Optimization of total harmonic current distortion and torque pulsation reduction in high-power induction motors using genetic algorithms

This paper presents a powerful application of genetic algorithm （GA） for the minimization of the total harmonic current distortion （THCD） in high-power induction motors fed by voltage source inverters, based on an approximate harmonic model. That is, having defined a desired fundamental output voltage, optimal pulse patterns （switching angles） are determined to produce the fundamental output voltage while minimizing the THCD. The complete results for the two cases of three and five switching instants in the first quarter period of pulse width modulation （PWM） waveform are presented. Presence of harmonics in the stator excitation leads to a pulsing-torque component. Considering the fact that if the pulsing-torques are at low frequencies, they can cause troublesome speed fluctuations, shaft fatigue, and unsatisfactory performance in the feedback control system, the 5th, 7th, 1 lth, and 13th current harmonics （in the case of five switching angles） are constrained at some pre-specified values, to mitigate the detrimental effects of low-frequency harmonics. At the same time, the THCD is optimized while the required fundamental output voltage is maintained.     

基于S3C44B0X直流电动机调速系统的实现

基于微处理器芯片S3C44B0X实现直流电动机的调压调速系统,主电路采用大功率GTR为开关器件构成的H型双极式电路,实现电动机正反转可逆调速。利用C语言编程控制S3C44B0X芯片的定时器来产生两路互补、宽度可调、死区补偿的脉冲波,控制H型电路中GTR的通断时间,以达到调节电机速度的目的。通过键盘输入和LED显示电路的设计对转速实时处理。     

CHEF Ⅲ型脉冲电泳仪获得清晰电泳效果的实验探索

CHEF Ⅲ型脉冲电泳仪是微生物种类鉴定、DNA大分子分离等基础科学研究中一个不可或缺的重要工具。该仪器可以快速、高效、准确地分离200 kb到6 Mb的DNA分子。因此,在染色体数目及染色体大小的确定、核型分析、遗传图谱分析、同源性检测分析等方面有关键性的作用。然而在实验过程中要使DNA分子完全、有效地分离,得到清晰、高效的条带却并非易事。本实验基于这些问题,经过一系列的探索研究,找到了稻瘟病菌及分子量标准酵母菌染色体分离所需要的最适条件,该条件能为分离其他真菌染色体提供借鉴与参考。     

英语词汇广度、深度知识与综合能力关系研究

对广东某高职院校81名非英语专业高职学生的英语词汇广度、深度知识和各项语言技能调研发现,被试之间的词汇知识水平和语言各项技能均存在着相当大的差距,二语习得连续系统的词汇知识越高,被试在各种语言技能的表现就越好,词汇深度知识对不同水平学生的预测力和影响模式各不相同,词汇深度知识比词汇广度对高分组和中间组的英语综合能力的影响程度更大,而阅读变量对低分组的语言水平预测力最大。     

杨氏双缝实验的数值模拟与分析

直接采用光场叠加方法运用数值计算模拟了杨氏双缝实验,研究了光源宽度、双缝缝宽、双缝间距、光源离双缝距离等因素对干涉条纹的影响.模拟的结果表明,光源宽度的增大、光源到双缝的距离的减小均会使得整个视场中干涉条纹的可见度均匀下降;双缝间距的增大会导致条纹可见度的不均匀下降和条纹密集度的增加.     

城市机动车道宽度探讨

本论文通过大量的资料收集与实地调研,在科学分析机动车道宽度影响因素及车辆行驶轨迹的基础上得出适宜于我国大多城市实际情况的车辆间的横向安全间距,并最终确定我国城市不同道路等级不同车型的车道宽度推荐值。     

Low‐intensity pulsed ultrasound ameliorates angiotensin II-induced cardiac fibrosis by alleviating inflammation via a caveolin-1-dependent pathway

ObjectiveCardiac hypertrophy and fibrosis are major pathological manifestations observed in left ventricular remodeling induced by angiotensin II (AngII). Low-intensity pulsed ultrasound (LIPUS) has been reported to ameliorate cardiac dysfunction and myocardial fibrosis in myocardial infarction (MI) through mechano-transduction and its downstream pathways. In this study, we aimed to investigate whether LIPUS could exert a protective effect by ameliorating AngII-induced cardiac hypertrophy and fibrosis and if so, to further elucidate the underlying molecular mechanisms.MethodsWe used AngII to mimic animal and cell culture models of cardiac hypertrophy and fibrosis. LIPUS irradiation was applied in vivo for 20 min every 2 d from one week before mini-pump implantation to four weeks after mini-pump implantation, and in vitro for 20 min on each of two occasions 6 h apart. Cardiac hypertrophy and fibrosis levels were then evaluated by echocardiographic, histopathological, and molecular biological methods.ResultsOur results showed that LIPUS could ameliorate left ventricular remodeling in vivo and cardiac fibrosis in vitro by reducing AngII-induced release of inflammatory cytokines, but the protective effects on cardiac hypertrophy were limited in vitro. Given that LIPUS increased the expression of caveolin-1 in response to mechanical stimulation, we inhibited caveolin-1 activity with pyrazolopyrimidine 2 (pp2) in vivo and in vitro. LIPUS-induced downregulation of inflammation was reversed and the anti-fibrotic effects of LIPUS were absent.ConclusionsThese results indicated that LIPUS could ameliorate AngII-induced cardiac fibrosis by alleviating inflammation via a caveolin-1-dependent pathway, providing new insights for the development of novel therapeutic apparatus in clinical practice.     

计算机辅助设计软件运行之硬件环境分析

计算机辅助设计主要涉及平面设计、机械制图、建筑效果图制作等领域,常用软件诸如Photoshop、AutoCAD、3dsMax等软件。这些软件的运行都会对计算机的硬件环境有很高的要求,文章将就其运行的硬件环境进行分析。     

材料硬度对喷丸组织强化效果的影响

目前用来表征金属材料表面力学特征最常见的指标是X射线衍射谱线的半高宽和显微硬度,人们普遍认为,材料的半高宽值越大,其硬度越高。许多从事喷丸研究的学从硬状态材料喷丸影响层半高宽减小的实验事实提出喷丸影响层发生了“加工软化”的观点,实验选用超高强度钢为实验材料,对其不同硬度的实验结果发现,喷丸使硬状态表面的半高宽大幅度减小,但使它们的表面屈服强度得到了提高。这说明用半高宽参量来推断表面的强度是不可靠的。     

梅菜地膜覆盖栽培试验

1999～2000 年于惠州梅菜原产地兼主产区—土桥进行了梅菜地膜覆盖栽培试验。结果表明: 该栽培法和常规栽培相比, 土壤温度、土壤含水量、土壤有机质含量和土壤孔隙度分别提高517 ℃、2615 %、41117 %和17114 % ,移栽后幼苗成活时间提早4d , 移栽后一个月幼苗株高和株幅分别提高1610 %和5116 % , 产量提高2918～5813 %.