Generation of bright soliton through the interaction of black solitons

a r X i v :p h y s i c s /0105007v 2 [p h y s i c s .o p t i c s ] 7 M a y 2001

Generation of Bright Soliton through the Interaction of Black Solitons

L.Losano 1,B.Baseia 2,and D.Bazeia 1

1

Departamento de F′?sica,Universidade Federal da Para′?ba,58051-970Jo?a o Pessoa,Para′?ba,Brazil 2

Departamento de F′?sica,Universidade Federal de Goi′a s,74001-970Goi?a nia,Goi′a s,Brazil

(February 2,2008)

We report on the possibility of having two black solitons interacting inside a silica ?ber that presents normal group-velocity dispersion,to generate a pair of solitons,a vector soliton of the black-bright type.The model obeys a pair of coupled nonlinear Schr¨o dinger equations,that follows in accordance with a Ginzburg-Landau equation describing the anisotropic XY model.We solve the coupled equa-tions using a trial-orbit method,which plays a signi?cant role when the Schr¨o dinger equations are reduced to ?rst order di?erential equations.PACS numbers:05.45.Yv,42.81.Dp,11.27.+d

Solitary waves and solitons are relevant to a variety of nonlinear physical processes.They have made per-haps the geatest experimental impact in the ?eld of non-linear ?ber optics,which are widely known to support solitons of several di?erent types [1–3].For instance,in silica ?bers there are optical solitons of the bright and dark types.They appear because the Kerr nonlinear-ity in silica is always described by a positive coe?cient,so that the sign of the group-velocity dispersion distin-guishes two di?erent types of solitons in silica ?bers:the bright soliton,for negative sign of the group-velocity dis-persion,and the dark soliton,for positive group-velocity dispersion.These two types of optical solitons were ?rst reported in Ref.[4],in the case of bright solitons,and in Ref.[5],in the case of dark solitons.They are solutions of the cubic nonlinear Schr¨o dinger equation,and they are characterized by having distinct pro?le:the bright soliton has vanishing asymptotic behavior,so they en-gender trivial topological behavior.On the other hand,dark solitons are characterized by non vanishing asymp-totic behavior,so the presence of topological pro?le is one important feature of dark solitons.The central char-acteristic of dark solitons is the presence of a dip in its center,which distinguishes two possibilities:black soli-tons,in the case the dip reaches the botton,that is,if the dip goes completely to zero,and gray solitons,in the other cases.

Although both bright and dark solitons are widely known to be present in ?bers,they are not exclusive of ?bers.They can also appear in other systems,in particu-lar in Bose-Einstein condensates (BEC),and in magnetic materials.The old prediction that an ideal gas of identi-cal bosons may condensate into a macroscopic quantum state has recently been accomplished:BECs of di?er-ent atomic elements were ?rst produced in [6–8],and are reviewed for instance in Ref.[9].Soom after this achiev-ment,the presence of bright solitons in a BEC was ?rst reported in Ref.[10],in the study of the dynamics of ul-tracold bosonic atoms loaded in an optical lattice,that is,in a lattice induced by the interference of an array of laser beams [11].The presence of dark solitons was

reported more recently in Refs.[12,13].The presence of bright or dark solitons in BEC is directly related to the physics of attractive or repulsive atomic interaction,respectivelly,in a mean-?eld description that follows in accordance with the Gross-Pitaevskii equation [14].In magnetic ?lms one ?nds dark solitons [15–17]in the form of a microwave magnetic envelope (MME).A good ex-ample of this was recently reported in Ref.[18],where one can ?nd an interesting way of generating dark MME solitons,which opens a new route for the investigation of dark solitons in magnetic systems.

In silica ?bers both black and bright solitons spring as solutions of the cubic non-linear Schr¨o dinger equation,with just a change in the sign of the term that controls the group-velocity dispersion in that equation.We illustrate the two possibilities considering the normalized equation that describes the electric ?eld envelope U =U (x,z )inside the optical ?ber

i ?U ±

2?2U ±

2

d 2u ±

u2?(x)goes to zero,reaching the botton of the electric ?eld envelope.

We consider the possibility of describing a more gen-eral situation.We think of using a single?ber,an optical medium with normal group-velocity dispersion. However,we illuminate the?ber with two distinct laser beams,having di?erent amplitudes and opposite circu-lar polarizations.The electric?elds are characterized by the envelopes U(x,z)and V(x,z),and the system is de-scribed by the two normalized equations

i ?U

2

?2U

?z?

1

?x2

+G(I)V=0(6)

We use I=|U|2+|V|2to describe the total intensity inside the?ber,and now the envelopes of two interacting laser beams inside the optical medium are characterized by the functions F(I)and G(I),which respond to non-linear Kerr interactions inside the silica?ber.

We describe the case of two di?erent laser beams,that interact inside the silica?ber with the envelope of the electric?elds in the form

U(x,z)=u(x)e iz(7)

V(x,z)=v(x)e irz(8) Here r is real and positive,and parametrizes the rela-tive propagation constant of

the vector

constituents.

We

substitute Eqs.(7)and(8)into Eqs.(5)and(6)to obtain 1

dx2

=?u+F r(u,v)u(9) 1

dx2

=?r v+G r(u,v)v(10)

We normalize the system in a way such that,in the ab-sence of v we get F r(u,0)=u2,and in the absence of u we get G r(0,v)=r2v2.In the?rst case,for v=0we get

1

dx2

=?u+u3(11) whose solutions are

u b(x)=±tanh(x?ˉx)(12) The second case is similar,leading to

v b(x)=± r tanh[√

1/r.Thus,in the following we will consider the case r∈(0,1).

0.5

1

1.5

2

–4–3–2–11234

x

FIG.1.The two black solitons,u2b(x)and v2b(x),repre-sented by thicker and thinner lines,respectively.They ap-pear inside the optical?ber when one of the two laser beams is turned o?.We use r=4/9.

The limit r→1describes the case of interactions be-tween laser beams of same amplitude but opposite circu-lar polarizations in an isotropic Kerr medium.This case is simpler,and can be described by a system of sym-metrically coupled nonlinear Schr¨o dinger equations.For the pair of symmetrically coupled equations,if we set F1(u,v)=G1(u,v)=u2+v2we get the well known Manakov model[25].This model can also be used to represent the isotropic XY model[26],which obeys the Ginzburg-Landau equation?A/?t=?2A/?x2+A?|A|2A,where A is complex.We use A=X+iY to show that for static con?gurations the above Ginzburg-Landau equation leads to the symmetrically coupled nonlinear Schr¨o dinger equations.We use this as a guide toward the more general asymmetric model,and we consider the anisotropic XY model,which is described by

?A

?x2

+A?|A|2A+αˉA(14) whereαis real.We use this model to investigate the case of two laser beams,in a medium such that F r(u,v)= u2+r(2r+1)v2and G r(u,v)=r2v2+r(2r+1)u2,that

obey F r(u,0)=u2and G r(0,v)=r2v2,as required to recuperate the case describing a single laser beam,when the other beam is turned o?.The form of the interaction is dictated by the anisotropic XY model,and by the two laser beams that enter the?ber.

The above considerations settle the problem.And now the key issue follows after recognizing that the coupled Schr¨o dinger equations can be seen as equations of motion

for static?elds that appear in models of

two

real scalar

?elds in bidimensional space-time[27].In the case under examination the system of two?elds is described by the potential

V(u,v)=1

2

(2r u v)2(15)

This potential has the general form[28–30]

V(u,v)=1

du

2

+

1

dv

2

(16)

where W=W(u,v)is given by

W(u,v)=?u+

1

2

d2u

2

d2v

1/r?2sech[2r(x?ˉx)](21) This result is very interesting:it shows that two black solitons in interaction inside the silica?ber generate a pair of solitons,one of the black type and the other of the bright type.In Fig.2we depict this non-trivial vec-tor soliton.It illustrate that the presence of bright soli-tons is not a privilege of speci?c?bers,that have anoma-lous group-velocity dispersion.We may say that the sec-ond laser beam sees the normal group-velocity disper-sion of the medium as an anomalous one,and this ap-pear through the presence of the?rst laser beam,which is responsible for changing the group-velocity dispersion inside the?ber.This phenomenon is new,and follows from the vector soliton(20)and(21).We notice that the vector soliton only exists for r∈(0,1/2),and the limit r→1/2leads us back to the scalar soliton u b(x). This model has the property that the limit r→1is triv-ial.This limit leads to the symmetric situation,which can be investigated after rotating the the(u,v)plane to (u+,u?),with u±=u±v.These transformations fac-torate the two-?eld system into two degenerate systems of a single?eld,that support no vector?eld solutions of the black and bright type.This shows that our model is asymmetric by construction,and the limit r→1leads to a trivial symmetric model.

The presence of the nontrivial black-bright vector soli-ton is easier to see if we integrate the coupled equations (18)and(19)once.This gives the?rst order equations

du

dx

=±2ruv(23)

The fact that the pair of second order equations(18)and (19)can be integrated to give the above pair of?rst or-der equations(22)and(23)is fundamental,since it is easier to integrate.In Field Theory this identi?es the Bogomol’nyi-Prasad-Sommer?eld bound[31];the solu-tions are stable and minimize the energy of the system [28,29].

0.2

0.4

0.6

0.8

1

–4–3–2–11234

x

FIG.2.The black(u22(x),thicker line)and bright(v22(x), thinner line)solitons that appear inside the optical?ber when both the laser beams are turned on.We use r=4/9.

We solve the?rst order equations using the trial or-bit method introduced in Ref.[32].We try the orbit u2+av2=1,for a being some real constant.We di?erentiate this expression and we use the?rst order equations(22)and(23)to obtain u2+r(1+2a)v2=1. This is compatible with the previous choice if and only if a=r/(1?2r).Thus the orbit is given by

u2+

1

r?2

v2=1(24)

It is an elliptical arc,that goes from(u=±1,v=0)to (u=?1,v=0)when x spans the entire real line.

We use the orbit(24)to write the?rst order Eq.(22) in the form du/dx=?2r(1?u2).It can be integrated easily.The result gives the solution(20).The other

solution(21)is obtained immediately from the orbit(24) obeyed by u and v.

We have found the vector soliton as a solution of the pair of?rst order equations(22)and(23).The approach is new,and involves two steps:the?rst consists in trans-forming the pair of second order Schr¨o dinger equations (18)and(19)into a pair of?rst order di?erential equa-tions;the second step deals with the trial orbit method introduced in Ref.[32].The trial orbit method was in-troduced to help solving second order equations of mo-tion for relativistic systems of coupled scalar?elds.In the present context,the e?ectiveness of the trial orbit method is direct,since we can use the?rst order equa-tions themselves to check if the orbit we trial is good, that is,if the trial orbit does not contradict the?rst or-der equations that follow from the equations of motions. This check is immediate,and provides a direct trial for the eligibility of the orbit under investigation.This fact does not appear in the original proposal in Ref.[32],since there it deals with second order di?erential equations. We see that when the potential is written in terms of W(u,v),in the form(16),the two equations of motion are written as

d2u

=W u W uv+W v W vv(26) dx2

where W u=?W/?u,etc.We associate to these equa-tions the pair of?rst order equations

du

=W v(27)

dx

We di?erentiate these?rst order equations to see that their solutions also solve the equations of motion.Thus, we can concentrate on the simpler task of solving?rst order equations to get solutions to the second order equa-tions.This is an important advantage,but it is restricted to work when the composite vector soliton presents non-trivial topological feature,as happens with dark solitons. This is not the case for bright solitons,that engender trivial topological behavior.Thus we may wander if it is possible to use two bright solitons to generate a compos-ite,bright-black vector soliton.Because the bright soli-tons are nontopological they cannot appear as solutions of?rst order equations,as recently shown in Ref.[33]. We thank A.F.Lima and P.C.Oliveira for discussions, and CAPES,CNPq,and PRONEX for partial support.

IELTS作文——Generation gap

Generation gap There always has been generation gap since the dawn of civilization. Old people act like a frog in the well. They are fully convinced with their ideas as ultimate and ideal. They ignore certain vital factors that are no longer valid in modern days. There is a great hue and cry raised by the elders and the young both that the communication between them has broken down and they accuse each other for and bemoan this state of affairs. They attribute it to generation gap. Majority in the society carries along with this moroseness and never pauses to think the why and how of the problem. 为什么？？ The elders are more critical of the younger generation with a big inventory of complaints against the young and the young mostly tend to ignore the grumbling, mumbling and occasional loud protestations of the older generation. But now and then they do protest. They resent the petting attitude of the elders. It is generally observed that the old behave like a frog in the well. They are fully convinced that the ideas they have had throughout their lives are the ultimate and ideal. They ignore certain vital factors that are no longer valid in the case of the modernity. There always has been generation gap since the dawn of civilization. The young have always deviated from the older standards and it was well that they did or there wouldn’t have been any progress today. The younger generation naturally differs in dress, food, habits etc, as all these were not available to the older generation. These changes are indicative of progress. With the passage of time when the society, right from the basic unit of the family through society and the entire humanity, is changing, how can the new generation be asked to stagnate or move bac kward to the ancestors’ way of life? In the olden days, in the Indian society the arranged marriage took place first and love between husband and the wife were thought to be a natural development. The moral standards differed in consonance with the contemporary situation, as human society is essentially a utilitarian one. The elders couldn’t have visualized what was to come in their lifetime i.e. live-in relationship, one night stand, car key pooling and fishing and things that are yet to come out in the open. It will be generally agreed that most fathers want their offspring to adopt the same profession that they themselves followed without giving due weight to the aptitude of the offspring. This causes tension between the elders and the children. The younger generation is more intellectually evolved than the preceding one. But the ego of the older people does not permit them to accept

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巧记字形方法多 主持人：收音机前的同学们，大家晚上好，欢迎收听龙广97频道的《名师学堂》节目，我是主持人小清。 我们在今天的节目现场还请来了奋斗小学二年级的各位同学们，欢迎你们。 首先我有一个问题问问现场的小同学们，你们都喜欢看书吗？（喜欢）（不喜欢） 书上的汉字你们都认识吗？（有的人是有的不认识） 不认识的字你们怎么才能认识呢？（问老师、问妈妈） 老师和妈妈是怎么教你们认字的？（现场随机提问） 那你们觉得书上不认识的字好学吗？（不好学，告诉好多遍都记不住） 你们喜不喜欢学那些不认识的字呀？（不喜欢，太枯燥了，不好玩） 那你们想不想让那些不认识的字变得好学好玩呢？（想） 特别想吗？大点声告诉我！（特别想） 好，今天呀，我就给你们请来了一位特别有本事的老师，这位老师能把字变成好听的歌，你们想不想听？（想听） 好，那现在《名师学堂》开讲了——上课铃声—— 有请哈尔滨市桥南小学赵家财老师（背景介绍：赵家财老师…… 主：赵老师你好 赵：主持人好，同学们好！ 同：老师好！ 主：赵老师，听说您在教孩子们识字方面有一个独门功夫！ 赵：谈不上什么独门功夫，只是在多年的教学当中，针对孩子们识字困难，自己爱琢磨，总结出来一些小方法，让孩子们喜欢上识字。 主：今天现场有好多同学都表达了自己不愿意识字的心情，您能让他们从今天开始就喜欢识字吗？ 赵：我试试看吧！ 主：好，那下边的时间就交给您了。 （赵老师和现场的同学们进行互动） 好的，同学们好！很高兴参加《名师学堂》这个节目，希望我讲的一些识字方法，对大家有一些帮助。 学习汉字我们不但要读准字音、理解字义，更要记住字形。记住字形是汉字学习的重点和难点。如果字形记不住，就会导致提笔忘字，写错别字等现象，影响阅读和表达，甚至会闹出笑话： 下面我先来讲一个关于写错别字的笑话。 有个同学在日记中写道：“今天下着小雨，我忘了带命，突然，我看见老师给我送命来了。”看完这句话，我笑得肚子都快疼起来了，原来他把“伞”写成“命”了。 我还听过这样一个笑话。一个中学生放暑假，去农村体验生活，住在房东老大娘家，老大娘十分关心他。有一天他给父母写了一封信：“爸爸妈妈，我现在住在房东老大狼家，和老大狼住在一起，每天早上她都把我咬醒……”父母看了他的信大惊失色，忙叫道：“快救救我儿子，他每天都跟狼在一起啊……”原来他把娘写成了狼，把叫写成了咬。 如果字形记不住，不但会闹出笑话，更为严重的是：一个错字还能导致一场战争的失败。我再给大家讲一个真实的故事。

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：

Generation_gap_中英对照

Generation gap 父母比我们年龄大，所以无论是生理上还是心理上，都要比我们成熟。 父母的经历和经验也比我们丰富，做事也比我们谨慎、周密。所以他们有能力采取适当的措施同子女进行沟通。如果父母没有做到这些而使自己与子女之间产生“代沟”，那么主要的责任在于父母。 从思想上讲 从现代教育上讲 子女所要接受的教育很多，而家庭教育则是子女接受教育中最为重要的教育内容之 一。"在谈及家庭教育必然要谈到父母与子女的关系问题。我们知道，一个良好的家庭环境必然会形成一个和睦而又温暖的家庭。如果家庭中各成员之间产生隔阂，必然会对子女的成长造成一定的影响。父母的言行和品德对子女有很大的影响。从子女一出生，父母就成了子女的启蒙老师，从此他们就担负着培养和教育子女的责任和义务，同时也是他们承担的社会责任。而父母的失职就可能给家庭蒙上一层阴影，造成家庭冷漠不和，以及子女的悲观、消极思想。 Intermsoffamilyeducation,parentsplayanimportantpartintherelationship between parents and children. We know that a good familyenvironmentisboundtoformaharmoniousandwarmfamily.Whatparents say and behave has a great influence on their children Negligenceoftheparentscancausechildren'spessimisticandnegativevalues.This is also one of the factors causing the generation gap. From the above arguments,we can draw a conclution thatthe generationgap is largely due to parents. 1/ 1

全面质量管理的常用方法一

全面质量管理的常用方法一 【本讲重点】 排列图 因果分析法 对策表方法 分层法 相关图法 排列图法 什么是排列图 排列图又叫巴雷特图，或主次分析图，它首先是由意大利经济学家巴雷特（Pareto）用于经济分析，后来由美国质量管理专家朱兰（J.M.Juran）将它应用于全面质量管理之中，成为全面质量管理常用的质量分析方法之一。 排列图中有两个纵坐标，一个横坐标，若干个柱状图和一条自左向右逐步上升的折线。左边的纵坐标为频数，右边的纵坐标为频率或称累积占有率。一般说来，横坐标为影响产品质量的各种问题或项目，纵坐标表示影响程度，折线为累计曲线。 排列图法的应用实际上是建立在ABC分析法基础之上的，它将现场中作为问题的废品、缺陷、毛病、事故等，按其现象或者原因进行分类，选取数据，根据废品数量和损失金额多少排列顺序，然后用柱形图表示其大小。因此，排列图法的核心目标是帮助我们找到影响生产质量问题的主要因素。例如，可以将积累出现的频率百分比累加达到70%的因素成为A类因素，它是影响质量的主要因素。 排列图的绘制步骤 排列图能够从任何众多的项目中找出最重要的问题，能清楚地看到问题的大小顺序，能了解该项目在全

体中所占的重要程度，具有较强的说服力，被广泛应用于确定改革的主要目标和效果、调查产生缺陷及故障的原因。因此，企业管理人员必须掌握排列图的绘制，并将其应用到质量过程中去。 一般说来，绘制排列图的步骤如图7-1所示，即：确定调查事项，收集数据，按内容或原因对数据分类，然后进行合计、整理数据，计算累积数，计算累积占有率，作出柱形图，画出累积曲线，填写有关事项。 图7-1 排列图的绘制步骤 排列图的应用实例 某化工机械厂为从事尿素合成的公司生产尿素合成塔，尿素合成塔在生产过程中需要承受一定的压力，上面共有成千上万个焊缝和焊点。由于该厂所生产的十五台尿素合成塔均不同程度地出现了焊缝缺陷，由此对返修所需工时的数据统计如表7-1所示。 表7-1 焊缝缺陷返修工时统计表 序号项目返修工时fi 频率 pi/% 累计频率 fi/% 类别 1焊缝气孔14860.460.4A 2夹渣5120.881.2A 3焊缝成型差208.289.4B 4焊道凹陷15 6.195.5B 5其他11 4.5100C 合计245100 缝成型差、焊道凹陷及其他缺陷，前三个要素累加起来达到了89.4%。根据这些统计数据绘制出如图7-2所示的排列图：横坐标是所列举问题的分类，纵坐标是各类缺陷百分率的频数。

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。

巧妙识别病句的12种方法

巧妙识别病句的12种方法： 病句，是指那些语言表达有误的句子，即不符合现代汉语的表达规则，或违反了客观事理的句子，前者是就语法方面而言的，后者是就逻辑方面而言的。中学生需要掌握的常见病句类型有六种，即语序不当、搭配不当、成分残缺或赘余、结构混乱、表意不明和不合逻辑。虽说这六种类型的病句都能考到，但在实际考试中，有几种常见的病句出错的方式出现的频率是非常高的，因此值得大家特别注意。而这些错误，我们可以通过标识来识别。 一．发现借宾短语开头的句子，看是否缺少主语。 在一个句子中，当介词或介词结构位于句首时，我们就应该仔细的分析这个句子的主谓宾等成分，如果没有主语，就属于介词结构在居首导致无主语的错误类型。这种类型的病句往往通过去掉居首介词来达到改正的目的。 例句: 1.通过阅读徐迟的《黄山记》，使我受到一次深刻的美感教育。（介 词位于居首，淹没主语，应删掉“通过”） 2.南北朝时期，由于北方民族的大融合和工商业经济的发展，为 隋朝统一全国创造了条件。（“由于”开头，导致句子无主语，应去掉“由于”） 二．发现句中有并列结构，看是否符合逻辑、是否语序错位、是否搭配得当。 这里所说的并列结构，主要是指动词并列、名词并列以及形容词

并列等。出现了并列结构，我们可以从是否符合逻辑、是否语序错位、是否搭配得当这三个方面去考虑。 例句： 1.我们的报刊、杂志、电视和一切出版物，更有责任做出表率。 （此句中“报刊、杂志”就属于“出版物”，这句话属于并列 名词搭配错误） 2.我们要认真讨论并听取王校长的发言。（逻辑语序不当，应是 先“听取”后“讨论”） 3.要办好一个企业，仍旧需要充分发挥个人的才智，集体的力量 和集思广益的效果。 （搭配不当，谓语“发挥”与宾语“集思广益的效果”不能搭 配） 三．发现具有两面意思的词语，如“是否”“能否”“优劣” “好坏”“成败”等，看前后是否对应。 一个句子如果出现这些词语，就应分析是否存在两面与一面不搭配的现象。 修改这类病句有两种方法，要么去掉句中的“能否”“是否”等词语，要么在句中的另一部分再加上“能否”或“是否”等词语。 例句： 1.一个关系到能否顺利择业的实际问题摆在他们的面前：必须会 使用电脑，必须会驾车，外语必须达到四级以上。（两面对一 面，前半部分包含了“能顺利择业”和“不能顺利择业”两个

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：

心理咨询的12种方法与案例分析

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when,while,as引导时间状语从句的区别

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