text:
|Publication number
|Publication type
|Application number
|Publication date
|May 8, 2012
|Priority date
|Nov 26, 2008
|Fee status
|Also published as
|Publication number
|Michael R. Hughes, James Hebert
|Original Assignee
|Flir Systems, Inc.
|Export Citation
|BiBTeX, EndNote, RefMan
|Patent Citations (27), Classifications (6), Legal Events (2)
|External Links: USPTO, USPTO Assignment, Espacenet
The present application claims the benefit under 35 U.S.C. �119(e) of U.S. provisional application Ser. No. 61/200,291, filed on Nov. 26, 2008, the disclosure of which is incorporated by reference herein in its entirety.
Generally, the present invention relates to a device package, such as an electronic package, with a corrosion resistant, moisture-tight seal with electromagnetic interference shielding properties, and a method of making such a package. More specifically, the present invention relates to a corrosion resistant device package having a magnesium housing and mating plastic cover comprising a plurality of electrically conductive and interconnected components.
It is a general problem that electronic devices and/or systems emit electromagnetic interference ("EMI") over various spectral bandwidths and the EMI emissions can be disruptive to the operation of the electronic device or system itself, or to independent but locally operating electronic devices or systems. While the EMI may be generated purposefully for various reasons, EMI is naturally produced by various electronic operations such as by fast current variations or the like. These can occur during the normal operation of electrical components such as resistors, capacitors, inductors, transistors, diodes, or the like. Alternately, fast current variations can be generated during the normal operation of motive electrical devices such as motors, solenoids or the like. In addition to EMI being generated by electrical components and motive electrical devices, current fluctuations along conductive pathways, e.g., through wires, bus bars, conductive traces, or the like leading to and from electrical components and motive electrical devices can also generate disruptive EMI emissions.
Generally, EMI emissions produce disruptive signal noise. The disruptive signal noise is generally at the EMI emission frequency and at harmonics thereof. Radio frequency interference ("RFI") bands, e.g., 50-1000 MHz, can be particularly disruptive to the operation of many devices by inducing disruptive radio signal noise into their otherwise noise-free signals. In particular, the operation of radio communication devices such as radio and television broadcasting systems, cellular telephone systems, and wireless computer network computers, and the like, can be adversely affected by RFI emissions emitted by unrelated devices.
Accordingly, EMI, and especially RFI emissions, in end-user products must be shielded or otherwise attenuated in a manner that reduces harmful EMI and RFI emissions to amplitude levels that are below the agreed upon EMI and RFI signal amplitudes at various signal bandwidths. Such amplitude levels are set by various regulatory agencies. Similarly, end-user products must also be capable of operating correctly when subjected to these same agreed upon EMI and RFI signal amplitudes levels at various bandwidths.
Additional problems are encountered when electronic devices and/or systems are used in harsh military or commercial environments. For instance, exposure to moisture, such as salt water or fog, may lead to corrosion or ingress of fluids. Accordingly, another desirable function of electronic device and/or system housings or packages is to resist corrosion and prevent fluid entry. Such systems that implement seals require a smooth interface to prevent water/moisture ingress. Most conductive paints are rough because of the metallic content of the paint.
Other functions of electronic devices and/or system housings or packages are to eliminate electrical shock hazards and to protect enclosed elements from damage by mechanical shock and or high g-forces. Other desirable functional characteristics of electronic device and/or system housings or packages are lightweight, easy of use, low cost, easy of manufacture and aesthetic appearance. Other desirable functional package characteristics may include forming a gas or liquid tight seal, ease of operator access, e.g., to replace a battery or the like, and a variety of convenient and functional interface access ports for providing electrical, mechanical, and other interfaces between the packaged electronic device or system and external devices or systems.
U.S. Pat. No. 6,763,576 to Watchko et al. discloses coating an interior surface of a housing with a metalized electrically conductive EMI shielding layer, which can include tin, nickel or an alloy of the two to resist corrosion. The housing can be made from magnesium or aluminum, among other metals, or plastics. The metal portion of the housing may be painted with a non-conductive paint. A conductive gasket may be used to provide electrical continuity between various mating housing parts. However, the reference does not disclose any means for protecting the exterior surface from corrosive materials, and the reference does not disclose masking any portion of the interior surface.
U.S. Pat. No. 7,446,265 to Krohto et al. discloses that electromagnetic interference shields may include an electrically conductive and grounded housing. The housing may be formed of a metal such as steel, aluminum, magnesium, or alternatively, a plastic or other polymeric material which is filled to form an electrically-conductive material. A conductive coating, such as an electrically-conductive paint, may be generally applied across the interior surfaces of the housing. A conductive gasket may be used to provide electrical continuity between different housing components. However, the reference does not disclose any means of protecting either the interior or exterior surface from corrosive materials, and the reference does not disclose masking any portion of the interior surface.
U.S. Patent Application Publication No. 2008/0273316 to Sarno et al. discloses a magnesium. Faraday shield, and U.S. Pat. No. 5,909,490 to Sokolich et al. discloses a magnesium EMI shield for a telephone. These references disclose the use of magnesium in EMI shields due to its low density and electrical conductivity. However, the references do not disclose any means of protecting either the interior or exterior surfaces from corrosive materials, and the references do not disclose masking any portion of the interior surface.
U.S. Pat. No. 4,988,550 discloses a masking tape for EMI shielding applications comprising, among other things, an adhesive layer and a metal foil layer adhered to the top of the adhesive layer. The tape is applied to a substrate that is sprayed with a paint, and the mask is then removed to reveal a conductive metal foil surface to which a conductive EMI shield can be mounted. However, the reference does not disclose a means of protecting both the interior and exterior surfaces from corrosive materials.
Thus, there still remains a need for an electronic package that comprises an electromagnetic shield, exhibits corrosion resistance on both the interior and exterior surfaces, and forms a water-tight seal.
The present invention concerns an electronic package comprising an electromagnetic interference shield having a series of interconnected electrically conductive components. The components form a tortuous electrically conductive path. Moreover, both the interior and exterior surfaces of the package are corrosion resistant, and the package further comprises a water tight seal.
In the accompanying drawings, which form a part of the specification and are to be read in conjunction therewith and in which like reference numerals are used to indicate like parts in the various views:
The present invention relates to a device package, such as an electronic system package, that is suitable for use in harsh military, industrial, or commercial environments. The package components, including a base enclosure and mating cover, comprise a series of interconnected electrically conductive materials, forming a tortuous electrically conductive path, that advantageously shield electromagnetic interference ("EMI"). The electrically conductive, EMI-shielding layers and other coated layers (e.g., insulative electrocoated paint layers) are smooth layers that provide corrosion resistance to the interior and exterior surfaces of the package. The device package is also designed such that its components form a water tight seal. Thus, innovatively, the package comprises a combination of components that synergistically shield electromagnetic interference, resist interior and exterior corrosion, and form a water tight seal.
Electronic system package 100 further includes a cover element 160. Cover 160 is sized and dimensioned to mate with the aperture 140, and to attach to base enclosure 110 to seal the hollow cavity 150. Electronic system package 100 further includes a gasket 170, which is sized to be captured between the top edge of cylindrical side wall 130 and cover 160. In addition, one or both of the top edge of side wall 130 and cover element 160 may include features such as channels or retainers for capturing and/or positioning gasket 170 in a desired position.
An electronic device or system, not shown, is housed within hollow cavity 150. Electronic device or system includes any device or system that emits electro-magnetic fields or is affected by same. Electronic device or system includes devices that emit or receive infrared radiation, such as IR cameras or sensors and IR binoculars or vision systems. The electronic device or system may be mechanically fastened to base enclosure 110 or to cover 160. In addition, one or both of base enclosure 110 and cover 160 may comprise a conductive element formed from an electrically conductive material, or base enclosure 110 and/or cover 160 may be formed with one or more electrically conductive layers formed therein or thereon, such that one or both of base enclosure 110 and cover 160 may become an element of the electrical device or electrical system. For example, base enclosure 110 and/or cover 160 can form an EFI shield or an antenna, among other things. Furthermore, base enclosure 110 and/or cover 160 can provide an electrical pathway from the interior of system package 100 to the outside.
Electronic system package 100 may further include a plurality of apertures 180 passing through any wall of the system package 100. Apertures 180 may comprise interface ports and may include electrical connectors, mechanical interfaces, fluid or gas ports, optical apertures, electromagnetic signal emitters and/or antennas, or any other aperture type as may be required. Generally, electronic system package 100, according to the present invention, is constructed as a corrosion resistant, water and moisture tight Faraday cage or shell or an EMI shield, preferably with base enclosure 110 comprising magnesium and cover 160 comprising a lighter weight injection moldable plastic.
Referring now to
Generally, an EMI shield is a barrier that confines EMI energy within one device and insulates that device from the EMI energy emitted by neighboring devices or from the surrounding environment. A Faraday cage is a particular type of EMI shield that is constructed from conducting materials. It blocks the effects of external electrical fields, because such external fields would produce a current on the Faraday cage but would not affect the functions of electrical systems, contained within the Faraday cage.
In the present invention, system package 100 forms an EMI-shielding Faraday cage, which is preferably constructed from a series of conductive materials that form a tortuous electrically conductive path 205, which continuously extends from the electrically conductive internal surfaces of cover 160, through conductive gasket 170, and into conductive base enclosure 110. The tortuous electrical conductive path 205 shown in
To protect against corrosion, electronic system package 100 is preferably coated with a corrosion resistant coating on one or more of its internal or external surfaces. Preferably, components that are made at least in part from metal are coated with a corrosion resistant coating. In one embodiment, base enclosure 110, which is preferably made from magnesium for high strength and electrical conductivity, is coated with an anti-corrosion coating that has a sufficient smoothness to cover the metal. Without being bound to any particular theory, the inventors of the present invention have discovered that the smoothness of the coating is advantageous against corrosion, because the smoothness of the coating minimizes microcracks from developing in the coating for corrosive agents, such as salt water or salt water vapor, to penetrate and attack the underlying metal. More advantageously, a smooth coating is also resistant to cracking due to thermal expansion and contraction of the underlying metal. It is known that metals have a high coefficient of thermal expansion. As metals, such as magnesium, expand and contract, microcracks represent stress concentrations that could compromise the integrity of the coating thereby exposing the metal to corrosive agents. Suitable anti-corrosion coatings include electrocoating, described below, which provide sufficient smoothness.
Referring back to
Conductive coating layers, including but not limited to those commercially available as CHO-SHIELD� 2000 series (commercially available from Chomerics of Woburn, Mass., a division of Parker Hannfin Corporation), are applied to certain internal surfaces of system package 100 in order to form portions of the electrical path 205 of the inventive Faraday cage. The preferred CHO-SHIELD 2000 series coatings are advantageous because they are lightweight and resistant to corrosive materials. In the present invention, conductive coating layer, preferably CHO-SHIELD 2002, which can adhere to polymers and which comprises a urethane binder with conductive copper filler, may be sprayed to coat the internal surface of cover 160, thereby forming conductive layer 250. Another conductive layer, preferably CHO-SHIELD 2003, which can adhere to metal and which also comprises a urethane binder with a conductive copper filler, may be sprayed to overlay portions of sidewall 130 of magnesium housing 110, thereby forming conductive layer 240. Conductive layer 240 carries electrical conductive path 205 to opening 230 and protects 230 in side wall 130 from corrosion. In this embodiment, electrical conductive path 205 comprises conductive layer 250 on cover 160, gasket 170, conductive layer 240 on side wall 130 that overlays opening 230 and the magnesium box enclosure 110.
Top cover 160 is preferably formed from a durable injection moldable plastic material such as urethane, and it is inherently able to withstand corrosion. The base enclosure 110 is preferably made of magnesium or a magnesium alloy, such as preferably the AZ31B magnesium-based alloy. Per standard ASTM International nomenclature, the AZ31B magnesium alloy has composition of approximately 3 wt. % aluminum (Al), 1 wt. % zinc (Zn), and the balance is substantially magnesium. Magnesium has a relatively high tensile strength (about 160 to 365 MPa, or about 23 to 53 ksi) and a relatively low density (about 1.738 g/cm3, which is approximately two-thirds the density of aluminum), which advantageously yield a relatively high strength-to-weight ratio (i.e., tensile strength/density). Accordingly, magnesium's strength and light weight make it a preferred metal for designing electronic system package 100, which may contain therein a variety of products including, but not limited to, IR cameras, IR binoculars, laptops, portable military equipment, and the like. Additionally, magnesium has good electrical conductivity (about 38.6% of IACS, or, the International Annealed Copper Standard), thereby allowing it to form a portion of the Faraday cage discussed above. Magnesium has a relatively high thermal conductivity (about 154.5 W�m−1�K−1) that is useful for dissipating thermal energy to the surrounding air. The aforementioned magnesium property values are from "Magnesium and Magnesium Alloys" in Metals Handbook Desk Edition, Second Edition, J. R. Davis (Ed.), 1998, p. 559-574, which is incorporated herein by reference in its entirety.
Magnesium, however, is susceptible to corrosion, because it is among the more electrochemically active structural metals. Consequently, magnesium has a high thermodynamic tendency to be corroded by water, and especially salt water or salt fog. Moreover, magnesium can also undergo so-called galvanic corrosion when exposed to other metals such as the metals contained in the electronic equipment protected by electronic system package 100. As discussed above, preferably, in the present invention, an electrocoating ("E-coat") paint process is used to coat the magnesium-based enclosure 110 in both the interior and exterior with a layer 220. As used herein, the term "electrocoating" is defined herein to mean any "method of painting where an electrically conductive work-piece is immersed in a paint bath and is coated by the application of electricity. Electrocoat is also referred to as E-coat, electrophoretic paint, electrodeposition paint, electrodip and electropaint." See Peter Hope, "Electrolyte Control in Small Scale Industrial Electrocoat Painting Processes," in Electrophoretic Deposition, Fundamentals and Applications: Proceedings of the International Symposium, A. Boccaccini et al. (Eds.), 2002, p. 167-174, which is incorporated herein by reference in its entirety. Similarly, electrocoat and electrocoated elements are coating or elements coated by the electrocoating process.
Electrocoating generally offers several advantages including automation, efficiency, low cost, and low emissions. More particularly, with respect to the present invention, it has been found that an E-coat paint process produces a smooth, durable finish—comparable to powder paint—that protects the metal, particularly magnesium, surface from corrosive elements. Powder paint is a coating or paint prepared by coating or spraying an element or object with electrostatically charged powder. The coated element is then heated to cure the powder in case of thermosetting powder or to melt the powder in case of thermoplastic powder. The paint powder can be ground to a fine powder to produce a smooth coating. Alternatively, CHO-SHIELD, which is also a smooth, corrosion resistant material, and powder paint can be used to coat magnesium-based housing 110. However, CHO-SHIELD is a relatively more expensive material than electrocoating and powder painting, and its use is preferably limited to select, masked-portions of housing 110, e.g. opening 230.
Before the magnesium-based housing 110 is electrocoated, substantially the entire magnesium-based housing 110 is coated with a chromate layer 210, which seals magnesium-based housing 110 and primes its surface for other coating layers. More particularly, a chromate chemical-conversion treatment converts the alkaline surface of magnesium to a more neutral pH, thereby allowing subsequently applied coatings to provide improved corrosion resistance. A variety of chromate treatments are known in the art including NH 35 (yellow chromate), or the Dow 19 chromate process, or any suitable process that conforms to the specification of SAE AMS-M-3171 Type VI (Society of Automotive Engineering, Aerospace Materials Specification), formerly MIL-M-3171 Type VI, which is incorporated herein by reference in its entirety.
After pretreating with chromate, substantially the entire magnesium housing 110, both on the interior and the exterior, is painted by an E-coat process to form anti-corrosion layer 220. An electrocoating process is based on the physical principle that opposite electrical charges are attracted to each other. Accordingly, in an E-coat process, pretreated metal parts such as magnesium housing 110 are dipped in a bath comprising deionized water (approximately 80-90 wt. %) and resinous paint (approximately 10-20 wt. %). The paint particles migrate under the influence of an electric field and are deposited onto an oppositely charged, chromate-treated magnesium surface. This process continues until substantially the entire surface is uniformly and smoothly coated with a paint that protects the underlying chromate-treated magnesium surface from corrosion. Thus, the process is an improvement over spraying and other means that may inadvertently leave certain areas unprotected from corrosion. After dipping in the paint bath, a metal part is removed, rinsed, and then cured so as to crosslink the resinous paint solids.
Generally, the electrocoating process can be anodic or cathodic and employ epoxy, acrylic, among other resins. In the anodic process, negatively charged paint particles are deposited on a positively charged metal part (serving as the anode), whereas in a cathodic process, positively charged paint particles are deposited on a negatively charged metal part (serving as the cathode). Epoxy electrocoatings are generally employed for improving corrosion resistance, whereas acrylic electrocoatings are generally employed for improving resistance to UV exposure. While any suitable electrocoating may be used, the present invention preferably uses a cathodic epoxy coating, such as epoxy coatings commercially available from Valmont Coatings Applied Coating Technology of Mendota Heights, Minn.
As discussed above, some areas of the magnesium housing 110 are intentionally masked from the E-coat paint to provide electrical access to base enclosure 110. In particular, any area of the magnesium housing 110 that will serve as a conductive pad, or the like, is masked from the E-coat paint process and/or the chromate priming process so as to maintain a path for electron flow into housing 110. One means of masking involves covering a particular area such as opening 230 with methyl-ethyl-ketone ("MEK") or equivalent solvent. Other means, as disclosed in U.S. Pat. No. 4,988,550, which is incorporated herein by reference in its entirety, involve using a masking tape to cover select areas during the E-coat paint process.
Particularly, in the present invention, opening 230 proximate aperture 140 is masked from the E-coat paint process. Masking may also be used before the appliance of the chromate priming process. Opening 230 is thereafter coated with a conductive material layer such as CHO-SHIELD� 2003. The CHO-SHIELD 2003 makes electrical contact with opening 230 and overlays the E-coat paint to a top edge of the top wall 260 to make electrical contact with gasket 170. In addition, other apertures passing through the magnesium housing 110 may be similarly masked.
According to another aspect of the present invention, the conductive gasket 170 as well as the mating edges of each of the top cover 160 and the side wall 130 of magnesium housing 110 are formed to fit together as a labyrinth that prevents moisture from passing therethrough. In other words, these various components form a water tight seal, which helps prevent the ingress of moisture at the conjunction of top cover 160 and magnesium housing 110.
An experiment was conducted to test the corrosion resistance, upon exposure to salt fog, of conductive gasket 170 and bottom e-coated magnesium housing 110. The experiment utilized test methods described in MIL-STD 810F military standard as well as CHO-TM100 (copy available from Chomerics of Woburn, Mass., a division of Parker Hannfin Corporation), which are both incorporated by reference in their entireties. In the experiment, test coupons were cycled in a salt fog chamber for 24 hour intervals, with 24 hours of drying in between, over a period of about five days. Deionized water was used in the coupon cleaning step.
As noted in Table 1 below, four magnesium test coupons comprising four layers were used in this experiment. For each test coupon, the bottom layer was comprised of magnesium (Mg). For test coupons 1 and 3, the bottom magnesium layer was coated with a chromate primer NH 35, whereas for test coupons 2 and 4, the bottom magnesium layer was electrocoated. For each test coupon, the NH 35 or electrocoated layer were overlayed with a conductive layer, e.g. CHO-SHIELD 2003. For test coupons 1 and 4, the CHO-SHIELD 2003 layer was overlayed with CHO-SEAL 1298 ("CS1298"), a conductive gasket (commercially available from Chomerics of Woburn, Mass., a division of Parker Hannfin Corporation) having a silver-aluminum (Ag—Al) conductive filler. For test coupons 2 and 3, the CHO-SHIELD 2003 was overlayed with CHO-SEAL 6308 ("CS6308"), a conductive gasket (commercially available from Chomerics of Woburn, Mass., a division of Parker Hannfin Corporation) having a nickel-carbon (Ni—C) conductive filler.
Table 1 below notes the weight loss of each test coupon, the average initial and final electrical resistivities, average thickness change, and observations about corrosion. The electrical resistivities are measures of a test coupon's ability to provide EMI shielding.
Test Coupon 1
Test Coupon 2
Test Coupon 3
Test Coupon 4
Weight loss
Weight lost
mOhm cm
mOhm cm
change (%)
Metal loss and
Slight pitting in a
Metal loss and
Slight to
deep fracturing
couple of areas of
moderate pitting
of outer edge.
outer edge.
fracturing of outer
around outer
Also, de-
Otherwise the
edge. Also, some
edge. Otherwise,
lamination of
coating and
de-lamination of
the coating and
CS2003 on back-
coupon were
CS2003 on front
coupon were
and backside.
From the experimental results synopsized in Table 1, it is apparent that test coupons 2 and 4, comprising CS2003/E-coated magnesium, provided the most protection in preventing galvanic corrosion after 48 hours of salt fog exposure, as noted by 0.6% and 1.3% weight loss, respectively. Test coupons 1 and 3, comprising CS2003/NH-35 coated magnesium, did not provide sufficient protection in preventing galvanic corrosion, as noted by the 6.5% and 3.7% weight loss, respectively.
Test coupon 2, comprising a CS6308 conductive gasket, was about 1.8 to about 2.2 times less corrosive than test coupon 3, comprising a CS1298 conductive gasket. Thus, test coupon 2 provided the better combination of material and coatings for protecting magnesium flanges in a corrosion environment.
In another experiment, the entire inventive electronic system package 100, housing an infrared camera, as shown in
While it is apparent that the illustrative embodiments of the invention disclosed herein fulfill the objectives of the present invention, it is appreciated that numerous modifications and other embodiments may be devised by those skilled in the art. Additionally, feature(s) and/or element(s) from any embodiment may be used singly or in combination with other embodiment(s). Therefore, it will be understood that the appended claims are intended to cover all such modifications and embodiments, which would come within the spirit and scope of the present invention.
|Cited Patent
|Filing date
|Publication date
|Sep 30, 1986
|Apr 5, 1988
|Motorola, Inc.
|Housing for vibration sensitive circuits
|Jul 28, 1989
|Jan 29, 1991
|Chomerics, Inc.
|Conductive masking laminate
|Feb 1, 1990
|Jun 4, 1991
|Obear Robert F
|Environment protected industrial microcomputer
|Jul 29, 1991
|Jun 9, 1992
|Shipley Company Inc.
|Coating composition
|Oct 27, 1989
|Jun 1, 1993
|Scientific-Atlanta, Inc.
|Pedestal assembly having an RFI/EMI labyrinth shield
|Sep 14, 1993
|Dec 5, 1995
|Mitsubishi Denki Kabushiki Kaisha
|Shielded enclosure for housing electronic components and manufacturing method thereof
|Oct 4, 1994
|Oct 1, 1996
|Northern Telecom Limited
|Integrated circuit packaging
|Jun 30, 1995
|Nov 5, 1996
|International Business Machines Corporation
|Electro-magnetic shielding structure having surface layers connected to each other at edges
|Sep 3, 1993
|Jan 21, 1997
|International Paper Company
|Laminated shielding material and method for shielding an enclosure therewith
|Sep 9, 1996
|Sep 15, 1998
|Gde Systems, Inc.
|Ruggedized container system and method
|Jul 7, 1997
|Jun 1, 1999
|Hughes Electronics Corporation
|Omnidirectional audio in a communications device
|Oct 6, 1997
|Jun 8, 1999
|Parker-Hannifin Corporation
|Corrosion-resistant, form-in-place EMI shielding gasket
|Jul 8, 1994
|Jul 20, 1999
|U.S. Philips Corporation
|Housing for appliances in the field of electrical datacommunication
|Aug 27, 1997
|Nov 9, 1999
|Nartron Corporation
|In-line module for attenuating electrical noise with male and female blade terminals
|Jun 1, 1999
|May 30, 2000
|Paes; Ned Z.
|Free-standing, portable tent assembly with flexible, electronic signal shielded enclosure
|May 11, 1999
|May 29, 2001
|Lucent Technologies, Inc.
|Circuit board RF shielding
|Jun 5, 2000
|Mar 12, 2002
|Expan Electronics Co., Ltd.
|Clip type conductive gasket
|Mar 27, 1998
|Dec 23, 2003
|Intel Corporation
|Magnetic gasket for fastening electronic components
|May 1, 2002
|Jul 20, 2004
|Parker-Hannifin Corporation
|Manufacture of electronics enclosure having a metallized shielding layer
|Jun 25, 2004
|Feb 6, 2007
|Northrop Grumman Corporation
|Non-ruggedized COTS display packaging for severe environment applications
|May 31, 2006
|Oct 30, 2007
|Motorola, Inc.
|Shield frame for a radio frequency shielding assembly
|Nov 24, 2005
|Nov 4, 2008
|Nok Corporation
|Electromagnetic wave shielding gasket
|Apr 14, 2006
|Nov 4, 2008
|Parker Hannifin Corporation
|Board level shielding module
|Apr 23, 2007
|Mar 3, 2009
|Hewlett-Packard Development Company, L.P.
|Enclosure and gasket assembly for reducing EMI
|Jan 10, 2008
|Mar 17, 2009
|Uber Co., Ltd.
|Electromagnetic shielding gasket and electronic device provided therewith
|Nov 22, 2006
|Nov 6, 2008
|Lightweight Rigid Case for Electronic Apparatus
|Nov 22, 2006
|Jun 14, 2007
|Rigid and lightweight electronic equipment casing
|U.S. Classification
|174/369, 174/386
|International Classification
|Cooperative Classification
|European Classification
|Nov 25, 2009
Owner name: FLIR SYSTEMS, INC., OREGON
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:HUGHES, MICHAEL R.;HEBERT, JAMES;REEL/FRAME:023572/0626
Effective date: 20091125
|Nov 2, 2015
|Fee payment
Year of fee payment: 4


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The Ecstacy of Loving God
Trances, Raptures, and the Supernatural Pleasures of Jesus Christ
John Crowder
This book is available for download with iBooks on your Mac or iOS device, and with iTunes on your computer. Books can be read with iBooks on your Mac or iOS device.
"though you have not seen Him, you love Him, and though you do not see Him now, but believe in Him, you greatly rejoice with joy inexpressible and full of glory," (1 Peter 1:8 NASB).
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- Category: Christianity
- Published: 01 December 2008
- Publisher: Destiny Image
- Seller: Destiny Image Publishers
- Print Length: 352 Pages
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text:
Sampling techniques such as Respondent-Driven Sampling (RDS) are widely used in epidemiology to sample "hidden" populations, such that properties of the network can be deduced from the sample. We consider how similar techniques can be designed that allow the discovery of the structure, especially the community structure, of networks. Our method involves collecting samples of a network by random walks and reconstructing the network by probabilistically coalescing vertices, using vertex attributes to determine the probabilities. Even though our method can only approximately reconstruct a part of the original network, it can recover its community structure relatively well. Moreover, it can find the key vertices which, when immunized, can effectively reduce the spread of an infection through the original network.
Citation: Yan B, Gregory S (2013) Identifying Communities and Key Vertices by Reconstructing Networks from Samples. PLoS ONE 8(4): e61006. doi:10.1371/journal.pone.0061006
Editor: Frank Havemann, Humboldt-Universität zu Berlin, Germany
Received: January 17, 2013; Accepted: March 5, 2013; Published: April 10, 2013
Copyright: © 2013 Yan, Gregory. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This research was partly funded by the University of Bristol Research Strategy Fund. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. No additional external funding was received for this study.
Competing interests: The authors have declared that no competing interests exist.
The representation of data as networks has become increasingly popular in recent years in diverse application areas, including social science, biology, and epidemiology. However, real-world datasets are often incomplete because it may be difficult or impossible to collect complete data with available time or resources. In the case of network data, techniques have been developed to estimate properties of a network from samples of it, and various methods devised to discover or predict missing information, which can then be added to the network. For example, there are numerous strategies for finding missing edges [1] and even for finding the correct sign or direction of existing edges, in the context of signed [2] and directed [3] networks, respectively.
In contrast to the "edge prediction" problem, we are concerned with a different form of incomplete network. We assume that all edges, and vertices, are present in the network, but that vertices may have incorrectly been duplicated. This kind of error is very common, for example, in bibliographic databases and in genealogy, where a single individual may be known by more than one name and therefore represented by more than one vertex. Our task is to take a network with possibly duplicated vertices and attempt to coalesce all duplicates into a single vertex. Clearly, this can be done perfectly only if the identity of each vertex is known. However, if we have only partial information about vertices, we can still estimate the probability that each pair of vertices represent the same individual, and therefore predict which pairs should be coalesced. Having reconstructed the network, we can then attempt to identify features of it, such as the communities or the vertices which are important in some sense.
One potential application of this is epidemiology. It is well known that the structure of a contact network strongly influences the spread of an infectious disease in it. For example, in community-structured networks, infections travel fast within communities but slowly between them [4], [5]. High-degree vertices also play an important role in spreading disease [6]: it is effective to control disease transmission by immunizing high-degree people in a disassortative social network. There are some other practical applications, for example, identifying key individuals in a criminal network [7].
Knowledge of the network structure could clearly be invaluable in disease control or crime prevention, etc. The problem is that it is often very difficult to discover the structure of real networks, especially social networks. However, it is often possible to obtain samples (subgraphs) of the network. In epidemiology, techniques such as Respondent-Driven Sampling (RDS) [8] and contact tracing (CT) [9] are often used for this purpose. Our idea is to reconstruct networks by collecting samples based on paths (sequences of adjacent vertices) starting from vertices that are randomly selected from the population, and using these to reconstruct the network.
Our technique works as follows. First, a member of the population is randomly selected as a "seed", which begins the first sample path. Then one of the neighbors of the seed is randomly selected and added to the end of the path. The process is repeated from the last vertex that was added to the path. If the selected neighbor already exists in any of the paths collected so far, we choose a different neighbor. The path stops growing if the latest vertex has no neighbors that have not already been sampled. When a path stops growing, a new path is started, beginning at a new randomly-selected seed. This is repeated until the total size (number of vertices) of all paths reaches a specified limit. We call this the Random Path Method (RPM). In our High-degree Path Method (HPM), we choose the highest-degree neighbor at each step, instead of a random one.
Both methods produce a set of paths: linear samples of the network about which we have complete information. In particular, the sampling strategy implies that we know the identity of every vertex in the paths, in order to avoid duplicates. For example, in the case of social networks, the members of these paths can be interviewed to obtain arbitrarily detailed information about them. In the second stage of our process, we convert each sample path to a sample tree, in which the seed becomes the root of the tree and the successor of each vertex v in the path becomes an offspring of v in the tree. Now a vertex v may have additional offspring in the tree: these are neighbors of v in the underlying network, and may (but need not) include v's predecessor and successor in the path. In the case of social networks, these additional offspring of v are "friends" of v which have been reported by v, but we do not have complete knowledge about them; in particular, they may be duplicated. Thus, a sample tree contains vertices of two types, which we call respondents and friends.
Each respondent is asked to provide a description of each chosen friend which, for practical reasons, is very unlikely to uniquely identify the friend. We use these descriptions to choose which pairs of vertices might represent the same individual, and coalesce them into a single vertex. Naturally, the success of this technique depends on the accuracy of descriptions (increased detail reduces the chance of incorrect matching) as well as on the size and number of the trees. Only if the trees cover the whole network and the descriptions are unique can we expect to reconstruct the underlying network perfectly. However, by exploiting knowledge of the frequency of individuals in the population matching each description, we can probabilistically coalesce vertices to build a large ensemble of possible networks, from which we can estimate some properties of the underlying network.
We explore this technique in the remainder of the paper. Essentially, we evaluate the similarity between the reconstructed network and the original underlying network, varying the features of the underlying network and the parameters of the sampling procedure. "Similarity" can be defined in several ways: similarity of edges, similarity of community structure, and similar ranking of various vertex properties. Finally, we use the technique to identify key vertices in a contact network for an infectious disease (i.e., those that might be important to the spread of infection) and immunize them. We find that choosing the key vertices from a relatively small sample can control the spread of infection almost as well as choosing them from the entire network.
The underlying network
We assume the existence of an a priori unknown network, which we call the underlying network. This is a simple undirected, unweighted network. Every vertex is characterized by a single, discrete-valued, attribute. For example, in a social network, this could represent any real-life property of the individual, such as gender, age, hair color, etc., or a tuple of them, e.g., (male, 34, brown). In general, this divides the vertices into a number (g) of categories. Therefore, without loss of generality, we assume that the attribute of v, av, is an integer in the range [1,g]. The distribution of attribute values can vary; for example, a uniform distribution could be used for age while a normal distribution is more realistic for height.
Sampling procedure
The first phase of our procedure collects a sample comprising a set of paths with a total size of approximately nr vertices:
- Choose any vertex s (that does not already appear in a path) from the underlying network, as seed.
- Add s to a new path.
- If size of all paths = nr, terminate.
- For the most recently added vertex v, try to obtain a neighbor u of v that is not in any path.
- If u is found, add u to current path and repeat from step 3.
- If u is not found, repeat from step 1.
In step 4, the vertex that we find must be a neighbor of v in the underlying network and must not have already been added to a path. This way we construct paths sequentially, until the total size is approximately the required size, nr.
In the second phase, we obtain from each respondent vertex v up to f "friends", which again must be neighbors of v in the underlying network. If v has more than f neighbors, any f of the neighbors can be chosen. If v has f neighbors or fewer, all of v's neighbors are chosen. The friends chosen by v are added as offspring of v in the sample tree. A vertex can be chosen as a friend even if it already appears in a tree. Finally, each friend vertex u is labeled with a "description" du: a set of categories that includes u's actual category. Descriptions are assumed to be correct but not necessarily precise. For example, if the vertex has (age) attribute 34 in the underlying network, its description in the sample tree could be, for example, {33,34} or {34,35,36}. If the same network vertex appears as a friend more than once, each occurrence may have a different (correct) description. The final trees contain nr+nf vertices: nr respondents and nf friends.
Figure 1(b) shows one possible set of sample trees, sampled from the underlying network of Figure 1(a), with vertices 1 and 3 as seeds. Notice that a vertex (e.g., 31) appears more than once in the trees (e.g., 31, 31', 31''), if it is a friend of more than one respondent.
A. Underlying network. B. Sample paths, with respondents in red and friends in green. C. True network. D. Reconstructed network: green vertices represent incorrectly coalesced pairs.
Network reconstruction
In this phase we attempt to convert the sample trees to a network by coalescing all vertices that represent the same vertex in the underlying network. If we could do this perfectly, we would end up with a subgraph of the underlying network which contains all nodes and edges that appear in the sample trees; we call this subgraph the true network. Figure 1(c) shows the true network corresponding to Figure 1(b).
Our network reconstruction algorithm repeatedly performs the following steps:
- Choose any two vertices u and v from the sample trees.
- Calculate the probability p that u and v represent the same individual.
- With probability p, coalesce u and v.
- If u is a respondent and v is a friend, the coalesced vertex is u, still labeled with au.
- If u and v are both friend vertices, the coalesced vertex is a friend vertex labeled with the description du ∩ dv.
These steps are repeated until the network size is reduced from nr+nf vertices to the desired size, nt.
The probability p calculated in step 2 depends on whether u and v are respondents or friends. If they are both respondents, p = 0 (all respondents are known to be distinct).
For respondent u and friend v:
- If there is an edge {u,v}, p = 0, because a respondent cannot choose himself as a friend.
- If au ∉ dv (u does not satisfy the description of v), p = 0.
- Otherwise,
(1)where Pr(dv) is the probability of an arbitrary vertex satisfying description dv. This is because there are, on average, nt Pr(dv) vertices satisfying that description and u is equally likely to be any of them.
For friend u and friend v:
- If u and v have a common neighbor (a respondent), p = 0, because all friends of a respondent are distinct.
- Otherwise,
(2)The probabilities Pr(d) depend on what is known about the underlying network. For example, if descriptions are ages (in years) and are uniformly distributed over a range of 50 years, Pr({34,35,36}) = 3/50. If we try to match two friend vertices with descriptions {33,34} and {34,35,36}, p would be (1/50)/(nt(2/50)(3/50)) = 50/6nt, assuming that nt is reasonably large.
Figure 1(d) shows one possible network produced by our network reconstruction. Most duplicate vertices have been coalesced correctly ({2,2'}, {23,23'}, and {31,31'}), but one pair ({27,28'}) has been merged wrongly, shown in green.
Experimental framework
In the next section, we evaluate our method empirically. In order to evaluate our reconstructed networks, we begin with a known underlying network and simulate our sampling procedure on it.
For the underlying network we use a selection of real social networks, listed in Table 1. We also use synthetic benchmark networks generated by the method of Lancichinetti et al. [10], which allows us to vary the parameters, especially the strength of community structure. The LFR networks have several parameters:
- n is the number of vertices.
- 〈k〉 and kmax are the average and maximum degree.
- τ1 and τ2 are the exponents of the power-law distribution of vertex degrees and community sizes.
- cmin and cmax are the minimum and maximum community size.
- μ is the mixing parameter: each vertex shares, on average, a fraction μ of its edges with vertices in other communities.
Having obtained or created the network, we then label the vertices with attributes which are integers in [1,g]; the number of categories, g, can be varied. The values are assigned randomly, according to a uniform or normal distribution. As an optional step, the network can then be made more assortative by swapping the attribute values of two vertices so that the values of neighboring vertices become more similar. By default, for most experiments in this paper, we use a normal distribution and do not try to increase assortativity.
In our Random Path Method, each seed is chosen randomly from the underlying network and each subsequent vertex is chosen randomly from the neighbors. In our High-degree Path Method, each seed is randomly chosen from vertices with degree 5 or more, and we always add the highest-degree neighbor to the path. The friends (at most f) of v are selected randomly from v's neighbors in the underlying network. The description attached to each friend is a randomly-chosen range of c (which can be varied) consecutive categories that includes the actual category of the corresponding vertex in the underlying network.
In our experiments, we assume that we know the size of the true network, nt, so that the network reconstruction phase stops coalescing vertices when that size is reached. This allows us to take the true network as the best possible reconstructed network. In real use, nt would not be known, but it should be possible to devise suitable alternative termination criteria; for example, to stop coalescing when the average degree (or other network property) of the reconstructed network reaches a realistic value.
Results and Discussion
Evaluation of the algorithm
First we evaluate our method for reconstructing networks: in particular, how its accuracy is affected by the properties of the underlying network and the parameters of the sampling procedure. Network properties are:
- Number of categories of vertex attributes, g.
- Distribution of vertex attributes: e.g., uniform or normal distribution.
- Whether the vertex attributes are assortative or non-assortative. In an assortative network we attempt to make vertex attributes similar to their neighbors', while attributes in the non-assortative network are randomly assigned.
- Strength of community structure, μ: each vertex shares, on average, a fraction μ of its edges with vertices in other communities.
By default, we use normally distributed, non-assortative, networks.
Parameters of the sampling procedure include:
- Number of neighbors named as friends, f.
- Number of consecutive categories in descriptions of friends, c. Increasing c reduces the precision of the description; for example, describing a friend's age to the nearest 5 years (c = 5) instead of giving the exact age in years (c = 1).
- Size of reconstructed network after coalescing, nt.
Default values that we use are f = 5 (a common value in surveys of friendship networks) and c = 1, while nt is set to 8% of the underlying network size; this is approximately the fraction used in some real surveys of "hidden populations" such as drug users. However, we also examine the effect of varying each of these parameters.
To measure the accuracy of the network reconstruction, we use coalescing precision, which we define as:(3)where a pair of vertices {u,v} in the sample trees is a coalesced pair if our method coalesces them, and a correct coalesced pair if (also) u and v represent the same vertex in the underlying network.
Figure 2 shows the effect of varying g on coalescing precision, for both assortative and non-assortative networks. A high g represents more accurate, less ambiguous, descriptions. As expected, the more information about descriptions obtained, the higher the precision. Our method performs better on non-assortative networks than assortative networks because, in the latter, the descriptions of vertices in sample trees are more likely to be similar and therefore harder to coalesce correctly. The High-degree Path Method performs better than the Random Path Method, and this is true of subsequent experiments; we discuss this in the conclusions.
Precision, for varying g, on assortative and non-assortative LFR networks with normal distribution with n = 1460, 〈k〉 = 20, kmax = 30, μ = 0.1, τ1 = 3, τ2 = 1, cmin = 10, and cmax = 20. A. Random Path Method. B. High-degree Path Method.
Figure 3 shows the effect of different distributions of vertex attributes for the underlying networks on coalescing precision. Our method works slightly better for uniform than for normal distribution; this is because, with a normal distribution, more individuals fall into a smaller number of categories, so the categories are less effective in distinguishing them.
Precision, for normal distribution and uniform distribution of vertex attributes, on non-assortative LFR networks with n = 1460, 〈k〉 = 20, kmax = 30, μ = 0.1, τ1 = 3, τ2 = 1, cmin = 10, and cmax = 20. A. Random Path Method. B. High-degree Path Method.
Figure 4 shows the effect of community structure on coalescing precision. The parameter μ controls the community structure of the underlying network. When we increase μ (for a less distinct community structure), the coalescing precision gradually falls. This is because, with a smaller μ, the vertices in each sample tree are more likely to belong to the same community and therefore any coalescing of them is more likely to be correct by chance.
Precision, varying μ on non-assortative LFR networks with normal distribution with n = 1460, 〈k〉 = 20, kmax = 30, τ1 = 3, τ2 = 1, cmin = 10, cmax = 20, and g = n. A. Random Path Method. B. High-degree Path Method.
As f increases, the sample trees tend to become larger, and so we need fewer of them because nt (the total size of all trees) is fixed. They also contain a larger fraction of friends, which carry less information than respondents and, unlike them, might be duplicated. Therefore, we expect worse results when f is larger. Figure 5 shows the coalescing precision when we vary f. In this example, the number of friends does not noticeably affect the coalescing precision of the method. Therefore, we use f = 5, because it is a common value in surveys of friendship.
Precision, varying f on non-assortative LFR networks with normal distribution with n = 1460, 〈k〉 = 20, kmax = 30, μ = 0.1, τ1 = 3, τ2 = 1, cmin = 10, cmax = 20, and g = n. A. Random Path Method. B. High-degree Path Method.
In reality, the descriptions of friends are not necessarily accurate, for example, a range of heights can be described for a friend. Therefore, we vary c, the number of categories in a range for describing friends. Figure 6 shows the effect of different ranges of categories on coalescing precision. As expected, a wider range results in lower precision because there are more pairs of vertices that could be (incorrectly) coalesced.
Precision, varying c on non-assortative LFR networks with normal distribution, with n = 1460, 〈k〉 = 20, kmax = 30, μ = 0.1, τ1 = 3, τ2 = 1, cmin = 10, cmax = 20, and g = n. A. Random Path Method. B. High-degree Path Method.
Community structure detection
The topological features of networks have attracted much attention in recent disease transmission research [5]. In particular, in a contact network, a disease spreads quickly between individuals inside communities and slowly between communities. Our hypothesis is that community structure in the underlying network can be predicted by the community structure found in the reconstructed network. We test this by using a good community detection algorithm (Infomap [15]) to detect communities in the reconstructed and true networks and then using the Normalized Mutual Information (NMI) measure to compare the partitions found in each network. However, we cannot use this to compare the partitions obtained in the underlying network and reconstructed network, because the reconstructed network omits most of the vertices and edges from the underlying network. Therefore, we use another measure, which we call community precision:(4)
Figure 7 shows a comparison of the partitions obtained in the true network and the reconstructed network by using NMI, and varying g. Figure 8 shows the community precision between the underlying and reconstructed networks. Both results show substantial similarity between the correct communities and those found in the reconstructed network. Figure 7 shows that community structure is found more accurately when the network is assortative even though the coalescing precision is lower (Figure 2). This is because, with our reconstruction method, even incorrect coalescing is likely to coalesce vertices that are in the same community if the network is assortative.
Normalized Mutual Information, varying g, with n = 1460, 〈k〉 = 20, kmax = 30, μ = 0.1, τ1 = 3, τ2 = 1, cmin = 10, and cmax = 20. A. Random Path Method. B. High-degree Path Method.
Community precision, varying g, with n = 1460, 〈k〉 = 20, kmax = 30, μ = 0.1, τ1 = 3, τ2 = 1, cmin = 10, and cmax = 20. A. Random Path Method. B. High-degree Path Method.
Rank correlation
In addition to detecting community structure, we are also interested in identifying the important vertices, which may be more important in spreading disease. Controlling (e.g., immunizing) key vertices could prevent a current or potential epidemic. In our experiments, we consider three vertex properties:
- degree(v). the number of neighbors of a vertex v. The vertices with high degree are important.
- kout(v). the number of neighbors of a vertex v in other communities. A vertex with a high kout is important because it is a "bridge" vertex.
- embeddedness(v). the fraction of neighbors of a vertex v that belong to the same community as this vertex [16]. A "bridge" vertex should have a low embeddedness. Embeddedness is related to the other two properties by the equation:
(5)We want to discover whether vertices in the reconstructed network that are "important" (according to each of these three properties) play the same role in the underlying network. The procedure follows the steps below:
- Calculate different properties for each of the vertices in the reconstructed network and the underlying network separately (ignoring vertices that do not occur in the reconstructed network).
- Rank the vertex lists according to those values.
- Compare the ranked lists of the reconstructed network and the underlying network by using a rank correlation coefficient. Spearman's rank correlation coefficient [17] has been chosen: this measures the similarity between two ranked lists of the same set of items.
Figures 9–12 show the results for our four real networks. In all cases, the similarity between the true network (TN) and underlying network (ULN) is less than perfect, because the true network lacks many of the edges present in the underlying network. The similarity between the reconstructed network (RCN) and true network increases with g. The similarity between the reconstructed network and underlying network is lower still but also increases with g. Degree is slightly better predicted than kout, while embeddedness is the hardest to predict of the three measures.
A. Degree (RPM). B. kout (RPM). C. Embeddedness (RPM). D. Degree (HPM). E. kout (HPM). F. Embeddedness (HPM).
A. Degree (RPM). B. kout (RPM). C. Embeddedness (RPM). D. Degree (HPM). E. kout (HPM). F. Embeddedness (HPM).
A. Degree (RPM). B. kout (RPM). C. Embeddedness (RPM). D. Degree (HPM). E. kout (HPM). F. Embeddedness (HPM).
A. Degree (RPM). B. kout (RPM). C. Embeddedness (RPM). D. Degree (HPM). E. kout (HPM). F. Embeddedness (HPM).
Disease simulation
In the last section, we showed that it is possible to predict certain vertex properties of a network from a sample, but only with moderate accuracy. Moreover, since the sample contains only a small fraction (8% in our experiments) of the underlying network, our method can predict nothing about the remaining 92% of vertices. The question is whether it is useful to have this imperfect information about the vertex properties of such a small sample of the network. We investigate this by using this information (the key vertices in the reconstructed network) to try to control the spread of disease in the underlying network.
The experiments are designed as follows:
- Calculate different properties for vertices in the reconstructed network (8% of the underlying network size) and order the list of vertices. We calculate the average value of each vertex property over 100 instances of such networks.
- Immunize the top-ranked vertices.
- Simulate a disease outbreak in the underlying network.
- Measure the total epidemic size, to assess the effectiveness of the control strategy.
We compare this method with an alternative whereby the actual value of each property is calculated using the whole underlying network. This is not feasible in real life because the underlying network is unknown, but can provide an upper bound for comparison with our strategies.
In step 3, we simulate the spread of an infectious disease using a susceptible-infected-recovered (SIR) model, taking the real-world networks in Table 1 as the underlying networks. We initially infect 0.2% of the vertices in the underlying network, then at each time step, there is a fixed probability (0.08) of the disease being transmitted to a susceptible vertex from each infectious neighbor, and a vertex remains infectious for a fixed period (four time steps).
Figures 13–16 (a) show results of the three strategies applied to the underlying network, together with a strategy of immunizing vertices selected randomly from the whole network. Figures 13–16 (b) and (c) show the same strategies where the vertex is chosen only from the reconstructed network with our two sampling methods. Because the latter is much smaller than the underlying network (8% of the size), the results are inevitably worse than choosing from the complete network, but still remarkably good. It may be thought that the immunization strategy is influenced only by which vertices appear in the sample trees, and hence reconstructed networks, rather than the values of the vertex properties. For example, vertices in sample trees naturally have a higher degree than average. To show that this is not the case, Figures 13–16 (b) and (c) also show a "random" strategy in which vertices are randomly selected from the reconstructed network. Here, because each reconstructed network contains a different set of vertices, we order vertices by the frequency with which they appear in reconstructed networks. Although this performs better than random selection from the whole underlying network, it is less good than our proposed strategies.
Effect on epidemic size, varying number of immunized vertices. A. Immunizing top-ranked vertices in underlying network. B. Immunizing top-ranked vertices in reconstructed network: Random Path Method. C. Immunizing top-ranked vertices in reconstructed network: High-degree Path Method.
Effect on epidemic size, varying number of immunized vertices. A. Immunizing top-ranked vertices in underlying network. B. Immunizing top-ranked vertices in reconstructed network: Random Path Method. C. Immunizing top-ranked vertices in reconstructed network: High-degree Path Method.
Effect on epidemic size, varying number of immunized vertices. A. Immunizing top-ranked vertices in underlying network. B. Immunizing top-ranked vertices in reconstructed network: Random Path Method. C. Immunizing top-ranked vertices in reconstructed network: High-degree Path Method.
Effect on epidemic size, varying number of immunized vertices. A. Immunizing top-ranked vertices in underlying network. B. Immunizing top-ranked vertices in reconstructed network: Random Path Method. C. Immunizing top-ranked vertices in reconstructed network: High-degree Path Method.
In summary, immunizing a small number of key vertices in the reconstructed network can control the spread of infection almost as well as immunizing the same number of key vertices in the underlying network. The kout strategy is usually the best in the underlying network, but degree is the best strategy in the reconstructed network.
Finally, we investigate how sensitive our method is to the size of the sample. In Figure 17 we plot the effect on epidemic size in two of our real networks. We immunize the top 1% of vertices, according to degree and kout, varying the size of the reconstructed network from which the vertices are chosen. The results suggest that our method is not particularly sensitive to the sample size, provided that the reconstructed network (size nt) is at least 5% of the underlying network size. It is worth mentioning that, although the underlying network is generally unknown, its size may be easy to estimate (e.g., the number of drug users in a city can be estimated from the city's population and the average prevalence of drug use). Therefore, the sample size (nr and nf) can be determined to make nt be approximately the desired fraction of the underlying network size.
Effect on epidemic size, varying the size of the reconstructed network. (a) Blogs (RPM). (b) Erdös1997 (RPM). (c) Blogs (HPM). (d) Erdös1997 (HPM).
We have described a sampling technique that allows some of the structure of networks to be recovered. Sampling strategies such as RDS [8] are already widely used in epidemiology to sample data from hidden populations. Indeed, Ref. [18] has examined the relation between community structure and RDS, showing that community structure in a network has an adverse effect on the sampling ability of RDS. However, RDS has not hitherto been used to find community structure in networks.
Our method does this by sampling trees and attempting to transform the trees to networks. The last step is a kind of missing data problem, in which the missing information is the identity of the pairs of vertices that represent the same individual. We solve this by using vertex attributes to calculate the probability that two vertices represent the same individual and coalesce them probabilistically. This is reminiscent of probabilistic linkage techniques, often used to combine data about the same individuals from multiple databases [19].
The results indicate that, not surprisingly, our method can reconstruct networks more accurately when descriptions are more precise. An interesting point is that community structure can be recovered quite well even when descriptions are not very accurate, because of the robustness of community detection methods. When the network features assortative mixing, which is common with community structure, the partitions found are even more accurate than in non-assortative networks. We also find that the ranking of vertices, with respect to degree and kout, can be estimated quite accurately. Even though our estimate applies only to a small fraction of the contact network, it is remarkable that the spread of disease can be controlled well by immunizing the key vertices discovered in this way.
We have actually described two methods: the High-degree Path Method (HPM) and the Random Path Method (RPM). The HPM generally performs better. This is because the sampled vertices have higher degree and are more likely to form larger sample trees, and therefore larger components, in the reconstructed network; these components contain more information about the network structure than a larger number of very small components. However, the RPM also works well and is more practical because it is usually easier to discover any neighbors of a respondent than to find all of them, as the HPM requires.
It remains to be seen how well the technique will work in real life. This depends largely on how accurately respondents describe their friends, which will vary according to the nature of the survey. To evaluate the reconstructed network, we would also need to have access to the real underlying network, which is rarely available.
One area for future work is clearly to test the techniques in practice, by targeting real members of a clearly defined small population whose network structure can be verified. This is likely to be quite expensive because of the need to interview respondents. Another idea is to modify our sampling procedure to make it interactive: for example, if the probability of coalescing two friend vertices (friends of respondents r1 and r2) is too low, we could ask r1 and r2 to provide more detailed descriptions of those friends, or we could provide r1's friend description to r2, for confirmation.
We would like to thank Caroline Colijn, Katy Turner, Harriet Mills, and Nick Fyson for comments on earlier experiments.
Author Contributions
Conceived and designed the experiments: BY SG. Performed the experiments: BY SG. Analyzed the data: BY SG. Contributed reagents/materials/analysis tools: BY SG. Wrote the paper: BY SG.
- 1. Lü L, Zhou T (2011) Link prediction in complex networks: a survey. Physica A 390: 1150–1170. doi: 10.1016/j.physa.2010.11.027
- 2.
Leskovec J, Huttenlocher D, Kleinberg J (2010) Predicting positive and negative links in online social networks. In: WWW 2010: Proceedings of the 19th International Conference on World Wide Web. Raleigh, North Carolina, USA, pp 641–650.
- 3. Guo F, Yang Z, Zhou T (2012) Predicting link directions via a recursive subgraph-based ranking. Available: arXiv 1206.2199. doi: 10.1016/j.physa.2013.03.025
- 4. Miller JC (2009) Spread of infectious diseases through clustered populations. J. R. Soc. Interface 6: 1121–1134. doi: 10.1098/rsif.2008.0524
- 5. Salathé M, Jones JH (2010) Dynamics and control of diseases in networks with community structure. PLoS Comput. Biol 6: e1000736. doi: 10.1371/journal.pcbi.1000736
- 6. Newman MEJ (2002) Assortative mixing in networks. Phys.Rev. Lett 89: 208701. doi: 10.1103/physrevlett.89.208701
- 7. Borgatti SP (2006) Identifying sets of key players in a network. Comput. Math. Organ. Theory 12: 21–34. doi: 10.1007/s10588-006-7084-x
- 8. Heckathorn DD (1997) Respondent-driven sampling: a new approach to the study of hidden populations. Social Problems 44: 174–199. doi: 10.1525/sp.1997.44.2.03x0221m
- 9. Eames KTD, Keeling MJ (2003) Contact tracing and disease control. Proc. R. Soc. B-Biol. Sci 270: 2565–2571. doi: 10.1098/rspb.2003.2554
- 10. Lancichinetti A, Fortunato S, Radicchi F (2008) Benchmark graphs for testing community detection algorithms. Phys. Rev. E 78: 046110. doi: 10.1103/physreve.78.046110
- 11. Guimerà R, Danon L, Diaz-Guilera A, Giralt F, Arenas A (2003) Self-similar community structure in a network of human interactions. Phys. Rev. E 68: 065103. doi: 10.1103/physreve.68.065103
- 12.
Gregory S (2007) An algorithm to find overlapping community structure in networks. In: Proceedings of the 11th European Conference on Principles and Practice of Knowledge Discovery in Databases (PKDD 2007). Berlin, Germany: Springer-Verlag, pp 91–102.
- 13. Leskovec J, Kleinberg J, Faloutsos C (2007) Graph evolution: densification and shrinking diameters. ACM Trans. Knowl. Discov. Data 1: 2. doi: 10.1145/1217299.1217301
- 14. Batagelj V, Mrvar A (2000) Some analyses of Erdös collaboration graph. Soc. Networks 22: 173–186. doi: 10.1016/s0378-8733(00)00023-x
- 15. Rosvall M, Bergstrom CT (2008) Maps of random walks on complex networks reveal community structure. Proc. Natl. Acad. Sci. USA 105: 1118–1123. doi: 10.1073/pnas.0706851105
- 16. Lancichinetti A, Kivelä M, Saramäki J, Fortunato S (2010) Characterizing the community structure of complex networks. PLoS ONE 5: e11976. doi: 10.1371/journal.pone.0011976
- 17.
Mendenhall W, Scheaffer RL, Wackerly DD (2002) Mathematical Statistics with Applications. CA: Duxbury Press.
- 18. Goel S, Salganik MJ (2009) Respondent-driven sampling as Markov chain Monte Carlo. Stat. Med 28: 2202–2229. doi: 10.1002/sim.3613
- 19. Jaro MA (1995) Probabilistic linkage of large public health data files. Stat. Med 14: 491–498. doi: 10.1002/sim.4780140510


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Energy & Renewables Companies in Bangladesh
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Clarke Energy
Office in Dhaka, BANGLADESH
Clarke Energy is a multinational specialist in the engineering, installation and maintenance of gas-fuelled power plants. Our facilities deliver fuel efficiency and help reduce carbon emissions. Applications include combined heat and power (CHP) with natural gas, biogas, landfill gas and coal gas. We are a the largest authorised distributor and service provider for GE's ...
Macherey-Nagel GmbH & Co. KG
Distributor in Baridhara, BANGLADESH
Macherey-Nagel is a specialist company for chemical analysis with five main product ranges: Water Analysis, Rapid Tests, Filtration, Chromatography and Bioanalysis. Our Water Analysis and Rapid Test product range supply test solutions for environmental monitoring and testing, specialising in the area of water and waste water analysis. Our portfolio for environmental ...
Tiger-Vac Inc. (USA)
Distributor in BANGLADESH
With over forty years of experience, Tiger-Vac has successfully established itself in the international market as a manufacturer of high quality Explosion Proof, Industrial Vacuum Cleaner and Cleanroom Vacuum Cleaner Systems. Tiger-Vac has accomplished this by listening to its clients and responding to their needs. Our many diverse clientele include the military, ...


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Health & Baby
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How to Protect Your Baby From Whooping Cough
As a parent, the thought of your baby getting whooping cough, or pertussis, may concern you. But you can take steps to protect your little one, even before he is born. In order to keep your baby safe, you'll need to protect yourself and your whole family. Pertussis vaccines don't completely wipe outRead Full Article
What to Do When Baby Refuses a Bottle
Not all babies take to a bottle right away. Try these tips to turn your feeding problems around. If you're calm and relaxed, your baby may be more receptive to the bottle. "Babies are sensitive creatures and pick up on stress in mom and dad," says Megan L. Shope, a certified doula supervisor. CreateRead Full Article
Measuring and Mixing Formula
No matter which type of formula you choose, it's important to measure and mix it properly so your baby safely gets the nutrition he needs. "Measuring and reconstituting infant formula is particularly important when it concerns low-birth-weight and premature babies," says David Saltzman, MD, a ChicagRead Full Article
Newborn Baths 101
For new parents, bath time can be daunting, with all that water and a slippery, wiggly baby. Eileen Costello, MD, a pediatrician at Brigham and Women's Hospital in Boston, helps new moms and dads understand how to keep their baby well-washed and safe. "For newborns, until the umbilical cord comes ofRead Full Article
Breastfeeding: Get the Support You Need
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5 New Mom Guilt Trips to Skip
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Newborn Care: What You Need for Baby
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Been walking around Sydney looking around for a dinner place, we passed by Maloney's Hotel and saw a sign about their Tuesday night "buffet" for $7.95, so we decided to try it. First you got to pay at the bar for the "buffet", but you are required to buy a beverage first before you can avail. So we got our sodas and then proceeded to the "buffet" table. I'm using the word "buffet" very loosely because when you say "buffet" it typically means All-you-can-eat, but it was not the case here. You can only fill up your plate once, and they have a waiter to give you only a small portion of their more expensive dishes like meats. It did not say anything on their sign about a one-plated buffet and the staff did not even inform us of this, we only found out from the waiter at the end of the table (when our plate was already filled with appetizers and rice!). It was already too late to pile up on the good stuff. It was very misleading especially for tourists like us. The food was not even exceptional. It was really a big disappointment for i thought Sydney was free from these kinds of superficial deception. I felt very cheated. I would not recommend this place for the fraud that they are!
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Comments Thread For: Boxingscene's 201 Y/E Awards: Prospect Of The Year
By Jake Donovan
If boxing is left with a 2010 season that was best known for what didnt take place at the top level, then at the very least it could have left us with hope and promise for the future.
It did.
While it remains a struggle to piece together all of the big fights for which the public clamors, it hasnt slowed the flow of traffic at the prospect level.
Thanks to stateside prospect-based series on various networks, more fighters than ever before are provided with the opportunity to make a name for themselves on the way up rather than being forced to toil in obscurity while awaiting their chance at prime time exposure.
Two stood out more so than any other, to where both are on the verge of title contention.
That they have both advanced to the contender stage before years end perhaps challenge the criteria that goes into recognizing the best prospects in the sport.
Still, that both are still on the rise qualifies them as fighters that continue to learn while they earn.
One started out a little further back than the other yet managed to catch up before the end of the year in terms of career progress.
With that comes the
BOXINGSCENE.COM 2010 PROSPECT OF THE YEAR MIGUEL ANGEL MIKEY GARCIA [Click Here To Read More]
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One fighter who I have yet seen mentioned as a candidate of prospect of the year in any website was Chris Martin. He had a breakout year this year with beating fellow prospect Chris Avalos and he went 5-0 this year.
I agree with Mickey Garcia winning it though. I just think Martin should have been in the honorable mention. I guess he didn't get any votes but nobody is mentioning him in any website. Dan Rafael did a top 25 and didn't mention him
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Dan Rafael forgot to include Kell Brook on the list. He also accidently included Mike Jones on the list. He must have meant to include Kell Brook.
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Cant wait to see Mikey Garcia take out Juan Manuel lopez!!!
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mikey had a great year.I expect canelo and mikey to do big things in 2011.
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Degale is better then all names mentioned
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I even did a write-up a few weeks ago pleading a case for Martin as the year's top prospect - http://www.boxingscene.com/?m=show&id=33960 ... I'm that much more embarrassed that the final draft excluded him, but I have since fixed it. Thanks for pointing it out.
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And, I missed the Martin article, good read I try to catch everything you do so I don't know how I missed it.
Good to see Martin get a mention. I think he was one of the most underrated prospects.
Good work.
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I have a project implemented in a (flawed) 3-tier architecture. My job is making it more generic so that it would be easy to add a new database into the project.
Concrete: there is a databaseFacade for an SQL database and i have to make it more generic so we can add multiple databases very easy. In this case writing it to a CSV file.
My idea in the database layer was to make a interface where all the methods are defined. Then having the database facade (depending which you want to use) implementing this interface so that it becomes more generic. Then i have some kind of DBmanager class. This DBmanager class will read out a config file so he knows what database to use. Based on this info he will create an instance of the interface and return this to the application layer.
However this is where I don't know if i'm correct. The application layer now has a DBmanager class (where everything is correctly encapsulated only 1 method is public for returning the facade) and after that the DBfacade.
Any thoughts about the correctness of this? Since I'm having doubts.


text: Theses and Dissertations (Economics) http://hdl.handle.net/10500/2887 2016-07-27T17:18:47Z 2016-07-27T17:18:47Z South African over-the-counter credit derivatives market : 2005-2015 Kennedy-Palmer, S http://hdl.handle.net/10500/21002 2016-07-20T12:43:15Z 2015-01-01T00:00:00Z South African over-the-counter credit derivatives market : 2005-2015 Kennedy-Palmer, S Credit derivatives played a large role in intensifying losses during the subprime lending crisis, which began in 2007 in the US and spiralled into a financial crisis in 2008. One of the major reasons for this descent into financial crisis was the uncertainty about the exposure of some systemically important financial institutions through their derivative positions, specifically credit derivative instruments such as credit default swaps (CDSs). Using data obtained from the SARB, the study found that prior to the crisis, the size of the South African OTC credit derivatives market was increasing steadily. However, the 2008 financial crisis temporarily stunted this growth, and the size of the market declined. Since 2010, the growth of the market has once again been on an upward trajectory. The study examines recent international and local regulations relating to OTC derivatives and makes policy recommendations for South Africa. 2015-01-01T00:00:00Z The sectorial employment intensity of growth in South Africa : 2000-2012 Mkhize, Njabulo Innocent http://hdl.handle.net/10500/20131 2016-04-20T06:14:27Z 2015-05-01T00:00:00Z The sectorial employment intensity of growth in South Africa : 2000-2012 Mkhize, Njabulo Innocent The rate of unemployment in South Africa remains stubbornly high despite vastly improved macroeconomic fundamentals and relatively high rates of economic growth for most of the post-1994 democratic era. Employment growth was much weaker than might have been expected given the improved economic outlook. This thesis investigates how the sectoral employment intensity of output growth in the eight non-agricultural sectors of the South African economy has evolved from 2000 to 2012, with a view to identifying key growth sectors that are employment intensive. An econometric model of the demand for labour is used to estimate employment elasticities in the major Standard Industrial Classification (SIC) divisions of the economy. The results suggest that aggregate employment and economic growth diverged and that jobless growth occurred in South Africa during the period under review. South Africa has become less labour intensive and more capital intensive, reflecting a structural adjustment that has weakened the employment-growth relationship. At the sectoral level, the results suggest the presence of a long-run relationship between employment and growth in finance and business services, manufacturing, transport and the utilities sectors. In particular, the results suggest that the tertiary sector performed best in terms of the employment intensity of output growth. This reflects the changing structure of the economy and the nature of employment shifting away from the primary towards the tertiary sectors. Investment in the tertiary sector may help to foster new employment opportunities and assist in improving the overall employment intensity of output growth in South Africa. 2015-05-01T00:00:00Z The accession of Ethiopia to the WTO in the context of its policy on "developmental state" Ermias Abede Addis http://hdl.handle.net/10500/19979 2016-03-09T10:18:15Z 2014-09-01T00:00:00Z The accession of Ethiopia to the WTO in the context of its policy on "developmental state" Ermias Abede Addis Unlike many other international instruments, accession to the WTO does not simply require the commitment of the government to sign and ratify the multilateral agreements. A country needs to make considerable legislative and administrative changes to comply with the standards of the WTO and its members to finalize the negotiation for accession. For governments with impure free market economy policy the challenges amplify. The government of Ethiopia publicly pronounces its adherence to the ideology of the developmental state. On the other hand the nucleus of WTO principles is progressive trade liberalization. Therefore, this dissertation tries to provide some reflection on the paradox created as a result of the divergence in priority between WTO principles and developmental state in the context of Ethiopian desire to join the organization. The research is an interdisciplinary work. The issues that will be discussed are not purely legal in their nature. They have legal, political and economic dimensions. And the main focus of the paper is on trade in services and foreign investment negotiation aspect of the accession. Furthermore the objective of the dissertation is to give some insight for policy makers about the challenges and opportunities that "Developmental State" ideology will pose in the accession process of Ethiopia to the WTO. The research is divided into five chapters. Chapter one gives introductory remarks about the concept of the developmental state and accession to the WTO. The limitations of the WTO accession process and an overview of the features of developmental state in the world and particularly in Ethiopia are also briefly discussed in the chapter. The origin and concept of developmental state in the world, in Africa and Ethiopia is discussed in some detail under chapter two. The chapter also tries to show the impact of developmental state policies in the laws of the country that are going to be deliberated in the process of accession. Chapter three is about accession to the WTO. In this chapter the requirements, benefits, challenges and procedures of accession are dealt in depth. The writer debates and tries to show the fact that the system is slowly shifting from rule based negotiation to power and precedent based negotiation. By analyzing the laws of Ethiopia that are inspired by the principles of developmental state against the legal and precedent requirements to join the WTO, I tried to correlate the findings of chapter two and three in chapter four. Specific strategies and advises on how to move the negotiation forward on certain areas are also outlined in this chapter. Finally, conclusion and my summarized recommendations are placed under chapter five. 2014-09-01T00:00:00Z Examining the effectiveness of the new Basel III banking standards : experience from the South African Customs Union (SACU) banks Musafare, Kidwell http://hdl.handle.net/10500/19156 2015-10-27T09:10:44Z 2015-02-01T00:00:00Z Examining the effectiveness of the new Basel III banking standards : experience from the South African Customs Union (SACU) banks Musafare, Kidwell This dissertation explored the efficacy of the new Basel III banking standards in SACU, grounded on the conjecture that they are not reflective of economies of SACU, but are merely an intensification of Basel II, rather than a substantial break with it. Firstly, loans and assets were tested for causality, since Basel III believes growth in these variables led to securitization. The leverage ratio has been introduced in Basel III as an anti-cyclical buffer. The OLS technique was employed to test for its significance in determining growth in bank assets. SACU feels the impact of debt, with credit is marginally treated in Basel III and is not introspective of the realities of its economies. ANOVA tests using debt, credit and GDP were done to determine a better method of addressing cyclicality. The leverage ratio was insignificant in Namibia, with debt and credit having momentous impacts on GDP in SACU. 2015-02-01T00:00:00Z


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Videoconferencing not only needs intra-stream synchronization to ensure the reconstruction quality of the stream, but also has real time requirement to satisfy the natural interaction between participants. This paper analyzed the components of end-to-end delay in the videoconferencing over wireless campus network with the objective of understanding how to reduce the delay as much as possible. Then a Network Resynchronization Delay Reduction (NRDR) algorithm was proposed to determine the optimal queuing deadline for frames in the network resynchronization, which dominates the end-to-end delay. The NRDR synthetically considers three performance metrics: the queuing delay, the discard probability of frames due to deadline misses, and the variation of discarded frames, in the attempt to obtain a compromise between the end-to-end delay and the intrastream synchronization quality. In the experiment, it was demonstrated that the NRDR is capable of providing the optimal synthesis performance, according to different requirements of videoconferencing participants.