发电厂直流系统接地故障分析与处理

分析发电厂直流系统接地故障的原因与危害,介绍了几种查找接地故障的方法,但因受直流系统分布电容的干扰,检测精度往往不够,需要进行改进,以提高直流系统的安全运行水平。     

Learning With Weblogs: Enhancing Cognitive and Social Knowledge Construction

This study investigated the impact of weblog use on individual learning in the context of university senior-level business education. As an emergent form of personal communication, weblogs enable people to publish their thoughts as webpages, and to share information and knowledge. Recognizing the potential impact of weblogs on knowledge expression and sharing, this research sought to empirically examine whether the continuous use of weblogs as online learning logs would affect student learning performance. The assumption was that effective use of weblogs promoted the constructivist models of learning by supporting both cognitive and social knowledge construction, and by reinforcing individual accountability in learning. Results from an Information Systems undergraduate course with 31 participants indicated that the performance of students' weblogs was a significant predictor of the learning outcome (while traditional coursework was not). Moreover, individuals' cognitive construction effort to build their own mental models and social construction effort to further enrich/expand knowledge resources appeared to be two key aspects of the constructivist learning with weblogs. Our results imply the potential benefit of using weblogs as a knowledge construction tool and a social learning medium     

关于移动平均过程两系数的推导

对经济预测方法中两公式给出了证明，两公式的系数被显式推导出来，这两个公式是时间序列模型公式，广泛用于经济预测之中，但文献上很难找到推导过程，本文的证明是基本的，无需高深数学知识即可理解．     

折反光学系统最佳红外像面位置的研究

较深入地研究了折反光学系统的红外像面,为确定实际的红外像面提出了一个新方法—计算从可见光边缘无色的弥散圆到红外最佳像面的距离。实践证明,这是确定这类光学系统最佳像面的一个方便、可靠的方法。     

RADIOACTIVE OR NATURAL TRACER。TECHNIQUES FOR LEAK DETERMINING OF DAM ABUTMENT

Infiltration and localization of preferential infiltration zones at the dam abutment are measured using radioactive tracer tests of flow in boreholes,meanwhile interconnection between boreholes and the energing water points is analysed.The theory and practice of radioactive tracer synthetic detective method are described to give methods and calculation formulae used under the condition of stable flow in single well to measure permeability coefficient and hydrostatic heads.Major single hole techniques including measurement for seepage line,velocity,rate of seepage flow and relationship of recharge of groundwater in aquifers are introduced briefly.The possibilities offered by natureal tracers are analysed,uincluding electric-conduct,pH-value and temperature of water as well as stable isotopes(D,^18O) and tritium.Furthermore,the sensibilities of this theory and methods were confirmed by detecting seepage flow field of Xinanjiang Dam.     

A Cellular Automata Based Rainfall-Runoff Model for Urban Inundation Analysis Under Different Land Uses

Recently many runoff models based on cellular automaton (CA) have been developed to simulate floods; however, the existing models cannot be readily applied to complex urban environments. This study proposes a novel rainfall-runoff model based on CA (RRCA) to simulate inundation. Its main contributions include a fine runoff generation process that considers 12 urban scenarios rather than a single land use type and the confluence process determined by the new transition rules considering water supply and demand (WS-WD transition rules). RRCA was compared with another CA based flood model (E2DCA). With the benchmark model, the results showed that there was good agreement, with an R-squared greater than 0.9, and that RRCA was more sensitive to waterlogging levels than E2DCA. Furthermore, the simulated vegetation interception, infiltration and drainage processes had varying degrees of impact on waterlogging. Corresponding measures can be taken in urban flood management according to the identification of areas experiencing drainage difficulties.

     

Toward practical adoption of i* framework: an automatic two-level layout approach

Requirements Engineering - Bridging the gap between academia and industry is an important issue to promote the practicality of i* framework. Researchers have been dealing with this issue from...     

基于双闭环系统的起重机位置控制技术研究

传统的起重机位置控制技术大多是以位移或速度为反馈量构成的单闭环控制,只能对系统的一个状态量进行控制,易造成系统的超调、振荡,难以实现真正意义上的位置控制;研究采用位移和速度的双闭环位置控制技术[1],以位移环为外环、速度环为内环,位移环根据位移的当前值与给定值的差,通过位移调节器给速度环提供给定速度,速度环通过速度调节器控制系统的运动速度,最终实现对系统的位置控制;通过对单闭环控制和双闭环控制的仿真结果对比分析,双闭环系统的位置和速度的控制精度均比单闭环精度高,最后通过实验,证明了双闭环系统在实践上的可行性。     

MMA7361L的高精度角度检测平台设计

倾角是许多控制系统中需要测量的一个重要参数。针对倾角测量,设计了一种基于ARM微控制器和加速度传感器的角度测量平台。该平台采用基于ARMCortex—M3内核的STM32F103VE为数据处理的核心,利用高精度加速度传感器MMA7361L为测角传感器,同时配置液晶屏和小型键盘实现了人机交互。该平台具有测量精度高、灵敏度高、价格低的特点,应用前景广阔。