Numerical investigation of cavitating flow behind the cone of a poppet valve in water hydraulic system

Computational Fluid Dynamics (CFD) simulations of cavitating flow through water hydraulic poppet valves were performed using advanced RNGk-epsilon turbulence model. The flow was turbulent, incompressible and unsteady, for Reynolds numbers greater than 43000. The working fluid was water, and the structure of the valve was simplified as a two dimensional axisymmetric geometrical model. Flow field visualization was numerically achieved. The effects of inlet velocity, outlet pressure, opening size as well as poppet angle on cavitation intensity in the poppet valve were numerically investigated. Experimental flow visualization was conducted to capture cavitation images near the orifice in the poppet valve with 30° poppet angle using high speed video camera. The binary cavitating flow field distribution obtained from digital processing of the original cavitation image showed a good agreement with the numerical result. Project supported by the National Natural Science Foundation of China (No. 59835160) and Scientific Research Foundation for Returned Overseas Chinese Scholars, State Education Ministry of China (No. 50175097)     

以经济增加值为核心的绩效评价体系与建设银行的改革

随着中国建设银行的股份制改造以及上市,追求银行价值最大化日益明确地成为银行首要经营目标.而经济增加值作为目前评价及度量企业经营绩效、创造长期价值、同时又最能体现股东价值增长的最好指标之一,无疑为建设银行加快改革,真正成为国际上具有核心竞争力的商业银行提供了一种科学的绩效评价之策.     

网络时代的高校思想政治教育工作的挑战与对策

网络技术的普及和发展,像一把双刃剑,给高校思想政治教育工作带来了机遇与挑战,它拓宽了高校思想政治工作的渠道,同时也引发许多问题,如何趋利避害进行网络思政教育是一个重要而迫切的课题.     

分布式技术在教材管理系统中的应用

本介绍了多层分布式结构的特点及采用分布式技术开发的高校教材管理系统。     

Field-study science classrooms as positive and enjoyable learning environments

We investigated differences between field-study classrooms and traditional science classrooms in terms of the learning environment and students’ attitudes to science, as well as the differential effectiveness of field-study classrooms for students differing in sex and English proficiency. A modified version of selected scales from the What Is Happening In this Class? questionnaire was used to assess the learning environment, whereas students’ attitudes were assessed with a shortened version of a scale from the Test of Science Related Attitudes. A sample of 765 grade 5 students from 17 schools responded to the learning environment and attitude scales in terms of both their traditional science classrooms and classrooms at a field-study centre in Florida. Large effect sizes supported the effectiveness of the field-studies classroom in terms of both the learning environment and student attitudes. Relative to the home school science class, the field-study class was considerably more effective for students with limited English proficiency than for native English speakers.     

Should Science be Taught in Early Childhood?

This essay considers the question of why we should teach science to K-2. After initial consideration of two traditional reasons for studying science, six assertions supporting the idea that even small children should be exposed to science are given. These are, in order: (1) Children naturally enjoy observing and thinking about nature. (2) Exposing students to science develops positive attitudes towards science. (3) Early exposure to scientific phenomena leads to better understanding of the scientific concepts studied later in a formal way. (4) The use of scientifically informed language at an early age influences the eventual development of scientific concepts. (5) Children can understand scientific concepts and reason scientifically. (6) Science is an efficient means for developing scientific thinking. Concrete illustrations of some of the ideas discussed in this essay, particularly, how language and prior knowledge may influence the development of scientific concepts, are then provided. The essay concludes by emphasizing that there is a window of opportunity that educators should exploit by presenting science as part of the curriculum in both kindergarten and the first years of primary school.     

ADAPT<Superscript>IT</Superscript>: Tools for training design and evaluation

This article describes a set of computerized tools that support the design and evaluation of competency-based training programs. The training of complex skills such as air traffic control and process control requires a competency-based approach that focuses on the integration and coordination of constituent skills and transfer of learning. At the heart of the training are authentic whole-task practice situations. The instructional design tools are based on van Merriënboer's 4C/ID^* methodology (1997). The article describes a training design tool (Core) that supports the analysis and design for competency-based training programs and an evaluation tool (Eval) that supports the subsequent revision of this training design.     

韩礼德系统语法语言分析的模式

:语言可以从不同角度加以研究。该文从六个方面简单阐述了系统语法大师M .A .K .Halliday语言分析的模式 ,主要内容包括 :语言的层次 ,链轴和选择轴 ,语法结构 ,语法单位 ,语法的级阶和语法系统     

An adaptive strategy for controlling chaotic system

This paper presents an adaptive strategy for controlling chaotic systems. By employing the phase space reconstruction technique in nonlinear dynamical systems theory, the proposed strategy transforms the nonlinear system into canonical form, and employs a nonlinear observer to estimate the uncertainties and disturbances of the nonlinear system, and then establishes a state-error-like feedback law. The developed control scheme allows chaos control in spite of modeling errors and parametric variations. The effectiveness of the proposed approach has been demonstrated through its applications to two well-known chaotic systems: Duffing oscillator and Rössler chaos.