Analysis and design of a three-phase current source solid-state VARcompensator

A reactive power compensation (RPC) system which uses a three-phase current-source force-commutated PWM (pulsewidth-modulated) rectifier is presented and analyzed. Pulsewidth modulation is also investigated as a means of reducing the size of reactive components. The proposed RPC system can compensate for leading and lagging displacement power factor. Other areas of investigation include the selection of rectifier input and output filter components and the closing of the loop around the reactive power command signal. finally, predicted results are verified experimentally     

On the numerical modelling of quasi‐static crack growth in linear elastic fracture mechanics

In this paper we present a strategy for the simulation of a propagating crack under mixed mode linear elastic conditions using a discontinuous finite element method. A key issue is to accurately compute the incremental change in the kink angle of the propagating crack during subsequent steps. We have chosen to work with a domain formulation of the material force vector as a criteria for the propagation direction. We describe the theoretical background together with the numerical implementation in detail and show some results for different loading conditions. Copyright © 2005 John Wiley & Sons, Ltd.     

Design aspects of synchronous PWM rectifier-inverter systems underunbalanced input voltage conditions

A complete analysis of a synchronous front-end PWM rectifier-inverter system under unbalanced input voltage conditions is presented. The analysis includes the harmonic assessment of input/output current and voltage waveforms. It is shown both theoretically and experimentally that input voltage unbalance generates uncharacteristic low-frequency harmonic components in the input and output currents. Special emphasis is given to the generation of a DC component in the inverter output voltage in the case in which the output frequency is twice the input frequency. System design curves for different degrees of unbalance for all major system components are reported. Key predicted results are confirmed experimentally     

Iterative speed improvement for solving slowly varying total least squares problems

Many problems in signal processing, modal analysis, system identification, etc., give rise to an overdetermined set of linear equations AX ≈ B. Whenever both the observation matrix B and the data matrix A are inaccurate, the total least squares (TLS) method is appropriate for estimating the unknown parameters X. Since the TLS solution is deduced from only one right singular vector or, in general, a basis of the right singular subspace associated with the smallest singular values of the data [A; B], the computational speed can be improved by only calculating those desired base vectors. If a priori information is available (e.g. the TLS solution at a previous time step when slowly varying sets of equations must be solved at each time instant), iterative methods are appropriate to compute those base vectors. It is shown in this paper that inverse iteration is the most efficient iterative technique for solving generic TLS problems of known rank.Two algorithms for subspace inverse iteration are presented. Their convergence properties and applicability in solving TLS problems are analysed. Based on the convergence rate and the operation counts in each iteration step, these iterative algorithms are compared in efficiency with the direct computation methods—classical TLS and partial TLS. In particular, the efficiency of these methods is illustrated in a practical real life problem, namely multiple input estimation of frequency response functions.     

Spark plasma sintering and decomposition of the Y<Subscript>3</Subscript>NbO<Subscript>7</Subscript>:Eu phase

The spark plasma sintering (SPS) of Eu³⁺-doped Y₃NbO₇ niobate phase was investigated to obtain dense ceramics. Although SPS allowed obtaining high-density ceramics, decomposition of the niobate phase occurred at high temperature and was promoted by the SPS process, which limited its use as an optical material. The niobate phase has been prepared by two synthesis methods: a solid-state route and a sol–gel method. The purity, density and microstructure of the dense ceramics were analyzed after spark plasma sintering. Translucent ceramics were only obtained from sol–gel powders after SPS at 1600 °C during 20 min with a heating rate of 5 °C/min. The sintering study of the pure niobate phase showed that during SPS process and especially in the presence of the high electrical field the Y₃NbO₇ phase is metastable at 1600 °C. A decomposition of the niobate compound is clearly demonstrated by luminescence measurements when high heating rates were used.     

Stress and phase purity analyses of diamond films deposited through laser-assisted combustion synthesis

Diamond films were deposited on silicon and tungsten carbide substrates in open air through laser-assisted combustion synthesis. Laser-induced resonant excitation of ethylene molecules was achieved in the combustion process to promote diamond growth rate. In addition to microstructure study by scanning electron microscopy, Raman spectroscopy was used to analyze the phase purity and residual stress of the diamond films. High-purity diamond films were obtained through laser-assisted combustion synthesis. The levels of residual stress were in agreement with corresponding thermal expansion coefficients of diamond, silicon, and tungsten carbide. Diamond-film purity increases while residual stress decreases with an increasing film thickness. Diamond films deposited on silicon substrates exhibit higher purity and lower residual stress than those deposited on tungsten carbide substrates.     

Polymer electrolyte membrane fuel cell contamination: Testing and diagnosis of toluene-induced cathode degradation

The effects of toluene contamination on the performance of polymer electrolyte membrane (PEM) fuel cells were investigated, using various levels of toluene concentration in the air streams, under different operational conditions and with different catalyst loadings. Constant-current polarization and electrochemical impedance spectroscopy (EIS) were conducted to analyze the poisoning behaviour of toluene. The severity of the contamination effect increased with an increase in both the current density and the toluene concentration, but decreased with an increase in both the relative humidity (RH) and the cathode-side Pt loading. The toluene-poisoned fuel cell could not be fully recovered by replacing toluene-contaminated air with pure air. EIS measurements revealed that both kinetic resistance and mass transfer resistance increased as a result of toluene contamination, while membrane resistance remained unchanged. However, the increase in kinetic resistance was a major contributor to cell performance degradation.     

Tyrosine phosphorylation of the juxtamembrane domain of the v-Fms oncogene product is required for its association with a 55-kDa protein

Tyrosine autophosphorylation of the v-Fms oncogene product results in the formation of high affinity binding sites for cellular proteins with Src homology 2 (SH2) domains that are involved in various signal cascades. Tryptic digestion of the autophosphorylated v-Fms and of its cellular counterpart, the feline c-Fms polypeptide, gave rise to at least six common major phosphopeptides, four of which have been characterized previously. Employing site-directed mutagenesis and phosphopeptide mapping of in vitro phosphorylated glutathione S-transferase v-Fms fusion proteins as well as full-length v-Fms molecules expressed in various cells, we show here that Tyr543 of the juxtamembrane domain and Tyr696 of the kinase insert domain constitute major autophosphorylation sites. Recombinant fusion proteins containing the tyrosine-phosphorylated kinase insert domain bind the growth factor receptor bound protein 2 and the p85 and p110 subunits of phosphatidylinositol 3'-kinase. In contrast, fusion proteins containing the juxtamembrane domain phosphorylated on Tyr543 fail to bind any of the known SH2 domain-containing cellular proteins but associate specifically with an as yet undefined 55-kDa cellular protein that by itself is phosphorylated on tyrosine.