Collective excitations of a trapped Bose-condensed gas

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大豆鼓粒期叶片荧光参数与叶绿素含

中作１８２Ｚｈｏｎｇｚｕｏ１８２
中作１８５Ｚｈｏｎｇｚｕｏ１８５
陕豆３０１Ｓｈａｎｄｏｕ３０１
承１３３７Ｃｈｅｎｇ１３３７
邯１５－１０５Ｈａｎ１５－１０５
邯１６－２７９Ｈａｎ１６－２７９
陕青豆１号Ｓｈａｎｑｉｎｇｄｏｕ１
中黄２２２Ｚｈｏｎｇｈｕａｎｇ２２２
中黄２２３Ｚｈｏｎｇｈｕａｎｇ２２３
，同时也是光合能力、营养胁迫和衰老进程
各阶段的良好指示剂
［４］
，可见测定叶绿素含量对大豆
产量及健康状况监测具有重要意义［５］。
常见的叶绿素含量测定方法有三种：第一种为比
绿素，然后用分光光度计进行比色测定，该方法能够准
且测定过程繁琐；第二种是用叶绿素计测定叶绿素的
相对含量［８－９］，该方法操作简单，时效性强，不需要破
新增供给量为１１２４０万吨，而国产大豆产量仅为
１６４０万吨［２］，远远不能满足国民需求，我国需求的大
豆主要依赖于进口，对我国大豆产业造成了巨大影响，
因此提高我国大豆产量迫在眉睫［２］。光合作用对大
豆产量具有重要影响，而叶绿素是光合作用必不可少
的物质
［３］
物育种工程项目（ＹＺＧＣ０９５），中央引导地方科技发展资金项目（ＹＤＺＪＳＸ２０２１Ｃ０１３）
作者简介：李方舟，男，助理研究员，主要从事大豆遗传育种与栽培研究。Ｅ⁃ｍａｉｌ：ｌｆｚ３８２８６２１＠１６３．ｃｏｍ
∗
通讯作者：古晓红，女，副研究员，主要从事大豆遗传育种与栽培研究。Ｅ⁃ｍａｉｌ：ｎｋｙｄｄｇｘｈ＠１２６．ｃｏｍ
冀２０１６Ｊｉ２０１６
安豆５８２０Ａｎｄｏｕ５８２０

英语单词

1. Typical of the grassland dwellers of the continent is the American antelope, or pronghorn. 美洲羚羊，或称叉角羚，是该大陆典型的草原动物。

2. Of the millions who saw Haley’s comet in 1986, how many people will live long enough to see it return in the twenty-first century. 1986年看见哈雷慧星的千百万人当中，有多少人能够长寿到足以目睹它在二十一世纪的回归呢？3. Anthropologists have discovered that fear, happiness, sadness, and surprise are universally reflected in facial expressions.人类学家们已经发现，恐惧，快乐，悲伤和惊奇都会行之于色，这在全人类是共通的。

4. Because of its irritating effect on humans, the use of phenol as a general antiseptic has been largely discontinued. 由于苯酚对人体带有刺激性作用，它基本上已不再被当作常用的防腐剂了。

5. In group to remain in existence, a profit-making organization must, in the long run, produce something consumers consider useful or desirable.任何盈利组织若要生存，最终都必须生产出消费者可用或需要的产品。

6. The greater the population there is in a locality, the greater the need there is for water, transportation, and disposal of refuse. 一个地方的人口越多，其对水，交通和垃圾处理的需求就会越大。

First-principle study of excitonic self-trapping in diamond

a rXiv:mtrl -th/9522v14Fe b1995First-principle study of excitonic self-trapping in diamond Francesco Mauri ∗and Roberto Car Institut Romand de Recherche Num´e rique en Physique des Mat´e riaux (IRRMA)IN-Ecublens 1015Lausanne,Switzerland Abstract We present a ﬁrst-principles study of excitonic self-trapping in diamond.Our calculation provides evidence for self-trapping of the 1s core exciton and gives a coherent interpretation of recent experimental X-ray absorption and emission data.Self-trapping does not occur in the case of a single valence exciton.We predict,however,that self-trapping should occur in the case of a valence biexciton.This process is accompanied by a large local relaxation of the lattice which could be observed experimentally.PACS numbers:61.80.−x,71.38.+i,71.35+z,71.55.−iTypeset using REVT E XDiamond presents an unusually favorable combination of characteristics that,in connection with the recent development of techniques for the deposition of thin diamondﬁlms,make this material a good candidate for many technological applications.Particularly appealing is the use of diamond in electronic or in opto-electronic devices,as e.g.UV-light emitting devices.Moreover,diamond is an ideal material for the construction of windows that operate under high power laser radiation or/and in adverse environments.It is therefore interesting to study radiation induced defects with deep electronic levels in the gap,since these can have important implications in many of these applications.Excitonic self-trapping is a possible mechanism for the formation of deep levels in the gap.The study of such processes in a purely covalent material,like diamond,is interesting also from a fundamental point of view.Indeed,excitonic self-trapping has been studied so far mostly in the context of ionic compounds,where it is always associated with,and often driven by,charge transfer eﬀects.In a covalent material the driving mechanism for self-trapping is instead related to the diﬀerence in the bonding character between the valence and the conduction band states.Both experimental data and theoretical arguments suggest the occurrence of self-trapping processes in diamond.In particular,a nitrogen(N)substitutional impurity induces a strong local deformation of the lattice[1–3]that can be interpreted as a self-trapping of the donor electron.The structure of a1s core exciton is more controversial[4–9].Indeed the similarity between an excited core of carbon and a ground-state core of nitrogen suggests that the core exciton should behave like a N impurity.However,the position of the core exciton peak in the diamond K-edge absorption spectra is only0.2eV lower than the conduction band minimum[4,7,8],while a N impurity originates a deep level1.7eV below the conduction band edge[10].On the other hand,emission spectra[8]suggest that a1s core exciton should self-trap like a N impurity.Finally,we consider valence excitations.In this case experimental evidence indicates that a single valence exciton is of the Wannier type,i.e.there is no self-trapping.To our knowledge,neither experimental nor theoretical investigations on the behavior of a valence biexciton in diamond have been performed,although simple scalingarguments suggest that the tendency to self-trap should be stronger for biexcitons than for single excitons.In this letter,we present a detailed theoretical study of excitonic self-trapping eﬀects in diamond.In particular,we have investigated the Born-Oppenheimer(BO)potential energy surfaces corresponding to a core exciton,a valence exciton and a valence biexciton in the context of density functional theory(DFT),within the local density approximation(LDA) for exchange and correlation.Our calculation indicates that the1s core exciton is on a diﬀerent BO surface in absorption and in emission experiments.Indeed X-ray absorption creates excitons in a p-like state as required by dipole selection rules.Subsequently the system makes a transition to an s-like state associated to a self-trapping distortion of the atomic lattice,similar to that found in the N impurity case.These results provide a coherent interpretation of the experimental data.In addition,our calculation suggests that self-trapping should also occur for a valence biexciton.This is a prediction that could be veriﬁed experimentally.Let us start by discussing a simple model[11,12].In diamond,the occupied valence and the lower conduction band states derive from superpositions of atomic sp3hybrids having bonding and antibonding character,respectively.Thus,when an electron,or a hole,or an electron-hole pair is added to the system,this can gain in deformation energy by relaxing the atomic lattice.Scaling arguments suggest that the deformation energy gain E def∝−1/N b, where N b is the number of bonds over which the perturbation is localized.This localization,due to quantum conﬁnement.The in turn,has a kinetic energy cost E kin∝+1/N2/3bbehavior of the system is then governed by the value of N b that minimizes the total energy E sum=E def+E kin.Since the only stationary point of E sum is a maximum,E sum attains its minimum value at either one of the two extrema N b=1or N b=∞.If the minimum occurs for N b=1,the perturbation is self-trapped on a single bond which is therefore stretched.If the minimum occurs for N b=∞,there is no self-trapping and the perturbation is delocalized.When N p particles(quasi-particles)are added to the system,one can showthat,for a given N b,E def scales as N2p,while E kin scales as N p.As a consequence,the probability of self-trapping is enhanced when N p is larger.This suggests that biexcitons should have a stronger tendency to self-trap than single excitons[12,13].In order to get a more quantitative understanding of self-trapping phenomena in dia-mond,we performed self-consistent electronic structure calculations,using norm-conserving pseudopotentials[14]to describe core-valence interactions.The wave-functions and the electronic density were expanded in plane-waves with a cutoﬀof35and of140Ry,respec-tively.We used a periodically repeated simple cubic supercell containing64atoms at the experimental equilibrium lattice constant.Only the wave-functions at theΓpoint were con-sidered.Since the self-trapped states are almost completely localized on one bond,they are only weakly aﬀected by the boundary conditions in a64atom supercell.The eﬀect of the k-point sampling was analysed in Ref.[3]where similar calculations for a N impurity were performed using the same supercell.It was found that a more accurate k-point sampling does not change the qualitative physics of the distortion but only increases the self-trapping energy by20%compared to calculations based on theΓ-point only[3].In order to describe a core exciton we adopted the method of Ref.[15],i.e.we generated a norm conserving pseudopotential for an excited carbon atom with one electron in the1s core level andﬁve electrons in the valence2s-2p levels.In our calculations for a valence exciton or biexciton we promoted one or two electrons,respectively,from the highest valence band state to the lowest conduction band state.Clearly,our single-particle approach cannot account for the(small)binding energy of delocalized Wannier excitons.However our approach should account for the most important contribution to the binding energy in the case of localized excitations.Structural relaxation studies were based on the Car-Parrinello(CP) approach[16].We used a standard CP scheme for both the core and the valence exciton, while a modiﬁed CP dynamics,in which the electrons are forced to stay in an arbitrary excited eigenstate[12,17],was necessary to study the BO surfaces corresponding to a valence biexciton.All the calculations were made more eﬃcient by the acceleration methods of Ref.[18].Weﬁrst computed the electronic structure of the core exciton with the atoms in the ideal lattice positions.In this case the excited-core atom induces two defect states in the gap:a non-degenerate level belonging to the A1representation of the T d point group,0.4eV below the conduction band edge,and a3-fold degenerate level with T2character,0.2eV below the conduction band edge.By letting the atomic coordinates free to relax,we found that the absolute minimum of the A1potential energy surface correponds to an asymmetric self-trapping distortion of the lattice similar to that found for the N impurity[3].In particular, the excited-core atom and its nearest-neighbor,labeled a and b,respectively,in Fig.1, move away from each other on the(111)direction.The corresponding displacements from the ideal sites are equal to10.4%and to11.5%of the bond length,respectively,so that the (a,b)-bond is stretched by21.9%.The other atoms move very little:for instance the nearest-neighbor atoms labeled c move by2.4%of the bond length only.This strong localization of the distortion is consistent with the simple scaling arguments discussed above.As a consequence of the atomic relaxation,the non-degenerate level ends up in the gap at1.5eV below the conduction band edge,while the corresponding wavefunction localizes on the stretched bond.The3-fold degenerate level remains close to the conduction band edge,but since the distortion lowers the symmetry from T d to C3v,the3-fold degenerate level splits into a2-fold degenerate E level and a non-degenerate A1level.In Fig.2we report the behavior of the potential energy surfaces corresponding to the ground-state,the A1and the T2core exciton states as a function of the self-trapping dis-tortion.Notice that the distortion gives a total energy gain of0.43eV on the A1potential energy surface.The same distortion causes an increase of the ground-state energy of1.29 eV.Our calculation indicates that the core-exciton behaves like the N impurity[3],support-ing,at least qualitatively,the validity of the equivalent core approximation.The similar behavior of the A1level in the core exciton and in the N impurity case was also pointed out recently in the context of semi-empirical CNDO calculations[9].The diﬀerences between the core exciton and the impurity[3]are only quantitative:in particular,the relaxationenergy and especially the distance of the A1level from the conduction band edge are smaller for the core exciton than for the N impurity.Our results suggest the following interpretation of the experimental data of Refs.[4,8]: (i)During X-ray absorption the atoms are in the ideal lattice positions.Dipole transitions from a1s core level to a A1valence level are forbidden,but transitions to the T2level are allowed.In our calculation the T2level is0.2eV lower than the conduction band edge,in good agreement with the core exciton peak observed in X-ray absorption spectra[4,8].(ii) On the T2BO potential energy surface the lattice undergoes a Jahn-Teller distortion which lowers its energy(see Fig.2).(iii)Since the LO phonon energy in diamond(0.16eV)is comparable to the energy spacing between the A1and the T2surfaces,which is less than 0.2eV after the Jahn-Teller distortion,the probability of a non-adiabatic transition from the T2to the A1surface is large.(iv)On the A1level the system undergoes a strong lattice relaxation resulting in a localization of the exciton on a single bond.(v)The self-trapping distortion induces a Stokes shift in the emitted photon energy.If the atomic relaxation were complete the Stokes shift would be equal to1.9eV,which correponds(see Fig.2) to the energy dissipated in the T2-A1transition(0.2eV),plus the energy gained by self trapping on the A1surface(0.43eV),plus the energy cost of the self-trapping distortion on the ground-state energy surface(1.29eV).The data reported in Ref.[8]show a shift of about1eV in the positions of the peaks associated to the1s core exciton in X-ray absorption and emission spectra.The emission peak is very broad,with a large sideband that corresponds to Stokes shifts of up to5eV.As pointed out in Ref.[8],this large sideband is likely to be the eﬀect of incomplete relaxation. This is to be expected since the core exciton lifetime should be comparable to the phonon period[8].As a consequence,the atomic lattice would be able to perform only a few damped oscillations around the distorted minimum structure during the lifetime of the core exciton.We now present our results for the valence excitations.While in the case of a single exciton the energy is minimum for the undistorted crystalline lattice,in the case of a biex-citon weﬁnd that the energy is minimized in correspondence of a localized distortion of theatomic lattice.This is characterized by a large outward symmetric displacement along the (111)direction of the atoms a and b in Fig.1.As a result the(a,b)-bond is broken since the distance between the atoms a and b is increased by51.2%compared to the crystalline bondlength.This distortion can be viewed as a kind of local graphitization in which the atoms a and b change from fourfold to threefold coordination and the corresponding hy-bridized orbitals change from sp3to sp2character.Again,in agreement with the model based on simple scaling arguments,the distortion is strongly localized on a single bond.As a matter of fact and with reference to the Fig.1,the atoms c and d move by1.2%of the bondlength,the atoms e and f move by2.3%,and the atoms not shown in theﬁgure by less than0.9%.The self-trapping distortion of the biexciton gives rise to two deep levels in the gap: a doubly occupied antibonding level,at1.7eV below the conduction band edge,and an empty bonding level,at1.6eV above the valence band edge.Both states are localized on the broken bond.In Fig.3we show how diﬀerent BO potential energy surfaces behave as a function of the self-trapping distortion of the valence biexciton.In particular,from thisﬁgure we see that,while for the biexciton there is an energy gain of1.74eV in correspondence with the self-trapping distortion,the same distortion has an energy cost of1.49eV for the single exciton,and of4.85eV for the unexcited crystal.We notice that,while DFT-LDA predicts self-trapping for the valence biexciton,it does not do so for the single exciton,in agreement with experiment.Similarly to the case of the core exciton the major experimental consequence of the self-trapping of the valence biexciton is a large Stokes shift in the stimulated-absorption spontaneous-emission cycle between the exciton and the biexciton BO surfaces.As it can be seen from Fig.3,this Stokes shift should be equal to3.23eV,i.e.to the sum of the energy gain of the biexciton(1.74eV)and of the energy cost of the exciton(1.49eV) for the self-trapping relaxation.The fundamental gap of diamond is indirect.Thus the spontaneous decay of a Wannier exciton in an ideal diamond crystal is phonon assistedand the radiative lifetime of the exciton is much longer than in direct gap semiconductors. However,after self-trapping of the biexciton,the translational symmetry is broken and direct spontaneous emission becomes allowed.As a consequence the radiative life time of the self-trapped biexciton is much smaller than that of the Wannier ing the DFT-LDA wavefunctions,we obtained a value of∼7ns for the radiative lifetime of the biexciton within the dipole approximation.This is several orders of magnitude larger than the typical phonon period.Therefore the self-trapping relaxation of the valence biexciton should be completed before the radiative decay.A self-trapped biexciton is a bound state of two excitons strongly localized on a single bond.Thus the formation of self-trapped biexcitons requires a high excitonic density.To realize this condition it is possible either to excite directly bound states of Wannier excitons, or to create a high density electron-hole plasma,e.g.by strong laser irradiation.In the second case many self-trapped biexcitons could be produced.This raises some interesting implications.If many self-trapped biexcitons are created,they could cluster producing a macroscopic graphitization.Moreover,since the process of self-trapping is associated with a relevant energy transfer from the electronic to the ionic degrees of freedom,in a high density electron hole plasma biexcitonic self-trapping could heat the crystal up to the melting point in fractions of a ps,i.e in the characteristic time of ionic relaxation.Interestingly,melting ofa GaAs crystal under high laser irradiation has been observed to occur in fractions of a ps[19].In Ref.[19]this phenomenon has been ascribed to the change in the binding properties due to the electronic excitations.Our study on diamond leads one to speculate that in a sub-picosecond melting experiment self-trapping phenomena could play an important role.In conclusion,we have studied excited-state BO potential energy surfaces of crystalline diamond within DFT-LDA.Our calculation predicts self-trapping of the core exciton and provides a coherent description of the X-ray absorption and emission processes,which com-pares well with the experimental data.Moreover,we also predict self-trapping of the valence biexciton,a process characterized by a large local lattice relaxation.This implies a strong Stokes shift in the stimulated absorption-spontaneous emission cycle of about3eV,whichcould be observed experimentally.It is a pleasure to thank F.Tassone for many useful discussions.We acknowledge support from the Swiss National Science Foundation under grant No.20-39528.93REFERENCES∗Present address:Departement of Physics,University of California,Berkeley CA94720, USA.[1]C.A.J.Ammerlaan,Inst.Phys.Conf.Ser.59,81(1981).[2]R.J.Cook and D.H.Whiﬀen,Proc.Roy.Soc.London A295,99(1966).[3]S.A.Kajihara et al,Phys.Rev.Lett.66,2010(1991).[4]J.F.Morar et al,Phys.Rev.Lett.54,1960(1985).[5]K.A.Jackson and M.R.Pederson,Phys.Rev.Lett.67,2521(1991).[6]J.Nithianandam,Phys.Rev.Lett.69,3108(1992).[7]P.E.Batson,Phys.Rev.Lett.70,1822(1993).[8]Y.Ma et al,Phys.Rev.Lett.71,3725(1993).[9]A.Mainwood and A.M.Stoneham,J.Phys.:Condens.Matter6,4917(1994).[10]R.G.Farrer,Solid State Commun.7,685(1969).[11]W.Hayes and A.M.Stoneham,Defects and defect processes in nonmetallic solids,(Wiley&Sons,New York,1985)pags.29-38.[12]F.Mauri,R.Car,(to be published).[13]The number of equal particles that can be accommodated on one bond of the crystal inthe same quantum state is limited by the Pauli principle.Thus no more than two holes or/and two electrons with opposite spins can be localized on one bond of a sp3bonded semiconductor.[14]G.Bachelet,D.Hamann,and M.Schl¨u ter,Phys.Rev.B26,4199(1982).[15]E.Pehlke and M.Scheﬄer,Phys.Rev.B47,3588(1993).[16]R.Car and M.Parrinello,Phys.Rev.Lett.55,2471(1985).[17]F.Mauri,R.Car and E.Tosatti,Europhys.Lett.24,431(1993).[18]F.Tassone,F.Mauri,and R.Car,Phys.Rev.B50,10561(1994).[19]orkov,I.L.Shumay,W.Rudolph,and T.Schroder,Opt.Lett.16,1013(1991);P.Saeta,J.-K.Wang,Y.Siegal,N.Bloembergen,and E.Mazur,Phys.Rev.Lett.67, 1023(1991);K.Sokolowski-Tinten,H.Schulz,J.Bialkowski,and D.von der Linde, Applied Phys.A53,227(1991).FIGURESFIG.1.Atoms and bonds in the ideal diamond crystal(left panel).Atoms and bonds after the self-trapping distortion associated with the valence biexciton(right panel).In this case the distance between the atoms a and b increases by51.2%.A similar but smaller distortion is associated with the core exciton:in this case the(a,b)distance is increased by21.9%.FIG.2.Total energy vs self-trapping distortion of the core-exciton.Theﬁgure displays the BO potential energy surfaces correponding to the ground-state,the A1,and the T2core exciton states.FIG.3.Total energy as a function of the self-trapping distortion of the biexciton.The BO energy surfaces correponding to the ground state,the valence exciton,and the valence biexciton are shown in theﬁgure.a b ce df(111)ground stateA 1−core excitonT 2−core excitonconduction ideal lattice distorted latticeground statebi−excitonexcitondistorted lattice ideal lattice。

英译汉。高英

Lesson 11)The one I am thinking of particularly is entered by Gothicarched gateway of aged brick and stone .You pass from the heat and glare of a big, open square into a cool, dark cavern which extends as far as the eye can see, losing itself in the shadowy distance.此时此刻我要说的集市的入口是一座古老的砖石结构的哥特式拱门，年代非常久远。

当你穿过一个烈日暴晒的大型露天广场，然后走进一个凉爽、幽暗的洞穴。

这洞穴一直一直向前延伸，一眼望不到尽头，最终消失在远处的阴影里。

2)It is a point of honor with the customers not to let the shopkeeper guess what it is she really likes and want until the last moment. 对于顾客来说，至关重要的一点是，不到最后一刻是不能让店主猜到她心里究竟中意哪样东西、想买哪样东西的.3)The seller ,on the other hand ,makes a point of protesting that the price he is charging is depriving him of all profit, and that he is sacrificing this because of his personal regard for the customer. 而在店主那一方来说，则是竭尽全力的让顾客相信，他开出的价钱使他根本无利可图，而他之所以愿意这样做完全是出于本人对顾客的敬重。

第四届冷原子会议会议安排July 5

40
[P16]
Jing Qian（钱静）
Efficient production of polar molecular Bose–Einstein condensates via an all-optical R-type atom–molecule adiabatic passage
41
[P17]
31
[P07]
Haichao Zhang（张海潮）
Demonstration of Neutral Atom Guiding via Radio-Frequency Field
32
[P08]
Shuyu Zhou（周蜀渝）
Double-well Array Trapping Atoms Based on Binary Optics ethod
会议安排July 5, Monday
Opening Ceremony
Presider
Liang Liu（刘亮）
8:30-9:00
Yuzhu Wang（王育竹）and Chaohui Ye（叶朝辉）
Opening Remarks
Sec. A
Presider
Li You（尤力）
9:00-9:30
Jun Ye（叶军）
Xing-Dong Zhao（赵兴东）
A magical polarization orientation for canceling the dipole-dipole
interaction in ultracold Bosonic dipolar gases
42
[P18]
Cheng-ling Bian（边成玲）
46
[P22]
K. Zhang（张可烨）

有道词典

We must accept finite disappointment, but we must never lose infinite hope. —Mattin Luther King我们必须接受失望，因为它是有限的，但千万不可失去希望，因为它是无穷的。

—马丁•路德•金A man can fail many times, but he isn't a failure until he begins to blame somebody else.一个人可以失败许多次，但是只要他没有开始责怪别人，他还不是一个失败者。

If you are too fortunate, you will not know yourself; if you are too unfortunate, nobody will know you.运气太好，见人不睬；运气太坏，无人理会。

Everyone has his inherent potential which is easily concealed by habbits, blured by time, and eroded by inertia.每个人都有潜在的能量，只是很容易被习惯所掩盖、被时间所迷离、被惰性所消磨。

Life is more like a battlefield. If you want something, you have to fight your best for it.生活就好比一个战场，如果你想得到一样东西，就必须拼命去争取。

When you're down and out, remember to keep your head up. When you're up and well, remember to keep your feet down.穷困潦倒时，要抬头挺胸；春风得意时，要脚踏实地。

2025届高中英语一轮复习：必修第三册 Unit 3 The world of science

Ⅳ.拔高词汇
1.invade 2.surrender
3.assault
4.swift 5.fate
vi.& vt._武__装__入__侵__；__侵__略__；__侵__犯___ vi.& vt._投__降__；__(_被__迫__)放__弃__，__交__出__ n._投__降__；__屈__服__；__屈__从___ n._攻__击__；__突__击__；__袭__击___ vt._猛__烈__攻__击__；__袭__击__；__侵__犯__(尤__指__构__成__犯__罪__)__ adj._迅__即__发__生__的__；__速__度__快__的__；__敏__捷__的__ n._命__中__注__定__的__事__(尤__指__坏__事__)_；__命__运__
速记词汇句型背诵
[拔高词汇]
1 mobilise (NAmE -ize) /'məʊbəlaɪz/
vt.& vi.组织；鼓动；动员
2 neutrality /njuː'træləti/ n.中立；中立状态
3 invade /ɪn'veɪd/
vi.& vt.武装入侵；侵略；侵犯
速记词汇句型背诵
默写词汇句型巩固
3._c_h_e_m_i_s_t_ →_c_h_e_m_i_s_tr_y_ →_c_h_e_m_i_c_a_l 4._b_i_o_lo_g_i_s_t _ →_b_io_l_o_g_y_ →_b_i_o_lo_g_i_c_a_l
n.化学家；药剂师；药房 n.化学 adj.化学的 n.生物学家 n.生理；生物学 adj.生物(学)的
但科学家们一致认为，如果富兰克林真的碰到了钥匙，他必定会被电死。

高级英语第二册词汇复习

lesson 1 Pub Talk and the King' s English : hard to follow or understand because full of puzzling parts，details，or relationships错综复杂的；难以理解的，难懂的----------------------------------------------------------------------------------: give way to one’s own desire尽情享受；从事于----------------------------------------------------------------------------------: wander aimlessly or idly；ramble漫步；闲逛----------------------------------------------------------------------------------: a person who converses；esp．one who enjoys and is skilled at conversation交谈者；(尤指)健谈者---------------------------------------------------------------------------------- : a short，entertaining account of some happening，usually personal or biographical轶事，逸事---------------------------------------------------------------------------------- : a close friend or companion 密友，知己----------------------------------------------------------------------------------: in or into a condition of ruin or catastrophe (婚姻)破坏的；失败的----------------------------------------------------------------------------------: (formerly)a soldier armed with a musket火枪手---------------------------------------------------------------------------------- : investigate for information；search发掘；调查(研究)---------------------------------------------------------------------------------- : a secluded，withdrawn，or inner place幽深处----------------------------------------------------------------------------------: aimlessly；at random随意地；无目的地---------------------------------------------------------------------------------- : an early form of chemistry，whose chief aims were to change baser metals into gold：a method or power of transmutation; esp. the seemingly miraculous change of a thing into something better炼金术；变化物质的方法或魔力----------------------------------------------------------------------------------: sharp in taste；sour；acid 辛辣的；尖酸的；刻薄的----------------------------------------------------------------------------------: a person found guilty of a crime and sentenced by a court罪犯----------------------------------------------------------------------------------: a farm laborer；peasant农民；庄稼人，乡下人----------------------------------------------------------------------------------: an open break in a previously friendly relationship分裂；失和----------------------------------------------------------------------------------: run or go hurriedly or quickly急驰，快跑---------------------------------------------------------------------------------- : a translation翻译----------------------------------------------------------------------------------: of，in or using twolanguages(用)两种语言的---------------------------------------------------------------------------------- : seize or stop on the way，before arrival at the intended place拦截；截断；截击。

高中英语book2unit1复习提纲

必修2 Unit 1 Cultural relics 一、单词__________________n. 遗物；遗迹；纪念物__________________adj. 稀有的；珍贵的__________________adj. 贵重的；有价值的__________________vi 幸免；幸存，生还__________________n. 花瓶__________________n. 朝代__________________n．龙__________________vt. 使吃惊；惊讶__________________adj. 令人吃惊的__________________vt. 挑选；选择__________________n．蜜；蜂蜜__________________n. 设计；图案；构思vt. 设计；计划；构思__________________adj. 奇特的；奇异的vt. 想象；设想；爱好___________________n. 风格；风度；类型___________________vt. 装饰，装修___________________n. 珠宝；宝石____________________n. 群；组；军队____________________n. 接待；接收；招待会____________________vt. 移动；搬开__________________n. 谜；神秘；神秘的事物____________________vt. 重建____________________adj. 本地的；当地的____________________n. 城堡____________________n. 审判；审讯；试验____________________n. 目击者；证人____________________n. 证据；根据____________________vi. 爆炸____________________n. 入口____________________n. 水手；海员；船员____________________vi. 下沉；沉下____________________n. 少女；女仆____________________adj. 非正式的____________________n/vi. 争论；辩论二、短语_________________________寻找_________________________属于_________________________作为报答；回报_________________________处于交战状态_________________________拆开；拆卸_________________________看重；器重_________________________很有价值________________________珍稀/重视某人/物_________________________故意做某事_________________________专门为…设计的_________________________流行地；时髦地______________________过时地；不受欢迎地_________________________被装饰有....._________________________某物丢了_________________________把…从…搬开_________________________消除恐惧_________________________毫无疑问......__________________________难怪.......世界众多奇迹/观之一______________________________________ _________________________某事仍然是个谜_____________________________前者_____________________________后者值得做某事be worth __________________________be worthy ___________________________________________________be worthwhile______________________________________________一条证据_____________________________________________________很明显；显然一场非正式的班级辩论___________________ ___________________________培养….兴趣三、重点句子1. 普鲁士国王威廉一当初世绝不可能想象到他送给俄罗斯人民的厚礼会有这样一段令人惊讶的历史。

每日一件趣事英语作文

Life is a tapestry woven with threads of ordinary moments and threads of the extraordinary. Just yesterday, I experienced an event that was nothing short of a delightful surprise, a testament to the fact that life can be as whimsical as it is unpredictable.It was a typical school day, filled with the usual hustle and bustle. The morning classes were a blur of notes and equations, and lunch was a hurried affair, as I was engrossed in a heated debate about the latest football match with my friends. But the real adventure began in the afternoon.Our English teacher, Mr. Thompson, was known for his unconventional teaching methods. He had a knack for turning the mundane into the magical, and today was no exception. As we filed into the classroom, we noticed something unusual. The desks were arranged in a circle, and in the center, there was a large, mysterious box.Good afternoon, class, Mr. Thompson greeted us with a twinkle in his eye. Today, were going to do something a little different. Ive brought a box filled with random objects. Each of you will pick one and write a short story based on it. The catch? You have to incorporate the object into the story in a meaningful way.The room buzzed with excitement as we each took turns picking an object from the box. I reached in and pulled out a small, antique key. It was old, with intricate engravings and a patina that spoke of years of use. I ran my fingers over the grooves, feeling a strange connection to the object.As I sat down to write, the story began to unfold in my mind. The key was no ordinary key it was a portal to another world. A world filled with magic, mystery, and adventure. I let my imagination run wild, weaving a tale of a young girl who discovers the key and embarks on a journey to unlock the secrets of her past.The story flowed from my pen, each sentence more captivating than the last. I was so engrossed in my writing that I barely noticed the passing of time. When I finally looked up, I realized that the class was over, and everyone was packing up their things.As we shared our stories, I was amazed by the creativity and imaginationof my classmates. There were tales of time travel, magical creatures, and hidden treasures. Each story was unique, a reflection of the individuals perspective and creativity.That day, I learned a valuable lesson. Life is full of surprises, and sometimes, all it takes is a simple object to spark a journey of creativity and selfdiscovery. The key I picked from the box was more than just a prop for a story it was a catalyst for a day filled with fun, imagination, and a deeper understanding of the power of storytelling.In the end, it wasnt just about the story I wrote. It was about the experience, the camaraderie, and the shared joy of creativity. It was a reminder that life is full of unexpected twists and turns, and that sometimes, the most ordinary moments can lead to the most extraordinaryadventures.So, the next time you find yourself in a routine, remember to look for the extraordinary in the ordinary. You never know when a simple object or a seemingly mundane moment might just be the key to unlocking a world of possibilities.。

环境污染严重和全球变暖解决倡议书英文作文

环境污染严重和全球变暖解决倡议书英文作文全文共3篇示例，供读者参考篇1An Important Message for the WorldHi everyone! My name is Jamie and I'm 10 years old. I have something really important to talk about today. It's about taking care of our planet Earth.Our beautiful planet is facing some huge problems. Have you noticed how the weather has been getting weirder and weirder? Things like crazy hurricanes, droughts where there's no rain for a long time, wildfires burning down forests, and glaciers melting rapidly. This is all because of global warming.What is global warming? It's when the temperature of the Earth slowly gets hotter and hotter. This is causing the climate to change in dangerous ways.Why is this happening? Mainly it's because of pollution from humans. We drive too many cars that pump out smoke and gases. Our factories release tons of smoke and chemicals into the air. We cut down forests that help absorb carbon dioxide. Cows on farms create lots of natural gas emissions. Basically, we'reputting too much "greenhouse gas" into the atmosphere, which traps heat and warms up the whole planet.So what's the big deal? Well, global warming means melting ice caps which raises the levels of the oceans. Many cities right by the ocean could someday be flooded! Warming temperatures wreck habitats for animals like polar bears who need ice to hunt. Droughts and heat waves make it hard to grow food crops. And the severe weather like hurricanes threatens many people's lives and homes.This is a major crisis, but I have hope we can fix it if we take action now. Every person needs to do their part. We can't leave this just to world leaders - we all have to pitch in as well!Here are some ideas for how kids and families can help:Use less electricity. Turn off lights when leaving a room. Unplug devices like TVs and computers when not using them so they don't waste energy. Take shorter showers to save hot water.Reduce, reuse, recycle! Cut down on plastic use. Bring reusable bags to the grocery store instead of taking new plastic ones. Recycle any plastic, glass, and metal items you use. Repurpose things instead of throwing them out. The less we waste, the better.Walk, bike, or take public transportation instead of driving a car when possible. Cars create a lot of pollution.Eat less meat and dairy. Cows create a lot of greenhouse gases. Have more meatless meals with vegetables, beans, tofu, etc.Plant trees! Trees absorb carbon dioxide, provide oxygen, prevent soil erosion, and give homes to wildlife. Having more trees makes a big difference.Support companies with good environmental practices. Choose products with less plastic packaging. Pick suppliers who use renewable energy sources like solar or wind power.Spread the word! Talk to your friends and family about global warming. The more people who understand this crisis, the better chance we have of solving it through group effort.In addition to those personal actions, we need our government leaders to make big changes too. They should:Pass laws that limit pollution from factories, vehicles, and businesses. Make companies follow strict environmental rules.Invest much more in clean, renewable energy sources like solar, wind, and hydroelectric power. Move away from fossil fuels like coal and oil.Put more funding toward environmental protection. We need to conserve resources, prevent habitats from being destroyed, protect endangered species, clean up polluted areas, and curb climate change.Work together with other world leaders on a global plan to reduce greenhouse emissions everywhere. We're all in this together as a planet!I also think we should have a new school subject just about the environment. Kids need to learn how to take care of the Earth. We can study climate change, conservation, sustainability, and eco-friendly practices. Protecting the planet should be a top priority!Some people might think, "I'm just one person, I can't make a difference." But that's not true! If every person makes an effort, it adds up in a huge way. We need everyone to change their daily habits. Kids can especially make a difference by nagging their parents to go green! Haha, just kidding...kind of.The Earth is our one and only home. We simply HAVE to take better care of it. The way humans are damaging the environment just cannot continue. The polar bears, rainforests, air quality, water supply - they all deserve to be protected for generations to come.We owe it to ourselves, our children, our grandchildren, and every human being yet to be born. I want them to be able to experience the beauty and wonders of nature, not just see it in pictures and videos. I want them to be able to breathe fresh, clean air and have a safe climate to live in. I want animals of all kinds to have their habitats preserved.It will take a lot of work, but we can do it! We have the ability to stop climate change from getting worse if we act now. Every person must change their daily habits, and our leaders need to seriously prioritize the environment. We should treat Every Day like it's Earth Day!The problem may seem too big to solve. But we kids are determined to have a bright future on a healthy planet Earth. The grown-ups need to join us on this incredibly important mission. Let's work together to heal our world before it's too late. The time is now to protect our one and only home. Who's with me?!篇2An Important Letter from a Kid About the EnvironmentDear Grown-Ups,My name is Jamie and I'm 10 years old. I'm writing to you today because I'm really worried about the environment andthink we all need to do more to take better care of our planet Earth.At school, we've been learning a lot about pollution, global warming, and climate change. It's pretty scary stuff! Did you know that the Earth is getting hotter and hotter every year because of things like burning too many fossil fuels and cutting down forests? The science teachers told us this extra heat is causing the polar ice caps to melt, sea levels to rise, extreme weather like hurricanes and droughts, and animals losing their habitats.It makes me really sad to think about polar bears having nowhere to live because their homes are melting away. Or forests being destroyed so animals like orangutans have to find new places to live. What if their new homes aren't good habitats and they can't find enough food? That would be terrible.The plastic pollution problem also looks really bad from what I've learned. Did you know there are huge islands of floating trash in the oceans that are literally the size of whole countries? That's just crazy! I saw pictures of beaches completely covered in plastic bottles, straws, bags and all kinds of other gross litter. My teacher said this plastic is really hurting andkilling marine life like whales, dolphins, sea turtles and so many other amazing ocean creatures.Apparently, a lot of this pollution comes from humans littering or improperly disposing of plastics. But a huge amount also comes from big factories and companies not being careful about containing their plastic waste. It just gets thrown out and makes its way into waterways that lead to the oceans. No wonder the fish are getting sick from eating all that junk!I feel like the grown-ups really need to do a much better job of fixing this giant plastic problem before it's too late. Couldn't we have better laws that force companies to use less plastic packaging and recycle way more? Also, shouldn't there be huge fines for companies that let plastic into the oceans? Getting tough on them might finally make them clean up their act.As for global warming, that seems really complicated to solve. But from what I've learned, a lot of it is caused by humans burning coal, oil and other fossil fuels that release greenhouse gases into the air. Those gases get trapped in the atmosphere and cause temperatures to go up.So it seems like we need to find better ways to make energy that don't involve burning stuff that pollutes the air so badly. Things like solar panels, wind turbines, hydro power from water,and geothermal power from the heat under the ground. They sound way cleaner to me!We also need to drive gas-powered cars and trucks a lot less. Maybe in the future we could get rid of those altogether and just have electric vehicles that don't pollute at all. How cool would that be? No more smelly exhaust coming from the cars on the road!Cutting down way fewer trees would probably also help a lot. Trees are known as the lungs of the planet because they absorb carbon dioxide and give out oxygen. So we need to protect forests instead of burning them down for new developments and farms. That just seems like such a waste to me.Anyway, those are some of the big things I think we need to work on to help stop messing up the environment with too much pollution and warming. It's going to be a huge effort by everyone though, not just a few people doing the right thing.Every grown-up needs to change some of their habits around the house, like:Using less electricity by turning off lights, unplugging devices, taking shorter showers, etc.Recycling way more stuff instead of just throwing it in the trashUsing re-usable shopping bags instead of plastic bagsDriving less by walking, biking or taking public transportation more oftenEating less meat and more vegetables since cows create a lot of greenhouse gasesBuying products with less plastic packagingNot littering and picking up plastic trash when you see itAnd companies need to change too:Shifting to renewable energy sources like solar and windUsing way less plastic in product packaging and shippingTreating and properly disposing of chemical waste instead of dumping itNot cutting down forests for developments and farmsComing up with creative ways to reduce their overall pollutionThe government should probably step in too with stricter environmental laws and regulations. Maybe give tax breaks topeople and companies that go green and punish those that keep polluting and warming the planet.I know solving these huge issues won't be easy. But we have to try for the sake of the environment and all the animals!I'm just a kid, but in a few years, it will be my generation running this planet. And believe me, we care way more about the environment than a lot of grown-ups seem to. So you all had better start making changes now before it's too late!I dream of a future where the air is fresh and clean, the animals can thrive in their natural habitats, and the gorgeous blue oceans are free of gross trash islands. A world with beautiful green forests that give us plenty of oxygen instead of being burned down. And sources of energy that don't overheat and pollute the planet through emissions.Maybe some grown-ups think that's just a silly kid's fantasy. But to me it just seems like common sense to take much better care of the only home we have - Mother Earth. She needs our help and we can't keep trashing her like this any more. It's time to step up our game, grown-ups!I really hope you all will start taking environmental issues way more seriously for the sake of my generation and those tocome after us. We need you to make big changes so we can inherit a clean, healthy world that we can actually keep living in without problems.Please don't let me and my friends down! The planet's future is in your hands.Sincerely,JamieA Concerned 10-Year-Old篇3Our Beautiful Earth Needs Our Help!Hi friends! My name is Lily and I'm 10 years old. I love playing outside, climbing trees, and exploring nature. But lately, I've been really worried about the health of our planet Earth. Have you noticed how the air sometimes looks dirty and smoggy? Or how there's so much trash littering our parks and oceans? It makes me sad to see Mother Nature suffering like this.The problem is that people aren't being very good caretakers of the Earth lately. We're polluting the environment way too much with our factories, cars, littering, and all the trash we create. It's like we're slowly poisoning our own home! All thispollution is also causing global warming, which means the whole planet is heating up way too much.What's so bad about global warming, you ask? Well, as the Earth gets hotter, it's causing the polar ice caps and glaciers to melt rapidly. This melting ice is raising the sea levels, which could one day flood many coastal cities where lots of people live. Yikes! Global warming is also messing up the weather and climate patterns, making some areas much hotter and drier, while causing other places to get a lot more extreme storms, hurricanes, and flooding.The changing climate is putting many animals and plants at risk of going extinct too because their habitats and food sources are disappearing. Imagine if your home was destroyed and you had no food to eat - that's how a lot of critters on Earth are feeling thanks to pollution and global warming. It's not fair to the animals and it's not fair to future kids like me who might not get to grow up enjoying all the amazing nature, plants, and creatures that I'm so lucky to have now.But you know what? I'm just a kid and there's only so much I can do alone to fix these huge environmental problems. That's why I'm writing this essay - to rally all my friends, adults, teachers,world leaders, and everyone to work together to help save our wonderful planet!Here are some of the things I think we should do to cut down on pollution and global warming:We need to drive less and walk, bike, take the bus, or carpool more whenever possible. Car emissions are a major source of air pollution and greenhouse gases that cause global warming. If we can use more environmentally-friendly transportation, it would make a huge difference!Let's all try really hard to reduce, reuse, and recycle as much as possible. Cutting down on the amount of energy, plastic, paper, and other waste we create will mean less pollution. We should also try to buy products with less wasteful packaging. Every little bit helps!Stop littering please It's so sad to see trash polluting our beautiful landscapes, beaches, and oceans. Put your trash in proper bins and pick up litter when you see it to help keep nature clean and protect animals.We need to push our leaders to pass laws that limit pollution from factories, cars, and other sources. Maybe there could be taxes on things that pollute a lot to encourage companies to gogreen. Profits shouldn't come before protecting the planet we all share.Conserve electricity and water! Things like leaving lights on, taking super long showers, and letting taps run wastefully requires power plants to work harder and burn more fossil fuels that pollute. Be mindful of your energy and water use.Plant more trees, gardens, and greenery! Trees and plants absorb carbon dioxide, provide homes for animals, and make our air fresher. Having lush, green spaces in urban areas helps offset some pollution too.Maybe scientists can invent new technologies to capture greenhouse gases so they don't go into the atmosphere. Or create more renewable energy sources that don't dirty our air like wind, solar, and hydro power. Gotta put those big brains to work to save Earth!We have to teach kids from a very young age how important it is to respect and protect the environment. Schools can have programs about conservation, recycling, and being good environmental citizens starting in kindergarten. That way, we'll all grow up knowing how to keep Earth healthy.Everyone needs to do their part by making simple changes in their daily habits and lifestyle to be more eco-friendly. Don't litter, try to consume less, walk or bike instead of drive sometimes, recycle, turn off lights when not using them, etc. Small acts multiplied by billions of people would be so powerful!If we all work together, wouldn't it be amazing if we could completely eliminate pollution and global warming one day? We could have fresh air to breathe, clean water to drink, thriving nature preserves full of animals, and the relief of knowing that the Earth is truly a healthy, sustainable home for all! What a wonderful dream to fight for!It might seem like very big problems for a little kid to try tackling, but I have to try. This is the only planet we've got and it's our shared home. We simply MUST take care of Mother Earth before the damage gets even worse. Global warming and environmental destruction affects every single plant, animal, and person - even kids like me.I don't want to grow up in a world where air pollution makes it hard to breathe, trash litters every landscape, animals are going extinct, and intense natural disasters are common due to climate change. I want to be able to play outside without smog, eat fresh foods that grew in healthy soil, swim in clean oceans,and see beautiful forests and coral reefs teeming with vibrant life.Keeping our air, land, and waters clean and protected should be one of humankind's most important priorities. We all need to make some big changes and sacrifices to our wasteful ways. It will be hard work, but if everyone does their part - governments, companies, communities, families, and kids - I'm hopeful we can reverse the damage and create a sustainable, healthy, and beautiful planet for all.Who's with me?! Let's get to work cleaning up our home, sweet Earth! Our future is depending on it. Together, our positive actions can create an amazing.worpd for the generations to come. The Earth is our one and only home...let's take good care of it!。

关于科技节的诗歌英语作文

In the heart of the city,where the pulse of progress beats, A festival of science,a spectacle,a feat.A celebration of minds,a gathering of the wise,Where the future unfolds,and the present is prized.Under the vast,starstudded sky,a canvas so grand,The architects of tomorrow,with their hands in the sand. They sculpt the unknown,with a vision so clear, Creating wonders that dazzle,and bring the world near.In the halls of discovery,where the curious roam, Experiments and innovations,a sight to behold in the dome. Robots dance and machines hum,a symphony of gears,A testament to human ingenuity,through the years.The young and the old,with eyes wide and bright,Gather to learn,to explore,to ignite the spark of might.The air is filled with excitement,a buzz of the new,As the festival of science,its magic imbues.From the depths of the ocean,to the heights of the sky,The marvels of science,they reach,they fly. Telescopes and microscopes,revealing the unseen, Expanding our horizons,and deepening our glean.In the realm of the digital,where data flows like a stream, Coding and algorithms,the language of the dream.Virtual worlds and simulations,a playground for the mind, Where the limits of reality,gently unwind.The festival is a beacon,a light in the dark,Guiding us towards knowledge,and a future thats stark.A reminder of our potential,our power to create,A world where science and humanity,beautifully,intermate.So let us raise our voices,in a chorus of praise,For the festival of science,in its many ways.A tribute to the thinkers,the doers,the dreamers,Whose work shapes our world,and makes the future seemers.As the sun sets on this day,and the stars take their place, The festival of science,leaves a lasting trace.A spark in the minds of all who attended,A promise of a future,thats bright,and splendid.。

我的父母在购物英语作文

Growing up in a family where both parents are avid shoppers has been an experience that has shaped my understanding of consumer culture and the importance of budgeting. My mother and father have always had a knack for finding the best deals and the most unique items, but their approach to shopping has also taught me valuable life lessons.My mother, a true bargain hunter, has an uncanny ability to spot a good deal from a mile away. She scours the internet, reads through flyers, and even has a knack for knowing when certain items will go on sale. This has led to our family enjoying a variety of products at a fraction of the cost. Her dedication to finding the best prices is not just about saving money its about the thrill of the hunt and the satisfaction of a job well done.On the other hand, my father takes a more calculated approach to shopping. He is meticulous in his research, often spending hours comparing products and reading reviews before making a purchase. His methodical nature ensures that we get the best quality for our money, and it has taught me the importance of patience and thoroughness in decisionmaking.One of the most memorable shopping experiences with my parents was during the Black Friday sales. The atmosphere was electric as we navigated through the crowded stores, each with a list of items we wanted to purchase. My mother was in her element, swiftly moving from one sale to another, while my father took his time, carefully considering each purchase.I watched as they balanced the excitement of the sales with the practicality of our needs.This experience was not just about the thrill of the chase or the satisfaction of a good deal it was also about the lessons I learned from my parents. I learned the importance of budgeting and the value of money. I saw how they managed to maintain a balance between indulging in the excitement of sales and the responsibility of managing our familys finances.Moreover, my parents shopping habits have also influenced my own approach to consumerism. I have learned to be discerning, to research before making a purchase, and to appreciate the value of a good deal. I have also learned to be mindful of the environmental impact of our consumption, opting for sustainable and ethically produced products whenever possible.In todays world, where consumerism is rampant, and the pressure to keep up with the latest trends is immense, my parents have instilled in me a sense of responsibility and mindfulness towards my consumption habits. They have shown me that shopping can be both a practical necessity and a source of enjoyment, but it should always be done with a clear understanding of our needs and the impact of our choices.In conclusion, my parents approach to shopping has been a significant influence in my life. It has taught me the importance of budgeting, the value of research, and the joy of finding a good deal. Their habits have shaped my understanding of consumer culture and have instilled in me a sense of responsibility towards my consumption habits. As I continue togrow and develop my own approach to shopping, I am grateful for the lessons they have taught me and the experiences we have shared together.。

六下英语四单元课文

六下英语四单元课文In the bustling city, the sun sets gracefully, casting a golden hue over the skyscrapers. Children rush home from school, their laughter echoing through the streets.At home, the aroma of dinner fills the air, a comforting reminder of family and warmth. The table is set, and the family gathers, sharing stories of the day, their faces lit with joy.In the evening, the young student opens their English book, eager to delve into the fourth unit. The pages are filled with colorful illustrations and engaging stories that capture their imagination.As they read, they are transported to a world of adventure, where they meet new friends and explore different cultures. Each sentence is a step forward, each word a new discovery.The vocabulary is challenging, but the context makes it easier to understand. The grammar is complex, yet the examples are clear and concise, guiding the young mind through the intricacies of the language.With each lesson, their confidence grows. They practice speaking, listening, reading, and writing, embracing the language as a tool for communication and expression.The unit culminates in a project, where the students showcase their understanding of the topics covered. Their presentations are creative and insightful, reflecting the depth of their learning.As the unit comes to an end, the student looks back with pride. They have not only learned English, but they have also gained a new perspective on the world around them.。

托福阅读TPO18-3 Lightning

LightningLightning is a brilliant flash of light produced by an electrical discharge from a storm cloud. The electrical discharge takes place when the attractive tension between a region of negatively charged particles and a region of positively charged particles becomes so great that the charged particles suddenly rush together. The coming together of the oppositely charged particles neutralizes the electrical tension and releases a tremendous amount of energy, which we see as lightning. The separation of positively and negatively charged particles takes place during the development of the storm cloud.The separation of charged particles that forms in a storm cloud has a sandwich-like structure. Concentrations of positively charged particles develop at the top and bottom of the cloud, but the middle region becomes negatively charged. Recent measurements made in the field together with laboratory simulations offer a promising explanation of how this structure of charged particles forms. What happens is that small (millimeter-to centimeter-size) pellets of ice form in the cold upper regions of the cloud. When these ice pellets fall, some of them strike much smaller ice crystals in the center of the cloud. The temperature at the center of the cloud is about -15℃ or lower. At such temperatures, the collision between the ice pellets and the ice crystals causes electrical charges to shift so that the ice pellets acquire a negative charge and the ice crystals become positively charged. Then updraft wind currents carry the light, positively charged ice crystals up to the top of the cloud. The heavier negatively charged ice pellets are left to concentrate in the center. This process explains why the top of the cloud becomes positively charged, while the center becomes negatively charged. The negatively charged region is large: several hundred meters thick and several kilometers in diameter. Below this large, cold, negatively charged region, the cloud is warmer than -15℃, and at these temperatures, collisions between ice crystals and falling ice pellets produce positively charged ice pellets that then populate a small region at the base of the cloud.Most lightning takes place within a cloud when the charge separation within the cloud collapses. However, as the storm cloud develops, the ground beneath the cloud becomes positively charged and lightning can take place in the form of an electrical discharge between the negative charge of the cloud and the positively charged ground. Lightning that strikes the ground is the most likely to be destructive, so even though it represents only 20 percent of all lightning, it has received a lot of scientific attention.Using high-speed photography, scientists have determined that there are two steps to the occurrence of lightning from a cloud to the ground. First, a channel, or path, is formed that connects the cloud and the ground. Then a strong current of electrons follows that path from the cloud to the ground, and it is that current that illuminates the channel as the lightning we see.The formation of the channel is initiated when electrons surge from the cloud base toward the ground. When a stream of these negatively charged electrons comes within 100 meters of the ground it is met by a stream of positively charged particles that comes up from the ground. When the negatively and positivelycharged streams meet, a complete channel connecting the cloud and the ground is formed. The channel is only a few centimeters in diameter, but that is wide enough for electrons to follow the channel to the ground in the visible form of a flash of lightning. The stream of positive particles that meets the surge of electrons from the cloud often arises from a tall pointed structure such as a metal flagpole or a tower. That is why the subsequent lightning that follows the completed channel often strikes a tall structure.Once a channel has been formed, it is usually used by several lightning discharges, each of them consisting of a stream of electrons from the cloud meeting a stream of positive particles along the established path. Sometimes, however, a stream of electrons following an established channel is met by a positive stream making a new path up from the ground. The result is a forked lightning that strikes the ground in two places.Paragraph1 : Lightning is a brilliant flash of light produced by an electrical discharge from a storm cloud. The electrical discharge takes place when the attractive tension between a region of negatively charged particles and a region of positively charged particles becomes so great that the charged particles suddenlyreleases amount of energy, which we see as lightning. The separation of positively and negatively charged particles takes place during the development of the storm cloud.1. According to paragraph 1, all of the following take place in the development of a flash of lightening EXCEPT○great tension between two oppositely charged regions○an increase in negatively charged particles over positively charged particles○oppositely charged particles coming together○the release of electrical energy in the form of visible light2.○distinct○growing○huge○immediateParagraph 2: The separation of charged particles that forms in a storm cloud has a sandwich-like structure. Concentrations of positively charged particles develop at the top and bottom of the cloud, but the middle region becomes negatively charged. Recent measurements made in the field together with laboratory simulations offer a promising explanation of how this structure of charged particles forms. What happens is that small (millimeter-to centimeter-size) pellets of ice form in the cold upper regions of the cloud. When these ice pellets fall, some of them strike much smaller ice crystals in the center of the cloud. The temperature at the center of the cloud is about -15℃ or lower. At such temperatures, the collision betweencharge and the ice crystals become positively charged. Then updraft wind currents carry the light, positively charged ice crystals up to the top of the cloud. The heavier negatively charged ice pellets are left to concentrate in the center. This process explains why the top of the cloud becomes positively charged, while the center becomes negatively charged. The negatively charged region is large: several hundred meters thick and several kilometers in diameter. Below this large, cold, negatively charged region, the cloud is warmer than -15℃, and at these temperatures, collisions between ice crystals and falling ice pellets produce positively charged ice pellets that then populate a small region at the base of the cloud.3.According to paragraph2, what causes ice crystal to become positively charged?○Collisions with ice pellets○Collisions with negatively charged ice crystals at the base of the cloud○Becoming concentrated in the central region of the cloud○Forming at a temperature greater than -15℃4.○reject○obtain○need○produce5. According to paragraph2, why are positively charged ice pellets produced in the lower part of thecloud?○Collisions between ice crystals and ice pellets increase in number in the lower part of the cloud.○The lower part of the cloud is smaller than the region above it.○More ice pellets than ice crystals reach the lower part of the cloud.○Temperature in the lower part of the cloud are warmer than -15℃.6.According to paragraph2, the middle region of a cloud becomes negatively charged due to all of thefollowing EXCEPT○a shift of electrical charged between ice pellets and ice crystals○negatively charged ice pellets that remain in the middle○a temperature of -15℃ or less○the development of a positive charge at the base of the cloud7.It can be inferred from paragraph 2 that part of the reason that the top of a storm cloud becomespositively charged is that○the top of the cloud is warmer than the middle of the cloud○the middle of the cloud is already occupied by positively charged particles○the negatively charged ice pellets are too heavy to be carried by the updrafts that move ice crystals ○collisions between ice pellets in the top of the cloud produce mainly positively charged particlesParagraph 3: Most lightning takes place within a cloud when the charge separation within the cloud collapses. However, as the storm cloud develops, the ground beneath the cloud becomes positively chargedeven though it represents only 20 percent of all lightning, it has received a lot of scientific attention.8.to explain why○this form of lightning has been investigated so much○this form of lightning is not as common as lightning within a cloud○scientific understanding of this form of lightning is important○the buildup of positive charge on the ground beneath a storm cloud can have serious consequencesParagraph 4: Using high-speed photography, scientists have determined that there are two steps to the occurrence of lightning from a cloud to the ground. First, a channel, or path, is formed that connects the cloud and the ground. Then a strong current of electrons follows that path from the cloud to the ground, and9.○opens○completes○lights○electrifiesthe ground. When a stream of these negatively charged electrons comes within 100 meters of the ground it is met by a stream of positively charged particles that comes up from the ground. When the negatively and positively charged streams meet, a complete channel connecting the cloud and the ground is formed. The channel is only a few centimeters in diameter, but that is wide enough for electrons to follow the channel to the ground in the visible form of a flash of lightning. The stream of positive particles that meets the surge of electrons from the cloud often arises from a tall pointed structure such as a metal flagpole or a tower. That is why the subsequent lightning that follows the completed channel often strikes a tall structure.10. According to paragraph5, which of the following is true of the stream of charged particles from theground?○It prevents streams of electrons from the cloud from striking the ground.○It completes a channel that connects the storm cloud with the ground.○It produces a stream of electrons from the cloud.○It widens the path made by the initial stream of electrons from the cloud.11.Which of the following claims about lightning strikes can be inferred from paragraph 5?○During a lightning strike the diameter of the channel the electrons follow is considerably enlarged beyond a few centimeters.○A building is unlikely to be hit by lightning unless it is at least 100 meters tall.○A building is hit by a lightning strike because the building itself has first determined the path the lightening then takes to it.○The light of a lightning strike first appears at the point where the streams of negative and positive particles meet.12.○started○intensified○finished○expectedThe formation of the channel is initiated when electrons surge from the cloud base toward the ground. When a stream of these negatively charged electrons comes within 100 meters of the ground it is met by a stream of positively charged particles that comes up from the ground. When the negatively and positively charged streams meet, a complete channel connecting the cloud and the ground is formed. The channel is only a few centimeters in diameter, but that is wide enough for electrons to follow the channel to the ground in the visible form of a flash of lightning. The stream of positive particles that meets the surge of electrons from the cloud often arises from a tall pointed structure such as a metal flagpole or a tower. That is why the subseq uent lightning that follows the completed channel often strikes a tall structure. ■Once a channel has been formed, it is usually used by several lightning discharges, each of them consisting of a stream of electrons from the cloud meeting a stream of positive particles along the established path. ■ Sometimes, however, a stream of electrons following an established channel is met by a positive stream making a new path up from the ground. ■ The result is a forked lightning that strikes the ground in two pla ces. ■13.Look at the four squares [■] that indicate where the following sentence could be added to the passage.The descending stream of electrons divides at the point where the new positive-stream channel intersects the established path.Where would the sentence best fit?14.Directions: An introductory sentence for a brief summary of the passage is provided below.Complete the summary by selecting the THERR answer choices that express the most important ideasin the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.Lightning takes place when a separation of a positive and negative electrical particles that develops in a storm could suddenly collapses.●●●○A storm cloud first develops a positively charged layer at the top, then a negatively charged middle layer, and finally, a positively charged layer at the bottom.○A separation of oppositely charged particles in clouds develops from collisions of falling ice pellets with ice crystals, from updrafts, and from temperature variations.○Lightning from cloud to ground follows a channel that forms when a stream of electrons moving down meets a stream of positive particles coming up from the ground.○Field studies, laboratory simulations, and high-speed photography have all been used to investigate the way charge separations develop in clouds.○Lightning from a cloud to the ground is more likely to be destructive than is lightning that takes place within a cloud.○Once a channel has been formed, it is usually used by several successive electrical discharges that illuminate the channel as flashes of lightning.参考答案：1．22．33．14．25．46．47．38．19．310． 211． 312． 113． 314． A separation of …Lightning from cloud to ground…Once a channel has …。

高考英语总复习第一部分基础考点聚焦 Unit5 The power of nature高效演练跟踪检测新人教版选修6

Unit 5 The power of natureⅠ单句语法填空1．The fear of all kinds of examinations can be a source of deep ____________(anxious) to many students.答案：anxiety2．To show our ____________(appreciate) fo r all your hard work, we’d like to give you a bonus.答案：appreciation3．(山东高考)____________(eat) at the cafeteria before, Tina didn’t want to eat there again.答案：Having eaten4．All the task____________(finish) ahead of time, they decided to go on holiday for a week.答案：having been finished5．Changbaishan is China’s largest nature reserve and is home ____________roe deer.答案：to6．Though on the same family, the bird varies ____________ size and color.答案：in7．She waved goodbye____________ her friends before boarding the plane.答案：to8．—Why are you so hurried?—My mother will get a bit ____________(anxiety) if I don’t get back on time.答案：anxious9．I____________(panic) when I saw smoke coming out of the engine.答案：panicked10．(2015·重庆高考书面表达)I’m writing to apply for “wild release”， in which you can put the books in the ____________(appoint) place, and other participants can have free access to them.答案：appointedⅡ单句改错1．The mother was standing at the gate, anxiously to see her son.anxiously→anxious 2．Lincoln had shot while watching a play in the Ford’s Theatre.had后加been 3．With all the houses being burnt to the ground, they had no place to live in.去掉being4．I was about to leave while the telephone rang.while→when5．After admiring the beautiful view, she made his way to the next destination.his→her6．As far as I know, it is absolute impossible to finish it in five days.absolute→absolutelyⅢ完成句子1．As a matter of fact, there is no point ____________________________(对考试惊慌失措)．答案：getting into a panic about the exams2．____________________________(没有其他可以求助的人), I had to come to see you. 答案：There being no one else to turn to3．____________________________(回答老师的问题后) she sat down and felt much more relaxed.答案：Having answered the teacher’s quest ions4．________________________(据说) some normal universities offer some students free education on condition that they return to their hometown to work as teachers. 答案：It is said that5．We ________________(保证) deliver your goods within a month.答案：guarantee to【写作素材】根据要求运用本单元所学知识完成下面小作文，并背诵成文。

2025版高考英语一轮总复习晨背素材选择性必修第二册Unit1Scientists(含答案)

高考英语一轮总复习：晨背素材选择性必修第二册 Unit 1 Science and Scientists Since the severe virus broke out, many people all over the world have been infected.Chinese outstanding，gifted and patriotic specialists in epidemiology and their assistants have been in charge of tracing the source of the virus in order to defend more people from being killed.They desired to produce vaccine to handle the deadly disease once and for all.Initially, with concrete proof collected, they suspected that wild bats were to blame.But by observing the virus with microscopes，they gathered solid and multiple statistics and mastered the framework of the virus, which gradually transformed their initial contradictory thinking.All the findings made them subscribe to the idea that the virus was not directly linked to the bats, which made the brilliant experts frustrated.This also cast a shadow on the experts, so they had to shift towards how to prevent the virus from spreading among people.Above all，the less we go out, the less likely we will come down with the deadly disease.Furthermore，taking in more protein and eating more vegetables are good choices as st but not least, what we should do is that we must wear masks outdoors.Thanks to these interventions，the threat of the severe virus in China saw a substantial decrease.What we have experienced has taught us to lead a healthy life such as drinking pure or boiled water and avoiding raw foods.In conclusion, under our motherland's leadership，we have achieved steady success, tears of happiness pouring down our cheeks.。

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In order to discuss the behavior of the elementary excitations in this limit it is convenient
2
to derive explicit equations for the density ρ(r, t) = |Φ(r, t)|2 and for the velocity ﬁeld v(r, t) = (Φ∗(r, t)∇Φ(r, t) − ∇Φ∗(r, t)Φ(r, t)) /2miρ(r, t). These equations can be directly
3
ρ0)/m for the change of the chemical potential (see Eqs.(4-5)). Assuming for simplicity an isotropic harmonic oscillator potential Vext(r) = ω02r2/2m, the equations of motion (2-3), after linearization, can be written in the useful form
normalization to the density ρ0. In the following we will look for solutions of the above equations by neglecting the kinetic energy pressure term 2m¯h√2 ρ0 ∇2√ρ0 in Eq.(4). This ap-
The main purpose of this work is to obtain an explicit, analytic solution of (1) holding when the repulsive interaction is large enough to make the kinetic energy pressure negligible compared to the external and interparticle interaction terms. When applied to the calculation of the ground state this limit corresponds to the Thomas-Fermi approximation and is reached for positive and large values of the adimensional parameter Na/a0 where a0 = (h¯/mω0)1/2 is the harmonic oscillator length characterizing the trap and N is the number of atoms. In the study of the elementary excitations this approximation corresponds to the hydrodynamic limit accounting, in homogeneous systems, for the propagation of phonons.
I-3850 Povo, Italy (February 1, 2008)
Abstract
By taking the hydrodynamic limit we derive, at T = 0, an explicit solution of the linearized time dependent Gross-Pitaevskii equation for the order parameter of a Bose gas conﬁned in a harmonic trap and interacting with repulsive forces. The dispersion law ω = ω0(2n2 + 2nℓ + 3n + ℓ)1/2 for the elementary excitations is obtained, to be compared with the prediction ω = ω0(2n + ℓ) of the noninteracting harmonic oscillator model. Here n is the number of radial nodes and ℓ is the orbital angular momentum. The eﬀects of the kinetic energy pressure, neglected in the hydrodynamic approximation, are estimated using a sum rule approach. Results are also presented for deformed traps and attractive forces. PACS numbers: 03.75.Fi, 05.30.Jp, 32.80.Pj, 67.90.+z
ih¯
∂ ∂t
Φ(r,
t)
=
−
h¯ 2 ∇2 2m
+
Vext(r) +
4πh¯2a m
|
Φ(r, t)
|2
Φ(r, t) .
(1)
Here Vext is the conﬁning potential and a is the s-wave scattering length. This equation neglects interaction eﬀects arising from the atoms out of the condensate. This is an accurate approximation for a dilute Bose gas at low temperatures where the depletion of the condensate is negligible. Diﬀerently from the homogeneous case, the Gross-Pitaevskii equation in the presence of an external potential admits stationary solutions not only for positive values of the scattering length, but also when a is negative. In the latter case a solution of metastable type is found provided the number of atoms in the trap is not too large [9–12]. The solutions of the time-dependent Eq.(1), after linearization, have the well known RPA structure and have been the object of a recent numerical investigation in the case of a trapped atomic gas [13].
Pitaevskii Eq.(1) and hold in the linear as well as in the non linear regimes. They have
the general structure of the dynamic equations of superﬂuids at zero temperature (see for
obtained starting from the time dependent Eq.(1) and take the form
∂ ∂tρΒιβλιοθήκη +∇(vρ)
=
0
(2)
and
m
∂ ∂t
v
+
∇(δµ
+
1 mv2) 2
=
0
(3)
where
δµ
=
Vext
+
4πh¯2a m
ρ
−
h¯2 2m√ρ
∇2√ρ
−
µ
(4)
example [7]). In particular Eq.(3) establishes the irrotational nature of the superﬂuid ﬂow.
The density ρ0 relative to the ground state is obtained setting v = 0 and δµ = 0. This
arXiv:cond-mat/9603126v1 18 Mar 1996
Collective excitations of a trapped Bose-condensed gas
S. Stringari
Dipartimento di Fisica, Universita` di Trento, and Istituto Nazionale di Fisica della Materia,
is the change of the chemical potential with respect to its ground state value µ. It is worth
noting that these equations do not involve any approximation with respect to the Gross-
Typeset using REVTEX 1
Almost 50 years ago Bogoliubov [1] derived his famous theory for the elementary excitations of a dilute Bose gas. This theory, originally applied to homogeneous systems, is now receiving a novel interest because of the experimental availability of Bose-condensed gases conﬁned in magnetic traps [2–4] (for a review on Bose-Einstein condensation see for instance Ref. [5]). The Bogoliubov theory can be shown [6] to correspond to the linear limit of the time dependent Gross-Pitaevskii [8] equation for the order parameter Φ