On the Shallow Decay of Some GRB Afterglows
a r
X
i
v
:a
s t
r o
-
p
h
/
4
2
1
19
v
1
5
F
e b
2
4
On the Shallow Decay of Some GRB Afterglows A.Panaitescu &P.Kumar Department of Astronomy,University of Texas at Austin Abstract.Half of the radio afterglows for which there is a good temporal coverage exhibit after 10days from the burst a decay which is shallower than at optical frequencies,contrary to what is expected within the simplest form of the standard model of relativistic ?reballs or jets.We investigate possible ways to decouple the radio and optical decays.First,the radio and optical emissions are assumed to arise from the same electron population and we allow for either a time-varying slope of the power-law distribution of electron energy or for time-varying microphysical parameters.Then we consider two scenarios where the radio and optical emissions arise in distinct parts of the GRB out?ow,either because the out?ow has an angular structure or because there is a long-lived reverse shock.We ?nd that the only the last scenario is compatible with the observations.The anomalous radio afterglows.The radio emission of all well-observed GRB afterglows decays after about day 10.This is consistent with what is expected in the standard ?reball model for GRB afterglows.In this model,the characteristic synchrotron frequency νi at which electrons with the typical post-shock energy e i =εi m p c 2Γ(Γbeing the ?reball Lorentz factor)radiate is νi ～30 E 0.03 2 εB 10d ?3/2GHz (1)where E is the ?reball’s kinetic energy per solid angle and the parameters εi and εB quantify the fraction of the post-shock energy imparted to electrons 1and to the magnetic ?eld.If the out?ow is collimated,the evolution of νi becomes faster,νi ∝t ?2,after the "jet-break"time when the jet start expanding laterally.Equation (1)indicates that,for reasonable afterglow parameters,the injection fre-
quency ν
i is expected to cross the radio domain around 10days,after which the radio
afterglow should decay as F r ∝t ?αr with αr =(3p ?1)/4for a ?reball interacting with a wind medium,αr =(3p ?3)/4for a ?reball decelerated by a uniform medium,and αr =p for jet spreading laterally.In the standard afterglow model,the optical light-curve decay is expected to be the same,apart from a difference |α
o ?αr |=1/4arising when
the cooling frequency (νc )is below the optical domain.
For ?ve radio afterglows (970508,980329,980703,000418,021004),the radio and optical decay indices are consistent with this basic "prediction"of the ?reball model,but it is not so for the other ?ve well-monitored radio afterglows (991208,991216,000301,000926,010222),which are shown in Figure 1.For these cases,it is natural
time (day)10?5
10?410?310?210?1100101F ν
(
m J
y
)
time (day)10?510?410?310?210?1100101F ν (
m J y
)
time (day)10?510?410?310?210?1
100101time (day)10?510?410?310?210?1100
101time (day)10?510?410?310?2
10?1100
101
time (day)10?5
10?4
10?310?210?1
100101
FIGURE 1.Radio (8GHz),Optical (5×1014Hz),and X-ray (5keV)light-curves for ?ve anomalous GRB afterglows whose radio light-curves decay slower than in the optical and for the afterglow 000418,for which the decays seen in these domains have the same indices,as expected in the simplest version of the standard ?reball/jet afterglow model.Power-law ?ts are indicated for each frequency range,errors are given in parentheses.
to investigate ?rst if the difference between the radio and optical decay indices could be caused by that the injection frequency ν
i remains above the radio domain (of typical
frequency νr ～10GHz)until the last radio measurements 2,usually around 100days
after the burst.According to equation (1),this requires electron and/or magnetic ?eld parameters close to equipartition (εi ,εB >～0.1),particularly if the jet-break time occurs at around 1day,as is the case for the afterglows 991216,000301,000926and 010222(see the break exhibited by their optical light-curves).
For ν
r <ν
i there are three relevant cases which yield a decaying radio emission.If
the GRB ejecta is spherical (or a suf?ciently wide jet),the radio light-curve decays only if the circumburst medium is a wind (r ?2density pro?le)and if ν
r <ν
c <ν
i ,in
which case α
r =2/3,as observed for the
afterglows 991216and 000926.If the GRB ejecta is collimated,a decaying radio light-curve can be obtained either for ν
i <νc or
for νc <ν
i .In the
former case αr =1/3,close to the value observed for the afterglow
010222,while the latter case yields αr =1,as seen in the afterglow 991208.Despite this
nice agreement between the expected and observed radio decay indices forνr<νi,none of the above cases actually work well.The?rst and third case require dense external media(homogeneous or wind-like)to maintainνc<νi until about100days,leading to self-absorbed sources at radio frequencies even at day10,which is inconsistent with the decaying radio light-curves,and to a synchrotron?ux atνi above100mJy at100days, which is1,000times larger than the radio?ux observed at that time.The second case leads to very tenuous external media,which are rather inconsistent with those expected for a massive star GRB progenitor.
Thus we have to investigate departures from the standard afterglow model in its simplest form that could account for the shallow radio decays observed for the above ?ve anomalous afterglows.Since theνr<νi case cannot explain all the properties of the radio afterglow emission,we will consider that the injection frequencyνi is below the radio domain when the radio decay is observed.In fact,the passage ofνi through this domain is the most natural cause for the onset of the radio decay seen at about 10days in the afterglows991208,000301,000926and010222,as well as in other afterglows whose radio and optical decay indices are consistent with the?reball model expectations.
These departures fall in two categories.In the?rst,we assume that the radio and optical emissions arise from the same region of the GRB?reball.If the same electron population gives both the radio and optical afterglows,then different decay indices can be obtained either if the slope p of the electron energy distribution is time-varying or if there is a spectral break between these two domains.In the second category,we assume that the radio and optical emissions arise from different?reball regions,as could be the case with a structured?reball or a long-lived reverse shock.We note that,in the scenarios that we describe below,involving time-varying afterglow parameters,the break seen in the optical light-curve of most afterglows shown in Figure1may arise from a rapid variation of the parameters under investigation and not necessarily from the tight collimation of the GRB out?ow.
Electron distribution with time-varying slope.We consider that,at all times of interest(1-100days after the burst),the electron distribution injected by the forward shock is a power-law of exponent?p that varies in time3.It is evident that,in this case,the radio and optical light-curves cannot both be power-laws in time.Given that optical measurements have smaller uncertainties,we can determine the evolution of the electron index p that yields a power-law optical light-curve and test the consequences of that evolution on the afterglow emission at other frequencies.
It can be shown that,in order to obtainαr<αo,the index p must increase in time, asymptotically approaching the value that the observedαr required if the index p were constant in time.Thus the optical afterglow spectrum should soften in time.For such a behavior of p,the radio light-curve should steepen in time,while the X-ray light-curve should decay faster that in the optical and should?atten in time.In general,these features are not quantitatively consistent with the multiwavelength observations of the
anomalous afterglows:the optical spectrum of991208appears to harden in time while
the decays of the X-ray light-curve of991216(during day1)and of the radio light-
curves of000926and010222(at100days)are much shallower than expected.Only for
000301the radio light-curve and optical spectrum are consistent with the consequences
of an evolving electron distribution index.4
Variable electron and magnetic?eld parameters.As the self-absorption and in-
jection break frequencies must be below the radio domain when the radio light-curves
decay,the only remaining break that could decouple the radio and optical decay indices
must be the cooling frequencyνc.However its evolution must be much faster than that for a constant magnetic parameterεB,to account for the magnitude of the observed αo?αr.Since we want,in fact,to explain not just the differenceαo?αr,but the ob-served values ofαr andαo,we must also allow for the electron energy parameterεi to be time-varying.We shall also consider that the?reball’s kinetic energy per solid angle
E(or the kinetic energy for a jet)is time-varying,either because of radiative losses or an energy injection in the?reball through some less relativistic ejecta which catch-up with the leading edge of the ejecta(which is decelerated by the interaction with the circumburst medium).
Because the quantities pertaining to the?reball dynamics are power-laws in the
observer time t,it is then natural to restrict our attention to time-varyingεi,εB,and E that evolve as power-laws with t:E∝t e,εi∝t i,εB∝t b.Radiative losses yield e≥?3/7 for a?reball interacting with a homogeneous medium,e≥?1/3if the medium is wind-like,and e≥?3/5for a spreading jet and any type of external https://www.sodocs.net/doc/5b7156857.html,ing standard equations for the afterglows spectral characteristics,we can calculate the decay indices for the radio and optical light-curves as functions of the parameters e,i and b and use the observedαr andαo to constraint them.
In this way it can be shown that,if there is no energy injection(e≤0),thenεi must
decrease in time whileεB must increase so fast that the magnetic?eld strength B∝ε1/2
B is constant or increases in time.This rather extreme requirement is somewhat alleviated if the external medium density increases with radius,as such a density pro?le leads to a faster evolution of the cooling frequency.If there is an energy injection,leading to e≥0, then there are solutions with constantεB,however the peak?ux and injection frequency evolutions implied by this scenario are in strong con?ict with those inferred from the radio emission of the afterglow991208.These conclusions apply to both a spherical ?reball and a collimated out?ow.
Structured out?ow.If the out?ow has a non-uniform angular distribution of the ki-netic energy per solid angle E,it is possible that the optical emission arises predomi-nantly from a core of higher E while the radio afterglow is emitted by a surrounding envelope of lower E.This possibility is suggested by the dependence of the injection frequencyνi on E(eq.[1]).For simplicity and maximal effect of the out?ow structure, we consider that both the core and envelope have an uniform distribution of E.In this scenario,the break exhibited by the afterglow optical light-curve is caused by the colli-mation of the core,while the onset of the radio decay is due to the passage through the
radio domain of theνi for the envelope emission.To explain the observedαr andαo,we must allow for different electron indices p in the out?ow core and envelope.
The test that this scenario must pass is that the radio and optical emissions are decou-pled.More speci?cally,the softening emission from the optical core must not overshine in the radio the emission from the envelope and the emission from the envelope must not be brighter in the optical than the faster decaying emission from the core.The?rst condition is equivalent to a lower limit on theνi frequency for the optical core at the time when the optical light-curve break is observed(which is the time when the core edge becomes visible to the observer).With the aid of equation(1),this leads to a lower limit on the injection frequency for the radio envelope at the time when the radio light-curve begins to decay.For the parameters of the radio and optical emission of the?ve anomalous afterglows,the latter lower limit falls invariably above10GHz,contrary to what is implied by the observed onset of the radio decay.The second condition leads to an upper limit on the cooling frequency for the envelope emission,which implies very dense external media and a self-absorbed radio emission,inconsistent with the observed radio decay.
Reverse shock.If there is a continuous in?ow of slower ejecta from the GRB pro-genitor into the leading edge of the GRB?reball,then the emission from the long-lived reverse shock crossing the incoming ejecta could dominate the radio afterglow emission, while the optical afterglow arises as usually from the forward shock.Given that a colli-mated out?ow undergoing lateral spreading and delayed energy injection loses angular uniformity,we restrict our attention to a spherical out?ow,which maintains its isotropy during the injection.
For simplicity,we parameterize the distribution of ejecta mass with Lorentz factor as a power-law,d M i/dΓ∝Γ?(q+1).The?reball energy can also vary in time(e.g. E∝t e),as described for a structured out?ow5.Just as for the scenario involving variable microphysical parameters,one can calculate the radio and optical decay indices as function of the parameters q and e,and then determine these parameters with the aid of observations.We?nd that the anomalous radio afterglows require q>3for a homogeneous medium,q>4for a wind medium,and e<1/3,indicating that the incoming ejecta can carry at most the same energy as the initial out?ow energy.
The reverse-forward shock scenario must also pass the test discussed above for a structured out?ow,leading to a lower limit on the forward shockνi frequency and an upper limit on the reverse shock cooling frequency.Two other constraints can be obtained by requiring that the forward shock yields the?ux normalization seen in the optical and that theνi frequency for the reverse shock crosses the radio domain when the onset of the radio fall-off is seen.These four requirements can be converted into constraints on the fundamental afterglow parameters E,εi,εB,and n(external medium density).For the anomalous afterglows we?nd that reasonable values of these parameters satisfy the observational requirements.
Note:More details on the features of the scenarios described here and the calculations behind the results presented can be found at astro-ph/0308273.
on the contrary的解析
On the contrary Onthecontrary, I have not yet begun. 正好相反，我还没有开始。 https://www.sodocs.net/doc/5b7156857.html, Onthecontrary, the instructions have been damaged. 反之，则说明已经损坏。 https://www.sodocs.net/doc/5b7156857.html, Onthecontrary, I understand all too well. 恰恰相反，我很清楚 https://www.sodocs.net/doc/5b7156857.html, Onthecontrary, I think this is good. ⑴我反而觉得这是好事。 https://www.sodocs.net/doc/5b7156857.html, Onthecontrary, I have tons of things to do 正相反，我有一大堆事要做 Provided by jukuu Is likely onthecontrary I in works for you 反倒像是我在为你们工作 https://www.sodocs.net/doc/5b7156857.html, Onthecontrary, or to buy the first good. 反之还是先买的好。 https://www.sodocs.net/doc/5b7156857.html, Onthecontrary, it is typically american. 相反，这正是典型的美国风格。 222.35.143.196 Onthecontrary, very exciting.
恰恰相反，非常刺激。 https://www.sodocs.net/doc/5b7156857.html, But onthecontrary, lazy. 却恰恰相反，懒洋洋的。 https://www.sodocs.net/doc/5b7156857.html, Onthecontrary, I hate it! 恰恰相反，我不喜欢！ https://www.sodocs.net/doc/5b7156857.html, Onthecontrary, the club gathers every month. 相反，俱乐部每个月都聚会。 https://www.sodocs.net/doc/5b7156857.html, Onthecontrary, I'm going to work harder. 我反而将更努力工作。 https://www.sodocs.net/doc/5b7156857.html, Onthecontrary, his demeanor is easy and nonchalant. 相反，他的举止轻松而无动于衷。 https://www.sodocs.net/doc/5b7156857.html, Too much nutrition onthecontrary can not be absorbed through skin. 太过营养了反而皮肤吸收不了. https://www.sodocs.net/doc/5b7156857.html, Onthecontrary, I would wish for it no other way. 正相反，我正希望这样 Provided by jukuu Onthecontrary most likely pathological. 反之很有可能是病理性的。 https://www.sodocs.net/doc/5b7156857.html, Onthecontrary, it will appear clumsy. 反之，就会显得粗笨。 https://www.sodocs.net/doc/5b7156857.html,
英语造句
一般过去式 时间状语：yesterday just now (刚刚) the day before three days ag0 a week ago in 1880 last month last year 1. I was in the classroom yesterday. I was not in the classroom yesterday. Were you in the classroom yesterday. 2. They went to see the film the day before. Did they go to see the film the day before. They did go to see the film the day before. 3. The man beat his wife yesterday. The man didn’t beat his wife yesterday. 4. I was a high student three years ago. 5. She became a teacher in 2009. 6. They began to study english a week ago 7. My mother brought a book from Canada last year. 8.My parents build a house to me four years ago . 9.He was husband ago. She was a cooker last mouth. My father was in the Xinjiang half a year ago. 10.My grandfather was a famer six years ago. 11.He burned in 1991
学生造句--Unit 1
●I wonder if it’s because I have been at school for so long that I’ve grown so crazy about going home. ●It is because she wasn’t well that she fell far behind her classmates this semester. ●I can well remember that there was a time when I took it for granted that friends should do everything for me. ●In order to make a difference to society, they spent almost all of their spare time in raising money for the charity. ●It’s no pleasure eating at school any longer because the food is not so tasty as that at home. ●He happened to be hit by a new idea when he was walking along the riverbank. ●I wonder if I can cope with stressful situations in life independently. ●It is because I take things for granted that I make so many mistakes. ●The treasure is so rare that a growing number of people are looking for it. ●He picks on the weak mn in order that we may pay attention to him. ●It’s no pleasure being disturbed whena I settle down to my work. ●I can well remember that when I was a child, I always made mistakes on purpose for fun. ●It’s no pleasure accompany her hanging out on the street on such a rainy day. ●I can well remember that there was a time when I threw my whole self into study in order to live up to my parents’ expectation and enter my dream university. ●I can well remember that she stuck with me all the time and helped me regain my confidence during my tough time five years ago. ●It is because he makes it a priority to study that he always gets good grades. ●I wonder if we should abandon this idea because there is no point in doing so. ●I wonder if it was because I ate ice-cream that I had an upset student this morning. ●It is because she refused to die that she became incredibly successful. ●She is so considerate that many of us turn to her for comfort. ●I can well remember that once I underestimated the power of words and hurt my friend. ●He works extremely hard in order to live up to his expectations. ●I happened to see a butterfly settle on the beautiful flower. ●It’s no pleasure making fun of others. ●It was the first time in the new semester that I had burned the midnight oil to study. ●It’s no pleasure taking everything into account when you long to have the relaxing life. ●I wonder if it was because he abandoned himself to despair that he was killed in a car accident when he was driving. ●Jack is always picking on younger children in order to show off his power. ●It is because he always burns the midnight oil that he oversleeps sometimes. ●I happened to find some pictures to do with my grandfather when I was going through the drawer. ●It was because I didn’t dare look at the failure face to face that I failed again. ●I tell my friend that failure is not scary in order that she can rebound from failure. ●I throw my whole self to study in order to pass the final exam. ●It was the first time that I had made a speech in public and enjoyed the thunder of applause. ●Alice happened to be on the street when a UFO landed right in front of her. ●It was the first time that I had kept myself open and talked sincerely with my parents. ●It was a beautiful sunny day. The weather was so comfortable that I settled myself into the
英语句子结构和造句
高中英语~词性~句子成分~语法构成 第一章节：英语句子中的词性 1.名词：n. 名词是指事物的名称，在句子中主要作主语.宾语.表语.同位语。 2.形容词;adj. 形容词是指对名词进行修饰~限定~描述~的成份，主要作定语.表语.。形容词在汉语中是（的）.其标志是: ous. Al .ful .ive。. 3.动词：vt. 动词是指主语发出的一个动作，一般用来作谓语。 4.副词：adv. 副词是指表示动作发生的地点. 时间. 条件. 方式. 原因. 目的. 结果.伴随让步. 一般用来修饰动词. 形容词。副词在汉语中是（地）.其标志是：ly。 5.代词：pron. 代词是指用来代替名词的词，名词所能担任的作用，代词也同样.代词主要用来作主语. 宾语. 表语. 同位语。 6.介词：prep.介词是指表示动词和名次关系的词，例如：in on at of about with for to。其特征：
介词后的动词要用—ing形式。介词加代词时，代词要用宾格。例如：give up her（him）这种形式是正确的，而give up she（he）这种形式是错误的。 7.冠词：冠词是指修饰名词，表名词泛指或特指。冠词有a an the 。 8.叹词：叹词表示一种语气。例如：OH. Ya 等 9.连词：连词是指连接两个并列的成分，这两个并列的成分可以是两个词也可以是两个句子。例如：and but or so 。 10.数词：数词是指表示数量关系词，一般分为基数词和序数词 第二章节：英语句子成分 主语：动作的发出者，一般放在动词前或句首。由名词. 代词. 数词. 不定时. 动名词. 或从句充当。 谓语：指主语发出来的动作，只能由动词充当，一般紧跟在主语后面。 宾语：指动作的承受着，一般由代词. 名词. 数词. 不定时. 动名词. 或从句充当. 介词后面的成分也叫介词宾语。 定语：只对名词起限定修饰的成分，一般由形容
六级单词解析造句记忆MNO
M A: Has the case been closed yet? B: No, the magistrate still needs to decide the outcome. magistrate n.地方行政官，地方法官，治安官 A: I am unable to read the small print in the book. B: It seems you need to magnify it. magnify vt.１．放大，扩大；２．夸大，夸张 A: That was a terrible storm. B: Indeed, but it is too early to determine the magnitude of the damage. magnitude n.１．重要性，重大；２．巨大，广大 A: A young fair maiden like you shouldn’t be single. B: That is because I am a young fair independent maiden. maiden n.少女，年轻姑娘，未婚女子 a.首次的，初次的 A: You look majestic sitting on that high chair. B: Yes, I am pretending to be the king! majestic a.雄伟的，壮丽的，庄严的，高贵的 A: Please cook me dinner now. B: Yes, your majesty, I’m at your service. majesty n.１．［Ｍ－］陛下（对帝王，王后的尊称）；２．雄伟，壮丽，庄严 A: Doctor, I traveled to Africa and I think I caught malaria. B: Did you take any medicine as a precaution? malaria n.疟疾 A: I hate you! B: Why are you so full of malice? malice n.恶意，怨恨 A: I’m afraid that the test results have come back and your lump is malignant. B: That means it’s serious, doesn’t it, doctor? malignant a.１．恶性的，致命的；２．恶意的，恶毒的 A: I’m going shopping in the mall this afternoon, want to join me? B: No, thanks, I have plans already. mall n.（由许多商店组成的）购物中心 A: That child looks very unhealthy. B: Yes, he does not have enough to eat. He is suffering from malnutrition.
base on的例句
意见应以事实为根据. 3 来自辞典例句 192. The bombers swooped ( down ) onthe air base. 轰炸机 突袭 空军基地. 来自辞典例句 193. He mounted their engines on a rubber base. 他把他们的发动机装在一个橡胶垫座上. 14 来自辞典例句 194. The column stands on a narrow base. 柱子竖立在狭窄的地基上. 14 来自辞典例句 195. When one stretched it, it looked like grey flakes on the carvas base. 你要是把它摊直, 看上去就象好一些灰色的粉片落在帆布底子上. 18 来自辞典例句 196. Economic growth and human well - being depend on the natural resource base that supports all living systems. 经济增长和人类的福利依赖于支持所有生命系统的自然资源. 12 1 来自辞典例句 197. The base was just a smudge onthe untouched hundred - mile coast of Manila Bay. 那基地只是马尼拉湾一百英里长安然无恙的海岸线上一个硝烟滚滚的污点. 6 来自辞典例句 198. You can't base an operation on the presumption that miracles are going to happen. 你不能把行动计划建筑在可能出现奇迹的假想基础上.
英语造句大全
英语造句大全English sentence 在句子中，更好的记忆单词！ 1、(1)、able adj. 能 句子：We are able to live under the sea in the future. (2)、ability n. 能力 句子：Most school care for children of different abilities. (3)、enable v. 使。。。能句子：This pass enables me to travel half-price on trains. 2、(1)、accurate adj. 精确的句子：We must have the accurate calculation. (2)、accurately adv. 精确地 句子：His calculation is accurately. 3、(1)、act v. 扮演 句子：He act the interesting character. （2）、actor n. 演员 句子：He was a famous actor. (3)、actress n. 女演员 句子：She was a famous actress. (4)、active adj. 积极的 句子：He is an active boy. 4、add v. 加 句子：He adds a little sugar in the milk. 5、advantage n. 优势 句子：His advantage is fight. 6、age 年龄n. 句子：His age is 15. 7、amusing 娱人的adj. 句子：This story is amusing. 8、angry 生气的adj. 句子：He is angry. 9、America 美国n.
(完整版)主谓造句
主语+谓语 1. 理解主谓结构 1) The students arrived. The students arrived at the park. 2) They are listening. They are listening to the music. 3) The disaster happened. 2．体会状语的位置 1) Tom always works hard. 2) Sometimes I go to the park at weekends.. 3) The girl cries very often. 4) We seldom come here. The disaster happened to the poor family. 3. 多个状语的排列次序 1) He works. 2) He works hard. 3) He always works hard. 4) He always works hard in the company. 5) He always works hard in the company recently. 6) He always works hard in the company recently because he wants to get promoted. 4. 写作常用不及物动词 1. ache My head aches. I’m aching all over. 2. agree agree with sb. about sth. agree to do sth. 3. apologize to sb. for sth. 4. appear (at the meeting, on the screen) 5. arrive at / in 6. belong to 7. chat with sb. about sth. 8. come (to …) 9. cry 10. dance 11. depend on /upon 12. die 13. fall 14. go to … 15. graduate from 16. … happen 17. laugh 18. listen to... 19. live 20. rise 21. sit 22. smile 23. swim 24. stay (at home / in a hotel) 25. work 26. wait for 汉译英： 1.昨天我去了电影院。 2.我能用英语跟外国人自由交谈。 3.晚上7点我们到达了机场。 4.暑假就要到了。 5.现在很多老人独自居住。 6.老师同意了。 7.刚才发生了一场车祸。 8.课上我们应该认真听讲。9. 我们的态度很重要。 10. 能否成功取决于你的态度。 11. 能取得多大进步取决于你付出多少努力。 12. 这个木桶能盛多少水取决于最短的一块板子的长度。
初中英语造句
【it's time to和it's time for】 ——————这其实是一个句型,只不过后面要跟不同的东西. ——————It's time to跟的是不定式（to do）.也就是说,要跟一个动词,意思是“到做某事的时候了”.如： It's time to go home. It's time to tell him the truth. ——————It's time for 跟的是名词.也就是说,不能跟动词.如： It's time for lunch.(没必要说It's time to have lunch) It's time for class.(没必要说It's time to begin the class.) They can't wait to see you Please ask liming to study tonight. Please ask liming not to play computer games tonight. Don’t make/let me to smoke I can hear/see you dance at the stage You had better go to bed early. You had better not watch tv It’s better to go to bed early It’s best to run in the morning I am enjoy running with music. With 表伴随听音乐 I already finish studying You should keep working. You should keep on studying English Keep calm and carry on 保持冷静继续前行二战开始前英国皇家政府制造的海报名字 I have to go on studying I feel like I am flying I have to stop playing computer games and stop to go home now I forget/remember to finish my homework. I forget/remember cleaning the classroom We keep/percent/stop him from eating more chips I prefer orange to apple I prefer to walk rather than run I used to sing when I was young What’s wrong with you There have nothing to do with you I am so busy studying You are too young to na?ve I am so tired that I have to go to bed early
The Kite Runner-美句摘抄及造句
《The Kite Runner》追风筝的人--------------------------------美句摘抄 1.I can still see Hassan up on that tree, sunlight flickering through the leaves on his almost perfectly round face, a face like a Chinese doll chiseled from hardwood: his flat, broad nose and slanting, narrow eyes like bamboo leaves, eyes that looked, depending on the light, gold, green even sapphire 翻译：我依然能记得哈桑坐在树上的样子，阳光穿过叶子，照着他那浑圆的脸庞。他的脸很像木头刻成的中国娃娃，鼻子大而扁平，双眼眯斜如同竹叶，在不同光线下会显现出金色、绿色，甚至是宝石蓝。 E.g.: A shadow of disquiet flickering over his face. 2.Never told that the mirror, like shooting walnuts at the neighbor's dog, was always my idea. 翻译：从来不提镜子、用胡桃射狗其实都是我的鬼主意。E.g.:His secret died with him, for he never told anyone. 3.We would sit across from each other on a pair of high
翻译加造句
一、翻译 1. The idea of consciously seeking out a special title was new to me., but not without appeal. 让我自己挑选自己最喜欢的书籍这个有意思的想法真的对我具有吸引力。 2.I was plunged into the aching tragedy of the Holocaust, the extraordinary clash of good, represented by the one decent man, and evil. 我陷入到大屠杀悲剧的痛苦之中，一个体面的人所代表的善与恶的猛烈冲击之中。 3.I was astonished by the the great power a novel could contain. I lacked the vocabulary to translate my feelings into words. 我被这部小说所包含的巨大能量感到震惊。我无法用语言来表达我的感情（心情）。 4，make sth. long to short长话短说 5.I learned that summer that reading was not the innocent(简单的) pastime(消遣) I have assumed it to be., not a breezy, instantly forgettable escape in the hammock(吊床)，( though I’ ve enjoyed many of those too ). I discovered that a book, if it arrives at the right moment, in the proper season, will change the course of all that follows. 那年夏天，我懂得了读书不是我认为的简单的娱乐消遣，也不只是躺在吊床上，一阵风吹过就忘记的消遣。我发现如果在适宜的时间、合适的季节读一本书的话，他将能改变一个人以后的人生道路。 二、词组造句 1. on purpose 特意，故意 This is especially true here, and it was ~. (这一点在这里尤其准确，并且他是故意的) 2.think up 虚构，编造，想出 She has thought up a good idea. 她想出了一个好的主意。 His story was thought up. 他的故事是编出来的。 3. in the meantime 与此同时 助记：in advance 事前in the meantime 与此同时in place 适当地... In the meantime, what can you do? 在这期间您能做什么呢？ In the meantime, we may not know how it works, but we know that it works. 在此期间，我们不知道它是如何工作的，但我们知道，它的确在发挥作用。 4.as though 好像，仿佛 It sounds as though you enjoyed Great wall. 这听起来好像你喜欢长城。 5. plunge into 使陷入 He plunged the room into darkness by switching off the light. 他把灯一关，房
改写句子练习2标准答案
The effective sentences:(improve the sentences!) 1.She hopes to spend this holiday either in Shanghai or in Suzhou. 2.Showing/to show sincerity and to keep/keeping promises are the basic requirements of a real friend. 3.I want to know the space of this house and when it was built. I want to know how big this house is and when it was built. I want to know the space of this house and the building time of the house. 4.In the past ten years,Mr.Smith has been a waiter,a tour guide,and taught English. In the past ten years,Mr.Smith has been a waiter,a tour guide,and an English teacher. 5.They are sweeping the floor wearing masks. They are sweeping the floor by wearing masks. wearing masks,They are sweeping the floor. 6.the drivers are told to drive carefully on the radio. the drivers are told on the radio to drive carefully 7.I almost spent two hours on this exercises. I spent almost two hours on this exercises. 8.Checking carefully,a serious mistake was found in the design. Checking carefully,I found a serious mistake in the design.
用以下短语造句
M1 U1 一. 把下列短语填入每个句子的空白处（注意所填短语的形式变化）： add up (to) be concerned about go through set down a series of on purpose in order to according to get along with fall in love (with) join in have got to hide away face to face 1 We’ve chatted online for some time but we have never met ___________. 2 It is nearly 11 o’clock yet he is not back. His mother ____________ him. 3 The Lius ___________ hard times before liberation. 4 ____________ get a good mark I worked very hard before the exam. 5 I think the window was broken ___________ by someone. 6 You should ___________ the language points on the blackboard. They are useful. 7 They met at Tom’s party and later on ____________ with each other. 8 You can find ____________ English reading materials in the school library. 9 I am easy to be with and _____________my classmates pretty well. 10 They __________ in a small village so that they might not be found. 11 Which of the following statements is not right ____________ the above passage? 12 It’s getting dark. I ___________ be off now. 13 More than 1,000 workers ___________ the general strike last week. 14 All her earnings _____________ about 3,000 yuan per month. 二.用以下短语造句： 1.go through 2. no longer/ not… any longer 3. on purpose 4. calm… down 5. happen to 6. set down 7. wonder if 三. 翻译： 1.曾经有段时间，我对学习丧失了兴趣。（there was a time when…） 2. 这是我第一次和她交流。（It is/was the first time that …注意时态） 3.他昨天公园里遇到的是他的一个老朋友。（强调句） 4. 他是在知道真相之后才意识到错怪女儿了。（强调句） M 1 U 2 一. 把下列短语填入每个句子的空白处（注意所填短语的形式变化）： play a …role (in) because of come up such as even if play a …part (in) 1 Dujiangyan(都江堰) is still ___________in irrigation(灌溉) today. 2 That question ___________ at yesterday’s meeting. 3 Karl Marx could speak a few foreign languages, _________Russian and English. 4 You must ask for leave first __________ you have something very important. 5 The media _________ major ________ in influencing people’s opinion s. 6 _________ years of hard work she looked like a woman in her fifties. 二.用以下短语造句： 1.make (good/full) use of 2. play a(n) important role in 3. even if 4. believe it or not 5. such as 6. because of
英语造句
English sentence 1、(1)、able adj. 能 句子：We are able to live under the sea in the future. (2)、ability n. 能力 句子：Most school care for children of different abilities. (3)、enable v. 使。。。能 句子：This pass enables me to travel half-price on trains. 2、(1)、accurate adj. 精确的 句子：We must have the accurate calculation. (2)、accurately adv. 精确地 句子：His calculation is accurately. 3、(1)、act v. 扮演 句子：He act the interesting character.（2）、actor n. 演员 句子：He was a famous actor. (3)、actress n. 女演员 句子：She was a famous actress. (4)、active adj. 积极的 句子：He is an active boy. 4、add v. 加 句子：He adds a little sugar in the milk. 5、advantage n. 优势 句子：His advantage is fight. 6、age 年龄n. 句子：His age is 15. 7、amusing 娱人的adj. 句子：This story is amusing. 8、angry 生气的adj. 句子：He is angry. 9、America 美国n. 句子：He is in America. 10、appear 出现v. He appears in this place. 11. artist 艺术家n. He is an artist. 12. attract 吸引 He attracts the dog. 13. Australia 澳大利亚 He is in Australia. 14.base 基地 She is in the base now. 15.basket 篮子 His basket is nice. 16.beautiful 美丽的 She is very beautiful. 17.begin 开始 He begins writing. 18.black 黑色的 He is black. 19.bright 明亮的 His eyes are bright. 20.good 好的 He is good at basketball. 21.British 英国人 He is British. 22.building 建造物 The building is highest in this city 23.busy 忙的 He is busy now. 24.calculate 计算 He calculates this test well. 25.Canada 加拿大 He borns in Canada. 26.care 照顾 He cared she yesterday. 27.certain 无疑的 They are certain to succeed. 28.change 改变 He changes the system. 29.chemical 化学药品