Microwave Absorption Peaks Signatures of Spin Dynamics in Cuprates

a r X i v :c o n d -m a t /9906053v 2 [c o n d -m a t .s t r -e l ] 17 J u n 1999Proc.of 1999U.of Miami Conf.on HTS (HTS99)

Microwave Absorption Peaks :Signatures of Spin Dynamics in Cuprates S.Sridhar and Z.Zhai Physics Department,Northeastern University,360Huntington Avenue,Boston,MA 02115A.Erb DPMC,Universit′e de Gen′e ve,CH-1211Gen′e ve 4,Switzerland Abstract.We show that a common feature of temperature-dependent microwave absorption is the presence of absorption peaks.ac loss peaks can arise when the internal T -dependent magnetic relaxation time crosses the measurement frequency.These features are observed in the insulating (Sr x Ca 14?x Cu 24O 41,La 5/3Sr 1/3NiO 4and Y Ba 2Cu 3O 6.0),pseudo-gap (T >T c in underdoped Y Ba 2Cu 3O 7?δ,Hg :1223and Hg :1201)and superconducting (T

gap-quasiparticle scenario,the data are consistent with mixed symmetry,e.g.d +s .While mixed symmetry is allowed in orthorhombic Y Ba 2Cu 3O 7?δ,it is not allowed in tetragonal Hg :1223.This suggests that the OP symmetry may be decoupled from the crystal symmetry.

2.The measured microwave absorption is signi?cantly higher than estimates

based upon d-wave calculations,using acceptable estimates of the scattering times.The discrepancies are very large(orders of magnitude)for all super-conductors such as Bi:2212,with the possible exception of Y Ba2Cu3O7?δ.

3.Anomalous state above T c:In materials such as Hg:1223,Hg:1201and un-

derdoped Y Ba2Cu3O7?δwe?nd that the surface resistance R s is not equal to the surface reactance X s(R s=X s).This indicates that the pseudogap state above T c is not a normal metal with ordinary Ohmic conductivity,and may signify the importance of magnetic contributions to the microwave impedance.

Thus the transition to the superconducting state takes place from an uncon-ventional state,and that suggests that sum rules may not hold[5].

4.The measured nonlinear response(which is a major limitation of the use of

the cuprate superconductors in microwave applications)is signi?cantly higher than estimates based upon d-wave calculations[6].

5.Internal Josephson e?ect:A unique feature of the cuprate superconductors is

the strong microwave response at very low?eld levels well below H c1.In ultra-clean Y Ba2Cu3O6.95samples,a nonlinear response which can be described as a single Josephson junction in the ab-plane,is observed[7].This can arise from

FIGURE1.Microwave absorption vs.T data for several cuprate materials.Note the presence of absorption peaks in all the data.(a)Sr14Cu24O41,(b)Y Ba2Cu3O6.02,(c)R s(top)andσ1 (bottom)for Y Ba2Cu3O6.95.The absorption peaks in R s and corresponding conductivity peaks are labeled A,B and C in panel(c).

a bulk Josephson e?ect between two superconducting components.Similar

behavior was also seen in Bi:2212single crystals[8].

6.Magnetic Recovery E?ect:A remarkable e?ect is the decrease of microwave

absorption for small applied dc?elds[9].A compelling interpretation of this e?ect is that small?elds reduce magnetic scattering[10].It is interesting to note that reduction of magnetic absorption by moment-orienting?elds is well-known in magnetic systems[11].

7.2nd Harmonic generation[12]:Frequently2nd harmonics are observed in many

microwave harmonic generation experiments.This is inconsistent with a time-reversal invariant state such as a pure d?wave OP,and must originate from extrinsic sources.A magnetic origin may well be possible.

To obtain a broad perspective on the microwave response of the cuprates,we have studied single crystal samples of a variety of cuprates,from superconductors such as Y:123,Hg:1223,Hg:1201,insulating or weakly doped members such as Y BCO6.0and insulating P rBaCuO,and the spin-ladder/chain compounds (Sr,Ca)?Cu?O.The measurements are carried out using very high Q su-perconducting cavities[13]that enable precision measurements of the microwave susceptibility and impedance.

A common feature that emerges from this wide data set of measurements is the presence of peaks in the temperature dependent microwave absorption,accom-panied by transition-like changes in the dispersion.The microwave loss is thus frequently non-monotonic and this behavior is not restricted to Y Ba2Cu3O7?δ. Remarkably such non-monotonic temperature dependent absorption is observed in insulating(Sr x Ca14?x Cu24O41and Y Ba2Cu3O6.0),pseudo-gap(above T c in under-doped Y Ba2Cu3O7?δ,Hg:1223and Hg:1201)and superconducting(below T c) states of the cuprates(see Fig.1(c)),and is a signature of spin dynamics in the microwave response.

The presence of non-monotonic temperature-dependence of the microwave ab-sorption,leading to peaks,presents an important clue,since it is not observed in any other type of superconductor.Instead,as discussed later in this paper,peaks in the microwave absorption are characteristic of magnetic dynamics.This raises the possibility that the microwave absorption in the cuprate superconductors is not due to quasiparticle dynamics,and instead is indicative of underlying spin dynam-ics.Hence the microwave response may be de-coupled from the underlying pairing symmetry of the superconducting OP.

Sr14Cu24O41

To illustrate the underlying physics,we discuss our recent microwave measure-ments on this spin chain/ladder material[14].The data shows a microwave absorp-tion peak as shown in Fig.1(a).This is accompanied by a drop in the microwave dispersion(not shown).The static magnetization does not show these changes, and hence this is a purely dynamic property.

The data in Fig.1(a)represents a microwave loss peak and can be described as spin freezing at microwave frequencies[14].The occurrence of loss peaks can be understood by considering a complex susceptibilityχ=χo/(1+iωτ)≡χ′+iχ′′. When the relaxation rateτ?1(T)varies rapidly with T and crosses the measurement frequencyω,a peak occurs whenωτ=1,this is shown in Fig. 2.Whenτ(T) increases with decreasing temperature T(Fig.2(a)),thenχ′shows a drop with decreasing T,as shown in the Fig.2(b),andχ′′shows a peak(Fig.2(c)). The experimental data for bothχ′andχ′′are in very good agreement with the middle and bottom panels of Fig.2,as we have shown in ref.21.Note that the changes in absorption(i.e.χ′′)and dispersion(χ′)can easily be mistaken for a superconducting transition without further information from static measurements.

The dominant relaxation mecha-

FIGURE2.(a)Temperature dependence of scat-tering rateτ?1and corresponding calculated varia-tion of(b)χ′and(c)χ′′for two di?erent frequencies. Note the loss peak observed in absorptionχ′′when ωτ=1.

in this material is due to spin-

relaxation at these tempera-Relaxation due to mobile

is rapidly suppressed because the charge ordering at around K?300K seen in synchrotron scattering[15].

Our experimental data on this thus provides clear and un-

evidence for microwave peaks due to spin dynamics in

cuprates,and also shows that

relaxation occurs at GHz fre-

in these materials.

YBa2Cu3O6.0

Our measurements on the par-

compound Y Ba2Cu3O6.0fur-

underscores the importance of

dynamics in microwave mea-

of the cuprates.Results forχ′′of Y Ba2Cu3O6.0measured at 10GHz are shown in Fig.1(b).The loss termχ′′shows a pronounced peak at around14K with an onset at50K which is accompanied by a corresponding feature inδχ′(T)(not

shown).Overall there are close similarities to the results of this material as well as other insulating cuprates such as the(Sr,Ca)?Cu?O family and also P rBaCuO.

A striking feature of the data in Fig.1(b)is the close similarity to zero-?eld μSR1/T1data shown in Fig.2of Niedermayer,et al.[16]on Y Ba2Cu3O6.0,in which also a peak is seen around22K.The close correspondence provides clear evidence that the10GHz measurements are studying the same spin dynamics seen

in theμSR experiment although at a di?erent(shorter)time scale.

Possible magnetic origin to absorption peaks in superconducting cuprates

In the conventional quasiparticle conductivity scenario,the peak is understood fromσ1=n qp(T)e2τ(T)/m as a competition between increasingτ(T)and decreas-ing n qp(T)with decreasing T.In a(non-quasiparticle)magnetic scenario,the peaks in surface resistance R s should be regarded as microwave absorption or loss peaks, rather than conductivity peaks.The peaks then occur due to the crossing of the magnetic relaxation timeτwith the measurement frequencyωas temperature T is varied.In a magnetic scenario,the peak is similar to loss peaks observed generally in ac driven relaxation systems,in which for T>T p(T p is the temperature at the absorption peak)the system relaxes in phase with the ac drive,while for T

Note that the absorption peak,which represents the out-of phase response,is necessarily accompanied by a decrease of the(in-phase)susceptibility[17].This is indeed what is observed even in the superconducting state.The peaks A,B and C are all accompanied by apparent decreases in the“penetration depth”or the reactive response.

A particularly clear example of the consequences of magnetism is our measure-ments on the anti-ferromagnetic superconductor DyNi2B2C,where T N=10.5K is greater than T c=6K[18].In the metallic AFM state above T c,we found that R s=X s.Both in the superconducting and AFM states,the data were analyzed in terms of a dynamic magnetic permeability contributionμ(ω,T)to the surface impedance since Z s=[iμ(ω,T)ω/σ]1/2.However the high frequency measurements do not distinguish between dynamic permeability and a dynamic conductivity con-tribution such as arising from a narrow Drude peak.In this material,the magnetic contribution is clearly identi?able as arising from the3-D AFM ordered state,whose in?uence extends into the superconducting state also,perhaps in the form of strong pairbreaking.

Although there are no3-D ordered magnetic states in the cuprates,there are lower dimensional structures such as stripes,arising from inhomogeneous hole doping of the parent AFM insulator.Recently,the presence of stripes in the cuprates[19]and nickelates[20]has been established experimentally and theo-retically[21,22].

The presence of stripes provides a plausible mechanism for spin contributions to the microwave response in the metallic pseudo-gap and superconducting states. The intrinsic inhomogeneity of the striped state leads naturally to unconventional (non-quasiparticle)transport[23].Since the region between the charge stripes is a disordered anti-ferromagnet,spin contributions to the microwave response could necessarily arise which are also similar to that in the pure spin chain/ladder com-pounds.

We have recently shown in the nickelate La5/3Sr1/3NiO4that stripe formation does lead to a microwave absorption peak[24].We have also con?rmed the glassy dynamics of stripes in this material.Thus we have shown that stripe formation can

lead to non-monotonic microwave absorption and hence stripes can potentially be the magnetic structures responsible for the absorption peaks seen in the cuprates. There is a close similarity of the data of La5/3Sr1/3NiO4and the Sr?Cu?O compounds discussed earlier,which shows that the microwave absorption peaks are typically observed below a charge ordering transition.This may well be happening in the cuprate superconductors also.

In summary,an extensive analysis of microwave data in the cuprate and related compounds suggests that the presence of microwave absorption peaks is a common signature of spin dynamics.The presence of these peaks in the superconducting state strongly suggests that conventional quasiparticle dynamics is not operative, but that these may be overwhelmed by strong contributions from spin dynamics, possibly due to the presence of stripes.

Discussions with K.Scharnberg are gratefully acknowledged.This research was supported by NSF-9711910and AFOSR-5710000349.

REFERENCES

1.H.Srikanth,et al.,Phys.Rev.B55,R14733(1997).

2.H.Srikanth,et al.,Phys.Rev.B57,7986(1998).

3.S.Hensen,G.M¨u ller,C.T.Rieck and K.Scharnberg,Phys.Rev.B56,6237(1997).

4.D.J.van Harlingen,Rev.Mod.Phys.,67,515(1995).

5.Z.Zhai,S.Sridhar,et.al,(to be published).

6.T.Dahm,et al.,J.of App.Phys.84,5662(1998).

7.Z.Zhai,et.al.,Physica C,282-287,1601(1997).

8.T.Jacobs,et al.,Rev.Sci.Instr.67,3757(1996).

9.D.P.Choudhury,et al.,IEEE TAS,7,No.2,p.1260-1263(1997).

10.M.A.Hein,Ch.Bauer,G.Muller,J.of Sup.,10,485(1997).

11.C.Poole and H.Farach,“Relaxation in Magnetic Resonance”,Academic Press,(New

York,1971).

12.D.P.Choudhury,J.S.Derov and S.Sridhar,(submitted to Appl.Phys.Lett.)

13.S.Sridhar and W.L.Kennedy,Rev.Sci.Instrum.59,531(1988).

14.Z.Zhai,et.al.,cond-mat/9903198.

15.D.E.Cox,et al.,Phys.Rev.B57,10750(1998).

16.Ch.Niedermayer,et al.,Phys.Rev.Lett.80,3843(1998).

17.This is true only if the response is purely relaxational andτincreases with decreasing

T.The in-phase susceptibility change can even be“ferromagnetic-like”,i.e.it can increase across T p in the presence of a restoring force.

18.D.P.Choudhury,H.Srikanth,S.Sridhar and P.C.Can?eld,Phys.Rev.B58,14490

(1998).

19.J.M.Tranquada,et al.,Phys.Rev.Lett.73,1003(1994).

20.S.-H.Lee and S.-W.Cheong,Phys.Rev.Lett.79,2514(1997).

21.V.J.Emery and S.A.Kivelson,Nature(London)374,434(1995).

22.S.R.White and D.Scalapino,Phys.Rev.Lett.80,1272(1998).

23.C.C.Tsuei,et al.,(preprint).

24.N.Hakim,et.al.,BAPS44,1658(1999).

图表与口诀记忆when、as、while的区别

图表与口诀记忆when、as、while的区别 1.图表与口诀前知识 关键是比较主从句子的动词，看其动词的持续性。瞬间的理解成点，持续的理解成线。主从关系有：点（点点、点线），线线，线点。 点：为瞬间动词，准确地称为“终止性动词”，指动词具有某种内在界限的含义，一旦达到这个界限，该动作就完成了。如come（来），一旦“到来”，该动作就不再继续下去了。 瞬间动词：arrive, begin, borrow, become, buy, catch, come, die, find, go，give, graduate, join, kill, lose, leave, marry, realize… 线：为非瞬间动词，准确地称为叫“延续性动词”。包括动态动词静态动词。 动态动词：live, sit, stand, study, talk, work, write… 静态动词（状态动词）：情感、看法、愿望等。Be, belong, consist, exist, feel, hate, have, hope, love, want… 兼有瞬时和非瞬时的动词：feel，look，move，run，work，write…，需要根据不同的语境判断。 2. when、as、while的区别一览表 【表格说明】：第一个点或者线表示从句谓语动词的持续性特征，黑点表示从句所表示的动作持续短，为瞬间动词，线表示持续长，为非瞬间动词。1~7为主句与从句所表示的动作时间有重合，第8为主句与从句所表示的动作不是同时发生，而是有先后顺序。 线线重相并发生， 长线” 【主句谓语为非瞬间动词中的 动态动词】 【记忆：等线动， 相并发生，但： 【主句谓语为非瞬间动词中的 静态动词】 【记忆：等线动，

when,while,as的区别

一、根据从句动作的持续性来区分 1.“主短从长”型：即主句是一个短暂性的动作，而从句是一个持续性动作，此时三者都可用。如： Jim hurt his arm while [when, as] he was playing tennis. 吉姆打网球时把手臂扭了。 As [When, While] she was waiting for the train, she became very impatient. 她在等火车时，变得很不耐烦。 注意：as用于引出一个持续性动词表示“在……期间”时，其谓语通常只能是那些含有动作和发展意味的动词，一般不能是那些不用于进行时态的动词(如be, seem, love, want, agree, see, know, have 等)，所以下面一句中的while不能换为as： A：I’m going to the post office. 我要去邮局。 B：While you are there, can you get me some stamps? 当你在邮局时，能帮我买几张邮票吗? 若主句与从句表示的是两个几乎同时发生的动作，含有类似汉语“刚要……就”“正要……却”的意思，英语一般要用as(也可用when)，且此时通常连用副词just。且此时，从句一般用进行时，主句用短暂性动词的一般时态。【注意与六区别】 I caught him just when [as] he was leaving the building. 他正要离开大楼的时候，我把他截住了。 Just as [when] the two men were leaving, a message arrived. 就在这两个人要离开的时候，突然有了消息。 2.“主长从长”型：即主句和从句为两个同时进行的动作或存在的状态，且强调主句动作或状态延续到从句所指的整个时间，此时通常要用while。如： I always listen to the radio while I’m driving. 我总是一边开车一边听收音机。 He didn’t ask me in; he kept me standing at the door while he read the me ssage. 他没有让我进去，他只顾看那张条子，让我站在门口等着。 但是，若主句和从句所表示的两个同时进行的动作含有“一边……一边”之意时，则习惯上要用as。如： He swung his arms as he walked. 他走路时摆动着手臂。 I couldn’t remember a story to tell the children, so I made one up as I went along. 我想不出有什么故事可给孩子讲了，只好现编现讲。 3.“主长从短”型：即主句是一个持续性动作，而从句是一个短暂性动作，此时可以用a s或when，但不能用while。如：

while、when和as的用法区别

as when while 的区别和用法 as when while的用法 一、as的意思是“正当……时候”,它既可表示一个具体的时间点，也可以表示一段时间。as可表示主句和从句的动作同时发生或同时持续，即“点点重合”“线线重合”；又可表示一个动作发生在另一个动作的持续过程中，即“点线重合”， 但不能表示两个动作一前一后发生。如果主句和从句的谓语动词都表示持续性的动作，二者均可用进行时，也可以一个用进行时，一个用一般时或者都用一般时。 1、As I got on the bus，he got off. 我上车，他下车。（点点重合）两个动作都是非延续性的 2、He was writing as I was reading. 我看书时，他在写字。（线线重合）两个动作都是延续性的 3、The students were talking as the teacher came in. 老师进来时，学生们正在讲话。（点线重合）前一个动作是延续性的，而后一个动作时非延续性的 二、while的意思是“在……同时（at the same time that )”“在……期间(for as long as, during the time that）”。从while的本身词义来看，它只能表示一段时间，不能表示具体的时间点。在时间上可以是“线线重合”或“点线重合”，但不能表示“点点重合”。例如： 1、He was watching TV while she was cooking. 她做饭时，他在看电视。（线线重合） 2、He was waiting for me while I was working. 我工作的时候，他正等着我。（线线重合） 3、He asked me a question while I was speaking. 我在讲话时，他问了我一个问题。（点线重合）

第七--when-while-as-区别及练习.

When while as区别 一、根据从句动作的持续性来区分 1、“主短从长”型：即主句是一个短暂性动作，而从句是一个持续性动作，此时三者都可用。如： Jim hurt his arm while［when， as］ he was playing tennis. 吉姆打网球时把手臂扭伤了。 2、“主长从长”型：即主句和从句为两个同时进行的动作或存在的状态，且强调主句动作或状态延续到从句所指的整个时间，此时通常要用while。 I always listen to the radio while I’m driving. 我总是一边开车一边听收音机。 He didn’t ask me in; he kept me standing at the door while he read the message. 他没有让我进去，他只顾看那张条子，让我站在门口等着。 但是，若主句和从句所表示的两个同时进行的动作含有“一边……一边”之意时，则习惯上要用as。如： He swung his arms as he walked. 他走路时摆动着手臂。 3、“主长从短”型：即主句是一个持续性动作，而从句是一个短暂性动作，此时可以用as 或when，但不能用while。如： It was raining hard when [as] we arrived. 我们到达时正下着大雨。 二、根据主句与从句动作是否同时发生来区分 1、若主句与从句表示的是两个同时发生的短暂性动作，含有类似汉语“一……就”的意思，英语一般要用as (也可用when)。如： The ice cracked as [when] I stepped onto it. 我一踩冰就裂了。 2、若主句与从句表示的是两个几乎同时发生的短暂性动作，含有类似汉语“刚要……就”“正要……却”的意思，英语一般要用as(也可用when)，且此时通常连用副词just。如： I caught him just when [as] he was leaving the building. 他正要离开大楼的时候，我把他截住了。 三、根据是否具有伴随变化来区分 若要表示主句动作伴随从句动作同时发展变化，有类似汉语“随着”的意思，英语习惯上要用as，而不用when或while。如： The room grew colder as the fire burnt down. 随着炉火逐渐减弱，房间越来越冷。 注：若不是引导从句，而是引出一个短语，则用with，不用as。如： With winter coming on, it’s time to buy warm clothes. 随着冬天到来，该买暖和衣裳了。 四、根据从句动作的规律性来区分 若暗示一种规律性，表示“每当……的时候”，英语一般要用when。如： It’s cold when it snows. 下雪时天冷。 五、根据主从句动作的先后顺序来区分 若主句与从句所表示的动作不是同时发生，而是有先后顺序时，一般要用when。

When while as的区别和用法(综合整理)

When while as的区别和用法 when的用法 当主句使用持续性动词时. Dave was eating,when the doorbell rang.门铃响时,大卫在吃饭. 2.一个动作紧接着另一个动作发生. When the lights went out, I lit some candles.灯灭了,我赶紧点上一些蜡烛. 3.谈论生命中的某一阶段,或过去的某段时间. His mother called him Robbie when he was a baby. 在他很小时,他妈妈叫他Robbin. 4.指"每一次" When I turn on the TV, smoke comes out the back. 每当我打开电视,就有烟从后面冒出. while/as 的用法 从句多为进行时,而且为持续性动词. I'll look after the children while you are making dinner. 你做饭,我来照顾孩子. 注意事项: (1) “主短从长”型：主句表示的是一个短暂性动作，从句表示的是一个持续性动作，三者都可用： He fell asleep when [while, as] he was reading. 他看书时睡着了。 Jim hurt his arm while［when，as］he was playing tennis. 吉姆打网球时把手臂扭伤了。 As［When，While］she was waiting for the train，she became very impatient. 她在等火车时，变得很不耐烦。 (2) “主长从长”型：若主、从句表示两个同时进行的持续性动作，且强调主句表示的动作延续到从句所指的整个时间，通常要用while： Don’t talk while you’re eating. 吃饭时不要说话。 I kept silent while he was writing. 在他写的时候，我默不做声。 但是，若主从句表示的两个同时进行的动作含有“一边…一边”之意思，通常用as：

精华!-微波办公室MWO仿真详细步骤

Microwave Office LC滤波器设计实例 【微波EDA网】Microwave Office 是一个强大的RF计算机辅助设计及仿真软件。它提供一整套完整的把你的设计思想转换为产品的设计环境和解决方案。使用较方便直观。下面应用它来设计一个滤波器。 其主界面如下图： （图1） 应用Microwave Office的整个设计过程可以主要分为以下几个步骤： 1．创建一个schematic电路原理图； 2．加入图表及物理量测量方法； 3．电路仿真； 4．调整电路； 5．创建变量； 6．最优化电路。 具体操作如下： 一、新建一个新的工程 1．选择下拉菜单的File > New Project; 2．选择File > Save Project As，给工程取个名字保存到本地磁盘。

二、设置工程默认的单位 1．选择下拉菜单中的Options > project options > Global Unit 设置为mm 2．修改其中的单位点击OK完成操作。 三、创建一个schematic原理图 1．选择菜单Project > Add Schematic > New Schematic 2．输入原理图的文件名例如：filter 四、放置元器件 1．按一下左下窗口的Elem，出现元件对话框 2．按一下其中的Lumped Element旁边的“+”号，扩展Lumped Element组 3．选择其下面的Inductor子组，再选中下方窗口显示IND模型，用鼠标左键选中并按住拖到schematic 窗口的合适位置出，释放左键。如需改动元件位置再用左键选择拖动即可。 4．再重复上述操作，在schematic中放置一共四个IND电感。并使他们连起来位置如图1所示。 5．选择Capacitor子组，再选中下方窗口中的CAP模型，拖动至schematic中放置位置如图1与电感连接。在拖动过程中按住左键并单击右键可以旋转器件(为什么我旋转不了？因为要在第3步把元件从左边的窗口往后边的电路图中拖的过程中才能旋转)。 五、连接导线 鼠标移至C1的下端节点此时鼠标形状改变，点中并拖动连接C2、C3的下面节点，完成连线。 六、在节点上放置端口 1．选择下拉菜单Schematic > Add Port； 2．移动鼠标到L1的左端放置端口1，并与L1连接； 3．重复上操作放置端口2连接L4的右端，见图1。 七、放置接地点 1．选择下拉菜单Schematic > Add Ground； 2．鼠标移动放置到C1的下节点。 八、编辑元件参数 双击元器件对应的参数即可修改其参数，修改L1和L4为15nH, L2和L3为30nH, C1和C3为8pF, C2为10pF。 九、确定仿真频率 1． Options > project options > Frequency Values 2．修改单位为MHz，输入100在Start field，1000在Stop field，输入10作为步长Step field。其余默认。单击Apply(一定要点击，否则设置无效！). 4．单击Ok完成仿真频率的设置 十、创建图表 1．右键工程视图中的Graphs组，选择Add Graph 2．输入名字“s21 and s11”选择Rectangular单击Ok。

when,while,as引导时间状语从句的区别

when，while，as引导时间状语从句的区别 when，while，as显然都可以引导时间状语从句，但用法区别非常大。 一、when可以和延续性动词连用，也可以和短暂性动词连用；而while和as只能和延续性动词连用。 ①Why do you want a new job when youve got such a good one already？（get 为短暂性动词）你已经找到如此好的工作，为何还想再找新的？ ②Sorry，I was out when you called me．（call为短暂性动词）对不起，你打电话时我刚好外出了。 ③Strike while the iron is hot．（is为延续性动词，表示一种持续的状态）趁热打铁。 ④The students took notes as they listened．（listen为延续性动词）学生们边听课边做笔记。 二、when从句的谓语动词可以在主句谓语动作之前、之后或同时发生；while 和as从句的谓语动作必须是和主句谓语动作同时发生。 1．从句动作在主句动作前发生，只用when。 ①When he had finished his homework，he took a short rest．（finished先发生）当他完成作业后，他休息了一会儿。 ②When I got to the airport，the guests had left．（got to后发生）当我赶到飞机场时，客人们已经离开了。 2．从句动作和主句动作同时发生，且从句动作为延续性动词时，when，while，as都可使用。 ①When ／While ／As we were dancing，a stranger came in．（dance为延续性动词）当我们跳舞时，一位陌生人走了进来。 ②When ／While ／As she was making a phonecall，I was writing a letter．（make为延续性动词）当她在打电话时，我正在写信。 3．当主句、从句动作同时进行，从句动作的时间概念淡化，而主要表示主句动作发生的背景或条件时，只能用as。这时，as常表示“随着……”；“一边……，一边……”之意。 ①As the time went on，the weather got worse．（as表示“随着……”之意） ②The atmosphere gets thinner and thinner as the height increases．随着高度的增加，大气越来越稀薄。 ③As years go by，China is getting stronger and richer．随着时间一年一年过去，中国变得越来越富强了。 ④The little girls sang as they went．小姑娘们一边走，一边唱。 ⑤The sad mother sat on the roadside，shouting as she was crying．伤心的妈妈坐在路边，边哭边叫。 4．在将来时从句中，常用when，且从句须用一般时代替将来时。 ①You shall borrow the book when I have finished reading it．在我读完这本书后，你可以借阅。 ②When the manager comes here for a visit next week，Ill talk with him about this．下周，经理来这参观时，我会和他谈谈此事。 三、when用于表示“一……就……”的句型中（指过去的事情）。 sb．had hardly（＝scarcely）done sth．when．．．＝Hardly ／Scarcely had sb．done sth．when．．．

When,While,As引导时间状语从句的区别

When，While，As引导时间状语从句的区别 when，while，as显然都可以引导时间状语从句，但用法区别非常大。 一、when可以和延续性动词连用，也可以和短暂性动词连用；而while和as 只能和延续性动词连用。 ① Why do you want a new job when you’ve got such a good one already？（get为短暂性动词）你已经找到如此好的工作，为何还想再找新的？ ②Sorry，I was out when you called me．（call为短暂性动词）对不起，你打电话时我刚好外出了。 ③Strike while the iron is hot．（is为延续性动词，表示一种持续的状态）趁热打铁。 ④ The students took notes as they listened．（listen为延续性动词）学生们边听课边做笔记。 二、when从句的谓语动词可以在主句谓语动作之前、之后或同时发生；while 和as从句的谓语动作必须是和主句谓语动作同时发生。 1．从句动作在主句动作前发生，只用 when。 ①When he had finished his homework，he took a short rest．（finished 先发生）当他完成作业后，他休息了一会儿。 ②When I got to the airport，the guests had left．（got to后发生）当我赶到飞机场时，客人们已经离开了。 2．从句动作和主句动作同时发生，且从句动作为延续性动词时，when，while，as都可使用。 ①When ／While ／As we were dancing，a stranger came in．（dance为延续性动词）当我们跳舞时，一位陌生人走了进来。 ②When ／While ／As she was making a phone call，I was writing a letter．（make为延续性动词）当她在打电话时，我正在写信。 3．当主句、从句动作同时进行，从句动作的时间概念淡化，而主要表示主句动作发生的背景或条件时，只能用 as。这时，as常表示“随着……”；“一边……，一边……”之意。 ① As the time went on，the weather got worse．（as表示“随着……”之意） ② The atmosphere gets thinner and thinner as the height increases．随着高度的增加，大气越来越稀薄。 ③As years go by，China is getting stronger and richer．随着时间一年一年过去，中国变得越来越富强了。 ④The little girls sang as they went．小姑娘们一边走，一边唱。 ⑤The sad mother sat on the roadside，shouting as she was crying．伤心的妈妈坐在路边，边哭边叫。 4．在将来时从句中，常用when，且从句须用一般时代替将来时。 ①You shall borrow the book when I have finished reading it．在我读完这本书后，你可以借阅。 ②When the manager comes here for a visit next week，Ill talk with him about this．下周，经理来这参观时，我会和他谈谈此事。 三、when用于表示“一……就……”的句型中（指过去的事情）。

When, while, as的区别和用法

When, while, as的区别和用法 版本一 (1) 若主句表示的是一个短暂性动作，从句表示的是一个持续性动作，三者都可用： He fell asleep when [while, as] he was reading. 他看书时睡着了。 【注】as 用于引出一个持续性动词表示“在……期间”时，其谓语通常只能是那些含有动作(action)和发展(development) 意味的动词，一般不能是那些不用于进行时态的动词(如be, seem, love, want, agree, see, know, have 等)，所以下面一句中的while 不能换为as： A：I’m going to the post office. 我要去邮局。 B：While you’re there, can you get me some stamps? 当你在邮局时，能帮我买几张邮票吗? (2) 若主、从句表示两个同时进行的持续性动作，且强调主句表示的动作延续到从句所指的整个时间，通常要用while： Don’t talk while you’re eating. 吃饭时不要说话。 I kept silent while he was writing. 在他写的时候，我默不做声。 但是，若主从句表示的两个同时进行的动作含有“一边…一边”之意思，通常用as： She sang as she went along. 她边走边唱。 (3) 若从句是一个短暂性动作，主句是一个持续性动作，可用as / when 但不用while： It was raining hard when [as] we arrived. 我们到达时正下着大雨。 (4) 若主从句表示的是两个同时(或几乎同时)发生的短暂性动作，用as / when： I thought of it just when [as] you opened your mouth. 就在你要说的时候，我也想到了。 (5) 若要表示两个正在发展变化的情况，相当于汉语的“随着”，一般用as： Things are getting better and better as time goes on. 随着时间的推移，情况越来越好。 As it grew darker, it became colder. 天色越晚，天气越冷。 (6) 表示“每当…的时候”(暗示一种规律性)，一般要用when： It’s cold when it snows. 下雪时天冷。 He smiles when you praise him. 你夸奖他时他总是笑笑。 (7) 若主从句所表示的动作不是同时发生，而是有先后顺序时，一般要用when： I will go home when he comes back. 他回来时，我就回家去。 (8) when 可用作并列连词，表示“这时(突然)”；while 也可以用作并列连词，表示“而”、“却”(表示对比)；但as 则没有类似用法： We were about to start when it began to rain. 我们正要出发，这时天开始下雨了。 He likes coffee, while she likes tea. 他喜欢咖啡，而她却喜欢茶。 (9) as 和when 后均可直接跟一个名词，构成省略句，但while 一般不这样用： As [When] a boy, he lived in Japan. 他小时候在日本。

第七whenwhileas区别及练习

When while as 区别 一、根据从句动作的持续性来区分 1、“主短从长”型：即主句是一个短暂性动作，而从句是一个持续性动作，此时三者都可 用。如： Jim hurt his arm while ［ when， as］ he was playing tennis. 吉姆打网球时把手臂扭伤了。 2、“主长从长”型：即主句和从句为两个同时进行的动作或存在的状态， 状态延续到从句所指的整个时间，此时通常要用while 。 且强调主句动作或 I always listen to the radio while I ’ m driving. 我总是一边开车一边听收音机。 He didn ’ t ask me in; he kept me standing at the door while he read the message. 他没有让我进去，他只顾看那张条子，让我站在门口等着。 但是，若主句和从句所表示的两个同时进行的动作含有“一边,, 一边”之意时，则习惯上 要用 as。如： He swung his arms as he walked. 他走路时摆动着手臂。 3、“主长从短”型：即主句是一个持续性动作，而从句是一个短暂性动作，此时可以用as 或when，但不能用 while 。如： It was raining hard when [as] we arrived.我们到达时正下着大雨。 二、根据主句与从句动作是否同时发生来区分 1、若主句与从句表示的是两个同时发生的短暂性动作，含有类似汉语 “一英语一般要用 as (也可用 when)。如： ,, 就的”意思，The ice cracked as [when] I stepped onto it. 我一踩冰就裂了。 2、若主句与从句表示的是两个几乎同时发生的短暂性动作，含有类似汉语“刚要“正要 ,, 却”的意思，英语一般要用 as(也可用 when)，且此时通常连用副词 ,, just。如： 就” I caught him just when [as] he was leaving the building. 他正要离开大楼的时候，我把他截住 了。 三、根据是否具有伴随变化来区分 若要表示主句动作伴随从句动作同时发展变化，有类似汉语“随着”的意思，英语习惯上要 用as，而不用 when 或 while 。如： The room grew colder as the fire burnt down.随着炉火逐渐减弱，房间越来越冷。 注：若不是引导从句，而是引出一个短语，则用with ，不用 as。如： With winter coming on, it ’ s time to buy warm clothes. 随着冬天到来，该买暖和衣裳了。 四、根据从句动作的规律性来区分 若暗示一种规律性，表示“每当,, 的时候”，英语一般要用when 。如：It ’s cold when it snows. 下雪时天冷。 五、根据主从句动作的先后顺序来区分 若主句与从句所表示的动作不是同时发生，而是有先后顺序时，一般要用when 。

when while as区别用法详解

when/while/as区别用法详解 when, while, as都可作"当……的时候"解，但它们之间也有差别。 若主句表示的是一个短暂性动作，从句表示的是一个持续性动作，三者都可用。 He fell asleep when/while/as he was reading. 他看书时睡着了。 when只表示一般的时间关系，它既可指时间的一点，也可指一段时间。用when时，从句的动作可与主句的动作同时发生，也可先于主句的动作，因此when用得最多。如： He was playing basketball when I saw him. 当我看见他的时候，他正在打篮球。 Don't forget to return this book for me, when you go to the library. 你去图书馆时，不要忘记替我还这本书。 while只能指一段时间，而不能指时间的一点。用while时，从句的动作或者与主句的动作同时发生，或者主句的动作是在从句的动作的进展过程中发生的。因此，从句中的谓语必须是表示延续性动作或状态的动词。这是while与when的主要差别。如： When we arrived in Beijing, it was raining. (arrive不是延续性的动词)我们到达北京时，天正在下雨。 Please do not trouble me while I am writing my homework. 我写作业时请不要打扰我。在用when和while连接的从句中，常省略与主句相同的主语和相应的be，而在as连接的从句中一般则不省略。如： He fell asleep while(he was)studying his grammar book.他在阅读语法书的时候睡着了。While in London,he studied music.他在伦敦的时候，研究音乐。 when 可用作并列连词，表示“这时(突然)”；while 也可以用作并列连词，表示“而”、“却”(表示对比)；但as 则没有类似用法： We were about to start when it began to rain. 我们正要出发，这时天开始下雨了。 He likes coffee, while she likes tea. 他喜欢咖啡，而她却喜欢茶。

when,while和as引导时间状语从句的用法

when, while 和 as 引导时间状语从句的用法 这三个词的意思很简单，都有“当……时候”的意思。但学生经常会问三个词的区别在哪儿，特别是在做选择题的时候。别说是学生，就我个人而言，做这样的选择题要保证百分之百的 正确也是不可能的。现根据大量的实例和个人的思考，做一点小结，供大家参考。 一、when 的用法 如果只从现象来看，when 从句用的最多的是一般过去时，而主句的时态没有限制，根据具 体情况而定。 When he was a child he was always trying out new ideas. 他小时候就常常试验一些新的设想。 when she came into my room I was just reading a book. 她走进我房间时，我正在看书。 Were you writing when the teacher came in? 老师进来的时候，你在写信吗？ Sorry，I was out when you called me. 对不起，你打电话来的时候我出去了。 He was on the point of leaving when someone knocked at the door. 他正要走,这时有人敲门。 I thought of it just when you opened your mouth. 就在你要说话的时候,我也想到了。 I had hardly[scarcely] closed my eyes when someone knocked at the door. 我刚一闭上眼，就有人在敲门了。 根据以上的例句，我们可以总结出一点：when 从句的A事件，相当于另一个事件B发生的时间点。也就是说，when 从句的重点不在动作本身发生的状态，而只是把它作为一个时间 点，所以when 多数情况下用的是一般过去时，则不用正在进行时。因为如果用正在进行时，它表示的就是一段时间而不是一个时间点了。根据这一点，有的文章补充说：when 从句的动词大多是瞬时动词。这种说法也可以参照。 实际上，when 从句也可以有其它的时态，但几乎也不用进行时，因为它也只是作为一个时 间参照点。例如： When I got to the airport，the guests had left. 当我赶到飞机场时，客人们已经离开了。 When he had finished his homework，he took a short rest． 当他完成作业后，他休息了一会儿。 Why do you want a new job when you have got such a good one already？ 你已经找到如此好的工作，为何还想再找新的？ You shall borrow the book when I have finished reading it.

状语从句中的when,while ,as用法汇总

状语从句中的when, while和as的用法 一．when，while，as在时间状语从句中的区别： ①三者均可表示“当……的时候”，如果主句表示的是短暂的动作，而从句表示的是一段时间，三者可通用。如： I met Kang Li as／when／while I was walking along the street． 当我沿街散步时碰见了康丽。 ②when可以和延续性动词连用，也可以和短暂性动词连用；而while和as只能和延续性动词连用。如： It was snowing when we got to the airport．当我们到达机场时，天正下着雪。 （不能用while） ③as强调主句与从句表示的动作同时发生，as常表示“随着……”；“一边……， 一边……；while强调主句表示的动作持续于while所指的整个时间内；when 可指主、从句所述动作同时或先后发生。如： As the time went on，the weather got worse．（as表示“随着……”之意） He sang as he went along．他边走边唱。 Please write while I read．我读的时候，请写下来。 When he reached home，he had a little rest．回到家后，他休息了一会儿。 ④when用于表示“一……就……”的句型中（指过去的事情）。 somebody had hardly（＝scarcely）done …when．．． ＝Hardly ／Scarcely had somebody done …when．．． ①I had hardly ／scarcely closed my eyes when someone knocked at the door． ＝Hardly ／Scarcely had I closed my eyes when someone knocked at the door．我刚一闭上眼，就有人在敲门了。 二.when, while和as都可引导让步状语从句： ①when引导让步状语从句，意为“尽管，虽然”相当于though或although: They stopped trying when they might have succeeded next time. ②while引导让步状语从句，相当于although ，是较为正式的书面语: While I am willing to go, I would like it better that you went. ③as引导让步状语从句必须倒装，从句中的表语，状语或动词原形置于句首，若表语为名词，前置时省略冠词。 Child as he is, he knows a lot. Much as I like it, I will not buy it, for it’s too expensive.

AWR_Microwave_Office设计套件的介绍

AWR_Microwave_Office设计套件的介绍随着电磁场和微波电路领域数值计算方法的发展，在最近几年出现了大量的电磁场和微波电路仿真软件。在这些软件中，多数软件都属于准3维或称为维电磁仿真软件。例如，Agilent公司的ADS（Advanced Design System）、AWR公司的Microwave Office、Ansoft 公司的Esemble、Serenade和CST公司的CST Design Studio等。目前，真正意义上的三维电磁场仿真软件只有Ansoft公司的HFSS、CST公司的Mafia、CST Microwave Studio、Zeland 公司的Fidelity和IMST GmbH公司的EMPIRE。从理论上讲，这些软件都能仿真任意三维结构的电磁性能。其中，HFSS （HFSS是英文高频结构仿真器（High Frequency Structure Simulator）的缩写）是一种最早出现在商业市场的电磁场三维仿真软件。因此，这一软件在全世界有比较大的用户群体。由于HFSS进入中国市场较早，所以目前国内的电磁场仿真方面HFSS的使用者众多，特别是在各大通信技术研究单位、公司、高校非常普及。

AWR_Microwave_Office设计套件是专门的微波/射频软件，Microwave Office软件是通过两个模拟器来对微波平面电路进行模拟和仿真的。对于由集总元件构成的电路, 用电路的方法来处理较为简便。该软件设有一个叫“VoltaireXL”的模拟器来处理集总元件构成的微波平面电路问题。而对于由具体的微带几何图形构成的分布参数微波平面电路则采用场的方法较为有效, 该软件采用的是一个叫“EMSight”的模拟器来处理任何多层平面结构的三维电磁场的问题。 由于这里意在着重于电磁场分析，所以仅涉及“EMSight”模拟器。下面是它的具体功能：“EMSight”模拟器是一个完整的三维电磁场模拟程序包, 它可用于平面高频电路和天线结构的分析。模拟器分析的电路都安装在一个矩形的金属包装盒内, 对于电路的层数和端口

微波冶金综述 2015年：Microwave-assisted metallurgy

Microwave-assisted metallurgy Zhiwei Peng1,2and Jiann-Yang Hwang*2,3 Microwave heating has been extensively explored in various fields of materials processing.This technology exhibits unique characteristics including volumetric and selective heating,which eventually lead to many exceptional advantages over conventional processing methods including both energy and cost savings,improved product quality,faster processing and greater eco-friendliness,making microwave heating appropriate for applications in metallurgy.This paper presents a critical review on the use of microwave energy in metallurgy,with emphasis on both fundamentals of microwave heating and recent experimental efforts on extractive metallurgy via pyrometallurgical and/or hydrometallurgical routes.Applications to metallurgical processes for extraction of various metals,including heavy metals(Fe,Ni,Co,Cu,Pb and Zn),light metals(Al and Mg),rare metals(Ti,Mo,W and Re)and precious metals(Au,Ag and Pt),are reviewed and discussed. Keywords:Microwave heating,Permittivity,Permeability,Pyrometallurgy,Hydrometallurgy,Materials pretreatment,Microwave reduction/leaching, Waste remediation Introduction Microwave heating has emerged as a unique and distin-guishing technology used for materials processing.1–4 The rapid advancement of this heating technology has inspired many more encouraging and successful applica-tions to metallurgy.The earliest application of micro-wave energy to metallurgy can be traced back to1960s when a patent for microwave treatment of iron ores was granted.5Around the same time,high-temperature microwave processing of oxide and sul?de minerals was reported.6Subsequent studies demonstrated strong microwave absorption in various metal-bearing minerals such as magnetite and pyrite.7Inspired by these dis-coveries,the direct reduction of metal oxides using microwave energy has been extensively explored since the early1990s.8–10It is largely documented that micro-wave reduction of many metal-bearing minerals could be achieved rapidly,which is attributed to the volumetric and selective heating characteristics of microwave heating. Consequently,there can be a considerable reduction in energy consumption and pollution(e.g.CO2and SO2 emissions)compared with conventional processes.11This cost saving,environmentally friendly feature is also accompanied by enhanced microwave heating character-istics(microwave absorption capabilities)of metal sources. Thus,microwave energy is?nding increasing applications in sub?elds of metallurgy,such as pretreatment of metal-bearing materials and metallurgical waste remediation.12 In many cases,the unique advantages of microwave heating were veri?ed by experimental observations. However,from studies over the past half century,it is recognised that there are still dif?culties that hinder the advancement of microwave-assisted metallurgy and more broad applications of the technology to materials proces-sing.Many challenges are confronted in the commercia-lisation and industrialisation of microwave-assisted metallurgy.13 As microwave energy is being used for the extraction of a variety of metals,this paper presents a critical and comprehensive review of the scienti?c literature on microwave-assisted metallurgy.The authors try to put emphasis on both the principles and applications of microwave heating associated with numerous metallurgi-cal processes for extraction of various metals including heavy metals(Fe,Ni,Co,Cu,Pb and Zn),light metals(Al and Mg),rare metals(Ti,Mo,W and Re)and precious metals(Au,Ag and Pt).Some key fundamentals of microwave heating that relate microwave–material inter-actions will be described by introducing the main microwave heating mechanisms,crucial physical para-meters(e.g.permittivity,permeability,microwave pene-tration depth,re?ection loss and impedance matching degree),and characteristics of microwave heating.This is followed by a brief introduction of features in microwave-assisted metallurgy and a detailed discussion on various applications to extractive metallurgy.Concluding remarks touch on major dif?culties that limit further development of microwave-assisted metallurgy followed by promising measures that address challenges faced with commercia-lisation and industrialisation. Microwave heating fundamentals Introduction to microwave heating Microwaves are electromagnetic waves with wavelengths from1mm to1m with corresponding frequencies 1School of Minerals Processing and Bioengineering,Central South University,Changsha,Hunan410083,China 2Department of Materials Science and Engineering,Michigan Technological University,Houghton,MI49931,USA 3Advanced Materials R&D Centre of WISCO,Beijing102211,China *Corresponding author,email jhwang@https://www.wendangku.net/doc/2618916560.html, ?2015Institute of Materials,Minerals and Mining and ASM International Published by Maney for the Institute and ASM International Received13March2014;accepted8August2014 DOI10.1179/1743280414Y.0000000042International Materials Reviews2015VOL60NO1 30