Electrical Performance of Static Induction Transistor with Mixed I-V Characteristics

The mixed non-saturating I-V characteristics of static induction transistor (SIT) are investigated.The optimum matching relations among the structural,material,and technological parameters are also presented.The technological experiments demonstrate that the channel parameters play a critical role in determining whether it is a mixed,triode-like or pentode-like I-V characteristics.The general control principles,methods,and criterions of fabrication parameters as well as the effect of control factor are analytically discussed.The results are useful for design and fabrication of SIT,especially for SIT with mixed I-V characteristics.

Non-linear characteristics of Rayleigh-Taylor instable perturbations

The direct numerical simulation method is adopted to study the non-linear characteristics of Rayleigh-Taylor instable perturbations at the ablation front of a 200 μm planar CH ablation target. In the simulation, the classical electrical thermal conductivity is included, and NND difference scheme is used. The linear growth rates obtained from the simulation agree with the Takabe formula. The ampli- tude distribution of the density perturbation at the ablation front is obtained for the linear growth case. The non-linear characteristics of Rayleigh-Taylor instable perturbations are analyzed and the numerical results show that the amplitude distributions of the compulsive harmonics are very different from that of the fundamental perturbation. The characteristics of the amplitude distributions of the harmonics and their fast growth explain why spikes occur at the ablation front. The numerical results also show that non-linear effects have relations with the phase differences of double mode initial perturbations, and different phase differences lead to varied spikes.

Water environmental planning considering the influence of non-linear characteristics

In practical water environmental planning, the influence of the non-linear characteristics on the benefit of environmental investment was seldom taken into consideration. This paper demonstrates that there exist a lot of non-linear behaviors in water environment by emphatically analyzing the influence of the non-linear characteristics of the economic scale, the meandering river and the model on water environmental planning, which will make a certain impact on the water environmental planning that sometimes cannot be neglected. This paper also preliminarily explores how to integrate the non-linear characteristics into water environmental planning. The results showed that compared with traditional methods, water environmental planning considering non-linear characteristics has its prevalence and it is necessary to develop the relevant planning theories and methods.

Analysis on Characteristic of Static Induction Transistor Using Mirror Method

A cylindrical gates model of the static induction transistor is proposed and mirror method is used to calculate the distribution of electric potential.The results show that:the potential barrier is directly determined by channel over pinched-off factor;gate efficiency η decreases as the gate dimension α 2 and shifted gate voltage are minished,and what differs from the first-order theory is that η will tend to zero at the shifted gate voltage tends to zero when V D=0;at low current,the voltage amplification factor μ increases as the drain current rising.When the drain current reaches certain degree,the voltage amplification factor keeps almost constant.In the end,an analytical description of SIT’s characteristic suited to both triode-like and mixed I-V characteristics are obtained.The predicted I-V curves are consistent perfectly with the reported experimental ones.

Influence of eddy current on transient characteristics of common rail injector solenoid valve

Influence of eddy current on transient characteristics of common rail injector solenoid valve was studied in this paper. Experimental investigations of drive current and power source volt- age of both drive current ascending and descending process were conducted on a common rail injec- tor solenoid valve. A new discretizing calculation method of solenoid valve flux linkage was put for- ward for the first time based on the experimental results and drive circuit principle, and flux linkage of both drive current ascending and descending process were evaluated. New inductance calculation methods for drive current ascending and descending process respectively were also presented. Influ- ence of parasitic inductance was evaluated. Results indicate that the air gap, under which the transi- ent flux linkage of the solenoid valve is the biggest, varies with drive current due to eddy current. Flux linkage of drive current descending process is bigger than that of drive current ascending process under the same drive current and the same air gap width. Eddy current can reduce the delay between the time that drive current begins to descend and the time that armature begins to move downward. Inductance of drive current descending process is bigger than that of drive current as- cending process over larger scope of drive current, but the difference becomes smaller with the in- creasing of air gap width. The differences of both flux linkage and inductance between drive current ascending and descending process are caused by the eddy current in core and armature materials.

Extraction Characteristics of Radio Frequency ICP Ion Source

An inductively coupled radio frequency ion source has been developed and its extraction characteristics measured. Beam current density up to 0.11 mA/ cm2 was obtained with argon at a rf discharge power of about 140 W. The dependences of ion beam on the discharge parameters such as rf source power, gas pressure and gas flow rate was studied.

Pyrolysis Characteristics and Kinetics of Municipal Solid Waste

Based on a systemic survey, the pyrolysis characteristics and apparent kinetics of the municipal solid waste （ MSW） under different conditions were researched using a special pyrolysis reactor, which could overcome the disadvantage of thermo-gravimetric analyzer. The thermal decomposition behaviour of MSW was investigated using thermo-gravimetric （ TG ） analysis at rates of 4.8,6.6,8.4, 12.0 and 13. 2 K/min. The pyrolysis characteristics of MSW were also studied in different function districts. The pyrolysis of MSW is a complex reaction process and three main stages are found according to the results. The first stage represents the degradation of cellulose and hemicellulose, with the maximum degradation rate occuring at 150℃ -200 ℃： the second stage represents dehydrochlorination and depolymerization of intermediate products and the differential thermogravimetric （ DTG ） curves have shoulder peaks at about 300℃： the third stage is the decomposition of the residual big molecular organic substance and lignin at 400 ℃- 600 ℃. Within the range of given experimental conditions, the results of non-linear fitting algorithm and experiment are in agreement with each other and the correlation coefficients are over0. 99. The kinetic characteristics are concerned with the material component and heating rate. The activation energy of reaction decreases with the increase of heating rate.

黑果枸杞中矿物元素溶出特性研究

黑果枸杞,茄科枸杞属,富含多种矿物质元素,这对人体生长发育有重要的生物学作用。黑果枸杞作为一种药食同源的物质,为了解其营养价值、指导健康食用及进一步功能开发,有必要分析矿物质溶出特性,并进行相关性分析。黑果枸杞样品制备以硝酸和过氧化氢为消解酸,微波消解仪制备消解液,以不同温度纯水浸提制备浸泡液,试验建立了电感耦合等离子体光谱法测定消解液和浸泡液中K、Na、Ca、Mg、Zn、Fe、Mn、Cu、Li、Sr十种矿物元素含量的实验方法,并进行了矿物元素溶出特性研究及相关性分析。在优化的光谱分析条件下,十种元素线性关系好(r>0.9995)、检出限低(<0.01 mg·L^(-1))、准确度高、精密度好。加标回收率在97.2%~101.8%之间,相对标准偏差小于1.99%。实验发现,黑果枸杞中矿物元素含量丰富,含量最高的是K,其次是Na、Ca、Mg,然后是Fe、Li和Sr,含量较低的是Mn、Zn、Cu。黑果枸杞中K/Na值大于8,属于典型的高钾低钠食品。Ca、Mg、Fe、Zn、Li、Sr、Mn、Cu也是人体中多种酶、激素和维生素中不可缺少的活性因子,是一种理想的食品。黑果枸杞浸泡液中,除Li与Ca、Zn、Fe之间,Mg与Zn之间关系不明显外,其余元素间呈显著正相关或极显著正相关。表明,各矿物质元素中不存在明显的拮抗作用。矿物质元素的溶出率与浸泡时间及提取温度有关。实验采用沸水和40℃纯水浸泡黑果枸杞样品,选取浸提时间5、10和20 min三个时间点研究提取温度及时间对溶出率的影响。十种元素中K、Na、Zn溶出率最高,可能是因为三种元素多以离子形式存在,容易提取。Ca、Mg、Sr、Mn、Cu含量差异大,溶出率相近,可能是价态相近,提取效率相近。Li溶出率受提取温度影响很大,沸水浸泡溶出率是40℃温水的的1.5~2倍,Fe在微量元素中含量最高,溶出率却最低,主要是由于Fe与蛋白质结合,不易萃取。试验数据可为健康食用黑果枸杞及进一步开发利用提供理论参考。

断层黏滑失稳过程声-电信号响应特征研究

为深入探索断层黏滑失稳的阶段特性以及声-电多源联合前兆特征,对含不同预制倾角断层的正长花岗岩开展了侧压分别为5、15、25MPa的双向剪切摩擦试验,观察和分析了断层黏滑失稳过程的力学行为以及声发射、电荷感应信号的时频响应特征。结果表明:(1)侧压和断层倾角改变了断层的黏滑特征,进而影响了感应电荷量和声发射事件震级。侧压越大,间黏滑和黏滑失稳阶段的电荷量占比以及电荷累积速度越大。相较于56º断层,45º断层黏滑失稳时基于振幅的统计指标b值更小,大尺度破裂占比更大。(2)声-电信号幅值的分形特征可以反映断层面黏滑错动释放能量的差异。声-电信号频域的阶段性响应特点可有效辨识实验室尺度下断层黏滑失稳的演化过程,可以将声-电信号主频幅值急剧提高作为断层黏滑失稳前兆特征之一。临近断层黏滑失稳时声发射和电荷感应参量(能量、分形维数、频谱幅值)均呈现明显的“突增”特性。(3)声-电信号能量突增与黏滑应力降之间具有较好的对应性,但并不完全同步。断层黏滑失稳时,声发射会先于电荷感应产生高幅值信号。仅采用单一声发射或电荷感应信号来预警有可能造成信息漏报、误报,需结合声发射和电荷感应信号特征以实现声-电二元信号的相互补充与验证。

基于镜像法的高频圆导线变压器漏感计算模型

高频变压器漏感是影响固态变压器功率传输特性及运行可靠性的一个重要参数,在设计阶段需要对其进行快速、精确的预测。由于数值法计算成本高昂,难以满足变压器设计阶段快速预测漏感的要求,目前常采用解析法计算漏感参数。基于一维磁场假设的计算模型忽略了绕组端部效应的影响,无法准确估计漏感。多数二维计算模型虽然考虑了横向漏磁通的影响,但泊松方程的求解及电流密度的级数表征导致其计算过程过于繁琐。因此,该文基于镜像原理准确提取磁芯窗口区域的漏磁场,推导该区域直流漏磁能量的解析表达式,并引入计及绕组集肤效应和邻近效应的频率相关因子,揭示宽频区间内漏感的衰减规律,建立能够同时考虑频变特性和绕组端部效应的漏感解析计算模型。最后,搭建漏感测量平台,针对具有不同孔隙率的变压器样机开展详细的实验研究。结果表明:所建模型的最大相对误差不超过5%,验证了该模型的准确性和有效性。

基于动态磁网络法大型感应电机阻抗参数及起动特性计算

为提高大型感应电机动态阻抗参数及起动特性计算的准确性及计算效率,构建了考虑电机转子转速变化引起气隙磁导变化的非线性动态磁网络模型。以一台6.5 MW大型感应电机为例,分析起动电流变化对电机内各处饱和程度的影响机理,在此基础上,根据磁力线路径及电机内饱和程度确定动态磁网络模型中的非线性磁导的计算方法。将动态磁网络模型与转子趋肤效应模型相结合,提出计及漏磁并考虑转子转速变化及饱和偏移现象的电机动态阻抗参数的计算方法。推导并建立基于转子多回路法的大型感应电机的动态数学模型,根据电机瞬态过程中的电磁耦合关系,确定动态数学模型与磁网络模型的动态耦合求解方法,提出大型电机瞬态过程中考虑电流、转速、饱和及趋肤程度变化的动态阻抗参数及起动特性的计算方法。通过与有限元计算结果及实验结果对比,验证了所提出计算方法的正确性。

计及风电PSS与PLL耦合对功角振荡影响的DFIG控制参数协调优化

双馈感应发电机(doubly fed induction generator,DFIG)装设电力系统稳定器(power system stabilizer,PSS),有助于抑制同步发电机间功角振荡,但抑制效果受DFIG锁相环(phase-locked loop,PLL)跟踪误差影响。考虑PSS与PLL耦合特性对功角振荡的影响,提出改善振荡抑制效果的DFIG控制参数协调优化算法。首先基于DFIG有功控制的分解等效结构绘制DFIG-PSS与锁相误差的耦合路径,提出耦合特性解析表达。然后建立耦合解析表达对控制参数的轨迹灵敏度向量,以向量2-范数之比定义耦合强度,量化耦合特性对功角振荡的影响程度。最后基于耦合强度指标,提出带有PLL参数动态不等式约束的多步优化模型,以协调DFIG控制参数取值,提高并网系统对功角振荡的抑制效果。仿真结果证实了耦合特性对功角振荡的影响,验证了所提协调优化算法的有效性。

考虑源荷特性的双馈风电机组动态减载协同调频控制

为使双馈风电机组(doubly fed induction generator,DFIG)的有功输出能响应电网频率的变化,有效参与电网频率调节,提高风电系统的稳定性,文中分析了虚拟惯性控制、下垂控制以及减载控制的基本原理,探究了相关参数对风电并网系统频率特性的影响。在此基础上,提出一种考虑系统源荷特性的动态减载协同调频控制策略。该策略结合源荷扰动情况实现减载率修正,通过MATLAB/SIMULINK仿真验证表明:当负荷波动时,该控制策略相较于固定减载调频使含风电系统在不同风速下的频率稳定性有了显著提高。

采用改进MPC提高储能系统电压暂态特性研究

储能系统通过换流器实现并网运行,常规换流器因为其开关频率低,在采样、计算环节存在延时导致储能系统暂态特性差,甚至引起整个电网不稳定。本文采用模型预测控制MPC(model predictive control)来实现储能系统功率快速响应,避免延时影响。引入功率权重价值函数在有功、无功MPC控制中,计算储能换流器输出电压最优值。针对因为滤波电感参数偏移导致的MPC模型不准确问题,本文采用电感误差补偿控制来提高模型精度。通过Matlab/Simulink仿真和实验来验证本文所提方案可提高储能系统暂态特性,有效消除误差对MPC控制性能的影响。

一株副干酪乳杆菌的抗炎抑菌作用分析

副干酪乳杆菌Lactobacillus paracasei是重要的益生菌之一。从贵州酸菜中分离得到的11株副干酪乳杆菌中筛选得到一株编号为GZ0613的菌株,体外表型研究显示,该菌株不溶血,对四环素等4种抗生素均表现为敏感,具有较好的耐酸耐盐能力和动物胃肠环境适应能力,对结肠癌细胞HT-29具有较强的黏附能力,对多种常见动物肠道致病菌有较强的生长抑制活性。通过葡聚糖硫酸钠(DSS)诱导建立小鼠结肠炎模型,比较空白对照组、DSS模型组与益生菌处理组小鼠炎症因子水平和炎症浸润程度、解剖学特征及肠道菌群结构之间的差异,结果表明,益生菌处理组小鼠血清中4个炎症因子IL-1β、IL-6、IL-8和TNF-α指标明显降低,脏器指数、结直肠长度及肠道菌群丰度和多样性更趋近于正常小鼠,说明该菌对DSS诱导的小鼠结肠炎有预防缓解作用,具有益生潜力,在动物功能性食品中具有应用前景。

考虑撬棒与直流卸荷协同保护动作特性的双馈风电场通用等值建模方法

低电压穿越(low voltage ride through,LVRT)期间撬棒(Crowbar)保护和直流卸荷(Chopper)保护的工作状态均对双馈风电机组(doubly fed induction generator,DFIG)的暂态响应特性有重要影响。传统等值方法往往只能识别与表征撬棒保护动作情况及其暂态特性,对于目前普遍的硬件协同保护场景而言,将造成等值误差,进而难以从电网侧准确描述风电接入后的动态特性及作用规律,在高比例风电场景下这样的误差将被放大,严重时可能会对电力系统安全稳定分析造成影响。因此,该文充分考虑双馈感应风机(doubly fed induction generator,DFIG)低电压穿越控制策略,揭示风机低电压穿越下两种保护协同动作特性,提出一种双馈型风电场通用等值方法,通过MATLAB/Simulink验证理论分析的正确性,并与仅考虑Crowbar保护的等值方法对比,说明所提等值建模方法的准确性。

考虑感应电机负荷特性的主动配电网电压模型预测控制

针对高比例新能源并网引发主动配电网电压越限问题,提出了一种考虑感应电机负荷特性的主动配电网电压模型预测控制方法。首先,通过建立感应电机负荷的稳态模型,分析了其有功和无功与并网点电压的耦合关系,提出考虑感应电机负荷特性的配电网状态估计方法,实现了对关键状态量的实时在线监测。然后,计及各类电压调节资源,构建考虑感应电机负荷特性的电压模型预测控制方法,并通过状态预测、滚动优化和反馈控制3个关键环节,在维持配电网电压安全的前提下,以最低调节成本实现感应电机负荷并网点电压与设定值的偏差最小化。最后,基于IEEE33节点系统算例进行仿真,验证了所提方法在提高状态估计精度、改善电压控制效果方面的有效性。

电感耦合等离子体质谱法结合化学计量学分析车前草药材中12种元素

目的建立同时测定车前草药材中12种元素的电感耦合等离子体质谱(ICP-MS)法,并进行化学计量学分析。方法射频功率为1800 W,等离子体气流量为15 L/min,载气流量为1 L/min,采样深度为12 mm,辅助器流量为1 L/min,雾化室温度为2.0℃,测量模式为动能歧视(KED)模式,碰撞气体积流量为6.0 mL/min,进样冲洗时间为35 s,蠕动泵泵速为50 r/min,扫描3次。根据3个产地15批车前草药材样品中12种元素的含量测定结果,建立特征图谱,并进行主成分分析。结果镉(Cd)、铅(Pb)、铜(Cu)、钠(Na)、锌(Zn)、钾(K)、铝(Al)、汞(Hg)、钙(Ca)、镁(Mg)、砷(As)、铁(Fe)质量浓度分别在0~100 ng/mL、0~100 ng/mL、0~500 ng/mL、0~500 ng/mL、0~1000 ng/mL、0~500 ng/mL、0~500 ng/mL、0~20 ng/mL、0~500 ng/mL、0~1000 ng/mL、0~100 ng/mL、0~1000 ng/mL范围内与仪器响应值线性关系良好(r≥0.9992,n=6);精密度、重复性、稳定性试验结果的RSD均小于5%;平均加样回收率为82.72%~91.10%,RSD为1.55%~4.69%(n=6)。15批车前草12种无机元素的平均含量分别为0.36,1.58,9.16,10.51,54.71,9.35,34.86,0.16,16.81,112.64,1.08,100.04 mg/kg。3个产地车前草药材中12种元素特征图谱的峰形基本相似。Mg、Fe、Zn、Al是车前草药材的特征元素;15批车前草药材样品的质量存在一定差异,其中贵州毕节所产的质量较好。结论建立的ICP-MS法操作简单、结果准确,可用于车前草药材中12种元素的含量测定;特征图谱及主成分分析可为车前草药材的开发利用和质量控制提供参考。

利用实用转矩公式计算液体变阻器电阻值的方法

介绍了水泥厂大型磨机采用绕线式电动机驱动及液体变阻器启动时,利用电动机实用转矩公式计算液体变阻器阻值的思路及方法。以球磨机为例,对比分析了按照液体变阻器说明书参考公式计算液体变阻器电阻值与采用电动机实用转矩公式计算液体变阻器初始外接电阻值的精确度及电动机启动时间。采用电动机实用转矩公式计算的电阻值更为精确,电动机启动时间更短,能够有针对性地选择和确定启动转矩值,充分利用电动机的电磁转矩特性,减少启动冲击过程,使设备运行更加平稳;同时,可有效改善液体变阻器的发热情况,缩短调试时间。需注意的是,计算平方转矩负载的启动时间时,由于其转矩随速度的升高而变大,可以采用平均负载转矩的方法近似计算启动时间。

水平井瞬变电磁边界远探测数值模拟与响应特征分析

为克服频率域电磁感应远探仪器过长的缺点,提出采用瞬变电磁远探测方法进行边界探测,给出了均匀地层中响应解析计算方法,基于COMSOL Multiphysics有限元数值软件,建立了层状地层水平井瞬变电磁远探测响应计算模型,并对其在地层界面识别时的响应特征进行了分析。结果显示:双对数坐标系下,均匀地层中瞬态电磁远探测响应随采集时间呈线性衰减规律,且地层电阻率越大,响应衰减越快,同时刻采集的响应值越小;在两层地层中,定义背景地层响应与层状地层响应差异为边界场响应,岩层边界会导致边界场产生局部极值,该极值点对应的时间与岩层电阻率对比度、探边距离以及仪器倾斜角度密切相关,增大收发线圈间距可导致边界场响应极值向晚期时刻移动;在三层地层中,瞬变电磁远探测响应同时包含岩层上边界和下边界的信息,在边界场响应中形成两个局部极值点。研究成果为瞬变电磁远探测打下良好基础。