bluuebunny/crossref_metadata_2025 huggingface dataset:
Monte Carlo‐based flood modelling framework for estimating probability weighted flood risk
Authors: Kalyanapu A.J. , Judi D.R. , McPherson T.N. , Burian S.J.
Published: September 2011

This study presents a new Monte Carlo‐based flood inundation modelling framework for estimating probability weighted flood risk using a computationally efficient graphics processing unit (GPU) two dimensional (2D) hydraulic model. The 2D flood model is programmed in the GPU framework providing a unique ability to run numerous simulations in a short period of time, permitting the integration of 2D hydraulic modelling into Monte Carlo analysis. The framework operates by performing many 2D flood simulations of randomly sampled input parameters to develop a spatially varied flood hazard map. The probabilistic framework is demonstrated using a 1% annual probability flood event and simulating 1000 different flood simulations by randomly selected peak flows of the Swannanoa River in Buncombe County, USA. The results, in general, display benefits of probabilistic flood risk approach compared with a single simulation approach. The latter approach underestimated 28% of flood risk relative to the former. As the number of simulations increased from 1 to 1000, areas identified as low danger and judgment zone increased by 87.4% and 36.8% respectively, whereas the high danger zone increased by 9.3%. In conclusion, the new Monte Carlo flood risk modelling framework has the ability to provide improved accuracy of flood risk and greater insight into the spatial distribution of flood risk.
WHAT IS THE FREQUENCY OF CARBOHYDRATE METABOLISM DISORDER IN CKD?
Authors: Basturk Taner , Unsal Abdulkadir
Published: September 2011

Objective: The objective of this paper is to detect the incidence of insulin resistance (IR) in Chronic Kidney disease (CKD) patients and the presence of impaired fasting glucose (IFG), impaired glucose tolerance (IGT) and diabetes mellitus (DM) in patients with/without IR.

Methods: We enrolled 113 patients with CKD. Biochemical parameters were investigated.

Results: IFG was found 59.3% of patients with CKD. Age (p = 0.012), BMI (p = 0.036), TG (p = 0.008), HbA1c(p = 0.002), hs‐CRP (p = 0.015) levels were higher in patients with IFG. According to the results of Oral glucose tolerance test (OGTT), 69% of patients with CKD had a detected carbohydrate metabolism disorder, 9.7% had DM, 59.3% had IGT. In patients with IFG 13.6% had DM, 31.8% IGT, in patients without IFG 4.2% had DM and 29.8% IGT. The mean HOMA‐IR and insulin levels were 3.03 ± 1, 97/11.9 ± 7.13. IR was detected 23% of patients with CKD. In patients with IR; FBG (p = 0.003), serum insulin (p = 0.001), TG (p = 0.05) and HbA1c (p = 0.004) levels were elevated. 31.3% of patients with IFG were found to be IR.

Conclusion: Carbohydrate metabolism disorder and insulin resistance are found in patients with CKD. Most patients with CKD who are elderly, obesity or overweight offer targets for additional risk factors. For these reasons, screening for DM may be recommended.
RENAL TRANSPLANT ACCEPTANCE STATUS, HEALTH‐RELATED QUALITY OF LIFE AND DEPRESSION IN DIALYSIS PATIENTS
Authors: Østhus Tone Brit Hortemo , Preljevic Valjbona , Sandvik Leiv , Dammen Toril , Os Ingrid
Published: September 2011

Health‐related quality of life (HRQOL) and depression in chronic dialysis patients, accepted (n = 122) or rejected (n = 93) for renal transplantation (Tx), were compared, whereas dialysis patients with pending acceptance status (n = 86) were followed for a median time of 3.6 years to assess whether HRQOL or depression predicted the likelihood of receiving a transplant. Clinical significant depression was present in 30% of the study patients. Less depression and better HRQOL were associated with being on the waiting list for Tx after adjusting for comorbidity, age, gender and dialysis vintage. During follow‐up, 55% of the dialysis patients in the group with pending acceptance were transplanted. The likelihood of receiving a renal graft was based on comorbidity and not on impaired HRQOL or depression. Follow‐up studies should investigate whether improved renal health after Tx translates into further improvement of HRQOL and less depression. Whether clinical depression and impaired HRQOL will impact graft survival needs to be explored.
Frequency of anemia of inflammation in patients with ankylosing spondylitis requiring anti‐TNFα drugs and therapy‐induced changes
Authors: NICCOLI Laura , NANNINI Carlotta , CASSARÀ Emanuele , KALOUDI Olga , CANTINI Fabrizio
Published: September 2011

Objective:  Primary: to evaluate the frequency of anemia of inflammation (AOI) in a clinical series of patients with ankylosing spondylitis (AS) requiring anti‐TNF (tumor necrosis factor) agents. Secondary: to examine anti‐TNF therapy‐induced changes in AOI.

Method:  Prospective, follow‐up, 6‐month study of all consecutive, new patients with AS requiring anti‐TNFα drugs observed between January 2004 and December 2008. AOI was defined according to WHO criteria. Primary outcome measure: the proportion of patients showing AOI at baseline. Secondary outcome measures: the proportion of patients achieving resolution of AOI at the 6‐month visit; the proportion of patients achieving any improvement in haemoglobin (Hb); the proportion of patients with any improvement in blood results.

Results:  One hundred and six patients (42 women and 64 men; mean age: 46 years) with AS were evaluated. Sixteen of these (15%) presented with AOI at baseline. After 6 months therapy 13 patients (81%) resolved AOI while two presented an Hb level reduction. After 6 months therapy we did not find a significant statistical improvement in red blood cell numbers (P = 0.85) and transferrin (P = 0.08) levels. Hb, mean corpuscular volume (MCV), iron, ferritin, C‐reactive protein (CRP) and erythrocyte sedimentation rate (ESR) improved reaching statistical significance (P = 0.0002, 0.0001, 0.001, 0.014; 0.007, 0.004, respectively).

Conclusion:  We found 15% frequency of AOI among a selected series of patients with AS. After 6 months of anti‐TNFα therapy AOI resolved in the majority of patients with significant improvement of Hb, MCV, CRP and ESR levels.
Familial rheumatoid arthritis in patients referred to rheumatology clinics of Tabriz, Iran
Authors: HAJALILOU Mehrzad , NOSHAD Hamid , KHABBAZI Ali R. , KOLAHI Susan , AZARI Maryam H. , ABBASNEGHAD Mohsen
Published: September 2011

Background:  The familial clustering of rheumatoid arthritis (RA) in first and second degree relatives of patients supports the role of genetic factors. The proportion of heredity in its development is roughly 60%; however, most individuals closely related to someone with RA do not get the disease. Considering the lack of sufficient data on the familial aggregation of RA in Iran, we designed this study for clarifying the familial prevalence of RA.

Objective:  To determine the prevalence of RA among relatives of patients with RA and to evaluate the mean disease onset age in relatives.

Methods:  In a longitudinal study from July 2008 to July 2010, we followed 210 unrelated patients with RA and their first and second degree relatives (FDR+ and SDR+), by interviewing and physical examination of those with symptoms, to ascertain prevalence. Familial RA was defined by presence of at least two siblings fulfilling the 1987 ACR criteria for RA.

Results:  We demonstrated that 17.6% of patients have at least one affected relative. The prevalence of RA in the family of studied patients was 0.83% (42 people). Thirty‐two in FDR+ and 10 people in SDR+ (2.53% and 0.26% of all family), also 1.12% in female relatives and 0.39% in male relatives had RA. The odds ratio for FDR/SDR was 2.52. The mean age at disease onset in relatives was 42.30 ± 1.51 years in FDR+ and 34.40 ± 2.10 years in the SDR+ group (0.03).

Conclusion:  The risk of RA is greatest in FDR+ and is likely to be due to a combination of inherited and environmental factors.
Triple labeling with three thymidine analogs reveals a well‐orchestrated regulation of hepatocyte proliferation during liver regeneration
Authors: Wu Yizhou , Guo Fuzheng , Liu Jin , Xiao Xueyuan , Huang Lingyun , He Dacheng
Published: September 2011

Aim:  After a two‐thirds partial hepatectomy (PHx) in rodents, the remaining cells will proliferate and restore the lost liver mass within 7 days. Previous studies have proved that the residual hepatocytes proliferate in a synchronous manner. However, the existing data can not reflect the chronicle of individual hepatocytes proliferation during liver regeneration.

Methods:  In this study, a combination of pulse and continuous labeling using three thymidine analogs, Bromodeoxyuridine (BrdU), Chlorodeoxyuridine (CldU) and Iododeoxyuridine (IdU), were used to analyze the cell proliferation of rat liver after PHx. This strategy allows us to follow an individual cell for more than one cell cycle and to define how many cells and which cells undergo multiple divisions.

Results:  The residual hepatocytes clustered into three subpopulations to initiate the proliferation sequentially, and the corresponding percentage of each was 32%, 17%, and 36%. Meanwhile, the remaining 15% of hepatocytes never proliferated. In addition, the periportal hepatocytes were the first to respond to PHx stimulation and re‐proliferated synchronously at 54 h. Furthermore, at least 11% of residual hepatocytes were identified to divide thrice or more.

Conclusion:  Based on the present analysis, we concluded a sequential model of the initial proliferation in residual hepatocytes, and for the first time, quantitatively elucidated the proliferation manner of three subpopulations during liver regeneration.
Audit Quality and the Market Valuation of Banks’ Allowance for Loan Losses*
Authors: Kanagaretnam Kiridaran , Krishnan Gopal V. , Lobo Gerald J. , Mathieu Robert
Published: September 2011

The recent banking crisis has led market participants to focus on the adequacy and quality of banks’ balance sheet items such as the allowance for loan losses. Beaver and Engel (1996) document that the capital market prices the nondiscretionary component of loan loss allowance negatively and the discretionary component less negatively. Using data from the pre‐crisis period and three measures of audit quality, auditor type (i.e., Big 5 versus non–Big 5), auditor industry specialization/expertise, and audit and nonaudit fees paid to auditors, we examine the effect of audit quality on the market valuation of the discretionary component of the allowance for loan losses. We find that, relative to the nondiscretionary component, the market valuation of the discretionary component of loan loss allowance is higher for banks audited by Big 5 auditors than for banks audited by non–Big 5 auditors. We also find that the relative market valuation of the discretionary component of loan loss allowance is increasing in auditor expertise. Regarding the impact of fees paid to auditors, we find that banks paying higher audit fees have higher relative market valuation of the discretionary component of the allowance for loan losses, but banks that pay higher nonaudit fees do not.
Annual Reporting and Accountability by Municipalities in Canada: An Empirical Investigation*
Authors: Blanco Huguette , Lennard John , Lamontagne Sylvain
Published: September 2011

Prior research regarding reporting and accountability by local governments in several countries has questioned the value of traditional annual reporting and the level of accountability to the public. This article reports on comparable research for local governments throughout Canada. The disclosure index methodology is used to evaluate the quality and quantity of information published in the annual reports and in the financial statements of Canadian local governments in 2003 with a comparison in 2005. Although all municipalities published audited financial statements, less than one‐third of municipalities published a comprehensive annual report in 2003. The results show an overall low disclosure index with significant improvements in 2005 compared to 2003 and significant differences across the country. The results, largely consistent with previously published international studies, raise questions about local government accountability and about the conceptual framework for local government reporting.
Static and Dynamic Characteristics of the Gas-Lubricated Spiral-Grooved Spool Bearing for Motion in the Axial Direction
Authors: Smalley A. J.
Published: September 2011

An analysis, based on the narrow groove theory, is presented for the closed, spiral-grooved spool bearing. Designs optimized for static stiffness are obtained for range of values of the groove extent parameter Y, and the characteristics of these designs under oscillatory motion are investigated over a wide frequency spectrum. It is shown that the geometry of the boundaries common to thrust and journal sections has an appreciable effect on the dynamic compliance of the bearing, and that a relief volume between the bearing sections can give rise to a gas film resonance, at which the compliance is strongly dependent on the dimensions of this volume. The beneficial effect of a thrust-bearing seal region with respect to this type of resonance is demonstrated, and it is shown that a design for optimum static stiffness differs considerably from one for optimum dynamic stiffness. It is the prediction of this analysis that a small sacrifice in static performance can lead to considerable gains in the performance under dynamic conditions.
Load Support of Spherical Squeeze-Film Gas Bearings
Authors: Beck J. V. , Strodtman C. L.
Published: September 2011

The steady-state ph distribution and the load support capability for a squeeze-film bearing in the form of a sphere, or portions of a sphere, are given for two cases, (a) when the sphere pulsates radially and (b) when the sphere motion is along the polar axis. Both small parameter and finite-difference results are given for loads in the radial and polar directions. It is shown that considerably more load support in both the radial and the polar directions is developed when the sphere pulsates radially. It is further shown that the load support can be improved by removing a portion of the sphere near the pole, thus venting the bearing to the ambient pressure.
Method of Theoretical Investigation of Externally Pressurized Gas-Lubricated Bearings
Authors: Stepanyants L. G. , Zablotsky N. D. , Sipenhov I. E.
Published: September 2011

An “unevenly distributed supercharging” pattern is suggested for treating externally pressurized bearings. The scheme simplifies the problem and is applicable in calculating any type of externally pressurized bearings Results of numerical integration of Reynolds’ equation for a section spherical bearing using this treatment are given.
Steady-State and Dynamic Analyses of Gas-Lubricated Hybrid Journal Bearings
Authors: Shapiro W.
Published: September 2011

The inherent limitations of load capacity and stability of hydrodynamic gas-lubricated bearings can be reduced by introducing external pressure and creating a hybrid bearing. Numerical computerized analyses of a hybrid journal bearing are discussed; separate developments are presented for steady-state and dynamic characteristics. The steady-state analysis provides performance over a wide range of operating parameters; the more complicated and lengthy dynamic analysis determines stability of the bearing-rotor system using geometry based upon steady-state results. Simplified flow charts of the computer programs are included. The analyses are applied to the preliminary design of a hybrid journal bearing.
Theory for Finite-Width High-Speed Self-Acting Gas-Lubricated Slider (and Partial-Arc) Bearings
Authors: Elrod H. G. , McCabe J. T.
Published: September 2011

The behavior of the pressure distribution within partial-arc and slider bearings under conditions of high-speed operation is investigated to provide an understanding of the basic phenomenon. Both the trailing-edge conditions and side-leakage effects are treated by asymptotic methods. A design example is given in which the edge effects on load capacity are computed as “corrections” to the infinite speed (Λ → ∞) solution.
Note on the Influence of the Heat Transfer Between the Surfaces as a Secondary Effect in Gas Lubrication
Authors: Constantinescu V. N.
Published: September 2011

The problem of gas lubrication is examined by taking into account the energy equation and variation of viscosity with temperature. The velocity profiles and the pressure differential equation are deduced. When the temperatures T0, T1 of the two lubricated surfaces are constant, simple corrections can be obtained in order to estimate the influence of unequal temperatures of the two surfaces on pressure distribution, load capacity, and friction stresses in self-acting films and on pressure distribution and mass flow in externally pressurized bearings. However, as the influence of the transversal heat transfer manifests only through the intermediary of the variation of viscosity with temperature, the isothermal analysis can further on be used, provided that one takes a mean value for the viscosity, corresponding to a mean temperature Tm = (T0 + T1)/2.
On the Influence of Magnetic and Electrical Fields in Gas Lubrication
Authors: Constantinescu V. N. , Dimofte F.
Published: September 2011

The paper examines some of the possibilities of MGD lubrication by considering some typical examples of external electromagnetic conditions and some simple types of bearings. Thus, for self-acting films, the case when an external tangential magnetic field combined with a transversal electrical field is studied. Pressures and load capacity are thus improved and, in addition, the friction forces can be diminished and even eliminated. For externally pressurized films, insulated surfaces subjected to an external transversal magnetic field can reduce the flow, provided that the Hartmann number has a sufficiently high value. Finally, it is pointed out that it is possible to produce pressures by electromagnetic means only. The electromagnetic pumping effect is produced, for instance, when a transversal electrical field is applied, combined with a tangential magnetic field, even when both lubricated surfaces are at rest. Some considerations concerning the practical possibilities of obtaining an electrically conductive gas at relatively low temperatures are also given.
Rolling Friction, I—Historical Introduction
Authors: Hersey Mayo D.
Published: September 2011

The earlier experiments on rolling friction are reviewed in this paper. It covers the period from Coulomb in 1785 to Whittemore and Petrenko in 1921, preceding the author’s work. Test data on solid cylinders as well as railway and wagon wheels are compared.
A Deep Groove Rolling Contact Parameter
Authors: Poon S. Y. , Haines D. J.
Published: September 2011

An analysis of the deep groove rolling contact problem reveals in the absence of relative spin between the elements the existence of a nondimensional parameter, characteristic of the problem, by which relevant factors such as load, geometrical configuration, elastic constants of the material, and coefficient of friction can be correlated. In this paper the existence of this nondimensional parameter is established and its use as an aid to the selection of bearing materials and parameters is considered.
Pitting of Steel Under Varying Speeds and Combined Stresses
Authors: Foord C. A. , Hingley C. G. , Cameron A.
Published: September 2011

A new loader is described for pitting research. It consists of a ball in a cylinder. Behind the ball is high-pressure oil which forces it against the moving counterface, which in its turn causes the ball to spin, and so remain centered in the cylinder. In the first part of the paper the effect of speed on pitting is studied using this loader. The results are correlated by a mathematical treatment of Way’s hydraulic crack-propagation hypothesis. The theory shows that high viscosity and compressibility and short transit times increase pitting life. Semiquantitative agreement is found between the new pitting theory and experiment. In the second part the action of combined stresses on pitting is investigated. The ball is loaded against a shaft mounted in a rotating-bending fatigue machine. It is found that a relatively small tensile bending stress reduces pitting life dramatically, whereas a small compressive bending stress completely inhibits pitting.
The Effect of Misalignment on the Fatigue Life of Cylindrical Roller Bearings Having Crowned Rolling Members
Authors: Harris T. A.
Published: September 2011

An analytical method is presented to determine the effect of misalignment on the performance of cylindrical roller bearings having crowned rolling members. This method utilizes a more representative load-contact deflection relationship than used in previous analyses, and further, can be employed to estimate the degree of crowning required for a given application. Fatigue-life reduction owing to misalignment, as predicted by this method, is much less severe than has been previously estimated analytically.
The Role of Lubrication in Biomechanical Joints
Authors: Mow V. C.
Published: September 2011

This paper attempts to present an overall picture of the various biomechanics problems in a synovial joint. Of particular interest is the lubrication mechanism between the articulating surfaces. A survey of pertinent information in regards to the constituents, i.e., the cartilage and the synovial fluid, indicates the possible types of constitutive equations which one must use to approximate their mechanical behavior. The approach is phenomenological. Further, the results of some of the lubrication theory are applied to the system under consideration. Using realistic physiological limits upon the loading and the speed of operation, the results seem to indicate that the mode of lubrication is elastorheodynamic. This is a term which describes the theory of lubrication in which the deformation of the cartilage and the non-Newtonian nature of the synovial fluid are considered. Finally, a list of problems is proposed. Their solutions are invaluable in settling the question of the proper description of the mechanism of synovial joints. Presently, research is under way in attacking one of these problems.
Salt Effects in Mucin Lubrication
Authors: McCutchen C. W. , Wilkins J. F.
Published: September 2011

Animal joints are lubricated by two complementary mechanisms. Weeping lubrication carries most of the joint load hydrostatically, leaving only a small fraction of the total to be carried by rubbing of the solid “skeletons” of the two cartilages. This rubbing is, in turn, lubricated by the synovial mucin; i.e., by long chain polymer molecules dissolved in the joint fluid. There is good evidence that the mucin molecules adsorb to the surfaces and provide boundary lubrication. In this paper we examine further this adsorption processs using a bearing whose two surfaces are rubber and glass, respectively. It is found that the lubricating ability of the mucin is good if it is applied to the bearing in a solution with about physiological salt concentration. At higher salt concentrations the lubrication is comparatively poor, while at zero salt concentration it is very bad indeed. If, on the other hand, the mucin is applied at physiological salt concentration, and then the salt and unadsorbed mucin are washed away with distilled water the lubrication remains good, and has, on occasion, even improved. Once the mucin has been adsorbed the entire range of salt concentration can be explored, with the lubrication becoming worse at high salt concentration and then recovering in greater or lesser degree when the salt is washed off. It seems, then, that the salt concentration affects lubrication in two ways. It can upset the adsorption of the lubricating film, and it can change the lubricating effectiveness of the film once it is adsorbed.
A Discrete-Continuum Approach to the Solution of the Contact of Rotating Circular Surfaces
Authors: Finkin E. F.
Published: September 2011

A new approach to the analysis of problems of surface contact is postulated, which takes into account the discrete nature of the process, but allows the simplicity of continuum methods, where possible; this is termed the discrete-continuum approach. The method is shown by developing the solution of the problem of the nominal interfacial pressure distribution and real area of contact density for rotating nominally flat but rough circular surfaces. The method allows the mathematical statement of the transitions which occur with surface wear, and thereby constitutes a mathematical description of some aspects of run-in. The method and solution to the present problem give insight into the nature of the pattern of contacts, and are therefore expected to find application in surface-contact temperature theory and in electrical-contact resistance theory.
Inward Pumping in Mechanical Face Seals
Authors: Findlay J. A.
Published: September 2011

The hydrodynamic characteristics which produce inward pumping in mechanical face seals are studied. Solutions to Reynolds’ equation for hydrodynamic lubrication are obtained using both the short-bearing approximation and numerical iterative methods. It is found that pumping in face seals results from combined radial eccentricity and misalignment, or one circumferential surface wave. Experimental results confirm the theory.
The Application of Elastohydrodynamic Lubrication Theory to Individual Asperity-Asperity Collisions
Authors: Fowles P. E.
Published: September 2011

Conventional elastohydrodynamic theory is modified and applied to the collision between two idealized surface asperities in an isothermal sliding system. Solutions for the pressure and film thickness between the asperities as functions of their overlap, the sliding speed, the pressure-viscosity coefficient of the lubricant, and the time since the initiation of the collision are obtained numerically for the first half of the collision process. It is shown that extremely high pressures and small film thicknesses are to be expected at the center of the contact region assuming the rheology of the lubricant film can be represented by that of the bulk lubricant.
An Experimental Study of High-Speed Rotors Supported by Air-Lubricated Foil Bearings—Part 1: Rotation in Pressurized and Self-Acting Foil Bearings
Authors: Licht L.
Published: September 2011

A high-speed rotor, supported by an air-lubricated foil bearing, is rotated in both the vertical and horizontal attitudes at speeds in excess of 60,000 rpm. The rotor is stable and free from “half-frequency” or “fractional-frequency” whirl instability encountered in conventional gas bearings. External pressurization is applied to separate the foil surfaces from the journal during the initial and final stages of rotation, with adequate self-acting support and foil separation established at relatively low transition speeds. In the pressurized mode of operation, the system is characterized by a series of ultra-harmonic resonances, of sharply defined frequencies, related by fractions to speeds of synchronous resonance. In the self-acting mode of operation, the response of the system to residual imbalance is influenced by both the foil bearing and by the pressurized thrust bearings. The magnitude of the air gap (clearance) is determined at various rotational speeds and compared with theoretically predicted results. The temperature rise of the foil with speed is measured at various locations in order to assess its contribution to clearance growth. The journal and foil surfaces are examined and it is found that the foil bearing is endowed with excellent wipe-wear characteristics.
An Experimental Study of High-Speed Rotors Supported by Air-Lubricated Foil Bearings—Part 2: Response to Impact and to Periodic Excitation
Authors: Licht L.
Published: September 2011

A high-speed rotor, supported by an air-lubricated foil bearing is stable at speeds up to and in excess of 60,000 rpm. “Natural frequencies” are determined at various rotational speeds from records of response following impact of the rotor housing. The foil-rotor system is subjected to periodic, unidirectional excitation by means of a vibrator (shake table) and the in-line and transverse responses are obtained in a frequency range 50–2000 cps. The behavior of the system is similar to that of a simple, damped oscillator, characterized by a single resonance in the low-frequency range. Experimentally determined values of resonant frequencies are in fairly good agreement with predicted results, based on a simplified theoretical formulation of the problem. Responses of rotors to (a) excitation of variable amplitude at resonance and to (b) excitation of variable amplitude at frequency equal to half the rotational speed are investigated. It is found that excitation and rotor excursion are nearly colinear, except in the neighborhood of resonance. Excitation at frequency equal to half the speed of rotation is not associated with large amplitudes of motion, wherein the foil bearing compares favorably with other types of fluid-film bearings.
Finite-Element Solution of the Incompressible Lubrication Problem
Authors: Reddi M. M.
Published: September 2011

A minimum principle for the transient incompressible Reynold’s equation, with the natural boundary conditions of prescribed pressure, as well as flow, is presented. The finite element method is introduced as the numerical counterpart of the Rayleigh-Ritz procedure. Flow computation is shown to be a natural corollary of the integral principle. Solutions of several test problems are presented.
A Theory for the Effects of Film Thickness and Normal Load in the Friction of Thin Films
Authors: Finkin E. F.
Published: September 2011

The effect of film thickness in solid friction is reviewed. Two regimes are distinguished: (a) increasing coefficient of friction with decreasing film thickness which occurs for ultrathin films and (b) decreasing coefficient of friction with decreasing film thickness which occurs for thin films. The former regime has previously been treated by the author; consequently, attention is focused on the latter regime. A review of the thin film phenomenon establishes that it is very much dependent on the type of deformation occurring at the contact and concludes that no single expression can uniquely describe it for all materials situations. A special theory is put forth for the contact situation corresponding to a model of an elastic layer of much less rigidity than its substrate and indenter. This situation corresponds to practically all naturally occurring and bonded nonmetallic solid lubricant films of industrial and scientific interest. It is shown that coefficient of friction f obeys the relation f ∝ 1/P for variable load P and constant thickness h, f ∝ h for constant load and variable film thickness, and f ∝ h/P for the general case. These expressions are verified by use of data from pin-on-disk tests, Falex tests, 4-ball tests, modified MacMillan tests, and other types of tests. The experimental data are for naturally formed graphite on diamond, SiO2 bonded PbO on stainless steel, and phenolic bonded 9MoS2-1 graphite films on steel and aluminum.
Hydrostatic Bearings for Cryogenic Rocket Engine Turbopumps
Authors: Reddecliff J. M. , Vohr J. H.
Published: September 2011

This paper summarizes an analytic and experimental investigation of hydrostatic bearings for use in high-pressure cryogenic rocket engine turbopumps. A hydrostatic bearing analysis was developed to predict bearing steady-state and time-dependent (stability) performance. The analysis accounts for the effects of turbulence, inertia, and compressibility in the fluid film. Bearing design charts were generated from the analysis to permit rapid prediction of bearing performance and to aid in the selection of optimum bearing configuration. Liquid hydrogen and liquid oxygen turbopump conceptual designs were prepared and the designs were used to establish hydrostatic bearing size and performance requirements. The turbopump designs included provision for operation when bearing supply pressure is insufficient to support the rotor. Two bearing designs, one LH2 and one LO2, were fabricated and tested in a test rig. Test bearing designs met turbopump requirements and included the turbopump start-stop rotor support provision. Experimental data for both test programs agreed well with steady-state predictions and the bearings were stable under all conditions. Both test bearing designs were in excellent mechanical condition after testing, which included 10 simulated turbopump start-stop cycles.
Stability Characteristics of Gyroscopes With Hydrodynamic-Grooved Rotor Bearings
Authors: Miura Hirofumi
Published: September 2011

Stability characteristics of a two-degree-of-freedom gyroscope having hydrodynamic-grooved rotor bearings are presented. The two types of oscillations of rotor are parallel whirling and conical whirling. The former is not so significant because the threshold rotor speed for instability is generally very high, and this result has been obtained in previous theories. The latter, in this case gimbals in motion, is very significant. Self-excited conical whirling which starts at low rotor speed and persists into higher ranges was observed. This instability is predictable from the theory presented. The agreement between theoretical and experimental frequency of self-excited oscillation is very good. For simplification, bearings are considered cylindrical, although the experimental apparatus has conical ones. Lubricant is incompressible.
Anisotropy of Sliding Damage on the (001) Surface of Copper Single Crystal
Authors: Soda Norimune , Sato Jun’Iti
Published: September 2011

Sliding tests are carried out on the (001) surface of a copper single crystal lubricated with liquid paraffin using a diamond cone slider. The experimental results show that widths of sliding tracks vary periodically with crystallographic directions. In the present experiment the surface is only deformed, and no wear debris is produced. The elastic anisotropy with respect to the direction of sliding is considered, and the distribution of slip traces around the track is observed on the (001) surface of copper. The results indicate that in the surface damage during sliding the plastic deformation and work-hardening are more important than elastic recovery of the surface.
Measurements of Leakage in Mechanical Face Seals
Authors: Findlay J. A.
Published: September 2011

The characteristics of mechanical face seals operating with hydrodynamic films were studied experimentally and analytically. Experimental and theoretical results are given showing the effects of gas cavities in the film and inward pumping. Photographs taken through the transparent test seal show the characteristics of the gas cavities. Experimental results are also given for the two fluid case, i.e., where the seal separates two different fluids; and for the case where inertia effects are important.
Hertzian Contact and Adhesion of Elastomers
Authors: Drutowski Richard C.
Published: September 2011

The contact of a hard sphere with a flat elastomer is examined both analytically and experimentally when adhesive stresses are present. Use of a transparent spherical indenter enables continuous measurement of contact size while the samples are pulled apart. For any combination of load and contact area, the superposition of a Hertz and a Boussinesq stress distribution separates the contact into a circular zone under compression and an outer annulus under tension. During separation, while the contact size decreases and the tensile annulus becomes a larger percentage of the total contact, the average tensile stress remains constant. This average adhesive is a material property which is easily measured and is shown to be invariant with respect to indenter radius and initial contact pressure. An application of this analysis to opaque indenters is described.
The Eccentric Face Seal with A Tangentially Varying Film Thickness
Authors: Sneck H. J.
Published: September 2011

It is shown analytically that face seal eccentricity combined with surface waviness can contribute an inward or outward leakage component to the total leakage flow depending on the phase angle between the eccentricity and the waviness.
Contact Region of a Hard Ball Rolling on a Viscoelastic Plate
Authors: Halaunbrenner J. , Kubisz A.
Published: September 2011

In the work presented, the contact region of a glass ball rolling without slip on a flat plate of viscoelastic material at various velocities was recorded. An interference microscope was used. Deformation of the base in the vicinity of the contact area was read from the interference picture obtained due to a narrow air gap between the ball and the base. The material of the base was characterized by creep and relaxation functions at constant temperature of (21 ± 0.5) deg C. The viscoelastic continuum of the base was replaced by the system of mutually independent vertical columns. By a subsequent twofold application of Boltzmann’s superposition principle, the diameter of the contact surface parallel to the velocity vector of the ball and depth of the concave track behind the ball were calculated. The results obtained were compared with observation data. Satisfactory agreement in cases where the shape of the contact area does not differ considerably from a circle (for small and great rolling velocities) was obtained.
Effects of Lubricants, Metals, Temperature, and Atmospheric Environments on Gear Load-Carrying Capacity
Authors: Baber B. B. , Anderson E. L. , Ku P. M.
Published: September 2011

Experimental gear load-carrying capacity results are presented for three different gear materials and a variety of lubricants of different chemical classes and viscosities, with emphasis on high-temperature operation in air and nitrogen environments. The lubricant-metal-atmosphere interaction was found to be complex and could not be predicted by simple means. With a given gear material in an air environment, load-carrying capacity was found to decrease with increasing temperature until a minimum value was reached, and then to increase with further increase in temperature. A substantial reduction in load-carrying capacity was noted when the air environment was replaced with nitrogen. In addition, the increase in load-carrying capacity noted at high temperatures in air environment was not observed when nitrogen environment was used. This general behavior was, however, quite different when another gear material was used.
On the Load Capacity of the MHD Journal Bearing
Authors: Dudzinsky S. J. , Young F. J. , Hughes W. F.
Published: September 2011

An analysis and experimental results are presented for a magnetohydrodynamic partial journal bearing using a liquid metal lubricant. An external magnetic field is applied axially along the journal, and current is permitted to flow between the journal and bearing. The analysis shows that increased load capacity can be achieved by supplying current from an external source. In addition, the analysis reveals the existence of an optimum Hartmann number at which the load capacity peaks for a given applied current. This optimum value is about 5 for a dimensionless current I¯ = −5 applied to a bearing with a width/diameter ratio of 1 and an eccentricity ratio of 0.6. Experimental results which demonstrate the increase in load capacity resulting from an externally applied current are presented graphically and compared with the theory.
On the Behavior of Grooved Plate Thrust Bearings With Compressible Lubricant
Authors: Wildmann M.
Published: September 2011

The equations for pressure and load for a grooved plate bearing are derived by assuming that the grooves are sinusoidal rather than square. The usual assumption of zero groove width is thus removed. The effects of groove width and lubricant compressibility are examined independently. Finally, limiting solutions for high compressibility numbers are obtained.
Boundary Conditions of a Viscous Flow Between Surfaces With Rolling and Sliding Motion
Authors: Tipei N.
Published: September 2011

The fluid motion between surfaces with different radii of curvature and velocities is studied, assuming that the viscous fluid is carried by the solid surfaces but does not fill up the whole space. The boundary conditions at the inlet are examined in connection with those at the outlet of the fluid film. It is shown that only a part of the fluid carried by the surfaces, depending on the velocities and the initial rates of flow ratio, penetrates into the contact zone. Thus an interpretation of the flow field is proposed, differering from the usually assumed shape of the streamlines, by assuming the existence of a counterflow at the inlet. By using some physical conditions in various representative situations, as well as an equilibrium condition for the vortex flow, the real quantity of fluid and the entry and exit points are determined. Thereafter, the film extent, pressure distribution, load-carrying capacity, and minimum film thickness are obtained. Tables are given with the characteristic angles of the fluid film as functions of the minimum film thickness-radius of curvature ratio. The calculated values are in a satisfactory agreement with the experiments of other authors, especially when using the Prandtl-Hopkins conditions at the outlet.
Rayleigh Step Journal Bearing: Part 1—Compressible Fluid
Authors: Hamrock B. J.
Published: September 2011

A linearized PH solution to the Reynolds equation was obtained while neglecting side leakage. The analysis was divided into two parts—the step and ridge regions. The pressure profile across the step and ridge region of the various pads which are placed around the journal was obtained from the linearized PH Reynolds equation. Knowing the pressure, the load components and attitude angle were calculated. The resulting equations were found to be a function of the bearing parameters (the eccentricity and compressibility number) and the step parameters (ratio of the stepped clearance to the ridge clearance, ratio of the angle extended by the ridge to the angle extended by the pad, and number of pads placed around the journal). The maximum load capacity can be determined by numerically differentiating the load with respect to the step bearing parameters while finding where the slope is zero. A series of data was run while varying the bearing parameters. The attitude angle was calculated for the various cases which were run.
Material Combinations for Hydrodynamic Inert Gas-Lubricated Bearings
Authors: Murray S. F.
Published: September 2011

Four promising material combinations were evaluated for use in hydrodynamic, gas-lubricated bearing applications. Three of these combinations were hard, wear-resistant materials; the fourth was a solid lubricant film mated against hardened steel. The test configuration was a single, tilting-pad, hydrodynamic test bearing which was deadweight loaded against a test shaft. Performance was evaluated by determining changes in the hydrodynamic behavior of the bearing during the test. All of the evaluations were made in an argon environment at temperatures of 350 F and 500 F. Each combination was subjected to one thousand starts and stops, at a stress of 4 psi, to evaluate low-speed sliding behavior. High-speed rub tests were then made by shock loading the pad against the shaft at 60,000 rpm. Two combinations were particularly effective in the start-stop tests. These were: A tungsten carbide coated pad running against an Al2O3 coated shaft, and a chrome oxide coated pad mated against a chrome oxide coated shaft. At high speed, the best combination was the self-mated chrome oxide coating. Some possible reasons for the effective performance of chrome oxide are advanced.
Measurement of Friction in Drawing, Extrusion, and Rolling
Authors: Evans W. , Avitzur B.
Published: September 2011

In the processes of plastic forming of metals, friction between the metal and the tools (dies) plays a crucial part. Forces, flow patterns, tool wear, and surface finish of the product as well as the capacity of the equipment (in rolling), all are affected by friction. A complete analysis of any process considers the coefficient of friction as a variable. A quantitative knowledge of the value of the coefficient of friction acting during processing is desired. This work proposes an experimental procedure for the evaluation of the coefficient of friction for processes like wire drawing and rod extrusion through an open die, for hydrostatic extrusion and for rolling.
Shaft Surface Finish Is an Important Part of the Sealing System
Authors: Heyn W. O.
Published: September 2011

Current specifications for shaft finishes to be used with shaft seals are inadequate. Many finishes which meet these current specifications do not perform well in sealing applications because they can cause either leakage or abrasive wear of the seal lip. The practice of leaving the selection of the process to produce the finish up to the shaft manufacturer may lead to poor performance of the sealing system. A new shaft finish specification is proposed which specifies a process to obtain a satisfactory sealing surface. It has been found that machine lead can be generated by plunge grinding. Grinding procedures for avoiding machine lead during plunge grinding are listed. In order to be certain that machine lead is not present, the surface must be inspected for it. Therefore, a special method for checking for machine lead is recommended.
Radial Load as a Lip Seal Design and Quality Control Factor
Authors: Schmitt W. A.
Published: September 2011

A new device for the measuring of radial load in the laboratory and quality control is described. Equations are derived for the evaluation of the radial load and the influence of materials and seal dimensions on the radial load are shown. Obtainable production tolerances for the radial load of a seal are discussed. Considerable changes of radial load due to working conditions can cause the failure of a seal. More attention should be paid to a thorough consideration of the working conditions before a seal is designed.
Process Control and Testing of Elastomers and Elastomeric Compositions
Authors: Carr J. J.
Published: September 2011

The paper presents a discussion of test equipment and procedures used to control raw polymers and compounded rubbers. The capabilities and uses of the Mooney Viscometer, Brabender Plasticorder, and Monsanto Oscillating Disk Rheometer are discussed. The data obtained during sampling stages and its value and subsequent application to monitoring production lots of elastomeric materials, are presented in an effort to show how close quality of conformance is maintained between prototype components and their mass-produced counterparts. The application and potential uses of Gas Chromatography as a means of polymer and finished compound identification is also described.
Some Aspects of Nonlinear Behavior in Lubricants Under Extreme Stress
Authors: Smith F. W.
Published: September 2011

A general basis for discussing nonlinearity in the flow of molecular fluids consists in applying the continuum mechanics of Coleman and Noll to a flow process governed by an Arrhenius activation energy equation. The theory predicts the familiar exponential increase of viscosity with pressure and a decrease in viscosity with high shear stress, and also predicts the existence of “normal stresses” under high shear stress. Schematic calculations are presented for the behavior of a lubricant under extreme stress.
Response of Viscoelastic Fluids in Dynamically Loaded Bearings
Authors: Tanner R. I.
Published: September 2011

The dynamic response of polymer fluids to small sinusoidal shearing motions may be characterized by their relaxation spectra. Recent experiments show that great changes can be induced in the relaxation spectrum by steady shearing of the sample. This is the case of most relevance to bearing studies in, for example, a dynamically loaded journal bearing. It is shown that almost all relaxation processes longer than a small multiple of the (shear rate)−1 are removed by steady shearing. This result implies that in a bearing undergoing dynamic loading with Fourier components which are low harmonics of the shaft speed a polymer fluid is expected to behave very like a quasi-Newtonian fluid with variable viscosity. The action of a sheared squeeze film is also considered and the implications for synovial joint lubrication are briefly mentioned.