bluuebunny/crossref_metadata_2025 huggingface dataset:
Non-Destructive High-Resolution Stiffness Mapping of Composite Engineered Surfaces
Authors: Gitis Norm , Khosla Vishal , Hermann Ilja , Vinogradov Michael
Published: June 2009

Experimental evaluation of hardness, adhesion and Young’s modulus has been performed on polyimide polymeric coatings used in LCD displays and on composite polymer-based materials used in automobiles and aircraft. A novel Universal Nano+Micro Tester UNMT-1 with a nano-analyzer module NA-2 has been utilized. It measures scratch-hardness of coatings and thin films, utilizing the same nano-tip for both scratching and nano-imaging under the constant load. It measures scratch-adhesion with the same diamond tip for both scratching and nano-imaging under the continuously-increasing load. It evaluates homogeneity of films and composite materials by simultaneous Young’s modulus and topography nano-mapping, with a diamond nano-tip in a tapping mode, while frequency and phase of its vibrations are analyzed. The Young’s modulus maps allowed us to evaluate the distribution of SiO/Si02 particles embedded in araldite, with varying SiO/Si02 concentration. While the topography images could not distinguish between the particles and polymeric matrix, the nano-mechanical maps revealed the effects of particle concentration and agglomeration on the local modulus of the material and the relationship between the SiO/Si02 uniformity and uniformity in modulus. The nano-scratches of 60-nm polyimide coatings at progressively increasing and constant loads generated adhesion and scratch-hardness data, respectively. Within the applied loads of 20 to 100 μN, we observed and determined both the critical load, at which the coating was delaminated from the glass substrate, and a corresponding lateral delamination force. The mutually complimentary nano-images and force graphs coincided nicely.
A Study of the Average Real Contact Pressure Between Rough Surfaces
Authors: Jackson Robert L. , Wilson W. Everett , Angadi Santosh
Published: June 2009

It is well known that the friction, wear, fatigue life, and contact resistance (electrical and thermal) are dependent on the contact between the rough profiles of the surfaces. Several different techniques have been used to model this contact (fractal, wavelet, statistical, multiscale, and deterministic methods). Several of these methods have found that the relationship between the real area of contact and load is linear. This suggests that there is a constant contact pressure between two surfaces (the average real contact pressure). Somewhat surprisingly, several works have found that this pressure may be greater than traditional hardness, even when the contact is heavily loaded and the contacts are deforming plastically. This mechanism is often called the asperity persistence. The current work uses a recent multiscale contact model and other theories to explain this mechanism and to help predict the average real contact pressure, especially during heavily loaded contacts.
Characterization of the Oil Condition by IR and Chemometrics
Authors: Felkel J. , Doerr N. , Varmuza K.
Published: June 2009

The acid number (AN) is considered an important indicator of oil condition, especially in terms of defining oil oxidation and the extent of acidification of used oils collected from two engines, each running with a different biogas. The results of chemometrical models comprising principal component analysis (PCA) for qualitative evaluation and partial least squares regression (PLS) for quantitative evaluation of used gas engine oils, respectively, are discussed. The investigations are based on infrared spectrometry and acid number measurements of monograde mineral-oil-based gas engine oils SAE 40. It is reported how IR spectrometry and chemometrics can be used to reveal the influence of the gas fuel type on oil aging (PCA) and for the indirect determination of the acid number (PLS). In contrast to the conventional time-consuming AN determination according to ASTM D 664, the joint use of IR spectrometry and chemometrics offers results within a few minutes. The chemometrical “measurement error” is in the range of precision and bias of the standard method.
A Plasticity Index, a Plasticity Number, and the Distribution of the Plastic Deformation Depth Based on a Fractal-Regular Contact Model
Authors: Wang Shao , Wang Huyi
Published: June 2009

A plasticity index and a plasticity number were proposed to indicate the severity of plastic deformation by considering the multi-scale and hierarchical nature of surface roughness. A distribution density function of the plastic deformation depth was introduced to characterize the evolution of plastic deformation with increasing load. By integrating this function, the fraction of the real contact area where plastic deformation depths are within any given range can be calculated.
Interfacial Forces and Friction on the Nanometer Scale
Authors: Ruths M.
Published: June 2009

In this tutorial, I will review the molecular origin of some of the forces that may be observed between interacting bodies, and the effects of such forces on adhesion and friction of surfaces and thin films at the atomic and nanoscopic scale.
Advances in Molecular Dynamics Simulations of Nanotribology
Authors: Chandross Michael
Published: June 2009

Molecular dynamics is the simulation method that is most amenable to the length and time scales of nanotribological experiments. The ability to track the individual motion of every atom in simulations has led to a detailed understanding of the underlying physics that is difficult to extract from experiment. While significant progress has been made in simulations over the past two decades, computational issues still limit the types of problems that can be approached, and the detailed understanding that results. Here we discuss recent advances in molecular dynamics simulations that push the bounds of simulation size, velocity, and chemistry. These state of the art simulation techniques have made great strides in allowing detailed comparisons to experimental results. These advances will be placed in context by addressing the barriers that remain and where future progress lies.
Nanotribological Simulations With Molecular Dynamics
Authors: Chandross Michael
Published: June 2009

The use of molecular dynamics (MD) simulations in nanotribology has made many advances in the past twenty years. While early simulations were limited to hundreds or thousands of atoms undergoing shear at 100 m/s, the current state of the art simulations in nanotribology approach millions of atoms with shear rates that can, in certain cases, match experiment. However, many of the exciting current simulations involve techniques that can be difficult for non-experts to understand. In this tutorial we hope to alleviate some of this confusion by reviewing the basic concepts that form the foundations of molecular dynamics (MD) simulations. This will include both a discussion of the method in general, was well as a focus on the use of MD in nanotribological simulations.
Multiscale Prediction of the Surface Separation Between Rough Surfaces
Authors: Wilson W. Everett , Jackson Robert L.
Published: June 2009

The current work considers the multiscale nature of surface roughness in a new model that predicts the real area of contact and surface separation, both as functions of load. By summing the distance between the two surfaces at all scales, a model of surface separation as a function of dimensionless load is also obtained. A previous rough surface multiscale contact model was based on stacked elastic-plastic spheres. This work uses stacked 3-D sinusoids to represent the asperities in contact at each scale of the surface. The results are also compared to several other existing rough surface contact models and experimental results. It appears that the statistical and multiscale models make different assumptions when considering surface separation. The statistical model does not consider the effect of deformation on the mean surface height, but the multiscale model does (the location of the mean height will change as the surface deforms). When deformation is included and the surface separation becomes zero, the surfaces must also come into complete contact.
Parametric Study of the Imbalance Response of a Squeeze Film Damper
Authors: Xing Changhu , Braun Minel J. , Li Hongmin
Published: June 2009

Rigid rotor models are widely used for the rotor-bearing stability analysis. This paper presents parametric studies for a squeeze film damper (SFD) using as parameters pressurization, the retainer spring support, and viscosity under the 2π- and π-film assumptions. The results are then validated by direct numerical simulation of the journal orbit.
Effect of Surface Roughness on Adhesion and Friction of Microfibers in Side Contact
Authors: Teodorescu Mircea , Majidi Carmel , Rahnejat Homer , Fearing Ronald S.
Published: June 2009

A multi-scale mathematical model is used to study the effect of surface roughness on the adhesion and friction of microfibers engaged in side contact. Results are compared to closed-form analytic approximations derived from linear elastic contact mechanics.
The Effects of Fuel Dilution With Biodiesel and Low Sulfur Diesel on Lubricant Acidity, Oxidation and Corrosion: A Bench Scale Study With CJ-4 and CI-4+ Lubricants
Authors: Watson Simon A. G. , Wong Victor W.
Published: June 2009

This study explored the effect of oil dilution with biodiesel and ultra low sulfur diesel fuel on acidity and corrosion in two lubricants with API service ratings of CJ-4 and CI-4+. The oils were diluted to levels of 0%, 5% and 10% with ultra low sulfur diesel fuel (ULSD), 20% biodiesel (B-20) and 100% biodiesel (B-100). For each case, the mixture of fuel and oil was subjected to oxidation tests using a procedure similar to ASTM D6594. The oxidation resistance of the CJ-4 and CI-4+ lubricants was similar in each case. The advanced formulation of the CJ-4 lubricant gave comparable overall performance to the CI-4+ lubricant, despite reduced levels of metallic additive compounds. The highest levels of lubricant degradation occurred when the lubricants were diluted with B-100. A substantial increase in acidity was observed when the oils were diluted with B-100. Moderate levels of copper and lead corrosion were observed in the tests with no fuel dilution, and dilution with ULSD. An order magnitude increase in corrosive wear was seen in the tests with B-100. Lower corrosion occurred with the CJ-4 lubricant.
Incipient Slip and Frictional Creep of Tyred Systems
Authors: Reina Saverio , Dini Daniele
Published: June 2009

This research presents a systematic study of the interfacial behaviour of tyred systems. A simplified two-dimensional contact model of an elastic strip, shrink-fitted onto a wheel, and subjected to different rolling contact conditions, has been developed. This model enables us to characterise the behaviour at the strip/substrate interface caused by a quasi-static application of moving loads on the surface of the layer. The solution is compared to the stationary load case and regimes of local slip, full stick, separation and frictional creep are identified and mapped for a variety of loading conditions, materials and geometries.
Viscoelastic Contact of Rough Surfaces in Relative Normal and Sliding Motion
Authors: Sepehri Ali , Farhang Kambiz
Published: June 2009

Mathematical formulae are derived for normal and tangential components of the contact force that depend not only on the proximity of the two surfaces but also the rate of approach and relative sliding. The development of the contact model is based on the asperity shoulder-shoulder contact leading to slanted asperity contact force. Thus an asperity force contains both normal and tangential components. Three dimensional consideration of asperity contact force yields directionally dependence of both the normal and tangential force components. A previously reported statistical approach is employed in which the dependence of the asperity normal and tangential contact force components on relative tangential velocity of two asperities are cast as corrective factors in the mathematical description of normal and tangential force components. The two corrective coefficients are the force directionality corrective coefficient and the force-velocity directionality corrective coefficient. Approximate equations are found for each of the normal and half-plane tangential force components that achieve accuracy within five (5) percent error.
Pressure Characteristics and Flow Patterns for a Porous Self-Circulating Hydrodynamic Bearing
Authors: Balasoiu Ana M. , Braun Minel J. , Moldovan Stefan I.
Published: June 2009

This paper presents the behavior of a porous cylindrical bearing that has a self-contained system that excludes the action of an external circulating pump for the lubricating fluid. The bearing contains a stationary porous bushing whose inner surface faces the active space of the bearing while the outer one faces a wrap-around reservoir. Under the cam-like effect of the eccentric shaft the fluid circulates in and out of the bearing clearance and reservoir respectively, without the help of an outside pump. The circulating mechanism is described and numerically simulated. The corresponding pressure profiles and flow patterns are also shown and discussed. The physical implementation of such a bearing system would lead to complete elimination of significant portions of the bearings lubricating circuit.
Three Dimensional Elastic-Plastic Contact of Nominally Flat Rough Surfaces Based on FEA-Based Constitutive Asperity Contact Relations and Including Asperity Shoulder Contact
Authors: Sepehri A. , Farhang K.
Published: June 2009

Three dimensional elastic-plastic contact of two nominally flat rough surfaces is considered. Equations governing the shoulder-shoulder contact of asperities are derived based on the asperity-asperity constitutive relations from a finite element model of their elastic-plastic interaction proposed by Kogut and Etsion [12]. Shoulder-shoulder asperity contact yields a slanted contact force consisting of both tangential (parallel to mean plane) and normal components. An analytical fusion technique is developed to combine the piecewise asperity level constitutive relations. This is shown to yield upon statistical summation the cumulative effect resulting in the contact force between two rough surfaces with two components, one in the normal direction and a half-plane tangential component.
A New Approach to End Effect Attenuation in Elastic Finite Length Line Contacts Between Revolution Bodies
Authors: Diaconescu Emanuel
Published: June 2009

There are many methods for attenuation of end effects in finite length line Hertz contacts. A new one is proposed herein by using an even polynomial generatrix for the equivalent rigid roller. The elastic contact between high order polynomial surfaces is used to get a nearly flat maximum pressure along the line contact. According to a reversed method, contact half-axes and central pressure are imposed. The longitudinal roller profile found numerically is indeed an even order polynomial. The method is validated numerically by a GC-DCFFT method.
Derivation of Reynolds Equation in Cylindrical Coordinates Applicable to Pin-on-Disk and CMP
Authors: Beschorner K. E. , Higgs C. F. , Lovell M. R.
Published: June 2009

Traditional tribology references typically provide the cylindrical (or polar) Reynolds equation, which may not be applicable when entrainment velocities vary with radius and/or angle. However, entrainment velocities are known to vary with angle for some cases of pin-on-disk contact and chemical mechanical polishing (CMP). A form of Reynolds equation is derived in this manuscript from the Navier-Stokes equations without entrainment velocity assumptions. Two case studies, related to pin-on-disk and CMP, are presented and results from the derived form of Reynolds equation are compared with results from the traditionally used form. Pressure distributions obtained from the two forms of Reynolds equation varied greatly in magnitude and in pressure shape. Therefore, a new form of the cylindrical Reynolds equation derived in this manuscript is used when entrainment velocities are known to vary with radius or angle.
The Mechanics of Adhesion: A Tutorial
Authors: Adams George G.
Published: June 2009

As the size of the contact region between two bodies decreases to the micro- and nano-scales, the effect of adhesion becomes increasingly important. In this tutorial, we review fundamental concepts of the mechanics of adhesion. Attention is placed on the contact of elastic bodies in which the shapes of the contacting bodies are locally spherical. We also discuss the use of spherical contact theory to model the adhesive contact of an asperity with a flat as part of a multi-asperity contact model.
Fluid-Crack Interaction in Lubricated Rolling-Sliding Contact
Authors: Lai J. , Ioannides E. , Wang J.
Published: June 2009

This paper reports on a theoretical study on the fluid-assisted surface cracking in lubricated rolling-sliding contact. An analytical 2D model, validated by the CFD simulations, is developed to describe the transient process of lubricant seepage into a surface-breaking crack during the contact loading. The fluid-crack interaction is studied by FE calculations.
A Multi-Scale Account of Friction-Vibration Interaction
Authors: Sepehri A. , Farhang K.
Published: June 2009

Using a nonlinear model of a two disk brake system, coupled equations of motion are found for their frictional interaction. 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 viscoelastic 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 decrease with decrease in the normal load and/or increase in structural damping of the system.
Tribological Tests of Friction Pair Materials for the GT-MHR Turbomachine Catcher Bearings
Authors: Baxi C. B. , Kodochigov N. G. , Belov S. E. , Borovkov M. N.
Published: June 2009

A power plant with high-temperature helium-cooled reactors (GT-MHR) (Figure 1) for electricity generation includes a turbomachine (TM) that provides helium circulation in the primary circuit and converts the coolant thermal power into electricity in the direct gas turbine cycle. Operability of the TM for the GT-MHR reactor plant (Figure 2) mainly depends on reliability of the electromagnetic suspension system for the vertical flexible rotor with a total weight of 67.7 tons and length of 29 meters. The electromagnetic suspension system for the TM rotor consists of axial and radial electromagnetic bearings (EMB), EMB control system, and catcher bearings (CB).
Development of a Bench Test Stand for High Speed Turbochargers
Authors: Kirk R. Gordon , Papke William J. , East James Thomas , Mueller Tobias , Newman Andrew Samuel
Published: June 2009

The design of a turbocharger test stand using high pressure compressed air is discussed in this paper. The turbocharger test stand will be used mainly for bearing testing and turbocharger shaft vibration measurement. The purpose of these measurements is to discover a bearing design that will increase the vibration stability of the turbocharger and reduce the amount of oil leakage past the shaft seals. This will ultimately reduce emissions and upkeep cost. This paper summarizes the details of the design and describes the calculations performed that assure the test stand will successfully power the turbo. The initial operation of the test stand indicates the desired operating speed can be achieved for future vibration testing.
Tribological Performance of Sub-Micron Scale Boric Acid Powder Additives for Extended Duration
Authors: Kabir M. A. , Higgs C. F. , Lovell M.
Published: June 2009

In this investigation, the friction and wear performance of sub-micron scale boric acid powder lubricant additives were studied during extended duration pin-on-disk experiments. The sub-micron (600 nm) and micro (4 μm) powder additives were created from 250 micron sized crystals using an 1800D SPEX Mill/Mixer. Lubricant combinations were prepared by homogeneously mixing the additives with canola oil in a vortex generator. Three different boric acid additives were investigated by combining 5.0 wt. % of 4 μm boric acid particles, 5.0 wt % of 600 nm sized boric acid particles, and a 5.0 wt % mixture of the 4 μm (2.5 wt. %) and 600 nm (2.5 wt. %) boric acid particles. A fourth additive, 5.0 wt. % of 0.5 – 5μm MoS2 powder, was also purchased and mixed with the canola oil to form a basis for comparison. It was determined that the oil mixed with a combination of micro and sub-micron scale boric acid powder additives exhibited better frictional performance than the oil mixed with micro or sub-micron boric acid additives.
Tribological Behavior of CrN and Al-Cr-N Coatings
Authors: Demas Nicholaos G. , Polycarpou Andreas A. , Polychronopoulou Kyriaki , Rebholz Claus
Published: June 2009

The tribological behavior of CrN and Al-Cr-N coatings prepared by twin electron-beam evaporation at 450°C was investigated. The composition, structure, mechanical and tribological properties of the coatings were determined using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) in combination with nanoindentation mechanical property measurements, scanning electron microscopy (SEM), and laboratory controlled ball-on-disc sliding experiments. It was found that all of the Al-Cr-N coatings exhibit higher hardness compared to CrN coatings. Also, the compositions of Al-Cr-N coatings with the lower Al content and lower Al/Cr ratios showed better tribological performance than the rest of the coatings.
Vibration and Acoustic Emission of Linear-Guideway Type Recirculating Linear Ball Bearings With One Artificial Defect in the Carriage
Authors: Ohta Hiroyuki , Matsuura Kazuya , Kato Soichro , Igarashi Yutaka
Published: June 2009

In machines with linear-guideway type recirculating linear ball bearings (linear bearings), to prevent shutdown of machines caused by unexpected-failures of linear bearings, there has been an increasing demand for the development of defect (especially flaking) detection techniques of linear bearings by using vibration or acoustic emission (AE) measurements. Although studies [1–3] on vibrations of linear bearings without defects have been carried out, work on vibrations and AE of defective linear bearings are few [4, 5].
Influence of the Weighting Material on Casing Wear in Impact-Sliding Test Condition
Authors: Chu Shengli , Fan Jianchun , Zhang Laibin , Yu Huiyuan
Published: June 2009

The weighting material in drilling fluid has very important effect on casing wear. By using the DCWT-1000 tester, a new impact-sliding tester for casing wear, a series of tests in impact-sliding work condition have been performed to investigate the effects of different weighting material doped in drilling fluid. The OE and SEM analysis presents that the iron ore powder doped in the drilling fluid led to the change in the wear mechanism from abrasive wear and adhesion wear to severe plastic flow and fatigue wear. The adhesion wear increasingly become severe with increasing iron ore powder content. While the barite doped in the drilling mud was beneficial to decreasing the adhesion wear and plastic deformation of the casing. Moreover, it is found that mixed weighting material with iron ore powder and barite in certain ratio has better effect on decreasing casing wear.
Coupled Thermo-Mechanical Modeling of Head-Disc Interface in Heat Assisted Magnetic Recording
Authors: Jandric Zoran , Peng Wei , Kiely James D. , Hsia Yiao-Tee
Published: June 2009

In Heat Assisted Magnetic Recording (HAMR), various thermal loads (laser, electrical current) subject the Head-Disc Interface (HDI) to intensive thermal strain / stress fields. The thermal strains, in terms of slider protrusion and media protrusion, significantly reduce the head-disc clearance and may lead to head-disc contact. Air bearings, by design, can passively adjust the fly height through so-called “self-compensation” to the protrusions. In this paper, an electro-thermo-mechanical model coupled with air bearing model has been developed to analyze the head flying characteristics under these thermal loads. The thermal protrusions induced by laser and current Joule heating, as well as their interactions, have been studied and verified with experimental results.
Oil Debris Detection Using Static and Dynamic Capacitance Measurements
Authors: Murali S. V. , Choy F. K. , Zhe J. , Carletta J. , Xia X.
Published: June 2009

This paper describes a capacitance sensing method to detect oil debris contents. Experimental investigations are conducted for both static and dynamic measurements. Static measurements are performed by inserting small metal wires into the oil sample between the two plate electrodes of a capacitor. With a gap of 7mm between the electrodes, it was found that the capacitance measurement can detect metal wires as small as 4 mils (101 μm) in diameter. While measurements of ferrous and the non-ferrous wires show certain measurable differences, a systematic difference between the two sets of measurements cannot be established. The dynamic measurements were conducted by measuring the changes in capacitance between two plate electrodes when a small particle was dropped into the oil between the two electrodes. The passage of a metal particle can be dynamically detected. It is expected that smaller metal debris particles can be detected by reducing the spacing between the two electrode plates in microchannels.
Detection of NM-Scale Scratches on High Gloss Metal Sheets by a Light Scattering Method
Authors: Bo¨hm J. , Bianchi D. , Jech M. , Brodmann R. , Vellekoop M.
Published: June 2009

This paper discusses a promising method to investigate high gloss finished metal surfaces. The main aim is to detect very shallow scratches on such surfaces. The method must be simple in its applicability, insensitive to external disturbances and sufficiently fast for application in monitoring industrial processes. To achieve this, the principle of light scattering is used by scanning a surface with a compact scattering light sensor using an LED as a light source (λ = 632.8nm). The reflected light is scattered into a specular part and a diffuse part, and collected by a one dimensional CCD-Array. The detected intensity distribution of the scattered light depends on the topography of the reflecting surface. Significant variations in the intensity profile will permit to identify the surface defects. With this system we were able to detect scratches on high gloss metal sheets with a typical width of 1 μm and a depth as small as 40 nm.
Effect of SWCNT on Tribological Behavior of Polymeric Nanocomposite
Authors: Zarrin Tahira , Ribeiro Rahul , Banda Sumanth , Ounaies Zoubeida , Liang Hong
Published: June 2009

The nanoscale structure of single-walled carbon nanotubes (SWCNTs) has unique properties. These nanostructured additives can induce unusual characteristic in many polymer matrix. In one of our recent experiments, it was found that when adding SWCNTs into a polyimide (PI) matrix, friction becomes a function of the concentration of the additive. In this research, we analyze the behavior of the SWCNTs-PI nano-composite using an approximation approach. We report that the frictional behavior of the nanocomposite is dominated by the elastic and plastic deformation through randomly dispersed SWCNTs under different loading conditions. At low concentration of SWCNTs, its elasticity dominates the properties of composite while at higher concentration, plastic behavior of tubes plays a major role in describing the properties of composite.
Evaluation of Supercritical Carbon Dioxide for Use in Fluid Film Bearings for Process Fluid Lubricated Machines
Authors: Bruckner Robert J.
Published: June 2009

Advanced closed loop power generation cycles are under consideration for a variety of terrestrial and aerospace power systems [1]. High pressure closed brayton cycles (CBC) and supercritical cycles (SCS) offer an advantage where the cycle working fluid can also be used as the lubricant for the fluid film bearings that support the high speed turbomachinery. Unfortunately the use of supercritical carbon dioxide as a lubricant is not well understood. In the supercritical condition fluids that are typically thought of as ideal gases take on a significantly different characteristic. While these fluids typically maintain gas-like absolute viscosities, their densities are liquid like. The combination of these effects leads to the emergence of inertial effects in fluid film bearings. In addition to the inertial effects that are brought on by the high fluid density, the temperature of the lubricant cannot be controlled independently of the thermodynamic process. This situation leads to technical challenges in maintaining dimensional stability and clearance control between the rotating and stationary surfaces of the bearings.
A Molecular Model of Asperity Contact and Comparison to Continuum Based Models
Authors: Huang Wei , Jackson Robert L.
Published: June 2009

Surface asperities can range widely in size. Therefore it is important to characterize the effect of size and scale on the contact mechanics. This work presents a molecular model of asperity contact in order to characterize small scale asperity contact. The model is also compared to existing continuum mechanics based models developed originally by Hertz for elastic contact and later expanded by others to include plasticity. It appears that the predictions can be related to each other and that the continuum material properties can be related to the properties describing the molecular forces.
Molecular Dynamics Simulation of Nanoindentation
Authors: Terrell Elon J. , Landry Eric , McGaughey Alan , Higgs C. Fred
Published: June 2009

A molecular dynamics model of a nanoindentation experiment was simulated in order to calculate the elastic modulus of several different Lennard-Jones (LJ) solids. It was found that the elastic modulus increased significantly as the depth of the potential well that describes the interactions between the atoms in the sample was increased.
Unloading Process in Elastic-Plastic Contact of a Rough Surface With a Flat
Authors: Sepehri A. , Farhang K.
Published: June 2009

Three dimensional elastic-plastic contact of a nominally flat rough surface and a flat is considered. The asperity level Finite Element based constitutive equations relating contact force and real contact area to the interference is used. The statistical summation of asperity interaction during unloading phase is derived in integral form. Approximate equations are found that describe in closed form contact load as a function of mean plane separation during unloading. The approximate equations provide accuracy to within 6 percent for the unload phase of the contact force.
Contact Force Simulation of Granular Media Using Explicit Finite Element Method
Authors: Kabir M. A. , Higgs C. F. , Lovell M. R.
Published: June 2009

Granular flow behavior is of fundamental interest to the engineering and scientific community because of the prevalence of these flows in the pharmaceutical, agricultural, food service, and powder manufacturing industries. When granular media come under external load, inter-particle forces in the granular media form an inhomogeneous distribution. In this study, a simulation of the contact forces in granular media was carried out using an explicit finite element method on a biaxial cell of approximately 2500 particles. Some of the key results included the capturing of normal force and tangential force distributions within a granular shear cell.
Simulation of Thermal Effects in Stationary and Sliding Electrical Contacts
Authors: Watkins Bobby G. , Streator Jeffrey
Published: June 2009

Sliding electrical contacts are subject to surface damage and wear, which can be enhanced by the heating at the interface arising from electrical contact resistance. For example, in electromagnetic launcher (EML) technology, thermally assisted wear processes can result in unacceptable levels of material loss at the armature-rail interface. The control of the interface tribology in sliding electrical contacts requires an understanding of the Joule heating in the vicinity of the interface. In the current study, a multiphysics numerical simulation is conducted of transient heat conduction in both a stationary and a sliding electrical contact. The interface under investigation consists of a flat-ended aluminum cylindrical pin sliding against an aluminum rail. Electrical contact resistance is modeled by introducing a thin layer of high resistivity between the pin and the rail. Results show that shortly after sliding has commenced, (1) the maximum temperature rise occurs in the bulk of the pin rather than at the interface, (2) the bulk of the Joule heat goes into the rail, and (3) that sliding can have a significant effect on the temperature field, even when the speed is quite low.
Layer Moleculecular Dynamic Diffusion Model of Nano-Meter Lubricant Film on Hard Disk Surfaces at High Rotating Speed
Authors: Zhang Bo , Chiba Hiroshi , Nakajima Akira
Published: June 2009

Spin-off experiments for PFPE Z25 were conducted by using a 3.5 inch disk at a constant speed of 10,000 rpm. The initial film thickness was set to about 2.4 nm for all the experiments while temperature was changed in a wide range. It is found that the rheological behavior of the film is quite different from that expected from the continuum. A novel model based on Fick’s law of diffusion was proposed, which is called the layer molecular dynamic diffusion (LMDD) model. The theoretical prediction was compared with the experimental results and a good agreement was obtained, verifying the effectiveness of the model.
Statistical Analysis of Contact-Induced Air Bearing Vibrations
Authors: Himes Adam , Budde Rick
Published: June 2009

Air bearing vibrations at nanometer clearance levels are a major impediment to reducing head media spacing. Modern air bearings typically exhibit debilitating self-excited vibrations at fly heights of about 1–2 nm. At this point, peak head media spacing and contact pressures will increase, leading to performance and reliability issues. There has been considerable work performed to understand and improve air bearing stability at and around the point of contact, resulting in numerous experimental methods and design concepts in the literature. An area where additional research is worthwhile is the statistical behavior of contact vibrations. This paper explores the time dependence of fly height by using a simplified 2D air bearing with a mechanics based contact simulation. A comparison with measurements of fly height vibration demonstrates the utility of the simplified model and underscores the importance of proper time scale considerations.
Lubricant for Probe-Based Ferroelectric Recording Devices
Authors: Yan Xiaoping , Joes Paul M. , Li Lei , Hsia Yiao-Tee
Published: June 2009

In a probe-based ferroelectric recording system a protective coating of lubricant provides low friction and a low wear rate as well as allows the continuous contact of the probe tip with the storage medium. SO5, a member of the commercially available electric connector lubricants polyphenyl ether (PPE), was experimentally proven effective as a lubricant in supporting this probe/media interface and has enabled the demonstration of the probe-based ferroelectric recording technology. The unique stability of SO5 lubricant in an electric field and in the presence of electrons makes this liquid particularly suitable for ferroelectric recording storage devices. A broad range of analytical techniques were used to identify this lubricant as a mixture of alkylated diphenyl ethers having varying molecular weight. A thin layer of this lubricant was uniformly coated on the probe media surface through a dip-lubing procedure. Its thermal stability and wettability was investigated in terms of the requirements for the successful application of this unique ferroelectric recording technology. The impact of this lubricant film on the read/write capability, durability and tribological performance was also explored.
RNA Interference-Mediated Silencing of the Respiratory Syncytial Virus Nucleocapsid Defines a Potent Antiviral Strategy
Authors: Alvarez Rene , Elbashir Sayda , Borland Todd , Toudjarska Ivanka , Hadwiger Philipp , John Mathias , Roehl Ingo , Morskaya Svetlana Shulga , Martinello Rick , Kahn Jeffrey , Van Ranst Mark , Tripp Ralph A. , DeVincenzo John P. , Pandey Rajendra , Maier Martin , Nechev Lubomir , Manoharan Muthiah , Kotelianski Victor , Meyers Rachel
Published: June 2009

We describe the design and characterization of a potent human respiratory syncytial virus (RSV) nucleocapsid gene-specific small interfering RNA (siRNA), ALN-RSV01. In in vitro RSV plaque assays, ALN-RSV01 showed a 50% inhibitory concentration of 0.7 nM. Sequence analysis of primary isolates of RSV showed that the siRNA target site was absolutely conserved in 89/95 isolates, and ALN-RSV01 demonstrated activity against all isolates, including those with single-mismatch mutations. In vivo, intranasal dosing of ALN-RSV01 in a BALB/c mouse model resulted in potent antiviral efficacy, with 2.5- to 3.0-log-unit reductions in RSV lung concentrations being achieved when ALN-RSV01 was administered prophylactically or therapeutically in both single-dose and multidose regimens. The specificity of ALN-RSV01 was demonstrated in vivo by using mismatch controls; and the absence of an immune stimulatory mechanism was demonstrated by showing that nonspecific siRNAs that induce alpha interferon and tumor necrosis factor alpha lack antiviral efficacy, while a chemically modified form of ALN-RSV01 lacking measurable immunostimulatory capacity retained full activity in vivo. Furthermore, an RNA interference mechanism of action was demonstrated by the capture of the site-specific cleavage product of the RSV mRNA via rapid amplification of cDNA ends both in vitro and in vivo. These studies lay a solid foundation for the further investigation of ALN-RSV01 as a novel therapeutic antiviral agent for clinical use by humans.
Molecular Epidemiology of KPC-Producing
Klebsiella pneumoniae
Isolates in the United States: Clonal Expansion of Multilocus Sequence Type 258
Authors: Kitchel Brandon , Rasheed J. Kamile , Patel Jean B. , Srinivasan Arjun , Navon-Venezia Shiri , Carmeli Yehuda , Brolund Alma , Giske Christian G.
Published: June 2009

Klebsiella pneumoniae
carbapenemase (KPC)-producing
Enterobacteriaceae
have become more common in the United States and throughout the world. We used pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) to examine the molecular epidemiology of KPC-producing
K. pneumoniae
isolates sent to the Centers for Disease Control and Prevention (CDC) for reference testing from 1996 to 2008. A dominant strain, sequence type 258 (ST 258), was found and likely accounts for 70% of the CDC's
K. pneumoniae
PFGE database. Isolates with PFGE patterns related to ST 258 were identified in 10 of the 19 U.S. states currently reporting KPC-producing
K. pneumoniae
, in addition to one isolate from Israel. KPC subtyping and analysis of the surrounding genetic environment were subsequently performed on 23 representative isolates. Thirteen isolates identified as ST 258 possessed either
bla
KPC-2
or
bla
KPC-3
and some variability in the Tn
4401
element upstream of the
bla
KPC
gene.
Escherichia coli
DH10B was successfully transformed by electroporation with KPC-encoding plasmid DNA from 20 of the 23 isolates. Restriction analysis of plasmid DNA prepared from transformants revealed a diversity of band patterns, suggesting the presence of different plasmids harboring the
bla
KPC
gene, even among isolates of the same ST.
VanA-Type Vancomycin-ResistantStaphylococcus aureus
Authors: Périchon Bruno , Courvalin Patrice
Published: June 2009

Since 2002, nine methicillin (meticillin)-resistantStaphylococcus aureus(MRSA) strains that are also resistant to vancomycin (VRSA) have been reported in the United States, including seven clinical isolates from Michigan. The strains harbor a plasmid-borne Tn1546element following conjugation from a glycopeptide-resistantEnterococcusstrain. In the second step, Tn1546transposed to a resident plasmid in five strains; the acquired plasmid behaved as a suicide gene delivery vector, and the incoming DNA had been rescued by illegitimate recombination. Surprisingly, combination of a glycopeptide with a β-lactam has a strong synergistic effect against VRSA, both in vitro and in an animal model, despite resistance of the strains to both drug classes when administered separately. This results from the fact that the late peptidoglycan precursors ending ind-alanine-d-lactate (d-Ala-d-Lac) that are mainly synthesized in the presence of glycopeptide inducers are not substrates for PBP2′, which is the only transpeptidase that remains active in the presence of oxacillin. One VRSA strain is partially dependent on vancomycin for growth due to a mutation in the hostd-Ala:d-Ala ligase, thus having to rely on the inducible resistance pathway for cell wall synthesis. Competition growth experiments in the absence of inducer between the MRSA recipient and isogenic VRSA transconjugant revealed a disadvantage for the transconjugant, accounting, in part, for the low level of dissemination of the VRSA clinical isolates. The association of multiple molecular and environmental factors has been implicated in the regional emergence of VRSA in Michigan.
Nukacin ISK-1, a Bacteriostatic Lantibiotic
Authors: Asaduzzaman Sikder M. , Nagao Jun-ichi , Iida Hiroshi , Zendo Takeshi , Nakayama Jiro , Sonomoto Kenji
Published: June 2009

We determined the mode of action of nukacin ISK-1. It did not cause membrane potential dissipation or the efflux of ATP or K
+
ions from the cells of a sensitive bacterial strain; however, it blocked the membrane depolarization activity of nisin. Nukacin ISK-1-treated cells had single arrangements of cells without the formation of a complete septum. A remarkable reduction in cell wall width was also observed, but cytoplasmic content was unaffected. We concluded that nukacin ISK-1 is bacteriostatic.
Comparative Analysis of the Locus of Enterocyte Effacement and Its Flanking Regions
Authors: Müller Daniel , Benz Inga , Liebchen Ariane , Gallitz Inka , Karch Helge , Schmidt M. Alexander
Published: June 2009

The attaching-and-effacing (A/E) phenotype mediated by factors derived from the locus of enterocyte effacement (LEE) is a hallmark of clinically important intestinal pathotypes ofEscherichia coli, including enteropathogenic (EPEC), atypical EPEC (ATEC), and enterohemorrhagicE. colistrains. Epidemiological studies indicate that the frequency of diarrhea outbreaks caused by ATEC is increasing. Hence, it is of major importance to further characterize putative factors contributing to the pathogenicity of these strains and to gain additional insight into the plasticity and evolutionary aspects of this emerging pathotype. Here, we analyzed the two clinical ATEC isolates B6 (O26:K60) and 9812 (O128:H2) and compared the genetic organizations, flanking regions, and chromosomal insertion loci of their LEE with those of the LEE of other A/E pathogens. Our analysis shows that the core LEE is largely conserved—particularly among genes coding for the type 3 secretion system—whereas genes encoding effector proteins display a higher variability. Chromosomal insertion loci appear to be restricted toselC,pheU, andpheV. In contrast, striking differences were found between the 5′- and 3′-associated flanking regions reflecting the different histories of the various strains and also possibly indicating different lines in evolution.
The Kennack Gneisses of the Lizard Complex, Cornwall, England: partial melts produced during ophiolite emplacement
Authors: Malpas J. , Langdon G. S.
Published: June 2009

The Kennack Gneisses are a series of migmatites and microgranites found at the base of the peridotite of the Lizard Ophiolite Complex. The gneisses were derived by metamorphism and anatexis of interbedded sediments and basalts of a lower ophiolite slice during displacement of the complex from the oceanic regime in Devonian times. Anatexis is thought to have taken place at temperatures of 700–800 °C and pressures of several kilobars, suggesting that heat was supplied locally by the thrusting of a hot peridotite sheet. Displacement and assembly of the ophiolite slices therefore probably took place not long after formation. Subsequent emplacement onto the Gramscatho beds was after considerable cooling.
Thermoluminescence dating of the Pleistocene Old Crow tephra and adjacent loess, near Fairbanks, Alaska
Authors: Berger Glenn W.
Published: June 2009

Two different thermoluminescence (TL) techniques have produced an average age of 109 ± 14 ka for the widespread Pleistocene Old Crown tephra, previously of uncertain age. A deposit of the tephra from the Halfway House site at Fairbanks, Alaska, was dated directly at 110 ± 12 ka by analyses of 4–11 μm glass, using the additive-dose TL technique. A lower age limit of 108 ± 16 ka for this tephra was obtained indirectly by analysis of 4–11 μm grains of loess just above it, using the partial-bleach TL technique.For this partial-bleach technique, the assumptions of "zeroing" of TL and of the saturating exponential form of the TL growth curves were checked by analyses of a surface loess deposited within the last century. Also, most or all of an unstable (anomalous fading) TL component was eliminated from the older polymineralic loess in only a few days by storing irradiated subsamples at elevated temperatures. In contrast, several months storage was required to achieve the same effect at room temperature for this sample.
40Ar–39Ar incremental heating study of mineral separates from the early Archean east Indian craton: implications for the thermal history of a section of the Singbhum Granite batholithic complex
Authors: Baksi Ajoy K. , Archibald D. A. , Sarkar S. N. , Saha A. K.
Published: June 2009

40Ar–39Ar incremental heating studies on mineral separates from three sets of rocks in the Singbhum craton in eastern India have helped unravel the thermochronometric history of the terrane and explain an earlier discrepancy between Sm–Nd (~3800 Ma) and Rb–Sr (~3100 Ma) whole-rock ages for the Older Metamorphic Tonalitic Gneiss (OMTG). High precision plateau ages for hornblende separates from the Older Metamorphic Group of rocks (OMG) suggest that this unit is older than 3300 Ma and that enclaves of both the OMTG and OMG within the batholithic complex cooled to ~500 °C at 3300 ± 15 Ma following engulfment in magma, forming the Singbhum Granite (SG). Results from a biotite separate from the OMTG imply that slow cooling continued to a temperature of ~300 °C at ~3160 Ma. Study of a feldspar separate from the Singbhum Granite, suggests final cooling (uplift?) through the ~150 °C isotherm ~660 Ma ago.We suggest that an earlier Rb–Sr whole-rock age of 3130 ± 85 Ma on the OMTG did not yield the crystallisation age, but rather the time of cooling to strontium retention temperature for the biotite in these rocks. We also demonstrate that for hornblende and mica from Archean rocks, 40Ar–39Ar incremental heating experiments can yield very high precision plateau ages (e.g., ± 2 to ± 5 Ma at 3300 Ma). In practice, however, we suggest this technique can separate events in the early Archean spaced ~30 Ma apart.