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Materials Science and Engineering A485 (2008) 403–408Effect of pulse magneticfield on microstructure of austeniticstainless steel during directional solidificationChangjiang Song a,Qiushu Li a,b,Haibin Li a,b,Qijie Zhai a,∗a School of Materials Science and Engineering,Shanghai University,Shanghai200072,Chinab Taiyuan University of Science and Technology,Taiyuan030024,ChinaReceived22June2007;received in revised form31July2007;accepted31July2007AbstractUsing directional solidification via zone melting,we investigated the effect of axial pulse magneticfield on microstructure and inter-face morphology of austenitic stainless steel over a wide range of growth rate(from planar to dendritic growth mode).Experimental results show that during directional solidification,applications of pulse magneticfield destabilize the interface morphology,i.e.it promotes planar–cellular–dendritic–cellular transition of growth mode under the same conditions.Analysis reveals that freezing rate oscillations caused by the pulse magneticfield may be responsible for this phenomenon.© 2007 Elsevier B.V. All rights reserved.Keywords:Pulse magneticfield;Directional solidification;Austenitic stainless steel;Electromagnetic force1.IntroductionApplications of current and magneticfield to material pro-cessing,so-called electromagnetic processing of material(EPM) has been widely studied in last two decades.And EPM has been successfully used to improve quality and properties of materi-als,such as grain refinement,improving interface stability and crystal quality during directional solidification,controlling crys-tal orientation,etc.[1–10].EPM was considered as an effective method to promote efficiency,fabricate high performance mate-rials,and develop advanced material processing technique.Now, the investigations were mainly focused on the applications of alternate currentfield,direct currentfield,pulse current,alternate magneticfield and static magneticfield[8–18].However,appli-cations of pulse magneticfield to material process have been seldom investigated.Directional solidification was frequently observed during melt solidification,and was important in many technological applications.The aim of this paper is to investigate the effect of the axial pulse magneticfield on the microstructure and solid/liquid(S/L)interface stability of austenitic stainless steel during directional solidification.∗Corresponding author.Tel.:+862156331218;fax:+862156331218.E-mail address:qjzhai@(Q.Zhai).2.ExperimentsThe setup used in this work was schematically shown in Fig.1,which mainly consists of generator of pulse magnetic field,heating coil,pulling mechanism,high purity alumina cru-cible and the coolant of liquid Ga–In–Sn alloy.The studied alloy was commercial austenitic stainless steel,whose composi-tion was shown in Table1.Its solidus and liquidus temperature are about1426.66◦C and1461.74◦C,respectively.The studied alloy were melted in an induction furnace and cast into cylinder bars with diameter of3mm and length of150mm.The experimental procedure was as follows:first,the pre-pared cylinder bar was placed in the high purity alumina crucible with inside diameter of3mm;second,the sample was slowly heated and melted to the predetermined temperature(1550◦C); third,holding5–8min for melt homogeneousness,the samples began to be pulled downward at a constant rate,and the pulse magneticfield was synchronously imposed on it;last,the sam-ple was quenched into liquid Ga–In–Sn alloy to observe the solid/liquid(S/L)interfaces at the predetermined time in steady-state growth stages.The frequency of pulse magneticfield was about4–5Hz,and a typical discharge course of power supply of pulsed magneticfield was shown in Fig.2.During the exper-iments,the sample was melted by the heating coil connected with high frequency(400kH)power supply,and the melt length was about15mm.A series of experiments were carried out0921-5093/$–see front matter© 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2007.07.079404 C.Song et al./Materials Science and Engineering A485 (2008) 403–408Fig.1.Sketch of experimental setup.Table 1Composition of austenitic stainless steel (wt.%)C 0.07Si 0.29Mn 0.70P 0.030S 0.002Ni 9.27Cr 17.47Ti 0.06FeBalancewith different pulling rate and different magnetic intensity under otherwise identical conditions.The temperature gradient at the S/L interfaces was measured by a B-type (Pt-30%Rh/Pt-6%Rh)thermocouple inserted the melt without magnetic field,the thermocouple moved together with samples during the measurement.It is difficult to measure the temperature in 3mm diameter samples,thus we measured the temperature gradient in a 5mm diameter sample under identical conditions,which was about 627K/cm in 5mm diametersampleFig.2.A discharge course of power supply of pulsed magnetic field.under identical conditions.The magnetic intensity was measured by an oersted-meter for strong magnetic field.The quenched samples were removed from the alumina cru-cible,and were cut along the symmetrical axis.The as-polished specimens were etched by the reagent of FeCl 3(18g)+HCl (30ml)+H 2O (100ml)for microstructure examination.The microstructure was examined by an optical microscope.3.ResultsWe mainly investigated the effect of the axial pulse magnetic field on S/L interface morphology at the pulling rate of 12,24,64,and 96␮m/s.The corresponding growth modes are planar,cel-lular,cellular–dendrite,and dendrite front growth,respectively.Fig.3shows the effect of pulse magnetic field on the longitudinal microstructure and interface morphology of austenitic stainless steel at the puling rate of 12␮m/s (grey phase is austenite phase,and black phase is ferritic phase).It indicates that without the pulse magnetic field,the growth mode is planar front growth as shown in Fig.3(a).When 0.50T pulse magnetic field is imposed,the disturbances appear on the growth interface as shown in Fig.3(b),which reveals onset of interface instability.When the magnetic intensity is 0.84T,the growth mode changes into the cellular front growth,as shown in Fig.3(c).And when the mag-netic intensity is 1.00T and 1.54T,the growth mode evolves into complex cellular–dendritic or dendritic front growth as shown in Fig.3(d and e).The above results show that application of the pulse magnetic field makes the growth mode transform from the planar to cellular to dendritic front growth at the pulling rate of 12␮m/s.Fig.4is the longitudinal microstructure and interface mor-phology at the pulling rate of 24␮m/s with different magnetic intensity.It reveals that without the pulse magnetic field,the growth mode is cellular front growth as shown in Fig.4(a).When the pulse magnetic field is applied,the side branch of cellular crystal begins to appear and gradually develop.The growth mode gradually transforms from cellular to dendritic front growth with increasing the magnetic intensity.Moreover,the primary spacing gradually decreases with increasing the magnetic intensity.Fig.5presents the longitudinal microstructures and interface morphology at the pulling rate of 64␮m/s with different mag-netic intensity.It exhibits that without the pulse magnetic field,the growth mode is cellular–dendritic front growth as shown in Fig.5(a).Application of 0.5T and 0.84T pulse magnetic field makes the growth mode evolve into dendritic front growth,as shown in Fig.5(b and c).Further increasing the magnetic inten-sity makes the growth mode evolve again into cellular–dendritic (or cellular)front growth as shown in Fig.5(d and e).And the primary spacing gradually becomes smaller with increasing the magnetic intensity.Fig.6shows the longitudinal microstructure and interface morphology at the pulling rate of 96␮m/s with different mag-netic intensity.It indicates that without the pulse magnetic field,the growth mode is dendritic front growth as shown in Fig.6(a).When 0.50T and 0.84T pulse magnetic field is applied,the growth mode transforms from dendritic to cellular front growth as shown in Fig.6(b and c).With further increasing magneticC.Song et al./Materials Science and Engineering A 485 (2008) 403–408405Fig.3.Longitudinal microstructure at the pulling rate of12␮m/s with different magnetic intensity:(a)0T,(b)0.50T,(c)0.84T,(d)1.00T,and(e)1.50T.intensity,the microstructure exhibits complex morphology as shown in Fig.6(d and e).That may enter the band-microstructure zone from the dendritic to planar transition at high growth rate,as observed by many researches[19–21].On the other hand,increase of the magnetic intensity does not make the pri-mary spacing decrease at the pulling rate of96␮m/s,inversely increase as shown in Fig.6(b and e).In the directional solidi-fication of Al–0.52wt.%Mn near the absolute stability[20,21], increasing freezing rate also makes primary spacings increase when growth mode transforms from the dendritic to planar front growth at high growth rate.Our experiments are similar to their experimental results.4.DiscussionsAccording to Trivedi and Kurz[19],microstructure of directional solidification exhibits planar–cellular–dendritic–cellular–planar transition due to the competition between differ-ent physical process(the convection effect is not considered). The solute diffusion length is defined as l D=D/V,the ther-mal diffusion length l T= T0/G,and the capillarity length d0=Γ/ T0(for an alloy),where D is the solute diffusion coef-ficients,V the growth rate, T0the equilibrium freezing range of the alloy,G the temperature gradient at the S/L interface and Γis the Gibbs–Thomson coefficient.For directionalsolidifica-Fig.4.Longitudinal microstructure at the pulling rate of24␮m/s with different magnetic intensity:(a)0T,(b)0.50T,(c)0.84T,(d)1.00T,and(e)1.50T.406 C.Song et al./Materials Science and Engineering A485 (2008) 403–408Fig.5.Longitudinal microstructure at the pulling rate of 64␮m/s with different magnetic intensity:(a)0T,(b)0.50T,(c)0.84T,(d)1.00T,and (e)1.50T.tion of the alloy,the transition growth rate can be expressed as follows:V c =DG T 0=DGkmC 0(k −1)for planar–cellular transition (1)V tr =DG k T 0=DGmC 0(k −1)for cellular–dendrite transition(2)V trh =D T 0aΓ=DmC 0(k −1)akΓfor dendrite–cellular(high rate)transition(3)where k is the equilibrium distribution coefficient,m the liquidus slope,C 0the initial alloy composition and a a constant.The equations show that transition velocity of growth mode increases with increasing the temperature gradient.The primary spacing is also a function of the growth rate and the temperature gradient.At low growth rate,the primary spacing decreases with increase of temperature gradient for constant growth rate and increase of growth rate for constant temperature gradient [12,22].The experimental results indicate that applications of the pulse magnetic field reduce the interface stability and promote planar–cellular–dendritic–cellular transition of growth mode,i.e.application of pulse magnetic field makes the transition velocity lower under otherwise identical conditions.Accord-ing to Eqs.(1)and (2),decrease of transition velocity may result from decrease of the temperature gradient at the S/L inter-face.However decrease of temperature gradient should result in increasing of primary spacing at low growth rate [12,22],which differs from the experimental results.Thus the experi-ment results cannot be explained by the changes of temperature gradient.When the pulse magnetic field is applied,it would produce the induction current in the melt.Interaction between pulse mag-netic field and the induction current gives rise to electromagnetic force toward the center of the melt.On the other hand,interaction between pulse magnetic field and the induction current caused by the high frequency current of heating coil also gives rise to electromagnetic force in the radial direction.The electromag-netic force periodically squeezes the melt,and result in melt flow.During the directional solidification,the melt flow can promote solution transmission,thus can decrease the solution build-up ahead of the interface,promote S/L interface stability and delay the transition from planar to cellular growth mode [23,24]and from cellular to dendritic growth mode [24,25].Therefore,the promotion of solution transmission by melt flow can’t also explain the reason for interface instability caused by application of pulse magnetic field.Application of magnetic field gives rise to change of Gibbs free energy of the liquid and solid.At constant pressure,the change of Gibbs free energy due to magnetic field can be written as [26,27]:d G =−S d T −μM d H(4)where G is Gibbs free energy,S the entropy,T the temperature,μthe magnetic permeability,M the magnetization intensity and H is the magnetic intensity.Due to difference of the magneti-zation intensity between the liquid and solid,application of the magnetic field can affect the liquidus and solidus temperature of the alloy.For example,Li et al.[28,29]found that the peritec-tic phase transformation temperature of Mn–Bi alloy increases about 20◦C in 10T magnetic field.The experimental results also suggest that application of pulse magnetic field can increasesC.Song et al./Materials Science and Engineering A 485 (2008) 403–408407Fig.6.Longitudinal microstructure at the pulling rate of96␮m/s with different magnetic intensity:(a)0T,(b)0.50T,(c)0.84T,(d)1.00T,and(e)1.50T.the liquidus and solidus temperature of austenitic stainless steel [30].Pulse magneticfield is periodic action of magneticfield on the melt.During action time of magneticfield,increase of the liquidus temperature would lead to greater constitutional super-cooling ahead of the S/L interface at the same melt temperature, which makes the advance rate of the interface increase,and the interface becomes instability.However,weakening and disap-pearance of the magneticfield make the liquidus temperature decrease and return to equilibrium state in absence of magnetic field.Consequently constitutional supercooling decreases,even overheating occurs at the interface.And the interface advance rate would decreases,even interface move backward due to remelting.Therefore,application of pulse magneticfield would causefluctuation of freezing rate.On the other hand,meltflow produced by electromagnetic force of pulse magneticfield can give rise to composition and temperaturefluctuation ahead of the S/L interface,which also can result in freezing ratefluc-tuation.The freezing ratefluctuation can lead to instability of interface and promote planar–cellular–dendritic–cellular tran-sition of growth mode.Moreover,the formed striations are clearly seen in the lower magnification microstructure in the steady-state growth stages of the samples with applied pulsed magneticfield,as shown in Figs.7(d and e)and8(d and e). The formed striations usually are caused by growth rate oscilla-tions of interface during the directional solidification.Increase of advance rate can make new cellular(or dendritic)crystal form either by branching or by nucleation.And decrease of advance rate can make the cellular(or dendritic)crystal ter-minate by overgrowth of other cellular(of dendritic)crystal. If there exists kinetic difference between formation and ter-mination of cellular(or dendritic)crystal.Thefluctuation of freezing rate can cause the average primary spacing to deviate (increase or decrease)from that at steady freezing rate[31,32]. It was theoretically and experimentally testified by Regel et al.in MnBi–Bi eutectic alloy[31,32].Consequently,thefreez-Fig.7.Longitudinal microstructure in the steady-state growth stages of the samples at the pulling rate of12␮m/s:(a)0T,(b)0.50T,(c)0.84T,(d)1.00T,and(e) 1.50T.408 C.Song et al./Materials Science and Engineering A485 (2008) 403–408Fig.8.Longitudinal microstructure in the steady-state growth stages of the samples at the pulling rate of 24␮m/s:(a)0T,(b)0.50T,(c)0.84T,(d)1.00T,and (e)1.50T.ing rate oscillations caused by pulsed magnetic field should be the origin of change of primary spacing in the experiments.It should be noted that further research is needed to well under-stand the action mechanism of pulsed magnetic field on the microstructure and interface morphology during the directional solidification.5.ConclusionsUsing directional solidification via zone melting,we inves-tigated the effect of axial pulse magnetic field on the microstructure and interface morphology of austenitic stain-less steel.Experimental results show that application of the pulse magnetic field reduces the interface stability and pro-motes planar–cellular–dendritic–cellular transition.Increasing magnetic intensity makes the primary spacing decrease at the pulling rate of 12,24and 64␮m/s.But increasing magnetic intensity makes the primary spacing increase at the pulling rate of 96␮m/s.Analysis reveals that freezing rate oscillations caused by the pulse magnetic field may be responsible for above phenomenon.AcknowledgementsThis work was supported by National Natural Science Foun-dation of China (No.:50274050),973Program of China (No.:2004CCA07000)and China Postdoctoral Science Foundation (No.:20070410716).We expressed our sincere thanks for their financial support.References[1]P.Lehmann,R.Moreau,D.Camel,R.Bolcato,Acta Mater.46(1998)4067–4079.[2]S.Asai,Sci.Technol.Adv.Mater.1(2000)191–200.[3]H.Conrad,Mater.Sci.Eng.A 287(2000)205–212.[4]A.Radjai,K.Miwa,T.Nishio,Metall.Mater.Trans.A 29(1998)1477–1484.[5]Y .-G.Sha,C.-H.Su,S.L.Lehoczky,J.Crystal Growth 173(1997)88–96.[6]O.P¨a tzold,I.Grants,U.Wunderwald,K.Jenkner,A.Cr¨o ll,G.Gerbeth,J.Crystal Growth 245(2002)237–246.[7]S.Asai,K.-S.Sassa,M.Tahashi,Sci.Technol.Adv.Mater.4(2003)455–460.[8]B.Ganapathysubramanian,N.Zabaras,J.Crystal Growth 276(2005)299–316.[9]Y .Wang,K.Kudo,Y .Inatomi,R.Ji,T.Motegi,J.Crystal Growth 284(2005)406–411.[10]B.A.Legrand,D.Chateigner,R.P.de la Bathie,R.Tournier,J.Magn.Magn.Mater.173(1997)20–28.[11]S.R.Coriell,G.B.McFadden,B.Billia,H.Nguyen Thi,Y .Dabo,J.CrystalGrowth 216(2000)495–500.[12]M.G¨u nd¨u z,E.C ¸adırlı,Mater.Sci.Eng.A 327(2002)167–185.[13]T.V .Savina,A.A.Nepomnyashchy,S.Brandon,A.A.Golovin,D.R.Lewin,J.Crystal Growth 237–239(2002)178–180.[14]O.Fornaro,H.A.Palacio,Scripta Mater.36(1997)439–445.[15]C.Song,Z.Xu,X.Liu,G.Liang,J.Li,Mater.Sci.Eng.A 393(2005)164–169.[16]C.-J.Song,Z.-M.Xu,G.Liang,J.-G.Li,Mater.Sci.Eng.A 424(2006)6–16.[17]C.Song,G.Liang,Z.Xu,J.Shen,J.Li,J.Mater.Process.Technol.180(2006)179–184.[18]C.Song,Z.Xu,J.Li,Mater.Sci.Forum 475–479(2005)281–284.[19]R.Trivedi,W.Kurz,Int.Mater.Rev.39(1994)49–74.[20]X.Geng,H.Fu,Sci.Technol.Adv.Mater.2(2001)209–212.[21]A.Ludwig,W.Kurz,Acta Mater.44(1996)3643–4654.[22]C.T.Rios,R.Caram,J.Crystal Growth 174(1997)65–69.[23]B.Kauerauf,G.Zimmermann,L.Murmann,S.Rex,J.Crystal Growth 193(1998)701–711.[24]R.Trivedi,H.Miyahara,P.Mazumder,E.Simsek,S.N.Tewari,J.CrystalGrowth 222(2001)365–379.[25]G.Grange,J.Gastaldi,C.Jourdan,B.Billia,J.Crystal Growth 151(1995)192–199.[26]J.-K.Choi,H.Ohtsuka,Y .Xu,W.Y .Choo,Scripta Mater.43(2000)221–226.[27]H.Wang,Effects of a High Magnetic Field on the Behavior of PrecipitatePhases in Alloys,Ph.D.thesis,Shanghai University,Shanghai,2002,pp.109–112.[28]X.Li,Z.M.Ren,Y .Fautrelle,Mater.Lett.60(2006)3379–3384.[29]Z.Ren,X.Li,Y .Sun,Y .Gao,K.Deng,Y .Zhong,Comp.Coupl.PhaseDiagrams Thermochem.30(2006)277–285.[30]Q.-S.Li,H.-B.Li,Q.-J.Zhai,J.Iron Steel Res.13(2006)69–72.[31]L.L.Regel,W.R.Wilcox,D.Popov,F.Li,Acta Astronaut.48(2001)101–108.[32]F.Li,L.L.Regel,W.R.Wilcox,J.Crystal Growth 223(2001)251–264.。

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螺线管结构参数对脉冲磁场的影响

螺线管结构参数对脉冲磁场的影响

第17卷 第5期 太赫兹科学与电子信息学报Vo1.17，No.52019年10月 Journal of Terahertz Science and Electronic Information Technology Oct.，2019文章编号：2095-4980(2019)05-0840-05螺线管结构参数对脉冲磁场的影响张广帅，宋志敏，孙 钧，吴 平，滕 雁，曹亦兵，范志强(西北核技术研究所高功率微波技术重点实验室，陕西西安 710024)摘 要：研究了线圈间距、匝数、个数以及不锈钢套筒对脉冲磁体产生磁场的影响规律。

在储能电容和电压不变的前提下，研究结果表明：增加线圈间距会导致磁感应强度降低，磁力线包络增大，但总电流达到峰值时刻减小；增加线圈匝数，峰值电流明显减小，会降低磁感应强度，但有利于抑制磁力线包络；增加并联线圈个数，有利于产生较长的均匀区，但是在供能一定的条件下，磁场强度有所降低，同时总电流达到峰值时刻减小。

总体来看，在一定均匀区长度的设计要求下，减少单个线圈匝数，增加并联线圈个数，能够得到磁感应强度更大、均匀性更好的磁场，但要考虑线圈承载电流的能力。

另外，不对称的阴阳极金属结构会导致磁场不对称分布，且磁感应强度达到峰值时刻要晚于总电流达到峰值的时刻。

关键词：高功率微波；螺线管脉冲磁体；均匀磁场中图分类号：O532 文献标志码：A doi：10.11805/TKYDA201905.0840Effect of solenoid pulsed magnet parameters on magnetic field ZHANG Guangshuai，SONG Zhimin，SUN Jun，WU ping，TENG Yan，CAO Yibing，FAN Zhiqiang. All Rights Reserved.(Science and Technology on High Power Microwave Laboratory，Northwest Institute of Nuclear Technology，Xi’an Shaanxi 710024，China) Abstract：The effect of structural parameters of solenoid pulsed magnet on magnetic field is studied, including the number of turns, the number of coils, the distance between multi-coils and stainless steelcylinder. Under the condition that the capacitor storing energy and the voltage which supplies power areboth constant, the amplitude of magnetic flux density is reduced and the fluctuation of magnetic field linesis increased contrarily when increasing the distance between multi-coils, but the total current reaches itspeak earlier. Increasing the number of turns in each coil can obviously reduce the peak of total current andthus the amplitude of magnetic flux density. However, it is beneficial for reducing the fluctuation ofmagnetic field lines. With the increasing of coils number, the length of uniform magnetic field regionbecomes longer, the amplitude of magnetic flux density is reduced with constant supplied energy, and thetotal current reaches its peak earlier. On the whole, when the length of uniform magnetic field region isconstant, decreasing the number of turns and increasing the number of coils are both effective ways to obtaina stronger magnetic flux density and better uniformity. But it is limited by the capacity of the coils to carrycurrent. In addition, the stainless steel cylinder causes the distribution of magnetic field to beasymmetrical, and the amplitude of magnetic flux density reaches its peak later than the total current does.Keywords：High Power Microwave(HPM)；solenoid pulse magnet；uniform magnetic field高功率微波(HPM)源通常需要外加引导磁场来约束产生HPM的强流相对论电子束[1–5]。

科技英语翻译试题2套

科技英语翻译试题2套

1答案请写在答题纸上。

Part one: Sentence Translation(30%)1.为此，必须对电路(circuit)的基本内容有一个很好的了解。

2.这个系数(coefficient)有待确定。

3.现有的教科书均没有提这一点。

4.由于反馈(feedback)在电子线路(electronic circuit)中起着重要作用，所以对它的研究极为重要。

5.有迹象表明，计算机的价格将进一步下跌。

6.这个方法的确管用，不过到底该在什么情况下使用它尚不清楚。

7.十年前该厂的产量比现在高五倍。

8.激光(laser)是二十世纪六十年代引入的一项新技术，它能穿透(pierce)特别硬的物质。

9.为使晶体管(transistor)正常工作，必须给其电极(electrode)加(apply)上合适的电压(voltage)。

10.代表磁场(magnetic field)的磁力线(magnetic line of force)是一些围绕该导线的同心圆(concentric circle)。

11.我们所谓的机器人(robot)实际上是能为人类做工的一种工具。

12.这类天线(antenna)和那类天线相比的优点是结构简单，效率高。

13.半导体(semiconductor)对光和热都很敏感(sensitive)，这两者都对导电率(conductivity)影响很大。

14.只有通过对系统性能进行研究我们才能了解其优缺点。

15.本书既讲了实际的设计方法，同时也讲述了理论问题，而重点放在一般概念上。

Part two: Mistakes Correction(30%)(Write down the corrected sentence on the answer sheet. )1. We are easy to determine the effect of new drug to patient.2. The direction of an electric current was decided before electrons were not discovered.3. Sound travel much less faster than light is.4. The price for this instrument is expensive.5. There are a few exceptions for this rule.6. The hotter the body will be, the more it radiates energy.7. The feature of this device is small in size and light in weight.8. That professor is very interesting in this topic.9. Our semiconductor industry comes into being at the end of 1950s.10. The both engineers are busy to design a type of new computer.11. Work equals to force multiplying distance.12. The new design instrument is in good quality.13. The ability for some elements to give off radiations is referred as theradioactivity.Part three:Read this article, translate the underlined sentences(15%), answer the questions (15%)and then summarize this article within 100 words (10%).The Dazzle of Lasers(激光)The acronym（首字母缩写词）"laser," describes how the device works: Light Amplification by Stimulated Emission of Radiation. In 1916 Einstein predicted that electrons(电子) in an atom could be deliberately stimulated to emit photons（光子） (light energy) of a certain wavelength. He was right. The laser must first be "pumped" with energy in a variety of ways so that the electrons are excited into higher energy states. But these high energy electrons are unstable--and fall back to a lower energy level. On the way down, their extra energy is released（释放）as light. That light is captured inside the laser and amplified by bouncing it back and forth between mirrors. The laser beam that emerges is amplified, monochromatic （单色的）, coherent light --and it shines with an unearthly power.Not until 1960 did Theodore Maiman, a 33-year-old engineer at Hughes Research Laboratories, build a homely four-inch cylinder containing a ruby rod encircled by a flash tube: the world's first working laser.More than two decades later, the laser has wrought a technological revolution. Lasers are an indispensable tool for delicate eye surgery, and doctors are using lasers experimentally to destroy cancerous tumors(肿瘤), unclog（使畅通） diseased arteries （动脉） and even treat herpes（疱疹）. Just as they provide new tools for health care, however, they also make possible new engines of destruction: recently Dr. Edward Teller, the father of the hydrogen bomb（氢弹）, called on President Reagon to urge that the United States build a space-based laser-weapon system that would use a nuclear bomb to fire brutally intense laser X-rays against enemy missiles in flight.Today pilots flying the new Boeing 767 and 757 aircraft navigate with the aid of new laser gyroscopes（陀螺仪）. Supermarket clerks use lasers to ring up prices at the checkout counter by "reading" universal bar-codes（条形码） printed on packages and canned goods. Powerful lasers cut and weld（焊） steel in factories from Detroit to Tokyo. Artists and filmmakers are beginning to use lasers for animation（动画）: at Lucasfilm, George Lucas has a team of computer wizards（奇才） developing a machinethat uses a computer-driven laser to draw animated images on film; a second film, with human actors, is then merged by laser with the graphics into a single seamless （无缝的） whole.How does the laser work? Anyone who has ever focused sunlight through a magnifying glass and watched paper or dry leaves snap into flames understands the power of concentrated light. Laser light is intense, concentrated light, too, but it works on a different principle. Shine sunlight through a prism（棱镜） and it breaks into the glorious colors of the rainbow. In the scientists' vocabulary, sunlight is "incoherent" --it is made up of a mix of wavelengths spanning the spectrum（光谱）from infrared（红外线） to ultraviolet（紫外线）. Laser light, on the other hand, is monochromatic and coherent－it shines at a single wavelength, and all the light waves march together in step like soldiers on parade（游行）.In the two decades since its invention, the laser has undergone a dramatic transformation: a wide variety of gas, solid-state, diode（二极管） and other lasers has been created. Each shines at a different wavelength; some pulse on and off, others operate continuously.When the laser moved out of the laboratory, one of its first and most significant applications was as a medical tool. Lasers are commonly used for delicate surgery inside the eye. In treating blood-vessel disorders resulting from complications(并发症) of diabetes（糖尿病）, doctors aim a fine beam of argon laser light（氩激光） through the pupil（瞳孔） of the eye and place up to 2000 tiny laser burns very closely around the back portion of the retina（视网膜）. These laser "welds" prevent harmful growth or rupture（断裂） of new, unwanted blood vessels.The very properties that make lasers dangerous --power and heat--are also being put to use to destroy some kinds of brain and spinal（脊髓的） tumors. Lasers have brought a new frontier to neurosurgery（神经外科）. They have made some inoperable tumors operable and high-risk tumors less high risk.Warfare is also changing as laser technology advances. Laser guidance systems have brought once unimaginable accuracy to artillery（炮）. In the near future, higher-intensity lasers may be used to blind the electronic sensory systems of aircraft, missiles, tanks and ships. And ultimately, some visionaries insists, the globe could be surrounded by a platoon（排） of orbiting battle stations armed with lasers capable of destroying planes and missiles within seconds of their beinglaunched.Just as they are opening new doors to medicine and military practices, lasers are also having a profound impact on communications. Instead of sunbeams, today's light-wave communication systems use laser light ricocheting through tiny glass fibers. Lasers generate light waves at extraordinarily high frequencies--in the range of trillions of cycles per second --which makes it possible to transmit enormous quantities of information. In addition, fiber-optic cables are cheaper than copper wire and are not subject to electromagnetic interference, or the annoying cross talk（串话） and static that plague（折磨） current systems. The big breakthrough was the semiconductor laser.Someday laser light may be piped through giant optic cables into deep ocean waters to create undersea farms; it may be beamed into space to talk to orbiting space stations. Lasers also may be used to fire extremely precise light pulses at DNA molecules, altering the structure of chromosomes（染色体） and thereby repairing defective genes --or even creating new forms of life. And eventually billions of lasers will link the world in a vast information network, a global village of light.1.How does the laser work?2.What is the difference between sunlight and the laser?3.Is the laser absolutely safe? If not, please explain.4.What are the advantages of the semiconductor laser in the communications field?5.In what fields is the laser applied?Part one:1.For this purpose, it is necessary to have a good understanding of the fundamentals of thecircuit.2.This coefficient remains to be determined.3.None of the textbook available mentions this point.4.Since feedback plays an important role in the electronic circuit, its study is very important.5.There is an indication that the price of computers will fall further.6.This method does work, but it is not clear in what condition it is that it should be used.7.The output of this factory 10 years ago is 6 times what it is now.8. A new technology introduced in the 1960s, laser can pierce very hard substances.9.For the transistor to work normally, it is necessary to apply a proper voltage across theelectrode.10.The magnetic lines of force representing the magnetic field are some concentric circlessurrounding the wire.11.What is called a robot is a tool which can do work for the human being.12.This type of antenna has the advantages over that one of simple structure and high efficiency.13.Semiconductors are sensitive to light and hear, both of which have a great impact onconductivity.14.Only through a study of the system’s performance is it possible to know its advantages anddisadvantages.15.This book discusses both practical design method and theoretical problems with emphasis onthe basic concept.Part two:1.It is easy to determine the effect of the new drug on the patient.2.The direction of the electric current had been decided before electrons were discovered.3.Sound travels much more slowly that light does.4.This instrument is expensive.5.There are a few exceptions to this rule.6.The hotter the body is, the more energy it radiates.7.This device is small and light.8.That professor is much interested in this topic.9.Our semiconductor industry came into being at the end of the 1950s.10.Both the engineers are busy designing a new type of computer.11.Work equals force multiplied by distance.12.The newly designed instrument is good in quality.13.The ability of some elements ot give off radiations is referred as the radioactivity.Part three:Translation:1. 20多年前，激光引发了一场技术革命。

magnetic_resonance_imaging1

magnetic_resonance_imaging1

There are three types of motion within an atom 1. Electrons spinning on their own axis 2. Electrons orbiting the nucleus 3. The nucleus spinning about its own axis
Hydrogen Carbon Nitrogen Oxygen Fluorine Sodium Phosphorus
1 13 15 17 19 23 31
The magnetic moment alignment
The alignment of the magnetic moment is measured as the total of the nuclear magnetic moments and is expressed as a vector sum The strength of the total magnetic moment is specific to every nucleus and determines the sensitivity to magnetic resonance
Diseased tissue, such as tumors, can be detected because the protons in different tissues return to their equilibrium state at different rates. By changing the parameters on the scanner this effect is used to create contrast between different types of body tissue.
美军雷达命名规则和雷达英文词汇

美军雷达命名规则和雷达英文词汇

美军雷达命名规范之宇文皓月创作按老美军用尺度MIL-STD-196D规定，其军用电子设备（包含雷达）根据联合电子类型命名系统（JETDS）。

名称由字母AN （陆军-海军联合命名系统）,一条斜线和另外三个字母组成。

三个字母暗示设备装置位置，设备类型和设备用途。

比方AN/SPS-49暗示舰载警戒雷达。

数字49标识特定装备，而且暗示该设备时JETDS规定的SPS类的第49种。

经过一次修改就在原型后附加一个字母如ABC，名称后加破折号，T和数字暗示丫是用来训练的。

名称后的括号内V暗示丫是可变系统，就是通过增加或减少设备来完成分歧功能的系统。

处于试验和研制中的系统有时在紧随正式名称后的括弧内用特殊标记来暗示，他们用来指明研究单位。

比方XB暗示海军研究实验室，XW暗示罗姆航空发展中心。

下面就把AN/***后面的三个字母的意思祥加说明。

JETDS设备符号装置位置（第一个字母）A 机载B 水下移动式，潜艇D 无人驾驶运载工具F 地面固定G 地面通用K 水陆两用M 地面移动式P 便携式S 水面舰艇T 地面可运输式U 通用V 地面车载W 水面或水下Z有人和无人驾驶空中运输工具设备类型（第二个字母）A 不成见光，热辐射设备C 载波设备D放射性检测，指示，计算设备E 激光设备G 电报，电传设备I 内部通信和有线广播J 机电设备K 遥测设备L 电子对抗设备M 气象设备N 空中声测设备P 雷达Q 声纳和水声设备R 无线电设备S专用设备，磁设备或组合设备T 电话（有线）设备V 目视和可见光设备W 武器特有设备X 传真和电视设备Y 数据处理设备设备用途（第三个字母）A 辅助装置B 轰炸C 通信（发射和接受）D 测向侦查或警戒E 弹射或投掷G 火控或探照灯瞄准H 记录K 计算M 维修或测试工具N导航（测高，信标，罗盘，测深，进场）Q 专用或兼用R 接收，无源探测S 探测或测距，测向，搜索T 发射W 自动飞行或遥控X 识别Y 监视和火控有源滤波器Active filter有源校正网络Active corrective network有源干扰Active jamming机载引导雷达 Airborne director radar机载动目标显示 Airborne MTI机载雷达 Airborne radar机载截击雷达 Airborne-intercept radar机载警戒雷达 Airborne warning radar模拟信号 Analog signal天线抗干扰技术Antenna anti-jamming technique天线增益 Antenna gain反辐射导弹 Anti-radiation missile背射天线 Backfire antenna回差 Backlash 轰炸雷达 Bombing radar平衡电感 Balancing inductor选频放大器 Bandpass amplifier战场侦察雷达 Battle-field search radar 盲区Blind zone闪烁干扰 Blinking jamming击穿功率 Breakdown power体效应二极管当地振荡器Bulk effect diode local oscillator宽带中频放大器Broad band intermediate frequency amplifier机柜、分机结构 Cabinet, subassembly标定误差 Calibrated error电子束管(阴极射线管) Cathode-ray tube(CRT)空腔型振荡器 Cavity Oscillator谐振腔 Cavity Resonator空腔稳频当地振荡器Cavity-Stabilized Local Oscillator干扰偶极子 Chaff Dipole信道化接收机 Channelized receiver 圆极化平面波Circularly polarized plane wave闭环控制系统（反馈控制系统）Close-loop control system (feed-back control system)杂波抑制 Clutter suppression同轴电缆 Coaxial cable 同轴谐振腔 Coaxial cavity同轴定向耦合器Coaxial directional coupler 同轴滤波器 Coaxial filter相干振荡器Coherent oscillator 相干动目标显示 Coherent MTI复调制干扰 Complex modulated jamming圆锥扫描雷达 Conical scan radar圆锥扫描天线 Conical Scanned Antenna连续波雷达接收机Continuous-wave radar receiver对比度 Contrast 卷积器 Convolutor变频损耗Conversion loss 相关时间Correlation time抗反辐射导弹措施Counter anti-radiation missile measures正交场器件（M型器件）Crossed-field devices(M-type devices)截止式衰减器Cut-Off Attenutor截止波长Cut-off wavelength连续波雷达发射机 CW Radar Transmitter直流阻抗 D.C. impedance直流谐振充电 D.C. resonant charging 直流谐振二极管充电 D.C. resonant diode charge数据处理 Data processing偏转线圈 Deflection coil延时充电电路 Delayed charging circuit介质移相器 Dielectric phase shifter介质干扰杆 Dielectric chaff rod数字滤波器 Digital filter数字匹配滤波器 Digital matched filter数字测距 Digital ranging引导雷达 Director radar多普勒雷达 Doppler Radar双门限检测器Double threshold detector 双T接头 Double T-junction等效负载Dummy load 天线收发开关DuplexerE面（H面）折叠双T E plane (H plane) magic-T天线的有效面积 Effective area of an antenna 有效辐射功率Effective radiation power(E.R.P.)电液伺服阀 Electro-hydraulic Servo value电磁兼容性 Electromagnetic compatibility电子抗干扰 Electronic anti-jamming电扫描天线 Electronic Scanned antenna电扫描雷达 Electronically Scanned Radar椭圆极化场矢量Elliptically Polarized Field Vector末制导雷达 End-guidance radar激励器（预调器、触发器）Exciter(premodulator, trigger)极窄脉冲雷达 Extra-short pulse radar快速付里叶变换 Fast Fourier Transform馈电网络Feed network 相控阵馈电网络Feed networks For Phased Array铁氧体移相器 Ferrite phase shifter火控雷达Fire control radar 频率捷变雷达Frequency agile radar调频雷达发射机 Frequency modulation radar transmitter引信干扰 Fuse jamming齿轮传动误差 Gear transmission error图形失真校正 Graphic distortion correction格雷戈伦天线 Gregarain antenna制导雷达 Guidance radar炮瞄雷达Gun directing radar 回旋管Gyrotron测高雷达 Height-finding radar水平极化场矢量Horizontally polarized field vector喇叭天线Horn antenna 环行电桥Hybrid ring液压泵 Hydraulic pump阻抗匹配Impedance match 天线阻抗匹配Impedance match of antenna输入阻抗 Input impedance 天线罩拔出相移Insertion phase of a radome阵列单元的孤立阻抗Isolated impedance of an array element天线间的隔离 Isolation between antennas干扰压制系数 Jamming blanket factor干扰调制样式 Jamming modulation type干扰信号带宽 Jamming signal band width速调管 Klystron激光雷达 Laser radar 线阵天线 Linear array antenna 负载阻抗 Load impedance低空搜索雷达 Low altitude surveillance radar 主振放大式发射机 M.O.P.A. transmitter磁脉冲调制器Magnetic pulse modulator 磁控管 Magnetron磁控管灯丝电压控制电路Magnetron filament voltage controlling Circuit主瓣零点宽度Main (major) lobe zero beamwidth航海雷达Marine radar 矩阵阵列Matrix array 气象雷达 Meteorological radar微波带通滤波器 Microwave band-pass filter 微波场效应晶体管放大器Microwave field effect transistor amplifier微波全息雷达 Microwave hologram radar微波低通滤波器 Microwave low-pass filter副瓣电平 Minor (side) lobe level机动雷达Movable radar 阵列天线的互耦Mutual coupling of an array antenna多模馈电器Multimode feed 多基地雷达Multistatic radar多端网络 Multiport network导航雷达Navigation radar 噪声调幅干扰Noise AM jamming噪声调幅调相干扰 Noise AM-PM jamming 归一化差斜率 Normalized difference slope单通道单脉冲雷达One-channel Monopulse Radar开环系统频率特性Open-loop system frequency characteristic运算放大器 Operational Amplifier超视距雷达 Over-the-horizon radar过压呵护电路 Overvoltage protection circuit 抛物柱面天线 Parabolic cylindrical antenna 参量检测器Parameter detector无源雷达Passive radar相位检波器Phase detector 移相器Phase detector相控阵天线Phased array antenna 锁相接收机 Phase-locked receiver相位扫描雷达 Phase-scanned radar脉冲压缩雷达Pulse compression radar 脉冲雷达接收机 Pulse radar receiver相控阵的量化误差Quantization error of a phased array雷达精度 Radar accuracy 雷达反侦察 Radar anti-reconnaissance天线罩 Radome采样频率Sampling frequency 舰载雷达Shipbased radar船用雷达Shipboard radar 侧视雷达Side-looking radar 旁瓣对消 Sidelobe Cancellation固体微波振荡器Solid state microwave oscillator合成孔径雷达 Synthetic radar目标识别雷达 Target-identification radar三通道单脉冲雷达接收机Three-channel monopulse radar receiverT型（Y型）环行器（结环行器）T-type (Y-type) circulator (junction circulator)静电控制超高频电子管（栅控管）UHF electronstatic control tubeV形波束雷达 V-beam radar压控晶体振荡器 Voltage controlled oscillator 波导谐振腔 Waveguide cavity天气雷达 Weather radar X-Y型天线座 X-Y type antenna pedestal八木天线 Yagi antenna雷达覆盖范围 Zone of radar coverage零轴漂移Zero-axsis drift雷达工作模式：目标捕获系统：The tention action system(该系统配备有嵌入式惯性导航系统和全球定位系统，可在雷达快速展开时提供雷达位置坐标。