bluuebunny/crossref_metadata_2025 huggingface dataset:
Factors affecting employee knowledge acquisition and application capabilities
Authors: Kim Soonhee , Lee Hyangsoo
Published: October 2010

Purpose

The paper aims to analyze the influences of organizational context and information technology (IT) applications on employees' perceptions of knowledge acquisition and application capabilities in five public and five private sector organizations in South Korea.

Design/methodology/approach

The paper analyzes how employees' perceptions of organizational context and IT affect employee knowledge acquisition and application capabilities in five public and five private sector organizations in South Korea. It discusses the results of regression analyses based on a survey of 322 public and private employees that explored their perceptions of organizational vision and goals, social networks, centralization, performance‐based reward systems, the usage of IT applications, and knowledge acquisition and application capabilities.

Findings

The results of a survey of public and private employees show that clear organizational vision and goals, social networks, and employee usage of IT applications are all positively associated with high levels of employee knowledge acquisition and application capabilities. Centralization, however, was negatively associated with employee knowledge acquisition and application capabilities. Social network and IT application utilization were both positively associated with public employees' knowledge acquisition and application capabilities. Performance‐based reward systems were positively associated with private employees' knowledge application capabilities only.

Originality/value

In 2000, the South Korean Government established a special task committee to develop knowledge management systems (KMS) in the public sector and to initiate KM strategies. Since 1997, major South Korean corporations have been developing KM information systems to allow employees to quickly respond to complex and evolving domestic and international market environments. Some of the knowledge management practices effectively implemented in these corporations have been selected as benchmarks for developing the government KMS in the South Korean Government. However, there is limited research on comparative studies of the factors affecting employee KM capabilities in public organizations and private in South Korea.
Doing business in China and India: a comparative approach
Authors: Quer Diego , Claver Enrique , Rienda Laura
Published: October 2010

Purpose

In recent years, China and India have been experiencing a process of economic and social transformation that is unprecedented in recent human history. The consequences of the spectacular resurgence of these two Asian giants are profound and far‐reaching, and are causing the centre of gravity of the world economy to be drawn inexorably toward these countries. The aim of this paper is to offer a comparative approach to the reality of China and India as regards business and strategic management.

Design/methodology/approach

The paper reviews previous literature that has focused on comparing various issues related to business and management in China and India.

Findings

The paper highlights the points of convergence and divergence in the developmental patterns of China and India, the key factors for success in each country, the entry modes that could be used and the business opportunities they offer.

Originality/value

The paper provides a comparison between China and India with regard to business and strategic management, analysing the main similarities and differences between the two Asian giants.
Patterns and motivations of successful women pursuing their careers in New Zealand call centres
Authors: Hunt Vivienne , Rasmussen Erling
Published: October 2010

Purpose

The purpose of this paper is to report on the experience of women working in New Zealand call centres after finding contrary evidence in the international research which suggests call centre work does not offer career opportunities for its mainly female workforce. The research seeks to explore the career progress of women in a selection of call centres to determine whether the New Zealand employment relations context contributed to outcomes different to those reported in the international research.

Design/methodology/approach

Case study methodology and six different call centre types were used to find 32 women who had experienced career progress. Semi‐structured in‐depth interviews were held with the women and senior management representatives at each organisation. Analysis of interview transcripts identified common themes and patterns across the case studies. Insights were gained from survey responses from 60 entry‐level workers, many of whom were return‐to‐work mothers, new immigrants or students.

Findings

The findings demonstrated that women were achieving considerable career success in the call centres investigated. Management practices accommodated their different labour market needs and respondents spoke about their passion and enjoyment of call centre work. The entry‐level workers reported that being part of the call centre workplace, allowed them to meet people, develop new skills and confidence while enhancing their career prospects. At many levels, call centre processes seemed to have enabled respondents to become competent, connected and confident workers.

Originality/value

Contrary to the international portrayal of call centre work and the career prospects for female workers the paper highlights the need for researchers to link employment outcomes to particular employment contexts.
The influence of changing climate on the ecology and management of selected Laurentian Great Lakes fisheries
Authors: Lynch A. J. , Taylor W. W. , Smith K. D.
Published: October 2010

The Laurentian Great Lakes Basin provides an ecological system to evaluate the potential effect of climate change on dynamics of fish populations and the management of their fisheries. This review describes the physical and biological mechanisms by which fish populations will be affected by changes in timing and duration of ice cover, precipitation events and temperature regimes associated with projected climate change in the Great Lakes Basin with a principal focus on the fish communities in shallower regions of the basin. Lake whitefish Coregonus clupeaformis, walleye Sander vitreus and smallmouth bass Micropterus dolomieu were examined to assess the potential effects of climate change on guilds of Great Lakes cold, cool and warm‐water fishes, respectively. Overall, the projections for these fishes are for the increased thermally suitable habitat within the lakes, though in different regions than they currently inhabit. Colder‐water fishes will seek refuge further north and deeper in the water column and warmer‐water fishes will fill the vacated habitat space in the warmer regions of the lakes. While these projections can be modified by a number of other habitat elements (e.g. anoxia, ice cover, dispersal ability and trophic productivity), it is clear that climate‐change drivers will challenge the nature, flexibility and public perception of current fisheries management programmes. Fisheries agencies should develop decision support tools to provide a systematic method for incorporating ecological responses to climate change and moderating public interests to ensure a sustainable future for Great Lakes fishes and fisheries.
Diagnosis and management of pituitary abscess: experiences from 33 cases
Authors: Liu Fuyi , Li Guilin , Yao Yong , Yang Yi , Ma Wenbin , Li Yongning , Chen Gao , Wang Renzhi
Published: October 2010

Objective  Pituitary abscess is a rare disorder with nonspecific presenting manifestations, often making a correct preoperative diagnosis difficult. To better determine the salient signs and symptoms of pituitary abscess and to evaluate the effectiveness of surgical and antibiotic therapies, we conducted a review of patients treated for pituitary abscess at the Peking Union Medical College Hospital (PUMCH).

Methods  A total of 33 consecutive patients referred to PUMCH between 1991 and 2007 were included. While 30 patients underwent surgery and antibiotic therapy, three patients accepted only antibiotic therapy. A complete history, a thorough record of signs and symptoms, pituitary imaging and biochemical panels were obtained for each patient.

Results  Most of the patients presented with complaints and symptoms consistent with a sellar mass, generally in the absence of any evidence of infection. Diabetes insipidus, hypopituitarism and headache were the most common clinical indicators. Typical magnetic resonance (MR) images after gadolinium injection demonstrated a sellar cystic mass with an enhanced rim. Although there were several recurrences, the abscess resolved in nearly all cases. Hypopituitarism generally did not recover, and hormone replacement therapy was usually necessary.

Conclusions  Presentation of diabetes insipidus, hypopituitarism and a sellar cystic mass with an enhanced rim may be suggestive of a pituitary abscess. For most patients, a transsphenoidal evacuation, followed by antibiotic therapy, is recommended. However, antibiotic therapy alone may be useful for acute cases. In our experience, pituitary abscesses can usually be treated, though the accompanying hypopituitarism is difficult to cure, and requiring lifelong hormonal replacement.
Water stress induces up‐regulation of DOF1 and MIF1 transcription factors and down‐regulation of proteins involved in secondary metabolism in amaranth roots (Amaranthus hypochondriacus L.)
Authors: Huerta‐Ocampo J. A. , León‐Galván M. F. , Ortega‐Cruz L. B. , Barrera‐Pacheco A. , De León‐Rodríguez A. , Mendoza‐Hernández G. , Barba de la Rosa A. P.
Published: October 2010

Roots are the primary sites of water stress perception in plants. The aim of this work was to study differential expression of proteins and transcripts in amaranth roots (Amaranthus hypochondriacus L.) when the plants were grown under drought stress. Changes in protein abundance within the roots were examined using two‐dimensional electrophoresis and LC/ESI‐MS/MS, and the differential expression of transcripts was evaluated with suppression subtractive hybridisation (SSH). Induction of drought stress decreased relative water content in leaves and increased solutes such as proline and total soluble sugars in roots. Differentially expressed proteins such as SODCu‐Zn, heat shock proteins, signalling‐related and glycine‐rich proteins were identified. Up‐regulated transcripts were those related to defence, stress, signalling (Ser, Tyr‐kinases and phosphatases) and water transport (aquaporins and nodulins). More noteworthy was identification of the transcription factors DOF1, which has been related to several plant‐specific biological processes, and MIF1, whose constitutive expression has been related to root growth reduction and dwarfism. The down‐regulated genes/proteins identified were related to cell differentiation (WOX5A) and secondary metabolism (caffeic acid O‐methyltransferase, isoflavone reductase‐like protein and two different S‐adenosylmethionine synthetases). Amaranth root response to drought stress appears to involve a coordinated response of osmolyte accumulation, up‐regulation of proteins that control damage from reactive oxygen species, up‐regulation of a family of heat shock proteins that stabilise other proteins and up‐regulation of transcription factors related to plant growth control.
Effect of Zataria multiflora Boiss. essential oil on colony morphology and ultrastructure of Aspergillus flavus
Authors: Gandomi Hassan , Misaghi Ali , Akhondzadeh Basti Afshin , Hamedi Hassan , Ramezani Shirvani Zahra
Published: October 2010

The mode of inhibitory action of Zataria multiflora Boiss. essential oil (EO) on the fungus, Aspergillus flavus, was studied by colony morphology examination, light microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The EO at concentrations used in this study suppressed the size of the colony as well as sporulation. SEM of mycelia treated with given concentrations of EO showed morphological alterations ranging from loss of turgidity and uniformity of mycelia at low concentrations of EO to evident destruction of the hyphae at higher concentration of EO. Semi‐thin sections of mycelia exposed to different concentrations of EO were analysed by light microscopy and revealed that the major change at level as low as 50 ppm of EO was limited to vacuolisation of cytoplasm resulting in cell swelling, while at higher concentrations, detachment of the cell membrane from the cell wall, deformation of mycelia and shedding the cytoplasm from the cell were the main alterations. These damages were well documented by TEM, which showed that the main sites of action of EO were the plasma membrane and cell wall. In conclusion, morphological and structural changes observed in this study may be one of the mechanisms involved in growth inhibition of the fungi and reducing aflatoxin production.
Frontonasal facial angle in chromosomally normal fetuses at 11+0 to 13+6 weeks
Authors: Vicario Roberta , Pirollo Linda Maria Azzurra , De Angelis Cristina , Narcisi Marianovella , Pietropolli Adalgisa , Piccione Emilio
Published: October 2010

Aim:  To establish the normal range of frontonasal angle (FNA) at 11+0 to 13+6 weeks of gestation and the feasibility of FNA measurement, evaluate the correlation of such a parameter with crown‐rump length (CRL) and nuchal translucency (NT) and assess the potential of FNA in improving the performance of first trimester sonographic and biochemical screening for trisomy 21.

Methods:  We conducted a prospective study in 400 singleton uncomplicated pregnancies. FNA was obtained during maternal screening for trisomy 21. NT thickness and FNA were measured by 2D ultrasound in a midsagittal plane of the fetal profile. FNA was measured between the line along the upper surface of the frontal bone and the superior edge of the nasal profile until the echogenic tip. Determination of maternal serum free β‐human chorionic gonadotropin (β‐hCG) and pregnancy‐associated plasma protein‐A (PAPP‐A) was committed and concomitantly evaluated by blood sample. Patient‐specific risk was calculated using Fetal Medicine Foundation software (Astraia Software GMBH, Munich, Germany).

Results:  Mean FNA increased with CRL from 119.80° at CRL 45 mm to 125.85° at CRL 84 mm. A significant association between the FNA and NT thickness was detected, while no significant association was found between FNA and serum PAPP‐A or β‐hCG.

Conclusion:  At 11+0 to 13+6 weeks FNA increases with fetal CRL and NT thickness. Such an increase is not related to serum biochemistry.
Raloxifene temporarily reduces arterial stiffness
Authors: Obayashi Satoshi , Terauchi Masakazu , Kato Kiyoko , Akiyoshi Mihoko , Kubota Toshiro
Published: October 2010

Aim:  Aortic stiffness is widely recognized as an important, independent determinant of cardiovascular risk. The cardio‐ankle vascular index (CAVI) has been developed to estimate vascular wall stiffness which is theoretically less affected by varied blood pressure. The purpose of this paper was to evaluate the change of CAVI during one‐year use of raloxifene (RLX).

Material & Methods:  Forty‐eight women who visited the menopausal clinic in Tokyo Medical and Dental University were enrolled in this study. Twenty‐two patients with osteopenia/osteoporosis (mean age 61.3 ± 1.1) out of 48 had RLX 60 mg/day (RLX group). The remaining 26 women (mean age 56.3 ± 1.0) had no medication and were recognized as younger, healthy control (control group). CAVI and ankle‐brachial index were measured every 6 months, compared among 0, 6 and 12 months, in respective group.

Results:  CAVI showed a significant positive correlation to age by the single linear regression analysis. Control group indicated no change of age‐adjusted CAVI through 12 months, but RLX group showed significant reduction of CAVI at 6 months and increased to the original level after 12 months. On the other hand, ankle‐brachial index change showed significant increase in control group, but slight increase in RLX group, suggesting no increased risk of arterial stenosis. Furthermore, CAVI in the relatively younger group (50 to 59 years; n = 11) indicated stronger reduction at 6 months than older group, suggesting high sensitivity to RLX treatment in the younger group.

Conclusion:  RLX treatment reduced CAVI value at 6 months which was superior in relatively younger group.
Nitric oxide participates in cold‐responsive phosphosphingolipid formation and gene expression in Arabidopsis thaliana
Authors: Cantrel Catherine , Vazquez Thomas , Puyaubert Juliette , Rezé Nathalie , Lesch Maria , Kaiser Werner M. , Dutilleul Christelle , Guillas Isabelle , Zachowski Alain , Baudouin Emmanuel
Published: October 2010

See also the Commentary by Gupta et al
.
A call for prospective studies in early‐stage ovarian cancer
Authors: Naik R , Ledermann J , Cross PA
Published: October 2010

Please cite this paper as: Naik R, Ledermann J, Cross P. A call for prospective studies in early‐stage ovarian cancer. BJOG 2010;117:1441–1443.
K‐Th‐Ti systematics and new three‐component mixing model of HED meteorites: Prospective study for interpretation of gamma‐ray and neutron spectra for the Dawn mission
Authors: USUI Tomohiro , McSWEEN Jr. Harry Y. , MITTLEFEHLDT David W. , PRETTYMAN Thomas H.
Published: October 2010

Abstract–The Dawn spacecraft carries a gamma‐ray and neutron detector (GRaND), which will measure and map the abundances of selected elements on the surface of asteroid 4 Vesta. We compare the variability of moderately volatile/refractory incompatible element ratios (K/Th and K/Ti) in howardite, eucrite, and diogenite (HED) meteorites with those in other achondrite suites that represent asteroidal crusts, because these ratios may be accurately measured by GRaND and likely reflect initial chemical compositions of the HED parent body. The K/Th and K/Ti variations can differentiate HED meteorites from angrites and some unique eucrite‐like lithologies. The results suggest that K, Th, and Ti abundances determined from GRaND data could not only confirm that Vesta is the parent body of HED meteorites but might also allow recognition of as‐yet unsampled compositional terranes on Vesta. Besides the K‐Th‐Ti systematics study, we propose a new three‐component mixing model for interpretation of GRaND spectra, required because the spatial resolution of GRaND is coarser than the spectral (compositional) heterogeneity of Vesta’s surface. The mixing model uses abundances of K, Ti, Fe, and Mg that will be analyzed more accurately than other prospective GRaND‐analyzed elements. We examine propagated errors due to GRaND analytical uncertainties and intrinsic errors that stem from an assumption introduced into the mixing model. The error investigation suggests that the mixing model can adequately estimate not only the diogenite/eucrite mixing ratio but also the abundances of most major and minor elements within the GRaND propagated errors.
A Comparative Thermal Analysis of Slot-Entry and Hole-Entry Hybrid Journal Bearings Lubricated With Non-Newtonian Lubricant
Authors: Garg H. C. , Kumar Vijay , Sharda H. B.
Published: October 2010

The effect of viscosity variation due to temperature rise and non-Newtonian behavior of the lubricant on the performance of hole-entry and slot-entry hybrid journal bearings system is the focus of this investigation. The performance characteristics of nonrecessed hybrid journal bearings operating with different flow controlling devices, i.e., constant flow valve, capillary, orifice, and slot restrictors, have been compared. Finite element method has been used to solve the Reynolds equation governing the flow of lubricant in the bearing clearance space along with the restrictor flow equation, energy equation and conduction equation using suitable iterative technique. The non-Newtonian lubricant has been assumed to follow the cubic shear stress law. The results indicate that variation in viscosity due to rise in temperature and non-Newtonian behavior of the lubricant affects the performance of nonrecessed hybrid journal bearing system quite significantly. The results further indicate that bearing performance can be improved by selecting a particular bearing configuration in conjunction with a suitable compensating device.
Microstructure and Wear Properties of Laser Clad (Ti,Mo)C Multiple Carbide Reinforced Fe-Based Composite Coating
Authors: Wang Xinhong , Zhang Min , Qu Shiyao
Published: October 2010

(Ti,Mo)C multiple carbide reinforced Fe-based composite coating was produced by laser melting a precursor mixture graphite, ferrotitanium (Fe–Ti), and ferromolybdenum (Fe–Mo) powders. The results showed that flowerlike and cubic type (Ti,Mo)C multiple carbides were formed during laser cladding process. The selective area diffraction pattern analysis indicated that (Ti,Mo)C crystallizes with cubic structure, which indicates that (Ti,Mo)C carbides were multiple carbides with Mo dissolved in the TiC structure. The formation of (Ti,Mo)C particles was achieved via a nucleation-growth mechanism during the laser cladding process. Increasing the amount of Fe–Mo in the reactants led to a decrease of carbide size and an increase of volume fraction of carbides. The coating possessed good cracking resistance when the amount of Fe–Mo was controlled within a range of 15 wt %. The Fe-based surface coating reinforced by (Ti,Mo)C multiple carbides gave an excellent wear resistance.
Investigation of Temperature Effects on Cavitation Erosion Behavior Based on Analysis of Erosion Particles
Authors: Saleh B. , Abouel-Kasem A. , El-Deen A. Ezz , Ahmed S. M.
Published: October 2010

The effect of temperature on the wear particles produced by vibratory cavitation erosion tests on Al-99.92 in distilled water was analyzed. Scanning electron microscope images of wear particles were obtained, forming a database for further analysis. This study showed that the variation of average particle size with temperature was very much similar to the variation of weight loss with temperature. The average particle size was maximum at 40°C. It was also observed that the average particle size was time dependent. The particle’s morphology features revealed that the predominant erosion mechanism was fatigue failure, irrespective of the temperature.
Multiple Normal Loading-Unloading Cycles of a Spherical Contact Under Stick Contact Condition
Authors: Zait Y. , Zolotarevsky V. , Kligerman Y. , Etsion I.
Published: October 2010

The multiple normal loading-unloading process of an elastic-plastic sphere by a rigid flat is analyzed using finite element method for stick contact condition and both kinematic and isotropic hardening models. The behavior of the global contact parameters as well as the stress field within the sphere tip is presented for several loading cycles. It was found that under stick contact condition, secondary plastification occurs even after the second loading cycle and that the hardening model used has little effect on the loading-unloading process. The cyclic loading process gradually converges into elastic shakedown.
Theoretical Modeling for Microgrooved Journal Bearings Under Mixed Lubrication
Authors: Ashihara Katsuhiro , Hashimoto Hiromu
Published: October 2010

In designing of engine bearings for automobiles, we need to establish a mixed lubrication model that considers the solid-to-solid contact between journal surfaces and bearing surfaces with microgroove. However, as far as we know, there is no literature treating such problems. This paper describes theoretical modeling for microgrooved bearings under the mixed lubrication conditions with experimental verifications and prediction of performance in the actual engine bearings. In this modeling, a sectional shape of the microgrooved bearing was approximated to be a circular sectional shape. Contact pressure between the journal surfaces and the bearing surfaces with microgroove was calculated using the Hertzian contact model and the effects of elastic deformation of bearing surface due to hydrodynamic and contact pressures were considered. A numerical calculation model was developed to predict bearing performance under the mixed lubrication condition in microgrooved journal bearings. Oil film thickness distributions, hydrodynamic and contact pressure distributions, and real contact area between the journal surfaces and the bearing surfaces with microgroove were obtained simultaneously by the theoretical model. Moreover, friction coefficients under mixed lubrication conditions were determined by the theoretical model and the calculated results were compared with experimental results using test rig. The calculated results successfully agreed with the experimental results and the applicability of the model was verified. Moreover, the model was applied to predict the performance of engine bearings. In the numerical results, real contact area occurred relative widely under low-speed conditions when engine was started but friction loss was not excessive because of low shearing velocity. On the other hand, under high-speed engine conditions, the friction loss was large in spite of narrow real contact area because of high shearing velocity. Under both low-speed and high-speed conditions, the real contacts will occur severely at the edge of the bearing in the axial direction and at the bearing angles from 50 deg to 110 deg in circumferential direction. In addition, an appropriate design of the microgrooved bearing was examined under mixed lubrication conditions. In the design of the microgrooves, a cooling effect and an enough amount of oil flow to the contact area are needed. As the results from parametric studies using present theoretical model, an influence of the depth of the microgroove was the largest on the cooling effect and the enough amount of oil flow. In the case of typical operation condition, it was found that 1.0 μm of the groove depth was the most appropriate.
A Mass-Conserving Complementarity Formulation to Study Lubricant Films in the Presence of Cavitation
Authors: Giacopini Matteo , Fowell Mark T. , Dini Daniele , Strozzi Antonio
Published: October 2010

A new mass-conserving formulation of the Reynolds equation is developed using the concept of complementarity. This new method overcomes the drawbacks previously associated with the use of such complementarity formulations for the solution of cavitation problems in which reformation of the liquid film occurs. Validation against a number of analytical and semi-analytical formulations, for a variety of problems including textured bearings and squeeze film dampers, is performed. The current formulation is shown to be in very good agreement with existing analytical and numerical mass-conserving solutions.
Research on the Effect of Whole Cylinder Block on EHL Performance of Main Bearings Considering Crankshaft Deformation for Internal Combustion Engine
Authors: Sun Jun , Cai Xiaoxia , Liu Liping
Published: October 2010

In this paper, the analyses of elastohydrodynamic lubrication (EHL) of crankshaft bearings considering the deformation of the whole cylinder block and crankshaft under load were carried out for the crankshaft bearing system of a four-stroke four-cylinder internal combustion engine. The lubrication of crankshaft bearing was analyzed by dynamic method. The deformation of bearing surface under pressure of oil film was calculated by compliance matrix method. The results show that when the crankshaft deformation under load is considered, compared with the results of not considering the deformation of cylinder block, the maximum film pressure decreases, the minimum film thickness increases, and the end leakage flow-rate and frictional coefficient of journal surface change little in an engine working cycle when considering the deformation of cylinder block. The models of the whole cylinder block and the single main bearing housing were used, respectively, to calculate the deformation of main bearing surface in the analyses. The results show that the calculation accuracy of the elastohydrodynamic lubrication analyses of crankshaft main bearings can be met basically by applying the simple model based on the single main bearing housing to calculate the elastic deformation of main bearing surface.
Effects of Some Solid Lubricants Suspended in Oil Toward Controlling the Wear Performance of a Cast Iron
Authors: Prasad B. K. , Rathod S. , Yadav M. S. , Modi O. P.
Published: October 2010

The present investigation deals with the examination of the sliding wear response of a gray cast iron in oil lubricated condition over a range of applied pressure. The composition of the oil lubricant was changed by adding 5.26 wt % solid lubricant particles. The solid lubricants used were graphite, talc, MoS2, and lead. The observed wear response of the samples has been substantiated through the characteristics of wear surfaces, subsurface regions, and debris particles and discussed in terms of specific response of different microconstituents, such as ferrite, pearlite, and graphite present therein. Operating wear mechanisms were assessed through the observed features of wear surfaces, subsurface regions, and debris. The wear rate increased with applied pressure. The slope of the wear rate versus pressure plots was low up to a critical pressure. This was followed by a sudden rise in the slope at higher pressures irrespective of the test environment. The frictional heating was affected by pressure in a manner practically identical to that of the wear rate. The presence of graphite, MoS2, and lead in the oil led to a substantial decrease in the wear rate and severity of frictional heating. The oil plus lead lubricant mixture was observed to offer best results in terms of reduced wear rate and lower frictional heating. This was followed by the ones containing graphite and MoS2 while talc caused the wear performance of the samples to deteriorate over that of the bare oil. However, the severity of frictional heating decreased in general in the oil containing solid lubricant particles. Seizure brought about high frictional heating and wear rate.
A Baseline Theory for the Design of Oil-Lubricated Centrally Pivoted Plane-Pad Thrust Bearings
Authors: Chang L.
Published: October 2010

A baseline theory is developed in this paper for the design of oil-lubricated centrally pivoted plane-pad thrust bearings. By focusing on the hydrodynamics generated by the viscosity-temperature effects of the lubricating oil, a mathematical model is derived with a single dimensionless parameter Wth. The nominal value of Wth is 0.1 for typical pad bearings in current industrial practice. The theory suggests two important design calculations for centrally pivoted plane-pad bearings: (1) The minimum oil film thickness in the bearing is about 0.65 of the film thickness determined using the classical isothermal lubrication theory with the pad pivoted at the maximum-load optimum location. Thus, by setting the film thickness to 1.54 times the design requirement, one may carry out design selections and calculations using the classical theory. (2) The friction in the bearing is about 1.7 times the value determined using the classical theory at the maximum-load optimum condition and with the film thickness equal to the design requirement. Thus, one may also use the classical theory to meaningfully calculate the friction and power loss in the centrally pivoted plane-pad bearing systems. The theory is developed based on fundamental lubrication science, order of magnitude analyses of the assumptions, and supporting evidence from numerical literature case studies. It would be a conservative baseline theory for the bearing design as other complicated and/or incidental mechanisms would help provide a design factor of safety.
Wear Characteristics of NiTi/Al6061 Short Fiber Metal Matrix Composite Reinforced With SiC Particulates
Authors: Akalin Ozgen , Ezirmik K. Vefa , Urgen Mustafa , Newaz Golam M.
Published: October 2010

Wear characteristics of Al6061 composites, reinforced with short NiTi fibers, were investigated. The NiTi/Al6061 composite samples were fabricated using pressure-assisted sintering process in ambient air where the NiTi fibers are aligned unidirectional in the Al matrix. In addition, NiTi/Al6061 composite with 5 wt % SiC particulates and monolithic Al6061 and Al6061 with 5 wt % SiC particulates were processed in similar conditions. The wear tests were performed using a reciprocating tribometer in ball-on-flat configuration where the counterbody material was martensitic steel. The effects of fiber isotropy and SiC reinforcements on wear resistance were experimentally investigated in dry sliding. Wear properties of the samples were studied using an optical profiler and a scanning electron microscope analysis. The results showed that transverse NiTi fibers improve the wear resistance significantly. Samples with transverse fiber orientation show mostly abrasive wear, whereas, monolithic and parallel samples show adhesive wear mechanism. In addition, SiC reinforcements improve the wear resistance of the composite and the monolithic samples. Since the Al6061 matrix material is smeared onto NiTi fibers in a short period, all composite samples show similar frictional characteristics after certain period of running in dry sliding.
A Dynamic Model for Vibration Studies of Deep Groove Ball Bearings Considering Single and Multiple Defects in Races
Authors: Patel V. N. , Tandon N. , Pandey R. K.
Published: October 2010

A dynamic model is reported herein for the study of vibrations of deep groove ball bearings having single and multiple defects on surfaces of inner and outer races. Masses of shaft, housing, races, and balls are considered in the modeling. The coupled solution of governing equations of motions is obtained using Runge–Kutta method. The model provides the vibrations of shaft, balls, and housing in time and frequency domains. Computed results from the model are validated with experimental results, which are generated using healthy and defective deep groove ball bearings. Characteristic defect frequencies and its harmonics are broadly investigated using both theoretical and experimental results. Comparison of vibration spectra for the cases having single and two defects on races reveals relatively higher velocity amplitudes with two defects. Good correlations between theoretical and experimental results are observed. Authors believe that this dynamic model can be used with confidence for the study and prediction of vibrations of healthy and defective deep groove ball bearings.
Investigation of Inclined Planar Rough Surfaces Contact From Static to Sliding
Authors: Ni Ting , Shi Xi
Published: October 2010

Due to the friction moment, when two flat rough surfaces come to sliding contact or quasi-sliding contact, there is an inclined angle between these two surfaces. A two degree-of-freedom inclined rough surface contact model is presented in this work and the effects of the angular displacement on the friction coefficient, interfacial forces, and interfacial moments for the elastic-plastic planar rough surfaces contact are investigated. The numerical simulations show that both interfacial forces and interfacial moments gain with the increase of the inclined angle while the friction coefficient decreases instead. In addition, for a given sliding mass block system, the effects of that friction coefficient and base sliding speed on the stability of the sliding contact are also discussed. The simulations indicate that a larger friction coefficient and a higher base sliding speed tend to turn over the mass block during the sliding.
Condition Monitoring of Molybdenum Disulphide Coated Thrust Ball Bearings Using Time-Frequency Signal Analysis
Authors: Kahirdeh Ali , Khonsari M. M.
Published: October 2010

A method for detection of wear in thrust ball bearings coated with molybdenum disulphide (MoS2) is presented. It employs an energy feature obtained from time-frequency representation of the vibration signal. Extensive experimental studies are conducted to verify the efficacy of the proposed method for fault diagnosis of MoS2 coating. These experiments are conducted under both oscillatory and unidirectional motions. The results of vibrations are corroborated with the friction coefficient from the onset of the motion until failure develops. Through monitoring of the energy in time-frequency domain as well as the coefficient of friction, three stages of coating life are identified. They are healthy period, developing damage, and failure. It is shown that the energy feature can detect whenever wear and damage appear and solid lubricant loses its lubrication capabilities.
A Study of Worn Hybrid Journal Bearing System With Different Recess Shapes Under Turbulent Regime
Authors: Nicodemus E. Rajasekhar , Sharma Satish C.
Published: October 2010

The objective of the present paper is to study analytically the influence of wear on the performance of a capillary-compensated, four-pocket, hybrid journal bearing system operating in a turbulent regime by considering various geometric shapes of recess. The present study deals with bearings having four different geometric shapes of recess, i.e., square, circular, elliptical, and triangular recessed bearings. The wear on the bearing surface is modeled using Dufrane’s abrasive wear model. The Reynolds equation based on Constantinescu’s turbulent lubrication theory has been solved using finite element method along with a restrictor flow equation as a constraint together with appropriate boundary conditions. The numerically simulated results have been presented for a wide range of nondimensional external loads, wear depth parameters, and Reynolds numbers. The numerically simulated results suggest that the combined influence of wear, turbulence, and geometric shape of recess significantly affects the bearing performance. It has been observed that a triangular recessed bearing provides a greater value of minimum fluid film thickness when operating in a turbulent regime. It is also noticed that direct fluid film stiffness coefficients get reduced significantly when bearings operate in a turbulent regime compared with a laminar regime. Further, it is observed that from the viewpoint of fluid film stiffness, a square recessed bearing is found to be most suitable when operating in a turbulent regime.
Does Thermal Conductivity Play a Role in Sliding Wear of Metals in Cryogenic Environment?
Authors: Basu Bikramjit , Mukhopadhyay Amartya , Mishra Ankit , Sarkar J.
Published: October 2010

The thermal conductivity of a metallic test piece is one of the principal parameters that influence the temperature buildup at tribocontacts and this normally plays an important role in the unlubricated dry sliding wear of metallic materials. It is, however, not clear whether thermal conductivity is an equally important parameter in the case of wear of metals at cryogenic temperatures, in particular, at liquid nitrogen temperature (LN2) of −196°C. In order to assess the influence of such a physical property of selected nonferrous metals on their tribological behavior in the LN2 environment, we have studied the friction and wear properties of high purity copper (Cu) and titanium (Ti) against the bearing grade steel. These two materials have been processed to produce samples of comparable hardness that have widely different thermal conductivities at room temperature and at test temperature. Wear tests were conducted at three different sliding speeds (0.89 m/s, 1.11 m/s, and 1.34 m/s) under 10 N load, and the friction and wear data were compared. Ti exhibited an order of magnitude higher wear rate (∼10−3 mm3/N m) as compared with Cu in identical test conditions. While evidences of abrasive wear and adhesive wear, without any oxidative wear, were found in worn Cu surfaces, worn Ti surfaces showed evidences of significant oxidative wear and mechanical damage of tribolayers. Higher wear rate in Ti appeared to be a result of oxidative wear of Ti, which seemed to be driven by the depletion of LN2 blanket at the tribocontacts under the influence of high flash temperature (14–76°C) as compared with the boiling temperature of LN2(−196°C). These results demonstrate that the materials with similar hardness subjected to identical LN2 wear test conditions can have significantly different wear rates because of the difference in the flash temperatures, which depend on the thermal conductivity of the test pieces.
Repeatability Estimation in Galling Resistance Testing
Authors: Hummel Scott R. , Helm Jeffrey
Published: October 2010

Galling is a severe form of mechanical surface damage, commonly observed in metals, that is accompanied by adhesive transfer, extensive plastic deformation, and/or cold-welding of the mating surfaces. It can lead to seizure or rapid failure of machine components. Stainless steels are particularly prone to galling. A new galling test and analysis method that reflects the statistical nature of galling is described. The new ASTM method (G196), which embodies a probabilistic approach to galling, is superior to an older ASTM test method (G98), which produces only a single threshold stress for a given combination of materials. A computer-modeled experiment involving a 300 series stainless steel is used to illustrate how the enhanced analysis can be applied to determine the repeatability of galling test results.
An Approach for Modeling Material Grain Structure in Investigations of Hertzian Subsurface Stresses and Rolling Contact Fatigue
Authors: Weinzapfel Nick , Sadeghi Farshid , Bakolas Vasilios
Published: October 2010

The continuum theory of elasticity and/or homogeneously discretized finite element models have been commonly used to investigate and analyze subsurface stresses in Hertzian contacts. These approaches, however, do not effectively capture the influence of the random microstructure topology on subsurface stress distributions in Hertzian contacts. In this paper, a finite element model for analyzing subsurface stresses in an elastic half-space subjected to a general Hertzian contact load with explicit consideration of the material microstructure topology is presented. The random internal geometry of polycrystalline microstructures is modeled using a 3D Voronoi tessellation, where each Voronoi cell represents a distinct material grain. The grains are then meshed using finite elements, and an algorithm was developed to eliminate poorly shaped elements resulting from “near degeneracy” in the Voronoi tessellations. Hertzian point and line contacts loads are applied as distributed surface loads, and the model’s response is evaluated with commercial finite element software ABAQUS. Internal stress results obtained from the current model compare well with analytical solutions from theory of elasticity. The influence of the internal microstructure topology on the subsurface stresses is demonstrated by analyzing the model’s response to an over rolling element using a critical plane approach.
Visco-Elastohydrodynamic Model of a Hydraulic Rod Seal During Transient Operation
Authors: Thatte Azam , Salant Richard F.
Published: October 2010

A visco-elastohydrodynamic model of a hydraulic rod seal during transient operation has been developed. The model includes analyses of the macro- and microscale deformation mechanics and contact mechanics, and the microscale fluid mechanics. Viscoelasticity enters the analysis through the deformation mechanics and through the contact mechanics. A hybrid finite element-finite volume computational framework is developed to solve the highly coupled governing equations. Viscoelasticity is seen to affect the leakage and friction characteristics of the seal through its effects on the changing fluid pressure and contact pressure distributions as the rod velocity and sealed pressure change during a cycle. Compared with purely elastic behavior, viscoelasticity increases the fluid pressure and the contact pressure significantly in the sealing region closest to the sealed end, shifts the fluid pressure peaks away from the sealed end during the instroke, and enhances the cavitation during the outstroke. It results in thicker fluid films and produces a significant increase in the Poiseuille flow during the instroke.
Identification of Synthetic Inducers and Inhibitors of the Quorum-Sensing Regulator LasR in
Pseudomonas aeruginosa
by High-Throughput Screening
Authors: Borlee Bradley R. , Geske Grant D. , Blackwell Helen E. , Handelsman Jo
Published: October 2010

We report the screening of 16,000 synthetic compounds for induction and inhibition of quorum sensing in a
Pseudomonas putida
N-acylated
l
-homoserine lactone (AHL) sensor strain engineered with the LasR transcriptional activator. LasR controls virulence gene expression in the opportunistic pathogen
Pseudomonas aeruginosa
and is of significant interest as a therapeutic target. Nine compounds that inhibit and 14 compounds that induce LasR activity were identified in our high-throughput screen.
Escherichia coliBinary Culture Engineered for Direct Fermentation of Hemicellulose to a Biofuel
Authors: Shin Hyun-Dong , McClendon Shara , Vo Trinh , Chen Rachel R.
Published: October 2010

Metabolic engineering has created severalEscherichia colibiocatalysts for production of biofuels and other useful molecules. However, the inability of these biocatalysts to directly use polymeric substrates necessitates costly pretreatment and enzymatic hydrolysis prior to fermentation. Consolidated bioprocessing has the potential to simplify the process by combining enzyme production, hydrolysis, and fermentation into a single step but requires a fermenting organism to multitask by producing both necessary enzymes and target molecules. We demonstrate here a binary strategy for consolidated bioprocessing of xylan, a complex substrate requiring six hemicellulases for complete hydrolysis. An integrated modular approach was used to design the two strains to function cooperatively in the process of transforming xylan into ethanol. The first strain was engineered to coexpress two hemicellulases. Recombinant enzymes were secreted to the growth medium by a method oflppdeletion with over 90% efficiency. Secreted enzymes hydrolyzed xylan into xylooligosaccharides, which were taken in by the second strain, designed to use the xylooligosaccharides for ethanol production. Cocultivation of the two strains converted xylan hemicellulose to ethanol with a yield about 55% of the theoretical value. Inclusion of other three hemicellulases improved the ethanol yield to 70%. Analysis of the culture broth showed that xylooligosaccharides with four or more xylose units were not utilized, suggesting that improving the use of higher xyloogligomers should be the focus in future efforts. This is the first demonstration of an engineered binary culture for consolidated bioprocessing of xylan. The modular design should allow the strategy to be adopted for a broad range of biofuel and biorefinery products.