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The relatively low intensity of the ionizing VUV radiation guarantees one-photon processes, in other words only one, fixed energy photon will be responsible for photoionization. The energy balance of photoionization comprises the internal energy and the adiabatic ionization energy of the neutral as well as the photon energy, the kinetic energy of the photoelectron and of the photoion. Because only threshold electrons are considered and the conservation of momentum holds, the last two terms vanish, and the internal energy of the photoion is known:
Scanning the photon energy corresponds to shifting the internal energy distribution of the parent ion. The parent ion sits in a potential energy well, in which the lowest energy exit channel often corresponds to the breaking of the weakest chemical bond, resulting in the formation of a fragment or daughter ion. A mass spectrum is recorded at every photon energy, and the fractional ion abundances are plotted to obtain the breakdown diagram. At low energies no parent ion is energetic enough to dissociate, and the parent ion corresponds to 100% of the ion signal. As the photon energy is increased, a certain fraction of the parent ions (in fact according to the cumulative distribution function of the neutral internal energy distribution) still has too little energy to dissociate, but some do. The parent ion fractional abundances decrease, and the daughter ion signal increases. At the dissociative photoionization threshold, E, all parent ions, even the ones with initially 0 internal energy, can dissociate, and the daughter ion abundance reaches 100% in the breakdown diagram.
If the potential energy well of the parent ion is shallow and the complete initial thermal energy distribution is broader than the depth of the well, the breakdown diagram can also be used to determine adiabatic ionization energies. | 7 | Physical Chemistry |
Because of resonance stabilization of the conjugate base, an α-hydrogen in an aldehyde is weakly acidic with a pK near 17. Note, however, this is much more acidic than an alkane or ether hydrogen, which has pK near 50 approximately, and is even more acidic than a ketone α-hydrogen which has pK near 20. This acidification of the α-hydrogen in aldehyde is attributed to:
* the electron-withdrawing quality of the formyl center and
* the fact that the conjugate base, an enolate anion, delocalizes its negative charge.
The formyl proton itself does not readily undergo deprotonation. | 0 | Organic Chemistry |
Reflection high energy electron diffraction - total reflection angle X-ray spectroscopy is a technique for monitoring the chemical composition of crystals. RHEED-TRAXS analyzes X-ray spectral lines emitted from a crystal as a result of electrons from a RHEED gun colliding with the surface.
RHEED-TRAXS is preferential to X-ray microanalysis (XMA)(such as EDS and WDS) because the incidence angle of the electrons on the surface is very small, typically less than 5°. As a result, the electrons do not penetrate deeply into the crystal, meaning the X-ray emission is restricted to the top of the crystal, allowing for real-time, in-situ monitoring of surface stoichiometry.
The experimental setup is fairly simple. Electrons are fired onto a sample causing X-ray emission. These X-rays are then detected using a silicon-lithium Si-Li crystal placed behind beryllium windows, used to maintain vacuum. | 3 | Analytical Chemistry |
The application of nanoparticles (NPs) are one of novel promising techniques to target biofilms due to their high surface-area-to-volume ratio, their ability to penetrate to the deeper layers of biofilms and the capacity to releasing antimicrobial agents in a controlled way. Studying NP-EPS interactions could provide deeper understanding on how to develop more effective nanoparticles. "smart release" nanocarriers that can penetrate biofilms and be triggered by pathogenic microenvironments to deliver drugs or multifunctional compounds, such as catalytic nanoparticles to aptamers, dendrimers, and bioactive peptides) have been developed to disrupt the EPS and the viability or metabolic activity of the embedded bacteria. Some factors that would alter the potentials of the NP to transport antimicrobial agents into the biofilm include physicochemical interactions of the NPs with EPS components, the characteristics of the water spaces (pores) within the EPS matrix and the EPS matrix viscosity. Size and surface properties (charge and functional groups) of the NPs are the major determinants of the penetration in and the interaction with the EPS. Another potential antibiofilm strategy is phage therapy. Bacteriophages, viruses that invade specific bacterial host cells, were suggested to be effective agents in penetrating biofilms. In order to reach the maximum efficacy to eradicate biofilms, therapeutic strategies need to target both the biofilm matrix components as well as the embedded microorganisms to target the complex biofilm microenvironment. | 1 | Biochemistry |
The journal is abstracted and indexed by:
*Cambridge Structural Database
*Chemical Abstracts Service
*Current Contents/Physical, Chemical & Earth Sciences
*Index Medicus/MEDLINE/PubMed
*Inspec
*PASCAL
*Science Citation Index Expanded
*Scopus
*VINITI Database RAS
According to the Journal Citation Reports, the journal has a 2021 impact factor of 3.520. | 7 | Physical Chemistry |
UV light (specifically, UV‑B) causes the body to produce vitamin D, which is essential for life. Humans need some UV radiation to maintain adequate vitamin D levels. According to the World Health Organization:
Vitamin D can also be obtained from food and supplementation. Excess sun exposure produces harmful effects, however.
Vitamin D promotes the creation of serotonin. The production of serotonin is in direct proportion to the degree of bright sunlight the body receives. Serotonin is thought to provide sensations of happiness, well-being and serenity to human beings. | 5 | Photochemistry |
Cancer can result from the loss of cell-cell interaction. In normal cells, growth is controlled by contact inhibition in which contact with neighboring cells causes a stunt in cell growth. Contact inhibition is thought to be mediated by cadherins, proteins that play an important role in cell adhesion. This inhibition prevents cells from piling up on top of one another and forming mounds. However, in cancerous cells where expression of E-cadherin is lost, contact inhibition is lost and results in uncontrolled growth or proliferation, tumor formation, and metastasis. | 1 | Biochemistry |
Direct effects of increasing CO concentrations in the atmosphere include increasing global temperatures, ocean acidification and a CO fertilization effect on plants and crops. | 2 | Environmental Chemistry |
In science and engineering, the parts-per notation is a set of pseudo-units to describe small values of miscellaneous dimensionless quantities, e.g. mole fraction or mass fraction. Since these fractions are quantity-per-quantity measures, they are pure numbers with no associated units of measurement. Commonly used are parts-per-million (ppm, ), parts-per-billion (ppb, ), parts-per-trillion (ppt, ) and parts-per-quadrillion (ppq, ). This notation is not part of the International System of Units (SI) system and its meaning is ambiguous. | 2 | Environmental Chemistry |
Glycosylation can also be effected using the tools of synthetic organic chemistry. Unlike the biochemical processes, synthetic glycochemistry relies heavily on protecting groups (e.g. the 4,6-O-benzylidene) in order to achieve desired regioselectivity. The other challenge of chemical glycosylation is the stereoselectivity that each glycosidic linkage has two stereo-outcomes, α/β or cis/trans. Generally, the α- or cis-glycoside is more challenging to synthesis. New methods have been developed based on solvent participation or the formation of bicyclic sulfonium ions as chiral-auxiliary groups. | 0 | Organic Chemistry |
Because of their resistant to cold water dissolution, which severely destroys the calcareous planktonic fossils at depth worldwide, Radiolarians has become one of the most commonly studied siliceous planktonic fossils for paleotemperature reconstruction.
Study of Radiolarians in the North Pacific deep sea cores has revealed that increases in both species diversity and abundance correspond to major glaciation events of the last 16 million years. Changes in Radiolarian compositions are also evident to reflect in general sea surface temperature.
By applying statistical analyses (Q-mode factor analysis), many quantitative studies of Radiolarian assemblages from surface sediments have established a transfer function which enables the estimation of paleo-sea surface temperature. For example, Pisias et al. (1997) were able to identify assemblages representative to the present Pacific biogeography and used these assemblages to predict sea surface temperature of the last glacier maximum. | 9 | Geochemistry |
Natural transformation is the viral transformation of cells without the interference of medical science. This is the most commonly considered form of viral transformation and includes many cancers and diseases, such as HIV, Hepatitis B, and T-cell Leukemia virus type I. | 1 | Biochemistry |
A screw axis (helical axis or twist axis) is a line that is simultaneously the axis of rotation and the line along which translation of a body occurs. Chasles' theorem shows that each Euclidean displacement in three-dimensional space has a screw axis, and the displacement can be decomposed into a rotation about and a slide along this screw axis.
Plücker coordinates are used to locate a screw axis in space, and consist of a pair of three-dimensional vectors. The first vector identifies the direction of the axis, and the second locates its position. The special case when the first vector is zero is interpreted as a pure translation in the direction of the second vector. A screw axis is associated with each pair of vectors in the algebra of screws, also known as screw theory.
The spatial movement of a body can be represented by a continuous set of displacements. Because each of these displacements has a screw axis, the movement has an associated ruled surface known as a screw surface. This surface is not the same as the axode, which is traced by the instantaneous screw axes of the movement of a body. The instantaneous screw axis, or instantaneous helical axis (IHA), is the axis of the helicoidal field generated by the velocities of every point in a moving body.
When a spatial displacement specializes to a planar displacement, the screw axis becomes the displacement pole, and the instantaneous screw axis becomes the velocity pole, or instantaneous center of rotation, also called an instant center. The term centro is also used for a velocity pole, and the locus of these points for a planar movement is called a centrode. | 3 | Analytical Chemistry |
In water–heavy water mixtures equilibria several species are involved: HO, HDO, DO, HO, DO, HDO, HDO, HO, DO. | 7 | Physical Chemistry |
Carboximidates are good electrophiles and undergo a range of addition reactions; with aliphatic imidates generally reacting faster than aromatic imidates. They can be hydrolyzed to give esters and by an analogous process react with amines (including ammonia) to form amidines. Aliphatic imidates react with an excess of alcohol under acid catalysis to form orthoesters RC(OR), aromatic imidates can also be converted but far less readily. | 0 | Organic Chemistry |
In some cases, energy loss features due to plasmon excitations are also observed. This can either be a final state effect caused by core hole decay, which generates quantized electron wave excitations in the solid (intrinsic plasmons), or it can be due to excitations induced by photoelectrons travelling from the emitter to the surface (extrinsic plasmons).
Due to the reduced coordination number of first-layer atoms, the plasma frequency of bulk and surface atoms are related by the following equation:
so that surface and bulk plasmons can be easily distinguished from each other.
Plasmon states in a solid are typically localized at the surface, and can strongly affect IMFP. | 7 | Physical Chemistry |
The sublimation sandwich method (also called the sublimation sandwich process and the sublimation sandwich technique) is a kind of physical vapor deposition used for creating man-made crystals. Silicon carbide is the most common crystal grown this way, though others crystals may also be created with it (notably gallium nitride).
In this method, the environment around a single crystal or a polycrystalline plate is filled with vapor heated to between 1600°C and 2100°C-- changes to this environment can affect the gas phase stoichiometry. The source-to-crystal distance is kept between 0.02-0.03mm (very low). Parameters that can affect crystal growth include source-to-substrate distance, temperature gradient, and the presence of tantalum for gathering excess carbon. High growth rates are the result of small source-to-seed distances combined with a large heat flux onto a small amount of source material with no more than a moderate temperature difference between the substrate and the source (0.5-10°C). The growth of large boules, however, remains quite difficult using this method, and it is better suited to the creation of epitaxial films with uniform polytype structures. Ultimately, samples with a thickness of up to 500µm can be produced using this method. | 3 | Analytical Chemistry |
In environmental management, water analysis is frequently deployed when pollution is suspected to identify the pollutant in order to take remedial action. The analysis can often enable the polluter to be identified. Such forensic work can examine the ratios of various components and can "type" samples of oils or other mixed organic contaminants to directly link the pollutant with the source.
In drinking water supplies the cause of unacceptable quality can similarly be determined by carefully targeted chemical analysis of samples taken throughout the distribution system.
In manufacturing, off-spec products may be directly tied back to unexpected changes in wet processing stages and analytical chemistry can identify which stages may be at fault and for what reason. | 9 | Geochemistry |
A metabolic network is the complete set of metabolic and physical processes that determine the physiological and biochemical properties of a cell. As such, these networks comprise the chemical reactions of metabolism, the metabolic pathways, as well as the regulatory interactions that guide these reactions.
With the sequencing of complete genomes, it is now possible to reconstruct the network of biochemical reactions in many organisms, from bacteria to human. Several of these networks are available online:
Kyoto Encyclopedia of Genes and Genomes (KEGG), EcoCyc, BioCyc and metaTIGER.
Metabolic networks are powerful tools for studying and modelling metabolism. | 1 | Biochemistry |
Jaroslav Heyrovský was born in Prague on December 20, 1890, the fifth child of Leopold Heyrovský, Professor of Roman Law at the Charles University in Prague, and his wife Clara, née Hanl von Kirchtreu. He obtained his early education at secondary school until 1909 when he began his study of chemistry, physics, and mathematics at the Charles University in Prague. From 1910 to 1914 he continued his studies at University College London, under Professors Sir William Ramsay, W. C. McC. Lewis, and F. G. Donnan, taking his B.Sc. degree in 1913. He was particularly interested in working with Professor Donnan, on electrochemistry.
During the First World War Heyrovský worked in a military hospital as a dispensing chemist and radiologist, which enabled him to continue his studies and to take his Ph.D. degree in Prague in 1918 and D.Sc. in London in 1921.
Heyrovský started his university career as assistant to Professor B. Brauner in the Institute of Analytical Chemistry of the Charles University, Prague; he was promoted to Associate Professor in 1922 and in 1926 he became the University's first Professor of Physical Chemistry.
Heyrovský's invention of the polarographic method dates from 1922 and he concentrated his whole further scientific activity on the development of this new branch of electrochemistry. He formed a school of Czech polarographers in the University, and was himself in the forefront of polarographic research. In 1950 Heyrovský was appointed as the Director of the newly established Polarographic Institute, which was incorporated into the Czechoslovak Academy of Sciences in 1952.
In 1926 Professor Heyrovský married Marie (Mary) Koranová, and the couple had two children, a daughter, Jitka, and a son, Michael.
Jaroslav Heyrovský died on March 27, 1967. He was interred in the Vyšehrad cemetery in Prague. | 3 | Analytical Chemistry |
The ENCODE project proposes to map all of the DHSs in the human genome with the intention of cataloging human regulatory DNA.
DHSs mark transcriptionally active regions of the genome, where there will be cellular selectivity. So, they used 125 different human cell types. This way, using the massive sequencing technique, they obtained the DHSs profiles of every cellular type. Through an analysis of the data, they identified almost 2.9 million distinct DHSs. 34% were specific to each cell type, and only a small minority (3,692) were detected in all cell types. Also, it was confirmed that only 5% of DHSs were found in TSS (Transcriptional Start Site) regions. The remaining 95% represented distal DHSs, divided in a uniform way between intronic and intergenic regions. The data gives an idea of the great complexity regulating the genetic expression in the human genome and the quantity of elements that control this regulation.
The high-resolution mapping of DHSs in the model plant Arabidopsis thaliana has been reported. Total 38,290 and 41,193 DHSs in leaf and flower tissues have been identified, respectively. | 1 | Biochemistry |
A use of ion chromatography can be seen in argentation chromatography. Usually, silver and compounds containing acetylenic and ethylenic bonds have very weak interactions. This phenomenon has been widely tested on olefin compounds. The ion complexes the olefins make with silver ions are weak and made based on the overlapping of pi, sigma, and d orbitals and available electrons therefore cause no real changes in the double bond. This behavior was manipulated to separate lipids, mainly fatty acids from mixtures in to fractions with differing number of double bonds using silver ions. The ion resins were impregnated with silver ions, which were then exposed to various acids (silicic acid) to elute fatty acids of different characteristics.
Detection limits as low as 1 μM can be obtained for alkali metal ions.
It may be used for measurement of HbA1c, porphyrin and with water purification. Ion Exchange Resins(IER) have been widely used especially in medicines due to its high capacity and the uncomplicated system of the separation process. One of the synthetic uses is to use Ion Exchange Resins for kidney dialysis. This method is used to separate the blood elements by using the cellulose membraned artificial kidney.
Another clinical application of ion chromatography is in the rapid anion exchange chromatography technique used to separate creatine kinase (CK) isoenzymes from human serum and tissue sourced in autopsy material (mostly CK rich tissues were used such as cardiac muscle and brain). These isoenzymes include MM, MB, and BB, which all carry out the same function given different amino acid sequences. The functions of these isoenzymes are to convert creatine, using ATP, into phosphocreatine expelling ADP. Mini columns were filled with DEAE-Sephadex A-50 and further eluted with tris- buffer sodium chloride at various concentrations (each concentration was chosen advantageously to manipulate elution). Human tissue extract was inserted in columns for separation. All fractions were analyzed to see total CK activity and it was found that each source of CK isoenzymes had characteristic isoenzymes found within. Firstly, CK- MM was eluted, then CK-MB, followed by CK-BB. Therefore, the isoenzymes found in each sample could be used to identify the source, as they were tissue specific.
Using the information from results, correlation could be made about the diagnosis of patients and the kind of CK isoenzymes found in most abundant activity. From the finding, about 35 out of 71 patients studied suffered from heart attack (myocardial infarction) also contained an abundant amount of the CK-MM and CK-MB isoenzymes. Findings further show that many other diagnosis including renal failure, cerebrovascular disease, and pulmonary disease were only found to have the CK-MM isoenzyme and no other isoenzyme. The results from this study indicate correlations between various diseases and the CK isoenzymes found which confirms previous test results using various techniques. Studies about CK-MB found in heart attack victims have expanded since this study and application of ion chromatography. | 3 | Analytical Chemistry |
The first modern definition of acids and bases in molecular terms was devised by Svante Arrhenius. A hydrogen theory of acids, it followed from his 1884 work with Friedrich Wilhelm Ostwald in establishing the presence of ions in aqueous solution and led to Arrhenius receiving the Nobel Prize in Chemistry in 1903.
As defined by Arrhenius:
* An Arrhenius acid is a substance that ionises in water to form hydrogen ions (); that is, an acid increases the concentration of H ions in an aqueous solution.
This causes the protonation of water, or the creation of the hydronium () ion. Thus, in modern times, the symbol is interpreted as a shorthand for , because it is now known that a bare proton does not exist as a free species in aqueous solution. This is the species which is measured by pH indicators to measure the acidity or basicity of a solution.
* An Arrhenius base is a substance that dissociates in water to form hydroxide () ions; that is, a base increases the concentration of ions in an aqueous solution.
The Arrhenius definitions of acidity and alkalinity are restricted to aqueous solutions and are not valid for most non-aqueous solutions, and refer to the concentration of the solvent ions. Under this definition, pure and HCl dissolved in toluene are not acidic, and molten NaOH and solutions of calcium amide in liquid ammonia are not alkaline. This led to the development of the Brønsted–Lowry theory and subsequent Lewis theory to account for these non-aqueous exceptions.
The reaction of an acid with a base is called a neutralization reaction. The products of this reaction are a salt and water.
In this traditional representation an acid–base neutralization reaction is formulated as a double-replacement reaction. For example, the reaction of hydrochloric acid (HCl) with sodium hydroxide (NaOH) solutions produces a solution of sodium chloride (NaCl) and some additional water molecules.
The modifier (aq) in this equation was implied by Arrhenius, rather than included explicitly. It indicates that the substances are dissolved in water. Though all three substances, HCl, NaOH and NaCl are capable of existing as pure compounds, in aqueous solutions they are fully dissociated into the aquated ions and . | 7 | Physical Chemistry |
More advanced direct reduction processes were developed at the beginning of the 20th century, when it became possible to smelt pre-reduced ores using the Martin-Siemens process or the electric arc furnace. Based on this technical and economic model, a number of processes were industrialized before World War II (the Krupp-Renn process adopted by the Shōwa Steel Works, the Chenot process, etc.). They remained confidential, however, and their profitability was generally debated.
Modern direct reduction processes, based on the use of natural gas instead of coal, were studied intensively in the 1950s. On December 5, 1957, the Mexican company Hylsa started up the first industrial production unit of this type in Monterrey, with the pre-reduced ore obtained destined for smelting in an electric arc furnace. As the production of pre-reduced ore with natural gas was economically viable, several plants were built in the late 1960s. As a cheap supply of natural gas was essential to their profitability, most plants were located in countries with gas deposits, in Latin America (where many were developed) and in the Middle East.
In 1970, worldwide production of pre-reduced iron ore reached 790,000 tonnes. The processes then in operation were the HYL process (680,000 tonnes produced), an SL/RN unit, a Purofer unit, and the first plant to use the Midrex process.
Although profitable and innovative, the processes invented did not ultimately prove to be a technological revolution capable of supplanting the traditional blast furnace-based process. However, the quantity of steel produced from pre-reduced materials grew steadily, outstripping world steel production:
* in 1976, installations in service totalled less than 5 Mt;
* in 1985, annual production was 11 Mt for an installed capacity of around 20 Mt, the difference being explained by fluctuations in energy costs;
* in 1991, production reached 20 Mt.
* in 1995, worldwide production of prereducts passed the 30 Mt mark for the first time.
* In 2010, 70 Mt were produced, 14% from HYL processes and 60% from the Midrex process. The latter accounts for most of the growth in natural gas-fired production of pre-reduced products, although since 2005 coal-fired processes have been making a strong comeback, mainly in India.
Packaging of pre-reduced iron ore is evenly divided between sponge iron and briquettes. Sponges are a highly porous metallic product, close to the original ore but highly pyrophoric, which limits their transport. They are therefore often subjected to hot compaction, which improves both product density and handling safety. In 2012, 45% of prereducts were transformed into briquettes in this way. | 8 | Metallurgy |
Of the 195 countries currently recognised by the United Nations, 141 use RHT and 54 use LHT on roads in general.
A country and its territories and dependencies are counted as one. Whichever directionality is listed first is the type that is used in general in the traffic category. | 4 | Stereochemistry |
In order for pathogenic bacteria to invade a cell, communication with the host cell is required. The first step for invading bacteria is usually adhesion to host cells. Strong anchoring, a characteristic that determines virulence, prevents the bacteria from being washed away before infection occurs. Bacterial cells can bind to many host cell surface structures such as glycolipids and glycoproteins which serve as attachment receptors. Once attached, the bacteria begin to interact with the host to disrupt its normal functioning and disrupt or rearrange its cytoskeleton. Proteins on the bacteria surface can interact with protein receptors on the host thereby affecting signal transduction within the cell. Alterations to signaling are favorable to bacteria because these alterations provide conditions under which the pathogen can invade. Many pathogens have Type III secretion systems which can directly inject protein toxins into the host cells. These toxins ultimately lead to rearrangement of the cytoskeleton and entry of the bacteria. | 1 | Biochemistry |
Any real measuring instrument has a limited range over which it can accurately measure absorbance. An instrument must be calibrated and checked against known standards if the readings are to be trusted. Many instruments will become non-linear (fail to follow the Beer–Lambert law) starting at approximately 2 AU (~1% transmission). It is also difficult to accurately measure very small absorbance values (below ) with commercially available instruments for chemical analysis. In such cases, laser-based absorption techniques can be used, since they have demonstrated detection limits that supersede those obtained by conventional non-laser-based instruments by many orders of magnitude (detection has been demonstrated all the way down to ). The theoretical best accuracy for most commercially available non-laser-based instruments is attained in the range near 1 AU. The path length or concentration should then, when possible, be adjusted to achieve readings near this range. | 7 | Physical Chemistry |
If the solvent is a liquid, then almost all gases, liquids, and solids can be dissolved. Here are some examples:
* Gas in liquid:
** Oxygen in water
** Carbon dioxide in water – a less simple example, because the solution is accompanied by a chemical reaction (formation of ions). The visible bubbles in carbonated water are not the dissolved gas, but only an effervescence of carbon dioxide that has come out of solution; the dissolved gas itself is not visible since it is dissolved on a molecular level.
* Liquid in liquid:
** The mixing of two or more substances of the same chemistry but different concentrations to form a constant. (Homogenization of solutions)
** Alcoholic beverages are basically solutions of ethanol in water.
* Solid in liquid:
** Sucrose (table sugar) in water
** Sodium chloride (NaCl) (table salt) or any other salt in water, which forms an electrolyte: When dissolving, salt dissociates into ions.
* Solutions in water are especially common, and are called aqueous solutions.
* Non-aqueous solutions are when the liquid solvent involved is not water.
Counterexamples are provided by liquid mixtures that are not homogeneous: colloids, suspensions, emulsions are not considered solutions.
Body fluids are examples of complex liquid solutions, containing many solutes. Many of these are electrolytes since they contain solute ions, such as potassium. Furthermore, they contain solute molecules like sugar and urea. Oxygen and carbon dioxide are also essential components of blood chemistry, where significant changes in their concentrations may be a sign of severe illness or injury. | 7 | Physical Chemistry |
Six affiliate societies focused on specific areas of materials science also fall under the ASM umbrella:
* The Heat Treating Society (HTS),
* The Thermal Spray Society (TSS),
* The International Metallographic Society (IMS),
* The Electronic Device Failure Analysis Society (EDFAS),
* The Failure Analysis Society (FAS), and
* The International Organization on Shape Memory and Superelastic Technology (SMST).
Each society is led by volunteers, produces specific technical content for members, and holds its own international event. | 8 | Metallurgy |
There are several surface measurement (including flasks and continuous in situ) networks including NOAA/ERSL, WDCGG, and RAMCES. The NOAA/ESRL Baseline Observatory Network, and the Scripps Institution of Oceanography Network data are hosted at the CDIAC at ORNL. The World Data Centre for Greenhouse Gases (WDCGG), part of GAW, data are hosted by the JMA. The Reseau Atmospherique de Mesure des Composes an Effet de Serre database (RAMCES) is part of IPSL.
From these measurements, further products are made which integrate data from the various sources. These products also address issues such as data discontinuity and sparseness. GLOBALVIEW- is one of these products.
Ongoing ground-based total column measurements began more recently. Column measurements typically refer to an averaged column amount denoted X, rather than a surface only measurement. These measurements are made by the TCCON. These data are also hosted on the CDIAC, and made publicly available according to the data use policy. | 2 | Environmental Chemistry |
Like all known forms of matter, liquids are fundamentally quantum mechanical. However, under standard conditions (near room temperature and pressure), much of the macroscopic behavior of liquids can be understood in terms of classical mechanics. The "classical picture" posits that the constituent molecules are discrete entities that interact through intermolecular forces according to Newton's laws of motion. As a result, their macroscopic properties can be described using classical statistical mechanics. While the intermolecular force law technically derives from quantum mechanics, it is usually understood as a model input to classical theory, obtained either from a fit to experimental data or from the classical limit of a quantum mechanical description. An illustrative, though highly simplified example is a collection of spherical molecules interacting through a Lennard-Jones potential.
For the classical limit to apply, a necessary condition is that the thermal de Broglie wavelength,
is small compared with the length scale under consideration. Here, is the Planck constant and is the molecule's mass. Typical values of are about 0.01-0.1 nanometers (Table 1). Hence, a high-resolution model of liquid structure at the nanoscale may require quantum mechanical considerations. A notable example is hydrogen bonding in associated liquids like water, where, due to the small mass of the proton, inherently quantum effects such as zero-point motion and tunneling are important.
For a liquid to behave classically at the macroscopic level, must be small compared with the average distance
between molecules. That is,
Representative values of this ratio for a few liquids are given in Table 1. The conclusion is that quantum effects are important for liquids at low temperatures and with small molecular mass. For dynamic processes, there is an additional timescale constraint:
where is the timescale of the process under consideration. For room-temperature liquids, the right-hand side is about 10 seconds, which generally means that time-dependent processes involving translational motion can be described classically.
At extremely low temperatures, even the macroscopic behavior of certain liquids deviates from classical mechanics. Notable examples are hydrogen and helium. Due to their low temperature and mass, such liquids have a thermal de Broglie wavelength comparable to the average distance between molecules. | 7 | Physical Chemistry |
It is far more difficult to produce a fermionic superfluid than a bosonic one, because the Pauli exclusion principle prohibits fermions from occupying the same quantum state. However, there is a well-known mechanism by which a superfluid may be formed from fermions: That mechanism is the BCS transition, discovered in 1957 by J. Bardeen, L.N. Cooper, and R. Schrieffer for describing superconductivity. These authors showed that, below a certain temperature, electrons (which are fermions) can pair up to form bound pairs now known as Cooper pairs. As long as collisions with the ionic lattice of the solid do not supply enough energy to break the Cooper pairs, the electron fluid will be able to flow without dissipation. As a result, it becomes a superfluid, and the material through which it flows a superconductor.
The BCS theory was phenomenally successful in describing superconductors. Soon after the publication of the BCS paper, several theorists proposed that a similar phenomenon could occur in fluids made up of fermions other than electrons, such as helium-3 atoms. These speculations were confirmed in 1971, when experiments performed by D.D. Osheroff showed that helium-3 becomes a superfluid below 0.0025 K. It was soon verified that the superfluidity of helium-3 arises from a BCS-like mechanism. | 7 | Physical Chemistry |
Empirical correlations are simple mathematical expressions intended to approximate a liquid's properties over a range of experimental conditions, such as varying temperature and pressure. They are constructed by fitting simple functional forms to experimental data. For example, the temperature-dependence of liquid viscosity is sometimes approximated by the function , where and are fitting constants. Empirical correlations allow for extremely efficient estimates of physical properties, which can be useful in thermophysical simulations. However, they require high quality experimental data to obtain a good fit and cannot reliably extrapolate beyond the conditions covered by experiments. | 7 | Physical Chemistry |
Thermocouples can generally be used in the testing of prototype electrical and mechanical apparatus. For example, switchgear under test for its current carrying capacity may have thermocouples installed and monitored during a heat run test, to confirm that the temperature rise at rated current does not exceed designed limits. | 8 | Metallurgy |
TFB is recruited by another translation factor, TBP, after it recognizes the TATA box and bends the DNA so transcription can initiate. TFB stabilizes the TBP-DNA complex so that the proteins can recruit RNA Polymerase and melt the DNA via a yet-unknown mechanism. This opening of the DNA is not an energy-dependent process in Archaea; since TFB, TBP, and RNAP are located more closely to each other than in Eukarya, the tightness of the proteins and their interactions may provide more areas of contact to open the DNA as well as physically strain the DNA, which leads to an open transcription complex.
TFB uses a zinc ion (Zn) as a cofactor and accepts one ion per subunit. | 1 | Biochemistry |
Sulfur diimides are chemical compounds of the formula S(NR). Structurally, they are the diimine of sulfur dioxide. The parent member, S(NH), is of only theoretical interest. Other derivatives where R is an organic group are stable and useful reagents. | 0 | Organic Chemistry |
In surface chemistry, the Hertz–Knudsen equation, also known as Knudsen-Langmuir equation describes evaporation rates, named after Heinrich Hertz and Martin Knudsen. | 7 | Physical Chemistry |
; (2001 September); Magnum opus
Pereras Magnum opus never loses sight of what is required to make a complete cricketer – in every sense of the word. Former England skipper Mike Brearley OBE has contributed the preface while the then Sri Lankas cricket coach, Davenall Whatmore, the foreword. It is the only self study training guide by an umpire for the players. It has won admiration and gained much recognition to the country from the cricketing world, which includes the ICC, MCC, ECB and even the prestigious Wisden Cricketers' Almanack (2002).
;Further Reading
* [http://thinkingcricket2.tripod.com/THINKING%20CRICKET.htm Thinking Cricket (February 2004)] Retrieved on 12 March 2009
* [http://www.island.lk/2001/11/11/sports05.html This is no ordinary cricket book but a well-thought out book of instructions. By Mahinda Wijesinghe (2001 November)] Retrieved on 12 March 2009 | 3 | Analytical Chemistry |
The reverse Krebs cycle, also known as reverse TCA cycle (rTCA) or reductive citric acid cycle, is an alternative to the standard Calvin-Benson cycle for carbon fixation. It has been found in strict anaerobic or microaerobic bacteria (as Aquificales) and anaerobic archea. It was discovered by Evans, Buchanan and Arnon in 1966 working with the photosynthetic green sulfur bacterium Chlorobium limicola. In particular, it is one of the most used pathways in hydrothermal vents by the Campylobacterota. This feature is very important in oceans. Without it, there would be no primary production in aphotic environments, which would lead to habitats without life. So this kind of primary production is called "dark primary production".
The cycle involves the biosynthesis of acetyl-CoA from two molecules of CO. The key steps of the reverse Krebs cycle are:
* Oxaloacetate to malate, using NADH + H
* Fumarate to succinate, catalyzed by an oxidoreductase, Fumarate reductase
* Succinate to succinyl-CoA, an ATP dependent step
* Succinyl-CoA to alpha-ketoglutarate, using one molecule of CO
* Alpha-ketoglutarate to isocitrate, using NADPH + H and another molecule of CO
* Citrate converted into oxaloacetate and acetyl-CoA, this is an ATP dependent step and the key enzyme is the ATP citrate lyase
This pathway is cyclic due to the regeneration of the oxaloacetate.
The bacteria Gammaproteobacteria and Riftia pachyptila switch from the Calvin-Benson cycle to the rTCA cycle in response to concentrations of HS. | 5 | Photochemistry |
The first publication of the structure of wheel shaped cluster anion, first determined for the nitrosyl derivative by Achim Müller et al. was announced in New Scientist as "Big Wheel rolls back the molecular frontier". Further work by the same group then refined the initial findings and determined the structure of the wheel produced in molybdate solutions as [MoOH(HO)]. The Mo-type cluster was then shown to be the basic structural type of molybdenum blue compounds obtained under slightly different conditions.
The structure of the big wheel is constructed from units containing 11 Mo atoms ({Mo}-type units), 14 of which are linked together to form the {Mo}-type cluster that has an external diameter of 3.4 nm. (12 {Mo}-type units are also involved in the construction of higher symmetrical spherical systems called Keplerates) These units consist of a central MoO bipyramid sharing edges with 5 MoO octahedra (an illustration of this is on page 155 of the review ). With 5 more linking MoO octahedra the repeating {Mo}-type unit is built up. | 7 | Physical Chemistry |
Two forces affect ionized atoms in a conductor: 1) The direct electrostatic force F, as a result of the electric field , which has the same direction as the electric field, and 2) The force from the exchange of momentum with other charge carriers F, toward the flow of charge carriers, is in the opposite direction of the electric field. In metallic conductors F is caused by a so-called "electron wind" or "ion wind".
The resulting force F on an activated ion in the electrical field can be written as
where is the electric charge of the ions, and the valences corresponding to the electrostatic and wind force respectively, the so-called effective valence of the material, the current density, and the resistivity of the material
Electromigration occurs when some of the momentum of a moving electron is transferred to a nearby activated ion. This causes the ion to move from its original position. Over time this force knocks a significant number of atoms far from their original positions. A break or gap can develop in the conducting material, preventing the flow of electricity. In narrow interconnect conductors, such as those linking transistors and other components in integrated circuits, this is known as a void or internal failure (open circuit). Electromigration can also cause the atoms of a conductor to pile up and drift toward other nearby conductors, creating an unintended electrical connection known as a hillock failure or whisker failure (short circuit). Both of these situations can lead to a malfunction of the circuit. | 7 | Physical Chemistry |
In iron and steel metallurgy, ledeburite is a mixture of 4.3% carbon in iron and is a eutectic mixture of austenite and cementite. Ledeburite is not a type of steel as the carbon level is too high although it may occur as a separate constituent in some high carbon steels. It is mostly found with cementite or pearlite in a range of cast irons.
It is named after the metallurgist Karl Heinrich Adolf Ledebur (1837–1906). He was the first professor of metallurgy at the Bergakademie Freiberg and discovered ledeburite in 1882.
Ledeburite arises when the carbon content is between 2.06% and 6.67%. The eutectic mixture of austenite and cementite is 4.3% carbon, FeC:2Fe, with a melting point of 1147 °C.
Ledeburite-II (at ambient temperature) is composed of cementite-I with recrystallized secondary cementite (which separates from austenite as the metal cools) and (with slow cooling) of pearlite. The pearlite results from the eutectoidal decay of the austenite that comes from the ledeburite-I at 723 °C. During more rapid cooling, bainite can develop instead of pearlite, and with very rapid cooling martensite can develop. | 8 | Metallurgy |
Like Wilson (1964), Renon & Prausnitz (1968) began with local composition theory, but instead of using the Flory–Huggins volumetric expression as Wilson did, they assumed local compositions followed
with a new "non-randomness" parameter α. The excess Gibbs free energy was then determined to be
Unlike Wilsons equation, this can predict partially miscible mixtures. However, the cross term, like Wohls expansion, is more suitable for than , and experimental data is not always sufficiently plentiful to yield three meaningful values, so later attempts to extend Wilsons equation to partial miscibility (or to extend Guggenheims quasichemical theory for nonrandom mixtures to Wilson's different-sized molecules) eventually yielded variants like UNIQUAC. | 7 | Physical Chemistry |
Corrosion fatigue is fatigue in a corrosive environment. It is the mechanical degradation of a material under the joint action of corrosion and cyclic loading. Nearly all engineering structures experience some form of alternating stress, and are exposed to harmful environments during their service life. The environment plays a significant role in the fatigue of high-strength structural materials like steel, aluminum alloys and titanium alloys. Materials with high specific strength are being developed to meet the requirements of advancing technology. However, their usefulness depends to a large extent on the degree to which they resist corrosion fatigue.
The effects of corrosive environments on the fatigue behavior of metals were studied as early as 1930.
The phenomenon should not be confused with stress corrosion cracking, where corrosion (such as pitting) leads to the development of brittle cracks, growth and failure. The only requirement for corrosion fatigue is that the sample be under tensile stress. | 8 | Metallurgy |
Samuel Van Leer was a well-known ironmaster and a United States Army officer during the American Revolutionary War. He started a military career with enthusiasm with his neighbor General Anthony Wayne in 1775. His furnace, Reading Furnace in Pennsylvania, supplied cannon and cannonballs for the Continental Army. Van Leers furnace was a center of colonial ironmaking and is associated with the introduction of the Franklin Stove, and the retreat of George Washingtons army following its defeat at the Battle of Brandywine, where they came for musket repairs. The location is listed as a temporary George Washington Headquarter.W Van Leer's children all joined the iron business as well. | 8 | Metallurgy |
A proton-exchange membrane, or polymer-electrolyte membrane (PEM), is a semipermeable membrane generally made from ionomers and designed to conduct protons while acting as an electronic insulator and reactant barrier, e.g. to oxygen and hydrogen gas. This is their essential function when incorporated into a membrane electrode assembly (MEA) of a proton-exchange membrane fuel cell or of a proton-exchange membrane electrolyser: separation of reactants and transport of protons while blocking a direct electronic pathway through the membrane.
PEMs can be made from either pure polymer membranes or from composite membranes, where other materials are embedded in a polymer matrix. One of the most common and commercially available PEM materials is the fluoropolymer (PFSA) Nafion, a DuPont product. While Nafion is an ionomer with a perfluorinated backbone like Teflon, there are many other structural motifs used to make ionomers for proton-exchange membranes. Many use polyaromatic polymers, while others use partially fluorinated polymers.
Proton-exchange membranes are primarily characterized by proton conductivity (σ), methanol permeability (P), and thermal stability.
PEM fuel cells use a solid polymer membrane (a thin plastic film) which is permeable to protons when it is saturated with water, but it does not conduct electrons. | 7 | Physical Chemistry |
The tetrathionate anion, , is a sulfur oxyanion derived from the compound tetrathionic acid, HSO. Two of the sulfur atoms present in the ion are in oxidation state 0 and two are in oxidation state +5. Alternatively, the compound can be viewed as the adduct resulting from the binding of disulfide| to SO. Tetrathionate is one of the polythionates, a family of anions with the formula [S(SO)]. Its IUPAC name is 2-(dithioperoxy)disulfate, and the name of its corresponding acid is 2-(dithioperoxy)disulfuric acid. The Chemical Abstracts Service identifies tetrathionate by the CAS Number 15536-54-6. | 8 | Metallurgy |
The technique of vibrational analysis with scanning probe microscopy allows probing vibrational properties of materials at the submicrometer scale, and even of individual molecules. This is accomplished by integrating scanning probe microscopy (SPM) and vibrational spectroscopy (Raman scattering or/and Fourier transform infrared spectroscopy, FTIR). This combination allows for much higher spatial resolution than can be achieved with conventional Raman/FTIR instrumentation. The technique is also nondestructive, requires non-extensive sample preparation, and provides more contrast such as intensity contrast, polarization contrast and wavelength contrast, as well as providing specific chemical information and topography images simultaneously. | 7 | Physical Chemistry |
After the mRNA is completed and cleaved off at the poly-A signal sequence, the left-over (residual) RNA strand remains bound to the DNA template and the RNA polymerase II unit, continuing to be transcribed. After this cleavage, a so-called exonuclease binds to the residual RNA strand and removes the freshly transcribed nucleotides one at a time (also called degrading the RNA), moving towards the bound RNA polymerase II. This exonuclease is XRN2 (5-3 Exoribonuclease 2) in humans. This model proposes that XRN2 proceeds to degrade the uncapped residual RNA from 5 to 3 until it reaches the RNA pol II unit. This causes the exonuclease to push off the RNA pol II unit as it moves past it, terminating the transcription while also cleaning up the residual RNA strand.
Similar to Rho-dependent termination, XRN2 triggers the dissociation of RNA polymerase II by either pushing the polymerase off of the DNA template or pulling the template out of the RNA polymerase. The mechanism by which this happens remains unclear, however, and has been challenged not to be the sole cause of the dissociation.
In order to protect the transcribed mRNA from degradation by the exonuclease, a 5 cap is added to the strand. This is a modified guanine added to the front of mRNA, which prevents the exonuclease from binding and degrading the RNA strand. A 3 poly(A) tail is added to the end of a mRNA strand for protection from other exonucleases as well. | 1 | Biochemistry |
In The United States, federal law recognizes a legal practice for the study of an item in hopes of obtaining a detailed understanding of the
way in which it works for the purpose of creating duplicate or superior products without the benefit of having the plans for the original item. The studied item must first have been legally obtained, not stolen or otherwise misappropriated. The purpose of intellectual property protection is to provide incentives to invest and to advance the collective knowledge. It is felt that deformulation or reverse engineering helps to educate and promote healthy competition. It is considered to be a learning tool which provides a path to making new, competitive products that perform better and at lower cost than what is currently on the market. Deformulation is often considered along with benchmarking, patent mapping, and other competitor intelligence gathering processes as a means of conducting day-to-day business.
Other countries may have different conceptions about intellectual property rights and about legal allowances for deformulation or reverse engineering of items. For information concerning the legal status of deformulation practices in other countries throughout the world it is advisable to consult with an expert on intellectual property law. | 3 | Analytical Chemistry |
As first shown in 2003, the auxiliary function of carotenoids as quenchers of singlet oxygen contributes to the photoprotective role of OCP has also been demonstrated under strong orange-red light, which are conditions where OCP cannot be photoactivated for its energy-quenching role. This is significant because all oxygenic phototrophs have a particular risk of oxidative damage initiated by singlet oxygen (O), which is produced when their own light-harvesting pigments act as photosensitizers. | 5 | Photochemistry |
Austempering is a hardening process that is used on iron-based metals to promote better mechanical properties. The metal is heated into the austenite region of the iron-cementite phase diagram and then quenched in a salt bath or other heat extraction medium that is between temperatures of . The metal is annealed in this temperature range until the austenite turns to bainite or ausferrite (bainitic ferrite + high-carbon austenite).
By changing the temperature for austenitization, the austempering process can yield different and desired microstructures. A higher austenitization temperature can produce a higher carbon content in austenite, whereas a lower temperature produces a more uniform distribution of austempered structure. The carbon content in austenite as a function of austempering time has been established. | 8 | Metallurgy |
Van de Flierdt grew up in rural western Germany. In 2000 van de Flierdt completed a diploma in Geology at the University of Bonn. She earned a PhD at ETH Zurich in 2003, working with Alexander Halliday. | 9 | Geochemistry |
The SCCmec found in methicillin-resistant Staphylococcus aureus likely originated in coagulase-negative staphylococcal species and was acquired by S. aureus.
Staphylococcal strains isolated from pig farms were found to carry several different types of SCCmec, suggesting that they may serve as a reservoir of these elements. | 1 | Biochemistry |
: M–R + M → M + M–R.
In redox-transmetalation a ligand is transferred from one metal to the other through an intermolecular mechanism. During the reaction one of the metal centers is oxidized and the other is reduced. The electronegativities of the metals and ligands is what causes the reaction to go forward. If M is more electronegative than M, it is thermodynamically favorable for the R group to coordinate to the less electronegative M. | 0 | Organic Chemistry |
The main component of a VIPA is a glass plate whose normal is slightly tilted with respect to the input light. One side (light input side) of the glass plate is coated with a 100% reflective mirror and the other side (light output side) is coated with a highly reflective but partially transmissive mirror. The side with the 100% reflective mirror has an anti-reflection coated light entrance area, through which a light beam enters the glass plate. The input light is line-focused to a line (focal line) on the partially transmissive mirror on the light output side. A typical line-focusing lens is a cylindrical lens, which is also part of the VIPA. The light beam is diverging after the beam waist located at the line-focused position.
After the light enters the glass plate through the light entrance area, the light is reflected at the partially transmissive mirror and the 100% reflective mirror, and thus the light travels back and forth between the partially transmissive mirror and the 100% reflective mirror.
It is noted that the glass plate is tilted as a result of its slight rotation where the axis of rotation is the focal line. This rotation/tilt prevents the light from leaving the glass plate out of the light entrance area. Therefore, in order for the optical system to work as a VIPA, there is a critical minimum angle of tilt that allows the light entering through the light entrance area to return only to the 100% reflective mirror. Below this angle, the function of the VIPA is severely impaired. If the tilting angle were zero, the reflected light from the partially transmissive mirror would travel exactly in reverse and exit the glass plate through the light entrance area without being reflected by the 100% reflective mirror. In the figure, refraction at the surfaces of the glass plate was ignored for simplicity.
When the light beam is reflected each time at the partially transmissive mirror, a small portion of the light power passes through the mirror and travels away from the glass plate. For a light beam passing through the mirror after multiple reflections, the position of the line-focus can be seen in the virtual image when observed from the light output side. Therefore, this light beam travels as if it originated at a virtual light source located at the position of the line-focus and diverged from the virtual light source. The positions of the virtual light sources for all the transmitted light beams automatically align along the normal to the glass plate with a constant spacing, that is, a number of virtual light sources are superimposed to create an optical phased array. Due to the interference of all the light beams, the phased array emits a collimated light beam in one direction, which is at a wavelength dependent angle, and therefore, an angular dispersion is produced. | 7 | Physical Chemistry |
The K factor or characterization factor is defined from Rankine boiling temperature °R=1.8Tb[k] and relative to water density ρ at 60°F:
K(UOP) =
The K factor is a systematic way of classifying a crude oil according to its paraffinic, naphthenic, intermediate or aromatic nature. 12.5 or higher indicate a crude oil of predominantly paraffinic constituents, while 10 or lower indicate a crude of more aromatic nature. The K(UOP) is also referred to as the UOP K factor or just UOPK. | 3 | Analytical Chemistry |
Ceramics are now commonly used in the medical fields as dental and bone implants. Surgical cermets are used regularly. Joint replacements are commonly coated with bioceramic materials to reduce wear and inflammatory response. Other examples of medical uses for bioceramics are in pacemakers, kidney dialysis machines, and respirators. | 7 | Physical Chemistry |
Streptavidin is a tetrameric protein expressed in Streptomyces avidinii. Because of Streptavidin's high affinity for vitamin H (biotin), Streptavidin is commonly used in the fields of molecular biology and biotechnology. The Strep-tag was originally selected from a genetic library to specifically bind to a proteolytically truncated "core" version of streptavidin. Over the years, the Strep-tag was systemically optimized, to permit a greater flexibility in the choice of attachment site. Further, its interaction partner, Streptavidin, was also optimized to increase peptide-binding capacity, which resulted in the development of Strep-Tactin. The binding affinity of Strep-tag to Strep-Tactin is nearly 100 times higher than from Strep-tag to Streptavidin. The so-called Strep-tag system, consisting of Strep-tag and Strep-Tactin, has proven particularly useful for the functional isolation and analysis of protein complexes in proteome research. | 1 | Biochemistry |
In chemistry and particularly biochemistry, an energy-rich species (usually energy-rich molecule) or high-energy species (usually high-energy molecule) is a chemical species which reacts, potentially with other species found in the environment, to release chemical energy.
In particular, the term is often used for:
* adenosine triphosphate (ATP) and similar molecules called high-energy phosphates, which release inorganic phosphate into the environment in an exothermic reaction with water:
:ATP + → ADP + P ΔG°' = −30.5 kJ/mol (−7.3 kcal/mol)
* fuels such as hydrocarbons, carbohydrates, lipids, proteins, and other organic molecules which react with oxygen in the environment to ultimately form carbon dioxide, water, and sometimes nitrogen, sulfates, and phosphates
* molecular hydrogen
* monatomic oxygen, ozone, hydrogen peroxide, singlet oxygen and other metastable or unstable species which spontaneously react without further reactants
* in particular, the vast majority of free radicals
* explosives such as nitroglycerin and other substances which react exothermically without requiring a second reactant
* metals or metal ions which can be oxidized to release energy
This is contrasted to species that are either part of the environment (this sometimes includes diatomic triplet oxygen) or do not react with the environment (such as many metal oxides or calcium carbonate); those species are not considered energy-rich or high-energy species. | 1 | Biochemistry |
Flavins (from Latin flavus, "yellow") refers generally to the class of organic compounds containing the tricyclic heterocycle isoalloxazine or its isomer alloxazine, and derivatives thereof. The biochemical source of flavin is the yellow B vitamin riboflavin. The flavin moiety is often attached with an adenosine diphosphate to form flavin adenine dinucleotide (FAD), and, in other circumstances, is found as flavin mononucleotide (or FMN), a phosphorylated form of riboflavin. It is in one or the other of these forms that flavin is present as a prosthetic group in flavoproteins. Despite the similar names, flavins (with "i") are chemically and biologically distinct from the flavanoids (with "a"), and the flavonols (with "o").
The flavin group is capable of undergoing oxidation-reduction reactions, and can accept either one electron in a two-step process or two electrons at once. Reduction is made with the addition of hydrogen atoms to specific nitrogen atoms on the isoalloxazine ring system:
In aqueous solution, flavins are yellow-coloured when oxidized, taking a red colour in the semi-reduced anionic state or blue in the neutral (semiquinone) state, and colourless when totally reduced. The oxidized and reduced forms are in fast equilibrium with the semiquinone (radical) form, shifted against the formation of the radical:
::Fl + FlH ⇌ FlH
where Fl is the oxidized flavin, FlH the reduced flavin (upon addition of two hydrogen atoms) and FlH the semiquinone form (addition of one hydrogen atom).
In the form of FADH, it is one of the cofactors that can transfer electrons to the electron transfer chain. | 1 | Biochemistry |
African swine fever virus (ASFV) is a large double-stranded DNA virus which replicates in the cytoplasm of infected cells and is the only member of the Asfarviridae family. The virus causes a lethal haemorraghic disease in domestic pigs. Some strains can cause death of animals within as little as a week after infection. In other species, the virus causes no obvious disease. ASFV is endemic to sub-Saharan Africa and exists in the wild through a cycle of infection between ticks and wild pigs, bushpigs and warthogs. | 1 | Biochemistry |
Genetic markers can be used to study the relationship between an inherited disease and its genetic cause (for example, a particular mutation of a gene that results in a defective protein). It is known that pieces of DNA that lie near each other on a chromosome tend to be inherited together. This property enables the use of a marker, which can then be used to determine the precise inheritance pattern of the gene that has not yet been exactly localized.
Genetic markers are employed in genealogical DNA testing for genetic genealogy to determine genetic distance between individuals or populations. Uniparental markers (on mitochondrial or Y chromosomal DNA) are studied for assessing maternal or paternal lineages. Autosomal markers are used for all ancestry.
Genetic markers have to be easily identifiable, associated with a specific locus, and highly polymorphic, because homozygotes do not provide any information. Detection of the marker can be direct by RNA sequencing, or indirect using allozymes.
Some of the methods used to study the genome or phylogenetics are RFLP, AFLP, RAPD, SSR. They can be used to create genetic maps of whatever organism is being studied.
There was a debate over what the transmissible agent of CTVT (canine transmissible venereal tumor) was. Many researchers hypothesized that virus like particles were responsible for transforming the cell, while others thought that the cell itself was able to infect other canines as an allograft. With the aid of genetic markers, researchers were able to provide conclusive evidence that the cancerous tumor cell evolved into a transmissible parasite. Furthermore, molecular genetic markers were used to resolve the issue of natural transmission, the breed of origin (phylogenetics), and the age of the canine tumor.
Genetic markers have also been used to measure the genomic response to selection in livestock. Natural and artificial selection leads to a change in the genetic makeup of the cell. The presence of different alleles due to a distorted segregation at the genetic markers is indicative of the difference between selected and non-selected livestock. | 1 | Biochemistry |
Progesterone is used as a medication. It is used in combination with estrogens mainly in hormone therapy for menopausal symptoms and low sex hormone levels in women. It may also be used alone to treat menopausal symptoms. Studies have shown that transdermal progesterone (skin patch) and oral micronized progesterone are effective treatments for certain symptoms of menopause such as hot flashes and night sweats, which are otherwise referred to as vasomotor symptoms or VMS.
It is also used in women to support pregnancy and fertility and to treat gynecological disorders. Progesterone has been shown to prevent miscarriage in women with 1) vaginal bleeding early in their current pregnancy and 2) a previous history of miscarriage. Progesterone can be taken by mouth, through the vagina, and by injection into muscle or fat, among other routes. | 0 | Organic Chemistry |
The scattering cross section of an object () is defined by the time-averaged power of the scattered wave () divided by the intensity of the incident wave (): .
Starting with the assumptions that a plasma object is small relative to the incident wavelength, thin relative to the skin depth, unmagnetized, and homogenous, the scattering cross-section of the plasma object can be determined by the following equation, where is the electron charge, is the electron mass, is the number of unbound electrons in the plasma object, is the geometrically-determined depolarization factor, is the incident wave circular frequency, is the plasma frequency, and is the effective momentum-transfer collisional frequency (not to be confused with collisional frequency).
(The above equation is derived from the Drude-Lorentz-Sommerfeld model. It neglects transient effects of electron motion and is only qualitatively applicable to Rayleigh scattering due to neglecting evanescence effects - strict consideration of boundary conditions is often required to capture the case of negative permittivity.). The total cross section can related to the cross section of an individual electron () according to the equation , since the electron motion will be in phase assuming that the plasma object is small relative to the incident wavelength.
The scattering regime is determined by the dominant term in the denominator. Collisional scattering refers to the assumption that , allowing the total scattering cross section to be expressed as:
The collisional scattering cross-section can also be expressed in terms of the Thomson scattering cross section (), which is independent of the plasma geometry and collisional frequency according to the following equation. | 7 | Physical Chemistry |
The temperature and pressure at which ordinary solid, liquid, and gaseous water coexist in equilibrium is a triple point of water. Since 1954, this point had been used to define the base unit of temperature, the kelvin, but, starting in 2019, the kelvin is now defined using the Boltzmann constant, rather than the triple point of water.
Due to the existence of many polymorphs (forms) of ice, water has other triple points, which have either three polymorphs of ice or two polymorphs of ice and liquid in equilibrium. Gustav Heinrich Johann Apollon Tammann in Göttingen produced data on several other triple points in the early 20th century. Kamb and others documented further triple points in the 1960s. | 2 | Environmental Chemistry |
In the idealized model, the chemical components of the and bulk phases remain unchanged except when approaching the dividing surface. The total moles of any component (Examples include: water, ethylene glycol etc.) remains constant in the bulk phases but varies in the surface phase for the real system model as shown below.
In the real system, however, the total moles of a component varies depending on the arbitrary placement of the dividing surface. The quantitative measure of adsorption of the -th component is captured by the surface excess quantity. The surface excess represents the difference between the total moles of the -th component in a system and the moles of the -th component in a particular phase (either or ) and is represented by:
where is the surface excess of the -th component, are the moles, and are the phases, and is the area of the dividing surface.
represents excess of solute per unit area of the surface over what would be present if the bulk concentration prevailed all the way to the surface, it can be positive, negative or zero. It has units of mol/m. | 7 | Physical Chemistry |
Monosaccharides which contain an aldehyde group are known as aldoses, and those with a ketone group are known as ketoses. The aldehyde can be oxidized via a redox reaction in which another compound is reduced. Thus, aldoses are reducing sugars. Sugars with ketone groups in their open chain form are capable of isomerizing via a series of tautomeric shifts to produce an aldehyde group in solution. Therefore, ketones like fructose are considered reducing sugars but it is the isomer containing an aldehyde group which is reducing since ketones cannot be oxidized without decomposition of the sugar. This type of isomerization is catalyzed by the base present in solutions which test for the presence of reducing sugars. | 0 | Organic Chemistry |
Linear triatomic molecules owe their geometry to their sp or spd hybridised central atoms. Well-known linear triatomic molecules include carbon dioxide (CO) and hydrogen cyanide (HCN).
Xenon difluoride (XeF) is one of the rare examples of a linear triatomic molecule possessing non-bonded pairs of electrons on the central atom. | 7 | Physical Chemistry |
The Boc group can be added to the amine under aqueous conditions using di-tert-butyl dicarbonate in the presence of a base such as sodium bicarbonate. Protection of the amine can also be accomplished in acetonitrile solution using 4-dimethylaminopyridine (DMAP) as the base.
Removal of the Boc in amino acids can be accomplished with strong acids such as trifluoroacetic acid neat or in dichloromethane or with HCl in methanol. A complication may be the tendency of the t-butyl cation intermediate to alkylate other nucleophiles; scavengers such as anisole or thioanisole may be used.
Selective cleavage of the N-Boc group in the presence of other protecting groups is possible when using AlCl.
Reaction with trimethylsilyl iodide in acetonitrile followed by methanol is a mild and versatile method of deprotecting Boc-protected amines.
The use of triethylsilane as a carbocation scavenger in the presence of trifluoroacetic acid in dichloromethane has been shown to lead to increased yields, decreased reaction times, simple work-up and improved selectivity for the deprotection of t-butyl ester and t-butoxycarbonyl sites in protected amino-acids and peptides in the presence of other acid-sensitive protecting groups such as the benzyloxycarbonyl, 9-fluorenylmethoxycarbonyl, O- and S-benzyl and t-butylthio groups. | 0 | Organic Chemistry |
CHNOPS and CHON are mnemonic acronyms for the most common elements in living organisms. "CHON" stands for carbon, hydrogen, oxygen, and nitrogen, which together make up more than 95 percent of the mass of biological systems. "CHNOPS" adds phosphorus and sulfur. | 1 | Biochemistry |
EosFP consists of 226 amino acids. It has a molecular mass of 25.8 kDa and its pI is 6.9. Eos has 84% identical residues to Kaede, a fluorescent protein that originated in a different scleractinian coral Trachyphyllia geoffroyi, but can also be irreversibly converted from a green to red emitting form using UV light. Excluding residues Phe-61 and His-62, the chromophore environment and chromophore itself are unaffected by photochemical modification. Wild-type EosFP has a tetrameric arrangement of subunits where each subunit has the same β-can structure as GFP. This structure includes an 11-stranded barrel and, down the central axis, the fluorophore-containing helix. | 1 | Biochemistry |
AOAC International's technical contributions center on the creation, validation, and global publication of reliable analytical test methods. Their areas of focus include, but are not limited to, safety of foods, beverages, dietary supplements, fertilizers, animal feeds, soil and water, and veterinary drugs. The aim of the test methods is to evaluate the purity of materials used in the production of foodstuffs, and their ingredients. The development of these analytical methods in achieved as part of a range of programs operated by AOAC. | 3 | Analytical Chemistry |
Mutations in K2.3 are suspected to be a possible underlying cause for several neurological disorders, including schizophrenia, bipolar disorder, Alzheimer's disease, anorexia nervosa and ataxia as well as myotonic muscular dystrophy. | 1 | Biochemistry |
A range of qualitative and quantitative tests have been developed to detect phosphate ions (PO) in solution. Such tests find use in industrial processes, scientific research, and environmental water monitoring. | 3 | Analytical Chemistry |
The first reported chemical synthesis of HMB was published in 1877 by the Russian chemists Michael and Alexander Zaytsev. HMB was isolated from the bark of Erythrophleum couminga (a Madagascan tree) in 1941 by Leopold Ružička. The earliest reported isolation of HMB as a human metabolite was by Tanaka and coworkers in 1968 from a patient with isovaleric acidemia.
The effects of HMB on human skeletal muscle were first discovered by Steven L. Nissen at Iowa State University in the . Nissen founded a company called Metabolic Technologies, Inc. (MTI) around the time of his discovery, which later acquired six HMB-related patents that the company has used to license the right to manufacture and incorporate HMB into dietary supplements. When it first became available commercially in the late 1990s, HMB was marketed solely as an exercise supplement to help athletes and bodybuilders build muscle. MTI subsequently developed two HMB-containing products, Juven and Revigor, to which Abbott Nutrition obtained the market rights in 2003 and 2008 respectively. Since then, Abbott has marketed Juven as a medical food and the Revigor brand of HMB as an active ingredient in food products (e.g., certain formulations of Ensure) and other medical foods (e.g., certain formulations of Juven). | 1 | Biochemistry |
Light production in Porichthys notatus has been found to be triggered through an adrenergic mechanism. The sympathetic nervous system of the fish is responsible for triggering bioluminescence in the photocytes. As a response to being triggered by an norepinepherine, epinephrine, or phenylephrine, the photocyte exhibits a quick flash and then emits light that slowly fades in intensity. Stimulation by isoproterenol was found to cause an only a slow fading illumination. The amplitude of the quick flash, referred to as the "fast response", was higher when the concentration of neurotransmitter stimulating it increased. A great dal of variation in luminescence was exhibited in the photocytes of different fish. Variation also existed depending on what time of year the photocytes were collected from the fish. Stimulation from phenylephrine was found to produce a less intense response than that of epinephrine or norepinephrine. Phentolamine was shown to inhibit the effect of stimulation by phenylephrine completely and of epinephrine and norepinephrine to a lesser degree. Clonidine was shown to have an inhibitory effect on the fast response but no effect on the slow response. The photocytes of Porichthys are known to be extensively innervated. | 1 | Biochemistry |
Walter was one of the youngest students of the Jagiellonian University in Kraków, where he studied history and chemistry in 1825–28. Subsequently, he studied at Berlin University, receiving a Ph.D. with his dissertation On Combination of Oxalic Acid and Alkali. Simultaneously he served as assistant to Professor Eilhard Mitscherlich.
On the outbreak of the November 1830 Uprising, he went to Warsaw and joined the Polish Army. He served as adjutant to Colonel Samuel Różycki, commander of the 7th infantry regiment. In 1831, aged 21, he was named professor of chemistry at the Jagiellonian University, but he left to Paris where he worked with Jean-Baptiste Dumas at the École Centrale des Arts et Manufactures. Here Walter began to teach analytical chemistry. He examined plant extracts and along with Pierre Joseph Pelletier he extracted toluene by distillation of pine resin in 1838. In 1840 they extracted octene (CH) from naphtha. Walter was able to demonstrate the substitution of carbon by sulphur in camphor in 1842. His achievements won him recognition from the French Academy. In sum, he isolated and studied 24 new chemical compounds, including toluene, biphenyl, nitrotoluene, cedrene, potassium hydroxide dihydrate, chromyl chloride, cumene, benzyl chloride, benzyl bromide, and menthene.
In 1847 he was decorated with the cross of the Legion of Honour. | 0 | Organic Chemistry |
Reducing nutrient inputs is a key precondition for restoration, but there are two caveats: Firstly it can take a long time, particularly because of the storage of nutrients in sediments. Secondly, restoration may need more than a simple reversal of inputs since there are sometimes several stable but very different ecological states. Recovery of eutrophicated lakes is slow, often requiring several decades.
In environmental remediation nutrient removal technologies include biofiltration, which uses living material to capture and biologically degrade pollutants. Examples include green belts, riparian areas, natural and constructed wetlands, and treatment ponds. | 2 | Environmental Chemistry |
*Thermal radiation emitted by a body at any temperature consists of a wide range of frequencies. The frequency distribution is given by Planck's law of black-body radiation for an idealized emitter as shown in the diagram at top.
*The dominant frequency (or color) range of the emitted radiation shifts to higher frequencies as the temperature of the emitter increases. For example, a red hot object radiates mainly in the long wavelengths (red and orange) of the visible band. If it is heated further, it also begins to emit discernible amounts of green and blue light, and the spread of frequencies in the entire visible range cause it to appear white to the human eye; it is white hot. Even at a white-hot temperature of 2000 K, 99% of the energy of the radiation is still in the infrared. This is determined by Wien's displacement law. In the diagram the peak value for each curve moves to the left as the temperature increases. | 7 | Physical Chemistry |
UTP also has the role of a source of energy or an activator of substrates in metabolic reactions, like that of ATP, but more specific. When UTP activates a substrate (like Glucose-1-phosphate), UDP-glucose is formed and inorganic phosphate is released.
UDP-glucose enters the synthesis of glycogen. UTP is used in the metabolism of galactose, where the activated form UDP-galactose is converted to UDP-glucose. UDP-glucuronate is used to conjugate bilirubin to a more water-soluble bilirubin diglucuronide. UTP is also used to activate amino sugars like Glucosamine-1-phosphate to UDP-glucosamine, and N-acetyl-glucosamine-1-phosphate to UDP-N-acetylglucosamine. | 1 | Biochemistry |
The approach relies on a combination of companion crops to be planted around and among maize or sorghum. Both domestic and wild grasses can help to protect the crops by attracting and trapping the stemborers. The grasses are planted in the border around the maize and sorghum fields where invading adult moths become attracted to chemicals emitted by the grasses themselves. Instead of landing on the maize or sorghum plants, the insects head for what appears to be a tastier meal. These grasses provide the "pull" in the "push–pull" strategy. They also serve as a haven for the borers natural enemies. Good trap crops include well-known grasses such as Napier grass (Pennisetum purpureum), Signal grass (Brachiaria brizantha), and Sudan grass (Sorghum vulgare sudanense'). Napier grass produces significantly higher levels of attractive volatile compounds (green leaf volatiles), cues used by gravid stemborer females to locate host plants, than maize or sorghum. There is also an increase of approximately 100-fold in the total amounts of these compounds produced in the first hour of nightfall by Napier grass (scotophase), the period at which stemborer moths seek host plants for laying eggs, causing the differential oviposition preference. However, many of the stemborer larvae, about 80%, do not survive, as Napier grass tissues produce sticky sap in response to feeding by the larvae, which traps them, causing the death of about 80% of larvae. | 1 | Biochemistry |
Electrical resistance heating is used by the environmental restoration industry for remediation of contaminated soil and groundwater. ERH consists of constructing electrodes in the ground, applying alternating current (AC) electricity to the electrodes and heating the subsurface to temperatures that promote the evaporation of contaminants. Volatilized contaminants are captured by a subsurface vapor recovery system and conveyed to the surface along with recovered air and steam. Similar to Soil vapor extraction, the air, steam and volatilized contaminants are then treated at the surface to separate water, air and the contaminants. Treatment of the various streams depends on local regulations and the amount of contaminant.
Some low volatility organic contaminants have a short hydrolysis half-life For contaminants like these, i.e. 1,1,2,2-Tetrachloroethane and 1,1,1-trichloroethane, hydrolysis can be the primary form of remediation. As the subsurface is heated the hydrolysis half-life of the contaminant will decrease as described by the Arrhenius equation. This results in a rapid degradation of the contaminant. The hydrolysis by-product may be remediated by conventional ERH, however the majority of the mass of the primary contaminant will not be recovered but rather will degrade to a by-product.
There are predominantly two electrical load arrangements for ERH: three-phase and six-phase. Three-phase heating consists of electrodes in a repeating triangular or delta pattern. Adjacent electrodes are of a different electrical phase so electricity conducts between them as shown in Figure 1. The contaminated area is depicted by the green shape while the electrodes are depicted by the numbered circles.
Six-phase heating consists of six electrodes in a hexagonal pattern with a neutral electrode in the center of the array. The six-phase arrays are outlined in blue in Figure 2 below. Once again the contaminated area is depicted by the green shape while the electrodes are depicted by the numbered circles. In a six-phase heating pattern there can be hot spots and cold spots depending on the phases that are next to each other. For this reason, six-phase heating typically works best on small circular areas that are less than 65 feet in diameter.
ERH is typically most effective on volatile organic compounds (VOCs). The chlorinated compounds perchloroethylene, trichloroethylene, and cis- or trans- 1,2-dichloroethylene are contaminants that are easily remediated with ERH. The table shows contaminants that can be remediated with ERH along with their respective boiling points. Less volatile contaminants like xylene or diesel can also be remediated with ERH but energy requirements increase as the volatility decreases.
Electrode spacing and operating time can be adjusted to balance the overall remediation cost with the desired cleanup time. A typical remediation may consist of electrodes spaced 15 to 20 feet apart with operating times usually less than a year. The design and cost of an ERH remediation system depends on a number of factors, primarily the volume of soil/groundwater to be treated, the type of contamination, and the treatment goals. The physical and chemical properties of the target compounds are governed by laws that make heated remediations advantageous over most conventional methods. The electrical energy usage required for heating the subsurface and volatilizing the contaminants can account for 5 to 40% of the overall remediation cost.
There are several laws that govern an ERH remediation. Dalton’s law governs the boiling point of a relatively insoluble contaminant. Raoult’s law governs the boiling point of mutually soluble co-contaminants and Henry’s law governs the ratio of the contaminant in the vapor phase to the contaminant in the liquid phase. | 2 | Environmental Chemistry |
The ability to quantitate the βhCG level is useful in monitoring germ cell and trophoblastic tumors, follow-up care after miscarriage, and diagnosis of and follow-up care after treatment of ectopic pregnancy. The lack of a visible fetus on vaginal ultrasound after βhCG levels reach 1500 mIU/mL is strongly indicative of an ectopic pregnancy. Still, even an hCG over 2000 IU/L does not necessarily exclude the presence of a viable intrauterine pregnancy in such cases.
As pregnancy tests, quantitative blood tests and the most sensitive urine tests usually detect hCG between 6 and 12 days after ovulation. It must be taken into account, however, that total hCG levels may vary in a very wide range within the first 4 weeks of gestation, leading to false results during this period. A rise of 35% over 48 hours is proposed as the minimal rise consistent with a viable intrauterine pregnancy. | 1 | Biochemistry |
Superconducting materials are characterized by the loss of resistance and two parameters: a critical temperature T and a critical magnetic field which brings the
superconductor to its normal state. In 1911, H. Kamerlingh Onnes discovered the superconductivity of mercury at a temperature below 4 K. Later,
other substances with superconductivity at temperatures up to 30 K were found. Superconductors prevent the penetration of the external magnetic field
into the sample when the magnetic field strength is less than the critical value. This effect was called the Meissner effect.
High-temperature superconductivity was discovered in the 1980s. Of the known compounds, the highest critical temperature T = 135 K belongs to
HgBaCaCuO.
Low-temperature superconductivity has found a theoretical explanation in the model of Bardeen, Cooper, and Schrieffer (BCS theory).
The physical basis of the model is the phenomenon of Cooper pairing of electrons. Since a pair of electrons carries an integer spin, the correlated states of the electrons can form a Bose–Einstein condensate.
An equivalent formalism was developed by Bogoliubov
and Valatin
Cooper pairing of nucleons takes place in ordinary nuclei. The effect manifests itself in the Bethe–Weizsacker mass formula, the last pairing term
of which describes the correlation energy of two nucleons. Because of the pairing, the binding energy of even-even nuclei systematically exceeds the binding energy of odd-even and
odd-odd nuclei. | 7 | Physical Chemistry |
Pseudo-response regulator (PRR) refers to a group of genes that regulate the circadian oscillator in plants. There are four primary PRR proteins (PRR9, PRR7, PRR5 and TOC1/PRR1) that perform the majority of interactions with other proteins within the circadian oscillator, and another (PRR3) that has limited function. These genes are all paralogs of each other, and all repress the transcription of Circadian Clock Associated 1 (CCA1) and Late Elongated Hypocotyl (LHY) at various times throughout the day. The expression of PRR9, PRR7, PRR5 and TOC1/PRR1 peak around morning, mid-day, afternoon and evening, respectively. As a group, these genes are one part of the three-part repressilator system that governs the biological clock in plants. | 1 | Biochemistry |
In crystalline metals, slip occurs in specific directions on crystallographic planes, and each combination of slip direction and slip plane will have its own Schmid factor. As an example, for a face-centered cubic (FCC) system the primary slip plane is {111} and primary slip directions exist within the direction, along the primary slip plane of , with the critical applied shear stress acting in the direction can be calculated by quickly determining if any of the dot product between the axial applied stress and slip plane, or dot product of axial applied stress and shear stress direction equal to zero. For the example cited above, the dot product of axial applied stress in the direction and shear stress resulting from the former in the direction yields a zero. For such a case, it is suitable to find a permutation of the family of the permutation direction for the shear stress slip direction has been chosen:
In a single crystal sample, the macroscopic yield stress will be determined by the Schmid factor of the single grain. Thus, in general, different yield strengths will be observed for applied stresses along different crystallographic directions. In polycrystalline specimens, the yield strength of each grain is different depending on its maximum Schmid factor, which indicates the operational slip system(s). The macroscopically observed yield stress will be related to the material's CRSS by an average Schmid factor, which is roughly 1/3.06 for FCC and 1/2.75 for body-centered cubic (BCC) structures.
The onset of plasticity in polycrystals is influenced by the number of available slip systems to accommodate incompatibilities at the grain boundaries. In the case of two adjacent, randomly oriented grains, one grain will have a larger Schmid factor and thus a smaller yield stress. Under load, this "weaker" grain will yield prior to the "stronger" grain, and as it deforms a stress concentration will build up in the stronger grain near the boundary between them. This stress concentration will activate dislocation motion in the available glide planes. These dislocations are geometrically necessary to ensure that the strain in each grain is equivalent at the grain boundary, so that the compatibility criteria are satisfied. G. I. Taylor showed that a minimum of five active slip systems are required to accommodate an arbitrary deformation. In crystal structures with fewer than 5 active slip systems, such as hexagonal close-packed (HCP) metals, the specimen will exhibit brittle failure instead of plastic deformation. | 8 | Metallurgy |
Coenzyme A was identified by Fritz Lipmann in 1946, who also later gave it its name. Its structure was determined during the early 1950s at the Lister Institute, London, together by Lipmann and other workers at Harvard Medical School and Massachusetts General Hospital. Lipmann initially intended to study acetyl transfer in animals, and from these experiments he noticed a unique factor that was not present in enzyme extracts but was evident in all organs of the animals. He was able to isolate and purify the factor from pig liver and discovered that its function was related to a coenzyme that was active in choline acetylation. Work with Beverly Guirard, Nathan Kaplan, and others determined that pantothenic acid was a central component of coenzyme A. The coenzyme was named coenzyme A to stand for "activation of acetate". In 1953, Fritz Lipmann won the Nobel Prize in Physiology or Medicine "for his discovery of co-enzyme A and its importance for intermediary metabolism". | 1 | Biochemistry |
The expression for the sound velocity of a liquid,
contains the bulk modulus K. If K is frequency-independent, then the liquid behaves as a linear medium, so that sound propagates without dissipation or mode coupling. In reality, all liquids show some dispersion: with increasing frequency, K crosses over from the low-frequency, liquid-like limit to the high-frequency, solid-like limit . In normal liquids, most of this crossover takes place at frequencies between GHz and THz, sometimes called hypersound.
At sub-GHz frequencies, a normal liquid cannot sustain shear waves: the zero-frequency limit of the shear modulus is 0. This is sometimes seen as the defining property of a liquid.
However, like the bulk modulus K, the shear modulus G is also frequency-dependent and exhibits a similar crossover at hypersound frequencies.
According to linear response theory, the Fourier transform of K or G describes how the system returns to equilibrium after an external perturbation; for this reason, the dispersion step in the GHz to THz region is also called relaxation. As a liquid is supercooled toward the glass transition, the structural relaxation time exponentially increases, which explains the viscoelastic behavior of glass-forming liquids. | 7 | Physical Chemistry |
It has already been mentioned that in HR-CS AAS lamp flicker noise is eliminated using correction pixels. In fact, any increase or decrease in radiation intensity that is observed to the same extent at all pixels chosen for correction is eliminated by the correction algorithm. This obviously also includes a reduction of the measured intensity due to radiation scattering or molecular absorption, which is corrected in the same way. As measurement of total and background absorption, and correction for the latter, are strictly simultaneous (in contrast to LS AAS), even the fastest changes of background absorption, as they may be observed in ET AAS, do not cause any problem. In addition, as the same algorithm is used for background correction and elimination of lamp noise, the background corrected signals show a much better signal-to-noise ratio compared to the uncorrected signals, which is also in contrast to LS AAS. | 3 | Analytical Chemistry |
ScerTF is a comprehensive database of position weight matrices for the transcription factors of Saccharomyces. | 1 | Biochemistry |
RNA-Seq captures DNA variation, including single nucleotide variants, small insertions/deletions. and structural variation. Variant calling in RNA-Seq is similar to DNA variant calling and often employs the same tools (including SAMtools mpileup and GATK HaplotypeCaller) with adjustments to account for splicing. One unique dimension for RNA variants is allele-specific expression (ASE): the variants from only one haplotype might be preferentially expressed due to regulatory effects including imprinting and expression quantitative trait loci, and noncoding rare variants. Limitations of RNA variant identification include that it only reflects expressed regions (in humans, <5% of the genome), could be subject to biases introduced by data processing (e.g., de novo transcriptome assemblies underestimate heterozygosity), and has lower quality when compared to direct DNA sequencing. | 1 | Biochemistry |
Polymerization-induced phase separation can be initiated either through thermally induced polymerization or photopolymerization. The process general occurs through spinodal decomposition, commonly resulting in the formation of co-continuous phases. | 7 | Physical Chemistry |
Graphene is viable for photothermal therapy. An 808 nm laser at a power density of 2 W/cm was used to irradiate the tumor sites on mice for 5 minutes. As noted by the authors, the power densities of lasers used to heat gold nanorods range from 2 to 4 W/cm. Thus, these nanoscale graphene sheets require a laser power on the lower end of the range used with gold nanoparticles to photothermally ablate tumors.
In 2012, Yang et al. incorporated the promising results regarding nanoscale reduced graphene oxide reported by Robinson et al. into another in vivo mice study., an order of magnitude lower than previously required power densities. This study demonstrates the higher efficacy of nanoscale reduced graphene oxide sheets as compared to both nanoscale graphene sheets and gold nanorods. | 5 | Photochemistry |
Bioluminescence in Amphiura filiformis and other species of sea star is widely believed to function in protection against predators. By attracting predators to one arm and losing the arm, the sea star is able to escape predation. | 1 | Biochemistry |
The PI curve can be applied to terrestrial and marine reactions but is most commonly used to explain ocean-dwelling phytoplankton's photosynthetic response to changes in light intensity. Using this tool to approximate biological productivity is important because phytoplankton contribute ~50% of total global carbon fixation and are important suppliers to the marine food web.
Within the scientific community, the curve can be referred to as the PI, PE or Light Response Curve. While individual researchers may have their own preferences, all are readily acceptable for use in the literature. Regardless of nomenclature, the photosynthetic rate in question can be described in terms of carbon (C) fixed per unit per time. Since individuals vary in size, it is also useful to normalise C concentration to Chlorophyll a (an important photosynthetic pigment) to account for specific biomass. | 5 | Photochemistry |
In electrochemistry, the Butler–Volmer equation (named after John Alfred Valentine Butler and Max Volmer), also known as Erdey-Grúz–Volmer equation, is one of the most fundamental relationships in electrochemical kinetics. It describes how the electrical current through an electrode depends on the voltage difference between the electrode and the bulk electrolyte for a simple, unimolecular redox reaction, considering that both a cathodic and an anodic reaction occur on the same electrode: | 7 | Physical Chemistry |
BVS was first developed by C. P. Chen and R. S. Lakes in 1989 in order to address the shortcomings of existing laboratory techniques for studying viscoelastic materials. It was later refined by M. Brodt et al. to improve the rigidity and resolution of the apparatus, which were sources of error in the original design. First used to study poly(methyl methacrylate) (PMMA), it has since seen applications in determining the properties of bone, capacitor dielectrics, high damping metals, and other such viscoelastic materials. | 7 | Physical Chemistry |
ABCC11 is a gene encoding an apical ATP-driven efflux transporter that has been found to transport a variety of lipophilic anions including cyclic nucleotides, estradiol glucuronide, steroid sulfates such as DHEA-S, and monoanionic bile acids. It is expressed and localized in apocrine glands, including in the axilla, the ceruminous glands in the auditory canal, and in the mammary gland. A single-nucleotide polymorphism (SNP) 538G→A in ABCC11 that leads to a G180R substitution in the encoded protein has been found to result in loss-of-function via affecting N-linked glycosylation and in turn causing proteasomal degradation of the protein. This polymorphism has been found to be responsible for the dry and white earwax phenotype, and is considered to be unique as it has been described as the only human SNP that has been found to determine a visible genetic trait. In addition to earwax phenotype, the ABCC11 genotype has been found to be associated with colostrum secretion from the breasts as well as normal axillary odor and osmidrosis (excessive axillary malodor).
A functional ABCC11 protein has been found to be essential for the presence of the characteristic strong axillary odor, with the 538G→A SNP leading to a loss of secretion of axillary malodorous precursors and a nearly complete loss of axillary odor in those who are homozygous for the polymorphism. Specifically, the secretion of the amino-acid conjugates 3M2H-Gln, HMHA-Gln, and Cys-Gly-(S) 3M3SH, which are precursors of key axillary malodorous compounds including the unsaturated or hydroxylated branched-chain fatty acids 3M2H and HMHA and the sulfanylalkanol 3M3SH, has been found to be abolished in homozygotic carriers of the SNP, and the odoriferous androstane steroids androstenone and androstenol and their precursors DHEA and DHEA-S have been found to be significantly reduced as well. Patients with axillary osmidrosis (538G/G or 538G/A genotype) were found to have significantly more numerous and relatively large axillary apocrine glands compared to controls with the A/A genotype. | 1 | Biochemistry |
Estimates of lake metabolism typically rely on the measurement of dissolved oxygen or carbon dioxide, or measurements of a carbon or oxygen tracer to estimate production and consumption of organic carbon. Oxygen is produced and carbon dioxide consumed through photosynthesis and oxygen is consumed and carbon dioxide produced through respiration. Here, organic matter is symbolized by glucose, though the chemical species produced and respired through these reactions vary widely.
Photosynthesis:
Respiration:
Photosynthesis and oxygen production only occurs in the presence of light, while the consumption of oxygen via respiration occurs in both the presence and absence of light. Lake metabolism terms include:
* GPP - gross primary production (e.g. total photosynthesis)
* R - total respiration
* - heterotrophic respiration
* - autotrophic respiration
* NEP - net ecosystem production = GPP - R
* NPP - net primary production = GPP - | 1 | Biochemistry |
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