bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Roughness Parameter and Grinding Angle on Coefficient of Friction When Sliding of Al–Mg Alloy Over EN8 Steel
Authors: Menezes Pradeep L. , Kishore  , Kailas Satish V.
Published: October 2006

Surface topography of harder mating surface plays an important role in metal forming operations as it predominantly controls the frictional behavior at the interface. In the present investigation, an inclined scratch tester was used to understand the effect of direction of surface grinding marks on interface friction and transfer layer formation. EN8 steel flats were ground to attain different surface roughnesses with unidirectional grinding marks. Al–Mg alloy pins were then scratched against the prepared EN8 steel flats. The grinding angle (angle between direction of scratch and grinding marks) was varied between 0 deg and 90 deg during the scratch tests. Scanning electron micrography of the contact surfaces revealed the transfer layer morphology. The coefficient of friction and transfer layer formation were observed to depend primarily on the direction of grinding marks of the harder mating surface, and independent of the surface roughness of harder mating surface. The grinding angle effect was attributed to the variation of plowing component of friction with grinding angle.
Dynamic Finite Element Simulations for Understanding Wheel-Rail Contact Oscillatory States Occurring Under Sliding Conditions
Authors: Saulot A. , Baillet L.
Published: October 2006

This paper presents a temporal study using dynamic finite element methods of the dynamic response of a 2D mechanical model composed of a deformable rotating disk (wheel) in contact with a deformable translating body (rail) with constant Coulomb friction. Under global sliding conditions, oscillatory states at specific frequencies occur in the contact patch even in the case of a constant friction coefficient. A parallel is drawn between the frequencies of these states and the modal analysis of the entire mechanical model. The influence on local contact conditions of parameters such as normal load, global sliding ratio, friction coefficient, and the transient value for applying sliding conditions is then evaluated. Finally, the consequences of these states on local rail plastic deformation are presented and correlated with rail corrugation occurring on straight tracks under acceleration and deceleration conditions.
Mixed Elastohydrodynamic Lubrication in a Partial Journal Bearing—Comparison Between Deterministic and Stochastic Models
Authors: Dobrica Mihai B. , Fillon Michel , Maspeyrot Patrick
Published: October 2006

The analysis of the mixed lubrication phenomena in journal and axial bearings represents nowadays the next step towards a better understanding of these devices, subjected to more and more severe operating conditions. While the theoretical bases required for an in-depth analysis of the mixed-lubrication regime have long been established, only small-scale numerical modeling was possible due to computing power limitations. This led to the appearance of averaging models, thus making it possible to generalize the trends observed in very small contacts, and to include them in large-scale numerical analyses. Unfortunately, a lack of experimental or numerical validations of these averaging models is observed, so that their reliability remains to be demonstrated. This paper proposes a deterministic numerical solution for the hydrodynamic component of the mixed-lubrication problem. The model is applicable to small partial journal bearings, having a few centimeters in width and diameter. Reynolds’ equation is solved on a very thin mesh, and pad deformation due to hydrodynamic pressure is taken into account. Deformation due to contact pressure is neglected, which limits the applicability of the model in those cases where extended contact is present. The results obtained with this deterministic model are compared to the stochastic solution proposed by Patir and Cheng, in both hydrodynamic and elastohydrodynamic regimes. The rough surfaces used in this study are numerically generated (Gaussian) and are either isotropic or oriented, having different correlation lengths. It is shown that the stochastic model of Patir and Cheng correctly anticipates the influence of roughness over the pressure field, for different types of roughness. However, when compared to the smooth surface solution, the correction introduced by this model only partially compensates for the differences observed with a deterministic analysis.
The Stribeck Curve: Experimental Results and Theoretical Prediction
Authors: Lu Xiaobin , Khonsari M. M. , Gelinck E. R. M.
Published: October 2006

The Stribeck curve plays an important role in identifying boundary, mixed, elastohydrodynamic, and hydrodynamic lubrication regimes. Recent advances in elastohydrodynamic lubrication together with rough surface interaction have made it possible to develop a methodology for predicting the trend of the Stribeck curve. In this paper, we report the results of a series of experiments performed on a journal bearing together with a theoretical prediction of the Stribeck-type behavior. Various loads and oil temperatures are considered. The comparison between the experimental results with a mixed elastohydrodynamic lubrication model for line contacts is indicative of good agreement.
The Influence of Adhesion and Sub-Newton Pull-Off Forces on the Release of Objects in Outer Space
Authors: Benedetti M. , Bortoluzzi D. , Da Lio M. , Fontanari V.
Published: October 2006

The theoretical background and the numerical modeling results of a ground-based verification activity of a critical space mission phase affected by adhesion issues are presented. Tribological models are first reviewed with an emphasis on the contact forces assessment and their relationship to the geometrical, material, and mechanical properties of the contacting metal bodies. An approach based on a finite element analysis of the contact, accounting for the adhesion forces, is then proposed for studying the contact behavior of smooth surfaces in vacuum. Some solutions aimed at reducing adhesion pull-off forces are discussed. Special emphasis is placed on the role of surface roughness in reducing adhesion. To this purpose, a fractal surface theory is used to estimate interaction forces. The obtained results are applied to discuss the role of adhesion on the release of a test mass under zero gravity as well as to suggest an appropriate detachment procedure that finds a specific application in a scientific space mission.
Determination of Steady-State Adhesive Wear Rate
Authors: Yang L. J.
Published: October 2006

A new equation has been formulated and found successful for modeling the wear rate of test specimens. It is capable of predicting the standard steady-state wear rate and the net steady-state wear rate with a FA value, an exponential function, of 0.99 and 0.999, respectively; and with deviations of about 19% and 36%, respectively. A methodology has also been proposed in this paper to enable the steady-state wear rate to be determined more accurately, consistently, and efficiently. The wear test will be divided into three stages: (i) To conduct the transient wear test; (ii) to predict the steady-state wear rate with the required sliding distance based on the transient wear data by using the new equation; (iii) to conduct confirmation runs to obtain the measured steady-state wear rate. The proposed methodology is supported by wear data obtained previously on aluminium based matrix composite materials. It is capable of giving more accurate steady-state wear rates, as well as saving a lot of testing time and labor, by reducing the number of trial runs required to achieve the steady-state wear condition. It will also give more consistent results since a common FA value will be used.
Surface Modification of AFM Si3N4 Probes for Adhesion/Friction Reduction and Imaging Improvement
Authors: Tao Zhenhua , Bhushan Bharat
Published: October 2006

Si 3 N 4 probes used for atomic force microscope exhibit large adhesion and friction resulting in artifacts of scanned image. In order to reduce adhesion and friction so as to reduce tip related artifacts, liquid lubricant (Z-TETRAOL) and fluorocarbon polymer (Fluorinert™) were applied on the Si3N4 probe. A comprehensive investigation of adhesion, friction, and wear of the uncoated/coated tips in both ambient air and various humidity levels as well as the influence of the coatings on the image resolution was performed. Experiments show that the coatings reduce the adhesion and friction of the Si3N4 tip, improve the initial image resolution, and exhibit less deterioration as compared to that of uncoated tip after scanning. The image degradation of an uncoated Si3N4 probe is also compared with that of an uncoated silicon probe. A probe cantilever deflection model was proposed to correlate the influence of the adhesion and friction with the image distortion.
Large-Scale Evaluation of Constrained Bearing Elements Made of Thermosetting Polyester Resin and Polyester Fabric Reinforcement
Authors: Samyn P. , Van Paepegem W. , Leendertz J. S. , Gerber A. , Van Schepdael L. , Degrieck J. , De Baets P.
Published: October 2006

Polymer composites are increasingly used as sliding materials for high-loaded bearings, however, their tribological characteristics are most commonly determined from small-scale laboratory tests. The static strength and dynamic coefficients of friction for polyester/polyester composite elements are presently studied on large-scale test equipment for determination of its bearing capacity and failure mechanisms under overload conditions. Original test samples have a diameter of 250 mm and thickness of 40 mm, corresponding to the practical implementation in the sliding surfaces of a ball-joint, and are tested at various scales for simulation of edge effects and repeatability of test results. Static tests reveal complete elastic recovery after loading to 120 MPa, plastic deformation after loading at 150 MPa and overload at 200 MPa. This makes present composite favorable for use under high loads, compared to, e.g., glass-fibre reinforced materials. Sliding tests indicate stick-slip for pure bulk composites and more stable sliding when PTFE lubricants are added. Dynamic overload occurs above 120 MPa due to an expansion of the nonconstrained top surface. A molybdenum-disulphide coating on the steel counterface is an effective lubricant for lower dynamic friction, as it favorably impregnates the composite sliding surface, while it is not effective at high loads as the coating is removed after sliding and high initial static friction is observed. Also a zinc phosphate thermoplastic coating cannot be applied to the counterface as it adheres strongly to the composite surface with consequently high initial friction and coating wear. Most stable sliding is observed against steel counterfaces, with progressive formation of a lubricating transfer film at higher loads due to exposure of PTFE lubricant. Composite wear mechanisms are mainly governed by thermal degradation of the thermosetting matrix (max. 162°C) with shear and particle detachment by the brittle nature of polyester rather than plastic deformation. The formation of a sliding film protects against fiber failure up to 150 MPa, while overload results in interlaminar shear, debonding, and ductile fiber pull-out.
Heat Treatment and Wear Characteristics of Al2O3 and TiC Particulate Reinforced AA6063 Al Alloy Hybrid Composites
Authors: Aziz M. Abdel , Mahmoud T. S. , Zaki Z. I. , Gaafer A. M.
Published: October 2006

In this article, the heat treatment and dry sliding wear behavior of Al-based AA6063 alloy reinforced with both TiC and Al2O3 ceramic particles were studied. The particles were synthesized by self-propagating high temperature synthesis (SHS) technique. The prepared composite alloy contains 5vol.%Al2O3 and 5vol.% TiC particles. The composite alloy was prepared by vortex method. To attain the peak hardness values of the alloys, age hardening behavior of the monolithic alloy and also the composite alloy was investigated. The wear tests were performed at room temperature using a pin-on-disk type apparatus. The results showed that the addition of TiC and Al2O3 particles increases the hardness of the AA6063 Al alloy and at the same time accelerates the aging kinetics. The sliding wear properties of AA6063 Al alloy were significantly improved by the addition of TiC and Al2O3 particles.
Two-Dimensional Adaptive-Surface Elasto-Plastic Asperity Contact Model
Authors: Liu Tianxiang , Liu Geng , Xie Qin , Wang Q. Jane
Published: October 2006

When contact problems are solved by numerical approaches, a surface profile is usually described by a series of discrete nodes with the same intervals along a coordinate axis. Contact computation based on roughness datum mesh may be time consuming. An adaptive-surface elasto-plastic asperity contact model is presented in this paper. Such a model is developed in order to reduce the computing time by removing the surface nodes that have little influence on the contact behavior of rough surfaces. The nodes to be removed are determined by a prescribed threshold. The adaptive-surface asperity contact model is solved by means of the element-free Galerkin-finite element coupling method because of its flexibility in domain discretization and versatility in node arrangements. The effects of different thresholds on contact pressure distribution, real contact area, and elasto-plastic stress fields in contacting bodies are investigated and discussed. The results show that this model can help reduce about 48% computational time when the relative errors are about 5%.
Low Friction and High Load Support Capacity of Slider Bearing With a Mixed Slip Surface
Authors: Wu C. W. , Ma G. J. , Zhou P. , Wu C. D.
Published: October 2006

The classical Reynolds theory reveals that a converging gap is the first necessary condition to generate a hydrodynamic pressure in a viscous fluid film confined between two solid surfaces with a relative sliding/rolling motion. For hundreds of years, the classical lubrication mechanics has been based on the frame of the Reynolds theory with no slip assumption. Recent studies show that a large boundary slip occurs on an ultrahydrophobic surface, which results in a very small friction drag. Unfortunately, such a slip surface also produces a small hydrodynamic pressure in a fluid film between two solid surfaces. This paper studies the lubrication behavior of infinite width slider bearings involving a mixed slip surface (MSS). The results of the study indicate that any geometrical wedges (gaps), i.e., a convergent wedge, a parallel gap, and even a divergent wedge, can generate hydrodynamic pressure in an infinite slider bearing with a mixed slip surface. It is found that with an MSS, the maximum fluid load support capacity occurs at a slightly divergent wedge (roughly parallel sliding gap) for an infinite width slider bearing, but not at a converging gap as what the classical Reynolds theory predicts. Surface optimization of a parallel sliding gap with a slip surface can double the hydrodynamic load support and reduce the friction drag by half of what the Reynolds theory predicts for an optimal wedge of a traditional slider bearing.
Elliptic Elastic Contact Between High Order Symmetrical Surfaces
Authors: Diaconescu Emanuel N.
Published: October 2006

This paper proves that a generalized Hertz pressure (the product of Hertz square root and an even polynomial of degree 2n with respect to coordinates) applied over elastic half-space boundary generates a polynomial normal displacement of degree 2n+2. Polynomial surface coefficients are combinations of elliptical integrals. The equation of rigid punch surface generating this pressure is derived, as well as the conditions in which an elliptical contact occurs. For second order surfaces, n=0, these results yield all Hertz formulas, whereas new formulas are derived for contact parameters between fourth, sixth, and eight order surfaces.
Rheological Characteristics and Turbulent Friction Drag and Heat Transfer Reductions of a Very Dilute Cationic Surfactant Solution
Authors: Wei Jinjia , Kawaguchi Yasuo , Yu Bo , Feng Ziping
Published: October 2006

Turbulent friction drag and heat transfer reductions and rheological characteristics of a very dilute cationic surfactant solution, cetyltrimethyl ammonium chloride (CTAC)/sodium salicylate (NaSal) aqueous solution, were experimentally investigated at various temperatures. It was found that there existed a critical temperature above which drag and heat transfer reductions disappeared and shear viscosities rapidly dropped to that of water. It was surmised that drag and heat transfer reductions had a certain relationship with rheological characteristics and a rheological characterization of CTAC∕NaSal surfactant solutions was performed to clarify this relationship. The effects of Reynolds number and fluid temperature and concentration on drag and heat transfer reductions were qualitatively explained by analyzing the measured shear viscosity data at different shear rates and solution temperatures and concentrations. The Giesekus model was found to fit the measured shear viscosities reasonably well for different temperatures and concentrations of the surfactant solution and the model parameter values obtained by fitting were correlated with temperature at certain solution concentrations. From the correlation results, the temperature effect on viscoelasticity of surfactant solutions was analyzed to relate the rheological characteristics with drag and heat transfer reduction phenomena.
Heat Transfer to Small Horizontal Cylinders Immersed in a Fluidized Bed
Authors: Friedman J. , Koundakjian P. , Naylor D. , Rosero D.
Published: October 2006

Heat transfer to horizontal cylinders immersed in fluidized beds has been extensively studied, but mainly in the context of heat transfer to boiler tubes in coal-fired beds. As a result, most correlations in the literature have been derived for cylinders of 25-50mm diameter in vigorously fluidizing beds. In recent years, fluidized bed heat treating furnaces fired by natural gas have become increasingly popular, particularly in the steel wire manufacturing industry. These fluidized beds typically operate at relatively low fluidizing rates (G∕Gmf<5) and with small diameter wires (1-6mm). Nusselt number correlations developed based on boiler tube studies do not extrapolate down to these small size ranges and low fluidizing rates. In order to obtain reliable Nusselt number data for these size ranges, an experimental investigation has been undertaken using two heat treating fluidized beds; one a pilot-scale industrial unit and the other a lab-scale (300mm diameter) unit. Heat transfer measurements were obtained using resistively heated cylindrical samples ranging from 1.3 to 9.5mm in diameter at fluidizing rates ranging from approximately 0.5×Gmf (packed bed condition) to over 10×Gmf using aluminum oxide sand particles ranging from dp=145-330μm (50–90 grit). It has been found that for all cylinder sizes tested, the Nusselt number reaches a maximum near 2×Gmf, then remains relatively steady (±5-10%) to the maximum fluidizing rate tested, typically 8-12×Gmf. A correlation for maximum Nusselt number is developed.
Measurement and Modeling of Condensation Heat Transfer Coefficients in Circular Microchannels
Authors: Bandhauer Todd M. , Agarwal Akhil , Garimella Srinivas
Published: October 2006

A model for predicting heat transfer during condensation of refrigerant R134a in horizontal microchannels is presented. The thermal amplification technique is used to measure condensation heat transfer coefficients accurately over small increments of refrigerant quality across the vapor-liquid dome (0<x<1). A combination of a high flow rate closed loop primary coolant and a low flow rate open loop secondary coolant ensures the accurate measurement of the small heat duties in these microchannels and the deduction of condensation heat transfer coefficients from measured UA values. Measurements were conducted for three circular microchannels (0.506<Dh<1.524mm) over the mass flux range 150<G<750kg∕m2s. Results from previous work by the authors on condensation flow mechanisms in microchannel geometries were used to interpret the results based on the applicable flow regimes. The heat transfer model is based on the approach originally developed by Traviss, D. P., Rohsenow, W. M., and Baron, A. B., 1973, “Forced-Convection Condensation Inside Tubes: A Heat Transfer Equation For Condenser Design,” ASHRAE Trans., 79(1), pp. 157–165 and Moser, K. W., Webb, R. L., and Na, B., 1998, “A New Equivalent Reynolds Number Model for Condensation in Smooth Tubes,” ASME, J. Heat Transfer, 120(2), pp. 410–417. The multiple-flow-regime model of Garimella, S., Agarwal, A., and Killion, J. D., 2005, “Condensation Pressure Drop in Circular Microchannels,” Heat Transfer Eng., 26(3), pp. 1–8 for predicting condensation pressure drops in microchannels is used to predict the pertinent interfacial shear stresses required in this heat transfer model. The resulting heat transfer model predicts 86% of the data within ±20%.
Thermohydraulics of Laminar Flow Through Rectangular and Square Ducts With Transverse Ribs and Twisted Tapes
Authors: Pramanik Debashis , Saha Sujoy K.
Published: October 2006

The heat transfer and the pressure drop characteristics of laminar flow of viscous oil through rectangular and square ducts with internal transverse rib turbulators on two opposite surfaces of the ducts and fitted with twisted tapes have been studied experimentally. The tapes have been full length, short length, and regularly spaced types. The transverse ribs in combination with full-length twisted tapes have been found to perform better than either ribs or twisted tapes acting alone. The heat transfer and the pressure drop measurements have been taken in separate test sections. Heat transfer tests were carried out in electrically heated stainless steel ducts incorporating uniform wall heat flux boundary conditions. Pressure drop tests were carried out in acrylic ducts. The flow was periodically fully developed in the regularly spaced twisted-tape elements case and decaying swirl flow in the short-length twisted tapes case. The flow characteristics are governed by twist ratio, space ratio, and length of twisted tape, Reynolds number, Prandtl number, rod-to-tube diameter ratio, duct aspect ratio, rib height, and rib spacing. Correlations developed for friction factor and Nusselt number have predicted the experimental data satisfactorily. The performance of the geometry under investigation has been evaluated. It has been found that on the basis of both constant pumping power and constant heat duty, the regularly spaced twisted-tape elements in specific cases perform marginally better than their full-length counterparts. However, the short-length twisted-tape performance is worse than the full-length twisted tapes. Therefore, full-length twisted tapes and regularly spaced twisted-tape elements in combination with transverse ribs are recommended for laminar flows. However, the short-length twisted tapes are not recommended.
Optimal Cool-Down in Linear and Nonlinear Thermoviscoelasticity and
the Effects of Initial Stress
Authors: Chen L. , Cao J. , Weitsman Y. J.
Published: October 2006

This article concerns the minimization of residual thermal stresses in geometrically constrained adhesive layers and thin polymeric composite lay-ups with emphasis on the role of initial stresses. Such residual stresses evolve during cure and subsequently during post-cure cool-down. The cure stresses play the role of initial stress superimposed on the thermoviscoelastic response that governs to cool-down phase. Optimization is achieved by following a time-temperature path that achieves the best counter play between temperature as a stress inducing and a stress reducing agent. When viscoelastic nonlinearity is considered such contradictory effect is played by stress itself, in which case an initial stress may have a beneficial effect.
The Thermo-Viscoelastic, Viscoplastic Characterization of Vetrotex 324∕Derakane 510A-40 Through Tg
Authors: Boyd Steven E. , Lesko John J. , Case Scott W.
Published: October 2006

The increased use of fiber reinforced plastics (FRPs) in ship topside structures necessitates the need to understand how such structures respond to fire exposure. For this reason we have characterized the nonlinear, thermo-viscoelastic behavior of Vetrotex 324∕Derakane 510A-40 using tensile loading of [±45]2S laminates. Nonlinearity is observed at elevated stress and temperatures above Tg. The data reduction sufficiently modeled the experimental master-curves over the whole temperature range, but suffered from inconsistencies in the creep data and recovery data, perhaps due to accumulated damage during the creep cycle. Our results indicate that the nonlinear viscoelastic behavior significantly contributes to structural behavior under fire loading conditions.
Continuum and Molecular-Level Modeling of Fatigue Crack Retardation in Self-Healing Polymers
Authors: Maiti Spandan , Shankar Chandrashekar , Geubelle Philippe H. , Kieffer John
Published: October 2006

A numerical model to study the fatigue crack retardation in a self-healing material (White et al., 2001, Nature, 409, pp. 794–797) is presented. The approach relies on a combination of cohesive modeling for fatigue crack propagation and a contact algorithm to enforce crack closure due to an artificial wedge in the wake of the crack. The healing kinetics of the self-healing material is captured by introducing along the fracture plane a state variable representing the evolving degree of cure of the healing agent. The atomic-scale processes during the cure of the healing agent are modeled using a coarse-grain molecular dynamics model specifically developed for this purpose. This approach yields the cure kinetics and the mechanical properties as a function of the degree of cure, information that is transmitted to the continuum-scale models. The incorporation of healing kinetics in the model enables us to study the competition between fatigue crack growth and crack retardation mechanisms in this new class of materials. A systematic study of the effect of different loading and healing parameters shows a good qualitative agreement between experimental observations and simulation results.
Long-Term Sustainability of a High-Energy, Low-Diversity Crustal Biome
Authors: Lin Li-Hung , Wang Pei-Ling , Rumble Douglas , Lippmann-Pipke Johanna , Boice Erik , Pratt Lisa M. , Lollar Barbara Sherwood , Brodie Eoin L. , Hazen Terry C. , Andersen Gary L. , DeSantis Todd Z. , Moser Duane P. , Kershaw Dave , Onstott T. C.
Published: October 2006

Geochemical, microbiological, and molecular analyses of alkaline saline groundwater at 2.8 kilometers depth in Archaean metabasalt revealed a microbial biome dominated by a single phylotype affiliated with thermophilic sulfate reducers belonging to
Firmicutes
. These sulfate reducers were sustained by geologically produced sulfate and hydrogen at concentrations sufficient to maintain activities for millions of years with no apparent reliance on photosynthetically derived substrates.
Functional Delivery of a Cytosolic tRNA into Mutant Mitochondria of Human Cells
Authors: Mahata Bidesh , Mukherjee Saikat , Mishra Sumita , Bandyopadhyay Arun , Adhya Samit
Published: October 2006

Many maternally inherited and incurable neuromyopathies are caused by mutations in mitochondrial (mt) transfer RNA (tRNA) genes. Kinetoplastid protozoa, including
Leishmania
, have evolved specialized systems for importing nucleus-encoded tRNAs into mitochondria. We found that the
Leishmania
RNA import complex (RIC) could enter human cells by a caveolin-1–dependent pathway, where it induced import of endogenous cytosolic tRNAs, including tRNA
Lys
, and restored mitochondrial function in a cybrid harboring a mutant mt tRNA
Lys
(
MT-TK
) gene. The use of protein complexes to modulate mitochondrial function may help in the management of such genetic disorders.
S6K1- and ßTRCP-Mediated Degradation of PDCD4 Promotes Protein Translation and Cell Growth
Authors: Dorrello N. Valerio , Peschiaroli Angelo , Guardavaccaro Daniele , Colburn Nancy H. , Sherman Nicholas E. , Pagano Michele
Published: October 2006

The tumor suppressor programmed cell death protein 4 (PDCD4) inhibits the translation initiation factor eIF4A, an RNA helicase that catalyzes the unwinding of secondary structure at the 5′ untranslated region (5′UTR) of messenger RNAs (mRNAs). In response to mitogens, PDCD4 was rapidly phosphorylated on Ser
67
by the protein kinase S6K1 and subsequently degraded via the ubiquitin ligase SCF
βTRCP
. Expression in cultured cells of a stable PDCD4 mutant that is unable to bind βTRCP inhibited translation of an mRNA with a structured 5′UTR, resulted in smaller cell size, and slowed down cell cycle progression. We propose that regulated degradation of PDCD4 in response to mitogens allows efficient protein synthesis and consequently cell growth.
Comment on "Stability via Asynchrony in
Drosophila
Metapopulations with Low Migration Rates"
Authors: Ranta Esa , Kaitala Veijo
Published: October 2006

Dey and Joshi (Reports, 21 April 2006, p. 434) studied replicate laboratory populations of
Drosophila
and reported that low migration led to asynchrony among subpopulations. We argue that this unexpected outcome may be due to variation in the initial size of the subpopulations and uncontrolled stochasticity in the experiments.
Response to Comment on "Stability via Asynchrony in
Drosophila
Metapopulations with Low Migration Rates"
Authors: Dey Sutirth , Joshi Amitabh
Published: October 2006

Ranta and Kaitala find asynchrony in our experiment unexpected and suggest stochasticity as a possible causal mechanism using simulated two-patch metapopulations. However, their mechanism can yield either subpopulation synchrony or asynchrony. We extend their approach to a nine-patch system approximating our experiment and show that asynchrony is not only not unexpected but extremely likely in real metapopulations with low migration.
Anisotropy and Corotation of Galactic Cosmic Rays
Authors: Amenomori M. , Ayabe S. , Bi X. J. , Chen D. , Cui S. W. , Danzengluobu  , Ding L. K. , Ding X. H. , Feng C. F. , Feng Zhaoyang , Feng Z. Y. , Gao X. Y. , Geng Q. X. , Guo H. W. , He H. H. , He M. , Hibino K. , Hotta N. , Hu Haibing , Hu H. B. , Huang J. , Huang Q. , Jia H. Y. , Kajino F. , Kasahara K. , Katayose Y. , Kato C. , Kawata K. , Labaciren  , Le G. M. , Li A. F. , Li J. Y. , Lou Y.-Q. , Lu H. , Lu S. L. , Meng X. R. , Mizutani K. , Mu J. , Munakata K. , Nagai A. , Nanjo H. , Nishizawa M. , Ohnishi M. , Ohta I. , Onuma H. , Ouchi T. , Ozawa S. , Ren J. R. , Saito T. , Saito T. Y. , Sakata M. , Sako T. K. , Sasaki T. , Shibata M. , Shiomi A. , Shirai T. , Sugimoto H. , Takita M. , Tan Y. H. , Tateyama N. , Torii S. , Tsuchiya H. , Udo S. , Wang B. , Wang H. , Wang X. , Wang Y. G. , Wu H. R. , Xue L. , Yamamoto Y. , Yan C. T. , Yang X. C. , Yasue S. , Ye Z. H. , Yu G. C. , Yuan A. F. , Yuda T. , Zhang H. M. , Zhang J. L. , Zhang N. J. , Zhang X. Y. , Zhang Y. , Zhang Yi , Zhaxisangzhu  , Zhou X. X.
Published: October 2006

The intensity of Galactic cosmic rays is nearly isotropic because of the influence of magnetic fields in the Milky Way. Here, we present two-dimensional high-precision anisotropy measurement for energies from a few to several hundred teraelectronvolts (TeV), using the large data sample of the Tibet Air Shower Arrays. Besides revealing finer details of the known anisotropies, a new component of Galactic cosmic ray anisotropy in sidereal time is uncovered around the Cygnus region direction. For cosmic-ray energies up to a few hundred TeV, all components of anisotropies fade away, showing a corotation of Galactic cosmic rays with the local Galactic magnetic environment. These results have broad implications for a comprehensive understanding of cosmic rays, supernovae, magnetic fields, and heliospheric and Galactic dynamic environments.
Molecular Imaging Using a Targeted Magnetic Resonance Hyperpolarized Biosensor
Authors: Schröder Leif , Lowery Thomas J. , Hilty Christian , Wemmer David E. , Pines Alexander
Published: October 2006

A magnetic resonance approach is presented that enables high-sensitivity, high-contrast molecular imaging by exploiting xenon biosensors. These sensors link xenon atoms to specific biomolecular targets, coupling the high sensitivity of hyperpolarized nuclei with the specificity of biochemical interactions. We demonstrated spatial resolution of a specific target protein in vitro at micromolar concentration, with a readout scheme that reduces the required acquisition time by >3300-fold relative to direct detection. This technique uses the signal of free hyperpolarized xenon to dramatically amplify the sensor signal via chemical exchange saturation transfer (CEST). Because it is ∼10,000 times more sensitive than previous CEST methods and other molecular magnetic resonance imaging techniques, it marks a critical step toward the application of xenon biosensors as selective contrast agents in biomedical applications.
Biotechnology and the Human Soul
Authors: Goldman Michael A.
Published: October 2006

Challenging Nature
. The Clash of Science and Spirituality at the New Frontiers of Life.
By Lee M. Silver
. Ecco (HarperCollins), New York, 2006. 460 pp. $26.95, C$34.95. ISBN 0-06-058267-7.

Proclaiming an unlimited promise for biotechnology, the author paints its varied critics as uniformly ignorant and blinded by spiritual beliefs.
Isolated Single-Cycle Attosecond Pulses
Authors: Sansone G. , Benedetti E. , Calegari F. , Vozzi C. , Avaldi L. , Flammini R. , Poletto L. , Villoresi P. , Altucci C. , Velotta R. , Stagira S. , De Silvestri S. , Nisoli M.
Published: October 2006

We generated single-cycle isolated attosecond pulses around ∼36 electron volts using phase-stabilized 5-femtosecond driving pulses with a modulated polarization state. Using a complete temporal characterization technique, we demonstrated the compression of the generated pulses for as low as 130 attoseconds, corresponding to less than 1.2 optical cycles. Numerical simulations of the generation process show that the carrier-envelope phase of the attosecond pulses is stable. The availability of single-cycle isolated attosecond pulses opens the way to a new regime in ultrafast physics, in which the strong-field electron dynamics in atoms and molecules is driven by the electric field of the attosecond pulses rather than by their intensity profile.
Dendritic Cell Stimulation by Mycobacterial Hsp70 Is Mediated Through CCR5
Authors: Floto R. Andres , MacAry Paul A. , Boname Jessica M. , Mien Tan Suet , Kampmann Beate , Hair James R. , Huey Oh Seen , Houben Edith N. G. , Pieters Jean , Day Cheryl , Oehlmann Wulf , Singh Mahavir , Smith Kenneth G. C. , Lehner Paul J.
Published: October 2006

An effective host immune response to mycobacterial infection must control pathogen dissemination without inducing immunopathology. Constitutive overexpression of mycobacterial heat shock protein (myHsp70) is associated with impaired bacterial persistence, but the immune-mediated mechanisms are unknown. We found that myHsp70, in addition to enhancing antigen delivery to human dendritic cells, signaled through the CCR5 chemokine receptor, promoting dendritic cell aggregation, immune synapse formation between dendritic cells and T cells, and the generation of effector immune responses. Thus, CCR5 acts as a pattern-recognition receptor for myHsp70, which may have implications for both the pathophysiology of tuberculosis and the use of myHsps in tumor-directed immunotherapy.
EFFECTIVE MASSES FOR DONOR BINDING ENERGIES IN QUANTUM WELL SYSTEMS
Authors: RAJASHABALA S. , NAVANEETHAKRISHNAN K.
Published: October 2006

The donor ionization energies in a quantum well and quantum dot with finite and infinite barriers are estimated for different well dimensions. Using the effective mass (EM) approximation, calculations are presented with constant effective mass and position dependent effective masses that are different for finite and infinite cases. Our results reduce to an approximate form used by X. H. Qi et al., Phys. Rev. B58 (1998) 10578 in the finite barrier model and that of L. E. Oliveira and L. M. Falicov, Phys. Rev. B34 (1986) 8676 in the infinite barrier case. Results are presented by taking the GaAs quantum well as an example. The use of constant effective mass of 0.067m0 is justified for well dimensions ≥a* where a* is an effective Bohr radius which is about 100 Å. While Qi et al. found a maximum of 22% variation in the binding energies due to mass variation, we obtained nearly 100% variation when mass variations are included correctly.
HEAD GESTURES, GAZE AND THE PRINCIPLES OF CONVERSATIONAL STRUCTURE
Authors: HEYLEN DIRK
Published: October 2006

Much of the work on embodied conversational agents is concerned with building computational models of nonverbal behaviors that can generate the right behavior in the appropriate context. In this paper, we discuss, from a linguistic and a conversation theoretic point of view, how nonverbal behaviors in conversations work. We look particularly at gaze and head movements. These play a variety of functions in face-to-face interactions. We show how these functions are structured by general principles governing cooperative actions and symbolic communication.
A DYNAMIC EMOTION REPRESENTATION MODEL WITHIN A FACIAL ANIMATION SYSTEM
Authors: TANGUY EMMANUEL , WILLIS PHILIP J. , BRYSON JOANNA J.
Published: October 2006

This paper presents the Dynamic Emotion Representation (DER), and demonstrates how an instance of this model can be integrated into a facial animation system. The DER model has been implemented to enable users to create their own emotion representation. Developers can select which emotions they include and how these interact. The instance of the DER model described in this paper is composed of three layers, each representing states changing over different time scales: behavior activations, emotions and moods. The design of this DER is discussed with reference to emotion theories and to the needs of a facial animation system. The DER is used in our Emotionally Expressive Facial Animation System (EE-FAS) to produce emotional expressions, to select facial signals corresponding to communicative functions in relation to the emotional state of the agent and also in relation to the comparison between the emotional state and the intended meanings expressed through communicative functions.
A PERCEPTUALLY-BASED THEORY OF MIND FOR AGENT INTERACTION INITIATION
Authors: PETERS CHRISTOPHER
Published: October 2006

We endow agents with the capability to open interactions based on their perception of the gaze and direction of attention of others in a virtual environment. The capability is geared towards the earliest part of interaction initiation, where agents may be at some distance from each other and may not initially have knowledge of each other's presence. An important idea in our work is that the start of interaction be initiated in a graceful manner involving exchanges of subtle cues before overt interaction commitments are made. Synthetic vision, attention and memory are used to implement the perceptually-based agent theory of mind. Theory of Mind is used to infer information about the intention of the other to interact based on their eye, head and body directions, locomotion and greeting gestures. An agent's interaction behavior is therefore driven not only by its interaction goal, but also by its theory of the goal of the other based on perception. We have implemented this system and used it to automate and evaluate social interaction behaviors between humans and agents in a virtual environment.
A STUDY IN USERS' PHYSIOLOGICAL RESPONSE TO AN EMPATHIC INTERFACE AGENT
Authors: PRENDINGER HELMUT , BECKER CHRISTIAN , ISHIZUKA MITSURU
Published: October 2006

This paper presents a novel method for evaluating the impact of animated interface agents with affective and empathic behavior. While previous studies relied on questionnaires in order to assess the user's overall experience with the interface agent, we will analyze users' physiological response (skin conductance and electromyography), which allows us to estimate affect-related user experiences on a moment-by-moment basis without interfering with the primary interaction task. As an interaction scenario, a card game has been implemented where the user plays against a virtual opponent. The findings of our study indicate that within a competitive gaming scenario, (i) the absence of the agent's display of negative emotions is conceived as arousing or stress-inducing, and (ii) the valence of users' emotional response is congruent with the valence of the emotion expressed by the agent. Our results for skin conductance could also be reproduced by assuming a local rather than a global baseline.
Density-Functional Theory for Complex Fluids
Authors: Wu Jianzhong , Li Zhidong
Published: October 2006

Density-functional theory (DFT) and its variations provide a fruitful approach to the computational modeling of the microscopic structures and phase behavior of soft-condensed matter. The methodology takes deep root in quantum mechanics but shares a mathematical similarity with a number of classical approaches in statistical mechanics. This review discusses different strategies commonly used to formulate the free-energy functional of complex fluids for either phenomena-oriented applications or as a generic description of the thermodynamic nonideality owing to various components of intermolecular forces. We emphasize the connections among different schemes of DFT approximations, their underlying assumptions, and inherent limitations. We also address extensions of equilibrium DFT to phenomenological theories for the dynamic properties of complex fluids and for the kinetics of phase transitions. In addition, we highlight the recent literature concerning applications of DFT to diverse static and time-dependent phenomena in complex fluids.
Species- and tissue-specific relationships between mitochondrial permeability transition and generation of ROS in brain and liver mitochondria of rats and mice
Authors: Panov Alexander , Dikalov Sergey , Shalbuyeva Natalia , Hemendinger Richelle , Greenamyre John T. , Rosenfeld Jeffrey
Published: October 2006

In animal models of neurodegenerative diseases pathological changes vary with the type of organ and species of the animals. We studied differences in the mitochondrial permeability transition (mPT) and reactive oxygen species (ROS) generation in the liver (LM) and brain (BM) of Sprague-Dawley rats and C57Bl mice. In the presence of ADP mouse LM and rat LM required three times less Ca2+ to initiate mPT than the corresponding BM. Mouse LM and BM sequestered 70% and 50% more Ca2+ phosphate than the rat LM and BM. MBM generated 50% more ROS with glutamate than the RBM, but not with succinate. With the NAD substrates, generation of ROS do not depend on the energy state of the BM. Organization of the respiratory complexes into the respirasome is a possible mechanism to prevent ROS generation in the BM. With BM oxidizing succinate, 80% of ROS generation was energy dependent. Induction of mPT does not affect ROS generation with NAD substrates and inhibit with succinate as a substrate. The relative insensitivity of the liver to systemic insults is associated with its high regenerative capacity. Neuronal cells with low regenerative capacity and a long life span protect themselves by minimizing ROS generation and by the ability to withstand very large Ca2+ insults. We suggest that additional factors, such as oxidative stress, are required to initiate neurodegeneration. Thus the observed differences in the Ca2+-induced mPT and ROS generation may underlie both the organ-specific and species-specific variability in the animal models of neurodegenerative diseases.
Contraction of insulin-resistant muscle normalizes insulin action in association with increased mitochondrial activity and fatty acid catabolism
Authors: Thyfault John P. , Cree Melanie G. , Zheng Donghai , Zwetsloot Jennifer J. , Tapscott Edward B. , Koves Timothy R. , Ilkayeva Olga , Wolfe Robert R. , Muoio Deborah M. , Dohm G. Lynis
Published: October 2006

Acute exercise can reverse muscle insulin resistance, but the mechanism(s) of action are unknown. With the use of a hindlimb perfusion model, we have found that acute contraction restores insulin-stimulated glucose uptake in muscle of obese Zucker rats to levels witnessed in lean controls. Previous reports have suggested that obesity-related insulin resistance stems from lipid oversupply and tissue accumulation of toxic lipid intermediates that impair insulin signaling. We reasoned that contraction might activate hydrolysis and oxidation of intramuscular lipids, thus alleviating “lipotoxicity” and priming the muscle for enhanced insulin action. Indeed, analysis of mitochondrial-derived acyl-carnitine esters suggested that contraction caused robust increases in β-oxidative flux and mitochondrial oxidation. As predicted, contraction decreased intramuscular triacylglycerol content; however, diacylglycerol and long chain acyl-CoAs, lipid intermediates presumed to trigger insulin resistance, were either unchanged or increased. In muscles from obese animals, insulin-stimulated tyrosine phosphorylation of the insulin receptor and insulin receptor substrate-1 remained impaired after contraction, whereas phosphorylation of the downstream signaling protein, AS160, was partially restored. These results suggest that acute exercise enables diabetic muscle to circumvent upstream defects in insulin signal transduction via mechanisms that are more tightly coupled to increased mitochondrial energy metabolism than the lowering of diacylglycerol and long chain acyl-CoA.
Regulation of Glutamate Release From Primary Afferents and Interneurons in the Spinal Cord by Muscarinic Receptor Subtypes
Authors: Zhang Hong-Mei , Chen Shao-Rui , Pan Hui-Lin
Published: October 2006

Activation of spinal muscarinic acetylcholine receptors (mAChRs) produces analgesia and inhibits dorsal horn neurons through potentiation of GABAergic/glycinergic tone and inhibition of glutamatergic input. To investigate the mAChR subtypes involved in the inhibitory effect of mAChR agonists on glutamate release, evoked excitatory postsynaptic currents (eEPSCs) were recorded in lamina II neurons using whole cell recordings in rat spinal cord slices. The nonselective mAChR agonist oxotremorine-M concentration-dependently inhibited the monosynaptic and polysynaptic EPSCs elicited by dorsal root stimulation. Interestingly, oxotromorine-M caused a greater inhibition of polysynaptic EPSCs (64.7%) than that of monosynaptic EPSCs (27.9%). In rats pretreated with intrathecal pertussis toxin, oxotremorine-M failed to decrease monosynaptic EPSCs but still partially inhibited the polysynaptic EPSCs in some neurons. This remaining effect was blocked by a relatively selective M3antagonist 4-DAMP. Himbacine, an M2/M4antagonist, or AFDX-116, a selective M2antagonist, completely blocked the inhibitory effect of oxotremorine-M on monosynaptic EPSCs. However, the specific M4antagonist MT-3 did not alter the effect of oxotremorine-M on monosynaptic EPSCs. Himbacine also partially attenuated the effect of oxotremorine-M on polysynaptic EPSCs in some cells and this effect was abolished by 4-DAMP. Furthermore, oxotremorine-M significantly decreased spontaneous EPSCs in seven of 22 (31.8%) neurons, an effect that was blocked by 4-DAMP. This study provides new information that the M2mAChRs play a critical role in the control of glutamatergic input from primary afferents to dorsal horn neurons. The M3and M2/M4subtypes on a subpopulation of interneurons are important for regulation of glutamate release from interneurons in the spinal dorsal horn.