Triaxial Test Simulations with Discrete Element Method and Hydrostatic Boundaries

A new boundary condition has been developed for the discrete element method. This boundary is different from the conventional periodic, rigid, or flexible boundries. This new boundary mechanism was developed to simulate triaxial tests. The new boundary, hydrostatic boundary, simulated the chamber fluid but not the rubber membrane. When a particle (ellipsoids in our simulations) contacts the hydrostatic boundary, pressure is developed. The interaction between the particle and the boundary is calculated analytically based on geometry. This hydrostatic boundary condition was implemented into an existing ellipsoidal discrete element code. Triaxial compression drained tests were performed with both periodic and hydrostatic boundaries. The result showed an increase in friction angle over the values observed from the periodic boundary mechanism. The result also closely resembles the experimental triaxial data. Thirteen specimens were generated and were used to investigate the following variables: particle shape, specimen size, and void ratio. A unique slope of the linear relationship between friction angle and void ratio was identified for monosize specimens of different particle shapes. It is found that the friction angle decreases as the aspect ratio increases provided that the void ratio of the two specimens is the same. The friction angle is linear proportional to the coordination number for monosize specimens regardless the specimen size. Also, the specimen size does not influence the behavior of two-size specimens.     

Image analysis for grain shape characterization in lamp filaments

Algorithms have been developed for appraising the quality of tungsten lamp filament wire microstructure with respect to its resistance to sag. They allow a numerical determination of grain aspect ratio, grain boundary contour, angle of boundary with wire diameter, and degree of grain boundary surface convolution. These values are combined algebraically to give a grain shape parameter (GSP) which reliably predicts how resistant the filament is to grain boundary sliding. Measurements are made of thermally etched grain boundaries on scanning electron microscopy (SEM) images of the surfaces on coiled filaments. Data are recorded and parameters computed by means of an image analyzer. The technique has been tested on samples made from the same wire modified in process to have varying strain after the last anneal. It has also been tested on samples purchased from various vendors. These applications indicate that the computed GSP is a sensitive predictor of filament creep resistance and reliably reflects variation in wire drawing strain after the last anneal.     

西秦岭不同矿带金矿床成矿流体及其物质来源探讨

西秦岭地区金矿资源丰富,找矿潜力巨大。为了探讨不同源区参与成矿的程度,对该区3个成矿亚带19个典型金矿床主成矿期流体包裹体及H、O、C、S稳定同位素特征进行研究,发现西秦岭地区成矿流体为岩浆水、变质水和大气降水混合来源,具有中低压、中低温和低盐度的特征,成矿物质为岩浆和沉积岩中碳酸盐岩的混合来源。西秦岭地区3个成矿亚带整体上具有明显的分带特征,自南向北其矿源具有从以混合来源为主向沉积来源过渡的趋势。     

Pathological human synovial fluids. Viscosity and boundary lubricating properties

On human synovial fluids obtained during operations from the knee joints of 80 patients with different joing disease, relative viscosity was measured at 3 different shear rates and the boundary lubrication was tested by the coefficient of friction in an artificial rubber/glass system. The results were evaluated in relation to the operative findings. The viscosity showed statistically significant differences between the synovial fluids from the knee joints with rheumatoid arthritis, osteoarthritis, and torn menisci, being lowest in rheumatoid synovial fluid and highest in synovial fluids from knee joints with torn menisci. Correlations were found in the variations in the viscosity and the degree of synovitis. The boundary lubrication also showed different values inrelation to the different diseases. Synovial fluid from knee joints with torn menisci seemed to act as the best lubricant and significantly better than rheumatoid synovial fluid. Variations in the boundary lubrications reflect successive degrees of cartilage degeneration.     

Actin disassembles reversibly during electrically induced recycling of synaptic vesicles in cultured neurons

We have studied depolarization-induced regulation of actin assembly in exocytotically active areas of dissociated chick sympathetic neurons. Active areas were identified with the fluorescent dye FM1-43 which labels synaptic vesicles that recycle in these regions. Exocytosis (electrically stimulated) was monitored in real time through depletion of FM1-43 fluorescence. To study depolarization-induced disassembly of actin in the FM1-43-stained regions, the cells were fixed after different periods of depolarization and stained with rhodamine phalloidin, which binds preferentially to the filamentous form of actin. In active regions, actin disassembles and reassembles during continuous 2 min depolarization. Actin disassembly that occurs after the first 25 s of depolarization was detected by a reduction in rhodamine phalloidin staining and confirmed by correlative electron microscopy. Immunogold staining revealed that actin is abundant throughout resting terminals. In some experiments, actin filaments were stabilized by loading cells with unlabelled phalloidin before stimulating secretion. Stabilizing the filaments does not alter the initial release but strongly reduces the release rate at later stages. These data are consistent with a model in which partial disassembly of actin filaments is necessary for facilitating the transport of vesicles within the terminal and reassembly is necessary for limiting that movement.     

湖南溆浦南江坪-龙王江-雁鹅界矿化带金锑资源的初步分析

湖南省溆浦县境内金锑资源较为丰富,存在有3条沿NE向展布的含金或金锑矿化带,属雪峰山金锑钨成矿带的一部分。南江坪-龙王江-雁鹅界金锑矿化带中有4个重点矿化地段,通过对该矿化带内的地层、岩性、构造和赋矿层位分析,认为在4个重点矿化地段中存在有可供开采的工业矿体。     

Uncertainty Analysis of Mound Monitoring for Recharged Water from Surface Spreading Basins

This study has conceptually reviewed issues related to implementation of a groundwater mound monitoring well (GMMW) for monitoring recharged water from a surface spreading basin with emphasis on uncertain hydrogeological conditions. For this, we selected a recharge site in the City of Mesa, Ariz., that is characterized with near-surface clay lenses of low permeability. A geostatistical simulation technique was used for generating hydrogeological fields under the recharge basin, using soil boring logs and historical hydrological data. More than 50 hydrogeological fields were generated and used for modeling. Five scenarios were formulated with varying parameter values and different initial and boundary conditions, and each scenario was evaluated with the 50 hydrogeological fields generated. Results of this study indicate that travel times to the mound may vary by over one order of magnitude and the use of a GMMW will only be practical for regulatory compliance in a homogeneous system.     

Static-Dynamic Analyses of Toroidal Shells

A corotational approach is used to analyze toroidal shells under static-dynamic loading. This approach decomposes the deformation into stretches and rigid-body rotations, examining the deformed state with respect to an orthogonal rigidly translated and rotated triad located at the point of interest on the deformed structure. The Jaumann stresses and strains are employed in the algorithm. Local and layerwise thickness stretching and shear warping functions are used to model the 3D behavior of the shell. These functions, developed through the use of the constitutive equations, enforce the continuity of stresses and displacements required at the ply interfaces and laminate surfaces. The model is validated against toroidal shell data available in the literature, and it shows good agreement.     

Aiming error under transformed spatial mappings suggests a structure for visual-motor maps.

Transformed spatial mappings were used to perturb normal visual–motor processes and reveal the structure of internal spatial representations used by the motor control system. In a 2-D discrete aiming task performed under rotated visual–motor mappings, the pattern of spatial movement error was the same for all Ss: peak error between 90° and 135° of rotation and low error for 180° rotation. A two-component spatial representation, based on oriented bidirectional movement axes plus direction of travel along such axes, is hypothesized. Observed reversals of movement direction under rotations greater than 90° are consistent with the hypothesized structure. Aiming error under reflections, unlike rotations, depended on direction of movement relative to the axis of reflection (H. A. Cunningham and M. Pavel, in press). RT and movement time effects were observed, but a speed-accuracy tradeoff was found only for rotations for which the direction-reversal strategy could be used. Finally, adaptation to rotation operates at all target locations equally but does not alter the relative difficulty of different rotations. Structural properties of the representation are invariant under learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Model for the alignment of actin filaments in endothelial cells subjected to fluid shear stress

Cultured vascular endothelial cells undergo significant morphological changes when subjected to sustained fluid shear stress. The cells elongate and align in the direction of applied flow. Accompanying this shape change is a reorganization at the intracellular level. The cytoskeletal actin filaments reorient in the direction of the cells' long axis. How this external stimulus is transmitted to the endothelial cytoskeleton still remains unclear. In this article, we present a theoretical model accounting for the cytoskeletal reorganization under the influence of fluid shear stress. We develop a system of integro-partial-differential equations describing the dynamics of actin filaments, the actin-binding proteins, and the drift of transmembrane proteins due to the fluid shear forces applied on the plasma membrane. Numerical simulations of the equations show that under certain conditions, initially randomly oriented cytoskeletal actin filaments reorient in structures parallel to the externally applied fluid shear forces. Thus, the model suggests a mechanism by which shear forces acting on the cell membrane can be transmitted to the entire cytoskeleton via molecular interactions alone.     

Results with the Clinicard analyser in a paediatric hospital (author's transl)

The most important chemical pathological investigations which require to be undertaken in the emergency laboratory of a paediatric hospital are of the serum electrolytes, blood glucose, cerebrospinal fluid glucose, blood urea nitrogen, total proteins, bilirubin and calcium. It is imperative to have the opportunity of controlling these parameters both during the day and night. In order to be independent of the presence of a technician we were interested in finding an instrument which can be used by untrained personnel and gives results of sufficient accuracy. Hence, the clinicard analyser was tested in regard to reproducibility and accuracy of results when used by highly-trained technicians and by persons without knowledge of laboratory work. It was established that the values obtained by these two groups are similar and sufficiently reproducible for emergency use. The accuracy of the instrument was tested with 2 charges of cuvettes and with different control sera. In the case of total proteins differences were found between the different control sera used. The values obtained for blood urea nitrogen and for blood glucose lay within the range given for Labtrol and for Seronorm. The accuracy of bilirubin was tested with 5 different control sera and all values lay within the ranged given by the factory. Calcium was tested with Labtrol and Fluinorm and also with sera and urines from different patients. The values were within the range given for the test sera and were comparable to those measured with the calcium analyser of EEL, but were about 7% lower than those determined using atomic absorption. The values obtained for cerebrospinal fluid glucose correlated well with those obtained by the routine method.     

Analytical solutions for steady and non-steady heat conduction with temperature dependent material values

A transformation well-known for a long time is used to transform the differential equation for heat conduction for temperature dependent material values into a differential equation written in a more simplified form. It is investigated how the initial and boundary conditions are transformed and in which cases the problem with variable material values can be solved by applying the solutions known for constant material values. For constant thermal diffusivity, this reduction is possible for boundary conditions of the first and second kind without limitation, for conditions of the third kind only in some cases. The results of different methods of calculation are compared in an example calculation. The series solution with transformation lies generally much closer to the numerically calculated temperature than the solution without transformation. The computing times for the series solution with transformation are reduced by a factor of 100. If the first minutes of the heating period are disregarded, the first term constitutes an excellent approximation. The computing time for the finite-difference method with transformation is 20% lower than without transformation.     

Calibration Accuracy for Constant Temperature Thermal Anemometer

Thermal anemometry is widely used to measure fluid velocity and boundary shear stress. Sensor calibration is required and results in a nonlinear equation with anemometer voltage as a function of fluid velocity or shear stress. Uncertainties in the parameters of the nonlinear equation are a source of uncertainty in measured values. A method for quantifying the calibration accuracy is presented using regression analysis with 95% confidence and prediction intervals. The proposed method is applied to shear stress measurements of a calibrated flush-mounted hot-film sensor. Shear stresses ranged from 0.6 to 6.8 Pa. Calibration accuracy was found to be within 15% of the absolute shear.     

Structural constraints on the coordination of concurrent rotations of the head and a steering device

Concurrent movements of different effectors are subject to structural constraints that facilitate certain patterns of coordination but impede others. The constraints for concurrent rotations of the head and a bimanually operated steering device were explored in two experiments. To indicate structural constraints, the difference between concurrent periodic rotations in same and different directions with respect to the variable error of synchronization was used. The first experiment showed less error for rotations in same directions than for rotations in opposite directions. In the second experiment, the same result was obtained with a horizontal and a backward-tilted steering wheel. Adding gaze shifts to head oscillations increased the accuracy of synchronization but did not affect the difference between both coordination patterns. In contrast to the synchronization of head and steering device, the variable error of synchronization of gaze and steering wheel did not differ between both modes of coordination; the error was again reduced when head oscillations were added to the saccades between eccentric fixation targets. This suggests space related (or allocentric) constraints, which most likely originate from concurrent specifications of movement directions in coupled spatiotopic maps so that the specification of rotations in the same direction is facilitated in comparison to rotations in opposite directions.     

The influence of orientation on the stress rupture properties of nickel-base superalloy single crystals

The influence of orientation on the stress rapture properties of MAR-M247 single crystals was studied. Stress rupture tests were performed at 724 MPa and 774 °C where the effect of anisotropy is prominent. The mechanical behavior of the single crystals was rationalized on the basis of the Schmid factors for the operative slip systems and the lattice rotations which the crystals underwent during deformation. The stress rupture lives at 774 °C were found to be greatly influenced by the lattice rotations required to produce intersecting slip, because second-stage creep does not begin until after the onset of intersecting slip. Crystals which required large rotations to become oriented for intersecting slip exhibited a large primary creep strain, a large effective stress level at the onset of steady-state creep, and consequently, a short stress rupture life. Those crystals having orientations within about 25° of the [001] exhibited significantly longer lives when their orientations were closer to the [001]-[011] boundary of the stereographic triangle than to the [001]-[1l 1] boundary, because they required smaller rotations to produce intersecting slip and the onset of second-stage creep. Thus, the direction off the [001], as well as the number of degrees off the [001], has a major influence on the stress rapture lives of single crystals in this temperature regime. REBECCA A. MacKAY, formerly Graduate Assistant, Case Western Reserve University, Cleveland, OH RALPH D. MAIER, formerly Assistant Professor, Case Western Reserve University     

Grain Structure Development During Friction Stir Welding of Single-Crystal Austenitic Stainless Steel

The high-resolution electron backscatter diffraction (EBSD) technique was used to study the grain boundary development and texture evolution during friction stir welding (FSW) in a single-crystal austenitic stainless steel. Strain-induced crystal rotations were found to be induced by simple shear deformation. With the crystal rotations, the single-crystal structure was broken up into a fine-grained polycrystalline aggregate in the stir zone. This process was deduced to be governed by continuous and discontinuous recrystallizations operating during the FSW process. The final texture which evolved in the stir zone was dominated by $ A/\bar{A}\left\{ {111} \right\} \, \langle 110 \rangle $ ideal simple shear orientations.     

胶东地区北泊金矿构造特征及其控矿作用

断裂是热液型矿床的主要成矿控矿构造。招远-平度断裂带经历了脆韧性-韧脆性演化过程,是胶东地区主要的成矿控矿构造。胶东矿集区总体表现出区域构造控制成矿区带、矿田构造控制矿床、矿区构造控制矿体以及强烈变形裂隙带控制矿脉的特征。成矿物质来自深源,甚至来自核-幔边界,在温度、压力等物理化学条件的控制下,深源含矿流体通过地幔热柱多级演化逐渐向上迁移,当达到断裂破裂强度时便会导致液压致裂,并快速贯入到有利的构造部位（如韧脆性-脆韧性剪切带、侵入岩体的内外接触带、密集的构造裂隙带以及各种脉岩与围岩接触带）聚集成矿。北泊金矿与莱西金矿的对比研究再次证实了这种认识,对指导深部地质找矿具有较好的借鉴作用。     

Friction of composite cushion bearings for total knee joint replacements under adverse lubrication conditions

Conventional joint replacements consist of a polished metallic or ceramic component articulating against a layer of polyethylene. Although the friction in the contact between these articulating surfaces is low, polyethylene wear is produced as a result of a boundary/mixed lubrication regime. Wear debris is generated by direct asperity contact, abrasion, adhesion and fatigue, and has been shown to cause adverse tissue reactions which can lead to joint failure. The introduction of soft compliant materials, similar in stiffness to articular cartilage, has shown that with cyclic loading and relative motion between the articulating surfaces typical of normal walking, a fluid film can be maintained through combined entraining and squeeze-film actions, and hence wear can be minimized. For 95 per cent of the time, however, we are not walking but standing still or moving slowly. A pendulum simulator has been used in the present study to investigate the effect of adverse tribological conditions which may lead to fluid film breakdown, such as severe cyclic loading, particularly in the swing phase, reduced sliding velocity, reduced stroke length and start-up after a period of constant loading. Friction of a model composite cushion knee bearing, manufactured from a graded modulus (20-1000 MPa) layer of polyurethane, sliding against a polished metal cylinder has been measured for various lubricants and the results have been analysed using a Stribeck assessment. Severe cyclic loading, decreased sliding velocity and decreased stroke length have been found to limit the degree of fluid entrainment previously allowed during the swing phase of normal walking, thus allowing breakdown of fluid films and elevated levels of friction and surface damage. Soft layer joint replacements must therefore be designed to operate with thick elastohydrodynamic fluid films to provide some degree of protection when tribological conditions become severe, or alternatively incorporate alternative boundary or mixed lubrication mechanisms. This study quantifies a potential limitation of the cushion bearing concept.     

Simple analysis and working equations for the solidification of cylinders and spheres

The analysis of solidification processes is complicated by a nonlinear boundary condition at the moving solid-liquid interface, and exact solutions are rare. Various attempts to predict the rate of solidification are available in the literature but most of the results seem to be of limited use for operation and design studies on metallurgical processes. In this article we present a physical model which can be solved analytically for the most commonly encountered boundary conditions; that is constant temperature at the cooling wall or finite heat transfer to the cooling fluid. The model is based on the assumption of a linear temperature profile in the solidified shell and a corresponding differential removal of internal energy. As a result one obtains a very simple expression for the soli-dification time as a function of the space variable and the pertinent system parameters. By comparison with numerical results the prediction error is shown to be less than 10 pet over a wide range of parameter combinations. In extreme situations, where a larger error may occur, equally accurate working equations can be generated by slightly modifying the basic results.     

Modeling Depth-Averaged Velocity and Boundary Shear in Trapezoidal Channels with Secondary Flows

The Shiono and Knight method (SKM) offers a new approach to calculating the lateral distributions of depth-averaged velocity and boundary shear stress for flows in straight prismatic channels. It accounts for bed shear, lateral shear, and secondary flow effects via 3 coefficients—f,λ, and Γ—thus incorporating some key 3D flow feature into a lateral distribution model for streamwise motion. The SKM incorporates the effects of secondary flows by specifying an appropriate value for the Γ parameter depending on the sense of direction of the secondary flows, commensurate with the derivative of the term Hρ(UV)d. The values of the transverse velocities, V, have been shown to be consistent with observation. A wide range of boundary shear stress data for trapezoidal channels from different sources has been used to validate the model. The accuracy of the predictions is good, despite the simplicity of the model, although some calibration problems remain. The SKM thus offers an alternative methodology to the more traditional computational fluid dynamics (CFD) approach, giving velocities and boundary shear stress for practical problems, but at much less computational effort than CFD.