Modeling and homogenization of textile reinforced composites based on the isogeometric analysis

In this contribution, the isogeometric analysis is used to compute the effective material properties of textile reinforced composites. The isogeometric analysis based on non-uniform rational B-splines (NURBS) provides an efficient approach for numerical modeling because there is no need for a mesh generation. There are further advantages such as the availability of a geometry representation based on NURBS in computer-aided design software and the possibility to apply different refinement methods which do not change the geometry of the numerical model. These properties motivate the combination of the isogeometric analysis with the homogenization method. Therefor, the unit cell model representing the inner architecture of a textile reinforced composite is defined using NURBS. In order to compute the effective mechanical properties of the heterogeneous material, the homogenization method with periodic boundary conditions is applied. Finally, two examples demonstrate the advantages of this approach. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the determination of the worst sampling error in a communication system for pulse-amplitude-modulated signals. I: The general model

We present a mathematical model of a communication system perturbed by statistical sampling errors (timing jitter). The aim is to find an ‘optimal’ impulse response for the system, the optimization problem actually being a minimax problem. that is we put the model into a game-theoretical framework. The basic game turns out to be a statistical game similar to those arising from estimation problems in statistics. Earlier results concerning least-favourable sampling error distributions published by Krabs and Vogel are supplemented by estimations of the number of support points of the least-favourable distribution. Furthermore, we state the existence of the saddle points of our game, which formerly has only been proved for some special cases. In the first part we treat the general situation, where one strategy set for the game—the set of all feasible impulse responses—forms a vector space with infinite dimension. In the second part we discuss the problem in the case that the impulse responses are restricted to a finite-dimensional subspace of the whole infinite-dimensional subspace.     

Hexamethylphosphorsäuretriamid als Ligand, 1. Mitt.: Tetrakis (hexamethylphosphorsäuretriamido)kobalt(II)

Calorimetric investigations on the formation of cobalt(II) solvates show, that the donor strength ofHMPT towards Co(II) is smaller, than is suggested by its donor number.¹H-NMR-spectra at different temperatures lead to the conclusion, that at room temperature in [Co(HMPT)₄]²⁺ the coordination center is “rattling” within the tetrahedron formed by the bulkyHMPT molecules.     

Dissociation and recombination of oxygen atoms produced in a microwave discharge. Part II. Theoretical calculations

In this study, the degree of dissociation and recombination of oxygen atoms produced by a microwave discharge in oxygen is examined by comparing a theoretical model of the kinetic mechanisms to chemical titration data. The results show that a one-dimensional, temperature-dependent model of the neutral species of the system can predict the oxygen atom concentration profile as measured by nitrogen dioxide titration. The model also indicates that the temperature of the gas is approximately 1000 K and that an overall gas temperature and velocity increase is due to electrical heating by the microwave discharge and not due to the enthalpy change of the species in the system.