bluuebunny/crossref_metadata_2025 huggingface dataset:
Engineering Applications of Synchrotron X-Rays and Neutrons and the FaME38 Project
Authors: Webster P. J. , Chen Z. , Hughes D. J. , Steuwer A. , Malard B. , Ratel N. , James M. N. , Ting S.-P.
Published: April 2008

Large Central Scientific Facilities such as the ESRF (the European Synchrotron Radiation Facility) and ILL (the European centre for neutron research), were set up to provide scientists with the advanced facilities they need to exploit neutron and synchrotron X-ray beams for scientific research. Engineers also conduct research at these Facilities, but this is less common as most practicing engineers generally have little or no knowledge of neutron or X-ray scattering, or of their considerable potential for engineering research, model validation, material development and for fatigue and failure analysis. FaME38 is the new joint support Facility for Materials Engineering, located at ILL-ESRF, set up to encourage and to facilitate engineering research by engineers at these facilities. It provides a technical and knowledge centre, a materials support laboratory, and the additional equipment and resources that academic and industrial engineers need for materials engineering research to become practicable, efficient and routine. It enables engineers to add the most advanced scientific diffraction and imaging facilities to their portfolio of diagnostic tools. These include non-destructive internal and through-surface strain scanning, phase analysis, radiography and tomography of engineering components. Synchrotron X-ray and neutron diffraction strain mapping is particularly suited for the rigorous experimental, non-destructive, validation of Finite Element and other computer model codes used to predict residual stress fields that are critical to the performance and lifetimes of engineering components. This paper discusses the FaME38 facility and demonstrates its utility in gaining fundamental insight into mechanical engineering problems through examples, including studies of railway rails, welds and peened surfaces that demonstrate the potential of neutron of synchrotron X-ray strain scanning for the determination of residual stress fields in a variety of engineering materials and critical components.
High-Energy Small- and Wide-Angle X-Ray Scattering: A Versatile Tool for Materials Analysis
Authors: Almer Jonathan
Published: April 2008

Acquisition of microstructural information during realistic service conditions is an ongoing need for fundamental materials insight and computational input. In addition, for engineering applications it is often important to be able to study materials over a wide range of penetration depths, from the surface to bulk. In this presentation we discuss developments at the Sector 1-ID beamline of the Advanced Photon Source (APS) to utilize high-energy x-ray scattering for such studies. The use of high-energies (~80 keV) provides a highly penetrating probe, with sampling depths up to several mm in most materials. Through the development and use of high-energy optics, we can perform both small- and wide-angle scattering (SAXS/WAXS), to probe a large range of sample dimensions in reciprocal space (ranging from Angstroms to hundreds of nanometers), with real space resolutions ranging from microns to mm.
Single-Wall Carbon Nanotube Polymer Composites: Investigating Their Percolative Behavior and Physical Performance
Authors: Ounaies Zoubeida , Park Cheol , Harrison Joycelyn
Published: April 2008

In this work, an approach to enhance the electroactive response of polymers is pursued. Single-wall carbon nanotubes (SWNT) nanoinclusions are dispersed in a piezoelectric polyimide. A qualitative assessment of dispersion is done using optical microscopy and high resolution scanning electron microscopy. Key requirements for the resulting nanocomposites are flexibility, and thermal and chemical stability. Electrical and dielectric properties of the SWNT-reinforced polyimide composites are investigated as a function of SWNT concentration. AC and DC conductivities are measured. The experimental dielectric constant was found to obey a percolation-like power law with a relatively low percolation threshold. It is found that addition of the SWNT in the polyimide composites facilitates poling and results in an increase of the piezoelectric properties of the composites. Furthermore, at higher SWNT concentration, a bending strain is observed at relatively low electric fields, indicating the potential of using these composites actuators. Current investigations illustrate the effects of SWNTs on dielectric, piezoelectric and electroactive properties. Further work is ongoing to assess the effect SWNTs on the mechanical and thermal properties of the polyimide matrix.
Properties of Electro-Active Paper and Its Potential as a Bio-Inspired Actuator for Special Applications
Authors: Kim Jaehwan , Jung Woochul , Craft William J. , Shelton John , Song Kyo , Choi Sang H. , Sankar Jag
Published: April 2008

On September 26, 2002, NASA announced that a consortium of six universities including: The University of Maryland, Virginia Tech, The University of Virginia, North Carolina A&T State University, North Carolina State University, and Georgina Tech had submitted the winning proposal for a National Institute of Aerospace. The Institute began formal operations in January of 2003 in Hampton, VA, and its mission included research, education, outreach, and technology transfer. One important focus of the NIA was to stimulate research among its member universities of potential benefit to NASA and to develop additional partnerships to further NIA focus areas. The work described in this paper is such an activity in bio-inspired actuator materials. This work was originally advocated and developed at Inha University, and it is being extended by teams from Inha University, North Carolina A&T State University, and NASA Langley so that the potential for these actuators as devices for special applications is better understood. This paper focuses on important performance characteristics of electro-active paper (EAPap) actuators and the potential of thes actuators to propel autonomous devices. EAPap is a paper that produces large displacement with small force under an electrical excitation. EAPap is made with chemically treated papers with electrodes on both outer surfaces. When electrical voltage is applied to the electrodes, a tip displacement is produced. One drawback in such actuators is that the actual power produced is variable, and the displacement is relatively unstable. Further, the performance tends to degrade in time and as a function of how the papers are processed. Environmental factors also impact the performance of the product including temperature and humidity. The use of such materials in ambulatory devices requires attention to these concerns and further research is needed to find what initial applications are most congruent with EAPap performance and service lift. In this paper, we have extended the knowledge base of EAPap to include additional ranges of temperature and humidity. We have also looked beyond the current tests on cantilevered beam actuators to segmented plate sections and have tested the ability of these actuators to perform as oscillatory devices both in and out of phase, and to chart their performance vs. time humidity and temperature thus emulating a rudimentary wing or walking assembly.
The Role of Intermetallics in Electromigration in Solder Pumps for Lead Free Solder Structure and Its Solder Pad Combination
Authors: Park S. B. , Iyer Ganesh R.
Published: April 2008

It is attempted to quantify the role of intermetallics for the electromigration in flip chip solder interconnects (C4). Intermetallics are formed at the interface of solder and metallic pad where they serve as metallic bonding agent. For the transition to the Pb-free solder interconnects, electromigration is one of the prime reliability concerns. It is observed that some flip chip solder interconnect fails earlier than the estimated time to failure. It is explained by the effect of intermetallics formed by solder and different matching pad metallurgies. This paper quantifies the role of the intermetallics in the time to failure for a system. A series of experiments are being conducted to determine the current exponent and activation energies of the Black’s equation for different solder and pad metallurgy combinations. Two test structures are proposed. The first test structure was made to study the role of the intermetallics and the second structure was made to characterize the pure solder’s electromigration.
Modeling of Combustion of Mono-Carbon Fuels Using the Rate-Controlled Constrained-Equilibrium Method
Authors: Ugarte Sergio , Metghalchi Mohamad , Keck James C.
Published: April 2008

Modeling of a non-equilibrium combustion process involves the solution of large systems of differential equations with as many equations as species present during the process. The process of chemical reaction and combustion is complicated since it may be governed by hundreds, sometimes thousands of microscopic rate processes. Integration of these equations simultaneously becomes more difficult with the complexity of the combustible. In order to reduce the size of these systems of equations, the Rate-Controlled Constrained-Equilibrium method (RCCE) has been proposed to model non-equilibrium combustion processes. This method is based on the Second Law of Thermodynamics, assuming that the evolution of a complex system can be described by a small number of rate-controlling reactions which impose slowly changing constraints on all allowed states of the system, therefore a non-equilibrium system will relax to its final equilibrium state through a sequence of rate controlled constrained equilibrium states. Oxidation induction times and concentration of species during a combustion process are found in a less complicated way with this method, as equations for constraints rather than for species determine the composition and evolution of the system. The time evolution of the system can be reduced since the number of constraints is much smaller than the number of species presents, so the number of equations to solve. The RCCE method has been applied to the stoichiometric combustion of mono-carbon fuels using 29 chemical species and 139 chemical reactions at different sets of pressure and temperature, ranging from 1 atm to 100 atm, and from 900 K to 1600 K respectively. Results of using 8, 9, 10 and 11 constraints compared very well to those of the detailed calculations at all conditions for the cases of formaldehyde (H2CO), methanol (CH3OH) and methane (CH4). For these systems, ignition delay times and major species concentrations were within 5% of the values given by detailed calculations, and computational saving times up to 50% have been met.
Thermal Design Correlations for Single- and Two-Phase Flow of R-407C in Meso-Scale Heat Exchangers
Authors: Shariff Yasir M. , Ravigururajan T. S.
Published: April 2008

The paper presents correlation development for an experimental database done on R-407C flow in meso-scale horizontal channels. Single-phase, two-phase subcooled, and two-phase saturated boiling flow correlations were developed. The variables considered in this study including essential design parameters, such as, channel diameter, coils pitch and diameter. For flow variables considered are the Reynolds number and the Prandtl number. The purpose of this study is to present new design correlations for flow boiling in a ternary refrigerant mixture at a meso-scale size. The relative influences of enhancement design parameters on friction factor and heat transfer were carried in this parametric analysis of the flow boiling correlations. The resulted correlations developed in this study are compared to available published correlations.
X-Ray Imaging of the Filling of “T” Shaped Microchannel Using a MEDIPIX2 Pixel Detector
Authors: Vabre A. , Manach E. , Gal O. , Legoupil S.
Published: April 2008

Fluid flows in “T” or “Y” shaped structures of microchannels are studied in order to develop modeling approaches as well as adapted measurement techniques. The applications of these structures are numerous and concern in particular biology and chemical engineering for which the integration of microchannels in lab-on-chip and/or microreactor is an important challenge. Our works concern the development of a measurement technique for the study of the filling of a “T” shaped microchannel structure by a liquid. In the studied channels, the experimental constraints are strong. Indeed, the space steps involved within the phenomena are very much reduced and vary from 1 to 10 μm. Moreover, the dynamics of the flow implies a high acquisition frequency, ranging from 10 to 100 Hz. Our technological choice is based on the measurement of the attenuation of an X-ray beam in the matter. The main advantage of this non-intrusive technique is that it can be implemented even in media opaque to visible light. Also, that X-ray techniques can theoretically reach a better space resolution than optical ones. The measurement technique is quantitative and a 3D measurement is achievable by tomography. These methods are validated for problems located at centimetric space steps and high acquisition frequencies, [1], [2]. The objective of this work is to match the microfluidics field requirement (space steps and attenuation contrast), while preserving high time frequencies. Our experimental bench consists of a X-ray generator, that makes possible to obtain high enlargements of the observed object whit a reduced blur in the image. The image is obtained by a pixel detector called Medipix2. This detector is under development within a European collaboration which gathers 16 partners around the CERN, the CEA being a partner. The main assets of this detector are its high space resolution, its operational photon counting mode and its high acquisition frequency. The presented works constitute a very first implementation and validation of the proposed technique for the microfluidics field. Experimental results are obtained and presented. They allow a measurement of the filling conditions of the “T” shape structure of microchannels. The orientations and research perspectives to improve the obtained results by the technique could be evaluated accurately and important basis of our work are now established and quantified for the future.
The Curvature Effect on the Heat Transfer at the End of a Bayonet Tube With Laminar Flows
Authors: Sun F. , Li H. , Drummond J. , Wang G.-X.
Published: April 2008

Bayonet tubes, simple refluent heat exchangers, are widely used to heat or cool a media when the heating/cooling agent is readily accessible from one side only. Many studies have been conducted to evaluate the heat transfer performance of bayonet tubes. The majority of these studies focus on the heat transfer in the annular section and little on the end surface. This paper presents a numerical simulation of the laminar flow and heat transfer in a bayonet tube. The simulation is first validated by the experimental data in the literature. The flow and heat transfer in bayonet tubes are then investigated with both flat and curved end surfaces. Both local and average Nusselt number on the end surfaces are calculated under various Re and geometry conditions. Effect of the end surface curvature is studied by comparing the performances of the flat and curved ended bayonet tubes.
Modeling of a 3-Dimensional Conjugate Heat Transfer on the Channel-Composite-Wall for Electronics Cooling
Authors: Yazawa K. , Yoshino H. , Nishino Y. , Nakagawa S. , Ishizuka M.
Published: April 2008

We report the modeling of a novel approach to passive heat transfer from electronic equipment through an enclosure wall with built-in vertical channels. This passive cooling method is based on the different temperature requirements between the enclosure surface and the internal heat-generating devices. This approach takes advantage of natural convection, known as the chimney effect, resulting from higher temperatures in vertically oriented channels. In addition to channel convection, the skin surface exposed to the environment dissipates the heat passively by both natural convection and radiation. The configuration of the wall and channels, termed a Channel-Composite-Wall (CCW), creates a novel form of passive cooling that we have analyzed and modeled. The inner side of the CCW is assumed to be uniformly heated. The three-dimensional flow regime is observed by means of PIV (particle image velocimetry) experiments and numerical studies. The unique velocity profile inside each channel is observed and can be regarded as similar to the flow in the differently heated parallel plates. The channel flow is modeled by breaking the channel down into two sections plus the exposed skin wall. Based on these observations, the relationship between the internal flow field and external convective flow can be considered to be handled separately. The thermal characteristic is also studied based on the correlations. The thermal conductivity and thickness of the solid partition of channels are found to be significant contributors to performance. The analytic model of the CCW was verified by numerical calculations and experiments. The model reasonably closely expresses the characteristics of this comprehensive conjugate heat transfer. The model can thus be used for the development of passively cooled electronics enclosure.
Microfabrication and Packaging Issues in the Development of a Planar Silicon Loop Heat Pipe, Using Si02 Fiber Wicks
Authors: Medis Praveen S. , Parimi Srinivas , Shuja Ahmed , Henderson H. Thurman , Suh Junwoo , Gerner Frank M.
Published: April 2008

The focus of this work is the physical development and performance of an infinitely expandable planar non-standard MEMS loop heat pipe, targeted for electronic cooling. The composition is principally semiconductor grade silicon, with some glass components, requiring neither internal pumps nor external power, except the waste heat which causes its operation. In as much as modern microelectronics is of a planar configuration, the cooling device surfaces (unlike the classical cylindrical heat pipe) should ideally also be planar. Here the authors report such a compatible planar heat pipe, infinitely expandable in surface area, using inexpensive batch processing and glass (silicon dioxide) fiber as the wick. Preliminary results have demonstrated 42 and 65 W/Cm2 in closed and open loop configurations, respectively. These power dissipating levels greatly exceed that required for most emerging CPU's and other electronics.
Analysis of Ultrafast Laser Propagation in Biological Tissues With Embedded Tumors and Large Blood Vessels
Authors: Zhou Jianhua , Zhang Yuwen , Chen J. K.
Published: April 2008

Time-resolved optical imaging technique offers the promise for development of safe, noninvasive, and inexpensive clinical imaging modalities with diagnostic ability. However, the presence of mismatched refractive-index boundaries in a soft tissue will tremendously change light propagation path, which in turn, makes the optical image obscure if not indiscernible. In this article, a time-resolved Monte Carlo model, which takes into account the photon reflection/transmission behavior at the mismatched refractive-index boundaries, is developed to investigate transient light propagation in biological tissues with embedded tumors and blood vessels. The results show that the temporal reflection signal displays two peak values when refractive-index mismatched foreign objects, such as tumors or blood vessels, are embedded in the tissue. One peak is a direct result arising from the pulse nature of the incident laser light, and the other is due to the backscattering from the refractive-index mismatched boundaries. This suggests that the occurrence of the "second peak" be an indication for the location and size of tumors inside the tissue.
Forced Convective Heat Transfer of Nanofluids in Microchannels
Authors: Jung Jung-Yeul , Oh Hoo-Suk , Kwak Ho-Young
Published: April 2008

Convective heat transfer coefficient and friction factor of a nanofluid in rectangular microchannel were measured. An integrated microsystem consisting of a single microchannel on one side and two localized heaters and five polysilicon temperature sensors along the channel on the other side were fabricated. Aluminum dioxide (Al2O3) nanofluids with various particle volume fractions were used in experiment to investigate the effect of the volume fraction of the nanoparticles to the convective heat transfer and fluid flow in microchannels. The convective heat transfer coefficient of the Al2O3 nanofluid in laminar flow regime was measured to be increased up to 15% compared to the distilled water at a volume fraction of 1.8 volume percent without major friction loss. The Nusselt number measured increases with increasing the Reynolds number in laminar flow regime. A new type of convective heat transfer correlation was proposed to correlate experimental data of heat transfer coefficient for nanofluids in microchannels.
Experimental Mapping of Local Heat Transfer Coefficients Under Multiple Piezoelectric Fans
Authors: Kimber Mark , Garimella Suresh , Raman Arvind
Published: April 2008

Piezoelectric fans have been shown to provide large enhancements in heat transfer over natural convection while consuming very little power. These fans consist of a piezoelectric material attached to a flexible cantilever. When driven at resonance, large oscillations at the cantilever tip cause fluid motion, which in turn, results in improved heat transfer rates. In this study, the local heat transfer coefficients are determined experimentally for piezoelectric fans vibrating close to an electrically heated stainless steel foil, and the entire temperature field is observed by means of an infrared camera. Various vibration amplitudes, distances from heater to fan tip (or gap), and fan pitches are considered for both single-fan and two-fan configurations in impinging orientations. Of particular interest is the increase in heat transfer performance with an additional fan present and the dependence of this increase on the variable parameters. Results show nearly uniform cooling within the envelope of vibration for single-fan experiments with small gaps, and the existence of an optimal gap distance which is dependent on vibration amplitude. The benefits of an additional fan include greater coverage area, but the resulting increase in peak convection coefficient is highly dependent on the fan pitch. Conditions exist where constructive interference is observed which causes a roughly 10% increase in peak convection coefficient while significantly increasing the coverage area. Understanding the local performance of piezoelectric fans provides an important tool to help implement these devices in practical cooling systems.
Synthesis and Thermoelectric Measurement of Individual Bismuth Nanowires
Authors: Moore Arden L. , Zhou Feng , Pettes Michael T. , Mavrokefalos Anastassios , Shi Li
Published: April 2008

It has been suggested by theoretical calculations that the thermoelectric figure of merit of bismuth (Bi) nanowires can be much higher than the bulk value because of quantum and classical size effects on electron and phonon transport in the nanowire. Recent advances in nanomaterials synthesis and characterization methods have enabled direct experimental investigation of the nanoscale size effects on thermoelectric properties. In this work, bismuth nanowires are synthesized by vapor deposition into the pores of anodic alumina membranes (AAMs) with variable pore sizes. The thermoelectric properties of individual Bi nanowires obtained from the AAMs were characterized using a new design of a microfabricated device. The presence of a highly stable bismuth oxide coating prohibited good electrical contact with the nanowire, but still allowed for thermal conductivity data to be obtained.
Coupled Electro-Thermal-Phase Change Modeling of a Chalcogenide Switch
Authors: Dhillon Navdeep Singh , Murthy Jayathi Y.
Published: April 2008

A coupled electro-thermal-phase change numerical model is developed to model the threshold and memory switching processes in a chalcogenide switch based on phase change memory (PCM) technology. Coupled electrical and thermal transport coupled to phase change and crystallization kinetics are solved. Charge transport has been implemented using simplified carrier continuity equations with a threshold switching model for electrical conductivity. Heat transfer is modeled using a Fourier model, accounting for latent heat through a fixed-grid enthalpy formulation. Phase change is modeled using the Johnson-Mehl equations for crystallization kinetics. Thermal conductivity and electrical resistivity changes due to phase change are modeled using a local percolation model. The charge transport and circuit equations are fully coupled with the heat transfer and phase change models to accurately simulate the switching process. SET and RESET pulses are simulated to demonstrate that the model is able to capture the underlying physics well.
Miniaturization of Electrostatic Fluid Accelerators
Authors: Hsu C. P. , Jewell-Larsen N. E. , Rollins A. C. , Krichtafovitch I. A. , Montgomery S. W. , Dibene J. T. , Mamishev A. V.
Published: April 2008

Existing thermal management methods for electronics do not meet technology needs and remain a major bottleneck in the evolution of computing, sensing, and information technology. The decreasing size of microelectronics components and the resulting increasing thermal output density require novel cooling solutions. Electrohydrodynamic ionic wind pumps, also known as electrostatic fluid accelerators (EFA), have the potential of becoming a critical element of electronic thermal management solutions. In order to take full advantage of EFA-based thermal management, it is essential to miniaturize EFA technology. This paper demonstrates the successful operation of a meso-scale microfabricated silicon EFA. A cantilever structure fabricated in bulk silicon with a radius of tip curvature of 25 μm is used as the corona electrode. The device was fabricated using a Deep Reactive Ion Etching (DRIE) microfabrication process. Forced convection cooling is demonstrated using infrared imaging, showing a 25°C surface temperature reduction over an actively heated substrate. The fabrication and test results of a meso-scale microfabricated EFA are presented in this paper.
Estimating the Effects of Interface Disorder on the Thermal Boundary Resistance Using a Virtual Crystal Approximation
Authors: Beechem Thomas , Graham Samuel
Published: April 2008

An analytical method is presented to estimate the effects of structural disorder on the thermal boundary resistance (TBR) between 2 materials. The current method is an extension of the diffuse mismatch model (DMM) where the interface is modeled as a virtual crystal of finite thickness with properties derived from those of the constituent materials. Using this virtual crystal extension, the predictive capabilities of the diffuse mismatch method are greatly increased with added insight into the sensitivity of materials to interface quality.
Pressure Drop and Heat Transfer in a Single-Phase Micro-Pin-Fin Heat Sink
Authors: Ho Abel M. Siu , Qu Weilin , Pfefferkorn Frank
Published: April 2008

The pressure drop and heat transfer characteristics of a single-phase micro-pin-fin heat sink were investigated experimentally. Fabricated from 110 copper, the heat sink consisted of 1950 staggered micro-pins with 200×200 μm2 cross-section by 670 μm height. Deionized water was employed as the cooling liquid. A coolant inlet temperature of 25°C, and two heat flux levels, q" eff = 50 W/cm2 and q" eff = 100 W/cm2, defined relative to the planform area of the heat sink, were tested. The inlet Reynolds number ranged from 93 to 634 for q" eff = 50 W/cm2, and 127 to 634 for q" eff = 100 W/cm2. The measured pressure drop and temperature distribution were used to evaluate average friction factor and local averaged heat transfer coefficient/Nusselt number. Predictions of the Moores and Joshi friction factor correlation and the Chyu et al. heat transfer correlation that were developed using macro-size pin-fin arrays were compared to micro-pin-fin heat sink data. While the Moores and Joshi correlation provide acceptable predictions, the Chyu et al. correlation overpredicted local Nusselt number data by a fairly large margin. These findings point to the need for further study of single-phase thermal/fluid transport process in micro-pin-fin heat sinks.
A Remediation Scheme to Global Warming: Engineering Biodegradable Aerosols With Maximum Scattering Potential
Authors: Attinger Daniel , Green Brendan
Published: April 2008

This exploratory study evaluates the following moderation scheme against global warming: deploying nanoparticles in the atmosphere in order to scatter a tiny amount of sunlight (1% or 2W/m2) up to space. Such a strategy could be a last-resort method to counteract unbearable effects of global warming. For particles made of a wide range of known materials, the scattering ability is defined to quantify how efficient the particle is at scattering sunlight. This scattering ability is a function of the particle radius and index of refraction, and is calculated by an in-house numerical code solving the Mie scattering equations. The code is validated against scattering calculations for SO2 particles published by Schwartz[1]. Our calculations show that an optimum particle size exists, which would minimize the amounts to be deployed in the atmosphere. Also, we evaluate the deployment of biodegradable nanoparticles, which would counteract global warming and minimize dangers related to their redeposition.
Thermal Design Guidelines for FC-BGA Package With Hot Spot Problem
Authors: Chen Eason , Lai Jeng Yuan , Wang Yu-Po , Hsiao C. S.
Published: April 2008

With the evolving function integration and power consumption of high-end IC applications, thermal management has become one of the most important concerns of semiconductor designers. In particular, hot spot problem, in recent years, has turned into a popular topic in IC chip thermal management that it comes from the uneven power consumptions in various logical blocks and results in local high temperature that would increase IC chip failure risks. In this paper, thermal evaluations for hot spot impacts on Flip-Chip Ball Grid Array (FC-BGA) packages were presented using CFD modeling technique. The evaluation topics covered hot spot power density effects on substrate designs and heat sink module characterizations including passive heat sink and fan heat sink performance under various hot spot conditions. Finally, thermal suggestions were concluded for package designers to improve the substrate design in substrate via arrangements to effectively dissipate hot spot source. Also heat sink module performance was derived for different ratings of hot spots and external heat sink performance is obtained for the hot spot impact elimination.
CFD Simulations of Flow and Pressure Distributions in Column Flow Type Fuel Cells
Authors: Ridenour Paul , Ma Zhigi , Selvarasu Naresh Kumar , Smotkin Eugene S. , Zhou Chenn Q.
Published: April 2008

Fuel cells are a growing new technology that can be applied in order to harness electrical energy out of hydrogen and hydrated air. When testing these devices however, pressure drops along the apparatus are strongly discouraged due to the fluctuation in gas volumetric flow rate that they incur. The design of the flow channels is critical to the fuel cell performance and water management. In this research, computational fluid dynamics (CFD) is used to analyze the gas manifold and a column channel inside of a fuel cell. The effect of the flow channel parameters on the flow rate and pressure drops are investigated to provide useful information to optimize the design of flow channels.
Optimization of Micro Channel Morphology
Authors: Vadnjal Aleksander , Catton Ivan
Published: April 2008

An increasing demand for a higher heat flux removal capability within a smaller volume for high power electronics led us to focus on micro channels in contrast to the classical heat fin design. A micro channel can have various shapes to enhance heat transfer, but the shape that will lead to a higher heat flux removal with a moderate pumping power needs to be determined. The standard micro-channel terminology is usually used for channels with a simple cross section, e.g. square, round, triangle, etc., but here the micro channel cross section is going to be expanded to describe more complicated and interconnected micro scale channel cross sections. The micro channel geometries explored are pin fins (in-line and staggered), parallel plates and sintered porous micro channels (see Fig.1). The problem solved here is a conjugate problem involving two heat transfer mechanisms; 1) porous media effective conductivity and 2) internal convective heat transfer coefficient. Volume averaging theory (VAT) is used to rigorously cast the point wise conservation of energy, momentum and mass equations into a form that represents the thermal and hydraulic properties of the micro channel (porous media) morphology. Using the resulting VAT based field equations, optimization of a micro channel heated from one side is used to determine the optimum micro channel morphology. A small square of 1 cm 2 is chosen as an example and the thermal resistance, 0C/W, and pressure drop are shown as a function of Reynolds number.
Travelling to China for the Beijing 2008 Olympic Games
Authors: Milne C J , Shaw M T M
Published: April 2008

The Beijing Olympics will be the world’s premier sporting event in 2008. Countries should begin planning for appropriate support for their Olympic athletes. Experienced medical staff should be appointed early and become familiar with the major medical or injury concerns of athletes and officials. Teams should assemble a comprehensive medical kit. Appropriate medical advice can ensure that athletes will arrive in Beijing in optimal condition. Medical issues particularly relevant to competitors at the Beijing Olympics include heat and humidity, waterborne diseases and air pollution. However, the air pollution probably represents less of a threat than previous media reports would indicate. The Olympic village and venues can be thought of as small enclaves located within a rapidly developing country.
Doppler ultrasonography of the anterior knee tendons in elite badminton players: colour fraction before and after match
Authors: Koenig M J , Torp-Pedersen S , Boesen M I , Holm C C , Bliddal H
Published: April 2008

Background

Anterior knee tendon problems are seldom reported in badminton players although the game is obviously stressful to the lower extremities.

Hypotheses

Painful anterior knee tendons are common among elite badminton players. The anterior knee tendons exhibit colour Doppler activity. This activity increases after a match. Painful tendons have more Doppler activity than tendons without pain.

Study design

Cohort study.

Methods

72 elite badminton players were interviewed about training, pain and injuries. The participants were scanned with high-end ultrasound equipment. Colour Doppler was used to examine the tendons of 64 players before a match and 46 players after a match. Intratendinous colour Doppler flow was measured as colour fraction (CF). The tendon complex was divided into three loci: the quadriceps tendon, the proximal patellar tendon and the insertion on the tibial tuberosity.

Results

Interview: Of the 72 players, 62 players had problems with 86 tendons in the lower extremity. Of these 86 tendons, 48 were the anterior knee tendons. Ultrasound: At baseline, the majority of players (87%) had colour Doppler flow in at least one scanning position. After a match, the percentage of the knee complexes involved did not change. CF increased significantly in the dominant leg at the tibial tuberosity; single players had a significantly higher CF after a match at the tibial tuberosity and in the patellar tendon both before and after a match. Painful tendons had the highest colour Doppler activity.

Conclusions

Most elite badminton players had pain in the anterior knee tendons and intratendinous Doppler activity both before and after match. High levels of Doppler activity were associated with self-reported ongoing pain.
Payments to injured professional jockeys in British horse racing (1996–2006)
Authors: Turner M , Balendra G , McCrory P
Published: April 2008

Objective:

To determine the direct and indirect cost of injuries in professional jockeys as a result of race riding.

Design:

Cohort study.

Setting:

Professional horse racing.

Participants:

Professional jockeys in the UK registered with the Jockey Club.

Main outcome measures:

Payouts under the Professional Riders Insurance Scheme (PRIS) for injuries sustained by professional jockeys, which were recorded by the Jockey Club injury database between 1996 and 2006 inclusive.

Results:

In the 11-year period of the study, there were 1328 injuries that resulted in jockeys missing a total of 71 509 days of racing, and as a result PRIS paid out £4 496 019 in compensation. Most injuries were minor, with a third of injured jockeys returning to race riding within 2 weeks and 45% of the claims receiving a payout of <£1000. Almost half the claims were due to fractures, with the clavicle being the most common site of injury. Joint dislocations accounted for the highest insurance payout and the longest time off racing.

Conclusions:

Horse racing is a sport known to have a high risk of injury. This study has found that almost £4.5 million was spent on the injuries that were reported to PRIS during the 11-year time period 1996–2006. This study sheds light on the overall injury cost in professional horse racing and will form the basis for more formal health economic analysis.
Characteristics of KIT-negative gastrointestinal stromal tumours and diagnostic utility of protein kinase C theta immunostaining
Authors: Lee H E , Kim M A , Lee H S , Lee B L , Kim W H
Published: April 2008

Aims:

To characterise KIT-negative gastrointestinal stromal tumours (GISTs) clinically, pathologically, immunohistochemically and genetically, and to establish the usefulness of protein kinase C theta (PKCθ) as a diagnostic marker in KIT-negative GIST.

Methods:

252 consecutive cases of GIST were evaluated for clinicopathological characteristics and immunostained for various antibodies. Mutational analyses ofKITand platelet-derived growth factor receptor α (PDGFRA) were also performed in 62 cases.

Results:

20 (7.9%) GISTs showed negative immunostaining for KIT. KIT-negative GISTs were more likely to originate from omentum or peritoneum, have an epithelioid histology, and be classified as high risk. The overall survival rate of patients with KIT-negative GISTs (5-year survival rate 68.7% (SD 10.7%)) was lower than that of patients with KIT-positive GISTs (5-year survival rate, 79.9% (3.0%)) (p = 0.042, log-rank test). Negative KIT expression was an independent prognostic factor in multivariate Cox regression analysis when the risk of aggressive behaviour and the status of imatinib treatment were adopted as covariates. KIT-negative GISTs also showed lower expression rates of CD34, Bcl-2, and PKCθ than KIT-positive GISTs; mutational analysis revealed that 30% of KIT-negative GISTs harboured aPDGFRAexon 18 mutation. Immunostaining on PKCθ showed that 93.9% of all GISTs expressed PKCθ protein. However, 21.9% of 64 mesenchymal tumours other than GIST also showed positivity on PKCθ.

Conclusions:

KIT-negative GISTs had characteristics that differ from those of KIT-positive GISTs, and negative KIT expression was an independent prognostic indicator for overall survival of patients. Although PKCθ is a sensitive diagnostic marker for GIST, its usefulness is limited because of low sensitivity and low specificity in KIT-negative GISTs.
The combined oxacillin resistance and coagulase (CORC) test for rapid identification and prediction of oxacillin resistance inStaphylococcusspecies directly from blood culture
Authors: Carey B E , Nicol L
Published: April 2008

The combined oxacillin resistance and coagulase (CORC) protocol for rapid identification and determination of oxacillin-susceptibility inStaphylococcusspp from blood culture is described. It incorporates a modified direct tube coagulase test (TCT) and a novel 4-hour multiplication-induction step, which increases the expression of staphylococcal PBP2a if present, facilitating detection by a commercial PBP2a latex agglutination kit. The protocol shows excellent sensitivity and specificity for determination of coagulase-positivity in staphylococci from patient blood cultures (96.8% (95% CI 81.5 to 99.8) and 100% (95% CI 75.9 to 100), respectively, n = 47), and for prediction of oxacillin resistance inS aureusdirectly from patient blood cultures (100% (95% CI 59.8 to 100) and 100% (95% CI 82.2 to 100), respectively (100% accuracy), n = 31) within 5 hours of blood culture positivity.
LATTICE CALCULATIONS ON THE SPECTRUM OF DIRAC AND DIRAC–KÄHLER OPERATORS
Authors: CAMPOS RAFAEL G. , LÓPEZ-LÓPEZ J. L. , VERA R.
Published: April 2008

We use a lattice formulation to study the spectra of the Dirac and the Dirac–Kähler operators on the 2-sphere. This lattice formulation uses differentiation matrices which yield exact values for the derivatives of polynomials, preserving the Leibniz rule in subspaces of polynomials of low degree and therefore, this formulation can be used to study the fermion–boson symmetry on the lattice. In this context, we find that the free Dirac and Dirac–Kähler operators on the 2-sphere exhibit fermionic as well as bosonic-like eigensolutions for which the corresponding eigenvalues and the number of states are computed. In the Dirac case these solutions appear in doublets, except for the bosonic mode with zero eigenvalue, indicating the possible existence of a supersymmetry of the square of the Dirac operator.
FUZZY FLUID MECHANICS IN THREE DIMENSIONS
Authors: RAJEEV S. G.
Published: April 2008

We introduce a rotation invariant short distance cutoff in the theory of an ideal fluid in three space dimensions, by requiring momenta to take values in a sphere. This leads to an algebra of functions in position space that is noncommutative. Nevertheless it is possible to find appropriate analogues of the Euler equations of an ideal fluid. The system still has a Hamiltonian structure. It is hoped that this will be useful in the study of possible singularities in the evolution of Euler (or Navier–Stokes) equations in three dimensions.
OPTIMAL ANTI-CLONING FOR REAL STATE
Authors: ZHANG LI-HUA , SHI BING , CAO ZHUO-LIANG
Published: April 2008

We present two optimal quantum anti-cloning machines for real state in two dimensions, i.e., input state lying in the x–z equator. The first anti-cloning machine produces two outputs which are orthogonal to the input, and the second one produces two anti-parallel outputs for a single input state. The optimal fidelities are also derived.
UTILISING JITTER NOISE IN THE PRECISE SYNCHRONISATION OF LASER PULSES
Authors: MINGESZ RÓBERT , GINGL ZOLTÁN , ALMÁSI GÁBOR , CSENGERI ATTILA , MAKRA PÉTER
Published: April 2008

We present a laser delay control system based on adaptive averaging which utilises the jitter noise of the laser to stabilise the delay more precisely. The system contains delay lines to measure and control the laser delay and a microcontroller that runs our control algorithm. The algorithm regulates the laser delay on the basis of the average of detected delay values, where the steps with which the delay is varied and the averaging length are chosen adaptively, depending on the distance from the target delay. Our complementary numerical simulations show that the jitter of the laser may play a beneficial role here: the error of the delay has a distinct minimum at a non-zero noise level. In a way similar to the dithering principle applied in analogue-to-digital conversion, averaging the noise-modulated detection instances yields a precision in setting the delay that is well beyond the resolution provided by detection time windows, and is close to the theoretical limit determined by the step size of the delay line we applied.
APPLICATION OF GENETIC ALGORITHMS FOR OVERALL OPTIMIZATION OF AN ACTIVE NOISE CONTROL SYSTEM IN AN ENCLOSURE
Authors: MONTAZERI ALLAHYAR , POSHTAN JAVAD , KAHAIE MOHAMMAD HOSSEIN
Published: April 2008

One of the main important aspects in designing an active control system is the optimization of position and number of sensors and actuators. In this paper this problem is addressed for the implementation of a multi-channel active noise control (ANC) system with the aim of global reduction of broadband noise in a telephone kiosk. This includes optimizing the locations for loudspeakers and microphones, finding proper size of the control system, i.e. the number of loudspeakers and microphones, and optimization of the control signals. The mean of acoustic potential energy in the enclosure in a frequency range of 50 Hz to 300 Hz is selected as the performance index for optimization purpose. Several genetic algorithms are proposed and compared to find the global minimum of this performance index. In order to have a better performance in reaching the global minimum, the parameters of these genetic algorithms are tuned, and the best genetic algorithm is selected among them. The main difference between the proposed algorithms is the used coding scheme. Numerical simulations of the acoustical potential energy and also sound pressure at the height where the head of a person may be located, confirms the optimality of the locations proposed by the genetic algorithm.
MODELING AND SIMULATION OF COUPLING EFFECT ON LOW FREQUENCY NOISE IN ADVANCED SOI MOSFETS
Authors: ZAFARI LEILY , JOMAAH JALAL , GHIBAUDO GERARD
Published: April 2008

Low frequency noise modeling and numerical simulation have been carried out to study the influence of the back interface quality and the silicon film thickness in Fully Depleted SOI MOSFETs, with special emphasis on the coupling effect. In devices with a standard film thickness, the noise level is higher than for an equivalent interface in bulk device, which could be a great concern for analog applications. On the other hand, it has been shown that in very thin SOI devices with a symmetrical structure (Double Gate architecture), the reduction of electric field in the silicon film, induces a conduction channel in the middle of the film, away from both interfaces which in turn reduces the scattering rate of carriers, decreasing the noise level.
CFD ANALYSIS OF CONJUGATE NATURAL CONVECTION IN A VERTICAL ANNULUS
Authors: REDDY P. VENKATA , NARASIMHAM G. S. V. L. , RAO S. V. RAGHURAMA , JOHNY T. , KASIVISWANATHAN K. V.
Published: April 2008

Conjugate natural convection in a vertical annulus with a centrally located vertical heat generating rod is studied numerically. The governing equations are discretized on a staggered mesh and are solved using a pressure-correction algorithm. A parametric study is performed by varying the Grashof number, aspect ratio, and the solid-to-fluid thermal conductivity ratio over wide ranges with the Prandtl number fixed at 0.7. Results are presented for the variation of several quantities of interest such as the local Nusselt numbers on the inner and outer boundaries, the axial variation of the centerline and interface temperatures, maximum solid, average solid and average interface temperature variations with Grashof number, and the average Nusselt number variation for the inner and outer boundaries with Grashof number. The average Nusselt number from the conjugate analysis is found to be between the Nusselt numbers of the isothermal and the isoflux cases. The average Nusselt numbers on the inner and outer boundaries show an increasing trend with the Grashof number. Correlations are presented for the Nusselt number and the dimensionless temperatures of interest in terms of the parameters of the problem.