The discovery of X-ray emission from the protostellar jet L1551 IRS5 (HH 154)

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近代物理学史(英文版)ppt课件

近代物理学史
The Modern History of Physics
土木15-8班王康杨程
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目录 Contents
I.经典物理学 II.现代物理学革命的序幕 III.相对论 IV.量子力学 V.原子结构理论的发展
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一、经典物理学/Classical Physics
Galileo and Newton, who founded in the 17th century classical physics. After the expansion of the various basic sectors in nineteenth Century to eighteenth Century to get a comprehensive, systematic and rapid development reached its glorious peak 由伽利略(1564—1642)和牛顿(1642—1727)等人于17世纪创立的经典物理学。经过18世纪在各个基础部门的拓展到19世纪得到了全面、系统和迅速的发展达到了它辉煌的顶峰。
• 本世纪20年代创立的量子力学理论为描述微观物体的行为提供了一个全新的框架，改变了我们最基本的测量原理，并为了解原子、分子和凝聚态物质的结构铺平了道路。因而导致了诸如半导体、光通讯等新兴技术的崛起，并为研制奇异材料和激光器件开辟了道路
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经典力学/Classical Mechanics
1. In l687 published "the mathematical principle of natural philosophy," Newton put forward three basic principle of dynamics and the law of universal gravitation.

scanning exercises

Reading skills for academic study: Scanning forspecific information.Exercise 1Read the following text quickly and fill in the table. What do the numbers given in the table refer to?Spoon-fed feel lost at the cutting edgeBefore arriving at university students will have been powerfully influenced by their school’s approach to learning particular subjects. Yet this is only rarely taken into account by teachers in higher education, according to new research carried out at Nottingham University, which could explain why so many students experience problems making the transition.Historian Alan Booth says there is a growing feeling on both sides of the Atlantic that the shift from school to university-style learning could be vastly improved. But little consensus exists about who or what is at fault when the students cannot cope. “School teachers commonly blame the poor quality of university teaching, citing factors such as large first-year lectures, the widespread use of inexperienced postgraduate tutors and the general lack of concern for students in an environment where research is dominant in career progression,” Dr Booth said.Many university tutors on the other hand claim that the school system is failing to prepare students for what will be expected of them at university. A-level history in particular is seen to be teacher-dominated, creating a passive dependency culture.But while both sides are bent on attacking each other, little is heard during such exchanges from the students themselves, according to Dr Booth, who has devised a questionnaire to test the views of more than 200 first-year history students at Nottingham over a three-year period. The students were asked about their experience of how history is taught at the outset of their degree programme. It quickly became clear that teaching methods in school were pretty staid.About 30 per cent of respondents claimed to have made significant use of primary sources (few felt very confident in handling them) and this had mostly been in connection with project work. Only 16 per cent had used video/audio; 2 per cent had experienced field trips and less than 1 per cent had engaged in role-play.Dr Booth found students and teachers were frequently restricted by the assessment style which remains dominated by exams. These put obstacles in the way of more adventurous teaching and active learning, he said. Of the students in the survey just 13 per cent felt their A-level course had prepared them very well for work at university. Three-quarters felt it had prepared them fairly well.One typical comment sums up the contrasting approach: “At A-level we tended to be spoon-fed with dictated notes and if we were told to do any background reading (which was rare) we were told exactly which pages to read out of the book”.To test this further the students were asked how well they were prepared in specific skills central to degree level history study. The answers reveal that the students felt most confident at taking notes from lectures and organising their notes. They were least able to give an oral presentation and there was no great confidence in contributing to seminars, knowing how much to read, using primary sources and searching for texts. Even reading and taking notes from a book were often problematic. Just 6 per cent of the sample said they felt competent at writing essays, the staple A level assessment activity.The personal influence of the teacher was paramount. In fact individual teachers were the cent re of students’ learning at A level with some 86 per cent of respondents reporting that their teachers had been more influential in their development as historians than the students’ own reading and thinking.The ideal teacher turned out to be someone who was enthusiastic about the subject; a good clear communicator who encouraged discussion. The ideal teacher was able to develop students involvement and independence. He or she was approachable and willing to help. The bad teacher, according to the survey, dictates notes and allows no room for discussion. He or she makes students learn strings of facts; appears uninterested in the subject and fails to listen to other points of view.No matter how poor the students judged their preparedness for degree-level study, however, there was a fairly widespread optimism that the experiencewould change them significantly, particularly in terms of their open mindedness and ability to cope with people.But it was clear, Dr Booth said, that the importance attached by many departments to third-year teaching could be misplaced. “Very often tutors regard the third year as the crucial time, allowing postgraduates to do a lot of the earlier teaching. But I am coming to the conclusion that the first year at university is the critical point of intervention”.Alison Utley, Times Higher Education Supplement. February 6th, 1998.Reading skills for academic study: Scanning forspecific information.Exercise 1 - AnswersRead the following text quickly and fill in the table. What do the numbers given in the table refer to?Reading skills for academic study: Scanning forspecific information.Exercise 2Read the following text quickly and answer the questions.1. W hen were X-rays discovered?2. W ho discovered them?3. W hat are the four characteristics of X-rays?The Discovery of X-raysExcept for a brief description of the Compton effect, and a few other remarks, we have postponed the discussion of X-rays until the present chapter because it is particularly convenient to treat X-ray spectra after treating optical spectra. Although this ordering may have given the reader a distorted impression of the historical importance of X-rays, this impression will be corrected shortly as we describe the crucial role played by X-rays in the development of modern physics.X-rays were discovered in 1895 by Roentgen while studying the phenomena of gaseous discharge. Using a cathode ray tube with a high voltage of several tens of kilovolts, he noticed that salts of barium would fluoresce when brought near the tube, although nothing visible was emitted by the tube. This effect persisted when the tube was wrapped with a layer of black cardboard. Roentgen soon established that the agency responsible for the fluorescence originated at the point at which the stream of energetic electrons struck the glass wall of the tube. Because of its unknown nature, he gave this agency the name X-rays. He found that X-rays could manifest themselves by darkening wrapped photographic plates, discharging charged electroscopes, as well as by causing fluorescence in a number of different substances. He also found that X-rays can penetrate considerable thicknesses of materials of low atomic number, whereas substances of high atomic number are relatively opaque. Roentgen took thefirst steps in identifying the nature of X-rays by using a system of slits to show that (1) they travel in straight lines, and that (2) they are uncharged, because they are not deflected by electric or magnetic fields.The discovery of X-rays aroused the interest of all physicists, and many joined in the investigation of their properties. In 1899 Haga and Wind performed a single slit diffraction experiment with X-rays which showed that (3) X-rays are a wave motion phenomenon, and, from the size of the diffraction pattern, their wavelength could be estimated to be 10-8 cm. In 1906 Barkla proved that (4) the waves are transverse by showing that they can be polarized by scattering from many materials.There is, of course, no longer anything unknown about the nature of X-rays. They are electromagnetic radiation of exactly the same nature as visible light, except that their wavelength is several orders of magnitude shorter. This conclusion follows from comparing properties 1 through 4 with the similarproperties of visible light, but it was actually postulated by Thomson several years before all these properties were known. Thomson argued that X-rays are electromagnetic radiation because such radiation would be expected to be emitted from the point at which the electrons strike the wall of a cathode ray tube. At this point, the electrons suffer very violent accelerations in coming to a stop and, according to classical electromagnetic theory, all accelerated charged particles emit electromagnetic radiations. We shall see later that this explanation of the production of X-rays is at least partially correct.In common with other electromagnetic radiations, X-rays exhibit particle-like aspects as well as wave-like aspects. The reader will recall that the Compton effect, which is one of the most convincing demonstrations of the existence of quanta, was originally observed with electromagnetic radiation in the X-ray region of wavelengths.Reading skills for academic study: Scanning forspecific information.Exercise 2 - AnswersRead the following text quickly and answer the questions.1. W hen were X-rays discovered?2. W ho discovered them?3. W hat are the four characteristics of X-rays?1. 18952. R oentgen3. 1. they travel in straight lines2. they are uncharged3. they are a wave motion phenomenon4. the waves are transverse。

中科院研究生院《固体物理》课程课件合集.pdf

X射线衍射
X射线衍射
X射线主要与电子云相互作用只考虑原子对X射线的弹性反射
晶面反射
相长干涉需要光程相等
bc ad dac bca
Bragg 把晶体对 X光的衍射当作由原子平面（晶面）的镜面反射，在满足镜面反射的衍射方向上，一个晶面内所有原子的散射波位相相同、相互叠加，形成相长干涉
晶体结构的探测
虽然点群和空间群理论以及晶格理论都是19世纪提出的，但直到1912年Laue发现了晶体X射线衍射现象之后才得以从实验上观测到晶体结构并证实了上述理论。
普通光学显微镜受分辨率的限制，无法观测原子排列，使用X光源，至今又没有可以使X光聚焦的透镜，所以只能依靠衍射现象来间接观测晶体中的原子排列。
这就是X射线衍射的劳厄条件；
可以证明劳厄条件和布拉格条件等价。
劳厄条件
k
k
G
h
k k Gh
k k
k
Gh
k
Ewald球
k k Gh
劳厄法
晶体取向固定，采用波长在 min 和max 之间的连续波长的X射线；
劳厄法
晶体取向固定，采用波长在 min 和max 之间的连续波长的X射线；
1.2
(nm )
eV 12
波长与晶格常数可比时，如波长 0.1nm 对应的能量 150 eV 。因此适合于晶体结构研究的是20~250eV的低能电子束。
电子带电，与原子相互作用强，穿透深度约几个原子层间距量级，因此低能电子衍射(Low Energy Electron Diffraction, LEED)主要用于晶体表面结构研究。
T (Rn ) (r ) (r Rn )
电子密度具有平移对称性

洛阳市九年级英语全册Unit12Lifeisfulloftheunexpected笔记重点大全

洛阳市九年级英语全册Unit12Lifeisfulloftheunexpected笔记重点大全单选题1、Steven told me that he ________ writing the report a week before. A．finishB．finishesC．finishingD．had finished答案：D句意：Steven告诉我他一周前就写完了报告。

考查过去完成时。

finish“完成”，根据“a week before”可知，从句时态用现在完成时，由宾语从句时态遵循“主过从过”原则可知，从句应该用过去的某种时态，所以空缺处应该用过去完成时，构成：主语+had+动词过去分词，故选D。

2、—The old man ________ all his money to the children in poor areas.—How kind he is!A．helped outB．gave awayC．sold outD．kept away答案：B句意：——那个老人把他所有的钱都捐给了贫困地区的孩子们。

——他多么善良啊！考查动词短语。

help out帮助脱困；give away赠送，捐赠；sell out卖光；keep away远离。

根据“all his money to the children in poor areas”可知，这位老人把钱都捐给了贫困地区的孩子们。

故选B。

3、The little girl set the fish free and watched it until it________in the river. A．showedB．flewC．disappearedD．died答案：C句意：小女孩把鱼放了出来，看着它消失在河里。

考查动词辨析。

showed展示；flew飞行；disappeared消失；died死亡。

根据“The little girl set the fish free.”小女孩把鱼放了出来。

怀念鲁润宝同志纪念鲁润宝先生逝世一周年-CiteSeerX

怀念鲁润宝同志在鲁润宝同志辞世2周年之际，鲁润宝先生的夫人（阎永勤）和他的孩子（鲁东宇）编纂出版了“鲁润宝文集”。

陈能宽先生还特地题写了书名。

谨将此书序言以及其中7篇英文文献转载于此，以誌纪念。

（李兴中，2010-10-25）纪念鲁润宝先生逝世一周年（代序言）鲁润宝先生，我的老朋友，你与世长辞已近一年了，你那微胖憨厚的形象一直留在我的脑海之中，你那刻苦钻研的精神永远使我钦佩。

回顾1990年前后，由于“冷聚变”科学问题的研讨，彼此相遇，结交为朋友，随着岁月的增长，我们由相识到相知，建立了深厚的友谊。

你从核物理、理论物理转向“冷聚变”研究，一开始就遇到很多困难，自然科学基金的申请又遭遇挫折，心里着急，也有怨气，但你那执着的劲头却令人感动。

我作为科技管理人员只能在一旁相劝。

因为“冷聚变”项目实属非共识有争议的项目，虽然蕴藏着大的创新，但从非共识到共识需要长期的争论。

而学术问题只能靠学术研究来判断，不能靠行政干预来解决。

因此我建议你最好继续做工作，争取在学术会议和学术刊物上多发表论文，让学术界了解和评议。

你努力工作，陆续发表了一些文章，尤其是1994年，提出了一种新的物理过程“电子——离子束缚态及其引发的核过程”，即“束缚态理论模型”的假说，并概述了这一新物理过程的特点，这是十分值得庆贺的进展。

不管这模型会引来什么样的争议，这种大胆创新的精神值得敬佩。

经过鍥而不舍的努力，查阅了各种文献资料，力图从不同领域中寻找能够支持这个假说的证据。

当你获得某点可能的佐证时，都兴奋地告诉我，我分享着你来之不易的喜悦。

后来，工作局面逐步打开，得到了一定的支持，工作条件获得改善，退休后你继续拼搏，单位也给予少量的但很珍贵的经费，保证了参加学术会议和查阅资料的费用。

你的夫人包揽了一切家务，让你能专心致志，集中精力于工作之中。

更多的刊物接受了你的稿件，在一些学术研讨会中，一些学者对你的新物理过程也甚感兴趣，论文被收入《21世纪100个交叉科学难题》专辑，还参加了2008年中国科协学会组织的新观点、新学说的学术沙龙，并作了三个专题报告。

X射线衍射的发现及其历史意义(麦振洪)

索末菲知道后,也意识到这个发现的重大意义, 于 1912 年 5 月4 日将上述材料密封上报巴伐利亚科学院,以确保他们在发现X射线晶体衍射的优先权。
劳厄把二维光栅衍射理论推广到三维光栅情况,得到了描述晶体衍射的劳厄方程 a (cosα0 - cosα) = hλ b (cosβ0 - cosβ) = kλ c (cosγ0 - cosγ) = lλ
波动光学是19 世纪物理学的重要成就之一,干涉和衍射是波动的两个主要特征,劳厄将一维光栅的衍射理论推广到二维光栅。
与艾瓦尔德讨论中,当艾瓦尔德谈及他的理论和通常色散理论的差异在于谐振子是排列成有规律的点阵。劳厄追
问,有何根据? 艾瓦尔德回答,晶体被认为具有这种内部的规律性。劳厄再问谐振子的间距有多大,艾瓦尔德说比可见光波长小得多,也许只有1/ 500～1/ 1000 ,确切值不知道。
对中国的影响
对自然科学发展的影响
诞生了X射线波谱学开拓了结构化学诞生了X射线晶体学催生了材料科学
(1909-2009)
In a public poll by the Science Museum in London: what is the most significant scientific invention?
1849年布拉维提出14种空间格子时讨论过倒易概念艾瓦尔德再发现，功不可没。
一战他投笔从戎，问及专业，X射线衍射理论，被分配到东线野战医院冲洗X射线透视底片。1916年东线无大战事，闲极无事，在野战医院重操旧业。
1916-1917发表X射线衍射动力学理论二战后积极提倡建立国际晶体学，主编《晶体学报》，为晶体学发展很大贡献。衍射几何学和X 射线衍射动力学理论
威尔逊(发明云雾室而获得诺贝尔物理奖)得知上述结果后,建议用解理的云母做X射线反射实验,因为解理面总是原子密排面。实验结果增强了小布拉格的信心,断然否定了老布拉格的粒子学说

(完整版)医学影像专业英语

(1)To prospectively evaluate the effect of heart rate, heart rate variability, and calcification dual-source computed tomography (CT) image quality and to prospectively assess diagnostic accuracy of dual-source CT for coronary artery stenosis. by using invasive coronary angiography as the reference standard.前瞻性评价心率、心率变异性及钙化双源计算机断层扫描成像质量的影响及对冠状动脉狭窄的双源性冠状动脉狭窄诊断的准确性评价。

以侵入性冠状动脉造影为参照标准。

(2)Chest radiography plays an essential role in the diagnosis of thoracic disease and is the most frequently performed radiologic examination in the United States. Since the discovery of X rays more than a century ago, advances in technology have yieled numerous improvements in thoracic imaging. Evolutionary progress in film-based imaging has led to the development of excellent screen-film systems specifically designed for chest radiography.胸部X线摄影中起着至关重要的作用在胸部疾病的诊断，是最常用的影像学检查在美国。

(完整版)医学影像专业英语

以侵入性冠状动脉造影为参照标准。

AND

T HE A STROPHYSICAL J OURNAL ,484:920È926,1997August 11997.The American Astronomical Society.All rights reserved.Printed in U.S.A.(STATISTICS OF FLUCTUATIONS IN THE SOLAR SOFT X-RAY EMISSIONS.AND S.U E N O 1M INESHIGEDepartment of Astronomy,Faculty of Science,Kyoto University,Sakyo-ku,Kyoto 606-01,JapanH.N EGOROInstitute of Space and Astronautical Science,Yoshinodai,Sagamihara,Kanagawa 226,JapanK.S HIBATASolar Physics Division,National Astronomical Observatory,Mitaka 181,JapanANDH.S.H UDSONSolar Physics Research Corporation,Institute of Space and Astronautical Science,Yoshinodai,Sagamihara,Kanagawa 226,JapanReceived 1996September 23;accepted 1997February 28ABSTRACTX-ray emission from the Sun Ñuctuates as a result of occasional Ñare events.We have calculated the power spectra of the solar soft X-ray variations using the photometric data of the GOES 6satellite.The data cover the period 1991September to 1994April,about 32months in total,and we have worked with 10minute averages.We Ðnd that the total power spectral densities (PSDs)have three distinct com-ponents;a Ñat or slightly decreasing low-frequency section,a 1/f -like moderate decline medium-frequency section,and steep decline high-frequency parts.The break frequencies separating three parts are Hz and 10~3.8Hz ,respectively.Such downward breaks are expected from the shot-f break^10~4.7noise (Ñarelike)character of solar X-ray emission,and we interpret the lower break frequency as indicat-ing an upper limit on Ñare timescales.These break frequencies do not vary appreciably with activity level.This suggests the existence of a universal mechanism for triggering Ñares in the solar corona.Moreover,the power-law index (where we assume PSD P f ~b ,f being frequency)of each part does not vary appreciably with the level of activity either;its average is b ^0.45,0.95,and 1.5,respectively.The overall shape of the PSD is quite similar to those of other astrophysical objects such as black hole can-didate stars and active galactic nuclei,albeit on a vastly di†erent scale.Subject headings:Sun:activity ÈSun:Ñares ÈSun:X-rays,gamma rays1.INTRODUCTIONIt is widely believed that solar Ñares are caused by a release of magnetic energy stored in the solar coronal Ðelds.If so,we may deÐne basic time and spatial scales,such as the Alfve n transit time over a pressure scale height.One might then expect that the pattern of Ñare occurrence would reÑect these typical scales.Interestingly,however,this is not the case:total energy outputs and peak intensities of Ñares are distributed rather smoothly.A power-law dependence of solar Ñares on peak intensity has been established through a number of observations (Drake 1971;Datlowe,Elcan,&Hudson et al.The 1974;Lin 1984;Dennis 1985).essence is that,although bigger Ñares occur less frequently than smaller Ñares,there is basically no preferential energy.We speculate that the occurrence of Ñares may not be the result of simple local physics but is somehow controlled globally.To investigate this possibility,thorough statistical studies of solar Ñares are indispensable.Many studies concerning the statistics of solar Ñares have been made so far,but most of them have treated solar Ñares as individual,independent events.To derive useful informa-tion,such as periodicities and noise properties,the tech-nique of power spectral densities (PSDs)is often used.In fact,there are some studies on long-term periodicities of solar Ñare occurrence et al.&Cliver (Rieger 1984;Kile Bai &Sturrock However,there have 1991;1991,1993).been few attempts to investigate high-frequency noise properties of these patterns.In the present study,we calcu-1ueno =kwasan.kyoto-u.ac.jp.late the PSD,using GOES 6data,and discuss the statistics of solar Ñares from viewpoints that di†er from previous ones.We shall describe the GOES 6data in The overall °2.light curves and the PSD will be presented in Solar °3.activity signiÐcantly decreased during this period.To see how the statistical nature changes with time,we divide the entire data set into 16subsets,each with a duration of 2months,and study the light curves and power spectra of each individual subset.The variation of each spectral parameter will also be displayed in In we focus on °3.°4the long-timescale periodicity of Ñare occurrence.The Ðnal section is devoted to summary and discussion on the sta-tistics of solar Ñares and its relation to X-ray Ñuctuation from other objects,such as black hole systems.2.DATAWe use the soft X-ray light curves from 1991September to 1994April obtained with GOES 6.The overall light curves are displayed in Clearly,the corona was Figure 1.rather active,producing large X-ray variations due to major Ñares only until the Ðrst half of 1993,and the number of large peaks decreased rapidly afterward.The GOES 6database contains soft X-ray Ñuxes (about 2È10keV)sampled at 3s intervals.Because of range changes in the logarithmic readout,the noise properties of a GOES light curve are complicated.In the concrete,the light curve with full time resolution shows steplike proÐles.To minimize this problem we have arbitrarily smoothed the data into 10minute bins,a total of 133,622samples in the 32month observation period.920FLUCTUATIONS IN SOLAR SOFT X-RAY EMISSION 921F IG .1a F IG .1bF IG .1.ÈAll of the soft X-ray light curves from the whole Sun obtained with GOES 6.The vertical axes are (a )on the linear scale and (b )on the logarithmic scale.3.POWER SPECTRUM OF SOLAR SOFT X -RAYVARIATIONS3.1.PSDs of Entire L ight CurvesWe calculate the PSD in the following way.At Ðrst,we transform the time of each data point,(j \1ÈJ ),into thet jcorresponding phase,for a given frequency,(i \1È/i ,j,f i N ).Next,we plot the normalized X-ray Ñux,(j \1ÈJ ),L (t j )against and Ðt these J data points bya straightx \sin (/i ,j )line:We also plot against y \cos L \a i x ]b i .L (t j )(/i ,j )and Ðt thedata again by a straight line:L \c i y ]d i .Finally,we sum the two squares of these declines,ai 2]c i 2,which corresponds to the PSD (except for a proportionalityconstant)at a frequency f i .The PSD of the entire time series is depicted in Figure 2.Here power spectra are averaged in frequency over equal intervals on the logarithmic scale;that is,we averaged over the intervals from to (i \1to N [1),where f i f i`1f i`1\fi (since 100.05^1.12).The peaks at lowfre-]100.05\1.12f i quencies reÑect structure in solar Ñare occurrence on theF IG .2.ÈPower spectral density of the whole time series of solar soft X-rays depicted in Power density is binned in the frequency direc-Fig.1.tion over the intervals from to where f i f i`1,f i`1\f i ]100.05\1.12f i.long timescale.At high frequencies,larger than D 10~5Hz,we can see a steepening of the spectrum to a 1/f -like decline.At Ðrst,we focus on the noise features at high frequencies.In order to increase the signal-to-noise ratio,we Ðrst calcu-lated PSDs for each of 16subsets with 2month durations (see for the deÐnition of subsets).We then averaged Table 1each PSD with frequency bins from to where f i f i`1,f i`1\fi]100.05,and Ðnally averaged the 16PSDs.shows Figure 3the averaged PSDs obtained in this way.Here the error bars show p /n 1@2,where p is the standard deviation of 16power spectra of each data subset and n is the number of data subsets,i.e.,n \16.We Ðnd that the solar PSDs appear to consist of two and possibly three distinct spectral domains.Break frequencies separating the three distinct parts with di†erent slopes are found at around f ^10~4.7Hz and f ^10~3.8Hz,respectively.These Ðxed frequencies were then used as limits of each domain for Ðts to power-law functions proportional to f ~b ,with b being a Ðtting parameter.The results of Ðtting are summarized in Table 2.Errors represent deviations of each PSD from the best-Ðt curve.It is interesting that these power-law indices are similar to those of a representative black hole candidate,Cyg X-1(cf.et al.see inset in and see Negoro 1995;Fig.3Table 2).What physical processes do these frequencies imply?Generally,if a single-Ñare light curve can be well represent-TABLE 1C ONTENTS OF S UBSETD ATASubset Start Time End Time Number (108s)(108s)Year and Month 1...... 3.9977280 4.05042181991Sep,Oct 2...... 4.0504320 4.10312741991Nov,Dec 3...... 4.1031360 5.15496801992Jan,Feb 4...... 4.1549760 4.20767101992Mar,Apr 5...... 4.2076800 4.26037441992May,Jun 6...... 4.2603840 4.31394181992Jul,Aug 7...... 4.3139520 4.36664701992Sep,Oct 8...... 4.3666560 4.41934981992Nov,Dec 9...... 4.4193600 4.47032901993Jan,Feb 10...... 4.4703360 4.52302981993Mar,Apr 11...... 4.5230400 4.57573701993May,Jun 12...... 4.5757440 4.62930501993Jul,Aug 13...... 4.6293120 4.68200901993Sep,Oct 14...... 4.6820160 4.73471391993Nov,Dec 15...... 4.7347200 4.78568701994Jan,Feb 16......4.78569604.83838981994Mar,Apr922UENO ET AL.Vol.484F IG.3.ÈPower spectral density for the32month data,which are averaged over time and frequency.The power spectrum of Cyg X-1obtained byNegorois also shown in the inset.(1992)ed by an exponential function of time[P exp([t/q),qbeing a constant],its power spectrum has aÑat-top proÐlewith a steep decline(P f~2)at high frequencies(LorentzianproÐle):S q (f)P(2nq f)21](2nq f)2.(1)In this case,the break frequency corresponds to f\(2nq)~1.To see the range of typical decay time q,we tried toÐt eachÑare light curve with an exponential func-tion for10bigÑares and20smallÑares present in the GOES data.Two such examples are displayed in One hasFigure4.TABLE2P OWER-L AW I NDEX OF T OTAL P OWER S PECTRUMFrequency RangeObject(Hz)Power-Law Index b Sun...........\10~4.70.45^0.0810~4.7to10~3.80.95^0.03[10~3.8 1.50^0.02 Cyg X-1......\10~1D0.010~1to100D0.9[100D1.5the longest decay time with s,whereas anotherqlongD8300has the shortest,s,among theÐtted data.Note,qshortD550however,that anyÑuctuations with even shorter duration (q\550s)have been suppressed byÐnite time resolution of our rebinning of the data(10minutes).The corresponding break frequencies are andflong^10~4.7fshort^10~3.5, respectively.These values agree well with the two break frequencies seen in The departure from the Lor-Figure3.entzian1/f2fallo†to high frequencies above10~4.7Hz could therefore be plausibly explained by a broad distribu-tion ofÑare decay times This means that we(Drake1971).may be able to reproduce by superposingFigure3Sq(f) with550\q\8300.In order to conÐrm this prediction,we performed PSD analyses of simulatedÑare light curves for the following two cases.In theÐrst case,we adopted20,000steps for the total observed time,and5and70steps for the shortest and longest durations ofÑares,respectively.In the second case, we again adopted20,000steps for the total time,but2and 20steps for the shortest and longest ones,respectively.In both simulations,the peak intensity distribution ofÑares was set to be N P P~1.8,which is consistent with previous observational studies.Time intervals between neighboring Ñares were simply assumed to be random,and the meanNo.2,1997FLUCTUATIONS IN SOLAR SOFT X-RAY EMISSION 923F IG .4.ÈSoft X-ray time proÐles of the solar Ñares (white squares )and the best-Ðt curve (solid line )for (a )the longest duration Ñare (1992May 3;22hr 48minutes)and (b )the shortest duration Ñare (1992May 28;13hr 26minutes)among the 32month data.interval equals 10and 9.1steps in the two cases,respec-tively.Moreover,Ñare durations were also taken to be random between the shortest and longest durations.We depict these two simulated light curves in and Figure 5smoothed power spectral densities in Apparently,Figure 6.the simulated light curves and PSDs are very similar to those observed.Quantitatively,we can predict that f short\10~1.50Hz and Hz in the Ðrst case,andf long\10~2.64Hz and Hz in the second f short \10~1.10f long \10~2.10case,by estimation from theshortest and the longest dura-tions,respectively.In fact,these values are found in simu-lated PSDs with good agreement.We thus (Fig.6),conÐrmed our interpretation of the shape of PSDs to be correct.The values of the upper break frequency,near 10~3.8Hz,are too close to the Nyquist frequency of our binning to beF IG .5.ÈSimulated light curves of Ñares.(a )Durations of Ñares are adopted as 5and 70steps,respectively,for the shortest and the longest ones.(b )Durations are set as 2and 20steps,respectively,for the shortest and the longest ones.These durations are taken to be at random between the shortest and longest durations.Time intervals between neighboring Ñares are also assumed to be random.On the other hand,the peak inten-sity distribution of Ñares was set to be N P P ~1.8.signiÐcant in this study.More quantitative discussion will be given in our next paper.Finally,we also examine periodicities in the occurrence of Ñares.In the PSDs we could Ðnd the apparent periodicities of 2.6,17.7,18.4,24.8,26.4,30.5,46.3,51.8,61.3,105,and 123days.&Sturrock also reported the period-Bai (1991)icities 25.5,51.0,76.5,102.0,127.5,and 153.0days before solar cycle 21.We have conÐrmed the periodicities of D 26,51,102,and 125days,but none with 76.5and 154days.Instead,we found the strong periodicity of 61.3days.These results are,however,very preliminary,and we need more detailed analysis to conÐrm our Ðndings in a future work.3.2.L ong -Term Changes of PSDsIn the previous subsection,we were concerned with the PSDs for the entire light curve.It is still open to question whether the power-law indices (or the break frequencies)of the PSDs remain the same all the time regardless of the di†erent magnitudes of Ñare activity.We thus next investi-gate the individual PSDs for each subset,Ðnding a variety of PSDs with di†erent shapes and magnitudes (see Table 3and Fig.5).To summarize,most PSDs show the three distinct com-ponents.If we denote the power-law indices of the com-ponents from lower to higher frequencies as and b 1,b 2,b 3,we usually Ðnd that is,the PSDis composed b 1\b 2\b 3;TABLE 3T IME V ARIATION OF P OWER -L AW I NDEXSubsetlog (f break )log (f break )Number b0b1(Hz)b2(Hz)b31.........0.031[4.550.66[3.70 1.52.........0.020[4.150.61[3.55 1.23.........0.17[4.600.92[3.80 1.34.........0.20[4.30 1.2[3.70 2.25.........0.11[4.65 1.1[3.90 3.06.........0.48[4.100.98[3.30 1.37.........0.46[4.55 1.8[3.750.908.........0.23[4.90 1.1[3.70 1.79.........0.036[4.500.73[3.85 1.410.........0.097[4.65 1.0[3.95 1.711.........0.18[4.300.87[3.60 2.112.........0.49[4.600.76[3.40 1.913...... 2.1[0.13[4.550.35[3.70 1.314.........0.38[4.15 1.1[3.45 1.715.........0.19[4.600.82[3.85 1.716......... 1.4[5.200.49[3.851.3924UENO ET AL.Vol.484F IG.6.ÈPower spectral density diagrams of simulated light curves ofÑares(a)PSD for the light curve with longer durations.(b)PSD for(Fig.5).the light curve with shorter durations.The di†erences of break frequenciescan be found.of aÑat part with a moderate decline part withb1D0,and a steep decline part with to f~2b2D f~1,b3D f~1.5from low to high frequencies,although these indices changefrom time to time There are not a few PSDs(Table3).having a1/f-like decline.Note again that the presence of thesteep decline part may be a†ected by theÐnite timeresolution.There are some exceptions:In the seventh subset,therelation among the power-law indices is Inb1\b3\b2.the16th subset,weÐnd In the13th subset,b2\b1^b3.the PSD appears to have four components.A steep declinealso appears at low frequencies(b1\b2\b3\b).On the other hand,the break frequencies did not changegreatly during the32months,although the meanÑuctua-F IG.7.ÈTime variations in the statistical properties of solarÑaresduring the32month data.(a)Variation of the power-law index at mediumfrequency.(b)Variation of the two break frequencies.The lower line(withlower frequencies)may show the longest durationÑare and the upper line(with higher frequencies)may show the shortest durationÑares.(c)Varia-tion of the solar activity.Values on the vertical axis show the soft X-rayÑux averaged over2months.tion amplitudes decreased appreciably.The variations inthe shapes of power spectra and the break frequencies arerather independent of the solar activity.In weFigure7depict the time variations of power-law indices,break fre-quencies,andÑare activity.The independence of the spec-tral parameters with time shows that the pattern ofÑareoccurrence does not depend on the level of activity.Thismay suggest the existence of a universal mechanism for trig-geringÑares in the solar corona.4.SUMMARY AND DISCUSSION4.1.Summary of Solar X-Ray FluctuationSoft X-rayÑuxes from the SunÑuctuate because large orsmallÑare events occur occasionally.By constructingpower spectra,we have found the following statistical fea-tures ofÑare occurrence.A1/f-likeÑuctuation appears at medium-frequencyregimes(f\10~4.7to10~3.8Hz)in the PSD.The breakfrequencies,which seem to correspond to inverses of themaximum and minimum duration ofÑares,are independentof the solar activity and do not change much with time.This1/f-like feature is quite reminiscent of X-ray variability fromother astronomical objects,such as Cyg X-1(black holecandidate)and the nuclei of active galaxies.We have alsofound that although the normalization of peak intensitieschanges,the overallÑuctuation properties(such as theNo.2,1997FLUCTUATIONS IN SOLAR SOFT X-RAY EMISSION925shape of the PSD)are more or less insensitive to the solar activity.From these features,we may conclude that the mecha-nism responsible for individual solarÑares is insensitive to the level of solar activity.Maybe the di†erent magnitudes of solar activity can be explained simply by the variation of the strength of helicity added to magneticÑux tubes in the solar convection zone.To connect this power-law distribution of solarÑares to the physics of individualÑares,&Hamilton andLu(1991) et al.propose that the solar coronal magneticÐeld Lu(1993)is in a self-organized critical state(SOC state),a critical state realized in a nonequilibrium open system Tang,(Bak,&Wiesenfeld The most outstanding feature of their 1988).model is that the system,following cellular automaton rules,spontaneously evolves to and steadily stays at an SOC state.In this state energy stored in magneticÐeld would be barely below its critical value,over which an energy-release event begins and leads to aÑare.The occurrence rate then shows a power-law dependence on size and lifetime of the event.We can expect1/f-likeÑuctuations on the energy dissipation in such a case,although the energy is injected randomly in time and space.If this is the case,solarÑares are like avalanches consisting of many small energy-release events,such as magnetic reconnec-tions.To summarize what we have learned through the present studies,the SOC model can naturally explain some of the observed statistical features,since the results are basically insensitive to the parameters of the physical system.If this model is usable,allÑarelike events,including nanoÑares and microÑares,can be understood in term of a common physical process.Although the present paper only presents the results of the PSD analyses,complementary information may be derived from the distributions of peak intensities of individ-ualÑares and intervals of adjacentÑares.It might be noted that the previous studies have shown that the distributions of peak intensities ofÑares can be well represented by power laws with indices c\1.8È1.9(cf.Yamashita,&Kakinuma,Enome et al.Dennis 1969;Drake1971;Datlowe1974;These distributions may contain 1985,1988;Shimizu1995).important physical information as follows:If this index is less than2.0,some additional heating mechanisms,such as nanoÑares are required to account for solar (Parker1988),coronal heating while otherwise coronal(Hudson1991),heating can be explained solely by various sizes ofÑares. Moreover,the distributions of intervals between adjacent peaks can be used to check whether the occurrence ofÑares is random or whether accumulation e†ects may exist. Detailed analyses using the GOES data will be presented in our next paper.4.2.Relationship to X-Ray Fluctuations fromBlack Hole ObjectsIt is also interesting to discuss the relationship between solar coronae and accretion disk coronae(cf.Galeev, Rosner,&Vaiana As mentioned1979;Takahara1979).already,1/f-likeÑuctuations are rather generally observed in X-ray radiation from stellar black hole candidates like Cyg X-1,neutron star X-ray binaries,and active galactic nuclei(see reviews by and&Makishima1988Pounds McHardy for more recent analysis see et al.1988;Negoroand references therein).The X-rayÈemitting regions of 1995these objects seem to be optically thin accretion disks domi-nated by magnetic pressure,where magneticÑares similar to solarÑares occasionally occur,giving rise to substantial Ñuctuations in X-ray emission(see Tajima,&Mat-Shibata,sumoto Kusunose,&Matsumoto 1990;Mineshige,1995, and references therein).It is thus of great importance to study the statistics of solar X-rayÑuctuations for consider-ing possible physical links between solar coronae and hot accretion disks.In particular,from PSDs the statistical features of solar and nonsolar X-rayÑuctuations are rather similar to each other.However,the absolute X-rayÑuxes from accretion disks are larger by many orders of magnitude than those from the solar corona,and the shapes of theÑare light curves are also rather di†erent from those of the X-ray shots in nonsolar sources.In the latter,mass accretion is another important factor in determining the shape of X-ray shot light curves.et al.in fact,have recently Manmoto(1996),succeeded in reproducing X-ray shot proÐles by time-dependent simulations of the accretion disk.When we consider these facts,it seems plausible that the mechanisms of creating solarÑares and X-rayÈemitting shots in accretion disks could be related(such as in an SOC model including magnetic reconnection;see,e.g.,Takeuchi, Mineshige,&Negoro In the solar interior,convec-1995).tion gives energy to the magneticÐeld.In accretion disks,in contrast,accreting gasÐrst acquires energy from gravita-tional potential well.The disk gas can then give energy to the magneticÐeld through ampliÐcation by the shearing motion of the gas and MHD instabilities associated with rotating disks.When the magnetic energy becomes compa-rable to internal energy of the disk gas,theÐeld will even-tually dissipate its energy via reconnection.The di†erence in shot characteristics,such as intensities,shot proÐles,and interval distributions,between the solar corona and an acc-retion disk source may arise from the di†erent physics involved.For accretion disks we mainly observe the accre-tion process of X-rayÈemitting blobs(powered by gravita-tional potential energy release due probably to magnetic reconnection),and such a source of energy is not available in the solar case.Furthermore,the solar soft X-ray radi-ation we analyze here does not represent the fundamental (direct)energy release in a solarÑare;it might be more appropriate to analyze the shot-noise properties of solar hard X-ray emission as a proxy for the fundamental energy-release mechanism.Finally,we need to o†er an explanation of the dimension-al constant we appear to have discovered,namely,the lower break frequency10~4.7Hz.It exceeds the Alfve n transit time of any basicÑare structure,but can be related to typical radiative cooling times forÑares limited in size scale to about1supergranule diameter(about50,000km).It is possible that this rough agreement suggests that the charac-teristic time is basically hydrodynamic in origin and does not reÑect the energy-release timescale itself.We are grateful to J.Kubota and T.Kato for useful comments and advice for analysis.This work was sup-ported in part by grants-in-aid from the Ministry of Educa-tion,Science,Sports,and Culture of Japan,06233101, 08640329(S.M.),and by NASA,NAS8-37334(H.S.H).926UENO ET AL.REFERENCEST.,&Sturrock,P.A.1991,Nature,350,Bai,1411993,ApJ,409,ÈÈÈ.476P.,Tang,C.,&Wiesenfeld,K.1988,Phys.Rev.A,38,Bak,364D.W.,Elcan,M.J.,&Hudson,H.S.1974,Sol.Phys.,39, Datlowe,155B.R.1985,Sol.Phys.,100,Dennis,465B.R.1988,Sol.Phys.,118,Dennis,49J.F.1971,Sol.Phys.,16,Drake,152A.A.,Rosner,R.,&Vaiana,G.S.1979,ApJ,229,Galeev,318H.S.1991,Sol.Phys.,133,Hudson,357T.,Yamashita,T.,&Enome,S.1969,Proc.Res.Inst.Atmo-Kakinuma,spherics Nagoya Univ.,16,127J.N.,&Cliver,E.W.1991,ApJ,370,Kile,442R.P.,Schwartz,R.A.,Kane,S.R.,Pelling,R.M.,&Hurley,K.C. 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广东省三校联考2023-2024学年高一下学期期中考试英语试题

广东省三校联考2023-2024学年高一下学期期中考试英语试题一、单项选择1．Many parts of China ________ very heavy rainfall in the past few days.A．have seen B．has seen C．had seen D．have been seen 2．The unemployment rate in this district ________ from 6% to 5% since two years ago.A．has been fallen B．fell C．has fallen D．had been fallen3．I am applying to the committee for being sent to our Denver branch to see how the previous marketing plan ________ out so far.A．carried B．have carriedC．has been carried D．have been carried4．Although a few have come and gone, the restaurant’s regular customers ________ the same for nearly 40 years.A．remained B．have remainedC．have been remained D．has been remained5．Hearing the news, she rushed out, ________ the book lying open on the table.A．left B．to leave C．leaving D．having left6．________ the address carefully, Tom clicked the button and sent the email to his professor.A．Checking B．Being checked C．To check D．Having checked 7．________ her mother after being separated for 20 years, she could not help________.A．Seen, crying B．To see, cry C．Seeing, crying D．Having seen, cry 8．________ by his research, Professor Salovey suggests that when predicting someone’s future success, their character, which ________ by EQ tests, might actually matter more than their IQ.A．Supported; is measured B．Supported; measuredC．Having been supported; being measured D．Having supported; measure9．________ to students who had not been involved in the study, they also showed a better understanding of the ________ students’ feelings.A．Comparing; disabling B．Compared; disabledC．Compared; disabling D．Comparing; disabled10．________ to a local zoo, the two lions are reported ________ well.A．Having sent; settling down B．Sent; to have settled downC．Sent; to settle down D．Having sent; to be settled down二、阅读理解The Nobel Prize has been awarded to women 60 times between 1901 and 2022. These women have made outstanding contributions to the worlds of medicine, science, literature and so on. Here are four of them.Dorothy Crowfoot HodgkinAward: Nobel Prize in ChemistryYear: 1964Dorothy Hodgkin was a British chemist whose interest in research began when, as a child, she received a chemistry book containing experiments with crystals. She studied at Oxford University and developed protein crystallography, which advanced the development of X-rays. This earned her the Nobel Prize.Gertrude B．ElionAward: Nobel Prize in Physiology or MedicineYear: 1988Gertrude Elion won the Nobel Prize for her discoveries of important principles for drug treatment. Elion had watched her grandfather die of cancer, so she decided to fight the disease throughout her life. Elion, together with George Hitchings, with whom she shared the award, created a system for drug production that relies heavily on biochemistry.Toni MorrisonAward: Nobel Prize in LiteratureYear: 1993Toni Morrison, whose book “Beloved” earned her the Pulitzer Prize and the American Book Award, was the first Black woman to ever receive the Nobel Prize in Literature. Born in Ohio, Morrison was a writer whose works are mostly about life in the Black community. She taught writing and served as an honorary professor at Princeton University.Esther DufloAward: Nobel Prize in EconomicsYear: 2019Esther Duflo shared her prize with her research colleagues Michael Kremer and Abhijit Banerjee, who is her husband. Duflo has spent much of her career at the Massachusetts Institute of Technology, where she earned her doctorate degree in 1999. Duflo and her partners were awarded the Nobel Prize for their approach to fighting poverty around the world.11．What won Dorothy Crowfoot Hodgkin the Nobel Prize?A．Her book about crystals.B．Her contribution to X-ray development.C．Her research on medicine.D．Her discovery of a new protein crystal. 12．What do Toni Morrison's books mainly focus on?A．Educational issues.B．Community service.C．Writing techniques.D．Black American's life.13．What do Gertrude B．Elion and Esther Duflo have in common?A．They won the Nobel Prize in the same year.B．They devoted themselves to fighting diseases.C．They shared the Nobel Prize together with others.D．Their life experiences committed them to their fields.I’m in the area of Noailles in Marseille, France’s second largest city and its main trade seaport. Some small shops sell vegetables, meat, and, it seems, all the spices of the Middle East. In addition to French, languages spoken on the busy streets include Arabic and African French. It all adds up to one of the most ethnically diverse cities in Europe.Close to the downtown street, I discover an Algerian restaurant, whose owner makes his signature dish-couscous with barley, not the usual wheat, using a recipe that hasn’t changed since the 1920s. Couscous is an necessary part of Marseille culture. The dish was added to the UNESCO’s Lists of Intangible Cultural Heritage in 2020.To be honest, before I travelled here, couscous had not been the first meal that came to mind when I thought of Marseille. It was bouillabaisse, the rich soup with olive oil, garlic and saffron. I imagined enjoying it at a small portside cafe. This was clearly a romantic fantasy. For one thing, there are no small cafes at historic city. For another, the restaurants do servebouillabaisse, but when I see the price at one place I am shocked: 69 euros! No bowl of soup should cost that much.I give up and end up two streets away from the old harbor in a new restaurant, Ourea. For28 euros, Chef Matthieu Roche serves a three-course lunch that includes tuna steaks and couscous.More and more young, talented people are discovering that Marseille is an ideal place to live. There is also a growing number of Parisians moving here every year. Tired of the rush and expense of life in larger cities, the newcomers come looking for the more relaxed Mediterranean way of life.Walking through these contrasting neighborhoods of Marseille. I think about the distinct communities here living in the same neighborhoods — together, side by side, but not mixed. They may also feel they are Marseillais first regardless of nationalities.14．Which word can best describe Marseille according to the first paragraph?A．Remote.B．Commercial.C．Industrial.D．Inland.15．What made the author leave the Algerian restaurant?A．The unreasonable charge.B．The unbearable flavor.C．The unsatisfying service.D．The noisy atmosphere.16．Why do the newcomers choose Marseille rather than other big cities?A．To make a fortune.B．To experience a dish.C．To learn a language.D．To live a leisurely life.17．In which column of a magazine can we probably read the text?A．Fashion.B．Food.C．Trade.D．Travel.It is reported that rail industry bosses are planning to phase out paper train tickets and shut almost 1 ,000 station ticket offices in England. The government says nothing has been decided. But the transport secretary, Grant Shapps, points out some stations sell only a handful of tickets each week and the vast majority of transactions( 交易) have moved online.Regardless of the outcome of the plan, the direction of travel is clear. In the name of modernization and cost-cutting, station ticket offices are likely to follow many high street bank branches and rural post offices into memory. For those who have grown used to the advantages of organizing travel via a smartphone, there will be little to mourn( 哀悼). But for people withoutonline access or skills, another small social barrier will have emerged. A recent report estimated that around 6% of households—1.5m homes—have no internet access. Millions more of us remain irregular and unconfident users of the internet. Most likely, as digital technology becomes the gatekeeper to everyday life, a significant minority risks being left behind.The shift online is unavoidable, but its fallout needs to be managed with more care. Technology should not be allowed to drive people to the side of their own lives, as anecdotal evidence suggests is increasingly the case. Ros Altmann, the former pensions minister, recently wrote of being contacted by an elderly woman who no longer drives to her local park, because she cannot download the car parking app required.The debate over ticket offices offers an opportunity to reflect more broadly on the increasing role of technology in our social landscape. Clearly, much more needs to be invested in helping marginalized(边缘化的) groups gain easy online access. Alternative offline options must be maintained for important services. Contactable telephone numbers and staffed public access points should always be available. This will cost more. But that is the price of being fair to those who find themselves on the wrong side of the digital divide.18．What forces the rail industry to phase out paper train tickets?A．Costs of internet access.B．Closure of station ticket offices.C．Sharp decline of offline transactions.D．Government’s efforts to digitize the industry. 19．Which of the following might fall victim to the plan?A．Rural post offices.B．Irregular internet users.C．Unconfident households.D．High Street bank branches.20．How does the author clarify his opinion in paragraph 3?A．By giving an example.B．By making a comparison.C．By citing research data.D．By offering statistical analysis.21．What does the author suggest in the last paragraph?A．Taking the digital divide fairly.B．Maintaining a diversity of service.C．Investing more in public transport.D．Slowing down the pace of modernization.An economist, Adam Smith, famously wrote that “it is not from the benevolence (慈善) of the butcher, the brewer or the baker, that we expect our dinner, but from their regard to their ownself-interest.” Like Smith, many economists today believe one’s self-interest is what drives competition and growth in market economies. Yet, in an increasingly interconnected society, it is even more crucial to have cooperative skills. Thus we should encourage cooperation to better prepare children for the future.Firstly, cooperation is an especially prized soft skill in the present age. As a study proves, soft skills such as good communication and empathy (共情) indicate outstanding employees as compared to technical skills or knowledge. In contrast, extremely competitive and individualistic behavior may damage social relations in the community of co-workers. Even the most competent employee may fail to pursue his goals effectively without others’ help.Moreover, encouraging cooperation boost children’s self-respect that better prepares them for the competitive world. Many modern societies are consumed by a crazy drive for success and the pressure to perform has infiltrated both classrooms and offices, causing higher rates of anxiety and depression among people. Teamwork can help an individual realize each has his or her own unique abilities and that another person’s strengths don’t discount his or her talents. Thus, cooperation can confirm children’s self-worth by correcting the insight that winning or paper achievement is the only measure of success.However, critics may claim adapting to competition should be given priority in education and parenting. To achieve one’s ambitions, one has to actively fight for opportunities and distinguish oneself from others. Nevertheless, since passion can already stimulate children to fulfill their ambitions, the need to encourage competition may be at the end of the day. As much as external competition can drive people to pursue excellence, internal motivation is at least equally or even more essential, and cooperation plays an instrumental role in helping one uncover one’s motivations.22．What can be inferred from Adam Smith’s words?A．Our society is increasingly interconnected.B．Our dinner is made out of the regards to markets.C．Self-interest pushes the development of economies.D．The butcher, the brewer or the baker is not sympathetic.23．What does the underlined word “infiltrated ” mean in paragraph 3 probably mean?A．Brightened.B．Decorated.C．Defended.D．Entered.24．Which of the following might the author agree with?A．Paper achievement is the only measure of success.B．One’s ambitions can be achieved through cooperation.C．Competition is not necessary for people to pursue excellence.D．Actively fighting for distinguishing oneself should be prioritized.25．What is the author’s purpose of writing this passage?A．To introduce the advantages of cooperation.B．To compare cooperation with competition.C．To suggest enhancing competitive skills.D．To advocate teaching children to cooperate.When it comes to solitary activities and bravery, going to a museum alone is something you should seek out. When I used to work at a large, encyclopedic museum, I would often wander through the galleries by myself on my lunch break or after work. 26 . So, why not take yourself on an independent date to a museum?When you visit a large museum alone, especially if there are certain artworks you you’re your heart set on seeing, you can set your own plan. 27 . You can go directly to the galleries you’re interested in and not waste time on art you have little or no desire to see.Enjoying a museum alone might help you enjoy solitude. Even if you’re a social butterfly, being alone is an inevitable part of life, so it’s important to learn to be comfortable being alone with yourself. A museum is an ideal way to intentionally practice this. 28 .If you go the route of remaining alone at a museum, you won’t have the distraction of social interaction. 29 . A museum is the perfect place to bring a sketchbook, sit down somewhere and draw what’s around you with no aim or judgment.30 . The thought of going to a place as public as a museum by yourself might be intimidating(令人生畏的), but I encourage you to try it out. You might discover another side to yourself, to the art or to other people that you wouldn’t have experienced otherwise.A．A museum is a wonderful place for self-reflectionB．You can welcome imagination in those quiet momentsC．You can be highly selective in how you plan your visitD．These were some of the most quiet, thoughtful parts of my dayE．As a result, you’ll be better equipped for those lonelier times in lifeF．A museum can be a great place for all seeking a quiet, reflective spaceG．Instead, you can focus on self-reflection, or you could look for inspiration三、完形填空In 2014,a sophomore student at the National Academy of Chinese Theatre Arts went with friends for a birthday 31 to Beijing Zoo. Little did he know that a chance 32 at the aquarium there would bring a lifelong 33 . As Xu Yitang gazed upon varieties of corals (珊瑚), a sense of wonder 34 him. Lost in the beauty and mystery of the creatures, he spent the entire afternoon in front of it.After he first saw corals at the aquarium, he began to 35 the local market to learn about coral farming from 36 who sell plants, fish, and corals. He also searched for information online. Before long, he had set up a small fish tank and started 37 a coral. “The coral is quite 38 and has extremely high requirements for water quality,” recalls Xu. “When I started growing coral, its 39 was not good.”As Xu gained knowledge about coral, including how to 40 factors like water temperature, pH levels and trace element concentrations (微量元素) during the cultivation process, his coral gradually started to 41 . As he knew more about the creature, he learned that coral reefs are 42 as “tropical rainforests” and “underwater gardens” of the ocean,providing a home for a quarter of all 43 life. However, with the 44 of the greenhouse effect, rising sea temperatures have led to coral decay. Xu felt an increasing sense of urgency and responsibility to protect them.After graduating from the university, he 45 the opportunity to become a coral conservationist and officially joined a research team in Hainan.31．A．cake B．celebration C．dinner D．card 32．A．miss B．approve C．encounter D．check 33．A．passion B．consumption C．invitation D．conclusion 34．A．washed over B．broke down C．faded away D．wandered about35．A．leave B．ask C．frequent D．tell 36．A．strangers B．merchants C．servants D．passengers 37．A．selling B．drawing C．making D．cultivating 38．A．strong B．beautiful C．huge D．fragile 39．A．shape B．state C．color D．length 40．A．cease B．obtain C．regulate D．predict 41．A．move B．die C．change D．flourish 42．A．known B．dressed C．used D．disguised 43．A．rare B．marine C．adorable D．artificial 44．A．strengthening B．decreasing C．switching D．expanding 45．A．lost B．devoted C．seized D．tackled四、语法填空阅读下面短文，在空白处填入1个适当的单词或括号内单词的正确形式。

医学影像诊断英语

医学影像诊断英语Diagnostic Imaging in MedicineThe field of diagnostic imaging has revolutionized the way healthcare professionals approach patient care. From the early days of X-rays to the cutting-edge technologies of modern imaging techniques, the evolution of this discipline has greatly enhanced our understanding of the human body and our ability to detect, diagnose, and monitor various medical conditions. In this essay, we will explore the significant role that diagnostic imaging plays in the field of medicine.One of the primary benefits of diagnostic imaging is its ability to provide healthcare professionals with a detailed and comprehensive view of the internal structures of the human body. Traditional physical examinations and laboratory tests can only provide limited information, but diagnostic imaging techniques, such as X-rays, computed tomography (CT) scans, magnetic resonance imaging (MRI), and ultrasound, allow healthcare providers to visualize organs, tissues, and even the smallest of anatomical details with remarkable clarity. This increased level of visual information has significantly improved the accuracy of diagnoses, enabling healthcareprofessionals to detect and identify a wide range of medical conditions at earlier stages, leading to more effective treatment and better patient outcomes.In the field of radiology, for instance, the use of X-rays has been a cornerstone of diagnostic imaging for over a century. X-rays, which are a form of electromagnetic radiation, are able to pass through the human body and create images that reveal the structure and density of internal organs and tissues. This technology has been instrumental in the diagnosis of fractures, lung diseases, and certain types of cancer, among other conditions. As technology has advanced, the quality and resolution of X-ray images have improved, allowing healthcare providers to make more informed decisions and provide more targeted treatments.Another important diagnostic imaging modality is the CT scan, which uses a series of X-ray images taken from different angles to create a detailed, three-dimensional representation of the body's internal structures. CT scans are particularly useful in the diagnosis of conditions that affect the brain, such as strokes, tumors, and head injuries, as well as in the evaluation of the abdominal and thoracic regions for a variety of medical issues.Magnetic resonance imaging (MRI), on the other hand, utilizes strong magnetic fields and radio waves to generate detailed imagesof the body's internal structures. Unlike X-rays and CT scans, MRI does not use ionizing radiation, making it a safer option for certain types of imaging, particularly in the diagnosis of neurological conditions and musculoskeletal injuries. MRI is also highly effective in the detection and monitoring of soft tissue diseases, such as multiple sclerosis, arthritis, and certain types of cancer.Ultrasound imaging, which uses high-frequency sound waves to create real-time images of the body's internal structures, is another important diagnostic tool. Ultrasound is particularly useful in the evaluation of the cardiovascular system, as it allows healthcare providers to visualize the heart and blood vessels, as well as in the assessment of pregnancy and fetal development. Ultrasound is also a valuable tool in the diagnosis of abdominal and pelvic conditions, such as gallbladder disease, kidney stones, and ovarian cysts.In addition to its diagnostic capabilities, diagnostic imaging also plays a crucial role in the planning and monitoring of medical treatments. For example, healthcare providers can use imaging techniques to guide the placement of surgical instruments, such as during minimally invasive procedures, or to monitor the progress of a patient's treatment, such as the response to cancer therapies. This integration of diagnostic imaging with treatment planning and monitoring has significantly improved the accuracy and effectiveness of medical interventions, leading to better patient outcomes andreduced healthcare costs.Moreover, the field of diagnostic imaging is continuously evolving, with the development of new and more advanced technologies. Innovations such as positron emission tomography (PET) scans, which can detect biochemical changes in the body, and hybrid imaging techniques, such as PET-CT and PET-MRI, which combine the strengths of multiple imaging modalities, have further enhanced the capabilities of diagnostic imaging in the detection and management of various medical conditions.As healthcare systems around the world strive to provide high-quality, cost-effective care, the importance of diagnostic imaging in modern medicine cannot be overstated. By providing healthcare professionals with detailed and accurate information about the state of a patient's health, diagnostic imaging has become an indispensable tool in the clinical decision-making process, leading to earlier diagnoses, more targeted treatments, and ultimately, better patient outcomes.In conclusion, the field of diagnostic imaging has played a pivotal role in the advancement of modern medicine. From the initial discovery of X-rays to the development of cutting-edge imaging technologies, the evolution of this discipline has transformed the way healthcare professionals approach patient care. By providingdetailed visual information about the internal structures of the human body, diagnostic imaging has become an essential component of comprehensive healthcare, enabling more accurate diagnoses, more effective treatments, and ultimately, improved patient outcomes.。

CT的基本知识

HU can be resolved by naked eye The difference of CT number
between normal liver and HCC is only about 10 HU
Proper window
WW=100；WL=50
white
Bone +1000
（WW）
Shortcomings of radiography
film
Overlapping
Magnification
Distortion
X-ray Poor contrast tube resolution
The spatial resolution of CT is inferior to traditional radiography.
Basic structure of CT
Scanning gantry Scanner table Computer Displayer Memory storage and Camera, etc
The X-ray tube and detectors are located inside the gantry, surrounding the patient
Air -1000
Remember: Always use suitable WW and WL in order to clearly observe the structures you want to see .
2.3 Classification of CT
According to the scanning pattern
COMPUTED TOMOGRAPHY
(CT)

超短超强激光辐照靶物质产生K-alpha源简介(投稿：光谱学与光谱分析)

超短超强激光辐照靶物质产生K-alpha 源简介王向贤（巢湖学院物理与电子科学系安徽巢湖 238000）摘要：超短超强激光与物质相互作用产生的K-alpha 线辐射，有准单能、发射区域小、时间短等优点，具有广泛的应用前景。

介绍了超短超强激光辐照靶物质产生K-alpha 源的基本原理及其主要研究内容，讨论了该领域的研究热点。

关键词：超短超强激光；K-alpha 源；基本原理引言：超短超强激光与物质相互作用产生的K-alpha 线辐射。

有准单能（几十个keV ）、发射区域小（微米量级），时间短（飞秒—皮秒量级）等优点[1,2]。

可广泛应用于惯性约束聚变背光照相，医学成像，光刻，时间分辨X 射线衍射等领域。

同时，超短超强激光与物质相互作用中超热电子辐射是强场物理的重要研究内容之一，而K-alpha 线的产生和超热电子直接相关，故可以通过研究K-alpha 线辐射研究超短超强激光与物质相关作用产生的超热电子。

一、超短超强激光辐照靶物质产生K-alpha 源的基本原理如图1所示，用超短超强激光脉冲辐照靶物质，如铝（Al ）、铜（Cu ）、金（Au ）等，激光与靶物质的耦合将产生超热电子，超热电子向靶中输运，碰撞电离1S 轨道电子，使得1S 轨道产生空穴，此时2P 轨道电子将向1S 轨道跃迁，产生K-alpha 光子辐射，产生的K-alpha 线辐射包括K-alpha1线和K-alpha2线[3]，分别对应于跃迁3/21/22221P S →和1/21/22221P S →。

图1 超短超强激光辐照靶物质产生K-alpha 光辐射的基本物理过程图2 超短超强激光辐照靶物质产生K-alpha光辐射的实验布局简图基于超短超强激光脉冲驱动的K-alpha源的实验布局如图2所示。

主激光经全反射镜反射后，被离轴抛面镜聚焦到铜等靶物质上。

X射线光谱仪（如：光子计数型CCD、晶体谱仪等）用于测量K－alpha线光谱，安装在与入射激光处于同一水平面的靶室法兰上（靶前、靶后位置均可），电子谱仪可同时在线测量实验产生的超热电子能谱。

大学英语综合教程 U2教案

Unit TwoLook Up at the StarsSuggested Teaching StepsLead-inText A➢Word & Sentence Study➢Structure StudyAfter-readingAdditional MaterialsLead-inDirections: Please watch the video clip and answer the questions.l . who was the speaker? what do you know about him?2 . According to the speaker, what are the ambitious experiments planned for the future?Tips:L.Stephen Hawking ( l942 — 20l8) was the former Lucasian Professor of Mathematics at the University of Cambridge and author of A Brief Hislory of Time which is an international bestseller.2.We will map the positions of billions of galaxies, better understand our place in the universe, and continue to explore space.Text A The Universe Gives up Its Deepest secret0ne of the greatest mysteries of the universe is about to be unraveled with the first detailed, threedimensional map of dark matter — the invisible material that makes up most of the cosmos.Astronomers announced yesterday that they have achieved the apparently impossible task of creating a picture of something that has defied every attempt to detect it since its existence was first postulated in l933.Scientists have known for many years that there is more to the universe than can be seen or detected through their telescopes but it is only now that they have been able to capture the first significant 3D image of this otherwise invisible material.Unlike the ordinary matter of the planets, stars and galaxies, which can be seen through telescopes or detected by scientific instruments, nobody has seen dark matter or knows what it is made of, though calculations suggest that it is at least six times bigger than the rest of the visible universe combined.A team of 70 astronomers from Europe, America and Japan used the Hubble Space Telescope to build up a picture of dark matter in a vast region of space where some of the galaxies date back to half the age of the universe —nearly 7 billion years.They used a phenomenon known as gravitational lensing, first predicted by Albert Einstein, to investigate an area of the sky nine times the size of a full moon. Gravitational lensing occurs when light from distant galaxies is bent by the gravitational influence of any matter that it passes on its journey through space.The scientists were able to exploit the technique by collecting the distorted light from half a million faraway galaxies to reconstruct some of the missing mass of the universe which isotherwise invisible to conventional telescopes.“We have, for the first time, mapped the large-scale distribution of dark matter in the universe,” the leading scientist said. “Dark matter is a mysterious and invisible form of matter, about which we know very little, yet it dominates the mass of the universe.”One of the most important discoveries to emerge from the study is that dark matter appears to form an invisible scaffold or skeleton around which the visible universe has formed.Although cosmologists have theorized that this would be the case, the findings are dramatic proof that their calculations are correct and that, without dark matter, the known universe that we can see would not be able to exist.“A filamentary web of dark matter is threaded through the entire universe, and acts as scaffolding within which the ordinary matter —including stars, galaxies and planets —can later be built,” the leading scientist said. “The most surprising aspect of our map is how unsurprising it is. Overall, we seem to understand really well what happens during the formation of structure and the evolution of the universe,” he said.The three-dimensional map of dark matter was built up by taking slices through different regions of space; much like a medical CT scanner builds a 3D image of the body by taking different X-ray “slices” in two dimensions.Data from the Hubble telescope was supplemented by measurements from telescopes on the ground, such as the Very Large Telescope of the European Southern Observatory and the Japanese Subaru telescope.Details of the dark matter map were released yesterday at the annual meeting of the American Astronomical society in Seattle and published online by the journal Nature. The map stretches half way back to the beginning of the universe and shows that dark matter has formed into “clumps” as it collapsed under gravity. Other matter then grouped around these clumps to form the visible stars, galaxies and planets.“The 3D information is vital to studying the evolution of the structures over cosmic time,” said another famous scientist.Astronomers have compared the task of detecting dark matter to the difficulty of photographing a city at night from the air when only street lights are visible.Scientists said the new images were equivalent to seeing a city, its suburbs and country roads in daylight for the first time. Major arteries and intersections become evident and a variety of neighborhoods are revealed.“Now that we have begun to map out where dark matter is, the next challenge is to determine what it is, and specifically its relationship to normal matter,” the leading scientist said. “We have answered the first question about where the dark matter is, but the ultimate goal will be to determine what it is.”Various experiments on Earth are under way to try to find out what dark matter is made of. One theory is that it is composed of mysterious sub-atomic particles that are difficult to detect because they do not interact with ordinary matter and so cannot be picked up and identified by conventional scientific instruments. Comparing the maps of visible matter and dark matter has already pointed to anomalies that could prove critical to the understanding of what constitutes dark matter.Detailed Study1.(Para. 2) Astronomers announced yesterday that they have achieved the apparently impossible task of creating a picture of something that has defied every attempt to detect it since its existence was first postulated in l933.【译文】昨天，天文学家声明：他们已完成了在此之前看似不可能完成的任务—— 自l933 年假设暗物质存在以来，人们一直尝试构建它的图像，但每次均以失败告终。

偶然的科学发现英语作文

偶然的科学发现英语作文Serendipity has played a pivotal role in the advancement of scientific knowledge throughout history Numerous groundbreaking discoveries have emerged not from meticulous planning and deliberate experimentation but rather from chance occurrences and unexpected observations These accidental scientific breakthroughs have profoundly shaped our understanding of the natural world and paved the way for technological innovations that have transformed our livesOne of the most famous examples of an accidental scientific discovery is the discovery of penicillin by Alexander Fleming in 1928 Fleming was conducting research on Staphylococcus bacteria when he noticed that a petri dish had been contaminated by a fungus Penicillium He observed that the areas of the dish around the fungus were clear of bacterial growth Fleming realized that the fungus must be producing an antibacterial substance which he later identified as the antibiotic penicillin This chance observation revolutionized the field of medicine and paved the way for the development of a wide range of life-saving antibioticsAnother notable example is the discovery of X-rays by WilhelmRöntgen in 1895 Röntgen was experimenting with cathode ray tubes when he noticed that a nearby fluorescent screen would glow even when the tube was covered Intrigued by this phenomenon Röntgen conducted further experiments and discovered that these mysterious rays could pass through human flesh but were blocked by denser materials like bone Through his accid ental discovery Röntgen opened up a new field of medical imaging and diagnostic tools that have become indispensable in modern healthcareThe microwave oven is another ubiquitous technology that emerged from an accidental scientific discovery In 1945 Percy Spencer a Raytheon engineer was testing a magnetron a key component of radar sets when he noticed that the candy bar in his pocket had melted This led him to realize that the microwaves being emitted by the magnetron were interacting with the chocolate causing it to heat up Further experimentation led to the development of the first microwave oven a technology that has revolutionized the way we prepare and consume foodThe discovery of radioactivity by Henri Becquerel in 1896 is another serendipitous breakthrough Becquerel was investigating the relationship between fluorescence and the emission of X-rays when he placed some uranium salts on top of a photographic platewrapped in black paper He expected the plate to remain unaffected but to his surprise the plate had become exposed indicating that the uranium salts were emitting their own invisible and penetrating rays Becquerel s accidental discovery of radioactivity paved the way for the development of nuclear physics and the use of radioactive materials in fields ranging from medicine to energy productionThe list of accidental scientific discoveries goes on from the vulcanization of rubber by Charles Goodyear to the discovery of the structure of DNA by James Watson and Francis Crick These chance occurrences and unintended observations have time and again challenged our understanding of the natural world and led to groundbreaking advancements that have improved the human conditionWhat is it about these accidental discoveries that makes them so impactful Firstly they often arise from a spirit of curiosity and a willingness to explore the unknown rather than a rigid adherence to a predetermined hypothesis Scientists who make accidental discoveries are typically open-minded flexible in their thinking and attuned to unexpected phenomena These qualities allow them to recognize the significance of chance events and to pursue lines of inquiry that may diverge from their original intentionsSecondly accidental discoveries tend to be transformative becausethey open up entirely new avenues of research and application The discovery of penicillin for example did not just lead to the development of a single antibiotic but rather catalyzed the entire field of antibiotics which has saved countless lives The discovery of X-rays likewise gave rise to a wide range of medical imaging techniques that have revolutionized healthcare In this way accidental discoveries have a multiplier effect generating cascades of further innovation and scientific progressFinally accidental discoveries often challenge our preconceptions and force us to revise our understanding of the natural world The discovery of radioactivity for instance upended the prevailing view of the atom as an indivisible and stable unit and ushered in the new field of nuclear physics Similarly the chance observation of the structure of DNA by Watson and Crick transformed our conception of genetics and heredity Breakthroughs that disrupt our existing models of the world are particularly valuable because they propel us to re-evaluate our assumptions and seek deeper truthsOf course not all accidental discoveries are immediately recognized for their significance and many go unnoticed or are dismissed as irrelevant at first But the history of science is replete with examples of chance occurrences that were ultimately revealed to be of immense importance The key is having an observant eye a curious mind and the willingness to explore unexpected phenomenaIn conclusion the role of serendipity in scientific discovery cannot be overstated Chance occurrences and unintended observations have time and again led to groundbreaking advancements that have transformed our understanding of the natural world and our ability to harness its power for the betterment of humanity As we continue to push the boundaries of scientific knowledge it is important that we cultivate an openness to the unexpected and a willingness to follow wherever the evidence may lead even if it diverges from our original intentions For it is often in the realm of the unanticipated that the most profound insights and innovations await。

2023-2024学年广东省广州市铁一中学高二下学期3月月考英语试题

2023-2024学年广东省广州市铁一中学高二下学期3月月考英语试题1. What I hate most is _______.A．laughing at B．to be laughed C．being laughed at D．being laughed2. This old castle is said ______ from designs by a famous architect in the 16th century.A．to build B．to have built C．to be built D．to have beenbuilt3. Our goal as educators is students to pursue their passions and achieve their dreams.A．inspired B．inspiring C．to inspire D．to be inspired 4. The pilot suggests that if you want to know how hard it is ________ in space, you can try eating while lying on one side.A．to swallow B．being swallowed C．to be swallowed D．swallowed5. Before the invention of the aeroplane, ________ in the sky like a bird was only a dream.A．flied B．to fly C．for flying D．man to fly6. ________ on the waiting list ________ will be selected for the leadership position in the non-profit organization?A．Who; do you think B．Whom; do you thinkC．Who; you think D．Whom; you think7. Last Sunday, Mr. Green asked Lily she had written to her mother .A．that; yesterday B．that; the day beforeC．whether; yesterday D．whether; the day before8. The policeman asked him ________ in a serious voice.A．where did he live B．where he livedC．where he lives in D．where does he live in9. If he comes back from work, I’ll tell him when ________ and visit him.A．will you come B．do you come C．you come D．you will come10. His pale face suggested that he__________ill and his teacher suggested that he__________to the hospital at once.A．should be; send B．was; should send C．was; be sent D．were; be sent11. Much unhappiness has been suffered by those people who have never recognized that it is as necessary to make themselves into whole and harmonious personalities as themselves clean, healthy and financially independent.A．kept B．keep C．to keep D．keeping12. They realized that the problem Ted put forward was difficult _______.A．to solve B．solved C．to be solved D．solving13. The discovery of gold in Australia led thousands to believe that a fortune ________.A．is made B．would made C．was to be made D．had made14. Her dress has become loose. She appears ______ weight.A．to lose B．being lost C．losing D．to have lost15. With an important test ______ after the vacation, I don’t think you can really have a good time.A．to take B．taking C．to be taken D．takenEvery day people joined archaeologists and artists in finding some of the year’s most dramatic discoveries. Below are some examples of 2023.“Naughty pupils”-ancient punishment method resurfacesArchaeologists discovered 18,000 ink-carved pieces of pottery-known as “ostraca”—at the site of Athribis early this year, and among them were hundreds of fragments(碎片)with a single symbol repeated front and back.Those scribbles(潦草的文字)are evidence of ‘naughty “pupils” being made to write lines, according to researchers a Germany’s University of Tuebingen. The fragments also included receipts, school texts, trade information and lists of names.Van Gogh peers out in hidden portraitThere is one more known van Gogh’s self-portrait in the world, and it was hidden behind a painting of a peasant woman. People made the discovery when they took an X-ray of one of his portraits from 1885 and discovered the artis t’s own image behind layers of cardboard and glue. While X-rays often reveal how artists-changed their compositions, the full self-portrait of van Gogh came as a huge surprise, who was known to reuse canvase(画布)to save money.Another treasure collection from SanxingduiThe Sanxingdui archaeological site has produced thousands of relics. The latest discovery, reported by Chinese state media in June includes 3,155 objects, a turtle shell-shaped box and a sacrificial altar among them. A team has been digging six places of the site, turning up more than 13,000 objects so far. Last year, the relics they uncovered included a golden mask, ivory artifacts(手工艺品)and a jade knife. The Sanxingdui culture still remains mysterious, as it left behind no written records or human remains, though many believe it to be part of the ancient kingdom of Shu, which ruled along the upper stream of the Yangtze River until it was conquered in 316 BC.16. What led to the researchers’ conclusion about the fragments?A．The repeated symbol. B．Trade information.C．Lists of pupils’ names.D．The mark of ink.17. Why did van Gogh hide his self-portrait in a painting?A．To keep away from X-rays.B．To save money.C．To make his works more mysterious.D．To help people find his composition.18. Which is the newly-unearthed relic of 2023 in Sanxingdui site?A．A jade knife. B．A golden mask.C．A written record. D．A turtle shell-shaped box.Twenty-two years ago, I won a Nobel Prize, together with Tim and Leland Hartwell, for our work on how cells control their division.The prize changed our lives. Suddenly you become a public figure being asked to do all sorts of things: to give lectures, quite often on topics you know little about; to sit on committees and reviews you are not always well qualified to be on; to visit countries you have barely heard of. It is like having a whole new extra job, with upwards of 500 requests a year.A recent study suggests that in general the extra commitments that Nobel winners take on result in fewer papers after their awards. There may be some truth to this given the extra demands on one’s time, but of course prestigious awards also allow new projects and research to be undertaken.What effects did the Nobel Prize have on my subsequent career and work? It has certainly helped me to get scientific leadership positions. Within a year of getting the prize I was offered and acceptedthe presidency of Rockefeller University in New York. Having the prize also helps to get things done. For example, I have been involved in the merging of two separate cancer research charities to form Cancer Research UK. And it has helped me support causes I care deeply about. I became an ambassador for Ukraine education and science to help raise money for schools in that shattered country. Moreover, having a Nobel does help attract high-quality research colleagues. I have just started three excellent new PhD students. It is a privilege for me to be able to pursue curiosity-driven research at this late stage of my career.However, one thing I am glad to say that the Nobel Prize did not influence was peer review from my fellow scientists, assessing the suitability of my own research for publication, and my grant applications for funding. My rejection rates have remained essentially the same before and after the prize. And that, of course, is exactly how it should be.19. What is the author’s purpose in writing paragraph 2?A．To share his pride in winning a Nobel.B．To express his regret at the changing of life.C．To show his self confidence in handling the extra jobs.D．To display his overburdened tasks after winning a Nobel.20. What does the underlined word “merging” in paragraph 4 mean?A．Competition. B．Comparison. C．Combination. D．Construction. 21. What is paragraph 4 mainly about?A．The special privileges the Nobel winner has.B．The positive impacts the Nobel Prize generates.C．The great contributions the Nobel winner makes.D．The scientific leadership the Nobel Prize provides.22. What message does the author mainly want to convey in the last paragraph?A．The spirit of science lies in seeking facts and truth.B．Winning a Nobel Prize has an impact on peer review.C．Extra commitments make Nobel winners less productive.D．The approval a Nobel winner receives is equal to rejection.The World Health Organization recently said that it planned to add gaming disorder(游戏成瘾)to its new list of disease classifications, angering the gaming industry but pleasing doctors who hope it may make treatment more easily available.Some US experts said it would make little difference when it comes to helping people with the disorder, although others said it would bring attention to a disorder that people sometimes don’trecognize. Many of us enjoy video games, but does playing our favorite game for a couple of hours every night mean we’re suffering from gaming disorder? Not, according to the WHO. The symptoms listed by the WHO include a lack of control over gaming, treating gaming more seriously than other life interests and daily activities, and continuing to play games despite the negative consequences that playing them might have. “The behavior pattern is enough to result in significant damage to one’s personal, family, or social life,”the WHO said.Meanwhile, Douglas Gentile of Iowa State University has carried out influential research into the cause of gaming addiction in young people. “I and many others had assumed that gaming is not really a problem but is a symptom of other problems,”he told NBC News. Many had thought it was simply a failure of self-control.To see if it was，Gentile’s team studied a group of children who had been gaming for several years. “We found that when kids became addicted，their anxiety increased…and their grades decreased,”Gentile said. When kids were able to b ack off from gaming, their symptoms disappeared, he added. Gentile thinks medical organizations should pay attention to the WHO’s proposal. “This isn’t an issue of opinion; it’s all issue of science,”he said. “This is a major scientific and medical organiz ation. They don’t do things lightly and without reason.”Dr Petros Levounis, chair of psychiatry at the New Jersey Medical School at Rutgers University, said that he hoped the WHO’s proposal would lead to more research into obsessive (过度的)behavior among al l types of people. “Now，there is renewed interest and excitement,” he said. 23. Which of the following is a sign of gaming disorder according to the WHO?A．Putting games before everything else.B．Keeping playing until winning the games.C．Playing games for several hours every night.D．Having a few hobbies besides playing games.24. Why is Gentile’s research mentioned?A．To explain the cause of gaming addiction.B．To show the influence of gaming disorder.C．To show the reasons behind the WHO’ s decision.D．To introduce the study that influenced the WHO’s proposal.25. What can we learn from what Levounis said?A．It needed further research to make it more convincing.B．It would do little to help people with gaming addiction.C．It would encourage new cures for gaming disorder.D．It would encourage studies about similar diseases.26. What does the author intend to tell us about gaming disorder?A．Its description. B．Controversial views.C．Its harmful effects. D．Explanations of the WHO’s decision. Each year, the world loses about 10 million hectares of forest—an area about the size of Iceland—because of cutting down trees. At that rate, some scientists predict the world’s forests could disappear in 100 to 200 years. To handle it, now researchers at Massachusetts Institute of Technology (MIT) have pioneered a technique to generate wood-like plant materials in a lab. This makes it possible to “grow” a wooden product without cutting down trees.In the lab, the researchers first take cells from the leaves of a young plant. These cells are cultured in liquid medium for two days, then moved to another medium which contains nutrients and two different hormones. By adjusting the hormone levels, the researchers can tune the physical and mechanical qualities of the cells. Next, the researchers use a 3D printer to shape the cell-based material, and let the shaped material grow in the dark for three months. Finally, the researchers dehydrate the material, and then evaluate its qualities.They found that lower hormone levels lead to plant materials with more rounded, open cells of lower density, while higher hormone levels contribute to the growth of plant materials with smaller but denser cell structures. Lower or higher density of cell structures makes the plant materials softer or more rigid, helping the materials grow with different wood-like characteristics. What’s more, it’s to be noted that the research process is about 100 times faster than the time it takes for a tree to grow to maturity!Research of this kind is ground-breaking. “This work demonstrates the great power of a technology,” says lead researcher, Jeffrey Berenstain. “The real opportunity here is to be at its best with what you use and how you use it. This technology can be tuned to meet the requirements you give about shapes, sizes, rigidity, and forms. It enables us to ‘grow’ any wooden product in a way that traditional agricultural methods can’t achieve.”27. Why do researchers at MIT conduct the research?A．To grow more trees. B．To protect plant diversity.C．To reduce tree losses. D．To predict forest disappearance.28. What does paragraph 2 mainly tell us about the lab research?A．Its theoretical basis. B．Its key procedures.C．Its scientific evidence. D．Its usual difficulties.29. What does the finding suggest about the plant materials?A．The hormone levels affect their rigidity.B．They are better than naturally grown plants.C．Their cells’ shapes mainly rely on their density.D．Their growth speed determines their characteristics.30. Why is the research ground-breaking according to Berenstain?A．It uses new biological materials in lab experiments.B．It revolutionizes the way to make wooden products.C．It challenges traditional scientific theories in forestry.D．It has a significant impact on worldwide plant growth.Art comes in two main categories: realistic and abstract. Realistic art aims to show real-life scenes, people, and objects exactly as they appear. It involves paying close attention to details, making things look like photographs. 31 . It’s more about expressing feelings, emotions, and ideas.Realistic art is easy to understand. Viewers can easily recognize what is portrayed. Take the Mona Lisa, for example—it’s a realistic painting of a lady with a mysterious smile. 32 , helping us to learn about the past.Unlike realistic art, abstract art is more about being creative. 33 . They use shapes, colors and patterns to express feelings and ideas. Abstract art means different things to different people. Some people enjoy trying to figure out what the artwork conveys.34 . Realistic art needs precision in drawing or sculpting to make things look real. Abstract art requires imagination to use shapes and colors in new ways. Many artists are skilled in both. They create realistic pieces to demonstrate their technical skills and abstract ones to display their creativity.As for personal preference, some people prefer the clear stories of realistic art while others are attracted to the mystery of abstract art, interpreting meanings in the shapes and forms. Together, the two kinds of art make the art world diverse and engaging. 35 .Wildlife has been greatly threatened in the modern age. There are species (物种) that are ________ every day. The white-naped crane is a typical example. So scientists are trying their best to________ the species from going out of existence.Chris and Tim work at a zoo, helping endangered cranes with their ________ . Emma, a female crane, has been in their ________ since she arrived in 2004.Born at an international crane foundation, Emma was ________ by human caretakers. This led to an unexpected consequence, though she had a wonderful time there. Emma had ________ taken herself as a crane and become deeply attached to humans. She refused to live with male cranes, and even had a ________ for killing some of them, which made it impossible for her to become a mother._____ , the two zookeepers didn't want to see the extinction (灭绝) of this precious species. With their patience and efforts, they successfully developed a ________ of artificial breeding (人工繁殖) and natural reproduction. This ________ Emma to give birth to five baby cranes.The two keepers are proud of their productive work. But before they can be ________ , more efforts must be made, because the population of the crane in the wild is on the ________ , and many other species appear headed toward extinction. ________ , not everyone has realized that wildlife has thoughts, feelings, and most importantly, equal rights to survive.How can we bridge the ever-widening gap that separates us from other animals? Chris and Tim offered us the ________ : human beings took it for granted that their brains held all the solutions, but maybe their hearts can be a better ________.36.A．growing B．migrating C．competing D．disappearing 37.A．ban B．save C．split D．remove38.A．abortion B．recreation C．reproduction D．administration 39.A．care B．eye C．mind D．story40.A．found B．chosen C．raised D．seized41.A．never B．always C．unluckily D．cheerfully42.A．gift B．skill C．concern D．reputation43.A．Therefore B．Moreover C．However D．Instead44.A．combination B．collection C．strategy D．system45.A．forced B．forbade C．taught D．enabled46.A．defeated B．grateful C．assured D．tolerant47.A．list B．rise C．agenda D．decline48.A．In contrast B．After all C．By the way D．On the contrary 49.A．course B．excuse C．answer D．reward50.A．guide B．treat C．example D．companion阅读下面短文，在空白处填入1个适当的单词或括号内单词的正确形式。

Xray基础知识

X射线物理与防护
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X射线的发现与发展
X射线的发现
X-ray 是由德国仑琴教授在1895年所发现。这种由真空管发出能穿透物体的辐射线，在电磁光谱上能量较可见光强，波长较短，频率较高，相类似之辐射线有宇宙射线等。
X射线机的发展简史
1. 离子X射线管阶段(1895~1912) 2. 电子X射线管阶段(1913~1928) 3. 旋转阳极X射线管阶段(1929~) 4. X射线影像增强器和X射线电视,电影阶段(1952~) 5. X射线计算机断层扫描装置(X-CT)(1972~) 6. 数字X射线机阶段
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X射线的防护
辐射损伤机理
X射线能引起构成机体细胞, 组织的原子或分子电离. 影响辐射损伤的因素: 辐射性质; 射线剂量; 剂量率; 照射方式; 受照
部位; 环境因素
实际工作中的防护
限制曝光时间, 曝光剂量做好个人屏蔽与防护
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X射线管特性
X射线管热容量
1HU=1.41•kV • mA • s
X射线管的生热和冷却曲线
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高压发生器简介
X-Ray Generator功能
提供电力给X-Ray Tube和其他系统组件; 控制影响影像品质之技术条件，如mA，kVp，sec.等
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缺陷
管电压脉动系数为100%. 射出大量有害X射线.
单相电路只取三相系统中的一相,负载功率较大时, 造成供电系统严重不平衡.

X射线的发现

The Discovery of X-rays X-射线的发现One hundred years ago this month, Wilhelm Conrad Rontgen cast thefirst x-ray images by chance 一百年前的这一个月,威廉.康德拉.伦琴意外地得到了第一张X-射线的图象by Graham FarmeloThe maid had to be dispatched several times to call him from his laboratory. 必须几次差遣侍女才能将他从实验室中叫出来When Wilhelm Conrad Rontgen, the head of the physics department at the University of Wurzburg, finally joined his wife at the dinner table, he was distracted, eating little and saying less.威廉.康德拉. 伦琴是伍尔兹伯格大学物理系系主任,当他终于和他的妻子一起坐在吃正餐的卓子旁时,他是心烦意乱的,吃得很少,说得更少.No sooner had they finished their meal than he returned to his work.他们一起吃完饭,他就回去工作了.It was November 8,1895. For several months, Rontgen had been investigating the behavior of cathode rays, later identified by other scientists as electrons.时间是1895年11月8日.几个月来,伦琴一直在研究后来由其他科学家确定为电子的阴极射线的特性.He knew that these rays, copiously produced in a special evacuated tube charged with high-voltage elctricity, penetrated only a few centimetersof air.他知道,在一个充有高压电的特制的真空管内大量产生的这些射线, 只能渗入几厘米的空气.And so he was astonished on that Friday evening before dinner to see flickering image so far away from the tube that it could not have been caused by the cathode rays, but it appeared only when they were present. 所以他对星期五晚餐前的傍晚,看到一个闪烁的图象离真空管这样远感到十分惊异,因为它不可能是由阴极射线引起的,但是只有当阴极射线存在的时候,它才出现.Rontgen pursued the matter intensively that night, failing to hear an elderly laboratory assistant knock at the door enter and leave. For days after, he ate and slept in his laboratory.(So preoccupied was he with this puzzle that he ignored a cardinal rule of experimentation he did not begin to take notes until nearly a week later. ) 那天晚上,伦琴全神贯注地考虑这一问题,以致连一个老的实验助手敲门和进出的声音都没有听到.以后几天,他吃住都在实验室.(他是这样全神贯注地思考这一难题,以致他忽略了实验室的一项基本规则-直到将近一个星期以后才开始记笔记).Only by repeating the experiment many times did Rontgen come to believe that a new type of ray had cast the image he saw. Because he did not know the nature of these rays, he called them x-ray--"X" for unknown. 只有通过重复这一实验许多次以后, 伦琴才开始相信一种新型的射线造成了他所看到的这幅图象.因为他不知道这些射线的性质,他就将其称为X-射线--"X"表示未知的.He told no one but his closest friend, Wthzburg zoologist Theodor H. Boveri, about the rays."I have discovered something interesting. " he said,"but I do not know whether or not my observations are correct. "关于这些射线,除了他的最亲密的朋友,伍尔兹伯格大学的动物学家 Theodor H.Boveri之外,他没有告诉任何人."我发现了一些有趣的东西,"他说," 但是我不知道我的观察是否正确."First to witness his experiments was his wife, Bertha whom he invitedinto his laboratory on the Sunday before Christmas. There he made aportrait exposing the bones in her left hand-the first permanent x-ray photograph of a part of the human body.首先亲眼看到他的实验的是他的妻子Bertha,是他在圣诞节前的星期天请她到他的实验室来的.他在那里拍摄了一幅展示她的左手骨骼的照片-第一张永久性的部分人体X-射线照片.The week after Christmas, Rontgen published a short paper, and by thefirst week of the new year, newspapers all over the world began reporting his discovery. Never before had a scientific breakthrough caused such excitement in the popular press. Any number of truly remarkable inventions emerged during the late 19th century, but the public was particularly fascinated by Rontgen`s find; it provide a wayto probe the human body without cutting it open.圣诞节后一个星期,伦琴发表了一篇简短的论文,到了新年的第一个星期,全世界的报纸都开始报导他的发现.在大众化的出版物中,以前没有哪一个科学上的突破引起这样大的激动.在十九世纪后期出现了许多真正很著名的发明,但是公众特别被伦琴的发现所迷住了,它提供了一种检查人体的方法,而不需要切开人体.The diagnostic potential of x-ray was grasped almost immediately. Within a month, surgeons in Europe and the U.S. were using them in a variety of ways. Perhaps the most bizarre early application was an attempt,described by the College of Physicians and Surgeons in New York City, "to reflect anatomic diagrams diagrams directly into the brainsof their students, making a much more enduring impression than the ordinary methods of learning anatomic details. " Some 20 years would pass before scientists determined the true nature of x- rays. All the same, Rontgen`s initial announcement proved to be one of the most celebrated in the history of physics-despite the several scientists atthe time who argued that it owed more to luck than to skill. 人们几乎立刻就抓住了用X-射线进行诊断的可能性.在一个月内,欧洲与美国的外科医生就以各种各样的方式应用它们. 也许最奇异的早期应用是纽约市内科与外科医生学院所描述的一种尝试,即"直接将解剖图反射到他们的学生的大脑中, 产生比学习解剖细节的普通方法更为持久的印象."大约过了20年,科学家们才确定了X- 射线的真正的性质.然而,伦琴最先宣布他的发现被证明在物理学的历史中是最有名的一个发现--尽管当时有几个科学家争辨说,这项发明更多的应归功于侥幸,而不是特殊的技巧.Cathode Rays 阴极射线Although he eventually attained celebrity as a physicist, Rontgen had originally planned to become an engineer. He was born in 1845 into a well-to-do(富有的)mercantile family(商人家庭)in the small town of Lennepin northwestern Germany and spent most of his childhood in the Netherlands. At age 20, he moved to Zurich(苏黎士)and three years later graduated witha bachelor`s degree in engineering from the Federal Institute of Technology. (三年后毕业于联邦理工学院,并且获的了工程学士的学位)Although Rontgen had not taken any experimental physics courses as an undergraduate, he decided to pursue graduate work in the field, persuadedin part by his mentor, August E.E. Kundt, professor of physics at the institute.虽然伦琴作为一个大学生没有学习过任何实验物理的课程,但是部分是在该学院的物理学教授,他的导师 August E. E. Kundt 的劝说下,他决定选择在该领域的研究生课程.After receiving his Ph.D. in 1869, Rontgen held a series of teaching positions at sundry(各式各样的)German universities. In collaboration with Kundt,he made careful studies of the behavior of matter and was, for example, the first to demonstrate(using a homemade thermometer) that it is easierto heat humid air than dry air. Other aspects of his work lent strongsupport to the unified theory of electricity and magnetism put forward inthe 1870s by Scottish mathematical physicist James Clerk Maxwell.他的另一方面的工作对十九世纪七十年代苏格兰的数学物理学家J.C.马克斯韦尔的一元化电磁理论提供了强有力的支持.Rontgen was 43 years old when he became professor of physics and director of the physical institute at the university in Wurzburg, a small, prosperous Bavarian city. On the second floor of the institute, heand his wife shared ample accommodations, including a study connectedto one of two private laboratories. This appointment must have givenhim considerable pleasure; 18 years earlier the university had not allowed him to pursue a position as a professor there, because he couldnot produce an Abitur, a certificate testifying that he had commpletedhigh school.当伦琴成为Wurzburg市这所大学的物理学教授和物理研究所的主任时,他才43岁.Wurzburg是一座较小的,但是繁荣兴旺的巴伐利亚城市.在研究所二楼,他和他的妻子分到了宽敞的宿舍,包括与两个专用实验室之一相连结的一个书房.这项任命使他非常高兴,18年前这所大学没有让他在这里担任教授职位,因为他不能出示证明他曾经完成了高中学业的毕业证书.Rontgen devoted a good deal of time to winning laboratory space, additional staff and other resources for the fledgling physics department at Wurzburg. By dint of his efforts, he sought to make it among the best in Geermany. His colleagues knew him to be a particularlyambitious, meticulous worker, who was extraordinarily knowledgeable about the latest developments in all areas of physics. Although he was sociable, during his entire working life he hardly exchanged a professional word with another physicist. 伦琴将大部分时间花在为Wurzburg大学初创的物理系争取实验室有更大的场所, 更多的职员与其他资源上.他企图凭借自己的努力,使Wurzburg大学物理系跻身德国最好的物理系之列.他的同事都知道他是一个特别有抱负的,细心的人,他对物理学所有领域中的最新进展都有非常透彻的了解.虽然他是爱交际的,但是在他的整个研究生涯中, 他几乎没有和另一个物理学家交换过专业上的只言片语.In June 1894 he began studying cathode rays, then an extrimely popular research topic. German physicist Eugen Goldstein of the University of Berlin had named these rays 18 years earlier. Goldsteinand several others established that cathode rays were negatively charged and that they traveled considerably slower than the speed of light. But one central puzzle remained:whereas most British physicists believed that these rays were particles, their German counterparts thought them to be disturbances in some all-pervasive ether.在1894年6月, 他开始研究阴极射线,当时那是一个极为普通的研究课题.18年前, 柏林大学的德国物理学家Eugen Goldstein 给这些射线命了名.Goldstein与其他几个人确定, 阴极射线带负电荷并且它们传播速度比光的速度慢得多. 但是仍有一个重要的难题没有解决:大部分英国物理学家认为这些射线是粒子,而他们的德国同行则认为它们是一些全弥漫性以太中的扰动.We shall probably never hnow Rontger`s motivation in turning his attention to cathode rays. His notebooks indicate that he was checking results obtained by two experimenters at the University of Bonn- the recently deceased Heinrich R. Hertz, the discoverer of radio waves, and his assistant, Philipp E. A. Lenard. Rontgen`s work was interrupted in the jall, when he was elected rector of the university, its highest office. Some scientists become addicted to the manifold pleasures of administration, but not Rontgen. By the autumn of the following year, he had returned to his laboratory.我们大概将永远不会知道伦琴将其注意力转向阴极射线的动机是什么.他的笔记本表明,他在检验无线电波的发现者--刚去世的赫兹与他的助手Philip E.A.Lenard在柏林大学进行的两项实验所获得的结果.在这一年的秋季,当伦琴被选为这个大学的校长这一最高职务的时候,他的研究被中断了. 一些科学家耽溺于行政管理的各种各样的乐趣,但是伦琴却不是这样.到了下一年秋天,他又回到了实验室去了.Discovery Day(发现日)Today a visitor to room 119A of the Technical College in Wurzburg can quickly tell that it is a special part of the buiding. It was in this high-ceilinged space, six meters square, overlooking the botanical gardens and leafy Pleicher Ring road(now called the Rontgen Ring) , that Rontgen made the discovery that was to astonish the world. Although this one-room museum does not contain the actual apparatus he used, it breathes history. It is no wonder that the college staff reverentially lower their voices when they usher visitors into the shrine. 今天凡是到伍尔兹伯格理工学院119A室的参观者都能够很快说出哪里是这栋建筑物的特别之处.就是在这个有高天花板,可俯瞰植物园与树叶覆盖的Pleicher环行路( 现称为伦琴环行路)的六平方米空间,伦琴做出了震惊世界的发现. 虽然这个仅有一室的博物馆没有陈列他实际用过的仪器,但是它散发出历史的气息.当这所学院的职员带领参观者走进这块圣地时,难怪他们都虔诚地把说话的声音压得很低.The night of Novenber 8, 1895, together with its seven-week aftermath of secrecy, is a rich source of fascination and speculation. Rontgen himself did much to fuel this interest, no doubt unintentionally, by his characteristic reticence and inscrutability, and also because he never gave a definitive account of what actually happened. The description here is, therefore, a version of the events, compiled fromRontgen`s reported comments and scant writings.1895年11月8日的晚上,加之该发现被保密七个星期的后果是吸引力与推测的丰富源泉. 由于伦琴特有的沉默寡言与不可思议,还因为他从不对实际发生了什么给予一个明确的说明,伦琴本人不是故意地给这种兴趣火上加油.所以,这里所描述的只是根据伦琴的已报导过的评论与与有限的文件而编辑的对这一事件的看法.The equipment he used to investigate cathode rays at that time among the best available. He preferred to build his own apparatus whenever possible, but most of the equipment for these experiments had been suppplied and designed by leading instrument makers. 他用来研究阴极射线的设备是当时可以得到的最好的设备.只要可能,他就宁可自己制造仪器, 但是用于这些实验的大部分设备则是由第一流仪器制造厂家提供和设计的.To prepare his cathode ray tube. Rontgen removed gas and vapor from it using a vacuum pump. In this standard procedure, the tube was pumped for three or four days to reduce the pressure to below about a thousandth of the usual atmospheric pressure. This low pressure enabled the cathode rays to pass as freely as possible through the tube , colliding only rarely with gas molecules.为了制备阴极射线管, 伦琴用真空泵从管子中除去气体与蒸气.在这一标准工艺过程中,管子被抽吸了3,4 天以便将压力减到大约通常大气压力的千分之一以下. 这样低的压力可以使阴极射线尽可能自由地通过管子,很少和气体分子碰撞.An induction coil, similar in principle to the transformer that generates the high-voltage sparks in a car`s engine, supplied the electric current. Rontgen`s transformer took a 20- volt suppplly from batteeries housed in the basement of the institute and converted it into individual pulses of about 35000 volts apiece. Every second about eight pulses were generated, catch one audibly accompanied by a loud crack coming from the electrical discharge between the ends of the secondary coil.一个原理上类似于汽车发动机中产生高压火花的变压器的感应线圈提供电流.伦琴的变压器从放在研究所的地下室内的电池中获得20伏电流,并将其转换为大约各35000伏的单个脉冲.每秒大约产生8次脉冲,每次脉冲都可以听到伴有来自次级线圈端部之间放电的响亮的噼啪喀啦声.Rontgen was working alone, as he normally did. He knew well that cathode rays caused a barium platinocyanide-coated screen to fluoresce with a characteristic green color. But he probably found this glow difficult to discern because he was partially color blind. so he darkened the room and blocked all light coming from the gaslit street outside. He also covered the cathode- ray tube with pieces of black cardboard, pasted together so that no visible light could escape from the tube.伦琴就像平常那样单独在进行研究.他很清楚,阴极射线能够使氰亚铂酸钡涂覆的屏幕产生具有特有绿色的荧光.但是他大概发现这种辉光很难辨识,因为他是部分色盲.于是他将房间遮起来,挡住来自外边街道上煤气灯的所有光线. 他也用粘贴在一起的黑卡片将阴极射线管盖上,以便使可见光不致从管中逸散出来.In the pitch black of the laboratory, hearing the coil snapping in the background, Rontgen happened to notice on his worktable a smallpiece of paper sparkling as though a single ray of light had fallen on it. This light, he realized, came from the letter "A" that a student had written on the sheet in platinocyanide solution. He must have been astonished: cathode rays could not have traveled the distance from his tube to the paper to reveal its markings. Further experiments indicated that indeed the flickering light was caused by something emitted from the tube more penetrating than cathode rays.在漆黑的实验室中,伦琴听到线圈在背景中劈拍作响,他偶然注意到在他的实验桌上有一小块纸在发火花,仿佛一道光线照在它上面. 他认为这道光线来自一个学生用氰亚铂酸盐溶液写在纸上的字母"A".他一定大吃一惊:阴极射线不能传播从真空管到纸这样远的距离来显示其痕迹. 进一步的实验表明,闪烁的光的确是由真空管内发射出来的东西引起的,它的穿透性比阴极射线更强."By accident,"Rontgen said, he discovered that this emanation went unhindered through a piece of black paper. He then demonstrated that it passed though a playing card. A thick book, he noted, cast a sharp shadow on the screen, giving a clear indication that he was observing rays of some kind, moving in straight lines. When he examined the exlent to which the rays penetrated metals, he had perhaps the biggest surprise of all. As he put a small piece of lead in the path of the rays , he saw not only the object`s dark shadow, but a fainter shadow in the shape of his thumb and finger as well. That shadow in turn enclosed another set outlining the bones of his hand."无意中"伦琴说,他发现这种发射出来的东西不受阻碍地穿过一张黑纸.他接着证明它穿过了一张扑克牌.他注意到, 一本厚书在屏幕上投下一个轮廓清晰的阴影,清楚地表明,他正在观察某种以直线移动的射线.当他检查这些射线穿透金属的程度时,他也许对这一切感到非常吃惊. 因为他放置了一小块铅在射线的通路上,他不仅看到了铅的较深的阴影,而且也看见了呈现他的大姆指与其他几个手指形状的模糊阴影. 那片阴影本身又包含勾画出他的手指骨骼的另一组阴影.Rontgen elucidated the properties of x-rays in a classic piece of experimentation. Using a magnet to deflect a beam of cathode rays so that it struck the side of the vacuum tube in different areas, he convinced himsellf--in a matter of minutes- - that the x- rays were emitted from the point at which the cathode rays hit the interior wall of the tube and not from any other point in the circuit. He also showed that magnetic forces did not affect x-rays, confirming that they had no electrical charge.伦琴用一个经典的实验阐明了X-射线的性质.用一块磁铁使一束阴极射线偏转,以致它照射在真空管侧面的不同区域以后,他确信, 在大约几分钟内--X-射线是阴极射线照在真空管的内壁那一点, 而不是电路上的任何其它点发出来的.他还指出,磁力不影响X-射线,证明它们不带电.Rontgen nixt determined that x-rays, like cathode rays, could darken a photographic plate. By placing objects between the source of the rays and the plate, he took permanent x-ray photographs, exploiting the deffering abilities of materials to transmit the rays. In taking these photographs, he pioneered three key areas of x-ray imaging. First, aphotograph of his closed wooden box of weights clearly revealed its contents, thus presaging the security application found at every airport check-in.(伦琴下一步测定了X-射线,它像阴极射线一样,能够使照相底板变黑.通过将物体放在射线源与底板之间,利用材料传送射线的不同能力, 他摄取了持久性的X-射线照片.在摄取这些照片中,他开发X-射线成像的三个关键性的领域. 首先,他的一幅装有重物的关闭了的木箱的图象,清楚地显露出它的内容物, 从而预示了在每个机场安全检查时的应用.)Second, an x-ray image of his hunting rifle revealed a flaw inside the metal of the gun:it was the first time a hidden structural fllaw had been exposed without destroying the object. Finally, and most startling of all, he took a permanent x-ray photograph of his wife`s left hand, revealing the bones and the rings that she was wearing. To produce this image, Bertha held her hand still against the plate for about 15 minuted, which gave her a dose of x- rays that dangerously exceeded the limits set in modern health and safety standards. Such are the hazards that pioneers unwittingly face.(第二,一幅他的猎枪的X- 射线图象揭示在枪的材料内部有一条裂缝: 一条隐藏在结构中的裂缝被揭露出来而没有毁坏物体这还是第一次.最后,并且也是所有三个领域中最使人吃惊的是, 他拍摄了一张他的妻子左手的永久性X-射线照片,显露出她的骨骼与她戴着的戒指.为了产生这幅图象,Bertha的手对着板保持静止不动约15分钟,她接受的X-射线的剂量危险地超过现代保健与安全标准所设定的极限.这是开拓者们不知不觉地面对的危险.)Rontgen carefully compared the properties of x- rays with those of visible light. Although both are electrically neutral and can cast sharp shadows, he found that in other ways, the x- ray appeared to deffer from light. He was unable to reflect them, nor could he refract them( he could not change their direction by making them traverse from one medium to another, for example, by passing them through a glass prism). In addition, he found no evidence that they could be diffracted (the rays did not bend around obstacles in their path).(伦琴仔细地比较了X-射线与可见光的特性. 虽然两者在电学上都是中性的而且能够投射边缘清楚的阴影,他发现在其他方面,X-射线似乎不同于光线.他既不能够反射X-射线,也不能使它们折射(他不能使4它们从一种介质穿向另一种介质,例如, 使它们通过玻璃棱镜而改变方向.)此外,他没有发现它们能够衍射的证据(这些射线在它们的通道中不会在障碍物周围弯曲).The similarifies between x-rays and light nonetheless led Rontgen to propose that they were in some way related. According to the theory put forward by Maxwell in 1873, light is an electromagnetic wave propagating in the ether, having electrical and magnetic signals vibrating perpendivular to the wave`s direction of motion. Rontgen tentatively suggested that the x-rays were vibrations in the ether in the same direction in which the rays were traveling. This speculation- -which turned out to be wrong--concluded his paper, On a New Kind of Rays, a Preliminary Communication, a masterpiece of experimental pphysics and concise reporting for which the University of Wurzburgreceives requests to this day.(然而,X-射线与光线间的类似性导致伦琴提出, 它们在某些方面是相近的.按照Maxwell在1873年提出的理论, 光是一种在以太中传播的电磁波,具有垂直于波运动方向振动的电磁信号.伦琴试探性地提出,X- 射线是在以太中的振荡,其方向与射线的传播方向相同.这一推测--被证明是错误的--是他的论文"关于一种新射线,初步信息"得出的结论.这是实验物理学的一篇杰作, 同时Wurzburg大学直至今天都接到获得这篇简报的要求.)Three days after Christmas in 1895, he gave the 10-page, handwritten manuscript to the secretary of the Wurzburger Physical Medical Society with the unusual requesst that it be published quickly. On New Year`s Day, after postingcoopies of his manuscript and photographs to several leading European physcists, he remarked to his wife:"Now there will be the devil to pay."(在1895年圣诞节后三天,他将一份十页的手稿交给伍尔兹伯格物理医学学会的秘书并提出一个异乎寻常的申请,要求早点出版它.将它的手稿副本与照片邮寄给欧洲的几个第一流的物理学家后的新年这一天,他对他的妻子说:" 现在将有无穷的后患了.")The Immediate Aftermath直接的后果In a few days Iwas disgusted with the business. I could not recognize my own work in the reports any more," Rontgen wrote to former assistant about a month after the news of his discovery broke. He was angry and upset by the initial newspaper stories, which seized on his remarkable photographs as though they represented by far the most immportant aspect of his experiments. Rontgen himself was for more interested in discovering both the true nature and the properties of x-ray."有几天我讨厌工作.我再也不能在报告中承认自己的工作," 他的发现这一新闻透露出去以后大约一个月,他写信告诉他以前的助手说.他生气了, 并且被报纸上最初的描述搞得心烦意乱,这些描述把重点放在他的著名的照片上,好像它们代表他的试验的最为重要的方面.伦琴自己更为感兴趣的是发现了X- 射线的真正的性质和特性.The first newspapeer account appeared on Sunday, January 5, in the Vienna Presse, and by January 16, word had reached the New York Times. Most scientists resd these reports before translations of the original paper became available, so it is not surprising that several experts did not initially believe them. Among these skeptics was Lord Kelvin of the University of Glasgow, regarded by many at the time as the greatest living scientist. Kelvin at first thought that the announcement was a hoax(he soon changed his mind).第一篇新闻报导出现在1月5日星期天的<维也纳新闻报导>中,到了1月16日,<纽约时报>也刊载了这一消息.在获得原文的译文之前, 大多数的科学家已经看过了这些报告, 因此有几个专家开始不相信这些报告是不足为奇的.在这些怀疑的人中有一个是格拉斯哥大学的Kelvin爵士,当时被许多人认为是活着的最伟大的科学家.Kelvin最初认为这一宣告是一个骗局(他很快改变了这一想法).The astonishing ability of x-rays to penerate matter gave rise to many cartoons that betrayed popular misunderstandings about the new rays. In addition the discovery stimulated a good deal of quackery( 庸医的医术). A London firm advertised its "x-ray-proof underclothing." and French enthusiasts(热心人)made attempts at "photographing the soul." In Iowa, a farmer reported that he had used the new rays to transform a 13-cent piece of metal into gold worth $153.X-射线穿透物质的惊人的能力引起起许多显示大众对这种新射线的误解的漫画.此外,这一发现激发了许多欺骗行为.一家伦敦的公司打广告宣传它的"防X-射线内衣",法国的热心人企图"拍摄灵魂的照片".在衣阿华州,一个农民报告,他已经用这种新射线将一块13厘米厚的金属变成了价值153美元的黄金.Engineers and photographers were on the whole even quicker than doctors to grasp the potential of x- ray devices. As the American journal Electrical Engineer commented in March 1896, "It is safe to say that there is probably no one possessed of a vacuum tube and an induction coil, who has not undertaken to repeat Professor Rontgen`s experiments." By the end of the year hundreds of crude x- ray machines were in operation. The first attempts at radiography were haphazard because its practitioners could only guess at the exposures needed to produce clear photographs. From 1899, doctors began to test the rays tor remedying cancer tuberculosis and various inflammations. Their success was unever and some patients and doctors suffered severe radiation burns.工程师与摄影者总的来说甚至比医生更快地了解了X-射线装置的潜在用处.正如美国的杂志<电气工程师>1896年3月号上所评论的,"可以说, 没有那一个拥有真空管与感应线圈的人,不会重复伦琴教授的实验."到了那一年的年底,已有数百个原始的X-射线机在运行之中.第一个辐射摄影的试验是偶然的事,因为它的专业人员仅仅能够推测产生清楚的照片所需的曝光时间.从1899年起,医生们开始试验性地将射线用于治疗癌症,肺结核病与各种炎症.他们的成功是参差不齐的, 并且有一些病人与医生遭受了严重的辐射灼伤.All the while, Rontgen tried to continue his research in an unaccustomed role--as an international celebrity. He did not answer most of the letters he received and refused all but two lecture invitations. One acceptance came in response to a summons from the Imperial Court in Berlin. He was asked to demonstrate his discovery on January 13 to the emperor, Wilhelm ll, whom Rontgen addmired for his politics and interest in science. After the successful demonstration, the emperor awarded Rontgen the Prussian Ordeer of the Crown and promptly commissioned three other scientists to investigate the military potential of the discovery. Rontgen knew of this work but neither helped nor hindered it.伦琴始终试图继续他的研究,他不习惯作为一个国际著名人士的角色.他对收到的信大部分都没有覆信,并且除了两次演讲外, 他谢绝了所有这样的邀请.有一次接受邀请,是为了响应来自柏林帝国宫廷的召唤. 他在1月13日向皇帝威廉二世表演他的发现,伦琴因为他的政策和对科学的兴趣而佩服他. 成功地表演以后, 皇帝授予伦琴普鲁士皇冠勋章并且迅速地委托其他的三个科学家来调查研究这一发现在军事上的潜力.伦琴知道这项工作,但是既不帮助他, 也不阻扰他.He gave a second lecture for the faculty and students at Wurzburg,。

第一章 1.1 世界放射医学发展简史

治疗后照片显示毛发脱落，但是有放射性溃疡形成
1896年芝加哥医生埃米尔·格鲁布(Emil Grubbe) 用X射线治疗乳腺癌
1896年，法国物理学家亨利·贝可勒尔（Henri Becquerel）发现铀盐的天然放射性
1896年，欧内斯特·卢瑟福(Ernest Rutherford)研究了铀的放射性，命名了α和β射线。
Otto Hahn
1895年，德国物理学家威廉·伦琴（Wilhelm Röntgen）发现X射线
伦琴夫人的手骨与戒指，拍摄于1895年12月22日核影像学诞生
1896年奥地利医生利奥波德·弗罗因德(Leopold Freund)用X射线治疗黑毛痣。开启了医学放射治疗
5岁的女孩背部有36×37cm的黑毛痣放射治疗后一周出现皮肤炎症
他的主要学术成就
放射性核素嬗变发现质子原子的有核模型人工核反应 α粒子散射实验
Ernest Rutherford 卢瑟福（1871－1937）
如果世界上设培养人才的诺贝尔奖的话，卢瑟福将是第1位获奖者，他的学生中有11位诺贝尔奖得主。
他从来没有树立过1个敌人，也从来没有失去过1位朋友。
发现铀核裂变的奥拓.哈恩及其助手
早期辐射损伤的报道
1923年乔治·德·海维希（George de Hevesy）研究了植物中放射性铅的吸收和分布，随后应用于活体的代谢研究，被认为是基础核医学之父
1926年医生赫尔曼·布鲁姆加特(Herrman Blumgart)用放射性核素研究了动静脉血管之间的循环时间，被认为是临床核医学之父
1895 1896 1898 1902
1911 1919 1920 1923 1934
1939 ……
Discovery of X-ray

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a r X i v :a s t r o -p h /0110112v 2 22 O c t 2001Astronomy &Astrophysics manuscript no.(will be inserted by hand later)Discovery of X-ray emission from the protostellar jet L1551IRS5(HH 154)F.Favata 1,C.V.M.Fridlund 1,G.Micela 2,S.Sciortino 2,and A.A.Kaas 31Astrophysics Division –Space Science Department of ESA,ESTEC,Postbus 299,NL-2200AG Noordwijk,The Netherlands2Osservatorio Astronomico di Palermo,Piazza del Parlamento 1,I-90134Palermo,Italy 3Nordic Optical Telescope,Apartado 474,E-38700Santa Cruz de la Palma,Canarias,SpainReceived date /Accepted dateAbstract.We have for the ﬁrst time detected X-ray emission associated with a protostellar jet,on the jet emanating from the L1551IRS5protostar.The IRS5protostar is hidden behind a very large absorbing column density,making the direct observation of the jet’s emission possible.The observed X-ray emission is likely associated with the shock “working surface”,i.e.the interface between the jet and the circumstellar medium.The X-ray luminosity emanating from the jet is,at L X ≃3×1029erg s −1,a signiﬁcant fraction of the luminosity normally associated with the coronal emission from young stars.The spectrum of the X-ray emission is compatible with thermal emission from a hot plasma,with a temperature of ≃0.5MK,fully in line with the temperature expected (on the basis of the jet’s velocity)for the shock front produced by the jet hitting the circumstellar medium.Key words.ISM:clouds –ISM:individual objects:L1551:HH 454–ISM:jets and outﬂows –Stars:formation –Stars:pre-main sequence –Radio lines:ISM1.IntroductionDuring the ﬁnal stages of the formation of low-mass stars (in the so-called classical T Tau phase)accretion of mate-rial from the proto-stellar nebula onto the Young Stellar Object (YSO)takes place through an accretion disk.Very often (and possibly always)the presence of the accretion disk is correlated with the presence of energetic polar out-ﬂows,that is,collimated jets of material being ejected perpendicularly to the disk,along its axis.Several models of the formation of the jet have been proposed,in most of which the jet is collimated by the presence of a (proto-stellar)magnetic ﬁeld.When these jets collide with the surrounding ambient medium –or with previously ejected material –they form a shock structure,which is directly observable in the form of so-called Herbig-Haro jets (e.g.Reipurth &Raga,1999).X-ray emission (and thus the presence of hot plasma,at temperatures in excess of several ×105K,up to ≃100MK during energetic ﬂares)has by now been observed in most stages of the formation of low-mass stars,ranging from the highly embedded,perhaps spherically accreting protostars (Class 0objects)to the ﬁnal stages of the pre-main sequence life of a star,the Weak-Line T Tau stage,2 F.Favata et al.:Discovery of X-ray emission from the protostellar jet L1551IRS5(HH154)2.The L1551IRS5outﬂowThe L1551cloud is one of the nearest(d≃140pc) sites of ongoing star formation,in which objects in sev-eral diﬀerent stages of the process are clearly visible,from deeply embedded,actively accreting(proto-)stars to the ﬁnal stages of star formation represented by the Weak-Line T Tau stars with no remaining circumstellar material. Several“canonical”examples of jets and outﬂows associ-ated with protostellar accretion are present in the region. In this paper we are mainly concerned with the jet asso-ciated with the IRS5source embedded in the L1551cloud and its associated outﬂow.L1551IRS5is a deeply embedded protostellar binary system(e.g.Rodriguez et al.,1998and references therein), eﬀectively invisible at optical wavelengths as it is hidden behind some≃150mag of visual extinction(Stocke et al., 1988;Smith et al.,1987;White et al.,2000)which most likely originates in the circumstellar accretion disk.The two Class0/1stars have a total luminosity of≃30L⊙.The two IRS5stars appear to be(jointly?)powering at least two observable outﬂows.A large(several arcmin) bipolar molecular outﬂow(actually theﬁrst discovered, Snell et al.,1980)and a much smaller(with a length of≃10arcsec)denser two-component jet(Fridlund& Liseau,1998),consisting of material at temperatures of T≃104K,thus visible in the emission lines of e.g.Hα, representative of recombination.The jet and the molecular outﬂow have been shown to be likely causally unrelated, given that the jet has a momentum insuﬃcient by sev-eral orders of magnitude to drive the molecular outﬂow (Fridlund&Liseau,1998).The jet moves at transverse velocity of200–400km s−1(Fridlund&Liseau,1994)and appears to end in a shock against the ambient medium(a “working surface”–Fridlund&Liseau,1998)3.Observations3.1.XMM-NewtonThe X-ray observations discussed in the this paper were obtained with the XMM-Newton observatory.A deep(50 ks)exposure of the star-forming region of the L1551cloud was obtained starting on Sep.92000at19:10UTC.All three EPIC cameras were active at the time of the obser-vation,in full-frame mode,with the mediumﬁlters.Data have been processed by us with the standard SAS V5.0.1pipeline system,concentrating,for the spec-tral analysis,on the EPIC-PN camera.In order to min-imize the unwanted contribution of non-X-ray events we have retained only the counts whose energy is in the0.3–7.9keV range.To deal with the time-varying background, we have applied a technique purposely developed at the Palermo Astronomical Observatory which maximizes the statistical signiﬁcance of weak sources by identifying and removing the fraction of the exposure time strongly af-fected by high-background episodes.In many XMM data sets most of the background is due to a small number of short(but intense)episodes–Fig.1.The top panel shows the total count rate as a function of time in the PN camera during the complete L1551XMM observation discussed in the present paper. The horizontal line is the chosen threshold value for back-groundﬁltering:time intervals during which the total PN count rate was above the line have been discarded from theﬁnal data set.The bottom panel shows the value of the merit function,as a function of the total accepted ob-serving time,which was used to determine the threshold. The merit function is optimized to yield an optimal data set for the detection of faint sources.mostly related to solar events–so that the background events are strongly concentrated in time.Removal of the small fraction of the observing time in which the high-background episodes are concentrated results in a much larger S/N ratio data set with a comparatively small loss of source photons.Fig.1shows the time evolution of the total count rate for the PN data set(in the top panel),to-gether with the threshold(shown by the horizontal line) above which the data are discarded.The threshold is dy-namically chosen by maximizing a merit function,deﬁned to optimize the detection of faint sources(which are back-ground,rather than photon-noise,dominated).The value of the merit function for the L1551PN observation is plot-ted in the lower panel of Fig.1as a function of the total accepted time.As a result of the overall procedure the initial data set of≃106photons collected during an exposure of≃56.8 ks for the MOS cameras and≃54.5ks for the PN camera, was reduced to a cleaned data set of≃250000photons collected in≃55ks for the MOS and≃51ks for the PN cameras,i.e with a judicious time and energyﬁltering we have been able to reduce the background level by a factor ≃4while rejecting only≃5%of the overall exposure time.F.Favata et al.:Discovery of X-ray emission from the protostellar jet L1551IRS5(HH 154)3Fig.2.The plot shows the diﬀerence (in arcsec)between the coordinate of the X-ray source as determined in the PN detector by the Pwdetect algorithm and their optical counterpart,for the 8bright X-ray sources (with more than 300counts)with unambiguous counterparts in the L1551XMM observation.The cleaned data set obtained by summing the data of the two MOS and one PN EPIC cameras has been searched for sources with the Wavelet Transform detec-tion algorithm also developed at Palermo Astronomical Observatory (Pwdetect ,Damiani et al.2001in prepa-ration).The characteristics of the XMM-Newton version of the algorithm are inherited from the version developed for the ROSAT PSPC (Damiani et al.,1997).The over-all analysis procedure follows the recipe described in more details by Sciortino et al.(2001).The L1551observation has been taken with the medium ﬁlters;in such a case we have derived that the value of the relative eﬃciency of the PN and of the individual MOS cameras is 2.94,hence the summed data set has a single MOS-equivalent cleaned exposure time of 2×55+2.94×51=260ks.In order to assess the source signiﬁcance threshold to adopt to ensure detection of the faintest sources a full set of simulations of empty ﬁelds with the same background level and the same exposure map as the summed data set needs to be run.Following this,a limiting threshold can be set which ensures e.g.a maximum of one spurious source per ﬁeld.While this has been done for the complete analysis of the full L1551exposure (and will be discussed in a future paper),the three X-ray sources discussed in the present paper are all well above the minimum thresh-old,and consequently their signiﬁcance is well above the spurious source threshold.The quality of the XMM aspect solution (“bore-sight correction”)was veriﬁed by comparing the positions of X-ray bright sources as determined in the PN detector bythe Pwdetect algorithm with the position of their op-tical counterparts.Only X-ray bright sources (with more than 300source counts in the PN camera)with single,unambiguous optical counterparts with good position de-termination were used,resulting in 8such sources being available in the L1551ﬁeld.The optical coordinates were obtained from the Simbad database.No signiﬁcant bias is present in the data,with a mean ∆RA =−0.33±1.46arcsec,and a mean ∆Dec =−0.15±1.85arcsec,so that the positional error for the faint sources is fully dominated by the photon noise coupled with the XMM point spread function.The extraction of source and background photons was performed using the xmmselect tool.Source photons have been extracted from a circular region of 45arcsec diameter,while background photons have been extracted from a region on the same CCD chip and at the same oﬀ-axis angle as for the source region.Response matri-ces (“arf ﬁles”)appropriate for the position and size of the source extraction regions have been computed for the EPIC PN camera.The spectral analysis has been per-formed using the XSPEC package,after rebinning the source spectra to a minimum of 20source counts per (vari-able width)bin.3.2.Ground-based observationsNew optical spectra and images of the IRS5jet have been obtained with the 2.6m Nordic Optical Telescope (NOT).The spectra were obtained in December 1999us-ing the echelle mode of the ALFOSC combined imager and spectrograph.The cross disperser/grating combination al-lowed for a spectral resolution of ≃1˚A at the wavelength of H α.The detector was a 2048×204815µm pixel CCD.A slit width of 1arcsec projected on the sky was used,and the integration time per spectrum was 3600s.The com-plete velocity ﬁeld of the jet was mapped in emission lines between 4800˚A and 7900˚A .For the purpose of evaluating shock velocities in this paper our interpretation is based on an analysis of the H αdata with the other lines used as a consistency check.A full analysis will be presented in a forthcoming paper.H βwas used together with H αin order to estimate the extinction towards the shocks in the L1551IRS5jet.For the identiﬁcation of the optical counterparts to the X-ray sources detected in the XMM image both new narrow band images (also obtained with the NOT)and already available HST images were used.The HST R -band WFPC2image of the jet region is shown in Fig.3together with the EPIC PN X-ray image;the position of the X-ray source associated with the L1551jet,together with the position of one of the background sources,is shown on the WFPC2image by a black circle.The size of the circle corresponds to the likely extent of the X-ray source as determined by the Pwdetect algorithm.The WFPC2image was obtained in February 1996with the F675W4 F.Favata et al.:Discovery of X-ray emission from the protostellar jet L1551IRS5(HH154)Fig.3.The left panel shows the region of L1551IRS5in X-rays,as seen in the XMM EPIC-PN camera,while the right panel shows a small part of the same region as seen in a1800s R-band CCD image obtained with the Hubble Space Telescope WFPC2camera.The size of the small detector(the WFPC2-PC chip)on the left part of the HST image is36.8arcsec,while the size of the X-ray image is9.3×6.3arcmin.The position of the two leftmost X-ray sources visible in the left panel is indicated on the R-band image by the circles.The leftmost X-ray point source is the one associated with L1551IRS5,while the other point source is one of the two background sources discussed in Sect.5.The nearly vertical alignment of bright pixels near the center-top of the X-ray image is due to“spill-over”from a bright source higher up in the image.(R-band)ﬁlter,and part of it is discussed in Fridlund& Liseau(1998).New narrow band images were also obtained with the NOT.These observations were carried out in March of 2001again using the ALFOSC,this time in imaging mode. Deep images integrated for1800s(Hα)and3600s(I-band)were obtained in order to detect possible new emis-sion knots,as well as to search for faint background or embedded sources shining through the molecular cloud(in possible association with the background X-ray sources discussed in Sect.5).A narrow bandﬁlter centered on the Hαline was used,while the I-bandﬁlter was centered on 7150˚A with a FWHM of1600˚A.Being several arcmin in size theﬁeld of view of the NOT images is signiﬁcantly larger than the WFPC2one,although with less spatial resolution and shallower limiting magnitude.4.X-ray emission from the L1551IRS5jetA faint X-ray source(the leftmost one in the left panel of Fig.3)is positionally coincident with the embedded source L1551IRS5and its jet.The background-subtracted count rate is only8.4×10−4cts s−1in the EPIC PN camera, so that the total number of source counts is limited to42 cts in the≃50ks exposure(with an equivalent number of background counts in the extraction box used,a cir-cle45arcsec in diameter).The low statistics allow a lim-ited amount of spectral information to be derived for the source.The resulting spectrum(shown in Fig.4)is soft, and can be reasonably described with a moderately ab-sorbed thermal ing a mekal model with an added interstellar absorption component in xspec gives a best-ﬁt temperature T=0.5±0.3×106K,with a moderate value of the best-ﬁt absorption(1.4±0.4×1022cm−2),cor-responding to an extinction of A V=7.3±2.1mag1.The null hypothesis probability for theﬁt is15%,i.e.theﬁt is,from the statistical point of view,fully acceptable.The limited statistics of the spectrum(and the correspond-ing small number of bins)do not allow to constrain the spectrum at a more detailed level.The full width at half power(FWHP)of the XMM point-spread function(PSF) for EPIC PN camera is≃14arcsec,signiﬁcantly larger than the size of the jets(whose visible length is≃10arc-sec).Thus,it is not possible to locate the precise site of the X-ray emission within the jet structure.5.Background sourcesTwo additional X-ray source are detected within the area on the sky that is dominated by the molecular outﬂow from L1551IRS5.The centroid positions,and background subtracted count-rates can be found in Table1.The po-sition of the brighter of the two against the molecular outﬂow is visibile in Fig.3.Neither of these sources can be associated with any visible object in the deep Hαand I-band images at these positions.F.Favata et al.:Discovery of X-ray emission from the protostellar jet L1551IRS5(HH154)5 Fig.4.The observed,background-subtracted EPIC PNX-ray spectrum of the X-ray source associated with theL1551IRS5jet.The best-ﬁt thermal(“mekal”)spectrum–whose parameters are given in Table1–is also shown.Bothχ2and K-S tests show that the X-ray emissionfrom these sources is constant to a high(≥90%)probabil-ity level.The spectra of these two sources are signiﬁcantlyharder than the spectrum of the source associated withthe L1551IRS5jet(the spectrum of the brighter of thetwo is shown in Fig.5),and can both be satisfactorilydescribed with an absorbed power-law spectrum,with in-dices varying between1.2and2.5.The absorbing columndensity is in both cases moderate,with A V between≃5and≃8magnitudes.The resulting column densities arethus similar to what is expected for the L1551molecu-lar cloud at these positions(Sandqvist&Bernes,1980).Given the X-ray spectral characteristics,as well as the lackof any visible candidate counterpart in our deep I-bandimages,we consider it likely that these sources are notassociated with the molecular L1551IRS5outﬂow,eventhough they are positionally coincident with(parts of)it.Rather,they are most likely to be extra-galactic X-raysources(plausibly active galactic nuclei)shining throughthe L1551cloud.Typical active galactic nuclei would have,on the basis of their high F X/F V ratio,optical magnitudesV>∼19,which would become V>∼24when the interven-ing column density is taken into account.Therefore theiroptical counterparts are not expected to be visible,on theoptical images presented here,againts the background ofthe molecular outﬂow emission.The spectra could in principle beﬁt also with a ther-mal spectrum,with a very high resulting temperature(T>∼100MK).While this temperature would not be in-compatible with coronal protostellar origin during e.g.anenergeticﬂare,the lack of any visible counterpart downto faint magnitudes(even though the absorbing columnis only a few magnitudes)and the constant light curve ofthe sources make this last hypothesis unlikely.The presence of two serendipitous X-ray sources in thePN image shown in Fig.3atﬂux levels of order10−14erg cm−2s−1is fully in line with the expected numberFig.5.The observed,background-subtracted EPIC PNX-ray spectrum of the X-ray source XMM J043126.9+180756.The best-ﬁt absorbed power-law spectrum–whose parameters are given in Table1–is also shown.density of background sources determined on the basisof the log N log S relationship for X-ray sources(see e.g.Hasinger et al.,2001),which predicts that at thisﬂux limit100to200sources per square degree should be present inany given X-ray observation.The area covered by X-rayimage of Fig.3is≃0.02square deg,so that the expectednumber of serendipitous sources is2to4.6.DiscussionHubble Space Telescope(HST)observations(Fridlund&Liseau,1998)indicate the presence of a number of shocksalong the extent of the IRS5jet.The jet is observed toend in a“working surface”against the ambient mediumat≃10arcsec from the presumed location of the sourcepowering it(see Figs.1and2of Fridlund&Liseau,1998).This shock feature is designated“knot D”in the nomen-clature of Neckel&Staude(1987)and Fridlund&Liseau(1994).We have measured the Hα/Hβratio towards theworking surface(knot D)of the jet.Assuming a type Bpure recombination spectrum(which is justiﬁed since wealso detect[O iii]5007˚A emission at this position–seebelow),weﬁnd A V to be4–6mag,depending on whichextinction law is applied.We alsoﬁnd that the extinctionis increasing in the direction towards IRS5along the jet(conﬁrming the result of Stocke et al.,1988).The absorb-ing column density,for the IRS5X-ray spectrum,is thuscompatible with the absorbing column density measuredtoward the visible jet(and in particular toward the shockfeature),making the association between the X-ray emis-sion and the jet plausible.Since as mentioned above theIRS5protostellar system is hidden behind a very thicklayer of absorbing material,corresponding to A V>∼150mag,it can be excluded that the X-ray photons–giventhe small absorbing column density and the lack of high-energy photons in the spectrum)–emanate from(or closeto)the photosphere/chromosphere of the protostars pow-6 F.Favata et al.:Discovery of X-ray emission from the protostellar jet L1551IRS5(HH154)Table 1.Coordinates,count rates and best-ﬁt spectral parameters for the three X-ray sources discussed in the present paper.Theﬁrst source is the one associated with the L1551IRS5jets,while the two other ones are the sources positionally associated with the L1551IRS5molecular outﬂow but most likely not physically associated with it.The count rate is given in units of counts per ks,while the column“σ”contains the signiﬁcance of the source detection in the combined MOS+PN image,in units of“equivalentσ”(i.e.obtained by integration of a Gaussian probability distribution).The absorbing column density is given in units of1022cm−2.For the X-ray source associated with the jets the bestﬁt temperature in MK is given,while for the two sources not associated with the outﬂows the best-ﬁt power-law index is given.The last column gives the(unabsorbed)X-rayﬂux in the0.3–5.0keV band in units of10−13 erg cm−2s−1.SourceαδrateσN(H)T F XSourceαδrateσN(H)γF X1+X ×(v shockF.Favata et al.:Discovery of X-ray emission from the protostellar jet L1551IRS5(HH154)70.8n2V,where n e is the electron density,n H the hydrogen density,and V is the volume of the emitting region(under the simplistic assumption of uniform density).Given that EM=1.1×1052cm−3(from the thermalﬁt to the X-ray data),assuming a density n e≃104cm−3(see above),one derives a volume V=1.4×1044cm3,which corresponds to a characteristic linear size l≃V1/3≃5×1014cm.This scale size is comparable to the upper limit for the size of the shock interface derived from the HST observations,≤1.0×1014cm,thus further supporting the identiﬁcation of the shock interface as the seat of the X-ray emission.7.ConclusionsWhile the energetic nature of the collimated jets observed to be originating from protostellar sources has been ev-ident for some time,no high-energy photons have up to now been observed from these phenomena.Here we report theﬁrst convincing evidence of X-ray emission from the protostellar jet associated with the IRS5protostar(s)in the L1551cloud.The X-ray source and the protostar and related jets are positionally coincident,and the small ab-sorbing column density observed for the X-ray spectrum (with an equivalent A V≃7mag,fully compatible with the absorbing column density observed in the optical to-wards the jet)allow us to exclude that the X-ray emission is associated with the protostellar sources(which are hid-den behind≃150mag of obscuration).The size of the jets(≃10arcsec)originating at L1551IRS5is smaller in angular extent than the XMM EPIC PSF(≃14arcsec), so that no inference is possible on spatial grounds about the possible detailed location of the origin of the X-ray emission.The emission from the IRS5jet is compatible with be-ing caused by thermal emission from a plasma heated to a moderate temperature(T≃0.5MK),equivalent to the shock temperature that is expected at the interface (“working surface”)between the jet and the surrounding circumstellar medium,on the basis of the observed jet ve-locity.This is regardless of whether it is a bow-shock or a reversed shock,which in itself is a function of whether the jet is denser than the ambient medium or vice versa. Fridlund&Liseau(1998)ﬁnd strong evidence for the jet being less dense than the surrounding medium.That con-clusion was reached by estimating the mass in the jet from the relative brightness of the shock,as well as discerning the ambient density from molecular line measurements. Our observation of X-rays from a≃0.5MK plasma is fully consistent with the conclusion of Fridlund&Liseau (1998).This is because the hypothesis of a“light”jet requires a high degree of ionization(so that we visually observe all the material present in the jet in recombina-tion radiation).A low degree of ionization at the observed shock velocities,would imply a plasma temperature well above1MK,which is incompatible with our X-ray data. We thus consider it most likely that the X-ray emission originates directly from a shock associated with the so-called knot D,and that our observations support the con-clusion of Fridlund&Liseau(1998)that the jet has a high degree of ionization.The presence of a soft X-ray source at the position of the shock associated with the jet is likely to have a signif-icant inﬂuence on the physical conditions of the accretion disk:while X-ray emission from the star’s corona is of-ten likely to be more powerful that the emission coming from the jet,most of the accretion disk(except for the innermost part)is eﬀectively shielded and not strongly il-luminated by the stellar coronal emission.The jet X-ray source on the other hand lies above the disk(if indeed it is located at the jet-circumstellar medium interface it is some1000AU above the disk),illuminating the disk from above.This X-rayﬂux can therefore ionize the disk material,and thus inﬂuence signiﬁcantly the disk physical conditions.Once more,if X-ray emission from protostel-lar jets is indeed a common feature,this would inﬂuence the protostellar environment signiﬁcantly.This will be in-vestigated in the future through detailed modelling of the relative contribution of the stellar coronal and jet X-ray luminosity to the ionization of the accretion disk. Acknowledgements.GM,SS acknowledge the partial support of ASI and MURST.This paper is based on observations ob-tained with XMM-Newton,an ESA science mission with in-struments and contributions directly funded by ESA Member States and the USA(NASA).Part of the data have been taken using ALFOSC,which is owned by the Instituto de Astroﬁsica de Andalucia(IAA)and operated at the Nordic Optical Telescope under agreement between IAA and the NBIfAFG of the Astronomical Observatory of Copenhagen. 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