New approach to power semiconductor devices modeling

The main problems occurring during high power device modeling are discussed in this paper. Unipolar and bipolar device properties are compared and the problems concerning high time-constant values related to the diffusion phenomena in the large base are explained. Traditional and novel concepts of power device simulation are presented. In order to make accurate and modern semiconductor device models widely accessible, a website has been designed and made available to Internet users, allowing them to perform simulations of electronic circuits containing high power semiconductor devices. In this software, a new distributed model of power diode has been included. Together with the existing VDMOS macromodel library, the presented approach can facilitate the design process of power circuits. In the future, distributed models of IGBT, BJT and thyristor will be added

EMI of large power systems: magnetic field calculation by substituting surface quantities for complex sources

The aim of this research is the elaboration of a method allowing simple simulation of electromagnetic interferences (EMI) of complex electric systems. The method presented in this paper allows the replacement of the electromagnetic active objects by simple closed surfaces that surround each source. The flux density components are calculated on these surfaces using standard 3D finite element software separately for each object. The magnetic flux density in every point of the free space around the system is calculated with an analytical formula. The main topic of the paper is the definition of the limits of the discussed method

Pb induces plant cell wall modifications - in particular - the increase of pectins able to bind metal ions level

Low - methylesterified pectin fraction, able to bind metal ions, is the cell wall compound which participates in land and water plant cell response to toxic metals. Protonemata of Funaria hygrometrica (Hedw.), root tips of Populus tremula x P.tremuloides and Lemna trisulca fronds, were used for studying the effects of Pb on plants cell walls (CW). The study were focused on the low- methylesterified pectins level and distribution. It was carried out by immunocytochemical methods, using JIM5 antibody which recognized lowmethylesterified pectins fraction - up 40%. Pb exposure resulted in the cell wall modifications in all investigated objects. The most striking result was the marked increase of the low-methylesterified pectins level. Moreover, cell walls thickenings were formed both in the moss protonemata and the poplar roots. The cell wall thickenings in both objects contained especially high level of low-methylesterified pectins. Simultaneously, cell wall thickenings accumulated extremely large and numerous Pb deposits. In many regions of the cell wall and cell wall thickenings the colocalization of low- methylesterified pectins and Pb deposits occurred. Low - methylesterified pectins level increased also in the cell walls of Lemna trisulca fronds and some of Pb deposits were colocalized with this pectin fraction in the CW. In fronds several Pb deposits occurred between plasma membrane and cell wall and only occasionally they were colocalized with lowmethylesterified pectins. However, in L. trisulca - cell wall was generally thicker in response to Pb. We did not observed almost any local cell wall thickenings as in Funaria and Populus. Taken these facts together we can conclude that plant cell walls were actively and intensively modified in response to Pb. In particular, the amount of low - methylesterified pectins, able to bind toxic Pb ions, markedly increased. Simultaneously, both cell wall and cell wall thickenings were the compartments which accumulate large amount of Pb. Hence, modified cell walls appear to be a very important repository for Pb2+ in different types of plant cells and different species. Detection of such a reaction in three different plant species and three different types of plant cells indicates that it may be more common plant tolerance strategy to Pb