Topology optimization with displacement constraints: a bilevel programming approach

We consider the minimum-compliance formulation of the truss topology problem with additional linear constraints on the displacements: the so-called displacement constraints. We propose a new bilevel programming approach to this problem. Our primal goal (upper-level) is to satisfy the displacement constraint as well as possible — we minimize the gap between the actual and prescribed displacement. Our second goal (lower level) is to minimize the compliance — we still want to find the stiffest structure satisfying the displacement constraints. On the lower level we solve a standard truss topology problem and hence we can solve it in the formulation suitable for the fast interior point alogrithms. The overall bilevel problem is solved by means of the so-called implicit programming approach. This approach leads to a nonsmooth optimization problem which is finally solved by a nonsmooth solver.     

Low-frequency quadrature mode birdcage resonator

The birdcage resonator is frequently used in conventional MRI because of its excellent attributes. Its use in low-field MRI is restricted to field strengths higher than, for example, 0.1 T, dependent on the size of the coil. This is because of the intrinsically low inductance value of the birdcage coils. Furthermore, the sensitivity of the birdcage at low field strengths is significantly lower when compared to, for example, the solenoid. Both problems can be overcome with the multiturn technique and a novel wound birdcage coil. The quadrature mode wound birdcage coil presented in this paper can be used at frequencies as low as 100 kHz. Its sensitivity is also increased when compared to the conventional strip-ring birdcage. Homogeneity effective volume, and methods to increase the resonator bandwidth to match the signal bandwidth are left intact. The latter is a typical low-field problem.     

Automatic reconstruction of 3D human arm motion from a monocular image sequence

A model-based approach to reconstruction of 3D human arm motion from a monocular image sequence taken under orthographic projection is presented. The reconstruction is divided into two stages. First, a 2D shape model is used to track the arm silhouettes and second-order curves are used to model the arm based on an iteratively reweighted least square method. As a result, 2D stick figures are extracted. In the second stage, the stick figures are backprojected into the scene. 3D postures are reconstructed using the constraints of a 3D kinematic model of the human arm. The motion of the arm is then derived as a transition between the arm postures. Applications of these results are foreseen in the analysis of human motion patterns. Received: 26 January 1996 / Accepted: 17 July 1997     

Czech project in history of mathematics

The paper describes the Czech project in the history of mathematics which was initiated at the Faculty of Mathematics and Physics of Charles University in Prague at the end of the eighties of the 20th century. Its main aim is to map the development of mathematical research in the Czech lands in the second half of the nineteenth and the first half of the twentieth century. The main result of this project is the production of monographs. These chart out the life and work of some prominent Czech personalities-mathematicians who have had substantial influence on the development of Czech mathematics. The aim of the project, the structure of the monographs and the general method are discussed in the paper.     

The PIBETA spectrometer for studying rare and forbidden decays of muons and pions

The construction and characteristics of the PIBETA spectrometer are described. This spectrometer is designed to implement a program of precise measurement of pion decay ^{+ 0} + e ⁺ + _e at the Paul Scherrer Institute (Switzerland). A spherical calorimeter, consisting of 240 crystals of pure CsI scintillator and embracing a solid angle of 3, is the main detector of the setup. In addition, the spectrometer is composed of an active collimator (which also acts as a beam degrader), a segmented active plastic target, two multiwire cylindrical proportional chambers, a 20-element cylindrical plastic hodoscope, and veto counters of cosmic muons.__________Translated from Pribory i Tekhnika Eksperimenta, No. 2, 2005, pp. 39–48.Original Russian Text Copyright © 2005 by Baranov, Kalinnikov, Karpukhin, Khomutov, A. Korenchenko, S. Korenchenko, Kravchuk, Kuchinskii, Mzhaviya, Rozhdestvenskii, Sidorkin, Tsamalaidze, Sakhelashvili, Frlez, Poanic, Li, Minehart, Smith, Stephens, Ziock, Bertl, Horisberger, Ritt, Schnyder, Wirtz, Ritchie, Supek, Kozlowski.     

Use of the Roughness Parameters Ssk and Sku to Control Friction—A Method for Designing Surface Texturing

The aim of this work was to show that with the use of the surface roughness parameters S_sk and S_ku we can predict tribological behavior of contact surfaces and use these parameters to plan surface texturing. This article presents a continuation of our research on virtual texturing and experimental work on surface textures in the form of channels. For this investigation, steel samples were laser surface textured in the shape of dimples with different spacings between the dimples and different dimple depths. The experimental results confirmed that the parameters S_sk and S_ku can be used to design the surface texturing, where a higher value of S_ku and more negative S_sk lead to lower friction.     

Substitution of nickel in Mg2Ni and its hydride with elements from groups XIII and XIV: An ab initio study

We have performed ab initio calculations with equilibrium supercells of the Mg₂Ni compound and its hydride Mg₂NiH₄ doped with elements X = Al, Ga, In, Si, Ge and Sn. Two concentrations of X in both structures have been set: (1) every 16th, and (2) every fourth Ni atom has been substituted by X. Total energy calculations yielded the Mg₂NiH₄ hydrogen absorption enthalpy ΔH_abs according to the chemical reaction Mg₂Ni + 2H₂ → Mg₂NiH₄. Reduction of the hydrogen absorption enthalpy was reported for both concentrations of X. When doping the Mg₂NiH₄ hydride with X = In in a low concentration (1), the value of hydrogen desorption enthalpy decreases from 68.22 to 55.96 kJ(mol H₂)^?1. Doping with X = In in a high concentration (2) further decreases the hydrogen desorption enthalpy to 5.50 kJ(mol H₂)^?1. Further, the electronic structure of Mg₂(Ni–In)H₄ hydride with a low In concentration indicates weaker Ni–H bonds in comparison with the pristine Mg₂NiH₄. Attraction between H and In atoms induced enhanced bonding between Mg and H atoms compared to the pristine Mg₂NiH₄.