Magnetomechanical coupling in transition metals

The Griineisen parameter is equal to about 2 for most substances. Its value is higher in the case of interactions, for example, electron-phonon and exchange interaction, magnetovolume instability. The parameter has very large values for Invar alloys and the coupling between thermal disorder and magnetic fluctuations dominates in finite-temperature properties.     

Haptic feedback in mixed-reality environment

The training process in industries is assisted with computer solutions to reduce costs. Normally, computer systems created to simulate assembly or machine manipulation are implemented with traditional Human-Computer interfaces (keyboard, mouse, etc). But, this usually leads to systems that are far from the real procedures, and thus not efficient in term of training. Two techniques could improve this procedure: mixed-reality and haptic feedback. We propose in this paper to investigate the integration of both of them inside a single framework. We present the hardware used to design our training system. A feasibility study allows one to establish testing protocol. The results of these tests convince us that such system should not try to simulate realistically the interaction between real and virtual objects as if it was only real objects.     

The effect of lithium oxide on the threshold field of ZnO varistors

Lithium oxide in form of Li₂CO₃ solution is added with contents of 0–200 ppm to two ZnO-based varistors standard formulations, once with Sb₂O₃ and the other without. According to Li₂CO₃ concentration, both threshold field and energy absorption capability evolution are studied. It is found that with the benefit of antimony, the lithium allows reaching high threshold field but concomitantly, low energy absorption capability. Without antimony, threshold fields up to 300 V/mm are attained, associated with a fair energy absorption capability. With 100 ppm of Li₂CO₃, optimum couple of values (315 V/mm; 115 J/cm³) is achieved. With 200 ppm of Li₂CO₃, threshold field exceeds 500 V/mm but energy absorption capability falls below 50 J/cm³. Correlations with SEM microstructures observations suggest that lithium increases voltage barrier height by decreasing donor density and that spinel phases (Zn₇Sb₂O₁₂) have detrimental effects on the electrical absorption capability by limiting the density of current, reducing the effective current path from one ZnO grain to another.     

An inverse-measure-based unilevel architecture for reliability-based design optimization

Reliability-based design optimization (RBDO) is a methodology for finding optimized designs that are characterized with a low probability of failure. Primarily, RBDO consists of optimizing a merit function while satisfying reliability constraints. The reliability constraints are constraints on the probability of failure corresponding to each of the failure modes of the system or a single constraint on the system probability of failure. The probability of failure is usually estimated by performing a reliability analysis. During the last few years, a variety of different formulations have been developed for RBDO. Traditionally, these have been formulated as a double-loop (nested) optimization problem. The upper level optimization loop generally involves optimizing a merit function subject to reliability constraints, and the lower level optimization loop(s) compute(s) the probabilities of failure corresponding to the failure mode(s) that govern(s) the system failure. This formulation is, by nature, computationally intensive. Researchers have provided sequential strategies to address this issue, where the deterministic optimization and reliability analysis are decoupled, and the process is performed iteratively until convergence is achieved. These methods, though attractive in terms of obtaining a workable reliable design at considerably reduced computational costs, often lead to premature convergence and therefore yield spurious optimal designs. In this paper, a novel unilevel formulation for RBDO is developed. In the proposed formulation, the lower level optimization (evaluation of reliability constraints in the double-loop formulation) is replaced by its corresponding first-order Karush–Kuhn–Tucker (KKT) necessary optimality conditions at the upper level optimization. Such a replacement is computationally equivalent to solving the original nested optimization if the lower level optimization problem is solved by numerically satisfying the KKT conditions (which is typically the case). It is shown through the use of test problems that the proposed formulation is numerically robust (stable) and computationally efficient compared to the existing approaches for RBDO.     

Fast and efficient methods for industrial floor assembly

In the wooden flooring manufacturing industry, floor quality is directly related to the positioning of the wooden slats. This process is labor intensive and, due to short decision times, even experienced employees can make bad decisions, which makes it hard to achieve high-quality standards. In this paper, we propose fast and efficient methods for use with an automatic assembly device. These assembly methods were evaluated on real-life data via computer simulation. Compared to the manual assembly process, which results in floors with 5% of defective joints, our automatic assembly methods resulted in almost perfect floors.     

Evaluation of Cyclic Softening in Silts and Clays

Procedures are presented for evaluating the potential for cyclic softening (i.e., onset of significant strains or strength loss) in saturated silts and clays during earthquakes. The recommended procedures are applicable for fine-grained soils with sufficient plasticity that they would be characterized as behaving more fundamentally like clays in undrained monotonic or cyclic loading. The procedures are presented in a form that is similar to that used in semiempirical liquefaction procedures. Expressions are developed for a static shear stress correction factor and a magnitude scaling factor. Guidelines and empirical relations are presented for determining cyclic resistance ratios based on different approaches to characterizing fine-grained soil deposits. The potential consequences of cyclic softening, and the major variables affecting such consequences, are discussed. Application of these procedures is demonstrated through the analysis of the Carrefour Shopping Center case history from the 1999 Kocaeli earthquake. The proposed procedures, in conjunction with associated liquefaction susceptibility criteria, provide an improved means for distinguishing between the conditions that do and those that do not lead to ground deformations in fine-grained soil deposits during earthquakes.     

Static Pushover Analyses of Pile Groups in Liquefied and Laterally Spreading Ground in Centrifuge Tests

Monotonic, static beam on nonlinear Winkler foundation (BNWF) methods are used to analyze a suite of dynamic centrifuge model tests involving pile group foundations embedded in a mildly sloping soil profile that develops liquefaction-induced lateral spreading during earthquake shaking. A single set of recommended design guidelines was used for a baseline set of analyses. When lateral spreading demands were modeled by imposing free-field soil displacements to the free ends of the soil springs (BNWF_SD), bending moments were predicted within ?8% to +69 (16th to 84th percentile values) and pile cap displacements were predicted within ?6 to +38%, with the accuracy being similar for small, medium, and large motions. When lateral spreading demands were modeled by imposing limit pressures directly to the pile nodes (BNWF_LP), bending moments and cap displacements were greatly overpredicted for small and medium motions where the lateral spreading displacements were not large enough to mobilize limit pressures, and pile cap displacements were greatly underpredicted for large motions. The effects of various parameter relations and alternative design guidelines on the accuracy of the BNWF analyses were evaluated. Sources of bias and dispersion in the BNWF predictions and the issues of greatest importance to foundation performance are discussed. The results of these comparisons indicate that certain guidelines and assumptions that are common in engineering design can produce significantly conservative or unconservative BNWF predictions, whereas the guidelines recommended herein can produce reasonably accurate predictions.     

A common formalism for the integral formulations of the forward EEG problem

The forward electroencephalography (EEG) problem involves finding a potential V from the Poisson equation inverted Delta x (sigma inverted Delta V) f, in which f represents electrical sources in the brain, and sigma the conductivity of the head tissues. In the piecewise constant conductivity head model, this can be accomplished by the boundary element method (BEM) using a suitable integral formulation. Most previous work uses the same integral formulation, corresponding to a double-layer potential. In this paper we present a conceptual framework based on a well-known theorem (Theorem 1) that characterizes harmonic functions defined on the complement of a bounded smooth surface. This theorem says that such harmonic functions are completely defined by their values and those of their normal derivatives on this surface. It allows us to cast the previous BEM approaches in a unified setting and to develop two new approaches corresponding to different ways of exploiting the same theorem. Specifically, we first present a dual approach which involves a single-layer potential. Then, we propose a symmetric formulation, which combines single- and double-layer potentials, and which is new to the field of EEG, although it has been applied to other problems in electromagnetism. The three methods have been evaluated numerically using a spherical geometry with known analytical solution, and the symmetric formulation achieves a significantly higher accuracy than the alternative methods. Additionally, we present results with realistically shaped meshes. Beside providing a better understanding of the foundations of BEM methods, our approach appears to lead also to more efficient algorithms.     

Preparation of Bi1−xSbx films by electrodeposition

A method has been developed to produce composition modulated Bi_1–x Sb _x alloys by electrodeposition. The electrolyte which consists of NaCl 4 M and HCl 1 M (pH 0) in aqueous medium, allows codeposition of bismuth and antimony to be accomplished at room temperature on glassy carbon. The composition of the films, their crystal structure, morphology and resistivity were studied as a function of electrochemical parameters and bath composition. It is shown that the electrodeposits are monophasic and exhibit a polycrystalline state. The obtained alloys represent a continuous series of solid solution. The film composition is dependent on the applied current density. The electrical resistivity is of the order of 3–7 m.