高压保护开关缓冲电路参数优化设计

目前的高压保护开关缓冲电路参数设计缺乏相关理论设计方法,同时缓冲电路方案由于设计过程中并未考虑分布电容影响,因此均为等参数设计方案,这种方法均压效果不够理想。为了解决目前参数设计中存在的问题,首先建立了含缓冲电路和杂散电感的MOSFET模型并对其关断过程进行了分析,从而得到了抑制电压尖峰的缓冲电路理论设计方法及表达式。针对串联均压未考虑分布电容的问题,通过构造等电位点,建立了含有分布电容的等效电路并进行分析,根据电荷方程等式得到了缓冲电路非等参数设计方法及表达式,该参数设计方法可以补偿分布电容造成的电压分布不均,并更好地指导高压保护开关的均压方案设计。为了验证参数设计的合理性进行了仿真分析,结果表明,最终得到的整体设计方案可以满足尖峰抑制以及均压的设计要求。     

Modified model of gate leakage currents in AlGaN/GaN HEMTs

It has been reported that the gate leakage currents are described by the Frenkel-Poole emission(FPE) model,at temperatures higher than 250 K.However,the gate leakage currents of our passivated devices do not accord with the FPE model.Therefore,a modified FPE model is developed in which an additional leakage current,besides the gate(Ⅰ_Ⅱ),is added.Based on the samples with different passivations,the Ⅰ_Ⅱ caused by a large number of surface traps is separated from total gate currents,and is found to be linear with respect to(φ_B-V_g)~(0.5).Compared with these from the FPE model,the calculated results from the modified model agree well with the I_g-V_g measurements at temperatures ranging from 295 K to 475 K.     

基于颗粒流的混凝土材料数值实验研究

混凝土材料是一种典型的非均质材料,其力学行为和破坏过程很复杂.本文利用PFC颗粒流软件的内嵌fish语言编写了骨料生成程序、边界条件控制程序,程序模拟了MTS伺服功能,实现了虚拟的混凝土单轴压缩试验.相对于一般有限元程序投放的骨料,文中骨料可以破裂.在生成的数值试件基础上,设计了单级配和全级配混凝土单轴压缩试验,并对其破裂形态、裂纹扩展过程、应力应变曲线和破裂过程能量变化规律进行了研究.利用该虚拟试验平台,可对混凝土的动、静力学特性进行系统研究.     

自预冷型四级高频脉冲管制冷机的研究

液氦温区在深空探测、甚长波红外探测、太赫兹探测、低温超导等众多领域中具有独特应用,基于此背景,本文开展了可直接获取液氦温区且具有实用意义的自预冷型四级高频脉冲管制冷机的理论和实验研究,建立制冷机的模型,对其关键结构参数和运行参数进行分析与优化.所研制的四级高频脉冲管制冷机在无外部预冷的条件下,最终获取到4.28 K的最...     

棠梨枝叶的化学成分研究

从棠梨枝叶(Pyrus pashia Buch.-Ham.ex D.Don)的甲醇提取物中分离得到了17个化合物,采用高分辨质谱、一维和二维核磁共振等现代波谱技术,鉴定上述化合物的结构分别为:pashinin A(1),天麻苷-7-O-顺式咖啡酸酯(2),天麻苷-7-O-反式咖啡酸酯(3),山奈酚-3-O-β-D-(6′′-O-对香豆酸酯)吡喃葡萄糖苷(4),山奈酚-3-O-β-D-(6′′-O-顺式对香豆酰)吡喃葡萄糖苷(5),天麻苷-7-O-对羟基苯甲酸酯(6),熊果苷(7),robustaside B(8),委陵菜酸(9),蔷薇酸(10),槲皮素3-O-β-D-吡喃葡萄糖苷(11),2R,3R-二氢槲皮素(12),木犀草素-4′-O-β-D-吡喃葡萄糖苷(13),芹黄素-4′-O-β-D-吡喃葡萄糖苷(14),5,7,4′-三羟基异黄酮-7-O-β-D-吡喃葡萄糖苷(15),染料木素(16),咖啡酸(17),其中化合物1和2为新化合物,化合物3为新的天然产物.除化合物17外,其余化合物均首次从该植物中分离得到.化合物1～3的抗肿瘤细胞活性实验表明其没有体外肿瘤细胞生长抑制活性(IC50>40μmol L-1);抗HIV病毒(HIV-1IIIB)实验显示:化合物1有极弱的抗HIV-1的活性,化合物4有弱的抗HIV-1的活性.     

Sc与Zr对Al-Mg-Mn合金力学性能和剥落腐蚀性能的影响

为了寻找Al-Mg-Mn合金力学性能和耐剥蚀性能的最佳组合,采用对比法探索Sc和Zr对Al-Mg-Mn合金力学性能和剥落腐蚀性能的影响,测定了含与不含微量Sc和Zr的Al-Mg-Mn合金板材在不同退火态的力学性能和剥落腐蚀性能,测量了它们的极化曲线.采用扫描电镜观察了合金的腐蚀微观形貌、用能谱仪分析了腐蚀产物的成分.采用光学显微镜和透射电子显微镜分析了合金的显微组织和力学性能、剥落腐蚀性能之间的关系.结果表明： 添加微量Sc和Zr能显著提高Al-Mg-Mn合金强度,改善合金强度和塑性的配合,而且Sc和Zr的添加没有引起合金耐剥蚀性能的明显下降.经过350 ℃/1 h退火的Al-Mg-Mn-Sc-Zr合金具有优良的力学性能和耐蚀性能组合.可通过添加微量Sc,Zr,减少Mg的含量,选择合理的退火工艺,使该类合金的力学性能和耐剥蚀性能达到理想组合.     

合成苯硫酚产物的气相色谱分析

苯硫酚广泛用作农药、医药的原料,有机合成中间体,阻聚剂,防腐剂以及橡胶塑解剂等。有关苯硫酚的气相色谱分离法,国外已有报道。针对合成苯硫酚的反应产物,我们采用10％丁二酸乙二醇聚酯(PEGS)2m不锈钢填充柱,以环己醇为内标,获得较好的分离测定结果。     

Novel Woods-Saxon stochastic resonance system for weak signal detection

We propose a joint exponential function and Woods–Saxon stochastic resonance(EWSSR)model.Because change of a single parameter in the classical stochastic resonance model may cause a great change in the shape of the potential function,it is difficult to obtain the optimal output signal-to-noise ratio by adjusting one parameter.In the novel system,the influence of different parameters on the shape of the potential function has its own emphasis,making it easier for us to adjust the shape of the potential function.The system can obtain different widths of the potential well or barrier height by adjusting one of these parameters,so that the system can match different types of input signals adaptively.By adjusting the system parameters,the potential function model can be transformed between the bistable model and the monostable model.The potential function of EWSSR has richer shapes and geometric characteristics.The effects of parameters,such as the height of the barrier and the width of the potential well,on SNR are studied,and a set of relatively optimal parameters are determined.Moreover,the EWSSR model is compared with other classical stochastic resonance models.Numerical experiments show that the proposed EWSSR model has higher SNR and better noise immunity than other classical stochastic resonance models.Simultaneously,the EWSSR model is applied to the detection of actual bearing fault signals,and the detection effect is also superior to other models.     

截面几何参数对帽型梁轴向冲击响应的影响

帽型梁结构作为汽车前纵梁主要部件,其轴向冲击变形模式和吸能特性是汽车被动安全设计的主要参考指标。为此,对带有倒角的帽型梁进行了初始能量为17.8kJ的落锤轴向冲击实验和数值模拟。保持梁结构的质量不变,对不带倒角和直角弯折的两种截面梁进行同等条件的数值模拟,在一定范围内探讨截面几何参数对帽型梁的变形模式、变形量、吸能总量、峰值载荷、平均碰撞载荷和碰撞力效率的影响。结果表明:对于带有倒角的帽型梁,其变形模式和变形量的计算结果与实验结果基本吻合,验证了计算模型的合理性;倒角的存在使结构变形模式从非紧凑型向紧凑型转变,提高了缓冲效果,降低了峰值载荷;弯折角度由93°变为90°时,对变形模式的影响较小,非直角弯折梁的吸能效果较直角弯折梁好。因此,截面几何参数对帽型梁结构的变形模式和吸能特性有一定影响。     

Synchronization and bidirectional communication without delay line using strong mutually coupled semiconductor lasers

This paper numerically demonstrates synchronization and bidirectional communication without delay line by using two semiconductor lasers with strong mutual injection in a face-to-face configuration.These results show that both of the two lasers' outputs synchronize with their input chaotic carriers.In addition,simulations demonstrate that this kind of synchronization can be used to realize bidirectional communications without delay line.Further studies indicate that within a small deviation in message amplitudes of two sides (±6%),the message can be extracted with signal-noise-ratio more than 10 dB;and the signal-noise-ratio is extremely sensitive to the message rates mismatch of two sides,which may be used as a key of bidirectional communication.