bluuebunny/crossref_metadata_2025 huggingface dataset:
Contact Behavior of Surfaces Containing Elliptical Asperities With Gaussian and Non-Gaussian Height Distributions
Authors: Jeng Yeau-Ren , Peng Shin-Rung
Published: September 2007

This study investigates the effects of asperity interactions on the mean surface separation and real contact area of rough surfaces containing elliptical asperities with Gaussian and non-Gaussian height distributions. The elastic-plastic contact behavior of surfaces with elliptical asperities with both single-mode and bimodal height distributions are studied. The results indicate that the effects of asperity interactions become more pronounced as the effective radius ratio of the asperities increases. The findings also reveal that the real contact load, the real contact area, and the surface contact mode observed for elliptical asperities are significantly different from those noted for spherical asperities. Furthermore, it is found that the form of the non-Gaussian height distribution has a significant effect on the contact mode of rough surfaces. Specifically, the contact mode of surfaces with a negatively skewed height distribution is found to be more elastic than that of surfaces with a Gaussian height distribution.
Static Friction Experiments and Verification of an Improved Elastic-Plastic Model Including Roughness Effects
Authors: Lee Chul-Hee , Polycarpou Andreas A.
Published: September 2007

An experimental study was conducted to measure the static friction coefficient under constant normal load and different interface conditions. These include surface roughness, dwell time, displacement rate, as well as the presence of traces of lubricant and wear debris at the interface. The static friction apparatus includes accurate measurement of friction, normal and lateral forces at the interface (using a high dynamic bandwidth piezoelectric force transducer), as well as precise motion control and measurement of the sliding mass. The experimental results show that dry surfaces are more dependent on the displacement rate prior to sliding inception compared to boundary lubricated surfaces in terms of static friction coefficient. Also, the presence of wear debris, boundary lubrication, and rougher surfaces decrease the static friction coefficient significantly compared to dry smooth surfaces. The experimental measurements under dry unlubricated conditions were subsequently compared to an improved elastic-plastic static friction model, and it was found that the model captures the experimental measurements of dry surfaces well in terms of the surface roughness.
A Three-Dimensional Semianalytical Model for Elastic-Plastic Sliding Contacts
Authors: Nélias Daniel , Antaluca Eduard , Boucly Vincent , Cretu Spiridon
Published: September 2007

A three-dimensional numerical model based on a semianalytical method in the framework of small strains and small displacements is presented for solving an elastic-plastic contact with surface traction. A Coulomb’s law is assumed for the friction, as commonly used for sliding contacts. The effects of the contact pressure distribution and residual strain on the geometry of the contacting surfaces are derived from Betti’s reciprocal theorem with initial strain. The main advantage of this approach over the classical finite element method (FEM) is the computing time, which is reduced by several orders of magnitude. The contact problem, which is one of the most time-consuming procedures in the elastic-plastic algorithm, is obtained using a method based on the variational principle and accelerated by means of the discrete convolution fast Fourier transform (FFT) and conjugate gradient methods. The FFT technique is also involved in the calculation of internal strains and stresses. A return-mapping algorithm with an elastic predictor∕plastic corrector scheme and a von Mises criterion is used in the plasticity loop. The model is first validated by comparison with results obtained by the FEM. The effect of the friction coefficient on the contact pressure distribution, subsurface stress field, and residual strains is also presented and discussed.
An Elliptical Elastic-Plastic Microcontact Model Developed for an Ellipsoid in Contact With a Smooth Rigid Flat
Authors: Lin Li Po , Lin Jen Fin
Published: September 2007

The determination of the elastoplastic deformation regime arising at the microcontact of a deformable ellipsoid and a rigid smooth flat was the main purpose of this study. One-eighth of an ellipsoid and a flat plate were taken as the contact bodies in the finite element analysis, and a mesh scheme of multisize elements was applied. Two observed phenomena regarding the contact pressures and the equivalent von Mises stresses formed at the contact area are given in order to identify the inception of the fully plastic deformation regime of an ellipsoid with an ellipticity ke. If the ellipticity (k) of an elliptical contact area is defined as the length ratio of the minor axis to the major axis, it is asymptotic to the ke value when the interference is sufficiently increased, irrespective of the ke value. The dimensionless interference regime associated with the elastoplastic deformation regime is narrowed by increasing the ellipticity of the ellipsoid (ke). Significant differences in the microcontact parameters such as the contact pressure, the contact area, and the contact load were found to be a function of the interference and the ke parameter of an ellipsoid. The interferences corresponding to the inceptions of the elastoplastic and fully plastic deformation regimes are both increased if the ke value is lowered. The interference, the contact area, and the contact load predicted by the present model for the behavior demonstrated at the inception of the elastoplastic deformation regime are lower than those obtained from the Horng model (Horng, J. H., 1998, “An Elliptical Elastic-Plastic Asperity Microcontact Model for Rough Surfaces,” ASME J. Tribol., 120, pp. 82–88) and the Jeng-Wang model (Jeng, Y. R., and Wang, P. Y., 2003, “An Elliptical Microcontact Model Considering Elastic, Elastoplastic, and Plastic Deformation,” ASME J. Tribol., 125, pp. 232–240). Big differences in the results of the average contact pressure, the contact area, and the contact load among the above microcontact models are discussed. The discrepancies are also explained from the developments of these models and boundary conditions set for the elastoplastic deformation regime.
Effects of Surface Roughness on Sliding Friction in Lubricated-Point Contacts: Experimental and Numerical Studies
Authors: Wang Shun , Hu Yuan-zhong , Wang Wen-zhong , Wang Hui
Published: September 2007

The objective of the present work is to investigate experimentally and numerically the influences of surface roughness, produced by typical machining processes, on friction performances in lubricated-point contacts. Prior to the full experimental investigation, a series of tests had been conducted to examine the experimental errors, resulting from repeated tests on the same specimen but at different tracks, with different amounts of lubricant supply, or after the sample reinstallation. Then, the effects of amplitude and texture of surface roughness on friction behavior are investigated in rotational and reciprocal-mode tests, respectively. The measured friction, averaged over the repeated tests and plotted as a function of sliding speed, shows Stribeck-type curves, which manifest the transition from full-film, mixed, to boundary lubrication. Results show that the roughness amplitude imposes a strong influence on the magnificence of friction and the route of lubrication transition. It is also observed that transverse roughness would give rise to a smaller friction coefficient than the longitudinal one under the same operating conditions. Moreover, the deterministic numerical solution of mixed lubrication has been extended to evaluate friction between rough surfaces over a wide range of lubrication regimes. The numerical simulation results are compared and agree very well with experiments.
Annular Component Transient Thermoelastic Analysis Using a State Space Approach
Authors: Yong Woon Yik , Keogh Patrick S.
Published: September 2007

Annular components are used widely in engineering systems and include bearing bushes and races, which may be exposed to extreme operating conditions. A method to establish the localized transient thermoelastic deformation of a homogeneous two-dimensional annular component is developed. The analysis is based on solving the thermoelasticity equations using a state space formulation for the Fourier components of the radial and tangential displacements. Two boundary conditions are considered, namely, rigid and resiliently mounted outer boundaries, both associated with stress free inner boundary conditions. The thermoelastic solution is then demonstrated for a transient temperature distribution induced by inner boundary frictional heating due to rotor contact, which is derived from a dynamic Hertzian pressure distribution. The application is to a relatively short auxiliary bearing for which a state of plane stress is appropriate. However, the thermoelastic analysis is generalized to cover cases of plane strain and plane stress.
Friction Coefficient as a Macroscopic View of Local Dissipation
Authors: Richard D. , Iordanoff I. , Berthier Y. , Renouf M. , Fillot N.
Published: September 2007

This paper presents an overview of a discrete element method approach to dry friction in the presence of a third body. Three dimensional computer simulations have been carried out to show the influence of the third body properties (and more specifically their adhesion) on friction coefficient and profiles of dissipated power. Simple interaction laws and a cohesive contact are set up to uncouple the key parameters governing the contact rheology. The model is validated through a global energy balance. As it is shown that dynamic friction coefficient can be explained only in terms of local energy dissipation, this work also emphasizes the fact that mechanism effects and third body rheology have important consequences on the energy generation and dissipation field. Therefore, asymmetries can arise and the surface temperature of first bodies can be significantly different even for the same global friction coefficient value. Such investigations highlight the fact that friction coefficient cannot be considered in the same way at the mechanism scale as at the contact scale where the third body plays a non-negligible role, although it has been neglected for years in thermal approaches to study of surfaces in contact.
Thermoelastohydrodynamic Behavior of Mechanical Gas Face Seals Operating at High Pressure
Authors: Thomas Sébastien , Brunetière Noël , Tournerie Bernard
Published: September 2007

A numerical modeling of thermoelastohydrodynamic mechanical face seal behavior is presented. The model is an axisymmetric one and it is confined to high pressure compressible flow. It takes into account the behavior of a real gas and includes thermal and inertia effects, as well as a choked flow condition. In addition, heat transfer between the fluid film and the seal faces is computed, as are the elastic and thermal distortions of the rings. In the first part of this paper, the influence of the coning angle on mechanical face seal characteristics is studied. In the second part, the influence of the solid distortions is analyzed. It is shown that face distortions strongly modify both the gap geometry and the mechanical face seal’s performance. The mechanical distortions lead to a converging gap, while the gas expansion, by cooling the fluid, creates a diverging gap.
The Impact of the Cavitation Model in the Analysis of Microtextured Lubricated Journal Bearings
Authors: Ausas Roberto , Ragot Patrick , Leiva Jorge , Jai Mohammed , Bayada Guy , Buscaglia Gustavo C.
Published: September 2007

In this paper, we analyze the impact of the cavitation model on the numerical assessment of lubricated journal bearings. We compare results using the classical Reynolds model and the so-called p-θ model proposed by Elrod and Adams [1974, “A Computer Program for Cavitation and Saturation Problems,” Proceedings of the First LEEDS-LYON Symposium on Cavitation and Related Phenomena in Lubrication, Leeds, UK] to fix the lack of mass conservation of Reynolds’ model. Both models are known to give quite similar predictions of load-carrying capacity and friction torque in nonstarved conditions, making Reynolds’ model the preferred model for its better numerical behavior. Here, we report on numerical comparisons of both models in the presence of microtextured bearing surfaces. We show that in the microtextured situation, Reynolds’ model largely underestimates the cavitated area, leading to inaccuracies in the estimation of several variables, such as the friction torque. This dictates that only mass-conserving models should be used when dealing with microtextured bearings.
The Influence of Injection Pockets on the Performance of Tilting-Pad Thrust Bearings—Part II: Comparison Between Theory and Experiment
Authors: Heinrichson Niels , Fuerst Axel , Santos Ilmar Ferreira
Published: September 2007

This is Part II of a two-part series of papers describing the effects of high-pressure injection pockets on the operating conditions of tilting-pad thrust bearings. The paper has two main objectives. One is an experimental investigation of the influence of an oil injection pocket on the pressure distribution and oil film thickness. Two situations are analyzed: (i) when the high-pressure oil injection is turned off and (ii) when the high-pressure injection is turned on. The other objective is to validate a numerical model with respect to its ability to predict the influence of such a pocket (with and without oil injection) on the pressure distribution and oil film thickness. Measurements of the distribution of pressure and oil film thickness are presented for tilting-pad thrust bearing pads of ∼100cm2 surface area. Two pads are measured in a laboratory test rig at loads of ∼1.5MPa and ∼4.0MPa and velocities of up to 33m∕s. One pad has a plain surface. The other pad has a conical injection pocket at the pivot point and a leading-edge taper. The measurements are compared to theoretical values obtained using a three-dimensional thermoelastohydrodynamic (TEHD) numerical model. At the low load, the theoretical pressure distribution corresponds well with the measured values for both pads, although the influence of the pocket is slightly underestimated. At the high load, large discrepancies exist for the pad with an injection pocket. It is argued that the discrepancies are due mainly to geometric inaccuracies of the collar surface, although they may to some extent be due to the simplifications employed in a Reynolds equation description of the pocket flow. The measured and theoretical values of oil film thickness compare well at low loads and velocities. At high loads and velocities, discrepancies grow to up to 25%. This is due to the accuracy of the measurements. When using hydrostatic jacking the model predicts the start-up behavior well.
Impact of Surfactant Structure on the Tribological Properties of Bentonite-Based Greases
Authors: Pogosian A. K. , Martirosyan T. R.
Published: September 2007

The development of new types of high-pressure plastic lubricants using natural minerals is of much importance. The effects of surfactant proportion and the structure of the nanoparticle thickener surface on the tribological properties of the bentonite-based grease were studied. The plastic lubricants that provide the best anti-friction and anti-wear properties were revealed to be the one that is modified by quaternary amine and urotropine-type ammonium salts. The surface ratio of bentonite particles modified by quaternary ammonium salts, which results in composite with the best tribological properties, was also revealed.
Investigation of the Tribological Properties of Surfactant-Modified MoS2 Microsized Spheres in Base Oil 500 SN
Authors: Fu Xun , Zhou Xiaodong , Shi Huaqiang , Wu Danmei , Hu Zhengshui
Published: September 2007

The tribological properties of MoS2 microsized spheres (MS-MoS2) with diameter of 0.5–3μm modified by self-prepared surfactant quaternary ammonium salt of 2-undecyl-1-dithioureido-ethyl-imidazoline (SUDEI) as an additive in base oil 500 SN were investigated and compared with those of commercial colloidal MoS2(CC-MoS2) on a four-ball tester and an Optimol SRV oscillating friction and wear tester in a ball-on-disk contact configuration. The worn surfaces of the bottom flat disk were examined with scanning electron microscopy and X-ray photoelectron spectroscopy. It was found that the MoS2 microsized spheres product was a much better extreme-pressure additive and antiwear and friction-reduction additive in 500 SN than commercial colloidal MoS2(CC-MoS2). Under the appropriate concentration of 0.1% and 0.25% for MS-MoS2 and CC-MoS2 and the load of 400N, the friction coefficient of MS-MoS2/oil and CC-MoS2/oil decreased about 25.0% and 12.5% and the wear volume loss decreased about 50.4% and 12.9% compared with the pure base stock. The boundary lubrication mechanism could be deduced as the effective chemical adsorption film formed by the long chain alkyl (C11H23) and active elements (S and N) in the surfactant SUDEI and tribochemical reaction film composed of the tribochemical reaction products.
A Modeling Approach for Predicting the Abrasive Particle Motion During Chemical Mechanical Polishing
Authors: Terrell Elon J. , Higgs III C. Fred
Published: September 2007

Chemical mechanical polishing (CMP) is a manufacturing process in which a wafer surface is polished by pressing it against a rotating pad that is flooded with slurry. The slurry itself is a fluid containing abrasive particles. Past experimentation has shown that the distribution of suspended particles in the slurry is significantly related to the distribution of material removal on the wafer during CMP. Therefore, this study involves the development and simulation of a model that predicts the kinematics and trajectory of the abrasive particles. The simulation results compare well to data from shear cell experiments data conducted by other researchers.
Ultra Mild Wear in Lubricated Tribology of an Aluminium Alloy
Authors: Das Sarmistha , Varalakshmi K. , Jayaram V. , Biswas S. K.
Published: September 2007

Flat faces of steel pins were slid on an eutectic aluminium silicon alloy under lubricated condition in the 1–100MPa mean contact pressure range and 0.2m∕s sliding speed. Two transition in wear rate were observed, at 10MPa and 70MPa. The wear rate in the 1–10MPa regime was found to be very small and within the measuring instrument resolution and also insensitive to contact pressure. The regime is designated ultramild wear. Lack of plastic flow, minimal fragmentation of silicon particles, and the presence of undistorted voids on the fractured and unfractured silicon particles in the subsurface suggest that the state of stress in the near surface region is elastic. Contact mechanical calculations demonstrate that at contact pressures <13.7MPa, the system is likely to shakedown to an elastic state.
Determination of the Fractal Scaling Parameter From Simulated
Fractal-Regular Surface Profiles Based on the Weierstrass-Mandelbrot
Function
Authors: Wang Shao , Shen Ji , Kin Chan Wai
Published: September 2007

A fractal dimension and a fractal roughness parameter are usually used to characterize a fractal surface. For a fractal-regular surface, a fractal domain length is also included. Such a formulation is based on an approximation using a constant value of the fractal scaling parameter that represents the ratio of the spatial frequencies of adjacent harmonic components in the Weierstrass–Mandelbrot (W-M) function. Although there were some reasons for assuming a constant value of 1.5 for the fractal scaling parameter, it is still left more or less arbitrary to adopt this assumption in fractal modeling of solid contact. In the present study, the fractal scaling parameter was treated as a variable rather than a constant by using a form of the W-M function with randomized phases based on a random walk formulation. A simple numerical scheme with clear graphical interpretation was developed to determine the value of the fractal scaling parameter. The fractal dimension, fractal roughness parameter, and fractal scaling parameter were all recovered with reasonable accuracy from numerically generated surface profiles.
Evaluation on Applicability of Reynolds Equation for Squared Transverse Roughness Compared to CFD
Authors: Li Jiang , Chen Haosheng
Published: September 2007

A discrete probability distribution function is used to represent the squared transverse roughness effect in a modified Reynolds equation, and the Reynolds equation is used to calculate the hydrodynamic lubrication in a slider-disk interface compared to the CFD method. When the roughness height is below 1% of the film thickness, the results acquired by the two methods are the same and the surface roughness does not show obvious effect on the lubrication results compared to that on the smooth surface. The load capacity and friction force increase as the roughness height increases when the roughness height exceeds 1% of the film thickness. Moreover, the forces acquired by Reynolds equations are smaller than those acquired by CFD, and the difference between them exceeds 10% when the roughness height is higher than 10% of the film thickness. Sidewall effect is considered to be the main reason for the difference, and the Reynolds equation is believed not suitable for calculating the effect of the squared transverse roughness in the hydrodynamic lubrication.
Effect of Lubrication Status of Bearing on Crankshaft Strength
Authors: Sun Jun , Gui Changlin
Published: September 2007

There is direct interaction between crankshaft and bearing in an internal combustion engine. The effect of lubrication status of bearing was not considered in the present calculation of crankshaft strength. A given oil film pressure distribution of bearing was generally used as load acted on journal. In this paper, a crankshaft-bearing system was taken as the study object. On the basis of lubrication analysis of misaligned bearing caused by crankshaft deformation, the stress and strength of-crankshaft were calculated using analytical oil film pressure of bearing as the load boundary condition. Crankshaft deformation and bearing load were calculated by whole crankshaft beam-element method. The lubrication of crankshaft bearing was analyzed by the kinetics method. Crankshaft stress was calculated by the finite-element method. The results show that when the effect of crankshaft deformation under load is considered, the offset distribution of oil film pressure of bearing appears and the highest oil film pressure increases remarkably, which result in the stresses of local area on fillet surface of crankshaft journal increase obviously and the safety factor of crankshaft decreases.
Acoustic Emission and Specific Film Thickness for Operating Spur Gears
Authors: Raja Hamzah R. I. , Mba D.
Published: September 2007

This paper presents experimental results correlating acoustic emission (AE) activity and the specific film thickness (λ) for operational spur gears. This relationship was established by spraying liquid nitrogen onto a rotating gear wheel, thereby reducing its operating temperature and controlling the specific film thickness for a range of load and speed conditions. It is concluded that the level of AE activity is dependent on the specific film thickness and the source of AE during meshing is predominately due to asperity contact. Furthermore, measurements of AE activity may offer an opportunity to quantify the level of asperity contact for meshing gears under a range of operating conditions.
A New Bypass Magnetorheological Fluid Damper
Authors: Hitchcock Gregory H. , Wang Xiaojie , Gordaninejad Faramarz
Published: September 2007

This study presents theoretical and experimental investigations of a novel external bypass, fail-safe, magnetorheological fluid (MRF) damper. A fail-safe MRF damper is referred to as a device that retains a minimum required damping capacity in the event of a power supply or electronic system failure. The new MRF device has a simple design, is compact, is capable of generating a considerable dynamic force range, and can be sized for specific vibration control applications. The theoretical formulation is developed based on the Herschel–Bulkley constitutive model for an annular flow. Experimental results are obtained to demonstrate the validity of the theoretical analysis.
Identification of Structural Stiffness and Damping Coefficients of a Shoed-Brush Seal
Authors: Delgado Adolfo , Andrés Luis San
Published: September 2007

The multiple-shoe brush seal, a variation of a standard brush seal, accommodates arcuate pads at the bristles’ free ends. This novel design allows reverse shaft rotation operation and reduces and even eliminates bristle wear, since the pads lift-off due to the generation of a hydrodynamic film during rotor spinning. This type of seal, able to work at both cold and high temperatures, not only restricts secondary leakage but also acts as an effective vibration damper. The dynamic operation of the shoed-brush seals, along with the validation of reliable predictive tools, relies on the appropriate estimation of the seal structural stiffness and energy dissipation features. Single-frequency external load tests conducted on a controlled motion test rig and without shaft rotation allow the identification (measurement) of the structural stiffness and equivalent damping of a 20-pad brush seal, 153mm in diameter. The seal energy dissipation mechanism, represented by a structural loss factor and a dry friction coefficient, characterizes the energy dissipated by the bristles and the dry friction interaction of the brush seal bristles rubbing against each other. The physical model used reproduces well the measured system motions, even for frequencies well above the identification range.
On the Fundamental Transverse Vibration Frequency of a Free-Free Thin Beam With Identical End Masses
Authors: Erturk A. , Inman D. J.
Published: September 2007

Current research in vibration-based energy harvesting and in microelectromechanical system technology has focused renewed attention on the vibration of beams with end masses. This paper shows that the commonly accepted and frequently quoted fundamental natural frequency formula for a beam with identical end masses is incorrect. It is also shown that the higher mode frequency expressions suggested in the referred work (Haener, J., 1958, “Formulas for the Frequencies Including Higher Frequencies of Uniform Cantilever and Free-Free Beams With Additional Masses at the Ends,” ASME J. Appl. Mech. 25, pp. 412) are also incorrect. The correct characteristic (frequency) equation is derived and nondimensional comparisons are made between the results of the previously published formula and the corrected formulation using Euler–Bernoulli beam assumptions. The previous formula is shown to be accurate only for the extreme case of very large end mass to beam mass ratios. Curve fitting is used to report alternative first order and second order polynomial ratio expressions for the first natural frequency, as well as for the frequencies of some higher modes.
Effects of Randomness on Band Gap Formation in Models of Fiber-Reinforced Composite Panels Having Quasirandom Fiber Arrangements
Authors: Cai Liang-Wu , Patil Shashidhar
Published: September 2007

Large-scale deterministic simulations are performed in order to observe the band gap formation in composite models having quasirandom fiber arrangements. Unidirectional fiber-reinforced composite panels are modeled in two-dimensional space with quasirandom fiber arrangements that can be qualified as “essentially regular with slight randomness.” Different quasirandom fiber arrangements are computationally generated using the same control parameters. Statistical parameters are used to quantitatively describe the fiber arrangements. Subsequently, a series of arrangements is generated from each base line arrangement by scaling up the coordinates of fiber centers, while the fiber diameter remains unchanged in order to study the effects of fiber spacing. Simulation results are compared with the corresponding case of ideally regular fiber arrangement. The most interesting observation is that the slight randomness in the fiber arrangements enhances the band gap phenomenon by introducing a few secondary band gaps adjacent to the primary band gap.
Circuits with Light at Nanoscales: Optical Nanocircuits Inspired by Metamaterials
Authors: Engheta Nader
Published: September 2007

A form of optical circuitry is overviewed in which a tapestry of subwavelength nanometer-scale metamaterial structures and nanoparticles may provide a mechanism for tailoring, patterning, and manipulating local optical electric fields and electric displacement vectors in a subwavelength domain, leading to the possibility of optical information processing at the nanometer scale. By exploiting the optical properties of metamaterials, these nanoparticles may play the role of “lumped” nanocircuit elements such as nanoinductors, nanocapacitors, and nanoresistors, analogous to microelectronics. I show that this concept of metamaterial-inspired nanoelectronics (“metactronics”) can bring the tools and mathematical machinery of the circuit theory into optics, may link the fields of optics, electronics, plasmonics, and metamaterials, and may provide road maps to future innovations in nanoscale optical devices, components, and more intricate nanoscale metamaterials.
Comment on "Organics Captured from Comet 81P/Wild 2 by the Stardust Spacecraft"
Authors: Spencer Maegan K. , Zare Richard N.
Published: September 2007

Sandford
et al
. (Reports, 15 December 2006, p. 1720) reported on organic compounds captured from Comet 81P/Wild 2 by the Stardust spacecraft. We emphasize the difficulty in assigning the origin of compounds detected diffusely along particle impact tracks and show that rapid heating of aerogel that has never been exposed to cometary particle capture can generate complex aromatic molecules from low-mass carbon impurities present in the aerogel.
A Classic Reconfigured
Authors: Laurel Brenda , Tow Rob
Published: September 2007

Human-Machine Reconfigurations
.
Plans and Situated Actions
. 2nd ed.
By Lucy A. Suchman
. Cambridge University Press, Cambridge, 2007. 326 pp. $80. ISBN 9780521858915. Paper, $29.99. ISBN 9780521675888.

The author provides a revision and extension of Plans and Situated Actions (1987), her groundbreaking anthropological analysis of interactions between humans and computers.
Athabasca Valles, Mars: A Lava-Draped Channel System
Authors: Jaeger W. L. , Keszthelyi L. P. , McEwen A. S. , Dundas C. M. , Russell P. S.
Published: September 2007

Athabasca Valles is a young outflow channel system on Mars that may have been carved by catastrophic water floods. However, images acquired by the High-Resolution Imaging Science Experiment camera onboard the Mars Reconnaissance Orbiter spacecraft reveal that Athabasca Valles is now entirely draped by a thin layer of solidified lava—the remnant of a once-swollen river of molten rock. The lava erupted from a fissure, inundated the channels, and drained downstream in geologically recent times. Purported ice features in Athabasca Valles and its distal basin, Cerberus Palus, are actually composed of this lava. Similar volcanic processes may have operated in other ostensibly fluvial channels, which could explain in part why the landers sent to investigate sites of ancient flooding on Mars have predominantly found lava at the surface instead.
Meter-Scale Morphology of the North Polar Region of Mars
Authors: Herkenhoff K. E. , Byrne S. , Russell P. S. , Fishbaugh K. E. , McEwen A. S.
Published: September 2007

Mars' north pole is covered by a dome of layered ice deposits. Detailed (∼30 centimeters per pixel) images of this region were obtained with the High-Resolution Imaging Science Experiment on board the Mars Reconnaissance Orbiter (MRO). Planum Boreum basal unit scarps reveal cross-bedding and show evidence for recent mass wasting, flow, and debris accumulation. The north polar layers themselves are as thin as 10 centimeters but appear to be covered by a dusty veneer in places, which may obscure thinner layers. Repetition of particular layer types implies that quasi-periodic climate changes influenced the stratigraphic sequence in the polar layered deposits, informing models for recent climate variations on Mars.
Accumulation and Erosion of Mars' South Polar Layered Deposits
Authors: Seu Roberto , Phillips Roger J. , Alberti Giovanni , Biccari Daniela , Bonaventura Francesco , Bortone Marco , Calabrese Diego , Campbell Bruce A. , Cartacci Marco , Carter Lynn M. , Catallo Claudio , Croce Anna , Croci Renato , Cutigni Marco , Placido Antonio Di , Dinardo Salvatore , Federico Costanzo , Flamini Enrico , Fois Franco , Frigeri Alessandro , Fuga Oreste , Giacomoni Emanuele , Gim Yonggyu , Guelfi Mauro , Holt John W. , Kofman Wlodek , Leuschen Carlton J. , Marinangeli Lucia , Marras Paolo , Masdea Arturo , Mattei Stefania , Mecozzi Riccardo , Milkovich Sarah M. , Morlupi Antonio , Mouginot Jeremie , Orosei Roberto , Papa Claudio , Paterno Tobia , del Marmo Paolo Persi , Pettinelli Elena , Pica Giulia , Picardi Giovanni , Plaut Jeffrey J. , Provenziani Marco , Putzig Nathaniel E. , Russo Federica , Safaeinili Ali , Salzillo Giuseppe , Santovito Maria Rosaria , Smrekar Suzanne E. , Tattarletti Barbara , Vicari Danilo
Published: September 2007

Mars' polar regions are covered with ice-rich layered deposits that potentially contain a record of climate variations. The sounding radar SHARAD on the Mars Reconnaissance Orbiter mapped detailed subsurface stratigraphy in the Promethei Lingula region of the south polar plateau, Planum Australe. Radar reflections interpreted as layers are correlated across adjacent orbits and are continuous for up to 150 kilometers along spacecraft orbital tracks. The reflectors are often separated into discrete reflector sequences, and strong echoes are seen as deep as 1 kilometer. In some cases, the sequences are dipping with respect to each other, suggesting an interdepositional period of erosion. In Australe Sulci, layers are exhumed, indicating recent erosion.
Spin Transition Zone in Earth's Lower Mantle
Authors: Lin Jung-Fu , Vankó György , Jacobsen Steven D. , Iota Valentin , Struzhkin Viktor V. , Prakapenka Vitali B. , Kuznetsov Alexei , Yoo Choong-Shik
Published: September 2007

Mineral properties in Earth's lower mantle are affected by iron electronic states, but representative pressures and temperatures have not yet been probed. Spin states of iron in lower-mantle ferropericlase have been measured up to 95 gigapascals and 2000 kelvin with x-ray emission in a laser-heated diamond cell. A gradual spin transition of iron occurs over a pressure-temperature range extending from about 1000 kilometers in depth and 1900 kelvin to 2200 kilometers and 2300 kelvin in the lower mantle. Because low-spin ferropericlase exhibits higher density and faster sound velocities relative to the high-spin ferropericlase, the observed increase in low-spin (Mg,Fe)O at mid-lower mantle conditions would manifest seismically as a lower-mantle spin transition zone characterized by a steeper-than-normal density gradient.
Universality Classes for Domain Wall Motion in the Ferromagnetic Semiconductor (Ga,Mn)As
Authors: Yamanouchi M. , Ieda J. , Matsukura F. , Barnes S. E. , Maekawa S. , Ohno H.
Published: September 2007

Magnetic domain wall motion induced by magnetic fields and spin-polarized electrical currents is experimentally well established. A full understanding of the underlying mechanisms, however, remains elusive. For the ferromagnetic semiconductor (Ga,Mn)As, we have measured and compared such motions in the thermally activated subthreshold, or “creep,” regime, where the velocity obeys an Arrhenius scaling law. Within this law, the clearly different exponents of the current and field reflect different universality classes, showing that the drive mechanisms are fundamentally different.
Dynamic Visualization of Thrombopoiesis Within Bone Marrow
Authors: Junt Tobias , Schulze Harald , Chen Zhao , Massberg Steffen , Goerge Tobias , Krueger Andreas , Wagner Denisa D. , Graf Thomas , Italiano Joseph E. , Shivdasani Ramesh A. , von Andrian Ulrich H.
Published: September 2007

Platelets are generated from megakaryocytes (MKs) in mammalian bone marrow (BM) by mechanisms that remain poorly understood. Here we describe the use of multiphoton intravital microscopy in intact BM to visualize platelet generation in mice. MKs were observed as sessile cells that extended dynamic proplatelet-like protrusions into microvessels. These intravascular extensions appeared to be sheared from their transendothelial stems by flowing blood, resulting in the appearance of proplatelets in peripheral blood. In vitro, proplatelet production from differentiating MKs was enhanced by fluid shear. These results confirm the concept of proplatelet formation in vivo and are consistent with the possibility that blood flow–induced hydrodynamic shear stress is a biophysical determinant of thrombopoiesis.
Free-Solution, Label-Free Molecular Interactions Studied by Back-Scattering Interferometry
Authors: Bornhop Darryl J. , Latham Joey C. , Kussrow Amanda , Markov Dmitry A. , Jones Richard D. , Sørensen Henrik S.
Published: September 2007

Free-solution, label-free molecular interactions were investigated with back-scattering interferometry in a simple optical train composed of a helium-neon laser, a microfluidic channel, and a position sensor. Molecular binding interactions between proteins, ions and protein, and small molecules and protein, were determined with high dynamic range dissociation constants (
K
d
spanning six decades) and unmatched sensitivity (picomolar
K
d
's and detection limits of 10,000s of molecules). With this technique, equilibrium dissociation constants were quantified for protein A and immunoglobulin G, interleukin-2 with its monoclonal antibody, and calmodulin with calcium ion Ca
2+
, a small molecule inhibitor, the protein calcineurin, and the M13 peptide. The high sensitivity of back-scattering interferometry and small volumes of microfluidics allowed the entire calmodulin assay to be performed with 200 picomoles of solute.
Asymmetric Catalysis of the Transannular Diels-Alder Reaction
Authors: Balskus Emily P. , Jacobsen Eric N.
Published: September 2007

Transannular chemical reactions are unparalleled in their ability to generate high degrees of stereochemical and architectural complexity in a single transformation. However, the successful application of this approach in synthesis depends on the ability to predict and control the outcome of the transannular reaction. Use of a chiral catalyst in this context represents an attractive, yet unused, strategy. This report describes a catalytic, asymmetric transannnular Diels-Alder (TADA) reaction that affords polycyclic products in high enantiomeric excess. This catalyst system can also alter the inherent diastereoselectivity of cyclizations with substrates containing chiral centers. Additionally, the catalytic enantioselective TADA has been used as the key step in a total synthesis of the sesquiterpene 11,12-diacetoxydrimane; this route may provide a general approach to the polycyclic carbon framework shared by many terpene natural products.
Density of Mars' South Polar Layered Deposits
Authors: Zuber Maria T. , Phillips Roger J. , Andrews-Hanna Jeffrey C. , Asmar Sami W. , Konopliv Alexander S. , Lemoine Frank G. , Plaut Jeffrey J. , Smith David E. , Smrekar Suzanne E.
Published: September 2007

Both poles of Mars are hidden beneath caps of layered ice. We calculated the density of the south polar layered deposits by combining the gravity field obtained from initial results of radio tracking of the Mars Reconnaissance Orbiter with existing surface topography from the Mars Orbiter Laser Altimeter on the Mars Global Surveyor spacecraft and basal topography from the Mars Advanced Radar for Subsurface and Ionospheric Sounding on the Mars Express spacecraft. The results indicate a best-fit density of 1220 kilograms per cubic meter, which is consistent with water ice that has ∼15% admixed dust. The results demonstrate that the deposits are probably composed of relatively clean water ice and also refine the martian surface-water inventory.
The Primitive Wrist of
Homo floresiensis
and Its Implications for Hominin Evolution
Authors: Tocheri Matthew W. , Orr Caley M. , Larson Susan G. , Sutikna Thomas , Jatmiko  , Saptomo E. Wahyu , Due Rokus Awe , Djubiantono Tony , Morwood Michael J. , Jungers William L.
Published: September 2007

Whether the Late Pleistocene hominin fossils from Flores, Indonesia, represent a new species, Homo floresiensis, or pathological modern humans has been debated. Analysis of three wrist bones from the holotype specimen (LB1) shows that it retains wrist morphology that is primitive for the African ape-human clade. In contrast, Neandertals and modern humans share derived wrist morphology that forms during embryogenesis, which diminishes the probability that pathology could result in the normal primitive state. This evidence indicates that LB1 is not a modern human with an undiagnosed pathology or growth defect; rather, it represents a species descended from a hominin ancestor that branched off before the origin of the clade that includes modern humans, Neandertals, and their last common ancestor.
Use of Antibody Avidity Assays for Diagnosis of Severe Acute Respiratory Syndrome Coronavirus Infection
Authors: Chan K. H. , Sonnenberg K. , Niedrig M. , Lam S. Y. , Pang C. M. , Chan K. M. , Ma S. K. , Seto W. H. , Peiris J. S. M.
Published: September 2007

An indirect immunofluorescent assay (Euroimmun AG, Luebeck, Germany) was used to investigate the avidity of immunoglobulin G (IgG), IgM, IgA, and total Ig (IgGAM) antibody responses to severe acute respiratory syndrome coronavirus (SARS CoV) infections. Serial serum samples from eight patients collected during the first, third, and ninth months after the onset of infection were evaluated. It was found that low-avidity IgG antibodies were detected in 15/15 (100%), 1/5 (20%), and 0/8 (0%) serum samples collected during the first, third, and ninth months after the onset of symptoms, respectively. Low-avidity antibodies of IgA and IgM subclasses were detected in 14/14 (100%) and 3/14 (21%) serum samples, respectively, collected in the first month after the onset of infection. However, IgA antibodies remained low in avidity in a proportion of patients even during late convalescence. As a consequence, IgG antibody avidity assays gave better discrimination between acute-phase and late-convalescent-phase serum samples than IgM, IgA, or IgGAM assays. In two of these patients, sequential serum samples were also tested for IgG avidity against human CoV strains OC43 and 229E in parallel. While SARS CoV infections induced an anamnestic IgG antibody response to the 229E and OC43 viruses, these cross-reactive antibodies remained of high avidity from early (the first month) postinfection. The results showed that assays to detect low-avidity antibody may be useful for discriminating early from late antibody responses and also for distinguishing anamnestic cross-reactive antibody responses from primary specific responses. This may be useful in some clinical situations.
Dried Blood Spots versus Sera for Detection of Rubella Virus-Specific Immunoglobulin M (IgM) and IgG in Samples Collected during a Rubella Outbreak in Peru
Authors: Helfand Rita F. , Cabezas Cesar , Abernathy Emily , Castillo-Solorzano Carlos , Ortiz Ana Cecilia , Sun Hong , Osores Fernando , Oliveira Lucia , Whittembury Alvaro , Charles Myrna , Andrus Jon , Icenogle Joe
Published: September 2007

Most persons with rubella virus-specific immunoglobulin M (IgM)- or IgG-positive sera tested positive (98% [
n
= 178] and 99% [
n
= 221], respectively) using paired filter paper dried blood spot (DBS) samples, provided that DBS indeterminate results were called positive. For persons with IgM- or IgG-negative sera, 97% and 98%, respectively, were negative using DBS.
Serum Reactivity against
Borrelia burgdorferi
OspA in Patients with Rheumatoid Arthritis
Authors: Hsieh Yu-Fan , Liu Han-Wen , Hsu Tsai-Ching , Wei James C.-C. , Shih Chien-Ming , Krause Peter J. , Tsay Gregory J.
Published: September 2007

Lyme arthritis and rheumatoid arthritis share common clinical features and synovial histology. It is unclear whether they also share similar pathogenesis. Previous studies have shown that the severity and duration of Lyme arthritis correlate directly with serum concentrations of antibody against outer surface protein A (OspA) of the causative pathogen
Borrelia burgdorferi
. We tested the sera of 68 subjects with rheumatoid arthritis, 147 subjects with other autoimmune diseases, and 44 healthy subjects who had never had Lyme disease, as well as sera of 16 patients who had Lyme disease, for reactivity against the
B. burgdorferi
OspA protein. The sera of about a quarter of the rheumatoid arthritis patients and a 10th of the autoimmune disease and Lyme disease patients reacted against OspA antigen. Of 50 rheumatoid arthritis patients who could be evaluated for disease severity, a 28-joint count disease activity score of >2.6 was noted for 11 of 15 (73%) patients whose sera reacted against OspA antigen and 13 of 35 (37%;
P
< 0.05) whose sera were nonreactive. Serum reactivity against OspA antigen is associated with the pathogenesis of rheumatoid arthritis.
Age-Stratified Prevalences of Pneumococcal-Serotype-Specific Immunoglobulin G in England and Their Relationship to the Serotype-Specific Incidence of Invasive Pneumococcal Disease Prior to the Introduction of the Pneumococcal 7-Valent Conjugate Vaccine
Authors: Balmer Paul , Borrow Ray , Findlow Jamie , Warrington Rosalind , Frankland Sarah , Waight Pauline , George Robert , Andrews Nick , Miller Elizabeth
Published: September 2007

Recent changes to the childhood immunization schedule in the United Kingdom have resulted in the inclusion of the 7-valent pneumococcal conjugate vaccine. However, the seroprevalence of pneumococcal antibodies in the population was unknown. To address this, we measured pneumococcal, age-specific immunoglobulin G (IgG) concentrations specific for nine serotypes by an assay run on the Bioplex platform, using 2,664 serum samples collected in England from 2000 to 2004. The lowest concentrations of IgG specific to all serotypes and the proportions of serotype-specific IgG concentrations of ≥0.35 μg/ml were observed in children aged <1 year. From 1 year on, there was a general increase in antibody levels with increasing age, and they remained high in adults. Maternal antibody was detected in young children aged <36 days but waned rapidly. Comparison of the age-specific seroprevalence of serotype-specific IgG to the serotype-specific incidence of invasive pneumococcal disease demonstrated a general inverse relationship for all age groups except the elderly. These data provide a baseline for natural immunity to the pneumococcal serotypes analyzed prior to the introduction of pneumococcal conjugate vaccine in the United Kingdom.