bluuebunny/crossref_metadata_2025 huggingface dataset:
Introduction of a Wheel-Rail and Wheel-Roller Contact Model for Independent Wheels in a Multibody Code
Authors: Bosso N. , Gugliotta A. , Soma` A.
Published: January 2009

This paper reports the introduction of a contact model on multibody codes to simulate both wheel/rail and wheel/roller contact for independent wheel railway vehicle. The contact model has been developed both through external subroutines (used to develop the friction model and the determination of the creepages) and using standard element of the MBS code (used to define the cinematic constraints of the wheel). This model can be introduced in a general railway vehicle model with no limitations: each “contact element” so defined can be applied between two bodies of the MBS the one representing the wheel, the other the rail or the roller. It is possible to choose among several algorithms to solve the friction problem: the Fastsim code, the Polach’s method, the linearized Kalker method or a simplified analytical method with saturation. It is also possible to perform simulations using constant value for the friction coefficient and for the normal load (fast simulations) or to use a non-linear law for the friction coefficient and the actual value for the normal load on the wheel. Due to the structure of the code it is possible to change the shape of the wheels profiles during the simulations even if at the moment this features has not been introduced in the code. Finally In the paper is compared the behavior of a bogie on rail and on roller.
Remote Ride Quality Monitoring of Acela Train Set Performance
Authors: Ackroyd Patrick , Angelo Steven , Nejikovsky Boris , Stevens Jeffrey
Published: January 2009

Federal Track Safety Standards require daily measurements of car body and truck accelerations on trains operating at speeds above 125-MPH. In compliance with this requirement, twelve high-speed Acela coaches, operating in the Northeast Corridor between Boston, MA, and Washington DC, have been equipped with remote monitoring systems. The systems provide continuous measurement of car body and truck motions, detect various acceleration events, tag them with GPS time and location information, and deliver the data to Central Processing Stations through wireless communications channels. The Central Processing Stations installed at the National Railroad Passenger Corporation (Amtrak) and ENSCO, Inc., headquarters provide email and pager notifications to designated Amtrak officers and also make the data available to them over secure Intranet and Internet connections. The overall architecture has multiple levels of protection and redundancy in order to ensure high reliability and availability of the service. The systems have been in continuous operation for over a year and provided a multitude of valuable information. Examples of system-reported acceleration events include events caused by track irregularities and train handling. The paper also describes some of the real-life operational scenarios and situations that arise when autonomous remote monitoring systems are used, including wireless communications coverage issues, GPS location pitfalls, and maintenance issues.
Optical Waveguide System for Solar Energy Utilization in Space
Authors: Nakamura T. , Case J. A. , Senior C. L. , Jack D. A. , Cuello J. L.
Published: January 2009

In the past 10 years, Physical Sciences Inc. has been developing the Optical Waveguide (OW) System for solar energy utilization. In this system, solar radiation is collected by the concentrator which transfers the concentrated solar radiation to the OW transmission line. The OW transmission line transports the solar radiation to the location of solar energy utilization. Applications of this system include: material processing and plant lighting in space as well as power generation. In this paper we present a review of our work conducted during the last 10 years on the lunar material processing and space-based plant growing.
Optimization of a Novel Combined Power/Refrigeration Thermodynamic Cycle
Authors: Lu Shaoguang , Goswami D. Yogi
Published: January 2009

A novel combined power/refrigeration thermodynamic cycle is optimized for thermal performance in this paper. The cycle uses ammonia-water binary mixture as a working fluid and can be driven by various heat sources, such as solar, geothermal and low temperature waste heat. It could produce power as well as refrigeration with power output as a primary goal. The optimization program, which is based on the Generalized Reduced Gradient (GRG) algorithm, can be used to optimize for different objective functions. Examples that maximize second law efficiency, work output and refrigeration output are presented, showing the cycle may be optimized for any desired performance parameter. In addition, cycle performance over a range of ambient temperatures was investigated. It was found that for a source temperature of 360K, which is in the range of flat plate solar collectors, both power and refrigeration outputs are achieved under optimum conditions. All performance parameters, including first and second law efficiencies, power and refrigeration output decrease as the ambient temperature goes up. On the other hand, for a source of 440K, optimum conditions do not provide any refrigeration. However, refrigeration can be obtained even for this temperature under non-optimum performance conditions.
Solar Air Conditioning Systems With PCM Solar Collectors
Authors: Gonza´lez Jorge E. , Alva S. Luis Humberto
Published: January 2009

This paper investigates the technical feasibility of using a compact, air-cooled, solar absorption air conditioning system when coupled to an innovative array of solar collectors. The particular absorption system of study is a single effect that uses lithium bromide and water as the absorbent and refrigerant fluid pair. The geographical location of interest is Puerto Rico and similar subtropical regions. The heat input to the absorption system generator is provided by an array of novels flat plate solar collectors that integrate the thermal storage component into them. The proposed collectors have a phase change material (PCM) integrated into them as a storage mechanism. The PCM-integrated solar collector eliminates the need of conventional storage tanks reducing cost and space. The present work uses a paraffin-graphite composite as the PCM to increase the conductivity of the PC matrix. The paraffin’s melting point is around 89°C that is appropriate for use in absorption systems. The mathematical model that describes the thermal process in the PCM is presented and differs from the analysis of conventional flat plate solar collectors. The proposed model for the PCM considers the temporal changes but not the spatial variations. The resulting set of equations for the fluid flow, the PCM, and the collector’s surface are solved simultaneously. Results for the collectors’ thermal performance are presented along with the effects of the composition of the PCM material. The thermal performance of an absorption machine coupled to an array of the proposed PCM’s solar collectors was investigated for nominal cooling capacities of 10.5, 14, and 17.5 kW. These cooling loads are suitable for a typical house or a small business building in Caribbean Islands. Computer simulations were conducted to evaluate the overall system’s performance when subjected to dynamic cooling loads. Within the computer model, heat and mass balances are conducted on each component of the system, including the solar collectors, the air-cooled condenser, and the air-cooled absorber. Comparisons are made with an absorption air conditioning system that uses a cooling tower with conventional flat plate collectors instead of air-cooled and PCM components. Useful information about physical dimensions of collectors, number of collectors needed, and efficiency of the overall system is presented.
A Simple Technique for Evaluating the Performance of Grid Connected Inverters
Authors: Schripsema Jason , Culik Jerry
Published: January 2009

One of the challenges associated with evaluating the reliability of a large number of grid-connected (GC) photovoltaic (PV) systems is the expense of the measurement and data logging equipment required to measure typical operating parameters for these system. In order to fully monitor a PV system, it is necessary to measure plane of array solar irradiance, solar spectrum, array temperature, DC voltage, and DC current as well as the AC voltage, AC current, and AC power produced by the inverter. This paper presents a technique for evaluating several aspects of the performance and reliability of a grid-connected PV system using just one AC power meter / data logger to record the minimum, maximum, and mean power produced by the system over small segments of time. The data can then be graphed to quickly identify a wide variety of inverter problems, several examples of which are presented.
Photocatalytic Oxidation of Toluene in Water From an Algae Pond With High Dissolved Oxygen Content
Authors: Vijayaraghavan Sanjay , Goswami D. Y.
Published: January 2009

Water in well-mixed ponds containing photosynthetic algae has been observed to have an extremely high Dissolved Oxygen (DO) content. Up to four times saturation levels of DO have been recorded. Since DO is known to have an important role in the photocatalytic oxidation of organic contaminants in water, it was hypothesized that a faster rate of contaminant destruction would be observed in water drawn from algae ponds supersaturated with DO. In order to verify this hypothesis a bench scale, batch type photoreactor was constructed. Some baseline tests were performed to investigate the influence of UV intensity, water pH and DO content on the photocatalytic destruction of toluene in water. An array of ultraviolet “blacklight” lamps in a lamp box was used to simulate solar ultraviolet radiation. First-order reaction rate constants were calculated from the destruction data, using a kinetic model proposed earlier. The reaction was found to proceed forward equally fast at pH 4 and 10. A power law relation was derived for the reaction rate dependence on UV intensity. Presence of DO in the water was found to be required for the reaction to go forward. Water from an algae pond, supersaturated with dissolved oxygen was spiked with toluene and destruction tests were then conducted in the same reactor. These tests did not show the expected improvement in destruction rates.
Solar Chimney Turbine: Part 1 of 2 — Design
Authors: Gannon Anthony J. , von Backstro¨m Theodore W.
Published: January 2009

The solar chimney is a simple renewable energy source consisting of three main components, a solar collector, chimney and turbine. Air under the collector is heated by the greenhouse effect. This less dense air rises up a chimney at the collector centre and drives an electricity-generating turbine. The operation of a solar chimney power plant is simple but high component efficiencies are needed for successful operation. A turbine design based on the design requirements for a full-scale solar chimney power plant is presented. The design integrates the turbine with the chimney. It is proposed that the chimney base legs be offset radially to act as inlet guide vanes and introduce pre-whirl before the rotor to reduce the exit kinetic energy. A three-step turbine design method is presented. A free vortex analysis method is used to determine the major turbine dimensions. A matrix throughflow method predicts the flow path through the inlet guide vanes and rotor. Finally the blade profiles are design using an optimization scheme coupled to a surface vortex method to achieve blades of minimum chord and low drag. The proposed turbine design can extract over 80% of the power available in the flow.
A Compact Model for Spherical Rough Contacts
Authors: Bahrami M. , Yovanovich M. M. , Culham J. R.
Published: January 2009

The contact of rough spheres is of high interest in many tribological, thermal, and electrical fundamental analyses. Implementing the existing models is complex and requires iterative numerical solutions. In this paper a new model is presented and a general pressure distribution is proposed that encompasses the entire range of spherical rough contacts including the Hertzian limit. It is shown that the non-dimensional maximum contact pressure is the key parameter that controls the solution. Compact expressions are proposed for calculating the pressure distribution, radius of the contact area, elastic bulk deformation, and the compliance as functions of the governing non-dimensional parameters. The present model shows the same trends as those of the Greenwood and Tripp model. Correlations proposed for the contact radius and the compliance are compared with experimental data collected by others and good agreement is observed.
The Actual Eyring Models for Thixotropy and Shear-Thinning: Experimental Validation and Application to EHD
Authors: Bair Scott
Published: January 2009

The Eyring sinh law is presently the most well accepted model for shear-thinning of EHD lubricants at high pressure. It was, however, not accepted for this purpose by Eyring who found it to be of only limited usefulness for thixotropy. Then, it is extremely important that these models receive a critical review using data obtained by modern methods to evaluate the actual Eyring models and show how they differ from the model in use today. Data from high-pressure viscometers were used to validate the actual Eyring models. The Ree-Eyring model for shear-thinning obeys time-temperature-pressure superposition. A film thickness calculation shows it to suffer from the same anomalous behavior in sliding contact as does the sinh law.
Combined Navier-Stokes and Bulk-Flow Analysis of Hybrid Bearings: Radial and Angled Injection
Authors: Helene Mathieu , Arghir Mihai , Frene Jean
Published: January 2009

The present work deals with the Navier-Stokes and bulk-flow analysis of hybrid bearings intended for use in aerospace applications. These bearings are expected to work at high rotational speeds and high feeding pressures. In such a case, the pressure in the shallow pockets of the bearing is no longer constant and is influenced by hydrostatic and hydrodynamic effects. It has been shown in the literature that the recess pressure pattern can have an important influence on the dynamic characteristics of the bearing. The present work investigates the pressure field in the recess of centered hybrid bearings with radial and angled injection by using a numerical Navier Stokes analysis. The recess pressure pattern is then subsequently characterized by combining these results with some parametric descriptions. For calculating the dynamic characteristics of the bearing, the parametric pressure pattern is then injected into a bulk-flow model that is an alternative analysis of the one introduced by San Andre´s [3, 4]. In order to evaluate the validity of the bulk-flow code, the numerical predictions are compared with experimental data taken from the literature for radial and angled injection. The favorable effect of the counter-rotating angled injection is then explained by using the velocity field issued from the Navier Stokes analysis and the pressure field given by the bulk-flow model.
Extracting Summit Roughness Parameters From Random Gaussian Surfaces Accounting for Asymmetry of the Summit Heights
Authors: Yu Ning , Polycarpou Andreas A.
Published: January 2009

The random Gaussian surface model proposed by Nayak is important to many statistical summit-based micro contact models. A Gaussian distribution is usually assumed for the summit heights as many surfaces have a Gaussian distribution of surface heights. In this work, based on Nayak’s models the skewness and kurtosis of the summit heights distribution are derived as a function of the bandwidth parameter α. The correctness of these two equations verified using a numerical scheme that generates random Gaussian surfaces with various α values. Also, practical contact simulations are performed to demonstrate the significance of the proposed equations and also to show the error of using a Gaussian distribution versus a correct asymmetric distribution for the summit heights.
Experimental and Numerical Investigation of Dynamic Instability in the Head Disk Interface at Proximity
Authors: Ambekar Rohit , Gupta Vineet , Bogy David B.
Published: January 2009

As the flying height decreases to achieve greater areal density in hard disk drives, different proximity forces act on the air bearing slider, which results in fly height modulation and instability. Identifying and characterizing these forces has become important for achieving a stable fly height at proximity. One way to study these forces is by examining the fly height hysteresis, which is a result of many constituent phenomena. The difference in the touchdown and takeoff rpm (hysteresis) was monitored for different slider designs, varying the humidity and lubricant thickness of the disks, and the sliders were monitored for lubricant pickup while the disks were examined for lubricant depletion and modulation. Correlation was established between the observed hysteresis and different possible constituent phenomena. One such phenomenon was identified as the Intermolecular Force from the correlation between the lubricant thickness and the touchdown velocity. Simulations using 3D dynamic simulation software explain the experimental trends.
Theoretical Investigation in Thermoelastohydrodynamic Lubrication With Non-Newtonian Lubricants Under Heavy Load Change
Authors: Mongkolwongrojn Mongkol , Thammakosol Kasame
Published: January 2009

The time-dependent thermal compressible elastohydrodynamic (EHD) lubrication of sliding line contact has been developed to investigate the effect of a sudden load change. The time-dependent modified Reynolds equation with non-Newtonian fluids has been formulated using power law’s model. In this study, the non-Newtonian dilatant fluids for liquids-solid lubricants have been purposed experimentally using the common solid particles namely, Molybdenum disulfide (MoS2) and Polytetrafluoroethylene (PTFE). The simultaneous systems of modified Reynolds and elasticity and energy equations with initial conditions were solved numerically using multigrid multilevel technique. The performance characteristics of the thermoelastohydrodynamic under line contact were presented with varying time for the pressure distribution, temperature distribution and oil film thickness. The transient response of the line contact between two surfaces was simulated under a heavy step load function. The coefficients of friction were also presented in this work at steady state condition with varying particle concentration. This simulation showed a significant effect of liquid-solid on thermoelastohydrodynamic (TEHD) lubrication under heavy load conditions.
Effect of Intermolecular Forces on the Static and Dynamic Performance of Air Bearing Sliders: Part II — Dependence of the Stability on Hamaker Constant, Suspension Preload and Pitch Angle
Authors: Gupta Vineet , Bogy David B.
Published: January 2009

Intermolecular and surface forces contribute significantly to the total forces acting on air bearing sliders for flying heights below 5nm. Their contributions to the total forces increase sharply with the reduction in flying height, and hence their existence can no longer be ignored in air bearing simulation for hard disk drives. Various experimentally observed dynamic instabilities can be explained by the inclusion of these forces in the model for low flying sliders. In this paper parametric studies are presented using a 3-DOF model to better understand the effect of the Hamaker constants, suspension pre load and pitch angle on the dynamic stability/instability of the sliders. A stiffness matrix is used to characterize the stability in the vertical, pitch and roll directions. The fly height diagrams are used to examine the multiple equilibriums that exist for low flying heights. It has been found that the system instability increases as the magnitude of the van der Waals force increases. It has also been found that higher suspension pre load and higher pitch angles tend to stabilize the system.
Vibration Monitoring and Damage Quantification of Faulty Ball Bearings
Authors: Choy F. K. , Zhou J. , Braun M. J. , Wang L.
Published: January 2009

More often then not, the rolling element bearings of rotating machinery are the mechanical components that are first prone to premature failure. Early warning of an impending bearing failure is vital to the safety and reliability of high-speed turbo-machinery. Presently, vibration monitoring is one of the most applied procedures in on-line damage and failure monitoring of rolling element bearings. This paper presents results from an experimental rotor-bearing test rig where quantified damage was induced in the supporting tapered ball bearings. Subsequently the vibration signature due to damage at the inner race of the bearing is examined. Four on-line vibration signature analyzing schemes are used concomitantly: (i) time averaging, (ii) frequency domain analysis, (iii) joint time-frequency analysis (Wigner-Ville and wavelet transforms) and (iv) chaotic vibration analysis (modified Poincare diagrams). The size/level of the damage is corroborated with the vibration amplitude and the resulting relationships are linearized to provide quantification criteria for bearing progressive failure prediction. The results from the above mentioned methodologies are compared for accuracy and redundancy, thus increasing the reliability for early detection of bearing damage and failure. It is shown that the use of the modified Poincare map can provide an effective way for identification and quantification of bearing damage in rolling element bearings.
Unsteady Analysis of a Mechanical Seal Using Duhamel’s Method
Authors: Salant Richard F. , Cao Bin
Published: January 2009

An unsteady numerical model of a mechanical seal, with mixed lubrication, has been developed. The thermal analysis is performed using Duhamel’s method is combination with a numerical experiment to determine Duhamel’s auxiliary function. The results using this semi-empirical approach compare well with those from a finite element analysis. The model has been used to predict the performance of a mechanical seal during startup and shutdown.
TEHD Analysis of Thrust Bearings With PTFE-Faced Pads
Authors: Glavatskih S. B. , Fillon Michel
Published: January 2009

Results of a combined theoretical and experimental investigation into the operation of thrust bearings with PTFE-faced pads are reported. Bearing performance is analysed in terms of temperature, power loss, oil film thickness and pressure. These parameters are first calculated using a THD model. The effect of PTFE facing on bearing thermal performance is then presented and discussed. A TEHD model is subsequently employed. Obtained TEHD results show that oil film thickness and temperature are strongly affected by the PTFE layer. Theoretical results are compared with measured temperature, oil film thickness and pressure.
Theoretical Modeling and Simulation of Piston Ring Assembly of an IC Engine
Authors: Mistry Kishore , Bhatt D. V. , Sheth N. R.
Published: January 2009

Frictional losses in an IC engine are observed between 17–19% of total induced horsepower. 35–45% frictional losses observed due to piston ring assembly only from the above-referred total frictional loss. Lubrication system is for reducing the frictional losses and under the total hydrodynamic lubrication system, if made it feasible, above referred losses can be reduced considerably. Wear normally observed at TDC and BDC during the power stroke. Experimental set-up is prepared by using used piston-cylinder assembly of an engine. Experiment methodology is adopted based on certain assumption and simulated the entire system with an extra drive system by an electric motor with a provision of various speed availability. Various pockets on cylinder liner of 2mm diameter are located on the periphery of cylinder liner to offer lubrication to the system. Care was taken to control the rate of lubrication flow with the help of control knob. Seven different profiles on piston ring were generated and measured. Friction force is calculated by power consumption measurement under different dynamic condition with a variation of 5-speed, 3- lubricants and different 8- types of piston ring geometry are experimented under different combination and results are tabulated. Graphs are plotted for friction force v/s speed for different lubricants and piston ring profiles. Effect of lubricants (SAE30, 15W40& 2T) and ring geometry are compared.
Experimental and Theoretical Study of Instantaneous Piston Assembly Friction in a Gasoline Engine
Authors: Mufti Riaz A. , Priest Martin , Chittenden Richard J.
Published: January 2009

A piston assembly friction model has been developed to predict the individual performance of compression rings, the oil control ring and the piston skirt. Validation of this model has been undertaken by comparing the predicted results with the experimental measurements of piston assembly friction in a gasoline engine under fired conditions using the IMEP (indicated mean effective pressure) method. The experimental results for an SAE 0W20 without friction modifier were compared with the predictions. The predicted results correlate very well with the measurements, especially at higher lubricant inlet temperatures. Piston skirt friction was predicted using both a simple concentric / cylinder model and a more realistic but computationally intensive method incorporating piston secondary motion. The results clearly indicate than the latter more realistic method is required to achieve satisfactory correlation with the measured data.
Prediction of Nano-Scale Wear: An Analytical Approach
Authors: Roy Chowdhury S. K.
Published: January 2009

When two surfaces touch each other, intimate contacts occur at the tips of the asperities and adhesional interaction between the solids arising out of the surface forces becomes significant. This effect need be considered in MEMs, micro-machines, magnetic storage systems other such situations where the surfaces are inherently smooth and loads are extremely low. Surfaces in these and many other tribological contacts may have sub-micron or even nanometric levels and the stochastic model for rough surfaces that typically applies to engineering surfaces is not suitable. The rough surface model is these circumstances must cover asperities ranging from nanometer to micrometer level and this essentially needs a fractal approach. The paper describes a theoretical study of adhesive wear at the contact between surfaces with nanometric level asperities at low loads using a fractal contact model and taking into account the surface forces. The model predicts wear between solids with wide range of material and surface properties. The results broadly confirm the experimental observation such as dependence of wear volume on normal load and also on adhesion due surface forces. Furthermore the fractal analysis gives a generalized solution and depending on the combinations of material and fractal parameters specific solutions, relevant to realistic situations may be arrived at, are obtained. Under certain parametric combinations high wear even under tensile load is predicted while near zero wear is expected for some another set of parameters. These predictions are certainly advantageous in the selection of surface and material properties in applications where loads are small and surfaces are ultra smooth.
Effects of Rolling Friction of the Balancing Balls on the Automatic Ball Balancer for Optical Disk Drives
Authors: Chao Paul C.-P. , Chiu Chi-Wei , Sung Cheng-Kuo , Leu Hui-Chung
Published: January 2009

This study is devoted to evaluate the performance of an automatic ball-type balance system (ABB) installed in optical disk drives (ODD) with consideration of the rolling friction between the balancing balls and the ball-containing race of the ABB. Researches have been conducted to study the performance of the ABB by investigating the nonlinear dynamics of the system; however, the rolling friction model adopted was a simple stick-slip type, which does not reflect the true contact dynamics between rolling balls and their races, leading to an inaccuracy in predicting ABB performance. In this study, a complete dynamic model of the ABB including a detailed rolling friction model based on contact mechanics is established. The method of multiple scales is then applied to formulate a scaled model to find all possible steady-state ball positions and analyze stabilities. It is found that possible steady-state residing positions of the ball inside the race are multiple and form continuous ranges. Numerical simulations and experiments are conducted to verify the validness of the theoretical findings. The obtained results are used to predict the level of residual vibration, with which the guidelines on dimension design and material choices of the ABB are distilled to achieve desired performance.
A Non-Phenomenological Account of Friction/Vibration Interaction in Rotary Systems
Authors: Farhang Kambiz , Lim Aik-Liang
Published: January 2009

The mathematical formulation relates the tribological events at micron-scale and the macroscopic scale vibration response of a two-disk brake system. This is accomplished by a visco-elastic account of interaction at the micron scale, its statistical quantification through the approximate analytical representation of the statistical expectation of contact force and the introduction of the contact force into the macro-scale dynamics of the two-disk system. Steady-state analysis of the system establishes the relation between friction torque and speed and supports observed behavior of many mechanical systems with friction. It is shown that, as a result of coupling of the macro-system’s dynamics and contact, there are combinations of parameters at the micro- and macro-scale that yield negative slope in friction torque/sliding speed relation, a well known source of dynamic instability. This results in an effective negative damping that tends to reduce with decrease in the normal load and/or increase in structural damping of the system.
Vision-Based Microtribological Characterization of Linear Microball Bearings
Authors: Tan X. , Modafe A. , Hergert R. , Ghalichechian N. , Shapiro B. , Baras J. S. , Ghodssi R.
Published: January 2009

Microball bearings can potentially provide robust and low friction support in micromachines such as micromotors and microgenerators. Their microtribological behavior needs to be investigated for design and control of such micromachines. In this paper a vision-based, non-intrusive measurement method is presented for characterization of friction in linear microball bearings. Infrared imaging is used to directly observe the dynamics of microballs and track the motion of bearing components. It is verified that microballs roll most of the time with occasional sliding or bumping resulting from fabrication nonuniformity. The friction-velocity curve demonstrates evident hysteresis. The dependence of frictional behavior on several factors is studied.
Finite Element and Gradient-Based Optimization Tools for Multi-Parameter Nanoindentation Characterization of Materials With Non-Linear Stress/Strain Behavior
Authors: Ovaert Timothy C. , Wang Jianjun
Published: January 2009

The nanoindentation method is becoming increasingly popular for materials characterization, particularly for thin-films, coatings, and other materials that do not easily lend themselves to standard mechanical test methods. However, nanoindentation methods are limited when it comes to their description of a material behavior that deviates from simple elastic or visco-elastic responses. In this paper, we describe a four-parameter constitutive model that has been implemented in a PC-based analysis tool that combines non-linear finite element modeling with data mining gradient-based optimization methods to solve for the unknown parameters from an experimental nanoindentation creep curve. This “VNDM” (virtual nanoindentation and data mining) method, then, is used to complement experimental nanoindentation creep tests for more thorough material characterization. The results verify that the parametric model is capable of describing a wide-range of material behavior, including elastic, visco-elastic, and visco-plastic responses.
Thermodynamics of Capillary Adhesion in MEMS
Authors: de Boer Maarten P. , de Boer P. C. T.
Published: January 2009

In this extended abstract, we briefly describe a thermodynamic model to treat capillary adhesion energies in MEMS. We first determine the constitutive laws of a capillary pendular ring bridging an asperity to a substrate. We find that the work of adhesion, W, depends on the surface separation rate. For the constant volume case (rapid surface separation), W = 2γ (where γ is the surface energy per unit area of the liquid-air interface), but if thermodynamic equilibrium is maintained (slow surface separation), W = γ. Thermodynamic analysis indicates that heat from the system walls can lower the work of adhesion at slow separation rates. We extend these constitutive laws to a simple multi-asperity surface in which the asperities are all of constant height. At low vapor partial pressures (p/psat), adhesion can be several orders of magnitude below γ because of incomplete wetting. As vapor partial pressure increases, condensing liquid fills in the geometric irregularities of the surface. As this filling takes place, W approaches 2γ for both the slow and rapid separation rates.
REVISITING MATRIX PRODUCT ON MASTER-WORKER PLATFORMS
Authors: DONGARRA JACK , PINEAU JEAN-FRANÇOIS , ROBERT YVES , SHI ZHIAO , VIVIEN FRÉDÉRIC
Published: January 2009

This paper is aimed at designing efficient parallel matrix-product algorithms for homogeneous master-worker platforms. While matrix-product is well-understood for homogeneous 2D-arrays of processors, there are two key hypotheses that render our work original and innovative:

— Centralized data. We assume that all matrix files originate from, and must be returned to, the master. The master distributes both data and computations to the workers. Typically, our approach is useful in the context of speeding up MATLAB or SCILAB clients running on a server (which acts as the master and initial repository of files).

— Limited memory. Because we investigate the parallelization of large problems, we cannot assume that full matrix panels can be stored in the worker memories and re-used for subsequent updates. The amount of memory available in each worker is expressed as a given number of buffers, where a buffer can store a square block of matrix elements. These square blocks are chosen so as to harness the power of Level 3 BLAS routines; they are of size 80 or 100 on most platforms.

We have devised efficient algorithms for resource selection (deciding which workers to enroll) and communication ordering (both for input and result messages), and we report a set of MPI experiments conducted on a platform at the University of Tennessee.
A SYSTEMATIC SCAN FOR 7-COLOURINGS OF THE GRID
Authors: JALSENIUS MARKUS , PEDERSEN KASPER
Published: January 2009

We study the mixing time of a systematic scan Markov chain for sampling from the uniform distribution on proper 7-colourings of a finite rectangular sub-grid of the infinite square lattice, the grid. A systematic scan Markov chain cycles through finite-size subsets of vertices in a deterministic order and updates the colours assigned to the vertices of each subset. The systematic scan Markov chain that we present cycles through subsets consisting of 2×2 sub-grids and updates the colours assigned to the vertices using a procedure known as heat-bath. We give a computer-assisted proof that this systematic scan Markov chain mixes in O( log n) scans, where n is the size of the rectangular sub-grid. We make use of a heuristic to compute required couplings of colourings of 2×2 sub-grids. This is the first time the mixing time of a systematic scan Markov chain on the grid has been shown to mix for less than 8 colours. We also give partial results that underline the challenges of proving rapid mixing of a systematic scan Markov chain for sampling 6-colourings of the grid by considering 2×3 and 3×3 sub-grids.
TOTALLY NON-COISOTROPIC DISPLACEMENT AND ITS APPLICATIONS TO HAMILTONIAN DYNAMICS
Authors: GÜREL BAŞAK Z.
Published: January 2009

In this paper, we prove the Conley conjecture and the almost existence theorem in a neighborhood of a closed nowhere coisotropic submanifold under certain natural assumptions on the ambient symplectic manifold. Essential to the proofs is a displacement principle for such submanifolds. Namely, we show that a topologically displaceable nowhere coisotropic submanifold is also displaceable by a Hamiltonian diffeomorphism, partially extending the well-known non-Lagrangian displacement property.
MAXIMUM PRINCIPLES AROUND AN EIGENVALUE WITH CONSTANT EIGENFUNCTIONS
Authors: CAMPOS J. , MAWHIN J. , ORTEGA R.
Published: January 2009

A class of linear operators L + λI between suitable function spaces is considered, when 0 is an eigenvalue of L with constant eigenfunctions. It is proved that L + λI satisfies a strong maximum principle when λ belongs to a suitable pointed left-neighborhood of 0, and satisfies a strong uniform anti-maximum principle when λ belongs to a suitable pointed right-neighborhood of 0. Applications are given to various types of ordinary or partial differential operators with periodic or Neumann boundary conditions.
The Relative Importance of Genetics and Environment on Mammographic Density
Authors: Ursin Giske , Lillie Elizabeth O. , Lee Eunjung , Cockburn Myles , Schork Nicholas J. , Cozen Wendy , Parisky Yuri R. , Hamilton Ann S. , Astrahan Melvin A. , Mack Thomas
Published: January 2009

Background: Although several environmental factors predict mammographic density, estimates of its heritability have been quite high. We investigated whether part of the presumed heritability might be attributed to differential sharing of modifiable risk factors in monozygotic (MZ) and dizygotic (DZ) twins.

Methods: We measured percent and absolute mammographic density using mammograms from 257 MZ and 296 DZ twin pairs. The correlation of intrapair mammographic density was compared according to zygosity across strata of modifiable risk factors. Portions of variance attributable to additive genetic factors, shared environment, and individual environment were calculated using a variance component methodology in the entire set, and within twin pairs stratified by environmental trait similarity.

Results: Both percent density and absolute mammographic density were more highly correlated between MZ twins than DZ twins, but the correlations varied across strata. Body mass index (BMI) and parity strongly predicted differences in mammographic density within MZ twin pairs. After adjusting for covariates, 53% of the total variance in percent density and 59% of that in absolute density seemed attributable to genetic effects, but these estimates varied greatly by stratum. For twins dissimilar on BMI (difference >2.5 kg/m2), the additive genetic component of absolute density was estimated at only 20% (±19%), and the common and individual environment at 21% (±14%) and 49%, respectively (P value for heterogeneity across BMI = 0.0001).

Conclusion: Our results confirm that the genome is an important determinant of mammographic density but suggest that an unknown portion of the mammographic density effect attributed to the genome may be due to shared modifiable environmental factors. (Cancer Epidemiol Biomarkers Prev 2009;18(1):102–12)
Male Circumcision and Serologically Determined Human Papillomavirus Infection in a Birth Cohort
Authors: Dickson Nigel P. , Ryding Janka , van Roode Thea , Paul Charlotte , Herbison Peter , Dillner Joakim , Skegg David C.G.
Published: January 2009

Circumcision has been reported to protect against infection with human papillomavirus (HPV) in men, but results have been inconsistent. We followed males in a birth cohort born in Dunedin, New Zealand, in 1972 and 1973 from age 3 to 32 years. Seropositivity at age 32 years for the oncogenic types HPV-16 and 18, and the nononcogenic types 6 and 11, was studied in relation to maternal reports of circumcision status at age 3 for 450 men. Seropositivity to any of these types was associated with lifetime number of sexual partners (P = 0.03), and lower moral-religious emphasis of the family of origin (P < 0.001). Circumcision was not found to be protective, with the adjusted odds ratio (95% confidence interval) for HPV6/11/16/18 seropositivity among the circumcised compared with the uncircumcised being 1.4 (0.89-2.2). (Cancer Epidemiol Biomarkers Prev 2009;18(1):177–83)
The Elevated Expression of a Mismatch Repair Protein Is a Predictor for Biochemical Recurrence After Radical Prostatectomy
Authors: Norris Alixanna M. , Gentry Michael , Peehl Donna M. , D'Agostino Ralph , Scarpinato Karin D.
Published: January 2009

Purpose: The inability to predict clinical outcome of prostate cancer is a major impediment to effective treatment decisions and patient counseling. New markers of recurrence are needed to improve the accuracy of risk assessment and treatment of prostate cancer. Our previous studies identified a mismatch repair protein, PMS2, to be elevated in prostate cancer; here, we investigate the prognostic potential of this marker. We hypothesized that the elevation of PMS2 would correlate with disease outcome.

Experimental Design: Retrospective quantitative immunohistochemistry was done to measure PMS2 in high-grade cancers of 166 men treated by radical prostatectomy with a biochemical recurrence rate of 56%. Associations between PMS2 levels, pathologic variables, and biochemical recurrence over time were determined.

Results: The mean level of PMS2 protein was consistently higher in both cancer-associated benign epithelium and cancer cells of patients who recurred, compared with nonrecurrent patients. PMS2 was an independent predictor of time-to-recurrence in Cox multivariate analyses and significantly stratified patients based on outcome. PMS2 was able to improve the sensitivity of total percent Gleason 4/5 as a risk factor for recurrence in this cohort.

Conclusions: PMS2 protein levels were shown to be a predictor of time-to-recurrence after surgery. This study is the first to document that the elevation of a mismatch repair protein negatively correlates with prognosis and has implications in patient diagnosis and molecular profiling. (Cancer Epidemiol Biomarkers Prev 2009;18(1):57–64)
The Association of Bone Mineral Density with Prostate Cancer Risk in the Osteoporotic Fractures in Men (MrOS) Study
Authors: Farhat Ghada N. , Taioli Emanuela , Cauley Jane A. , Zmuda Joseph M. , Orwoll Eric , Bauer Douglas C. , Wilt Timothy J. , Hoffman Andrew R. , Beer Tomasz M. , Shikany James M. , Daniels Nicholas , Chan June , Fink Howard A. , Barrett-Connor Elizabeth , Parsons J. Kellogg , Bunker Clareann H. ,   for the Osteoporotic Fractures in Men (MrOS) Study Group
Published: January 2009

We investigated the association of bone mineral density (BMD) measures with prostate cancer (PCa) risk in older men enrolled in the Osteoporotic Fractures in Men Study. We hypothesized that men with higher BMD, a marker of exposure to endogenous sex hormones, would have an increased incidence of PCa. The cohort included 4,597 men (89% White, 65 years or older) with no prior history of PCa. Baseline total body, total hip, and spine BMD were assessed using dual energy X-ray absorptiometry. Prostate cancer was confirmed by review of medical records. Cox regression was used to assess the association of BMD quartiles with incident PCa, adjusting for age, body mass index, and other covariates. During an average follow-up of 5.2 years, 5.6% (n = 255) of men developed PCa. Total body BMD was inversely associated with incident PCa, with a significant trend for decreasing PCa risk with increasing BMD quartiles (Ptrend = 0.007). Men in the highest total body BMD quartile had a 41% reduced risk for PCa (hazard ratio, 0.59; 95% confidence interval, 0.40-0.86), compared with men in the lowest quartile. Total hip and spine BMD did not exhibit significant relationships with PCa. Associations of BMD measures differed for low-grade (Gleason sum, 2-6) versus high-grade tumors (Gleason sum, ≥7). Significant inverse relationships with high-grade disease were noted at the total body and total hip sites. However, no associations were observed with low-grade disease. Our results provide support for an inverse association between BMD and PCa risk. Possible pathophyisological mechanisms linking BMD and PCa should be elucidated. (Cancer Epidemiol Biomarkers Prev 2009;18(1):148–54)
Vitamin D Receptor Polymorphisms and Breast Cancer Risk: Results from the National Cancer Institute Breast and Prostate Cancer Cohort Consortium
Authors: McKay James D. , McCullough Marjorie L. , Ziegler Regina G. , Kraft Peter , Saltzman Barbara S. , Riboli Elio , Barricarte Aurelio , Berg Christine D. , Bergland Goran , Bingham Sheila , Brustad Magritt , Bueno-de-Mesquita H. Bas , Burdette Laurie , Buring Julie , Calle Eugenia E. , Chanock Stephen J. , Clavel-Chapelon Françoise , Cox David G. , Dossus Laure , Feigelson Heather Spencer , Haiman Christopher A. , Hankinson Susan E. , Hoover Robert N. , Hunter David J. , Husing Anika , Kaaks Rudolph , Kolonel Laurence N. , Le Marchand Loic , Linseisen Jakob , McCarty Catherine A. , Overvad Kim , Panico Salvatore , Purdue Mark P. , Stram Daniel O. , Stevens Victoria L. , Trichopoulos Dimitrios , Willett Walter C. , Yuenger Jeffrey , Thun Michael J.
Published: January 2009

Background: Vitamin D is hypothesized to lower the risk of breast cancer by inhibiting cell proliferation via the nuclear vitamin D receptor (VDR). Two common single nucleotide polymorphisms (SNP) in the VDR gene (VDR), rs1544410 (BsmI), and rs2228570 (FokI), have been inconsistently associated with breast cancer risk. Increased risk has been reported for the FokI ff genotype, which encodes a less transcriptionally active isoform of VDR, and reduced risk has been reported for the BsmI BB genotype, a SNP in strong linkage disequilibrium with a 3′-untranslated region, which may influence VDR mRNA stability.

Methods: We pooled data from 6 prospective studies in the National Cancer Institute Breast and Prostate Cancer Cohort Consortium to examine associations between these SNPs and breast cancer among >6,300 cases and 8,100 controls for each SNP using conditional logistic regression.

Results: The odds ratio (OR) for the rs2228570 (FokI) ff versus FF genotype in the overall population was statistically significantly elevated [OR, 1.16; 95% confidence interval (95% CI), 1.04-1.28] but was weaker once data from the cohort with previously published positive findings were removed (OR, 1.10; 95% CI, 0.98-1.24). No association was noted between rs1544410 (BsmI) BB and breast cancer risk overall (OR, 0.98; 95% CI, 0.89-1.09), but the BB genotype was associated with a significantly lower risk of advanced breast cancer (OR, 0.74; 95% CI, 0.60-0.92).

Conclusions: Although the evidence for independent contributions of these variants to breast cancer susceptibility remains equivocal, future large studies should integrate genetic variation in VDR with biomarkers of vitamin D status. (Cancer Epidemiol Biomarkers Prev 2009;18(1):297–305)