Fuzzy risk index for power transformer failures due to external short-circuits

A novel methodology to assess the risk of power transformer failures caused by external faults, such as short-circuit, taking the paper insulation condition into account, is presented. The risk index is obtained by contrasting the insulation paper condition with the probability that the transformer withstands the short-circuit current flowing along the winding during an external fault. In order to assess the risk, this probability and the value of the degree of polymerization of the insulating paper are regarded as inputs of a type-2 fuzzy logic system (T2-FLS), which computes the fuzzy risk level. A Monte Carlo simulation has been used to find the survival function of the currents flowing through the transformer winding during a single-phase or a three-phase short-circuit. The Roy Billinton Test System and a real power system have been used to test the results.     

Wavelet power,entropy and bispectrum applied to AE signals for damage identification and evaluation of corroded galvanized steel

Acoustic emission (AE) signals obtained from scratch tests on hot dip galvanized samples with different corrosion levels were processed by wavelet transform (WT) analysis. Wavelet power was distributed in different frequency bands, according to damage mechanisms. The frequency bands were automatically obtained by searching for the relative minima of the wavelet entropy of signals and appropriate clustering methods. Correlation between the different mechanisms was corroborated by bispectrum analysis (BA). The damage evaluation entailed studying the evolution of the wavelet power in a specific frequency band, which corresponded to the fracture of the zeta phase columns of the galvanized coating. Results showed damage to increase along with the level of corrosion, but adherence was not dramatically affected in the studied corrosion range. The application of two signal-processing techniques, WT and BA, contributed to the consistency of our results. Besides the addressed technological application, we could demonstrate that that signal-processing techniques, when applied carefully, and results classified with care, are able to contribute to what is certainly an important problem, specially in cases like the treated here, where a complete physical theory relating damage and AE is not yet available.     

Hydrodynamic characterization of a needle sparger rectangular bubble column: Homogeneous flow, static bubble plume and oscillating bubble plume

In this work a detailed experimental hydrodynamic characterization of a needle sparger rectangular bubble column has been performed. The liquid velocity profiles and bubble plume oscillation frequency have been measured by means of laser Doppler anemometry (LDA), and the bubble velocity map by particle image velocimetry (PIV). In this way, the influence of the superficial gas velocity, liquid height and aeration pattern on the column flow structure was analysed. A highly uniform upward flow structure with down flow near the walls was obtained by means of a full-length aeration pattern. This flow structure was preserved even for high gas fractions values. The partial-length aeration patterns with the aerated zone (defined as the aerated width divided by the column width) larger than 0.7 provide a bubble plume and two pure liquid vortical structures in the column bottom, although they are static in nature. With aerated zones lower than 0.6, an oscillating bubble plume is obtained. A non-dimensional analysis of bubble plume oscillation frequency shows a dependence of bubble plume behaviour with the aerated zone. In this way, two different types of bubble plume oscillations, namely confined bubble plume oscillation and free bubble plume oscillation, are introduced and analysed.     

Four‐parameter beta distribution estimation and skewness test

Sequential tolerance control (STC) is a tolerance control methodology used in discrete parts manufacturing. Recently, an adaptive sphere‐fitting method for STC (ASF–STC) was developed to account for potential skewness in manufacturing operations' distributions, a factor not considered in conventional STC. ASF–STC offers significant improvements over conventional STC when such skewness exists. The direction of skewness of an operations' distribution is a necessary input to ASF–STC. Thus, a novel approach to determining the skewness of a distribution for small sample sizes is presented here. ASF–STC has an additional requirement of distribution information for each operation. The beta distribution is an ideal candidate here, as it is very flexible in shape. The literature on four‐parameter beta estimation is very limited, and their performance for small sample sizes is poor. STC was designed for low‐volume production, thus the estimation for small sample sizes is necessary here. This study presents a heuristic, based on the method of moments estimates for a beta distribution, that estimates the four parameters for a beta distribution with small sample size. Several computational results are provided to compare this heuristic to the best‐known procedure, with the heuristic found to perform better for the test problems considered. Copyright © 2002 John Wiley & Sons, Ltd.     

Audio-visual speech asynchrony detection using co-inertia analysis and coupled hidden markov models

This paper addresses the subject of liveness detection, which is a test that ensures that biometric cues are acquired from a live person who is actually present at the time of capture. The liveness check is performed by measuring the degree of synchrony between the lips and the voice extracted from a video sequence. Three new methods for asynchrony detection based on co-inertia analysis (CoIA) and a fourth based on coupled hidden Markov models (CHMMs) are derived. Experimental comparisons are made with several methods previously used in the literature for asynchrony detection and speaker location. The reported results demonstrate the effectiveness and superiority of the proposed new methods based on both CoIA and CHMMs as asynchrony detection methods.     

Strain-life fatigue predictions for sintered steels with nonzero mean stress

Several approximate models have been utilized for fatigue life prediction. Some of these models are available for mean stress (or strain) correction on fatigue life, when nonzero mean stress (or strain) is applied. In this paper, the most commonly used empirical strain-life models for fatigue life predictions, for materials subjected to variable amplitude loads, are described. Experimental results of fatigue tests, where the specimens of sintered steels were subjected to partial random loads, are presented and compared with those results obtained theoretically by the models. The utilization of the various models and their influence on results are discussed.     

Analytical expression for the non-isothermal effectiveness factor: the nth-order reaction in a slab geometry

The problem of calculating the effectiveness factor for a porous slab of catalyst pellet under non-isothermal conditions has been revisited. An exact formal analytical solution was obtained for a nth-order (integer n?0), exothermic and irreversible chemical reaction. Numerical calculations where performed, and an analytical formula was obtained for the very fast reaction limit. In addition, a fairly simple formula, which was called the low beta approximation, was developed and tested to be valid for low values of the thermicity group β?0.1.     

Integration in Europe of human genetics results obtained by Spaniards in the USA: A historical perspective

The mobility of Spanish biochemists from Europe to the United States over the past 80 years (1927–2006) is approached from a historical perspective. The academic community on human genetics has awarded this emigrated Spanish community with the Nobel prize as well as other awards from European foundations. The vertical/horizontal integration methodology offers an opportunity to understand the extremely satisfactory history of a small European community overseas. To piece the puzzle together, continuous reference is made to the theory of systems. To test and use this holistic history, the circulation of the knowledge produced on cancer has been studied as intrinsically related to time by using the algorithmic historiography. Francisco Duran Reynals and Severo Ochoa have been selected as examples of the vertical integration. The former one because he was the director of an important collaborator, his own wife; the latter, as the founder of a Spanish specific research school in America based in his own work. The simultaneous stay of several young Spanish scientists at the Columbia University (Mariano Barbacid, Manuel Perucho and ángel Pellicer) serves to design the horizontal integration, to create a holon hierarchy to reflect the criteria of subsidiarity and acceptability, and to focus on the Spanish discoveries and contributions to cancer research. The transatlantic flows of knowledge generated by the Spanish elite of biochemists in the USA from 1927 on define a network of geographical displacements. As a result, the social structure thus visualizes the identity of the international mobility of scientists who leave for Europe/USA, and their return to Spain. A model of the brain drain of professionals to the USA, that retain 80% of the Spanish cancer researchers, is developed. A version of theis paper was a contribution to: 2nd International Conference of the European Society for the History of Science (Cracow, Sept. 2006).     

Novel mesoporous aluminosilicate supported palladium-rhodium catalysts for diesel upgrading: I. Preparation and characterisation

Bimetallic PdRh (with Pd/Rh mole ratio = 2/1) catalysts supported on a mesoporous aluminosilicate have been prepared and three methods of metal incorporation in the support have been compared: direct incorporation into the synthesis gel, impregnation and ion-exchange. Physico-chemical characterisations (nitrogen adsorption–desorption, hydrogen chemisorption, transmission electron microscopy, X-ray photoelectron and extended X-ray absorption fine structure spectroscopies), as well as simulated coking and regeneration tests are described. The dispersion, metal particle size and the formation of bimetallic particles within the material depend on the method of metal incorporation. Direct incorporation and ion-exchange methods lead to co-existence of PdRh intermetallic aggregates and segregated Pd; on the other hand, the impregnation method leads to the formation of very small and well dispersed PdRh alloy particles, with Pd preferentially located on the alloy particle surface.