PAM GTO inverter with quasi resonant dc link

Contents This paper presents a technique for realizing PAM capability in the case of a resonant dc link three phase inverter equipped with GTO thyristors. A new quasi resonant dc link circuit together with a sinusoidal PAM for an inverter fed drive are proposed in order to reduce the power losses in the machine and in the inverter. An improved dynamic behavior is also discussed in the paper. The harmonic analysis of the output voltage is presented for different operation modes.

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PAM-Wechselrichter mit quasiresonantem Zwischenkreis und GTO-Thyristoren

Übersicht In der Arbeit wird ein auf einen Wechselrichter mit GTO-Thyristoren angewandtes PAM-Verfahren vorgestellt. Der Wechselrichter wird von einem Gleichstromzwischenkreis mit Resonanzkreis gespeist. Es wird ein quasiresonanter Kreis zur Verringerung der Verluste im Wechselrichter und in der Asynchronmaschine vorgeschlagen. Durch die Steuerung des Wechselrichters erzielt man ein besseres dynamisches Verhalten des Antriebssystems. Eine Analyse der Harmonischen der Ausgangsspannung wird für verschiedene Betriebsweisen durchgeführt.

     

Pesticide measurements from the first national environmental health survey of child care centers using a multi-residue GC/MS analysis method

The U.S. Department of Housing and Urban Development, in collaboration with the U.S. Consumer Product Safety Commission and the U.S. Environmental Protection Agency, characterized the environments of young children (<6 years) by measuring lead, allergens, and pesticides in a randomly selected nationally representative sample of licensed institutional child care centers. Multi-stage sampling with clustering was used to select 168 child care centers in 30 primary sampling units in the United States. Centers were recruited into the study by telephone interviewers. Samples for pesticides, lead, and allergens were collected at multiple locations in each center by field technicians. Field sampling was conducted from July through October 2001. Wipe samples from indoor surfaces (floors, tabletops, desks) and soil samples were collected at the centers and analyzed using a multi-residue GC/MS analysis method. Based on the questionnaire responses, pyrethroids were the most commonly used pesticides among centers applying pesticides. Among the 63% of centers reporting pesticide applications, the number of pesticides used in each center ranged from 1 to 10 and the frequency of use ranged from 1 to 107 times annually. Numerous organophosphate and pyrethroid pesticides were detected in the indoor floor wipe samples. Chlorpyrifos (0.004-28 ng/cm2), diazinon (0.002-18 ng/cm2), cis-permethrin (0.004-3 ng/cm2), and     

Power active filter for controlled three-phase rectifier

Contents This paper presents a power active filter with inductive storage that permits a very good compensation of the higher current harmonics generated in the mains by a controlled or uncontrolled three-phase rectifier.

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Aktives Leistungsfilter für einen gesteuerten Stromrichter

Übersicht In der Arbeit wird ein aktives Leistungsfilter mit induktivem Speicher beschrieben, das eine bessere Kompensation der von einem gesteuertem Stromrichter erzeugten Stromharmonischen erlaubt.

     

Latent attractors: a model for context-dependent place representations in the hippocampus

Cells throughout the rodent hippocampal system show place-specific patterns of firing called place fields, creating a coarse-coded representation of location. The dependencies of this place code--or cognitive map--on sensory cues have been investigated extensively, and several computational models have been developed to explain them. However, place representations also exhibit strong dependence on spatial and behavioral context, and identical sensory environments can produce very different place codes in different situations. Several recent studies have proposed models for the computational basis of this phenomenon, but it is still not completely understood. In this article, we present a very simple connectionist model for producing context-dependent place representations in the hippocampus. We propose that context dependence arises in the dentate gyrus-hilus (DGH) system, which functions as a dynamic selector, disposing a small group of granule and pyramidal cells to fire in response to afferent stimulus while depressing the rest. It is hypothesized that the DGH system dynamics has "latent attractors," which are unmasked by the afferent input and channel system activity into subpopulations of cells in the DG, CA3, and other hippocampal regions as observed experimentally. The proposed model shows that a minimally structured hippocampus-like system can robustly produce context-dependent place codes with realistic attributes.     

使用Lloyd Relaxation的物体表面网格化

根据输入的物体表面点云生成与表面点云拓扑结构一致且几何形状接近的三角网格,在计算机图形学建模中具有很重要的作用,提出一种基于Lloyd relaxation的模型表面点云网格化方法.首先从输人点云中随机选取一些样本点,样本点的数目可以指定;然后运用扩展的Lloyd relaxation算法将这些样本点沿着物体表面移动;当得到一个近似均匀的样本点分布后,运用改进的"crust"算法根据这些样本点生成三角网格.通过在每次relaxation过程中减少网格和曲面间体积的方法,使生成的三角网格与原始表面点云的几何形状接近.实验结果证明,该方法能正确、有效地生成输入点云模型的三角网格,并可以运用在三维物体表面重建和网格简化上.     

Recombination Through Different Types of Localized States in Organic Solar Cells

Recombination in bulk heterojunction solar cells is explored by observing the result of prolonged white light illumination, thermal annealing to high temperature, and chemical doping. Measurements of the photocurrent spectral response, the steady state photocurrent‐voltage characteristics, transient photoconductivity and the dark forward bias current on polymer:fullerene solar cells provide information about the density of states and the electronic properties. Illumination generates deep localized states in the interface gap, which act as recombination centers and also increase the diode ideality factor. Annealing induces both nanostructural and electronic changes. The coarsening of the domain structure reduces the probability that excitons reach the interfaces and also reduces the charge transfer absorption. At the same time annealing broadens the exponential band tails and increases the recombination rate. Doping introduces shallow states near the fullerene conduction band, which also act as recombination centers. The results show that recombination is through localized states of different character, depending on the circumstances.     

The moderating effects of personal reputation on accountability-strain relationships.

Although felt accountability has predicted positive outcomes in some studies, it has demonstrated anxiety-provoking properties in others. This inconsistency has led researchers to search for moderating variables that explain why felt accountability promotes or impedes favorable outcomes. Building on these studies, the authors examine the moderating effects of personal reputation on the felt accountability-strain relationship. As hypothesized, the results indicate that a positive personal reputation ameliorated the strain reactions caused by felt accountability. In particular, as felt accountability increased, individuals with strong personal reputations experienced less job tension and depressed mood at work, as well as more job satisfaction, but individuals with weak personal reputations experienced the opposite outcomes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)