脉冲激光作用于硅的受激发光特性

用脉冲激光作用在硅基上产生表面等离子体波,在氧气和空气氛围中加工生成硅氧化量子点结构,有很强的光致荧光（PL）发光,发光效率可达20%;经高温快速退火处理后,在700 nm波长邻域观察到受激发光峰,检测到明显的光学增益和阈值行为,其受激发光峰最窄的半高宽可达0.5 nm。通过第一性原理模拟计算,发现硅氧化量子点结构表面钝化成键的类型与密度是形成受激发光的关键,并由此提出相应的物理模型。     

步进电动机的驱动与控制分析

步进电动机是一种将电脉冲信号转换成机械角位移的电磁机械装置。由于所用电源是脉冲电源,所以也称为脉冲马达。步进电动机的工作方式和一般电动机的不同,是采用脉冲控制方式工作的。只有按一定规律对各相绕组轮流通电,步进电动机才能实现转动。因此,只要控制输入电脉冲的数量及频率就可精确控制步进电动机的转角及转速。因此它是一种高效而优化的驱动与控制工具.     

超光速物理学

昆虫学家长期以来一直以为黄蜂实在太愚蠢，以致它们都不能通过视觉进行相互识别。它们微小的头脑可能使它们没有足够的脑汁来识别单个的     

后张法预应力钢绞线初始应力与推算伸长值的确定方法

文章介绍了在后张法预应力筋张拉的应力应变双控中,采用解析法推算张拉初始应力时预应力筋伸长值的方法.     

R&D投资系统管理

R＆D投资活动是一个受多种因素影响和制约的系统过程,其高技术特征使其结果的不确定性和风险比传统投资项目更大。在系统分析企业内外因素与研究开发投资效率关系的基础上,指出提高企业R＆D项目成功率,必须运用系统管理的思想,加强R＆D项目的初始决策、过程控制与要素投入、中止决策、风险控制和外部性及内化等的管理水平。     

“孝”文化背后的重生祈望

孝意识是中华伦理道德的原点精神,中国传统文化中的伦理道德思想莫不发端于孝意识。在儒家思想学说中,孝占有极其重要的地位,它的伦理及政治功能向来为人们所重视。综合考察孝的宗教、哲学意义及人文伦理意义,才能合理解释其对中国社会文化的深远影响。     

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.     

A novel current-sharing scheme based on magamp

The magamp （magnetic amplifier） is widely used in power supplies due to its low cost, simplicity and other advantages. This paper discusses a novel application of the magamp in switching power supplies, where the magamp is used to regulate pulse width modulation （PWM） instead of power signal in the main circuit. This method extends the application of the magamp in power supplies, and makes it possible to further regulate control signal when PWMs have been generated. Based on this applica- tion, a new current-sharing （CS） scheme using the magamp is proposed, which uses a modified inner loop CS structure. In this scheme PWMs are generated by one main controller, and CS is achieved by regulating PWMs using a magamp in each module. Compared with traditional application of the magamp, the new CS scheme can be used in most topologies and only requires magamps of low power capacity. Then a test circuit of parallel power supply is developed, in which CS is achieved by a PWM regulator with the magamp. The proposed scheme is also used to upgrade an electroplate power to make it capable of paralleling supplies. Experimental results show that the proposed scheme has good CS performance.     

西北地区水资源利用障碍及水权制度的建立

水资源是经济、社会发展的基础性资源。在西部大开发机遇下,西北干旱区的水资源短缺,成为制约西北经济、社会、环境发展的瓶颈,也使我国可持续发展受到影响。西北地区水资源短缺的原因不仅有西北属于干旱半干旱地区的内因,还有人为的水污染、水资源浪费等外因,更重要的原因是制度不健全。文章针对建设节水型社会的背景,从政府管理、技术改进、水权制度内涵及水权市场运作原则方面提出解决西北水资源短缺问题的根本性措施。