bluuebunny/crossref_metadata_2025 huggingface dataset:
Migratory history of the giant mottled eel (Anguilla marmorata) in the Bonin Islands of Japan
Authors: Chino N. , Arai T.
Published: October 2009

Chino N, Arai T. Migratory history of the giant mottled eel (Anguilla marmorata) in the Bonin Islands of Japan. Ecology of Freshwater Fish 2010: 19: 19–25. © 2009 John Wiley & Sons A/S

Abstract –  In order to elucidate the migratory history and habitat use of the giant mottled eel Anguilla marmorata, in the Bonin Islands of Japan, strontium (Sr) and calcium (Ca) concentrations in otoliths were examined by X‐ray electron microprobe analysis. The X‐ray intensity map and line analyses showed three fluctuation patterns: (i) freshwater residence, (ii) continuous residence in brackish water, and (iii) residence in freshwater after recruitment, while returning to brackish water. Based on these results and previous studies, the migratory behaviours of A. marmorata appear to differ in each habitat in response to inter‐ and intra‐specific competition. The results suggest that A. marmorata has a flexible pattern of migration, with an ability to adapt to various habitats and salinities.
Insights on endemism: comparison of the duration of the marine larval phase estimated by otolith microstructural analysis of three amphidromous Sicyopterus species (Gobioidei: Sicydiinae) from Vanuatu and New Caledonia
Authors: Lord C. , Brun C. , Hautecœur M. , Keith P.
Published: October 2009

Lord C, Brun C, Hautecœur M, Keith P. Insights on endemism: comparison of the duration of the marine larval phase estimated by otolith microstructural analysis of three amphidromous Sicyopterus species (Gobioidei: Sicydiinae) from Vanuatu and New Caledonia. Ecology of Freshwater Fish 2010: 19: 26–38. © 2009 John Wiley & Sons A/S

Abstract –  The microstructure of otoliths of three amphidromous gobies (Sicydiinae) of the genus Sicyopterus has been analysed. One of these species, Sicyopterus lagocephalus has a widespread distribution whereas the other two are endemic (Sicyopterus aiensis, from Vanuatu and Sicyopterus sarasini, from New Caledonia). The microstructural analysis of the otoliths showed that the duration of the marine larval phase is significantly shorter for both endemic species than for the cosmopolitan species (131 ± 3.4 days for S. lagocephalus, 79.2 ± 4.6 days for S. aiensis and 76.5 ± 3.9 days for S. sarasini). These results led us to infer that it could be one of the factors explaining endemism. We have also improved our knowledge on the processes undergone during the marine phase by studying the growth of the otolith. This work allowed us to propose possible migration routes. These species’ reproduction period has also been studied by back‐calculating hatching dates. All these elements improve our understanding of the life‐history traits and dispersion strategies of these species, which is crucial to implementing conservation measures in order to protect them and their environment, both threatened by anthropogenic actions.
Interaction Energy Analysis of Peptide can Predict the Possibilities of Mimetics by its Retroinverso Isomer
Authors: Rai Jagdish
Published: October 2009

It has been previously reported that the retroinverso analog of S peptide cannot mimic the S peptide, whereas the retroinverso analog of foot‐and‐mouth disease virus antigen can mimic the foot‐and‐mouth disease virus antigen. The structures of S peptide, foot‐and‐mouth disease virus antigen, and their retroinverso analogs are known. Here, we have attempted to explain the structural basis of mimetics at the level of atomic interactions by elaborating upon the Guptasarma’s hypothesis. Using interaction energy analysis of S peptide and foot‐and‐mouth disease virus antigen, we propose that if the energy of the CO and NH backbone atoms’ non‐covalent interactions with all other atoms is negligible as compared with the energy of other non‐covalent interactions, then the retroinverso isomer can mimic the original peptide/protein. Previous work has established that the structure of the inverso analog of a protein will be the mirror image of the protein, and it will only recognize the respective mirror image substrate/binding partner. The retro peptide conformation that can be superimposed on all side chains in any conformation of the original peptide does not exist in the conformational space of the peptides.
Imprinting Status of GαS, NESP55, and XLαs in Cell Cultures Derived from Human Embryonic Germ Cells: GNAS Imprinting in Human Embryonic Germ Cells
Authors: Crane Janet L. , Shamblott Michael J. , Axelman Joyce , Hsu Stephanie , Levine Michael A. , Germain‐Lee Emily L.
Published: October 2009

GNAS is a complex gene that through use of alternative first exons encodes signaling proteins Gαs and XLαs plus neurosecretory protein NESP55. Tissue‐specific expression of these proteins is regulated through reciprocal genomic imprinting in fully differentiated and developed tissue. Mutations in GNAS account for several human disorders, including McCune‐Albright syndrome and Albright hereditary osteodystrophy, and further knowledge of GNAS imprinting may provide insights into variable phenotypes of these disorders. We therefore analyzed expression of Gαs, NESP55, and XLαs prior to tissue differentiation in cell cultures derived from human primordia germ cells. We found that the expression of Gαs was biallelic (maternal allele: 52.6%± 2.5%; paternal allele: 47.2%± 2.5%; p= 0.07), whereas NESP55 was expressed preferentially from the maternal allele (maternal allele: 81.9%± 10%; paternal allele: 18.1%± 10%; p= 0.002) and XLαs was preferentially expressed from the paternal allele (maternal allele: 2.7%± 0.3%; paternal allele: 97.3%± 0.3%; p= 0.007). These results demonstrate that imprinting of NESP55 occurs very early in development, although complete imprinting appears to take place later than 5–11 weeks postfertilization, and that imprinting of XLαs occurs very early postfertilization. By contrast, mprinting of Gαs most likely occurs after 11 weeks postfertilization and after tissue differentiation.
Molecular phylogeny of selected Old World Astragalus (Fabaceae): incongruence among chloroplast trnL‐F, ndhF and nuclear ribosomal DNA ITS sequences
Authors: Kazemi Marzie , Kazempour Osaloo Shahrokh , Asghar Maassoumi Ali , Rastegar Pouyani Eskandar
Published: October 2009

This study reports maximum parsimony and Bayesian phylogenetic analyses of selected Old World Astragalus using two chloroplast fragments including trnL‐F and ndhF and the nuclear ribosomal internal transcribed spacer (nrDNA ITS). A total of 52 taxa including 34 euploid Old World and New World Astragalus, one aneuploid species from the Neo‐Astragalus clade as a representative and 14 other Astragalean taxa, plus Cheseneya astragalina and two species of Caragana as outgroups were analyzed for both trnL‐F and nrDNA ITS regions. ndhF was analyzed in 30 taxa and the same number for the combination of these three datasets were examined. In general, the trnL‐F dataset and the ndhF and nrDNA ITS datasets generated more or less the same clades within Astragalus. However, in the trnL‐F and ndhF phylogenies, Astragalus species are not gathered in a single clade, the so‐called Astragalus s.s., as indicated by the nrDNA ITS tree. Visual inspection of these three phylogenies revealed that they were inconsistent regarding the position and relationships of Astragalus hemsleyi, A. ophiocarpus, A. annularis–A. epiglottis/Astragalus pelecinus,A. echinatus and A. arizonicus. Incongruence length difference test suggested that the trnL‐F, ndhF and nrDNA ITS datasets were incongruent. In spite of this, phylogenetic analyses of the combined datasets as one unit or as three partitions generated trees that were topologically similar as a mix of the cpDNA and the nrDNA ITS trees. However, the combined dataset provided more resolved and statistically supported clades. The recently described A. memoriosus appeared closely related to A. stocksii (both from sect. Caraganella) based on both trnL‐F and nrDNA ITS sequences.
Changes in the distributions of epiphytic lichens in southern Sweden using a new statistical method
Authors: Lättman Håkan , Milberg Per , Palmer Michael W. , Mattsson Jan‐Eric
Published: October 2009

Past studies on changes in species distribution have mainly been based on analysis of range boundaries. In contrast, the method used here evaluates shifts in species’ geographic centroids within a predefined area. We used presence/absence data on epiphytic lichens collected 1986 and 2003 from 64 sites in southern Sweden. A centroid was calculated each year, for each lichen species and substrate. The distance of centroid movement was evaluated in a permutation procedure. In total, 56 lichen species on 22 tree species were involved in the analyses, yielding 30 cases that had sufficient sample sizes both years to be evaluated. Out of these, three exhibited a significant movement of their centroid. The shift of lichen centroids of Hypogymnia physodes (L.) Nyl. and Vulpicida pinastri (Scop.) J.‐E. Mattsson & M. J. Lai on the tree species Juniperus communis L. was 50 and 151 km with the direction 27° and 48°, respectively. For Hypogymnia physodes on Pinus sylvestris L., corresponding values were 41 km and 30°. The northnortheast shifts of these species in Sweden could be a response to a warming climate.
Evolution, phylogeography and taxonomy of allopolyploid Dactylorhiza (Orchidaceae) and its implications for conservation
Authors: Nordström Sofie , Hedrén Mikael
Published: October 2009

This review is based on recent molecular studies of Dactylorhiza (Orchidaceae). Most of the studies have focused on the allotetraploid members of the genus in general and on D. majalis ssp. lapponica in particular. It was concluded that most of the allotetraploid taxa have derived from hybridizations between the parental lineages D. maculata s.l. and D. incarnata s.l., with D. maculata s.l. serving as the seed parent. Evidence of multiple origins was found both among northern European allotetraploids as well as among Greek allotetraploids. Introgression from both parental lineages and hybridizations between independently derived polyploid lineages was also detected. The three morphologically similar taxa D. majalis ssp. traunsteineri, ssp. lapponica and ssp. russowii should be treated as one and most of the Greek allotetraploids should be regarded as regional variants of the southeastern European D. majalis ssp. cordigera. The Balkans and the Alps most probably served as refugia for the genus during the last glaciations and at least two waves of immigration reached Scandinavia. Finally, we suggest that the conservation of allotetraploid Dactylorhiza should emphasize important geographic areas and habitats and that the allopolyploids should have the same conservation status as the diploids.
Analysis of Revenue Maximization Under Two Movie‐Screening Policies
Authors: Dawande Milind , Drobouchevitch Inna , Rajapakshe Tharanga , Sriskandarajah Chelliah
Published: October 2009

A few weeks before the start of a major season, movie distributors arrange a private screening of the movies to be released during that season for exhibitors and, subsequently, solicit bids for these movies (from exhibitors). Since the number of such solicitations far exceeds the number of movies that can be feasibly screened at a multiplex (i.e., a theater with multiple screens), the problem of interest for an exhibitor is that of choosing a subset of movies for which to submit bids to the distributors. We consider the problem of the selection and screening of movies for a multiplex to maximize the exhibitor's cumulative revenue over a fixed planning horizon. The release times of the movies that can potentially be selected during the planning horizon are known a priori. If selected for screening, a movie must be scheduled through its obligatory period, after which its run may or may not be extended. The problem involves two primary decisions: (i) the selection of a subset of movies for screening from those that can potentially be screened during the planning horizon and (ii) the determination of the duration of screening for the selected movies. We investigate two basic and popular screening policies: preempt‐resume and non‐preempt. In the preempt‐resume policy, the screening of a movie can be preempted and resumed in its post‐obligatory period. In the non‐preempt policy, a movie is screened continuously from its release time until the time it is permanently withdrawn from the multiplex. We show that optimizing under the preempt‐resume policy is strongly NP‐hard while the problem under the non‐preempt policy is polynomially solvable. We develop efficient algorithms for the problem under both screening policies and show that the revenue obtained from the preempt‐resume policy can be significantly higher as compared with that from the non‐preempt policy. Our work provides managers of multiplexes with valuable insights into the selection and screening of movies and offers an easy‐to‐use computational tool to compare the revenues obtainable from adopting these popular policies.
Optimal Acquisition Quantities in Remanufacturing with Condition Uncertainty
Authors: Galbreth Michael R. , Blackburn Joseph D.
Published: October 2009

The condition of the used products acquired by remanufacturing firms often varies widely. A firm can manage this variation by acquiring a quantity of used items that exceeds demand, enabling it to remanufacture a subset of the acquired items in the best condition. As more excess items are acquired, the firm can increase its selectivity and lower its remanufacturing costs. In this paper, we examine the tradeoff of acquisition and scrapping costs vs. remanufacturing costs when used product condition is widely varying and uncertain. We derive acquisition quantities that minimize total expected costs for several representations of condition variability and remanufacturing cost structures. We find that, when costs are linear, the optimal acquisition quantity has a closed form and increases with the square root of the degree of condition variability. Our models are based on experience with remanufacturers of cell phones and imaging supplies, and application of our results is illustrated using example data from industry.
A respiratory response to the activation of the muscle metaboreflex during concurrent hypercapnia in man
Authors: Lykidis Christos K. , Kumar Prem , Vianna Lauro C. , White Michael J. , Balanos George M.
Published: October 2009

In this study, we aimed to assess the ventilatory and cardiovascular responses to the combined activation of the muscle metaboreflex and the ventilatory chemoreflex, achieved by postexercise circulatory occlusion (PECO) and euoxic hypercapnia (end‐tidal partial pressure of CO2 7 mmHg above normal), respectively. Eleven healthy subjects (4 women and 7 men; 29 ± 4.4 years old; mean ±s.d.) undertook the following four trials, in random order: 2 min of isometric handgrip exercise followed by 2 min of PECO with hypercapnia; 2 min of isometric handgrip exercise followed by 2 min of PECO while breathing room air; 4 min of rest with hypercapnia; and 4 min of rest while breathing room air. Ventilation was significantly increased during exercise in both the hypercapnic (+3.17 ± 0.82 l min−1) and the room air breathing trials (+2.90 ± 0.26 l min−1; all P < 0.05). During PECO, ventilation returned to pre‐exercise levels when breathing room air (+0.52 ± 0.37 l min−1; P > 0.05), but it remained elevated during hypercapnia (+3.77 ± 0.23 l min−1; P < 0.05). The results indicate that the muscle metaboreflex stimulates ventilation with concurrent chemoreflex activation. These findings have implications for disease states where effort intolerance and breathlessness are linked.
Episodic spinal serotonin receptor activation elicits long‐lasting phrenic motor facilitation by an NADPH oxidase‐dependent mechanism
Authors: MacFarlane P. M. , Mitchell G. S.
Published: October 2009

Phrenic long‐term facilitation (pLTF) is a serotonin (5‐HT)‐dependent augmentation of phrenic motor output induced by acute intermittent hypoxia (AIH). AIH‐induced pLTF requires spinal NADPH oxidase activity and reactive oxygen species (ROS) formation. Since 5‐HT receptor activation stimulates NADPH oxidase activity in some cell types, we tested the hypothesis that episodic spinal 5‐HT receptor activation (without AIH) is sufficient to elicit an NADPH oxidase‐dependent facilitation of phrenic motor output (pMF). In anaesthetised, artificially ventilated adult male rats, episodic intrathecal 5‐HT injections (3 × 6 μl injections at 5 min intervals) into the cerebrospinal fluid (CSF) near cervical spinal segments containing the phrenic motor nucleus elicited a progressive increase in integrated phrenic nerve burst amplitude (i.e. pMF) lasting at least 60 min post‐5‐HT administration. Hypoglossal (XII) nerve activity was unaffected, suggesting that effective doses of 5‐HT did not reach the brainstem. A single 5‐HT injection was without effect. 5‐HT‐induced pMF was dose dependent, but exhibited a bell‐shaped dose–response curve. Activation of different 5‐HT receptor subtypes, specifically 5‐HT2versus 5‐HT7 receptors, may underlie the bell‐shaped dose–response curve via a mechanism of ‘cross‐talk’ inhibition. Pre‐treatment with NADPH oxidase inhibitors, apocynin or diphenylenodium (DPI), blocked 5‐HT induced pMF. Thus, episodic spinal 5‐HT receptor activation is sufficient to elicit pMF by an NADPH oxidase‐dependent mechanism, suggesting common mechanisms of ROS formation with AIH‐induced pLTF. An understanding of the mechanisms giving rise to AIH‐induced pLTF and 5‐HT induced pMF may inspire novel therapeutic strategies for respiratory insufficiency in diverse conditions, such as sleep apnoea, cervical spinal injury or amyotrophic lateral sclerosis.
Effects of Differential Scheme and Viscosity Model on Rough-Surface Point-Contact Isothermal EHL
Authors: Liu Yuchuan , Wang Q. Jane , Zhu Dong , Wang Wenzhong , Hu Yuanzhong
Published: October 2009

This paper discussed the computational accuracy of rough-surface point-contact isothermal elastohydrodynamic lubrication (EHL) analysis by investigating the effects of differential scheme, viscosity-pressure, and shear-thinning models. An EHL experiment with multitransverse ridges was employed as simulated target. Four differential schemes, including the combined and the separate first-order and second-order backward schemes, were investigated. It is found that the separate second-order backward scheme offers the best results based on the comparison with the experimental data, with which two roughness derivatives may be fully or partially canceled each other; thus, the discretization error induced by roughness can be reduced. The consistency of differential schemes is an important issue for the separate schemes. The Yasutomi free-volume viscosity-pressure model and the Eyring rheological model are found to yield the numerical simulations the closest to experimental results.
An Offshore Risk Analysis Method Using Fuzzy Bayesian Network
Authors: Ren J. , Jenkinson I. , Wang J. , Xu D. L. , Yang J. B.
Published: October 2009

The operation of an offshore installation is associated with a high level of uncertainty because it usually operates in a dynamic environment in which technical and human and organizational malfunctions may cause possible accidents. This paper proposes a fuzzy Bayesian network (FBN) approach to model causal relationships among risk factors, which may cause possible accidents in offshore operations. The FBN model explicitly represents cause-and-effect assumptions between offshore engineering system variables that may be obscured under other modeling approaches like fuzzy reasoning and Monte Carlo risk analysis. The flexibility of the method allows for multiple forms of information to be used to quantify model relationships, including formally assessed expert opinions when quantitative data are lacking in early design stages with a high level of innovation or when only qualitative or vague statements can be made. The model is also a modular representation of uncertain knowledge due to randomness and vagueness. This makes the risk and safety analysis of offshore engineering systems more functional and easier in many assessment contexts. A case study of the collision risk between a floating production, storage and offloading unit and the authorized vessels due to human errors during operation is used to illustrate the application of the proposed model.
Second-Order Low-Frequency Wave Forces on a SPM Offloading Tanker in Shallow Water
Authors: Ma S. , Kim M. H. , Shi S.
Published: October 2009

This paper studies the influence of three different calculation methods of the second-order low-frequency (LF) wave-force quadratic transfer functions (QTFs) for a single point mooring (SPM) tanker system in relatively shallow water region. The multivessel-mooring hawser coupled dynamic analysis is used to simulate the floater relative motions and mooring and hawser tensions. Because the SPM tanker is deployed in shallow water region and the slowly varying drift motions are to be dominant in typical operational conditions, the accurate calculation of LF wave-force QTFs become important especially for mooring and hawser-tension prediction. The practically popular Newman’s approximation and another approximation excluding complicated free-surface integrals are used to calculate the LF QTFs on the offloading tanker and they are compared with the complete QTF results. Further comparison is carried out by calculating the resulting LF wave-force spectra and motion time histories and analyzing their impacts on hawser and mooring line tensions. Through the example studies, the limitation of the Newman’s approximation in the case of shallow water and longer period irregular waves is underscored.
The Motion of Floating Systems: Nonlinear Dynamics in Periodic and Random Waves
Authors: Ellermann Katrin
Published: October 2009

Floating systems, such as ships, barges, or semisubmersibles, show a dynamical behavior, which is determined by their internal structure and the operating conditions caused by external forces e.g., due to waves and wind. Due to the complexity of the system, which commonly includes coupling of multiple components or nonlinear restoring forces, the response can exhibit inherently nonlinear characteristics. In this paper different models of floating systems are considered. For the idealized case of purely harmonic forcing they all show nonlinear behavior such as subharmonic motion or different steady-state responses at constant operating conditions. The introduction of random disturbances leads to deviations from the idealized case, which may change the overall response significantly. Advantages and limitations of the different mathematical models and the applied numerical techniques are discussed.
A Study of Airborne Wear Particles Generated From a Sliding Contact
Authors: Olofsson Ulf , Olander Lars , Jansson Anders
Published: October 2009

Recently, much attention has been paid to the influence of airborne particles in the atmosphere on human health. Sliding contacts are a significant source of airborne particles in urban environments. In this study airborne particles generated from a sliding steel-on-steel combination are studied using a pin-on-disk tribometer equipped with airborne-particle counting instrumentation. The instrumentation measured particles in size intervals from 0.01μm to 32μm. The result shows three particle size regimes with distinct number peaks: ultrafine particles with a size distribution peak around 0.08μm, fine particles with a peak around 0.35μm, and coarse particles with a peak around 2 or 4μm. Both the particle generation rate and the wear rate increase with increasing sliding velocity and contact pressure.
Theoretical and Experimental Study on Dynamic Coefficients and Stability for a Hydrostatic/Hydrodynamic Conical Bearing
Authors: Hong Guo , Xinmin Lai , Shaoqi Cen
Published: October 2009

This paper presents a theoretical study and experimental method to recognize the dynamic performance (stiffness and damping coefficients) of an externally pressurized deep/shallow pockets hybrid conical bearing compensated by flat capillary restrictors. The equations governing the flow of fluid film in the conical bearing together with the pressure boundary condition and the restrictor flow equation are solved by using the finite element method. A delicate test rig is constructed and bearings having a big end diameter of 97 mm, a length of 90 mm, and a radial clearance of 0.02–0.025 mm are analyzed. It is assumed that the fluid film force of the hydrostatic/hydrodynamic conical bearing is characterized by a set of linear stiffness and damping coefficients. The experiment used the impulse excitation method to recognize these coefficients and established their characteristics under different operating conditions. Numerical results are compared with the experimental results. The stability parameters of hybrid conical, hydrodynamic, and hydrostatic bearings are compared. The results show that the hybrid conical bearing has the advantages of high load carrying capability and high stability under small eccentricity.
Thermal Modeling and Experimental Investigation for Laser Assisted Milling of Silicon Nitride Ceramics
Authors: Shen Xinwei , Lei Shuting
Published: October 2009

This study is motivated by the fact that temperature control is very important for the success of laser assisted milling. A transient three-dimensional thermal model is developed using finite element analysis for laser assisted milling (LAMill) of silicon nitride ceramics, and then validated through a series of experiments of laser assisted face milling. This study aims to explore the thermal characteristics in LAMill of silicon nitride ceramics and thus provide guidelines on parameter selection for future operations. In addition, heat generation associated with machining is considered, and the effects of laser power, feed, and cutting speed on temperature are investigated. Simulation results show that heat generation associated with machining can be neglected. Laser power is one critical parameter for successful operation of LAMill. Moreover, both feed and cutting speed can affect the operating temperatures by varying feed rate; however, once feed rate is fixed, they have a little impact on the operating temperatures.
Tribological Characterization of Machining at Very Small Contact Areas
Authors: Lovell Michael R. , Cohen P. , Menezes Pradeep L. , Shankar R.
Published: October 2009

When machining miniaturized components, the contact conditions between the tool and the workpiece exhibit very small contact areas that are on the order of 10−5 mm2. Under these conditions, extremely high contact stresses are generated, and it is not clear whether macroscopic theories for the chip formation, cutting forces, and friction mechanisms are applicable. For this reason, the present investigation has focused on creating a basic understanding of the frictional behavior in very small scale machining processes so that evaluations of standard macroscale models could be performed. Specialized machining experiments were conducted on 70/30 brass materials using high-speed steel tools over a range of speeds, feeds, depths of cut, and tool rake angles. At each operating condition studied, the friction coefficient and the shear factor τk were obtained. Based on the experimental results, it was determined that the standard macroscopic theory for analyzing detailed friction mechanisms was insufficient in very small scale machining processes. An approach that utilized the shear factor, in contrast, was found to be better for decoupling the physical phenomena involved. Utilizing the shear factor as an analysis parameter, the parameters that significantly influence the friction in microscale machining processes were ascertained and discussed.
Effects of Rolling Direction and Lubricant on Friction in Sheet Metal Forming
Authors: Liu Xiaojun , Liewald Mathias , Becker Dina
Published: October 2009

Lubrication and friction at workpiece-tool interface play an important role in product quality control of sheet metal forming process. Surface microstructures of sheets have a great influence on the development of lubrication films. In order to investigate the effects of the rolling direction of aluminum alloy sheet and lubricant on the friction behavior in sheet metal forming, strip drawing test was used. The sample used was electric discharge texturing (EDT) surface. Lubricants, both with and without additives, were used. The strip drawing tests were performed at angles between the sliding and rolling directions of 0–90 deg. Variations in the sheet surface topography were analyzed by comparing the sheet surface microstructures and its 3D surface parameters before and after the strip drawing test. Results of the strip drawing tests indicate that the kind and amount of lubricant have great influences on friction at the interface, and the lubricant with additives benefits improving the friction behavior between the sheet and the tool. The EDT surface of the aluminum alloy sheet has an anisotropic frictional property during deep drawing process due to different angles between the sliding and rolling directions. When the sliding direction is parallel to the rolling direction, the coefficient of friction has the highest value. When the angle between the sliding and rolling directions increases, the coefficient of friction decreases. The surface microstructure of the sheets after the strip drawing test at different angles between the sliding and rolling directions has been modified, and its 3D surface parameters decrease significantly to a different degree.
Linear Stability Analysis of the Herringbone Groove Journal Bearings in Microsystems: Consideration of Gas Rarefaction Effects
Authors: Li Wang-Long , Shen Rui-Wen
Published: October 2009

The dynamic performance of the herringbone groove journal bearings (HGJBs) with the effects of gas rarefaction taken into account is considered for applications in microsystems. Two important parameters (the Knudsen number Kn and the tangential momentum accommodation coefficients, TMACs or the accommodation coefficients, ACs) that affect gas rarefaction significantly are considered. Small variations in film thickness and pressure from the equilibrium state are substituted into the transient modified molecular gas lubrication (MMGL) equation, which considers effects of gas rarefactions with the Poiseuille and Couette flow rate correctors. The gas film in the rotor-bearing system is modeled as stiffness and damping elements with coefficients dependent on the exciting frequency. The dynamic coefficients are then obtained by solving the linearized MMGL equations. The equations of motion of the rotor as well as the dynamic coefficients are performed for the present linear stability analysis. Due to the exciting frequency-dependent nature of the dynamic coefficients, an iterative method with the golden section technique is introduced in the linear stability analysis of rotor-bearing systems. The critical mass parameters and the related threshold speed are computed and discussed. The results of this study prove that HGJBs in microsystems can operate at concentric conditions at very high speeds.
Impulse-Load Dynamics of Squeeze Film Gas Bearings for a Linear Motion Guide
Authors: Ono Yuji , Yoshimoto Shigeka , Miyatake Masaaki
Published: October 2009

This paper deals with a noncontact moving table using squeeze-film gas bearings for a linear motion guide, and investigates the dynamic behavior of the moving table under impulse load, experimentally and numerically, to clarify the dynamic characteristics of a squeeze-film gas bearing. This squeeze bearing for a noncontact moving table uses piezoelectric actuators as an ultrasonic vibrator to make the bearing surface vibrate at the ultrasonic resonant frequency of the bearing plate. The squeeze-film pressure is generated in the gap beneath the vibrating bearing surface and can support the moving table without any contact. It was consequently found that the numerical calculation method presented in this paper could predict well the dynamic behavior of the moving table using the squeeze-film gas bearing under impulse load.
Enhancement of Wear Resistance of Copper With Tungsten Addition (≤20 wt %) by Powder Metallurgy Route
Authors: Maji Poulami , Dube R. K. , Basu Bikramjit
Published: October 2009

Copper–tungsten composite materials are developed for applications such as electrical contacts, resistance electrodes, and contact tips in welding guns as well as for components requiring higher wear resistance. In addition to the aspect of improved performance, it is scientifically interesting to assess the tribological properties, and therefore the objectives of the present work include, to determine the role of W additions in improving the fretting wear resistance of Cu for electrical applications, to determine the optimum concentration for W additions, and to identify the mechanisms responsible for fretting wear improvements. In addressing these issues, a planned set of fretting wear tests were conducted on powder metallurgically processed Cu–W composites (maximum W content of 20 wt %) against steel counterbody under varying load (up to 10 N) for 10,000 cycles. It has been observed that at lower loads of 2 N, the coefficient of friction (COF) recorded was ∼0.9 for the Cu–20 wt % W/steel, whereas it was ∼0.85 for a pure Cu/steel couple. Under similar operating conditions with the increase in load, the COF decreases to 0.5 at 10 N load, irrespective of the composition of the Cu–W composite. Furthermore, the incorporation of 5 wt % W has reduced the volumetric wear loss by 4–6 folds in comparison to unreinforced Cu. The addition of even higher percentage of W has led to increase its wear resistance by ∼10 folds. Under the investigated conditions, the wear rate systematically decreases with the increase in load for all the tested Cu–W composites. Based on the topographical observation of worn surfaces, it is observed that wear mechanisms for the Cu and Cu–W composites are tribochemical wear, adhesive wear, and abrasive wear. The incorporation of harder W particles (5 wt % or more) help in abrading the steel ball and in forming a dense tribolayer of FexOy, which effectively reduces wear rate and hence, increases wear resistance of the Cu–W composite surface in reference to unreinforced Cu.
A Review of Rolling Contact Fatigue
Authors: Sadeghi Farshid , Jalalahmadi Behrooz , Slack Trevor S. , Raje Nihar , Arakere Nagaraj K.
Published: October 2009

Ball and rolling element bearings are perhaps the most widely used components in industrial machinery. They are used to support load and allow relative motion inherent in the mechanism to take place. Subsurface originated spalling has been recognized as one of the main modes of failure for rolling contact fatigue (RCF) of bearings. In the past few decades a significant number of investigators have attempted to determine the physical mechanisms involved in rolling contact fatigue of bearings and proposed models to predict their fatigue lives. In this paper, some of the most widely used RCF models are reviewed and discussed, and their limitations are addressed. The paper also presents the modeling approaches recently proposed by the authors to develop life models and better understanding of the RCF.
A Mechanistic Model for Time-Dependent Fatigue
Authors: Majumdar S. , Maiya P. S.
Published: October 2009

Elevated-temperature failure of structural materials (e.g., austenitic stainless steels, low-alloy steels) used in energy-conversion systems can occur by fatigue, creep, or by interactive processes involving creep, fatigue, and environment. The fracture surfaces of these materials exhibit a variety of microstructural features depending upon the type of material, strain rate, temperature, environment, hold times, and sequence of waveshapes. These microstructural observations have been used as a guide in the formulation of generalized damage-rate equations that include interaction between a crack and cavities in a given environment. Crack-propagation rate as well as total life of a fatigue specimen have been calculated by integrating the damage-rate equations over the inelastic strain history of the specimen, and compared with experimental results.
Structural Integrity: Evolution of a Technology
Authors: Wells A. A.
Published: October 2009

This paper deals mainly with technical features of fracture control as a contribution to structural integrity. An attempt has been made to illustrate how scientific method can be further applied to daily production. The objective is to achieve a meaningful and desirable discipline, without introducing a plethora of expensive tests and their consequential delays, or the development of more artificial and unnecessary situations between adversaries. This is an objective of quality assurance, which aims to require and encourage good housekeeping over the whole of a fabricating activity. Many of the requirements may be mundane, and relate to proof that the selected materials and processes have been adhered to without, or only with agreed substitutions. The importance of this activity should be thoroughly recognized with respect to the achievement of structural integrity, and its organization deserves the most profound study and respect.
The Effects of Low Temperature Magnetic Cycling on the Properties of Ferromagnetic Materials
Authors: Collins J. D.
Published: October 2009

The interaction of dislocations with magnetic domain walls and the low energy response of dislocations at cryogenic temperatures have been investigated as a means of improving the structure sensitive properties of steel. Both cutting tools and carburized surfaces have shown an improvement when subjected to a cyclic magnetic field in the temperature range of 77 K to room temperature (RT). An annealing effect of the treatment suggests it may be a low energy substitution for conventional thermal tempering in specific applications.
Vibratory Stress Relief: A Fundamental Study of Its Effectiveness
Authors: Dawson R. , Moffat D. G.
Published: October 2009

Techniques have been devised for inducing consistent residual stress distributions into cantilever beams and for measuring their variation through the section. Commercial vibratory stress relief procedures have been simulated using a laboratory shaker, and it has been shown that resonant vibration techniques are capable of producing almost complete surface stress relief in specimens of hot rolled mild steel, cold drawn mild steel, and an aluminium alloy. The variables involved in the process are examined and conclusions are reached regarding cyclic strain amplitudes, cycle numbers, and frequency and fatigue effects.
Void Nucleation Effects in Biaxially Stretched Sheets
Authors: Chu C. C. , Needleman A.
Published: October 2009

The effects of void nucleation occurring during the deformation history on forming limit curves are considered for both in-plane and punch stretching employing a constitutive model of a porous plastic solid. Both plastic strain controlled and stress controlled nucleation processes are simulated by a two parameter void nucleation criterion. For in-plane stretching, plastic strain controlled nucleation can have, in certain circumstances, a significantly destabilizing effect on the forming limit curve. However, within the framework of plane stress theory which neglects the enhancement of the hydrostatic stress due to necking, a stress controlled nucleation process is not found to be significantly destabilizing. In punch stretching a ductile rupture criterion, which limits the maximum volume fraction of voids, as well as the appearance of a well defined thickness trough, is adopted as a localized necking criterion. Only plastic strain controlled void nucleation is considered here in out-of-plane stretching. The resulting forming limit curves have the same shape as those obtained previously with void nucleation neglected.
Fracture Mode Transitions in Aged Ultra-High Strength 18Ni (350) Maraging Steel
Authors: Rack H. J.
Published: October 2009

The influence of test temperature on the blunt notch and precracked fracture toughness behavior of aged 18Ni (350) maraging steel has been examined. Both toughness measurements exhibit a decrease with decreasing test temperature. The tough-to-brittle transition observed in the precracked fracture toughness samples is similar to that previously reported for the tensile ductility of this alloy and can be associated with a gradual change in fracture mode, from microvoid coalescence at elevated temperatures to quasi-cleavage at low temperatures. This fracture mode transition is suppressed to lower temperatures in the blunt notch samples. Here the fracture behavior is complicated by the presence of a shear failure region immediately below the notch root. It is suggested that it is the development of this shear failure region which controls the fracture resistance of blunt notched aged 18Ni (350) maraging steel. Apparently shear initiation requires the attainment of a critical strain at the surface of the notch root, with this strain decreasing with decreasing test temperature.
Near-Threshold Fatigue Crack Growth in 2 1/4 Cr-1Mo Pressure Vessel Steel in Air and Hydrogen
Authors: Ritchie R. O. , Suresh S. , Moss C. M.
Published: October 2009

As part of an ongoing program to examine subcritical flaw growth in candidate steels for proposed coal gasifier pressure vessels, an initial study is made of characteristics of ultralow growth rate fatigue crack propagation in thick-section, normalized 2 1/4 Cr-1Mo pressure vessel steel (ASTM A387, Class 2 Grade 22). Crack propagation data are generated over a wide range of growth rates, from 10−8 to 10−2 mm/cycle, for load ratios between 0.05 and 0.80 at ambient temperatures in low pressure environments of moist air, dry hydrogen gas and dry argon gas. Particular emphasis is placed on behavior at near-threshold growth rates, below 10−6 mm/cycle, approaching the so-called threshold stress intensity for fatigue crack growth, ΔK0. Near-threshold growth rates, in addition to showing a marked sensitivity to load ratio, are found to be significantly enhanced in gaseous hydrogen compared to air. Similar environmentally-enhanced growth is observed in argon gas. To account for such results, previous models of threshold behavior based on environmental factors (e.g., hydrogen embrittlement) are questioned, and a new approach is presented in terms of the role of oxide debris from moist environments in promoting crack closure. This oxide-induced closure model is found to be consistent with most experimental observations of near-threshold fatigue crack propagation behavior and is proposed as a mechanism for environmental effects at ultra-low growth rates.
A Probabilistic Approach to Fatigue Crack Growth Rate
Authors: Tsurui Akira , Igarashi Akito
Published: October 2009

A probabilistic model for fatigue crack growth proposed by K. P. Oh is modified in some respects. Under more natural assumptions than Oh’s it is derived that the rate of fatigue crack growth is proportional to some power of the range of the stress intensity factor. It is also shown that the exponent ranges from 2 to 4.
A Comparative Study of Two State-Variable Constitutive Theories
Authors: Delph T. J.
Published: October 2009

Direct quantitative comparisons are drawn between the predictions of two state-variable constitutive theories, that of Hart and a recently-proposed theory due to Robinson, for a number of simple uniaxial load histories. The predictions of the two theories agree well in relaxation, constant strain-rate, and constant stress creep simulations. However, substantial differences may be noted in simulations involving more complex loading histories. These differences are discussed within the context of the structure of the theories and comparisons are drawn with real material behavior.
Creep Crack Growth Under LEFM Conditions
Authors: Pilkington R. , Smith E.
Published: October 2009

The paper presents an outline model for creep crack growth under LEFM conditions. The incremental nature of the crack propagation process is taken into account, and a theoretical analysis shows that the relation between crack tip stress intensification and crack growth rate is not unique.
A Criterion for Low-Cycle Fatigue Failure Under Biaxial States of Stress
Authors: Lefebvre D. , Neale K. W. , Ellyin F.
Published: October 2009

The plastic strain energy required for failure in low-cycle biaxial fatigue is estimated using the energy in uniaxial fatigue and assumptions from the theory of plasticity. A criterion for high-strain multiaxial fatigue of the form Δε¯pΔσ¯=KNƒc is developed, where the equivalent stress amplitude Δσ and the equivalent plastic strain amplitude Δεp are based on the von Mises yield function of plasticity. The parameters K and c are assumed to depend on the mechanical properties of the material and to be functions of the stress ratio. These functions can be evaluated from uniaxial fatigue data and are compared with tests performed on thin-walled tubes of mild steel at different stress ratios. The proposed criterion seems to yield a promising approach for the low-cycle fatigue analysis of metals under biaxial states of stress.
Abrasive Wear in Machining: Experiments With Materials of Controlled Microstructure
Authors: Ramalingam S. , Wright P. K.
Published: October 2009

Evidence is presented to show that hard inclusions in iron-base alloys degrade machinability by reducing cutting tool life. Machining experiments have been carried out on Fe-C-Silica and Fe-C-Alumina powder metal compacts containing varying amounts of abrasive. In addition, two stainless steels have been compared. One of these was titanium stabilized hence containing hard TiC particles; the other was unstabilized and free of such particles. In all these experiments the tool wear rate increased with volume fraction of hard inclusions. Abrasive wear mechanisms have been identified using detailed metallography. When machining with high-speed steels, rake face wear by abrasion occurs by a plastic plowing process and this is enhanced if the tool is thermally weakened. When machining with cemented carbide tools the results indicate that the temperatures in the crater region are high enough for the same plastic plowing of tool material to occur. By contrast, temperatures at the flank face are 300–400°C lower and the wear processes are of a different nature.
Application of Finite Element Calculations to Residual Stress Measurements
Authors: Schajer G. S.
Published: October 2009

The use of finite element calculations is assessed as a means of analysis of the strain relaxation data from a measurement of residual stress by a material removal method. This application is important because it allows a greater flexibility of choice for specimen shape, materials, and experimental procedure than would be possible if only analytic or experimental calibrations are used. Three possible applications are described using the hole-drilling method as an example, and comparisons of calculated results and experimental measurements are presented.
Stress Intensity Factors for Corner Cracked Holes Under General Loading Conditions
Authors: Grandt A. F. , Kullgren T. E.
Published: October 2009

A linear elastic analysis is conducted with the finite element-alternating method for quarter-elliptical corner cracks located at fastener holes. Mode-one stress intensity factors are presented along the crack periphery for a crack face pressure loading which can be represented by a third order polynomial. Results are also given for remote tensile loading applied perpendicular to the crack plane. Two example problems describe application of the polynomial crack face pressure solutions to other loading configurations through a simple linear superposition.