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Latest VO developments at Paris VO Data Center
NASA Astrophysics Data System (ADS)
Le Sidaner, P.; Dubernet, M.-L.; Simon, G.; Aboudarham, J.; Baillard, A.; Barache, C.; Boone, F.; Chilingarian, I.; Dantel-Fort, M.; Desert, J. M.; Didelon, P.; Egret, D.; Guibert, J.; Hebrard, G.; Lainey, V.; Magnard, F.; Marmo, C.; Martin, J. M.; Pelat, D.; Renié, C.; Sarkissian, A.; Schneider, J.; Theureau, G.; Vachier, F.
Paris VO Data Center aims at providing VO access to its databases ressources, at participating to international standards developments, at implementing VO compliant simulation codes and data visualisation and analysis softwares. We will present some of the latest VO developments involving ressources from Paris VO Data Center, i.e, the first simple spectra access for data of the Nançay radiotelescope observatory, a validator for Simple Spectra Access protocols and its implementation tools, a Cone-search access to the exoplanet catalog, a pipeline for images processing to make them "science-ready" in vo-format, implementation of Simple Image Access using Geographic Information System in databases. Developments involving other ressources may be found in their own contributions to this meeting.
Latest VO development at VO-Paris Data Centre
NASA Astrophysics Data System (ADS)
Le Sidaner, P.; Dubernet, M.-L.; Simon, G.; Aboudarham, J.; Baillard, A.; Barache, C.; Boone, F.; Chilingarian, I.; Dantel-Fort, M.; Didelon, P.; Egret, D.; Guibert, J.; Hebrard, G.; Lainey, V.; Magnard, F.; Marmo, C.; Martin, J. M.; Normand, J.; Pelat, D.; Renié, C.; Sarkissian, A.; Savalle, R.; Shih, A.; Schneider, J.; Theureau, G.; Vachier, F.
VO-Paris Data Center aims at providing VO access to its databases resources, at participating to the development of interoperability standards, at implementing VO-compliant simulation codes and data visualization and analysis software. We will present some of the latest VO development involving resources from Paris VO Data Center, i.e, the first simple spectral access for data of the Nancay radio-telescope, a validator for Simple Spectra Access protocols and its implementation tools, a Cone-search access to the exoplanet catalog, a pipeline for image processing to make them "science-ready" and converting into VO-format, implementation of Simple Image Access using Geographic Information System in databases. Developments involving other resources may be found in their own contributions to this meeting.
NASA Astrophysics Data System (ADS)
Plante, R.; Fitzpatrick, M.; Graham, M.; Tody, D.; Young, W.
We introduce two products for accessing the VO from Python: PyVO and VOClient. PyVO is built on the widely-used Astropy package and is well suited for integrating automated access to astronomical data into highly customizable scripts and applications for data analysis in Python. VOClient is built on a collection of C-libraries and is well suited for integrating with multi-language analysis packages. It also provides a framework for integrating legacy software into the Python environment. In this demo, we will run through several examples demonstrate basic data discovery and retrieval of data. This includes finding archives containing data of interest (VO registry), retrieving datasets (SIA, SSA), and exploring (Cone Search, SLAP). VOClient features some extended capabilities including the ability to communicate to other desktop applications from a script using the SAMP protocol.
VO for Education: Archive Prototype
NASA Astrophysics Data System (ADS)
Ramella, M.; Iafrate, G.; De Marco, M.; Molinaro, M.; Knapic, C.; Smareglia, R.; Cepparo, F.
The number of remote control telescopes dedicated to education is increasing in many countries, leading to correspondingly larger and larger amount of stored educational data that are usually available only to local observers. Here we present the project for a new infrastructure that will allow teachers using educational telescopes to archive their data and easily publish them within the Virtual Observatory (VO) avoiding the complexity of professional tools. Students and teachers anywhere will be able to access these data with obvious benefits for the realization of grander scale collaborative projects. Educational VO data will also be an important resource for teachers not having direct access to any educational telescopes. We will use the educational telescope at our observatory in Trieste as a prototype for the future VO educational data archive resource. The publishing infrastructure will include: user authentication, content and curation validation, data validation and ingestion, VO compliant resource generation. All of these parts will be performed by means of server side applications accessible through a web graphical user interface (web GUI). Apart from user registration, that will be validated by a natural person responsible for the archive (after having verified the reliability of the user and inspected one or more test files), all the subsequent steps will be automated. This means that at the very first data submission through the webGUI, a complete resource including archive and published VO service will be generated, ready to be registered to the VO. The efforts required to the registered user will consist only in describing herself/himself at registration step and submitting the data she/he selects for publishing after each observation sessions. The infrastructure will be file format independent and the underlying data model will use a minimal set of standard VO keywords, some of which will be specific for outreach and education, possibly including VO
Tools and services from the French VO
NASA Astrophysics Data System (ADS)
Genova, F.; French Vo Teams
The French VO (Action Spécifique Observatoires Virtuels France - ASOV), a joint e action of INSU and CNES, coordinates French participation in the VO for astronomy, solar, heliospheric and space plasma physics, and the study of the planets. It supports teams which develops VO services to uptake VO standards and methods, in particular by organizing tutorials for developers, provides forums for discussion, and funds travel of French participants to IVOA meetings. INSU, on behalf of the French VO, is a member of the IVOA and of Euro-VO, and coordinates the Euro-VO Data Center Alliance, which will be funded by the European Commission as a Coordination Action of the Infrastructure, Communication Network Development program from September 1, 2006. ASOV was created in 2004. Within a few years it has succeeded in creating a national community of VO developers. Several teams participate very actively in the IVOA Interoperability standard development, and collaborate with IT laboratories on VO-related subjects. Most French astronomy laboratories are involved in the development of VO-oriented services and tools, with a wide diversity of actions (observation archives/`science ready' data, value-added data bases and services; tools for visualisation, image analysis, . . . ; software suites; numerical simulations/theoretical astronomy services, thematic services). A recent census received more than 40 answers describing projects at different scales, some operational, some in development. Details on French VO teams and ASOV actions are available from the French VO Web site:
ERIC Educational Resources Information Center
Milner, Jacob
Voice over Internet Protocol (VoIP) is everywhere. The technology lets users make and receive phone calls over the Internet, transporting voice traffic alongside data traffic such as instant messages (IMs) and e-mail. While the number of consumer customers using VoIP increases every week, the technology is finding its way into K-12 education as…
Tunable VO2/Au hyperbolic metamaterial
NASA Astrophysics Data System (ADS)
Prayakarao, S.; Mendoza, B.; Devine, A.; Kyaw, C.; van Dover, R. B.; Liberman, V.; Noginov, M. A.
Vanadium dioxide (VO2) is known to have a semiconductor-to-metal phase transition at ˜68 °C. Therefore, it can be used as a tunable component of an active metamaterial. The lamellar metamaterial studied in this work is composed of subwavelength VO2 and Au layers and is designed to undergo a temperature controlled transition from the optical hyperbolic phase to the metallic phase. VO2 films and VO2/Au lamellar metamaterial stacks have been fabricated and studied in electrical conductivity and optical (transmission and reflection) experiments. The observed temperature-dependent changes in the reflection and transmission spectra of the metamaterials and VO2 thin films are in a good qualitative agreement with theoretical predictions. The demonstrated optical hyperbolic-to-metallic phase transition is a unique physical phenomenon with the potential to enable advanced control of light-matter interactions.
A Planetary Science VO prototype
NASA Astrophysics Data System (ADS)
Erard, S.; Le Sidaner, P.; Berthier, J.; Cecconi, B.; Henry, F.; Lamy, L.; Chauvin, C.; Savalle, R.; Jacquey, C.; André, N.; Schmitt, B.
The goal of the JRA4 Work Package of Europlanet-RI was to set the basis for a European Virtual Observatory in Planetary Science. The objective in this first step was to save time during searches in big archives and small databases, as well as to facilitate data access and visualization. The system is based on a new access protocol based on TAP, a specific client to query the available services, and intensive recycling of tools developed for the Astronomy VO. Some new databases were also produced in the EuroPlaNet-RI framework and are available in this context. This system should be extensible to all fields of Planetary Science, and open to external data providers.
Radiation absorbed dose estimates for oxygen-15 radiopharmaceuticals (H2( V)O, C VO, O VO) in newborn infants
Powers, W.J.; Stabin, M.; Howse, D.; Eichling, J.O.; Herscovitch, P.
In preparation for measurement of regional cerebral oxygen metabolism by positron emission tomography, radiation absorbed dose estimates for 19 internal organs, blood, and total body were calculated for newborn infants following bolus intravenous administration of H2( V)O and brief inhalation of C VO and O VO. Cumulated activity for each radiopharmaceutical was calculated from a compartmental model based on the known biologic behavior of the compound. Values for mean absorbed dose/unit cumulated activity (S) for internal organs and total body were based on a newborn phantom. S was separately calculated for blood. Total radiopharmaceutical absorbed dose estimates necessary to measure cerebral oxygen metabolism in a 3.51-kg infant based on 0.7 mCi/kg H2( V)O and 1 mCi/kg C VO and O VO were determined to be 1.6 rad to the lung (maximum organ dose), 0.28 rad to the marrow, 0.46 rad to the gonads, and 0.22 rad to total body. These values are similar to those for current clinical nuclear medicine procedures employing /sup 99m/Tc in newborn infants.
Cabling specialist Connectix examines the growing potential for healthcare sector use of VoIP technology and highlights the importance of correct cabling infrastructure as a carrier of both voice and high-speed data traffic. PMID:18494421
Magnetic Irreversibility in VO2/Ni Bilayers
NASA Astrophysics Data System (ADS)
de La Venta, Jose; Lauzier, Josh; Sutton, Logan
The temperature dependence of the coercivity and magnetization of VO2/Ni bilayers was studied. VO2 exhibits a well-known Structural Phase Transition (SPT) at 330-340 K, from a low temperature monoclinic (M) to a high temperature rutile (R) structure. The SPT of VO2 induces an inverse magnetoelastic effect that strongly modifies the coercivity and magnetization of the Ni films. In addition, the growth conditions allow tuning of the magnetic properties. Ni films deposited on top of VO2 (M) show an irreversible change in the coercivity after the first cycle through the high temperature phase, with a corresponding change in the surface morphology of VO2. On the other hand, the Ni films grown on top of VO2 (R) do not show this irreversibility. These results indicate that properties of magnetic films are strongly affected by the strain induced by materials that undergo SPT and that it is possible to control the magnetic properties by tuning the growth conditions.
NASA Technical Reports Server (NTRS)
Wennersten, Miriam Dvorak; Banes, Anthony Vince; Boegner, Gregory J.; Dougherty, Lamar; Edwards, Bernard L.; Roman, Joseph; Bauer, Frank H. (Technical Monitor)
NASA Goddard Space Flight Center has built an open architecture, 24 channel space flight GPS receiver. The CompactPCI PiVoT GPS receiver card is based on the Mitel/GEC Plessey Builder-2 board. PiVoT uses two Plessey 2021 correlators to allow tracking of up to 24 separate GPS SV's on unique channels. Its four front ends can support four independent antennas, making it a useful card for hosting GPS attitude determination algorithms. It has been built using space quality, radiation tolerant parts. The PiVoT card will track a weaker signal than the original Builder 2 board. It also hosts an improved clock oscillator. The PiVoT software is based on the original Plessey Builder 2 software ported to the Linux operating system. The software is POSIX complaint and can easily be converted to other POSIX operating systems. The software is open source to anyone with a licensing agreement with Plessey. Additional tasks can be added to the software to support GPS science experiments or attitude determination algorithms. The next generation PiVoT receiver will be a single radiation hardened CompactPCI card containing the microprocessor and the GPS receiver optimized for use above the GPS constellation. PiVoT was flown successfully on a balloon in July, 2001, for its first non-simulated flight.
Towards a VO compliant ESO science archive
NASA Astrophysics Data System (ADS)
Padovani, Paolo
Data centres have a major role in the Virtual Observatory (VO), as they are the primary source of astronomical data. The VO cannot (and does not) dictate how a data centre handles its own archive. However, 'VO-layer' is needed to 'translate' any locally defined parameter to the standard (i.e., International Virtual Observatory Alliance compliant) ones. The longer term vision of the VO is also to hide away any observatory/telescope/instrument specific detail and work in astronomical units, for example, 'wavelength range' and not grism or filter name. Data providers are then advised to systematically collect metadata ('data about data') about the curation process, assign unique identifiers, describe the general content (e.g., physical coverage) of a collection, and provide interface and capability parameters of public services. Finally, the VO will work at its best with high-level ('science-ready') data, so that the VO user is spared as much as possible any complex and time consuming data reduction. Data centres should then make an effort to provide such data.
MAST in the Context of VO Activities
NASA Astrophysics Data System (ADS)
Kamp, I.; Thompson, R.; Conti, A.; Fraquelli, D.; Kimball, T.; Levay, K.; Shiao, B.; Smith, M.; Somerville, R.; White, R. L.
In the past year, the Multimission Archive at the Space Telescope Science Institute (MAST) has taken major steps in making MAST's holdings available using VO-defined protocols and standards, and in implementing VO-based tools. For example, MAST has implemented the Simple Cone Search protocol, and all MAST mission searches may be returned in the VOTable format, allowing other archives to use MAST data for their VO applications. We have made many of our popular High Level Science Products available through Simple Image Access Protocol (SIAP), and are implementing the VO Simple Spectral Access Protocol (SSAP). The cross correlation of VizieR catalogs with MAST missions is now possible and illustrates the integration of VO services into MAST. The user can easily display the results from searches within MAST using the plotting tool VOPlot. MAST also participates in the NVO registry service. Thus, the user can harvest MAST holdings simultaneously with data from many other surveys and missions through the VO DataScope Data Inventory Service.
Scalable architecture for VoIP privacy
NASA Astrophysics Data System (ADS)
Medvinsky, Alexander
An access network for Voice over IP (VoIP) clients (e.g. DOCSIS-based HFC network) often provides a privacy service. However, such a privacy service is limited only to that access network. When VoIP packets are carried over an open IP network or over a network with some connections to the Internet, it is desirable to provide an end-to-end privacy service where each VoIP packet is encrypted at the source and decrypted at the terminating endpoint. Clearly, public key encryption cannot be applied to each voice packet; the performance would be unacceptable regardless of the choice of a public key algorithm. The only alternative is for the two VoIP endpoints to negotiate a shared symmetric key. Since VoIP connections are established only for duration of a phone call, the end-to-end key negotiation needs to occur during each call setup. And it should not noticeably delay the call setup phase. In order to provide end-to-end privacy, it is not sufficient to encrypt all messages between the two endpoints. It is important that the two endpoints authenticate each other - validate each other's identity. Without authentication an adversary might trick two VoIP clients to negotiate keys with her and then sit in the middle of their conversation and record each VoIP packet, before forwarding it to the intended destination. However, direct authentication of the two VoIP endpoints is not always possible in telephony networks - in particular when caller ID blocking services are enabled. To support such anonymity services, it may be sufficient to authenticate not the identity of the caller but the fact that it is a valid subscriber and that all subsequent signaling and voice traffic will be coming from the same source. The PacketCable specifications provide an example of a VoIP architecture with end-to-end privacy that meets the above stated criteria. This paper describes the PacketCable end-to-end privacy approach and suggests additional mechanisms that may be used to further
NASA Technical Reports Server (NTRS)
Wennersten, Miriam; Banes, Vince; Boegner, Greg; Clagnett, Charles; Dougherty, Lamar; Edwards, Bernard; Roman, Joe; Bauer, Frank H. (Technical Monitor)
NASA Goddard Space Flight Center has built an open architecture, 24 channel spaceflight Global Positioning System (GPS) receiver. The compact PCI PiVoT GPS receiver card is based on the Mitel/GEC Plessey Builder 2 board. PiVoT uses two Plessey 2021 correlators to allow tracking of up to 24 separate GPS SV's on unique channels. Its four front ends can support four independent antennas, making it a useful card for hosting GPS attitude determination algorithms. It has been built using space quality, radiation tolerant parts. The PiVoT card works at a lower signal to noise ratio than the original Builder 2 board. It also hosts an improved clock oscillator. The PiVoT software is based on the original Piessey Builder 2 software ported to the Linux operating system. The software is posix compliant and can be easily converted to other posix operating systems. The software is open source to anyone with a licensing agreement with Plessey. Additional tasks can be added to the software to support GPS science experiments or attitude determination algorithms. The next generation PiVoT receiver will be a single radiation hardened compact PCI card containing the microprocessor and the GPS receiver optimized for use above the GPS constellation.
Synthesis and Electrochemical Properties of Nano-VO2 (B).
Yang, Yun; Lu, Yong; Wang, Wei; Feng, Chuanqi; Yang, Shuijin
The nano-VO2 (B) has been self-assembly synthesized by hydrothermal method using different templates, which may give them some interesting properties. The as-prepared samples were characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The electrochemical properties of the samples were investigated. The results show that the hexadecyltrimethyl ammonium bromide (CTAB) (soft template) was used to obtain the VO2 (B1) nanobelts. The flake graphite (hard template) was taken to get the VO2 (B2) nanosheets. The VO2 (B1) nanobelts have higher initial capacity to compare with VO2 (B2). But the VO2 (B2) nanosheets showed better cycling performance than that of VO2 (B1) nanobelts. The nano VO2 (B2) is a promising anode material for lithium ion battery application. PMID:27455666
SPLAT-VO: Spectral Analysis Tool for the Virtual Observatory
NASA Astrophysics Data System (ADS)
Castro-Neves, Margarida; Draper, Peter W.
SPLAT-VO is an extension of the SPLAT (Spectral Analysis Tool, ascl:1402.007) graphical tool for displaying, comparing, modifying and analyzing astronomical spectra; it includes facilities that allow it to work as part of the Virtual Observatory (VO). SPLAT-VO comes in two different forms, one for querying and downloading spectra from SSAP servers and one for interoperating with VO tools, such as TOPCAT (ascl:1101.010).
Euro-VO-Coordination of virtual observatory activities in Europe
NASA Astrophysics Data System (ADS)
Genova, Françoise; Allen, Mark G.; Arviset, Christophe; Lawrence, Andy; Pasian, Fabio; Solano, Enrique; Wambsganss, Joachim
The European Virtual Observatory Euro-VO has been coordinating European VO activities through a series of projects co-funded by the European Commission over the last 15 years. The bulk of VO work in Europe is ensured by the national VO initiatives and those of intergovernmental agencies. VO activities at the European level coordinate the work in support of the three "pillars" of the Virtual Observatory: support to the scientific community, take-up by the data providers, and technological activities. Several Euro-VO projects have also provided direct support to selected developments and prototyping. This paper explains the methodology used by Euro-VO over the years. It summarises the activities which were performed and their evolutions at different stages of the development of the VO, explains the Euro-VO role with respect to the international and national levels of VO activities, details the lessons learnt for best practices for the coordination of the VO building blocks, and the liaison with other European initiatives, documenting the added-value of European coordination. Finally, the current status and next steps of Euro-VO are briefly addressed.
Properties of VO 2 thin film prepared with precursor VO(acac) 2
NASA Astrophysics Data System (ADS)
Pan, Mei; Zhong, Hongmei; Wang, Shaowei; Liu, Jie; Li, Zhifeng; Chen, Xiaoshuang; Lu, Wei
Both pure and tungsten (W)- or chromium (Cr)-doped vanadium dioxide (VO 2) thin films have been deposited by the sol-gel method on Si substrate using VO(acac) 2 as a precursor. XRD, Raman and atomic force microscopy (AFM) measurements showed the high (1 1 0) orientation of the films. It was found that the temperature coefficient of resistivity (TCR) values of the films around room temperature could be adjusted by impurity doping. Compared with the un-doped VO 2 films, the W-doping leads to larger TCR values, while the Cr-doping leads to smaller ones. The TCR value is linearly dependent on the impurity at room temperature. The largest TCR value of 5.2/% K -1 was obtained for 20/at% W-doped VO 2 film.
ERIC Educational Resources Information Center
Schaffhauser, Dian
School districts have by and large had great results implementing VoIP, which has become the conduit for delivering expanded functionality, achieving greater internal control, and gaining freedom from onerous monthly phone bills. But demonstrating a financial return on what is a substantial investment can be an elusive effort. The goal of…
ERIC Educational Resources Information Center
Young, Dan
Internet Protocol (IP) Telephony, or voice-over IP (VoIP), has proved to be a wise decision for many organizations. This technology crosses the boundaries of public and private networks, enterprise and residential markets, voice and data technologies, as well as local and long-distance services. The convergence of voice and data into a single,…
ERIC Educational Resources Information Center
Branzburg, Jeffrey
Cablevision, Comcast, Verizon, and many other high-speed broadband Internet providers are now also offering telephone services through "Voice over Internet Protocol" (VoIP). This technology sends ordinary telephone calls over the Internet rather than over telephone lines. While impractical without the use of a broadband Internet connection, with…
Polycrystalline VO2 thin films via femtosecond laser processing of amorphous VO x
NASA Astrophysics Data System (ADS)
Charipar, N. A.; Kim, H.; Breckenfeld, E.; Charipar, K. M.; Mathews, S. A.; Piqué, A.
Femtosecond laser processing of pulsed laser-deposited amorphous vanadium oxide thin films was investigated. Polycrystalline VO2 thin films were achieved by femtosecond laser processing in air at room temperature. The electrical transport properties, crystal structure, surface morphology, and optical properties were characterized. The laser-processed films exhibited a metal-insulator phase transition characteristic of VO2, thus presenting a pathway for the growth of crystalline vanadium dioxide films on low-temperature substrates.
Lessons Learned in Building VO Resources: Binding Together Several VO Standards into an Operational Service
NASA Astrophysics Data System (ADS)
Chilingarian, I.; Bonnarel, F.; Louys, M.; Le Sidaner, P.
The International Virtual Observatory Alliance (IVOA) developed numerous interoperability standards during the last several years. Most of them are quite simple to implement from the technical point of view and even contain "SIMPLE" in the title. Does it mean that it is also simple to build a working VO resource using those standards? Yes and no. "Yes" because the standards are indeed simple, and "no" because usually one needs to implement a lot more than it was thought in the beginning of the project so the time management of the team becomes difficult. In our presentation we will start with a basic case of a simple spectral data collection. Then we will describe several examples of "small" technologically advanced VO resources built in CDS and VO-Paris and will show that many standards are hidden from managers' eyes at the initial stage of the project development. The projects will be: (1) the GalMer database providing access to the results of numerical simulations of galaxy interactions; (2) the full spectrum fitting service that allows one to extract internal kinematics and stellar populations from spectra of galaxies available in the VO. We conclude that: (a) with the existing set of IVOA standards one can already build very advanced VO-enabled archives and tools useful for scientists; (b) managers have to be very careful when estimating the project development timelines for VO-enabled resources.
Werbach, Kevin
Internet telephony, or VoIP, is rapidly replacing the conventional kind. This year, for the first time, U.S. companies bought more new Internet-phone connections than standard lines. The major driver behind this change is cost. But VoIP isn't just a new technology for making old-fashioned calls cheaper, says consultant Kevin Werbach. It is fundamentally changing how companies use voice communications. What makes VoIP so powerful is that it turns voice into digital data packets that can be stored, copied, combined with other data, and distributed to virtually any device that connects to the Internet. And it makes it simple to provide all the functionality of a corporate phone-call features, directories, security-to anyone anywhere there's broadband access. That fosters new kinds of businesses such as virtual call centers, where widely dispersed agents work at all hours from their homes. The most successful early adopters, says Werbach, will focus more on achieving business objectives than on saving money. They will also consider how to push VoIP capabilities out to the extended organization, making use of everyone as a resource. Deployment may be incremental, but companies should be thinking about where VoIP could take them. Executives should ask what they could do if, on demand, they could bring all their employees, customers, suppliers, and partners together in a virtual room, with shared access to every modern communications and computing channel. They should take a fresh look at their business processes to find points at which richer and more customizable communications could eliminate bottlenecks and enhance quality. The important dividing line won't be between those who deploy Vol P and those who don't, or even between early adopters and laggards. It will be between those who see Vol P as just a new way to do the same old things and those who use itto rethink their entire businesses. PMID:16171218
Epitaxial stabilization and phase instability of VO2 polymorphs
Lee, Shinbuhm; Ivanov, Ilia N.; Keum, Jong K.; Lee, Ho Nyung
The VO2 polymorphs, i.e., VO2(A), VO2(B), VO2(M1) and VO2(R), have a wide spectrum of functionalities useful for many potential applications in information and energy technologies. However, synthesis of phase pure materials, especially in thin film forms, has been a challenging task due to the fact that the VO2 polymorphs are closely related to each other in a thermodynamic framework. Here, we report epitaxial stabilization of the VO2 polymorphs to synthesize high quality single crystalline thin films and study the phase stability of these metastable materials. We selectively deposit all the phases on various perovskite substrates with different crystallographic orientations. By investigating the phase instability, phonon modes and transport behaviours, not only do we find distinctively contrasting physical properties of the VO2 polymorphs, but that the polymorphs can be on the verge of phase transitions when heated as low as ~400 °C. Our successful epitaxy of both VO2(A) and VO2(B) phases, which are rarely studied due to the lack of phase pure materials, will open the door to the fundamental studies of VO2 polymorphs for potential applications in advanced electronic and energy devices. PMID:26787259
Epitaxial stabilization and phase instability of VO2 polymorphs.
Lee, Shinbuhm; Ivanov, Ilia N; Keum, Jong K; Lee, Ho Nyung
The VO2 polymorphs, i.e., VO2(A), VO2(B), VO2(M1) and VO2(R), have a wide spectrum of functionalities useful for many potential applications in information and energy technologies. However, synthesis of phase pure materials, especially in thin film forms, has been a challenging task due to the fact that the VO2 polymorphs are closely related to each other in a thermodynamic framework. Here, we report epitaxial stabilization of the VO2 polymorphs to synthesize high quality single crystalline thin films and study the phase stability of these metastable materials. We selectively deposit all the phases on various perovskite substrates with different crystallographic orientations. By investigating the phase instability, phonon modes and transport behaviours, not only do we find distinctively contrasting physical properties of the VO2 polymorphs, but that the polymorphs can be on the verge of phase transitions when heated as low as ~400 °C. Our successful epitaxy of both VO2(A) and VO2(B) phases, which are rarely studied due to the lack of phase pure materials, will open the door to the fundamental studies of VO2 polymorphs for potential applications in advanced electronic and energy devices. PMID:26787259
Epitaxial stabilization and phase instability of VO2 polymorphs
NASA Astrophysics Data System (ADS)
Lee, Shinbuhm; Ivanov, Ilia N.; Keum, Jong K.; Lee, Ho Nyung
The VO2 polymorphs, i.e., VO2(A), VO2(B), VO2(M1) and VO2(R), have a wide spectrum of functionalities useful for many potential applications in information and energy technologies. However, synthesis of phase pure materials, especially in thin film forms, has been a challenging task due to the fact that the VO2 polymorphs are closely related to each other in a thermodynamic framework. Here, we report epitaxial stabilization of the VO2 polymorphs to synthesize high quality single crystalline thin films and study the phase stability of these metastable materials. We selectively deposit all the phases on various perovskite substrates with different crystallographic orientations. By investigating the phase instability, phonon modes and transport behaviours, not only do we find distinctively contrasting physical properties of the VO2 polymorphs, but that the polymorphs can be on the verge of phase transitions when heated as low as ~400 °C. Our successful epitaxy of both VO2(A) and VO2(B) phases, which are rarely studied due to the lack of phase pure materials, will open the door to the fundamental studies of VO2 polymorphs for potential applications in advanced electronic and energy devices.
Epitaxial stabilization and phase instability of VO2 polymorphs
Lee, Shinbuhm; Ivanov, Ilia N.; Keum, Jong K.; Lee, Ho Nyung
The VO2 polymorphs, i.e., VO2(A), VO2(B), VO2(M1) and VO2(R), have a wide spectrum of functionalities useful for many potential applications in information and energy technologies. However, synthesis of phase pure materials, especially in thin film forms, has been a challenging task due to the fact that the VO2 polymorphs are closely related to each other in a thermodynamic framework. Here, we report epitaxial stabilization of the VO2 polymorphs to synthesize high quality single crystalline thin films and study the phase stability of these metastable materials. We selectively deposit all the phases on various perovskite substrates with different crystallographic orientations. Bymore » investigating the phase instability, phonon modes and transport behaviours, not only do we find distinctively contrasting physical properties of the VO2 polymorphs, but that the polymorphs can be on the verge of phase transitions when heated as low as ~400 °C. In conclusion, our successful epitaxy of both VO2(A) and VO2(B) phases, which are rarely studied due to the lack of phase pure materials, will open the door to the fundamental studies of VO2 polymorphs for potential applications in advanced electronic and energy devices.« less
VO2 kinetics during submaximal exercise following simulated weightlessness
NASA Technical Reports Server (NTRS)
Convertino, V. A.; Sandler, H.
A study is presented of the effects of deconditioning following 7 days of continuous head-down (-6 degrees) bedrest on changes in steady-state VO2, O2, and recovery VO2 during the performance of constant-load exercises. The deconditioning effects of bedrest on the physical working capacity were manifested in the subjects by significant changes in VO2 kinetics following the 7 days of head-down bedrest. While the subjects demonstrated the ability to attain similar steady-state VO2, simulated weightlessness using head-down bedrest resulted in a reduction of total VO2 capacity and an increase in the O2 deficit and VO2 halftime during submaximal constant-load exercise. It is concluded that this change in VO2 kinetics was induced by reexposure of the cardiovascular system to the +1 Gz (upright) environment.
Electrical oscillation in Pt/VO{sub 2} bilayer strips
Wang, Ying; Qi, Long; Xu, Yanjun; Wu, Yihong; Chai, Jianwei; Wang, Shijie; Yang, Yumeng; Tanaka, Hidekazu
We report on the observation of stable electrical oscillation in Pt/vanadium dioxide (VO{sub 2}) bilayer strips, in which the Pt overlayer serves the dual purposes of heating up the VO{sub 2} and weakening the electric field in the VO{sub 2} layer. Systematic measurements in an ultrahigh vacuum nanoprobe system show that the oscillation frequency increases with the bias current and/or with decreasing device dimension. In contrast to most VO{sub 2}-based oscillators reported to date, which are electrically triggered, current-induced Joule heating in the Pt overlayer is found to play a dominant role in the generation of oscillation in Pt/VO{sub 2} bilayers. A simple model involving thermally triggered transition of VO{sub 2} on a heat sink is able to account for the experimental observations. The results in this work provide an alternative view of the triggering mechanism in VO{sub 2}-based oscillators.
Modular VO oriented Java EE service deployer
NASA Astrophysics Data System (ADS)
Molinaro, Marco; Cepparo, Francesco; De Marco, Marco; Knapic, Cristina; Apollo, Pietro; Smareglia, Riccardo
The International Virtual Observatory Alliance (IVOA) has produced many standards and recommendations whose aim is to generate an architecture that starts from astrophysical resources, in a general sense, and ends up in deployed consumable services (that are themselves astrophysical resources). Focusing on the Data Access Layer (DAL) system architecture, that these standards define, in the last years a web based application has been developed and maintained at INAF-OATs IA2 (Italian National institute for Astrophysics - Astronomical Observatory of Trieste, Italian center of Astronomical Archives) to try to deploy and manage multiple VO (Virtual Observatory) services in a uniform way: VO-Dance. However a set of criticalities have arisen since when the VO-Dance idea has been produced, plus some major changes underwent and are undergoing at the IVOA DAL layer (and related standards): this urged IA2 to identify a new solution for its own service layer. Keeping on the basic ideas from VO-Dance (simple service configuration, service instantiation at call time and modularity) while switching to different software technologies (e.g. dismissing Java Reflection in favour of Enterprise Java Bean, EJB, based solution), the new solution has been sketched out and tested for feasibility. Here we present the results originating from this test study. The main constraints for this new project come from various fields. A better homogenized solution rising from IVOA DAL standards: for example the new DALI (Data Access Layer Interface) specification that acts as a common interface system for previous and oncoming access protocols. The need for a modular system where each component is based upon a single VO specification allowing services to rely on common capabilities instead of homogenizing them inside service components directly. The search for a scalable system that takes advantage from distributed systems. The constraints find answer in the adopted solutions hereafter sketched. The
Oxidizing annealing effects on VO2 films with different microstructures
NASA Astrophysics Data System (ADS)
Dou, Yan-Kun; Li, Jing-Bo; Cao, Mao-Sheng; Su, De-Zhi; Rehman, Fida; Zhang, Jia-Song; Jin, Hai-Bo
Vanadium dioxide (VO2) films have been prepared by direct-current magnetron sputter deposition on m-, a-, and r-plane sapphire substrates. The obtained VO2 films display different microstructures depending on the orientation of sapphire substrates, i.e. mixed microstructure of striped grains and equiaxed grains on m-sapphire, big equiaxed grains on a-sapphire and fine-grained microstructure on r-sapphire. The VO2 films were treated by the processes of oxidation in air. The electric resistance and infrared transmittance of the oxidized films were characterized to examine performance characteristics of VO2 films with different microstructures in oxidation environment. The oxidized VO2 films on m-sapphire exhibit better electrical performance than the other two films. After air oxidization for 600 s at 450 °C, the VO2 films on m-sapphire show a resistance change of 4 orders of magnitude over the semiconductor-to-metal transition. The oxidized VO2 films on a-sapphire have the highest optical modulation efficiency in infrared region compared to other samples. The different performance characteristics of VO2 films are understood in terms of microstructures, i.e. grain size, grain shape, and oxygen vacancies. The findings reveal the correlation of microstructures and performances of VO2 films, and provide useful knowledge for the design of VO2 materials to different applications.
Cloudspace: virtual environments in the VO
NASA Astrophysics Data System (ADS)
Graham, M. J.; Williams, R. D.
The grid community is moving towards providing on-demand computing in the form of virtual workspaces - abstracted execution environments that are dynamically made available to authorized clients. In part this is a reaction to market forces represented by such commercial initiatives as Amazon EC2 and in part a solution to hot service deployment. One danger, though, is that a multiplicity of implementations will lead to a lack of interoperability. Such a concern in the VO regarding distributed data storage led to the development of VOSpace, a lightweight abstraction layer that sits on top of existing storage solutions such as SRB. In this paper, we introduce Cloudspace, a resource-oriented extension of VOSpace, that incorporates UWS, the VO pattern for managing asynchronous services, to form a natural habitat for virtual environments in the VO. A notable feature of the Cloudspace concept is that distributed data and computing can be managed seamlessly through a single mechanism thus making the astronomer's life easier as we move into a new era of sophisticated computational astronomy.
ESA Science Archives and associated VO activities
NASA Astrophysics Data System (ADS)
Arviset, Christophe; Baines, Deborah; Barbarisi, Isa; Castellanos, Javier; Cheek, Neil; Costa, Hugo; Fajersztejn, Nicolas; Gonzalez, Juan; Fernandez, Monica; Laruelo, Andrea; Leon, Ignacio; Ortiz, Inaki; Osuna, Pedro; Salgado, Jesus; Tapiador, Daniel
ESA's European Space Astronomy Centre (ESAC), near Madrid, Spain, hosts most of ESA space based missions' scientific archives, in planetary (Mars Express, Venus Express, Rosetta, Huygens, Giotto, Smart-1, all in ESA Planetary Science Archive), in astronomy (XMM-Newton, Herschel, ISO, Integral, Exosat, Planck) and in solar physics (Soho). All these science archives are operated by a dedicated Science Archives and Virtual Observatory Team (SAT) at ESAC, enabling common and efficient design, development, operations and maintenance of the archives software systems. This also ensures long term preservation and availability of such science archives, as a sustainable service to the science community. ESA space science data can be accessed through powerful and user friendly user interface, as well as from machine scriptable interface and through VO interfaces. Virtual Observatory activities are also fully part of ESA archiving strategy and ESA is a very ac-tive partner in VO initiatives in Europe through Euro-VO AIDA and EuroPlanet and worldwide through the IVOA (International Virtual Observatory Alliance) and the IPDA (International Planetary Data Alliance).
A novel inorganic precipitation-peptization method for VO2 sol and VO2 nanoparticles preparation: Synthesis, characterization and mechanism.
Li, Yao; Jiang, Peng; Xiang, Wei; Ran, Fanyong; Cao, Wenbin
In this paper, a simple, safe and cost-saving precipitation-peptization method was proposed to prepare VO2 sol by using inorganic VOSO4-NH3⋅H2O-H2O2 reactants system in air under room temperature. In this process, VOSO4 was firstly precipitated to form VO(OH)2, then monometallic species of VO(O2)(OH)(-) were formed through the coordination between VO(OH)2 and H2O2. The rearrangement of VO(O2)(OH)(-) in a nonplanar pattern and intermolecular condensation reactions result in multinuclear species. Finally, VO2 sol is prepared through the condensation reactions between the multinuclear species. After drying the obtained sol at 40°C, VO2 xerogel exhibiting monoclinic crystal structure with the space group of C2/m was prepared. The crystal structure of VO2 nanoparticles was transferred to monoclinic crystal structure with the space group of P21/c (VO2(M)) by annealing the xerogel at 550°C. Both XRD and TEM analysis indicated that the nanoparticles possess good crystallinity with crystallite size of 34.5nm as estimated by Scherrer's method. These results suggest that the VO2 sol has been prepared successfully through the proposed simple method. PMID:26433476
UkrVO: Astroplates and the Joint Digitized Archive
NASA Astrophysics Data System (ADS)
Vavilova, I.; Pakuliak, L.; Protsyuk, Y.; Shlyapnikov, A.; Golovnya, V.; Yizhakevych, O.; Shatokhina, S.; Kazantseva, L.; Virun, N.; Kashuba, S.
The UkrVO (Ukrainian VO) database consists of about 150,000 astronegatives and 50,000 CCD-frames containing the unique astroinformation for formulation of important scientific tasks. This database is compiled from observations conducted in 1898-2011 years at observational sites of 8 Ukrainian observatories with about 50 instruments. The Joint Digital Archive (JDA) of photographic observations has become the UkrVO astroplate's core. Now the UkrVO Joint Digitized Archive covers about 40,000 astroplates, from which 15,000 are digitized. They were performed with a flatbed scanner EpsonExpression 10000XL with 16-bit gray levels, resolution of 1200-1600 dpi. Digitized images are stored in TIFF and FITS formats. Current version of UkrVO site for JDA and other information is placed on http://ukr-vo.org.
Integrating legacy software toolkits into China-VO system
NASA Astrophysics Data System (ADS)
Wang, Xiao-Qian, Cui, Chen-Zhou, Zhao, Yong-Heng
Virtual Observatory (VO) is a collection of data-archives and software toolkits. It aims to provide astronomers research resources with uniformed interfaces, using advanced information technologies. In this article, we discuss the necessaries and feasibilities of integrating legacy software toolkits into China-VO system at first; then analyse granularity about integrating. Three general integrating methods are given in detail. At last, we introduce an instance of integrating "Image Magick" - an software for image processing and discuss more about VO integration.
PyVO: Python access to the Virtual Observatory
NASA Astrophysics Data System (ADS)
Graham, Matthew; Plante, Ray; Tody, Doug; Fitzpatrick, Mike
PyVO provides access to remote data and services of the Virtual observatory (VO) using Python. It allows archive searches for data of a particular type or related to a particular topic and query submissions to obtain data to a particular archive to download selected data products. PyVO supports querying the VAO registry; simple data access services (DAL) to access images (SIA), source catalog records (Cone Search), spectra (SSA), and spectral line emission/absorption data (SLAP); and object name resolution (for converting names of objects in the sky into positions). PyVO requires both AstroPy and NumPy.
Security Research on VoIP with Watermarking
NASA Astrophysics Data System (ADS)
Hu, Dong; Lee, Ping
With the wide application of VoIP, many problems have occurred. One of the problems is security. The problems with securing VoIP systems, insufficient standardization and lack of security mechanisms emerged the need for new approaches and solutions. In this paper, we propose a new security architecture for VoIP which is based on digital watermarking which is a new, flexible and powerful technology that is increasingly gaining more and more attentions. Besides known applications e.g. to solve copyright protection problems, we propose to use digital watermarking to secure not only transmitted audio but also signaling protocol that VoIP is based on.
Direct synthesis of thermochromic VO2 through hydrothermal reaction
NASA Astrophysics Data System (ADS)
Alie, David; Gedvilas, Lynn; Wang, Zhiwei; Tenent, Robert; Engtrakul, Chaiwat; Yan, Yanfa; Shaheen, Sean E.; Dillon, Anne C.; Ban, Chunmei
Thermochromic VO2 was directly synthesized using hydrothermal techniques. The effects of formation conditions on the structure and morphology of the final product were studied through X-ray diffraction (XRD), and scanning electron microscopy (SEM). Unique hollow sphere morphology was observed for the synthesized VO2 powders. Ex-situ XRD studies after heat treatment confirmed the thermal stability of the VO2 structure. Thermochromic properties, as a consequence of the reversible structural transformation between monoclinic VO2 and tetragonal phases, were observed by Fourier transform infrared spectroscopy (FTIR).
Study of Thermal properties of VO2 and multilayer VO2 thin films for application in Thermal Switches
NASA Astrophysics Data System (ADS)
Zhu, Gaohua
Ultrafast nature of the phase transition near room temperature in VO2 makes it attractive material for applications in electronics and optical devices however utilization of corresponding drastic change in thermo-physical properties are rarely reported. In this study we investigate thermal and electronic properties of VO2 thin films on various substrates across the transition temperature to seek possibility of utilizing VO2 based thermal switches for applications in thermal devices. In addition, the interfacial heat transfer in VO2/metal multilayer thin film is mediated by phonons at low temperature, and when temperature is elevated beyond phase transition temperature, the interface thermal conductance is mediated mainly by both phons and electrons. VO2-multilayers approach is studied to utilize the switching interface thermal conductance in order to obtain higher thermal conductivity switch ratio than what can be achieved in intrinsic VO2. Thermal conductivities and interface thermal conductance of VO2 and VO2 multilayer thin films are measured using the time-domain thermoreflectance (TDTR) method. We will discuss interplay of phononic and electronic component to thermal conductivity in the light of Wiedemann-Franz law across the metal to insulator state of VO2 films.
VO-compliant workflows and science gateways
NASA Astrophysics Data System (ADS)
Castelli, G.; Taffoni, G.; Sciacca, E.; Becciani, U.; Costa, A.; Krokos, M.; Pasian, F.; Vuerli, C.
Workflow and science gateway technologies have been adopted by scientific communities as a valuable tool to carry out complex experiments. They offer the possibility to perform computations for data analysis and simulations, whereas hiding details of the complex infrastructures underneath. There are many workflow management systems covering a large variety of generic services coordinating execution of workflows. In this paper we describe our experiences in creating workflows oriented science gateways based on gUSE/WS-PGRADE technology and in particular we discuss the efforts devoted to develop a VO-compliant web environment.
Flexible thermochromic window based on hybridized VO2/graphene.
Kim, Hyeongkeun; Kim, Yena; Kim, Keun Soo; Jeong, Hu Young; Jang, A-Rang; Han, Seung Ho; Yoon, Dae Ho; Suh, Kwang S; Shin, Hyeon Suk; Kim, TaeYoung; Yang, Woo Seok
Large-scale integration of vanadium dioxide (VO2) on mechanically flexible substrates is critical to the realization of flexible smart window films that can respond to environmental temperatures to modulate light transmittance. Until now, the formation of highly crystalline and stoichiometric VO2 on flexible substrate has not been demonstrated due to the high-temperature condition for VO2 growth. Here, we demonstrate a VO2-based thermochromic film with unprecedented mechanical flexibility by employing graphene as a versatile platform for VO2. The graphene effectively functions as an atomically thin, flexible, yet robust support which enables the formation of stoichiometric VO2 crystals with temperature-driven phase transition characteristics. The graphene-supported VO2 was capable of being transferred to a plastic substrate, forming a new type of flexible thermochromic film. The flexible VO2 films were then integrated into the mock-up house, exhibiting its efficient operation to reduce the in-house temperature under infrared irradiation. These results provide important progress for the fabrication of flexible thermochromic films for energy-saving windows. PMID:23758656
Electronic structure and insulating gap in epitaxial VO2 polymorphs
Lee, Shinbuhm; Meyer, Tricia L.; Sohn, Changhee; Lee, Donghwa; Nichols, John A.; Lee, Dongkyu; Seo, Sung Seok Ambrose; Freeland, John W.; Noh, Tae Won; Lee, Ho Nyung
Here, determining the origin of the insulating gap in the monoclinic VO2(M1) is a long-standing issue. The difficulty of this study arises from the simultaneous occurrence of structural and electronic transitions upon thermal cycling. Here, we compare the electronic structure of the M1 phase with that of single crystalline insulating VO2(A) and VO2(B) thin films to better understand the insulating phase of VO2. As these A and B phases do not undergo a structural transition upon thermal cycling, we comparatively study the origin of the gap opening in the insulating VO2 phases. By x-ray absorption and optical spectroscopy, we findmore » that the shift of unoccupied t2g orbitals away from the Fermi level is a common feature, which plays an important role for the insulating behavior in VO2 polymorphs. The distinct splitting of the half-filled t2g orbital is observed only in the M1 phase, widening the bandgap up to ~0.6 eV. Our approach of comparing all three insulating VO2 phases provides insight into a better understanding of the electronic structure and the origin of the insulating gap in VO2.« less
VoIP makes voice heard--functionality is up.
Wade, Phil; Wakelam, Mathew
Phil Wade, sales and marketing director, and Mathew Wakelam, VoIP product manager, at alarm and communication specialist Static Systems Group, discuss wireless VoLP's potential in healthcare establishments and examine how, in particular, the technology can be successfully integrated with nurse call systems. PMID:18552104
Integrating Cluster Data into the VO Infrastructure
NASA Astrophysics Data System (ADS)
Richards, P. J.; Perry, C. H.
The UK Cluster Data Centre (UKCDC) has provided access to Cluster data products since the launch of the Cluster spacecraft in 2000. In keeping with the aim of providing the widest possible access to the Space Physics community, the UKCDC has participated in several projects to advance the interoperability of their data holdings within the emerging international VO infrastructure. These activities include AstroGrid in the UK, ESA's SpaceGrid and participation in the NASA led Space Physics Archive Search and Extract (SPASE) Consortium. Although, as demonstrated by SpaceGrid, the technology exists to build the VO infrastructure, the main obstacle to progress has been the absence of a metadata standard used by Data Centres and other data providers. The Cluster Active Archive (CAA), which is providing an archive of Cluster high resolution data, has a comprehensive metadata dictionary which is used to describe all Cluster data products. The UKCDC is ingesting into the CAA the summary and primary data products being used during the mission for event monitoring. As part of this activity, the CAA metadata is also being translated into SPASE metadata and the UKCDC is in the process of building a SPASE registry of the data products available at the UKCDC and also data access services developed according to the SPASE standards. The experience gained as the SPASE standard matures will form the basis for building a SPASE registry and services for access to the Cluster archive.
Microstructures and thermochromic characteristics of VO2/AZO composite films
NASA Astrophysics Data System (ADS)
Xiao, Han; Li, Yi; Yuan, Wenrui; Fang, Baoying; Wang, Xiaohua; Hao, Rulong; Wu, Zhengyi; Xu, Tingting; Jiang, Wei; Chen, Peizu
A vanadium dioxide (VO2) thin film was fabricated on a ZnO doped with Al (AZO) conductive glass by magnetron sputtering at room temperature followed by annealing under air atmosphere. The microstructures and optical properties of the thin film were studied. The results showed that the VO2/AZO composite film was poly-crystalline and the AZO layer did not change the preferred growth orientation of VO2. Compared to the VO2 film fabricated on soda-lime glass substrate through the same process and condition, the phase transition temperature of the VO2/AZO composite film was decreased by about 25 °C, thermal hysteresis width narrowed to 6 °C, the visible light transmittance was over 50%, the infrared transmittances before and after phase transition were 21% and 55%, respectively at 1500 nm.
Integrating the IA2 Astronomical Archive in the VO: The VO-Dance Engine
NASA Astrophysics Data System (ADS)
Molinaro, M.; Laurino, O.; Smareglia, R.
Virtual Observatory (VO) protocols and standards are getting mature and the astronomical community asks for astrophysical data to be easily reachable. This means data centers have to intensify their efforts to provide the data they manage not only through proprietary portals and services but also through interoperable resources developed on the basis of the IVOA (International Virtual Observatory Alliance) recommendations. Here we present the work and ideas developed at the IA2 (Italian Astronomical Archive) data center hosted by the INAF-OATs (Italian Institute for Astrophysics - Trieste Astronomical Observatory) to reach this goal. The core point is the development of an application that from existing DB and archive structures can translate their content to VO compliant resources: VO-Dance (written in Java). This application, in turn, relies on a database (potentially DBMS independent) to store the translation layer information of each resource and auxiliary content (UCDs, field names, authorizations, policies, etc.). The last token is an administrative interface (currently developed using the Django python framework) to allow the data center administrators to set up and maintain resources. This deployment, platform independent, with database and administrative interface highly customizable, means the package, when stable and easily distributable, can be also used by single astronomers or groups to set up their own resources from their public datasets.
Data access service of China-VO
NASA Astrophysics Data System (ADS)
Sang, Jian; Zhao, Yong-Heng; Cui, Chen-Zhou
With the development of technologies and the implementation of large quantity of astronomical observation projects, astronomy faces data avalanche and has entered an information era. A basic aim of the Virtual Observatory is to provide uniform access to highly distributed, complicated, huge astronomical datasets, and to realize federation of global astronomical data resources, so that astronomers can obtain required data efficiently and conveniently for their research. China Virtual Observatory (China-VO) project designs and implements astronomical data access services based on Grid technology, and provides uniform interface to Grid client application. In this paper, we introduce the data access service toolkit development using Globus Toolkit, the Grid services encapsulation of catalogs according to the latest astronomical data standards recommended by International Virtual Observatory Alliance, the implements of catalog Cone Search access service. Furthermore, we also introduce how to construct other Grid services using above data access services.
Epitaxial Ni/VO2 heterostructures on Si (001)
NASA Astrophysics Data System (ADS)
Singamaneni, Srinivasa Rao; Foley, Gabrielle; Prater, John; Narayan, Jay
VO2 is a strongly correlated oxide, undergoes a first order metal-insulator (MIT) well above the room temperature 340K. Previous works have shown that the stress associated with structural changes across MIT, VO2 can produce significant changes in magnetic properties of over layer ferromagnetic films such as Ni. This control of the magnetic properties could be very important to many technological applications. However, the current use of r-sapphire as substrate can be restrictive in the microelectronics industry. The previous works focused their studies on polycrystalline Ni and VO2 films, which do not allow the precise controlling of the associated properties due to poor reproducibility of polycrystalline films. We have investigated the magnetic and electronic properties of Ni/VO2 films when epitaxially integrated on Si (001) by pulsed laser deposition using domain matching epitaxy paradigm. Ni was grown both in nanoscale islands and layered form. The XRD results showed that the Ni, VO2and YSZ layers were grown epitaxially in single out of plane orientations. We found that the hysteresis in resistance vs. temperature curves in VO2 thin films was retained even when it is in close proximity with the Ni layer which helped confirm that VO2 layer preserves its characteristic features, revealed the fingerprint magnetic features of Ni layer. We will present and discuss our comprehensive experimental findings.
SIP-CCME cooperation in multimedia VoIP network
NASA Astrophysics Data System (ADS)
Grądkowska, Magdalena; Popiel, Piotr; Sobańska, Katarzyna
VoIP is a fast-developing technology which allows making telephone calls using a data network like the Internet. VoIP converts the voice signal from the telephone into a digital signal that travels over the Internet and then converts it back at the other end so that speaking to anyone with a regular phone number is possible. VoIP may also enable the direct calls from a computer with the use of a conventional telephone or a microphone. Some services using VoIP may only allow you to call other people using the same VoIP service, but others may allow you to call anyone who has a telephone number. First condition is a broadband Internet connection for VoIP technology to work. There are two major advantages of VOIP: lower cost and increased functionality. In the paper the integration of two networks, one with a CCME based installation and the other with a full Asterisk/SIP voicemail deployment is presented. The goal was to allow dialing between VoIP's telephony from different networks and evaluate a quality of connection with the use of certain codecs.
Chapter 44: Introduction to Publishing in the VO
NASA Astrophysics Data System (ADS)
Plante, R. L.; Greene, G.
As part of our introductory tour of the VO at the beginning of this book, we introduced registries as one way to begin finding useful data and services. We also saw how applications, like DataScope, can use registries behind the scenes to discover data resources for us. In Chapter 41, we took a closer look at the registry framework, where we introduced concepts and terms such as resources, identifiers, and resource metadata and described how they are used to aid data discovery. Another important capability of the VO is that users can also be publishers. In the VO, we consider something as published if you can use VO facilities to find it. In this chapter, we will take an overall look at the process of publishing data and services to the VO. An important part of publishing, we will see, is registering a collection or service with a VO registry. We will look at that this process in more detail through a visit to one publishing registry. Much of the information presented in this chapter has been adapted from the document "How to Publish to the NVO" (Plante 2007), available from the US-VO web site. This document is updated regularly to provide data and service providers with "first steps" information on publishing and provides pointers to additional resources.
Depressed Phase Transition in Solution-Grown VO2 Nanostructures
Whittaker, L.; Jaye, C; Fu, Z; Fischer, D; Banerjee, S
The first-order metal-insulator phase transition in VO{sub 2} is characterized by an ultrafast several-orders-of-magnitude change in electrical conductivity and optical transmittance, which makes this material an attractive candidate for the fabrication of optical limiting elements, thermochromic coatings, and Mott field-effect transistors. Here, we demonstrate that the phase-transition temperature and hysteresis can be tuned by scaling VO{sub 2} to nanoscale dimensions. A simple hydrothermal protocol yields anisotropic free-standing single-crystalline VO{sub 2} nanostructures with a phase-transition temperature depressed to as low as 32 C from 67 C in the bulk. The observations here point to the importance of carefully controlling the stochiometry and dimensions of VO{sub 2} nanostructures to tune the phase transition in this system.
Density functional theory study of rutile VO2 surfaces
NASA Astrophysics Data System (ADS)
Mellan, Thomas A.; Grau-Crespo, Ricardo
We present the results of a density functional theory investigation of the surfaces of rutile-like vanadium dioxide, VO2(R). We calculate the surface energies of low Miller index planes and find that the most stable surface orientation is the (110). The equilibrium morphology of a VO2(R) particle has an acicular shape, laterally confined by (110) planes and topped by (011) planes. The redox properties of the (110) surface are investigated by calculating the relative surface free energies of the non-stoichiometric compositions as a function of oxygen chemical potential. It is found that the VO2(110) surface is oxidized with respect to the stoichiometric composition, not only at ambient conditions but also at the more reducing conditions under which bulk VO2 is stable in comparison with bulk V2O5. The adsorbed oxygen forms surface vanadyl species much more favorably than surface peroxo species.
Audio CAPTCHA for SIP-Based VoIP
NASA Astrophysics Data System (ADS)
Soupionis, Yannis; Tountas, George; Gritzalis, Dimitris
Voice over IP (VoIP) introduces new ways of communication, while utilizing existing data networks to provide inexpensive voice communications worldwide as a promising alternative to the traditional PSTN telephony. SPam over Internet Telephony (SPIT) is one potential source of future annoyance in VoIP. A common way to launch a SPIT attack is the use of an automated procedure (bot), which generates calls and produces audio advertisements. In this paper, our goal is to design appropriate CAPTCHA to fight such bots. We focus on and develop audio CAPTCHA, as the audio format is more suitable for VoIP environments and we implement it in a SIP-based VoIP environment. Furthermore, we suggest and evaluate the specific attributes that audio CAPTCHA should incorporate in order to be effective, and test it against an open source bot implementation.
Structural, optical, and magnetic properties of FeVO3
NASA Astrophysics Data System (ADS)
Singh, Pooja; Gupta, Anurag; Dogra, Anjana
We report the structural, optical, and magnetic properties of polycrystalline FeVO3 synthesized by solid state reaction technique.While FeVO3 has rhombohedral crystal structure with space group R-3c (167) identical to the parentα-Fe2O3, the lattice volume reduces due to the replacement of Fe3+ with V3+ having smaller ionic radii. The most remarkable outcome of doping is reduction in band gap from 2.1 (α-Fe2O3) to 1.5 eV (FeVO3), which is favorable for photo-electrochemical applications. Although the canted ferromagnetism persists in FeVO3, an enhancement in magnetic moment is observed as compared to the parent compound.
Temperature-controlled surface plasmon resonance in VO (2) nanorods.
Lopez, R; Haynes, T E; Boatner, L A; Feldman, L C; Haglund, R F
The optical properties of VO(2) nanoparticles formed in an amorphous SiO(2) host by stoichiometric ion implantation of vanadium and oxygen and thermal annealing have been determined and correlated with the particle size and morphology. The results show that that the temperature-controlled semiconductor-to-metal phase transition of the VO(2) nanophase precipitates turns on the classical surface plasmon resonance, with specific features that depend on the size and aspect ratio of the VO(2) particles. This effect improves the optical contrast between the metallic and semiconducting states in the near-IR region of the spectrum as a result of dielectric confinement that is due to the SiO(2) host. A fiber-optic application is demonstrated, as is the ability to control the characteristics of the phase transition by using ion implantation to dope the VO(2) nanoparticles with tungsten or titanium ions. PMID:18026439
The Euro-VO Registry, Re-engineering the Back-end
NASA Astrophysics Data System (ADS)
Arviset, C.; Perdikeas, M.; Osuna, P.; Gonzalez, J.
The Euro-VO Registry, located, developed and operated at ESAC, is one of the full searchable registries available worldwide, gathering information about all VO-compliant resources. The Euro-VO Registry serves as a registration point for European - and other countries- VO actors and data centres wishing to publish VO services. It harvests other registries to ensure its completeness so VO applications developers and VO users can use it to discover all VO resources, from Europe and from all other VO projects. The Euro-VO Registry provides as well a harvesting interface to other registries in the world to make sure the European VO services are also included in all other worldwide full registries. In particular, the new Euro-VO registry will be supporting the new RegTAP search interface for the relational registry allowing arbitrary ADQL queries against its contents over a compliant TAP service. The recently obsolete (for future developments) SOAP-based legacy search interface will also be supported for backwards compatibility purposes. Furthermore, in the context of the IVOA, some quality control and curation procedures for the registry resources are being defined. The Euro-VO Registry implements these procedures to ensure the high quality of the VO resources it references. This paper gives an overview of the recent development of the new Euro-VO Registry, together with its new curation facilities, both of which are being performed under a contract awarded to Neuropublic, under ESA special initiative to Greece.
The preparation of a plasmonically resonant VO2 thermochromic pigment.
Bai, Huaping; Cortie, Michael B; Maaroof, Abbas I; Dowd, Annette; Kealley, Catherine; Smith, Geoffrey B
Vanadium dioxide (VO(2)) undergoes a reversible metal-insulator transition, normally at approximately 68 degrees C. While the properties of continuous semi-transparent coatings of VO(2) are well known, there is far less information available concerning the potential use of discrete VO(2) nanoparticles as a thermochromic pigment in opaque coatings. Individual VO(2) nanoparticles undergo a localized plasmon resonance with near-infrared light at about 1100 nm and this resonance can be switched on and off by simply varying the temperature of the system. Therefore, incorporation of VO(2) nanoparticles into a coating system imbues the coating with the ability to self-adaptively modulate its own absorptive efficiency in the near-infrared. Here we examine the magnitude and control of this phenomenon. Prototype coatings are described, made using VO(2) powder produced by an improved process. The materials are characterized using calorimetry, x-ray diffraction, high-resolution scanning electron microscopy, transmission electron microscopy, and by measurement of optical properties. PMID:19417455
The preparation of a plasmonically resonant VO2 thermochromic pigment
NASA Astrophysics Data System (ADS)
Bai, Huaping; Cortie, Michael B.; Maaroof, Abbas I.; Dowd, Annette; Kealley, Catherine; Smith, Geoffrey B.
Vanadium dioxide (VO2) undergoes a reversible metal-insulator transition, normally at ~68 °C. While the properties of continuous semi-transparent coatings of VO2 are well known, there is far less information available concerning the potential use of discrete VO2 nanoparticles as a thermochromic pigment in opaque coatings. Individual VO2 nanoparticles undergo a localized plasmon resonance with near-infrared light at about 1100 nm and this resonance can be switched on and off by simply varying the temperature of the system. Therefore, incorporation of VO2 nanoparticles into a coating system imbues the coating with the ability to self-adaptively modulate its own absorptive efficiency in the near-infrared. Here we examine the magnitude and control of this phenomenon. Prototype coatings are described, made using VO2 powder produced by an improved process. The materials are characterized using calorimetry, x-ray diffraction, high-resolution scanning electron microscopy, transmission electron microscopy, and by measurement of optical properties.
Fair Scheduling for Delay-Sensitive VoIP Traffic
NASA Astrophysics Data System (ADS)
Ahmed, Shawish; Jiang, Xiaohong; Horiguchi, Susumu
With the wide expansion of voice services over the IP networks (VoIP), the volume of this delay sensitive traffic is steadily growing. The current packet schedulers for IP networks meet the delay constraint of VoIP traffic by simply assigning its packets the highest priority. This technique is acceptable as long as the amount of VoIP traffic is relatively very small compared to other non-voice traffic. With the notable expansion of VoIP applications, however, the current packet schedulers will significantly sacrifice the fairness deserved by the non-voice traffic. In this paper, we extend the conventional Deficit Round-Robin (DRR) scheduler by including a packet classifier, a Token Bucket and a resource reservation scheme and propose an integrated packet scheduler architecture for the growing VoIP traffic. We demonstrate through both theoretical analysis and extensive simulation that the new architecture makes it possible for us to significantly improve the fairness to non-voice traffic while still meeting the tight delay requirement of VoIP applications.
Electric field induced metal-insulator transition in VO2 thin film based on FTO/VO2/FTO structure
NASA Astrophysics Data System (ADS)
Hao, Rulong; Li, Yi; Liu, Fei; Sun, Yao; Tang, Jiayin; Chen, Peizu; Jiang, Wei; Wu, Zhengyi; Xu, Tingting; Fang, Baoying
A VO2 thin film has been prepared using a DC magnetron sputtering method and annealing on an F-doped SnO2 (FTO) conductive glass substrate. The FTO/VO2/FTO structure was fabricated using photolithography and a chemical etching process. The temperature dependence of the I-V hysteresis loop for the FTO/VO2/FTO structure has been analyzed. The threshold voltage decreases with increasing temperature, with a value of 9.2 V at 20 °C. The maximum transmission modulation value of the FTO/VO2/FTO structure is 31.4% under various temperatures and voltages. Optical modulation can be realized in the structure by applying an electric field.
VO2 kinetics and metabolic contributions whilst swimming at 95, 100, and 105% of the velocity at VO2max.
Sousa, Ana C; Vilas-Boas, João P; Fernandes, Ricardo J
A bioenergetical analysis of swimming at intensities near competitive distances is inexistent. It was aimed to compare the transient VO2 kinetics responses and metabolic contributions whilst swimming at different velocities around VO2max. 12 trained male swimmers performed (i) an incremental protocol to determine the velocity at VO2max (vVO2max) and (ii) three square wave exercises from rest to 95, 100, and 105% of vVO2max. VO2 was directly measured using a telemetric portable gas analyser and its kinetics analysed through a double-exponential model. Metabolic contributions were assessed through the sum of three energy components. No differences were observed in the fast component response (τ1--15, 18, and 16 s, A1--36, 34, and 37 mL · kg(-1) · min (-1), and Gain--32, 29, and 30 mL · min (-1) at 95, 100, and 105% of the vVO2max, resp.) but A2 was higher in 95 and 100% compared to 105% intensity (480.76 ± 247.01, 452.18 ± 217.04, and 147.04 ± 60.40 mL · min (-1), resp.). The aerobic energy contribution increased with the time sustained (83 ± 5, 74 ± 6, and 59 ± 7% for 95, 100, and 105%, resp.). The adjustment of the cardiovascular and/or pulmonary systems that determine O2 delivery and diffusion to the exercising muscles did not change with changing intensity, with the exception of VO2 slow component kinetics metabolic profiles. PMID:25045690
Chemical and sonochemical approaches to the formation of VO{sub 2} films and VO{sub 2}-impregnated materials
Keppens, V.; Mandrus, D.; Boatner, L.A.
A new chemical and chemical/ultrasonic approach to the preparation of VO{sub 2} films and VO{sub 2}-impregnated bulk materials has been developed. In this approach, a V{sub 2}O{sub 5} sol prepared by quenching is used to coat SiO{sub 2} substrates. The resulting gel-film is heat treated in a reducing atmosphere to form a film identified as VO{sub 2} from the results of X-ray diffraction and both optical and resistivity measurements, which reveal the phase transition characteristic of vanadium dioxide. The advantage of this approach to the formation of VO{sub 2} is that the V{sub 2}O{sub 5} sol can be used to impregnate porous materials, which are then heated treated to form an optically active composite material. The switching properties of the VO{sub 2} films are investigated using optical and resistivity measurements, and the results are compared to those obtained for VO{sub 2}-films prepared by more-conventional methods.
VO-Dance an IVOA tools to easy publish data into VO and it's extension on planetology request
NASA Astrophysics Data System (ADS)
Smareglia, R.; Capria, M. T.; Molinaro, M.
Data publishing through the self standing portals can be joined to VO resource publishing, i.e. astronomical resources deployed through VO compliant services. Since the IVOA (International Virtual Observatory Alliance) provides many protocols and standards for the various data flavors (images, spectra, catalogues … ), and since the data center has as a goal to grow up in number of hosted archives and services providing, the idea arose to find a way to easily deploy and maintain VO resources. VO-Dance is a java web application developed at IA2 that addresses this idea creating, in a dynamical way, VO resources out of database tables or views. It is structured to be potentially DBMS and platform independent and consists of 3 main tokens, an internal DB to store resources description and model metadata information, a restful web application to deploy the resources to the VO community. It's extension to planetology request is under study to best effort INAF software development and archive efficiency.
The Effect of Habitual Smoking on VO2max
NASA Technical Reports Server (NTRS)
Wier, Larry T.; Suminski, Richard R.; Poston, Walker S.; Randles, Anthony M.; Arenare, Brian; Jackson, Andrew S.
VO2max is associated with many factors, including age, gender, physical activity, and body composition. It is popularly believed that habitual smoking lowers aerobic fitness. PURPOSE: to determine the effect of habitual smoking on VO2max after controlling for age, gender, activity and BMI. METHODS: 2374 men and 375 women employed at the NASA/Johnson Space Center were measured for VO2max by indirect calorimetry (RER>=1.1), activity by the 11 point (0-10) NASA Physical Activity Status Scale (PASS), BMI and smoking pack-yrs (packs day*y of smoking). Age was recorded in years and gender was coded as M=1, W=0. Pack.y was made a categorical variable consisting of four levels as follows: Never Smoked (0), Light (1-10), Regular (11-20), Heavy (>20). Group differences were verified by ANOVA. A General Linear Models (GLM) was used to develop two models to examine the relationship of smoking behavior on VO2max. GLM #1(without smoking) determined the combined effects of age, gender, PASS and BMI on VO2max. GLM #2 (with smoking) determined the added effects of smoking (pack.y groupings) on VO2max after controlling for age, gender, PASS and BMI. Constant errors (CE) were calculated to compare the accuracy of the two models for estimating the VO2max of the smoking subgroups. RESULTS: ANOVA affirmed the mean VO2max of each pack.y grouping decreased significantly (p<0.01) as the level of smoking exposure increased. GLM #1 showed that age, gender, PASS and BMI were independently related with VO2max (R2 = 0.642, SEE = 4.90, p<0.001). The added pack.y variables in GLM #2 were statistically significant (R2 change = 0.7%, p<0.01). Post hoc analysis showed that compared to Never Smoked, the effects on VO2max from Light and Regular smoking habits were -0.83 and -0.85 ml.kg- 1.min-1 respectively (p<0.05). The effect of Heavy smoking on VO2max was -2.56 ml.kg- 1.min-1 (p<0.001). The CE s of each smoking group in GLM #2 was smaller than the CE s of the smoking group counterparts in GLM #1
One-step hydrothermal conversion of VO2(B) into W-doped VO2(M) and its phase transition and optical switching properties
NASA Astrophysics Data System (ADS)
Zhang, Yifu; Zhang, Xiongzhi; Huang, Yu; Huang, Chi; Niu, Fei; Meng, Changgong; Tan, Xiaoyu
W-doped monoclinic vanadium dioxide VO2(M) nanobelts have been transformed from VO2(B) nanobelts in the presence of tungstic acid by a facile one-step hydrothermal route for the first time. The as-prepared samples were characterized by X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and variable-temperature infrared spectroscopy (IR). The results show that W atoms are doped into the crystal lattice of VO2(M) matrix, and the morphology and size of the as-obtained VO2(M) nanobelts are dependent on that of the precursor VO2(B). The phase transition temperature (Tc) of W-doped VO2(M) can be tuned by W doping. The variable-temperature IR reveals that the as-synthesized W-doped VO2(M) nanobelts have outstanding thermochromic characters and optical switching properties.
Thermochromic characteristics of Ti-doped VO2 thin film
NASA Astrophysics Data System (ADS)
Lee, Hwasoo; Ko, Kyung Hyun; Choi, Jun Oh
Utilizing metal-to-insulator transition (MIT) properties of V-oxide film, stable VO2 phase is necessary. In sputtering deposition of VO2, simple target preparation and high deposition rate are recommendable. For this, VO2 film was deposited on quartz substrate by RF magnetron sputter system under low working pressure using V2O5 target. Due to the lower sputtering yield of oxygen compared to vanadium, oxygen ion contents is usually deficient from that of target. So, the reduction of V ions was a result of charge compensation with the oxygen ions. Under lower working pressure, deposition rate become higher so that this deficiency is getting larger to cause further reduction to destabilize VO2. Preventing this, titanium oxide co-deposition was suggested to enrich oxygen source. When TiO2 was used, Ti ion has stable +4 charge state so that extra oxygen sputtered prevents V ion reduction below +4 state. But, in case of TiO, Ti ions were oxidized from +2 to +3 and +4 state and V ions with less oxidation potential should be reduced to +3 or so. Pure VO2 film had MIT at 66°C and large resistivity ratio of 4 orders of magnitude from 30°C to 90°C. Under low working pressure, (V2O5 + TiO2) system yield fairly good films, while films with poor or absence of MIT were produced with TiO case.
Proposal of Secure VoIP System Using Attribute Certificate
NASA Astrophysics Data System (ADS)
Kim, Jin-Mook; Jeong, Young-Ae; Hong, Seong-Sik
VoIP is a service that changes the analogue audio signal into a digital signal and then transfers the audio information to the users after configuring it as a packet; and it has an advantage of lower price than the existing voice call service and better extensibility. However, VoIP service has a system structure that, compared to the existing PSTN (Public Switched Telephone Network), has poor call quality and is vulnerable in the security aspect. To make up these problems, TLS service was introduced to enhance the security. In practical system, however, since QoS problem occurs, it is necessary to develop the VoIP security system that can satisfy QoS at the same time in the security aspect. In this paper, a user authentication VoIP system that can provide a service according to the security and the user through providing a differential service according to the approach of the users by adding AA server at the step of configuring the existing VoIP session is suggested. It was found that the proposed system of this study provides a quicker QoS than the TLS-added system at a similar level of security. Also, it is able to provide a variety of additional services by the different users.
Synthesis, characterization and formation mechanism of metastable phase VO{sub 2}(A) nanorods
Cheng, X.H.; Xu, H.F.; Wang, Z.Z.; Zhu, K.R.; Li, G.; Jin, Shaowei
Graphical abstract: - Highlights: • Pure phases of VO{sub 2}(B) and VO{sub 2}(A) were prepared by a facile hydrothermal method. • Belt-like particles prepared at 180 °C was indexed as monoclinic VO{sub 2}(B) phase. • Rod-like particles prepared at 230 °C was indexed as tetragonal VO{sub 2}(A) phase. • VO{sub 2}(A) nanorods resulted from VO{sub 2}(B) nanobelts by assembly and crystal adjustment. - Abstract: Pure phase VO{sub 2}(A) nanorods were synthesized via the reduction of V{sub 2}O{sub 5} by oxalic acid during the hydrothermal treatment. Two sets of samples were prepared by varying both system temperature and reaction time under a filling ratio of 0.40 for observing the formation and evolution of VO{sub 2}(A) nanorods. Structures were characterized by X-ray diffraction, scanning and transmission electron microscopies, respectively. It was found that VO{sub 2}(B) was firstly formed and then transformed into VO{sub 2}(A) as the increasing system temperature or extending reaction time. An assembling and following crystal adjustment was proposed for explanation the formation process of VO{sub 2}(A) from VO{sub 2}(B). For VO{sub 2}(A) nanorods, the phase transition temperature of 169.7 °C was higher than that of the VO{sub 2}(A) bulk, it might be ascribed to the lower crystallinity or nonstoichiometry in VO{sub 2}(A) nanorods. VO{sub 2} nanostructures with controllable phases and properties should find their promising applications in a single VO{sub 2} nanodevice.
Relationship between body and leg VO2 during maximal cycle ergometry
NASA Technical Reports Server (NTRS)
Knight, D. R.; Poole, D. C.; Schaffartzik, W.; Guy, H. J.; Prediletto, R.; Hogan, M. C.; Wagner, P. D.
It is not known whether the asymptotic behavior of whole body O2 consumption (VO2) at maximal work rates (WR) is explained by similar behavior of VO2 in the exercising legs. To resolve this question, simultaneous measurements of body and leg VO2 were made at submaximal and maximal levels of effort breathing normoxic and hypoxic gases in seven trained male cyclists (maximal VO2, 64.7 +/- 2.7 ml O2.min-1.kg-1), each of whom demonstrated a reproducible VO2-WR asymptote during fatiguing incremental cycle ergometry. Left leg blood flow was measured by constant-infusion thermodilution, and total leg VO2 was calculated as the product of twice leg flow and radial arterial-femoral venous O2 concentration difference. The VO2-WR relationships determined at submaximal WR's were extrapolated to maximal WR as a basis for assessing the body and leg VO2 responses. The differences between measured and extrapolated maximal VO2 were 235 +/- 45 (body) and 203 +/- 70 (leg) ml O2/min (not significantly different). Plateauing of leg VO2 was associated with, and explained by, plateauing of both leg blood flow and O2 extraction and hence of leg VO2. We conclude that the asymptotic behavior of whole body VO2 at maximal WRs is a direct reflection of the VO2 profile at the exercising legs.
Direct synthesis of thermochromic VO{sub 2} through hydrothermal reaction
Alie, David; Gedvilas, Lynn; Wang, Zhiwei; Tenent, Robert; Engtrakul, Chaiwat; Yan, Yanfa; Shaheen, Sean E.; Dillon, Anne C.; Ban, Chunmei
Thermochromic VO{sub 2} was directly synthesized using hydrothermal techniques. The effects of formation conditions on the structure and morphology of the final product were studied through X-ray diffraction (XRD), and scanning electron microscopy (SEM). Unique hollow sphere morphology was observed for the synthesized VO{sub 2} powders. Ex-situ XRD studies after heat treatment confirmed the thermal stability of the VO{sub 2} structure. Thermochromic properties, as a consequence of the reversible structural transformation between monoclinic VO{sub 2} and tetragonal phases, were observed by Fourier transform infrared spectroscopy (FTIR). - Graphical abstract: Thermochromic VO{sub 2} crystals with hollow spherical and asterisk shape were directly synthesized using hydrothermal techniques. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) studies confirmed the thermal stability and the reversible thermochromic properties of the VO{sub 2} structure. - Highlights: • One-step synthesis of thermochromic VO{sub 2} monoclinic phase, and VO{sub 2} (A and B phases) using hydrothermal technique. VO{sub 2} (A), VO{sub 2} (B). • Identification of the relationship between synthesis conditions and the morphology/structure of the final products. • Formation of VO{sub 2} monoclinic phase with an interesting hollow sphere shape. • Demonstration of superior thermal stability of the VO{sub 2} monoclinic phase. • Characterizing the thermochromic properties of VO{sub 2} monoclinic phase.
Solution-processed phase-change VO(2) metamaterials from colloidal vanadium oxide (VO(x)) nanocrystals.
Paik, Taejong; Hong, Sung-Hoon; Gaulding, E Ashley; Caglayan, Humeyra; Gordon, Thomas R; Engheta, Nader; Kagan, Cherie R; Murray, Christopher B
We demonstrate thermally switchable VO2 metamaterials fabricated using solution-processable colloidal nanocrystals (NCs). Vanadium oxide (VOx) NCs are synthesized through a nonhydrolytic reaction and deposited from stable colloidal dispersions to form NC thin films. Rapid thermal annealing transforms the VOx NC thin films into monoclinic, nanocrystalline VO2 thin films that show a sharp, reversible metal-insulator phase transition. Introduction of precise concentrations of tungsten dopings into the colloidal VOx NCs enables the still sharp phase transition of the VO2 thin films to be tuned to lower temperatures as the doping level increases. We fabricate "smart", differentially doped, multilayered VO2 films to program the phase and therefore the metal-insulator behavior of constituent vertically structured layers with temperature. With increasing temperature, we tailored the optical response of multilayered films in the near-IR and IR regions from that of a strong light absorber, in a metal-insulator structure, to that of a Drude-like reflector, characteristic of a pure metallic structure. We demonstrate that nanocrystal-based nanoimprinting can be employed to pattern multilayered subwavelength nanostructures, such as three-dimensional VO2 nanopillar arrays, that exhibit plasmonic dipolar responses tunable with a temperature change. PMID:24377298
Europlanet IDIS: Connecting Planetary Science VO Services with SAMP
NASA Astrophysics Data System (ADS)
Cecconi, Baptiste; Jacquey, Christian; Erard, Stéphane; Le Sidaner, Pierre; Andre, Nicolas; Bourrel, Nataliya; Berthier, Jerome; Gangloff, Michel; Renard, Benjamin; Hitier, Richard
IDIS (Integrated and Distributed Information System) is part of the Europlanet project. Its purpose is to develop a prototype of a planetology Virtual Observatory (VO). In the frame of its participation to this project, and in collaboration with VO-Paris (Virtual Observatory Paris Data Centre), the CDPP (Data Centre for Plasma Physics, based in Toulouse) has developed tools to describe, query and access data in the frame of Planetary Sciences. In particular, SAMP (Simple Application Messaging Protocol) has been used to connect the new services with existing tools such as Aladin, VOSpec, SPlat or TOPCAT. We present here a few examples and prototypes of VO integration success for Planetary Sciences. The EuroPlaNet-RI project is funded by the European Commission under the 7th Framework Program, grant 228319 "Capacities Specific Programme".
Successive phase transitions in the orthovanadate TmVO3
NASA Astrophysics Data System (ADS)
Sarkar, Tapati; Ivanov, Sergey A.; Bazuev, G. V.; Nordblad, Per; Mathieu, Roland
Synthesis and crystal structure, magnetization and heat capacity measurements of phase pure polycrystalline TmVO3 are reported. TmVO3 was stabilized in the orthorhombic structure by thermal treatment of the precursor TmVO4 in a reducing atmosphere. Magnetization and heat capacity measurements reveal the presence of several successive structural and magnetic phase transitions in this compound. At T = 108 K, the sample undergoes a transition from a paramagnetic state to an antiferromagnetic state, followed by a second transition at 78 K which is related to spin and orbital reorientation. The heat capacity measurements reveal the presence of a third transition in the paramagnetic state (at T = 175 K), which corresponds to a structural phase transition and orbital ordering. At low temperatures (~15 K) and weak fields, there is an anomaly in the magnetization, which may be associated with antiferromagnetic short range ordering of the Tm3+ ions.
Spectroscopic characteristics of GdVO4: Dy3+ crystal
NASA Astrophysics Data System (ADS)
Ning, Kaijie; He, Xiaoming; Zhang, Lianhan; Liu, Youchen; Yin, Jigang; Zhang, Peixing; Chen, Guangzhu; Wang, Xiangyong; Chen, Zhe; Shi, Chunjun; Hong, Jiaqi; Hang, Yin
Room temperature optical absorption, emission spectrum of GdVO4: Dy3+ crystal grown by Czochralski (CZ) method were measured and analyzed. Spectral parameters were calculated in the framework of the Judd-Ofelt theory. The GdVO4: Dy3+ crystal showed two intense and relatively broad absorption bands in UV wavelength range centered at 390 and 453 nm and two prominent emission peaks located at blue 485 and yellow 575 nm. The corresponding absorption and emission cross sections were estimated and the luminescence decay curve was analyzed. Optical spectroscopy investigations indicate that GdVO4: Dy3+ crystal would be a promising blue and yellow solid state laser material.
Phase stabilization of VO2 thin films in high vacuum
NASA Astrophysics Data System (ADS)
Zhang, Hai-Tian; Eaton, Craig; Ye, Hansheng; Engel-Herbert, Roman
A new growth approach to stabilize VO2 on Al2O3 in high vacuum is reported by reducing vanadium oxytriisopropoxide (VTIP) with vanadium metal. Phase stabilization and surface wetting behavior were studied as a function of growth parameters. The flux balance of VTIP to V in combination with growth temperature was identified to be critical for the growth of high quality VO2 thin films. High V fluxes were required to suppress the island formation and to ensure a coalesced film, while too high V fluxes ultimately favored the formation of the undesired, epitaxially stabilized V2O3 phase. Careful optimization of growth temperature, VTIP to V ratio, and growth rate led to high quality single phase VO2 thin films with >3.5 orders of magnitude change in resistivity across the metal-to-insulator transition. This approach opens up another synthesis avenue to stabilize oxide thin films into desired phases.
Thermochromic VO2 on Zinnwaldite Mica by pulsed laser deposition
NASA Astrophysics Data System (ADS)
Mathevula, L.; Ngom, B. D.; Kotsedi, L.; Sechogela, P.; Doyle, T. B.; Ghouti, M.; Maaza, M.
VO2 thin films have been deposited by pulsed laser deposition on Zinnwaldite Mica substrates. The crystal structure, chemical composition, morphology were determined and the semiconductor/metal transition (SMT) properties of the deposited films were investigated. Without any post annealing, the films exhibit a textured nature with a VO2 (0 1 1) preferred crystallographic orientation and an elevated thermal variation of the electric resistance ratio RS/RM through the SMT at T ≈ 68 °C of the order of 104 and a narrow ∼7 °C hysteresis. In addition, the growth of the VO2 crystallites seem to be governed likely by a Volmer-Weber or Stranski-Krastanov mechanisms and certainly not a Frank-van Der Merwe process.
The NOAO NVO Portal: Client-Side VO
NASA Astrophysics Data System (ADS)
Gasson, D.; Fuentes, E.; Miller, C. J.
The NOAO National Virtual Observatory (NVO) portal is a recently deployed web application for one-stop discovery, analysis, and access to VO-compliant imaging data and services. The NOAO NVO portal utilizes Simple Image Access Protocol (SIAP) services provided by some astronomical archives. The portal also utilizes a number of SOAP-based VO web services (WESIX, Sesame, etc). We discuss the design decisions and technology choices that were made in the NOAO NVO portal code to facilitate the use of IVOA standards and VO data/services. This includes a new Virtual Observatory library written for Ruby: an interpreted scripting language for quick and easy object-oriented programming. We provide an overview of VORuby and how it is utilized in the NOAO NVO Portal.
Accuracy of the VO2peak prediction equation in firefighters
Background A leading contributing factor to firefighter injury and death is lack of fitness. Therefore, the Fire Service Joint Labor Management Wellness-Fitness Initiative (WFI) was established that includes a focus on providing fitness assessments to all fire service personnel. The current fitness assessment includes a submaximal exercise test protocol and associated prediction equation to predict individual VO2peak as a measure of fitness. There is limited information on the accuracy, precision, and sources of error of this prediction equation. This study replicated previous research by validating the accuracy of the WFI VO2peak prediction equation for a group of firefighters and further examining potential sources of error for an individual firefighters' assessment. Methods The sample consisted of 22 firefighters who completed a maximal exercise test protocol similar to the WFI submaximal protocol, but the test was terminated when firefighters reached a maximal level of exertion (i.e., measured VO2peak). We then calculated the predicted VO2peak based on the WFI prediction equation along with individual firefighters' body mass index (BMI) and 85% of maximum heart rate. The data were analyzed using paired samples t-tests in SPSS v. 21.0. Results The difference between predicted and measured VO2peak was -0.77 ± 8.35 mL•kg-1•min-1. However, there was a weak, statistically non-significant association between measured VO2peak and predicted VO2peak (R2 = 0.09, F(1,21) = 2.05, p = 0.17). The intraclass correlation coefficient (ICC = 0.215, p > 0.05) and Pearson (r = 0.31, p = 0.17) and Spearman (ρ = 0.28, p = 0.21) correlation coefficients were small. The standard error of the estimate (SEE) was 8.5 mL•kg-1•min-1. Further, both age and baseline fitness level were associated with increased inaccuracy of the prediction equation. Conclusions We provide data on the inaccuracy and sources of error for the WFI VO2peak
Lattice effects in HoVo 3 single crystal
NASA Astrophysics Data System (ADS)
Sikora, M.; Marquina, C.; Ibarra, M. R.; Nugroho, A. A.; Palstra, T. T. M.
We report the study of lattice effects in the Mott insulator HoVO 3 performed by means of linear thermal expansion on a single crystal in the temperature range 10-290 K. The holmium orthovanadate HoVO 3 reveals gradual orbital ordering (OO) below TOO=200 K and orders antiferromagnetically at TN=113 K. A first-order structural phase transition takes place at TS˜38 K, which is probably accompanied by change of the OO type and hence the type of antiferromagnetic spin ordering.
Infrared-sensitive electrochromic device based on VO2
NASA Astrophysics Data System (ADS)
Nakano, M.; Shibuya, K.; Ogawa, N.; Hatano, T.; Kawasaki, M.; Iwasa, Y.; Tokura, Y.
The field-effect transistor (FET) provides an electrical switching function of current flowing through a channel surface by external voltage. Here, we report on a field-effect device that enables electrical switching of optical transmittance as well as conventional electrical current. We investigated optical properties of vanadium dioxide (VO2) thin film under the presence of electric field generated at the interface between VO2 and ionic liquid in a FET geometry, and found that the device exhibits clear electrochromic effect with large ON/OFF contrast only in the infrared region, potentially beneficial for energy-saving smart window applications as a voltage-tunable transparent heat-cutting filter.
RegTAP - a New API to the VO Registry
NASA Astrophysics Data System (ADS)
Demleitner, M.
The Virtual Observatory (VO) Registry is a comprehensive directory of astronomical services maintained collaboratively by major data centers across the globe. Until now, the API to the Registry as used by clients and users relied on several outdated standards, and has interoperability issues with more advanced queries. With RegTAP, there is now a relational schema exposed via the VO's Table Access Protocol as implemented by many clients, and several compliant services already exist. While many users will just use UIs operating RegTAP , both advanced users and client authors will want to directly operate the API. This paper provides an overview of RegTAP.
Phase Transformation of VO2 Nanoparticles Assisted by Microwave Heating
Sikong, Lek.
The microwave assisted synthesis nowadays attracts a great deal of attention. Monoclinic phase VO2 (M) was prepared from NH4VO3 and H2C2O4 · 2H2O by a rapid microwave assisted technique. The synthesis parameters, microwave irradiation time, microwave power, and calcinations temperature were systematically varied and their influences on the structure and morphology were evaluated. The microwave power level has been carried out in range 180–600 W. TEM analysis demonstrated nanosized samples. The structural and morphological properties were measured using XRD, TEM, and thermal analyses. The variations of vanadium phase led to thermochromic properties. PMID:24688438
Urchin-like m-LaVO{sub 4} and m-LaVO{sub 4}/Ag microspheres: Synthesis and characterization
Chen, Limiao; Wu, Min; Wang, Dan; Zhou, Le; Yu, Na; Zhang, Peisen; Huang, Jianhan; Liu, Xiaohe; Qiu, Guanzhou
The semiconductor nanostructures decorated with noble metals have attracted increasing attention due to their interesting physical and chemical properties. In this work, urchin-like monoclinic (m-) LaVO{sub 4} microspheres were prepared by a hydrothermal method and used as a template to fabricate Ag nanoparticle-decorated m-LaVO{sub 4} composites. The morphology and structure were characterized by transmission electron microscope, high-resolution transmission electron microscope, scanning electron microscope, and energy-dispersive X-ray. It was found that Ag nanoparticles with narrow size distribution were uniformly loaded on urchin-like m-LaVO{sub 4} microspheres, and the resulted composite microspheres showed distinct surface plasmon absorption band compared to pure m-LaVO{sub 4} microspheres. Photocatalytic activities of as-prepared samples were examined by studying the degradation of methyl orange solutions under visible-light irradiation (> 400 nm). Results clearly showed that urchin-like m-LaVO{sub 4}/Ag microspheres possess much higher photocatalytic activity than pure m-LaVO{sub 4} microspheres and P25. - Highlights: • m-LaVO{sub 4}/Ag composites microspheres were fabricated by a hydrothermal method. • m-LaVO{sub 4} microspheres show higher photocatalytic activity than m-LaVO{sub 4} microspheres. • m-LaVO{sub 4}/Ag microspheres exhibit a good stability.
Time-resolved emission spectroscopy of gadolinium vanadate ceramics (GdVO4:Bi3+)
NASA Astrophysics Data System (ADS)
Leppert, J.; Peudenier, S.; Bayer, E.; Grabmaier, B. C.; Blasse, G.
The preparation of GdVO4:Bi3+ ceramics is indicated. Bismuth shows a strong tendency to evaporate during the sintering process. Time-resolved emission spectroscopy shows for sufficiently low Bi3+ concentrations subsequently: blue VO{4/3-}emission with a decay time corresponding to the transfer rate (106 s-1), yellow VO{4/3-}-Bi3+ emission, rare-earth impurity emission and VO{4/3-}-Bi3+ afterglow.
Estimation of VO2 Max: A Comparative Analysis of Five Exercise Tests.
ERIC Educational Resources Information Center
Zwiren, Linda D.; And Others
Thirty-eight healthy females measured maximal oxygen uptake (VO2max) on the cycle ergometer and treadmill to compare five exercise tests (run, walk, step, and two tests using heart-rate response on the bicycle ergometer) in predicting VO2max. Results indicate that walk and run tests are satisfactory predictors of VO2max in 30- to 39-year-old…
Matching of Male and Female Subjects Using VO2 Max.
ERIC Educational Resources Information Center
Cureton, Kirk J.
The increasing use of various VO2 max expressions as test measures is a problem because the magnitude of sex difference varies considerably with each expression. A valid match of male and female test subjects would consider physical activity history and the amount of endurance exercise done in the previous year. (Author/FG)
Direct and continuous synthesis of VO2 nanoparticles.
Powell, M J; Marchand, P; Denis, C J; Bear, J C; Darr, J A; Parkin, I P
Monoclinic VO2 nanoparticles are of interest due to the material's thermochromic properties, however, direct synthesis routes to VO2 nanoparticles are often inaccessible due to the high synthesis temperatures or long reaction times required. Herein, we present a two-step synthesis route for the preparation of monoclinic VO2 nanoparticles using Continuous Hydrothermal Flow Synthesis (CHFS) followed by a short post heat treatment step. A range of particle sizes, dependent on synthesis conditions, were produced from 50 to 200 nm by varying reaction temperatures and the residence times in the process. The nanoparticles were characterised by powder X-ray diffraction, Raman and UV/Vis spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The nanoparticles were highly crystalline with rod and sphere-like morphologies present in TEM micrographs, with the size of both the rod and spherical particles being highly dependent on both reaction temperature and residence time. SEM micrographs showed the surface of the powders produced from the CHFS process to be highly uniform. The samples were given a short post synthesis heat treatment to ensure that they were phase pure monoclinic VO2, which led to them exhibiting a large and reversible switch in optical properties (at near-IR wavelengths), which suggests that if such materials can be incorporated into coatings or in composites, they could be used for fenestration in architectural applications. PMID:26497868
Direct and continuous synthesis of VO2 nanoparticles
NASA Astrophysics Data System (ADS)
Powell, M. J.; Marchand, P.; Denis, C. J.; Bear, J. C.; Darr, J. A.; Parkin, I. P.
Monoclinic VO2 nanoparticles are of interest due to the material's thermochromic properties, however, direct synthesis routes to VO2 nanoparticles are often inaccessible due to the high synthesis temperatures or long reaction times required. Herein, we present a two-step synthesis route for the preparation of monoclinic VO2 nanoparticles using Continuous Hydrothermal Flow Synthesis (CHFS) followed by a short post heat treatment step. A range of particle sizes, dependent on synthesis conditions, were produced from 50 to 200 nm by varying reaction temperatures and the residence times in the process. The nanoparticles were characterised by powder X-ray diffraction, Raman and UV/Vis spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The nanoparticles were highly crystalline with rod and sphere-like morphologies present in TEM micrographs, with the size of both the rod and spherical particles being highly dependent on both reaction temperature and residence time. SEM micrographs showed the surface of the powders produced from the CHFS process to be highly uniform. The samples were given a short post synthesis heat treatment to ensure that they were phase pure monoclinic VO2, which led to them exhibiting a large and reversible switch in optical properties (at near-IR wavelengths), which suggests that if such materials can be incorporated into coatings or in composites, they could be used for fenestration in architectural applications.
Covert Channels in SIP for VoIP Signalling
NASA Astrophysics Data System (ADS)
Mazurczyk, Wojciech; Szczypiorski, Krzysztof
In this paper, we evaluate available steganographic techniques for SIP (Session Initiation Protocol) that can be used for creating covert channels during signaling phase of VoIP (Voice over IP) call. Apart from characterizing existing steganographic methods we provide new insights by introducing new techniques. We also estimate amount of data that can be transferred in signalling messages for typical IP telephony call.
A minimal model for the structural energetics of VO2
NASA Astrophysics Data System (ADS)
Kim, Chanul; Marianetti, Chris; The Marianetti Group Team
Resolving the structural, magnetic, and electronic structure of VO2 from the first-principles of quantum mechanics is still a forefront problem despite decades of attention. Hybrid functionals have been shown to qualitatively ruin the structural energetics. While density functional theory (DFT) combined with cluster extensions of dynamical mean-field theory (DMFT) have demonstrated promising results in terms of the electronic properties, structural phase stability has not yet been addressed. In order to capture the basic physics of the structural transition, we propose a minimal model of VO2 based on the one dimensional Peierls-Hubbard model and parameterize this based on DFT calculations of VO2. The total energy versus dimerization in the minimal mode is then solved numerically exactly using density matrix renormalization group (DMRG) and compared to the Hartree-Fock solution. We demonstrate that the Hartree-Fock solution exhibits the same pathologies as DFT+U, and spin density functional theory for that matter, while the DMRG solution is consistent with experimental observation. Our results demonstrate the critical role of non-locality in the total energy, and this will need to be accounted for to obtain a complete description of VO2 from first-principles. The authors acknowledge support from FAME, one of six centers of STARnet, a Semiconductor Research Corporation program sponsored by MARCO and DARPA.
Optical diffraction in ordered VO2 nanoparticle arrays
NASA Astrophysics Data System (ADS)
Lopez, Rene; Feldman, Leonard; Haglund, Richard
The potential of oxide electronic materials as multifunctional building blocks is one of the driving concepts of the field. In this presentation, we show how nanostructured particle arrays with long-range order can be used to modulate an optical response through exploiting the metal-insulator transition of vanadium dioxide. Arrays of VO2 nanoparticles with long-range order were fabricated by pulsed laser deposition in an arbitrary pattern defined by focused ion-beam lithography. The interaction of light with the nanoparticles is controlled by the nanoparticle size, spacing and geometrical arrangement and by switching between the metallic and semiconducting phases of VO2. In addition to the near-infrared surface plasmon response observed in previous VO2 studies, the VO2 nanoparticle arrays exhibit size-dependent optical resonances in the visible region that likewise show an enhanced optical contrast between the semiconducting and metallic phases. The collective optical response as a function of temperature gives rise to an enhanced scattering state during the evolving phase transition, while the incoherent coupling between the nanoparticles produces an order-disorder-order transition.
Magnetic and Ferroelectric Anisotropy in Multiferroic FeVO4
NASA Astrophysics Data System (ADS)
Abdelhamid, Ehab; Dixit, Ambesh; Kimura, Kenta; Kimura, Tsuyoshi; Jayakumar, Onattu; Naik, Vaman; Naik, Ratna; Lawes, Gavin; Nadgorny, Boris
FeVO4 has been studied as a model system for understanding the magnetoelectric interaction mechanisms in low symmetry multiferroics. Triclinic FeVO4 is characterized by two antiferromagnetic phase transitions, occurring at TN 1 = 22 K and TN 2 = 15 K, with the latter transition signaling a break in the space inversion symmetry, accompanied by the development of a non-collinear magnetic order which induces ferroelectricity. Earlier measurements on polycrystalline FeVO4 doped with magnetic (Cr and Mn) as well as non magnetic (Zn) dopants indicate the stability of the two antiferromagnetic transition temperatures. In this work, single crystals of both undoped and doped FeVO4 were grown from flux. To track the changes in lattice parameters induced by changing the doping concentration (measured by EDAX), XRD and Raman spectra were obtained. By recording the magnetization along two different crystal orientations, we were able to confirm the easy magnetic axis in this structure. Finally, we obtain the crystal's ferroelectric polarization along two different directions in an attempt to further understand the mechanism responsible for the ferroelectric transition. This work is supported by the NSF under DMR-1306449.
Multi-VO support in IHEP's distributed computing environment
NASA Astrophysics Data System (ADS)
Yan, T.; Suo, B.; Zhao, X. H.; Zhang, X. M.; Ma, Z. T.; Yan, X. F.; Lin, T.; Deng, Z. Y.; Li, W. D.; Belov, S.; Pelevanyuk, I.; Zhemchugov, A.; Cai, H.
Inspired by the success of BESDIRAC, the distributed computing environment based on DIRAC for BESIII experiment, several other experiments operated by Institute of High Energy Physics (IHEP), such as Circular Electron Positron Collider (CEPC), Jiangmen Underground Neutrino Observatory (JUNO), Large High Altitude Air Shower Observatory (LHAASO) and Hard X-ray Modulation Telescope (HXMT) etc, are willing to use DIRAC to integrate the geographically distributed computing resources available by their collaborations. In order to minimize manpower and hardware cost, we extended the BESDIRAC platform to support multi-VO scenario, instead of setting up a self-contained distributed computing environment for each VO. This makes DIRAC as a service for the community of those experiments. To support multi-VO, the system architecture of BESDIRAC is adjusted for scalability. The VOMS and DIRAC servers are reconfigured to manage users and groups belong to several VOs. A lightweight storage resource manager StoRM is employed as the central SE to integrate local and grid data. A frontend system is designed for user's massive job splitting, submission and management, with plugins to support new VOs. A monitoring and accounting system is also considered to easy the system administration and VO related resources usage accounting.
Pressure-induced transformations in PrVO4 and SmVO4 and isolation of high-pressure metastable phases.
Errandonea, Daniel; Achary, S Nagabhusan; Pellicer-Porres, Julio; Tyagi, Avesh K
Zircon-type PrVO4 and SmVO4 have been studied by high-pressure Raman spectroscopy up to 17 GPa. The occurrence of phase transitions has been detected when compression exceeds 6 GPa. The transformations are not reversible. Raman spectra of the high-pressure phases show similarities with those expected for a monazite-type phase in PrVO4 and a scheelite-type phase in SmVO4.The high-pressure phases have been also synthesized using a large-volume press and recovered at ambient conditions. X-ray diffraction measurements of the metastable products recovered after decompression confirms the monazite (PrVO4) and scheelite (SmVO4) structures of the high-pressure phases. Based upon optical properties of the reported new polymorphs, novel applications for rare-earth vanadates are proposed, including photocatalytic hydrogen production. PMID:23600563
Visible light driven photocatalysis and antibacterial activity of AgVO{sub 3} and Ag/AgVO{sub 3} nanowires
Singh, Anamika; Dutta, Dimple P.; Ballal, A.; Tyagi, A.K.; Fulekar, M.H.
Graphical abstract: - Highlights: • Ag/AgVO{sub 3} and pure AgVO{sub 3} nanowires synthesized by sonochemical process. • Characterization done using XRD, SEM, TEM, EDX and BET analysis. • Visible light degradation of RhB by Ag/AgVO{sub 3} within 45 min. • Antibacterial activity of Ag/AgVO{sub 3} demonstrated. - Abstract: Ag/AgVO{sub 3} nanowires and AgVO{sub 3} nanorods were synthesized in aqueous media via a facile sonochemical route. The as-synthesized products were characterized by X-ray diffraction, Brunauer–Emmett–Teller surface area analysis, scanning electron microscopy together with an energy dispersion X-ray spectrum analysis, transmission electron microscopy and UV–vis diffuse reflectance spectroscopy. The results revealed that inert atmosphere promotes the formation of Ag/AgVO{sub 3} nanowires. The photocatalytic studies revealed that the Ag/AgVO{sub 3} nanowires exhibited complete photocatalytic degradation of Rhodamine B within 45 min under visible light irradiation. The antibacterial activity of Ag/AgVO{sub 3} nanowires was tested against Escherechia coli and Bacillus subtilis. The minimum growth inhibitory concentration value was found to be 50 and 10 folds lower than for the antibiotic ciprofloxacin for E. coli and B. subtilis, respectively. The antibacterial properties of the β-AgVO{sub 3} nanorods prove that in case of the Ag dispersed Ag/AgVO{sub 3} nanowires, the enhanced antibacterial action is also due to contribution from the AgVO{sub 3} support.
Current Status of VO Compliant Data Service in Japanese Virtual Observatory
NASA Astrophysics Data System (ADS)
Shirasaki, Y.; Komiya, Y.; Ohishi, M.; Mizumoto, Y.; Ishihara, Y.; Tsutsumi, J.; Hiyama, T.; Nakamoto, H.; Sakamoto, M.
In these years, standards to build a Virtual Observatory (VO) data service have been established with the efforts in the International Virtual Observatory Alliance (IVOA). We applied these newly established standards (SSAP, TAP) to our VO service toolkit which was developed to implement earlier VO standards SIAP and (deprecated) SkyNode. The toolkit can be easily installed and provides a GUI interface to construct and manage VO service. In this paper, we describes the architecture of our toolkit and how it is used to start hosting VO service.
The ROI of VoIP: Everybody Says VoIP Saves Big Bucks. But Does It?
ERIC Educational Resources Information Center
Villano, Matt
Advocates of Voice over Internet Protocol (VoIP) say it saves money on long distance calls by sending them over the Internet, improves communication by eliminating the Private Branch Exchange (PBX), and offers a host of neat features such as call forwarding, e-mail accessible voicemail, and more. When it comes to measuring the dollars-and-cents…
Synthesis of novel photocatalytic RGO-InVO{sub 4} nanocomposites with visible light photoactivity
Shen, Jianfeng; Li, Xianfu; Huang, Weishi; Li, Na; Ye, Mingxin
Graphical abstract: A facile method for preparation of reduced graphene oxide (RGO) sheets supported indium vanadate (InVO{sub 4}) photocatalysts is reported. The visible light response and adsorption ability of RGO-InVO{sub 4} nanocomposites is greatly improved, which can effectively remove methyl orange and Cr (VI) from water. - Highlights: • Supramolecular photocatalyst of RGO-InVO{sub 4} was achieved. • Reduction of GO and preparation of RGO-InVO{sub 4} was simultaneous. • The prepared RGO-InVO{sub 4} shows high photocatalytic activity and adsorption capacity under visible light. • In situ growth of uniform InVO{sub 4} particles on RGO sheets is facile and efficient - Abstract: In this study, we report a facile method for preparation of reduced graphene oxide (RGO) sheets supported indium vanadate (InVO{sub 4}) photocatalysts. A wide range of characterization techniques, such as Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction, Thermogravimetric analysis and Transmission electron microscopy were applied to characterize the obtained composites. The results indicated that the composites consist of uniformly dispersed InVO{sub 4} nanocrystals on RGO sheets. Visible light responses of RGO-InVO{sub 4} nanocomposites are greatly improved as compared with the bulk InVO{sub 4}. The as-prepared RGO-InVO{sub 4} nanocomposites can effectively remove methyl orange and Cr (VI) from water under visible light irradiation, which can be used as novel photocatalysts for environmental protection.
Improving the Accuracy of Predicting Maximal Oxygen Consumption (VO2peak)
NASA Technical Reports Server (NTRS)
Downs, Meghan E.; Lee, Stuart M. C.; Ploutz-Snyder, Lori; Feiveson, Alan
Maximal oxygen (VO2pk) is the maximum amount of oxygen that the body can use during intense exercise and is used for benchmarking endurance exercise capacity. The most accurate method to determineVO2pk requires continuous measurements of ventilation and gas exchange during an exercise test to maximal effort, which necessitates expensive equipment, a trained staff, and time to set-up the equipment. For astronauts, accurate VO2pk measures are important to assess mission critical task performance capabilities and to prescribe exercise intensities to optimize performance. Currently, astronauts perform submaximal exercise tests during flight to predict VO2pk; however, while submaximal VO2pk prediction equations provide reliable estimates of mean VO2pk for populations, they can be unacceptably inaccurate for a given individual. The error in current predictions and logistical limitations of measuring VO2pk, particularly during spaceflight, highlights the need for improved estimation methods.
Improving the Accuracy of Predicting Maximal Oxygen Consumption (VO2pk)
NASA Technical Reports Server (NTRS)
Downs, Meghan E.; Lee, Stuart M. C.; Ploutz-Snyder, Lori; Feiveson, Alan
Maximal oxygen (VO2pk) is the maximum amount of oxygen that the body can use during intense exercise and is used for benchmarking endurance exercise capacity. The most accurate method to determineVO2pk requires continuous measurements of ventilation and gas exchange during an exercise test to maximal effort, which necessitates expensive equipment, a trained staff, and time to set-up the equipment. For astronauts, accurate VO2pk measures are important to assess mission critical task performance capabilities and to prescribe exercise intensities to optimize performance. Currently, astronauts perform submaximal exercise tests during flight to predict VO2pk; however, while submaximal VO2pk prediction equations provide reliable estimates of mean VO2pk for populations, they can be unacceptably inaccurate for a given individual. The error in current predictions and logistical limitations of measuring VO2pk, particularly during spaceflight, highlights the need for improved estimation methods.
Aqueous citrato-oxovanadate(IV) precursor solutions for VO2: synthesis, spectroscopic investigation and thermal analysis.
Peys, Nick; Adriaensens, Peter; Van Doorslaer, Sabine; Gielis, Sven; Peeters, Ellen; De Dobbelaere, Christopher; De Gendt, Stefan; Hardy, An; Van Bael, Marlies K
An aqueous precursor solution, containing citrato-VO(2+) complexes, is synthesized for the formation of monoclinic VO2. With regard to the decomposition of the VO(2+) complexes towards vanadium oxide formation, it is important to gain insights into the chemical structure and transformations of the precursor during synthesis and thermal treatment. Hence, the conversion of the cyclic [V4O12](4-) ion to the VO(2+) ion in aqueous solution, using oxalic acid as an acidifier and a reducing agent, is studied by (51)Vanadium nuclear magnetic resonance spectroscopy. The citrate complexation of this VO(2+) ion and the differentiation between a solution containing citrato-oxalato-VO(2+) and citrato-VO(2+) complexes are studied by electron paramagnetic resonance and Fourier transform infra-red spectroscopy. In both solutions, the VO(2+) containing complex is mononuclear and has a distorted octahedral geometry with a fourfold R-CO2(-) ligation at the equatorial positions and likely a fifth R-CO2(-) ligation at the axial position. Small differences in the thermal decomposition pathway between the gel containing citrato-oxalato-VO(2+) complexes and the oxalate-free gel containing citrato-VO(2+) complexes are observed between 150 and 200 °C in air and are assigned to the presence of (NH4)2C2O4 in the citrato-oxalato-VO(2+) solution. Both precursor solutions are successfully used for the formation of crystalline vanadium oxide nanostructures on SiO2, after thermal annealing at 500 °C in a 0.1% O2 atmosphere. However, the citrato-oxalato-VO(2+) and the oxalate-free citrato-VO(2+) solution result in the formation of monoclinic V6O13 and monoclinic VO2, respectively. PMID:25005054
VO2 thermochromic smart window for energy savings and generation
NASA Astrophysics Data System (ADS)
Zhou, Jiadong; Gao, Yanfeng; Zhang, Zongtao; Luo, Hongjie; Cao, Chuanxiang; Chen, Zhang; Dai, Lei; Liu, Xinling
The ability to achieve energy saving in architectures and optimal solar energy utilisation affects the sustainable development of the human race. Traditional smart windows and solar cells cannot be combined into one device for energy saving and electricity generation. A VO2 film can respond to the environmental temperature to intelligently regulate infrared transmittance while maintaining visible transparency, and can be applied as a thermochromic smart window. Herein, we report for the first time a novel VO2-based smart window that partially utilises light scattering to solar cells around the glass panel for electricity generation. This smart window combines energy-saving and generation in one device, and offers potential to intelligently regulate and utilise solar radiation in an efficient manner.
UkrVO Joint Digitized Archive and Scientific Prospects
NASA Astrophysics Data System (ADS)
Vavilova, I. B.; Pakuliak, L. K.; Protsyuk, Yu. I.; Shlyapnikov, A. A.; Savanevich, V. E.; Kondrashova, N. N.; Yatsenko, A. I.; Andruk, V. N.
The UkrVO (Ukrainian Virtual Observatory) database consists of about 200 000 astronomical photographic plates and 500 000 CCD frames containing unique astronomical information for formulating important scientific tasks. This database is compiled from observations conducted in 1898--2011 at the observing sites of 8 Ukrainian observatories, with about 60 instruments. This paper deals with some principal scientific projects where the UkrVO data\\-bases are used, namely, the creation of the Joint Digitized Archive (JDA); compilation of new stellar catalogues; search for optical counterparts of gamma-ray bursts; spectroscopic study of solar flares and solar active formations; development of software for searches for new small bodies of the solar system.
Applicability of Emerging Resource Discovery Standards to the VO
NASA Astrophysics Data System (ADS)
Dolensky, Markus
The Virtual Observatory (VO) will be one of the first applications belonging to a new generation of network services which are commonly referred to as the Semantic Web. As the name indicates the Semantic Web is supposed to represent its contents and usage in a systematic and decentralized way. In order to achieve this goal a number of new protocols and standards are currently defined. The Semantic Web is still in its early stages and therefore it is not surprising that there is a moderate number of evolving standards and systems out there with more or less comparable scope. It is the purpose of this paper to evaluate the applicability of a number of those evolving technologies to the VO.
Structural and physical properties of BiVO{sub 3}
Singh, M. P. Razavi, F. S.
We report the phase stabilization and properties of BiVO{sub 3} (BVO) thin films, grown on (001) SrTiO{sub 3} and LaAlO{sub 3}, using the pulsed laser deposition technique. Bi and V are in 3+ oxidation states as measured by using x-ray photoelectrons spectroscopy. BVO exhibits a Curie-Weiss paramagnetic behaviour and about −26 K Weiss temperature. This demonstrates the presence of a strong correlation effect due to the spin fluctuation. Additionally, these films exhibit a semiconducting behaviour owing to the thermally activated conduction process. A plausible explanation of the observed properties is presented by comparing with the closely related LaVO{sub 3} and other orthovanadates.
Bandwidth broker architecture for VoIP QoS
NASA Astrophysics Data System (ADS)
Kim, Keith; Mouchtaris, Petros; Samtani, Sunil; Talpade, Rajesh; Wong, Larry
We present a scalable architecture for assuring Quality of Service to VoIP applications in an Internet Service Provider's network. This architecture is based on the Differentiated Services and Bandwidth Broker models, and can also be used by other resource-sensitive applications. In this paper, we elaborate on a number of significant issues involved in the design, implementation, deployment and use of the Bandwidth Broker. The Call Agent architecture is used as the VoIP application. We describe the Bandwidth Broker prototype that is used to validate our approach. Our findings suggest that it is feasible to use the Bandwidth Broker architecture for assuring QoS, and a trade-off exists between the granularity of resource requests and call-setup delay.
VO2 thermochromic smart window for energy savings and generation
Zhou, Jiadong; Gao, Yanfeng; Zhang, Zongtao; Luo, Hongjie; Cao, Chuanxiang; Chen, Zhang; Dai, Lei; Liu, Xinling
The ability to achieve energy saving in architectures and optimal solar energy utilisation affects the sustainable development of the human race. Traditional smart windows and solar cells cannot be combined into one device for energy saving and electricity generation. A VO2 film can respond to the environmental temperature to intelligently regulate infrared transmittance while maintaining visible transparency, and can be applied as a thermochromic smart window. Herein, we report for the first time a novel VO2-based smart window that partially utilises light scattering to solar cells around the glass panel for electricity generation. This smart window combines energy-saving and generation in one device, and offers potential to intelligently regulate and utilise solar radiation in an efficient manner. PMID:24157625
Epitaxial growth of VO{sub 2} by periodic annealing
Tashman, J. W.; Paik, H.; Merz, T. A.; Lee, J. H.; Moyer, J. A.; Schiffer, P.; Misra, R.; Mundy, J. A.; Spila, T.; Schubert, J.; Muller, D. A.; Schlom, D. G.
We report the growth of ultrathin VO{sub 2} films on rutile TiO{sub 2} (001) substrates via reactive molecular-beam epitaxy. The films were formed by the cyclical deposition of amorphous vanadium and its subsequent oxidation and transformation to VO{sub 2} via solid-phase epitaxy. Significant metal-insulator transitions were observed in films as thin as 2.3 nm, where a resistance change ΔR/R of 25 was measured. Low angle annular dark field scanning transmission electron microscopy was used in conjunction with electron energy loss spectroscopy to study the film/substrate interface and revealed the vanadium to be tetravalent and the titanium interdiffusion to be limited to 1.6 nm.
In situ high-pressure synchrotron X-ray diffraction study of the structural stability in NdVO{sub 4} and LaVO{sub 4}
Errandonea, D.; Achary, S.N.; Tyagi, A.K.; Bettinelli, M.
Highlights: • NdVO{sub 4} and LaVO{sub 4} were studied under high pressure using synchrotron powder XRD. • Both compounds exhibit first-order phase transitions. • In NdVO{sub 4} the transition involves a symmetry breaking and in LaVO{sub 4} is isomorphic. • The crystal structures of the high-pressure phases are assigned. • Axial and bulk compressibilities are determined. - Abstract: Room-temperature angle-dispersive X-ray diffraction measurements on zircon-type NdVO{sub 4} and monazite-type LaVO{sub 4} were performed in a diamond-anvil cell up to 12 GPa. In NdVO{sub 4}, we found evidence for a non-reversible pressure-induced structural phase transition from zircon to a monazite-type structure at 6.5 GPa. Monazite-type LaVO{sub 4} also exhibits a phase transition but at 8.6 GPa. In this case the transition is reversible and isomorphic. In both compounds the pressure induced transitions involve a large volume collapse. Finally, the equations of state and axial compressibilities for the low-pressure phases are also determined.
Effect of W addition on the electrical switching of VO2 thin films
NASA Astrophysics Data System (ADS)
Rajeswaran, Bharathi; Umarji, Arun M.
Vanadium Oxide has been a frontrunner in the field of oxide electronics because of its metal-insulator transition (MIT). The interplay of different structures of VO2 has played a crucial role in deciding the magnitude of the first order MIT. Substitution doping has been found to introduce different polymorphs of VO2. Hence the role of substitution doping in stabilizing the competing phases of VO2 in the thin film form remains underexplored. Consequently there have been reports both discounting and approving such a stabilization of competing phases in VO2. It is reported in the literature that the bandwidth of the hysteresis and transition temperature of VO2 can be tuned by substitutional doping of VO2 with W. In this work, we have adopted a novel technique called, Ultrasonic Nebulized Spray Pyrolysis of Aqueous Combustion Mixture (UNSPACM) to deposit VO2 and W- doped VO2 as thin films. XRD and Raman spectroscopy were used to investigate the role of tungsten on the structure of VO2 thin films. Morphology of the thin films was found to be consisting of globular and porous nanoparticles of size ˜ 20nm. Transition temperature decreased with the addition of W. We found that for 2.0 at % W doping in VO2, the transition temperature has reduced from 68 o C to 25 o C. It is noted that W-doping in the process of reducing the transition temperature, alters the local structure and also increases room temperature carrier concentration.
Indirect estimation of VO2max in athletes by ACSM's equation: valid or not?
Koutlianos, N; Dimitros, E; Metaxas, T; Cansiz, M; Deligiannis, AS; Kouidi, E
Aim: The purpose of this study was to assess the indirect calculation of VO2max using ACSM's equation for Bruce protocol in athletes of different sports and to compare with the directly measured; secondly to develop regression models predicting VO2 max in athletes. Methods: Fifty five male athletes of national and international level (mean age 28.3 ± 5.6 yrs) performed graded exercise test with direct measurement of VO2 through ergospirometric device. Moreover, 3 equations were used for the indirect calculation of VO2max: a) VO2max= (0.2 · Speed) + (0.9 · Speed · Grade) + 3.5 (ACSM running equation), b) regression analysis model using enter method and c) stepwise method based on the measured data of VO2. Age, BMI, speed, grade and exercise time were used as independent variables. Results: Regression analysis using enter method yielded the equation (R=.64, standard error of estimation [SEE] = 6.11): VO2max (ml·kg-1·min-1) = 58.443 - (0.215 · age) - (0.632 · BMI) - (68.639 · grade) + (1.579 · time) while stepwise method (R = .61, SEE = 6.18) led to: VO2max (ml·kg-1·min-1) = 33.971 - (0.291 · age) + (1.481 · time). The calculated values of VO2max from these regression models did not differ significantly from the measured VO2max (p>.05). On the contrary, VO2max calculated from the ACSM's running equation was significantly higher from the actually measured value by 14.6% (p <.05). Conclusions: In conclusion, it seems that ACSM's equation is not capable of accurately predicting VO2max in athletes aged 18-37 years using Bruce protocol. Only the regression models were correlated moderately with the actually measured values of VO2max. PMID:24376318
Pulmonary and leg VO2 during submaximal exercise: implications for muscular efficiency
NASA Technical Reports Server (NTRS)
Poole, D. C.; Gaesser, G. A.; Hogan, M. C.; Knight, D. R.; Wagner, P. D.
Insights into muscle energetics during exercise (e.g., muscular efficiency) are often inferred from measurements of pulmonary gas exchange. This procedure presupposes that changes of pulmonary O2 (VO2) associated with increases of external work reflect accurately the increased muscle VO2. The present investigation addressed this issue directly by making simultaneous determinations of pulmonary and leg VO2 over a range of work rates calculated to elicit 20-90% of maximum VO2 on the basis of prior incremental (25 or 30 W/min) cycle ergometry. VO2 for both legs was calculated as the product of twice one-leg blood flow (constant-infusion thermodilution) and arteriovenous O2 content difference across the leg. Measurements were made 3-5 min after each work rate imposition to avoid incorporation of the VO2 slow component above the lactate threshold. For all 17 subjects, the slope of pulmonary VO2 (9.9 +/- 0.2 ml O2.W-1.min-1) was not different (P greater than 0.05) from that for leg VO2 (9.2 +/- 0.6 ml O2.W-1.min-1). Estimation of "delta" efficiency (i.e., delta work accomplished divided by delta energy expended, calculated from slope of VO2 vs. work rate and a caloric equivalent for O2 of 4.985 cal/ml) using pulmonary VO2 measurements (29.1 +/- 0.6%) was likewise not significantly different (P greater than 0.05) from that made using leg VO2 measurements (33.7 +/- 2.4%). These data suggest that the net VO2 cost of metabolic "support" processes outside the exercising legs changes little over a relatively broad range of exercise intensities. Thus, under the conditions of this investigation, changes of VO2 measured from expired gas reflected closely those occurring within the exercising legs.
Passively mode-locked Yb:LuVO4 oscillator
NASA Astrophysics Data System (ADS)
Rivier, Simon; Mateos, Xavier; Liu, Junhai; Petrov, Valentin; Griebner, Uwe; Zorn, Martin; Weyers, Markus; Zhang, Huaijin; Wang, Jiyang; Jiang, Minhua
Passive mode locking of the ytterbium doped orthovanadate crystal Yb:LuVO4 is reported for the first time. We demonstrate what we believe to be the shortest pulses directly generated with an Yb-doped crystalline laser using a semiconductor saturable absorber. The pulses at 1036 nm have a duration as short as 58 fs for an average power of 85 mW.
TeleInViVo: a collaborative volume visualization application.
Coleman, J; Savchenko, A; Goettsch, A; Wang, K; Bono, P; Littlefield, R; Macedonia, C
Converging technologies in the areas of networks, volume visualization algorithms, and computer performance have made possible the development of a new tool for collaboration, which extends the reach of health professionals, and other consumers of volumetric data around the world. TeleInViVo(tm) is a three-dimensional (3D) collaborative volume visualization tool for medical applications. It extends the capabilities of InViVo(tm), a fast volume visualization tool developed at the Fraunhofer IGD, Darmstadt, Germany [1-3], with efficient and intuitive network collaboration features for remote consultation and new modes of interaction. The software runs on both UNIX and Windows NT platforms. TeleInViVo provides a high degree of interactivity for the medical professional when interacting with the patient data, facilitates explanation and communication between field personnel and medical experts located far from the field, and permits viewing of the data in a multitude of ways designed to support rapid and accurate diagnosis. Current efforts involve architectural enhancements to support multiuser, distributed telemedical scenarios. The application includes the following features: Volume and subvolume data transmission at user specified resolution, Synchronization cues, Integration of Immersion Probe(tm), a 6 degree-of-freedom input device, for ergonomic 3D data exploration, Tools for measuring distances, Tools for planning instrument path, Arbitrary cutting planes in real time, Interactive segmentation tools, Virtual video recorder and playback (cine loops), 3D stereo mode. TeleInViVo is an essential part of the MUSTPAC-1 portable 3D ultrasound system developed by Battelle Pacific Northwest Labs, Richland, WA. PMID:10168908
Chapter 11: Web-based Tools - VO Region Inventory Service
NASA Astrophysics Data System (ADS)
Good, J. C.
As the size and number of datasets available through the VO grows, it becomes increasingly critical to have services that aid in locating and characterizing data pertinent to a particular scientific problem. At the same time, this same increase makes that goal more and more difficult to achieve. With a small number of datasets, it is feasible to simply retrieve the data itself (as the NVO DataScope service does). At intermediate scales, "count" DBMS searches (searches of the actual datasets which return record counts rather than full data subsets) sent to each data provider will work. However, neither of these approaches scale as the number of datasets expands into the hundreds or thousands. Dealing with the same problem internally, IRSA developed a compact and extremely fast scheme for determining source counts for positional catalogs (and in some cases image metadata) over arbitrarily large regions for multiple catalogs in a fraction of a second. To show applicability to the VO in general, this service has been extended with indices for all 4000+ catalogs in CDS Vizier (essentially all published catalogs and source tables). In this chapter, we will briefly describe the architecture of this service, and then describe how this can be used in a distributed system to retrieve rapid inventories of all VO holdings in a way that places an insignificant load on any data supplier. Further, we show and this tool can be used in conjunction with VO Registries and catalog services to zero in on those datasets that are appropriate to the user's needs. The initial implementation of this service consolidates custom binary index file structures (external to any DBMS and therefore portable) at a single site to minimize search times and implements the search interface as a simple CGI program. However, the architecture is amenable to distribution. The next phase of development will focus on metadata harvesting from data archives through a standard program interface and distribution
Europlanet IDIS: Adapting existing VO building blocks to Planetary Sciences
NASA Astrophysics Data System (ADS)
Cecconi, Baptiste; Jacquey, Christian; Erard, Stéphane; Le Sidaner, Pierre; Andre, Nicolas; Bourrel, Nataliya; Berthier, Jerome; Gangloff, Michel
IDIS (Integrated and Distributed Information System) is part of the Europlanet project. Its purpose is to develop a prototype of a planetology Virtual Observatory (VO). In the frame of its participation to this project, and in collaboration with VO-Paris (Virtual Observatory Paris Data Centre), the CDPP (Data Centre for Plasma Physics, based in Toulouse) has developed a data model to describe the wide variety of data products that can be found in the planetology community, which includes a wide variety of science thematics such as plasma physics, planetary surfaces, interiors, atmospheres or small bodies. This data model is making extensive use of existing standards provided by various groups (IVOA, IPDA, SPASE...) and its scope is to describe the scientific content of datasets, in order to be able to locate and retrieve data files corresponding to a given request. Two generic protocols has been identified for data exchange: PDAP (Planetary Data Access Protocol), developed by IPDA and Obs-TAP (Observation Table Access Protocol), developed by IVOA. In this latter case, Obs-TAP has been adapted to better fit to the planetology community; this protocol is called IDIS-TAP. The data model and the protocols are now tested in collaboration with VO-Paris and other Europlanet IDIS partners. The EuroPlaNet-RI project is funded by the European Commission under the 7th Framework Program, grant 228319 "Capacities Specific Programme".
Nonreciprocal switching of VO2 thin films on microstructured surfaces
NASA Astrophysics Data System (ADS)
Adams, Charles; Karakurt, Ismail; Leiderer, Paul; Boneberg, Johannes; Haglund, Richard
Vanadium dioxide is a strongly correlated electron material that undergoes an insulator-to-metal transition at approximately 340 K, with a corresponding large change in its optical and electronic properties. By depositing a VO2 thin film on a planar hexagonal close-packed array of 1.54 μm diameter silica microspheres, we constructed a laser-triggered thin film optical switch that exhibits different fluence thresholds for the insulator-metal transition (IMT) depending on the direction of illumination. The IMT was triggered by a ns Nd:YAG laser (532 nm) from two directions normal to the substrate while monitoring the transmission with a near-IR diode laser. Due to the focusing effects of the microspheres, the fluence required for switching the VO2 was 2.4 times higher when the switching laser was incident from the film (top) side of the array than from the microsphere (bottom) side. Through both the experiments and simulations, we find evidence for strong nonlinear near-field absorption in the VO2.
Workflow in Astronomy : the VO France Workflow Working Group experience
NASA Astrophysics Data System (ADS)
Schaaff, A.; Petit, F. L.; Prugniel, P.; Slezak, E.; Surace, C.
The French Action Spécifique Observatoires Virtuels has created the Workflow Working Group in 2005. Its aim is to explore the use of the Workflow paradigm in the astronomical domain. The first consensus was the definition of a Workflow as a sequence of tasks realized in a controlled context (at various levels: intelligence in the choice of the algorithms, flow control, etc.), based on use cases studies, in an architecture which takes into account VO standards. The current roadmap is to provide scientific use cases in several domains (image, spectrum, simulation, data mining, etc.) and to improve them mainly with VO existing tools. Another important point is to develop collaborations with the IT community (links to EGEE, ...). Use cases are useful to compare the pertinence of the possible workflow models and to understand how to implement it as efficiently as possible with the existing tools (ex. : AstroGrid, AÏDA, WebCom-G, etc.). The execution (local machine, cluster, grid) through this kind of tools and the use of VO functionalities (Web Services, Grid, VOSpace, etc.) becomes almost transparent.
Raman phonons in multiferroic FeVO4 crystals
NASA Astrophysics Data System (ADS)
Zhang, An-Min; Liu, Kai; Ji, Jian-Ting; He, Chang-Zhen; Tian, Yong; Jin, Feng; Zhang, Qing-Ming
Multiferroic materials are promising candidates for next-generation multi-functional devices, because of the coexistence of multi-orders and the coupling between the orders. FeVO4 has been confirmed to be a multiferroic compound, since it exhibits both ferroelectricity and antiferromagnetic ordering at low temperatures. In this paper, we have performed careful Raman scattering measurements on high-quality FeVO4 single crystals. The compound has a very rich phonon structure due to its low crystal symmetry (P - 1) and at least 47 Raman-active phonon modes have been resolved in the low and hightemperature spectra. Most of the observed modes are well assigned with aid of first-principles calculations and symmetry analysis. The present study provides an experimental basis for exploring spin-lattice coupling and the mechanism of multiferroicity in FeVO4 Project supported by the National Basic Research Program of China (Grant No. 2012CB921701), the National Natural Science Foundation of China (Grant Nos. 11174367 and 11004243), the China Postdoctoral Science Foundation, the Fundamental Research Funds for the Central Universities, and the Research Funds of Renmin University of China (Grant Nos. 10XNI038, 14XNLF06, and 14XNLQ03).
Optical properties and electronic band structure of BiMg2PO6, BiMg2VO6, BiMg2VO6:Pr3+ and BiMg2VO6:Eu3+
NASA Astrophysics Data System (ADS)
Barros, A.; Deloncle, R.; Deschamp, J.; Boutinaud, P.; Chadeyron, G.; Mahiou, R.; Cavalli, E.; Brik, M. G.
The luminescence properties of the yellow pigment BiMg2VO6 are revisited and those of BiMg2PO6, BiMg2VO6:Pr3+ and BiMg2VO6:Eu3+ are described. It is shown that the undoped systems exhibit broad band emission in the green or orange spectral regions, but only upon UV or near UV excitation. In contradiction with a previous report, we found that the blue, host absorbed, photons are lost non-radiatively and do not contribute to the luminescence processes in BiMg2VO6. To understand these experimental results, the optical properties of BiMg2VO6 and BiMg2PO6 are theoretically analysed on the basis of electronic structure diagrams calculated by the DFT method. It is found that the optical transitions are mostly localised within [VO4]3- units or non-regular Bi3+ ions and occur in the UV or near UV regions. The luminescence of the trivalent lanthanide dopants is weak (Eu3+) or unobserved (Pr3+) in BiMg2VO6 which is explained by inefficient energy migration in the host lattice to the impurity sites.
In situ Raman spectroscopy study of metal-enhanced hydrogenation and dehydrogenation of VO2.
Wu, Hao; Fu, Qiang; Bao, Xinhe
Vanadium dioxide (VO2) has a phase transition from insulator to metal at 340 K, and this transition can be strongly modified by hydrogenation. In this work, two dimensional (2D) VO2 sheets have been grown on Si(1 1 1) surfaces through chemical vapor deposition, and metal (Au, Pt) thin films were deposited on VO2 surfaces by sputtering. The hydrogenation and dehydrogenation of VO2 and metal-decorated VO2 structures in H2 and in air were in situ studied by Raman. We found that hydrogenation and dehydrogenation temperatures have been significantly decreased with the VO2 surface decorated by Au and Pt. The enhanced hydrogenation and dehydrogenation reactions can be attributed to catalytic dissociation of H2 and O2 molecules on metal surfaces and subsequent spillover of dissociated H and O atoms to the oxide surfaces. PMID:27603090
Carbon quantum dots coated BiVO{sub 4} inverse opals for enhanced photoelectrochemical hydrogen generation
Nan, Feng; Shen, Mingrong; Fang, Liang E-mail: email@example.com; Kang, Zhenhui E-mail: email@example.com; Wang, Junling
Carbon quantum dots (CQDs) coated BiVO{sub 4} inverse opal (io-BiVO{sub 4}) structure that shows dramatic improvement of photoelectrochemical hydrogen generation has been fabricated using electrodeposition with a template. The io-BiVO{sub 4} maximizes photon trapping through slow light effect, while maintaining adequate surface area for effective redox reactions. CQDs are then incorporated to the io-BiVO{sub 4} to further improve the photoconversion efficiency. Due to the strong visible light absorption property of CQDs and enhanced separation of the photoexcited electrons, the CQDs coated io-BiVO{sub 4} exhibit a maximum photo-to-hydrogen conversion efficiency of 0.35%, which is 6 times higher than that of the pure BiVO{sub 4} thin films. This work is a good example of designing composite photoelectrode by combining quantum dots and photonic crystal.
Carbon quantum dots coated BiVO4 inverse opals for enhanced photoelectrochemical hydrogen generation
NASA Astrophysics Data System (ADS)
Nan, Feng; Kang, Zhenhui; Wang, Junling; Shen, Mingrong; Fang, Liang
Carbon quantum dots (CQDs) coated BiVO4 inverse opal (io-BiVO4) structure that shows dramatic improvement of photoelectrochemical hydrogen generation has been fabricated using electrodeposition with a template. The io-BiVO4 maximizes photon trapping through slow light effect, while maintaining adequate surface area for effective redox reactions. CQDs are then incorporated to the io-BiVO4 to further improve the photoconversion efficiency. Due to the strong visible light absorption property of CQDs and enhanced separation of the photoexcited electrons, the CQDs coated io-BiVO4 exhibit a maximum photo-to-hydrogen conversion efficiency of 0.35%, which is 6 times higher than that of the pure BiVO4 thin films. This work is a good example of designing composite photoelectrode by combining quantum dots and photonic crystal.
Optimization of thermochromic VO2 based structures with tunable thermal emissivity
NASA Astrophysics Data System (ADS)
Voti, R. Li; Larciprete, M. C.; Leahu, G.; Sibilia, C.; Bertolotti, M.
In this paper, we design and simulate VO2/metal multilayers to obtain a large tunability of the thermal emissivity of infrared (IR) filters in the typical mid wave IR window of many infrared cameras. The multilayer structure is optimized to realise a low emissivity filter at high temperatures useful for military purposes. The values of tunability found for VO2/metal multilayers are larger than the value for a single thick layer of VO2.
Effect of Oxide Buffer Layer on the Thermochromic Properties of VO2 Thin Films
NASA Astrophysics Data System (ADS)
Koo, Hyun; Xu, Lu; Ko, Kyeong-Eun; Ahn, Seunghyun; Chang, Se-Hong; Park, Chan
VO2 thin films were deposited on soda lime glass substrates with ZnO, TiO2, SnO2, and CeO2 thin films applied as buffer layers between the VO2 films and the substrates in order to investigate the effect of buffer layer on the formation and the thermochromic properties of VO2 film. Buffer layers with thicknesses over 50 nm were found to affect the formation of VO2 film, which was confirmed by XRD spectra. By using ZnO, TiO2, and SnO2 buffer layers, monoclinic VO2 (VO2(M)) film was successfully fabricated on soda lime glass at 370 °C. On the contrary, films of VO2(B), which is known to have no phase transition near room temperature, were formed rather than VO2(M) when the film was deposited on CeO2 buffer layer at the same film deposition temperature. The excellent thermochromic properties of the films deposited on ZnO, TiO2, and SnO2 buffer layers were confirmed from the temperature dependence of electrical resistivity from room temperature to 80 °C. Especially, due to the tendency of ZnO thin film to grow with a high degree of preferred orientation on soda lime glass at low temperature, the VO2 film deposited on ZnO buffer layer exhibits the best thermochromic properties compared to those on other buffer layer materials used in this study. These results suggest that deposition of VO2 films on soda lime glass at low temperature with excellent thermochromic properties can be achieved by considering the buffer layer material having structural similarity with VO2. Moreover, the degree of crystallization of buffer layer is also related with that of VO2 film, and thus ZnO can be one of the most effective buffer layer materials.
Impact of VoIP and QoS on Open and Distance Learning
ERIC Educational Resources Information Center
Saxena, P. C.; Jasola, Sanjay; Sharma, Ramesh C.
Voice over Internet Protocol (VoIP) is becoming a reality in many organizations. The potential for mobility in voice over wi-fi networks will derive demand for the technology. Wireless VoIP is poised to rival VoIP as an alternative telephony tool. Internet has been used to transport data in the form of packet. In the past, Internet did not support…
Gas-phase reactivity of metavanadate [VO3]- towards methanol and ethanol: experiment and theory.
Waters, Tom; Wedd, Anthony G; O'Hair, Richard A J
The gas-phase reactivity of the metavanadate anion [VO3]- towards methanol and ethanol was examined by a combination of ion-molecule reaction and isotope labelling experiments in a quadrupole ion-trap mass spectrometer. The experimental data were interpreted with the aid of density functional theory calculations. [VO3]- dehydrated methanol to eliminate water and form [VO2(eta2-OCH2)]-, which features an [eta2-C,O-OCH2]2- ligand formed by formal removal of two protons from methanol and which is isoelectronic with peroxide. [VO3]- reacted with ethanol in an analogous manner to form [VO2(eta2-OCHCH3)]-, as well as by loss of ethene to form [VO2(OH)2]-. The calculations predicted that important intermediates in these reactions were the hydroxo alkoxo anions [VO2(OH)(OCH2R)]- (R: H, CH3). These were predicted to undergo intramolecular hydrogen-atom transfer to form [VO(OH)2(eta1-OCHR)]- followed by eta1-O-->eta2-C,O rearrangements to form [VO(OH)2(eta2-OCHR)]-. The latter reacted further to eliminate water and generate the product [VO2(eta2-OCHR)]-. This major product observed for [VO3]- is markedly different from that observed previously for [NbO3]- containing the heavier Group 5 congener niobium. In that case, the major product of the reaction was an ion of stoichiometry [Nb, O3, H2]- arising from the formal dehydrogenation of methanol to formaldehyde. The origin of this difference was examined theoretically and attributed to the intermediate alkoxo anion [NbO2(OH)(OCH3)]- preferring hydride transfer to form [HNbO2(OH)]- with loss of formaldehyde. This contrasts with the hydrogen-atom-transfer pathway observed for [VO2(OH)(OCH3)]-. PMID:17661322
Insights into Stabilization of the 99TcVO Core for Synthesis of 99TcVO Compounds
McGregor, Donna; Burton-Pye, Benjamin P.; Lukens, Wayne W.; Howell, Robertha C.; Francesconi, Lynn C.
Synthesis of technetium-99 (99Tc; t1/2: 2.1 105 years, max: 253 keV) materials is of importance in studies of the nuclear fuel cycle where Tc is a major fission product (6percent thermal yield from 235U and 239Pu), in understanding radioactive tank waste composition, and in identifying 99mTc compounds for nuclear medicine imaging. One of the most useful synthetic starting materials, (NBu4)TcOCl4, is susceptible to disproportionation in water to form TcO4 and TcIV species, especially TcO2 2H2O. This unwanted reaction is especially problematic when working with ligands bearing hard donor atoms, such as oxygen, where the stability with the soft TcV=O3+ core may be low. Polyoxometalates (POMs) are such ligands. They possess defect sites with four hard oxygen atoms and show low (ca. 108) stability constants with transition metals. Tc complexes of POMs are molecular-level models for Tc metal oxide solid-state materials and can provide information on coordination and redox environments of metal oxides that stabilize low-valent Tc. In order to synthesize pure Tc POM complexes [TcVO(1-P2W17O61)]7 (TcVO-1) and [TcVO(2-P2W17O61)]7 (TcVO-2) from (NBu4)TcOCl4, we have identified strategies that minimize formation of TcIV species and optimize the formation of pure TcV species. The parameters that we consider are the amount of ethylene glycol, which is employed as a transfer ligand to prevent hydrolysis of (NBu4)TcOCl4, and the precipitating agent. The TcIV species that contaminates the non-optimized syntheses is likely a TcIV -oxido-bridged dimer [TcIV-(-O)2-TcIV]. We also employ a novel procedure where the 2 ligand is photoactivated and reduced (in the presence of a sacrificial electron donor) to subsequently reduce TcVIIO4 to an isolatable TcVO-2 product that is remarkably free of TcIV.
Efficient removal rhodamine B over hydrothermally synthesized fishbone like BiVO{sub 4}
Lin, Xue; Li, Hongji; Yu, Lili; Zhao, Han; Yan, Yongsheng; Liu, Chunbo; Zhai, Hongjv
Graphical abstract: - Highlights: • Fishbone like BiVO{sub 4} product was synthesized through hydrothermal method. • BiVO{sub 4} sample was characterized by various characterization technologies. • Fishbone like BiVO{sub 4} presented outstanding photocatalytic performance. - Abstract: Fishbone like BiVO{sub 4} product has been successfully synthesized by a hydrothermal method without using any surfactant or template. The pH value was found to play an important role in the formation of this morphology. The band gap of the as-prepared fishbone like BiVO{sub 4} sample was estimated to be about 2.36 eV from the onset of UV–vis diffuse reflectance spectrum (UV–vis DRS) of the photocatalyst. The as-prepared fishbone like BiVO{sub 4} sample exhibited excellent visible-light-driven photocatalytic efficiency. Over this catalyst, the 100% degradation of rhodamine B (Rh B) (0.005 mmol L{sup −1}) was obtained after visible light irradiation (λ > 420 nm) for 180 min. This is much higher than that of bulk BiVO{sub 4} sample prepared by solid-state reaction. The reason for the differences in the photocatalytic activities of fishbone like BiVO{sub 4} sample and bulk BiVO{sub 4} sample was further investigated.
EPR study of VO2+ doped glycine zinc sulphate single crystal
NASA Astrophysics Data System (ADS)
Prabakaran, R.; Subramanian, P.
Single crystals Of GZS:VO2+ were grown by slow evaporation of solvent at room temperature. The EPR study was carried out at room temperature. Single crystal rotations in each of the three mutually orthogonal planes indicate single site occupation of VO2+ in the lattice. g and A tensors were calculated from the recorded EPR spectra. The principal values of g and A indicates existence of rhombic symmetry around the VO2+ ion. From the direction cosines of the g and A tensors, the locations of VO2+ in the lattice have been identified as substitutional site.
Temperature dependence of thermal conductivity of VO2 thin films across metal-insulator transition
NASA Astrophysics Data System (ADS)
Kizuka, Hinako; Yagi, Takashi; Jia, Junjun; Yamashita, Yuichiro; Nakamura, Shinichi; Taketoshi, Naoyuki; Shigesato, Yuzo
Thermal conductivity of a 300-nm-thick VO2 thin film and its temperature dependence across the metal-insulator phase transition (TMIT) were studied using a pulsed light heating thermoreflectance technique. The VO2 and Mo/VO2/Mo films with a VO2 thickness of 300 nm were prepared on quartz glass substrates: the former was used for the characterization of electrical properties, and the latter was used for the thermal conductivity measurement. The VO2 films were deposited by reactive rf magnetron sputtering using a V2O3 target and an Ar-O2 mixture gas at 645 K. The VO2 films consisted of single phase VO2 as confirmed by X-ray diffraction and electron beam diffraction. With increased temperature, the electrical resistivity of the VO2 film decreased abruptly from 6.3 × 10-1 to 5.3 × 10-4 Ω cm across the TMIT of around 325-340 K. The thermal conductivity of the VO2 film increased from 3.6 to 5.4 W m-1 K-1 across the TMIT. This discontinuity and temperature dependence of thermal conductivity can be explained by the phonon heat conduction and the Wiedemann-Franz law.
Spectroscopic analysis in the virtual observatory environment with SPLAT-VO
NASA Astrophysics Data System (ADS)
Škoda, P.; Draper, P. W.; Neves, M. C.; Andrešič, D.; Jenness, T.
SPLAT-VO is a powerful graphical tool for displaying, comparing, modifying and analysing astronomical spectra, as well as searching and retrieving spectra from services around the world using Virtual Observatory (VO) protocols and services. The development of SPLAT-VO started in 1999, as part of the Starlink StarJava initiative, sometime before that of the VO, so initial support for the VO was necessarily added once VO standards and services became available. Further developments were supported by the Joint Astronomy Centre, Hawaii until 2009. Since end of 2011 development of SPLAT-VO has been continued by the German Astrophysical Virtual Observatory, and the Astronomical Institute of the Academy of Sciences of the Czech Republic. From this time several new features have been added, including support for the latest VO protocols, along with new visualization and spectra storing capabilities. This paper presents the history of SPLAT-VO, its capabilities, recent additions and future plans, as well as a discussion on the motivations and lessons learned up to now.
RGO/InVO4 hollowed-out nanofibers: Electrospinning synthesis and its application in photocatalysis
NASA Astrophysics Data System (ADS)
Ma, Dong; Zhang, Yanxiang; Gao, Mengchun; Xin, Yanjun; Wu, Juan; Bao, Nan
A composite of reduced graphene oxide (RGO) and InVO4 nanofiber was successfully synthesized by an electrospinning technique. The as-collected fibers were calcined at 420 °C in air and then calcined at 550 °C in nitrogen gas to remove polyvinyl pyrrolidone (PVP), which could enable InVO4 to crystallize and protect the RGO from oxidation. The InVO4 in the composite illustrated a hollowed-out fibrous morphology and orthorhombic phase, and RGO nanosheets were nested in the InVO4 nanofibers. The hybrid RGO could produce more hydroxyl groups and a higher oxygen vacancy density on the surface of RGO/InVO4 composite. Compared with pure InVO4, the light absorption range of the as-prepared RGO/InVO4 composite was expanded. In Rh B degradation, the RGO/InVO4 hybrid nanofibers displayed a higher photocatalytic activity than pure InVO4 nanofibers. The enhanced photocatalytic activity might be ascribed to the role of RGO as an electron transporter and acceptor in the composite, which could effectively inhibit the charge recombination and facilitate the charge transfer. The exported electron could attack an O2 molecule to facilitate the generation of •O2- and •OH for the photodegradation process of Rh B.
Microwave synthesis and photocatalytic activity of Tb(3+) doped BiVO4 microcrystals.
Wang, Ying; Liu, Fuyang; Hua, Yingjie; Wang, Chongtai; Zhao, Xudong; Liu, Xiaoyang; Li, Hongdong
Tb(3+) doped BiVO4 has been successfully synthesized by a simple microwave-assisted hydrothermal method at 140°C for 30min. The structure, morphology and optical property of the Tb(3+) doped BiVO4 products have been systematically investigated. This study indicates that the incorporation of Tb(3+) could induce the conversion of structure from monoclinic to tetragonal for BiVO4. Furthermore, the as-obtained Tb(3+) doped BiVO4 samples showed an obvious morphological change: the hollow square rod-like BiVO4 crystal gradually changed to spindle-like crystal. The Tb(3+) doped BiVO4 products exhibited extraordinary photocatalytic activity for Methylene Blue (MB) degradation under visible light irradiation. The doped BiVO4 at a molar ratio of 2at% (Tb and Bi) with a mixture of monoclinic and tetragonal phases showed and prominent photocatalytic degradation rate, which reached 99.9% in 120min. The results suggest that the differences in the photocatalytic activity of these BiVO4 crystals with different Tb(3+) doping concentrations can be attributed to the change of crystalline phases, and the coexistence of the monoclinic/tetragonal phases in BiVO4 products, which improve the efficient charge separation and transportation. PMID:27565962
Ultrafast dynamics during the photoinduced phase transition in VO2
NASA Astrophysics Data System (ADS)
Wegkamp, Daniel; Stähler, Julia
The phase transition of VO2 from a monoclinic insulator to a rutile metal, which occurs thermally at TC = 340 K, can also be driven by strong photoexcitation. The ultrafast dynamics during this photoinduced phase transition (PIPT) have attracted great scientific attention for decades, as this approach promises to answer the question of whether the insulator-to-metal (IMT) transition is caused by electronic or crystallographic processes through disentanglement of the different contributions in the time domain. We review our recent results achieved by femtosecond time-resolved photoelectron, optical, and coherent phonon spectroscopy and discuss them within the framework of a selection of latest, complementary studies of the ultrafast PIPT in VO2. We show that the population change of electrons and holes caused by photoexcitation launches a highly non-equilibrium plasma phase characterized by enhanced screening due to quasi-free carriers and followed by two branches of non-equilibrium dynamics: (i) an instantaneous (within the time resolution) collapse of the insulating gap that precedes charge carrier relaxation and significant ionic motion and (ii) an instantaneous lattice potential symmetry change that represents the onset of the crystallographic phase transition through ionic motion on longer timescales. We discuss the interconnection between these two non-thermal pathways with particular focus on the meaning of the critical fluence of the PIPT in different types of experiments. Based on this, we conclude that the PIPT threshold identified in optical experiments is most probably determined by the excitation density required to drive the lattice potential change rather than the IMT. These considerations suggest that the IMT can be driven by weaker excitation, predicting a transiently metallic, monoclinic state of VO2 that is not stabilized by the non-thermal structural transition and, thus, decays on ultrafast timescales.
Thermochromic light scattering from particulate VO2 layers
NASA Astrophysics Data System (ADS)
Montero, José; Ji, Yu-Xia; Granqvist, Claes G.; Niklasson, Gunnar A.
Particulate layers of thermochromic (TC) VO2 were made by reactive DC magnetron sputtering of vanadium onto In2O3:Sn-coated glass. The deposits were characterized by scanning electron microscopy, atomic force microscopy, and X-ray diffraction. Specular and diffuse optical transmittance and reflectance were recorded in the 300-2500-nm wavelength range and displayed pronounced TC effects. These properties could be reconciled with a semi-quantitative model based on Lorentz-Mie theory applied to the distribution of particle sizes and accounting for particle shapes by the Grenfell-Warren approach with equal-volume-to-area spheres.
Publishing Planetary Data to the VO using DaCHS
NASA Astrophysics Data System (ADS)
Demleitner, M.
Publishing to the Virtual Observatory has many advantages, but between standards compliance, registration, data organisation, and server operation it is also requires a nontrivial effort if starting from scratch. The DaCHS software from the German Astrophysical Virtual Observatory offers a packaged solution letting publishers concentrate on working with their own data and metadata as much as possible. For the planetary community, publishing is further facilitated by built-in support for the EPN-TAP data model. This contribution will show a typical publishing workflow together with a brief overview of how DaCHS meshes in with the VO and Web-based data usage.
Giant magnetocaloric effect in antiferromagnetic DyVO4 compound
NASA Astrophysics Data System (ADS)
Midya, A.; Khan, N.; Bhoi, D.; Mandal, P.
We have investigated the magnetic and magnetocaloric properties of DyVO4 by magnetization and heat capacity measurements. χ(T) shows antiferromagnetic to paramagnetic transition at TNDy~3.5 K. The compound undergoes a metamagnetic transition and exhibits a huge entropy change. The maximum values of magnetic entropy change (ΔSM), adiabatic temperature change (ΔTad) and refrigerant capacity (RC) reach 26 J kg-1 K-1, 17 K, and 526 J kg-1, respectively for a field change of 0-8 T. Moreover, the material is highly insulating and exhibits no thermal and field hysteresis, satisfying the necessary conditions for a good magnetic refrigerant material.
Ezzine Yahmed, Safa; Ayed, Meriem; Zid, Mohamed Faouzi; Driss, Ahmed
A new vanadium oxide, potassium bis-(dioxovanad-yl) phosphate, β-K(VO2)2(PO4), has been synthesized by a solid-state reaction. In the title compound, the [V2PO8] framework is built up from infinite pyramidal [V2O8]∞ and [VPO7]∞ chains linked together by V-O-P bridges, leading to a three-dimensional framework which delimits two types of inter-secting tunnels running along [100] and [010] in which the four unique K(+) ions, showing coordination numbers of nine and ten, are located. PMID:23476311
The Effect of Aging on Relationships between Lean Body Mass and VO2max in Rowers.
Kim, Chul-Ho; Wheatley, Courtney M; Behnia, Mehrdad; Johnson, Bruce D
Aging is associated with a fall in maximal aerobic capacity as well as with a decline in lean body mass. The purpose of the study was to investigate the influence of aging on the relationship between aerobic capacity and lean body mass in subjects that chronically train both their upper and lower bodies. Eleven older rowers (58±5 yrs) and 11 younger rowers (27±4 yrs) participated in the study. Prior to the VO2max testing, subjects underwent a dual energy X-ray absorptiometry scan to estimate total lean body mass. Subsequently, VO2max was quantified during a maximal exercise test on a rowing ergometer as well as a semi-recumbent cycle ergometer. The test protocol included a pre-exercise stage followed by incremental exercise until VO2max was reached. The order of exercise modes was randomized and there was a wash-out period between the two tests. Oxygen uptake was obtained via a breath-by-breath metabolic cart (Vmax™ Encore, San Diego, CA). Rowing VO2max was higher than cycling VO2max in both groups (p<0.05). Older subjects had less of an increase in VO2max from cycling to rowing (p<0.05). There was a significant relationship between muscle mass and VO2max for both groups (p<0.05). After correcting for muscle mass, the difference in cycling VO2max between groups disappeared (p>0.05), however, older subjects still demonstrated a lower rowing VO2max relative to younger subjects (p<0.05). Muscle mass is associated with the VO2max obtained, however, it appears that VO2max in older subjects may be less influenced by muscle mass than in younger subjects. PMID:27479009
The Effect of Aging on Relationships between Lean Body Mass and VO2max in Rowers
Kim, Chul-Ho
Aging is associated with a fall in maximal aerobic capacity as well as with a decline in lean body mass. The purpose of the study was to investigate the influence of aging on the relationship between aerobic capacity and lean body mass in subjects that chronically train both their upper and lower bodies. Eleven older rowers (58±5 yrs) and 11 younger rowers (27±4 yrs) participated in the study. Prior to the VO2max testing, subjects underwent a dual energy X-ray absorptiometry scan to estimate total lean body mass. Subsequently, VO2max was quantified during a maximal exercise test on a rowing ergometer as well as a semi-recumbent cycle ergometer. The test protocol included a pre-exercise stage followed by incremental exercise until VO2max was reached. The order of exercise modes was randomized and there was a wash-out period between the two tests. Oxygen uptake was obtained via a breath-by-breath metabolic cart (Vmax™ Encore, San Diego, CA). Rowing VO2max was higher than cycling VO2max in both groups (p<0.05). Older subjects had less of an increase in VO2max from cycling to rowing (p<0.05). There was a significant relationship between muscle mass and VO2max for both groups (p<0.05). After correcting for muscle mass, the difference in cycling VO2max between groups disappeared (p>0.05), however, older subjects still demonstrated a lower rowing VO2max relative to younger subjects (p<0.05). Muscle mass is associated with the VO2max obtained, however, it appears that VO2max in older subjects may be less influenced by muscle mass than in younger subjects. PMID:27479009
Investigation of Terahertz Emission from BiVO4/Au Thin Film Interface
NASA Astrophysics Data System (ADS)
Kumar, Nishant; Abdi, Fatwa F.; Trzesniewski, Bartek; Smith, Wilson A.; Planken, Paul C. M.; Adam, Aurèle J. L.
We demonstrate emission of terahertz pulses from a BiVO4/Au thin film interface, illuminated with femtosecond laser pulses. Based on the experimental observations, we propose that the most likely cause of the THz emission is the Photo-Dember effect caused by the standing wave intensity distribution formed at the BiVO4/Au interfaces.
Submaximal Treadmill Exercise Test to Predict VO[subscript 2]max in Fit Adults
ERIC Educational Resources Information Center
Vehrs, Pat R.; George, James D.; Fellingham, Gilbert W.; Plowman, Sharon A.; Dustman-Allen, Kymberli
This study was designed to develop a single-stage submaximal treadmill jogging (TMJ) test to predict VO[subscript 2]max in fit adults. Participants (N = 400; men = 250 and women = 150), ages 18 to 40 years, successfully completed a maximal graded exercise test (GXT) at 1 of 3 laboratories to determine VO[subscript 2]max. The TMJ test was completed…
Epitaxial growth of higher transition-temperature VO2 films on AlN/Si
NASA Astrophysics Data System (ADS)
Slusar, Tetiana; Cho, Jin-Cheol; Kim, Bong-Jun; Yun, Sun Jin; Kim, Hyun-Tak
We report the epitaxial growth and the mechanism of a higher temperature insulator-to-metal-transition (IMT) of vanadium dioxide (VO2) thin films synthesized on aluminum nitride (AlN)/Si (111) substrates by a pulsed-laser-deposition method; the IMT temperature is TIMT ≈ 350 K. X-ray diffractometer and high resolution transmission electron microscope data show that the epitaxial relationship of VO2 and AlN is VO2 (010) ‖ AlN (0001) with VO2 [101] ‖ AlN [ 2 1 ¯ 1 ¯ 0 ] zone axes, which results in a substrate-induced tensile strain along the in-plane a and c axes of the insulating monoclinic VO2. This strain stabilizes the insulating phase of VO2 and raises TIMT for 10 K higher than TIMT single crystal ≈ 340 K in a bulk VO2 single crystal. Near TIMT, a resistance change of about four orders is observed in a thick film of ˜130 nm. The VO2/AlN/Si heterostructures are promising for the development of integrated IMT-Si technology, including thermal switchers, transistors, and other applications.
Transient VO2 Characteristics in Children at the Onset of Steady-Rate Exercise.
ERIC Educational Resources Information Center
Freedson, Patty S.; And Others
Transient oxygen uptake (VO2) was studied in 28 children ranging in age from seven to fourteen. It was found that the VO2 halftime is similar to that of adults and that younger children attained a steady rate quicker than older children. (Authors/FG)
Occurrence of Siliceous Impact Melt in Netschaëvo IIE? A FIB-TEM Study
NASA Astrophysics Data System (ADS)
Hamann, C.; Van Roosbroek, N.; Greshake, A.; Pittarello, L.; Hecht, L.; Debaille, V.; Wirth, R.; Claeys, Ph.
A silicate inclusion in a sample of the Netschaëvo IIE iron meteorite was studied with FIB-TEM. We present petrographic features indicating that this inclusion is quenched impact melt and suggest that Netschaëvo is an impact melt breccia.
Removing the thermal component from heart rate provides an accurate VO2 estimation in forest work.
Dubé, Philippe-Antoine; Imbeau, Daniel; Dubeau, Denise; Lebel, Luc; Kolus, Ahmet
Heart rate (HR) was monitored continuously in 41 forest workers performing brushcutting or tree planting work. 10-min seated rest periods were imposed during the workday to estimate the HR thermal component (ΔHRT) per Vogt et al. (1970, 1973). VO2 was measured using a portable gas analyzer during a morning submaximal step-test conducted at the work site, during a work bout over the course of the day (range: 9-74 min), and during an ensuing 10-min rest pause taken at the worksite. The VO2 estimated, from measured HR and from corrected HR (thermal component removed), were compared to VO2 measured during work and rest. Varied levels of HR thermal component (ΔHRTavg range: 0-38 bpm) originating from a wide range of ambient thermal conditions, thermal clothing insulation worn, and physical load exerted during work were observed. Using raw HR significantly overestimated measured work VO2 by 30% on average (range: 1%-64%). 74% of VO2 prediction error variance was explained by the HR thermal component. VO2 estimated from corrected HR, was not statistically different from measured VO2. Work VO2 can be estimated accurately in the presence of thermal stress using Vogt et al.'s method, which can be implemented easily by the practitioner with inexpensive instruments. PMID:26851474
Effect of Toe Clips During Bicycle Ergometry on VO2 max.
ERIC Educational Resources Information Center
Moffat, Roger S.; Sparling, Phillip B.
Eight men participated in three randomized maximal oxygen uptake tests to investigate the hypothesis that the use of toe clips on bicycle ergometers produced a higher VO2 max. No significant difference in mean VO2 max or performance time was observed. (Author/MT)
Non-Exercise Estimation of VO[subscript 2]max Using the International Physical Activity Questionnaire
ERIC Educational Resources Information Center
Schembre, Susan M.; Riebe, Deborah A.
Non-exercise equations developed from self-reported physical activity can estimate maximal oxygen uptake (VO[subscript 2]max) as well as sub-maximal exercise testing. The International Physical Activity Questionnaire is the most widely used and validated self-report measure of physical activity. This study aimed to develop and test a VO[subscript…
Electronic structure and insulating gap in epitaxial VO2 polymorphs
Lee, Shinbuhm; Meyer, Tricia L.; Sohn, Changhee; Lee, Donghwa; Nichols, John A.; Lee, Dongkyu; Seo, Sung Seok Ambrose; Freeland, John W.; Noh, Tae Won; Lee, Ho Nyung
Here, determining the origin of the insulating gap in the monoclinic VO2(M1) is a long-standing issue. The difficulty of this study arises from the simultaneous occurrence of structural and electronic transitions upon thermal cycling. Here, we compare the electronic structure of the M1 phase with that of single crystalline insulating VO2(A) and VO2(B) thin films to better understand the insulating phase of VO2. As these A and B phases do not undergo a structural transition upon thermal cycling, we comparatively study the origin of the gap opening in the insulating VO2 phases. By x-ray absorption and optical spectroscopy, we find that the shift of unoccupied t2g orbitals away from the Fermi level is a common feature, which plays an important role for the insulating behavior in VO2 polymorphs. The distinct splitting of the half-filled t2g orbital is observed only in the M1 phase, widening the bandgap up to ~0.6 eV. Our approach of comparing all three insulating VO2 phases provides insight into a better understanding of the electronic structure and the origin of the insulating gap in VO2.
47 CFR 51.913 - Transition for VoIP-PSTN traffic.
Code of Federal Regulations, 2013 CFR
... 47 Telecommunication 3 2013-10-01 2013-10-01 false Transition for VoIP-PSTN traffic. 51.913... (CONTINUED) INTERCONNECTION Transitional Access Service Pricing § 51.913 Transition for VoIP-PSTN traffic. (a... originates and/or terminates in IP format shall be subject to a rate equal to the relevant...
47 CFR 51.913 - Transition for VoIP-PSTN traffic.
Code of Federal Regulations, 2012 CFR
... 47 Telecommunication 3 2012-10-01 2012-10-01 false Transition for VoIP-PSTN traffic. 51.913... (CONTINUED) INTERCONNECTION Transitional Access Service Pricing § 51.913 Transition for VoIP-PSTN traffic. (a... originates and/or terminates in IP format shall be subject to a rate equal to the relevant...
47 CFR 51.913 - Transition for VoIP-PSTN traffic.
Code of Federal Regulations, 2014 CFR
... 47 Telecommunication 3 2014-10-01 2014-10-01 false Transition for VoIP-PSTN traffic. 51.913... (CONTINUED) INTERCONNECTION Transitional Access Service Pricing § 51.913 Transition for VoIP-PSTN traffic. (a... originates and/or terminates in IP format shall be subject to a rate equal to the relevant...
Pressure-induced phase transitions and metallization in VO2
NASA Astrophysics Data System (ADS)
Bai, Ligang; Li, Quan; Corr, Serena A.; Meng, Yue; Park, Changyong; Sinogeikin, Stanislav V.; Ko, Changhyun; Wu, Junqiao; Shen, Guoyin
We report the results of pressure-induced phase transitions and metallization in VO2 based on synchrotron x-ray diffraction, electrical resistivity, and Raman spectroscopy. Our isothermal compression experiments at room temperature and 383 K show that the room temperature monoclinic phase (M 1 ,P 21/c ) and the high-temperature rutile phase (R ,P 42/m n m ) of VO2 undergo phase transitions to a distorted M 1 monoclinic phase (M 1' ,P 21/c ) above 13.0 GPa and to an orthorhombic phase (CaCl2-like, P n n m ) above 13.7 GPa, respectively. Upon further compression, both high-pressure phases transform into a new phase (phase X ) above 34.3 and 38.3 GPa at room temperature and 383 K, respectively. The room temperature M 1 -M 1' phase transition structurally resembles the R -CaCl2 phase transition at 383 K, suggesting a second-order displacive type of transition. Contrary to previous studies, our electrical resistivity results, Raman measurements, as well as ab initio calculations indicate that the new phase X , rather than the M 1' phase, is responsible for the metallization under pressure. The metallization mechanism is discussed based on the proposed crystal structure.
What governs skeletal muscle VO2max? New evidence.
Richardson, R S
Recent investigations into the determinants of skeletal muscle maximal oxygen consumption (VO2) have provided further evidence regarding the role of O2 supply and demand in governing exercise metabolism. Specifically, four studies utilizing both animal and human exercise models are highlighted here: 1) the role of the diffusive O2 component was examined in the exercising canine gastrocnemius muscle by a rightward shift in the O2 dissociation curve while maintaining O2 delivery constant; 2) the role of peripheral and central components was examined by studying the human quadriceps muscle, already recognized to have a very high mass specific O2 delivery, under conditions of increased (hyperoxia) and reduced O2 availability (hypoxia); 3) the role of intracellular PO2 in the progressive increase in lactate efflux from skeletal muscle from submaximal to maximal effort; and finally 4) the role of intracellular PO2 itself as a determinant of maximal mitochondrial O2 consumption. In summary, these investigations illustrate 1) the importance of the diffusion gradient from blood to muscle cell; 2) illustrate that even in functionally isolated trained skeletal muscle the highest recorded metabolic rates can be increased by increasing O2 supply; 3) that a constant intracellular PO2 during graded exercise is therefore unrelated to increasing lactate efflux; and 4) that only in hyperoxia does trained human skeletal muscle approaching very high mitochondrial metabolic limits, as shown by a disproportionate increase in intracellular PO2 for the recorded change in VO2max. PMID:10647536
Mel-cepstrum-based steganalysis for VoIP steganography
NASA Astrophysics Data System (ADS)
Kraetzer, Christian; Dittmann, Jana
Steganography and steganalysis in VoIP applications are important research topics as speech data is an appropriate cover to hide messages or comprehensive documents. In our paper we introduce a Mel-cepstrum based analysis known from speaker and speech recognition to perform a detection of embedded hidden messages. In particular we combine known and established audio steganalysis features with the features derived from Melcepstrum based analysis for an investigation on the improvement of the detection performance. Our main focus considers the application environment of VoIP-steganography scenarios. The evaluation of the enhanced feature space is performed for classical steganographic as well as for watermarking algorithms. With this strategy we show how general forensic approaches can detect information hiding techniques in the field of hidden communication as well as for DRM applications. For the later the detection of the presence of a potential watermark in a specific feature space can lead to new attacks or to a better design of the watermarking pattern. Following that the usefulness of Mel-cepstrum domain based features for detection is discussed in detail.
VO2 Kinetics and Metabolic Contributions Whilst Swimming at 95, 100, and 105% of the Velocity at VO2 max
Sousa, Ana C.; Vilas-Boas, João P.; Fernandes, Ricardo J.
A bioenergetical analysis of swimming at intensities near competitive distances is inexistent. It was aimed to compare the transient VO2 kinetics responses and metabolic contributions whilst swimming at different velocities around VO2max. 12 trained male swimmers performed (i) an incremental protocol to determine the velocity at VO2max (vVO2max) and (ii) three square wave exercises from rest to 95, 100, and 105% of vVO2max. VO2 was directly measured using a telemetric portable gas analyser and its kinetics analysed through a double-exponential model. Metabolic contributions were assessed through the sum of three energy components. No differences were observed in the fast component response (τ1—15, 18, and 16 s, A1—36, 34, and 37 mL · kg−1 · min−1, and Gain—32, 29, and 30 mL · min−1 at 95, 100, and 105% of the vVO2max, resp.) but A2 was higher in 95 and 100% compared to 105% intensity (480.76 ± 247.01, 452.18 ± 217.04, and 147.04 ± 60.40 mL · min−1, resp.). The aerobic energy contribution increased with the time sustained (83 ± 5, 74 ± 6, and 59 ± 7% for 95, 100, and 105%, resp.). The adjustment of the cardiovascular and/or pulmonary systems that determine O2 delivery and diffusion to the exercising muscles did not change with changing intensity, with the exception of VO2 slow component kinetics metabolic profiles. PMID:25045690
Theoretical characterization of vanadyl and VO3+ cations in gas phase
NASA Astrophysics Data System (ADS)
Almenia, S.; Mogren Al Mogren, M.; Ben Abdallah, D.; Linguerri, R.; Hochlaf, M.
We investigate VO2+ and VO3+ ions theoretically. The electronic computations are performed using multi reference configuration interaction approaches in conjunction with the aug-cc-pV5Z basis set. VO2+ potential possesses a Morse-like shape instead of the common volcanic shape since both the charge retaining (V2+ + O) and charge separating (V+ + O+) dissociation channels are almost coinciding in energy. Its intense blue color is due to the A2Π-X2Δ transition. We predict VO3+ as metastable. For bound states, we derived a set of accurate spectroscopic parameters. We estimate the adiabatic double and triple ionization energies of VO to be 22.5 eV and 50.9 eV.
Evaluating the perceived voice quality on VoIP network using interpolated FIR filter algorithm
NASA Astrophysics Data System (ADS)
Pal Singh, Harjit; Singh, Sarabjeet; Sarin, R. K.; Singh, Jasvir
Voice over Internet Protocol (VoIP) is a popular communication service nowadays. VoIP reduces the cost of call transmission by passing voice and video packets through the available bandwidth for data packets through Internet protocol. The quality of the VoIP signal is degraded due to the various network impairments. The proposed scheme, interpolated finite impulse response, is implemented as post-processor after decoding the signal in VoIP system. The performance of the proposed scheme is evaluated for various network conditions. The results of the proposed scheme are measured with the objective measurement methods for signal quality evaluation. The performance of the proposed system is compared with the existing techniques for quality improvement in VoIP system. The results show much improvement in speech quality with the proposed scheme in comparison to other similar schemes.
Hydrothermal growth of VO2 nanoplate thermochromic films on glass with high visible transmittance
NASA Astrophysics Data System (ADS)
Zhang, Jiasong; Li, Jingbo; Chen, Pengwan; Rehman, Fida; Jiang, Yijie; Cao, Maosheng; Zhao, Yongjie; Jin, Haibo
The preparation of thermochromic vanadium dioxide (VO2) films in an economical way is of interest to realizing the application of smart windows. Here, we reported a successful preparation of self-assembly VO2 nanoplate films on TiO2-buffered glass by a facile hydrothermal process. The VO2 films composed of triangle-shaped plates standing on substrates exhibit a self-generated porous structure, which favors the transmission of solar light. The porosity of films is easily controlled by changing the concentration of precursor solutions. Excellent thermochromic properties are observed with visible light transmittance as high as 70.3% and solar modulating efficiency up to 9.3% in a VO2 film with porosity of ~35.9%. This work demonstrates a promising technique to promote the commercial utilization of VO2 in smart windows.
Thermochromic properties of VO2 thin film on SiNx buffered glass substrate
NASA Astrophysics Data System (ADS)
Koo, Hyun; You, HyunWoo; Ko, Kyeong-Eun; Kwon, O.-Jong; Chang, Se-Hong; Park, Chan
VO2 thin films were deposited on soda lime glass substrates with silicon nitride sodium-diffusion barrier layer as diffusion barrier, in order to investigate the effect of sodium ion diffusion on the formation of VO2. SiNx layers with thicknesses over 30 nm were found to successfully prevent sodium ion diffusion in VO2 thin film and also contribute to the formation of VO2 thin film, which was confirmed by XRD spectra and XPS measurements. The change of infrared transmittance at 2500 nm wavelength with temperature change from room temperature to 80 °C was increased significantly, and the optical hysteresis width of the sample decreased by almost 6 K as well. The results suggest that applying diffusion barrier can improve the thermochromic properties of the VO2 films for energy-saving smart coatings, and silicon nitride can be one of the effective materials to prevent sodium ion diffusion.
Self-Assembly and Horizontal Orientation Growth of VO2 Nanowires
Cheng, Chun; Guo, Hua; Amini, Abbas; Liu, Kai; Fu, Deyi; Zou, Jian; Song, Haisheng
Single-crystalline vanadium dioxide (VO2) nanostructures have attracted an intense research interest recently because of their unique single-domain metal-insulator phase transition property. Synthesis of these nanostructures in the past was limited in density, alignment, or single-crystallinity. The assembly of VO2 nanowires (NWs) is desirable for a "bottom-up" approach to the engineering of intricate structures using nanoscale building blocks. Here, we report the successful synthesis of horizontally aligned VO2 NWs with a dense growth mode in the [1-100]quartz direction of a polished x-cut quartz surface using a simple vapor transport method. Our strategy of controlled growth of VO2 NWs promisingly paves the way for designing novel metal-insulator transition devices based on VO2 NWs. PMID:24965899
Hydrothermal growth of VO2 nanoplate thermochromic films on glass with high visible transmittance.
Zhang, Jiasong; Li, Jingbo; Chen, Pengwan; Rehman, Fida; Jiang, Yijie; Cao, Maosheng; Zhao, Yongjie; Jin, Haibo
The preparation of thermochromic vanadium dioxide (VO2) films in an economical way is of interest to realizing the application of smart windows. Here, we reported a successful preparation of self-assembly VO2 nanoplate films on TiO2-buffered glass by a facile hydrothermal process. The VO2 films composed of triangle-shaped plates standing on substrates exhibit a self-generated porous structure, which favors the transmission of solar light. The porosity of films is easily controlled by changing the concentration of precursor solutions. Excellent thermochromic properties are observed with visible light transmittance as high as 70.3% and solar modulating efficiency up to 9.3% in a VO2 film with porosity of ~35.9%. This work demonstrates a promising technique to promote the commercial utilization of VO2 in smart windows. PMID:27296772
Selective growth of single phase VO{sub 2}(A, B, and M) polymorph thin films
Srivastava, Amar; Saha, Surajit; Rotella, Helene; Pal, Banabir; Kalon, Gopinadhan; Mathew, Sinu; Motapothula, Mallikarjuna; Dykas, Michal; Yang, Ping; Okunishi, Eiji; Sarma, D. D.; Venkatesan, T.
We demonstrate the growth of high quality single phase films of VO{sub 2}(A, B, and M) on SrTiO{sub 3} substrate by controlling the vanadium arrival rate (laser frequency) and oxidation of the V atoms. A phase diagram has been developed (oxygen pressure versus laser frequency) for various phases of VO{sub 2} and their electronic properties are investigated. VO{sub 2}(A) phase is insulating VO{sub 2}(B) phase is semi-metallic, and VO{sub 2}(M) phase exhibits a metal-insulator transition, corroborated by photo-electron spectroscopic studies. The ability to control the growth of various polymorphs opens up the possibility for novel (hetero)structures promising new device functionalities.
Hydrothermal growth of VO2 nanoplate thermochromic films on glass with high visible transmittance
Zhang, Jiasong; Li, Jingbo; Chen, Pengwan; Rehman, Fida; Jiang, Yijie; Cao, Maosheng; Zhao, Yongjie; Jin, Haibo
The preparation of thermochromic vanadium dioxide (VO2) films in an economical way is of interest to realizing the application of smart windows. Here, we reported a successful preparation of self-assembly VO2 nanoplate films on TiO2-buffered glass by a facile hydrothermal process. The VO2 films composed of triangle-shaped plates standing on substrates exhibit a self-generated porous structure, which favors the transmission of solar light. The porosity of films is easily controlled by changing the concentration of precursor solutions. Excellent thermochromic properties are observed with visible light transmittance as high as 70.3% and solar modulating efficiency up to 9.3% in a VO2 film with porosity of ~35.9%. This work demonstrates a promising technique to promote the commercial utilization of VO2 in smart windows. PMID:27296772
Voltage switching of a VO{sub 2} memory metasurface using ionic gel
Goldflam, M. D.; Liu, M. K.; Chapler, B. C.; Stinson, H. T.; Sternbach, A. J.; McLeod, A. S.; Basov, D. N.; Zhang, J. D.; Geng, K.; Royal, M.; Jokerst, N. M.; Smith, D. R.; Kim, Bong-Jun; Averitt, R. D.; Kim, H-T.
We demonstrate an electrolyte-based voltage tunable vanadium dioxide (VO{sub 2}) memory metasurface. Large spatial scale, low voltage, non-volatile switching of terahertz (THz) metasurface resonances is achieved through voltage application using an ionic gel to drive the insulator-to-metal transition in an underlying VO{sub 2} layer. Positive and negative voltage application can selectively tune the metasurface resonance into the "off" or "on" state by pushing the VO{sub 2} into a more conductive or insulating regime respectively. Compared to graphene based control devices, the relatively long saturation time of resonance modification in VO{sub 2} based devices suggests that this voltage-induced switching originates primarily from electrochemical effects related to oxygen migration across the electrolyte–VO{sub 2} interface.
Silica-shell encapsulation and adhesion of VO2 nanowires to glass substrates: integrating solution-derived VO2 nanowires within thermally responsive coatings
NASA Astrophysics Data System (ADS)
Pelcher, Kate E.; Crawley, Matthew R.; Banerjee, Sarbajit
The binary vanadium oxide VO2 undergoes a reversible insulator—metal phase transition in response to increasing temperature accompanied by an orders of magnitude alteration of optical transmittance; the low-temperature monoclinic phase of VO2 is infrared-transmissive, whereas the high-temperature rutile phase is infrared-reflective. This remarkable property portends applications in thermally responsive spectral mirrors that can modulate infrared transmittance as a function of temperature. Using a modified Stöber process, we demonstrate the constitution of conformal SiO2 shells around the VO2 nanowires. The SiO2 shells enhance the robustness of the VO2 nanowires towards thermal oxidation; the thickness of the shells is observed to depend on the reaction time. Notably, the deposition of conformal shells does not deleteriously impact the metal—insulator transitions of the VO2 nanowire cores. A modification of this approach allows for the VO2 nanowires to be embedded within a SiO2 matrix bonded to glass. The applied coatings are strongly adhered to glass as evaluated using standardized ASTM methods. The coatings exhibit promising thermochromic response and attenuate transmission of near-infrared radiation with increasing temperature.
Synthesis, surface and optical properties of Ag2Cu(VO3)4 and Cu(VO3)2 vanadates
NASA Astrophysics Data System (ADS)
Qiao, Xuebin; Wan, Yingpeng; Li, Yuze; Qin, Lin; Seo, Hyo Jin
Ag2Cu(VO3)4 and Cu(VO3)2 were prepared via the sol-gel chemical synthesis. The phase formation was confirmed by X-ray powder polycrystalline diffraction (XRD) measurements. The surface properties were measured with the scanning electron microscope (SEM), energy dispersive spectra (EDS), transmission electron microscopy (TEM), and nitrogen adsorption-desorption isotherms. The optical properties and the band-gap structures were investigated. The vanadates have efficient optical absorption in the UV to visible wavelength region with an indirect allowed transition. Ag2Cu(VO3)4 has smaller band gap (1.85 eV) than that of Cu(VO3)2 (2.03 eV). The narrowed band gap is due to the hybridization between the Ag-4d and O-2p in the valence band. The photocatalysis was investigated by photodegradation of methylene blue (MB) solutions excited by the light with wavelength longer than 420 nm. Correspondingly Ag2Cu(VO3)4 has more efficient photocatalytic activity on MB photodegradation than that of Cu(VO3)2. The photocatalytic mechanisms were suggested according to the band positions and the trapping experiments.
Single crystal and magnetic structures of maricite-type AgMnVO{sub 4}
Ben Yahia, Hamdi; Shikano, Masahiro; Gaudin, Etienne; Avdeev, Maxim; Ling, Chris D.
Single crystals of the ternary manganese vanadate AgMnVO{sub 4}, were grown using AgVO{sub 3} flux. The structure was determined from single crystal X-ray diffraction data. The magnetic structure and properties of AgMnVO{sub 4} were characterized by magnetic susceptibility, specific heat, and low-temperature neutron powder diffraction measurements. AgMnVO{sub 4} crystallizes in the maricite-type structure with space group Pnma, a=9.5393(12), b=6.8132(9), c=5.3315(7) Å and Z=4. AgMnVO{sub 4} contains MnO{sub 4} chains made up of edge-sharing MnO{sub 6} octahedra, and these chains are interlinked by the VO{sub 4} and AgO{sub 4} tetrahedra. The specific heat measurements indicate a 3D-antiferromagnetic ordering at ∼12.1 K and the neutron powder diffraction measurements at 5 K show that the Mn{sup 2+}magnetic moments are antiferromagnetically coupled within the chains which are antiferromagnetically coupled to each other. - Graphical abstract: The AgMnVO{sub 4} crystals could be grown in AgVO{sub 3} flux and the magnetic structure was determined from neutron powder diffraction data. The spins in each MnO{sub 4} chain along [0 1 0] are antiferromagnetically coupled, while these antiferromagnetic chains are antiferromagnetically coupled along [0 0 1] but have a non-collinear arrangement along [1 0 1]. - Highlights: • We have been able to grow AgMnVO{sub 4} single crystals, using AgVO{sub 3} flux. • We solved its crystal structure using single crystal data. • We carried out magnetic susceptibility and specific heat measurements. • We solved the magnetic structure from low-temperature neutron powder diffraction data. • We compared the magnetic structure to that of NaFePO{sub 4}.
Time to Exhaustion at the VO2max Velocity in Swimming: A Review
Fernandes, Ricardo J.; Vilas-Boas, J. Paulo
The aim of this study was to present a review on the time to exhaustion at the minimum swimming velocity corresponding to maximal oxygen consumption (TLim-vVO2max). This parameter is critical both for the aerobic power and the lactate tolerance bioenergetical training intensity zones, being fundamental to characterize it, and to point out its main determinants. The few number of studies conducted in this topic observed that swimmers were able to maintain an exercise intensity corresponding to maximal aerobic power during 215 to 260 s (elite swimmers), 230 to 260 s (high level swimmers) and 310 to 325 s (low level swimmers), and no differences between genders were reported. TLim-vVO2max main bioenergetic and functional determinants were swimming economy and VO2 slow component (direct relationship), and vVO2max, velocity at anaerobic threshold and blood lactate production (inverse relationship); when more homogeneous groups of swimmers were analysed, the inverse correlation value between TLim-vVO2max and vVO2max was not so evident. In general, TLim-vVO2max was not related to VO2max. TLim-vVO2max seems also to be influenced by stroking parameters, with a direct relationship to stroke length and stroke index, and an inverse correlation with stroke rate. Assessing TLim-vVO2max, together with the anaerobic threshold and the biomechanical general parameters, will allow a larger spectrum of testing protocols application, helping to build more objective and efficient training programs. PMID:23486651
VO{sub 2} (A): Reinvestigation of crystal structure, phase transition and crystal growth mechanisms
Rao Popuri, Srinivasa; Artemenko, Alla; Labrugere, Christine; Miclau, Marinela; Villesuzanne, Antoine; Pollet, Michaël
Well crystallized VO{sub 2} (A) microrods were grown via a single step hydrothermal reaction in the presence of V{sub 2}O{sub 5} and oxalic acid. With the advantage of high crystalline samples, we propose P4/ncc as an appropriate space group at room temperature. From morphological studies, we found that the oriented attachment and layer by layer growth mechanisms are responsible for the formation of VO{sub 2} (A) micro rods. The structural and electronic transitions in VO{sub 2} (A) are strongly first order in nature, and a marked difference between the structural transition temperatures and electronic transitions temperature was evidenced. The reversible intra- (LTP-A to HTP-A) and irreversible inter- (HTP-A to VO{sub 2} (M1)) structural phase transformations were studied by in-situ powder X-ray diffraction. Attempts to increase the size of the VO{sub 2} (A) microrods are presented and the possible formation steps for the flower-like morphologies of VO{sub 2} (M1) are described. - Graphical abstract: Using a single step and template free hydrothermal synthesis, well crystallized VO{sub 2} (A) microrods were prepared and the P4/ncc space group was assigned to the room temperature crystal structure. Reversible and irreversible phase transitions among different VO{sub 2} polymorphs were identified and their progressive nature was highlighted. Attempts to increase the microrods size, involving layer by layer formation mechanisms, are presented. - Highlights: • Highly crystallized VO{sub 2} (A) microrods were grown via a single step hydrothermal process. • The P4/ncc space group was determined for VO{sub 2} (A) at room temperature. • The electronic structure and progressive nature of the structural phase transition were investigated. • A weak coupling between structural and electronic phase transitions was identified. • Different crystallite morphologies were discussed in relation with growth mechanisms.
Preparation and thermochromic properties of Ce-doped VO{sub 2} films
Song, Linwei; Zhang, Yubo; Huang, Wanxia; Shi, Qiwu; Li, Danxia; Zhang, Yang; Xu, Yuanjie
Graphical abstract: This effect of doping concentration on the phase transition temperature of VO{sub 2} films demonstrates that the phase transition temperature is decreasing along with the increase of the Ce dopant concentrations. After doping Ce, the transition temperature of VO{sub 2} film changes appreciably. Highlights: ► Ce-doped VO{sub 2} films were prepared on muscovite substrate by inorganic sol–gel method for the first time. ► The cerium existing in the VO{sub 2} films in the form of Ce{sup 4+} and Ce{sup 3+} was substituted for part of V atoms in the lattice. ► Ce doping could remarkably reduce the particle size of the Ce-doped films compared with undoped films. ► The phase transition temperature of Ce-doped VO{sub 2} films decreased appreciably with maintaining high-quality phase transition. - Abstract: Mixture of cerium (III) nitrate hexahydrate and vanadium pentaoxide powder were used as precursor to prepare Ce-doped VO{sub 2} films on the muscovite substrate by inorganic sol–gel method. SEM, XRD and XPS were used to investigate the morphologies and structures of VO{sub 2} films. The results show that the VO{sub 2} films grow on the muscovite substrate with preferred orientated (0 1 1) plane and the Ce exists in the form of Ce{sup 4+} and Ce{sup 3+} replacing part of V atoms in the lattice. The infrared transmittance change was measured from room temperature to the temperature above the metal–insulator transition. The films have excellent thermochromic performance. The metal–insulator transition temperature of VO{sub 2} films changes appreciably with Ce doped, which decreases by 4.5 °C per 1 at.% doping. Furthermore, Ce doping could remarkably reduce the particle size of VO{sub 2} films.
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Effects of training on muscle O2 transport at VO2max
NASA Technical Reports Server (NTRS)
Roca, J.; Agusti, A. G.; Alonso, A.; Poole, D. C.; Viegas, C.; Barbera, J. A.; Rodriguez-Roisin, R.; Ferrer, A.; Wagner, P. D.
To quantify the relative contributions of convective and peripheral diffusive components of O2 transport to the increase in leg O2 uptake (VO2leg) at maximum O2 uptake (VO2max) after 9 wk of endurance training, 12 sedentary subjects (age 21.8 +/- 3.4 yr, VO2max 36.9 +/- 5.9 ml.min-1.kg-1) were studied. VO2max, leg blood flow (Qleg), and arterial and femoral venous PO2, and thus VO2leg, were measured while the subjects breathed room air, 15% O2, and 12% O2. The sequence of the three inspirates was balanced. After training, VO2max and VO2leg increased at each inspired O2 concentration [FIO2; mean over the 3 FIO2 values 25.2 +/- 17.8 and 36.5 +/- 33% (SD), respectively]. Before training, VO2leg and mean capillary PO2 were linearly related through the origin during hypoxia but not during room air breathing, suggesting that, at 21% O2, VO2max was not limited by O2 supply. After training, VO2leg and mean capillary PO2 at each FIO2 fell along a straight line with zero intercept, just as in athletes (Roca et al. J. Appl. Physiol. 67: 291-299, 1989). Calculated muscle O2 diffusing capacity (DO2) rose 34% while Qleg increased 19%. The relatively greater rise in DO2 increased the DO2/Qleg, which led to 9.9% greater O2 extraction. By numerical analysis, the increase in Qleg alone (constant DO2) would have raised VO2leg by 35 ml/min (mean), but that of DO2 (constant Qleg) would have increased VO2leg by 85 ml/min, more than twice as much. The sum of these individual effects (120 ml/min) was less (P = 0.013) than the observed rise of 164 ml/min (mean). This synergism (explained by the increase in DO2/Qleg) seems to be an important contribution to increases in VO2max with training.
VO2 Off Transient Kinetics in Extreme Intensity Swimming
Sousa, Ana; Figueiredo, Pedro; Keskinen, Kari L.; Rodríguez, Ferran A.; Machado, Leandro; Vilas-Boas, João P.; Fernandes, Ricardo J.
Inconsistencies about dynamic asymmetry between the on- and off- transient responses in oxygen uptake are found in the literature. Therefore, the purpose of this study was to characterize the oxygen uptake off-transient kinetics during a maximal 200-m front crawl effort, as examining the degree to which the on/off regularity of the oxygen uptake kinetics response was preserved. Eight high level male swimmers performed a 200-m front crawl at maximal speed during which oxygen uptake was directly measured through breath-by-breath oxymetry (averaged every 5 s). This apparatus was connected to the swimmer by a low hydrodynamic resistance respiratory snorkel and valve system. Results: The on- and off-transient phases were symmetrical in shape (mirror image) once they were adequately fitted by a single-exponential regression models, and no slow component for the oxygen uptake response was developed. Mean (± SD) peak oxygen uptake was 69.0 (± 6.3) mL·kg-1·min-1, significantly correlated with time constant of the off- transient period (r = 0.76, p < 0.05) but not with any of the other oxygen off-transient kinetic parameters studied. A direct relationship between time constant of the off-transient period and mean swimming speed of the 200-m (r = 0.77, p < 0.05), and with the amplitude of the fast component of the effort period (r = 0.72, p < 0.05) were observed. The mean amplitude and time constant of the off-transient period values were significantly greater than the respective on- transient. In conclusion, although an asymmetry between the on- and off kinetic parameters was verified, both the 200-m effort and the respectively recovery period were better characterized by a single exponential regression model. Key points The VO2 slow component was not observed in the recovery period of swimming extreme efforts; The on and off transient periods were better fitted by a single exponential function, and so, these effort and recovery periods of swimming extreme efforts are
TAPAS, a VO archive at the IRAM 30-m telescope
NASA Astrophysics Data System (ADS)
Leon, Stephane; Espigares, Victor; Ruíz, José Enrique; Verdes-Montenegro, Lourdes; Mauersberger, Rainer; Brunswig, Walter; Kramer, Carsten; Santander-Vela, Juan de Dios; Wiesemeyer, Helmut
Astronomical observatories are today generating increasingly large volumes of data. For an efficient use of them, databases have been built following the standards proposed by the International Virtual Observatory Alliance (IVOA), providing a common protocol to query them and make them interoperable. The IRAM 30-m radio telescope, located in Sierra Nevada (Granada, Spain) is a millimeter wavelength telescope with a constantly renewed, extensive choice of instruments, and capable of covering the frequency range between 80 and 370 GHz. It is continuously producing a large amount of data thanks to the more than 200 scientific projects observed each year. The TAPAS archive at the IRAM 30-m telescope is aimed to provide public access to the headers describing the observations performed with the telescope, according to a defined data policy, making as well the technical data available to the IRAM staff members. A special emphasis has been made to make it Virtual Observatory (VO) compliant, and to offer a VO compliant web interface allowing to make the information available to the scientific community. TAPAS is built using the Django Python framework on top of a relational MySQL database, and is fully integrated with the telescope control system. The TAPAS data model (DM) is based on the Radio Astronomical DAta Model for Single dish radio telescopes (RADAMS), to allow for easy integration into the VO infrastructure. A metadata modeling layer is used by the data-filler to allow an implementation free from assumptions about the control system and the underlying database. TAPAS and its public web interface (
AMDA/IDIS demonstrator for planetary plasma VO
NASA Astrophysics Data System (ADS)
Jacquey, C.; André, N.; Cecconi, B.; Génot, V.; Gangloff, M.; Budnik, E.; Pallier, E.; Bouchemit, M.
We present a demonstrator developed at CDPP (Centre de Données de Physique des Plasmas, http://cdpp.cesr.fr ) which applies on the MAPSKP database (http://mapskp.cesr.fr/). The demonstrator consists of three main components: a set of web-services offered on the MAPSKP database, a searchable registry using the SPASE (http://www.spase-group.org/) datamodel and the AMDA service (http://cdpp-amda.cesr.fr/). The former is a web based easy-to-use tool which allows to exploit data coming from its local database or distant databases, as the MAPSKP one for example. The functionalities offered by AMDA include visualisation, computation of user-edited parameters, visual search and automated search on the content of the data. We will show what has been learned from this experience in regard of future planetology VO to be built.
Reactive evaporation of anomalous blue VO/sub 2/
Case, F.C.
Thin films of vanadium dioxide exhibit a thermally induced semiconductor-to-metal phase transition near 67/sup 0/ C. In most deposition conditions, the transition is accompanied by large changes in optical properties at infrared wavelengths, but with only slight visible contrast. Recently, reactive evaporation at high temperatures and in stringent process conditions of so-called blue VO/sub 2/ has been reported (G. A. Nyberg and R. A. Buhrman, J. Vac. Sci. Technol. A 2, 301 (1984)). These films exhibit a striking blue-to-red transition in transmitted light. In this paper, a new technique for thin-film growth of anomalous vanadium dioxide will be presented. The primary steps in the process are the reactive evaporation of vanadium oxide at ambient temperature followed by anneal in flowing oxygen. Optical and microstructural data for material deposited on sapphire and fused quartz substrates will be compared to standard vanadium oxide.
Active terahertz nanoantennas based on VO2 phase transition.
Seo, Minah; Kyoung, Jisoo; Park, Hyeongryeol; Koo, Sukmo; Kim, Hyun-sun; Bernien, Hannes; Kim, Bong Jun; Choe, Jong Ho; Ahn, Yeong Hwan; Kim, Hyun-Tak; Park, Namkyoo; Park, Q-Han; Ahn, Kwangjun; Kim, Dai-sik
Unusual performances of metamaterials such as negative index of refraction, memory effect, and cloaking originate from the resonance features of the metallic composite atom(1-6). Indeed, control of metamaterial properties by changing dielectric environments of thin films below the metallic resonators has been demonstrated(7-11). However, the dynamic control ranges are still limited to less than a factor of 10,(7-11) with the applicable bandwidth defined by the sharp resonance features. Here, we present ultra-broad-band metamaterial thin film with colossal dynamic control range, fulfilling present day research demands. Hybridized with thin VO(2) (vanadium dioxide) (12-18) films, nanoresonator supercell arrays designed for one decade of spectral width in terahertz frequency region show an unprecedented extinction ratio of over 10000 when the underlying thin film experiences a phase transition. Our nanoresonator approach realizes the full potential of the thin film technology for long wavelength applications. PMID:20469898
Correlation between surface morphology and electrical properties of VO2 films grown by direct thermal oxidation method
NASA Astrophysics Data System (ADS)
Yoon, Joonseok; Park, Changwoo; Park, Sungkyun; Mun, Bongjin Simon; Ju, Honglyoul
We investigate surface morphology and electrical properties of VO2 films fabricated by direct thermal oxidation method. The VO2 film prepared with oxidation temperature at 580 °C exhibits excellent qualities of VO2 characteristics, e.g. a metal-insulator transition (MIT) near 67 °C, a resistivity ratio of ∼2.3 × 104, and a bandgap of 0.7 eV. The analysis of surface morphology with electrical resistivity of VO2 films reveals that the transport properties of VO2 films are closely related to the grain size and surface roughness that vary with oxidation annealing temperatures.
Structural, photophysical and photocatalytic properties of novel Bi2AlVO7.
Luan, Jingfei; Zhao, Wei; Feng, Jingwei; Cai, Hongling; Zheng, Zheng; Pan, Bingcai; Wu, Xiaoshan; Zou, Zhigang; Li, Yongmei
Bi(2)AlVO(7) was prepared by solid-state reaction technique for the first time and the structural and photocatalytic properties of Bi(2)AlVO(7) and Bi(2)InTaO(7) were investigated. The results showed that Bi(2)AlVO(7) crystallized in the tetragonal crystal system with space group I4/mmm. In addition, the band gaps of Bi(2)AlVO(7) and Bi(2)InTaO(7) were estimated to be about 2.06 and 2.81 eV. The photocatalytic degradation of aqueous methylene blue (MB) dye with Bi(2)AlVO(7) or Bi(2)InTaO(7) as catalyst was investigated under visible light irradiation. Bi(2)AlVO(7) showed higher photocatalytic activity compared with Bi(2)InTaO(7) for photocatalytic degradation of MB under visible light irradiation. Complete removal of aqueous MB dye was realized after visible light irradiation for 160 min with Bi(2)AlVO(7) as the photocatalyst. The reduction of the total organic carbon (TOC) and the formation of inorganic products, SO(4)(2-) and NO(3)(-) revealed the continuous mineralization of aqueous MB dye during the photocatalytic process. The possible photocatalytic degradation pathway of aqueous MB dye was revealed under visible light irradiation. PMID:18842341
Synthesis and photocatalytic performances of BiVO 4 by ammonia co-precipitation process
NASA Astrophysics Data System (ADS)
Yu, Jianqiang; Zhang, Yan; Kudo, Akihiko
This paper reports the preparation and photocatalytic performance of Bismuth vanadate (BiVO 4) by a facile and inexpensive approach. An amorphous BiVO 4 was first prepared by a co-precipitation process from aqueous solutions of Bi(NO 3) 3 and NH 4VO 3 using ammonia. Followed by heating treatment at various temperatures, the amorphous phase converted to crystalline BiVO 4 with a structure between monoclinic and tetragonal scheelite. The crystallization of BiVO 4 occurred at about 523 K, while the nanocrystalline BiVO 4 were formed with a heat-treatment of lower than 673 K. However, when the heat-treatment was carried out at 773 K, the accumulation of nanocrystals to bulk particles was observed. The photocatalytic performances of the materials were investigated by O 2 evolution under visible-light, and MB decomposition under solar simulator. The results demonstrated that the crystalline structure is still the vital factor for the activities of both reactions. However, the crystallinity of BiVO 4 gives a major influence on the activity of O 2 evolution, whereas the surface area, plays an important role for photocatalytic MB decomposition.
Terbium-Doped VO2 Thin Films: Reduced Phase Transition Temperature and Largely Enhanced Luminous Transmittance.
Wang, Ning; Duchamp, Martial; Dunin-Borkowski, Rafal E; Liu, Shiyu; Zeng, XianTing; Cao, Xun; Long, Yi
Vanadium dioxide (VO2) is a well-known thermochromic material with large IR modulating ability, promising for energy-saving smart windows. The main drawbacks of VO2 are its high phase transition temperature (τ(c) = 68°C), low luminous transmission (T(lum)), and weak solar modulating ability (ΔT(sol)). In this paper, the terbium cation (Tb(3+)) doping was first reported to reduce τ(c) and increase T(lum) of VO2 thin films. Compared with pristine VO2, 2 at. % doping level gives both enhanced T(lum) and ΔT(sol) from 45.8% to 54.0% and 7.7% to 8.3%, respectively. The T(lum) increases with continuous Tb(3+) doping and reaches 79.4% at 6 at. % doping level, representing ∼73.4% relative increment compared with pure VO2. This has surpassed the best reported doped VO2 thin films. The enhanced thermochromic properties is meaningful for smart window applications of VO2 materials. PMID:26729057
Electrochemical properties of VO-flyash composite for lithium polymer battery
NASA Astrophysics Data System (ADS)
Kim, Jong-Uk; Gu, Hal-Bon
A VO-flyash composite electrode for a lithium/polymer battery (LPB) was developed. We investigated XRD diffraction and electrochemical properties of vanadium oxide (VO)-flyash composite with polyvinylidene (PVDF)/polyacrylonitrile (PAN)-based polymer electrolyte as a function of mixing ratio. The discharge capacity of VO-flyash with 50 wt.% V 2O 5 in PVDF-PAN-PC 5EC 5iClO 4 electrolyte was 150 and 128 mAh/g at 1 and 10 cycles, respectively. The discharge capacity of VO-flyash with 85 wt.% V 2O 5 was 195 mAh/g at 10 cycles. The capacity retention of VO-flyash anode with 3 wt.% V 2O 5 was higher than that of VO-flyash cathode with 85 wt.% V 2O 5. The VO-flyash with 3 wt.% V 2O 5 composite anode in PVDF/PAN-based electrolyte shows good capacity with cycling.
Handover Management for VoWLAN Based on Estimation of AP Queue Length and Frame Retries
NASA Astrophysics Data System (ADS)
Niswar, Muhammad; Kashihara, Shigeru; Tsukamoto, Kazuya; Kadobayashi, Youki; Yamaguchi, Suguru
Switching a communication path from one Access Point (AP) to another in inter-domain WLANs is a critical challenge for delay-sensitive applications such as Voice over IP (VoIP) because communication quality during handover (HO) is more likely to be deteriorated. To maintain VoIP quality during HO, we need to solve many problems. In particular, in bi-directional communication such as VoIP, an AP becomes a bottleneck with the increase of VoIP calls. As a result, packets queued in the AP buffer may experience a large queuing delay or packet losses due to increase in queue length or buffer overflow, thereby causing the degradation of VoIP quality for the Mobile Nodes (MNs) side. To avoid this degradation, MNs need to appropriately and autonomously execute HO in response to the change in wireless network condition, i.e., the deterioration of wireless link quality and the congestion state at the AP. In this paper, we propose an HO decision strategy considering frame retries, AP queue length, and transmission rate at an MN for maintaining VoIP quality during HO. Through simulation experiments, we then show that our proposed method can maintain VoIP quality during HO by properly detecting the wireless network condition.
Efficient solar-driven water splitting by nanocone BiVO4-perovskite tandem cells.
Qiu, Yongcai; Liu, Wei; Chen, Wei; Chen, Wei; Zhou, Guangmin; Hsu, Po-Chun; Zhang, Rufan; Liang, Zheng; Fan, Shoushan; Zhang, Yuegang; Cui, Yi
Bismuth vanadate (BiVO4) has been widely regarded as a promising photoanode material for photoelectrochemical (PEC) water splitting because of its low cost, its high stability against photocorrosion, and its relatively narrow band gap of 2.4 eV. However, the achieved performance of the BiVO4 photoanode remains unsatisfactory to date because its short carrier diffusion length restricts the total thickness of the BiVO4 film required for sufficient light absorption. We addressed the issue by deposition of nanoporous Mo-doped BiVO4 (Mo:BiVO4) on an engineered cone-shaped nanostructure, in which the Mo:BiVO4 layer with a larger effective thickness maintains highly efficient charge separation and high light absorption capability, which can be further enhanced by multiple light scattering in the nanocone structure. As a result, the nanocone/Mo:BiVO4/Fe(Ni)OOH photoanode exhibits a high water-splitting photocurrent of 5.82 ± 0.36 mA cm(-2) at 1.23 V versus the reversible hydrogen electrode under 1-sun illumination. We also demonstrate that the PEC cell in tandem with a single perovskite solar cell exhibits unassisted water splitting with a solar-to-hydrogen conversion efficiency of up to 6.2%. PMID:27386565
Efficient solar-driven water splitting by nanocone BiVO4-perovskite tandem cells
Qiu, Yongcai; Liu, Wei; Chen, Wei; Chen, Wei; Zhou, Guangmin; Hsu, Po-Chun; Zhang, Rufan; Liang, Zheng; Fan, Shoushan; Zhang, Yuegang; Cui, Yi
Bismuth vanadate (BiVO4) has been widely regarded as a promising photoanode material for photoelectrochemical (PEC) water splitting because of its low cost, its high stability against photocorrosion, and its relatively narrow band gap of 2.4 eV. However, the achieved performance of the BiVO4 photoanode remains unsatisfactory to date because its short carrier diffusion length restricts the total thickness of the BiVO4 film required for sufficient light absorption. We addressed the issue by deposition of nanoporous Mo-doped BiVO4 (Mo:BiVO4) on an engineered cone-shaped nanostructure, in which the Mo:BiVO4 layer with a larger effective thickness maintains highly efficient charge separation and high light absorption capability, which can be further enhanced by multiple light scattering in the nanocone structure. As a result, the nanocone/Mo:BiVO4/Fe(Ni)OOH photoanode exhibits a high water-splitting photocurrent of 5.82 ± 0.36 mA cm−2 at 1.23 V versus the reversible hydrogen electrode under 1-sun illumination. We also demonstrate that the PEC cell in tandem with a single perovskite solar cell exhibits unassisted water splitting with a solar-to-hydrogen conversion efficiency of up to 6.2%. PMID:27386565
The heart rate VO2 relationship of aerobic dance: a comparison of target heart rate methods.
Scharff-Olson, M; Williford, H N; Smith, F H
The purpose of this study was to examine the relationship between heart rate (HR) and oxygen consumption (VO2) for aerobic dance exercise. Therefore, eleven females completed 20 minutes of aerobic dance with continuous monitoring of HR and VO2. These physiological responses were analyzed with correlation/regression techniques. The results showed that for aerobic dance to produce a response in excess of 50% of VO2 max, the target HR must be approximately 80% of the age-predicted HR max or greater. In contrast, previously reported data for treadmill running shows that 50% of VO2 max is achieved at approximately 65% of age-predicted HR max in females. The maximum heart rate reserve (Karvonen) method was also found to underestimate the actual VO2 of AD. With the Karvonen method, the target heart rate must approximate 65% of maximum HR reserve in order to elicit a VO2 response which is representative of 50% of VO2 max. These data support recent research which illustrates that target heart rate prescriptions derived from treadmill testing may fail to accurately place AD participants in the recommended training zone. PMID:1293420
The VO-Dance web application at the IA2 data center
NASA Astrophysics Data System (ADS)
Molinaro, Marco; Knapic, Cristina; Smareglia, Riccardo
Italian center for Astronomical Archives (IA2, http://ia2.oats.inaf.it) is a national infrastructure project of the Italian National Institute for Astrophysics (Istituto Nazionale di AstroFisica, INAF) that provides services for the astronomical community. Besides data hosting for the Large Binocular Telescope (LBT) Corporation, the Galileo National Telescope (Telescopio Nazionale Galileo, TNG) Consortium and other telescopes and instruments, IA2 offers proprietary and public data access through user portals (both developed and mirrored) and deploys resources complying the Virtual Observatory (VO) standards. Archiving systems and web interfaces are developed to be extremely flexible about adding new instruments from other telescopes. VO resources publishing, along with data access portals, implements the International Virtual Observatory Alliance (IVOA) protocols providing astronomers with new ways of analyzing data. Given the large variety of data flavours and IVOA standards, the need for tools to easily accomplish data ingestion and data publishing arises. This paper describes the VO-Dance tool, that IA2 started developing to address VO resources publishing in a dynamical way from already existent database tables or views. The tool consists in a Java web application, potentially DBMS and platform independent, that stores internally the services' metadata and information, exposes restful endpoints to accept VO queries for these services and dynamically translates calls to these endpoints to SQL queries coherent with the published table or view. In response to the call VO-Dance translates back the database answer in a VO compliant way.
Chapter 35: Describing Data and Data Collections in the VO
NASA Astrophysics Data System (ADS)
Kent, B. R.; Hanisch, R. J.; Williams, R. D.
The list of numbers: 19.22, 17.23, 18.11, 16.98, and 15.11, is of little intrinsic interest without information about the context in which they appear. For instance, are these daily closing stock prices for your favorite investment, or are they hourly photometric measurements of an increasingly bright quasar? The information needed to define this context is called metadata. Metadata are data about data. Astronomers are familiar with metadata through the headers of FITS files and the names and units associated with columns in a table or database. In the VO, metadata describe the contents of tables, images, and spectra, as well as aggregate collections of data (archives, surveys) and computational services. Moreover, VO metadata are constructed according to rules that avoid ambiguity and make it clear whether, in the example above, the stock prices are in dollars or euros, or the photometry is Johnson V or Sloan g. Organization of data is important in any scientific discipline. Equally crucial are the descriptions of that data: the organization publishing the data, its creator or the person making it available, what instruments were used, units assigned to measurement, calibration status, and data quality assessment. The Virtual Observatory metadata scheme not only applies to datasets, but to resources as well, including data archive facilities, searchable web forms, and online analysis and display tools. Since the scientific output flowing from large datasets depends greatly on how well the data are described, it is important for users to understand the basics of the metadata scheme in order to locate the data that they want and use it correctly. Metadata are the key to data discovery and data and service interoperability in the Virtual Observatory.
Lasing of Yb in a mixed YGdVO4 crystal with bistability and polarization switching
NASA Astrophysics Data System (ADS)
Liu, Junhai; Zhang, Huaijin; Mateos, Xavier; Han, Wenjuan; Petrov, Valentin
The orthovanadate crystals YVO4, GdVO4, and LuVO4 attract much attention as promising host materials for the trivalent Yb-ion since such crystals are characterized by large absorption and emission cross sections, broad absorption and emission bands, and higher thermal conductivities than most of the other Yb-doped materials. More interestingly, their laser operation is characterized by optical bistability, apparently a unique feature of Yb-doped vanadates, not found so far in other Yb-lasers or even in other solid-state lasers. The optically "passive" vanadates, YVO4, GdVO4, and LuVO4, as well as the stoichiometric YbVO4 exhibit the same zircon structure and continuous isostructural solid solutions can be expected. The absorption and emission spectra of Yb0.0054:Y0.3481Gd0.6465VO4, a specific compound in the mixed Ybt:YxGd1-x-tVO4 series, inherit the spectroscopic features of both Yb:YVO4 and Yb:GdVO4. We found that this Yb-doped solid solution also displays optical bistability in continuous-wave (cw) laser operation. The strongly pronounced bistability extends from Pabs=1.9 W to Pabs=3.4 W while the output power amounts to 0.98 W at the upthreshold. Distinct from the previously reported Yb:LuVO4 laser, coexistence and switching of the σ and π polarization states occur along with emission wavelength shift in the bistability region upon decreasing the pump power. Increasing the output coupling reduces the bistability region while expanding the coexistence region for the σ and π polarization states.
Lithium-inserted vanadium dioxide (LixVO2) thin films
NASA Astrophysics Data System (ADS)
Khan, Mohammad S. R.
Thermochromic switching between a low-temperature and high-temperature less transparent state is possible in thin films based on vanadium dioxide (VO2). The critical temperature Tc at which the transition takes place in VO2 is on the order of 68 degrees Celsius which can be depressed towards a comfortable temperature by several techniques, including dopants. Dopants can be inserted by electrochemical means. This work is an exploratory study of the electrochromism of LixVO2 with a view to 'smart window' applications. Thin films of LixVO2 (0 less than or equal to x less than or equal to 0.43) were made by reactive sputtering and annealing electrolyte of LiClO4 and propylene carbonate. A maximum lithium content of x equals 0.43 was accomplished. Optical spectral response at wavelength pertinent to solar radiation was reported. Lithium insertion increased the transmittance gradually and reversibly i.e. LixVO2 showed electrochromism and bleached under Li insertion. LixVO2 also showed thermochroism, although to a smaller degree than VO2 and was most transparent at low temperature. Temperature- dependent electrical conductivity and thermoelectric power measurements were also performed. A conductivity transition by approximately 3 orders of magnitude was seen at approximately 60 degrees Celsius in VO2. This transition decreased in proportion with the amount of Li intercalation and was less than one order of magnitude in Li0.43VO2. Lithiation also decreased Tc by a few degrees Celsius. The thermoelectric power showed a well defined increase when Tc was exceeded.
Synthesis and Structure of ACa 9(VO 4) 7 Compounds, A=Bi or a Rare Earth
NASA Astrophysics Data System (ADS)
Evans, J. S. O.; Huang, J.; Sleight, A. W.
Phases of the type ACa9(VO4)7 have been prepared where A can be a trivalent rare earth cation or Bi3+. The structure of BiCa9(VO4)7 was determined from single crystal X-ray diffraction data. The space group is R3 with a=10.8511(2) and c=38.0505(9) at 120 K and Z=6. The structure is related to that of Ca3(VO4)2, but a site partially occupied by Ca in Ca3(VO4)2 is completely vacant in BiCa9(VO4)7. All the ACa9(VO4)7 phases prepared showed a significant second harmonic signal. For the rare-earth compounds, the magnitude of the signal was comparable to that of KH2PO4; a value three times higher was found for BiCa9(VO4)7.
Raman study of phonon modes in ErVO4 single crystals
NASA Astrophysics Data System (ADS)
Guedes, I.; Hirano, Y.; Grimsditch, M.; Wakabayashi, N.; Loong, C.-K.; Boatner, L. A.
The phonon modes of a pure ErVO4 crystal were determined at room temperature using Raman scattering methods, and the observed frequencies were assigned according to group theory in terms of the internal modes of the VO43- ions and the external modes of the Er(VO4) lattice. The assignments of the phonon modes match well with the overall phonon systematics of the rare-earth orthovanadate series, and the results presented here reinforce the general trend of bonding strength in the zircon series of RVO4, RAsO4, and RPO4 materials.
Probing orbital ordering in LaVO3 epitaxial films by Raman scattering
NASA Astrophysics Data System (ADS)
Vrejoiu, I.; Himcinschi, C.; Jin, L.; Jia, C.-L.; Raab, N.; Engelmayer, J.; Waser, R.; Dittmann, R.; van Loosdrecht, P. H. M.
Single crystals of Mott-Hubbard insulator LaVO3 exhibit spin and orbital ordering along with a structural change below ≈140 K. The occurrence of orbital ordering in epitaxial LaVO3 films has, however, been little investigated. By temperature-dependent Raman scattering spectroscopy, we probed and evidenced the transition to orbital ordering in epitaxial LaVO3 film samples fabricated by pulsed-laser deposition. This opens up the possibility to explore the influence of different epitaxial strain (compressive vs. tensile) and of epitaxy-induced distortions of oxygen octahedra on the orbital ordering, in epitaxial perovskite vanadate films.
Influence of prior exercise on VO2 kinetics subsequent exhaustive rowing performance.
Sousa, Ana; Ribeiro, João; Sousa, Marisa; Vilas-Boas, João Paulo; Fernandes, Ricardo J
Prior exercise has the potential to enhance subsequent performance by accelerating the oxygen uptake (VO2) kinetics. The present study investigated the effects of two different intensities of prior exercise on pulmonary VO2 kinetics and exercise time during subsequent exhaustive rowing exercise. It was hypothesized that in prior heavy, but not prior moderate exercise condition, overall VO2 kinetics would be faster and the VO2 primary amplitude would be higher, leading to longer exercise time at VO2max. Six subjects (mean ± SD; age: 22.9±4.5 yr; height: 181.2±7.1 cm and body mass: 75.5±3.4 kg) completed square-wave transitions to 100% of VO2max from three different conditions: without prior exercise, with prior moderate and heavy exercise. VO2 was measured using a telemetric portable gas analyser (K4b(2), Cosmed, Rome, Italy) and the data were modelled using either mono or double exponential fittings. The use of prior moderate exercise resulted in a faster VO2 pulmonary kinetics response (τ1 = 13.41±3.96 s), an improved performance in the time to exhaustion (238.8±50.2 s) and similar blood lactate concentrations ([La(-)]) values (11.8±1.7 mmol.L(-1)) compared to the condition without prior exercise (16.0±5.56 s, 215.3±60.1 s and 10.7±1.2 mmol.L(-1), for τ1, time sustained at VO2max and [La(-)], respectively). Performance of prior heavy exercise, although useful in accelerating the VO2 pulmonary kinetics response during a subsequent time to exhaustion exercise (τ1 = 9.18±1.60 s), resulted in a shorter time sustained at VO2max (155.5±46.0 s), while [La(-)] was similar (13.5±1.7 mmol.L(-1)) compared to the other two conditions. Although both prior moderate and heavy exercise resulted in a faster pulmonary VO2 kinetics response, only prior moderate exercise lead to improved rowing performance. PMID:24404156
Influence of Prior Exercise on VO2 Kinetics Subsequent Exhaustive Rowing Performance
Sousa, Ana; Ribeiro, João; Sousa, Marisa; Vilas-Boas, João Paulo; Fernandes, Ricardo J.
Prior exercise has the potential to enhance subsequent performance by accelerating the oxygen uptake (VO2) kinetics. The present study investigated the effects of two different intensities of prior exercise on pulmonary VO2 kinetics and exercise time during subsequent exhaustive rowing exercise. It was hypothesized that in prior heavy, but not prior moderate exercise condition, overall VO2 kinetics would be faster and the VO2 primary amplitude would be higher, leading to longer exercise time at VO2max. Six subjects (mean ± SD; age: 22.9±4.5 yr; height: 181.2±7.1 cm and body mass: 75.5±3.4 kg) completed square-wave transitions to 100% of VO2max from three different conditions: without prior exercise, with prior moderate and heavy exercise. VO2 was measured using a telemetric portable gas analyser (K4b2, Cosmed, Rome, Italy) and the data were modelled using either mono or double exponential fittings. The use of prior moderate exercise resulted in a faster VO2 pulmonary kinetics response (τ1 = 13.41±3.96 s), an improved performance in the time to exhaustion (238.8±50.2 s) and similar blood lactate concentrations ([La−]) values (11.8±1.7 mmol.L−1) compared to the condition without prior exercise (16.0±5.56 s, 215.3±60.1 s and 10.7±1.2 mmol.L−1, for τ1, time sustained at VO2max and [La−], respectively). Performance of prior heavy exercise, although useful in accelerating the VO2 pulmonary kinetics response during a subsequent time to exhaustion exercise (τ1 = 9.18±1.60 s), resulted in a shorter time sustained at VO2max (155.5±46.0 s), while [La−] was similar (13.5±1.7 mmol.L−1) compared to the other two conditions. Although both prior moderate and heavy exercise resulted in a faster pulmonary VO2 kinetics response, only prior moderate exercise lead to improved rowing performance. PMID:24404156
Controlled synthesis of m-BiVO4 dendrites for enhanced photocatalytic activity
NASA Astrophysics Data System (ADS)
Li, Di; Shi, Weidong; Zheng, Wenjun
Well-defined m-BiVO4 dendrites have been synthesized using a simple hydrothermal method without adding organic surfactant. A series of time-dependent experiments were conducted to investigate the shape formation mechanism of the m-BiVO4 dendrites. Furthermore, the corresponding growth mechanism which involved the Ostwald ripening process has been discussed. The m-BiVO4 dendrites showed great enhanced activity in the visible-light photocatalytic degradation of Rhodamine B (RhB) solution which might be attributed to the special morphology.
Electrical control of terahertz nano antennas on VO2 thin film.
Jeong, Young-Gyun; Bernien, Hannes; Kyoung, Ji-Soo; Park, Hyeong-Ryeol; Kim, Hyun-Sun; Choi, Jae-Wook; Kim, Bong-Jun; Kim, Hyun-Tak; Ahn, Kwang Jun; Kim, Dai-Sik
We demonstrate an active metamaterial device that allows to electrically control terahertz transmission over more than one order of magnitude. Our device consists of a lithographically defined gold nano antenna array fabricated on a thin film of vanadium dioxide (VO(2)), a material that possesses an insulator to metal transition. The nano antennas let terahertz (THz) radiation funnel through when the VO(2) film is in the insulating state. By applying a dc-bias voltage through our device, the VO(2) becomes metallic. This electrically shorts the antennas and therefore switches off the transmission in two distinct regimes: reversible and irreversible switching. PMID:22108973
VoIP Session Capacity Expansion with Packet Transmission Suppression Control in Wireless LAN
NASA Astrophysics Data System (ADS)
Morioka, Yasufumi; Higashino, Takeshi; Tsukamoto, Katsutoshi; Komaki, Shozo
This paper proposes a VoIP (Voice over Internet Protocol) session capacity expansion method that uses periodic packet transmission suppression control for wireless LANs. The proposed method expands the VoIP session capacity of an AP without critically degrading the QoS (Quality of Service) of all stations. Simulation results show the proposed method with 0.5% packet suppression control on each station expands a VoIP session capacity by up to 5% compared to a legacy method while satisfying required QoS for all stations.
Prior Knowledge of Trial Number Influences the Incidence of Plateau at VO2max
Gordon, Dan; Caddy, Oliver; Merzbach, Viviane; Gernigon, Marie; Baker, James; Scruton, Adrian; Keiller, Don; Barnes, Richard
The purpose of this study was to assess the VO2max plateau response at VO2max during a series of pre-determined trials. METHODS: Ten male well-trained athletes (age, 23.0 ± 3.2; height, 183.3 ± 5.5 cm; mass 77.5 ± 11.1 Kg; VO2max 66.5 ± 5.0 ml.kg-1,min-1), but who were VO2max testing naïve and with prior-knowledge of trial number completed four incremental tests to volitional exhaustion, separated by ~72-h for the determination of VO2max and gas exchange threshold. Throughout all trials VO2max was recorded on a breath-by-breath basis using a pre-calibrated metabolic cart, using a plateau criterion of Δ VO2 ≤1.5 ml.kg-1.min-1 over the final 2 consecutive 30 s sampling periods. A significant difference was observed between trial-1 and trial-4 for plateau incidence (p = 0.0285) rising from 20% in trial-1 to a 70% response rate in trial-4. Furthermore a significant difference was observed for VO2dif (difference between criterion value and Δ VO2) in trial-1, 1.02 ± 1.69 ml.kg-1.min-1 (p = 0.038), with non-significant differences observed for all other trials, despite a non-significant difference for VO2max across all trials (p > 0.05). Finally, a significant difference was observed for effort perception (RPE) at volitional exhaustion between trial-1 (17.7 ± 1.3) and trial-4 (19.0 ± 1.4) (p = 0.0052). These data indicate that prior-knowledge of trial number can influence the manifestation of the VO2 plateau in a group of well-trained male athletes, thereby suggesting that a form of effort control is established in order to preserve the finite anaerobic capacity. Key points In well-trained athletes the incidence of plateau at VO2max increases in conjunction with an increase in trial number and the associated sensations of pain and fatigue. By informing the participant of the number of trials to be completed a closed-loop condition is developed whereby effort in all trials is compared to a perceptually developed template. Closed-loop condition leads to a
Energy star compliant voice over internet protocol (VoIP) telecommunications network including energy star compliant VoIP devices
Kouchri, Farrokh Mohammadzadeh
A Voice over Internet Protocol (VoIP) communications system, a method of managing a communications network in such a system and a program product therefore. The system/network includes an ENERGY STAR (E-star) aware softswitch and E-star compliant communications devices at system endpoints. The E-star aware softswitch allows E-star compliant communications devices to enter and remain in power saving mode. The E-star aware softswitch spools messages and forwards only selected messages (e.g., calls) to the devices in power saving mode. When the E-star compliant communications devices exit power saving mode, the E-star aware softswitch forwards spooled messages.
Synthesis, crystal structure and optical properties of BiMgVO 5
NASA Astrophysics Data System (ADS)
Benmokhtar, S.; El Jazouli, A.; Chaminade, J. P.; Gravereau, P.; Guillen, F.; de Waal, D.
The new vanadate BiMgVO 5 has been prepared and its structure has been determined by single crystal X-ray diffraction: space group P21/n, a=7.542(6) Å, b=11.615(5) Å, c=5.305(3) Å, β=107.38(5)°, wR2=0.0447, R=0.0255. The structure consists of [Mg 2O 10] and [Bi 2O 10] dimers sharing their corners with [VO 4] tetrahedra. The ranges of bond lengths are 2.129-2.814 Å for Bi-O; 2.035-2.167 Å for Mg-O and 1.684-1.745 Å for V-O. V-O bond lengths determined from Raman band wavenumbers are between 1.679 and 1.747 Å. An emission band overlapping the entire visible region with a maximum around 650 nm is observed.
Selective scanning tunneling microscope light emission from rutile phase of VO2.
Sakai, Joe; Kuwahara, Masashi; Hotsuki, Masaki; Katano, Satoshi; Uehara, Yoichi
We observed scanning tunneling microscope light emission (STM-LE) induced by a tunneling current at the gap between an Ag tip and a VO2 thin film, in parallel to scanning tunneling spectroscopy (STS) profiles. The 34 nm thick VO2 film grown on a rutile TiO2 (0 0 1) substrate consisted of both rutile (R)- and monoclinic (M)-structure phases of a few 10 nm-sized domains at room temperature. We found that STM-LE with a certain photon energy of 2.0 eV occurs selectively from R-phase domains of VO2, while no STM-LE was observed from M-phase. The mechanism of STM-LE from R-phase VO2 was determined to be an interband transition process rather than inverse photoemission or inelastic tunneling processes. PMID:27460183
Temperature-driven and photo-induced MIT behaviors of VO2 nanowires
NASA Astrophysics Data System (ADS)
Sohn, Ahrum; Kim, Dong-Wook; Byun, Ji-Won; Baik, Jeong Min
VO2 shows a metal-insulator transition (MIT) and structural phase transition (SPT) at critical temperature (Tc) of 343K. It has been known that the MIT and SPT behaviors of VO2 can be tuned by external stimuli such as light, electric-field, and strain. We carried out comparative studies of MIT behaviors of VO2 nanowires during heating-cooling cycles with and without illumination using several light sources (red, blue, and UV). Light can induce change in Tc and hysteresis width of the resistance change. We have investigated influences of light on SPT during MIT. In this presentation, we will discuss possible physical origins for the photo-induced effects on the MIT behaviors of the VO2 nanowires.
VoIP for Telerehabilitation: A Pilot Usability Study for HIPAA Compliance
Watzlaf, Valerie R.; Ondich, Briana
Consumer-based, free Voice and video over the Internet Protocol (VoIP) software systems such as Skype and others are used by health care providers to deliver telerehabilitation and other health-related services to clients. Privacy and security applications as well as HIPAA compliance within these protocols have been questioned by practitioners, health information managers, and other healthcare entities. This pilot usability study examined whether four respondents who used the top three, free consumer-based, VoIP software systems perceived these VoIP technologies to be private, secure, and HIPAA compliant; most did not. While the pilot study limitations include the number of respondents and systems assessed, the protocol can be applied to future research and replicated for instructional purposes. Recommendations are provided for VoIP companies, providers, and clients/consumers. PMID:25945194
LaVo4: Eu Phosphor Films with Enhanced Eu Solubility
Hwang, Harold
Eu doped rare-earth orthovanadates are known to be good red phosphor materials. In particular, LaVO{sub 4}:Eu is a promising candidate due to the low Eu-site point symmetry, and thus high dipole transition probability within Judd-Ofelt theory. However, the low solubility limit (< 3 mol %) of Eu in LaVO{sub 4} prevents its efficient use as a phosphor. We present optical evidence of enhanced Eu solubility as high as 10 mol % in LaVO{sub 4}:Eu thin films grown by pulsed laser deposition and postannealing. The photoluminescent intensity exceeded that of YVO{sub 4}:Eu thin films when excited below the host bandgap, indicating stronger direct emission of Eu in LaVO{sub 4}.
Phase Transition in strongly-correlated VO2: Time-domainAssignment of Cause and Effect
Cavalleri, A.; Dekorsy, Th.; Chong, H.H.; Kieffer, J.C.; Schoenlein, R.W.
We establish time-domain hierarchy between structural andelectronic effects in the strongly correlated system VO2. Theinsulator-to-metal transition is driven directly by structural changerather than by electron-electron correlations.
The characteristics of Au:VO2 nanocomposite thin film for photo-electricity applications
NASA Astrophysics Data System (ADS)
Zhu, Yabin; Na, Jie; He, Fan; Zhou, Yueliang
Au nanoparticles have been fabricated on normal glass substrates using nanosphere lithography (NSL) method. Vanadium dioxide has been deposited on Au/glass by reactive radio frequency (rf) magnetron sputtering. The structure and composition were determined by X-ray diffraction and X-ray photoelectron spectroscope. Electrical and optical properties of bare VO2 and Au:VO2 nanocomposite thin films were measured. Typical hysteresis behavior and sharp phase transition were observed. Nanopartical Au could effectively reduce the transition temperature to 40 °C. The transmittance spectrum for both Au:VO2 nanocomposite thin film shows high transmittance under transition temperature and low transmittance above transition temperature. The characteristics present the Au:VO2 nanocomposite thin film can be used for applications, such as "smart window" or "laser protector".
Predictors of VO2Peak in children age 6- to 7-years-old.
Dencker, Magnus; Hermansen, Bianca; Bugge, Anna; Froberg, Karsten; Andersen, Lars B
This study investigated the predictors of aerobic fitness (VO2PEAK) in young children on a population-base. Participants were 436 children (229 boys and 207 girls) aged 6.7 ± 0.4 yrs. VO2PEAK was measured during a maximal treadmill exercise test. Physical activity was assessed by accelerometers. Total body fat and total fat free mass were estimated from skinfold measurements. Regression analyses indicated that significant predictors for VO2PEAK per kilogram body mass were total body fat, maximal heart rate, sex, and age. Physical activity explained an additional 4-7%. Further analyses showed the main contributing factors for absolute values of VO2PEAK were fat free mass, maximal heart rate, sex, and age. Physical activity explained an additional 3-6%. PMID:21467593
Selective scanning tunneling microscope light emission from rutile phase of VO2
NASA Astrophysics Data System (ADS)
Sakai, Joe; Kuwahara, Masashi; Hotsuki, Masaki; Katano, Satoshi; Uehara, Yoichi
We observed scanning tunneling microscope light emission (STM-LE) induced by a tunneling current at the gap between an Ag tip and a VO2 thin film, in parallel to scanning tunneling spectroscopy (STS) profiles. The 34 nm thick VO2 film grown on a rutile TiO2 (0 0 1) substrate consisted of both rutile (R)- and monoclinic (M)-structure phases of a few 10 nm-sized domains at room temperature. We found that STM-LE with a certain photon energy of 2.0 eV occurs selectively from R-phase domains of VO2, while no STM-LE was observed from M-phase. The mechanism of STM-LE from R-phase VO2 was determined to be an interband transition process rather than inverse photoemission or inelastic tunneling processes.
Business Collaborations in Grids: The BREIN Architectural Principals and VO Model
NASA Astrophysics Data System (ADS)
Taylor, Steve; Surridge, Mike; Laria, Giuseppe; Ritrovato, Pierluigi; Schubert, Lutz
We describe the business-oriented architectural principles of the EC FP7 project "BREIN" for service-based computing. The architecture is founded on principles of how real businesses interact to mutual benefit, and we show how these can be applied to SOA and Grid computing. We present building blocks that can be composed in many ways to produce different value systems and supply chains for the provision of computing services over the Internet. We also introduce the complementary BREIN VO concept, which is centric to, and managed by, a main contractor who bears the responsibility for the whole VO. The BREIN VO has an execution lifecycle for the creation and operation of the VO, and we have related this to an application-focused workflow involving steps that provide real end-user value. We show how this can be applied to an engineering simulation application and how the workflow can be adapted should the need arise.
VoIP for Telerehabilitation: A Pilot Usability Study for HIPAA Compliance.
Watzlaf, Valerie R; Ondich, Briana
Consumer-based, free Voice and video over the Internet Protocol (VoIP) software systems such as Skype and others are used by health care providers to deliver telerehabilitation and other health-related services to clients. Privacy and security applications as well as HIPAA compliance within these protocols have been questioned by practitioners, health information managers, and other healthcare entities. This pilot usability study examined whether four respondents who used the top three, free consumer-based, VoIP software systems perceived these VoIP technologies to be private, secure, and HIPAA compliant; most did not. While the pilot study limitations include the number of respondents and systems assessed, the protocol can be applied to future research and replicated for instructional purposes. Recommendations are provided for VoIP companies, providers, and clients/consumers. PMID:25945194
Chapter 18: Web-based Tools - NED VO Services
NASA Astrophysics Data System (ADS)
Mazzarella, J. M.; NED Team
The NASA/IPAC Extragalactic Database (NED) is a thematic, web-based research facility in widespread use by scientists, educators, space missions, and observatory operations for observation planning, data analysis, discovery, and publication of research about objects beyond our Milky Way galaxy. NED is a portal into a systematic fusion of data from hundreds of sky surveys and tens of thousands of research publications. The contents and services span the entire electromagnetic spectrum from gamma rays through radio frequencies, and are continuously updated to reflect the current literature and releases of large-scale sky survey catalogs. NED has been on the Internet since 1990, growing in content, automation and services with the evolution of information technology. NED is the world's largest database of crossidentified extragalactic objects. As of December 2006, the system contains approximately 10 million objects and 15 million multi-wavelength cross-IDs. Over 4 thousand catalogs and published lists covering the entire electromagnetic spectrum have had their objects cross-identified or associated, with fundamental data parameters federated for convenient queries and retrieval. This chapter describes the interoperability of NED services with other components of the Virtual Observatory (VO). Section 1 is a brief overview of the primary NED web services. Section 2 provides a tutorial for using NED services currently available through the NVO Registry. The "name resolver" provides VO portals and related internet services with celestial coordinates for objects specified by catalog identifier (name); any alias can be queried because this service is based on the source cross-IDs established by NED. All major services have been updated to provide output in VOTable (XML) format that can be accessed directly from the NED web interface or using the NVO registry. These include access to images via SIAP, Cone- Search queries, and services providing fundamental, multi
Mobile telephones: a comparison of radiated power between 3G VoIP calls and 3G VoCS calls.
Jovanovic, Dragan; Bragard, Guillaume; Picard, Dominique; Chauvin, Sébastien
The purpose of this study is to assess the mean RF power radiated by mobile telephones during voice calls in 3G VoIP (Voice over Internet Protocol) using an application well known to mobile Internet users, and to compare it with the mean power radiated during voice calls in 3G VoCS (Voice over Circuit Switch) on a traditional network. Knowing that the specific absorption rate (SAR) is proportional to the mean radiated power, the user's exposure could be clearly identified at the same time. Three 3G (High Speed Packet Access) smartphones from three different manufacturers, all dual-band for GSM (900 MHz, 1800 MHz) and dual-band for UMTS (900 MHz, 1950 MHz), were used between 28 July and 04 August 2011 in Paris (France) to make 220 two-minute calls on a mobile telephone network with national coverage. The places where the calls were made were selected in such a way as to describe the whole range of usage situations of the mobile telephone. The measuring equipment, called "SYRPOM", recorded the radiation power levels and the frequency bands used during the calls with a sampling rate of 20,000 per second. In the framework of this study, the mean normalised power radiated by a telephone in 3G VoIP calls was evaluated at 0.75% maximum power of the smartphone, compared with 0.22% in 3G VoCS calls. The very low average power levels associated with use of 3G devices with VoIP or VoCS support the view that RF exposure resulting from their use is far from exceeding the basic restrictions of current exposure limits in terms of SAR. PMID:25352159
Size and composition-controlled fabrication of VO2 nanocrystals by terminated cluster growth
Anders, Andre; Slack, Jonathan
A physical vapor deposition-based route for the fabrication of VO2 nanoparticles is demonstrated, consisting of reactive sputtering and vapor condensation at elevated pressures. The oxidation of vanadium atoms is an efficient heterogeneous nucleation method, leading to high nanoparticle throughtput. Fine control of the nanoparticle size and composition is obtained. Post growth annealing leads to crystalline VO2 nanoparticles with optimum thermocromic and plasmonic properties.
Broadband terahertz generation using the semiconductor-metal transition in VO2
NASA Astrophysics Data System (ADS)
Charipar, Nicholas A.; Kim, Heungsoo; Mathews, Scott A.; Piqué, Alberto
We report the design, fabrication, and characterization of broadband terahertz emitters based on the semiconductor-metal transition in thin film VO2 (vanadium dioxide). With the appropriate geometry, picosecond electrical pulses are generated by illuminating 120 nm thick VO2 with 280 fs pulses from a femtosecond laser. These ultrafast electrical pulses are used to drive a simple dipole antenna, generating broadband terahertz radiation.
Resistance modulation in VO2 nanowires induced by an electric field via air-gap gates
NASA Astrophysics Data System (ADS)
Kanki, Teruo; Chikanari, Masashi; Wei, Tingting; Tanaka, Hidekazu; The Institute of Scientific; Industrial Research Team
Vanadium dioxide (VO2) shows huge resistance change with metal-insulator transition (MIT) at around room temperature. Controlling of the MIT by applying an electric field is a topical ongoing research toward the realization of Mott transistor. In this study, we have successfully switched channel resistance of VO2 nano-wire channels by a pure electrostatic field effect using a side-gate-type field-effect transistor (SG-FET) viaair gap and found that single crystalline VO2 nanowires and the channels with narrower width enhance transport modulation rate. The rate of change in resistance ((R0-R)/R, where R0 and R is the resistance of VO2 channel with off state and on state gate voltage (VG) , respectively) was 0.42 % at VG = 30 V in in-plane poly-crystalline VO2 channels on Al2O3(0001) substrates, while the rate in single crystalline channels on TiO2 (001) substrates was 3.84 %, which was 9 times higher than that using the poly-crystalline channels. With reducing wire width from 3000 nm to 400 nm of VO2 on TiO2 (001) substrate, furthermore, resistance modulation ratio enhanced from 0.67 % to 3.84 %. This change can not be explained by a simple free-electron model. In this presentation, we will compare the electronic properties between in-plane polycrystalline VO2 on Al2O3 (0001) and single crystalline VO2 on TiO2 (001) substrates, and show experimental data in detail..
Sodium calcium orthovanadate, NaCa4(VO4)3.
Ben Yahia, Hamdi; Gaudin, Etienne; Darriet, Jacques
Single crystals of sodium tetracalcium trivanadium dodecaoxide were prepared by melting a powder sample of NaCa4(VO4)3 at 1673 K, followed by slow cooling to room temperature. The compound crystallizes in the Pnma space group and is isostructural with the mineral silicocarnotite, Ca5(PO4)2SiO4. The structure is composed of isolated VO4 tetrahedra linked by sodium and calcium cations disordered over eight- and seven-coordinated sites. PMID:15997052
Which are the best VO2 sampling intervals to characterize low to severe swimming intensities?
de Jesus, K; Guidetti, L; de Jesus, K; Vilas-Boas, J P; Baldari, C; Fernandes, R J
Cardiorespiratory response in swimming has been used to better understand aerobic performance, especially by assessing oxygen uptake (VO2). The current study aimed to compare different VO2 time-averaging intervals throughout low to severe swimming intensities, hypothesizing that VO2 values are similar for different time averages at low to moderate and heavy swimming intensities, but not for the severe domain. 20 male trained swimmers completed an incremental protocol of 7×200 m until exhaustion (0.05 m/s increments and 30 s intervals). VO2 was measured by a portable gas analyser connected to a snorkel system. 6 time average intervals (breath-by-breath, 5, 10, 15, 20 and 30 s) were compared for all the protocol steps. Breath-by-breath and 5 s average exhibited higher VO2 values than averages≥10 s for all swimming intensities (P≤0.02; partial η(2)≤0.28). VO2 values did not differ between 10, 15, 20 and 30 s averages throughout the incremental protocol (P>0.05; partial η(2)≤0.05). Furthermore, 10 and 15 s averages showed the lowest VO2 mean difference (0.19 mL( · )kg(-1 · )min(-1)). For the 6 time average intervals analysed, 10 and 15 s averages were those that showed the lowest changes on VO2 values. We recommended the use of 10 and 15 s time averaging intervals to determine relevant respiratory gas exchange parameters along a large spectrum of swimming intensities. PMID:24892654
Patterns of Senescence in Human Cardiovascular Fitness: VO2max in Subsistence and Industrialized Populations
Pisor, Anne C.; Gurven, Michael; Blackwell, Aaron D.; Kaplan, Hillard; Yetish, Gandhi
Objectives This study explores whether cardiovascular fitness levels and senescent decline are similar in the Tsimane of Bolivia and Canadians, as well as other subsistence and industrialized populations. Among Tsimane, we examine whether morbidity predicts lower levels and faster decline of cardiovascular fitness, or whether their lifestyle (e.g., high physical activity) promotes high levels and slow decline. Alternatively, high activity levels and morbidity might counterbalance such that Tsimane fitness levels and decline are similar to those in industrialized populations. Methods Maximal oxygen uptake (VO2max) was estimated using a step test heart rate method for 701 participants. We compared these estimates to the Canadian Health Measures Survey and previous studies in industrialized and subsistence populations. We evaluated whether health indicators and proxies for market integration were associated with VO2max levels and rate of decline for the Tsimane. Results The Tsimane have significantly higher levels of VO2max and slower rates of decline than Canadians; initial evidence suggests differences in VO2max levels between other subsistence and industrialized populations. Low hemoglobin predicts low VO2max for Tsimane women while helminth infection predicts high VO2max for Tsimane men, though results might be specific to the VO2max scaling parameter used. No variables tested interact with age to moderate decline. Conclusions The Tsimane demonstrate higher levels of cardiovascular fitness than industrialized populations, but levels similar to other subsistence populations. The high VO2max of Tsimane is consistent with their high physical activity and few indicators of cardiovascular disease, measured in previous studies. PMID:24022886
VoIP Implementation and Experiments on a Mobile Wireless AdHoc Network
NASA Astrophysics Data System (ADS)
Zhang, Hongqi; Yang, Oliver; Zhao, Jiying
We have implemented a testbed to study the performance of VoIP in wireless ad hoc networks. The ASNC (Adaptive Source Network-rate Control) scheme is used to battle packet loss by feeding MOS (Mean Opinion Score) and loss information back to the sender. Our different VoIP experiments with measurements on delay, packet loss rate and MOS have validated the feasibility and efficiency of our scheme. It further verifies the simulator we used in the initial investigation.
VO2 (A): Reinvestigation of crystal structure, phase transition and crystal growth mechanisms
NASA Astrophysics Data System (ADS)
Rao Popuri, Srinivasa; Artemenko, Alla; Labrugere, Christine; Miclau, Marinela; Villesuzanne, Antoine; Pollet, Michaël
Well crystallized VO2 (A) microrods were grown via a single step hydrothermal reaction in the presence of V2O5 and oxalic acid. With the advantage of high crystalline samples, we propose P4/ncc as an appropriate space group at room temperature. From morphological studies, we found that the oriented attachment and layer by layer growth mechanisms are responsible for the formation of VO2 (A) micro rods. The structural and electronic transitions in VO2 (A) are strongly first order in nature, and a marked difference between the structural transition temperatures and electronic transitions temperature was evidenced. The reversible intra- (LTP-A to HTP-A) and irreversible inter- (HTP-A to VO2 (M1)) structural phase transformations were studied by in-situ powder X-ray diffraction. Attempts to increase the size of the VO2 (A) microrods are presented and the possible formation steps for the flower-like morphologies of VO2 (M1) are described.
VO(2max) and Microgravity Exposure: Convective versus Diffusive O(2) Transport.
Ade, Carl J; Broxterman, Ryan M; Barstow, Thomas J
Exposure to a microgravity environment decreases the maximal rate of O2 uptake (VO(2max)) in healthy individuals returning to a gravitational environment. The magnitude of this decrease in VO(2max) is, in part, dependent on the duration of microgravity exposure, such that long exposure may result in up to a 38% decrease in VO(2max). This review identifies the components within the O(2) transport pathway that determine the decrease in postmicrogravity VO(2max) and highlights the potential contributing physiological mechanisms. A retrospective analysis revealed that the decline in VO(2max) is initially mediated by a decrease in convective and diffusive O(2) transport that occurs as the duration of microgravity exposure is extended. Mechanistically, the attenuation of O(2) transport is the combined result of a deconditioning across multiple organ systems including decreases in total blood volume, red blood cell mass, cardiac function and mass, vascular function, skeletal muscle mass, and, potentially, capillary hemodynamics, which become evident during exercise upon re-exposure to the head-to-foot gravitational forces of upright posture on Earth. In summary, VO(2max) is determined by the integration of central and peripheral O(2) transport mechanisms, which, if not maintained during microgravity, will have a substantial long-term detrimental impact on space mission performance and astronaut health. PMID:25380479
Visible light photocatalytic activity of BiVO4 particles with different morphologies
NASA Astrophysics Data System (ADS)
Lin, Xue; Yu, Lili; Yan, Lina; Li, Hongji; Yan, Yongsheng; Liu, Chunbo; Zhai, Hongju
Bismuth vanadate (BiVO4) particles with different morphologies were synthesized by a one-step hydrothermal process and their optical and photocatalytic properties were investigated. Their crystal structure and microstructures were characterized using X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). XRD patterns demonstrate that the as-prepared samples are monoclinic cell. FESEM shows that BiVO4 crystals can be fabricated in different morphologies by simply manipulating the reaction parameters of hydrothermal process. The UV-visible diffuse reflectance spectra (UV-vis DRS) reveal that the band gaps of BiVO4 photocatalysts are about 2.07-2.21 eV. The as-prepared BiVO4 photocatalysts exhibit higher photocatalytic activities in the degradation of rhodamine B (Rh B) under visible light irradiation (λ > 420 nm) compared with traditional N-doped TiO2 (N-TiO2). Furthermore, wheat like BiVO4 sample reveals the highest photocatalytic activity. Up to 100% Rh B is decolorized after visible light irradiation for 180 min. The reason for the difference in the photocatalytic activities for BiVO4 samples obtained at different conditions were systematically studied based on their shape, size and the variation of local structure.
Band Theory for the Electronic and Magnetic Properties of VO2 Phases
NASA Astrophysics Data System (ADS)
Shen, Xiao; Xu, Sheng; Hallman, Kent; Haglund, Richard; Pantelides, Sokrates
VO2 is widely studied for the insulator-metal transition between the monoclinic M1 (insulator) and rutile R (metal) phases. Recent experiments show that in addition to the M1 and R phases, VO2 has a rich phase diagram including a recently identified metallic monoclinic phase, making the material particularly intriguing. The origin of the band gap in the insulating phase of VO2 has been a subject of debate. It was suggested that the insulating phase cannot be described by band theory and thus strong correlations must be invoked. However, recent band calculations using density functional theory (DFT) with a hybrid functional and standard pseudopotentials correctly obtains a band gap for the M1 insulating phase. Subsequent calculations, however, found that the magnetic properties of VO2 phases are not correctly described by such calculations. Here we present DFT calculations using a tuned hybrid functional and hard pseudopotentials that reproduce both the band gaps and the magnetic properties of the known VO2 phases. Thus, it is appropriate to use band theory to describe VO2 phases without invoking strong correlations. Furthermore, using the band theory treatment, we identify a candidate for the metallic monoclinic phase. Doe DE-FG02-09ER46554, NSF EECS-1509740.
Straining to observe the M2 phase in epitaxial VO2 films
NASA Astrophysics Data System (ADS)
Quackenbush, Nicholas; Wahila, Matthew; Piper, Louis; Paik, Hanjong; Holtz, Megan; Huang, Xin; Brock, Joel; Muller, David; Schlom, Darrell; Woicik, Joseph; Arena, Dario
It has been more than a decade since it was shown that the transition temperature TMIT of VO2 in epitaxial thin films can be tuned by compressive and tensile strain along the rutile c-axis. Since this discovery, uniaxial strain studies of VO2 nanobeams have demonstrated that compressive strain indeed lowers TMIT, thus stabilizing the metallic rutile phase. However, even minor tensile strain induces an intermediate insulating monoclinic M2 phase. Whether this phase can be stabilized in thin films remains contentious owing to the constraints of sample and/or interface quality. Here, we present hard x-ray photoelectron spectroscopy and temperature-dependent soft x-ray absorption spectroscopy of high quality ultrathin epitaxial VO2 films on TiO2 (001) and (100) substrates. The VO2/TiO2(001) are absent of intermediate phases and maintain a MIT similar to unstrained VO2, while the VO2/TiO2(100) films display a stable M2 phase between the M1 and rutile endpoint phases. We discuss our findings in terms of differences between uniaxial and biaxial strain. This research is supported by the National Science Foundation under DMR-1409912.
Multiferroicity and spiral magnetism in FeVO{sub 4} with quenched Fe orbital moments
Daoud-Aladine, A.; Chapon, L. C.; Kundys, B.; Martin, C.; Simon, C.; Radaelli, P. G.; Brown, P. J.
FeVO{sub 4} has been studied by heat capacity, magnetic susceptibility, electric polarization and single-crystal neutron-diffraction experiments. The triclinic crystal structure is made of S-shaped clusters of six Fe{sup 3+} ions, linked by VO{sub 4}{sup 3-} groups. Two long-range magnetic ordering transitions occur at T{sub N1}=22 K and T{sub N2}=15 K. Both magnetic structures are incommensurate and below T{sub N2}, FeVO{sub 4} becomes weakly ferroelectric coincidentally with the loss of the collinearity of the magnetic structure in a very similar fashion than in the classical TbMnO{sub 3} multiferroic material. However we argue that the symmetry considerations and the mechanisms invoked to explain these properties in TbMnO{sub 3} do not straightforwardly apply to FeVO{sub 4}. First, the magnetic structures, even the collinear structure, are all acentric so that ferroelectricity in FeVO{sub 4} is not correlated with the fact magnetic ordering is breaking inversion symmetry. Regarding the mechanism, FeVO{sub 4} has quenched orbital moments that questions the exact role of the spin-orbit interactions.
Synthesis and characterization of VO2-based thermochromic thin films for energy-efficient windows.
Batista, Carlos; Ribeiro, Ricardo M; Teixeira, Vasco
Thermochromic VO2 thin films have successfully been grown on SiO2-coated float glass by reactive DC and pulsed-DC magnetron sputtering. The influence of substitutional doping of V by higher valence cations, such as W, Mo, and Nb, and respective contents on the crystal structure of VO2 is evaluated. Moreover, the effectiveness of each dopant element on the reduction of the intrinsic transition temperature and infrared modulation efficiency of VO2 is discussed. In summary, all the dopant elements--regardless of the concentration, within the studied range-- formed a solid solution with VO2, which was the only compound observed by X-ray diffractometry. Nb showed a clear detrimental effect on the crystal structure of VO2. The undoped films presented a marked thermochromic behavior, specially the one prepared by pulsed-DC sputtering. The dopants effectively decreased the transition of VO2 to the proximity of room temperature. However, the IR modulation efficiency is markedly affected as a consequence of the increased metallic character of the semiconducting phase. Tungsten proved to be the most effective element on the reduction of the semiconducting-metal transition temperature, while Mo and Nb showed similar results with the latter being detrimental to the thermochromism. PMID:21711813
Continuous tuning of W-doped VO{sub 2} optical properties for terahertz analog applications
Karaoglan-Bebek, G.; Hoque, M. N. F.; Fan, Z.; Bernussi, A. A.; Holtz, M.
Vanadium dioxide (VO{sub 2}), with its characteristic metal-insulator phase transition, is a prospective active candidate to realize tunable optical devices operating at terahertz (THz) frequencies. However, the abrupt phase transition restricts its practical use in analog-like continuous applications. Incorporation of tungsten is a feasible approach to alter the phase transition properties of thin VO{sub 2} films. We show that amplitude THz modulation depth of ∼65%, characteristic phase transition temperature of ∼40 °C, and tuning range larger than 35 °C can be achieved with W-doped VO{sub 2} films grown on sapphire substrates. W-doped VO{sub 2} films can also be used to suppress Fabry-Perot resonances at THz frequencies but at temperatures much lower than that observed for undoped VO{sub 2} films. The gradual phase transition temperature window allows for precise control of the W-doped VO{sub 2} optical properties for future analog based THz devices.
Impact of thermal expansion of substrates on phase transition temperature of VO2 films
NASA Astrophysics Data System (ADS)
Sakai, Joe; Zaghrioui, Mustapha; Matsushima, Masaaki; Funakubo, Hiroshi; Okimura, Kunio
Non-epitaxial, (010)M1-oriented VO2 thin films were grown on various substrates [amorphous SiO2, Si (001), Al2O3 (0001), and CaF2 (001)] with Pt (111)/SiO2 buffer layers. Phase transition from MoO2-type monoclinic to rutile-type tetragonal structures of these VO2 layers was investigated with temperature-controlled micro-Raman spectroscopy. It was confirmed that substrates with larger thermal expansion coefficient cause larger out-of-plane lattice spacings of both Pt and VO2, and thus lower transition temperatures of VO2 films, as a result of higher in-plane shrinkage during cooling from the deposition temperature. The transition temperatures and aM1/2 lengths, estimated from bM1 lengths, of present samples were compared with previous reports in a strain—temperature phase diagram. The present results fit with previous reports better by assuming that in-plane lattice aspect ratio of VO2 films is not clamped by the substrates but is flexible during the temperature change. Thermal expansion of substrates is an essential parameter to be taken into account when one considers device application of the phase transition properties of VO2 films, especially thick or non-epitaxial.
Influence of lattice distortion on phase transition properties of polycrystalline VO2 thin film
NASA Astrophysics Data System (ADS)
Lin, Tiegui; Wang, Langping; Wang, Xiaofeng; Zhang, Yufen; Yu, Yonghao
In this work, high power impulse magnetron sputtering was used to control the lattice distortion in polycrystalline VO2 thin film. SEM images revealed that all the VO2 thin films had crystallite sizes of below 20 nm, and similar configurations. UV-vis-near IR transmittance spectra measured at different temperatures showed that most of the as-deposited films had a typical metal-insulator transition. Four-point probe resistivity results showed that the transition temperature of the films varied from 54.5 to 32 °C. The X-ray diffraction (XRD) patterns of the as-deposited films revealed that most were polycrystalline monoclinic VO2. The XRD results also confirmed that the lattice distortions in the as-deposited films were different, and the transition temperature decreased with the difference between the interplanar spacing of the as-deposited thin film and standard rutile VO2. Furthermore, a room temperature rutile VO2 thin film was successfully synthesized when this difference was small enough. Additionally, XRD patterns measured at varied temperatures revealed that the phase transition process of the polycrystalline VO2 thin film was a coordinative deformation between grains with different orientations. The main structural change during the phase transition was a gradual shift in interplanar spacing with temperature.
Activation of peroxymonosulfate by BiVO4 under visible light for degradation of Rhodamine B
NASA Astrophysics Data System (ADS)
Liu, Yang; Guo, Hongguang; Zhang, Yongli; Tang, Weihong; Cheng, Xin; Liu, Hongwei
A photocatalytic system involving visible light and BiVO4 (Vis/BiVO4) in the presence of peroxymonosulfate (PMS) has been developed to oxidize the target pollutant Rhodamine B (RhB) in aqueous solution. It was found that PMS could enhance the photocatalytic efficiency of BiVO4 and could be activated to promote the removal of RhB with sulfate radicals, hydroxyl radicals and superoxide radicals. Critical impacting factors in the Vis/BiVO4/PMS system were investigated concerning the influence of PMS concentration, solution pH, catalyst dosage, initial concentration of RhB and the presence of anions (Cl- and CO32-). In addition, by using isopropanol, tert-butanol, 1,4-benzoquinone and ethylenediamine tetraacetic acid disodium salt as probe compounds, the main active species were demonstrated including radSO4-, radOH and radO2- in the system, and a detail photocatalytic mechanism for the Vis/BiVO4/PMS system was proposed. Finally, up to 10 intermediate products of RhB were identified by GC/MS, included benzenoid organic compounds, organic acids and three nitrogenous organic compounds. This study provides a feasible way to degrade organic pollutants in wastewater using BiVO4 with PMS under visible light.
Synthesis and characterization of VO2-based thermochromic thin films for energy-efficient windows
Thermochromic VO2 thin films have successfully been grown on SiO2-coated float glass by reactive DC and pulsed-DC magnetron sputtering. The influence of substitutional doping of V by higher valence cations, such as W, Mo, and Nb, and respective contents on the crystal structure of VO2 is evaluated. Moreover, the effectiveness of each dopant element on the reduction of the intrinsic transition temperature and infrared modulation efficiency of VO2 is discussed. In summary, all the dopant elements--regardless of the concentration, within the studied range-- formed a solid solution with VO2, which was the only compound observed by X-ray diffractometry. Nb showed a clear detrimental effect on the crystal structure of VO2. The undoped films presented a marked thermochromic behavior, specially the one prepared by pulsed-DC sputtering. The dopants effectively decreased the transition of VO2 to the proximity of room temperature. However, the IR modulation efficiency is markedly affected as a consequence of the increased metallic character of the semiconducting phase. Tungsten proved to be the most effective element on the reduction of the semiconducting-metal transition temperature, while Mo and Nb showed similar results with the latter being detrimental to the thermochromism. PMID:21711813
Synthesis and characterization of VO2-based thermochromic thin films for energy-efficient windows
NASA Astrophysics Data System (ADS)
Batista, Carlos; Ribeiro, Ricardo M.; Teixeira, Vasco
Thermochromic VO2 thin films have successfully been grown on SiO2-coated float glass by reactive DC and pulsed-DC magnetron sputtering. The influence of substitutional doping of V by higher valence cations, such as W, Mo, and Nb, and respective contents on the crystal structure of VO2 is evaluated. Moreover, the effectiveness of each dopant element on the reduction of the intrinsic transition temperature and infrared modulation efficiency of VO2 is discussed. In summary, all the dopant elements--regardless of the concentration, within the studied range-- formed a solid solution with VO2, which was the only compound observed by X-ray diffractometry. Nb showed a clear detrimental effect on the crystal structure of VO2. The undoped films presented a marked thermochromic behavior, specially the one prepared by pulsed-DC sputtering. The dopants effectively decreased the transition of VO2 to the proximity of room temperature. However, the IR modulation efficiency is markedly affected as a consequence of the increased metallic character of the semiconducting phase. Tungsten proved to be the most effective element on the reduction of the semiconducting-metal transition temperature, while Mo and Nb showed similar results with the latter being detrimental to the thermochromism.
Properties of VO2 Films Sputter-Deposited from V2O5 Target
NASA Astrophysics Data System (ADS)
Tsai, Kuang-Yue; Chin, Tsung-Shune; Shieh, Han-Ping D.
Rutile VO2 is a thermochromic material that exhibits a reversible metal-insulator phase transition upon thermal cycling. A new deposition process of rutile VO2 from a V2O5 target was developed using reactive oxygen instead of hydrogen. Adjusting the substrate temperature and the oxygen flow ratio changes the compositions and phases of the as-deposited films into rutile VO2 under optimum deposition conditions on the Si and thick glass substrates. Crystalline phases analyzed by X-ray diffraction shows the relationship among V4O9, V6O13, and VO2 films prepared under different deposition conditions. Analysis by AFM shows that VO2 films grown at higher substrate temperatures have larger grain size. The optical switching property of VO2 was measured at a wavelength of 1.5 μm and transition temperature around 45°C was also measured. Inhomogeneity and the strained structure of the film are suggested to be the reasons of transition temperature lower than typical reported value because the impurity in the target is too low to be detected quantatively by ICP.
Tailoring Multilayered BiVO4 Photoanodes by Pulsed Laser Deposition for Water Splitting.
Murcia-López, Sebastián; Fàbrega, Cristian; Monllor-Satoca, Damián; Hernández-Alonso, María D; Penelas-Pérez, Germán; Morata, Alex; Morante, Juan R; Andreu, Teresa
Pulsed laser deposition (PLD) is proposed as promising technique for the fabrication of multilayered BiVO4-based photoanodes. For this purpose, bare BiVO4 films and two heterojunctions, BiVO4/SnO2 and BiVO4/WO3/SnO2, have been prepared using consecutive ablation of assorted targets in a single batch. The ease, high versatility and usefulness of this technique in engineering the internal configuration of the photoanode with stoichiometric target-to-substrate transfer are demonstrated. The obtained photocurrent densities are among the highest reported values for undoped BiVO4 without oxygen evolution catalysts (OEC). A detailed analysis of the influence of SnO2 and WO3 layers on the charge transport properties because of the changes at the internal FTO/semiconductor interface is performed through transient photocurrent measurements (TPC), showing that the BiVO4/WO3/SnO2 heterostructure attains a significant decrease in the internal losses and reaches high photocurrent values. This study is expected to open the door to the fabrication of other systems based on ternary (or even more complex) metal oxides as photoanodes for water splitting, which is a promising alternative for obtaining materials able to fulfill the different requierements in the development of more efficient systems for this process. PMID:26804929
Transport phenomena in SrVO3 thin films
NASA Astrophysics Data System (ADS)
Gu, Man; Wolf, Stuart; Lu, Jiwei; University of Virginia Team
Bulk SrVO3 (SVO) with a 3d1 electronic configuration has been found to exhibit metallic and Pauli paramagnetic behavior. We have obtained epitaxial SVO films grown on various substrates (STO, SLAO, LSAT and LAO) using a pulsed electron-beam deposition (PED) technique. The film transport properties were found to be strongly dependent on the substrate. A 40 nm SVO film deposited on an STO substrate exhibited metallic behavior with the electrical resistivity following a T2 law that corresponds to a Fermi liquid system, the resistance ratio R(300K)/R(2K) was ~ 1.66. Hall measurements showed that the mobility increased slightly as the temperature was decreased. A small positive out-of-plane magnetoresistance was observed, it was only 0.045% at 5 K and 7 Tesla. SVO films with the same thickness grown on SLAO, LSAT and LAO showed semiconducting behavior, the different transport properties in the SVO films could be attributed to the compressive film strain or the different film-substrate interfaces.
Photoinducing the hidden M2 phase in VO2
NASA Astrophysics Data System (ADS)
Walko, D. A.; Smith, R. K.; Wen, Haidan; Dichiara, A. D.; Jeong, Jaewoo; Samant, Mahensh G.; Parkin, Stuart S. P.
We used time-resolved x-ray diffraction to study photoinduced structural phase transitions in a 170-nm-thick VO2 film grown on sapphire (1,0,-1,0). Heating the unstrained film from room temperature induces the well-known phase transition from the monoclinic (M1) phase directly to the high-temperature tetragonal rutile (R) phase. In contrast, upon ultrafast optical excitation, the phase transition depends strongly on the laser intensity. At low fluences, the film is partially transformed into the monoclinic M2 phase, a phase which generally is observed only in doped or strained materials. Above a threshold at higher fluences, a small portion of the film is transformed into the M2 phase, decaying on a time scale of a few nanoseconds, while the majority of the film is transformed into the R phase which can persist for tens of nanoseconds. We further discuss the effects of laser wavelength on the efficiency of producing the M2 phase. Work at the Advanced Photon Source supported by DOE Contract No. DE-AC02-06CH11357.
Ab initio study of optical excitations in VO2
NASA Astrophysics Data System (ADS)
Coulter, John; Gali, Adam; Manousakis, Efstratios
Motivated by recent experimental efforts to fabricate p-n junctions from transition metal oxides (TMOs) and a recent theoretical study claiming TMOs to be good absorbers and promising materials for efficient carrier multiplication, we study the optical properties of a prototypical TMO, the insulator M1 phase of vanadium dioxide (VO2), by ab initio methods. We applied the Bethe-Salpeter equations (BSE) to calculate the optical properties, starting from self-consistent GW quasi-particle energy levels and states. In contrast to expectations, the exciton binding energy obtained by BSE is in good agreement with the experiment. We find that the electron-electron interaction is very strong which makes this material promising for efficient carrier multiplication that might lead to an enhanced efficiency in photo-voltaics applications. To illustrate this more quantitatively, we calculated the impact ionization rate within the independent quasiparticle approximation, and find that the rate is significantly higher than silicon in the region of highest solar intensity, due to the strong multiple carrier excitations.
Enabling OpenID Authentication for VO-integrated Portals
NASA Astrophysics Data System (ADS)
Plante, R.; Yekkirala, V.; Baker, W.
To support interoperating services that share proprietary data and other user-specific information, the VAO Project provides login services for browser-based portals built on the open standard, OpenID. To help portal developers take advantage of this service, we have developed a downloadable toolkit for integrating OpenID single sign-on support into any portal. This toolkit provides APIs in a few languages commonly used on the server-side as well as a command-line version for use in any language. In addition to describing how to use this toolkit, we also discuss the general VAO framework for single sign-on. While a portal may, if it wishes, support any OpenID provider, the VAO service provides a few extra features to support VO interoperability. This includes a portal's ability to retrieve (with the user's permission) an X.509 certificate representing the authenticated user so that the portal can access other restricted services on the user's behalf. Other standard features of OpenID allow portals to request other information about the user; this feature will be used in the future for sharing information about a user's group membership to enable sharing within a group of collaborating scientists.
The Gaia Archive at ESAC: a VO-inside archive
NASA Astrophysics Data System (ADS)
Gonzalez-Nunez, J.
The ESDC (ESAC Science Data Center) is one of the active members of the IVOA (International Virtual Observatory Alliance) that have defined a set of standards, libraries and concepts that allows to create flexible,scalable and interoperable architectures on the data archives development. In the case of astronomy science that involves the use of big catalogues, as in Gaia or Euclid, TAP, UWS and VOSpace standards can be used to create an architecture that allows the explotation of this valuable data from the community. Also, new challenges arise like the implementation of the new paradigm "move code close to the data", what can be partially obtained by the extension of the protocols (TAP+, UWS+, etc) or the languages (ADQL). We explain how we have used VO standards and libraries for the Gaia Archive that, not only have producing an open and interoperable archive but, also, minimizing the developement on certain areas. Also we will explain how we have extended these protocols and the future plans.
Charge sensing by altering the phase transition in VO2
NASA Astrophysics Data System (ADS)
Kumar, Suhas; Esfandyarpour, Rahim; Davis, Ronald; Nishi, Yoshio
We use vanadium dioxide to sense changes in surface charge accumulation and explore possibilities of sensing presence of large polar molecules. It was shown last year that surface charge accumulation can cause bulk delocalization. It was also shown that surface charge accumulation can cause a decrease in the insulator-metal transition temperature of vanadium dioxide. We use this concept and replace the surface charges with molecules that have a net polarization. We used biotinylated bovine serum albumin (BBSA) and streptavidin in our experiments. We observed a change in the potential and current at which the switching of resistance happened. This implied a change in the power and hence the temperature at which the Mott transition happened. When these molecules are held on the surface of VO2, we postulate that they transfer charges, which is what we are sensing as changes in the temperature at which a phase transition happens. We believe this shows the possibility of sensing a variety of molecules that are of interest to biologists, chemists and environmentalists. Equal contribution as Author 1.
Photocatalytic and photoelectrochemical water oxidation over metal-doped monoclinic BiVO(4) photoanodes.
Parmar, Kanak Pal Singh; Kang, Hyun Joon; Bist, Amita; Dua, Piyush; Jang, Jum Suk; Lee, Jae Sung
The visible-light-induced water oxidation ability of metal-ion-doped BiVO(4) was investigated and of 12 metal ion dopants tested, only W and Mo dramatically enhanced the water photo-oxidation activity of bare BiVO(4); Mo had the highest improvement by a factor of about six. Thus, BiVO(4) and W- or Mo-doped (2 atom %) BiVO(4) photoanodes about 1 μm thick were fabricated onto transparent conducting substrate by a metal-organic decomposition/spin-coating method. Under simulated one sun (air mass 1.5G, 100 mW cm(-2)) and at 1.23 V versus a reversible hydrogen electrode, the highest photocurrent density (J(PH)) of about 2.38 mA cm(-2) was achieved for Mo doping followed by W doping (J(PH) ≈ 1.98 mA cm(-2)), whereas undoped BiVO(4) gave a J(PH) value of about 0.42 mA cm(-2). The photoelectrochemical water oxidation activity of W- and Mo-doped BiVO(4) photoanodes corresponded to the incident photon to current conversion efficiency of about 35 and 40 % respectively. Electrochemical impedance spectroscopy and Mott-Schottky analysis indicated a positive flat band shift of about 30 mV, a carrier concentration 1.6-2 times higher, and a charge-transfer resistance reduced by 3-4-fold for W- or Mo-doped BiVO(4) relative to undoped BiVO(4). Electronic structure calculations revealed that both W and Mo were shallow donors and Mo doping generated superior conductivity to W doping. The photo-oxidation activity of water on BiVO(4) photoanodes (undoped
Validation of a Ramp Running Protocol for Determination of the True VO2max in Mice
Ayachi, Mohamed; Niel, Romain; Momken, Iman; Billat, Véronique L.; Mille-Hamard, Laurence
In the field of comparative physiology, it remains to be established whether the concept of VO2max is valid in the mouse and, if so, how this value can be accurately determined. In humans, VO2max is generally considered to correspond to the plateau observed when VO2 no longer rises with an increase in workload. In contrast, the concept of VO2peak tends to be used in murine studies. The objectives of the present study were to determine whether (i) a continuous ramp protocol yielded a higher VO2peak than a stepwise, incremental protocol, and (ii) the VO2peak measured in the ramp protocol corresponded to VO2max. The three protocols (based on intensity-controlled treadmill running until exhaustion with eight female FVB/N mice) were performed in random order: (a) an incremental protocol that begins at 10 m.min−1 speed and increases by 3 m.min−1 every 3 min. (b) a ramp protocol with slow acceleration (3 m.min−2), and (c) a ramp protocol with fast acceleration (12 m.min−2). Each protocol was performed with two slopes (0 and 25°). Hence, each mouse performed six exercise tests. We found that the value of VO2peak was protocol-dependent (p < 0.05) and was highest (59.0 ml.kg 0.75.min−1) for the 3 m.min−2 0° ramp protocol. In the latter, the presence of a VO2max plateau was associated with the fulfillment of two secondary criteria (a blood lactate concentration >8 mmol.l−1 and a respiratory exchange ratio >1). The total duration of the 3 m.min−2 0° ramp protocol was shorter than that of the incremental protocol. Taken as a whole, our results suggest that VO2max in the mouse is best determined by applying a ramp exercise protocol with slow acceleration and no treadmill slope. PMID:27621709
High TIMT insulator-to-metal transition of the VO2 films on AlN/Si substrate
NASA Astrophysics Data System (ADS)
Slusar, Tetiana; Cho, Jin-Cheol; Kim, Bong-Jun; Kim, Hyun-Tak
Electronical and structural properties of the VO2 thin films are strongly affected by growth conditions and underlying substrate providing a flexibility of their functional parameters. We present a new VO2/AlN/Si heterostructure, where VO2 is characterized by an excellent insulator-to-metal transition (IMT) occurred at a higher temperature TIMT than that typical for single crystals. Mentioned characteristics are associated with growth mechanism of the film and its epitaxial alignment with respect to the substrate. In particular, the TIMT upshift in VO2/AlN/Si is explained by a stable crystallographic configuration in the plane of the VO2 film as well as a tensile deformation of a monoclinic a-axis formed by tilted and dimerized V4+-V4+, responsible for strong electron correlations. Moreover, proposed synergy of VO2 and Si is able to make new results for advanced materials fabrication and development of switching devices of new generation.