Understanding metallic bonding: Structure,process and interaction by Rasch analysis

This paper reports the results of a survey of 3006 Year 10–12 students on their understandings of metallic bonding. The instrument was developed based on Chi's ontological categories of scientific concepts and students' understanding of metallic bonding as reported in the literature. The instrument has two parts. Part one probed into students' understanding of metallic bonding as (a) a submicro structure of metals, (b) a process in which individual metal atoms lose their outermost shell electrons to form a ‘sea of electrons’ and octet metal cations or (c) an all-directional electrostatic force between delocalized electrons and metal cations, that is, an interaction. Part two assessed students' explanation of malleability of metals, for example (a) as a submicro structural rearrangement of metal atoms/cations or (b) based on all-directional electrostatic force. The instrument was validated by the Rasch Model. Psychometric assessment showed that the instrument possessed reasonably good properties of measurement. Results revealed that it was reliable and valid for measuring students' understanding of metallic bonding. Analysis revealed that the structure, process and interaction understandings were unidimensional and in an increasing order of difficulty. Implications for the teaching of metallic bonding, particular through the use of diagrams, critiques and model-based learning, are discussed.     

Conceptual difficulties experienced by senior high school students of electrochemistry: Electric circuits and oxidation-reduction equations

The purpose of this research was to investigate students' understanding of electrochemistry following a course of instruction. A list of conceptual and propositional knowledge statements was formulated to identify the knowledge base necessary for students to understand electric circuits and oxidation-reduction equations. The conceptual and propositional knowledge statements provided the framework for the development of a semistructured interview protocol which was administered to 32 students in their final year of high school chemistry. The interview questions about electric circuits revealed that several students in the sample were confused about the nature of electric current both in metallic conductors and in electrolytes. Students studying both physics and chemistry were more confused about current flow in metallic conductors than students who were only studying chemistry. In the section of the interview which focused on oxidation and reduction, many students experienced problems in identifying oxidation-reduction equations. Several misconceptions relating to the inappropriate use of definitions of oxidation and reduction were identified. The data illustrate how students attempted to make sense of the concepts of electrochemistry with the knowledge they had already developed or constructed. The implications of the research are that teachers, curriculum developers, and textbook writers, if they are to minimize potential misconceptions, need to be cognizant of the relationship between physics and chemistry teaching, of the need to test for erroneous preconceptions about current before teaching about electrochemical (galvanic) and electrolytic cells, and of the difficulties experienced by students when using more than one model to explain scientific phenomena.     

Story of fission

The discovery of nuclear fission is the culmination of sustained efforts involving many scientists led by Hahn and Meitner to understand the production of artificial radioactivity induced by neutrons bombarding uranium. The large energy release in this process was almost immediately used for both military and civilian purposes. It also started the largescale funding of scientific research by governments across the world. Nuclear energy is one of the clean sources of energy and contributes very little to global warming.     

Conductance oscillations through an aharonov-bohm ring with a quantum gate

１　Ｉｎｔｒｏｄｕｃｔｉｏｎ　Ｑｕａｎｔｕｍｃｏｈｅｒｅｎｔｔｒａｎｓｐｏｒｔｉｎｍｅｓｏｓｃｏｐｉｃｓｙｓｔｅｍｈａｓｂｅｅｎｉｎｖｅｓｔｉｇａｔｅｄｅｘｔｅｎｓｉｖｅｌｙｉｎｔｈｅｐａｓｔｄｅｃａｄｅ．Ｍｏｔｉｖａｔｅｄｂｙｓｏｍｅｒｅｃｅｎｔｅｘｐｅｒｉｍｅｎｔｓ,ｍａｄｅｂｙＹａｃｏｂｙｅｔａｌ．［１］ａｎｄＢｕｋｓｅｔａｌ．［２］,ｐｈａｓｅｓｅｎｓｉｔｉｖｅｔｒａｎｓｐｒｏｔｉｎａｎＡｈａｒｏｎｏｖｂｏｈｍ（ＡＢ）ｒｉｎｇｗｉｔｈａｑｕａｎｔｕｍｄｏｔ（ＱＤ）ｅｍｂｅｄｄｅｄ…     

超热电子的产生与输运背向辐射的实验研究

报道了在20TW fs激光器上,采用电子磁谱仪和光学CCD积分成像相机,分别对激光-固体靶的相互作用,在靶背方向产生的超热电子能谱及其光学渡越辐射进行的测量。能谱测量结果显示：超热电子能谱呈双温类-麦克斯韦分布,拟合的温度分别为90keV和280keV,平均温度为185keV,这与已知的温度定标率较好地吻合;光学渡越辐射测量结果显示：光学渡越辐射是由于超热电子输运穿越固体靶所致,而辐射区域呈圆盘状、有发散角、有光强分布;如果考虑超热电子的产生和加热机制,则占主导地位的加热机制是共振吸收对电子的加热。     

通过带有量子门的Aharonov-Casher环的自旋极化电导振荡

1 Introduction Since some experi ments made by Yacoby,et al.[1],and Schuster ,et al.[2],that first measured electrontransmission phase through a quantum dot ( QD) ,phase sensitive transports in open mesoscopic ringwith a QD have been extensively investiga…     

安徽省工业化水平与能源使用效率的协整检验

利用协整理论和误差修正模型,考察了安徽省1993～2008年工业化发展水平与能源使用效率间的关系。结果显示:能源使用效率的提高有利于促进工业化水平的增长,且两者间互为因果关系,但短期内能源使用效率对工业化水平影响不显著。对此,安徽省应继续调整产业结构,提高能源利用效率,缓解经济增长对能源的需求。     

以昂尼斯气体为工质的斯特林热机循环效率

以昂尼斯气体为工质,推导出斯特林热机循环的回热损失、输出功及效率的表达式.经过验证,以理想气体、范德瓦尔斯气体、Redlich-Kwong气体和Dieterici气体为工质时,斯特林循环的回热损失、输出功及效率均可由以昂尼斯气体为工质时的形式得出.     

Giant magnetoresistance

The 2007 Nobel Prize in Physics was awarded to Albert Fert and Peter Grünberg for the discovery of giant magnetoresistance (GMR). GMR is achieved in metallic multilayers, where the resistance of the multilayer changes considerably by the application of a magnetic field. This has paved the way for high density data storage in magnetic media. (left) Debakanata Samal is a research scholar at the Deaprtment of Physics at IISc, Bangalore. His research interests are in magnetotransport in oxide multilayers, spintronics. (right) P S Anil Kumar is an Asst. Professor at the Department of Physics, IISc Bangalore. His research interests are in spintronics, magnetic nano-structures, surface-and thin-film magnetism, magnetotransport in metallic multilayers and oxides, and spin-polarized electron scattering.     

问题教学的“过程化”研究

问题教学是指以问题为中心的教学,它是把教学内容化作问题,引导学生通过解决问题从而掌握知识、形成能力、养成心理品质的过程。以数学教学中数学概念的形成过程、数学定理、公式和法则的发现及推导过程、数学问题解决的认知过程为例,探究问题教学的“过程化”。     

Fermion number fractionization

Solitons emerge as non-perturbative solutions of non-linear wave equations in classical and quantum theories. These are non-dispersive and localised packets of energy — remarkable properties for solutions of non-linear differential equations. In the presence of such objects, the solutions of Dirac equation lead to the curious phenomenon of ‘fractional fermion number’. Under normal conditions the fermion number takes strictly integral values. In this article, we describe this accidental discovery and its manifestation in polyacetylene chains, which has led to the development of organic conductors. (left) Kumar Rao is a Postdoctoral Fellow at PRL, Ahmedabad. He is interested in particle physics phenomenology as probed in particle colliders and formal aspects of quantum field theory. (right) Narendra Sahu is currently a postdoctoral fellow at Lancaster University, UK. His main research area includes Cosmology and Astroparticle physics. Currently he is working on dark matter and matter anti-matter asymmetry of the universe. (center) P K Panigrahi’s research interests are in the area of quantum computation, solitons in Bose Einstein condensates & nonlinear optical media. He is also deeply interested in science education and derives pleasure from long weekend walks.     

Perspectives on the metallic interconnects for solid oxide fuel cells

The various stages and progress in the development of interconnect materials for solid oxide fuel cells (SOFCs) over the last two decades are reviewed. The criteria for the application of materials as interconnects are highlighted. Interconnects based on lanthanum chromite ceramics demonstrate many inherent drawbacks and therefore are only useful for SOFCs operating around 1000 ℃. The advance in the research of anode-supported flat SOFCs facilitates the replacement of ceramic interconnects with metallic ones due to their significantly lowered working temperature. Besides, interconnects made of metals or alloys offer many advantages as compared to their ceramic counterpart. The oxidation response and thermal expansion behaviors of various prospective metallic interconnects are examined and evaluated. The minimization of contact resistance to achieve desired and reliable stack performance during their projected lifetime still remains a highly challenging issue with metallic interconnects. Inexpensive coating materials and techniques may play a key role in pro moting the commercialization of SOFC stack whose interconnects are constructed of some current commercially available alloys. Alternatively, development of new metallic materials that are capable of forming stable oxide scales with sluggish growth rate and sufficient electrical conductivity is called for.     

Supporting Communication in a Collaborative Discovery Learning Environment: the Effect of Instruction

We present a study on the effect of instruction on collaboration in a collaborative discovery learning environment. The instruction we used, called RIDE, is built upon four principles identified in the literature on collaborative processes: Respect, Intelligent collaboration, Deciding together, and Encouraging. In an experimental study, a group of learners (ages 15–17) receiving this instruction was compared to a control group. The learners worked in dyads on separate computers in a shared discovery learning environment in the physics domain of collisions, communicating through a chat channel. Qualitative and quantitative analyses of the logged actions in the learning environment and the chat protocols showed that the RIDE instruction can lead to more constructive communication, and improved discovery learning activities, as expected, although no direct effect on discovery learning results was found. This study shows the benefits of providing instruction on effective communication and the learning process in a collaborative discovery learning situation.     

正常金属-量子点-超导系统的共振隧穿

研究了正常金属-量子点-超导系统的输运特性,并考虑了相互作用在点上和对势在超导一边,输运特性依赖于库仑阻塞效应和Andreev反射的竞争,在有限温度下,电导对门压展现出一系列的峰,它们取决于量子点的能级间隔和电荷能.不同种类共振峰的详细分析也被给出.     

非理想气体的卡诺循环

把范德瓦尔斯气体和昂尼斯气体作为工作物质，计算其卡诺循环的效率，与理想气体卡诺循环的效率相同，进一步说明卡诺定理的正确性．     

A First Course in Electrical Engineering

This article describes the introductory two-semester course in electrical engineering that has been developed over a period of five years at Princeton University. The aims of the course are to provide an introduction to the field of electrical engineering via the basic concepts of electricity and magnetism (which are developed through Maxwell's equations in the integral form), to apply these concepts in developing the fundamentals of energy conversion and circuit theory, and to carry forward, in a continuous and integrated way, a modern treatment of network analysis. Thus, the treatment proceeds from field ideas to circuits and physical apparatus, and to their mathematical models. With the circuit relations formulated, attention turns to the analysis of networks, starting with network topology and extending through pole-zero ideas. The treatment stops just short of the Laplace transform. This course is intended to serve as a foundation for subsequent courses such as electronic circuits, energy conversion, and advanced network analysis and synthesis, and has been developed with the purpose of providing the student with a unifying point of view for these varied topics.     

Simple operated multipurpose temperature control cryostat

A suitable simple optical cryostat for optical, magneto-optical, electrical and thermo-electrical measurements was designed. It is suitable for use in a magnetic pool gap as narrow as less than 1 cm. Throughout a long period of time, the heat diffusion process of the cryostat can be easily operated at slow increase in sample temperature in a range 1.25 K/min at 200 K that will be reduced gradually to 0.66 K at room temperature. Liquid nitrogen was used to cool down the temperature. During the operation, the change in the measured energy gap of a semiconductor sample and other physical parameters resulting from the change of temperature can be corrected through the temperature coefficient of that parameter at the corresponding temperature. The cryostat was successfully used for all experiments mentioned above to measure the properties of a single crystal of GaP (Gallium Phosphate) semiconductor.     

一种面向业务领域的web服务发现方法以及支撑框架

针对UDDI关键字匹配带来的服务发现精度低,以及难以从功能相同的多个web服务中选择合适服务的问题,提出一种新的面向业务领域的web服务发现方法和相关框架.当用户请求服务时,根据功能请求从实际服务中抽取出服务簇,然后由业务信息属性等非功能性属性进行协商,确定出适合的服务并与用户请求绑定,而整个发现过程对用户来说都是透明的.通过建立一个基于旅游领域的原型系统IPVita来测试和支持此框架.     

关于电源能量的传输问题

通过对进入电阻和电容器内的能流的计算，分析了电源能量的传输问题．结果表明，电源的能量是通过电磁场传输出去的，通电电线的作用是提供所需的电磁场．     

Energy harvesting from pavement via polyvinylidene fluoride: hybrid piezo-pyroelectric effects

In the USA, there are over 4 million miles (6 million km) of roadways and more than 250 million registered vehicles. Energy lost in the pavement system due to traffic-induced vibration and deformation is enormous. If effectively harvested, such energy can serve as an alternative sustainable energy source that can be easily integrated into the transportation system. It is well known that most piezoelectric materials are also pyroelectric materials, which convert temperature change into electricity. However, the potential of polyvinylidene fluoride (PVDF) as a hybrid piezo-pyroelectric energy harvester has been seldom studied. The uniqueness of this study lies in that the electrical responses of PVDF under coupled mechanical and thermal stimulations are investigated. Through a series of well controlled experiments, it is found that there exists an interesting coupling phenomenon between piezoelectric and pyroelectric effects of PVDF: the voltage generated by simultaneous mechanical and thermal stimulations is the algebraic sum of voltages generated by separate stimulations. This means that there is neither strengthening nor weakening coupling effect when the piezoelectric and pyroelectric phenomena are coupled. This also makes the modeling process of the hybrid piezoelectric and pyroelectric effect straightforward. An estimation of power generation through piezoelectric and pyroelectric effect is conducted, and the overall effects of temperature on hybrid piezo-pyroelectric energy harvesting are discussed.