《英语作业team学习.pptx》由会员分享,可在线阅读,更多相关《英语作业team学习.pptx(22页珍藏版)》请在taowenge.com淘文阁网|工程机械CAD图纸|机械工程制图|CAD装配图下载|SolidWorks_CaTia_CAD_UG_PROE_设计图分享下载上搜索。
1、contentscreditabilityitensemodal verbfirst person voicelexical items第1页/共22页 creditabilityReputable publisher or journalSample oneJournal:science Impact Factor:31.477 Cited:1235 Sample twoJournal:PRL Impact Factor:7.728 Cited:13330 Sample threeJournal:science Impact Factor:31.477 Cited:1702 Sample f
2、ourJournal:PRL Impact Factor:7.728 Cited:8520 第2页/共22页 creditabilityAuthors credentialAuthorFieldsKnown forSample 1Eli YablonovitchPhysics,Electrical Engineering Photonic CrystalSample 2Yoel FinkProfessor at MITOmnidirectional reflectorsSample 3D.R.SmithDirector at Duke UniversityMetamaterials Sampl
3、e 4J.B.PendryTheoretical PhysicistInvisibility cloak第3页/共22页Abstractp叙述结论或建议时,可使用现在时、臆测动词或may,should,could等助动词p介绍背景资料时,如果描述普遍事实,应使用现在时 如果对某种研究现状和趋势的概述,则使用现在完成时It has been recognized for some time that the spontaneous emission by atoms is not necessarily a fixed and immutable property of the coupling
4、 between matter and space,but that it can be controlled by modification of the properties of the radiation field.This is equally true in the solid state,where spontaneous emission plays a fundamental role in limiting the performance of semiconductor lasers,heterojunction bipolar transistors,and sola
5、r cells.If a three-dimensionally periodic dielectric structure has an electromagnetic band gap which overlaps the electronic band edge,then spontaneous emission can be rigorously forbidden.第4页/共22页Abstractp概述实验程序、方法时,通常用过去时p描述应用前景、领域时,通常用将来时A design criterion that permits truly omnidirectional refle
6、ctivity for all polarizations of incident light over a wide selectable range of frequencies was used in fabricating an all-dielectric omnidirectional reflector consisting of multilayer films.The reflector was simply constructed as a stack of nine alternating micrometer-thick layers of polystyrene an
7、d tellurium and demonstrates omnidirectional reflection over the wavelength range from 10 to 15 micrometers.Because the omnidirectionality criterion is general,it can be used to design omnidirectional reflectors in many frequency ranges of interest.Potential uses depend on the geometry of the system
8、.For example,coating of an enclosure will result in an optical cavity.A hollow tube will produce a low-loss,broadband waveguide,whereas a planar film could be used as an efficient radiative heat barrier or collector in thermoelectric devices.第5页/共22页Introductionp描述特定研究领域中最近的某种趋势,或者强调表发生的事件对现在的影响时,常采
9、用现在完成时p叙述有关现象或普遍事实和对其他人研究成果的引用时,句子的主要动词多使用现在时It has been recognized for some time that the spontaneous emission by atoms is not necessarily a fixed and immutable property of the coupling between matter and space,but that it can be controlled by modification of the properties of the radiation field.R
10、ecently there have been experiments in which the spontaneous emission by Rydberg atoms and by Penning-trapped electrons has been inhibited in a microwave cavity which had no electromagnetic modes at the transition frequency.Such a capability is no less important in the solid state where spontaneous
11、emission in the form of electron-hole radiative recombination plays a decisive role.For direct-gap semiconductors it is commonplace for the internal spontaneous emission quantum efficiency of electron-hole recombination to exceed 90%even at room temperature.第6页/共22页Materials and Methodsp描述的内容为不受时间影响
12、的事实,实验步骤或计算的过程、公式的推导、模型的建立等,采用一般现在时In principle the internal spontaneous emission is thus never really lost and the overall emission is diminished by the factor n2.p描述的内容为特定、过去的行为或事件,则采用过去式Although such a system has been analyzed extensively in the literature,the possibility of omnidirectional refle
13、ctivity was not recognized until recently.第7页/共22页Resultsp对研究结果进行说明或由其得出一般性推论时,多用现在时p叙述或总结研究结果的内容为关于过去的事实,所以通常采用过去时The PS-Te structure does not have a complete photonic band gap.Its omnidirectional reflectivity is due instead to the restricted phase space available to the propagating states of the s
14、ystem.The materials and processes were chosen for their low cost and applicability to large area coverage.The possibility of achieving omnidirectional reflectivity itself is not associated with any particular choice of materials and can be applied to many wavelengths of interest.Our structure offers
15、 metallic-like omnidirectional reflectivity for a wide range of frequencies and at the same time is of low loss.In addition,it allows the flexibility of frequency selection.第8页/共22页The frequency of modal verb CanMayCouldShouldMustSample 1167004Sample 2211201Sample 3254815Sample 4110103第9页/共22页Can(能力
16、)The currents that flow when this resonance is activated couple strongly to an applied magnetic field,yielding an effective permeability that can reach quite high values.Such an inhibition can be much more complete than in a metallic waveguide since dielectric structures can in principle be lossless
17、.A lower limit can now be placed on the minimum refractive index difference required to assure that a gap will open up in the electromagnetic spectrum.The engineered response of metamaterials has had a dramatic impact on the physics,optics,and engineering communities,because metamaterials can offer
18、electromagnetic properties that are difficult or impossible to achieve with conventional,naturally occurring materials.第10页/共22页May(可能)As we look to higher frequencies,on the other hand,conventional magnetism tails off and artificial magnetism may play an increasingly important role.Nevertheless we
19、may conclude that inhibited spontaneous emission is a real possibility in semiconductor lasers,but that it may require further materials development before the benefits are fully felt.Although such an inhomogeneous collection may not satisfy our intuitive definition of a material,an electromagnetic
20、wave passing through the structure cannot tell the difference.In general these limits should be easy to satisfy,but it may be difficult to find a common lattice-matched pair of materials with a sufficiently large index difference.第11页/共22页Must(必然)Therefore,I must conclude that inhibited spontaneous
21、emission is already incorporated to the maximum permissible degree in the most modern solar-cell designs.In solar cells radiative emission does indeed play the key role,but as with lasers it cannot be completely eliminated since it must coexist with light absorption from the surrounding space.Any ma
22、terial destined for use in the MRI environment must not perturb the quasi-static magnetic field pattern,thus excluding the use of all conventional magnetic materials.A starting point for this discussion is the observation by Einstein that spontaneous emission must inescapably coexist with absorption
23、 and stimulated emission.第12页/共22页The comparison of I and We use frequencyIWeSample 143Sample 20 4Sample 3020Sample 4223nArticles in the humanities and social science InArticles in the science and engineering We第13页/共22页I(主观观点)In Fig.1,I sketch the focusing action of such a slab,assuming that the re
24、fractive index.I conclude that inhibited spontaneous emission due to an electromagnetic band gap can be a significant effect in solid-state physics and may someday have a role to play in the study of semiconductor lasers.In this Letter I want to challenge the traditional limitation on lens performan
25、ce and propose a class of“superlenses,”and to suggest a practical scheme for implementing such a lens.Therefore I suggest that the direct-gap semiconductors are a natural physical system for the study of inhibited spontaneous emission.第14页/共22页We(客观规律)We turn now toward the role of spontaneous emiss
26、ion in heterojunction bipolar transistors and solar cells.We choose the axis of the lens to be the z axis.Maxwells equations tell us that第15页/共22页Frequency of passive and active voice 引言结论Sample 1主动3/31/1 被动0/30/1Sample 2主动7/105/6被动3/101/6nActive voice -subjective but directnPassive voice-objective
27、but discontinuous第16页/共22页pPassive voiceIn Eq.(I)it is assumed that the doping density is negligible compared to the injected density so that n=p.The three-dimensional periodicity of the index of refraction leads to an fcc reciprocal lattice for electromagnetic waves with the classic Brillouin zone
28、as illustrated in Fig.2(c).pActive voiceTherefore I suggest that the direct-gap semiconductors are a natural physical system for the study of inhibited spontaneous emission.In this paper,I analyze the different aspects of inhibited spontaneous emission appropriate to each of these cases.Therefore,I
29、must conclude that inhibited spontaneous emission is already incorporated to the maximum permissible degree in the most modern solar-cell designs.The passive and active voice choice第17页/共22页Synonyms(同义词转换)It has been recognized for some time that the spontaneous emission by atoms is not necessarily
30、a fixed and immutable property of the coupling between matter and space,but that it can be controlled by modification of the properties of the radiation field.Recently there have been experiments in which the spontaneous emission by Rydberg atoms and by Penning-trapped electrons has been inhibited i
31、n a microwave cavity which had no electromagnetic modes at the transition frequency.It will be neither feasible nor desirable to eliminate spontaneous emission entirely if the function of the semiconductor happens to be the emission or the absorption of light itself.Examples of this would be the sem
32、iconductor laser and the solar cell,respectively.In those cases the goal would be to restrict the spontaneous emission to only those electromagnetic modes which are absolutely necessary.In other functions such as the heterojunction bipolar transistor,where the radiation field would preferably be abs
33、ent,all spontaneous emission should be suppressed if possible.第18页/共22页Synonyms(同义词转换)It has been recognized for some time that the spontaneous emission by atoms is not necessarily a fixed and immutable property of the coupling between matter and space,but that it can be controlled by modification o
34、f the properties of the radiation field.Recently there have been experiments in which the spontaneous emission by Rydberg atoms and by Penning-trapped electrons has been inhibited in a microwave cavity which had no electromagnetic modes at the transition frequency.It will be neither feasible nor des
35、irable to eliminate spontaneous emission entirely if the function of the semiconductor happens to be the emission or the absorption of light itself.Examples of this would be the semiconductor laser and the solar cell,respectively.In those cases the goal would be to restrict the spontaneous emission
36、to only those electromagnetic modes which are absolutely necessary.In other functions such as the heterojunction bipolar transistor,where the radiation field would preferably be absent,all spontaneous emission should be suppressed if possible.第19页/共22页Nominalization(动词名词化)The prohibition of wave pro
37、pagation in the forbidden gap makes these periodic dielectric structures valuable as highly ideal reflective mirrors,for example,for use in Fabry-Perotresonators.Such an inhibition can be much more complete than in a metallic waveguide since dielectric structures can in principle be lossless.第20页/共22页Thank you.第21页/共22页感谢您的观看!第22页/共22页