Factorization of Rational Matrices in Sampled-Data Systems Design

Special features of factorization procedures for two types of rational matrices encountered in H ₂ and H optimization problems for sampled-data systems are considered. A rigorous estimate of the characteristic polynomial of the H ₂-optimal closed-loop system is given.     

Admission control and resource optimization for multiple-user OFDMA Cognitive Radio systems

In Cognitive Radio (CR) systems, the fluctuating nature of the available frequency resource due to Primary Users (PUs) activity necessitates the introduction of admission and eviction measures at the CR system if a guaranteed Quality of Service (QoS) is required by Real Time (RT) Secondary Users (SUs). This problem has been recently addressed in the literature with simplified assumptions that might become unrealistic in practical system setups. In this paper, we tackle the problem of admission and eviction control of RT SUs in multiple-user Orthogonal Frequency Division Multiple Access (OFDMA) CR systems and propose new solutions that are practical and efficient at the same time. In particular, we propose three different ways to install a Resource Buffer Zone (RBZ) at the time of admission to limit future call drops resulting from fluctuating PU activity. We also study the effect of PU activity on the feasibility of the resource allocation problem and propose three different methods to resolve system outages once they occur. Numerical results obtained through Monte Carlo simulations demonstrate the efficacy of the proposed techniques.     

Mechanisms of action of isothiocyanates in cancer chemoprevention: an update

Isothiocyanates (ITC), derived from glucosinolates, are thought to be responsible for the chemoprotective actions conferred by higher cruciferous vegetable intake. Evidence suggests that isothiocyanates exert their effects through a variety of distinct but interconnected signaling pathways important for inhibiting carcinogenesis, including those involved in detoxification, inflammation, apoptosis, and cell cycle and epigenetic regulation, among others. This article provides an update on the latest research on isothiocyanates and these mechanisms, and points out remaining gaps in our understanding of these events. Given the variety of ITC produced from glucosinolates, and the diverse pathways on which these compounds act, a systems biology approach, in vivo, may help to better characterize their integrated role in cancer prevention. In addition, the effects of dose, duration of exposure, and specificity of different ITC should be considered.     

Multilevel coding for multiple-antenna transmission

The application of powerful coding for transmission over multiple-input/multiple-output channels is discussed. The authors emphasize that as an immediate consequence of the mutual information chain rule, multilevel coding (MLC) constitutes the optimum coded modulation scheme. On the other hand, simple bit-interleaved coded modulation (BICM) is only a convenient alternative for the case of two transmit and one receive antennas when combined with orthogonal space-time block codes. Starting from MLC, the authors further propose a hybrid coded modulation scheme, which favorably combines the advantages of MLC and BICM.     

Thermochemische Plasmawärmebehandlung von metallischen Werkstoffen

Thermochemical Plasma Heat Treatment of Metals Thermochemical plasma heat treatment of metals has a number of advantages over conventional processes. This paper describes the basic principles, the plasma process equipment and the effect of the main parameters. Reasons for the great advantages and versatilities of plasma heat treatment are reported. The major subject is plasma nitriding and plasma nitrocarburizing of steels and titanium alloys. The presented results show how the great number of independent process parameters allow to produce surface layers with specific microstructure and properties.     

Performance of coded modulation employing differential encodingover Rayleigh fading channels

Multilevel coding and bit-interleaved coded modulation employing differential encoding and non-coherent reception over flat fading channels are assessed. To achieve high bandwidth efficiencies mixed amplitude/phase modulation is performed. It is shown that multiple symbol detection only provides gains for multilevel coding as Gray labelling of the differential symbols is not possible     

Iterative interference cancellation for DS-CDMA systems with highsystem loads using reliability-dependent feedback

In this paper, coded transmission over time-variant multipath Rayleigh-fading channels employing direct-sequence code division multiple access (DS-CDMA) is considered. Assuming ideal knowledge of the actual channel state and randomly chosen spreading sequences, we show that iterative multi-user interference suppression based on adapted minimum mean-squared error (MMSE) filters combined with serial successive cancellation and single user decoding can reach near optimum performance within a few iteration cycles. This holds even for doubly loaded systems, i.e., when the number of users K in the system is two times as large as the spreading factor N. Further, we evidence that for sufficiently reliable symbol estimates soft decision feedback can be replaced by hard decision feedback without any performance degradation but with significant savings in complexity     

On the Determination of Charge Profiles in Epitaxial Layers of ZnSe by Capacitance Measurements

The doping profile in semiconducting epitaxial layers is often deduced from the behavior of the capacitance of a Schottky contact evaporated onto the surface of the layer as a function of the bias voltage. It is shown on the example of Au/ZnSe/GaAs heterostructures that the heterojunction with the substrate in series with this Schottky contact leads to erroneous profiles, if no special care is taken in the choice of the frequency used in measuring the capacitance. This frequency must be chosen below the cutoff frequency which is apparent in the graphs of the capacitance vs the frequency.     

Steady state analysis of electronic circuits by cubic and exponential splines

Multitone Harmonic Balance (HB) is widely used for the simulation of the quasiperiodic steady state of RF circuits. HB is based on a Fourier expansion of the unknown waveforms and is state-of-the-art. Unfortunately, trigonometric polynomials exhibit poor convergence properties in cases where the signal is not quasi-sinusoidal which leads to a prohibitive run-time even for small circuits. Moreover, the approximation of sharp transients leads to the well-known Gibbs phenomenon, which cannot be reduced by an increase of Fourier coefficients. In this paper, we present an alternative approach based on alternatively cubic or exponential splines for a (quasi-) periodic steady state analysis. Unlike trigonometric basis function, a spline basis solves for a variational problem, i.e., the cubic spline minimizes the curvature. Because of their compact support, spline bases are better suited for waveforms with sharp transients. Furthermore, we show that the amount of work for coding of splines is negligible if an implementation of HB is available. In general, designers are mainly interested in spectra and not in waveforms. Therefore, a method for calculating the spectrum from a spline basis is derived too.