bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimizing Ground Water Observation Networks in Irrigation Areas Using Principal Component Analysis
Authors: Khan S. , Chen H. F. , Rana T.
Published: August 2008

Ground water monitoring networks can provide vital information for sustainable water resources management. This involves the measurement of ground water level, solute concentration, or both. This article deals with the former. It optimizes network distribution of piezometer or data sampling wells to effectively monitor ground water levels under an irrigation region while retaining adequate overall measurement accuracy. This article presents a structured process for applying principal component analysis (PCA) in optimizing a ground water monitoring network in an irrigation area of Australia. The PCA functions, distributed with the MATLAB package, were used to determine relative contributions of individual piezometers in capturing the spatiotemporal variation of ground water levels. Kriging gridding interpolation algorithm was used to render the data surface presentations and determine spatial differences in piezometeric surfaces using different number of data sets. The results show that the overall difference of ground water level between the original piezometer network and the optimized networks after the PCA process was applied is less than 20%, while the total number of piezometers in the optimized network is reduced by 63%, which will save the time and cost to monitor ground water levels in the irrigation area.
Nitrate Removal Rates in a 15‐Year‐Old Permeable Reactive Barrier Treating Septic System Nitrate
Authors: Robertson W.D. , Vogan J.L. , Lombardo P.S.
Published: August 2008

Permeable reactive barriers (PRBs) have gained popularity in recent years as a low‐cost method for ground water remediation. However, their cost advantage usually requires that these barriers remain maintenance free for a number of years after installation. In this study, sediment cores were retrieved from a pilot‐scale PRB consisting of a sand and wood particle (sawdust) mixture that has been in continuous operation for 15 years treating nitrate from a septic system plume in southern Ontario (Long Point site). Reaction rates for the 15‐year‐old media were measured in dynamic flow column tests and were compared to rates measured in year 1 using the same reactive mixture. Nitrate removal rates in the 15‐year‐old media varied, as expected, with temperature in the range of 0.22 to 1.1 mg N/L/d at 6 °C to 10 °C to 3.5 to 6.0 mg N/L/d at 20 °C to 22 °C. The latter rates remained within about 50% of the year 1 rates (10.2 ± 2.7 mg N/L/d at 22 °C). Near the end of the year 15 column test, media particles >0.5 mm in diameter, containing most of the wood particles, were removed from the reactive media by sieving. Nitrate removal subsequently declined by about 80%, indicating that the wood particles were the principal energy source for denitrification. This example shows that some denitrifying PRBs can remain maintenance free and be adequately reactive for decades.
Origin and Fate of Industrial Ammonium in Anoxic Ground Water—15N Evidence for Anaerobic Oxidation (Anammox)
Authors: Clark Ian , Timlin Robert , Bourbonnais Annie , Jones Katie , Lafleur Dennis , Wickens Kevin
Published: August 2008

Elevated ammonium concentrations in pump‐and‐treat effluent from a volatile organic compounds–contaminated municipal aquifer originate from two industrial sources: infiltration of drainage from the blending operations of a fertilizer company (FC) located in the recharge area ( of 500 to 700 parts per million [ppm] N and of 150 to 300 ppm N) and leakage from waste water treatment ponds maintained by an adjacent chemical company (CC) ( of 50 to 70 ppm N, with no ). Geochemical and isotope data are used to trace the mechanisms for the strong attenuation observed between the source areas and the municipal ground water treatment wells ( < 10 ppm N). Conservative mixing calculations demonstrate a loss of and along the flowpath relative to K+ and Cl−. Reactive loss of in these anoxic ground water is attributed to anaerobic oxidation by anammox bacteria. Lines of evidence leading to this conclusion include (1) loss of both and under anoxic conditions along the flowpath; (2) a progressive enrichment of and , indicating reactive loss of ammonium and nitrate; (3) values greater than coexisting , which precludes loss by nitrification to ; and (4) significant N2 overpressuring with increasing values. Anaerobic ammonium oxidation by anammox bacteria uses nitrate as the electron donor: . The recently discovered anammox reaction is more energetically favorable than denitrification and is now considered to play a major role in the global nitrogen cycle. It has been observed in waste water bioreactors and sea water but not previously in ground water.
Comparison of the Anti‐inflammatory Activities of Imidazole Antimycotics in Relation to Molecular Structure
Authors: Steel Helen C. , Tintinger Gregory R. , Anderson Ronald
Published: August 2008

The objective of this study was to compare the anti‐inflammatory potencies of the imidazole antimycotics, fluconazole, itraconazole, ketoconazole and voriconazole (0.5 and 5 μm) in relation to their molecular structures. Anti‐inflammatory activity was determined according to the magnitude of inhibition of production of leukotriene B4 and influx of Ca2+ following activation of the cells with the chemo‐attractant platelet‐activating factor (200 nm), using enzyme‐linked immunosorbent assay and spectrofluorometric procedures, respectively. Treatment of platelet‐activating factor‐activated neutrophils with the imidazole antimycotics resulted in inhibition of production of leukotriene B4 and attenuation of Ca2+ influx, the order of potency being itraconazole > ketoconazole > fluconazole = voriconazole. These observations demonstrate the requirement for both the diazole/triazole moiety (all four agents), and the substituted phenylpiperazinyl ether side chain (itraconazole and ketoconazole only) for maximal anti‐inflammatory activity of this class of pharmacological agents.
Medieval Jewish Biblical Commentaries and the State ofParshanutStudies
Authors: Kalman Jason
Published: August 2008

This article surveys recent developments in the field ofParshanutstudies. It explores the editing, publication, and translation of new text editions of medieval commentaries and provides an overview of current debates concerning the development of Karaite exegesis and the school ofpeshatcommentary in Northern France. Using a case study of medieval Jewish commentaries on the book of Job it highlights those biblical exegetes who are currently receiving scholarly attention and the types of questions being asked about them and the works they composed. Finally, some topics for future research are highlighted.
Midrash and the Hebrew Bible
Authors: Kern‐Ulmer Rivka
Published: August 2008

Midrash is the particular mode of interpreting the Hebrew Bible that was developed by the rabbis of late antiquity in the Land of Israel. Midrash rendered Scripture relevant to the needs of a specific period in time. Definitions of midrash, the scope of midrashic activity, and its applicability to multiple interpretive strategies are widely disputed among scholars. This essay examines inner‐biblical interpretation, definitions of midrash, midrash scholarship, classifications of midrash, the boundaries of the genre midrash, midrasic exegesis, and various theological assumptions of midrash.
On the Syntax and Semantics of Evidentials
Authors: Speas Peggy
Published: August 2008

In some languages, every declarative sentence includes a morpheme specifying the speaker's evidence or source of information. This article provides an overview of the central theoretical questions addressed in recent research on Evidential morphemes. First, I discuss the question of whether Evidentials constitute a coherent closed‐class system, independent of other systems of grammar. Next, I briefly consider the evidence for an Evidential head in the syntactic representation. Finally, I review the ways in which Evidentials resemble and differ from epistemic modals.
Evolution, Path Dependence and Economic Geography
Authors: MacKinnon Danny
Published: August 2008

This article provides a review of research on evolution and path dependence in economic geography. While economic geographers have long been interested in regional economic change, the period since the early 1990s has witnessed a more explicit concern with questions of evolution and adaptation. Indeed, the notion that the economic landscape is ‘path‐dependent’ has been described as one of the most exciting ideas in economic geography. Evolutionary economic geography (EEG) can be seen as comprised of two main strands of literature, focusing on: path dependency, institutions and lock‐in; and evolution, routines and complexity. Rather than viewing EEG as a separate enterprise, I suggest that there is a need to link evolution to institutional and political economy approaches within a theoretically plural economic geography. After outlining the contribution of evolutionary economics and the two key strands of EEG, the article discusses some key issues for evolutionary research in economic geography.
Non‐Native Plant Invasion of the Hawaiian Islands
Authors: Gillespie Thomas W. , Chu Jasmine , Pau Stephanie
Published: August 2008

The Hawaiian Islands hold a unique geographic position that has resulted in plant species with remarkable evolutionary adaptations to island life as well as the highest proportion of plant endemism (90%) in the world. Polynesians and Europeans significantly reduced the extent of native vegetation types, and Europeans introduced non‐native plants that have become highly invasive. The Hawaiian Islands have been extremely susceptible to invasion due to the fact that they are oceanic islands; they contain low intensities of competition; they have altered disturbance regimes; and a relatively short time has passed since non‐native plant introductions, suggesting that the situation can only get worse. African grasses, Leucaena leucocephala, Psidium sp., Miconia calvescens, and Schinus terebinthifolius, are some of the most aggressive invasive plant species in the Hawaiian Islands. Species databases, remote sensing methods, and geographic information system analyses are currently being developed and will be extremely important for identifying the extent and threat of invasive plants. The three main methods of invasive plant removal include manual/mechanical removal, herbicide application, and biological controls. A number of federal, state, and non‐profit organizations are involved with the management of invasive plant species in the Hawaiian Islands. However, much more attention must be paid to protecting some of the most unique and endangered ecosystems on the planet.
Ultraviolet Radiation as a Limiting Factor in Leaf Expansion and Development
Authors: Wargent Jason J. , Moore Jason P. , Roland Ennos A. , Paul Nigel D.
Published: August 2008

Reductions in leaf growth are a commonly observed response to ultraviolet radiation, but the underlying mechanisms remain poorly defined. This study examined the response of leaves exposed to a UV environment across a range of organizational scales, including leaf expansion rate, epidermal cell size and number, biomechanical properties, leaf–water relations and activity of cell‐wall peroxidases. Two experimental approaches were used; Lettuce (Lactuca sativaL.) plants were propagated under (a) supplementary UV‐B (9 kJ m−2 day−1) in controlled environment (CE) conditions, and (b) field conditions, where plants were placed under three horticultural films with differing UV transmissions. In both experiments, UV‐B caused the greatest reductions in leaf expansion and final leaf size, with some reductions attributable to UV‐A wavelengths. In supplementary UV‐B conditions, adaxial cell size was reduced, while in field plants, both cell size and cell number were lower in an increased UV environment, as was the case with abaxial cells in CE plants. Although leaf turgor and leaf extensibility were not affected by UV wavelengths, breaking strain of leaf tissue was decreased under supplementary UV‐B. Cell‐wall peroxidase activity was increased in both supplementary UV conditions and in the field, where only a zero UV environment showed no upregulation of cell‐wall peroxidase.
Antithrombin effect on coagulation and fibrinolytic profiles after living donor liver transplantation: a pilot study
Authors: KANEKO J. , SUGAWARA Y. , TAMURA S. , TOGASHI J. , MATSUI Y. , MAKUUCHI M.
Published: August 2008

Early after liver transplantation, patients are in a hypercoagulable state because of an imbalance between coagulation and fibrinolysis because of the slow recovery of depleted anticoagulant proteins. Antithrombin (AT) is used in anticoagulant protocols to prevent thrombosis. The subjects of the present study were 17 men and eight women that underwent living donor liver transplantation. The initial 15 cases were administered AT concentrate (1500 U/day) on postoperative days (POD) 1 through 3 (AT group) and the following 10 consecutive cases were not administered AT (control). AT, thrombin‐AT complex, plasmin‐alpha2 plasmin inhibitor complex, thrombomodulin, fibrin degradation product D‐dimer (FDP‐DD) level, prothrombin time international normalized ratio, activated partial thromboplastin time, and platelet counts were measured. In the AT group, AT activity was maintained at levels >80% for 5 days after transplantation. In the control group, AT activity did not return to normal during the first 2 weeks after the operation. FDP‐DD levels were significantly higher in the control group than in the AT group (P < 0.05). Six patients in the control group and three patients in the AT group required transfusions with platelet concentrate (P < 0.05). AT supplementation might reduce FDP‐DD levels and prevent decreased platelet counts in the early stages after liver transplantation.
How Much Does Expertise Reduce Behavioral Biases? The Case of Anchoring Effects in Stock Return Estimates
Authors: Kaustia Markku , Alho Eeva , Puttonen Vesa
Published: August 2008

We use data from surveys involving 300 Scandinavian financial market professionals and 213 university students to conduct three controlled experiments in which we manipulate the background information given to subjects. We find a very large anchoring effect in the students' long‐term stock return expectations, that is, their estimates are influenced by an initial starting value. Professionals show a much smaller anchoring effect, but it nevertheless remains statistically and economically significant, even when we restrict the sample to more experienced professionals. We also find that the professionals are not conscious of the impact of historical returns on their expectations.
Corporate Debt Issuance and the Historical Level of Interest Rates
Authors: Barry Christopher B. , Mann Steven C. , Mihov Vassil T. , Rodríguez Mauricio
Published: August 2008

Using a sample that comprises more than 14,000 new issues of corporate debt for the period 1970‐2001, we examine the relation between debt issues and the level of interest rates relative to historical levels. Consistent with recent survey evidence, we find that companies issue more debt, more debt relative to investment spending, and more debt compared to equity when interest rates are low relative to historical rates. The effects continue to hold when we control for other variables that influence debt issuance and when we account for refinancing.
What Is the Cost of Financial Flexibility? Theory and Evidence for Make‐Whole Call Provisions
Authors: Powers Eric , Tsyplakov Sergey
Published: August 2008

Firms commonly incorporate make‐whole call provisions in their newly issued debt, presumably to improve their ability to retire debt early if circumstances require. In return for increased financial flexibility, firms must compensate bondholders with additional (incremental) yield. To estimate theoretical incremental yields, we use and calibrate a structural model for a large sample of callable and noncallable US corporate bonds issued between 1995 and 2004. In a frictionless model where calls occur only when they are in‐the‐money, theoretical incremental yields average approximately 2 basis points (bp). In an extended model that incorporates taxes, transactions costs, and randomly occurring exogenous events requiring early bond retirement, incremental yields average approximately 5 bp. Empirical analysis, however, indicates that observed incremental yields are significantly greater than model‐generated values, averaging between 13 and 24 bp. In the later years of our sample period, however, observed incremental yields begin to converge to model‐generated values.
The Impact of Past Syndicate Alliances on the Consolidation of Financial Institutions
Authors: Champagne Claudia , Kryzanowski Lawrence
Published: August 2008

The impact of past syndicate alliances on the consolidation of financial institutions is examined. The odds of two lenders combining increases with the intensity and exclusivity of their prior syndicated loan alliances. The impact is higher for international mergers and acquisitions (M&As) and for prior syndicate co‐relationships where the acquirer and target were participant and lead, respectively. The odds of a particular lender being a target decreases as its return on equity (ROE) and earnings/price (E/P) ratios increase and as its size and growth opportunities decrease. The intensity and exclusivity of the syndicated loan alliances leading up to M&A announcements are significantly higher for non‐US versus US M&As. The significantly lower short‐ and long‐term performances for both acquirers and targets with prior syndicate co‐involvements disappear in the presence of control variables that account for the less frequent use of cash payments, the greater incidence of divestitures, and the higher percentage of shares acquired through their M&As. Acquirers with versus those without past syndicate target co‐involvements exhibit greater outperformance for control‐firm benchmarked ROEs and lower underperformance for control‐firm and prior‐to‐M&A benchmarked ROEs.
How Preussag Became TUI: A Clinical Study of Institutional Blockholders and Restructuring in Europe
Authors: Dittmann Ingolf , Maug Ernst , Schneider Christoph
Published: August 2008

Between 1997 and 2004, Preussag, a diversified German conglomerate of “old economy” businesses, transformed itself into TUI, a company focused almost entirely on tourism and logistics. We analyze how Preussag executed this change, and how the change contributed to Preussag's underperformance in the stock market. We find that only the divestitures created value, that the strategy to invest in tourism destroyed value, and that the acquisition premiums Preussag paid were mostly unjustified. The case shows how divestiture programs increase the liquid resources available to management and casts doubt on the positive governance role of institutional blockholders.
Fourteen new di‐ and tetranucleotide microsatellite loci for the critically endangered Indian tiger (Panthera tigris tigris)
Authors: SHARMA R. , STUCKAS H. , MOLL K. , KHAN I. , BHASKAR R. , GOYAL S. P. , TIEDEMANN R.
Published: August 2008

We describe 11 dinucleotide and three tetranucleotide microsatellite loci for the critically endangered Indian tiger,Panthera tigris tigris. All of them were polymorphic with four to nine alleles per locus and an observed heterozygosity between 0.13 and 1.0. All primers also amplify microsatellite loci in leopard,Panthera pardus,and 12 primer pairs yielded reproducible results in domestic cat,Felis catus.These new microsatellites specifically developed for Indian tiger — in combination with those already available — comprise a reasonable number of loci to genetically analyse wild and captive populations of this illustrative species and might allow for recognition of individual tigers.
Development of nine microsatellite markers for Pomacentrus amboinensis
Authors: JONES DAVID B. , JERRY DEAN R. , MCCORMICK MARK I. , BAY LINE K.
Published: August 2008

The relatively long pelagic larval duration of Pomacentrus amboinensis, a tropical fish, suggests the potential for long‐distance dispersal; however, several nongenetic studies have found substantial self‐recruitment at one location. To analyse patterns of connectivity of this species, primers for nine independent microsatellite loci were developed for P. amboinensis using a magnetic bead enrichment protocol. Twenty individuals from one location were analysed and observed heterozygosities ranged from 0.7 to 0.95. Eight of nine loci were in Hardy–Weinberg equilibrium and no evidence of linkage or null alleles were found.
Development of polymorphic microsatellite markers in Hessian fly, Mayetiola destructor (Say)
Authors: SCHEMERHORN BRANDON J. , CRANE YAN M. , MORTON PHILIP K.
Published: August 2008

A microsatellite library was prepared from size‐selected genomic DNA of Hessian fly (Mayetiola destructor). Approximately 81% of recovered clones hybridized with microsatellite motif‐specific probes. Subsequently, 2350 clones were sequenced. Sixty‐two individual flies from laboratory strains were used to test for reliability and polymorphism in 50 of the microsatellites by gel electrophoresis; 18 were further tested with capillary electrophoresis. Of these, 17 behaved as a polymorphic single locus appropriate for population analysis.
Beyond Politics and Positions: A Call for Collaboration Between Family Court and Domestic Violence Professionals
Authors: Salem Peter , Dunford‐Jackson Billie Lee
Published: August 2008

The domestic violence advocacy and family court communities have each grown dramatically over the last three decades. Although these professional communities share many values in common, they often find themselves at odds with one another on a host of issues. This article examines the practical, political, definitional, and ideological differences between the two communities and calls for them to join forces and collaborate on behalf of children and families.
What is your diagnosis? Ventral neck mass in a dog
Authors: Fernandez Nicole J. , Clark Edward G. , Larson Victoria S.
Published: August 2008

Abstract: A 14‐year‐old male Labrador Retriever was presented for lethargy and collapse. On physical examination, numerous abnormalities were found, including a large ventral neck mass (100 cm3) in the area of the thyroid gland. Fine‐needle aspirates revealed 2 apparent populations of cells: one suspected to be a well‐differentiated thyroid carcinoma, and the other consisting of large pleomorphic to spindloid cells suggestive of sarcoma. Two days later, the dog died at home. A full necropsy was not performed, but examination of the head and neck revealed a well‐encapsulated mass adjacent to the cranial trachea and larynx. A section of the mass was evaluated histologically and a diagnosis of anaplastic thyroid carcinoma was made. Immunohistochemical evaluation with antibodies to thyroglobulin, cytokeratin, and vimentin confirmed distinct populations of malignant epithelial and malignant mesenchymal cells, and the diagnosis was amended to thyroid carcinosarcoma. Thyroid carcinosarcoma is a rare neoplasm in dogs in which the cell type comprising the mesenchymal component can vary. Immunochemistry to demonstrate the 2 cell types may be necessary to differentiate thyroid carcinosarcoma from anaplastic thyroid carcinoma.
In vitro heparinization of canine whole blood with low molecular weight heparin (dalteparin) significantly and dose‐dependently prolongs heparinase‐modified tissue factor‐activated thromboelastography parameters and prothrombinase‐induced clotting time
Authors: Jessen Lisbeth R. , Wiinberg Bo , Jensen Asger L. , Kjelgaard‐Hansen Mads , Jensen Kate H. , Pedersen Lotte B. , Kristensen Annemarie T.
Published: August 2008

Background: Low‐molecular‐weight heparin (LMWH) is being used increasingly in veterinary medicine for both treatment and prophylaxis of thromboembolic disease, but no predictable patient‐side method exists to monitor its effect.

Objectives: The aim of this study was to evaluate thromboelastography (TEG) and prothombinase‐induced clotting time (PiCT) assays for detecting hemostatic alterations following in vitro heparinization of canine whole blood with dalteparin (Fragmin).

Methods: Citrated whole‐blood samples were collected from 7 clinically healthy dogs. Dalteparin was added at concentrations of 0, 0.156, 0.625, 1.25, and 2.5 U/mL of whole blood. TEG was performed using heparinase cups with tissue factor (TF, 1:50,000) and kaolin as activators. Reaction time (R), clotting time (K), angle (α), and maximum amplitude (MA) were recorded. PiCT and anti‐FXa activity were measured in plasma.

Results: With TF, increasing concentrations of dalteparin significantly prolonged R and K and significantly decreased α and MA. K, α, and MA ratios were significantly different from baseline at all dalteparin concentrations and R was significantly different from baseline at concentrations of 0.625, 1.25, and 2.5 U/mL. With kaolin, only R was significantly different from baseline at dalteparin concentrations of 0.625 and 2.5 U/mL. PiCT detected dalteparin concentrations ≤ 0.625 U/mL, with a good linear correlation (r2=.96, P<.0001).

Conclusion: These results suggest that TF‐activated TEG and PiCT assays should be further evaluated as promising new methods for evaluating the effect of LMWH, using doses in the recommended clinical range and prospective clinical studies.
A Pin-on-Disk Experimental Study on a Green Particulate-Fluid Lubricant
Authors: Kabir M. A. , Higgs C. Fred , Lovell Michael R.
Published: August 2008

The present investigation analyzes a green, petroleum-free lubricant that is produced by mixing two environmentally benign components—canola oil and boric acid powder. To study the influence of boric acid particle size and solid volume fraction on the proposed lubricant performance, pin-on-disk experiments were conducted with spherical copper pins (radius 6.5mm) and aluminum disks (Ra=1.35μm). Friction coefficient measurements were taken at more than 20 distinct operating conditions while varying the lubrication condition (unlubricated, boric acid, canola oil, boric acid/canola oil mixture), boric acid volume fraction, and boric acid particle size. Based on the experiments, it was determined that a solid volume fraction of 7% with 350–700μm particles was the optimum green particulate lubricant candidate for minimizing the friction at the conditions tested. This work also uncovered an inverse relationship between the friction coefficient and boric acid particle size (in canola oil at 7% solid fraction). Micrographs of the pin and disk wear track were analyzed to study this frictional behavior of the interface materials. Additionally, rheological tests were conducted to measure the viscosity of the canola oil and boric acid powder mixture as a function of particle size, and it was found that the viscosity increased with particle size over the size range tested. Finally, the results indicated that the boric acid-canola oil lubricant mixture demonstrated excellent potential for use as lubricants in industrial applications such as sheet metal forming.
An Investigation of Rolling Element Vibrations Caused by Local Defects
Authors: Arslan H. , Aktürk N.
Published: August 2008

In this paper, a shaft-bearing model is developed in order to investigate the rolling element vibrations for an angular contact ball bearing with and without defects. The shaft-bearing assembly is considered as a mass-spring system. The system shows a nonlinear characteristic under dynamic conditions. The equations of motion in radial and axial directions were obtained for shaft and rolling elements, and they were solved simultaneously with a computer simulation program. Additionally, the effect of localized defects on running surfaces (i.e., inner ring, outer ring, and ball) on the vibration of the balls is investigated. Vibration of rolling elements in the radial direction is analyzed in time and frequency domains. Characteristic defect frequencies and their components can be seen in the frequency spectra of rolling element vibrations. Comparison of the obtained results with similar studies available in literature showed reasonable qualitative agreement.
The Effects of Interfacial Particles on the Contact of an Elastic Sphere With a Rigid Flat Surface
Authors: Bozkaya Dinçer , Müftü Sinan
Published: August 2008

In chemical mechanical polishing (CMP), a rigid wafer is forced on a rough elastomeric polishing pad, while a slurry containing abrasive particles flows through the interface. One of the important factors that influence the material removal rate in CMP is the magnitude of contact force transmitted to the abrasive particles trapped at the contact interface. The total push-down force is distributed to the direct contact between the wafer and the pad, and to the three-body contact between the wafer, the pad, and the abrasive particles. The presence of the abrasive particles alters the asperity contact, which otherwise can be described by Hertz contact relationships. In this study, the effect of the interfacial particles on the single asperity contact is investigated. An approach used by Greenwood and Tripp (1967, “The Elastic Contact of Rough Spheres,” ASME J. Appl. Mech., 34, pp. 153–160) to study the contact of rough spheres is utilized since the presence of the particles provides a rough character to the contact. The results show that the contact behavior becomes non-Hertzian with decreasing contact force and increasing elastic modulus, particle size, and particle concentration. The role of the interfacial particles is to spread the contact over a larger area while lowering the maximum contact pressure at the center of contact predicted by Hertz contact. The conditions required to transfer the contact force on the particles effectively are also described.
Air Bearing Surface Designs in Consideration of Thermomechanical Actuation Efficiency
Authors: Zhang Shuyu , Lee Sung-Chang , Kim Dongman , Ferber Joerg , Strom Brian , Tyndall George
Published: August 2008

Thermomechanical actuation (TMA) at the transducer region of the air bearing surface (ABS) protrudes from the transducer toward the recording media. This actuation induces a change in the air bearing pressure and a concomitant lift of the slider. The actual actuation in flying height divided by the TMA protrusion, defined as the TMA efficiency, is intimately coupled to the ABS design. After introducing an expression describing the changes in the air bearing forces due to the TMA protrusion, three approaches are proposed that facilitate the optimization of the ABS design for improving the TMA efficiency. These approaches include (a) reducing the air bearing pressure, (b) reducing the size of the TMA affected area, and (c) decoupling the peak air bearing pressure area from the TMA affected area. To illustrate these approaches, several ABS designs are evaluated by comparing their TMA efficiencies.
A Potential Elastohydrodynamic Origin of Load-Support and Coulomb-Like Friction in Lung∕Chest Wall Lubrication
Authors: Butler James P. , Loring Stephen H.
Published: August 2008

During normal breathing, the mesothelial surfaces of the lung and chest wall slide relative to one another. Experimentally, the shear stresses induced by such reciprocal sliding motion are very small, consistent with hydrodynamic lubrication, and relatively insensitive to sliding velocity, similar to Coulomb-type dry friction. Here we explore the possibility that shear-induced deformation of surface roughness in such tissues could result in bidirectional load-supporting behavior, in the absence of solid-solid contact, with shear stresses relatively insensitive to sliding velocity. We consider a lubrication problem with elastic blocks (including the rigid limit) over a planar surface sliding with velocity U, where the normal force is fixed (hence the channel thickness is a dependent variable). One block shape is continuous piecewise linear (V block) and the other continuous piecewise smoothly quadratic (Q block). The undeformed elastic blocks are spatially symmetric; their elastic deformation is simplified by taking it to be affine, with the degree of shape asymmetry linearly increasing with shear stress. We find that the V block exhibits nonzero Coulomb-type starting friction in both the rigid and the elastic case, and that the smooth Q block exhibits approximate Coulomb friction in the sense that the rate of change of shear force with U is unbounded as U→0, shear force ∝U1∕2 in the rigid asymmetric case and ∝U1∕3 in the (symmetric when undeformed) elastic case. Shear-induced deformation of the elastic blocks results in load-supporting behavior for both directions of sliding. This mechanism could explain load-supporting behavior of deformable surfaces that are symmetrical when undeformed and may be the source of the weak velocity dependence of friction seen in the sliding of lubricated, but rough, surfaces of elastic media such as the visceral and parietal pleural surfaces of the lung and chest wall.
Influence of Two-Sided Surface Waviness on the EHL Behavior of Rolling/Sliding Point Contacts Under Thermal and Non-Newtonian Conditions
Authors: Yang Peiran , Cui Jinlei , Jin Z. M. , Dowson D.
Published: August 2008

The influence of the transversely and/or longitudinally oriented surface waviness on the lubricating behavior in the rolling/sliding elliptic contact composed of two steel bodies and lubricated with a non-Newtonian lubricant was investigated theoretically with full numerical solution of the thermal elastohydrodynamic lubrication. The entrainment velocity was assumed to be along the minor axis of the Hertzian contact ellipse. The waviness of each surface was given by a sinusoidal function. The non-Newtonian flow of the lubricant was described by the Eyring model with a constant Eyring shear stress at the ambient pressure and temperature. The velocity of the faster surface was assumed to be four times as that of the slower surface in order not only to highlight the thermal and non-Newtonian effects, but also to ensure a cyclic solution when both surfaces were with transversely oriented waviness. Starting from a quasisteady solution, the cyclic time-dependent solution was achieved numerically time step by time step. The results show that the thermal and non-Newtonian effects can be enlarged significantly by the surface waviness, and the worst configuration of the surface topography is that both surfaces are with longitudinal waviness.
Nonlinear Dynamic Behavior of a Rigid Rotor Supported by Hydrostatic
Squeeze Film Dampers
Authors: Bouzidane A. , Thomas M. , Lakis A. A.
Published: August 2008

This research project aims to study the nonlinear dynamic behavior of a rigid rotor supported by hydrostatic squeeze film dampers (HSFDs). The investigated HSFD consists of four hydrostatic bearing flat pads fed by capillary restrictors. A nonlinear hydrostatic squeeze film damper model is developed, and the results are compared with those obtained using a linear approach. The effect of unbalance eccentricity on the vibration response and the transmitted force of the HSFD are investigated using the linear and nonlinear models. The results show good agreement between the linear and nonlinear methods when the unbalance force is small. However, as the unbalance forces become larger, the results obtained using the linear models cease to be representative of the real behavior of rotor dynamics and a nonlinear approach must be conducted. The effects of supply pressure, viscosity, pressure ratio, and rotational speed on the response and the force transmitted to the HSFD are investigated using a nonlinear approach.
A Probabilistic Model to Characterize Erosion-Oxidation Damage on Boiler Grade Steel Impacted by Solid Particle
Authors: Das S. K. , Hegde Shubha , Godiwalla K. M. , Mehrotra S. P. , Dey P. K.
Published: August 2008

A probabilistic model based methodology has been applied to describe the relative rate of material loss from the steel surface subjected to simultaneous action of high temperature oxidation and mechanical erosion. Growth of the oxide scales is treated deterministically and erosion is described using an established probabilistic modeling methodology. Oxidation is described with a parabolic growth law to quantify the rate of growth of the oxide scales, namely, nickel, iron, and chromium, respectively. In consonance with the published model, erosion is treated using a probabilistic methodology as spatially random phenomena on the oxide surface. The model has been applied to predict the relative erosive loss of material as a function of time resulted as a consequence of influence oxidation on mechanical erosion in a synergetic manner.
A Finite Element Based Study on the Elastic-Plastic Transition Behavior in a Hemisphere in Contact With a Rigid Flat
Authors: Shankar S. , Mayuram M. M.
Published: August 2008

An axisymmetrical hemispherical asperity in contact with a rigid flat is modeled for an elastic perfectly plastic material. The present analysis extends the work (sphere in contact with a flat plate) of Kogut–Etsion Model and Jackson–Green Model and addresses some aspects uncovered in the above models. This paper shows the critical values in the dimensionless interference ratios (ω∕ωc) for the evolution of the elastic core and the plastic region within the asperity for different Y∕E ratios. The present analysis also covers higher interference ratios, and the results are applied to show the difference in the calculation of real contact area for the entire surface with other existing models. The statistical model developed to calculate the real contact area and the contact load for the entire surfaces based on the finite element method (FEM) single asperity model with the elastic perfectly plastic assumption depends on the Y∕E ratio of the material.
Scale Effects in Generalized Newtonian Elastohydrodynamic Films
Authors: Kudish Ilya I. , Kumar P. , Khonsari M. M. , Bair Scott
Published: August 2008

The estimation or prediction of elastohydrodynamic lubrication (EHL) film thickness requires knowledge of the lubricant properties. Today, in many instances, the lubricant properties have been obtained from a measurement of the central film thickness and the assumption of a classical Newtonian film-thickness formula. This technique has the practical advantage of using an effective pressure-viscosity coefficient, which compensates for shear-thinning. We have shown by a perturbation analysis of limiting cases for fluid with Carreau rheology (represented by Newtonian and power fluid) and by a full EHL numerical solution for Carreau fluid that the practice of extrapolating from a laboratory scale measurement of film thickness to the film thickness of an operating contact may substantially overestimate the film thickness in the real machine if the machine scale is smaller and the lubricant is shear-thinning within the inlet zone. The intention here is to show that errors result from extrapolation of Newtonian formulas to different scale and not to provide advice regarding quantitative engineering calculations.
A New Approach to Modeling Surface Defects in Bearing Dynamics Simulations
Authors: Ashtekar Ankur , Sadeghi Farshid , Stacke Lars-Erik
Published: August 2008

A dynamic model for deep groove and angular contact ball bearings was developed to investigate the influence of race defects on the motions of bearing components (i.e., inner and outer races, cage, and balls). In order to determine the effects of dents on the bearing dynamics, a model was developed to determine the force-deflection relationship between an ellipsoid and a dented semi-infinite domain. The force-deflection relationship for dented surfaces was then incorporated in the bearing dynamic model by replacing the well-known Hertzian force-deflection relationship whenever a ball/dent interaction occurs. In this investigation, all bearing components have six degrees-of-freedom. Newton’s laws are used to determine the motions of all bearing elements, and an explicit fourth-order Runge–Kutta algorithm with a variable or constant step size was used to integrate the equations of motion. A model was used to study the effect of dent size, dent location, and inner race speed on bearing components. The results indicate that surface defects and irregularities like dent have a severe effect on bearing motion and forces. Furthermore, these effects are even more severe for high-speed applications. The results also demonstrate that a single dent can affect the forces and motion throughout the entire bearing and on all bearing components. However, the location of the dent dictates the magnitude of its influence on each bearing component.
Computation of Sliding Friction and Ratcheting Strain of Sintered and Hardened Steels Under Contact Fatigue Conditions
Authors: Govindarajan N. , Gnanamoorthy R.
Published: August 2008

Fatigue properties of powder metallurgy parts are affected mainly by the porosity fraction. Even though it has inferior mechanical and physical properties over the conventional materials, the application of powder metallurgy products in automotive fields is seen in recent trends. The rolling-sliding contact fatigue behavior of sintered and hardened steels has been investigated by performing experiments that represent practical sliding friction coefficient component prevailing in the medium- and heavy-duty bearings and gears. Introduction of sliding friction coefficient changes the typical failure pattern and wear rate of sintered and hardened steels. The sliding friction has been computed from available models and compared with the experimental data. The ratcheting strain has also been predicted for sintered and hardened steels for various contact pressures and sliding friction coefficients. The maximum value of this strain is responsible for surface crack initiation. The wear particle analysis is carried out for the sintered and hardened steels under rolling-sliding contact fatigue conditions. The ferrogram slides for pore free steel under the rolling-sliding contact fatigue conditions are also prepared to study the effect of porosity in wear mechanism. The characteristics of wear morphology and the size, shape, and concentration of worn particles for sintered and hardened steels are also analyzed for various rolling-sliding contact fatigue conditions.
A Statistical Damage Mechanics Model for Subsurface Initiated Spalling in Rolling Contacts
Authors: Raje Nihar , Sadeghi Farshid , Rateick Richard G.
Published: August 2008

Fatigue lives of rolling element bearings exhibit a wide scatter due to the statistical nature of the rolling contact fatigue failure process. Empirical life models that account for this dispersion do not provide insights into the physical mechanisms that lead to this scatter. One of the primary reasons for dispersion in lives is the stochastic nature of the bearing material. Here, a damage mechanics based fatigue model is introduced in conjunction with the idea of discrete material representation that takes the effect of material microstructure explicitly into account. Two sources of material randomness are considered: (1) the topological randomness due to geometric variability in the material microstructure and (2) the material property randomness due to nonuniform distribution of properties throughout the material. The effect of these variations on the subsurface stress fields in rolling element line contacts is studied. The damage model, which incorporates cyclic damage accumulation and progressive degradation of material properties with rolling contact cycling, is used to study the mechanisms of subsurface initiated spalling in bearing contacts. Crack initiation as well as propagation stages are modeled using damaged material zones in a unified framework. The spalling phenomenon is found to occur through microcrack initiation below the surface where multiple microcracks coalesce and subsequent cracks propagate to the surface. The computed crack trajectories and spall profiles are found to be consistent with experimental observations. The microcrack initiation phase is found to be only a small fraction of the total spalling life and the scatter in total life is primarily governed by the scatter in the propagation phase of the cracks through the microstructure. Spalling lives are found to follow a three-parameter Weibull distribution more closely compared to the conventionally used two-parameter Weibull distribution. The Weibull slopes obtained are within experimentally observed values for bearing steels. Spalling lives are found to follow an inverse power law relationship with respect to the contact pressure with a stress-life exponent of 9.35.
Thermomechanical Analysis of Elastoplastic Bodies in a Sliding Spherical Contact and the Effects of Sliding Speed, Heat Partition, and Thermal Softening
Authors: Chen W. Wayne , Wang Q. Jane
Published: August 2008

A thermomechanical analysis of elasto-plastic bodies is a necessary step toward the understanding of tribological behaviors of machine components subjected to both mechanical loading and frictional heating. A three-dimensional thermoelastoplastic contact model for counterformal bodies has been developed, which takes into account steady state heat flux, temperature-dependent strain hardening behavior, and interaction of mechanical and thermal loads. The fast Fourier transform and conjugate gradient method are the underlying numerical algorithms used in this model. Sliding of a half-space over a stationary sphere is simulated with this model. The friction-induced heat is partitioned into two bodies based on surface temperature distributions. In the simulation, the sphere is considered to be fully thermoelastoplastic, while the half-space is treated to be thermoelastic. Simulation results include surface pressure, temperature rise, and subsurface stress and plastic strain fields. The paper also studies the influences of sliding speed and thermal softening on contact behaviors for sliding speed ranging three orders of magnitude.
Combined Effects of Shear Thinning and Viscous Heating on EHL Characteristics of Rolling/Sliding Line Contacts
Authors: Kumar Punit , Khonsari M. M.
Published: August 2008

The combined influence of shear thinning and viscous heating on the behavior of film thickness and friction in elastohydrodynamic lubrication (EHL) rolling/sliding line contacts is investigated numerically. The constitutive equation put forward by Carreau is incorporated into the model to describe shear thinning. An extensive set of numerical simulations is presented. Comparison of the film thickness predictions with published experiments reveals good agreement, and it is shown that thermal effect plays an important role in the precise estimation of EHL film thickness and friction coefficient. Parametric simulations show that thermal effect in shear-thinning fluids is strongly affected by the power-law index used in the Carreau equation. Comparisons of prediction of the Newtonian fluid model are presented to quantify the degree to which it overestimates the film thickness.