Interfacial waves between piezoelectric and piezomagnetic half-spaces with magneto-electro-mechanical imperfect interface

Abstract

We study the propagation of shear horizontal waves between the interface of piezoelectric and piezomagnetic half-spaces with a magneto-electro-mechanical imperfect contact. Mechanical, electrical and magnetical imperfections are modelled by means of a spring, a capacitor and a inductor, respectively. A general expression for the dispersion relation not reported previously in literature is given in an explicit form, with the diverse limit cases analysed in detail. In some of these limit cases, new expressions are also obtained which predict the existence of interfacial waves. In the other cases, when already reported results exist, a comparison with them is done. Some physical interpretations are derived from the limit cases. The influence of mechanical, electrical and magnetical imperfect contacts are shown in some numerical examples.     

Preparation and properties of a left-handed metamaterial composite

A left-handed metamaterial (a YIG/Ag composite with adjustable negative permittivity and permeability) was prepared by an in situ synthesis process, and its characterisation, microstructure, electrical conductivity, dielectric loss and magnetic properties studied. A negative permittivity behaviour with a Fano-like resonance is ascribed to plasma oscillation of delocalised electrons from silver conducting networks. As the silver content increases, the turbine loss increases, which greatly enhances the electromagnetic wave consumption capacity inside the material and leads to a stronger electromagnetic absorption and shielding performance. The dielectric loss near the percolation threshold is due to the combined effects of polarisation and conduction. The capacitive character is responsible for positive permittivity, and the inductive character leads to negative permittivity. LC resonance results in the Fano-like resonance, leading to the permittivity changing from negative to positive. Gyromagnetic spin rotation, domain wall motion and percolation characteristic of YIG/Ag composites cause frequency dispersion of the permeability. The YIG/Ag composite with double negative characteristics provides prospects for electromagnetic shielding application.     

High-pressure phase transition and lattice dynamics of rock-salt and FeSi-type phases of MgS

A phase transition of MgS under high pressure is investigated using a first-principles method. It is found from energy-volume calculations that the rock-salt (B1) phase of MgS transforms into a FeSi-type (B28) phase at 143?GPa. The calculated ground-state parameters in the B1 phase are in excellent agreement with available experimental and theoretical data. Ab initio phonon calculations are also performed to investigate the structural behaviour of MgS under high pressure. An unstable transverse acoustic mode and a phase transition from B1 to B28 phase at ~143.7?GPa driven by this soft mode are predicted. The B28 structure of MgS is stable up to 350?GPa according to lattice dynamics calculations.     

Distance stability analysis in multidimensional scaling using the jackknife method

Stability or sensitivity analysis is an important topic in data analysis that has received little attention in the application of multidimensional scaling (MDS), for which the only available approaches are given in terms of a coordinate‐based analytical jackknife methodology. Although in MDS the prime interest is in assessing the stability of the points in the configuration, this methodology may be influenced by imprecisions resulting from the inherently necessary Procrustes method. This paper proposes an analytical distance‐based jackknife procedure to study stability and cross‐validation in MDS in terms of the jackknife distances, which is not influenced by the Procrustes method. For each object, the corresponding jackknife estimated points are considered as naturally clustered points, and stability and cross‐validation are analysed in terms of the MDS distances arising from the jackknife procedure, on the basis of a weighted cluster‐MDS algorithm. A jackknife‐relevant configuration is also proposed for cross‐validation in terms of coordinates, in a cluster‐MDS framework.     

规则多边图形的离散度与图形信号认知绩效的关系

用实验方法研究规则多边图形的离散度与图形信号认知绩效的关系。实验的自变量是图形的离散度参数,因变量是单位时间图形信号的视觉通道信息传递量。实验的刺激材料是２５个离散度为０．３～０．７的规则多边图形。刺激材料的呈现与被试的反应记录都由计算机控制。结果表明：离散度适中（０．５左右）及偏小的图形信号认知绩效较高,离散度从０．５增大到０．６,认知绩效迅速下降,离散度继续增大,认知绩效仍有下降,但趋势平缓。     

The geometric representation of similarity and dissimilarity. Extension to measures of dispersion and comments on the distance model of subjective dissimilarity

In psychometrics and mathematical taxonomy dissimilarity is commonly geometrically represented by the Euclidean (Minkowski) distance function. This is only a part of a general geometric representation of similarity and dissimilarity (Junge, 1978). Gini's index (or ratio) and Pearson's coefficient of variation, used in economics as measures of income distribution inequality, are known in mathematical statistics as standardized measures of dispersion. It is shown that both measures can be identified with the general geometric representation of similarity and dissimilarity.     

Interfacial waves between two piezoelectric half-spaces with electro-mechanical imperfect interface

We study the propagation of shear horizontal waves between the interface of two piezoelectric materials with an electro-mechanical imperfect contact. Mechanical and electrical imperfections are modeled by means of a spring and a capacitor, respectively. The corresponding mathematical expressions for the imperfect contact are given in this article. The system of differential equations for the waves in the considered half-space is derived and the associate solutions are found. A general expression for the dispersion relation, not reported previously in the literature, is given in an explicit form, with the diverse limit cases analyzed in detail. In some of these limit cases, new expressions are also obtained, which predict the existence of interfacial waves. In the other cases, where already reported results exist, a comparison with them is done. Some physical interpretations are derived from the limit cases. The influence of mechanical and electrical imperfect contacts are shown in some numerical examples.     

Cluster differences scaling with a within-clusters loss component and a fuzzy successive approximation strategy to avoid local minima

Cluster differences scaling is a method for partitioning a set of objects into classes and simultaneously finding a low-dimensional spatial representation ofK cluster points, to model a given square table of dissimilarities amongn stimuli or objects. The least squares loss function of cluster differences scaling, originally defined only on the residuals of pairs of objects that are allocated to different clusters, is extended with a loss component for pairs that are allocated to the same cluster. It is shown that this extension makes the method equivalent to multidimensional scaling with cluster constraints on the coordinates. A decomposition of the sum of squared dissimilarities into contributions from several sources of variation is described, including the appropriate degrees of freedom for each source. After developing a convergent algorithm for fitting the cluster differences model, it is argued that the individual objects and the cluster locations can be jointly displayed in a configuration obtained as a by-product of the optimization. Finally, the paper introduces a fuzzy version of the loss function, which can be used in a successive approximation strategy for avoiding local minima. A simulation study demonstrates that this strategy significantly outperforms two other well-known initialization strategies, and that it has a success rate of 92 out of 100 in attaining the global minimum.     

Robust techniques for testing heterogeneity of variance effects in factorial designs

Several ways of using the traditional analysis of variance to test heterogeneity of spread in factorial designs with equal or unequaln are compared using both theoretical and Monte Carlo results. Two types of spread variables, (1) the jackknife pseudovalues ofs ² and (2) the absolute deviations from the cell median, are shown to be robust and relatively powerful. These variables seem to be generally superior to the Z-variance and Box-Scheffé procedures.This research was sponsored by Public Health Service Training Grant MH-08258 from the National Institute of Mental Health. The author thanks Mark I. Appelbaum, Elliot M. Cramer, and Scott E. Maxwell for their helpful criticisms of this paper. An earlier version of this work was presented at the Annual Meeting of the Psychometric Society, Murray Hill, New Jersey, April, 1976.     

薪酬水平和薪酬差距对企业运营结果影响的元分析

以国内外113篇企业薪酬水平和薪酬差距领域的实证研究(254个效应值, 438880家企业)为样本, 采用基于结构方程模型的元分析方法检验了企业平均薪酬水平、垂直薪酬差距和水平薪酬差距对企业创新、绩效和离职等运营结果的影响。元分析结果显示, 平均薪酬水平不仅能够显著提升企业的创新和绩效水平, 也会抑制企业内部的离职水平; 垂直和水平薪酬差距对企业绩效的主效应并不显著, 但其对企业创新具有显著的抑制作用, 并能够显著提升企业的离职水平。进一步的调节效应检验表明, 国家地域因素调节了薪酬水平与企业绩效之间的关系, 即中国企业的平均薪酬水平对企业绩效的促进作用显著高于美国企业。研究结果对于企业的薪酬管理具有一定的借鉴意义。