High-Redshift Quasars Found in Sloan Digital Sky Survey Commissioning Data VI. Sloan Digita
- 格式:pdf
- 大小:1017.34 KB
- 文档页数:34
Combustion and NO x emission characteristics of a retrofitted down-fired 660MW e utility boiler at different loadsZhengqi Li ⇑,Guangkui Liu,Qunyi Zhu,Zhichao Chen,Feng RenSchool of Energy Science and Engineering,Harbin Institute of Technology,92,West Dazhi Street,Harbin 150001,Chinaa r t i c l e i n f o Article history:Received 7September 2010Received in revised form 23November 2010Accepted 20January 2011Available online 12February 2011Keywords:Down-fired boiler RetrofitCarbon content in fly ash Thermal efficiencya b s t r a c tIndustrial experiments were performed for a retrofitted 660MW e full-scale down-fired boiler.Measure-ments of ignition of the primary air/fuel mixture flow,the gas temperature distribution of the furnace and the gas components in the furnace were conducted at loads of 660,550and 330MW e .With decreasing load,the gas temperature decreases and the ignition position of the primary coal/air flow becomes farther along the axis of the fuel-rich pipe in the burner region under the arches.The furnace temperature also decreases with decreasing load,as does the difference between the temperatures in the burning region and the lower position of the burnout region.With decreasing load,the exhaust gas temperature decreases from 129.8°C to 114.3°C,while NO x emissions decrease from 2448to 1610mg/m 3.All three loads result in low carbon content in fly ash and great boiler thermal efficiency higher than 92%.Com-pared with the case of 660MW e before retrofit,the exhaust gas temperature decreased from 136to 129.8°C,the carbon content in the fly ash decreased from 9.55%to 2.43%and the boiler efficiency increased from 84.54%to 93.66%.Ó2011Elsevier Ltd.All rights reserved.1.IntroductionReserves of anthracite and lean coal are abundant and globally distributed.The use of anthracite and lean coal,which have low-volatility contents,presents difficulties in ignition and burnout.More and more research has been conducted around the world to solve these problems.At present,down-fired combustion is widely applied in the power industry to consume low-volatility coals,and its main merit is that it achieves a high degree of burn-out by prolonging the residence time of pulverized-coal in the fur-nace.However,a practical down-fired boiler operation still suffers from the problems of high carbon content in the fly ash and poor flame stabilization at low load without oil support firing.Precise understanding of the behavior of char particles in pul-verized-coal combustion systems is critical in determining funda-mental processes that occur during heterogeneous bustion data obtained for full-scale equipment can give the combustion and NO x emission characteristics of real combustors,in particular the turbulent flow of industrial coal flames.As a re-sult,studies using full-scale equipment are highly desirable and a necessity.In the surrounds of wall-fired boilers,measurements are made of the local mean concentrations of O 2,CO,CO 2,and NO x ,gas temperatures,and char burnout through several observ-ing doors in the utility boilers [1–5].Experiments have also been performed for tangentially fired boilers [6–9].However,for down-fired boilers adopting Foster Wheeler technology,there has only been the work of Li et al.,who measured the gas temperature,gas species concentrations in the furnace and carbon content in the fly ash in a 300MW e boiler before and after retrofit [10–14].In the present study,in situ experiments were carried out for a 660MW e down-fired pulverized-coal boiler after retrofit;this unit has the maximum capacity of any currently used worldwide [15].Measurements of ignition of the primary air/fuel mixture flow,the gas temperature distribution of the furnace and the gas compo-nents in the furnace were made for this full-scale boiler at the rated,middle and half loads.The collected data were used to deter-mine the combustion and NO x emissions characteristics of the boi-ler at different loads.The results obtained from these experiments help solve similar problems and benefit the design and operation of 600MW e and 1000MW e down-fired boilers,and the data can be used to support theoretical and numerical calculations.2.The utility boilerThe investigated 660MW e boiler,having the largest capacity of any down-fired boiler in the world,was made by Foster Wheeler (FW)Corp.Fig.1a is a schematic diagram of the furnace.Arches di-vide the furnace into two:the lower furnace below the arches and the upper furnace above the arches.Originally,36cyclone burners were arranged on the arches to produce a W-shaped flame.The fuel-rich flow streaming from the cyclone nozzle is near the0306-2619/$-see front matter Ó2011Elsevier Ltd.All rights reserved.doi:10.1016/j.apenergy.2011.01.048Corresponding author.Tel.:+8645186418854;fax:+8645186412528.E-mail address:green@ (Z.Li).water-cooled wall while the fuel-leanflow jetting from the fuel-lean pipe faces the furnace center.Under the arches,there are three tiers of secondary air denoted D,E and F,all of which are fed into the furnace horizontally.Details of the specific structure of this kind of boiler can be found in the literature[10–13].During practical operation,the boiler suffers from great resis-tance and serious abrasion of the cyclone and high carbon content infly ash up to7–10%.Fuel-richflows form after the separation of the coal/airflows in the cyclones.The swirl intensities of fuel-rich flows decrease at the exits under the effect of the adjustable vane, which provides great resistance.The fuel-richflows with residual swirl have little rigidity and abrade the nozzles of the cyclones [16].The secondary air under the arches enters the furnace horizon-tally and mixes prematurely with the fuel-richflow.This reduces the down-forwardflow and space for combustion and decreases the temperature in the lower furnace,which causes a series of problems including the delayed ignition of pulverized-coal and high carbon content in thefly ash[13,17].There is fuel-leanflow with low momentum and shallow penetration depth near the furnace center, which readily shortens theflame and reduces upflow to the burnout region quickly.This is also a reason for the poor burnout degree of coal particles and high carbon content in thefly ash[18].In2009,Li et al.retrofitted the combustion system with many items.Fig.1b is a schematic diagram of the retrofitted combustion system.A fuel louver concentrator replaced the original cyclone as it has much lower resistance than the cyclone.The fuel/airflowfirst passes through the louver concentrator and separates into fuel-rich flow and fuel-leanflow.The fuel-richflow further divides into two and is injected into the furnace through the original primary air ducts facing the furnace center while the fuel-leanflow as vent air is injected into the furnace near the wall.The vent air ducts are con-trolled by valves.The horizontal secondary air is modified by the F-tier secondary air with an angle of declination of20°.In this retrofitted boiler,measurements were conducted at loads of660,550and330MW e with a constant opening of the vent air valves.3.Data acquisition methods and experimental conditionsThe formal in situ experiments were carried out in the2026tph down-fired pulverized-coal boiler to investigate certain aspects of the combustion process and NO x formation in the furnace.During the experiments,soot blowing and sewer bleeding were not per-mitted.The coal used in the experiments was a mixture of anthra-cite and lean coal.Sample characteristics of coals before and after retrofit are presented in Table1.The following parameters were measured:(1)The gas temper-ature of the furnace was measured with a leucoscope through observing doors in the front,rear and side walls.The layout of the observing doors is shown in Fig.2.The measurement error is 50°C.(2)The gas temperature of the furnace was measured with a nickel chromium–nickel silicon thermocouple through observing doors1,2and3.As shown in Fig.2,observing door1is in the air-flow zone of the tier D and E slots,observing door2is in the airflow zone of the tier F slots,and observing door3is above the arches. The end of the bare thermocouple was exposed in the furnace,so the temperature measured should be higher than the local gas temperature because of highflame radiation.However,because of radiation between the bare thermocouple and the water-cooled wall,and the close proximity of the two,the temperature mea-sured should be lower than the local gas temperature.The calcula-tions have indicated that in the region of highest temperature the ‘‘true’’temperature do not exceed the measured one by more than 8%[3,19].The thermocouples used were thoroughly checked be-fore leaving the factory,giving high confidence in the temperature measurement results.To minimize errors due to ash deposition,Table1Characteristics of the coal used in the experiments before and after retrofit.Quantity Before retrofit After retrofitProximate analysis,wt.%(as received)Volatile10.729.29Ash30.8431.51Moisture0.54 2.48Fixed carbon57.9056.72Net heating value(kJ/kg)23,53121,250Ultimate analysis,wt.%(as received)Carbon59.7059.48Hydrogen 2.95 2.52Oxygen 3.81 3.53Nitrogen0.820.83Sulfur 1.340.79Z.Li et al./Applied Energy88(2011)2400–24062401the thermocouples were frequently retracted from the furnace and, where necessary,any deposits were carefully removed.Moreover, the probes were replaced if there was any thermal distortion ob-served.(3)The primary air/flow temperature distribution was measured with the same thermocouple inserted parallel to the axis of the fuel-rich pipe,as shown in Fig.1.(4)Gas compositions were sampled using a water-cooled stainless steel probe2.5m in length for analysis of the local mean O2,CO and NO x concentrations.As shown in Fig.3,the probe comprised a centrally located10mm (inner diameter)tube,through which quenched samples were evacuated,surrounded by a tube for probe cooling.The probe was cleaned frequently by blowing high-pressure air through it to maintain a constant suction rate.The water-cooled probe was inserted into the furnace through observing doors1–3(see Fig.2).The gases withdrawn were analyzed online using a Testo 350M system.Theflue gas after the air heater was also analyzed online.Calibrations with standard mixtures including zero concen-trations were performed before each measurement session.The measurement error for O2and CO2concentrations was1%,while that for CO and NO x concentrations was50ppm.(5)Unburnt car-bon infly ash was determined by collectingfly ash using a particle-sampling device with constant suction speed.Values of the main operating parameters for the three operating loads are listed in Table2.4.Results and discussionFig.4shows the gas temperature distribution of the fuel-burn-ing zone along the cyclone axes of the burners;zero points were set at the tips of the burner nozzles in the furnace.With decreasing load,the gas temperature decreases and the ignition position of the primary coal/airflow becomes farther along the axis of the fuel-rich pipe in the burner region under the arches,especially as the load decreases from550to330MW e.For the rated load,the gas temperature rises rapidly as the measurement point extends to lower positions,exceeding1000°C at a position400mm from the end of the fuel-rich nozzle and exceeding1200°C at 1400mm.For the load of550MW e,the gas temperature is a little lower than that for the rated load in the burner region,exceeding 1000°C at a position800mm from the fuel-rich nozzle.For the half load,the gas temperature rises slowly and the temperature gradi-ent is lower than in the other two cases,barely reaching1000°C at 2400mm.The mass ratio of coal/air decreases as the load decreases,indi-cating that the concentration of pulverized-coal falls in the primary air and the momentum of coal/airflow decreases,resulting in aTable2Boiler operating conditions and measurement results.Quantity Before retrofit After retrofit660MW e660MW e550MW e330MW eTotalflux of the primary air(kg/s)121127110.574Temperature of the primaryair(°C)130124125114Totalflux of the secondaryair(kg/s)657620511396Temperature of thesecondary air(°C)398405397362 Coal feeding rate(ton/h)268.6282.7244.6147.7 O2at the furnace exit(dryvolume%)3.35 2.58 2.02 5.31O2influe gases(dry volume%)4.76 3.99 3.047.27NO x influe gas(mg/m3at6%O2dry)1181244821631610Carbon infly ash(%)9.55 2.43 6.02 3.24 Exhaust gas temperature(°C)136129.8119.3114.3Thermal efficiency of the boiler(%)84.5493.6692.5992.862402Z.Li et al./Applied Energy88(2011)2400–2406shallower penetration depth and shorter residence time of the pri-mary coal/airflow in the lower furnace.For these reasons,the gas temperature measured along the axis direction of the fuel-rich pipe decreases and the ignition of the primary coal/airflow in the bur-ner region under the arches is farther along the axis.The mass ratio of coal/air is defined to indicate the coal concen-tration in the primary air.As the load falls from660to330MW e, the mass ratio of coal/air drops from0.618to0.554,which indi-cates an obvious decrease in the coal concentration;thus,the heat and time needed for coal ignition increase.This is one of the rea-sons for the low gas temperature in the burner region and far igni-tion position of the coal particles at half load.For the load of 550MW e,the mass ratio of coal/air is0.615,which is little different to that for the rated load.Furthermore,the quantity of primary air and coal feed rate both decrease as the load decreases,as does the momentum of coal/airflow,leading to shallow penetration of the pulverized-coal in the lower furnace.The short residence times then lower the overall temperature of the burner zone to the ex-tent that the fuel-richflow cannot obtain sufficient heat from the recirculating up-flowing gases(see Fig.1).Fig.5presents furnace gas temperature variations as measured using the thermocouple inserted through observing doors1–3.On the whole,the gas temperature measured through observing doors 1–3decreases with decreasing load.In the case of the temperature distribution measured through observing door1,the gas tempera-turefirst increases and then decreases because some of the high-temperature gas recirculates into the near-wall zone.As the measurement points move deeper into the furnace,the measured temperature begins to fall as the thermocouple enters the fuel-rich flow.At the rated load,the gas temperature is steadily around 1000°C at points further than1400mm,while for the load of 550MW e,the measured temperature is a little lower.At the same position but for a load of330MW e,the temperature falls below 700°C gradually,indicating that the fuel-richflow has not ignited. This temperature sequence is the same as that for the temperature gradients of the fuel-richflow mentioned above,indicating that ignition conditions worsen as the load decreases.In the cases of measuring the temperature through observing doors2and3,once the temperature reached1250°C,no further measurements were taken at deeper positions for the simple rea-son of protecting the thermocouple from burnout.From the rela-tively limited temperature distribution,Fig.5shows that in the zone near observing door2,the temperature rises rapidly at loads of660and550MW e,and at400mm,temperatures already exceed 1250°C.This indicates that coal burns more intensely in the lower furnace in both cases.At the load of330MW e,the temperature rises to nearly1200°C at the position1800mm from the side wall, increasing more slowly than in the other two cases.As illustrated above for the gas temperature in the burner region,the momentum of coal/airflow at half load is low,which results in a shallow pen-etration depth and short residence time of the primary coal/air flow and low furnace temperature in the lower furnace.Further-more,the F-tier air accounts for a large proportion of the secondary air entering the furnace under the arches;therefore,much of the air does not take part in combustion immediately,which decreases the temperature in the region near observing door2.In the zones near observing door3above the arches,the temperature increases to more than1100°C at a load of330MW e,which is just a little lower than the temperature near observing door2.This can be ex-plained by the delay in the fuel-richflow ignition causing much of the fuel to burn in the upper furnace.Fig.6presents furnace temperature variations measured through observing doors for the three loads.The furnace tempera-tures shown in Fig.6are averages of values measured through observing doors at the same level.In the three cases,gas tempera-ture peaks are all in the lower furnace,and the distances from the peak positions to the exit of the furnace are relatively large.Resi-dence times for coal burning in the higher-temperature zone are thus longer,which favors fuel burnout.The difference between temperatures in the burning region and the lower position of the burnout region decreases as the load decreases,and is just35°C at a load of330MW e.This is because the momentum of coal/air flow decreases,which results in a shallower penetration depth and shorter residence time of the primary coal/airflow in the lower furnace;the ignition position becomes farther from the fuel-rich nozzle,and more pulverized-coal combusts completely in the upper furnace.Moreover,the temperature in the furnace decreases with the decreasing load.The reason for this is that the total heatZ.Li et al./Applied Energy88(2011)2400–24062403provided to the furnace also falls with decreasing load,decreasing the furnace temperature.Fig.7shows the variations in gas species concentrations in the zones near observing doors1–3.Gas species concentration mea-surements begin400mm from the side wall to avoid the effect of an air leak.In all three cases,the O2concentration sequence is C(door1)>C(door2)>C(door3),which describes well theflow of coal as illustrated in Fig.1b.Fuel-richflowsfirst inject down-ward into the furnace and then reverse their direction upwards in the down-fired boiler.The coal/airflows pass sequentially through the observation doors1,2,and3and O2is consumed con-tinuously along the path of theflame.Thus,in each case,the O2 concentration in the zone near observation door1was the highest, that in the zone near observation door2was intermediate and that near observation door3was the lowest.In the airflowflow zone of the D and E tiers and in the zone near the wall,a great quantity of hot gas lowers the measured O2con-centration.When the measurement points are deeper and closer to the fuel-richflow,the measured value increases.O2concentra-tions near observing door1increase with decreasing load,espe-cially from550to330MW e.For loads of660and550MW e,at the position1800mm from the wall,O2concentrations are nearly 14%,suggesting that the fuel-richflow is beginning to react and a certain amount of O2is being consumed.For the load of 330MW e,however,O2concentrations are higher than18%,indi-cating that the fuel-richflow has not ignited,which agrees with the conclusion drawn from the temperature analysis.In the near-wall zone of observing doors2and3,O2concentrations at half load are higher than in the other two cases,even as high as8%in the near-wall zone of observing door3.At all three loads,CO concentrations strictly rule contrary to O2 concentrations.In the zones near observing doors1–3,the higher the O2concentration,the lower the CO concentration.In the air-flowflow zone of the D and E tiers,CO concentrations decrease with decreasing load because of the delayed ignition of the fuel/ airflow.In the near-wall zone of observing doors2and3,CO con-centrations in the case of the half load are lower than in the other two cases because of the highly oxidizing atmosphere in the furnace.2404Z.Li et al./Applied Energy88(2011)2400–2406In the zone near port1at loads of660and550MW e,volatiles are released and form a certain amount of NO x.However,biased combustion restricts the formation of NO x,and hence,NO x concen-tration here is only645mg/m3and630mg/m3respectively at a position1800mm from the wall.However,for the load of 330MW e,the NO x concentration is as high as3706mg/m3at the same position,because the high O2concentrations form the strong oxidative atmosphere near the observing door1.Moreover,the fuel/airflows with weak rigidity mix with the fuel gas quickly in the furnace;these are the reason for the high NO x concentration. Compared with those measured through observing door1,NO x concentrations for660and550MW e operation increase rapidly in the airflow zone of observing door2because fuel–NO forms con-stantly with further combustion of the pulverized-coal and ther-mal NO increasingly forms under the high-temperature condition in the lower furnace.The NO x concentration at a load of 550MW e is lower than that for the rated load because of the re-duced fuel–NO formation with a lower coal feed rate and the low-er-furnace temperature in this zone.In the case of330MW e,NO x concentrations decrease sharply,because the reducing atmosphere become higher with a great amount of O2consuming.In the zone near observing door3,the NO x concentration decreases with decreasing load.Table2lists results obtained for theflue gas after the air hea-ter.It is obvious that as the load decreases,the exhaust gas tem-perature decreases from129.8°C to114.3°C,while NO x emissions decrease from2448to1610mg/m3.Overall,the NO x content in theflue gas at the three loads was at high levels, exceeding the proposed Chinese emission standard for anthracite (1100mg/Nm3).To decrease these emissions,further technolo-gies,such as over-fire air[15,20],selective catalytic reduction and selective non-catalytic reduction[21,22]should be taken into account.All three loads result in low carbon content in thefly ash and great boiler thermal efficiency higher than92%.The O2 concentrations at the furnace exit when operating at660and 550MW e were2.58%and2.02%,respectively,with the small dif-ference between the two caused by thefluctuation of air supply during operation.The carbon in thefly ash at a load of550MW e was6.02%,which is higher than that at660MW e because the lower-furnace temperature was lower by as much as50°C than the temperature at the higher operating load.To enhance heat absorption in the reheater and to ensure sufficient temperature of the reheat steam,the method of increasing the excess air coef-ficient is commonly adopted when operated at330MW e.Thus, the O2concentration at the furnace exit at330MW e was5.31%, much higher than that at660or550MW e.Despite the high O2 concentration,the quantity of air supplied,including both pri-mary and secondary air,was low for the330MW e case,being only63%of the quantity supplied at660MW e and76%of the quantity supplied at660MW e,as shown in Table2.Therefore, the mean velocity of the fuel gas was lower and the residence time of pulverized-coal was longer in the furnace.These factors explain the high degree of burnout of pulverized-coal and low carbon content in thefly ash.Table2also shows the main operating parameters and mea-surement results at a load of660MW e before the combustion sys-tem retrofit.After retrofit,the exhaust gas temperature decreased from136to129.8°C,the carbon content in thefly ash decreased from9.55%to 2.43%and the boiler efficiency increased from 84.54%to93.66%.However,the NO x content in theflue gas (O2=6%)was higher than before the retrofit,because premature ignition of the pulverized-coal prolonged the residence time of coal particles in the lower furnace with high temperature.Furthermore, the O2concentration in theflue gas decreased from4.76%to3.99%, which increased the NO x concentration after conversion of O2at 6%.5.ConclusionIndustrial experiments were performed in a retrofitted 660MW e full-scale down-fired boiler.Measurements of ignition of the primary air/fuel mixtureflow,gas temperature distribution of the furnace and the gas components in the furnace were con-ducted at loads of660,550and330MW e.The results were as follows.With decreasing load,the gas temperature decreases and the ignition position of the primary coal/airflow becomes farther along the axis of the fuel-rich pipe in the burner region under the arches, especially as the load decreases from550to330MW e.With decreasing load,the gas temperature measured through observing doors1–3decreases,the ignition conditions worsen. Moreover,the combustion intensity of pulverized-coal reduces in the lower furnace.The furnace temperature also decreases with decreasing load,as does the difference between temperatures in the burning region and in the lower position of the burnout region.O2concentrations near observing door1increase with decreas-ing load,while O2concentrations at half load are higher than in the other two cases in the near-wall zone of observing doors2and3. CO concentrations strictly rule contrary to O2concentrations.The higher the O2concentration,the lower the CO concentration near observing doors1–3.NO x concentrations(O2=6%)near observing door1were low at loads of660and550MW e than at the load of 330MW pared with those measured through observing door 1,NO x concentrations for660and550MW e operation increase rapidly in the airflow zone of observing door2while NO x concen-trations at the load of330MW e decrease.In the zone near observ-ing door3,the NO x concentration decreases with decreasing load.With decreasing load,the exhaust gas temperature decreases from129.8°C to114.3°C,while NO x emissions decrease from 2448to1610mg/m3.All three loads result in low carbon content in thefly ash and great boiler thermal efficiency higher than92%.Compared with the case of660MW e before retrofit,the exhaust gas temperature decreased from136to129.8°C,the carbon con-tent in thefly ash decreased from9.55%to2.43%and the boiler efficiency increased from84.54%to93.66%.AcknowledgmentThis work was sponsored by the Hi-Tech Research and Development Program of China(863Program)(Contract No. 2006AA05Z321).References[1]Li ZQ,Jing JP,Liu GK,Chen ZC,Liu CL.Measurement of gas species,temper-atures,char burnout,and wall heatfluxes in a200-MWe lignite-fired boiler at different loads.Appl Energy2010;87:1217–30.[2]Li ZQ,Jing JP,Chen ZC,Ren F,Xu B,Wei HD,et bustion characteristicsand NO x emissions of enhanced ignition-dual register and central-fuel-rich swirl burners in a300-MWe wall-fired pulverized coal utility bust Sci Technol2008;180:1370–94.[3]Costa M,Azevedo JLT,Carvalho bustion characteristics of a front-wall-fired pulverized coal300MW e utility bust Sci Technol 1997;129:277–93.[4]Costa M,Silva P,Azevedo JLT.Measurements of gas species,temperature,andchar burnout in a low-NO x pulverized coal-fired utility bust Sci Technol2003;175:271–89.[5]Costa M,Azevedo JLT.Experimental characterization of an industrialpulverized coal-fired furnace under deep staging bust Sci Technol2007;179:1923–35.[6]Kouprianova VI,Tanetsakunvatanab V.Optimization of excess air for theimprovement of environmental performance of a150MW boilerfired with Thai lignite.Appl Energy2003;74:445–53.[7]Li S,Xu TM,Hui SE,Wei XL.NO x emission and thermal efficiency of a300MW eutility boiler retrofitted by air staging.Appl Energy2009;86:1797–803.Z.Li et al./Applied Energy88(2011)2400–24062405[8]Toshikazu T,Hirofumi O,Dernjatinc P,Savolainenc K.Reducing the minimumload and NO x emissions for lignite-fired boiler by applying a stable-flame concept.Appl Energy2003;74:415–24.[9]Li ZQ,Yang LB,Qiu PH,Sun R,Chen LZ,Sun SZ.Experimental study of thecombustion efficiency and formation of NO x in industrial pulverized coal combustion.Int J Energy Res2004;28:511–20.[10]Li ZQ,Ren F,Zhang J,Zhang XH,Chen ZC,Chen LZ.Influence of vent air valveopening on combustion characteristics of a down-fired pulverized-coal 300MW e utility boiler.Fuel2007;86:245–62.[11]Ren F,Li ZQ,Jing JP,Zhang XH,Chen ZC,Zhang JW.Influence of the adjustablevane position on theflow and combustion characteristics of a down-fired pulverized-coal300MW e utility boiler.Fuel Process Technol2008;89: 1297–305.[12]Li ZQ,Ren F,Chen ZC,Wang JJ,Chen Z,Zhang JW.Influence of oil atomized aironflow and combustion characteristics in a300MW e down-fired –Pac J Chem Eng2010;5:488–96.[13]Li ZQ,Ren F,Chen ZC,Chen Z,Wang JJ.Influence of declivitous secondary air oncombustion characteristics of a down-fired300-MWe utility boiler.Fuel 2010;89:410–6.[14]Li ZQ,Ren F,Chen ZC,Liu GK,Xu ZX.Improved NO x emissions and combustioncharacteristics for a retrofitted down-fired300-MWe utility boiler.Environ Sci Technol2010;44:3926–31.[15]Garcia-Mallol JA,Steitz T,Chu CY,Jiang PZ.Ultra-low NO x advanced FW archfiring:central power station applications.In:2nd US China NO x and SO2 control workshop,Dalian;2005.[16]Zhang J.Experimental study and numerical simulation on separation char-acteristics of cyclone separator of downfired boiler.Harbin:School of Energy Science and Engineering,Harbin Institute of Technology;2006[in Chinese]. [17]Ren F,Li ZQ,Chen ZC,Wang JJ,Chen Z.Influence of the down-draft secondaryair on the furnace aerodynamic characteristics of a down-fired boiler.Energy Fuels2009;23:2437–43.[18]Ren F,Li ZQ,Chen ZC,Xu ZX,Yang GH.Experimental investigations into gas/particleflows in a down-fired boiler:influence of the vent air ratio.Energy Fuels2010;24:1592–602.[19]De DS.Measurement offlame temperature with a multi-elementthermocouple.J Inst Energy1981;54:113–6.[20]Li ZQ,Ren F,Liu GK,Shen SP,Chen ZC.Influence of the overfire air ratio on theNO x emission and combustion characteristics of a down-fired300MW e utility boiler.Environ Sci Technol2010;44:6510–6.[21]Sounak R,Hegde MS,Giridhar M.Catalysis for NO x abatement.Appl Energy2010;86:2283–97.[22]Liang ZY,Ma XQ,Lin H,Tang YT.The energy consumption and environmentalimpacts of SCR technology in China.Appl Energy2010.doi:10.1016/ j.apenergy.2010.10.010.2406Z.Li et al./Applied Energy88(2011)2400–2406。
1000 0569/2020/036(06) 1705 18ActaPetrologicaSinica 岩石学报doi:10 18654/1000 0569/2020 06 04榴辉岩中单斜辉石 石榴子石镁同位素地质温度计评述黄宏炜1 杜瑾雪1 柯珊2HUANGHongWei1,DUJinXue1 andKEShan21 中国地质大学地球科学与资源学院,北京 1000832 中国地质大学地质过程与矿产资源国家重点实验室,北京 1000831 SchoolofEarthSciencesandResources,ChinaUniversityofGeosciences,Beijing100083,China2 StateKeyLaboratoryofGeologicalProcessesandMineralResources,ChinaUniversityofGeosciences,Beijing100083,China2019 11 14收稿,2020 04 08改回HuangHW,DuJXandKeS 2020 Reviewontheclinopyroxene garnetmagnesiumisotopegeothermometersforeclogites ActaPetrologicaSinica,36(6):1705-1718,doi:10 18654/1000 0569/2020 06 04Abstract Theremarkableequilibriummagnesiumisotopefractionationbetweenclinopyroxeneandgarnetobservedineclogitesmakesitapotentialhigh precisiongeothermometer Therefore,thispaperselects64pairsofclinopyroxene garnetmagnesiumisotopedataofeclogitesintheChinesesouthwesternTianshanorogen,intheDabie SuluorogenandintheKaapvaalcratonintheSouthAfricafromliteratures Then,wescreened50pairsofdatathatreachtheequilibriummagnesiumisotopefractionationbytheδ26MgCpx δ26MgGrtdiagram Usingthesemagnesiumisotopeequilibriumfractionationdata,wecalculatedpeaktemperaturesofeclogitesbymagnesiumisotopegeothermometersofHuangetal (2013)throughfirst principlescalculationandWangetal (2012)andLietal (2016)throughempiricalestimation,andcomparedthemwiththepeaktemperaturesgivenbyothergeothermometers Byanalyzingthecalculationresults,itisfoundthatfororogeniceclogites,thecalculationresultsofthegeothermometerofHuangetal (2013)areconsistentwiththosepreviouslyobtainedbytraditionalgeothermometersandphaseequilibriamodeling,whilethecalculationresultsofthegeothermometersofWangetal (2012)andLietal (2016)aresignificantlylower Forthecratoneclogites,thecalculationresultsofallthethreemagnesiumisotopegeothermometersaresignificantlydifferentfromresultsoftraditionalgeothermometersbymorethan50℃,whichismostprobablycausedbyre equilibriumofmagnesiumisotopeduringearlyretrogrademetamorphismathightemperatures Thisindicatesthatthesethreemagnesiumisotopegeothermometersarenotapplicableforthecratoneclogites Basedontheabovedata,themethodofempiricalestimationisusedtocalibrateanewclinopyroxene garnetmagnesiumisotopegeothermometer,whichisΔ26MgCpx Grt=1 11×106/[T(K)]2(R2=0 92).Inaddition,thispaperalsobrieflydiscussesapplicationprospectoftheclinopyroxene garnetmagnesiumisotopegeothermometersandtheproblemsthatshouldbepaidattentiontoduringapplication Keywords Eclogites;Isotopegeothermometer;Magnesiumisotope;Clinopyroxene garnet摘 要 榴辉岩中单斜辉石和石榴子石之间显著的镁同位素平衡分馏,使其成为一种具有潜力的高精度地质温度计。
DOI: 10.1126/science.1094786, 441 (2004);304Science et al.Mitchell S. Abrahamsen,Cryptosporidium parvum Complete Genome Sequence of the Apicomplexan, (this information is current as of October 7, 2009 ):The following resources related to this article are available online at/cgi/content/full/304/5669/441version of this article at:including high-resolution figures, can be found in the online Updated information and services,/cgi/content/full/1094786/DC1 can be found at:Supporting Online Material/cgi/content/full/304/5669/441#otherarticles , 9 of which can be accessed for free: cites 25 articles This article 239 article(s) on the ISI Web of Science. cited by This article has been /cgi/content/full/304/5669/441#otherarticles 53 articles hosted by HighWire Press; see: cited by This article has been/cgi/collection/genetics Genetics: subject collections This article appears in the following/about/permissions.dtl in whole or in part can be found at: this article permission to reproduce of this article or about obtaining reprints Information about obtaining registered trademark of AAAS.is a Science 2004 by the American Association for the Advancement of Science; all rights reserved. The title Copyright American Association for the Advancement of Science, 1200 New York Avenue NW, Washington, DC 20005. (print ISSN 0036-8075; online ISSN 1095-9203) is published weekly, except the last week in December, by the Science o n O c t o b e r 7, 2009w w w .s c i e n c e m a g .o r g D o w n l o a d e d f r o m3.R.Jackendoff,Foundations of Language:Brain,Gram-mar,Evolution(Oxford Univ.Press,Oxford,2003).4.Although for Frege(1),reference was established rela-tive to objects in the world,here we follow Jackendoff’s suggestion(3)that this is done relative to objects and the state of affairs as mentally represented.5.S.Zola-Morgan,L.R.Squire,in The Development andNeural Bases of Higher Cognitive Functions(New York Academy of Sciences,New York,1990),pp.434–456.6.N.Chomsky,Reflections on Language(Pantheon,New York,1975).7.J.Katz,Semantic Theory(Harper&Row,New York,1972).8.D.Sperber,D.Wilson,Relevance(Harvard Univ.Press,Cambridge,MA,1986).9.K.I.Forster,in Sentence Processing,W.E.Cooper,C.T.Walker,Eds.(Erlbaum,Hillsdale,NJ,1989),pp.27–85.10.H.H.Clark,Using Language(Cambridge Univ.Press,Cambridge,1996).11.Often word meanings can only be fully determined byinvokingworld knowledg e.For instance,the meaningof “flat”in a“flat road”implies the absence of holes.However,in the expression“aflat tire,”it indicates the presence of a hole.The meaningof“finish”in the phrase “Billfinished the book”implies that Bill completed readingthe book.However,the phrase“the g oatfin-ished the book”can only be interpreted as the goat eatingor destroyingthe book.The examples illustrate that word meaningis often underdetermined and nec-essarily intertwined with general world knowledge.In such cases,it is hard to see how the integration of lexical meaning and general world knowledge could be strictly separated(3,31).12.W.Marslen-Wilson,C.M.Brown,L.K.Tyler,Lang.Cognit.Process.3,1(1988).13.ERPs for30subjects were averaged time-locked to theonset of the critical words,with40items per condition.Sentences were presented word by word on the centerof a computer screen,with a stimulus onset asynchronyof600ms.While subjects were readingthe sentences,their EEG was recorded and amplified with a high-cut-off frequency of70Hz,a time constant of8s,and asamplingfrequency of200Hz.14.Materials and methods are available as supportingmaterial on Science Online.15.M.Kutas,S.A.Hillyard,Science207,203(1980).16.C.Brown,P.Hagoort,J.Cognit.Neurosci.5,34(1993).17.C.M.Brown,P.Hagoort,in Architectures and Mech-anisms for Language Processing,M.W.Crocker,M.Pickering,C.Clifton Jr.,Eds.(Cambridge Univ.Press,Cambridge,1999),pp.213–237.18.F.Varela et al.,Nature Rev.Neurosci.2,229(2001).19.We obtained TFRs of the single-trial EEG data by con-volvingcomplex Morlet wavelets with the EEG data andcomputingthe squared norm for the result of theconvolution.We used wavelets with a7-cycle width,with frequencies ranging from1to70Hz,in1-Hz steps.Power values thus obtained were expressed as a per-centage change relative to the power in a baselineinterval,which was taken from150to0ms before theonset of the critical word.This was done in order tonormalize for individual differences in EEG power anddifferences in baseline power between different fre-quency bands.Two relevant time-frequency compo-nents were identified:(i)a theta component,rangingfrom4to7Hz and from300to800ms after wordonset,and(ii)a gamma component,ranging from35to45Hz and from400to600ms after word onset.20.C.Tallon-Baudry,O.Bertrand,Trends Cognit.Sci.3,151(1999).tner et al.,Nature397,434(1999).22.M.Bastiaansen,P.Hagoort,Cortex39(2003).23.O.Jensen,C.D.Tesche,Eur.J.Neurosci.15,1395(2002).24.Whole brain T2*-weighted echo planar imaging bloodoxygen level–dependent(EPI-BOLD)fMRI data wereacquired with a Siemens Sonata1.5-T magnetic reso-nance scanner with interleaved slice ordering,a volumerepetition time of2.48s,an echo time of40ms,a90°flip angle,31horizontal slices,a64ϫ64slice matrix,and isotropic voxel size of3.5ϫ3.5ϫ3.5mm.For thestructural magnetic resonance image,we used a high-resolution(isotropic voxels of1mm3)T1-weightedmagnetization-prepared rapid gradient-echo pulse se-quence.The fMRI data were preprocessed and analyzedby statistical parametric mappingwith SPM99software(http://www.fi/spm99).25.S.E.Petersen et al.,Nature331,585(1988).26.B.T.Gold,R.L.Buckner,Neuron35,803(2002).27.E.Halgren et al.,J.Psychophysiol.88,1(1994).28.E.Halgren et al.,Neuroimage17,1101(2002).29.M.K.Tanenhaus et al.,Science268,1632(1995).30.J.J.A.van Berkum et al.,J.Cognit.Neurosci.11,657(1999).31.P.A.M.Seuren,Discourse Semantics(Basil Blackwell,Oxford,1985).32.We thank P.Indefrey,P.Fries,P.A.M.Seuren,and M.van Turennout for helpful discussions.Supported bythe Netherlands Organization for Scientific Research,grant no.400-56-384(P.H.).Supporting Online Material/cgi/content/full/1095455/DC1Materials and MethodsFig.S1References and Notes8January2004;accepted9March2004Published online18March2004;10.1126/science.1095455Include this information when citingthis paper.Complete Genome Sequence ofthe Apicomplexan,Cryptosporidium parvumMitchell S.Abrahamsen,1,2*†Thomas J.Templeton,3†Shinichiro Enomoto,1Juan E.Abrahante,1Guan Zhu,4 Cheryl ncto,1Mingqi Deng,1Chang Liu,1‡Giovanni Widmer,5Saul Tzipori,5GregoryA.Buck,6Ping Xu,6 Alan T.Bankier,7Paul H.Dear,7Bernard A.Konfortov,7 Helen F.Spriggs,7Lakshminarayan Iyer,8Vivek Anantharaman,8L.Aravind,8Vivek Kapur2,9The apicomplexan Cryptosporidium parvum is an intestinal parasite that affects healthy humans and animals,and causes an unrelenting infection in immuno-compromised individuals such as AIDS patients.We report the complete ge-nome sequence of C.parvum,type II isolate.Genome analysis identifies ex-tremely streamlined metabolic pathways and a reliance on the host for nu-trients.In contrast to Plasmodium and Toxoplasma,the parasite lacks an api-coplast and its genome,and possesses a degenerate mitochondrion that has lost its genome.Several novel classes of cell-surface and secreted proteins with a potential role in host interactions and pathogenesis were also detected.Elu-cidation of the core metabolism,including enzymes with high similarities to bacterial and plant counterparts,opens new avenues for drug development.Cryptosporidium parvum is a globally impor-tant intracellular pathogen of humans and animals.The duration of infection and patho-genesis of cryptosporidiosis depends on host immune status,ranging from a severe but self-limiting diarrhea in immunocompetent individuals to a life-threatening,prolonged infection in immunocompromised patients.Asubstantial degree of morbidity and mortalityis associated with infections in AIDS pa-tients.Despite intensive efforts over the past20years,there is currently no effective ther-apy for treating or preventing C.parvuminfection in humans.Cryptosporidium belongs to the phylumApicomplexa,whose members share a com-mon apical secretory apparatus mediating lo-comotion and tissue or cellular invasion.Many apicomplexans are of medical or vet-erinary importance,including Plasmodium,Babesia,Toxoplasma,Neosprora,Sarcocys-tis,Cyclospora,and Eimeria.The life cycle ofC.parvum is similar to that of other cyst-forming apicomplexans(e.g.,Eimeria and Tox-oplasma),resulting in the formation of oocysts1Department of Veterinary and Biomedical Science,College of Veterinary Medicine,2Biomedical Genom-ics Center,University of Minnesota,St.Paul,MN55108,USA.3Department of Microbiology and Immu-nology,Weill Medical College and Program in Immu-nology,Weill Graduate School of Medical Sciences ofCornell University,New York,NY10021,USA.4De-partment of Veterinary Pathobiology,College of Vet-erinary Medicine,Texas A&M University,College Sta-tion,TX77843,USA.5Division of Infectious Diseases,Tufts University School of Veterinary Medicine,NorthGrafton,MA01536,USA.6Center for the Study ofBiological Complexity and Department of Microbiol-ogy and Immunology,Virginia Commonwealth Uni-versity,Richmond,VA23198,USA.7MRC Laboratoryof Molecular Biology,Hills Road,Cambridge CB22QH,UK.8National Center for Biotechnology Infor-mation,National Library of Medicine,National Insti-tutes of Health,Bethesda,MD20894,USA.9Depart-ment of Microbiology,University of Minnesota,Min-neapolis,MN55455,USA.*To whom correspondence should be addressed.E-mail:abe@†These authors contributed equally to this work.‡Present address:Bioinformatics Division,Genetic Re-search,GlaxoSmithKline Pharmaceuticals,5MooreDrive,Research Triangle Park,NC27009,USA.R E P O R T S SCIENCE VOL30416APRIL2004441o n O c t o b e r 7 , 2 0 0 9 w w w . s c i e n c e m a g . o r g D o w n l o a d e d f r o mthat are shed in the feces of infected hosts.C.parvum oocysts are highly resistant to environ-mental stresses,including chlorine treatment of community water supplies;hence,the parasite is an important water-and food-borne pathogen (1).The obligate intracellular nature of the par-asite ’s life cycle and the inability to culture the parasite continuously in vitro greatly impair researchers ’ability to obtain purified samples of the different developmental stages.The par-asite cannot be genetically manipulated,and transformation methodologies are currently un-available.To begin to address these limitations,we have obtained the complete C.parvum ge-nome sequence and its predicted protein com-plement.(This whole-genome shotgun project has been deposited at DDBJ/EMBL/GenBank under the project accession AAEE00000000.The version described in this paper is the first version,AAEE01000000.)The random shotgun approach was used to obtain the complete DNA sequence (2)of the Iowa “type II ”isolate of C.parvum .This isolate readily transmits disease among numerous mammals,including humans.The resulting ge-nome sequence has roughly 13ϫgenome cov-erage containing five gaps and 9.1Mb of totalDNA sequence within eight chromosomes.The C.parvum genome is thus quite compact rela-tive to the 23-Mb,14-chromosome genome of Plasmodium falciparum (3);this size difference is predominantly the result of shorter intergenic regions,fewer introns,and a smaller number of genes (Table 1).Comparison of the assembled sequence of chromosome VI to that of the recently published sequence of chromosome VI (4)revealed that our assembly contains an ad-ditional 160kb of sequence and a single gap versus two,with the common sequences dis-playing a 99.993%sequence identity (2).The relative paucity of introns greatly simplified gene predictions and facilitated an-notation (2)of predicted open reading frames (ORFs).These analyses provided an estimate of 3807protein-encoding genes for the C.parvum genome,far fewer than the estimated 5300genes predicted for the Plasmodium genome (3).This difference is primarily due to the absence of an apicoplast and mitochondrial genome,as well as the pres-ence of fewer genes encoding metabolic functions and variant surface proteins,such as the P.falciparum var and rifin molecules (Table 2).An analysis of the encoded pro-tein sequences with the program SEG (5)shows that these protein-encoding genes are not enriched in low-complexity se-quences (34%)to the extent observed in the proteins from Plasmodium (70%).Our sequence analysis indicates that Cryptosporidium ,unlike Plasmodium and Toxoplasma ,lacks both mitochondrion and apicoplast genomes.The overall complete-ness of the genome sequence,together with the fact that similar DNA extraction proce-dures used to isolate total genomic DNA from C.parvum efficiently yielded mito-chondrion and apicoplast genomes from Ei-meria sp.and Toxoplasma (6,7),indicates that the absence of organellar genomes was unlikely to have been the result of method-ological error.These conclusions are con-sistent with the absence of nuclear genes for the DNA replication and translation machinery characteristic of mitochondria and apicoplasts,and with the lack of mito-chondrial or apicoplast targeting signals for tRNA synthetases.A number of putative mitochondrial pro-teins were identified,including components of a mitochondrial protein import apparatus,chaperones,uncoupling proteins,and solute translocators (table S1).However,the ge-nome does not encode any Krebs cycle en-zymes,nor the components constituting the mitochondrial complexes I to IV;this finding indicates that the parasite does not rely on complete oxidation and respiratory chains for synthesizing adenosine triphosphate (ATP).Similar to Plasmodium ,no orthologs for the ␥,␦,or εsubunits or the c subunit of the F 0proton channel were detected (whereas all subunits were found for a V-type ATPase).Cryptosporidium ,like Eimeria (8)and Plas-modium ,possesses a pyridine nucleotide tran-shydrogenase integral membrane protein that may couple reduced nicotinamide adenine dinucleotide (NADH)and reduced nico-tinamide adenine dinucleotide phosphate (NADPH)redox to proton translocation across the inner mitochondrial membrane.Unlike Plasmodium ,the parasite has two copies of the pyridine nucleotide transhydrogenase gene.Also present is a likely mitochondrial membrane –associated,cyanide-resistant alter-native oxidase (AOX )that catalyzes the reduction of molecular oxygen by ubiquinol to produce H 2O,but not superoxide or H 2O 2.Several genes were identified as involved in biogenesis of iron-sulfur [Fe-S]complexes with potential mitochondrial targeting signals (e.g.,nifS,nifU,frataxin,and ferredoxin),supporting the presence of a limited electron flux in the mitochondrial remnant (table S2).Our sequence analysis confirms the absence of a plastid genome (7)and,additionally,the loss of plastid-associated metabolic pathways including the type II fatty acid synthases (FASs)and isoprenoid synthetic enzymes thatTable 1.General features of the C.parvum genome and comparison with other single-celled eukaryotes.Values are derived from respective genome project summaries (3,26–28).ND,not determined.FeatureC.parvum P.falciparum S.pombe S.cerevisiae E.cuniculiSize (Mbp)9.122.912.512.5 2.5(G ϩC)content (%)3019.43638.347No.of genes 38075268492957701997Mean gene length (bp)excluding introns 1795228314261424ND Gene density (bp per gene)23824338252820881256Percent coding75.352.657.570.590Genes with introns (%)553.9435ND Intergenic regions (G ϩC)content %23.913.632.435.145Mean length (bp)5661694952515129RNAsNo.of tRNA genes 454317429944No.of 5S rRNA genes 6330100–2003No.of 5.8S ,18S ,and 28S rRNA units 57200–400100–20022Table parison between predicted C.parvum and P.falciparum proteins.FeatureC.parvum P.falciparum *Common †Total predicted proteins380752681883Mitochondrial targeted/encoded 17(0.45%)246(4.7%)15Apicoplast targeted/encoded 0581(11.0%)0var/rif/stevor ‡0236(4.5%)0Annotated as protease §50(1.3%)31(0.59%)27Annotated as transporter 69(1.8%)34(0.65%)34Assigned EC function ¶167(4.4%)389(7.4%)113Hypothetical proteins925(24.3%)3208(60.9%)126*Values indicated for P.falciparum are as reported (3)with the exception of those for proteins annotated as protease or transporter.†TBLASTN hits (e Ͻ–5)between C.parvum and P.falciparum .‡As reported in (3).§Pre-dicted proteins annotated as “protease or peptidase”for C.parvum (CryptoGenome database,)and P.falciparum (PlasmoDB database,).Predicted proteins annotated as “trans-porter,permease of P-type ATPase”for C.parvum (CryptoGenome)and P.falciparum (PlasmoDB).¶Bidirectional BLAST hit (e Ͻ–15)to orthologs with assigned Enzyme Commission (EC)numbers.Does not include EC assignment numbers for protein kinases or protein phosphatases (due to inconsistent annotation across genomes),or DNA polymerases or RNA polymerases,as a result of issues related to subunit inclusion.(For consistency,46proteins were excluded from the reported P.falciparum values.)R E P O R T S16APRIL 2004VOL 304SCIENCE 442 o n O c t o b e r 7, 2009w w w .s c i e n c e m a g .o r g D o w n l o a d e d f r o mare otherwise localized to the plastid in other apicomplexans.C.parvum fatty acid biosynthe-sis appears to be cytoplasmic,conducted by a large(8252amino acids)modular type I FAS (9)and possibly by another large enzyme that is related to the multidomain bacterial polyketide synthase(10).Comprehensive screening of the C.parvum genome sequence also did not detect orthologs of Plasmodium nuclear-encoded genes that contain apicoplast-targeting and transit sequences(11).C.parvum metabolism is greatly stream-lined relative to that of Plasmodium,and in certain ways it is reminiscent of that of another obligate eukaryotic parasite,the microsporidian Encephalitozoon.The degeneration of the mi-tochondrion and associated metabolic capabili-ties suggests that the parasite largely relies on glycolysis for energy production.The parasite is capable of uptake and catabolism of mono-sugars(e.g.,glucose and fructose)as well as synthesis,storage,and catabolism of polysac-charides such as trehalose and amylopectin. Like many anaerobic organisms,it economizes ATP through the use of pyrophosphate-dependent phosphofructokinases.The conver-sion of pyruvate to acetyl–coenzyme A(CoA) is catalyzed by an atypical pyruvate-NADPH oxidoreductase(Cp PNO)that contains an N-terminal pyruvate–ferredoxin oxidoreductase (PFO)domain fused with a C-terminal NADPH–cytochrome P450reductase domain (CPR).Such a PFO-CPR fusion has previously been observed only in the euglenozoan protist Euglena gracilis(12).Acetyl-CoA can be con-verted to malonyl-CoA,an important precursor for fatty acid and polyketide biosynthesis.Gly-colysis leads to several possible organic end products,including lactate,acetate,and ethanol. The production of acetate from acetyl-CoA may be economically beneficial to the parasite via coupling with ATP production.Ethanol is potentially produced via two in-dependent pathways:(i)from the combination of pyruvate decarboxylase and alcohol dehy-drogenase,or(ii)from acetyl-CoA by means of a bifunctional dehydrogenase(adhE)with ac-etaldehyde and alcohol dehydrogenase activi-ties;adhE first converts acetyl-CoA to acetal-dehyde and then reduces the latter to ethanol. AdhE predominantly occurs in bacteria but has recently been identified in several protozoans, including vertebrate gut parasites such as Enta-moeba and Giardia(13,14).Adjacent to the adhE gene resides a second gene encoding only the AdhE C-terminal Fe-dependent alcohol de-hydrogenase domain.This gene product may form a multisubunit complex with AdhE,or it may function as an alternative alcohol dehydro-genase that is specific to certain growth condi-tions.C.parvum has a glycerol3-phosphate dehydrogenase similar to those of plants,fungi, and the kinetoplastid Trypanosoma,but(unlike trypanosomes)the parasite lacks an ortholog of glycerol kinase and thus this pathway does not yield glycerol production.In addition to themodular fatty acid synthase(Cp FAS1)andpolyketide synthase homolog(Cp PKS1), C.parvum possesses several fatty acyl–CoA syn-thases and a fatty acyl elongase that may partici-pate in fatty acid metabolism.Further,enzymesfor the metabolism of complex lipids(e.g.,glyc-erolipid and inositol phosphate)were identified inthe genome.Fatty acids are apparently not anenergy source,because enzymes of the fatty acidoxidative pathway are absent,with the exceptionof a3-hydroxyacyl-CoA dehydrogenase.C.parvum purine metabolism is greatlysimplified,retaining only an adenosine ki-nase and enzymes catalyzing conversionsof adenosine5Ј-monophosphate(AMP)toinosine,xanthosine,and guanosine5Ј-monophosphates(IMP,XMP,and GMP).Among these enzymes,IMP dehydrogenase(IMPDH)is phylogenetically related toε-proteobacterial IMPDH and is strikinglydifferent from its counterparts in both thehost and other apicomplexans(15).In con-trast to other apicomplexans such as Toxo-plasma gondii and P.falciparum,no geneencoding hypoxanthine-xanthineguaninephosphoribosyltransferase(HXGPRT)is de-tected,in contrast to a previous report on theactivity of this enzyme in C.parvum sporo-zoites(16).The absence of HXGPRT sug-gests that the parasite may rely solely on asingle enzyme system including IMPDH toproduce GMP from AMP.In contrast to otherapicomplexans,the parasite appears to relyon adenosine for purine salvage,a modelsupported by the identification of an adeno-sine transporter.Unlike other apicomplexansand many parasitic protists that can synthe-size pyrimidines de novo,C.parvum relies onpyrimidine salvage and retains the ability forinterconversions among uridine and cytidine5Ј-monophosphates(UMP and CMP),theirdeoxy forms(dUMP and dCMP),and dAMP,as well as their corresponding di-and triphos-phonucleotides.The parasite has also largelyshed the ability to synthesize amino acids denovo,although it retains the ability to convertselect amino acids,and instead appears torely on amino acid uptake from the host bymeans of a set of at least11amino acidtransporters(table S2).Most of the Cryptosporidium core pro-cesses involved in DNA replication,repair,transcription,and translation conform to thebasic eukaryotic blueprint(2).The transcrip-tional apparatus resembles Plasmodium interms of basal transcription machinery.How-ever,a striking numerical difference is seenin the complements of two RNA bindingdomains,Sm and RRM,between P.falcipa-rum(17and71domains,respectively)and C.parvum(9and51domains).This reductionresults in part from the loss of conservedproteins belonging to the spliceosomal ma-chinery,including all genes encoding Smdomain proteins belonging to the U6spliceo-somal particle,which suggests that this par-ticle activity is degenerate or entirely lost.This reduction in spliceosomal machinery isconsistent with the reduced number of pre-dicted introns in Cryptosporidium(5%)rela-tive to Plasmodium(Ͼ50%).In addition,keycomponents of the small RNA–mediatedposttranscriptional gene silencing system aremissing,such as the RNA-dependent RNApolymerase,Argonaute,and Dicer orthologs;hence,RNA interference–related technolo-gies are unlikely to be of much value intargeted disruption of genes in C.parvum.Cryptosporidium invasion of columnarbrush border epithelial cells has been de-scribed as“intracellular,but extracytoplas-mic,”as the parasite resides on the surface ofthe intestinal epithelium but lies underneaththe host cell membrane.This niche may al-low the parasite to evade immune surveil-lance but take advantage of solute transportacross the host microvillus membrane or theextensively convoluted parasitophorous vac-uole.Indeed,Cryptosporidium has numerousgenes(table S2)encoding families of putativesugar transporters(up to9genes)and aminoacid transporters(11genes).This is in starkcontrast to Plasmodium,which has fewersugar transporters and only one putative ami-no acid transporter(GenBank identificationnumber23612372).As a first step toward identification ofmulti–drug-resistant pumps,the genome se-quence was analyzed for all occurrences ofgenes encoding multitransmembrane proteins.Notable are a set of four paralogous proteinsthat belong to the sbmA family(table S2)thatare involved in the transport of peptide antibi-otics in bacteria.A putative ortholog of thePlasmodium chloroquine resistance–linkedgene Pf CRT(17)was also identified,althoughthe parasite does not possess a food vacuole likethe one seen in Plasmodium.Unlike Plasmodium,C.parvum does notpossess extensive subtelomeric clusters of anti-genically variant proteins(exemplified by thelarge families of var and rif/stevor genes)thatare involved in immune evasion.In contrast,more than20genes were identified that encodemucin-like proteins(18,19)having hallmarksof extensive Thr or Ser stretches suggestive ofglycosylation and signal peptide sequences sug-gesting secretion(table S2).One notable exam-ple is an11,700–amino acid protein with anuninterrupted stretch of308Thr residues(cgd3_720).Although large families of secretedproteins analogous to the Plasmodium multi-gene families were not found,several smallermultigene clusters were observed that encodepredicted secreted proteins,with no detectablesimilarity to proteins from other organisms(Fig.1,A and B).Within this group,at leastfour distinct families appear to have emergedthrough gene expansions specific to the Cryp-R E P O R T S SCIENCE VOL30416APRIL2004443o n O c t o b e r 7 , 2 0 0 9 w w w . s c i e n c e m a g . o r g D o w n l o a d e d f r o mtosporidium clade.These families —SKSR,MEDLE,WYLE,FGLN,and GGC —were named after well-conserved sequence motifs (table S2).Reverse transcription polymerase chain reaction (RT-PCR)expression analysis (20)of one cluster,a locus of seven adjacent CpLSP genes (Fig.1B),shows coexpression during the course of in vitro development (Fig.1C).An additional eight genes were identified that encode proteins having a periodic cysteine structure similar to the Cryptosporidium oocyst wall protein;these eight genes are similarly expressed during the onset of oocyst formation and likely participate in the formation of the coccidian rigid oocyst wall in both Cryptospo-ridium and Toxoplasma (21).Whereas the extracellular proteins described above are of apparent apicomplexan or lineage-specific in-vention,Cryptosporidium possesses many genesencodingsecretedproteinshavinglineage-specific multidomain architectures composed of animal-and bacterial-like extracellular adhe-sive domains (fig.S1).Lineage-specific expansions were ob-served for several proteases (table S2),in-cluding an aspartyl protease (six genes),a subtilisin-like protease,a cryptopain-like cys-teine protease (five genes),and a Plas-modium falcilysin-like (insulin degrading enzyme –like)protease (19genes).Nine of the Cryptosporidium falcilysin genes lack the Zn-chelating “HXXEH ”active site motif and are likely to be catalytically inactive copies that may have been reused for specific protein-protein interactions on the cell sur-face.In contrast to the Plasmodium falcilysin,the Cryptosporidium genes possess signal peptide sequences and are likely trafficked to a secretory pathway.The expansion of this family suggests either that the proteins have distinct cleavage specificities or that their diversity may be related to evasion of a host immune response.Completion of the C.parvum genome se-quence has highlighted the lack of conven-tional drug targets currently pursued for the control and treatment of other parasitic protists.On the basis of molecular and bio-chemical studies and drug screening of other apicomplexans,several putative Cryptospo-ridium metabolic pathways or enzymes have been erroneously proposed to be potential drug targets (22),including the apicoplast and its associated metabolic pathways,the shikimate pathway,the mannitol cycle,the electron transport chain,and HXGPRT.Nonetheless,complete genome sequence analysis identifies a number of classic and novel molecular candidates for drug explora-tion,including numerous plant-like and bacterial-like enzymes (tables S3and S4).Although the C.parvum genome lacks HXGPRT,a potent drug target in other api-complexans,it has only the single pathway dependent on IMPDH to convert AMP to GMP.The bacterial-type IMPDH may be a promising target because it differs substan-tially from that of eukaryotic enzymes (15).Because of the lack of de novo biosynthetic capacity for purines,pyrimidines,and amino acids,C.parvum relies solely on scavenge from the host via a series of transporters,which may be exploited for chemotherapy.C.parvum possesses a bacterial-type thymidine kinase,and the role of this enzyme in pyrim-idine metabolism and its drug target candida-cy should be pursued.The presence of an alternative oxidase,likely targeted to the remnant mitochondrion,gives promise to the study of salicylhydroxamic acid (SHAM),as-cofuranone,and their analogs as inhibitors of energy metabolism in the parasite (23).Cryptosporidium possesses at least 15“plant-like ”enzymes that are either absent in or highly divergent from those typically found in mammals (table S3).Within the glycolytic pathway,the plant-like PPi-PFK has been shown to be a potential target in other parasites including T.gondii ,and PEPCL and PGI ap-pear to be plant-type enzymes in C.parvum .Another example is a trehalose-6-phosphate synthase/phosphatase catalyzing trehalose bio-synthesis from glucose-6-phosphate and uridine diphosphate –glucose.Trehalose may serve as a sugar storage source or may function as an antidesiccant,antioxidant,or protein stability agent in oocysts,playing a role similar to that of mannitol in Eimeria oocysts (24).Orthologs of putative Eimeria mannitol synthesis enzymes were not found.However,two oxidoreductases (table S2)were identified in C.parvum ,one of which belongs to the same families as the plant mannose dehydrogenases (25)and the other to the plant cinnamyl alcohol dehydrogenases.In principle,these enzymes could synthesize protective polyol compounds,and the former enzyme could use host-derived mannose to syn-thesize mannitol.References and Notes1.D.G.Korich et al .,Appl.Environ.Microbiol.56,1423(1990).2.See supportingdata on Science Online.3.M.J.Gardner et al .,Nature 419,498(2002).4.A.T.Bankier et al .,Genome Res.13,1787(2003).5.J.C.Wootton,Comput.Chem.18,269(1994).Fig.1.(A )Schematic showing the chromosomal locations of clusters of potentially secreted proteins.Numbers of adjacent genes are indicated in paren-theses.Arrows indicate direc-tion of clusters containinguni-directional genes (encoded on the same strand);squares indi-cate clusters containingg enes encoded on both strands.Non-paralogous genes are indicated by solid gray squares or direc-tional triangles;SKSR (green triangles),FGLN (red trian-gles),and MEDLE (blue trian-gles)indicate three C.parvum –specific families of paralogous genes predominantly located at telomeres.Insl (yellow tri-angles)indicates an insulinase/falcilysin-like paralogous gene family.Cp LSP (white square)indicates the location of a clus-ter of adjacent large secreted proteins (table S2)that are cotranscriptionally regulated.Identified anchored telomeric repeat sequences are indicated by circles.(B )Schematic show-inga select locus containinga cluster of coexpressed large secreted proteins (Cp LSP).Genes and intergenic regions (regions between identified genes)are drawn to scale at the nucleotide level.The length of the intergenic re-gions is indicated above or be-low the locus.(C )Relative ex-pression levels of CpLSP (red lines)and,as a control,C.parvum Hedgehog-type HINT domain gene (blue line)duringin vitro development,as determined by semiquantitative RT-PCR usingg ene-specific primers correspondingto the seven adjacent g enes within the CpLSP locus as shown in (B).Expression levels from three independent time-course experiments are represented as the ratio of the expression of each gene to that of C.parvum 18S rRNA present in each of the infected samples (20).R E P O R T S16APRIL 2004VOL 304SCIENCE 444 o n O c t o b e r 7, 2009w w w .s c i e n c e m a g .o r g D o w n l o a d e d f r o m。
a rXiv:as tr o-ph/998255v123Aug1999Accepted –To appear in The Astrophysical Journal.Parsec-Scale Images of Flat-Spectrum Radio Sources in Seyfert Galaxies C.G.Mundell Department of Astronomy,University of Maryland,College Park,MD,20742,USA;A.S.Wilson 1Department of Astronomy,University of Maryland,College Park,MD,20742,USA;J.S.Ulvestad National Radio Astronomy Observatory,P.O.Box O,Socorro,NM,87801,USA;A.L.Roy 2National Radio Astronomy Observatory,P.O.Box O,Socorro,NM,87801,USA ABSTRACT We present high angular resolution (∼2mas)radio continuum observations of five Seyfert galaxies with flat-spectrum radio nuclei,using the VLBA at 8.4GHz.The goal of the project is to test whether these flat-spectrum cores represent thermal emission from the accretion disk,as inferred previously by Gallimore et al.for NGC 1068,or non-thermal,synchrotron self-absorbed emission,which is believed to be responsible for more powerful,flat-spectrum nuclear sources in radio galaxies and quasars.In four sources (T0109−383,NGC 2110,NGC 5252,Mrk 926),the nuclear source is detected but unresolved by the VLBA,indicating brightness temperatures in excess of 108K and sizes,on average,less than 1pc.We argue that the radio emission is non-thermal and synchrotron self-absorbed in these galaxies,but Doppler boosting by relativistic outflows is not required.Synchrotron self-absorption brightness temperatures suggest intrinsic source sizes smaller than ∼0.05−0.2pc,for these four galaxies,the smallest of which corresponds to a light-crossing time of ∼60light days or 104gravitational radii for a 108M ⊙black hole.In one of these galaxies (NGC 2110),there is alsoextended(∼0.2pc)radio emission along the same direction as the400-pc scalejet seen with the VLA,suggesting that the extended emission comes from thebase of the jet.In another galaxy(NGC4388),theflat-spectrum nuclear sourceis undetected by the VLBA.We also present MERLIN and VLA observations ofthis galaxy and argue that the observed,flat-spectrum,nuclear radio emissionrepresents optically thin,free-free radiation from dense thermal gas on scales≃0.4to a few pc.It is notable that the two Seyfert galaxies with detectedthermal nuclear radio emission(NGC1068and NGC4388)both have largeX-ray absorbing columns,suggesting that columns in excess of≃1024cm−2areneeded for such disks to be detectable.Subject headings:accretion disks—galaxies:active—galaxies:jets—galaxies:nuclei—galaxies:Seyfert1.IntroductionIt has become generally accepted that supermassive black holes(SBH)lie at the center of most,if not all,galaxies(e.g.,Richstone et al.,1998;van der Marel,1999),with some lying dormant and others being triggered into an active phase to produce active galactic nuclei(AGN)(e.g.,Haehnelt&Rees,1993;Silk&Rees,1998).The power source for this activity is thought to be accretion of material onto the SBH,with the infalling material forming an accretion disk which,depending on detailed conditions,then regulates the fueling rate(e.g.Narayan&Yi,1994;Kato,Fukue&Mineshige,1998;Blandford& Begelman,1998).The radius to which these accretion disks extend(and hence become more easily observable)is not well established,but current AGN unification schemes advocate a geometrically thick and clumpy torus(e.g.Krolik&Begelman,1988;Krolik and Lepp, 1989;Pier&Krolik,1992)or warped thin disk(Miyoshi et al.,1995;Greenhill et al.,1995; Herrnstein,Greenhill&Moran,1996;Pringle,1996;Maloney,Begelman&Pringle,1996) which hides the nucleus when viewed edge-on.Our viewing angle with respect to the torus or disk is then responsible for the observed differences between narrow-line AGNs(e.g Seyfert2’s),in which our view of the nuclear broad-line region is obscured(edge-on view), and unobscured(pole-on view)broad-line AGNs(e.g.Seyfert1’s).Indirect evidence in support of such tori includes the discovery of broad lines in the polarized(hence scattered) light of Seyfert2s(Antonucci&Miller,1985;Tran,1995),sharp-edged bi-cones of ionized gas(e.g.,Wilson&Tsvetanov,1994)photo-ionized by anisotropic nuclear UV radiation (perhaps originating from the accretion disk and further collimated by the torus),large gas column densities(1023−25cm−2)to the nuclei of Seyfert2’s,inferred from photoelectricabsorption of soft X-rays(Turner et al.,1997)and strong mid-infrared emission in both Seyfert types(e.g.,Antonucci,1993;Alonso-Herrero,Ward&Kotilainen,1996).Recent,high-resolution studies at optical and radio wavelengths have begun to provide more direct evidence for‘nuclear’disks on size-scales ranging from the∼100-1000-pc diameter dusty disks imaged by HST(Jaffe et al.,1993;Ford et al.,1994;Carollo et al., 1997)and millimeter interferometry(Baker&Scoville,1998;Downes&Solomon,1998)to pc-scale disks inferred from HI and free-free absorption studies(Mundell et al.,1995;Carilli et al.,1998;Peck&Taylor,1998;Wilson et al.,1998;Taylor et al.,1999;Ulvestad,Wrobel &Carilli,1999),down to the0.25-pc warped,edge-on,Keplerian maser disk in NGC4258, imaged by the VLBA(Miyoshi et al.,1995,Greenhill et al.,1995;Herrnstein,et al.,1996).Theoretical work indicates that UV/X-ray radiation from the central engine can heat, ionize and evaporate the gas on the inner edge of the torus(Pier&Voit,1995;Balsara& Krolik,1993;Krolik&Lepp,1989).Indeed,simple Str¨o mgren sphere arguments suggest a radius for the ionized region of R(pc)=1.5(N⋆/1054s−1)1/3(n e/105cm−3)−2/3,where N⋆is the number of nuclear ionizing photons per second and n e is the electron density. Recalling the typical density n e∼105−6cm−3of the ionized disk in NGC1068(see below), we expect R∼0.3−1.5pc which is comparable to the tenths of pc to∼pc-scale resolutions achievable with the VLBA for nearby Seyferts.Recent high angular resolution VLBA radio observations of the archetypal Seyfert2galaxy,NGC1068,by Gallimore et al.(1997),have shown that emission from one of the radio components(‘S1’)may be associated with the inner,ionized edge of the torus.This radio component has aflat or rising(towards higher frequencies)spectrum,suggesting it contains the AGN,and a brightness temperature of up to4×106K;it is elongated perpendicular to the inner radio ejecta and extends over∼40 mas(3pc).The radiation mechanism may be free-free thermal emission(Gallimore et al., 1997),direct synchrotron emission(Roy et al.,1998)or Thomson scattering of a nuclear flat-spectrum synchrotron self-absorbed radio core(itself not detected)by the electrons at the inner edges of the torus(Gallimore et al.,1997;Roy et al.,1998).This discovery highlights the possibility of using the VLBA to image the pc-scale disks or tori in other Seyfert galaxies.However,flat-spectrum radio sources in AGNs often represent non-thermal synchrotron self-absorbed radio emission with a much higher brightness temperature(>108K)than is characteristic of component S1in NGC1068. High resolution radio observations are thus required to distinguish between the two emission processes.In the present paper,we report parsec-scale VLBA imaging offive Seyfert galaxies withflat-spectrum radio cores and hundred-pc scale,steep-spectrum,radio jets and lobes.Two of these galaxies also exhibit ionization cones with sharp,straight edges and axes aligned with the radio ejecta.Our goal is to determine whether theflat spectrumnuclear radio emission represents thermal emission from the accretion disk/obscuring torus or synchrotron self-absorbed emission from a compact radio core source.The paper is organized as follows;Sections2and3describe the sample selection, observations and reduction techniques whilst in Section4,the results of the study are presented.Section5discusses possible scenarios for the observed radio emission including direct non-thermal radiation from the AGN,emission from supernovae or supernova remnants produced in a starburst,or thermal emission from the accretion disk.The observed brightness temperatures are discussed in the context of the NGC1068result and comparison is made with other types of active nuclei such as radio galaxies,radio-loud and radio-quiet quasars.Section6summarizes the conclusions.Throughout,we assume H0=75km s−1Mpc−1and q0=0.5.2.Sample SelectionThe radio emission of Seyfert galaxies imaged at resolutions0.′′1–1′′almost always has the steep spectrum characteristic of optically thin synchrotron radiation.Flat spectrum cores are rare.In order to identify galaxies that may contain radio components similarto‘S1’in NGC1068,we have reviewed both published(e.g.,Ulvestad&Wilson,1989, and earlier papers in this series atλ6cm andλ20cm;Kukula et al.,1995at3.6cm)and unpublished(Wilson,Braatz&Dressel at3.6cm)VLA‘A’configuration surveys and other interferometric studies(e.g.,Roy et al.,1994).In selecting candidate galaxies for VLBA observations,we used the following criteria:•The radio component that is coincident with the optical nucleus(the position of which is known to≈0.′′2accuracy–e.g.,Clements,1981,1983),has aflat spectrum(α≤0.4, S∝ν−α)between20cm and6cm or3.6cm with the VLA in‘A’configuration.This component must also be unresolved in the VLA‘A’configuration at2cm and/or3.6cm.•Theflux density of this component exceeds5mJy at3.6cm(for comparison,the total flux density of component‘S1’in NGC1068at this wavelength is14mJy).•There is,in addition,extended,‘linear’(double,triple or jet-like),steep spectrum radio emission on the hundreds of parsecs–kiloparsec scales,or well-defined,optical ionization cones.The reason for this last criterion is to define the axis of ejection of the radio components and thus the expected axis of the accretion disk.We found only six(excluding NGC1068)Seyfert galaxies that satisfy these three criteria in the entire sample of about130imaged in the‘A’configuration.We omit one ofthem because of its unfavorable declination(–44◦),leavingfive for imaging with the VLBA. These galaxies are T0109−383,NGC2110,NGC4388,NGC5252and Mrk926.3.Observations and Reduction3.1.VLBA ObservationsThe observations were obtained with the10-element VLBA(Napier et al,1994)at8.4 GHz during observing runs in1997and1998,details of which are given in Table1.Dual circular polarizations(Right&Left)were recorded for all sources,and only the parallel hands(i.e.RR and LL)were correlated.T0109−383,NGC2110and Mrk926were recorded with a32-MHz bandwidth and two-bit sampling(8MHz per IF,4IFs,2polarizations)and NGC4388and NGC5252were recorded with a16-MHz bandwidth and two-bit sampling.The target sources are too weak to obtain estimates of the phase errors using standard VLBI self-calibration/imaging techniques(e.g.Walker,1995);instead the targets were observed in phase referencing mode,in which frequent observations of a nearby bright calibrator are interleaved with target scans and used for fringefitting,which corrects the large phase errors,delays(phase variations as a function of frequency)and delay rates (phase variations as a function of time)present in the data(Beasley&Conway,1995). As described below,extending the coherence time in this way improves the signal-to-noise ratio and enables an image of the target source to be made,which can then be usedas a starting model for subsequent cycles of self-calibration.Target source plus phase calibrator cycle times are shown in Table1.This method is similar to that used on smaller, connected-element arrays,such as the VLA(known as‘phase calibration’),but is more problematic for VLBI due to larger and more rapidly varying phase errors.Rapid changes in the troposphere at8.4GHz therefore require short switching times to satisfy the condition that the change in atmospheric phase be less than a radian over the switching interval,thus enabling reliable phase connection,without2π-radian ambiguities,for successful imaging of the target source(Beasley&Conway,1995).In addition,less frequent observations were made of a bright calibrator(‘phase check’)source.Data editing and calibration followed standard methods(Greisen&Murphy,1998) and used the NRAO Astronomical Image Processing System(aips)(van Moorsel,Kemball &Greisen,1996).Amplitude scales were determined from standard VLBA antenna gain tables,maintained by NRAO staff,and measurements of T sys made throughout the run. In addition,all data for source elevations below∼5◦were removed,and the antennas at Hancock(HN),and North Liberty(NL)were deleted from the NGC5252dataset as nofringes were detected to HN,and NL showed poor phase stability due to bad weather.The final phase corrections,interpolated over time,were used as a guide for additional data editing.Despite short switching times between galaxy and phase calibrator,poor tropospheric conditions and uncertainty in the target source position prevented immediate imaging of the phase-referenced target sources using all the data.Observations of the‘phase check’source were therefore used to verify the quality of the phase referencing,before applying the phase corrections to the target sources,and to provide ancillary calibration such as manual pulse calibration and amplitude calibration checks.After imaging the phase calibrator to verify that the corrections derived from fringe fitting were valid,phase,delay and rate corrections were applied to the‘check source’,from phase calibrator scans that were adjacent in time to the check source.Many baselines displayed poor phase coherence at some point in the observing run,preventing a coherent image of the source from being produced initially from the whole dataset.Instead,small time ranges(e.g.around1hour),within which the majority of antennas had less rapidly varying phases,were selected to be used in the initial stages of the imaging process.The ‘check’source,with calibration applied from the phase calibrator,was imaged for the selected small time range.The resultant image was then used as an input/starting model for subsequent cycles of self-calibration.This self-calibration process then enabled the remaining data to be fully calibrated and used to make afinal image of the‘check’source. Thefinal structure,flux and position of each‘check’source compared well with previously published images(e.g.Browne et al.,1998;Fey&Charlot,1997)and images produced from our data using self-calibration alone.This method provides an independent consistency check on the phase referencing,increasing our confidence in the images of the target sources. Only one‘check’source(J0044-3530)was not successfully imaged due to insufficient data (i.e.only3minutes at very low elevation).The target sources were then imaged using the same method,with natural and uniform data weighting.The uniformly weighted images (with robust parameter0-Briggs,1995)are shown in Figure1.The naturally weighted images,with more sensitivity to extended emission,were used to derive the brightness temperature limits to possible thermal emission from the program galaxies;these limits are ∼30%lower than those derived from the uniformly weighted images shown in this paper.The uncertainty in theflux scale is taken to be∼5%and is included in the total uncertainties influx densities quoted in Table2.These errors were derived by adding,in quadrature,the5%amplitude scale error,the r.m.s.noise in thefinal image and the error in the Gaussianfitting.The accuracy of the target source positions is dominated by the uncertainty in theposition of the phase calibrators(∼0.4–14mas;see Table1).Additional positional errors, due to the transfer of phase corrections from the phase calibrator to the target source,are negligible due to the promixity of each calibrator to its target source.3.2.MERLIN observationsNGC4388was not detected by the present VLBA observations.We therefore obtained and analyzed MERLINλ6-cm(4.993-GHz)archival data for NGC4388,which was observed on7th December,1992with six antennas.Phase referencing was performed with regular observations of1215+113,interleaved throughout the observing run and3C286was used for flux and bandpass calibration.Aflux of7.087Jy for3C286was adopted,assuming a total flux density of7.382Jy(Baars et al.,1977)and correcting for MERLIN resolution effects. After initial gain-elevation corrections and amplitude calibration using MERLIN software, the data were transferred to aips for all subsequent phase and amplitude calibration,data editing and imaging.Dual polarizations were recorded for a15-MHz bandwidth,centered at4.993GHz,but the right circular polarization data were removed due to instrumental problems,resulting in afinal image of the left circular polarization only(Figure2).4.ResultsFiveflat-spectrum-core Seyferts,were observed with the VLBA at8.4GHz.Four of thefive sources were detected(T0109−383,NGC2110,NGC5252,Mrk926)and show compact,unresolved cores with brightness temperatures T B>108K,total luminosities at 8.4GHz of∼1021W Hz−1and sizes,on average,less than1pc.In addition to the core emission,NGC2110shows extended emission which may represent the inner parts of the radio jets,and NGC5252may be marginally extended(Figure1).NGC4388is not detected with the VLBA,but is detected at5GHz with MERLIN(Figure2).Wefind no evidence for emission(to a3-σlimit of T B∼106K)extended perpendicular to the hundred-pc scale radio emission in T0109−383,NGC2110,NGC5252or Mrk926,as would be expected for emission from an accretion disk,but we discuss the possibility of thermal emission from NGC4388(Section5.4).The measured and derived properties of each source are listed in Table2,while more detailed properties of NGC2110and NGC4388are given in Tables3 and4respectively.The properties of each source are discussed more fully below.Distances are calculated assuming H0=75km s−1Mpc−1and q0=0.5,except for NGC4388which is assumed to be at the distance of the Virgo cluster,taken to be16Mpc.4.1.T0109−383T0109−383(NGC424)is a highly inclined(∼75◦)early-type((R)SB(r)0/a–de Vaucouleurs et al.1991)Seyfert galaxy at a distance of46.6Mpc.The nucleus ofT0109−383,originally classified as a Seyfert type2(Smith,1975),exhibits strong line emission from highly ionized species such as[Fe vii]λ5720,6086and[Fe x]λ6374(Fosbury &Sansom,1983;Penston et al.,1984).Analysis of the continuum emission from thefar IR to the far UV and decomposition of the Hα–[N ii]blend led Boisson&Durret (1986)to suggest a re-classification of T0109−383to a Seyfert1.The recent discoveryof broad components to the Hαand Hβlines,along with emission from Fe ii,confirms the type1classification(Murayama et al.,1998).VLA images of the radio emissionat6and20cm,show the nuclear radio source to consist of an unresolved core with aflat spectrum(α206=0.17±0.07)betweenλ6andλ20cm,and a weaker,secondary,steep spectrum component≃1.′′4east of the core(Ulvestad&Wilson,1989).Similar radio structure is seen in the8.4-GHz VLA image(Braatz,Wilson&Dressel,unpublished), shown in Figure1,with the core spectrum remaining relativelyflat(α63.5=0.21)between6 and3.5cm(Morganti et al.,1999).The results of Gaussianfitting to the8.4-GHz VLBA image(Figure1),given in Table2,show the sub-pc scale nuclear emission to be unresolved, with a peak brightness of T B>8.1×108K,adopting a source size smaller than half of the beamsize.The peak and integrated8.4-GHz VLAfluxes for the core,10.4mJy beam−1 and11.2mJy respectively,are in excellent agreement with those measured from the VLBA image(Table2),indicating that little nuclear emission was missed by the VLBA.A similar peak brightness of10.4mJy beam−1is found in the3.5-cm ATCA image of Morganti et al. (1999),while their slightly higher integratedflux includes some of the emission≃1′′E and W of the nucleus(Ulvestad&Wilson,1989;Figure1).The excellent agreement between the nuclearλ3.6-cmfluxes in observations spanning∼six years indicates no significant variability.In the VLBA image,we detected no extended emission in the N-S direction(as might be expected from a parsec-scale,thermal disk if the arcsec-scale,steep spectrum,E-W emission in the VLA image is interpreted as emission from nuclear ejecta)brighter than ∼1.3×106K(3σin the naturally weighted image)and more extended than0.27pc(half of the beamsize in the naturally weighted image).4.2.NGC2110NGC2110was initially classified as a Narrow Line X-ray Galaxy,NLXG,(Bradt et al., 1978),and lies in an S0/E host galaxy(Wilson,Baldwin&Ulvestad,1985)at a distanceof30.4Mpc.Such NLXG’s have a sufficient column of dust to the nucleus to obscure the broad line region,thus leading to a Seyfert2classification of the optical spectrum,but an insufficient gas column to attenuate the2–10keV emission,so the hard X-ray luminosity is comparable to those of Seyfert1’s(Weaver et al.,1995a;Malaguti et al.,1999).Early radio observations found NGC2110to be a strong radio source(Bradt et al.,1978)and subsequent VLA imaging(Ulvestad&Wilson,1983;1984b)showed symmetrical,jet-like radio emission,extending∼4′′in the N-S direction and straddling a central compact core.A more recent VLA A-configuration image atλ3.6cm,obtained by Nagar et al.(1999)and shown in Figure1,contains a wealth of complex structure.Ulvestad&Wilson(1983)found the spectrum of the core to be relativelyflat(spectral indexα206∼0.36±0.05)betweenλ20 cm andλ6cm,but becoming steeper(α62∼0.96±0.09)betweenλ6cm andλ2cm(assuming no time variability).Using theλ3.6-cm coreflux measurement of Nagar et al.(1999)and ignoring variability or resolution effects gives spectral indices ofα63.6=0.61andα3.62=1.31, also suggesting a steepening of the spectrum at higher frequencies.The radio continuum emission of NGC2110,imaged with the VLBA atλ3.6cm and shown in Figure1,consists of a compact core,presumably the nucleus,and slightly extended emission which is most pronounced to the north.The results offitting a single-component Gaussian are given in Table2;the fact that the integratedflux is significantly higher than the peakflux also suggests the source is resolved.Resolved structure is also evident in the time-averaged(u,v)data(not shown),consistent with an unresolved point source(with a flux density of∼8mJy)superimposed on an extended“halo”with approximate dimensions of2.5(N-S)×0.5(E-W)mas.Preliminary two-component Gaussianfits to the image are also consistent with an unresolved point source and an extended component.We therefore subtracted an8-mJy point source(in the(u,v)plane using the aips task uvsub)positioned at the peak of the3.6cm VLBA image,and studied the residual emission.This emission is extended both north and south of the core by∼0.7mas,consistent with emission from the inner regions of the northern and southern jets.Using the brightness of8mJy beam−1for the unresolved component and assuming an upper limit to the source size of0.94×0.36mas(half of the beamsize),wefind T B> 6.0×108K.In addition to the core and extended emission,the Gaussianfits suggest the presence of a third component,centered∼1.95mas north of the core;its size and direction of elongation are not well constrained.This component may be a knot in the northern jet.A summary of thefitted properties of each component is given in Table3.The total VLBA-detectedflux density of the source(zero baselineflux measured in the uv plane)is30mJy.Thisflux density is lower than the previously measured VLA core flux of77.6mJy at this frequency(Nagar et al.,1999),presumably due to the high spatialresolution of the present observations and missing short spacings of the VLBA compared to the VLA,thereby reducing our sensitivity to extended structure.This may also explain why we detect no VLBA counterpart to the small eastern extension present in theλ3.6-cm VLA image,which contains about3.6mJy offlux and extends approximately0.′′5east of the core(Nagar et al.,1999).Alternatively,the extension in the VLA image may be a result of instrumental effects caused by the source position being close to the celestial equator and the short duration of the snapshot observation,an effect termed‘equator disease’(Antonucci&Ulvestad,1985).In the VLBA image,we detect no extended emission in the E-W direction(such as might be expected from a parsec-scale thermal disk)brighter than 3.1×106K(3σin the naturally weighted image),and more extended than0.07pc(one half of the E-W beamsize in the naturally weighted image).4.3.NGC4388NGC4388is a nearby,edge-on spiral galaxy(SB(s)b pec-Phillips&Malin,1982) which is thought to lie close to the centre of the Virgo cluster(Phillips&Malin,1982)and may be tidally disturbed by nearby cluster core galaxies M84or IC3303(Corbin,Baldwin &Wilson,1988).Ionization cones extend approximately perpendicular to the disk(Pogge, 1988;Corbin et al.,1988;Falcke,Wilson&Simpson,1998)and the kinematics of the ionized gas in the narrow line region(NLR)shows a complex combination of rotation and outflow(Corbin et al.1988;Veilleux,1991;Veilleux et al.,1999).The nucleus is variously classified as Seyfert type1or2,with the high galactic inclination and obscuring dust lanes making unambiguous classification difficult(Falcke et al.,1998).Shields&Filippenko (1988)report broad,off-nuclear Hαemission,but subsequent IR searches for broad lines such as Paβ(Blanco,Ward&Wright,1990;Ruiz,Rieke&Schmidt,1994)and Brαand Brγ(Veilleux,Goodrich&Hill,1997)have failed to detect a broad nuclear component.Previous radio continuum images of NGC4388(Stone et al.,1988;Carral,Turner& Ho,1990;Hummel&Saikia,1991;Falcke et al.,1998)show complex,extended structure, both along the galactic plane and perpendicular to it.A recent3.5cm VLA image of the extended radio emission(Falcke et al.,1998)shows,in more detail,the‘hour-glass’-shaped radio outflow to the north of the galactic plane,and the compact(∼1.′′9separation)central double,which were suggested by earlier images.In Section4.3.1we concentrate on the radio emission from the northern component of the compact radio double,which shows a flat spectrum up to2cm(Carral,Turner&Ho,1990)and is thought to be the nucleus,and in Section4.3.2,we discuss the extended emission to the SW.4.3.1.The nucleusAs stated earlier,NGC4388is not detected in the8.4-GHz VLBA observations, with a3-σbrightness temperature limit of T B∼<2.2×106K(σ=63.2µJy/beam with a beam size of2.52×1.46mas in the naturally weighted map,with a factor1.7applied to correct for decorrelation due to residual imperfections in the phase referencing corrections, estimated using the check source).We do,however,detect emission from NGC4388at λ6cm with MERLIN.The uniformly weighted MERLIN image(Figure2)shows emission from two components,labelled M1and M2,the stronger of which we identify with the nucleus and discuss in more detail here,while M2is discussed in Section4.3.2.The nuclear component M1,has a peak brightness of1.2mJy beam−1which corresponds to a brightness temperature T B>2.4×104K at5GHz(beamsize91×39.5mas,see Table4).The nucleus is unresolved in the MERLIN data,indicating that the source size is intermediate between the MERLIN and VLBA beam sizes.However,a combination of the MERLIN and VLBA results with published spectral index information can further constrain the source size.Earlier radio observations of NGC4388have found the nuclear spectrum to beflat from1.49GHz to15GHz.The spectral index was measured to beα=0.26between1.49 GHz and4.86GHz with a relatively large beamsize of1.′′2(Hummel&Saikia,1991)and Carral et al.(1990)report aflat spectrum up to15GHz with an upper limit to the nuclear size of70mas.Including the VLA8.4GHz coreflux of Kukula et al(1995)suggests that the spectrum of the nucleus may be very slightly inverted between8.4GHz and15GHz (α=–0.05)but within the errors it can be taken asflat.We therefore used the measured MERLIN5-GHz peakflux to derive predicted VLBA8.4GHzfluxes of the nucleus,for spectral indices of bothα=0.0and0.26,and converted these predictedfluxes to brightness temperatures,assuming the source is unresolved by the representative VLBA beamsize of 2.52×1.46mas.These predicted temperatures are listed in Table4and are above the detection threshold of the VLBA observations for a source size equal to or smaller than the VLBA beam.The larger predicted brightness temperature,for a source size equal to the VLBA beam,of T B≃8.3×106K is,however,only3.8times greater than our3-σ,VLBA detection limit and so the solid angle of the source need only be3.8times larger than the VLBA beamsize to be undetected.We therefore constrain the size of the nucleus to be∼> 3.7mas(α=0.0)or∼>0.3pc.Sensitive,high angular resolution VLBA observations at lower frequencies such as2.3GHz and1.4GHz are required to determine the actual size and structure of the nucleus in NGC4388.。
非线性光学部分介质在强激光场作用下产生的极化强度与入射辐射场强之间不再是线性关系,而是与场强的二次、三次以至于更高次项有关,这种关系称为非线性。
凡是与非线性有关的光学现象称为非线性光学现象,属于非线性光学的研究内容。
非线性光学一方面研究光辐射在非线性介质中传播时由于和介质的非线性相互作用自身所受的影响,另一方面则研究介质本身在光场作用下所表现出的特性。
在光通信中,主要是进入高速通信,10g,尤其是40G,随着入纤光功率的增强,非线性效应逐渐显现,系统设计必须加以考虑这方面的影响,于是在40G里面变出现了形形色色的编码。
以下切入正题1、《Nonlinear Fiber Optics》和《Applications of Nonlinear Fiber Optics》Agrawl ,这2本书从书名大家应该也可以看出是偏重于光纤通信应用的,目前第一个已经到第四版,第二个为第二版了,包括中译本,论坛都有,大家可以搜索下就可以都看到了。
/viewthread. ... =nonlinear%2Boptics/viewthread. ... =nonlinear%2Boptics2、Boyd W.R的《nonlinear optics》3rdW. Boyd教授在2002年被任命为Rochester大学M. Parker Givens Professor of Optics,lz发的应该是第二版,该书1992年第一版,第二版在第一版的基础上增加了很多新内容,并对以前的内容做了不少修订,在2008年的4月,该书又出了第三版。
整体来说,该书内容比较深,学校里的高年级研究生和一般研究人员可参考。
W.Boyd今年5月份曾代表美国光学学会来南京开会下载链接:/viewthread. ... =nonlinear%2Boptics3、华裔学者沈元镶的《非线性光学原理》沈是这方面非常牛b的,他的导师算是非线性光学方面的开创者吧,并因此获得了诺贝尔奖。
⼝径为地球⼤⼩的虚拟天⽂望远镜EHT⼝径为地球⼤⼩的虚拟天⽂望远镜EHT为了看清遥远的天体M87,我们需要⼀台与众不同的望远镜。
EHT =事件视界望远镜的英⽂缩写,也是⼀个国际性天⽂观测组织的名称。
2017年EHT活动的分布在六个地理位置⼋个站点。
[EHT Collaboration等2019]EHT是⼀种的虚拟望远镜,它通过结合来⾃全球各地的⽆线电阵列和⼯具的同步观测⽽创建。
对于今天发布的M87图像,观测是由亚利桑那州,夏威夷,墨西哥,智利,西班⽛和南极的六个地点,⼋台望远镜拍摄的。
EHT通过执⾏⾮常长的基线⼲涉测量来⼯作;通过在世界各地组合不同的望远镜,EHT可以像望远镜⼀样⼯作,其有效尺⼨与其最长基线 - 组件望远镜之间的距离相同。
通过这种⽅式,EHT能够实现前所未有的分辨率:理论上它可以在1.3 mm的观察波长下分辨到低于百万分之⼆⼗五分之⼀秒⾃EHT⼤胆的成像计划⾸次启动以来,已有⼗多年了。
随着现有设施的升级和新设施的建成,科学家们耐⼼地等待着 - 在2017年4⽉,最终有条件获得M87事件视界的⾸次美⾊。
2017年4⽉四天观察到M87的⿊洞。
天⽓⼀直很好 - 全⾏星! - 在这些观测期间,允许EHT科学家结合⼋个望远镜的数据并重建⿊洞的图像。
他们所看到的是预测的闪亮:⼀圈光线跨越约38-44微⽶,环的南部看起来⽐其他部分更亮。
/////////////////////////////////////////////////////////////////////⼀⽀由200多名天⽂学家组成的国际团队,包括来⾃⿇省理⼯学院海斯塔克天⽂台的科学家,已经捕获了第⼀个⿊洞直接图像。
他们通过协调四⼤洲⼋个主要⽆线电观测台的⼒量,完成了这项⾮凡的壮举,作为⼀个虚拟的地球⼤⼩的望远镜⼀起⼯作。
在今天发表的特刊“天体物理学杂志快报”上发表的⼀系列论⽂中,该团队揭⽰了Messier 87中⼼的超⼤质量⿊洞的四幅图像,或者是处⼥座星系团中的⼀个星系M87,距今5500万光年。
Quasi-Normal Modes of Stars and Black HolesKostas D.KokkotasDepartment of Physics,Aristotle University of Thessaloniki,Thessaloniki54006,Greece.kokkotas@astro.auth.grhttp://www.astro.auth.gr/˜kokkotasandBernd G.SchmidtMax Planck Institute for Gravitational Physics,Albert Einstein Institute,D-14476Golm,Germany.bernd@aei-potsdam.mpg.dePublished16September1999/Articles/Volume2/1999-2kokkotasLiving Reviews in RelativityPublished by the Max Planck Institute for Gravitational PhysicsAlbert Einstein Institute,GermanyAbstractPerturbations of stars and black holes have been one of the main topics of relativistic astrophysics for the last few decades.They are of partic-ular importance today,because of their relevance to gravitational waveastronomy.In this review we present the theory of quasi-normal modes ofcompact objects from both the mathematical and astrophysical points ofview.The discussion includes perturbations of black holes(Schwarzschild,Reissner-Nordstr¨o m,Kerr and Kerr-Newman)and relativistic stars(non-rotating and slowly-rotating).The properties of the various families ofquasi-normal modes are described,and numerical techniques for calculat-ing quasi-normal modes reviewed.The successes,as well as the limits,of perturbation theory are presented,and its role in the emerging era ofnumerical relativity and supercomputers is discussed.c 1999Max-Planck-Gesellschaft and the authors.Further information on copyright is given at /Info/Copyright/.For permission to reproduce the article please contact livrev@aei-potsdam.mpg.de.Article AmendmentsOn author request a Living Reviews article can be amended to include errata and small additions to ensure that the most accurate and up-to-date infor-mation possible is provided.For detailed documentation of amendments, please go to the article’s online version at/Articles/Volume2/1999-2kokkotas/. Owing to the fact that a Living Reviews article can evolve over time,we recommend to cite the article as follows:Kokkotas,K.D.,and Schmidt,B.G.,“Quasi-Normal Modes of Stars and Black Holes”,Living Rev.Relativity,2,(1999),2.[Online Article]:cited on<date>, /Articles/Volume2/1999-2kokkotas/. The date in’cited on<date>’then uniquely identifies the version of the article you are referring to.3Quasi-Normal Modes of Stars and Black HolesContents1Introduction4 2Normal Modes–Quasi-Normal Modes–Resonances7 3Quasi-Normal Modes of Black Holes123.1Schwarzschild Black Holes (12)3.2Kerr Black Holes (17)3.3Stability and Completeness of Quasi-Normal Modes (20)4Quasi-Normal Modes of Relativistic Stars234.1Stellar Pulsations:The Theoretical Minimum (23)4.2Mode Analysis (26)4.2.1Families of Fluid Modes (26)4.2.2Families of Spacetime or w-Modes (30)4.3Stability (31)5Excitation and Detection of QNMs325.1Studies of Black Hole QNM Excitation (33)5.2Studies of Stellar QNM Excitation (34)5.3Detection of the QNM Ringing (37)5.4Parameter Estimation (39)6Numerical Techniques426.1Black Holes (42)6.1.1Evolving the Time Dependent Wave Equation (42)6.1.2Integration of the Time Independent Wave Equation (43)6.1.3WKB Methods (44)6.1.4The Method of Continued Fractions (44)6.2Relativistic Stars (45)7Where Are We Going?487.1Synergism Between Perturbation Theory and Numerical Relativity487.2Second Order Perturbations (48)7.3Mode Calculations (49)7.4The Detectors (49)8Acknowledgments50 9Appendix:Schr¨o dinger Equation Versus Wave Equation51Living Reviews in Relativity(1999-2)K.D.Kokkotas and B.G.Schmidt41IntroductionHelioseismology and asteroseismology are well known terms in classical astro-physics.From the beginning of the century the variability of Cepheids has been used for the accurate measurement of cosmic distances,while the variability of a number of stellar objects(RR Lyrae,Mira)has been associated with stel-lar oscillations.Observations of solar oscillations(with thousands of nonradial modes)have also revealed a wealth of information about the internal structure of the Sun[204].Practically every stellar object oscillates radially or nonradi-ally,and although there is great difficulty in observing such oscillations there are already results for various types of stars(O,B,...).All these types of pulsations of normal main sequence stars can be studied via Newtonian theory and they are of no importance for the forthcoming era of gravitational wave astronomy.The gravitational waves emitted by these stars are extremely weak and have very low frequencies(cf.for a discussion of the sun[70],and an im-portant new measurement of the sun’s quadrupole moment and its application in the measurement of the anomalous precession of Mercury’s perihelion[163]). This is not the case when we consider very compact stellar objects i.e.neutron stars and black holes.Their oscillations,produced mainly during the formation phase,can be strong enough to be detected by the gravitational wave detectors (LIGO,VIRGO,GEO600,SPHERE)which are under construction.In the framework of general relativity(GR)quasi-normal modes(QNM) arise,as perturbations(electromagnetic or gravitational)of stellar or black hole spacetimes.Due to the emission of gravitational waves there are no normal mode oscillations but instead the frequencies become“quasi-normal”(complex), with the real part representing the actual frequency of the oscillation and the imaginary part representing the damping.In this review we shall discuss the oscillations of neutron stars and black holes.The natural way to study these oscillations is by considering the linearized Einstein equations.Nevertheless,there has been recent work on nonlinear black hole perturbations[101,102,103,104,100]while,as yet nothing is known for nonlinear stellar oscillations in general relativity.The study of black hole perturbations was initiated by the pioneering work of Regge and Wheeler[173]in the late50s and was continued by Zerilli[212]. The perturbations of relativistic stars in GR werefirst studied in the late60s by Kip Thorne and his collaborators[202,198,199,200].The initial aim of Regge and Wheeler was to study the stability of a black hole to small perturbations and they did not try to connect these perturbations to astrophysics.In con-trast,for the case of relativistic stars,Thorne’s aim was to extend the known properties of Newtonian oscillation theory to general relativity,and to estimate the frequencies and the energy radiated as gravitational waves.QNMs werefirst pointed out by Vishveshwara[207]in calculations of the scattering of gravitational waves by a Schwarzschild black hole,while Press[164] coined the term quasi-normal frequencies.QNM oscillations have been found in perturbation calculations of particles falling into Schwarzschild[73]and Kerr black holes[76,80]and in the collapse of a star to form a black hole[66,67,68]. Living Reviews in Relativity(1999-2)5Quasi-Normal Modes of Stars and Black Holes Numerical investigations of the fully nonlinear equations of general relativity have provided results which agree with the results of perturbation calculations;in particular numerical studies of the head-on collision of two black holes [30,29](cf.Figure 1)and gravitational collapse to a Kerr hole [191].Recently,Price,Pullin and collaborators [170,31,101,28]have pushed forward the agreement between full nonlinear numerical results and results from perturbation theory for the collision of two black holes.This proves the power of the perturbation approach even in highly nonlinear problems while at the same time indicating its limits.In the concluding remarks of their pioneering paper on nonradial oscillations of neutron stars Thorne and Campollataro [202]described it as “just a modest introduction to a story which promises to be long,complicated and fascinating ”.The story has undoubtedly proved to be intriguing,and many authors have contributed to our present understanding of the pulsations of both black holes and neutron stars.Thirty years after these prophetic words by Thorne and Campollataro hundreds of papers have been written in an attempt to understand the stability,the characteristic frequencies and the mechanisms of excitation of these oscillations.Their relevance to the emission of gravitational waves was always the basic underlying reason of each study.An account of all this work will be attempted in the next sections hoping that the interested reader will find this review useful both as a guide to the literature and as an inspiration for future work on the open problems of the field.020406080100Time (M ADM )-0.3-0.2-0.10.00.10.20.3(l =2) Z e r i l l i F u n c t i o n Numerical solutionQNM fit Figure 1:QNM ringing after the head-on collision of two unequal mass black holes [29].The continuous line corresponds to the full nonlinear numerical calculation while the dotted line is a fit to the fundamental and first overtone QNM.In the next section we attempt to give a mathematical definition of QNMs.Living Reviews in Relativity (1999-2)K.D.Kokkotas and B.G.Schmidt6 The third and fourth section will be devoted to the study of the black hole and stellar QNMs.In thefifth section we discuss the excitation and observation of QNMs andfinally in the sixth section we will mention the more significant numerical techniques used in the study of QNMs.Living Reviews in Relativity(1999-2)7Quasi-Normal Modes of Stars and Black Holes 2Normal Modes–Quasi-Normal Modes–Res-onancesBefore discussing quasi-normal modes it is useful to remember what normal modes are!Compact classical linear oscillating systems such asfinite strings,mem-branes,or cavitiesfilled with electromagnetic radiation have preferred time harmonic states of motion(ωis real):χn(t,x)=e iωn tχn(x),n=1,2,3...,(1) if dissipation is neglected.(We assumeχto be some complex valuedfield.) There is generally an infinite collection of such periodic solutions,and the“gen-eral solution”can be expressed as a superposition,χ(t,x)=∞n=1a n e iωn tχn(x),(2)of such normal modes.The simplest example is a string of length L which isfixed at its ends.All such systems can be described by systems of partial differential equations of the type(χmay be a vector)∂χ∂t=Aχ,(3)where A is a linear operator acting only on the spatial variables.Because of thefiniteness of the system the time evolution is only determined if some boundary conditions are prescribed.The search for solutions periodic in time leads to a boundary value problem in the spatial variables.In simple cases it is of the Sturm-Liouville type.The treatment of such boundary value problems for differential equations played an important role in the development of Hilbert space techniques.A Hilbert space is chosen such that the differential operator becomes sym-metric.Due to the boundary conditions dictated by the physical problem,A becomes a self-adjoint operator on the appropriate Hilbert space and has a pure point spectrum.The eigenfunctions and eigenvalues determine the periodic solutions(1).The definition of self-adjointness is rather subtle from a physicist’s point of view since fairly complicated“domain issues”play an essential role.(See[43] where a mathematical exposition for physicists is given.)The wave equation modeling thefinite string has solutions of various degrees of differentiability. To describe all“realistic situations”,clearly C∞functions should be sufficient. Sometimes it may,however,also be convenient to consider more general solu-tions.From the mathematical point of view the collection of all smooth functions is not a natural setting to study the wave equation because sequences of solutionsLiving Reviews in Relativity(1999-2)K.D.Kokkotas and B.G.Schmidt8 exist which converge to non-smooth solutions.To establish such powerful state-ments like(2)one has to study the equation on certain subsets of the Hilbert space of square integrable functions.For“nice”equations it usually happens that the eigenfunctions are in fact analytic.They can then be used to gen-erate,for example,all smooth solutions by a pointwise converging series(2). The key point is that we need some mathematical sophistication to obtain the “completeness property”of the eigenfunctions.This picture of“normal modes”changes when we consider“open systems”which can lose energy to infinity.The simplest case are waves on an infinite string.The general solution of this problem isχ(t,x)=A(t−x)+B(t+x)(4) with“arbitrary”functions A and B.Which solutions should we study?Since we have all solutions,this is not a serious question.In more general cases, however,in which the general solution is not known,we have to select a certain class of solutions which we consider as relevant for the physical problem.Let us consider for the following discussion,as an example,a wave equation with a potential on the real line,∂2∂t2χ+ −∂2∂x2+V(x)χ=0.(5)Cauchy dataχ(0,x),∂tχ(0,x)which have two derivatives determine a unique twice differentiable solution.No boundary condition is needed at infinity to determine the time evolution of the data!This can be established by fairly simple PDE theory[116].There exist solutions for which the support of thefields are spatially compact, or–the other extreme–solutions with infinite total energy for which thefields grow at spatial infinity in a quite arbitrary way!From the point of view of physics smooth solutions with spatially compact support should be the relevant class–who cares what happens near infinity! Again it turns out that mathematically it is more convenient to study all solu-tions offinite total energy.Then the relevant operator is again self-adjoint,but now its spectrum is purely“continuous”.There are no eigenfunctions which are square integrable.Only“improper eigenfunctions”like plane waves exist.This expresses the fact that wefind a solution of the form(1)for any realωand by forming appropriate superpositions one can construct solutions which are “almost eigenfunctions”.(In the case V(x)≡0these are wave packets formed from plane waves.)These solutions are the analogs of normal modes for infinite systems.Let us now turn to the discussion of“quasi-normal modes”which are concep-tually different to normal modes.To define quasi-normal modes let us consider the wave equation(5)for potentials with V≥0which vanish for|x|>x0.Then in this case all solutions determined by data of compact support are bounded: |χ(t,x)|<C.We can use Laplace transformation techniques to represent such Living Reviews in Relativity(1999-2)9Quasi-Normal Modes of Stars and Black Holes solutions.The Laplace transformˆχ(s,x)(s>0real)of a solutionχ(t,x)isˆχ(s,x)= ∞0e−stχ(t,x)dt,(6) and satisfies the ordinary differential equations2ˆχ−ˆχ +Vˆχ=+sχ(0,x)+∂tχ(0,x),(7) wheres2ˆχ−ˆχ +Vˆχ=0(8) is the homogeneous equation.The boundedness ofχimplies thatˆχis analytic for positive,real s,and has an analytic continuation onto the complex half plane Re(s)>0.Which solutionˆχof this inhomogeneous equation gives the unique solution in spacetime determined by the data?There is no arbitrariness;only one of the Green functions for the inhomogeneous equation is correct!All Green functions can be constructed by the following well known method. Choose any two linearly independent solutions of the homogeneous equation f−(s,x)and f+(s,x),and defineG(s,x,x )=1W(s)f−(s,x )f+(s,x)(x <x),f−(s,x)f+(s,x )(x >x),(9)where W(s)is the Wronskian of f−and f+.If we denote the inhomogeneity of(7)by j,a solution of(7)isˆχ(s,x)= ∞−∞G(s,x,x )j(s,x )dx .(10) We still have to select a unique pair of solutions f−,f+.Here the information that the solution in spacetime is bounded can be used.The definition of the Laplace transform implies thatˆχis bounded as a function of x.Because the potential V vanishes for|x|>x0,the solutions of the homogeneous equation(8) for|x|>x0aref=e±sx.(11) The following pair of solutionsf+=e−sx for x>x0,f−=e+sx for x<−x0,(12) which is linearly independent for Re(s)>0,gives the unique Green function which defines a bounded solution for j of compact support.Note that for Re(s)>0the solution f+is exponentially decaying for large x and f−is expo-nentially decaying for small x.For small x however,f+will be a linear com-bination a(s)e−sx+b(s)e sx which will in general grow exponentially.Similar behavior is found for f−.Living Reviews in Relativity(1999-2)K.D.Kokkotas and B.G.Schmidt 10Quasi-Normal mode frequencies s n can be defined as those complex numbers for whichf +(s n ,x )=c (s n )f −(s n ,x ),(13)that is the two functions become linearly dependent,the Wronskian vanishes and the Green function is singular!The corresponding solutions f +(s n ,x )are called quasi eigenfunctions.Are there such numbers s n ?From the boundedness of the solution in space-time we know that the unique Green function must exist for Re (s )>0.Hence f +,f −are linearly independent for those values of s .However,as solutions f +,f −of the homogeneous equation (8)they have a unique continuation to the complex s plane.In [35]it is shown that for positive potentials with compact support there is always a countable number of zeros of the Wronskian with Re (s )<0.What is the mathematical and physical significance of the quasi-normal fre-quencies s n and the corresponding quasi-normal functions f +?First of all we should note that because of Re (s )<0the function f +grows exponentially for small and large x !The corresponding spacetime solution e s n t f +(s n ,x )is therefore not a physically relevant solution,unlike the normal modes.If one studies the inverse Laplace transformation and expresses χas a com-plex line integral (a >0),χ(t,x )=12πi +∞−∞e (a +is )t ˆχ(a +is,x )ds,(14)one can deform the path of the complex integration and show that the late time behavior of solutions can be approximated in finite parts of the space by a finite sum of the form χ(t,x )∼N n =1a n e (αn +iβn )t f +(s n ,x ).(15)Here we assume that Re (s n +1)<Re (s n )<0,s n =αn +iβn .The approxi-mation ∼means that if we choose x 0,x 1, and t 0then there exists a constant C (t 0,x 0,x 1, )such that χ(t,x )−N n =1a n e (αn +iβn )t f +(s n ,x ) ≤Ce (−|αN +1|+ )t (16)holds for t >t 0,x 0<x <x 1, >0with C (t 0,x 0,x 1, )independent of t .The constants a n depend only on the data [35]!This implies in particular that all solutions defined by data of compact support decay exponentially in time on spatially bounded regions.The generic leading order decay is determined by the quasi-normal mode frequency with the largest real part s 1,i.e.slowest damping.On finite intervals and for late times the solution is approximated by a finite sum of quasi eigenfunctions (15).It is presently unclear whether one can strengthen (16)to a statement like (2),a pointwise expansion of the late time solution in terms of quasi-normal Living Reviews in Relativity (1999-2)11Quasi-Normal Modes of Stars and Black Holes modes.For one particular potential(P¨o schl-Teller)this has been shown by Beyer[42].Let us now consider the case where the potential is positive for all x,but decays near infinity as happens for example for the wave equation on the static Schwarzschild spacetime.Data of compact support determine again solutions which are bounded[117].Hence we can proceed as before.Thefirst new point concerns the definitions of f±.It can be shown that the homogeneous equation(8)has for each real positive s a unique solution f+(s,x)such that lim x→∞(e sx f+(s,x))=1holds and correspondingly for f−.These functions are uniquely determined,define the correct Green function and have analytic continuations onto the complex half plane Re(s)>0.It is however quite complicated to get a good representation of these func-tions.If the point at infinity is not a regular singular point,we do not even get converging series expansions for f±.(This is particularly serious for values of s with negative real part because we expect exponential growth in x).The next new feature is that the analyticity properties of f±in the complex s plane depend on the decay of the potential.To obtain information about analytic continuation,even use of analyticity properties of the potential in x is made!Branch cuts may occur.Nevertheless in a lot of cases an infinite number of quasi-normal mode frequencies exists.The fact that the potential never vanishes may,however,destroy the expo-nential decay in time of the solutions and therefore the essential properties of the quasi-normal modes.This probably happens if the potential decays slower than exponentially.There is,however,the following way out:Suppose you want to study a solution determined by data of compact support from t=0to some largefinite time t=T.Up to this time the solution is–because of domain of dependence properties–completely independent of the potential for sufficiently large x.Hence we may see an exponential decay of the form(15)in a time range t1<t<T.This is the behavior seen in numerical calculations.The situation is similar in the case ofα-decay in quantum mechanics.A comparison of quasi-normal modes of wave equations and resonances in quantum theory can be found in the appendix,see section9.Living Reviews in Relativity(1999-2)K.D.Kokkotas and B.G.Schmidt123Quasi-Normal Modes of Black HolesOne of the most interesting aspects of gravitational wave detection will be the connection with the existence of black holes[201].Although there are presently several indirect ways of identifying black holes in the universe,gravitational waves emitted by an oscillating black hole will carry a uniquefingerprint which would lead to the direct identification of their existence.As we mentioned earlier,gravitational radiation from black hole oscillations exhibits certain characteristic frequencies which are independent of the pro-cesses giving rise to these oscillations.These“quasi-normal”frequencies are directly connected to the parameters of the black hole(mass,charge and angu-lar momentum)and for stellar mass black holes are expected to be inside the bandwidth of the constructed gravitational wave detectors.The perturbations of a Schwarzschild black hole reduce to a simple wave equation which has been studied extensively.The wave equation for the case of a Reissner-Nordstr¨o m black hole is more or less similar to the Schwarzschild case,but for Kerr one has to solve a system of coupled wave equations(one for the radial part and one for the angular part).For this reason the Kerr case has been studied less thoroughly.Finally,in the case of Kerr-Newman black holes we face the problem that the perturbations cannot be separated in their angular and radial parts and thus apart from special cases[124]the problem has not been studied at all.3.1Schwarzschild Black HolesThe study of perturbations of Schwarzschild black holes assumes a small per-turbation hµνon a static spherically symmetric background metricds2=g0µνdxµdxν=−e v(r)dt2+eλ(r)dr2+r2 dθ2+sin2θdφ2 ,(17) with the perturbed metric having the formgµν=g0µν+hµν,(18) which leads to a variation of the Einstein equations i.e.δGµν=4πδTµν.(19) By assuming a decomposition into tensor spherical harmonics for each hµνof the formχ(t,r,θ,φ)= mχ m(r,t)r Y m(θ,φ),(20)the perturbation problem is reduced to a single wave equation,for the func-tionχ m(r,t)(which is a combination of the various components of hµν).It should be pointed out that equation(20)is an expansion for scalar quantities only.From the10independent components of the hµνonly h tt,h tr,and h rr transform as scalars under rotations.The h tθ,h tφ,h rθ,and h rφtransform asLiving Reviews in Relativity(1999-2)13Quasi-Normal Modes of Stars and Black Holes components of two-vectors under rotations and can be expanded in a series of vector spherical harmonics while the components hθθ,hθφ,and hφφtransform as components of a2×2tensor and can be expanded in a series of tensor spher-ical harmonics(see[202,212,152]for details).There are two classes of vector spherical harmonics(polar and axial)which are build out of combinations of the Levi-Civita volume form and the gradient operator acting on the scalar spherical harmonics.The difference between the two families is their parity. Under the parity operatorπa spherical harmonic with index transforms as (−1) ,the polar class of perturbations transform under parity in the same way, as(−1) ,and the axial perturbations as(−1) +11.Finally,since we are dealing with spherically symmetric spacetimes the solution will be independent of m, thus this subscript can be omitted.The radial component of a perturbation outside the event horizon satisfies the following wave equation,∂2∂t χ + −∂2∂r∗+V (r)χ =0,(21)where r∗is the“tortoise”radial coordinate defined byr∗=r+2M log(r/2M−1),(22) and M is the mass of the black hole.For“axial”perturbationsV (r)= 1−2M r ( +1)r+2σMr(23)is the effective potential or(as it is known in the literature)Regge-Wheeler potential[173],which is a single potential barrier with a peak around r=3M, which is the location of the unstable photon orbit.The form(23)is true even if we consider scalar or electromagnetic testfields as perturbations.The parameter σtakes the values1for scalar perturbations,0for electromagnetic perturbations, and−3for gravitational perturbations and can be expressed asσ=1−s2,where s=0,1,2is the spin of the perturbingfield.For“polar”perturbations the effective potential was derived by Zerilli[212]and has the form V (r)= 1−2M r 2n2(n+1)r3+6n2Mr2+18nM2r+18M3r3(nr+3M)2,(24)1In the literature the polar perturbations are also called even-parity because they are characterized by their behavior under parity operations as discussed earlier,and in the same way the axial perturbations are called odd-parity.We will stick to the polar/axial terminology since there is a confusion with the definition of the parity operation,the reason is that to most people,the words“even”and“odd”imply that a mode transforms underπas(−1)2n or(−1)2n+1respectively(for n some integer).However only the polar modes with even have even parity and only axial modes with even have odd parity.If is odd,then polar modes have odd parity and axial modes have even parity.Another terminology is to call the polar perturbations spheroidal and the axial ones toroidal.This definition is coming from the study of stellar pulsations in Newtonian theory and represents the type offluid motions that each type of perturbation induces.Since we are dealing both with stars and black holes we will stick to the polar/axial terminology.Living Reviews in Relativity(1999-2)K.D.Kokkotas and B.G.Schmidt14where2n=( −1)( +2).(25) Chandrasekhar[54]has shown that one can transform the equation(21)for “axial”modes to the corresponding one for“polar”modes via a transforma-tion involving differential operations.It can also be shown that both forms are connected to the Bardeen-Press[38]perturbation equation derived via the Newman-Penrose formalism.The potential V (r∗)decays exponentially near the horizon,r∗→−∞,and as r−2∗for r∗→+∞.From the form of equation(21)it is evident that the study of black hole perturbations will follow the footsteps of the theory outlined in section2.Kay and Wald[117]have shown that solutions with data of compact sup-port are bounded.Hence we know that the time independent Green function G(s,r∗,r ∗)is analytic for Re(s)>0.The essential difficulty is now to obtain the solutions f±(cf.equation(10))of the equations2ˆχ−ˆχ +Vˆχ=0,(26) (prime denotes differentiation with respect to r∗)which satisfy for real,positives:f+∼e−sr∗for r∗→∞,f−∼e+r∗x for r∗→−∞.(27) To determine the quasi-normal modes we need the analytic continuations of these functions.As the horizon(r∗→∞)is a regular singular point of(26),a representation of f−(r∗,s)as a converging series exists.For M=12it reads:f−(r,s)=(r−1)s∞n=0a n(s)(r−1)n.(28)The series converges for all complex s and|r−1|<1[162].(The analytic extension of f−is investigated in[115].)The result is that f−has an extension to the complex s plane with poles only at negative real integers.The representation of f+is more complicated:Because infinity is a singular point no power series expansion like(28)exists.A representation coming from the iteration of the defining integral equation is given by Jensen and Candelas[115],see also[159]. It turns out that the continuation of f+has a branch cut Re(s)≤0due to the decay r−2for large r[115].The most extensive mathematical investigation of quasi-normal modes of the Schwarzschild solution is contained in the paper by Bachelot and Motet-Bachelot[35].Here the existence of an infinite number of quasi-normal modes is demonstrated.Truncating the potential(23)to make it of compact support leads to the estimate(16).The decay of solutions in time is not exponential because of the weak decay of the potential for large r.At late times,the quasi-normal oscillations are swamped by the radiative tail[166,167].This tail radiation is of interest in its Living Reviews in Relativity(1999-2)。
《星海求知:天文学的奥秘》期末考试及答案一、单选题(题数:50,共?50.0?分)1、各种寻找系外行星的方法中,“产量”最多的是()。
A、视向速度法B、凌星法C、直接成像法D、不清楚正确答案:B?2、银河系的中心方向主要位于哪个星座?()A、天琴B、天鹰C、人马D、天蝎正确答案:C?3、开普勒探测器使用的搜寻系外行星的方法是()。
A、视向速度法B、凌星法C、直接成像法D、微透镜法正确答案:B?4、黑洞、白洞和虫洞当中,目前可以视为已经有观测证据的是()。
A、黑洞B、白洞C、虫洞D、都没有正确答案:A?5、上弦月相对于朔月的日月角距变化了()度。
A、45B、90C、180D、270正确答案:B?6、“三起源”不包括()的起源问题。
B、天体C、生命D、人类正确答案:D?7、“不同历史时期宇宙膨胀速度不同”,这里“不同历史时期”相比于现代,几乎不会考虑()时期。
A、137亿年前B、50亿年前C、10亿年前D、旧石器时代正确答案:D?8、由于岁差原因,现在的黄道春分点已经位于()星座的位置。
A、白羊B、金牛C、双鱼正确答案:C?9、以下现象,不是由太阳活动导致的是()。
A、日冕物质喷射B、极光C、黑子D、太阳周年视运动正确答案:D?10、太阳系前五大卫星当中,质量与其所属行星质量最接近的是:()A、木卫三B、月球C、土卫六D、木卫四正确答案:B?11、宇宙标准模型中,时间是宇宙创生的()秒之后开始的。
A、10^(-4)B、10^(-10)C、10^(-36)D、10^(-44)正确答案:A?12、人类目前认识到的全部的宇宙物质,占全部宇宙物质的份额接近()。
A、.05B、.25C、.5D、1正确答案:A?13、大爆炸模型在()年代正式确立为标准宇宙模型。
A、1930年代-1940年代B、1940年代-1950年代C、1970年代-1980年代D、1980年代-1990年代正确答案:C?14、以下生物组合与“动物-植物-真菌-原核生物-原生生物”的分类顺序不一致的是()。
Stabilized high-power laser system forthe gravitational wave detector advancedLIGOP.Kwee,1,∗C.Bogan,2K.Danzmann,1,2M.Frede,4H.Kim,1P.King,5J.P¨o ld,1O.Puncken,3R.L.Savage,5F.Seifert,5P.Wessels,3L.Winkelmann,3and B.Willke21Max-Planck-Institut f¨u r Gravitationsphysik(Albert-Einstein-Institut),Hannover,Germany2Leibniz Universit¨a t Hannover,Hannover,Germany3Laser Zentrum Hannover e.V.,Hannover,Germany4neoLASE GmbH,Hannover,Germany5LIGO Laboratory,California Institute of Technology,Pasadena,California,USA*patrick.kwee@aei.mpg.deAbstract:An ultra-stable,high-power cw Nd:Y AG laser system,devel-oped for the ground-based gravitational wave detector Advanced LIGO(Laser Interferometer Gravitational-Wave Observatory),was comprehen-sively ser power,frequency,beam pointing and beamquality were simultaneously stabilized using different active and passiveschemes.The output beam,the performance of the stabilization,and thecross-coupling between different stabilization feedback control loops werecharacterized and found to fulfill most design requirements.The employedstabilization schemes and the achieved performance are of relevance tomany high-precision optical experiments.©2012Optical Society of AmericaOCIS codes:(140.3425)Laser stabilization;(120.3180)Interferometry.References and links1.S.Rowan and J.Hough,“Gravitational wave detection by interferometry(ground and space),”Living Rev.Rel-ativity3,1–3(2000).2.P.R.Saulson,Fundamentals of Interferometric Gravitational Wave Detectors(World Scientific,1994).3.G.M.Harry,“Advanced LIGO:the next generation of gravitational wave detectors,”Class.Quantum Grav.27,084006(2010).4. B.Willke,“Stabilized lasers for advanced gravitational wave detectors,”Laser Photon.Rev.4,780–794(2010).5.P.Kwee,“Laser characterization and stabilization for precision interferometry,”Ph.D.thesis,Universit¨a t Han-nover(2010).6.K.Somiya,Y.Chen,S.Kawamura,and N.Mio,“Frequency noise and intensity noise of next-generationgravitational-wave detectors with RF/DC readout schemes,”Phys.Rev.D73,122005(2006).7. B.Willke,P.King,R.Savage,and P.Fritschel,“Pre-stabilized laser design requirements,”internal technicalreport T050036-v4,LIGO Scientific Collaboration(2009).8.L.Winkelmann,O.Puncken,R.Kluzik,C.Veltkamp,P.Kwee,J.Poeld,C.Bogan,B.Willke,M.Frede,J.Neu-mann,P.Wessels,and D.Kracht,“Injection-locked single-frequency laser with an output power of220W,”Appl.Phys.B102,529–538(2011).9.T.J.Kane and R.L.Byer,“Monolithic,unidirectional single-mode Nd:Y AG ring laser,”Opt.Lett.10,65–67(1985).10.I.Freitag,A.T¨u nnermann,and H.Welling,“Power scaling of diode-pumped monolithic Nd:Y AG lasers to outputpowers of several watts,”mun.115,511–515(1995).11.M.Frede,B.Schulz,R.Wilhelm,P.Kwee,F.Seifert,B.Willke,and D.Kracht,“Fundamental mode,single-frequency laser amplifier for gravitational wave detectors,”Opt.Express15,459–465(2007).#161737 - $15.00 USD Received 18 Jan 2012; revised 27 Feb 2012; accepted 4 Mar 2012; published 24 Apr 2012 (C) 2012 OSA7 May 2012 / Vol. 20, No. 10 / OPTICS EXPRESS 1061712. A.D.Farinas,E.K.Gustafson,and R.L.Byer,“Frequency and intensity noise in an injection-locked,solid-statelaser,”J.Opt.Soc.Am.B12,328–334(1995).13.R.Bork,M.Aronsson,D.Barker,J.Batch,J.Heefner,A.Ivanov,R.McCarthy,V.Sandberg,and K.Thorne,“New control and data acquisition system in the Advanced LIGO project,”Proc.of Industrial Control And Large Experimental Physics Control System(ICALEPSC)conference(2011).14.“Experimental physics and industrial control system,”/epics/.15.P.Kwee and B.Willke,“Automatic laser beam characterization of monolithic Nd:Y AG nonplanar ring lasers,”Appl.Opt.47,6022–6032(2008).16.P.Kwee,F.Seifert,B.Willke,and K.Danzmann,“Laser beam quality and pointing measurement with an opticalresonator,”Rev.Sci.Instrum.78,073103(2007).17. A.R¨u diger,R.Schilling,L.Schnupp,W.Winkler,H.Billing,and K.Maischberger,“A mode selector to suppressfluctuations in laser beam geometry,”Opt.Acta28,641–658(1981).18. B.Willke,N.Uehara,E.K.Gustafson,R.L.Byer,P.J.King,S.U.Seel,and R.L.Savage,“Spatial and temporalfiltering of a10-W Nd:Y AG laser with a Fabry-Perot ring-cavity premode cleaner,”Opt.Lett.23,1704–1706 (1998).19.J.H.P¨o ld,“Stabilization of the Advanced LIGO200W laser,”Diploma thesis,Leibniz Universit¨a t Hannover(2009).20. E.D.Black,“An introduction to Pound-Drever-Hall laser frequency stabilization,”Am.J.Phys.69,79–87(2001).21.R.W.P.Drever,J.L.Hall,F.V.Kowalski,J.Hough,G.M.Ford,A.J.Munley,and H.Ward,“Laser phase andfrequency stabilization using an optical resonator,”Appl.Phys.B31,97–105(1983).22. A.Bullington,ntz,M.Fejer,and R.Byer,“Modal frequency degeneracy in thermally loaded optical res-onators,”Appl.Opt.47,2840–2851(2008).23.G.Mueller,“Beam jitter coupling in Advanced LIGO,”Opt.Express13,7118–7132(2005).24.V.Delaubert,N.Treps,ssen,C.C.Harb,C.Fabre,m,and H.-A.Bachor,“TEM10homodynedetection as an optimal small-displacement and tilt-measurement scheme,”Phys.Rev.A74,053823(2006). 25.P.Kwee,B.Willke,and K.Danzmann,“Laser power noise detection at the quantum-noise limit of32A pho-tocurrent,”Opt.Lett.36,3563–3565(2011).26. A.Araya,N.Mio,K.Tsubono,K.Suehiro,S.Telada,M.Ohashi,and M.Fujimoto,“Optical mode cleaner withsuspended mirrors,”Appl.Opt.36,1446–1453(1997).27.P.Kwee,B.Willke,and K.Danzmann,“Shot-noise-limited laser power stabilization with a high-power photodi-ode array,”Opt.Lett.34,2912–2914(2009).28. ntz,P.Fritschel,H.Rong,E.Daw,and G.Gonz´a lez,“Quantum-limited optical phase detection at the10−10rad level,”J.Opt.Soc.Am.A19,91–100(2002).1.IntroductionInterferometric gravitational wave detectors[1,2]perform one of the most precise differential length measurements ever.Their goal is to directly detect the faint signals of gravitational waves emitted by astrophysical sources.The Advanced LIGO(Laser Interferometer Gravitational-Wave Observatory)[3]project is currently installing three second-generation,ground-based detectors at two observatory sites in the USA.The4kilometer-long baseline Michelson inter-ferometers have an anticipated tenfold better sensitivity than theirfirst-generation counterparts (Inital LIGO)and will presumably reach a strain sensitivity between10−24and10−23Hz−1/2.One key technology necessary to reach this extreme sensitivity are ultra-stable high-power laser systems[4,5].A high laser output power is required to reach a high signal-to-quantum-noise ratio,since the effect of quantum noise at high frequencies in the gravitational wave readout is reduced with increasing circulating laser power in the interferometer.In addition to quantum noise,technical laser noise coupling to the gravitational wave channel is a major noise source[6].Thus it is important to reduce the coupling of laser noise,e.g.by optical design or by exploiting symmetries,and to reduce laser noise itself by various active and passive stabilization schemes.In this article,we report on the pre-stabilized laser(PSL)of the Advanced LIGO detector. The PSL is based on a high-power solid-state laser that is comprehensively stabilized.One laser system was set up at the Albert-Einstein-Institute(AEI)in Hannover,Germany,the so called PSL reference system.Another identical PSL has already been installed at one Advanced LIGO site,the one near Livingston,LA,USA,and two more PSLs will be installed at the second #161737 - $15.00 USD Received 18 Jan 2012; revised 27 Feb 2012; accepted 4 Mar 2012; published 24 Apr 2012 (C) 2012 OSA7 May 2012 / Vol. 20, No. 10 / OPTICS EXPRESS 10618site at Hanford,WA,USA.We have characterized the reference PSL and thefirst observatory PSL.For this we measured various beam parameters and noise levels of the output beam in the gravitational wave detection frequency band from about10Hz to10kHz,measured the performance of the active and passive stabilization schemes,and determined upper bounds for the cross coupling between different control loops.At the time of writing the PSL reference system has been operated continuously for more than18months,and continues to operate reliably.The reference system delivered a continuous-wave,single-frequency laser beam at1064nm wavelength with a maximum power of150W with99.5%in the TEM00mode.The active and passive stabilization schemes efficiently re-duced the technical laser noise by several orders of magnitude such that most design require-ments[5,7]were fulfilled.In the gravitational wave detection frequency band the relative power noise was as low as2×10−8Hz−1/2,relative beam pointingfluctuations were as low as1×10−7Hz−1/2,and an in-loop measurement of the frequency noise was consistent with the maximum acceptable frequency noise of about0.1HzHz−1/2.The cross couplings between the control loops were,in general,rather small or at the expected levels.Thus we were able to optimize each loop individually and observed no instabilities due to cross couplings.This stabilized laser system is an indispensable part of Advanced LIGO and fulfilled nearly all design goals concerning the maximum acceptable noise levels of the different beam pa-rameters right after installation.Furthermore all or a subset of the implemented stabilization schemes might be of interest for many other high-precision optical experiments that are limited by laser noise.Besides gravitational wave detectors,stabilized laser systems are used e.g.in the field of optical frequency standards,macroscopic quantum objects,precision spectroscopy and optical traps.In the following section the laser system,the stabilization scheme and the characterization methods are described(Section2).Then,the results of the characterization(Section3)and the conclusions(Section4)are presented.ser system and stabilizationThe PSL consists of the laser,developed and fabricated by Laser Zentrum Hannover e.V.(LZH) and neoLASE,and the stabilization,developed and integrated by AEI.The optical components of the PSL are on a commercial optical table,occupying a space of about1.5×3.5m2,in a clean,dust-free environment.At the observatory sites the optical table is located in an acoustically isolated cleanroom.Most of the required electronics,the laser diodes for pumping the laser,and water chillers for cooling components on the optical table are placed outside of this cleanroom.The laser itself consists of three stages(Fig.1).An almostfinal version of the laser,the so-called engineering prototype,is described in detail in[8].The primary focus of this article is the stabilization and characterization of the PSL.Thus only a rough overview of the laser and the minor modifications implemented between engineering prototype and reference system are given in the following.Thefirst stage,the master laser,is a commercial non-planar ring-oscillator[9,10](NPRO) manufactured by InnoLight GmbH in Hannover,Germany.This solid-state laser uses a Nd:Y AG crystal as the laser medium and resonator at the same time.The NPRO is pumped by laser diodes at808nm and delivers an output power of2W.An internal power stabilization,called the noise eater,suppresses the relaxation oscillation at around1MHz.Due to its monolithic res-onator,the laser has exceptional intrinsic frequency stability.The two subsequent laser stages, used for power scaling,inherit the frequency stability of the master laser.The second stage(medium-power amplifier)is a single-pass amplifier[11]with an output power of35W.The seed laser beam from the NPRO stage passes through four Nd:YVO4crys-#161737 - $15.00 USD Received 18 Jan 2012; revised 27 Feb 2012; accepted 4 Mar 2012; published 24 Apr 2012 (C) 2012 OSA7 May 2012 / Vol. 20, No. 10 / OPTICS EXPRESS 10619power stabilizationFig.1.Pre-stabilized laser system of Advanced LIGO.The three-staged laser(NPRO,medium power amplifier,high power oscillator)and the stabilization scheme(pre-mode-cleaner,power and frequency stabilization)are shown.The input-mode-cleaner is not partof the PSL but closely related.NPRO,non-planar ring oscillator;EOM,electro-optic mod-ulator;FI,Faraday isolator;AOM,acousto-optic modulator.tals which are longitudinally pumped byfiber-coupled laser diodes at808nm.The third stage is an injection-locked ring oscillator[8]with an output power of about220W, called the high-power oscillator(HPO).Four Nd:Y AG crystals are used as the active media. Each is longitudinally pumped by sevenfiber-coupled laser diodes at808nm.The oscillator is injection-locked[12]to the previous laser stage using a feedback control loop.A broadband EOM(electro-optic modulator)placed between the NPRO and the medium-power amplifier is used to generate the required phase modulation sidebands at35.5MHz.Thus the high output power and good beam quality of this last stage is combined with the good frequency stability of the previous stages.The reference system features some minor modifications compared to the engineering proto-type[8]concerning the optics:The external halo aperture was integrated into the laser system permanently improving the beam quality.Additionally,a few minor designflaws related to the mechanical structure and the optical layout were engineered out.This did not degrade the output performance,nor the characteristics of the locked laser.In general the PSL is designed to be operated in two different power modes.In high-power mode all three laser stages are engaged with a power of about160W at the PSL output.In low-power mode the high-power oscillator is turned off and a shutter inside the laser resonator is closed.The beam of the medium-power stage is reflected at the output coupler of the high power stage leaving a residual power of about13W at the PSL output.This low-power mode will be used in the early commissioning phase and in the low-frequency-optimized operation mode of Advanced LIGO and is not discussed further in this article.The stabilization has three sections(Fig.1:PMC,PD2,reference cavity):A passive resonator, the so called pre-mode-cleaner(PMC),is used tofilter the laser beam spatially and temporally (see subsection2.1).Two pick-off beams at the PMC are used for the active power stabilization (see subsection2.2)and the active frequency pre-stabilization,respectively(see subsection2.3).In general most stabilization feedback control loops of the PSL are implemented using analog electronics.A real-time computer system(Control and Data Acquisition Systems,CDS,[13]) which is common to many other subsystems of Advanced LIGO,is utilized to control and mon-itor important parameters of the analog electronics.The lock acquisition of various loops,a few #161737 - $15.00 USD Received 18 Jan 2012; revised 27 Feb 2012; accepted 4 Mar 2012; published 24 Apr 2012 (C) 2012 OSA7 May 2012 / Vol. 20, No. 10 / OPTICS EXPRESS 10620slow digital control loops,and the data acquisition are implemented using this computer sys-tem.Many signals are recorded at different sampling rates ranging from16Hz to33kHz for diagnostics,monitoring and vetoing of gravitational wave signals.In total four real-time pro-cesses are used to control different aspects of the laser system.The Experimental Physics and Industrial Control System(EPICS)[14]and its associated user tools are used to communicate with the real-time software modules.The PSL contains a permanent,dedicated diagnostic instrument,the so called diagnostic breadboard(DBB,not shown in Fig.1)[15].This instrument is used to analyze two different beams,pick-off beams of the medium power stage and of the HPO.Two shutters are used to multiplex these to the DBB.We are able to measurefluctuations in power,frequency and beam pointing in an automated way with this instrument.In addition the beam quality quantified by the higher order mode content of the beam was measured using a modescan technique[16].The DBB is controlled by one real-time process of the CDS.In contrast to most of the other control loops in the PSL,all DBB control loops were implemented digitally.We used this instrument during the characterization of the laser system to measure the mentioned laser beam parameters of the HPO.In addition we temporarily placed an identical copy of the DBB downstream of the PMC to characterize the output beam of the PSL reference system.2.1.Pre-mode-cleanerA key component of the stabilization scheme is the passive ring resonator,called the pre-mode-cleaner(PMC)[17,18].It functions to suppress higher-order transverse modes,to improve the beam quality and the pointing stability of the laser beam,and tofilter powerfluctuations at radio frequencies.The beam transmitted through this resonator is the output beam of the PSL, and it is delivered to the subsequent subsystems of the gravitational wave detector.We developed and used a computer program[19]to model thefilter effects of the PMC as a function of various resonator parameters in order to aid its design.This led to a resonator with a bow-tie configuration consisting of four low-loss mirrors glued to an aluminum spacer. The optical round-trip length is2m with a free spectral range(FSR)of150MHz.The inci-dence angle of the horizontally polarized laser beam is6◦.Theflat input and output coupling mirrors have a power transmission of2.4%and the two concave high reflectivity mirrors(3m radius of curvature)have a transmission of68ppm.The measured bandwidth was,as expected, 560kHz which corresponds to afinesse of133and a power build-up factor of42.The Gaussian input/output beam had a waist radius of about568µm and the measured acquired round-trip Gouy phase was about1.7rad which is equivalent to0.27FSR.One TEM00resonance frequency of the PMC is stabilized to the laser frequency.The Pound-Drever-Hall(PDH)[20,21]sensing scheme is used to generate error signals,reusing the phase modulation sidebands at35.5MHz created between NPRO and medium power amplifier for the injection locking.The signal of the photodetector PD1,placed in reflection of the PMC, is demodulated at35.5MHz.This photodetector consists of a1mm InGaAs photodiode and a transimpedance amplifier.A piezo-electric element(PZT)between one of the curved mirrors and the spacer is used as a fast actuator to control the round-trip length and thereby the reso-nance frequencies of the PMC.With a maximum voltage of382V we were able to change the round-trip length by about2.4µm.An analog feedback control loop with a bandwidth of about 7kHz is used to stabilize the PMC resonance frequency to the laser frequency.In addition,the electronics is able to automatically bring the PMC into resonance with the laser(lock acquisition).For this process a125ms period ramp signal with an amplitude cor-responding to about one FSR is applied to the PZT of the PMC.The average power on pho-todetector PD1is monitored and as soon as the power drops below a given threshold the logic considers the PMC as resonant and closes the analog control loop.This lock acquisition proce-#161737 - $15.00 USD Received 18 Jan 2012; revised 27 Feb 2012; accepted 4 Mar 2012; published 24 Apr 2012 (C) 2012 OSA7 May 2012 / Vol. 20, No. 10 / OPTICS EXPRESS 10621dure took an average of about65ms and is automatically repeated as soon as the PMC goes off resonance.One real-time process of CDS is dedicated to control the PMC electronics.This includes parameters such as the proportional gain of the loop or lock acquisition parameters.In addition to the PZT actuator,two heating foils,delivering a maximum total heating power of14W,are attached to the aluminum spacer to control its temperature and thereby the roundtrip length on timescales longer than3s.We measured a heating and cooling1/e time constant of about2h with a range of4.5K which corresponds to about197FSR.During maintenance periods we heat the spacer with7W to reach a spacer temperature of about2.3K above room temperature in order to optimize the dynamic range of this actuator.A digital control loop uses this heater as an actuator to off-load the PZT actuator allowing compensation for slow room temperature and laser frequency drifts.The PMC is placed inside a pressure-tight tank at atmospheric pressure for acoustic shield-ing,to avoid contamination of the resonator mirrors and to minimize optical path length changes induced by atmospheric pressure variations.We used only low-outgassing materials and fabri-cated the PMC in a cleanroom in order to keep the initial mirror contamination to a minimum and to sustain a high long-term throughput.The PMCfilters the laser beam and improves the beam quality of the laser by suppress-ing higher order transverse modes[17].The acquired round-trip Gouy phase of the PMC was chosen in such a way that the resonance frequencies of higher order TEM modes are clearly separated from the TEM00resonance frequency.Thus these modes are not resonant and are mainly reflected by the PMC,whereas the TEM00mode is transmitted.However,during the design phase we underestimated the thermal effects in the PMC such that at nominal circu-lating power the round-trip Gouy-phase is close to0.25FSR and the resonance of the TEM40 mode is close to that of the TEM00mode.To characterize the mode-cleaning performance we measured the beam quality upstream and downstream of the PMC with the two independent DBBs.At150W in the transmitted beam,the circulating power in the PMC is about6.4kW and the intensity at the mirror surface can be as high as1.8×1010W m−2.At these power levels even small absorptions in the mirror coatings cause thermal effects which slightly change the mirror curvature[22].To estimate these thermal effects we analyzed the transmitted beam as a function of the circulating power using the DBB.In particular we measured the mode content of the LG10and TEM40mode.Changes of the PMC eigenmode waist size showed up as variations of the LG10mode content.A power dependence of the round-trip Gouy phase caused a variation of the power within the TEM40mode since its resonance frequency is close to a TEM00mode resonance and thus the suppression of this mode depends strongly on the Gouy phase.We adjusted the input power to the PMC such that the transmitted power ranged from100W to 150W corresponding to a circulating power between4.2kW and6.4kW.We used our PMC computer simulation to deduce the power dependence of the eigenmode waist size and the round-trip Gouy phase.The results are given in section3.1.At all circulating power levels,however,the TEM10and TEM01modes are strongly sup-pressed by the PMC and thus beam pointingfluctuations are reduced.Pointingfluctuations can be expressed tofirst order as powerfluctuations of the TEM10and TEM01modes[23,24].The PMC reduces thefield amplitude of these modes and thus the pointingfluctuations by a factor of about61according to the measuredfinesse and round-trip Gouy phase.To keep beam point-ingfluctuations small is important since they couple to the gravitational wave channel by small differential misalignments of the interferometer optics.Thus stringent design requirements,at the10−6Hz−1/2level for relative pointing,were set.To verify the pointing suppression effect of the PMC we used DBBs to measure the beam pointingfluctuations upstream and downstream #161737 - $15.00 USD Received 18 Jan 2012; revised 27 Feb 2012; accepted 4 Mar 2012; published 24 Apr 2012 (C) 2012 OSA7 May 2012 / Vol. 20, No. 10 / OPTICS EXPRESS 10622Fig.2.Detailed schematic of the power noise sensor setup for thefirst power stabilizationloop.This setup corresponds to PD2in the overview in Fig.1.λ/2,waveplate;PBS,polar-izing beam splitter;BD,glassfilters used as beam dump;PD,single element photodetector;QPD,quadrant photodetector.of the PMC.The resonator design has an even number of nearly normal-incidence reflections.Thus the resonance frequencies of horizontal and vertical polarized light are almost identical and the PMC does not act as polarizer.Therefore we use a thin-film polarizer upstream of the PMC to reach the required purity of larger than100:1in horizontal polarization.Finally the PMC reduces technical powerfluctuations at radio frequencies(RF).A good power stability between9MHz and100MHz is necessary as the phase modulated light in-jected into the interferometer is used to sense several degrees of freedom of the interferometer that need to be controlled.Power noise around these phase modulation sidebands would be a noise source for the respective stabilization loop.The PMC has a bandwidth(HWHM)of about 560kHz and acts tofirst order as a low-passfilter for powerfluctuations with a-3dB corner frequency at this frequency.To verify that the suppression of RF powerfluctuations is suffi-cient to fulfill the design requirements,we measured the relative power noise up to100MHz downstream of the PMC with a dedicated experiment involving the optical ac coupling tech-nique[25].In addition the PMC serves the very important purpose of defining the spatial laser mode for the downstream subsystem,namely the input optics(IO)subsystem.The IO subsystem is responsible,among other things,to further stabilize the laser beam with the suspended input mode cleaner[26]before the beam will be injected into the interferometer.Modifications of beam alignment or beam size of the laser system,which were and might be unavoidable,e.g., due to maintenance,do not propagate downstream of the PMC tofirst order due to its mode-cleaning effect.Furthermore we benefit from a similar isolating effect for the active power and frequency stabilization by using the beams transmitted through the curved high-reflectivity mirrors of the PMC.2.2.Power stabilizationThe passivefiltering effect of the PMC reduces powerfluctuations significantly only above the PMC bandwidth.In the detection band from about10Hz to10kHz good power stability is required sincefluctuations couple via the radiation pressure imbalance and the dark-fringe offset to the gravitational wave channel.Thus two cascaded active control loops,thefirst and second power stabilization loop,are used to reduce powerfluctuations which are mainly caused by the HPO stage.Thefirst loop uses a low-noise photodetector(PD2,see Figs.1and2)at one pick-off port #161737 - $15.00 USD Received 18 Jan 2012; revised 27 Feb 2012; accepted 4 Mar 2012; published 24 Apr 2012 (C) 2012 OSA7 May 2012 / Vol. 20, No. 10 / OPTICS EXPRESS 10623of the PMC to measure the powerfluctuations downstream of the PMC.An analog electronics feedback control loop and an AOM(acousto-optic modulator)as actuator,located upstream of the PMC,are used to stabilize the power.Scattered light turned out to be a critical noise source for thisfirst loop.Thus we placed all required optical and opto-electronic components into a box to shield from scattered light(see Fig.2).The beam transmitted by the curved PMC mirror has a power of about360mW.This beam isfirst attenuated in the box using aλ/2waveplate and a thin-film polarizer,such that we are able to adjust the power on the photodetectors to the optimal operation point.Afterwards the beam is split by a50:50beam splitter.The beams are directed to two identical photode-tectors,one for the control loop(PD2a,in-loop detector)and one for independent out-of-loop measurements to verify the achieved power stability(PD2b,out-of-loop detector).These pho-todetectors consist of a2mm InGaAs photodiode(PerkinElmer C30642GH),a transimpedance amplifier and an integrated signal-conditioningfilter.At the chosen operation point a power of about4mW illuminates each photodetector generating a photocurrent of about3mA.Thus the shot noise is at a relative power noise of10−8Hz−1/2.The signal conditioningfilter has a gain of0.2at very low frequencies(<70mHz)and amplifies the photodetector signal in the im-portant frequency range between3.3Hz and120Hz by about52dB.This signal conditioning filter reduces the electronics noise requirements on all subsequent stages,but has the drawback that the range between3.3Hz and120Hz is limited to maximum peak-to-peak relative power fluctuations of5×10−3.Thus the signal-conditioned channel is in its designed operation range only when the power stabilization loop is closed and therefore it is not possible to measure the free running power noise using this channel due to saturation.The uncoated glass windows of the photodiodes were removed and the laser beam hits the photodiodes at an incidence angle of45◦.The residual reflection from the photodiode surface is dumped into a glassfilter(Schott BG39)at the Brewster angle.Beam positionfluctuations in combination with spatial inhomogeneities in the photodiode responsivity is another noise source for the power stabilization.We placed a silicon quadrant photodetector(QPD)in the box to measure the beam positionfluctuations of a low-power beam picked off the main beam in the box.The beam parameters,in particular the Gouy phase,at the QPD are the same as on the power sensing detectors.Thus the beam positionfluctuations measured with the QPD are the same as the ones on the power sensing photodetectors,assuming that the positionfluctuations are caused upstream of the QPD pick-off point.We used the QPD to measure beam positionfluctuations only for diagnostic and noise projection purposes.In a slightly modified experiment,we replaced one turning mirror in the path to the power sta-bilization box by a mirror attached to a tip/tilt PZT element.We measured the typical coupling between beam positionfluctuations generated by the PZT and the residual relative photocurrent fluctuations measured with the out-of-the-loop photodetector.This coupling was between1m−1 and10m−1which is a typical value observed in different power stabilization experiments as well.We measured this coupling factor to be able to calculate the noise contribution in the out-of-the-loop photodetector signal due to beam positionfluctuations(see Subsection3.3).Since this tip/tilt actuator was only temporarily in the setup,we are not able to measure the coupling on a regular basis.Both power sensing photodetectors are connected to analog feedback control electronics.A low-pass(100mHz corner frequency)filtered reference value is subtracted from one signal which is subsequently passed through several control loopfilter stages.With power stabilization activated,we are able to control the power on the photodetectors and thereby the PSL output power via the reference level on time scales longer than10s.The reference level and other important parameters of these electronics are controlled by one dedicated real-time process of the CDS.The actuation or control signal of the electronics is passed to an AOM driver #161737 - $15.00 USD Received 18 Jan 2012; revised 27 Feb 2012; accepted 4 Mar 2012; published 24 Apr 2012 (C) 2012 OSA7 May 2012 / Vol. 20, No. 10 / OPTICS EXPRESS 10624。
2022年新高考模拟卷语文5(原卷版)解析如果说高考是一场战役,那么头脑就是抢,学识就是子弹,铃声就是信号,考卷就是目标,答题就是拼杀,成绩就是胜利。
高考之战在即,让我们扛起抢,子弹上膛,聆听信号,冲向目标,英勇拼杀,多取最后的胜利!下面是高考店铺为大家编辑整理的“2022年高考语文模拟卷(新高考专用)(解析版)”此文本仅供参考,欢迎阅读。
一、非连续性文本阅读阅读下面的文字,完成各题材料一:“中国天眼”身在法地,但在科学家眼中,它心系深空,是一座“天空实验室”。
到现在为止,应该没有天文学家上过太空,但他们却是最了解宇宙的一群人,靠的是什么?不少人小时候索试过用曝光的胶片观看日食,还有动手能力更强的,用两个放大镜自制过光学望远镜。
望远镜就是天文学家了解宇宙的必备工具。
但射电望远镜不同于人们熟悉的光学望远镜、它不能直接成像,而是抓取目标的无线电信号,用数据说话。
天文学家利用“天眼”开展工作,有点类似移动靶射击运动,需要不断地选取目标、瞄准目标射击、分析结果。
据北京大学教授、中科院国家天文台研究员李柯伽介绍,第一步要考虑望远镜频率是否合适、灵敏度是否足够、目标是不是在可视范围内,以便确定观测源的坐标,形成观测列表。
第二步是望远镜控制部门执行观测。
如何精确控制“天眼”瞄准动辄光年之外的目标?简单地说,一是通过天体坐标计算出望远镜所需的“姿态”,二是驱动电机控制望远镜的“姿态”。
因为地球在不停自转和公转,这样的观测比移动靶射击复杂得多,要不断地修正望远镜的位置,不断地瞄准目标,并确保一直命中靶心。
第三步是通过编程来分析数据。
外表安静的“天眼”,内心澎湃,每秒最高传输数据38G。
海量的数据,基本没有手动分析的可能,所以天文学家都是“程序员”,用大数据手段实现天地“连线”。
前辈科学家发现的物理定律,我们在物理实验室里做实验,结果都能验证定律为真。
在“天空实验室”里呢?那可不一定。
天文学跟物理学密不可分,大尺度时空结构、宇宙演化、高能天体(如黑洞、脉冲星等)都是以广义相对论为重要理论基础的。
arXiv:astro-ph/0103228v1 15 Mar 2001SubmittedtoTheAstronomicalJournalHigh-RedshiftQuasarsFoundinSloanDigitalSkySurveyCommissioningDataVI.SloanDigitalSkySurveySpectrographObservations1
ScottF.Anderson2,XiaohuiFan3,GordonT.Richards4,DonaldP.Schneider4,MichaelA.Strauss5,DanielE.VandenBerk6,JamesE.Gunn5,GillianR.Knapp5,DavidSchlegel5,WolfgangVoges7,BrianYanny6,NetaA.Bahcall5,J.Brinkmann8,RobertBrunner9,IstvanCsab´ai10,11,MamoruDoi12,MasatakaFukugita13,3,ˇZeljkoIvezi´c5,DonaldQ.Lamb14,JonLoveday15,RobertH.Lupton5,TimothyA.McKay16,JeffreyA.Munn17,R.C.Nichol18,G.P.Szokoly19,andDonaldG.York14
emailaddresses:anderson@astro.washington.edu,fan@sns.ias.edu,gtr@astro.psu.edu,dps@astro.psu.edu,strauss@astro.princeton.edu,danvb@fnal.gov–2–ABSTRACTWepresentresultsonover100high-redshiftquasarsfoundintheSloanDigitalSkySurvey(SDSS),usingautomatedselectionalgorithmsappliedtoSDSSimagingdataandwithspectroscopicconfirmationobtainedduringroutinespectroscopicoperationsoftheSloan2.5-mtelescope.TheSDSSspectracoverthewavelengthrange3900–9200˚Aataspectralresolutionof1800,andhavebeenobtainedfor116quasarswithredshiftsgreaterthan3.94;92oftheseobjectswerepreviouslyuncataloged,significantlyincreasingthecurrenttallyofpublishedz>4quasars.Thepaperalsoreportsobservationsoffiveadditionalnewz>4.6quasars;allwerefoundfromtheSDSSimagingsurveyandspectroscopicallyconfirmedwithdatafromtheApachePointObservatory’s3.5-mtelescope.Thei′magnitudesofthequasarsrangefrom18.03to20.56.Ofthe97newobjectsinthispaper,13areBroadAbsorptionLinequasars.Fivequasars,includingoneobjectataredshiftof5.11,have20cmpeakfluxdensitiesgreaterthan1mJy.Twoofthequasars,bothatz≈4.5,haveveryweakemissionlines;oneoftheseobjectsisaradiosource.Nineteenofthenewly-discoveredobjectshaveredshiftsabove4.6,andthemaximumredshiftisz=5.41;amongobjectsreportedtodate,thelatteristhethirdhighestredshiftAGN,andpenultimateinredshiftamongluminousquasars.
Subjectheadings:cosmology:earlyuniverse—quasars:individual1.IntroductionThepastfewyearshaveseenadramaticincreaseinboththenumberofknownhigh-redshiftquasarsandinthehighestquasarredshift.Largeareasurveys,usingmulticolorselectiontechniques,haveidentifiedanumberofquasarsatredshiftslargerthan5.0,includingoneobjectataredshiftof5.80(Fanetal.2000b).Surveysusingphotographicplates(e.g.,Kennefick,Djorgovski,&deCarvalho1995b;Storrie-Lombardietal.2000,Sharpetal.2001)andCCDs(theSloanDigitalSkySurvey(SDSS);Yorketal.2000)havenowproducedadatabaseofwellover100quasarswithredshiftslargerthanfour.Giventhecurrentpaceofdiscovery,weexpectthenumberofsuchquasarswillincreasebymanyfactorsinthenearfuture.
InthisseriesofpaperswehavealreadypresentedSDSSdiscoveriesofmorethan100quasarswithredshiftslargerthan3.5(fourquasarswithredshiftslargerthan4.95);allwereinitiallyidentifiedinSDSSimagingdataandspectroscopicconfirmationwasobtainedusingtheApachePointObservatory3.5-m,Hobby-Eberly,andKecktelescopes(seeSchneideretal.2001forasummaryoftheSDSShigh-redshiftquasars).TheSDSSspectrographsbeganoperationin–3–early2000(seeCastanderetal.2001),andinthepastyearhavereturnedspectraofnearly9000quasars;fortheinitialresultsoftheSDSSquasarsurveyseeRichardsetal.(2001b)andVandenBerketal.(2001).InthispaperwereportthefirstresultsoftheSDSSspectroscopicsurveyforhigh-redshiftquasars:116quasars(92previouslyunknown)withredshiftslargerthan3.94identifiedbycommissioningversionsoftheSDSSQuasarTargetSelectionSoftware;thefinalversionofthiscodeispresentedinRichardsetal.(2001a).Inaddition,wealsodescribefivenewz>4.6quasarsthatwerefoundintheSDSSimagingdataandspectroscopicallyconfirmedwiththeApachePointObservatory3.5-mtelescope.FindingchartsforallobjectslackingpublishedidentificationsaregiveninFigure1.
TheSDSSimagingobservationsandtargetselectionaredescribedin§2,andthespectroscopicobservationsofthequasarcandidatesarepresentedin§3.Thepropertiesofthequasarsarereviewedin§4,andabriefdiscussionappearsin§5.ThroughoutthispaperwewilladoptthecosmologicalmodelwithH0=50kms−1Mpc−1,Ω0=1.0,andΛ=0.0.
2.SloanDigitalSkySurveyImagingandQuasarTargetSelectionTheSloanDigitalSkySurveyusesaCCDcamera(Gunnetal.1998)onadedicated2.5-mtelescope(Siegmundetal.2001)atApachePointObservatory,NewMexico,toobtainimagesinfivebroadopticalbandsover10,000deg2ofthehighGalacticlatitudeskycenteredapproximatelyontheNorthGalacticPole.Thefivefilters(designatedu′,g′,r′,i′,andz′)covertheentirewavelengthrangeoftheCCDresponse(Fukugitaetal.1996;Fanetal.2001).Photometriccalibrationisprovidedbysimultaneousobservationswitha20-inchtelescopeatthesamesite.Thesurveydataprocessingsoftwaremeasuresthepropertiesofeachdetectedobjectintheimagingdata,anddeterminesandappliesbothastrometricandphotometriccalibrations(Pieretal.2001;Luptonetal.2001).Atthetimeofthiswriting(March2001)substantiallymorethan1000sq.deg.havebeenobservedwiththeSDSS,althoughsomeofthedatadonotmeetthestrictsurveyrequirements.ThefindingchartsinFigure1weremadefromi′-banddatatakenwiththeSDSSsurveycamera.