Muon spin relaxation study of amorphous Hf2Co

Muon spin relaxation measurements were carried out in zero magnetic field on amorphous Hf₂Co. The results obtained and comparison with the behaviour of the muon in crystalline Hf₂Co (A. Baudry, P. Boyer, L.P. Ferreira, S.W. Harris, S. Miraglia and L. Pontonnier, J. Phys.: Condens. Matter, 4 (1992) 5025) indicate that muons occupy interstitial sites without Co atoms in first-neighbour positions and diffuse through those sites, suggesting the existence of some degree of short-range order in the amorphous structure. Muon diffusion cannot be described by a single thermally activated process and is faster in the amorphous alloy than in the crystalline alloy.     

Fatigue behaviour of a phenolic matrix composite

This paper presents results of a fatigue life investigations carried out in plate specimens of a fibre-glass-reinforced phenolic matrix composite. Tensile and Young's modulus data were obtained at four different testing temperatures (room temperature, 100, 150 and 200 °C). The fatigue S−N data were obtained at room temperature only and for two stress ratio values (R=0 and 0.4). Fatigue and tensile behaviour was assesesed in the composite with the fibres aligned in the longitudinal loading direction. The results were obtained for two values of volume fraction (0.28 and 0.42) and three different glass surface treatments. A detailed comparison of fatigue results is given taking into account several fatigue parameters and also the testing variables. Results of observations of SEM fracture surfaces are also presented.     

Analysis and Design of Robust Controllers Using the Interval Diophantine Equation

In this paper the design of pole placement feedback controllers for interval plants is addressed within an Interval Analysis framework. Three main topics connected by the concept of interval Diophantine equation are treated: a relatively straightforward investigation about robust coprimeness of interval polynomials, a reliable computing approach for the design of pole placement controllers in the presence of inaccuracies of interval type, and the design of robust controllers with regional pole placement specifications. After explicitly characterizing a convex subset of robust controllers, the problem of designing non-fragile controllers is formulated as a design centering problem, which is then solved by a global optimization algorithm. Numerical examples illustrate the main characteristics of the approach proposed.This paper has been partially supported by grants from Conselho Nacional de Desenvolvimento Científico e Tecnológico–Brazil.     

Mesh‐independent p‐orthotropic enrichment using the generalized finite element method

This paper is aimed at presenting a simple yet effective procedure to implement a mesh‐independent p‐orthotropic enrichment in the generalized finite element method. The procedure is based on the observation that shape functions used in the GFEM can be constructed from polynomials defined in any co‐ordinate system regardless of the underlying mesh or type of element used. Numerical examples where the solution possesses boundary or internal layers are solved on coarse tetrahedral meshes with isotropic and the proposed p‐orthotropic enrichment. Copyright © 2002 John Wiley & Sons, Ltd.     

Propagation of flicker in electric power networks due to windenergy conversions systems

Wind energy conversion systems (WECS) produce fluctuating output power, which may cause voltage fluctuations and flicker. Flicker assessment in networks may be difficult since its evaluation requires long computing time and special procedures to calculate the flicker severity index, Pst. In this paper, a frequency domain method to study flicker propagation is presented. This method is based on propagation of frequency components from WECS output currents throughout the grid. In this way, a fast flicker analysis in a network of any size can be performed. Also, an algorithm for flicker measurement in the frequency domain, which allows Pst calculation, is proposed. Several study cases have been performed, and results have been compared with time domain simulations, showing good agreement between them     

Computationally efficient methods for bit-error rate evaluation inweakly coherent optical systems

A semianalytical method to estimate the bit-error rate performance of nonsynchronous ASK and FSK optical heterodyne systems is presented. This approach takes into account numerous system details with an accuracy similar to Monte-Carlo simulation, but with a computation time reduced by several orders of magnitude. An analytical approximation, based on a closed-form expression for the decision variable moment generating function, is also presented. The results obtained with the semianalytical method and the analytical approximation are compared to Monte-Carlo simulation results and to measurements obtained on a practical FSK system     

Screening of supports for the immobilization of pectinmethylesterase from acerola (Malpighia glabra L)

A partially purified extract of pectinmethylesterase (PME) from acerola fruit was immobilized on various supports: glass, celite, chrysotile, agarose, concanavalin A Sepharose 4B, egg shell, polyacrylamide and gelatin. In addition, reticulation with glutaraldehyde was assessed, as well as the use of gelatin in the presence of celite, glass and silica. The highest immobilization yields were obtained when the pectinmethylesterase was immobilized in concanavalin A Sepharose 4B (81.7%) and in gelatin‐water (78.0%). Copyright © 2004 Society of Chemical Industry     

Uniform Polarization Scattering With Fiber-Coil-Based Polarization Controllers

A detailed study of fiber-coil-based polarization controllers (PCs) is performed. First, a method to deterministically calculate the PC configuration in order to transform between any two states of polarization is presented. In a second stage, the case in which the configuration angles are randomly changed is studied. The cases of a single PC and of the system obtained with the concatenation of several PCs are analyzed. For both cases, a general expression for the variance of the Stokes parameters is obtained. Using this expression, it is demonstrated that it is possible to achieve uniform polarization scattering using a concatenation of fiber-coil-based PCs. Finally, it is shown that fiber-coil-based PCs can be used to emulate both first- and second-order polarization-mode dispersions