Accurate near-field calculation in the rigorous coupled-wave analysis method

The rigorous coupled-wave analysis (RCWA) is one of the most successful and widely used methods for modeling periodic optical structures. It yields fast convergence of the electromagnetic far-field and has been adapted to model various optical devices and wave configurations. In this article, we investigate the accuracy with which the electromagnetic near-field can be calculated by using RCWA and explain the observed slow convergence and numerical artifacts from which it suffers, namely unphysical oscillations at material boundaries due to the Gibb's phenomenon. In order to alleviate these shortcomings, we also introduce a mathematical formulation for accurate near-field calculation in RCWA, for one- and two-dimensional straight and slanted diffraction gratings. This accurate near-field computational approach is tested and evaluated for several representative test-structures and configurations in order to illustrate the advantages provided by the proposed modified formulation of the RCWA.Comment: 13 pages, 12 figure

The impact of cultural dissonance and acculturation orientations on immigrant students' academic performance

Indexación: Scopus; Scielo; Redalyc.Prior research has documented meaningful differences between school performance of immigrant and native students. Multicultural education has been associated with academic failure of foreign students. e aim of this study was to examine the impact of a set of psychosocial variables on the perceived academic achievement of first generation immigrant adolescents from public secondary schools in Northern Spain. Results showed that 46% of the variability in foreign students’ perceived academic performance was explained by home-school cultural dissonance. We also explored the impact of acculturation orientation to separation, perception of discrimination from teachers, school adjustment, and psychological well-being in academic performance. Any multicultural education context should take into account psychosocial adjustment, given its influence on academic performance of all studentsSe han hallado diferencias significativas entre el rendimiento académico de los inmigrantes y el de los estudiantes nativos. Sin embargo, hay una escasa evidencia acerca de los aspectos psicosociales de este fenómeno. El objetivo de este estudio fue examinar el impacto de un conjunto de variables psicosociales: disonancia cultural y orientaciones de aculturación en el rendimiento académico percibido de adolescentes inmigrantes de primera generación de centros de Educación Secundaria en el Norte de España. Los resultados mostraron que alrededor del 46% de la variabilidad en el rendimiento era explicada por la disonancia cultural entre escuela y hogar. Cualquier contexto de educación multicultural ha de tomar en consideración el ajuste psicosocial, dada su influencia en el rendimiento académico de los estudiantes.http://www.redalyc.org/jatsRepo/647/64753989003/index.htm

Diagnostic methods of frequency response analysis for power transformer winding a review

Abstract: Monitoring and diagnosis of power transformers in power systems have been investigated and discussed for the past decades. Earlier detect power transformer winding failures is recommended for both manufacturing process and also for power system operators. One of the most powerful and accurate tool for sufficient winding deformation detection is considered Frequency Response Analysis (FRA) among other diagnostic methods. In this paper a review of diagnostic methods of FRA for power transformer winding are presented. Different methods of transformer winding diagnosis, with their benefits and drawbacks where investigated. Moreover, possible windings failures, diagnostic methods of FRA in Off-line and On-line power transformers, detailed advantages and disadvantages of two major types of FRA are presented. The paper was able to show that some uncertainties have not been eliminated completely

Small power, three to one phase matrix converter for wind generators

Abstract: This paper will investigate the use of a three-to-one Matrix converter to synchronize the electrical energy and condition the output of the wind generator. A Matrix converter is a direct ACAC solution, removing the need for large smoothing capacitors in a typical rectifier/inverter solution. This paper will briefly review the Matrix converter operational theory. A simulation and the practical results of a three-to-one phase matrix converter for varying input frequencies are also presented. The conclusion shows that the proposal is a viable solution for small power wind harvesting

The performance of distance protection relay on series compensated line under fault conditions

Abstract: This paper presents the behaviour of the distance protection relays on a series compensated transmission line under fault conditions. Series compensation presents distance protection elements with unorthodox line impedance and as a result the relays may operate incorrectly. Sub-harmonic oscillations and non-linearity of the line impedance are some of the challenges introduced by series compensation of transmission lines. The study is carried out in a Digsilent power factory environment and results pertaining to the response of the distance relay on a 400 kV series compensated line under fault conditions are presente

Using PSIM to investigate harmonic control for boost-type PWM rectifiers

Abstract: Static power converters produce harmonics due to the nature of the conversion process. This paper will investigate two variations of current mode control for three-phase power converters ensuring reduced harmonic pollution and power factor improvement. The first method employed uses a Fryze current reference and the second method utilises a balanced three-phase sinusoidal reference. Both control techniques are simulated under unbalanced and distorted supply conditions using the PSIM simulation platform. The results are presented showing that using the Fryze current reference is the best choice