A discretized proportional base driver for Silicon Carbide Bipolar Junction Transistors

Silicon Carbide Bipolar Junction Transistors require a continuous base current in the on-state. This base current is usually made constant and is corresponding to the maximum collector current and maximum junction temperature that is foreseen in a certain application. In this paper, a discretized proportional base driver is proposed which will reduce, for the right application, the steady-state power consumption of the base driver. The operation of the proposed base driver has been verified experimentally, driving a 1200V/40A SiC BJT in a DC-DC boost converter. In order to determine the potential reduction of the power consumption of the base driver, a case with a dc-dc converter in an ideal electric vehicle driving the new European drive cycle has been investigated. It is found that the steady-state power consumption of the base driver can be reduced by approximately 63 %. The total reduction of the driver consumption is 2816 J during the drive cycle, which is slightly more than the total on-state losses for the SiC BJTs used in the converter. © 2013 IEEE.

Development and characterization of polymorphic microsatellite loci in the endangered Yangtze finless porpoise (Neophocaena phocaenoides asiaeorientalis)

The finless porpoise (Neophocaena phocaenoides) is one of the smallest cetacean species widely distributed in the shallow coastal waters of the Indo-Pacific Oceans. The population size of the Yangtze subspecies (N. p. asiaeorientalis) has sharply decreased in the last two decades and access to objective data on its population structure and genetic diversity would be of great assistance for their proper management. Here we report on the isolation of nine polymorphic microsatellite using the "Fast Isolation by AFLP of Sequences Containing repeats" (FIASCO) protocol. Polymorphism was assessed using 30 porpoise individuals randomly sampled in the Yangtze River. The number of alleles per locus varies from 2 to 9, with an average value of 5.56, whereas the ranges of observed and expected heterozygosi ties were 0.300-0.633 (mean 0.496) and 0.473-0.804 (mean 0.659), respectively.

Changes in the plankton community following introduction of filter-feeding planktivorous fish

1. We conducted enclosure experiments in a shallow eutrophic lake, in which a biomass gradient of the filter-feeding planktivore, silver carp, Hypophthalmichthys molitrix Valenciennes, was created, and subsequent community changes in both zooplankton and phytoplankton were examined. 2. During a summer experiment, a bloom of Anabaena flos-aquae developed (approximate to 8000 cells mL(-1)) solely in an enclosure without silver carp. Concurrent with, or slightly preceding the Anabaena bloom, the number of rotifer species and their abundance increased from seven to twelve species (1700-14 400 organisms L-1) after the bloom in this fish-free enclosure. Protozoans and bacteria were generally insensitive to the gradient of silver carp biomass. 3. During an autumn experiment, on the other hand, large herbivorous crustaceans were more efficient than silver carp in suppressing the algae, partly because the lower water temperature (approximate to 24 degrees C) inhibited active feeding of this warm-water fish and also formation of algal colonies. Heterotrophic nanoflagellate and bacterial densities were also influenced negatively by the crustaceans. 4. Correspondence analysis (CA) was applied to the weekly community data of zooplankton and phytoplankton. A major effect detected in the zooplankton community was the presence/absence of silver carp rather than the biomass of silver carp, whereas that in the phytoplankton community was the fish biomass before the Anabaena bloom, but shifted to the presence/absence of the fish after the bloom.

Fabrication of Ge nano-dot heterojunction phototransistors for improved light detection at 1.55 mu m

Heterojunction phototransistors (HPTs) with several Ge/Si nano-dot layers as the absorption region are fabricated to obtain improved light detectivity at 1.55 mu m. The HPT detectors are of n-p-n type with ten layers of Ge(8ML)/Si(45nm) incorporated in the base-collector junction and are grown by an ultrahigh-vacuum chemical-vapor deposition system. The detectors are operated with normal incidence. Because of the good quality of the grown material and fabrication process, the dark current is only 0.71pA/mu m(2) under 5 V bias and the break-down voltage is over 20 V. Compared to the positive-intrinsic-negative (PIN) reference detector with the same absorption layer, the responsivity is improved over 17 times for normal incidence at 1.55 mu m.

Lateral intersubband photocurrent study on InAs/InAlas/InP self-assembled nanostructures

We present lateral intersubband photocurrent (PC) study on self-assembled InAs/InAIAs/InP(001) nanostructures in normal incidence. With the help of interband excitation, a broad PC signal has been observed in the photon energy range of 150-630 meV arising from the bound-to-continuum intersubband absorption in the InAs nanostructures. The large linewidth of the intersubband PC signal is due to the size inhomogeneity of the nanostructures. With the increase of the interband excitation the intersubband PC signal firstly increases with a redshift of PC peak and reaches its maximum, then decreases with no peak shift. The increase and redshift of the PC signal at low excitation level can be explained by the state filling effect. However, the decrease of PC signal at high excitation level may be due to the change of the mobility and lifetime of the electrons. The intersubband PC signal decreases when the temperature is increased, which can be explained by the decrease of the mobility and lifetime of the electrons and the thermal escape of electrons.

黄土高原子午岭林区6个典型群落优势种的热值和养分特征

能量流动、物质循环和信息传递共同构成了生态系统三大功能。能量是维持生态系统功能与过程的动力,Jordan(1971)认为能量比干物质更能反映出群落对自然资源(特别是太阳能)的利用情况。Long(1934)率先用热值来表示植物所含能量的多少,此后关于植物热值的研究工作逐渐展开。我国的植物热值研究始于20世纪80年代(杨福囤等,1983;祖元刚等,1986),主要集中在海南(林益明等,2000)、福建(林益明等,2004)、广东(任海等,1999)和浙江(郝朝运等,2006)等热带亚热带植物群落以及内蒙古羊草草原(鲍雅静等,2003),但有关黄土高原地区的植被热值研究尚未见报道。子午岭林区是黄土高原主要的天然次生林区,其植被主要是在弃耕地基础上逐渐恢复起来的(邹厚远等,2002)。由于自然因素与人为因素的影响,子午岭的植被在恢复时间上存在较大差异,形成了处于不同演替阶段的各种植被群落类型。本研究选取的6个代表性植被群落分别是沙棘(Hippophae rhamnoides)群落、山杨(Populus davidiana)群落、白桦(Betula platyphylla)群落、油松(Pinus tabulaeform...

子午岭地区植被演替过程中土壤养分及酶活性特征研究

选择植被自然恢复不同年限的阳坡梁坡地作为研究对象,采用时空互代法研究子午岭地区植被恢复过程中土壤养分和酶活性的变化。结果表明,植被恢复140 a内,不同土层土壤有机质含量、全氮含量、蔗糖酶活性、脲酶活性、碱性磷酸酶活性和过氧化氢酶活性增加,且表土层(0~20 cm)土壤养分含量和酶活性高于下层土壤(20~40 cm)。以裸露地为对照,土壤0~20 cm土层,有机质含量、全氮含量、蔗糖酶活性、脲酶活性、碱性磷酸酶活性和过氧化氢酶活性分别增加了23.8%~534.9%、9.3%~300.0%、213.6%~521.5%、40.4%~286.5%、22.7%~232.2%和3.2%~22.4%,土壤速效磷含量呈现波动变化,过氧化氢酶活性变化幅度比其他三种酶低。土壤有机质含量与全氮、速效磷含量密切相关;土壤蔗糖酶与土壤有机质、全氮均为极显著的相关关系(0.930/0.918);土壤脲酶活性与全氮含量相关系数最高(0.804);土壤碱性磷酸酶活性与有机质、全氮含量都呈极显著相关(0.977/0.984);土壤过氧化氢酶活性与全氮含量极显著相关,相关系数达0.996。

自组织生长InAs量子点的发光性质研究

通过对加InGaAs自组织生长量子点的变温光致发光谱以及时间分辨谱的研究，发现低温下量子点的发光强度和光生载流子的寿命不变；中间温度区载流子寿命随温度升高而变大；更高温度时，发光强度和载流子寿命均随温度升高而快速下降。

Improved Epitaxy of 3C-SiC Layers on Si(100) by New CVD/LPCVD System

Single crystalline 3C-SiC epitaxial layers are grown on φ50mm Si wafers by a new resistively heated CVD/LPCVD system, using SiH_4, C_2H_4 and H_2 as gas precursors. X-ray diffraction and Raman scattering measurements are used to investigate the crystallinity of the grown films. Electrical properties of the epitaxial 3C-SiC layers with thickness of 1 ～ 3μm are measured by Van der Pauw method. The improved Hall mobility reaches the highest value of 470cm~2/(V·s) at the carrier concentration of 7.7 * 10~(17)cm~(-3).

Optoelectronic Smart Pixels Comprising Flip-Chip-Bonded GaAs/AlGaAs MQW Detectors and Modulators on Silicon CMOS Circuit

于2010-11-23批量导入