High power devices in wide bandgap semiconductors

Silicon carbide (SiC) semiconductor devices for high power applications are now commercially available as discrete devices. Recently Schottky diodes are offered by both USA and Europe based companies. Active switching devices such as bipolar junction transistors (BJTs), field effect transistors (JFETs and MOSFETs) are now reaching the market. The interest is rapidly growing for these devices in high power and high temperature applications. The main advantages of wide bandgap semiconductors are their very hi...     

经济型补偿柜调试仪

介绍了一种使用三相工频电源,利用2个小功率变压器和若干开关组成的补偿柜调试仪,与传统继保仪相比具有极高的经济性,能够较好地满足补偿柜的调试需要。     

负荷功率因数对配电变电站电压稳定性的影响

对配电变电站的电压稳定性原理进行仿真,分析表明,在负荷有功一定的情况下,负荷功率因数的下降对电压稳定性将会产生两个方面的影响:负荷无功-电压特性曲线上升,与之相对应的电网无功-电压特性曲线下降,从而使配电变电站的电压稳定性显著下降。     

能源管理系统实施中供配电系统改造方案

针对钢铁企业能源管理最基本的供配电系统以及供配电系统改造的内容作了较为详细的介绍。根据供配电系统的变电站现场配置情况,提出了供配电系统的3种改造方案,并就每种改造方案在什么情况下采用以及需要注意的事项进行探讨。     

Speech intelligibility measured with shortened versions of Callsign Acquisition Test (CAT)

The Callsign Acquisition Test (CAT) is a new speech intelligibility test developed by the Human Research and Engineering Directorate of the U.S. Army Research Laboratory (ARL-HRED). CAT uses the phonetic alphabet and digit stimuli combined together to form 126 test items.

Objective

The purpose of this study was to assess the reliability of data collected with shorter versions of CAT.

Design

A total of 5 shorter versions of the original list (CAT-120, CAT-60, CAT-40, CAT-30, and CAT-24) were formed and evaluated using 19 participants. Each of the subsets of CAT was presented in pink noise at signal-to-noise ratios (SNRs) of −6 dB and −9 dB.

Results

Results showed that shortened CAT lists have the capability of providing the same predictive power as the full CAT with good test-retest reliability.

Conclusions

Under the experimental conditions of this study, any of the shorter versions of the CAT can be utilized in place of the full version to reduce testing times with no effect on predictive power.     

New GOES imager algorithms for cloud and active fire detection and fire radiative power assessment across North, South and Central America

Vegetation fires are a key global terrestrial disturbance factor and a major source of atmospheric trace gases and aerosols. Therefore, many earth-system science and operational monitoring applications require access to repetitive, frequent and well-characterized information on fire emissions source strengths. Geostationary imagers offer important temporal advantages when studying rapidly changing phenomena such as vegetation fires. Here we present a new algorithm for detecting and characterising active fires burning within the imager footprints of the Geostationary Operational Environmental Satellites (GOES), including consideration of cloud-cover and calculation of fire radiative power (FRP), a metric shown to be strongly related to fuel consumption and smoke emission rates. The approach is based on a set of algorithms now delivering near real time (NRT) operational FRP products from the Meteosat Spinning Enhanced Visible and Infra-Red Imager (SEVIRI) imager (available from http://landsaf.meteo.pt/), and the GOES processing chain presented here is designed to deliver a compatible fire product to complete geostationary coverage of the Western hemisphere. Results from the two GOES imagers are intercompared, and are independently verified against the well regarded MODIS cloud mask and active fire products. We find that the detection of cloud and active fires from GOES matches that of MODIS very well for fire pixels having FRP > 30 MW, when the GOES omission error falls to less than 10%. The FRP of fire clusters detected near simultaneously by both GOES and MODIS have a bias of only 22 MW, and a similar bias is found when comparing near-simultaneous GOES East and GOES West FRP observations. However, many fire pixels having FRP < 30 MW remain undetected by GOES, probably unavoidably since it has a much coarser spatial resolution than MODIS. Adjustment using data from the less frequent but more accurate views obtained from high spatial resolution polar orbiting imagers could be used to bias correct regional FRP totals. Temporal integration of the GOES FRP record indicates that during the summer months, biomass burning combusts thousands of millions of tonnes of fuel daily across the Americas. Comparison of these results to those of the Global Fire Emissions Database (GFEDv2) indicate strong linear relationships (r² > 0.9), suggesting that the timely FRP data available from a GOES real-time data feed is likely to be a suitable fire emissions source strength term for inclusion in schemes aiming to forecast the concentrations of atmospheric constituents affected by biomass burning.     

仿真软件在高频电路实验教学中的应用

Multisim10是原理电路设计、电路功能测试的仿真软件.该文利用Multisim10对高频电路中的功率放大器和正弦波振荡器进行了分析,其结果符合理论推导.将Multisim10引入到高频实验教学中,不但能提高学生的学习兴趣,帮助学生更好理解原理电路以及相关特性的测试方法,而且还能提高学生的电路设计能力.     

变压器空载补偿在企业节能的应用

在高供高计的用电企业中,变压器空载时的无功损耗往往由电网供给,影响电网输送能力,另外造成企业用电功率因数偏低,产生高额的力调电费。该文采用低压自动空载补偿的方法,减少变压器空载时从电网中消耗的无功功率,从而提高功率因数,节约企业生产成本。     

Improving content visibility for high‐ambient‐illumination viewable display and energy‐saving display

Abstract— Nowadays, low‐contrast viewing of LC displays (LCDs) occurs very often, which includes the viewing of mobile LCDs at high ambient illumination and the viewing of LCDs at low‐power mode. These cases result in low‐content visibility and low contrast, leading to an unpleasant viewing experience. In this paper, a technique to improve the perceived contrast and visibility of images at low‐contrast viewing conditions is proposed. The proposed approach enhances image brightness with content and ambient adaptive image brightening and highlights visual parts and boundaries with non‐photorealistic rendering. The proposed technique enables longer battery life for mobile LC devices and makes mobile LC devices viewable at high ambient illumination. It also enables TVs with extreme low‐power consumption and smart‐grid responsive TVs.     

Adaptive predistortion using threshold decomposition‐based piecewise linear modeling

A new adaptive predistortion approach for nonlinear power amplifiers based on the piecewise linear (PWL) approximation of nonlinear functions is presented. The PWL model is obtained using threshold decomposition (TD) of the input‐output characteristics. The TD based PWL model is used to develop a baseband predistorter using both the direct and the indirect learning architectures. The proposed predistorter is proved to provide a better performance in suppressing nonlinear distortion than conventional polynomial predistorters and a reduced hardware complexity as compared to lookup table (LUT) approach. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.