Future galactic supernova neutrino signal What can we learn

Future galactic supernova neutrino signal What can we learn
Future galactic supernova neutrino signal What can we learn

a r

X

i

v

:n u

c

l

-

t h /

1

1

1

1

6

v

1

7

N

o

v

2

1

Future galactic supernova neutrino signal:What can we learn??P.Vogel Physics Department,Caltech,Pasadena,CA 91125,USA February 8,2008Abstract The next supernova in our galaxy will be detected by a variety of neutrino detectors.In this lecture I discuss the set of observables needed to constrain the models of supernova neutrino emission.They are the ?ux normalizations,and average energies,of each of the three expected components of the neutrino ?ux:νe ,ˉνe ,and νx (all the other four ?avors combined).I show how the existing,or soon to be operational,neutrino detectors will be able to determine the magnitude of these observables,and estimate the corresponding rates.1Introduction When neutrinos from supernova 1987A were detected by the Kamiokande [1]and IMB [2]collabora-tions,a new era of neutrino astrophysics began.Despite the limited statistics (11events in Kamiokande and 8events in IMB)the observation con?rmed that the core collapse supernovae emit most of their binding energy (a few ×1053erg)in neutrinos,that the duration of the neutrino emission is ~10seconds,and that the average energy of the neutrinos (at least of the ˉνe ,which were the only ?avor actually seen)is ~15MeV,close to expectations.The observation of SN1987A lead to a ?ood of papers analyzing its consequences (for a relatively early review,see e.g.[3]),which is only very slowly diminishing with time.Historically,there were seven supernovae in our galaxy proper recorded in the past thousand years,and none in the last three centuries (some were not core-collapse SN which emit neutrinos,though).All of them were relatively close to the solar system,so it is di?cult to estimate the true rate averaged

over the whole galaxy from this record.Consensus estimate of core-collapse supernova rate in our galaxy is about three times per century [4].Thus,the next Galactic supernova neutrino burst can come at any time,tomorrow or in several decades.It is likely that neutrinos from such supernova will be detected by a variety of detectors,with much better statistics than for SN1987A.Thus a wealth of new information is expected from such unique event which cannot be repeated in the productive lifetime of an average physicist.(Unfortunately,the present or planned neutrino detectors are unable to observe supernovae in even the nearest galaxy,Andromeda,about 700kpc away.)Here I discuss some of the lessons that should,and hopefully will,be extracted from the neutrino signal of the next supernova in our galaxy.

There are several areas of physics that will greatly bene?t from the supernova neutrino observations.They can be divided into three broad categories:

1.)Neutrino properties;mass,mixing,decay,etc.In particular,one could use the time-of-?ight of the neutral current signal (dominantly νμand ντ)to reach sensitivity to masses of about 30eV

for these neutrinos[5,6].This would represent an improvement by more than three orders of magnitude for the mass associated withνμ,and by almost six orders of magnitude for the mass associated withντwhen compared to the present direct neutrino mass limits[7].If,moreover, the neutrino emission is abruptly truncated by the collapse of the proto-neutron star into a black hole,one can use this sharp cut-o?in the neutrino signal to improve the time-of-?ight sensitivity to masses of~6eV forνμandντand to~1.8eV forνe[8].

2.)Supernova properties.From the neutrino signal it might be possible to determine the lumi-

nosities and average energies of all three components of the neutrino?ux:νe,ˉνe,andνx(this notation will be used from now on collectively forνμ,ντand their antiparticles).

3.)Supernova https://www.360docs.net/doc/3c2822777.html,ing the angular distribution of the products of the neutrino induced

signal,or the timing of the signal recorded in widely separated detectors,it might be possible to?nd the direction towards the supernova independently,or prior to,of the optical signal(for the discussion of this item,see[9]).

I refer to the listed references regarding the items1.)and3.)and in the following I will concentrate on the item2.)-the determination of supernova properties from the neutrino signal.My aim is going to be a de?nition of a‘template’,i.e.,a recipe how to determine the required quantities and what signal and statistical accuracy one may expect using the existing,or soon to be operational, detectors.Substantial deviations from this template will mean either that the supernova behaves in an unexpected way,or that neutrino oscillations a?ect the signal.Obviously,general analysis of all possibilities is impossible before the fact.However,the existence of such a template might help in preparing the detectors for the supernova signal,particularly those like SuperKamiokande,SNO, KamLAND or Borexino,which are built for a di?erent purpose.

I will consider a‘standard’supernova(for a review of Type-II supernova theory see[10]),approx-imately at the center of the galaxy,at the distance from Earth of10kpc.The binding energy,which is essentially fully emitted in neutrinos,is assumed to be3×1053ergs.It is easy to understand the magnitude of the binding energy E B by using the simple estimate

E B?3

R

,where R=10km,M?1.4M⊙.(1)

Neutrinos are trapped in the hot and dense protoneutron star.The mean free path of neutrinos,λ=

1

c

R2

neutrino?avors are di?erent,the position of their neutrinospheres,and hence also the decoupling temperatures,will be di?erent as well.Theνx neutrinos undergo only neutral current interactions, hence their mean free path is longest,and thus their decoupling temperature will be highest.Bothνe andˉνe have in addition also charged current interactions.Moreover,since the star contains many more neutrons than protons,theνe mean free path will be shorter(sinceνe interact with neutrons)than theˉνe mean free path(sinceˉνe interact with protons).Hence a hierarchy of decoupling temperatures (or mean energies)is expected,

T(νx)(~8MeV)>T(ˉνe)(~5MeV)>T(νe)(~3.5MeV),(4) or

Eνx ~25MeV> Eˉνe ~16MeV> Eνe ~11MeV.(5) At the same time,one expects that the total luminosity will be equally shared by all neutrino ?avors,so averaged over time

E B

Lν ?

cm?2s?1,(7)

Eν (MeV)

for the assumed10seconds emission time.With such a?ux and a typical cross section of~10?41 cm2,one expects few hundred charged current interactions with protons in1kton of water,and few tens of events in1kton of iron(or other heavy target).Clearly,very large detectors,operating for a long time,are needed.

Thus the challenge for supernova neutrino observers is to detect separately the three expected components of the neutrino?ux:theνe component through the charged reaction on bound neutrons (i.e.,on nuclei),theˉνe component most easily through the charged current reaction on free protons, and theνx component through neutral current reactions.For each of these components one should determine,ideally,not only the total rate,proportional to Lν/ Eν σ(Eν)f(Eν)dEν,(f(Eν)is the normalized energy distribution;typically assumed to be the Fermi-Dirac thermal one)but also the temperature,or equivalently Eν .If,and only if this program can be accomplished,can one reach reliable conclusions about supernova astrophysics and/or neutrino oscillations.

2Detectingˉνe andνe through charged current reactions

It is relatively easy to detectˉνe,since most detectors contain free protons and one can utilize the reactionˉνe+p→e++n with large cross section and a characteristic signature of the time and position correlated positron and neutron.

The cross section is well known.Neglecting the small neutron recoil energy(~E2ν/M p),one can simply relate the positron energy to the incoming neutrino energy,

E(0)e=Eν??,?=M n?M p=1.293MeV.(8)

The di?erential cross section to this(M p→∞)order is

dσ2 (f2+3g2)+(f2?g2)v(0)e cosθ E(0)e p(0)e,σ0=G2F cos2θC

1MeV2 ×10?42cm2=2π2/m5e

charged current induced events in the case of oscillations.One drawback is that the corresponding cross sections for both reactions are rather uncertain.In fact,the two recent calculations of these quantities[16,17]di?er by about a factor of two.Thus,if the lead based supernova detectors are ever build,experimental determination of these cross sections will be necessary.

3Detectingνx neutrinos through neutral current scattering

The supernovaνx,i.e.νμandντwith their antiparticles,do not have enough energy to induce charged current(CC)interactions.Thus,they can be detected only through their neutral current (NC)scattering.In order to detect the NC scattering one has to?nd,?rst of all,the appropriate signature,i.e.a reaction that can be clearly recognized and separated from the CC channels.Since NC scattering is?avor blind,the contribution of theνe andˉνe scattering has to be subtracted in order to isolate theνx e?ect.This condition more or less eliminates neutrino-electron scattering,where the νe andˉνe contribution dominates.However,in semileptonic NC scattering the cross section typically increases fast with energy,and hence theνx contribution will dominate the NC yield.(The fact that there are four?avors in theνx?ux helps as well.)

The other di?culty is that in a typical NC reaction there is no spectral information;only the number of events per unit time can be measured.Generally,the scattering rate(per s)is:

L(t??t(E))

dN NC

10?42cm2

1MeV D 2 det.mass

1053ergs

16O

Figure1:Schematic illustration of the detection scheme for supernovaνx neutrinos in waterˇCerenkov

.

by the NCνx scattering.

Thus,there will be a rather accurate information on the rate of the NC events.By combining the data from di?erent detectors,one can try to determine theνx luminosity and temperature separately. This should be possible,at least crudely,since the mentioned reactions,while all proportional to the νx luminosity,will have slightly di?erent dependence on neutrino energy in the various respective cross sections.

4Neutrino elastic scattering on protons

Ideally,one would like to use NC scattering combined with some spectrum information,not just rate as in the previous section.As stressed previously also,the seemingly obvious candidate process,neutrino -electron scattering,will be dominated by theνe andˉνe scattering,and thus is not very convenient to study theνx scattering.

In detectors with low detection threshold,such as the scintillator based KamLAND and Borexino,

one can,in principle use for this purpose the elastic scattering on protons1

.The corresponding

di?erential cross section is

π (c2A+c2V)?(c2A?c2V)T p M p Eν±2c M c A T p 1The content of this section is based on the suggestion of John Beacom,for details see[19].

Let us assume that one will be able to extract from measurement some spectral information on the recoiling protons.Would that make it possible to distinguish the cases in which the νx luminosity and temperature conspire in such a way that they lead to the same total number of events,and therefore are indistinguishable based only on Eq.(11)?The answer is yes,and how this could be accomplished is illustrated in Fig. 4.One can see that the proton recoil spectra sensitively depend on the neutrino temperature,with the ratio of the low and high energy yields decreasing with the increasing temperature.In a detailed simulation [19]the power of such discrimination was demonstrated by taking into account the statistical ?uctuation of the expected data.As shown in Fig.5one expects about 10%resolution on both the νx temperature and total energy carried by these neutrinos.

It should be stressed once more that the considered NC signal is independent of neutrino oscillations into ‘active’?avors,i.e.νe ?νμ,τand obviously νμ?ντ.If this signal can be in fact detected,it would measure the luminosity and temperature of the hottest component of the supernova neutrino emission spectrum.

00.250.50.751 1.25 1.5 1.752

Effective energy (MeV)00.2

0.4

0.6

0.8

1

1.21.4

1.6

1.82

R a t i o o f r a t e s T=6,E νx

=4.2T=7,E νx

=2.75T=8,E νx

=2T=9,E νx

=1.6T=10,E νx

=1.3Figure 4:Ratio of proton yields,as a function of the e?ective quenched energy,to the standard case of T =8Mev,and the total energy emitted in νx equal to 2×1053erg.All considered cases result in the same total number of events above the threshold of 200keV of the e?ective energy.

456789101112

T [MeV]

01

2

34567

8

E t o t 4νx [1053 e r g @ 10 k p c ]T ν = 6, E tot

4νx = 4.2 T ν = 10, E tot 4νx = 1.4T ν = 8, E tot 4νx = 2Figure 5:Monte Carlo simulation of the combined ?t to T νx and the total energy carried by such

neutrinos,E tot 4νx

.5Conclusions

In this lecture I have shown how,through the combination of the existing (or soon to be operational)detectors,one can determine simultaneously and independently the luminosities and average energies (or temperatures)of the three expected components,νe ,ˉνe and νx ,of the next Galactic supernova neutrino ?ux.For a ‘standard’supernova near the center of our galaxy,at 10kpc,I have estimated the corresponding count rates,neglecting for a moment the possible e?ects of neutrino oscillations.

Having this set of quantities will make it possible to verify,or ?nd deviations,from the basic assumptions about the supernova neutrino emission:the equal luminosity in each of the six neutrino ?avors,and the hierarchy of decoupling temperatures.Also,one should be able to determine the total emitted energy,essentially the supernova binding energy,and the total neutrino ?uence.Such observables will,in turn,severely constrain theoretical models of supernova neutrino emission,and allow one to deduce conclusions about the possible role of neutrino oscillations.

Most of the original results reported here were obtained in a highly pleasurable collaboration with John Beacom.The work was supported by the US DOE contract DE-FG03-88ER40397.

References

[1]K.Hirata et al.,Phys.Rev.Lett.58(1987)1490

[2]R.Bionta et al.,Phys.Rev.Lett.58(1987)1494

[3]D.N.Schramm and J.W.Truran,Phys.Rep.189(1990)89

[4]S.van den Bergh,Phys.Rep.204(1991)385;G.A.Tamman,W.L¨o?er and A.Schr¨o der,

Astrophys.J.Suppl.92(1994)487

[5]J.F.Beacom and P.Vogel,Phys.Rev.D58(1998)053010

[6]J.F.Beacom and P.Vogel,Phys.Rev.D58(1998)093012

[7]D.E.Groom et al.(Particle Data Group),Eur.Phys.J.15(2000)1

[8]J.F.Beacom,R.N.Boyd and T.Mezzacappa,Phys.Rev.Lett.85(2000)3568

[9]J.F.Beacom and P.Vogel,Phys.Rev.D60(1999)033007

[10]H.A.Bethe,Rev.Mod.Phys.62(1990)801

[11]S.E.Woosley et al.,Astrophys.J433(1994)229

[12]H.-T.Janka in Valcano Workshop1992, F.Giovannelli and G.Mannocchi editors,(Italian

Physical Soc.,Vulcano,1993)

[13]P.Vogel and J.F.Beacom,Phys.Rev.D60(1999)053003

[14]W.C.Haxton,Phys.Rev.D36(1987)2283

[15]E.Kolbe,https://www.360docs.net/doc/3c2822777.html,nganke,and P.Vogel,to be published

[16]G.M.Fuller,W.C.Haxton,and G.C.McLaughlin,Phys.Rev.D59(1999)085005

[17]E.Kolbe and https://www.360docs.net/doc/3c2822777.html,nganke,Phys.Rev.C63(2001)025802

[18]https://www.360docs.net/doc/3c2822777.html,nganke,P.Vogel,and E.Kolbe,Phys.Rev.Lett.76(1996)2629

[19]J.F.Beacom,W.M.Farr,and P.Vogel,in preparation.

1995年诺贝尔物理学奖——中微子和重轻子的发现

1995年诺贝尔物理学奖——中微子和重轻子的发现 1995年诺贝尔物理学奖的一半授予美国加州斯坦福大学的佩尔(Martin L.Perl,1927—),奖励他发现了τ轻子①,另一半授予美国加利福尼亚州欧文(Lrvine)加州大学的莱因斯(Frederick Reines,1918—),奖励他检测到了中微子。 佩尔和莱因斯是对轻子物理学作出重大贡献的两位美国物理学家。这是继鲍威尔(1950年发现π介子),张伯伦与西格雷(1959年发现反质子),丁肇中与里克特(1976年发现J/ψ粒子),鲁比亚和范德米尔(1984年发现W±、z0粒子),莱德曼、施瓦茨和斯坦博格(1988年发现中微子有不同属性),夏帕克(1992年发明多丝正比室)等人之后,国际科学界又一次将诺贝尔物理学奖这一殊荣授予实验高能粒子物理学领域的科学家,人数占本世纪后半叶的总领奖人数的12%。 从这一统计数字可以看出,50年代以来,实验高能粒子物理学的成就非常突出,是物理学界引以为豪的领域之一。 提到中微子的发现,应该先讲讲几件先驱的贡献。中微子的概念是1930年泡利首先提出的。当时摆在物理学家面前的疑难问题中有一个涉及β衰变。β衰变和α衰变及γ衰变不一样,放射性元素发出的β电子能量是连续分布的,不像α和γ射线具有明确的分立谱。而原子核的能态差是确定的,显然β衰变的连续谱是一种反常现象,不符合能量守恒定律的要求。是某种未知的过程在起作用,把能量带走了,还是能量守恒定律不适用于β衰变?在这个疑难问题面前,玻尔甚至都准备放弃能量守恒定律的普适性,他提出也许能量守恒定律只适用于统计性的过程。泡利是一位思想极为活跃的理论家,他在一封给同行的公开信中提出:“原子核中可能存在一种自旋为1/2,服从不相容原理的电中性粒子”。β衰变中失踪的能量也许就是这一察觉不到的中性粒子——中微子带走的。 费米支持泡利的设想,他在1934年正式提出β衰变理论,很好地解释了β能谱的连续性问题,不久这一理论得到了正电子衰变实验的肯定。然而,由于这种微小的中性粒子既不荷电,又不参与强相互作用,质量微不足道,它的存在一直未能得到实验验证。人们只能从能量和角动量的分析,论证这一幽灵式的基本粒子的存在和所起的作用。 在众多的探讨中微子的实验方案中,中国物理学家王淦昌提出的方案格外引人注意。他在40年代初从中国的抗战大后方向美国《物理评论》杂志提交了一篇简短的论文,建议把普通β衰变末态的三体,变为K俘获的二体,就有可能间接观测到中微子的存在。他还特别指出,可取Be→Li作为实验对象。这一建议立即受到实验物理学家的重视。1952年美国的戴维斯果然用这一方法取得了与理论预期值相符的实验结果,初步肯定了中微子的客观存在。 就在这个时候,直接捕捉中微子的工作也开始了。1953年美国洛斯阿拉莫斯(Los Alamos)科学实验室的莱因斯和考恩(ClydeL.Cowan,Jr)领导的实验小组按下列方案探测到反中微子:

英语口语课自我介绍英语口语大赛自我介绍

英语口语课自我介绍-英语口语大赛 自我介绍 口语比赛自我介绍 小学英语口语竞赛自我介绍1 小学英语口语竞赛自我介绍 Dear teachers and classmates, thank you for giving me such a chance to introduce myself,thanks. 亲爱的老师们、同学门,感谢大家给了我这样一个机会来做自我介绍,这是我莫大的荣幸。I’m xxxxxx from chijiayu Primary school. I’mic and drawing pictures. 在我的课余时间,我喜欢骑自行车,听音乐和画画。 I like rabbit very much. It has two long ears and a short tail. It’s as lovely as me. Am I right? 我非常喜欢小兔子。它有两个长长的耳朵和一个短尾巴,和我

一样的可爱。我说的对吗?I like English very much, and I want to be an English teacher in my hometown in the future. 我非常喜欢英语,我以后要在家乡当一名英语老师。 Because my hometown is a mountain village, many children can’t speak English well. 因为我的家乡是一个山村,许多孩子不能很好地说英语。 I’m very confident. Because “Where there is a will, there is a way”. I believe my dream will come true. 我非常有信心,因为“有志者,事竟成。”我相信我的理想最终会实现。That’s all. Thank you for listening. 谢谢大家的聆听。小学英语口语竞赛自我介绍 胡可 Dear teachers and classmates, thank you for giving me such a chance to introduce ’s my great honor. I’m Hu Ke from Class 1, Grade 5. I’m ten years old.

中微子的发现

中微子的发现 背景 从运动学理论可以知道,当一个粒子衰变为两个粒子时,动量和动能守恒,末态粒子的能量应为确定值。而1914年,查德威克在实验中发现β衰变中放出的电子的能谱为连续谱,这意味着电子有各种不同的能量。这是什么原因呢? 对查德威克发现的现象,梅特纳认为:原子发射的电子能量都具有观察到的最大值,最终观察到的是电子经过别的过程损失一定能量后的次级电子。艾利斯(C.D.Ellis)和伍斯特(W.A.Wooster)设计了一个实验,运用一个量能器把所有产生的粒子收集起来,即使初级电子的能量被次级过程重新分配,也能从收集到的总能量算出每次β衰变放出的平均能量,它应当等于观察到的电子能谱极大值。可是,1927年他们的实验结果表明,量能器得到的只是最后射出的电子能量,其平均值与连续谱相符,而看不到次级发射的其它能量。由此可见并没有什么次级过程起作用的迹象。 面对这种困惑形势,玻尔对能量守恒理论提出了质疑。玻尔的主张遭到激烈的反对,狄拉克表示:“我宁可不惜任何代价来保持能量的严格守恒。”泡利也不同意玻尔的观点,1930年,他提出:β衰变中,可能存在一种电中性的粒子带走了电子一部分能量。他把这一电中性的粒子称为中微子。泡利的这一建议是很大胆的,因为这样的粒子是很难直接探测出来的,但这一假设可以使人们摆脱有关核结构理论及β衰变所遇到的困境。 1933年10月的索尔维会议对中微子概念的发展具有重大意义。泡利在会上再次介绍了他对这个新粒子的看法。尽管海森伯还持有怀疑态度,费米却对它做了肯定,并且已经认识到它与中子的区别。那届索尔维会议后仅两个月,费米即在核的质子-中子模型的基础上,发表了有关β衰变的理论。他用相对论量子力学描述费米子,又利用狄拉克辐射理论的产生与湮灭算符及遵从二次量子化的方法导出了寿命公式和β衰变的连续能谱公式,成功的完成了他的β衰变理论。费米的β衰变理论,不仅圆满地解释了整个β衰变过程,澄清了有关β衰变的疑难,同时也确立了有关核结构的理论。按照费米的理论,在β衰变里,中微

石墨烯介绍

1石墨烯概述-结构及性质 1.1 石墨烯的结构 石墨烯是一种由碳原子以sp2杂化连接形成的单原子层二维晶体,碳原子规整的排列于蜂窝状点阵结构单元之中,如图1所示。每个碳原子除了以σ键与其他三个碳原子相连之外,剩余的π电子与其他碳原子的π电子形成离域大π键,电子可在此区域内自由移动,从而使石墨烯具有优异的导电性能。同时,这种紧密堆积的蜂窝状结构也是构造其他碳材料的基本单元,如图2所示,单原子层的石墨烯可以包裹形成零维的富勒烯,单层或者多层的石墨烯可以卷曲形成单壁或者多壁的碳纳米管。 图1 石墨烯的结构示意图 图2石墨烯:其他石墨结构碳材料的基本构造单元,可包裹形成零维富勒烯,卷曲形成一维 碳纳米管,也可堆叠形成三维的石墨 1.2石墨烯的性质 石墨烯独特的单原子层结构,决定了其拥有许多优异的物理性质。如前所述,石墨烯中的每个碳原子都有一个未成键的π 电子,这些电子可形成与平面垂直的π轨道,π 电子可在这种长程π 轨道中自由移动,从而赋予了石墨烯出色的导电性能。研究表明室温下载流子在石墨烯中的迁移率可达到15000cm2/(V·s),相当于光速的1/300,在特定条件,如液氦的温度下,更是可达到250000cm2/(V·s),远远超过其他半导体材料,如锑化铟、砷化镓、硅半

导体等。这使得石墨烯中的电子的性质和相对论性的中微子非常相似。并且电子在晶格中的移动是无障碍的,不会发生散射,使其具有优良的电子传输性质。同时,石墨烯独特的电子结构还使其表现出许多奇特的电学性质,比如室温量子霍尔效应等。由于石墨烯中的每个碳原子均与相邻的三个碳原子结合成很强的σ 键,因此石墨烯同样表现出优异的力学性能。最近,哥伦比亚大学科学家利用原子力显微镜直接测试了单层石墨烯的力学性能,发现石墨烯的杨氏模量约为1100GPa,断裂强度更是达到了130GPa,比最好的钢铁还要高100 倍。石墨烯同样是一种优良的热导体。因为在未掺杂石墨中载流子密度较低,因此石墨烯的传热主要是靠声子的传递,而电子运动对石墨烯的导热可以忽略不计。其导热系数高达5000W/(m·K), 优于碳纳米管,更是比一些常见金属,如金、银、铜等高10 倍以上。除了优异的传导性能及力学性能之外,石墨烯还具有一些其他新奇的性质。由于石墨烯边缘及缺陷处有孤对电子,使石墨烯具有铁磁性等磁性能。由于石墨烯单原子层的特殊结构,使石墨烯的理论比表面积高达2630m2/g。石墨烯也具备独特的光学性能,单层石墨烯在可见光区的透过率达97%以上。这些特性使石墨烯在纳米器件、传感器、储氢材料、复合材料、场发射材料等重要领域有着广泛的应用前景。 图3石墨烯的应用 2石墨烯聚酯复合材料的制备方法 由于石墨烯优异的性质以及低的成本,石墨烯作为聚合物纳米填料被广泛报道。为了获得优异性能的聚合物/石墨烯复合材料,首先要保证石墨烯在聚合物基体中均匀分散。石墨烯的分散与制备方法、石墨烯表面化学、橡胶种类以及石墨烯-橡胶界面有着密切关系。聚合物/石墨烯复合材料的制备方法主要有溶液共混、熔体加工、原位聚合和乳液共混四种方法。 2.1 溶液共混法 溶液共混法主要是采用聚合物本身聚合体系的有机溶剂,充分分散石墨烯于体系中,随着体系聚合反应进行,最后石墨烯均匀分散并充分结合于聚合物基体中,得到石墨烯/聚合物复合材料的一种方法。通常先制备氧化石墨烯作为前驱体,对其进行功能化改性使之能在聚合体系溶剂中分散,还原后与聚合物进行溶液共混,从而制备石墨烯/聚合物复合材料。通过溶液共混制备复合材料的关键是将石墨烯及其衍生物均匀分散在能溶解聚合物的溶剂中。

英语口语课教案

英语口语课教案标准化工作室编码[XX968T-XX89628-XJ668-XT689N]

口语课:H e a l t h y e a t i n g(健康饮食) 老师: 李世琰班级: 英语专业098班 教学辅助: 电脑多媒体 Teaching Objectives(教学目标): 一、知识技能目标: 1.认识并掌握有关食物及健康饮食习惯的单词、词组; 2.用英语表达哪些是健康食物,哪些是垃圾食物,以及为什么; 3.总结平衡膳食的定义,并且能提出一些健康建议。 二、情感态度目标:了解有关营养饮食的基本常识和培养健康的饮食习惯。 三、文化意识目标:了解外国的不同饮食习惯,培养和扩大文化意识。 教学重难点: 1.教学重点:如何区分健康食品以及垃圾食品并且会用英语表达;. 2.教学难点: 教会学生如何自如表达自己的意见和建议并且帮助学生总结出平 衡膳食的定义。 教学方法: 1. Pair work and Group work (小组合作,交流式教学) 2. Discussion and cooperative learning (自主探究、合作探究) 3. Task-based approach (任务式教学) 教学步骤: Part 1 导入(Warming up) 1.以一句话:“Everybody needs foods, so do I”及麦当劳、肯德基的相关 饮食引入话题。 (1-2 分钟) (For example: “Have you had lunch or breakfast in McDonald’s or KFC? Do you like the food there? Which one do you prefer?” The purpose of this part is to stimulate Ss’ interest and call their attention to the topic. ) Part 2 知识展示(presentation) 1、在电脑屏幕上展示食物的图片,然后把学生分成两组竞赛,看哪组的同学 认识的食物单词多,然后教师教导朗读(5-6分钟) 2、老师先展示如何使用句型:“I think that (or the food name) is junk/healthy food because….”来描述什么是健康食品,什么是垃圾食品。 然后把学生按4人分成一组进行讨论练习,老师给出了对话该涉及的内容范 围:What is the name of the food? / What nutrition(营养物质)does it mainly contain? (10分钟) Part 3: 活动任务--- 做调查报告(10分钟) 给学生发一张表格,引导学生按照表格询问周围3个左右的同学,了解同学间 的饮食习惯,并能提出一些健康建议,提问两个左右的同学课堂展示。 Name(名字)Breakfast (早餐)Snacks(零 食) Lunch(午 餐) Dinner (晚 餐)

英语口语课自我介绍

英语口语课自我介绍 在进行英语的口语课时,需要做好自我介绍,那么应该如何做自我介绍呢?下面是WTT分享给大家的英语口语课自我介绍,欢迎阅读。 英语口语课自我介绍篇 1 Hello everyone, my name is Lee. This is really a great honor to have this opportunity, and I believe I can make good performance today. Now I will introduce myself briefly. I am 20 years old,born in Guangdong province, south of China, and I am a senior student at Guangdong **University. My major is English. And I will receive my bachelor degree after my graduation in June. In the past four years, I spent most of my time on study. I passed CET4 and CET6 with a ease and acquired basic theoretical and practical knowledge of Language. Besides, I have attended several Speech competition held in Beijing, which really showed our professional advantages. I have taken a tour to some big factories and companies, through which I got a deep understanding of English for application. Compared to developed countries, unfortunately, although we have made extraordinary progress since 1998, our packaging industry is still underdeveloped, messy and unstable, and the situation of employees in the field is awkward. But I have full confidence in its bright future if only our economy can be kept at the growth pace still. I guess you may be interested in why I choose this job. I would like to tell you that this job is one of my lifelong goals. If I can work here,I will work hard. As to my character, I cannot describe it well, but I know I am optimistic and confident. Sometimes I prefer to stay alone, reading and listening to the music, but I am not lonely, for I like to chat with my classmates about almost everything. My favorite pastime is to play volleyball, to play cards or to surf online. From life at university, I learn how to balance study and entertainment. By the way, I was an actor in our amazing drama club. I have a few glorious memories on stage. That

第六章 地球的演化与形成(习题)

第六章地球的演化与形成 一填空题 1. 节肢动物的三叶虫在(寒武)纪和(奥陶)纪繁盛,到(二叠)纪末期全部绝灭。 2. 早古生代是海生(无脊椎)动物和低等(植物)繁盛的时代。 3. 早古生代是海生无脊椎动物大发展的时期,其中主要类别包括(三叶虫)、(头足类)、(笔石)及(腕足类)。 4. 新生代因(哺乳)动物繁盛而被称为(哺乳)动物的时代 5. 劳亚大陆和冈瓦纳之间的古大洋为(古特提斯)洋。 6. 陆生脊椎动物最早出现在(泥盆)纪 7. 爬行动物最早出现在(石炭)纪 8. 晚古生代海生无脊椎动物以(腕足)类、(珊瑚)类、(有孔虫)和(菊石)最为繁盛。 9. 志留纪的标准化石有(笔石)、(珊瑚)和(腕足)类。 10. 地史上第一次形成广泛陆相沉积的时代是(志留)纪 11. 加里东运动发生在(志留)纪 12. 因(泥盆)纪裸蕨植物特别繁盛而被称为裸蕨植物的时代 13. 三叠纪初期,全球只有一个大陆,称为(联合大陆) 14. 地球上发现的最古老的岩石年龄为( 4200 )Ma 15. 早寒武世形成的地层称为(下)寒武(统)或早寒武世地层 16. 地质年代单位与年代地层单位的对应关系:宙(宇);代(界);纪(系);世(统) 二选择题 1. 裸子植物在()时代最为繁盛 泥盆纪 第四纪 中生代 寒武纪 2. 被子植物在()时代最为繁盛 早古生代 新生代

晚古生代 3. 地球上最原始的生命出现在() 1600Ma 3200Ma 2300Ma 1900Ma 4. 裸蕨植物的特点是() 无根茎叶的分化 根茎叶已完全分化 已有明显的根部,但茎叶尚未分化 只有根和茎,没有真正的叶部 5. 地球上首次出现大规模出现森林的时代为() 白垩纪 石炭纪 新第三纪 泥盆纪 6. 世界最早的成煤期为() 侏罗纪 石炭纪 寒武纪

说明文阅读专项训练110:《中微子,关乎宇宙起源之谜》

中微子,关乎宇宙起源之谜 ①日本“顶级神冈”中微子探测器项目已正式启动,计划于2027年开始收集数据。该项目由日本主导、英国和加拿大等国参与,目的是阐明物质的起源及基本粒子的“大统一理论”,揭开宇宙起源之谜。 ②中微子是宇宙中数量最多的基本粒子之一。基本粒子是已知的最小粒子,它们不能像原子那样被分成更小的粒子,是构造宇宙中一切的基本元素。而中微子又是最轻的物质粒子,迄今还未能测出它的确切质量,但至少比电子还要轻100万倍。它们无处不在,如太阳发光、核反应堆发电、岩石的天然放射性衰变等核物理过程中都会产生,就连我们每个人也会因体内的钾-40衰变而每天发射约4亿个中微子。 ③中微子的最大特点就是几乎不与任何物质反应。不管是人体还是地球,在它看来,都是极为空旷、可以自由穿梭的空间。我们感觉不到它的存在,科学上探测也极为困难。因此,中微子的发现和研究过程,饱含着几代科研人员的心血。 ④1930年,奥地利科学家泡利为了解释原子核衰变中能量似乎不守恒的现象,预言了中微子的存在,认为就是这种“永远找不到的粒子”偷偷带走了能量。经过20多年的寻找,美国科学家科万和莱因斯终于在核反应堆旁探测到中微子,证明了它的存在。莱因斯因此获得了1995年诺贝尔物理学奖。 ⑤1968年,美国科学家戴维斯在地下1500米深的废弃金矿中进行实验,首次探测到了来自太阳的中微子,证实太阳无穷无尽的能量来自氢核聚变。1987年,日本科学家小柴昌俊在第一代神冈实验中,探测到了来自超新星的中微子。他们二人因此都获得了2002年诺贝尔物理学奖。此后,戴维斯进一步提高测量精度,却发现太阳中微子的数量比理论预言的要少得多,被称为“太阳中微子失踪之谜”。此后,小柴昌俊的学生梶田隆章发现,宇宙射线在大气层中产生的中微子也比预期少,称为“大气中微子丢失之谜”。 ⑥中微子为什么比预计的少?1998年,梶田隆章在升级后的第二代神冈实验中发现,大气中微子比预期少,是因为在飞行过程中自发变成了其他种类的中微子,这一现象就是中微子振荡。他也因此获得了2015年诺贝尔物理学奖。 ⑦中微子振荡现象证明了中微子有质量,尽管质量极其小,但会影响宇宙的起源和演化。根据已知的物理规律,在宇宙早期,正反物质应该成对产生,数量是一样的。但在现在的宇宙中,并没有发现大量反物质存在的迹象。为什么宇宙只由正物质构成?反物质到哪里去了?这是宇宙起源必须回答的关键问题。中微子振荡会带来一个意外的结果,即正反粒子的行为可以不一样,很有可能造成反物质消失。因此,全面了解中微子振荡,是破解“反物质消失之谜”的重要一环。 ⑧由于中微子难以探测,解决这些谜团需要巨大的探测器,获取更精确的数据。日本前两代神冈实验坚持自己的优势方向,掌握核心技术,持之以恒地探索,取得了巨大突破。此次启动的第三代实验“顶级神冈”将建造一个26万吨的水探测器,造价约8亿美元。此前,中国的江门中微子实验和美国的深层地下中微子实验也已开始建设。三个实验间既竞争又互补,联合分析能显著提高发现能力。新一代的中微子实验,也许有一天可以揭开宇宙起源的谜题。 11.(3分)①-③段,概括中微子的三个特点。 12.(3分)判断下列句子使用的说明方法,每空只填一项。 (1)但至少比电子还要轻100万倍。()()(2)它们无处不在,如太阳发光、核反应堆发电、岩石的天然放射性衰变等。() 13.(3分)莱因斯、戴维斯和小柴昌俊获得诺贝尔物理学奖的原因分别是什么? 14.(2分)中微子和揭开宇宙起源谜题有何关系?根据文章内容概括提炼。

英语口语课三分钟演讲稿

英语口语课三分钟演讲稿 ladies and gentleen , gd afternn! i? ver glad t stand here and give u a shrt speeh tda tpi is uth i hpe u ill lie it , and fund the iprtane in ur uth s that re herish it first i ant t as u se questins: 1、 d u n hat is uth? 2、h d u aster ur uth? uth uth is nt a tie f life, it is a state f ind it is nt rs hees , red lips and supple nees, it is a atter f the etins : it is the freshness it is the freshness f the deep springs f life uth eans a teperaental predinane f urage ver tiidit f the appetite , fr adventure ver the lve f ease this ften exists in a an f 60 re than a b f 20 nbd grs ld erel b a nuber f ears e gr ld b deserting ur ideals ears rinle the sin , but t give up enthusias rinles the sul rr , fear , self –distrust bs the heart and turns the spirit ba t dust hether 60 f 16 , there is in ever huan being s heart the lure f nders, the unfailing hildlie appetite f hat?s next and the f the gae f living in the enter f ur heart and heart there?s a ireless statin : s lng as it reeives essages f beaut , hpe ,heer, urage and per fr en and fr the infinite, s lng as u are ung hen the aerials are dn , and ur spirit is vered ith sns f niis and the ie f

英语口语自我介绍范文3篇

英语口语自我介绍范文3篇 英语口语自我介绍要如何去准备呢?学生们是不是为它绞尽脑汁呢?下面是小编收集整理的英语口语自我介绍,欢迎阅读借鉴,更多资讯请继续关注自我介绍栏目。 英语口语自我介绍范文1:Hello everyone, my name is Lee. This is really a great honor to have this opportunity, and I believe I can make good performance today. Now I will introduce myself briefly. I am 20 years old,born in Guangdong province, south of China, and I am a senior student at Guangdong **University. My major is English. And I will receive my bachelor degree after my graduation in June. In the past four years, I spent most of my time on study. I passed CET4 and CET6 with a ease and acquired basic theoretical and practical knowledge of Language. Besides, I have attended several Speech competition held in Beijing, which really showed our professional advantages. I have taken a tour to some big factories and companies, through which I got a deep understanding of English for application. Compared to developed countries, unfortunately, although we have made extraordinary progress since 1998, our packaging industry is still underdeveloped, messy and unstable, and the situation of

石墨烯介绍

获奖者2010年10月5日,2010年诺贝尔物理学奖被授予英国曼彻斯特大学的安德烈·海姆和康斯坦丁·诺沃肖洛夫,以表彰他们在石墨烯材料方面的研究。 PPT1安德烈·海姆,1958年10月出生于俄罗斯,拥有荷兰国籍,父母为德国人。1987 年在俄罗斯科学院固体物理学研究院获得博士学位。他于2001年加入曼彻斯特大学,现任物理学 教授和纳米科技中心主任。之前拥有此荣誉头衔的人包括卢瑟福爵士,卢瑟福于1907-1919年在曼 彻斯特大学工作。 他至今发表了超过150篇的文章,其中有发表在自然和科学杂志上的。他获得的奖项包括2007 年的Mott Prize和2008年的Europhysics Prize。2010年成为皇家学会350周年纪念荣誉研究教授。 在2000年他还获得“搞笑诺贝尔奖”——通过磁性克服重力,让一只青蛙悬浮在半空中。10年 后的2010年他获得诺贝尔物理学奖。 2010年医学奖:荷兰的两位科学家发现哮喘症可用过山车治疗。 和平奖:英国研究人员证实诅咒可以减轻疼痛。 PPT2康斯坦丁·诺沃肖洛夫,1974年出生于俄罗斯,具有英国和俄罗斯双重国籍。2004年在荷兰奈梅亨大学获得博士学位。是安德烈·海姆的博士生。 曼彻斯特大学目前任教的诺贝尔奖得主人数增加到4名,获得诺贝尔奖的历史总人数为25位。发现 石墨属于混晶,为片层结构,层内由共价键相连,层间由分子间作用力相连。共价键是比较牢固的,但分子间作用力(范德华力)小得多。因此,石墨的单层是牢固的,而层间作用力很小,极易脱落。 2004年,他们发现了一种简单易行的新途径。他们强行将石墨分离成较小的碎片,从碎片中剥离出较薄的石墨薄片,然后用一种特殊的塑料胶带粘住薄片的两侧,撕开胶带,薄片也随之一分为二。不断重复这一过程,就可以得到越来越薄的石墨薄片,而其中部分样品仅由一层碳原子构成——他们制得了石墨烯。 结构

英语口语自我介绍带翻译

英语口语自我介绍带翻译 本文是关于英语口语自我介绍带翻译,仅供参考,希望对您有所帮助,感谢阅读。 英语口语课上老师喜欢学生用英文来做自我介绍,这不仅能锻炼口语还能相互认识。下面就和大家分享三篇英语口语自我介绍带翻译,欢迎阅读。 1 Everybody is good! My name is han mei, 11 years old this year, WanZaiXian recreation town in the third primary school. You want to know about me? Next, I will introduce myself to you. I, do not look beautiful, oval face, a pair of not quite not small eyes, a kind of short nose, often hang a faint smile, I usually wear uniforms. I like reading a book. Because reading can not only enrich the knowledge, still can quiet heart, in short reading can have benefits. "The book read times since its righteousness, see", this is my motto, learning should be like reading a book as carefully, and read more, want to think more, look more, ability to grasp the full text. "Books are the ladder of the progress of mankind", man without knowledge fish like that without water, knowledge to people is important, today's earnest efforts to get a better life and future of tomorrow, so, each student should study hard. Sometimes, I read a book will also see more fascinating! I study are good moral character is also good, still take a county miyoshi students! I was a teacher in the eyes of a good student, the students have a good example. In the class as a monitor, everybody said I'm honest, study hard, but I the only disappointment is too timid, and rarely speak in class. Look, this is me, a timid quiet girl. I listened, you are willing to make friends with me?

中微子的振荡实验和理论

中微子的振荡实验和理论 华南师范大学物理与电信工程学院物理学勷勤创新班 作者:黄慧敏蔡莹邱小欢麦展风 摘要:,本文主要通过对中微子振荡实验及其理论的阐述,加深对中微子以及中微子振荡的认识,以及阐述对中微子振动实验发展的展望 关键词:中微子振荡 MSN效应质量差 Abstract:This article states the theory and the experiment of neutrino oscillation for illustrating the current situation and expectation of development of the nertrino oscillation’s experiment . Key word:neutrino oscillation .MSN reaction.mess diffirence. 1、引言 大亚湾中微子实验宣布发现了一种新的中微子振荡,并测量到其振荡几率,这一实验结果不仅使我们更深入了解了中微子的基本特性,更为未来进行中微子实验破解“反物质消失之谜”奠定科学基础。 1998年在日本Takayama召开的的世界中微子大会上,日本物理学家宣布他们的超神冈国际合作组发现了大气中微子震荡,成为了物理学界的头号新闻。 粒子物理学经典模型认为,中微子的质量为零,在相互作用中轻子数守恒,中微子不会从一种类型转变成另外一种类型。现在超神冈实验组发现了中微子振荡,这表明了中微子具有质量,中微子可以从μ中微子转变成其他类型的中微子,轻子数也随之不守恒,这推动了物理学的进一步发展。 1930年,为了解释核的β衰变中电子的能力是一个连续谱,泡利引入了中微子这种新型粒子,但人们一直没能从实验中验证中微子的存在。1941年,我国著名物理学家王淦昌先生建议利用原子核的K电子俘获测原子核的反冲能量来证明中微子的存在。历经10年,于1952年此实验获得成功,证明了中微子是一个客观存在的粒子。 中微子,顾名思义,是固有质量极其微小的中性粒子。由于难以探测,我们对中微子的了解非常有限,至今还存在大量未解之谜。中微子有3种类型:电子中微子、μ子中微子、τ子中微子,这三种中微子两两之间转换,可以有三种振荡模式。其中太阳中微子振荡称之为theta12振荡,大气中微子为theta23振荡。

英语口语课三分钟演讲范文大全

英语口语课三分钟演讲范文大全 英语不是自己的母语,要演讲起来,绝对不是一件容易的事,三分钟,用来表达自己的中心意思,会不会够?下面是小编分享的几篇英语口语课三分钟演讲范文,一起来看看吧。 英语口语课三分钟演讲范文篇一 Far and away the most important holiday in China is Spring Festival, also known as the Chinese New Year. To the Chinese people it is as important as Christmas to people in the West. The dates for this annual celebration are determined by the lunar calendar rather than the GREgorian calendar. so the timing of the holiday varies from late January to early February. To the ordinary Chinese, the festival actually begins on the eve of the lunar New Years Day and ends on the fifth day of the first month of the lunar calendar. But the 15th of the first month, which normally is called the Lantern Festival, means the official end of the Spring Festival in many parts of the country.

英语口语课自我介绍_自我介绍

英语口语课自我介绍_自我介绍 英语口语课自我介绍篇1Hello everyone, my name is Lee. This is really a great honor to have this opportunity, and I believe I can make good performance today. Now I will introduce myself briefly. I am 20 years old,born in Guangdong province, south of China, and I am a senior student at Guangdong **University. My major is English. And I will receive my bachelor degree after my graduation in June. In the past four years, I spent most of my time on study. I passed CET4 and CET6 with a ease and acquired basic theoretical and practical knowledge of Language. Besides, I have attended several Speech competition held in Beijing, which really showed our professional advantages. I have taken a tour to some big factories and companies, through which I got a deep understanding of English for application. Compared to developed countries, unfortunately, although we have made extraordinary progress since 1998, our packaging industry is still underdeveloped, messy and unstable, and the situation of employees in the field is awkward. But I have full confidence in its bright future if only our economy can be kept at the growth pace still. I guess you may be interested in why I choose this job. I would like to tell you that this job is one of my lifelong goals. If I can work here,I will work hard. As to my character, I cannot describe it well, but I know I am optimistic and confident. Sometimes I prefer to stay alone, reading and listening to the music, but I am not lonely, for I like to chat with my classmates about almost everything. My favorite pastime is to play volleyball, to play cards or to surf online. From life at university, I learn how to balance study and entertainment. By the way, I was an actor in our amazing drama club. I have a few glorious memories on stage. That is my pride... 英语口语课自我介绍篇2Good morning. I am glad to be here for this interview. First let me introduce myself. My name is , 24. I come from ,the capital of Province. I graduated from the department of University in July ,2001.In the past two years I have been prepareing for the postgraduate examination while I have been teaching in NO. middle School and I was a head-teacher of a class in junior grade two.Now all my hard work has got a result since I have a chance to be interview by you . I am open-minded ,quick in thought and very fond of history.In my spare time,I have broad interests like many other youngers.I like reading books, especially those about Frequently I exchange with other people by making comments in the forum on line.In addition ,during my college years,I was once a Net-bar technician.So, I have a comparative good command of network application.I am able to operate the computer well.I am skillful in searching for information in Internet.I am a football fan for years.Italian team is my favorite.Anyway,I feel great pity for our country’s team. I always believe that one will easily lag behind unless he keeps on learning .Of course, if I am given a chance to study in this famous University,I will stare no effort to master a good command of advance. 英语口语课自我介绍篇3Good morning , ladies and gentlemen It is my great honor to have this opportunity to introduce myself. and I hope I could make a good performance today, eventually become a member of your school. Now let me introduce myself please. I'm a graduate student from **** UNIVERSITY . My name is *** ,**years old. ,

相关文档
最新文档