Twelve shear surface waves guided by clamped/free boundaries in magneto-electro-elastic materials

It is shown that surface waves with twelve different velocities in the cases of different magneto-electrical boundary conditions can be guided by the interface of two identical magneto-electro-elastic half-spaces. The plane boundary of one of the half-spaces is clamped while the plane boundary of the other one is free of stresses. The 12 velocities of propagation of these surface waves are obtained is explicit forms. It is shown that the number of different surface wave velocities decreases from 12 to 2 if the magneto-electro-elastic material is changed to a piezoelectric material.Comment: 7 pages, no figure

An Empirical Bayes Approach for Distributed Estimation of Spatial Fields

In this paper we consider a network of spatially distributed sensors which collect measurement samples of a spatial field, and aim at estimating in a distributed way (without any central coordinator) the entire field by suitably fusing all network data. We propose a general probabilistic model that can handle both partial knowledge of the physics generating the spatial field as well as a purely data-driven inference. Specifically, we adopt an Empirical Bayes approach in which the spatial field is modeled as a Gaussian Process, whose mean function is described by means of parametrized equations. We characterize the Empirical Bayes estimator when nodes are heterogeneous, i.e., perform a different number of measurements. Moreover, by exploiting the sparsity of both the covariance and the (parametrized) mean function of the Gaussian Process, we are able to design a distributed spatial field estimator. We corroborate the theoretical results with two numerical simulations: a stationary temperature field estimation in which the field is described by a partial differential (heat) equation, and a data driven inference in which the mean is parametrized by a cubic spline

Armenia's 'Middle Class': Stability Characteristics and the Challenge of Erosion

This article will give a systematic overview of the main features of the middle class in Armenia based on their self-perception as captured in representative surveys. Typically, respondents identifying themselves as 'middle class' mostly have a university-level education, are employed, and are young or middle-aged. Evidence of upward social and economic mobility and progress in life are other important factors for self-identification as 'middle class'. However, has stagnation set in? This article analyses the threats that might lead to the erosion of Armenia's middle class. A limited access to professional education and healthcare services, the precariousness of employment, and the many impediments to small- and middle-sized enterprise development were the most prominent threats identified in a number of sociological studies