bluuebunny/crossref_metadata_2025 huggingface dataset:
Lessons From Single Cell Organisms: Insights Into the Antimicrobial and Toxic Effects of Peritoneal Dialysate Bases
Authors: Diskin Charles J
Published: October 2009

Although it was first described over a quarter of a century ago, the mechanisms behind the antimicrobial activity of fresh peritoneal dialysate have been poorly understood. Recent insight into the biochemistry appears to suggest that at least part of the effect resides in the salts of the carboxylic acids. An understanding of the metabolic pathways of both sensitive and resistant organisms has not only led to an understanding of the mechanisms of the antimicrobial effect, but also may have provided the insight for future studies to reduce toxicity to the peritoneal membrane. While our knowledge base in this area is still evolving, an improved understanding of the biochemical basis of both the antibacterial effect and toxicity of the salts of carboxylic acids in peritoneal dialysate can only prove useful.
Physical Activity Is Necessary to Prevent Deterioration of the Walking Ability of Patients Undergoing Maintenance Hemodialysis
Authors: Kutsuna Toshiki , Matsunaga Atsuhiko , Matsumoto Takuya , Ishii Akira , Yamamoto Kazuya , Hotta Kazuki , Aiba Naoko , Takagi Yutaka , Yoshida Atsushi , Takahira Naonobu , Masuda Takashi
Published: October 2009

Maintenance of the walking ability is very important for smooth continuation of maintenance hemodialysis (HD). The aim of the present study was to clarify the physical activity level in daily living that HD patients should maintain to prevent deterioration of their walking ability. Outpatients undergoing maintenance HD, consisting of 65 males and 88 females with a mean age of 64 ± 11 years, were recruited for the present study. Their physical activity level was recorded over a week with an accelerometer. The physical activity level in daily living was defined as the sum of the lengths of time for which the patients were engaged in physical activity of light or greater intensity during the day, and expressed as the average duration per day. The walking ability was assessed by the normal walking speed and maximum walking speed. Data were analyzed using the receiver operating characteristic (ROC) curve, and the cut‐off point for the physical activity time was determined to predict deterioration of the walking ability. In the prediction of deterioration of the normal and maximum walking speeds, the areas under the ROC curve for the physical activity time were 0.78 (95% confidence interval, 0.69–0.87, P < 0.001) and 0.75 (95% confidence interval, 0.63–0.86, P < 0.001), respectively. Moreover, the ROC curve revealed that the cut‐off point for the physical activity time to prevent deterioration of the normal and maximum walking speeds was 50 min/day. Thus, HD patients should engage in physical activity for at least 50 min/day to prevent deterioration of their walking ability.
BOOTSTRAP CONFIDENCE INTERVALS FOR THE KINETIC PARAMETERS OF DEGRADATION OF ANTHOCYANINS IN GRAPE POMACE
Authors: MISHRA D.K. , DOLAN K.D. , YANG L.
Published: October 2009

Because of the growing interest in nutraceuticals and their health benefits, it is important to develop tools for modeling degradation of nutraceuticals in low‐moisture‐ and high‐temperature‐heated foods. The objective of this study was to estimate the kinetic parameters for the degradation of anthocyanins in grape pomace and to calculate the bootstrap confidence interval (CI), which is a more realistic estimate of the true CI than the commonly used asymptotic CI. Thermal and kinetic parameters for unsteady‐state conduction‐heated foods (grape pomace) were estimated separately using an inverse problem technique. Rate constant (kr) and activation energy (Ea) for the degradation of anthocyanins in grape pomace were estimated, and the 95% bootstrap CIs were calculated and compared with the 95% asymptotic CIs. Grape pomace at 42% moisture content (wet basis) in steel cans (radius 0.027 m, and height 0.073 m) was heated in a steam retort at 126.7C. Anthocyanin retention was measured by high‐performance liquid chromatography. The retention values were used to estimate kinetic parameters, which were k113.9C = 0.0606/min and Ea = 65.32 kJ/mol. Asymptotic CIs for k113.9Cand Ea were 0.052 and 0.068, and 23.3 and 102.7, respectively. Bootstrap 95% CIs for k113.9Cand Ea were 0.053 and 0.066, and 49.08 and 104.9, respectively. Bootstrap confidence band and bootstrap prediction band (PB) for anthocyanin retention were smaller than asymptotic confidence and PBs, respectively. The smaller width of the bootstrap bands, which are considered more accurate than asymptotic bands, allows more accurate process design and cost‐savings, potentially leading to higher‐quality nutraceutical products.

PRACTICAL APPLICATIONS

Thermal and kinetic parameters for unsteady‐state conduction‐heated foods (grape pomace) were estimated separately using nonlinear regression techniques. This non‐isothermal method of estimating thermal and kinetic parameters is fast, convenient and more accurate than the isothermal method. Also, for certain application such as low‐moisture solids at high temperatures, isothermal experiments are not feasible. There is much more information gained from the type of plot presented here than from the typical plot with only one fitted line showing the mean values. The smaller width of the bootstrap bands, which are considered more accurate than asymptotic bands, allows more accurate process design and cost‐savings, potentially leading to higher‐quality nutraceutical products.
Relative Efficiency of the Fuzzy p‐Value Approach to Hypothesis Testing
Authors: Kuk Anthony Y. C. , Xu Jinfeng
Published: October 2009

In missing data problems, it is often the case that there is a natural test statistic for testing a statistical hypothesis had all the data been observed. A fuzzy p‐value approach to hypothesis testing has recently been proposed which is implemented by imputing the missing values in the “complete data” test statistic by values simulated from the conditional null distribution given the observed data. We argue that imputing data in this way will inevitably lead to loss in power. For the case of scalar parameter, we show that the asymptotic efficiency of the score test based on the imputed “complete data” relative to the score test based on the observed data is given by the ratio of the observed data information to the complete data information. Three examples involving probit regression, normal random effects model, and unidentified paired data are used for illustration. For testing linkage disequilibrium based on pooled genotype data, simulation results show that the imputed Neyman Pearson and Fisher exact tests are less powerful than a Wald‐type test based on the observed data maximum likelihood estimator. In conclusion, we caution against the routine use of the fuzzy p‐value approach in latent variable or missing data problems and suggest some viable alternatives.
Delving into the “Institutional Black Box”: Revealing the Attributes of Sustainable Urban Water Management Regimes1
Authors: Van De Meene Susan J. , Brown Rebekah R.
Published: October 2009

van de Meene, Susan J. and Rebekah R. Brown, 2009. Delving into the “Institutional Black Box”: Revealing the Attributes of Sustainable Urban Water Management Regimes.Journal of the American Water Resources Association(JAWRA) 45(6):1448‐1464.

Abstract: This paper is based on the proposition that the transition to sustainable urban water management has been hampered by the lack of insight into attributes of a sustainable urban water regime. Significant progress has been made in developing technical solutions to advance urban water practice, however it is the co‐evolution of the socio‐institutional and technical systems that enable a system‐wide transition. A systematic analysis of 81 empirical studies across a range of practice areas was undertaken to construct a schema of the sustainable urban water regime attributes. Attributes were identified and analyzed using a framework of nested management regime spheres: the administrative and regulatory system, inter‐organizational, intra‐organizational, and human resources spheres. The regime is likely to involve significant stakeholder involvement, collaborative inter‐organizational relationships, flexible and adaptive organizational cultures, and motivated and engaging employees. Comparison of the constructed sustainable and traditional regime attributes reveals that to realize sustainable urban water management in practice a substantial shift in governance is required. This difference emphasizes the critical need for explicitly supported strategies targeted at developing each management regime sphere to further enable change toward sustainable urban water management.
Reading ability and stereoacuity with combined implantation of refractive and diffractive multifocal intraocular lenses
Authors: Chen Weirong , Meng Qianli , Ye Haiyun , Liu Yizhi
Published: October 2009

Purpose:  To evaluate reading ability and stereoscopic vision with combined implantation of refractive and diffractive multifocal intraocular lenses (IOLs).

Methods:  Thirty‐one cataract patients (62 eyes) were assigned to receive either a ReZoom NXG1 IOL in the dominant eye and a Tecnis ZM900 IOL in the fellow eye (MIOL group), or Sensar AR40e IOLs bilaterally (SIOL group). The uncorrected visual acuity (UCVA) at 500 cm, best spectacle‐corrected visual acuity (BSCVA) at 500 cm, reading acuity, reading speed, near stereoacuity and questionnaire were assessed 3 months postoperatively.

Results:  Three months postoperatively, monocular and binocular UCVA and BSCVA at 500 cm showed no significant differences in both groups. The uncorrected reading acuity and reading speed in the MIOL group were significantly better than those in the SIOL group and were similar to that with correction in the SIOL group. The uncorrected mean near stereoacuity in the MIOL group was significantly better than that in the SIOL group (69 ± 50 seconds of arc in the MIOL group versus 180 ± 160 seconds of arc in the SIOL group). Patients in the MIOL group had a high level of satisfaction and more than 80% of them had an increased independence from spectacles for brief reading.

Conclusion:  The combined implantation of refractive and diffractive multifocal IOLs was effective in improving reading ability and near stereoacuity with a good visual quality.
Associations between chronic glycosylated haemoglobin (HbA1c) level and macular volume in diabetes patients without macular oedema
Authors: Yeung Ling , Sun Chi‐Chin , Ku Wan‐Chen , Chuang Lan‐Hsin , Chen Chih‐Hung , Huang Bi‐Yu , Ting Ming‐Kuo , Yang Ko‐Jen
Published: October 2009

Acta Ophthalmol. 2010: 88: 753–758

Purpose:  This study aimed to examine the correlation between glycosylated haemoglobin (HbA1c) level and macular volume in diabetes patients without diabetic macular oedema (DMO).

Methods:  We carried out an observational, cross‐sectional study. Patients who had diabetes mellitus (DM) of ≥ 10 years duration without DMO were included. Only one eye of each patient was selected for analysis. Eyes with proliferative diabetic retinopathy were excluded. Central subfield thickness (CST), central subfield volume (CSV) and total macular volume (TMV) were measured by optical coherence tomography (OCT). Chronic HbA1c level was defined as the mean HbA1c value in the year prior to enrolment.

Results:  We included 97 eyes from 97 patients (47 women, 50 men; mean age 62.2 years). They included eight type 1 and 89 type 2 DM patients. The mean duration of DM was 15.5 years. Forty‐two (43%) eyes had no diabetic retinopathy and 55 (57%) eyes had non‐proliferative diabetic retinopathy. In statistical analysis, CST (mean 188.80 ± 27.64 μm; r = 0.220, p = 0.030), CSV (mean 0.149 ± 0.021 mm3; r = 0.213, p = 0.036) and TMV (mean 6.497 ± 0.715 mm3; r = 0.299, p = 0.003) positively correlated with chronic HbA1c level (7.95 ± 1.29%). The linear regression model showed that chronic HbA1c level (standardized coefficient 0.253; p = 0.013) and age (standardized coefficient − 0.206; p = 0.040) were factors significantly related to TMV.

Conclusions:  Chronic HbA1c level positively correlates with macular thickness and volume in patients with DM of ≥ 10 years duration without DMO. Our results suggest that subclinical macular volume and thickness changes may occur before DMO becomes clinically evident. Early tight glycaemic control prior to the onset of DMO may play an important role in preventing the deterioration of macular function by altering macular haemodynamics.
The Effect of Added Rotation on Crosshead Bearing Performance
Authors: Takasaki M. , Ettles C. M. McC.
Published: October 2009

Crosshead bearings in two stroke engines operate under severe conditions of lubrication since the sliding velocity of the bearing parts is very low and oscillatory. A computational model is developed to find the effect of intermittently increasing the speed of rotation by indexing the pin through a few degrees of rotation at some part of the 360 deg cycle. It is found that the best position for added rotation is at bottom dead center and that the improvement in minimum film thickness is approximately proportional to the amount of extra rotation. Quite small amounts of pin indexing (ten degrees) can produce a worthwhile increase in film thickness.
A New Numerical Technique for Computing Surface Elastic Deformation Caused by a Given Normal Pressure Distribution
Authors: Hou Keping , Zhu Dong , Wen Shizhu
Published: October 2009

This paper presents a new numerical method for computing the elastic normal surface displacement field caused by a given normal pressure distribution. The pressure function is approximated by a piecewise biquadratic polynomial on the whole domain analyzed, and the deformation of every node is expressed as a linear combination of the nodal pressures whose coefficients can be combined into a deformation matrix. Consequently, the iterative calculation of elastic deformation is simplified and the amount of work is greatly reduced. It has been proved, in addition, that the numerical accuracy of the new method is higher than that of some others.
On The Role of a Non-Newtonian Fluid in Short Bearing Theory
Authors: Buckholz R. H.
Published: October 2009

The importance of rheological properties of lubricants has arisen from the realization that non-Newtonian fluid effects are manifested over a broad range of lubrication applications. In this paper a theoretical investigation of short journal bearings performance characteristics for non-Newtonian power-law lubricants is given. A modified form of the Reynolds’ equation for hydrodynamic lubrication is studied in the asymptotic limit of small slenderness ratio (i.e., bearing length to diameter, L/D = λ→0). Fluid film pressure distributions in short bearings of arbitrary azimuthal length are studied using matched asymptotic expansions in the slenderness ratio. The merit of the short bearing approach used in solving a modified Reynolds’ equation by the method of matched asymptotic expansions is emphasized. Fluid film pressure distributions are determined without recourse to numerical solutions to a modified Reynolds’ equation. Power-law rheological exponents less than and equal to one are considered; power-law fluids exhibit reduced load capacities relative to the Newtonian fluid. The cavitation boundary shape is determined from Reynolds’ free surface condition; and the boundary shape is shown to be independent of the bearing eccentricity ratio.
A Theoretical Study of Stability of a Rigid Rotor Under the Influence of Dilute Viscoelastic Lubricants
Authors: Mukherjee A. , Bhattacharyya R. , Rao Dasary A. M.
Published: October 2009

An attempt is made to study theoretically the stability of a symmetrical, horizontal, rigid rotor mounted on two identical short bearings. Dilute viscoelastic solutions are used as lubricants. Experimental studies reveal that at high shear rates, which occur in the journal bearing clearance space, the Weissenberg effect is degraded while the relaxation time remains unaltered. Harnoy proposed a constitutive equation which decouples the Weissenberg effect and relaxation time may be used to depict the constitutive relations for lubricants under above-mentioned conditions. The study reveals that an apparent inertia tensor, arising out of linearized elasto-viscous acceleration dependent forces, has a predominant effect on the stability of such a rotor. As the stability map is considerably modified by the use of viscoelastic lubricants, the high speed instability limits are extended providing an incentive for using this type of lubricants. However, some new instability patches show off which correspond to lower speeds of a rotor. Nature of their instabilities is still to be established. A rotor may, however, be so designed that it never falls inside such patches of instability during its operation and speeding up period.
Hydrodynamic Lubrication of Rigid Nonconformal Contacts in Combined Rolling and Normal Motion
Authors: Ghosh M. K. , Hamrock J. , Brewe D.
Published: October 2009

A numerical solution to the problem of hydrodynamic lubrication of rigid point contacts with an isoviscous, incompressible lubricant has been obtained. The hydrodynamic load-carrying capacity under unsteady (or dynamic) conditions arising from the combined effects of squeeze motion superposed upon the entraining motion has been determined for both normal approach and separation. Superposed normal motion considerably increases net load-carrying capacity during normal approach and substantially reduces net load-carrying capacity during separation. Geometry has also been found to have a significant influence on the dynamic load-carrying capacity. The ratio of dynamic to steady state load-carrying capacity increases with increasing geometry parameter for normal approach and decreases during separation. The cavitation (film rupture) boundary is also influenced significantly by the normal motion, moving downstream during approach and upstream during separation. For sufficiently high normal separation velocity the rupture boundary may even move upstream of the minimum-film-thickness position. Sixty-three cases were used to derive a functional relationship for the ratio of the dynamic to steady state load-carrying capacity β in terms of the dimensionless normal velocity parameter q (incorporating normal velocity, entraining velocity, and film thickness) and the geometry parameter α. The result is expressed in the form β={α−0.028sech(1.68q)}1/q The ratio of the dynamic to steady state peak pressures in the contact ξ increases considerably with increasing normal velocity parameter during normal approach, with a similar decrease during separation. The ratio is expressed as a function of q and α by ξ={α−0.032sech(2q)}1/q
Improving the Wear Resistance of Austenitic Alloys by Surface Treatment
Authors: Whittle R. D. T. , Scott V. D.
Published: October 2009

The surface hardening of a number of different austenitic alloys by thermochemical treatment and their subsequent behavior to unlubricated sliding wear is described. It is shown that nitriding, nitrocarburizing (Tufftriding) and boronizing processes generally produce hard compact layers on the metal substrate and that wear behavior is related to metal composition as well as to type of chemical treatment. The results demonstrate also that the wear performance of such surface-treated austenitic materials can compare favorably with that of a commercially nitrided ferritic alloy, provided that metal core properties are not adversely affected by the processing.
Study of Residual Stresses Induced by Sliding Wear
Authors: Mairey D. , Sprauel J. M. , Chuard M. , Mignot J.
Published: October 2009

A XC carbon steel disk was submitted to the friction of a 100 C 6 steel bearing ball on a pin-on-disk tribometer. The geometry of the surface was periodically measured as was the state of the stresses, on a single point of the wear track using a very simple location process. The wear track was quickly grooved while the normal stresses (parallel to the plane of the surface) increased fast. The shearing stresses remain weak.
Comparison of Surface Damage Caused by Sliding Wear and Cavitation Erosion on Mechanical Face Seals
Authors: Okada Tsunenori , Iwai Yoshiro , Hosokawa Yukio
Published: October 2009

To clarify the dangerous surface damage in mechanical seals, both sliding wear and vibratory cavitation erosion tests were performed on sintered carbon materials. The differences in damage between cavitation erosion and sliding wear were investigated through observation of surface topographies and volume losses. Roughness, Ra, of worn surface is rather small, about 1 μm in the worst case, and is independent of the worn depth. In cavitation erosion, however, Ra of eroded surface increases rapidly and thereafter attains a large steady value (3.6 μm- 11 μm for various carbon materials) with increasing eroded depth regardless of the cavitation intensity. The sliding surfaces of actual operating mechanical seals were compared with our test results and thus it was concluded that the severe damage in the mechanical seals is caused by the concentrated repetition of cavitation erosion. Furthermore, the wear and cavitation erosion resistance were compared among the various carbon seal materials. From these results, it has become clear that the cavitation erosion test is important to find out the quality of mechanical seal materials.
Implications of Thermoelastic Instability for the Design of Brakes
Authors: Barber J. R. , Beamond T. W. , Waring J. R. , Pritchard C.
Published: October 2009

Thermal distortion in brakes due to frictional heating causes localized contact and high temperatures (hot spots) with consequent thermal damage to the sliding components. This paper examines the effect of brake design and operating parameters on the maximum temperature reached. Previous solutions for steady-state sliding are reviewed and the effects of hot spots being in intermittent contact due to the geometric design of the brake are discussed. Approximate solutions for transient thermoelastic contact are extended to the case of uniform deceleration to determine the duration of the stop for which thermoelastic effects will be significant. If the stop is sufficiently slow for hot spots to develop, the temperatures will generally be high. However, high temperatures are also reached in sufficiently rapid stops due to the high rate of energy dissipation. An optimum is found between these extremes.
Effects of Turbulence and Viscosity Variation on the Dynamic Coefficients of Fluid Film Journal Bearings
Authors: Wilcock D. F. , Pinkus O.
Published: October 2009

Many high-speed or large fluid film bearings operate in the turbulent regime. However, relatively little consideration has been given to the effects of turbulence and of the variation in viscosity on the dynamic stiffness and damping characteristics of the bearings. Since the dynamic behavior of the rotor supported on such bearings is often closely tied to the bearing dynamic coefficients, knowledge of them may be critical to both the design and the in-place correction of rotor instabilities. These effects are here considered in some detail on the basis of computer calculated analytical results, both in general dimensionless terms and with regard to a specific numerical example.
Performance of Water-Lubricated Flat Spiral Groove Bearings
Authors: Furuishi Yoshiro , Suganami Takuya , Yamamoto Sakuei , Tokumitsu Kiyonori
Published: October 2009

The 8.6 cm diameter spiral groove bearings, solid type and support type, are designed for water-lubricated thrust application. The load-carrying capacity limit is obtained experimentally. The major conclusions are as follows: (1) The load-carrying capacity depends significantly upon the deformations of the bearing and the runner, which are caused by the temperature and hydrodynamic pressure distributions. (2) The load-carrying capacity limit is determined primarily by the surface roughness and the film thickness, and the maximum value of the load-carrying capacity obtained in this experiment is above 5 × 104 N. (3) The support type bearing gives better load-carrying capacity than the solid type.
Optimum Parallel Step-Sector Lubricated With an Incompressible Fluid
Authors: Hamrock B. J.
Published: October 2009

The dimensionless parameters normally associated with a step-sector thrust bearing are the film thickness ratio, the dimensionless step location, the number of sectors, the radius ratio, and the angular extent of the lubrication feed groove. The present paper will determine the optimum number of sectors and the parallel step configuration for a step-sector thrust bearing while considering load capacity or stiffness and assuming an incompressible fluid.
Transient Temperatures in the Vicinity of an Asperity Contact
Authors: Gecim B. , Winer W. O.
Published: October 2009

The two dimensional, transient temperature distribution in the vicinity of a small, stationary, circular heat source is derived. The source is assumed to be acting on the surface of a relatively much larger body which can be treated as semi-infinite. Formulations both with and without surface convection are considered. Successive integral transforms are used to obtain a direct solution of the governing differential equation. The transient of local temperature rise is found to be very short and very localized in the immediate vicinity of the source. The auxiliary problem of pure convective cooling, i.e., no heat input, is also presented. The initial temperature distribution is taken to be the steady distribution already derived with the heat input. The transient of local temperature in cooling-off is found to be even shorter. In both the main and the auxiliary problems, the governing parameters are source radius, heat flux, thermal conductivity and thermal diffusivity. The convective coefficient does not have a significant effect. This study is intended to represent the thermal behavior of a single asperity in an apparent area of contact. The auxiliary problem represents the cooling-off of the asperity as it moves out from the apparent contact; or it may also be the cooling-off between two consecutive asperity collisions within an apparent contact. The analysis can also be applied to multiple sources acting simultaneously, provided that they are located sufficiently far away from each other, and thermal interaction is negligible. Because the heat generated at the asperity interface must be partitioned, a partition coefficient is derived in the appendix.
Material Response to Rolling Contact Loading
Authors: Voskamp A. P.
Published: October 2009

The material response to rolling contact loading has been analyzed using quantitative X-ray diffraction methods. This has led to the discovery of preferred crystalline orientation in very narrow subsurface regions of endurance-tested 6309 deep groove ball bearing inner rings. The high hydrostatic pressure field, derived from the load-induced three-dimensional stress field in each Hertzian contact load cycle, allows substantial microplastic deformation to be accommodated in the subsurface layers. This microplastic deformation is accompanied by transformation of retained austenite, decay of martensite and the development of texture and residual stresses, one of which is a subsurface tensile stress in a direction normal to the surface. Both the preferred orientation and the tensile residual stress allow for crack propagation parallel to the rolling contact surface. Based on these findings, an outline of a qualitative model for rolling contact fatigue is presented.
The Damping Capacity of a Sealed Squeeze Film Bearing
Authors: Dede M. M. , Dogan M. , Holmes R.
Published: October 2009

The purpose of this paper is to establish a theoretical model to represent a sealed squeeze-film damper bearing and to assess it against results from a test rig, simulating the essential features of a medium-sized gas turbine aero engine.
Sliding Contact Between Dissimilar Elastic Cylinders
Authors: Hills D. A. , Sackfield A.
Published: October 2009

The problem considered is contact between two dissimilar elastic cylinders, having their axes parallel and sliding in a direction normal to the axes. The traction distribution is determined, as are the resultant stresses generated in each body. It is found that the stresses well within the body are not changed greatly from a classical Hertz analysis, where coupling between the normal and shear tractions is neglected, but that there is a first order modification of surface tensile stresses.
An Experimental Investigation of the Film-to-Substrate Bond Strength of Sputtered Thin Film Using a Semi-Quantitative Test Method
Authors: Ting Bond-Yen , Ramalingam S. , Winer W. O.
Published: October 2009

The experimentally measured adhesion strength of thin films of titanium and titanium nitride deposited on aluminum and AISI 304 stainless steel substrates are reported. A semi-quantitative test method presented and discussed in a companion paper was used to measure the film-to-substrate bond strength. The test results obtained show that the surface cleaning and preparation procedures used prior to film deposition dominate thin film adhesion. The results obtained also show that thin soft and hard films with film-to-substrate bond strength sufficient for heavily loaded tribological applications can be produced with magnetron sputtering techniques.
Steel Composition Effects on Grindability and Rolling Contact Fatigue Resistance of Bearing Steels
Authors: Torrance A. A. , Stokes R. J. , Howes T. D.
Published: October 2009

Measurements of the grindability of a bearing quality AISI 1070 steel show that it is far less susceptible to grinding burn than is AISI 52100 steel. Whereas the behavior in this respect of AISI 52100 steel has been shown to correlate well with Malkin’s thermal model, the behavior of the AISI 1070 material did not show such good correlation, even when the difference in thermal conductivity of the two materials was taken into account. It was shown, however, that the more empirically based model of Peters et al. could provide a useful prediction for AISI 1070 steel and subsequently also for the AISI 52100 steel. Rolling contact tests indicate that its fatigue resistance is as good as that of AISI 52100, so it would seem to merit serious consideration as a cheaper alternative material for mass produced bearings.
Annular Compressible Squeeze Films
Authors: Blech J. J.
Published: October 2009

The exact solution for annular isothermal squeeze films in either parallel or tilting simple harmonic motion of small amplitude is derived. Pressure distributions, forces and moments are given for any inner to outer radius ratio. Comparison of cutoff frequencies with approximate values of previous works indicates that for low inter to outer radius, there exist deviations between the approximate frequencies to the present values. Damping forces correlate well with Green and Etsion’s work for low squeeze numbers and moderately large inner to outer radius ratios.
Melt Friction and Pin-on-Disk Devices
Authors: Stiffler A. Kent
Published: October 2009

A melt concept is proposed to explain the tribology of unlubricated metal pin-on-disk sliding at high speeds. A squeeze film model of the melt film is developed which depends on the continually forming melt to give steady-state load support. Expressions are derived for the film thickness, coefficient of friction, and wear. The theory is applied to pin-on-disk data available in the literature. There is good agreement between theory and experiment for the friction coefficient. The results for wear are inconclusive. A significant factor affecting the findings is surface roughness.
The Contact Between Arbitrarily Curved Bodies of Finite Dimensions
Authors: de Mul J. M. , Kalker J. J. , Fredriksson B.
Published: October 2009

A new method is described for the analysis of the contact between two bodies of linearly elastic materials in the absence of friction. No specific assumptions are made about the curvature of the bodies. Though based on commonly used half-space theory, approximations are introduced to take into account the finite dimensions of the bodies. The model has been implemented in a computer program and verified by means of FEM analysis. The applicability of the technique to lubricated tribological contacts is demonstrated.
Development of a Three-Dimensional Noncontact Digital Optical Profiler
Authors: Wyant J. C. , Koliopoulos C. L. , Bhushan B. , Basila D.
Published: October 2009

A noncontact three-dimensional optical profiler for measuring surface roughness is described. The system consists of a reflection microscope, Mirau interferometer with a reference surface mounted on a piezoelectric transducer, CID detector array, frame grabber, and micro-computer. Interferometric phase-shifting techniques are used to obtain surface height information. The height measurements are processed by a computer to obtain topographical statistical parameters, which are useful in predicting tribological and magnetic performances of the head-media interface in magnetic storage systems. Sample data are presented for magnetic media (tape, floppy disk, and rigid disk), a magnetic head, a silicon wafer, and a glass slide.
Temperature Measurement of Microscopic Areas Within a Simulated Head/Tape Interface Using Infrared Radiometric Technique
Authors: Gulino R. , Bair S. , Winer W. O. , Bhushan B.
Published: October 2009

This study concerns the infrared measurement of steady-state and transient temperatures of microscopic areas within the contact region formed by a magnetic tape passing over a simulated recording head. This research demonstrates that the tape surface temperature can be measured within specific limits of response time and sensitivity. Due to its high tranmissivity in the relevant infrared band, sapphire was chosen as the material to be used in the fabrication of a simulated recording head. A Barnes RM2A infrared microscope was the principle radiometer used, while a best effort was made in scanning with an AGA Thermovision 750. The friction force versus load characteristics of the head-magnetic tape interface were also observed. The high speed measurements were divided into two regimes; non-contact hydrodynamic film region, and tape-head contact regime. The temperature measurements displayed a strong correlation with the measured friction force versus load curve. Almost no temperature rise was found in the noncontact hydrodynamic film region while a temperature rise of a few degrees Celsius was found when there was tape-head contact. The results with the AGA Thermovision 750 were consistent with the measurements obtained with the Barnes RM2A.
The Lubrication of Unidirectional Striated Roughness: Consequences for Some General Roughness Theories
Authors: To̸nder Kristian
Published: October 2009

Relations expressing the effects of unidirectional striated roughness on hydrodynamic quantities, relative to the normal x–y coordinate system are derived. It is shown that the angle between the direction of the grooves and that of motion may be expressed by the Kubo-Peklenik number, γ, for random striations. A comparison between the ensuing results and those claimed by other authors to be valid for area-distributed random roughness, is made. The two sets are identical for γ equal to unity, regardless of autocorrelation functions, but strong arguments indicating this correspondence to hold for all γ’s are presented. It is concluded that the results are, in general, valid for unidirectional striations only.
Modeling of Oil-Film Forces in Squeeze-Film Bearings
Authors: Burrows C. R. , Sahinkaya M. N. , Kucuk N. C.
Published: October 2009

The role played by bearings in determining the dynamic characteristics of rotor-bearing systems is well known. This has led to various attempts to model oil-film force coefficients in terms of linearized stiffness and damping elements. The inadequacy of these theoretical coefficients to predict performance under certain conditions has led some authors to propose the use of nonlinear models. An alternative philosophy, developed in this paper, is to retain a linear model structure and seek to determine optimized coefficient values using modern parameter estimation techniques. It is shown that these estimated linearized parameters predict system performance more accurately than the theoretical linear coefficients; particularly when the rotor is operating near a critical speed.
A Numerical Model for the Elastic Frictionless Contact of Real Rough Surfaces
Authors: Webster M. N. , Sayles R. S.
Published: October 2009

A computer model for the dry, frictionless contact of real rough surfaces is presented. The model uses data directly recorded from a stylus measuring instrument and as a confirmation of the model it is shown to reproduce “smooth case” results with a high level of accuracy. Results are given for two important applications of the technique. The first considers the analysis of the contact pressure and displacements for a bearing surface including a debris induced dent in the contact zone. The results go someway to providing an explanation of early life failure often associated with debris contaminated oil. Secondly the relationship between load and real contact area is studied for a sample set of surface profiles. The results obtained are compared with random process theory. It is proposed that the numerical model represents a different approach to rough surface contact allowing certain assumptions about the nature of surface roughness to be relaxed.
Wear of Thermochemically Produced Nitrogen Stainless Steel
Authors: Campillo Illanes B. F. , Sarkar A. D.
Published: October 2009

Thermochemically produced stainless steels with varying nitrogen content were slid dry on high carbon martensitic steel counterfaces using a pin bush machine. The running-in wear was high but the steady state wear decreased with increased nitrogen contents of the steels. A work hardened layer formed on the pins, the degree of hardening increasing with the nitrogen content of the steels. The hard pins caused a considerable amount of wear of the bushes, possibly, by ploughing. The pins wore by transfer and oxidation and, by interfacial shear and, probably, brittle fracture of the work hardened layer at a heavy load.
Analysis of Traction Forces in a Precision Traction Drive
Authors: Kannel J. W. , Dow T. A.
Published: October 2009

A theory for the shear stress between a rough elastic cylinder and a cylinder with a soft layer has been developed. The theory is based on a Fourier transform approach for the elasticity equations coupled with surface deflection equations for transient contacts. For thick layers (h > .001 in.) the shear stress on the surface approaches the shear of the layer alone. The elastic shear deflection (∼100 μin.) as a result of the tangential load is significant and increases if a surface layer such as a thin coating is added to one or both cylinders. The predicted interfacial shear stresses are considerably altered by surface roughness on uncoated surfaces and these effects are ameliorated by the addition of a thin soft surface coating.
Pressure and Squeeze Effects on the Dynamic Characteristics of Elastomer O-Rings Under Small Reciprocating Motion
Authors: Green I. , Etsion I.
Published: October 2009

A test procedure is described by which quick measurements of stiffness and damping coefficients of elastomer O-rings can be made for a wide range of the parameters affecting O-ring dynamics. Tests were performed to investigate the effects of squeeze and pressure on the dynamic characteristics of Nitrile (Buna N) and Fluorocarbon (Viton 75) O-rings. Results of these tests are presented and discussed.
Steady Temperatures in a Rotating Cylinder—Some Variations in the Geometry and the Thermal Boundary Conditions
Authors: Gecim B. , Winer W. O.
Published: October 2009

Three cases are studied as variations in the geometry and the thermal boundary conditions pertinent to the classical flash temperature theory. First, the case of multiple surface heat sources is considered. It is shown that the relative location of the sources is the critical factor in predicting the local temperatures at each contact. Second, the case of a short cylinder (or a disk) is analyzed. In addition to the lateral surface boundary conditions, convective cooling from the side faces is considered. It is shown that a considerable reduction in bulk temperature can be achieved by effective cooling from the side faces. Third, the case of a hollow cylinder is studied where, in addition to the outer boundary conditions, uniform internal heating (or cooling) is considered. It is demonstrated that the bulk temperature can be varied significantly by changing the magnitude (and direction) of the internal heat flux. In both the second and the third cases, over a wide range of the pertinent parameters, it is shown that the local temperature rise remains virtually unchanged.
High-Speed Noncontact Profiling of Pavement Surface Texture and Its Significance
Authors: Wambold J. C. , Henry J. J.
Published: October 2009

It is generally agreed that the friction between a tire and a wet pavement (skid resistance) is controlled by the surface texture characteristics. Therefore, by measuring the relevant parameters describing texture, or by measuring a physical process dependent on texture, regression techniques can be used to relate skid resistance to the chosen texture parameter or process. Two scales of texture are of particular importance: microtexture (small-scale asperities) and macrotexture (large-scale asperities). This paper describes work performed to: (1) review candidate macrotexture and microtexture measurement methods that can be made at highway speeds (at or about 64 km/h [40 mph]), which are presently used or have potential for use in pavement texture measurement; (2) design and build a prototype of the most promising method; and (3) evaluate the effects of pavement surface texture on skid resistance. A prototype noncontact vision system that makes texture measurements at highway speeds was developed, and several improvements were made to upgrade the system to provide an improved prototype. Both hardware and software enhancements have yielded a texture measurement system that can obtain pavement macrotexture data in a fast, efficient, and reliable way.
An Optimum Connecting Rod Design Study—A Lubrication Viewpoint
Authors: Goenka Pawan K. , Oh Kong Ping
Published: October 2009

The effect of support structure on the performance of a connecting rod bearing is analyzed by elastohydrodynamic lubrication theory. The support structure is modified iteratively until an optimum design is obtained. With the connecting rod of a typical gasoline engine as an example, it was found that a 150 percent improvement in film thickness and a 34 percent reduction in peak pressure can be obtained by changing the structural design. This design, however, increases the peak octahedral shear stress in the rod. Structural design changes considered were found to have surprisingly little effect on the power loss of the bearing.
Determination of High Water Fluid Properties Using a Capillary Viscometer
Authors: Mickelson R. W. , Sulick E. H.
Published: October 2009

A simple capillary viscometer was used to demonstrate how one obtains the true shear stress-shear rate rheological properties of a polymer solution. The methodology, described in this paper, shows how the pressure drop caused by the friction of the liquid flowing through the tube is separated from the pressure drops associated with entrance and exit effects and the elastic energy of the polymer solution.
Dynamics of Gas-Lubricated Slider Bearings in Magnetic Recording Disk Files—Part II: Numerical Simulation
Authors: Miu D. K. , Bogy D. B.
Published: October 2009

This two part paper presents the experimental observation and numerical simulation of the dynamic response of self-acting gas-lubricated slider bearings used to maintain the sub-micron spacings between the Read/Write transducers and the rotating disks in magnetic recording disk files. In this Part II, a factored implicit finite difference scheme is used to integrate the Reynolds lubrication equation, which describes the isothermal compressible fluid flow within the bearing region, and a fourth order Runge-Kutta method is used to solve the equations of motion, which describe the slider dynamics. Using this numerical model, the theoretical slider response due to a rectangular step in the disk surface is obtained. Excellent correlation is observed between theory and experiment. Results are presented to illustrate the effects of step size, step location, and surface velocity on the dynamic performance of slider bearings.
Test Results For Round-Hole-Pattern Damper Seals: Optimum Configurations and Dimensions for Maximum Net Damping
Authors: Childs D. W. , Kim Chang-Ho
Published: October 2009

Test results are presented for nine annular seals which use a roughened stator and smooth rotor to yield an increase in net damping as compared to conventional smooth-rotor / smooth-stator annular seals. Round-hole roughness patterns are used to achieve the desired stator roughness. The results presented demonstrate that the maximum net damping is achieved by (a) a hole pattern which takes up about 34 percent of the surface area, and (b) hole depths which are about three times the radial clearances. When compared to a smooth seal, the optimum configuration increases net damping by 37 percent, while reducing leakage by 46 percent and direct stiffness by 23 percent. Comparisons of experiment to theory are generally satisfactory for hole-patterns near the optimum area ratio of 34 percent. However, the theory is unsatisfactory for seals which have a substantially higher percentage of the surface area taken up by holes.
The Strength of Some Non-Hertzian Plane Contacts
Authors: Sackfield A. , Hills D. A.
Published: October 2009

The problem of plane elastic contact between a symmetrical indentor and a half-plane is addressed. The form of the contacting profile of the indentor is represented in terms of Chebyshev polynomials, and the resulting stress-field is deduced, for both static and sliding contact. It is shown that by making the profile somewhat flatter than a cylinder a large load may be sustained without yielding. Practical implications of the result, including profiles needed to attain optimal contact conditions, are discussed.
Flow of a Fluid of the Differential Type in a Journal Bearing
Authors: Kacou A. , Rajagopal K. R. , Szeri A. Z.
Published: October 2009

The flow of a homogeneous incompressible non-Newtonian fluid of the differential type between infinite eccentric rotating cylinders is discussed within the context of the lubrication approximation. The problem is studied by means of a perturbation and the effects of the non-Newtonian parameters are delineated. It is found that the load carrying capacity of the bearing can be significantly altered by the non-Newtonian character of the fluid.
Effects of Gas Entrainment on Squeeze Film Damper Performance
Authors: Feng N. S. , Hahn E. J.
Published: October 2009

Squeeze film dampers are frequently used for stabilization and/or vibration control of rotating machinery. Theoretical analyses to date generally assume an incompressible lubricant. In practice, however, depending on the capacity of the lubricant reservoir, the lubricant at damper inlet contains varying amounts of dissolved gas, which come out of solution to form a “spongy” gas-liquid mixture during damper operation. This paper examines theoretically and experimentally the effects such entrained gases have on damper performance, particularly on damper load capacity and the likelihood of multistable operation. It is shown that under certain operating conditions, a significant delay in the onset of bistable operation is predicted, depending on the fluid film model employed. Preliminary tests indicate that at low bearing parameter values (B ≐ 0.02), the homogeneous compressible film model using the Hayward rather than the Isbin viscosity relationship for gas-liquid mixtures provides the best prediction of damper performance. Of the incompressible film models, the zero pressure truncation predictions are generally quite satisfactory and superior to the commonly used π-film predictions.