bluuebunny/crossref_metadata_2025 huggingface dataset:
Rab3a interacting molecule (RIM) and the tethering of pre‐synaptic transmitter release site‐associated CaV2.2 calcium channels
Authors: Wong Fiona K. , Stanley Elise F.
Published: October 2009

Biochemical and physiological evidence suggest that pre‐synaptic calcium channels are attached to the transmitter release site within the active zone by a molecular tether. A recent study has proposed that ‘Rab3a Interacting Molecule’ (RIM) serves as the tether for CaV2.1 channels in mouse brain, based in part on biochemical co‐immunoprecipitation (co‐IP) using a monoclonal antibody, mRIM. We previously argued against this idea for CaV2.2 calcium channel at chick synapses based on experiments using a different anti‐RIM antibody, pRIM1,2: while staining for the two proteins co‐localized and co‐varied at the transmitter release face, consistent with an association, they failed to co‐IP from a synaptosome membrane lysate. RIM is, however, a family of proteins and we tested the possibility that the mRIM antibody used in the more recent study identifies a particular channel‐tethering variant. We find that co‐immunostaining with mRIM and anti‐CaV2.2 antibody neither co‐localized nor co‐varied at the transmitter release face and the two proteins did not co‐IP, arguing against a common protein complex and a key CaV2.2 scaffolding role for RIM at the active zone. The differing results might be reconciled, however, in a model where a RIM family member contributes to a protein bridge that anchors the pre‐fusion secretory vesicle to the calcium channel protein complex.
Viral entry mechanisms: cellular and viral mediators of herpes simplex virus entry
Authors: Akhtar Jihan , Shukla Deepak
Published: October 2009

Herpes simplex virus type‐1 and type‐2 are highly prevalent human pathogens causing life‐long infections. The process of infection begins when the virions bind heparan sulfate moieties present on host cell surfaces. This initial attachment then triggers a cascade of molecular interactions involving multiple viral and host cell proteins and receptors, leading to penetration of the viral nucleocapsid and tegument proteins into the cytoplasm. The nucleocapsid is then transported to the nuclear membrane and the viral DNA is released for replication in the nucleus. Recent studies have revealed that herpes simplex virus entry or penetration into cells may be a highly complex process and the mechanism of entry may demonstrate unique cell‐type specificities. Although specificities clearly exist, past and ongoing studies demonstrate that herpes simplex virus may share certain common receptors and pathways that are also used by many other human viruses. This minireview helps to shed light on recent revelations on the herpes simplex virus entry process.
Death‐associated protein kinase (DAPK) and signal transduction: regulation in cancer
Authors: Michie Alison M. , McCaig Alison M. , Nakagawa Rinako , Vukovic Milica
Published: October 2009

Death‐associated protein kinase (DAPK) is a pro‐apoptotic serine/threonine protein kinase that is dysregulated in a wide variety of cancers. The mechanism by which this occurs has largely been attributed to promoter hypermethylation, which results in gene silencing. However, recent studies indicate that DAPK expression can be detected in some cancers, but its function is still repressed, suggesting that DAPK activity can be subverted at a post‐translational level in cancer cells. This review will focus on recent data describing potential mechanisms that may alter the expression, regulation or function of DAPK.
Retrospective Analysis of Long‐term Lipid Apheresis at a Single Center
Authors: Koziolek Michael J , Hennig Ulrich , Zapf Antonia , Bramlage Carsten , Grupp Clemens , Armstrong Victor W , Strutz Frank , Müller Gerhard A
Published: October 2009

We retrospectively analyzed 10 906 lipid apheresis sessions (heparin‐induced lipoprotein precipitation, direct adsorption of lipoproteins, double filtration plasmapheresis, dextran sulfate adsorption, and immunoadsorption) in 38 patients who were consecutively treated in our department during the last 20 years. The incidences of major cardiovascular events (MACE) (death, cerebrovascular accident, myocardial infarction, limb amputation, and renal vascular involvement) were taken separately as primary end‐points or as a combined end‐point. The time‐course of secondary end‐points (coronary and extracranial status of arteries, left ventricular function, occlusive artery disease, and calculated glomerular filtration rate [cGFR]) were also evaluated, as well as the extent of the reduction in plasma lipids and lipoproteins and the incidence of therapy associated side‐effects. MACE decreased from 7.02% events per patient per year at the start of lipid apheresis to 1.17% during lipid apheresis and the rate of myocardial revascularization decreased from 22.8% to 3.8% per patient per year. Classical (diabetes mellitus, arterial hypertension, and smoking history), as well as novel risk factors (cGFR < 60 mL/min, statin withdrawal, mixed hyperlipoproteinemia, and elevated lipoprotein (a)) were associated with an elevated risk for MACE. All applied methods had comparable effects. All lipid apheresis methods proved to be safe and suitable for long‐term treatment. The present data demonstrate that treatment with lipid apheresis is very effective and leads to long‐term reduction in cardiovascular mortality and morbidity.
Genetic control of invasive plants species using selfish genetic elements
Authors: Hodgins Kathryn A. , Rieseberg Loren , Otto Sarah P.
Published: October 2009

Invasive plants cause substantial environmental damage and economic loss. Here, we explore the possibility that a selfish genetic element found in plants called cytoplasmic male sterility (CMS) could be exploited for weed control. CMS is caused by mutations in the mitochondrial genome that sterilize male reproductive organs. We developed an analytical model and a spatial simulation to assess the use of CMS alleles to manage weed populations. Specifically, we examined how fertility, selfing, pollen limitation and dispersal influenced extinction rate and time until extinction in populations where CMS arises. We found that the introduction of a CMS allele can cause rapid population extinction, but only under a restricted set of conditions. Both models suggest that the CMS strategy will be appropriate for species where pollen limitation is negligible, inbreeding depression is high and the fertility advantage of females over hermaphrodites is substantial. In general, spatial structure did not have a strong influence on the simulation outcome, although low pollen dispersal and intermediate levels of seed dispersal tended to reduce population extinction rates. Given these results, the introduction of CMS alleles into a population of invasive plants probably represents an effective control method for only a select number of species.
A Fluid Film Squeezed Between Two Rotating Parallel Plane Surfaces
Authors: Hamza E. A.
Published: October 2009

This paper is concerned with the motion of a fluid film squeezed between two rotating parallel plane surfaces. Attention is given to the case of impulsive squeezing and impulsive rotation. Approximate analytic solutions are obtained and a numerical solution to the full nonlinear equations of motion is presented. The results show that the centrifugal inertial forces increase the radial outflow and reduce considerably the load capacity while the noncentrifugal inertial forces increase the torque.
Stability of Multirecess Hybrid-Operating Oil Journal Bearings
Authors: Chen Y. S. , Wu H. Y. , Xie P. L.
Published: October 2009

An analysis and a numerical solution using finite difference method to predict the dynamic performance of multirecess hybrid-operating oil journal bearings are presented. The linearized stiffness and damping coefficients of a typical capillary-compensated bearing with four recesses are computed for various design parameters. The corresponding stiffness and the stability threshold of the bearing are then obtained, and the opposite influences of the hydrodynamic action on them are demonstrated. The effect of rotor flexibility on the onset of self-excited whirl is discussed, and a method is given to determine the stability threshold of a rotor-hybrid bearing system.
Plane Slider Bearing Load Due to Fluid Inertia—Experiment and Theory
Authors: Tichy J. A. , Chen S.-H.
Published: October 2009

Experimental measurements of load in a simulated plane slider bearing have been performed. The flow is laminar but modified Reynolds numbers up to 30 are obtained. In comparison with actual bearings, large film thickness and slow velocity are used to avoid experimental difficulties and isolate the inertia effect. The load is found to have increased by 100 percent relative to lubrication theory at modified Reynolds number about ten. Most existing inertia theories predict only a small effect at this Reynolds number. A simple theory is proposed to account for this discrepancy, combining existing models which have considered an inlet pressure jump and small Reynolds number perturbation analysis.
Evaluation of Various Approximate Solutions for Fluid Inertia Effects on the Dynamic Performance of a Stepped Thrust Bearing
Authors: Haruyama Y. , Kazamaki T. , Mori A. , Mori H.
Published: October 2009

Based on the Navier-Stokes equations in which the pressure is assumed to be constant across the film thickness, various approximate solutions and the exact one for the dynamic performance of an infinitely wide, stepped thrust bearing in a laminar flow regime are presented under the assumption of a small harmonic vibration. From comparison of the approximate solutions with the exact one, it is concluded that some kind of averaging approach in which the time dependent term is treated exactly while the convective inertia terms are averaged out across the film thickness gives close approximations in a wide range of designing conditions, and that the other kind of averaging approach in which all the inertia terms including the time dependent term are averaged out across the film thickness gives fairly good approximations.
Stability, Load Capacity, Stiffness, and Damping Advantages of the Double Pocket Journal Bearing
Authors: Nicholas J. C.
Published: October 2009

The double pocket bearing design is discussed and compared to the plain three axial groove bearing. Rigid rotor stability, load capacity, and stiffness and damping curves are shown for the two bearing designs illustrating the stability and load capacity advantages of the double pocket bearing. Results show that placing double opposing stepped pockets in the top pads of a three axial groove bearing is a simple, inexpensive, expedient modification that is effective in suppressing oil whirl instability. Furthermore, the bottom plain pad retains the load carrying capacity of the original three axial groove design. Frequency spectrums substantiating the stabilizing ability of the double pocket design are shown for a test stand instability problem.
A Generalized Integral Numerical Solution Method for Lubrication Problems
Authors: Khader M. S.
Published: October 2009

A generalized numerical method for solving Reynolds equation of lubrication is developed. The method is general for the Reynolds equation in its one and two dimensional forms. The present numerical technique is based on converting the differential form of Reynolds equation to an integral form and using there with a universal singular solution of a unit source Poisson’s type equation. A fast efficient iterative numerical scheme is then employed for solving the integral equation for the pressure distribution. The paper is divided into two parts, the first is devoted to the method development while the second part is confined to the application of the method to different problems related to bearings.
The Oxidational Wear of High-Chromium Ferritic Steel on Austenitic Stainless Steel
Authors: Allen C. B. , Quinn T. F. J. , Sullivan J. L.
Published: October 2009

Experiments are described in which high-chromium ferritic steel pins were slid, without lubrication, against austenitic stainless steel disks, under loads varying from 7 to 95N and speeds varying from 0.23 to 3.3 ms−1. Although no external heating was supplied, all the worn surfaces were oxidized, as also was the wear debris, indicating that some form of mild wear always occurred under these conditions. Measurements were made, using a special tilt correction facility on the Scanning Electron Microscope, of the thicknesses of the oxide formed both on the pin and the disk surfaces, due to the evolution of frictional heating at the interface. The division of heat at the interface was also deduced from thermocouple measurements. These measurements, combined with the surface model used as the basis for the Oxidational Wear Theory, are shown to give rise to independent estimates of the contact temperature (Tc), the number of contacts beneath the pin at any instant (N), and the radius (a) of each of those contacts, that are consistent with those obtained in earlier published experiments involving the mild wear of low-alloy steels. In these earlier experiments, the validity of the estimates of N, Tc and “a,” depended upon the validity of the choice of Arrhenius Constant used in the Oxidational Wear Theory. The correlation between the two sets of estimates is discussed. Suggestions are made for further work to validate the Oxidational Theory of the mild wear of these industrially-important materials, particularly at elevated temperatures.
A New Method of Evaluating Metal-Working Lubricants
Authors: Ramaraj T. C. , Shaw M. C.
Published: October 2009

When two identical penny shaped disks mounted one above the other are upset simultaneously in uniaxial compression, they deform differently if friction on the upper die surface may be covered by a thin film of teflon which results in essentially zero friction there while the lower die surface corresponds to a lubricant-die material-work material combination to be evaluated. After deformation, the thickness of the upper disk at its center (h1) will be less than the central thickness of the lower disk (h2) if friction on the lower die surface is greater than on the upper die surface. The ratio h1/h2 provides a sensitive measure of the difference in frictional resistance on the upper and lower die surfaces and may be used to evaluate different lubricant-die material-work material-die finish combinations for different degrees of reduction. Representative experimental results are presented and discussed.
A High Pressure-Short Time Shear Strength Analyzer for Lubricants
Authors: Jacobson B.
Published: October 2009

High pressure rheology of lubricants under transient pressure and shear stress loads is studied experimentally. The total compression time is about 140 μs and the maximum pressure during the impact time is 5.5 GPa. The results from this high speed test apparatus agree well with static tests of the shear strength increase with pressure up to 2.2 GPa.
The Elastohydrodynamic Solution of Journal Bearings Under Dynamic Loading
Authors: Oh K. P. , Goenka P. K.
Published: October 2009

The Newton-Raphson algorithm was used in conjunction with Murty’s algorithm and the finite-element method to analyze the elastohydrodynamic lubrication of a journal bearing under dynamic loading. Cavitation boundary conditions were used. A realistic compliance matrix and load schedule were used in the illustrative example. Solutions for the film pressure, the film thickness and its rate of change with time were obtained as functions of the crank angle.
Frictional Properties of a Surface Covered With Soft Metal Film (Interference Effect of Soft Metal Film Deformation Between Two Protuberances)
Authors: Kato Shinobu , Marui Etsuo , Tachi Kiyoo
Published: October 2009

The frictional characteristic is examined with reference to a model considering the interference effect of plastic flow (deformation) in soft metal film, when a two-protuberance indentor is slid on a surface covered by electroplated soft metal film. The result is compared with that of a single-protuberance indentor. The coefficient of friction in a two-protuberance indentor, where the interference effect exists, is lower than in a single-protuberance indentor, where the interference effect does not. This fact can well be explained with the configuration of plastic flow line on protuberances described by deforming soft metal film, and the corresponding contact pressure distribution between protuberances and a surface.
The Mechanism of Friction in Boundary Lubrication
Authors: Komvopoulos K. , Saka N. , Suh N. P.
Published: October 2009

The primary friction mechanism between boundary-lubricated sliding surfaces was investigated. Experiments were performed on well-polished aluminum, copper, and chromium using mineral oil lubricant. It was found that the prevailing boundary lubrication model, which is based on the adhesion between asperities and shearing of the lubricant film, cannot account for the formation of plowing grooves on polished surfaces. Scanning electron micrographs of the worn surfaces and surface profiles have shown that plowing is the dominant mechanism of friction in boundary lubrication. Theoretical analysis has shown that the coefficient of friction depends on the sharpness and the size of the entrapped wear debris or the surface asperities, and the interfacial “frictional” conditions. Reasonable agreement was obtained between theoretical and experimental friction coefficients.
The Reduction of Adhesion by Ion Implantation
Authors: Hirano M. , Miyake S.
Published: October 2009

The effects of boron and argon ion implantation on the tribological characteristics of SUS440C stainless steel, sliding against a SUS440C ball (unimplanted) were investigated at room temperature using a friction test apparatus employing a ball-plate geometry in the absence of a lubricant. Wear performance was estimated using a profilometer tracing of the specimen wear track. Boron implantation reduced both the friction and wear of SUS440C. The friction coefficient of SUS440C was reduced from 0.75 to 0.15. SEM observations of wear track topography suggest that the reduction of the friction coefficient can be attributed to reduced adhesion due to boron implantation. The friction coefficient of the boron implanted layer decreased with an increase in the total ion dose. Argon implantation was carried out to distinguish the effects of implantation from the influence of contamination. Argon implantation increased the friction coefficient from 0.8 to 1.0 in contrast with boron implantation.
A Semi-Quantitative Method for Thin Film Adhesion Measurement
Authors: Ting Bond-Yen , Winer W. O. , Ramalingam S.
Published: October 2009

Film deposition techniques are used in several applications. In tribology, wear and friction can be changed significantly by depositing a thin film on the contacting surfaces. A vital factor for this application is the adhesion between the film and the substrate. Due to high contact stresses in many tribological applications, high adhesion is required. Measurement of adhesion is therefore important if coated elements are to be used with confidence. A method has been developed for the measurement of adhesion which uses a composite model. This method is presented in this paper. A one-dimensional elastic analysis is sufficient to determine adhesion strength. In this method an interfacial shear stress is generated at the film-to-substrate interface by imposing a strain difference between the film and substrate. This interfacial shear stress is used to evaluate film adhesion. If the film-substrate adhesion is less than the shear stress applied to the interface the film will debond; otherwise, it will remain adhered to the substrate. The analysis developed yields a quantitative expression for the interfacial shear strength. Therefore the adhesion can be quantitatively determined.
Formulas for Moderately Elliptical Hertzian Contacts
Authors: Greenwood J. A.
Published: October 2009

For small ellipticities the Hertzian contact pressure and approach can be obtained to a good approximation by using the formulae for circular contact with an equivalent radius of curvature (AB) −1/2, where A and B are the principal relative curvatures. For higher ellipticities (AB(A + B)/2)−1/3 should be used to find the contact area and pressure; an equivalent radius for finding the approach is also given. The ellipticity of the contact can be estimated from the asymptotic equation (a/b) ≈ (B/A)2/3.
Dynamically Loaded Journal Bearings: A Finite Element Treatment for Rigid and Elastic Surfaces
Authors: LaBouff G. A. , Booker J. F.
Published: October 2009

Hydrodynamic lubrication of dynamically loaded journal bearings with both rigid and flexible housings is treated by a unified computational procedure based on the finite element method. Numerical examples show effects of mesh density and housing flexibility under steady and periodic loading.
Starvation in Dynamically Loaded Flexible Short Journal Bearings
Authors: van der Tempel L. , Moes H. , Bosma R.
Published: October 2009

A starvation model is incorporated in a previously presented numerical method for calculating film thicknesses inflexible short journal bearings under dynamic load. The system of elastohydrodynamic integro-differential equations is now coupled with continuity equations for the lubricant, considering central circumferential oil grooves and a constant supply pressure. An important application of this method is the connecting rod bearing in medium speed combustion engines. Results for several groove geometries are compared with those for a fully flooded bearing.
Effects of Surface Roughness on Lubrication in Cold Rolling of Metals
Authors: Lu S. S. , Chuang Y. H.
Published: October 2009

Experiments were conducted on a laboratory rolling mill to assess the effects of surface roughness on lubrication in the cold rolling of thin steel and aluminum strips by measuring the forward slip, frictional power, roll force, and change in surface roughness. Adverse lubricating conditions indicated by higher forward slip and frictional power were found when a strong longitudinal directionality was present on the initial strip surface. Favorable lubricating conditions were found when the initial strip surface had strong transverse directionality because of the ease of bringing lubricant into the roll gap and formation of oil pockets on the strip surface.
Simulation of Random Surface Roughness-Induced Contact Vibrations at Hertzian Contacts During Steady Sliding
Authors: Soom Andres , Chen Jern-Wen
Published: October 2009

Random normal contact vibrations, excited by surface irregularities swept through the contact region of Hertzian contacts during sliding, are studied using digital simulation techniques. The input disturbances are modeled as random time processes with specified spectral content in the spatial wavenumber and frequency domains. The Hertzian contact stiffness is modeled directly or through a bilinear approximation. The contact vibration spectra and resulting mean square contact loading are obtained from the simulations. A comparison with previous measurements shows good agreement between the simulation and experimental results.
Growth Mechanism of Subsurface Crack Due to Hertzian Contact
Authors: Kaneta M. , Murakami Y. , Okazaki T.
Published: October 2009

The variations of three-dimensional mixed mode stress intensity factors for a circular crack under a Hertzian contact pressure moving over the surface are calculated by taking into account both the frictional forces between the crack faces and between the contact surfaces. The circular (penny shaped) crack is assumed to be embeded parallel to the surface. The crack opening occurs near the leading crack tip as well as near the trailing crack tip depending on the pass of the contact load. The crack propagates mainly Mode II, though application of a high surface traction or a heavy contact load can induce the tensile mode crack growth. When the surface traction is directed from left to right, the left side crack tip propagates parallel to the surface and the right side crack tip extends toward the surface.
A Generalized Squeezing Flow of a Power-Law Fluid Between Two Plane Annuli
Authors: Elkouh A. F. , Nigro N. J. , Glowacz A.
Published: October 2009

A generalization of the problem of laminar squeezing flow of a non-Newtonian fluid between plane annular surfaces is presented. The generalization considers the effect of difference in the pressures at the inner and outer boundaries. The fluid is assumed to be incompressible, and the non-Newtonian behavior of the fluid is described by a power-law model. Expressions for the pressure distribution and load capacity are presented along with tables that are used for obtaining numerical results.
Stokes Roughness Effects on Hydrodynamic Lubrication. Part II—Effects Under Slip Flow Boundary Conditions
Authors: Mitsuya Y.
Published: October 2009

Stokes roughness effects on hydrodynamic lubrication are studied in the slip flow regime. Slip flow boundary conditions for Navier-Stokes equations are derived, assuming that the fluid on a surface slips due to the molecular mean free path along the surface, even if the surface is rough. The perturbation method for Navier-Stokes equations, which was derived in Part I of this report, is then applied. Slip flow effects on load carrying capacity and frictional force are numerically clarified for both Stokes and Reynolds roughnesses. In the slip flow regime, second-order quantities induced by Stokes effects, such as flow rate, load carrying capacity, and frictional force are in proportion to the wavenumber squared. This phenomenon relative to the quantities being proportional is also the same as that in the continuum flow regime. As a result of velocity slippage, the load carrying capacity in Stokes roughness is found to decrease more than in Reynolds roughness for incompressible films, while the relationship is reversed for compressible films having a high compressibility number. The simulation of random roughness, which is generated by numerical means, clarifies one important result: the average slip flow effects associated with random Stokes roughness become similar to the slip flow effects in deterministic sinusoidal Stokes roughness, whose wavelength and height are statistically equivalent to those of random roughness. Although attention should be given to the fact that Stokes effects on random roughness demonstrate considerable scattering with the continuum flow, such scattering diminishes with the slip flow.
A Thermohydrodynamic Solution of Pivoted Thrust Pads: Part I—Theory
Authors: Jeng M. C. , Zhou G. R. , Szeri A. Z.
Published: October 2009

The object is construction of a thermohydrodynamic theory of thrust bearings. The bearing pad has the geometry of an annular sector and is supported in one point; about this point it is free to pivot. The film shape is arbitrary, thus permitting specification of thermal-elastic deformation and/or crowning of the pad. The lubricant which is interposed between bearing pad and runner has temperature dependent viscosity. The lubricant flow may be laminar or turbulent. The numerical method employed in this work is the method of Finite Differences for the pressure equation and Galerkin’s method with B-spline test functions for the energy equation.
A Thermohydrodynamic Solution of Pivoted Thrust Pads: Part III—Linearized Force Coefficients
Authors: Jeng M. C. , Szeri A. Z.
Published: October 2009

This is Part III, of a three-part sequence of papers on pivoted thrust pads. In this paper we calculate the linearized spring and damping coefficients of pivoted pads. Both the stiffness and the damping are shown to be strongly influenced by the degree of crowning. Spherical crowning is employed here to simulate pad deformation under the combined action of pressure and heat.
Thermo-Elasto-Hydrodynamic-Analysis of Step and Diaphragm Thrust Bearing
Authors: Tieu A. K.
Published: October 2009

In this paper, the beneficial effects of elastic diaphragm deflection within a confined inlet area are demonstrated when it is incorporated in a conventional tilting bearing (diaphragm tilting bearing), step bearing (step and diaphragm bearing), and parallel bearing (diaphragm bearing). Rigid support of the diaphragm pad is required to utilize full potential of this bearing. The step and diaphragm pad provides a physical bearing that has the capacity approaching the optimum bearing which was based on numerical optimization.
Mixing Inlet Temperatures in Hydrodynamic Bearings
Authors: Heshmat H. , Pinkus O.
Published: October 2009

Cold and hot lubricant mixing at the inlet to a hydrodynamic bearing has been an unresolved and critical problem in determining bearing performance. The paper offers a conceptual and experimental investigation of the mechanism of mixing in the groove, in terms of the relevant flows and temperatures. The carryover from pad to pad of the discharging hot fluid film, the flow dynamics in the groove and the effects of cavitation are all determined in detail in the light of available experiments. Results of an extensive series of tests aimed at measuring the mixing inlet temperatures as a function of a range of operating conditions and bearing sizes are correlated in terms of an appropriate mixing function. Empirical equations based on the above correlation for the determination of the inlet temperatures are then given for both thrust and journal bearings.
Estimating the Severity of Sub-Synchronous Shaft Vibrations Within Fluid Film Journal Bearings
Authors: McHugh J. D.
Published: October 2009

Frequency analyzers sometimes show that shaft proximity probe signals have both a subsynchronous and synchronous component. For shafts supported on fluid-film bearings, a widely-held concern exists over any subsynchronous vibrations, even when the levels are limited in magnitude. Little information has existed for judging the impact of such vibrations on the bearing. In the present paper, a rational method is developed for estimating the dynamic load imposed on a bearing by combinations of sub-synchronous and synchronous vibration. Curves are provided for several bearing geometries which can be used to estimate the maximum dynamic load produced by such vibrations. The curves may also be used to estimate the combination of sub-synchronous and one-per-rev shaft vibrations permissible for some limiting dynamic bearing load.
The Effects of Fluid Inertia Forces in Parallel Circular Squeeze Film Bearings Lubricated With Pseudo-Plastic Fluids
Authors: Hashimoto Hiromu , Wada Sanae
Published: October 2009

The effects of fluid inertia forces in parallel circular squeeze film bearings lubricated with pseudo-plastic fluids are examined theoretically. In the derivation of lubrication equation, the cubic equation obtained from the empirical flow curves for pseudo-plastic fluids is used as the relation between shear stress and shear strain rate, and the inertia term in the momentum equation is approximated by the mean value averaged across the film thickness. Numerical solutions for the film pressure of circular bearings lubricated with Newtonian and pseudo-plastic fluids under the sinusoidal squeeze motion are presented in graphical form and the effects of inertia forces on the film pressure are determined.
Entry Flow in a Narrow Channel of Varying Gap With One Sliding Surface
Authors: Tichy J. A.
Published: October 2009

An upstream potential flow analysis is performed for the entrance region of a narrow channel in the presence of fluid inertia forces. Existing thin film solutions for slider bearings have an anomalous singularity in the pressure gradient, due to the parabolic nature of the thin film equations. Although the geometry of the present paper is somewhat different than that of the slider bearing, the problem of the singularity is resolved and some information can be obtained regarding inlet flow in the more practical slider bearing case. The potential core flow solution consists of a uniform flow first-order solution, which accelerates due to the narrowing of the bearing, and a second-order displacement solution which decelerates due to the growth of boundary layers. The resulting pressure and velocity behavior are illustrated. To form a uniformly valid solution, the present upstream analysis must be matched to the downstream (thin film) result.
Adsorption Studies With Radiolabeled Zinc Dialkyldithiophosphate
Authors: Otto K. , Sorek H.
Published: October 2009

Adsorption of zinc di-n-octyldithiophosphate synthesized with radioactive 65Zn has been studied on iron, steel, silica, and carbon. Adsorption on iron powder in an inert atmosphere is described by Elovich kinetics and Langmuir type isotherms. Adsorption equilibrium was not complete even after ten days. Results indicate activated chemisorption with an apparent activation energy of 15 kJ/mol (3.6 kcal/mol) on relatively uniform adsorption sites. Adsorbent composition, oxygen concentration, and solution contaminants, such as methanol, strongly influence adsorption capacity. Monolayer coverage, derived from the Langmuir isotherm, is in reasonable agreement with differently derived literature values. Pronounced variations observed on different adsorbents are thought to be caused by catalytic decomposition or oxidation of ZDDP. Because of this sensitivity, it appears that laboratory studies with simplified systems cannot provide much information on the actual structure of an antiwear layer formed in practical multicomponent lubricants.
Experimental Investigation of Cutting Fluid Interaction in Machining
Authors: Naerheim Yngve , Smith Tennyson , Lan Ming-Shong
Published: October 2009

Scanning Auger analysis of fracture surfaces of chips from cutting 4340 steel bars and 4130 steel tubing using CCl4 as a model cutting fluid provide evidence that it is possible for cutting fluid or vapor to penetrate into the chip along fissures created during chip formation. Similar analysis of the rake face on the tools provide evidence of partial penetration between the tool and chip as well. The effect of the penetration is to reduce the energy required for the cutting process by facilitating the chip formation and reducing the adhesion forces between the tool and chip. The penetration can be explained by the capillary action of fissures that provide reactive surfaces and fast propagation paths for the cutting fluid and vapor.
Fast Approach for Calculating Film Thicknesses and Pressures in Elastohydrodynamically Lubricated Contacts at High Loads
Authors: Houpert L. G. , Hamrock B. J.
Published: October 2009

The film thicknesses and pressures in elastohydrodynamically lubricated contacts have been calculated for a line contact by using an improved version of Okamura’s approach. The new approach allows for lubricant compressibility, the use of Roelands viscosity, a general mesh (nonconstant step), and accurate calculations of the elastic deformations. The new approach is described, and the effects on film thickness, pressure, and pressure spike of each of the improvements are discussed. Successful runs have been obtained at high pressure (to 4.8 GPa) with low CPU times.
Theory Versus Experiment for the Rotordynamic Coefficients of Annular Gas Seals: Part 1—Test Facility and Apparatus
Authors: Childs D. W. , Nelson C. E. , Nicks C. , Scharrer J. , Elrod D. , Hale K.
Published: October 2009

A facility and apparatus are described for determining the rotordynamic coefficients and leakage characteristics of annular gas seals. The apparatus has a current top speed of 8000 cpm with a nominal seal diameter of 15.24 cm (6 in.). The air-supply unit yields a seal pressure ratio of approximately 7. The inlet tangential velocity can also be controlled. An external shaker is used to excite the test rotor. The apparatus has the capability to independently calculate all rotordynamic coefficients at a given operating condition with one excitation frequency.
The Tribological Behavior of an Automotive Cam and Flat Lifter System
Authors: Bair S. , Griffioen J. A. , Winer W. O.
Published: October 2009

In order to thoroughly characterize the cam/tappet contact, a simulator was designed and constructed which presents a lifter which is stationary except for rotation. The cam instead moves through the lift curve so that the contact remains essentially in the horizontal plane. Three components of contact force on the lifter are measured. A series of eight nominally flat lifter foot materials were investigated for frictional loss as a function of speed. In addition, the effects of oil temperature, running in, lifter rotation and lifter foot spherical radius was studied. With one of the lifters (Al2O3) the surface temperature of the cam was measured at peak lift employing an infrared scanning system. Peak temperatures in excess of 300° C were observed for some operating conditions. Preliminary measurements were made with a roller lifter. The loss per revolution ranged from 1.75 J to 3.9 J for the flat followers. The roller follower loss was 18 percent of that of the flat follower for similar conditions.
A Review of DOE ECUT Tribology Surveys
Authors: Dake L. S. , Russell J. A. , Debrodt D. C.
Published: October 2009

Experts estimate that in 1978 over four quadrillion Btu of energy were lost in the United States because of simple friction and wear. The Energy Conversion and Utilization Technology Program (ECUT) in the U.S. Department of Energy commissioned six surveys from various experts in the field of tribology to learn about the causes of these energy losses and how to reduce them. The surveys included: 1) identification of typical tribology energy sinks in industry, 2) reduction of tribological losses in utilities and transportation, 3) tribological research needed for advanced heat engines, 4) energy conservation potential of new surface modifications, 5) identification of current tribology work sponsored by the government, and 6) an assessment of industrial research needs. A summary of the major findings of each survey is included in this paper.
A Finite Element Analysis of Contact Stress and Strain in an Elastic Film on a Rigid Substrate—Part I: Zero Friction
Authors: Ihara T. , Shaw M. C. , Bhushan B.
Published: October 2009

The stresses and strains in a semi-infinite homogeneous body indented by a rigid sphere is a classical problem first investigated by Hertz. The special case of a thin elastic layer on a rigid substrate indented by a rigid sphere is considered here using a finite element approach. This is a problem of interest in the hardness testing of thin sheet material and in engineering design when the applied load is axially directed. When the applied load has a frictional (tangential) component, the results are of particular interest in tribology. The study is divided into two parts. The first considers purely axial loading while the second part, presented in a companion paper, considers a combination of axial and tangential loading. Results in both cases are compared with the well known Hertz solution.
A Finite Element Analysis of Contact Stress and Strain in an Elastic Film on a Rigid Substrate—Part II: With Friction
Authors: Ihara T. , Shaw M. C. , Bhushan B.
Published: October 2009

Deformation and elastic stress characteristics are considered for a thin elastic film on a rigid substrate when loaded by a rigid cylindrical indentor in conjunction with different amounts of friction. Friction tends to move the point of maximum shear stress from below the loaded surface into this surface, particularly when the elastic film is thin relative to the width of contact. Increased friction also increases the magnitude of the horizontal tensile stress (σx) in the free top surface and moves it closer to the trailing edge of the indentor. Friction has a rather negligible influence on the depth of deformation for a given loading condition but substantially increases the magnitude of the peak normal stress in the loaded surface and moves it toward the leading edge of the indentor.
Stress Intensity Factors for Small Cracks in the Rim of Disks and Rings Subjected to Rolling Contact
Authors: Lei T. S. , Bhargava V. , Hahn G. T. , Rubin C. A.
Published: October 2009

The influence of the residual stresses attending the plastic deformation of a rim on the cyclic crack growth driving force produced by repeated two-dimensional rolling contacts is evaluated. The residual stresses are estimated for disks and rings with different geometries. Values of the Mode II and Mode I stress intensity range, ΔKI and ΔKII, are derived for small, subsurface cracks from the variations in the stress intensity factors with position of the contact for rolling in the absence of surface shear tractions. The calculations take into account (i) steady-state contact stresses generated by a relative peak pressure of po/k = 5; (ii) the radial and circumferential residual stresses, (iii) the frictional resistance on the crack faces; (iv) the crack inclination, and (v) the relative ratios of the inner and outer ring radii. A prediction of the crack initiation and growth rate for high strength steel is illustrated.
Experimental Investigation of the Shear Strength of Lubricants Subjected to High Pressure and Temperature
Authors: Ho¨glund E. , Jacobson B.
Published: October 2009

In order to evaluate the relationship between limiting shear strength and pressure for a lubricant an experimental apparatus has been built. Pressures up to 2.2 GPa and temperatures up to 200°C are attainable simultaneously. Thus the limiting shear strength-pressure relationship has been surveyed in a wide range. Several types of natural and synthetic lubricants have been tested. The results show that all the mineral oils tested behave in quite a similar way. Synthetic lubricants do not show this behaviour, but the relationship between limiting shear strength and pressure depends strongly upon the chemical base of the synthetic lubricants. The behaviour of grease does not differ from that of liquid lubricants. The pressures at which the lubricants change from a liquid to a solid behaviour have also been measured.
Behavior of an Oscillating Oil Squeeze Film
Authors: Parkins D. W. , Woollam J. H.
Published: October 2009

This paper records observations of the behavior of an oil film subject to an oscillatory squeeze motion of its containing surfaces. In the experimental apparatus, the square upper surface oscillated at a frequency within the range 5–45 Hz and contained two pressure transducers. A fixed transparent lower surface facilitated viewing of cavitation patterns and their position relative to the pressure transducers. A computer controlled technique enabled these patterns to be photographed at any selected point in the oscillatory cycle, and synchronized with the corresponding instantaneous oil film pressure and thickness. The effect is given of vibratory amplitude, frequency and initial oil film thickness upon the steady force generated by the oscillatory squeeze motion. A previously identified cavitation regime has been shown to be more complex than hitherto supposed. Four sub-regimes have been tentatively identified. Their characteristics are described, together with photographs of typical sequences of cavitation patterns in each subregime, at identified times in the pressure and film thickness cycle. The effects of surrounding oil depth upon the vibratory amplitude at which cavitation first appears, is described. Descriptions are given of the sub-regime appearing at onset, and any changes thereto appearing with further increases in vibratory amplitude.
Test Results for Sawtooth-Pattern Damper Seals: Leakage and Rotordynamic Coefficients
Authors: Childs D. , Garcia F.
Published: October 2009

Test results consisting of direct and transverse force coefficients are presented for eleven, sawtooth-pattern, damper-seal configurations. The designation “damper” seal refers to a seal which uses a deliberately roughened stator and smooth rotor, as suggested by von Pragenau [1], to increase the net seal damping force. The designation “sawtooth-pattern” refers to a stator-roughness pattern whose cross section normal to the axis of the seal resembles saw teeth with the teeth direction opposing fluid motion in the direction of shaft rotation. The sawtooth pattern yields axial grooves in the stator which are interrupted by spacer elements which act as flow constrictions or “dams.” Sawtooth-pattern seals had more damping than smooth seals but less than the round-hole-pattern seals tested previously. Stiffness of sawtooth and round-hole-pattern seals were comparable. Leakage of maximum-damping configurations was greater for sawtooth-pattern than for round-hole-pattern seals; both types of seals leaked substantially less than did smooth seals. If damping is sacrificed, sawtooth-pattern seals can be designed to leak less than round-hole-pattern seals.
Analysis for Rotordynamic Coefficients of Helically-Grooved Turbulent Annular Seals
Authors: Kim Chang-Ho , Childs D. W.
Published: October 2009

An analysis for helically-grooved turbulent annular seals is developed to predict leakage and dynamic coefficients, as related to rotordynamics. The grooved surface pattern is formulated as an inhomogeneous directivity in surface shear stress. The governing equations, based on both Hirs’ turbulent lubrication theory and “fine-groove” theory, are expanded in the eccentricity ratio to yield zeroth and first-order perturbation solutions. The zeroth-order equations define the steady-state leakage and the circumferential velocity development due to wall shear for a centered rotor position. The first-order equations define perturbations in the pressure and axial and circumferential velocity fields due to small motion of the rotor about the centered position. Numerical results are presented for proposed grooved seals in the High Pressure Oxygen Turbopump (HPOTP) of the Space Shuttle Main Engine (SSME) and for a water-pump application. The results show that an optimum helix angle exists from a rotordynamic stability viewpoint. Further, a properly designed helically-grooved stator is predicted to have pronounced stability advantages over other currently used seals.
Parallel Sliding Load Support in the Mixed Friction Regime. Part 2—Evaluation of the Mechanisms
Authors: Lebeck A. O.
Published: October 2009

When two parallel surfaces slide parallel to each other in the presence of a liquid, classical lubrication theory shows that no load carrying capacity should result. In Part 1 of this work the experimental data showing that such load support does occur are reviewed. In this paper several of the proposed mechanisms for parallel sliding load support are evaluated by combining the mechanism with a mixed friction model and comparing predictions to experimental results. Both water and oil type bearings are considered. While there are exceptions, it has been found that in general the thermal wedge, microasperity lubrication, microasperity collisions, and squeeze effects cannot account for the large apparent load support in the experimental cases studied. However, small deviations from parallel geometry have a strong effect and can easily account for the observed load support, but several questions remain. It is concluded that future investigations should be directed to developing a better understanding of how favorable macrogeometries might be developed and searching for other sources of pressure generation in parallel sliding.
Impact on Reynolds Theory on Bearing and Seal Design
Authors: Shapiro Wilbur
Published: October 2009

The governing equation of lubrication theory was developed by Osborne Reynolds in 1886. Two-dimensional solutions to this equation were not obtained until many years afterwards, first by electric analog techniques and then by digital computer. Solving the equation has produced tremendous advances in bearing design and development and insight into the mechanisms of lubricating film behavior. This paper concentrates on some of the developments for solving the Reynolds’ equation and some applications that have followed a better understanding of fluid-film phenomena.