Thermal simulation for geometric optimization of metallizedpolypropylene film capacitors

In this paper, the authors use an analytical model to calculate the losses in the metallized polypropylene film capacitors. The model is validated experimentally for capacitors having the same capacitance but different geometry. For each group of capacitors, a temperature distribution in the roll is assumed with the aim of optimizing its thermal performance. It appears that the heating of a long capacitor is higher than that of an equivalent flat capacitor subjected to the same electric stresses     

Radar cross section measurements using near-field radar imaging

In this paper a technique to obtain the far-field scattering signature of bodies, using near-field measurements, is proposed. The method is based on near-field radar imaging techniques. The backscattered field data are collected in a controlled environment over a large frequency band and aspect angle using a near-field antenna. A focused radar image of the body is generated. Probe correction to compensate for the radiation pattern of the interrogating antenna is conducted during the two-dimensional imaging of the object. The contribution from each scattering center to the total backscattered far-field is obtained from the radar image. The proposed technique is applied to obtain the far-field radar cross section (RCS) for an object from near-field measurements conducted in an anechoic chamber at the University of Pretoria, South Africa     

Nonlinear black-box modeling in system identification: a unified overview

A nonlinear black-box structure for a dynamical system is a model structure that is prepared to describe virtually any nonlinear dynamics. There has been considerable recent interest in this area, with structures based on neural networks, radial basis networks, wavelet networks and hinging hyperplanes, as well as wavelet-transform-based methods and models based on fuzzy sets and fuzzy rules. This paper describes all these approaches in a common framework, from a user's perspective. It focuses on what are the common features in the different approaches, the choices that have to be made and what considerations are relevant for a successful system-identification application of these techniques. It is pointed out that the nonlinear structures can be seen as a concatenation of a mapping form observed data to a regression vector and a nonlinear mapping from the regressor space to the output space. These mappings are discussed separately. The latter mapping is usually formed as a basis function expansion. The basis functions are typically formed from one simple scalar function, which is modified in terms of scale and location. The expansion from the scalar argument to the regressor space is achieved by a radial- or a ridge-type approach. Basic techniques for estimating the parameters in the structures are criterion minimization, as well as two-step procedures, where first the relevant basis functions are determined, using data, and then a linear least-squares step to determine the coordinates of the function approximation. A particular problem is to deal with the large number of potentially necessary parameters. This is handled by making the number of ‘used’ parameters considerably less than the number of ‘offered’ parameters, by regularization, shrinking, pruning or regressor selection.     

Structural studies on γ-MnO2 by transmission electron microscopy

Single-crystal electron diffraction patterns were obtained on five specimens of -MnO₂: one natural, two electrolytical (EMD) and two chemical (CMD) samples. EMDs are best described by the orthorhombic structure proposed by De Wolff which is derived from the ramsdellite structure. A CMD prepared from MnCO₃ fits the hexagonal cell of -MnO₂. Flaky grains from the natural sample and fibres from a CMD prepared from Mn(NO₃)₂ are hexagonal with a new cell:a 0.494,c 0.539 nm. No simple relation between chemical composition, morphology and structure could be found.     

The Zr-Ni-Cr system at 1000 °C in the ZrCr2-ZrNi-Ni-Cr region

The isothermal section of the Zr-Ni-Crternary system was determined at 1000 °C in the ZrCr₂-ZrNiNi-Cr region. The nature and composition of the phases involved in the different equilibria were determined by metallographic analysis, electron probe microanalysis (EPMA), and x-ray powder diffraction (XRD) analysis. Substitution of Cr by Ni in the Laves phase ZrCr₂ is possible in large quantities resulting in the formation of ternary Laves phases. However formation of the ZrNi₂ compound was not observed. This substitution reduces the content of Zr and induces transformations from C15 to C14 and to the C15 structure through two two-phase regions.     

Supporting multiple perspectives in feature-based configuration

Feature diagrams have become commonplace in software product line engineering as a means to document variability early in the life cycle. Over the years, their application has also been extended to assist stakeholders in the configuration of software products. However, existing feature-based configuration techniques offer little support for tailoring configuration views to the profiles of the various stakeholders. In this paper, we propose a lightweight, yet formal and flexible, mechanism to leverage multidimensional separation of concerns in feature-based configuration. We propose a technique to specify concerns in feature diagrams and to generate automatically concern-specific configuration views. Three alternative visualisations are proposed. Our contributions are motivated and illustrated through excerpts from a real web-based meeting management application which was also used for a preliminary evaluation. We also report on the progress made in the development of a tool supporting multi-view feature-based configuration.     

Optical modes for BiNem® LCDs

Abstract— We report on theoretical simulations and measurements of the optics of BiNem® displays, taking into account not only the luminance at normal incidence, but contrast ratio and color shift over the viewing hemisphere as well. Transmissive and reflective BiNem® modes were optimized differently, emphasizing contrast in transmission and paperlike, white appearance in reflection.     

Experimental Data Highlighting the Role of Surface Fracture Energy in Quasi-Static Confined Comminution

Since the pioneering work of Griffith, Linear Elastic Fracture Mechanics has been widely experimentally validated and successfully developed in solid mechanics modeling. However, recent theoretical models applying the energy balance found in Griffith theory specifically for quasi-static confined comminution have until now not been systematically confronted to experiments. In this study, we analyze data of compression tests on crushable sand, where grain breakage has been triggered by flooding the initially dry material at constant stresses. We consider a partition of the dissipation between surface fracture energy and the rearrangement of fragments and grains surrounding crushed particles. Our results show that the role of the surface fracture energy is stressdependent and that its influence becomes less significant at high stresses.     

Potential of solar heat pipe vacuum collectors in the desiccant cooling process: Modelling and experimental results

Desiccant cooling is an alternative technique to vapour compression systems. When thermally driven at moderate temperatures, it can be coupled to solar collectors. The use of flat-plate collectors and air collectors has demonstrated low efficiency in the coupling process and so a low potential of solar energy use in desiccant cooling. In this paper the use of heat pipe vacuum tube (HPVT) collectors in a solar desiccant cooling set up is investigated. First, a model for the collectors is proposed and experimentally validated under various operating conditions. A model of the storage tank taking into account thermal stratification is also validated. The experimentally evaluated efficiency of the HPVT collectors for one operating day varies between 0.6 and 0.7. Finally, simulation of the solar desiccant plant cooling a building is performed for different climates over a summer season. The solar fraction and the overall efficiency of the solar plant are calculated for this period and the potential of the vacuum tube collectors is evaluated for application to the desiccant cooling process.