Express Method for Estimation of Tensile Strength and Crack Resistance of Brittle Media

The procedure is proposed for estimating the crack resistance and tensile strength of rocks by the results of experiments on disk samples with holes. The gradient approach to the strength problem is employed in processing the experimental data.     

The complexity of economic equilibria for house allocation markets

We prove NP-completeness of deciding the existence of an economic equilibrium in so-called house allocation markets. House allocation markets are markets with indivisible goods in which every agent holds exactly one copy of some good.     

An intrinsic observer for a class of Lagrangian systems

We propose a new design method of asymptotic observers for a class of nonlinear mechanical systems: Lagrangian systems with configuration (position) measurements. Our main contribution is to introduce a state (position and velocity) observer that is invariant under any changes of the configuration coordinates. The observer dynamics equations, as the Euler-Lagrange equations, are intrinsic. The design method uses the Riemannian structure defined by the kinetic energy on the configuration manifold. The local convergence is proved by showing that the Jacobian of the observer dynamics is negative definite (contraction) for a particular metric defined on the state-space, a metric derived from the kinetic energy and the observer gains. From a practical point of view, such intrinsic observers can be approximated, when the estimated configuration is close to the true one, by an explicit set of differential equations involving the Riemannian curvature tensor. These equations can be automatically generated via symbolic differentiations of the metric and potential up to order two. Numerical simulations for the ball and beam system, an example where the scalar curvature is always negative, show the effectiveness of such approximation when the measured positions are noisy or include high frequency neglected dynamics.     

An exploratory study of adolescent's perceptions of the Web

Abstract The purpose of this exploratory study was to investigate the influence of two individual characteristics (Web experience and academic focus) of adolescents on the Web perception, using off-line questionnaires (a Lickert response scale) constituted on the basis of a series of interviews. Questions concerned: perceptions about the nature of information found in the Web; 'strategies' of access to the interesting Internet sites and the reliability of different information resources (libraries, television, Web, etc.). Results lead to the assumption that adolescents with high Web experience became more critical, less confident and less enthusiastic than adolescents with low Web experience and that, in some dimensions, perceptions of literature students are different to those of science students. Even if some interesting results were obtained, further research is needed to explore users' perceptions related to individuals' characteristics and to determine the generalisability of the influences identified in this exploratory study.     

Customer service providers' attitudes relating to customer service and customer satisfaction in the customer-server exchange.

The authors proposed and tested a model describing the relationship between customer service providers' perceptions and attitudes toward their service-related duties and their customers' perceptions of satisfaction with their service experiences. Results indicated that the perception of having standards for service delivery in an organization is strongly related to line-level employees' perceptions of support from coworkers and supervisors. Perceived support from coworker, was significantly related to service providers' customer orientation, whereas perceived support from supervisors showed a weaker relationship to a customer orientation. Ultimately, service providers' customer orientation was strongly related to customers' satisfaction with service. Finally, a set of post hoc analyses indicated that coworker and supervisory support explained a greater proportion of incremental variance in the model than did perceived organizational support alone. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Determination of shear strength values according to EN 408

This paper presents the results of 382 shear tests carried out according to EN 408. The test pieces consisted of spruce (Picea abies) and varied in density and ring width orientation (radial, tangential and at an angle of 45° to the steel plates). In addition pieces containing pith and knots were tested. The paper discusses problems observed when using this test configuration and shows that the test results do not support the characteristic shear strength values as given in EN 338. Moreover, the test results do not support the relationship between characteristic shear strength and characteristic bending strength as given in EN 384.

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Résumé Cet article présente les résultats de 382 essais de cisaillement menés conformément à EN 408. Les éprouvettes d’essai sont en épicéa (Picea abies) et présentent une variabilité en termes de masse volumique et d’orientation des cernes d’accroissement (radiale, tangentielle, à un angle de 45° par rapport aux plaques métalliques). Des éprouvettes supplémentaires contenant du cœur et des nœuds ont également été testées. L’article évoque les problèmes qui ont été mis en évidence lors de l’utilisation de ce dispositif expérimental et montre que les résultats expérimentaux ne sont pas en accord avec les valeurs caractéristiques de résistance au cisaillement données dans EN 338. De plus, ces résultats ne confirment pas la relation entre résistance caractéristique au cisaillement et résistance caractéristique à la flexion telle que stipulée dans EN 384.

     

Uranium(III) in aqueous solutions: Preparation,properties, synthesis of solid compounds

Published data on the preparation procedures, stability, and complexation of U(III) in aqueous solutions are summarized and correlated. Reactions with inorganic and organic free radicals studied by the flash radiolysis method, the spectroscopic properties, the extraction and ion-exchange behavior of U(III), and methods for isolation of solid U(III) compounds from aqueous solutions are discussed.     

常减压蒸馏装置换热网络的节能优化

利用夹点技术理论对耗能严重的某炼油厂常减压蒸馏装置进行用能诊断分析;并结合热力学原理得到两种优化换热网络,节能效果显著。