实际指数脉冲电场对细胞跨膜电位的影响

为了进一步增大细胞跨膜电位峰值,提高脉冲电场电穿孔效率,基于相关文献中球形单细胞多层介电模型的细胞跨膜电位计算方法,分析了实际RC指数衰减脉冲上升沿时间对细胞跨膜电位的影响。通过Matlab软件对细胞跨膜电位的传递函数频率响应进行了仿真分析,结果表明:不同频段的电场对细胞跨膜电位的影响不同。建立了一种改进的RC指数衰减脉冲模型,并进行了仿真计算,结果表明:脉冲电场上升沿时间对细胞跨膜电位有很大影响:上升沿时间越小,频率响应就越高,减小上升沿时间可以提高细胞跨膜电位峰值。仿真结论对改进脉冲电场发生电路的结构和参数设计,以增大细胞跨膜电位峰值并提高电穿孔效率提供了理论依据。     

脉冲氙灯电流峰值与电容充电电压的线性模拟

为了提高调节脉冲氙灯的效率,研究了脉冲氙灯电流峰值与电容初始电压之间的关系,并在此基础上量化分析了脉冲氙灯参数对电流峰值的影响。实验分组分别测量了具有不同充气气压、电极间距以及灯管内径等参数的脉冲氙灯工作在不同电容初始电压条件下的电流峰值。实验发现,电容初始电压在1.75~4.25 k V范围内,电流峰值与电容充电电压有着良好的线性关系。对此进行了线性函数模拟,得到模拟结果与实验测量结果的相对误差5%。通过计算分析充气气压、电极间距以及内径等条件与模拟线性函数斜率的关系,验证了所得结果的正确性以及研究方法的合理性,为脉冲氙灯电流峰值的研究提供了一种新的方法。同时发现灯管内径对脉冲氙灯电流峰值影响十分强烈,充气气压对电流峰值影响相对较弱。这些现象对于新型脉冲氙灯的研制、选用及调试都有参考意义。     

电除尘用脉冲高压电源的研制

本文介绍了一种新式电除尘用脉冲高压电源，其输出电压参数为：直流基础电压ＵＤＣ＝－（０－４０）ｋＶ，脉冲电压幅值Ｕｍ＝－（４０－８０）ｋＶ，脉冲宽度τ＝４４μｓ，脉冲前沿时间τｒ＝１．４μｓ，脉冲重复频率ｆ＝５０－４００Ｈｚ。电源对每次脉冲放电未用完能量具有回收功能。经比较该电源的主要性能指标优于国外同类产品。     

MOSFET在感应叠加型高压双方波脉冲发生装置中的应用

为了获得脉冲间距较小并且可随时调节的高压方波脉冲,利用MOSFET响应快、重复频率高的特点研制出了感应叠加型固态高压双脉冲发生装置,该装置主要由8个感应叠加模块组成,每个感应叠加模块由18个并联的功率MOSFET构成。每个功率MOSFET具有专用的驱动电路,该驱动电路由雪崩晶体管产生的触发脉冲进行同步触发。通过测试,所搭建的8个模块感应叠加装置具有输出高压大电流双方波脉冲的能力,在10Ω负载条件下输出的高压大电流双脉冲的峰值电压达3.6 k V、峰值电流达360 A。输出脉冲底部不平坦度10%。通过优化调节雪崩触发脉冲的时间一致性,获得的输出高压脉冲的上升沿和下降沿时间分别为20 ns及30 ns。通过调整雪崩触发脉冲源输出的双触发脉冲的脉宽和脉冲间隔,可调节输出高压双脉冲的脉宽及脉冲间隔。     

T型三电平IGBT驱动的优化设计与测试

针对所研制的T型三电平绝缘栅双极型晶闸管(IGBT)驱动装置,研究了门极驱动电阻的计算、模块寄生参数的测算及寄生参数对测试结果的影响,进一步研究了双脉冲测试中尖峰电压不对称的原因并提出解决途径。在双脉冲测试平台上,通过测试IGBT模块接线端子间的电压及流过它们的电流在第二个脉冲关断时刻的波形,利用测定的电压峰值和电流变化率,计算出IGBT模块内部寄生的杂散电感大小。结果表明,双脉冲测试中尖峰电压不对称的现象是由IGBT模块内部引线造成的杂散电感严重不对称造成的。此处介绍的测试方法为检测驱动装置、调整驱动参数和优化测试结果提供了良好的依据。     

800kV雷电电磁脉冲场模拟器的研制

为了模拟雷电放电过程中产生的电磁脉冲场,建立了雷电模拟系统的等效电路模型,分析了各种电路参数对模拟器输出波形的影响;根据等效电路各参数,利用Marx发生器作为雷电电磁脉冲源,使用有界波模拟器作为场传输装置,研制了雷电电磁脉冲模拟系统,在有界波传输线内产生上升时间和半波宽度可变的双指数电场波,用来模拟雷雷击过程中产生的雷电电磁脉冲辐射场。测量结果表明,合理选择参数可以在有界波传输线内模拟1.2/50μs的雷电电磁脉冲远场电磁波;输出波形的峰值场强、波前时间和半峰值时间的变异系数表明该模拟器具有良好的重复性;并且传输线内峰值场强和Marx发生器充电电压有比较好的线性关系。     

离散随机SVPWM中概率密度函数的表征与选择

针对连续随机空间矢量脉宽调制(space vector pulse width modulation, SVPWM)技术在永磁同步电机驱动系统中对高度集中的PWM谐波能量分散效果不理想问题，提出一种基于Beta分布的离散混合双随机SVPWM技术。首先，基于调制理论分析传统SVPWM技术的开关函数与电压PWM谐波之间的内在联系，并根据开关函数中调制参数的组合形式不同对随机SVPWM技术进行分类。然后，从预定义的离散序列中随机选择开关频率因子和脉冲位置因子以实现开关函数中开关频率和脉冲位置的离散随机化，同时基于Beta分布和均匀分布对离散随机序列进行优化，以改善离散随机SVPWM技术的PWM谐波抑制效果，使得频域中的谐波能量分散到更多频率分量处。通过实验平台测试，结果显示基于Beta分布的离散双随机调制技术相较于传统随机脉宽调制技术谐波峰值降低了53%,表明引入Beta分布的离散混合双随机SVPWM技术具有更优的谐波散射效果，同时还具有与传统SVPWM技术相当的驱动效率。     

吸收比和极化指数浅析

以吸收比作为试品绝缘状况的判比指标有其不确定性,不能确切有效地作出判断。极化指数与试品绝缘良好程度呈单调变化的正比关系,无不确定性。但是,用绝缘电阻值Ｒ６０ｓ、吸收比Ｋ＝ Ｒ６０ｓ ／Ｒ１５ｓ 或极化指数ＰＩ＝ Ｒ１０ｍ ｉｎ ／Ｒ１ｍ ｉｎ 等一项参数来规范１ 个电阻—时间动态过程,以此作为绝缘性能的判比指标,将会带来很大的局限性。因此,遴选更理想的绝缘判比参量应作为当前的重要研究课题。     

带并联短路支节的超宽谱双极脉冲转换器研究

研制了一个带并联短路支节的超宽谱双极脉冲转换器并给出其工作原理和波过程分析。输入脉宽 6ns和2ns的电压脉冲得到了电压峰—峰值接近输入电压峰值的双极性脉冲。研究表明 ,通过改变短路线的长度和特性阻抗可调节双极脉冲的相对位置和幅值比率 ,双极脉冲波形的稳定性完全取决于输入的单极性脉冲稳定性     

基于H桥-MPC电路的高压脉冲发生器设计

针对强电磁脉冲用于工业及生活污水有机物降解研究,设计并研制了采用H桥式逆变电路和磁脉冲压缩(MPC)电路为核心结构的小型高重复频率高压脉冲发生器.该装置输出电压脉冲为双指数电压波,脉宽为纳秒到微秒级别可调,上升前沿时间为纳秒级,脉冲峰值为0～20 kV,脉冲重复频率为0～300 Hz.采用H桥电路结构,初级储能电容可直接连接充电电源,省去缓冲电路.绝缘栅双极型晶体管(IGBT)在零电流和零电压条件下关断,关断损耗非常小.经实验证实电压和电流上升时间及脉冲宽度都为百纳秒级,电压峰值可接近20 kV.所设计电源很好的满足了污水放电有机物质降解的研究及应用,此外还可以推广到其他研究及工业应用领域,如气体放电等离子体研宄等.这里的研究对高压脉冲发生器的设计、研制及应用具有一定的指导意义.     

一款高精度90°移相器实用电路的设计

用RC元件及相应电路设计低频固定频率90°±Δφ移相器是人们常用的方案,然而RC移相器元件的老化、环境(尤其是温度)的变化严重地影响了移相器的稳定性。本文采用了一系列措施:(1)选用低温度系数的精密阻容元件;(2)对阻容元件进行老化处理;(3)分别测量元件的温度系数;(4)用相反温度系数的阻容元件按一定的比例进行补偿等,使RC元件温度系数达到±1ppm/℃以内。对90°±Δφ移相器的温度试验表明,电路的温度系数达到2.88ppm/℃。文中还给出所选用的部分国内外RC元件实测的温度系数,对读者利用RC元件设计某些高稳定性电路(如HPF、BPF、LPF等)有重要的参考价值。     

RC框架结构地震倒塌性能分析

本文提出了以最大层间位移角和损伤指数双向控制的地震倒塌准则,选取已有的地震动记录,基于增量动力分析方法揭示了楼层高度、结构高宽比、框架柱轴压比及楼板约束强度等诸主要影响因素对RC框架结构地震倒塌易损性能的影响规律,进而对其抗地震倒塌能力进行了定量化的评价。本文的研究为评估RC框架结构体系的抗地震倒塌性能提供了一定的理论支撑和工程意义。     

Efficient 1.94-μm Tm:YALO laser

Laser emission from Tm:YALO is observed over the range 1.93-2.00 μm. A model including reabsorption loss and polarization effects, predicting the output wavelength as a function of laser parameters, is used to design a Tm:YALO laser with output restricted to 1.94 μm, without employing a tuning element. This laser is potentially useful for medical applications, offing to the strong absorption coefficient at 1.94 μm in liquid water (twice that of the 2.02-μm Tm:YAG laser and four times that of the 2.09-μm Ho:YAG laser)     

电子引伸计数据采集系统的设计

针对力学实验或生产加工的实际功能需求,以高性能单片机STC89C52RC为核心设计开发了1套电子引伸计微机数据采集系统.系统硬件电路以高精度斩波稳零型运算放大器TLC2652为信号放大芯片、以16位Σ-△型A/D转换芯片AD7705为模数转换器件,下位单片机程序采用Keil C51进行编写,系统上位机软件应用VB进行设...     

A method of diagnosing reversible converters of alternating current electric locomotives

Failures of reversible converters (RCs) in ac electric locomotives can cause failures of ac locomotive power equipment. Depending on their severity, the electric locomotive can be placed in one of several different modes, from partial loss of function to complete halting. With this in mind, it becomes important to develop (upgrade) diagnostic support of RCs and decide on a procedure of diagnostics that would make it possible to identify defects of RCs not only in the running mode, but also in the stationary mode, during scheduled and unscheduled repairs of an electric locomotive. To provide a more reliable evaluation of the technical condition of the RC functional control, is necessary to check the connections between the converter parts. It is also important that the diagnostics allows modifications of input signals supplied to the converter inlet, depending on the results of a scheduled check for specifying the diagnosis and troubleshooting. The stationary automated diagnostics system makes it possible to determine the technical condition of an RC in the rectifier mode in stationary conditions and is intended for use in testing an RC exposed to simulated operational effects. In the current phase of development, the diagnostics system allows evaluation of the capacity and correctness of implementing the RC control algorithm in all four adjustment zones, as well as identification of RC leg interruptions. Together with the algorithm for RC diagnostics, the suggested method makes it possible to conduct functional tests and identify a particular defect, as well as check the operation of the RC by monitoring the work of the converter as a single diagnosed object before the RC is installed on the locomotive. This will ensure faster and more reliable diagnostics and make it possible to almost completely avoid the use of RCs with unidentified defects.     

Ce-Al-Cu非晶合金制备及非晶形成能力

为研究Ce-Al-Cu非晶合金的制备及非晶形成能力（GFA）,采用熔体旋淬法制备了Ce70AlxCu30-x（x=5,10,13）、Ce80-xAlxCu20（x=10,15,20）和Ce90-xAl10Cux（x=15,20,25）非晶合金薄带。用X-射线衍射法（XRD）进行物相表征,用差示扫描量热法（DSC）测量样品在加热过程中的相变规律,对合金的非晶形成能力与非晶形成能力的参数（Tg、Tx、Tm、Tl、Trg、η）进行分析。结果表明,Ce含量的适当增加和Al含量的适当降低有利于降低Trg,有利于非晶形成;Cu含量的改变对非晶的形成产生极大的影响,但当Cu的原子分数为20%时,Tg最低,对Tx和Tl的影响亦不大;Ce70Al10Cu20相对此合金的其他成分点具有更好的非晶形成能力,且快淬速度为15 m/s时非晶形成能力最好。     

动态电路初始值的研究

储能元件初始值的确定对研究动态电路的分析至关重要。通过对四个典型的RC常态电路、病态电路的电容初始电压及冲激电流的分析,系统、深入地探讨了RC常态电路、病态电路在有界电源激励下的初始值的确定,并得出在病态电路中的电容电流必是冲激电流的重要结论和三种RC病态电路电容电压初始值的求解方法。从理论上更深入了对RC病态电路初始值乃至电路暂态响应的认识,解决了RC病态电路初始值求解难的问题。     

Tm-Doped Fiber Lasers: Fundamentals and Power Scaling

We describe fundamental measurements of the properties of thulium (Tm)-doped silica and power scaling studies of fiber lasers based on the material. Data on the high-lying Tm:silica energy levels, the first taken to our knowledge, indicate that pumping at 790 nm is unlikely to lead to fiber darkening via multiphoton excitation. Measurement of the cross-relaxation dynamics produces an estimate that, at the doping levels used, as much as 80% of the decay of the Tm level pumped is due to cross relaxation. Using a fiber having a 25- $mu$m-diameter, 0.08 numerical aperture (NA) core, we observed fiber laser efficiencies as high as 64.5% and output powers of 300 W (around 2040 nm) for 500 W of launched pump power, with a nearly diffraction-limited beam. At these efficiencies, the cross-relaxation process was producing 1.8 laser photons per pump photon. We generated 885 W from a multimode laser using a 35-$mu$ m, 0.2-NA core fiber and set a new record for Tm-doped fiber laser continuous-wave power.      

High-power/high-brightness diode-pumped 1.9-/spl mu/m thulium and resonantly pumped 2.1-/spl mu/m holmium lasers

We report high power (>36 W) with beam propagation factor M/sup 2//spl sim/2 in a diode end-pumped Tm:LiYF/sub 4/ (Tm:YLF) laser generating output near the 1.91-/spl mu/m region. Using the 1.91-/spl mu/m emission and high brightness achieved with the Tm:YLF laser we resonantly end-pump the Holmium /sup 5/I/sub 7/ manifold in Ho:YAG and demonstrate /spl sim/19 W of continuous-wave (CW) output. The diode-to-Holmium optical to-optical conversion efficiency achieved is /spl sim/18%. Using a CW pumped and repetitively Q-switched configuration, the Tm:YLF pumped Ho:YAG laser achieves >16 W of output power with an M/sup 2//spl sim/1.48 at 15 kHz. A Q-switched frequency range of 9 to >50 kHz is also achieved.     

Influence of doping concentration on the power performance of diode-pumped continuous-wave Tm/sup 3+/:YAlO/sub 3/ lasers

We investigated the effect of thulium ion concentration on the continuous-wave (CW) power performance of diode single-end-pumped thulium-doped YAlO/sub 3/ (Tm:YAP) lasers. Three samples with 1.5%, 3%, and 4% Tm/sup 3+/ concentration were examined at 18/spl deg/C. Lifetime and fluorescence measurements were further performed to assess the strength of cross relaxation and nonradiative decay. Our results showed that in single-end-pumped configurations, the best CW power performance was obtained with the 1.5% Tm:YAP sample, and laser performance of the samples degraded monotonically with increasing Tm/sup 3+/ concentration. By using 9.5 W of incident pump power at 797 nm, a maximum of 1430 mW of output power was obtained with the 1.5% Tm:YAP sample and 2% output coupler. We discuss how the effects of cross relaxation, reabsorption, nonradiative decay, and internal heating vary with increasing concentration. Spectroscopic measurements and rate-equation analysis suggest that cross relaxation should already be effective in samples with 1.5% Tm/sup 3+/ ion concentration and doping concentrations larger than 4% will lead to degradation in power performance due to higher nonradiative decay rates and larger reabsorption losses.