a r X i v :c o n d -m a t /0109038v 1 4 S e p 2001Adiabatic stabilization of excitons in intense terahertz laser
Ren-Bao Liu and Bang-Fen Zhu
Center for Advanced Study,Tsinghua University,Beijing 100084,People’s Republic of China
High-precise calculation of near-infrared absorption and transient spectra in bulk semiconductors
irradiated by an intense terahertz (THz)laser shows that,the ionization rate of the ground-state
exciton,probed through the dynamic Fano resonance,may decrease with the increase of the THz
laser intensity.This counterintuitive e?ect indicates the excitons are stabilized against the ?eld-
ionization.The much lower Rydberg energy and “atomic unit”of laser intensity for excitons,and the
possibility of creating excitons from the “vacuum state”allow observing the excitonic stabilization
in experiments,in contrast to the case of atomic stabilization.
PACS numbers:https://www.doczj.com/doc/897845185.html,,78.20.Jq,32.80.Fb,42.50.Md In accordance to Einstein’s theory of the photoelectric e?ect,an electron can be stripped from its atom by light beams with su?ciently high frequency.As the intensity of a light beam is increased,the stripping probability of the electron increases owing to the increasing number of photon impacts.Surprisingly,since the late 1980’s,theoretical investigations and numerical simulations [1–6]have predicted that when the electric ?eld,associated with a laser of su?ciently high intensity and frequency,approaches or exceeds the electrostatic ?eld between the electron and the ion in an atom,the wave function of the irradiated atom may be distorted adiabatically into a distribution with two well separated peaks.The peak spacing increases with increasing the ?eld intensity,thus the atomic electron spends more time far away from the nucleus,and the ionization rate slows down dramatically till almost totally suppressed.In other words,the adia-batic stabilization of the atom occurs.The observation of this atomic stabilization e?ect is,however,extremely di?cult.Firstly,for the atomic ground state,the high-frequency and high-intensity con-dition requires an extreme ultraviolet laser with intensity
larger than an atomic unit (～3.51×1016W/cm 2),which
seems not available in the near future.Secondly,and
more vitally,su?ciently slow turn-on is demanded for
the laser pulse to adiabatically drive the atomic ground
state into a stable dressed state;during the rise time of
the super-intense laser pulse,however,substantial ion-
ization has already been inevitable [7],which prevents
the e?ect from observation.Some researchers even ar-
gued that it was impossible to observe such an adiabatic
stabilization of atoms [8,9].In fact,except for a few dis-
putable indications for the stabilization of high Rydberg
states [10],so far there is no unambiguous experimental
evidence for the atomic stabilization.
It is compelling to settle the debate whether this e?ect
exists or not.Apart from the pure curiosity in basic re-
search,the atomic stabilization is also of importance in
potential application,such as the high harmonic genera-tion [11]and quantum computation [12],as it can quench the undesired ionization and dephasing caused by the in-tense laser that is used to drive electrons or to manipulate a qubit in an atom.In this Letter,we report on the adiabatic stabiliza-tion of hydrogen-atom-like excitons in semiconductors.The excitonic stabilization (XS),in contrast to its atomic counterpart,is de?nitely an observable e?ect,owing to the basic characteristic of excitons that they are created from “vacuum”of carriers by the interband optical exci-tation.In our study,the dressed exciton states are pre-pared by weak near-infrared (NIR)laser pulses in semi-conductors in the presence of a quasi-continuous tera-hertz (THz)?eld,as in most recent experiments on the dynamical Franz-Keldysh e?ect [13–15].The ionization rate or lifetime of the dressed excitons can be directly ex-tracted by monitoring either the linewidth of absorption peaks or the decay time of transient signals.Thus the “turn-on”problem is safely circumvented as long as the pulsed interband excitation and the following dephasing process of excitons are well covered by the ?attop region of the THz laser pulse.Moreover,the present laboratory gear is already ready for observing the XS e?ect.Due to the small e?ec-tive mass μand large dielectric constant ε,an exciton has much smaller binding energy E B than the hydrogen atom does,and the “excitonic unit”for laser intensity (∝μ4/ε5.5)in a typical semiconductor like GaAs is about 10orders of magnitude smaller than the atomic unit.So,the “high-intensity and high-frequency”requirement for the XS can readily be ful?lled by the free-electron lasers operating with MW/cm 2power and THz frequency [16].Our investigation is based on the high-precise calcula-tion of interband optical spectra,which includes properly the Coulomb interaction,the nonperturbative ac-?eld,and the contribution of continuum states.To avoid un-necessary complexity,the excitonic state is treated within the simple e?ective-mass approximation.Then the mo-tion equation for the relative motion of an electron-hole
pair is
iˉh?tψ(r,t)=(?H?iγ2)ψ(r,t)+χ(t)e?i?0tδ(r),(1)
?H≡E
g ?
ˉh2
4πεr
+eF z cos(ωt),(2)
where E
g
is the band gap,F is the?eld strength of the THz laser associated with frequencyωand linearly polar-ized in the z direction,χ(t)denotes the NIR pulse exci-
tation centered at?0,andγ2is an interband dephasing-rate due to phonon scattering.The THz laser is assumed
in a continuous wave(cw)form,because its microsec-ond duration[16]is much longer than the picosecond interband excitation and dephasing process.This model system is mathematically equivalent to a hydrogen atom in an intense laser except that the electron-hole pair is generated by the NIR laser.
Without the Coulomb coupling,the eigensolution of the time-dependent Hamiltonian(Eq.(2))is the Volkov state[17],which,as the basis set,reads
|k,m =e imωt?ia F k z cos(ωt)+i U p
2μ
+U p+mˉhω,denote the sideband index and the wavevector,respectively.Here U p≡e2F2
μω2is the classical ex-
cursion amplitude of an electron in the ac-electric?eld,
and|?k is the Bloch-state with accelerating quasimomen-
tum k?eF
γ2+(??E g+E B)2
,
indicating the occurrence of the DFR.By?tting the
0ωpeak,the ionization rateΓcan be extracted via
γ≈γ2+Γ/2.As shown in Fig.2,γ(hence the ioniza-
tion rate)increases with the laser intensity until F≈16
kV/cm(correspondingly,I≈1.0MW/cm2[21]and
a F≈1.28a B).Beyond that critical?eld strength,the
ionization rate commences to decrease,and approaches
zero at F≈28kV/cm,clearly demonstrating the XS
e?ect.
Γcan also be obtained analytically in the high-
frequency approximation[23].When the wavefunction
dichotomy is negligible for medium a F(say a F<3a B),
a compact result forΓof the ground state[23]can be derived as
Γ≈ nω>E B32π2a F 2 10J2n(a F k n x)dx, where k2n=nω?E B.When?eld is enhanced so that a F k n approaches or exceeds1,due to rapid oscillation of the Bessel function,the integration over x diminishes. Physically,this originates from the destructive interfer-ence of the out-going waves scattered from di?erent part of the initial state.On the other hand,the stretching of the state along the?eld will reduce the wavefunction peak,contributing additionally to the XS.
Fano interference is one of fundamental channels for irreversible decay[24,25],so the XS can also be directly observed in the time domain by monitoring the transient optical signal after a pulsed excitation.The time-resolved interband polarization is calculated for several THz-?eld strengths and plotted in Fig.3.The duration of the NIR pulseτis then set to be2/ω,and the central frequency is chosen for each?eld strength to be resonant with the brightest transition,namely?0?E g=?4,?2,2,5,and 6meV for F=0,8,16,20,and30kV/cm,respectively. To single out the dephasing induced by the DFR only, the reformulated signal P(t)≡P(t)exp(γ2t)is plotted. At?nite?eld,the optical signal roughly oscillates with the period of T≡2π/ω,because the states in the KH po-tential oscillate periodically in the laboratory frame.The modulation beat superimposed on the fast oscillation re-sults from the quantum interference between the Floquet states with di?erent quasienergy.The dynamic Fano in-terference between the discrete state and the continuum opens a new channel for interband dephasing,leading to the decay of the transient signal.The XS e?ect is ver-i?ed by the fact that the dephasing rate calculated for F>16kV/cm begins to decrease,consistent with the variation trend of the ionization rate as shown in Fig.2. For F=30kV/cm(I≈3.6MW/cm2[21]),the decay of the signal almost disappear.To measure the transient signals,nonlinear optical experiments like four-wave mix-ing are usually adopted,in which many-body correlation is important sometimes[26]and may induce new inter-esting e?ects on XS,which,however,is out of the scope of our present study.
Fig.4displays snapshots of the probability distribu-tion of the exciton wavepacket resonantly excited by a pulse(?0?E g=8.88meV)withτ=20/ω,corre-sponding to the spectral width0.5meV.When the NIR-excitation pulse is over,the wavepacket performs almost perfect periodic swinging along the z?axis with the turn-ing points located at about±?z a F,except for an overall exponential decay due to the ionization.This periodic behavior is veri?ed by the time-dependence of the opti-cal signal(see the inset).Because of the inter-sideband mixing,the wavepacket shape varies drastically within a period,in contrast to the unchanged shape of the period-ically oscillating wavepacket in the KH potential without inter-sideband coupling[1].All these demonstrate that a quasi-bound Floquet state is formed in the strong THz-?eld,and justify our ascribing the suppression of the Fano broadening and dephasing rate to the adiabatic XS.
In summary,the novel excitonic stabilization e?ect,a counterpart of the atomic stabilization e?ect,has been predicted and explored nonperturbatively in a coupled system of semiconductors and intense THz-?elds by high-precise calculation.
This work was supported by the National Science Foundation of China,and R.B.L was also supported by China Postdoctoral Science Foundation.
[17]D.M.Volkov,Z.Phys.94,250(1935).
[18]H. A.Kramers,Collected Scienti?c Papers(North-
Holland,Amsterdam,1956),p.866;W.C.Henneberger, Phys.Rev.Lett.21,838(1968).
[19]R.B.Liu and B.F.Zhu,J.Phys.:Condens.Matter12,
L741(2000).
[20]S.Glutsch,D.S.Chemla,and F.Bechstedt,Phys.Rev.
B54,11592(1996).
[21]Here we use the intensity inside the material with relative
dielectric constantε/ε0=9.0.The vacuum value is larger by about1.3.
[22]U.Fano,Phys.Rev.124,1866(1961).
[23]M.Pont,Phys.Rev.A44,2141(1991);44,2152(1991).
[24]U.Siegner,M.-A.Mycek,S.Glutsch,and D.S.Chemla,
Phys.Rev.Lett.74,470(1995).
[25]C.P.Holfeld,F.L¨o ser,M.Sudzius,K.Leo,D.M.Whit-
taker,and K.K¨o hler,Phys.Rev.Lett.81,874(1998).
[26]D.S.Chemla and J.Shah,Nature411,549(2001). FIG.1.Linear absorption spectrum for several THz-?eld strengths indicated by F.The upper-right inset shows,as an example,the Fano resonance?tting process for F=24 kV/cm,where the squares are the?tted data.The lower-right inset shows schematically the sideband structure of the Flo-quet-state excitonic spectrum.
FIG.2.Fano broadening constant versus the THz-?eld strength.
FIG.3.Real-time dependence of the interband polariza-tion for various THz-?eld strength indicated by F,in which the curves are o?set for clarity.The intensity pro?le of the NIR pulse(the dotted curve)is also shown for comparison. FIG.4.Probability distribution of the NIR-pulse-excited wavepacket at several time instant within a period T for the THz-?eld of F=24kV/cm.The inset shows the semi-logarithmic plots of the intensity of the NIR pulse(dot-ted line)and transient interband optical signal(|P(t)|2,solid line)as functions of time,and the time snatch(marked by the bar)where the snapshots are made.
?-E g (meV)
-1001020
α(?) (a r b . u n i t s )0
8
16
20
24
30
F (kV/cm)
510
+ω
?ω
0ω
24 kV/cm
F (kV/cm)0510********
γ (m e V )
1.0
1.2
1.4
1.6
1.8
ωt /(2π)0102030
|!
(t
)|
2
(
a
r b .
u
n
i t s ) F (KV/cm)=0830
1620
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第一章导论 宏观经济学研究的问题 研究的问题是一个国家整体经济的运作情况以及政府如何运用经济政策来影响国家整体经济的运作。 宏观经济学的研究内容 研究内容之一：长期经济增长 一国生产的商品和劳务总量的增加，既GDP的增加或人均GDP的增加。 研究内容之二：经济周期 短期经济活动的急剧收缩和扩张。一个国家会出现经济增长加速和增长下降甚至出现负增长等周期性现象。 研究内容之三：失业 有劳动能力并寻求工作但找不到工作的现象。 研究内容之四：通货膨胀 一般物价水平普遍、持续、大规模上升的现象。 研究内容之五：国际经济 研究内容之六：宏观经济政策 政府的宏观经济政策主要包括财政政策和货币政策等。 财政政策：由政府的税收政策和支出政策组成。 货币政策：主要指在中央银行的控制下如何决定和调整一个国家的货币供给的增长速度。 宏观经济学的研究方法 第一，宏观经济学把一个经济体系中所有的市场综合为三个市场：金融市场、商品和服务市场以及劳动力市场；把经济行为主体综合成三类：家庭、企业和政府；研究三类经济行为主体如何在上述三类市场中发生行为并相互作用。 第二，宏观经济分析建立在微观经济个体行为分析基础上。如果对宏观经济现象的解释与微观经济个体理性行为不相一致，则就缺乏其微观经济学基础。 第三，宏观经济学在观察现实经济现象的基础上，加上必要的假设，建立起理论模型，然后再用现实世界中的数据来检验理论模型。 ★经济模型有两种变量：内生变量（一个模型要解释的变量）与外生变量（一个模型视为给定的变量） ★经济模型往往是用数学术语说明 ★经济模型具有多样性，但一个模型仅仅适用于解释经济的一个方面。 宏观经济模型的关键特征：价格伸缩性与黏性 宏观经济学的研究方法 实证分析方法 均衡分析方法 静态、比较静态和动态分析方法
小学生个人读书事迹简介怎么写800字 书,是人类进步的阶梯,苏联作家高尔基的一句话道出了书的重要。书可谓是众多名人的“宠儿”。历来,名人说出关于书的名言数不胜数。今天小编在这给大家整理了小学生个人读书事迹,接下来随着小编一起来看看吧! 小学生个人读书事迹1 “万般皆下品,惟有读书高”、“书中自有颜如玉,书中自有黄金屋”,古往今来,读书的好处为人们所重视,有人“学而优则仕”,有人“满腹经纶”走上“传道授业解惑也”的道路……但是,从长远的角度看,笔者认为读书的好处在于增加了我们做事的成功率,改善了生活的质量。 三国时期的大将吕蒙,行伍出身,不重视文化的学习,行文时,常常要他人捉刀。经过主君孙权的劝导,吕蒙懂得了读书的重要性,从此手不释卷,成为了一代儒将,连东吴的智囊鲁肃都对他“刮目相待”。后来的事实证明,荆州之战的胜利,擒获“武圣”关羽,离不开吕蒙的“运筹帷幄,决胜千里”,而他的韬略离不开平时的读书。由此可见,一个人行事的成功率高低,与他的对读书,对知识的重视程度是密切相关的。 的物理学家牛顿曾近说过,“如果我比别人看得更远,那是因为我站在巨人的肩上”,鲜花和掌声面前,一代伟人没有迷失方向,自始至终对读书保持着热枕。牛顿的话语告诉我们,渊博的知识能让我们站在更高、更理性的角度来看问题,从而少犯错误,少走弯路。
读书的好处是显而易见的,但是,在社会发展日新月异的今天,依然不乏对读书,对知识缺乏认知的人,《今日说法》中我们反复看到农民工没有和用人单位签订劳动合同,最终讨薪无果;屠户不知道往牛肉里掺“巴西疯牛肉”是犯法的;某父母坚持“棍棒底下出孝子”,结果伤害了孩子的身心,也将自己送进了班房……对书本,对知识的零解读让他们付出了惨痛的代价,当他们奔波在讨薪的路上,当他们面对高墙电网时,幸福,从何谈起?高质量的生活,从何谈起? 读书,让我们体会到“锄禾日当午,汗滴禾下土”的艰辛;读书,让我们感知到“四海无闲田,农夫犹饿死”的无奈;读书,让我们感悟到“为报倾城随太守,西北望射天狼”的豪情壮志。 读书的好处在于提高了生活的质量,它填补了我们人生中的空白,让我们不至于在大好的年华里无所事事,从书本中,我们学会提炼出有用的信息,汲取成长所需的营养。所以,我们要认真读书,充分认识到读书对改善生活的重要意义,只有这样,才是一种负责任的生活态度。 小学生个人读书事迹2 所谓读一本好书就是交一个良师益友,但我认为读一本好书就是一次大冒险,大探究。一次体会书的过程,真的很有意思,咯咯的笑声,总是从书香里散发;沉思的目光也总是从书本里透露。是书给了我启示,是书填补了我无聊的夜空,也是书带我遨游整个古今中外。所以人活着就不能没有书,只要爱书你就是一个爱生活的人,只要爱书你就是一个大写的人,只要爱书你就是一个懂得珍惜与否的人。可真所谓
关于坚持的英语演讲稿 Results are not important, but they can persist for many years as a commemoration of. Many years ago, as a result of habits and overeating formed one of obesity, as well as indicators of overall physical disorders, so that affects my work and life. In friends to encourage and supervise, the participated in the team Now considered to have been more than three years, neither the fine rain, regardless of winter heat, a day out with 5:00 time. The beginning, have been discouraged, suffering, and disappointment, but in the end of the urging of friends, to re-get up, stand on the playground. 成绩并不重要，但可以作为坚持多年晨跑的一个纪念。多年前，由于庸懒习惯和暴饮暴食，形成了一身的肥胖，以及体检指标的全盘失常，以致于影响到了我的工作和生活。在好友的鼓励和督促下，参加了晨跑队伍。现在算来，已经三年多了，无论天晴下雨，不管寒冬酷暑，每天五点准时起来出门晨跑。开始时，也曾气馁过、痛苦过、失望过，但最后都在好友们的催促下，重新爬起来，站到了操场上。 In fact, I did not build big, nor strong muscles, not a sport-born people. Over the past few years to adhere to it, because I have a team behind, the strength of a strongteam here, very grateful to our team, for a long time, we encourage each other, and with sweat, enjoying common health happy. For example, Friends of the several run in order to maintain order and unable to attend the 10，000 meters race, and they are always concerned about the brothers and promptly inform the place and time, gives us confidence and courage. At the same time, also came on their own inner desire and pursuit for a good health, who wrote many of their own log in order to refuel for their own, and inspiring. 其实我没有高大身材，也没健壮肌肉，天生不属于运动型的人。几年来能够坚持下来，因为我的背后有一个团队，有着强大团队的力量，在这里，非常感谢我们的晨跑队，长期以来，我们相互鼓励着，一起流汗，共同享受着健康带来的快
1.How to build a business that lasts100years 0:11Imagine that you are a product designer.And you've designed a product,a new type of product,called the human immune system.You're pitching this product to a skeptical,strictly no-nonsense manager.Let's call him Bob.I think we all know at least one Bob,right?How would that go? 0:34Bob,I've got this incredible idea for a completely new type of personal health product.It's called the human immune system.I can see from your face that you're having some problems with this.Don't worry.I know it's very complicated.I don't want to take you through the gory details,I just want to tell you about some of the amazing features of this product.First of all,it cleverly uses redundancy by having millions of copies of each component--leukocytes,white blood cells--before they're actually needed,to create a massive buffer against the unexpected.And it cleverly leverages diversity by having not just leukocytes but B cells,T cells,natural killer cells,antibodies.The components don't really matter.The point is that together,this diversity of different approaches can cope with more or less anything that evolution has been able to throw up.And the design is completely modular.You have the surface barrier of the human skin,you have the very rapidly reacting innate immune system and then you have the highly targeted adaptive immune system.The point is,that if one system fails,another can take over,creating a virtually foolproof system. 1:54I can see I'm losing you,Bob,but stay with me,because here is the really killer feature.The product is completely adaptive.It's able to actually develop targeted antibodies to threats that it's never even met before.It actually also does this with incredible prudence,detecting and reacting to every tiny threat,and furthermore, remembering every previous threat,in case they are ever encountered again.What I'm pitching you today is actually not a stand-alone product.The product is embedded in the larger system of the human body,and it works in complete harmony with that system,to create this unprecedented level of biological protection.So Bob,just tell me honestly,what do you think of my product? 2:47And Bob may say something like,I sincerely appreciate the effort and passion that have gone into your presentation,blah blah blah-- 2:56(Laughter) 2:58But honestly,it's total nonsense.You seem to be saying that the key selling points of your product are that it is inefficient and complex.Didn't they teach you 80-20?And furthermore,you're saying that this product is siloed.It overreacts, makes things up as it goes along and is actually designed for somebody else's benefit. I'm sorry to break it to you,but I don't think this one is a winner.
关于工作的优秀英语演讲稿 Different people have various ambitions. Some want to be engineers or doctors in the future. Some want to be scientists or businessmen. Still some wish to be teachers or lawers when they grow up in the days to come. Unlike other people, I prefer to be a farmer. However, it is not easy to be a farmer for Iwill be looked upon by others. Anyway,what I am trying to do is to make great contributions to agriculture. It is well known that farming is the basic of the country. Above all, farming is not only a challenge but also a good opportunity for the young. We can also make a big profit by growing vegetables and food in a scientific way. Besides we can apply what we have learned in school to farming. Thus our countryside will become more and more properous. I believe that any man with knowledge can do whatever they can so long as this job can meet his or her interest. All the working position can provide him with a good chance to become a talent. 1 ————来源网络整理，仅供供参考
一、S/S技术介绍 1、原理 固化/稳定化(solidification/stabilization S/S)是将污染土壤与能聚结成固体的黏结剂混合，从而将污染物捕获或固定在固体结构中的技术。这两个术语常结合使用但它们具有不同的含义：固化是在废物中添加固化剂，使其转变为不可流动固体或形成紧密固体的过程。 稳定化是将污染物转变为低溶解度、低迁移性及低毒性的物质的过程；稳定化不一定改变污染土壤的物理性状。 2、优缺点 优点 a)能快速控制污染物 b)对多重金属污染有明显优势 c)处理费用低 d)工艺过程简单 e)处理周期短 f)固化物能用于其它用途(如：建筑材料)缺点 a)不能有效去除重金属污染物毒 性 b)不能很好去除重金属污染物的 含量 c)土壤被破坏 d)需要大量固化剂 3、特殊金属处理 多价态金属（As、Cr）：通常需要使用氧化剂和还原剂进行处理 a)As：固化前先进行氧化处理，从3价转化成5价 b)Cr：固化前进行还原处理，从6价转化成3价 Hg：自然状态下具有挥发性 需进行预处理：采用活性炭吸附或反应形成HgS沉淀 4、常用参数及其作用 二、主要固化/稳定化材料 1、主要S/S材料 a)固化剂：水泥、火山灰、改性粘土、热塑材料 b)稳定化剂：腐殖酸、磷酸盐、石灰、氧化镁、铁盐
c)吸附剂：沸石、粘土、活性炭 d)其他：硫化物、聚硫化物、螯合物、水玻璃、污泥 2、可用作修复材料的副产物和废物 a)有机物：生物质固体物质、粪肥、堆肥、沼渣、造纸污泥、木屑、乙醇生产副产物 b)pH调节剂：石灰、草木灰、粉煤灰、制糖石灰渣、水泥窑石灰窑灰、赤泥、石灰稳定污泥 c)矿物质：铸造砂、钢渣、硫酸污泥、石膏、水处理污泥 三、搅拌混合与工程 1、异位稳定化 a)挖掘污染土壤 b)筛分污染土壤，除去大颗粒物质，减少污染土壤的稳定化量 c)对筛除的大颗粒物质进行清洗 d)对筛下土壤添加（粉末或泥浆添加），并混合均匀 e)养护（28d）和老化 f)检测和处置 四、浸出与评估 1、评估与测试 a)抗压强度 b)渗透系数 c)判断固化/稳定化处理过程成功与否主要是根据被处理过的有毒有害污染物抵抗自然界中可导 致污染物释放的物理及化学过程的能力，通过毒性浸出试验来确定 d)抗环境PH和Eh变化的能力 e)长期环境行为和环境影响（固结剂同污染物的相互作用、碳酸化、硫酸盐和氯化物侵蚀、风化 等） f)微观结构（XRD、SEM、EDX） g)风险评价 2、固化块性能评估 a)UCS：最低值要求，平均值要求； b)渗透系数：最高值要求，平均值要求，如：5x10-6to 1x10-6cm/sec ； c)浸出实验：最高值要求，平均值要求； d)场地概念模型
个人先进事迹简介 01 在思想政治方面,xxxx同学积极向上,热爱祖国、热爱中国共产党,拥护中国共产党的领导.利用课余时间和党课机会认真学习政治理论,积极向党组织靠拢. 在学习上,xxxx同学认为只有把学习成绩确实提高才能为将来的实践打下扎实的基础,成为社会有用人才.学习努力、成绩优良. 在生活中,善于与人沟通,乐观向上,乐于助人.有健全的人格意识和良好的心理素质和从容、坦诚、乐观、快乐的生活态度,乐于帮助身边的同学,受到师生的好评. 02 xxx同学认真学习政治理论,积极上进,在校期间获得原院级三好生,和校级三好生,优秀团员称号,并获得三等奖学金. 在学习上遇到不理解的地方也常常向老师请教,还勇于向老师提出质疑.在完成自己学业的同时,能主动帮助其他同学解决学习上的难题,和其他同学共同探讨,共同进步. 在社会实践方面,xxxx同学参与了中国儿童文学精品“悦”读书系,插画绘制工作,xxxx同学在班中担任宣传委员,工作积极主动,认真负责,有较强的组织能力.能够在老师、班主任的指导下独立完成学院、班级布置的各项工作. 03 xxx同学在政治思想方面积极进取,严格要求自己.在学习方面刻苦努力,不断钻研,学习成绩优异,连续两年荣获国家励志奖学金；作
为一名学生干部,她总是充满激情的迎接并完成各项工作,荣获优秀团干部称号.在社会实践和志愿者活动中起到模范带头作用. 04 xxxx同学在思想方面,积极要求进步,为人诚实,尊敬师长.严格 要求自己.在大一期间就积极参加了党课初、高级班的学习,拥护中国共产党的领导,并积极向党组织靠拢. 在工作上,作为班中的学习委员,对待工作兢兢业业、尽职尽责 的完成班集体的各项工作任务.并在班级和系里能够起骨干带头作用.热心为同学服务,工作责任心强. 在学习上,学习目的明确、态度端正、刻苦努力,连续两学年在 班级的综合测评排名中获得第1.并荣获院级二等奖学金、三好生、优秀班干部、优秀团员等奖项. 在社会实践方面,积极参加学校和班级组织的各项政治活动,并 在志愿者活动中起到模范带头作用.积极锻炼身体.能够处理好学习与工作的关系,乐于助人,团结班中每一位同学,谦虚好学,受到师生的好评. 05 在思想方面,xxxx同学积极向上,热爱祖国、热爱中国共产党,拥护中国共产党的领导.作为一名共产党员时刻起到积极的带头作用,利用课余时间和党课机会认真学习政治理论. 在工作上,作为班中的团支部书记,xxxx同学积极策划组织各类 团活动,具有良好的组织能力. 在学习上,xxxx同学学习努力、成绩优良、并热心帮助在学习上有困难的同学,连续两年获得二等奖学金. 在生活中,善于与人沟通,乐观向上,乐于助人.有健全的人格意 识和良好的心理素质.
尊敬的领导，老师，亲爱的同学们， 大家好！我是5班的梁浩东。今天早上我坐车来学校的路上，我仔细观察了路上形形色色的人，有开着小车衣着精致的叔叔阿姨，有市场带着倦容的卖各种早点的阿姨，还有偶尔穿梭于人群中衣衫褴褛的乞丐。于是我问自己，十几年后我会成为怎样的自己，想成为社会成功人士还是碌碌无为的人呢，答案肯定是前者。那么十几年后我怎样才能如愿以偿呢，成为一个受人尊重，有价值的人呢？正如我今天演讲的题目是：自主管理。 大家都知道爱玩是我们孩子的天性，学习也是我们的责任和义务。要怎样处理好这些矛盾，提高自主管理呢？ 首先，我们要有小主人翁思想，自己做自己的主人，要认识到我们学习，生活这一切都是我们自己走自己的人生路，并不是为了报答父母，更不是为了敷衍老师。 我认为自主管理又可以理解为自我管理，在学习和生活中无处不在，比如通过老师，小组长来管理约束行为和同学们对自身行为的管理都属于自我管理。比如我们到一个旅游景点，看到一块大石头，有的同学特别兴奋，会想在上面刻上：某某某到此一游话。这时你就需要自我管理，你需要提醒自己，这样做会破坏景点，而且是一种素质低下的表现。你设想一下，如果别人家小孩去你家墙上乱涂乱画，你是何种感受。同样我们把自主管理放到学习上，在我们想偷懒，想逃避，想放弃的时候，我们可以通过自主管理来避免这些，通过他人或者自己的力量来完成。例如我会制定作息时间计划表，里面包括学习，运动，玩耍等内容的完成时间。那些学校学习尖子，他们学习好是智商高于我们吗，其实不然，在我所了解的哪些优秀的学霸传授经验里，就提到要能够自我管理，规范好学习时间的分分秒秒，只有辛勤的付出，才能取得优异成绩。 在现实生活中，无数成功人士告诉我们自主管理的重要性。十几年后我想成为一位优秀的，为国家多做贡献的人。亲爱的同学们，你们们？让我们从现在开始重视和执行自主管理，十几年后成为那个你想成为的人。 谢谢大家！
关于工作的英语演讲稿 【篇一：关于工作的英语演讲稿】 关于工作的英语演讲稿 different people have various ambitions. some want to be engineers or doctors in the future. some want to be scientists or businessmen. still some wish to be teachers or lawers when they grow up in the days to come. unlike other people, i prefer to be a farmer. however, it is not easy to be a farmer for iwill be looked upon by others. anyway,what i am trying to do is to make great contributions to agriculture. it is well known that farming is the basic of the country. above all, farming is not only a challenge but also a good opportunity for the young. we can also make a big profit by growing vegetables and food in a scientific way. besides we can apply what we have learned in school to farming. thus our countryside will become more and more properous. i believe that any man with knowledge can do whatever they can so long as this job can meet his or her interest. all the working position can provide him with a good chance to become a talent. 【篇二：关于责任感的英语演讲稿】 im grateful that ive been given this opportunity to stand here as a spokesman. facing all of you on the stage, i have the exciting feeling of participating in this speech competition. the topic today is what we cannot afford to lose. if you ask me this question, i must tell you that i think the answer is a word---- responsibility. in my elementary years, there was a little girl in the class who worked very hard, however she could never do satisfactorily in her lessons. the teacher asked me to help her, and it was obvious that she expected a lot from me. but as a young boy, i was so restless and thoughtless, i always tried to get more time to play and enjoy myself. so she was always slighted over by me. one day before the final exam, she came up to me and said, could you please explain this to me? i can not understand it. i
Dear teacher and colleagues: my topic is on “spare time”. It is a huge blessing that we can work 996. Jack Ma said at an Ali's internal communication activity, That means we should work at 9am to 9pm, 6 days a week .I question the entire premise of this piece. but I'm always interested in hearing what successful and especially rich people come up with time .So I finally found out Jack Ma also had said :”i f you don’t put out more time and energy than others ,how can you achieve the success you want? If you do not do 996 when you are young ,when will you ?”I quite agree with the idea that young people should fight for success .But there are a lot of survival activities to do in a day ,I want to focus on how much time they take from us and what can we do with the rest of the time. As all we known ,There are 168 hours in a week .We sleep roughly seven-and-a-half and eight hours a day .so around 56 hours a week . maybe it is slightly different for someone . We do our personal things like eating and bathing and maybe looking after kids -about three hours a day .so around 21 hours a week .And if you are working a full time job ,so 40 hours a week , Oh! Maybe it is impossible for us at
关于人英语演讲稿(精选多篇) 关于人的优美句子 1、“黑皮小子”是我对在公交车上偶遇两次的一个男孩的称呼代号。一听这个外号，你也定会知道他极黑了。他的脸总是黑黑的；裸露在短袖外的胳膊也是黑黑的；就连两只有厚厚耳垂的耳朵也那么黑黑的，时不时像黑色的猎犬竖起来倾听着什么；黑黑的扁鼻子时不时地深呼吸着，像是在警觉地嗅着什么异样的味道。 2、我不知道，如何诠释我的母亲，因为母亲淡淡的生活中却常常跳动着不一样的间最无私、最伟大、最崇高的爱，莫过于母爱。无私，因为她的爱只有付出，无需回报；伟大，因为她的爱寓于
普通、平凡和简单之中；崇高，是因为她的爱是用生命化作乳汁，哺育着我，使我的生命得以延续，得以蓬勃，得以灿烂。 3、我的左撇子伙伴是用左手写字的，就像我们的右手一样挥洒自如。在日常生活中，曾见过用左手拿筷子的，也有像超级林丹用左手打羽毛球的，但很少碰见用左手写字的。中国汉字笔画笔顺是左起右收，适合用右手写字。但我的左撇子伙伴写字是右起左收的，像鸡爪一样迈出田字格，左看右看，上看下看，每一个字都很难看。平时考试时间终了，他总是做不完试卷。于是老师就跟家长商量，决定让他左改右写。经过老师引导，家长配合，他自己刻苦练字，考试能够提前完成了。现在他的字像他本人一样阳光、帅气。 4、老师，他们是辛勤的园丁，帮助着那些幼苗茁壮成长。他们不怕辛苦地给我们改厚厚一叠的作业，给我们上课。一步一步一点一点地给我们知识。虽然
他们有时也会批评一些人，但是他们的批评是对我们有帮助的，我们也要理解他们。那些学习差的同学，老师会逐一地耐心教导，使他们的学习突飞猛进。使他们的耐心教导培养出了一批批优秀的人才。他们不怕辛苦、不怕劳累地教育着我们这些幼苗，难道不是美吗？ 5、我有一个表妹，还不到十岁，她那圆圆的小脸蛋儿，粉白中透着粉红，她的头发很浓密，而且好像马鬓毛一样的粗硬，但还是保留着孩子一样的蓬乱的美，卷曲的环绕着她那小小的耳朵。说起她，她可是一个古灵精怪的小女孩。 6、黑皮小子是一个善良的人，他要跟所有见过的人成为最好的朋友！这样人人都是他的好朋友，那么人人都是好友一样坦诚、关爱相交，这样人与人自然会和谐起来，少了许多争执了。 7、有人说，老师是土壤，把知识化作养分，传授给祖国的花朵，让他们茁壮成长。亦有人说，老师是一座知识的桥梁，把我们带进奇妙的科学世界，让