Ferroelastic Properties of Lead Zirconate Titanate Ceramics

To increase the reliability of multilayer actuators, calculation of the mechanical stress inside the device during operation is important. This paper shows that the small-signal value of the elastic constant s is not sufficient to describe the complicated behavior of lead zirconate titanate (PZT) ceramics. Therefore, compressive strain and depolarization have been measured as a function of large-signal stress applied parallel to the poling direction. The nonlinear dependence of the strain and depolarization can clearly be explained by domain processes. Soft and hard PZT ceramics have been investigated. In hard PZT, domain switching appears at higher stresses than in soft PZT. Moreover, in hard PZT, the domains partly switch back during unloading. The critical stress (coercive stress) necessary for a domain-switching process shows a dependence on the Zr:Ti ratio that is quite similar to the dependence of the electric coercive field. The influence of an electric field applied parallel to the poling direction and superimposed on the compression experiment also has been examined. The coercive stress depends linearly on the electric field. The linear coefficient of this relation is given by the ratio of depolarization to compressive strain caused by domain switching.     

Context Effects on Lexical Choice and Lexical Activation.

Speakers are regularly confronted with the choice among lexical alternatives when referring to objects, including basic-level names (e.g., car) and subordinate-level names (e.g., Beetle). Which of these names is eventually selected often depends on contextual factors. The present article reports a series of picture-word interference experiments that explored how the designated target name (basic level vs. subordinate level) and contextual constraints rendering the name alternative either appropriate or inappropriate affect lexical activation and lexical choice. The experimental data demonstrate clear context effects on the eventual lexical choice. However, they also show that alternative nonselected object names are phonologically activated, even if a constraining context makes these alternative names currently inappropriate. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Iterative solution of boundary element approximations for electric and magnetic fields

The calculation of potentials in homogeneous and isotropic media by the boundary element method has the advantage that a harmonic solution of Laplace's equation is obtained for given approximated boundary conditions. The technique leads to the solution of linear systems with full matrices of dimension 1000–10,000 for medium- and large-sized three-dimensional problems, An efficient solution procedure of the linear systems is required. While the iterative solution of the large and sparse linear systems arising from the finite difference or the finite element method is well documented, the systems resulting from the boundary element method are typically solved by direct methods. However, in many cases an iterative solver needs far fewer operations to achieve a sufficient accuracy. Importantly, there are many alternative methods, each of them well suited for different types of problem. Here, we provide an overview of state-of-the-art iterative solvers. We will discuss the particular methods that have been successfully applied to systems arising from field calculations in the high-voltage engineering by the boundary element method. The selection of appropriate methods is discussed. We demonstrate that iterative solutions can be much faster than direct solvers with regards to the number of operations. Furthermore, these solvers are optimally suited for today's supercomputers because they can be efficiently vectorized and parallelized.