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1.
INTRODUCTION Metamaterials are periodic metallic structures exhibiting unique properties not existing in natural materials. They are also called backward wave mate- rials, double negative materials, or left-handed mate- rials (LHM) in particular, in which the vectors E, H and k form a left-handed system. Since the idea pro- posed by Veselago (1968), metamaterials have at- tracted great interest in the last years (Smith et al., 2000; Pendry, 2000; Smith and Kroll, 2000; Shelby et al., …  相似文献   

2.
In this paper, we summarize some recent activities in the field of metamaterial research at the National University of Singapore （NUS）. Integral equations are applied for electromagnetic modelling of supernatural materials. Some special characteristics of the metamaterials are shown. Moreover, quasi-static Lorentz theory and numerical method （i.e., the method of moments for solving the electric field integral equation） and the transmission line theory are both presented to obtain the effective constitutive relations of metamaterials, respectively. Finally, feasibility of fabricating metamaterials based on analysis of equivalent transmission line model in the microwave spectrum and even higher is also shown and correspondingly some broad-bandwidth and low-loss metamaterial structures are designed and synthesized.  相似文献   

3.
INTRODUCTION In recent years metamaterials, more commonly referred to as left-handed materials, have stimulated great interests in the scientific and engineering field. These artificial materials, which were first theorized by Veselago (1968) and experimentally realized by Shelby et al.(2001), can exhibit specific electromag- netic properties not commonly found in nature. The approach of using transmission line theory was veri- fied to be an efficient design tool for metamaterials applica…  相似文献   

4.
Encapsulation of different guestspecies such as molecules and ions inside carbon nanotubes （CNTs） has been reported in the literatures during the last 15 years and repre sents an exciting development of nanoengineering of novel materials and composites. The reported nanocomposite mate rials show the semiconducting properties with potential applications in nanosensors, nanounits and nanocircuits as well as advanced energy transfer and storage properties, and encompass manufacturing for novel nanowires, nanoelectronic devices with properties designed with optoelectronic, spin tronic and nanomagnetic qualities. This review reports on a wide range of encapsulation references with particular focus on single molecules, atomic chains, metal halides and polymers encapsulated inside CNTs. The encapsulation methods and the chemical and physical qualities of these novel materials are crucial for the future manufacturing of novel innovations in nanotechnology, and represent therefore the current stateof theart of encapsulation methods in advanced manufacturing.  相似文献   

5.
罗英梅 《海外英语》2011,(7):153-154
The current study is concerned with the integration of English reading and writing in a program which is delivered jointly by Henan University(HU) in Kaifeng and Victoria University(VU) in Melbourne.Currently,English writing and reading have irrelevant teaching contents.In order to make better use the Chinese and Australian teachers’ English expertise to enhance students’ English proficiency in the joint program,VU and HU initiated this case study of coordination and cooperation at a curriculum and delivery planning level for reading and writing.By analyzing research data,this paper aims to measure the effectiveness of integration of writing and reading,to identify students’ acceptance of the collaboration of writing and reading and also to explore alternative ways of designing the teaching materials in an Australia-China English course.The main findings of the research project relate to student confidence,knowledge,motivation which are greatly improved when reading and writing materials are closely-related;trial groups’ writing proficiency showed twice greater improvement than that of control group;integration of reading and writing better uses Australian and Chinese teachers’ English expertise;over 90% of the students comment that the specially-designed materials are useful and would like to continue learning in this way if possible.  相似文献   

6.
Chinese tourism becomes a thriving field with the promotion of China reform and opening policy and the rapid development of social economy. The translation of tourist materials thus weighs a lot in the economic development and cross-cultural communication. But the condition is not satisfactory, there are still existing some problems in the translation of tourist publicity materials. Therefor the readers can’t receive the equal information that the original text expressed. Based on this fact,the paper attempts to analyze what pragmatic failures there are in the translation of tourist materials and to analyze how the Pragmaticmarkedness Equivalence Principle(PMEP) approach can be applied to the translation of tourist publicity materials to achieve the translation equivalence.  相似文献   

7.
According to the observance of ELT(English Language Training)classes in China,the selection of reading materials becomes a big problem.Most teachers there are in a traditional way of following the textbooks,and regard texts given in those books as the sole resource of teaching materials.However,those texts are not ideal for all situations,and when there are problems,we need to make improvements instead of sticking to the authority of textbooks.In this paper the author will illustrate the necessity of adapting reading textbooks mainly in a Chinese ELT context and set forth some corresponding suggestions about adaption in different cases.  相似文献   

8.
INTRODUCTION Due to market pressures for improvements in productivity, reliability, ductility, wear resistance and profitability of mechanical systems, manufacturers are placing increasing demands on available materials.Economic constraints require that these materials are inexpensive and easily available. In order to enhance the surface properties of today’s materials, producers of components are turning to different surface finish and treatments. There are several techniques available …  相似文献   

9.
Introduction Materials development is both a field of study and a practical undertaking. As a field it studies the principles and procedures of the design, implementation and evaluation and adaptation of language teaching materials, by teachers for their own classrooms and by materials writers for sale or distribution. Ideally these two aspects of materials development are interactive in that the theoretical studies inform and are informed by the development and use of classroom materials （e. g. Tomlinson 1998c）.  相似文献   

10.
A Novel Electromagnetic Bandgap Structure for Filter   总被引：1，自引：0，他引：1  
Electromagnetic bandgap (EBG) materials are periodic structures capable of prohibiting the propagation of electromagnetic waves within a certain band of frequencies. This characteristic of EBG has wide application. The structures to be studied here are mainly planar EBG materials of two dimensions, which are periodic arrays of holes etched in the ground plane of a conventional microstrip line. EBG structures are calculated with finite-difference time-domain (FDTD) method in this paper. Technique of the perfectly matched layer is used for the absorption of electromagnetic waves in FDTD. The FDTD method is programmed with the blend of C^ and Matlab languages, which makes the program both simple and fast computing. A kind of new EBG structure is brought out through a lot of experiments and analyses. A filter with wide stop-band and another filter with two stop-bands are designed.  相似文献   

11.
INTRODUCTIONInvestigationofphotonicbandgap(PBG)materialsiscurrentlyoneofthemostactivefron-tiersinengineeringandphysics.PBGmaterialshaverecentlyemergedasanewmultidisciplinaryfieldofstudy(Kesleretal.,1996;Yablonovitch,1994;SimovskiandHe,2001).APBGstructurecanhaveabandgapwithinwhichelectromagnetic(EM)wavepropagationispreventedinalldirec-tions(Joannopoulosetal.,1997;Ozbayetal.,1994).Foratwo-dimensionalPBGmaterial,thepropagationofanEMwavewithinitsbandgapispreventedinalldirectionswithin…  相似文献   

12.
A new photonic bandgap (PBG) cover for a patch antenna with a photonic bandgap substrate is introduced. The plane wave expansion method and the FDTD method were used to calculate such an antenna system. Numerical results for the input return loss, radiation pattern, surface wave, and the directivity of the antennas are presented. A comparison between the conventional patch antenna and the new PBG antenna is given. It is shown that the new PBG cover is very efficient for improving the radiation directivity. The physical reasons for the improvement are also given. Project supported by the National Natural Science Foundation of China (No. 90101024) and the Science and Technologies of Zhejiang Provinc (No. ZD0002)  相似文献   

13.
This study has explored the parents’ regulation strategies that were more likely to support children’s self-regulation in learning situations with computers. These strategies have been analysed by means of new grids involving seven categories of behaviour: cognitive strategies relating to identification of objective, exploration of means, attention and evaluation; motivational strategies; and socio-communicative strategies such as joint attention and request. 62 7-year-old children from Quebec families were examined with their mothers and fathers. The children were asked to complete two learning tasks that involved using LOGO software to draw a picture. Results indicated that parents’ regulation varied depending on their gender; a higher directivity was observed in mothers, more specifically through some specific strategies. Analysis of variance on repeated measures showed that, during the session, there was a decrease in the specification of the objective, the initiation of joint attention and of behaviour regulation in parents; and an improvement of the identification of the objective, planning and self-evaluation in children. Correlations between parental regulation and children’s self-regulation strategies indicated positive links concerning strategies relating to joint attention and to motivation; and negative links concerning strategies relating to the exploration of means and evaluation. A good adjustment of the parents’ regulation and the children’s self-regulation correlated positivel with success in the task. Methodological implications are proposed for research and psycho-educative intervention.  相似文献   

14.
This study was designed to illuminate the state of education in Taiwan by constructing Educational Indicator Systems. The study, sponsored by the National Science Council between 1998 and 2000, was the first comprehensive indicator project to cover all educational levels in Taiwan. Various research methods were used, including panel discussion, conference, setting up website, Delphi technique, questionnaires and visits to 14 international organizations and government agencies. In the process, two educational indicator systems based upon the “Context-Input-Process-Progress” (CIPP) model were formulated: “Taiwan’s Educational Indicator System by educational level” (TEIS by el) with 99 indicators, and “Significant Indicators of Taiwan’s Education” (SITE) with 34 indicators. Finally, some limitations and suggestions were offered for the future development of Educational Indicator Systems.  相似文献   

15.
The 4TPS-PS parallel platform designed for a stabilization and automatic tracking system is a novel lower-mobility parallel mechanism. In the first part of this paper, the structure of the platform is described and the kinematics model is built. The workspace of the platform is defined as the full reachable rotation workspace when the Z coordinate dimension of the upper plate varies continuously. A fast searching method of the full reachable workspace is presented, after which the inverse kinematics of the platform is deduced. The forward and inverse solutions of the speed and force of the platform are deduced. According to the characteristic of the 4TPS-PS platform’s structure, a fast searching algorithm of the maximum generalized speed and maximum generalized force output by the upper plate is put forward based on the forward and inverse solutions of the platform’s speed and force. The 4TPS-PS platform prototype built by the State Key Laboratory of Fluid Power Transmission and Control of China is taken as the research subject. The full reachable rotation workspace of the prototype is computed out and analyzed. The curves of maximum generalized speed and maximum generalized force of the prototype are computed out and plotted. Finally, the com- puting and analyzing results of the operating characteristics are confirmed through the experiment.  相似文献   

16.
We describe research carried out with a prospective secondary biology teacher, whom we shall call Miguel. The teacher’s conceptions of the nature of science and of learning and teaching science were analyzed and compared with his classroom practice when teaching science lessons. The data gathering procedures were interviews analyzed by means of cognitive maps and classroom observations. The results reflected Miguel’s relativist conceptions of the nature of science that were consistent with his constructivist orientation in learning and teaching. In the classroom, however, he followed a strategy of transmission of external knowledge based exclusively on teacher explanations, the students being regarded as mere passive receptors of that knowledge. Miguel’s classroom behavior was completely contrary to his conceptions, which were to reinforce the students’ alternative ideas through debate, and not by means of teacher explanation.  相似文献   

17.
The puzzle as to how bats navigate without colliding with obstacles and hunt tiny mosquitoes in complete darkness remained unanswered for nearly 140 years after Lazzaro Spallanzani, who proposed at the close of the 18th century that bats possess a ‘sixth sense’ for orientation. Donald Griffin solved the puzzle in 1938 with the help of world’s first ultrasound microphone devised by the American physicist G W Pierce. Griffin called this sixth sense ‘echolocation’, which enables bats and marine mammals such as whales, dolphins and porpoises to lead active lives under the cover of darkness. In this article we describe the life of Donald Griffin and how he proved the existence of echolocation in bats.  相似文献   

18.
INTRODUCTION It is well known that micro-tremor observation is one of the most convenient methods for investi- gating the dynamic characteristics of the surface ground and the affected structure (Bard, 1998; Dow- rick, 1997). Micro-tremor is a kind of geophysics information related to soil formation of site, corre- sponding to engineering geological condition. The frequency characteristics of micro-tremor can be obtained by spectral analyses of its signals, which can be used to probe into…  相似文献   

19.
This is a documentary study of education abroad policy in the People’s Republic of China (PRC) between 1978 and 2009. By examining the dynamics underpinning the PRC state’s efforts to shape the flow of Chinese students and scholars from and into China, this article reveals the major strategies that have enabled education abroad to become a source of brain gain. It argues that China’s brain gain strategies feature three characteristics: a proactive diplomatic approach to international educational relations; strategic dependence on foreign higher education resources and a decentralized economic mechanism to raise foreign-trained human capital. The paper concludes by discussing the implications of Chinese experience for our understanding of the complex and dynamic relations between the state, the market, universities and international relations as relating to cross-border academic mobility, international educational relations, and national development in a globalizing world.  相似文献   

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