On the solvability of extended Riccati equations

The Kalman-Yakubovich-Popov lemma, which gives necessary and sufficient conditions for solvability of matrix Lur'e-Riccati equations, is a milestone in modern control theory. There are, however, important and general extensions of this lemma that have not been studied yet. Starting with the absolute stability theory with semidefinite frequency domain function, we generalize here this lemma to the sign indefinite case-a research that is motivated by new problems on passivity and H/sub /spl infin// control theory.     

A typology of course of motion in simulated environments based on Bézier curve analysis

This paper proposes a novel method of analysing trajectories followed by people while they perform navigational tasks. The results indicate that modelling trajectories with Bézier curves provides a basis for the diagnosis of navigational patterns. The method offers five indicators: goodness of fit, average curvature, number of inflexion points, lengths of straight line segments, and area covered. Study results, obtained in a virtual environment show that these indicators carry important information about user performance, specifically spatial knowledge acquisition. Corina Sas is a Lecturer in the field of human–computer interaction in the Computing Department at Lancaster University. She holds bachelor degrees in Computer Science and Psychology and an M.A. in Industrial Psychology from Romania. She received her Ph.D. degree in Computer Science from University College Dublin in 2004. Her research interests include user modelling, adaptive systems, data mining, spatial cognition, user studies and individual differences. She has published in various journals and international conferences in these areas. Nikita Schmidt is a Postdoctoral Research Fellow at University College Dublin (UCD). He received his Ph.D. degree from UCD in 2004 and M.Sc. from St-Petersburg State University, Russia in 1994. His research interests include pervasive, ubiquitous and location-aware computing, embedded systems, hardware-close software development and tree-structured data. His work experience is a mix of industry and academia.     

An approach to surface retouching and mesh smoothing

In this paper, we discuss a novel, fast, practical algorithm for surface modification of geometric objects. A space-mapping technique is used to transform a given or damaged part of a surface into a different shape in a continuous manner. The proposed approach is used for surface-retouching and mesh-smoothing problems. The technique, in fact, is based on a local processing of polygonal data that can be applied to the fairing of 3D meshes. We consider shape transformation as a general type of operation for surface modification and attempt to approach the problem from a single point of view, namely, that of the space-mapping technique based on the implementation of radial-basis functions. Experimental results are included to demonstrate the functionality of our mesh-modeling tool.     

Convergence of the least-squares method with a polynomial regularizer for the infinite-dimensional autoregression equation

Consideration was given to the estimation of the unknown parameters of a stable infinite-dimensional autoregressive model from the observations of a random time series. The class of such models includes an autoregressive moving-average equation with a stable moving-average part. A modified procedure of the least-squares method was used to identify the unknown parameters. For the infinite-dimensional case, the estimates of the least-squares method were proved to be strong consistent. In addition, presented was a fact on convergence of the semimartingales that is of independent interest.This work was supported in part by the Russian Foundation for Basic Research, projects nos. 01-01-00306, 04-01-00084, and project no. 00-15-96-028 for the Russian Scientific Schools.Translated from Avtomatika i Telemekhanika, No. 1, 2005, pp. 100–117.Original Russian Text Copyright © 2005 by Barabanov, Gel.This paper was recommended for publication by B.M. Miller, a member of the Editorial Board     

Study of the coupling between human head and cellular phone helical antennas

The interaction between normal-mode helical antennas and human head models is analyzed, using both a novel accurate semi-analytical method and finite-difference time-domain (FDTD) simulations. The semi-analytical method is based on the combination of Green's functions theory with the method of moments (Green/MoM) and is able to model arbitrarily shaped wire antennas radiating in the close proximity of layered lossy dielectric spheres representing simplified models of the human head. The purpose of the development of the Green/MoM technique is to provide a reliable tool for preliminary (worst case) estimation of human head exposure to the field generated by different antenna configurations with emphasis on the helical antenna, representing the most diffused antenna type used in modern cellular handsets. Furthermore, the accurate semi-analytical character of the Green/MoM technique permits the accuracy assessment of purely numerical techniques, such as the FDTD, which is currently the most widely used computational method in mobile communication dosimetric problems, since it allows modeling of anatomically based head models. After appropriate benchmarking, FDTD simulations are used to study the interaction between a heterogeneous anatomically correct model of the human head exposed to a normal-mode helix monopole operating at 1710 MHz mounted on the top of a metal box representing a realistic mobile communication terminal. The study of both canonical and realistic exposure problems includes computations of specific absorption rates (SARs) inside the human head, total power absorbed by the head and assessment of antenna performance. Emphasis is placed on the comparative dosimetric assessment between adults and children head models.     

Nature of Cooper Instability of Spin Polarons in Cuprate High-$$T_\mathrm{c}$$ Superconductors

It is shown that the exchange interaction in the subsystem of localized moments of copper ions can trigger a Cooper instability in the ensemble of spin-polaron quasiparticles in cuprate high-temperature superconductors. It is important that, inherent to cuprates, strong coupling between Fermi and spin degrees of freedom leads on the one hand to formation of spin-polaron quasiparticles and, on the other hand, allows to transfer the interaction between Bose degrees of freedom onto the interaction between Fermi quasiparticles. The solution of the integral equation for the d-wave superconducting order parameter is well consistent with the available experimental data.     

Design and performance of asymmetric supported membranes for oxygen and hydrogen separation

Producing syngas and hydrogen from biofuels is a promising technology in the modern energy. In this work results of authors’ research aimed at design of supported membranes for oxygen and hydrogen separation are reviewed. Nanocomposites were deposited as thin layers on Ni–Al foam substrates. Oxygen separation membranes were tested in CH₄ selective oxidation/oxi-dry reforming. The hydrogen separation membranes were tested in C₂H₅OH steam reforming. High oxygen/hydrogen fluxes were demonstrated. For oxygen separation membranes syngas yield and methane conversion increase with temperature and contact time. For reactor with hydrogen separation membrane a good performance in ethanol steam reforming was obtained. Hydrogen permeation increases with ethanol inlet concentration, then a slight decrease is observed. The results of tests demonstrated the oxygen/hydrogen permeability promising for the practical application, high catalytic performance and a good thermochemical stability.     

Ion-implantation studies on perpendicular media

Magnetic and structural properties of ion implanted perpendicular recording media have been investigated. Effects of 12C+ ion implantation with the doses of 2 x 10(11), 10(13), 10(14) and 10(16) ions/cm2 in the magnetic recording layer of conventional granular and continuous perpendicular media are reported in this paper. Implantation with the highest fluence of 10(16) ions/cm2 resulted in change of the magnetization reversal mechanism, thereby reducing coercivity. In continuous media the implanted ions cause increase in pinning defects, leading to an increase in coercivity. In contrast, high dose was found to cause similar change in the crystallographic properties of both the granular and continuous media.