High-Redshift Quasars Found in Sloan Digital Sky Survey Commissioning Data VI. Sloan Digita

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Submitted to The Astronomical Journal High-Redshift Quasars Found in Sloan Digital Sky Survey Commissioning Data VI.Sloan Digital Sky Survey Spectrograph Observations 1Scott F.Anderson 2,Xiaohui Fan 3,Gordon T.Richards 4,Donald P.Schneider 4,Michael A.Strauss 5,Daniel E.Vanden Berk 6,James E.Gunn 5,Gillian R.Knapp 5,David Schlegel 5,Wolfgang Voges 7,Brian Yanny 6,Neta A.Bahcall 5,J.Brinkmann 8,Robert Brunner 9,Istvan Csab′a i 10,11,Mamoru Doi 12,Masataka Fukugita 13,3,ˇZeljko Ivezi′c 5,Donald https://www.sodocs.net/doc/f42536590.html,mb 14,Jon Loveday 15,Robert H.Lupton 5,Timothy A.McKay 16,Je?rey A.Munn 17,R.C.Nichol 18,G.P.Szokoly 19,and Donald G.York 14email addresses:anderson@https://www.sodocs.net/doc/f42536590.html,,fan@https://www.sodocs.net/doc/f42536590.html,,gtr@https://www.sodocs.net/doc/f42536590.html,,dps@https://www.sodocs.net/doc/f42536590.html,,strauss@https://www.sodocs.net/doc/f42536590.html,,

danvb@https://www.sodocs.net/doc/f42536590.html,

ABSTRACT

We present results on over100high-redshift quasars found in the Sloan Digital Sky Survey(SDSS),using automated selection algorithms applied to SDSS imaging

data and with spectroscopic con?rmation obtained during routine spectroscopic

operations of the Sloan2.5-m telescope.The SDSS spectra cover the wavelength range

3900–9200?A at a spectral resolution of1800,and have been obtained for116quasars

with redshifts greater than3.94;92of these objects were previously uncataloged,

signi?cantly increasing the current tally of published z>4quasars.The paper also

reports observations of?ve additional new z>4.6quasars;all were found from the

SDSS imaging survey and spectroscopically con?rmed with data from the Apache

Point Observatory’s3.5-m telescope.The i′magnitudes of the quasars range from

18.03to20.56.Of the97new objects in this paper,13are Broad Absorption Line

quasars.Five quasars,including one object at a redshift of5.11,have20cm peak?ux

densities greater than1mJy.Two of the quasars,both at z≈4.5,have very weak

emission lines;one of these objects is a radio source.Nineteen of the newly-discovered

objects have redshifts above4.6,and the maximum redshift is z=5.41;among objects

reported to date,the latter is the third highest redshift AGN,and penultimate in

redshift among luminous quasars.

Subject headings:cosmology:early universe—quasars:individual

1.Introduction

The past few years have seen a dramatic increase in both the number of known high-redshift quasars and in the highest quasar https://www.sodocs.net/doc/f42536590.html,rge area surveys,using multicolor selection techniques,have identi?ed a number of quasars at redshifts larger than5.0,including one object at a redshift of5.80(Fan et al.2000b).Surveys using photographic plates(e.g.,Kenne?ck, Djorgovski,&de Carvalho1995b;Storrie-Lombardi et al.2000,Sharp et al.2001)and CCDs(the Sloan Digital Sky Survey(SDSS);York et al.2000)have now produced a data base of well over 100quasars with redshifts larger than four.Given the current pace of discovery,we expect the number of such quasars will increase by many factors in the near future.

In this series of papers we have already presented SDSS discoveries of more than100quasars with redshifts larger than3.5(four quasars with redshifts larger than4.95);all were initially identi?ed in SDSS imaging data and spectroscopic con?rmation was obtained using the Apache Point Observatory3.5-m,Hobby-Eberly,and Keck telescopes(see Schneider et al.2001for

a summary of the SDSS high-redshift quasars).The SDSS spectrographs began operation in

early2000(see Castander et al.2001),and in the past year have returned spectra of nearly9000 quasars;for the initial results of the SDSS quasar survey see Richards et al.(2001b)and Vanden Berk et al.(2001).In this paper we report the?rst results of the SDSS spectroscopic survey for high-redshift quasars:116quasars(92previously unknown)with redshifts larger than3.94identi?ed by commissioning versions of the SDSS Quasar Target Selection Software;the ?nal version of this code is presented in Richards et al.(2001a).In addition,we also describe?ve new z>4.6quasars that were found in the SDSS imaging data and spectroscopically con?rmed with the Apache Point Observatory3.5-m telescope.Finding charts for all objects lacking published identi?cations are given in Figure1.

The SDSS imaging observations and target selection are described in§2,and the spectroscopic observations of the quasar candidates are presented in§3.The properties of the quasars are reviewed in§4,and a brief discussion appears in§5.Throughout this paper we will adopt the cosmological model with H0=50km s?1Mpc?1,?0=1.0,andΛ=0.0.

2.Sloan Digital Sky Survey Imaging and Quasar Target Selection

The Sloan Digital Sky Survey uses a CCD camera(Gunn et al.1998)on a dedicated

2.5-m telescope(Siegmund et al.2001)at Apache Point Observatory,New Mexico,to obtain images in?ve broad optical bands over10,000deg2of the high Galactic latitude sky centered approximately on the North Galactic Pole.The?ve?lters(designated u′,g′,r′,i′,and z′) cover the entire wavelength range of the CCD response(Fukugita et al.1996;Fan et al.2001). Photometric calibration is provided by simultaneous observations with a20-inch telescope at the same site.The survey data processing software measures the properties of each detected object in the imaging data,and determines and applies both astrometric and photometric calibrations (Pier et al.2001;Lupton et al.2001).At the time of this writing(March2001)substantially more than1000sq.deg.have been observed with the SDSS,although some of the data do not meet the strict survey requirements.The?nding charts in Figure1were made from i′-band data taken with the SDSS survey camera.

The high photometric accuracy,good image quality,and?ve wavelength bands covering the optical and near-infrared of the SDSS imaging survey produce an extremely e?ective data base from which to identify quasars.Since the spectra of quasars and stars di?er considerably, multicolor surveys have long been the primary technique employed to optically select quasars(e.g., Schmidt&Green1983and references therein).Fan(1999)calculated the expected location,as a function of redshift,of quasars in SDSS color-space;his results suggested that the SDSS could e?ectively identify quasars at most redshifts below≈5-6.Richards et al.(2001b)presented the SDSS colors of more than2600quasars with0

The presence of the i′and z′?lters in the SDSS camera make it possible to e?ectively identify high-redshift quasars.The combination of the strong Lymanαemission line,substantial absorption due to the Lymanαforest,and the smooth continuum longward of the Lymanαemission line cause the SDSS colors of most quasars with redshifts above≈3.3to be considerably di?erent than SDSS colors of stars(e.g.,Fan1999;Fan et al.1999;Richards et al.2001b).As one increases the quasar redshift above≈5.8,the Lymanαemission line leaves the i′band and enters the z′?lter,so detections of most z≈6quasars will rely on only one?lter(see Fan2000b).To date,the SDSS high-redshift quasar selection e?ciency(number of quasars divided by the number of quasar candidates)is approximately60–70%(e.g.,Fan et al.2001;Schneider et al.2001)for objects with i?<20.0;this is a much higher value than that achieved in previous investigations in this?eld.The contaminants in the SDSS high-redshift quasar candidates are late-type stars, narrow emission line galaxies at low redshift,and“E+A galaxies”at z≈0.4(Fan et al.1999).

One of the primary goals of the SDSS is to obtain spectra of a sample of≈100,000quasars selected from the SDSS imaging data(York et al.2000).The SDSS Quasar Target Selection Algorithm uses information from the SDSS photometric catalogs(e.g.,morphology,magnitude) to produce a list of quasar candidates to be included in the SDSS spectroscopic survey.The details of the selection are given in Richards et al.(2001a).One of the primary tasks of the SDSS commissioning period was to re?ne the quasar selection technique;during this time a number of versions of the quasar selection algorithm were used.

It is important to note that the objects described in this paper do not constitute a complete sample.Although most of the objects were identi?ed by an automated selection technique,the details of the selection procedure varied from?eld to?eld as the e?ectiveness of the algorithm was tested during the commissioning period.

The planned SDSS complete sample is expected to consist of objects whose colors are distinct from those of stars with153.0quasars with15

3.Spectroscopy of Quasar Candidates

The SDSS spectroscopic survey is carried out by two?ber-fed double spectrographs mounted at the Cassegrain focus of the SDSS2.5-m telescope(see York et al.2000;Castander et al.2001; and Uomoto et al.2001for details).Each spectrograph contains blue(3900-6200?A)and red (5800-9200?A)beams that produce spectra at a resolution of≈1800.A total of320?bers enter

each spectrograph;a single observation covers targets located in a3?diameter?eld.The?bers subtend a diameter of3′′on the sky,and because of mechanical constraints the?bers must be separated by at least55′′.In each?eld,32of the640?bers are assigned to measuring the sky,and approximately eight?bers are used for photometric standards and three?bers observe reddening standards.Typically about100quasar candidate spectra are taken in a45-minute observation of a?eld.For this paper we considered spectroscopic observations of138?elds,which cover an e?ective area of approximately700sq deg;nearly9000quasar spectra have been obtained to date.

The data,along with the associated calibration frames,are processed by the SDSS Spectroscopic Pipeline(Frieman et al.2001),which removes instrumental e?ects,extracts the spectra,calculates the wavelength calibration,subtracts the sky spectrum and removes the atmospheric absorption bands,and performs the?ux calibration.The spectra are then classi?ed (e.g.,star,galaxy,quasar)and redshifts are determined by the pipeline software.

We selected objects whose redshifts,as determined by the SDSS spectroscopic pipeline software,were larger than3.95,and supplemented this list by visually inspecting the processed spectra and identifying objects whose redshifts appeared to be four or larger.A visual inspection of these candidates produced a set of116quasars with redshifts ranging from3.94to5.41. Although the C IV emission line lies beyond the red cuto?of the spectrograph when the redshift exceeds4.8,the quality of the spectra and the distinctive appearance of the Lymanα+N V emission line and Lymanαforest region in these objects allows single-line redshifts to be assigned with high con?dence.SDSS spectra of27of the quasars are displayed in Figure2.

The high quality of the data is particularly notable given that the spectra,of objects with i?≈20,were obtained with a2.5-m telescope in modest length exposures(less than an hour in clear,good seeing conditions).

An additional?ve z>4.6quasars,identi?ed as high-redshift candidates in the SDSS imaging data,were spectroscopically con?rmed with the Double Imaging Spectrograph on the Apache Point Observatory3.5-m telescope.The spectra covered the wavelength range4000-10,000?A, with a spectral resolution of12?A(blue camera)and23?A(red camera);all exposure times were 3600s.(For details of the instrument con?guration see Fan et al.1999).Redshifts for these?ve objects were determined using the techniques described in Fan et al.(2001).The spectra of the ?ve quasars are shown in Figure3.

4.Discussion

Table1provides basic data(uniform and of high quality)for all121quasars.The object name format is SDSSp Jhhmmss.ss+ddmmss.s,where the coordinate equinox is J2000,and the “p”refers to the preliminary nature of the astrometry.The reported magnitudes are based on a preliminary photometric calibration;to indicate this,the?lters have an asterisk instead of a prime superscript(e.g.,g?rather than g′).The estimated astrometric accuracies in each coordinate

are0.10′′and the calibration of the photometric measurements is accurate to0.04magnitudes in the g′,r′,and i′?lters and0.06magnitudes in the u′and z′bands.Throughout the text,object names will frequently be abbreviated as SDSShhmm+ddmm.

Slightly more than80%(97)of the quasars in Table1were previously unknown,including all ?ve of the z>4.6“APO”objects.Eighteen of the objects had been previously identi?ed in SDSS data;they are included in this study because of the improved photometry and the newly obtained SDSS spectra.Four quasars in Table1were discovered by the Automated Plate Measuring facility (APM)survey(see Storrie-Lombardi et al.2000),and two quasars are Palomar Sky Survey(PSS) objects(Kenne?ck,Djorgovski,&de Carvalho1995b).The?nal column in Table1provides the references for all24of the previously known quasars independently recovered here.

The locations of the quasars in SDSS color space are shown in Figure4.As expected from the predictions of Fan(1999)and demonstrated by previous SDSS high-redshift quasar studies (e.g.,see summary in Schneider et al.2001),the colors of quasars with redshifts between4.0 and4.6are well-separated from the colors of stars in the(g??r?),(r??i?)diagram(the distance between stars and a typical quasar at this redshift is approximately one magnitude).At redshifts above≈4.6the(r??i?),(i??z?)diagram becomes a very useful aid,because at these redshifts the errors in the g??r?color can become large due to Lyman-limit systems entering the g?band.

Figure5shows the relationship between the(r??i?)color and redshift for the121quasars in Table1.Between redshifts of4.0and4.5,the mean color slightly increases,and the colors in this redshift range have a dispersion about the mean of0.10-0.15mag.At redshifts above4.5,when the Lymanαemission line moves from the r′to the i′?lter and the Lymanαforest blankets the r′bandpass,the(?r??i?)measurements rapidly increase to1.5and larger.The large dispersion in the color at z>4.5is likely to arise from the variation in strength of the Lymanαforest along di?erent lines of sight.

The redshift distribution of the quasars in Table1is shown in Figure6.The numbers decline rapidly with redshift(only about10%of the objects have z>4.8),and there is a slight dip near z=4.5due to the di?culty of separating quasars of this redshift from the stellar locus(see Fan et al.2001)using the early commissioning selection algorithm.Figure7displays the distribution of i?magnitudes of the quasars.The bulk of the objects have19.2

These objects are moderately luminous quasars;3C273,which has M B=?27.0in our adopted cosmology,would appear in our sample(i?<20.6)out to a redshift of approximately4.8. The most luminous objects in Table1are over two magnitudes brighter than3C273.

The sample includes nineteen new quasars with z>4.6,including three new quasars with z>5:SDSS0231?0728,SDSS0756+4104,and SDSS0913+5919.

The sample contains one set of quasars that are relatively close together on the sky: SDSS1108?0059(z=4.01)and SDSS1108?0058(z=4.56)are separated by only80′′.The

projected comoving separation of the lines of sight at z=4.01is approximately500kpc.

Sixteen of the121quasars,and13of the97newly discovered ones,are either certain or probable BAL quasars;this is consistent with the10%BAL fraction found in optically selected quasars at lower redshift(Weymann et al.1991).The spectra of many of the quasars have narrow absorption line systems,both intervening and intrinsic.

Five quasars in Table1have peak20cm(FIRST)?ux densities greater than2.5mJy.Two objects which are not included in the FIRST survey area were detected by the NRAO VLA Sky Survey(NVSS,Condon et al.1998;see notes on individual objects).An additional two quasars were detected by FIRST,but were fainter than than the NVSS limit.Four of the radio quasars were previously known;only?ve of the97newly discovered quasars are radio sources above the≈1mJy level.One of?ve quasars,SDSS0913+5919(z=5.11),is a luminous radio source (18.1mJy at20cm),and is the most distant known radio-loud quasar.This fraction of radio detections(≤10%)is comparable to the results found in previous studies of high-redshift quasars (e.g.,Schmidt et al.1995b,Stern et al.2000a).

None of the quasars are found in the ROSAT All-Sky Survey(RASS)Bright Source Catalog (Voges et al.1999;Schwope et al.2000),which has a?ux limit of2.4×10?12erg cm?2s?1in the0.5to2.0keV band.This result is not unexpected given that with the exception of a few unusual sources(e.g.,blazars),high-redshift quasars have X-ray?uxes well below the catalog limit (Kaspi,Brandt,&Schneider2000).One quasar,SDSS1737+5828,may have been detected in the RASS Faint Source Catalog(Voges et al.2000),but the optical/X-ray match is far from certain (see notes on individual objects).

Notes on Individual Objects

SDSSp J003126.80+150739.6(z=4.20):This radio-loud quasar has a?ux density of42.2mJy at20cm from the NVSS.

SDSSp J012004.83+141108.3(z=4.71):This object contains deep C IV and Si IV BAL features,and there may be strong Lymanβ+O VI emission.The spectrum was taken with the APO3.5-m telescope;the data for this object are displayed in Figure3.

SDSSp J015032.87+143425.6(z=4.14):The spectrum of this quasar shows very deep,very broad Si IV and C IV absorption troughs,and also has a narrow,associated absorption line system.

SDSSp J015642.11+141944.4(z=4.30):Strong BAL features are apparent in this spectrum, and lines from a given ion have multiple,broad components.

SDSSp J023137.65?072854.5(z=5.41):This object has the highest redshift in our current sample,and is the AGN with the third largest known redshift(following the luminous SDSS quasar with z=5.80found by Fan et al.2000b,and a low luminosity AGN at z=5.50found by Stern et al.2000b).While the redshift relies especially on the strong line atλ=7800?A,the redshift is not in doubt given the characteristic line pro?le and continuum discontinuity,plus the presence of a Lyman limit system at a rest wavelength of910?A.There is also strong evidence for Lymanβ+O VI and N V emission at a consistent redshift.The absorption just shortward of the Lymanαemission line is exceptionally strong;the?ux appears to drop to zero.This object was observed twice with the SDSS spectrographs,and the two spectra both indicate a redshift of5.41. SDSSp J023923.47?080105.1(z=4.00):This possible BAL quasar appears to have shallow, high-velocity C IV absorption and exceptionally strong O IV+Lymanβemission.

SDSSp J024447.79?081606.1(z=4.03):At i?=18.03,this quasar is both the brightest and the most luminous(M B≈?29.3,assuming an ultraviolet-optical spectral index of?0.5)object in the sample.

SDSSp J024457.19?010809.9(z=3.96):This bright(i?=18.33)BAL quasar is an unpublished PSS object.

SDSSp J025204.29+003136.9(z=4.10):The spectrum of this object displays deep,broad C IV absorption and strong,multi-component Si IV absorption.

SDSSp J025647.06?085041.4(z=4.21):This is a BAL quasar with weak absorption features, the most prominent of which is probably due to N V.

SDSSp J033005.32?053709.0(z=4.09):The spectrum of this BAL quasar shows two narrow C IV features superposed on a broad C IV absorption trough.

SDSSp J034946.61?065730.3(z=3.95):The spectrum of this BAL quasar has broad,shallow Si IV and C IV absorption features.

SDSSp J075618.4+410408.6(z=5.09):This quasar has the fourth largest redshift discovered by the SDSS.

SDSSp J083946.22+511202.8(z=4.39):The FIRST survey measurement of a20cm peak ?ux density of40.50mJy indicates that this is a radio-loud quasar.

SDSSp J085210.89+535949.0(z=4.20):This is a BAL quasar with a deep C IV absorption feature.

SDSSp J085634.93+525206.4(z=4.72):This object is a BAL quasar;it has a series of broad, deep absorption features.The precise redshift is uncertain given the nature of the BAL features. SDSSp J091316.56+591921.5(z=5.11):This quasar has the second largest redshift in our sample,and is near the faint limit of the SDSS spectroscopic survey.The spectrum(see Figure2) is of modest signal-to-noise ratio,and there is only one signi?cant emission feature,but the spectral region centered on≈7500?A displays all the characteristics of Lymanαemission line at z=5.11.The radio?ux from the object is18.1mJy(NVSS);this is a powerful radio quasar. SDSSp J102043.83+000105.8(z=4.30):This quasar was detected by the FIRST survey at a peak?ux density of1.68mJy at20cm.

SDSSp J110826.32+003706.8(z=4.41):This is a BAL quasar with strong,smooth Si IV and C IV absorption features.

SDSSp J123937.18+674020.8(z=4.40):The spectrum of this object displays C IV absorption and what may be an N V absorption feature;we tentatively classify this as a BAL quasar. SDSSp J130216.13+003032.1(z=4.50):This object has very weak emission lines;the spectrum appears quite similar to the z=4.62object reported by Fan et al.(1999).

SDSSp J141332.36?004909.7(z=4.14):It is not clear whether this object is a bona?de BAL or if the C IV and Si IV absorption features are formed from narrow multi-component“associated”absorption.The Lymanβ+O VI emission line is exceptionally strong.

SDSSp J144231.73+011055.3(z=4.56):This quasar was detected by the FIRST survey at a peak?ux density of1.07mJy at20cm.The spectrum is nearly bereft of emission lines,similar to the z=4.62object reported by Fan et al.(1999);also compare to SDSS1302+0030noted above. SDSSp J160501.21?011220.6(z=4.92):This quasar was discovered by Fan et al.(2000a);it is the highest redshift BAL yet published,and has the by far largest value of r??i?(2.37±0.15) in our sample.

SDSSp J162048.74+002005.7(z=4.09):The spectrum of this quasar displays a wealth of absorption phenomena:strong,broad C IV,multi-component Si IV,perhaps Lymanα+N V,and strong,broad O IV.

SDSSp J173744.87+582829.5(z=4.94):This quasar is possibly X-ray detected in the RASS Faint Source Catalog(1RXS J173739.9+582823)with an unabsorbed?ux in the0.1–2.4keV band of7.3×10?14erg s?1cm?2.The centroid of this X-ray source(≈7photons)is40′′from the SDSS position,and the chance of at least one unrelated RASS X-ray source superposition in our sample of over one hundred quasars is non-negligible(about25%).A higher spatial resolution X-ray image(e.g.,from Chandra)would clarify the identi?cation.If con?rmed,SDSS1737+5828 would be the highest redshift X-ray source yet detected in the RASS.

5.Summary

Calculations based on the measured high-redshift luminosity function(e.g.,Schmidt,Schneider &Gunn1995a;Kenne?ck,Djorgovski&de Carvalho1995a)and the expected performance of the SDSS camera predicted that the SDSS should produce a sample of well over a thousand quasars at redshifts above four(e.g.,Schneider1999),and that the SDSS automated selection algorithm could identify quasars as distant as a redshift of six.The early results,presented in this paper,are promising.Although less than10%of the survey area has been observed spectroscopically,and much of the work to date has been spent?ne-tuning both the equipment and the software,the SDSS has already,in“survey mode”,selected more than100such objects.We are particularly encouraged by the discovery of the quasar at redshift5.41;this object,and the other z≈5.0 quasars in this paper,show that such objects can be found in an automated manner.

The SDSS commissioning was completed in Fall2000,and the survey has now o?cially commenced.The quasars in this paper do not constitute a complete sample because they were identi?ed with a variety of selection criteria during the commissioning period.We expect that in each year of operation the SDSS will discover150-200quasars will redshifts larger than four,and ?ve to ten quasars with redshifts larger than?ve,all found with well-de?ned,uniform selection criteria.

This work was supported in part by National Science Foundation grants PHY00-70928(XF), AST99-00703(GTR and DPS),and AST00-71091(MAS).XF and MAS acknowledge additional support from the Princeton University Research Board,and a Porter O.Jacobus Fellowship,and XF acknowledges support from a Frank and Peggy Taplin Fellowship.

The Sloan Digital Sky Survey20(SDSS)is a joint project of The University of Chicago, Fermilab,the Institute for Advanced Study,the Japan Participation Group,The Johns Hopkins University,the Max-Planck-Institute for Astronomy(MPIA),the Max-Planck-Institute for Astrophysics(MPA),New Mexico State University,Princeton University,the United States Naval Observatory,and the University of Washington.Apache Point Observatory,site of the SDSS telescopes,is operated by the Astrophysical Research Consortium(ARC).Funding for the project has been provided by the Alfred P.Sloan Foundation,the SDSS member institutions,the National Aeronautics and Space Administration,the National Science Foundation,the U.S.Department of Energy,Monbusho,and the Max Planck Society.

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Stern,D.,Djorgovski,S.G.,Perley,R.A.,de Carvalho,R.R.,&Wall,J.V.2000a,AJ,119,1526 Stern,D.,Spinrad,HJ.,Eisenhardt,P.,Bunker,A.J.,Dawson,S.,Stanford,S.,&Elston,R.2000, ApJ,533,L75

Storrie-Lombardi,L.J.,Irwin,M.J.,McMahon,R.G.,&Hook,I.M.2000,MNRAS,in press/astro-ph/0012446

Uomoto,A.,et al.2001,in preparation

Vanden Berk,D.E.,Richards,G.T.,Bauer,A.,et al.2001,AJ,submitted

Voges,W.,et al.1999,A&A,349,389

Voges,W.,et al.2000,IAUC,7432

York,D.G.,Adelman,J.,Anderson,J.E.,Anderson,S.F.,et al.2000,AJ,120,1579 Weymann,R.J.,Morris,S.L.,Foltz,C.B.,&Hewett,P.C.1991,ApJ,373,23

Figure Captions

Fig.1.—(a-d)Finding charts for the98quasars in this paper that lack published identi?cations; each individual chart is100′′on a side.All frames are i′images taken with the SDSS camera.The small arrow in the lower left of each chart indicates the direction of north;all charts have“sky”parity,so east is located90?counterclockwise from north.

Fig. 2.—(a-i)Spectra of27of the quasars taken with the SDSS spectrographs.The spectral resolution is approximately1800;data points shortward of4250?A are not displayed as they have very low signal-to-noise ratio.Displayed are all the z>4.8objects,BALs,and the two z≈4.5 quasars with extremely weak emission lines.

Fig. 3.—Apache Point Observatory Spectra of the?ve z>4.6quasars taken with the Double Imaging Spectrograph on the Apache Point Observatory’s3.5-m telescope.The spectral resolution is approximately23?A,and the exposure times are all3600s.Only data from the red beam are displayed as these objects produce little signal below5500?A.

Fig.4.—Locations of the121quasars in the(g??r?),(r??i?)(left panel)and(r??i?),(i??z?) (right panel)color-color diagrams.The quasars are coded by redshift;triangles represent redshifts less than4.6and circles are z>4.6quasars.The points and contours represent the colors of10,000 stars.

Fig.5.—The(r??i?)color of the121quasars as a function of redshift.Note the sudden reddening at z≈4.5as the Lymanαemission line enters the i′band.

Fig. 6.—The redshift distribution of the121quasars.Note the steep decline as one moves to larger redshifts.The dip at z≈4.5is due to a drop in the detection e?ciency at these redshifts of the quasar selection algorithm used during SDSS commissioning(see Fan et al.2001).

Fig.7.—The distribution of the i?magnitudes of the121quasars.The sharp cuto?near i?≈20.5 is due to the brightness limit of the SDSS spectroscopic survey.Fourteen of the objects have i?<19.

003126.80+150739.6003749.19+155208.4005006.35-005319.3012004.83+141108.3015032.87+143425.6 015642.11+141944.4015704.10+122858.3020651.37+121624.4023137.65-072854.5023923.47-081005.1 024447.79-081606.1024457.19-010809.9025039.17-065405.1025159.41-084258.1025204.29+003136.9 025518.58+004847.6025647.06-085041.4031213.98-062658.8032226.10-055824.7033119.67-074143.1 033305.32-053709.0033344.43-060625.2033406.99-063406.5034109.35-064805.1034541.51-072315.3

034946.61-065730.3073147.01+364346.5075103.96+424211.6075618.14+410408.6075652.07+450258.9 075732.89+441424.7080159.25+433625.0080549.94+482345.9081054.88+460357.9081241.12+442129.0 083046.28+474646.5083103.00+523533.6083212.37+530327.4083324.57+523955.0083946.22+511202.8 084811.52-001418.0085151.27+020756.1085210.89+535949.0085430.18+004213.6085634.93+525206.4 090242.08-002125.9090440.64+535038.8090532.15-001430.5091016.79+575331.1091316.56+591921.5

092038.49+564235.9092256.20+561849.3094056.02+584830.2094108.36+594725.8094917.17+602104.5 095000.17+620318.6095151.17+594556.2100154.87+630818.0100413.14+630437.4101053.52+644832.0 102043.82+000105.8102332.08+633508.1103309.21+644351.1104008.10+651429.3104040.14-001540.9 104351.20+650647.7105254.60-000625.9105602.37+003222.0105902.73+010404.1110247.29+663519.5 110819.16-005824.0110826.32+003706.8111224.18+004630.4123937.18+674020.8125433.57-003922.7

125759.22-011130.3130216.13+003032.1132447.26-031358.3134723.09+002158.9135057.86-004355.3

135134.46-003652.2135423.00-003906.2144231.73+011055.3144407.63-010152.8144617.35-010131.2 152443.19+011358.9162048.74+002005.7170804.91+602202.0171014.52+592326.5171224.92+560625.0 171530.49+645319.3171808.67+551511.2172007.20+602823.9173744.87+582829.5220008.66+001744.8

221644.02+001348.3222050.80+001959.1234147.27+001551.9

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Excel_VBA实例教程_查找单元格

Excel VBA实例教程查找单元格 1、使用Find方法 在Excel中使用查找对话框可以查找工作表中特定内容的单元格，而在VBA中则使用Find方法，如下面的代码所示。 01.Sub RngFind() 02. Dim StrFind As String 03. Dim Rng As Range 04. StrFind = InputBox("请输入要查找的值:") 05. If Trim(StrFind) <> "" Then 06. With Sheet1.Range("A:A") 07. Set Rng = .Find(What:=StrFind, _ 08. After:=.Cells(.Cells.Count), _ 09. LookIn:=xlValues, _ 10. LookAt:=xlWhole, _ 11. SearchOrder:=xlByRows, _ 12. SearchDirection:=xlNext, _ 13. MatchCase:=False) 14. If Not Rng Is Nothing Then 15. Application.Goto Rng, True 16. Else 17. MsgBox "没有找到该单元格!" 18. End If 19. End With 20. End If 21.End Sub 代码解析： RngFind过程使用Find方法在工作表Sheet1的A列中查找InputBox函数对话框中所输入的值，并查找该值所在的第一个单元格。 第6到第13行代码在工作表Sheet1的A列中查找InputBox函数对话框中所输入的值。应用于Range 对象的Find方法在区域中查找特定信息，并返回Range对象，该对象代表用于查找信息的第一个单元格。如果未发现匹配单元格，就返回Nothing，语法如下： 01.expression.Find(What, After, LookIn, LookAt, SearchOrder, SearchDirection, MatchCase, MatchByte, SerchFormat) 复制代码参数expression是必需的，该表达式返回一个Range对象。 参数What是必需的，要搜索的数据，可为字符串或任意数据类型。 参数After是可选的，表示搜索过程将从其之后开始进行的单元格，必须是区域中的单个单元格。查找时是从该单元格之后开始的，直到本方法绕回到指定的单元格时，才对其进行搜索。如果未指定本参数，搜索将从区域的左上角单元格之后开始。 在本例中将After参数设置为A列的最后一个单元格，所以查找时从A1单元格开始搜索。 参数LookIn是可选的，信息类型。 参数LookAt是可选的，可为XlLookAt常量的xlWhole 或xlPart之一。 参数SearchOrder是可选的，可为XlSearchOrder常量的xlByRows或xlByColumns之一。 参数SearchDirection是可选的，搜索的方向，可为XlSearchDirection常量的xlNext或xlPrevious 之一。

vast的中文释义

vast的发音：英音 [ vɑ:st ]；美音 [ v?st ] vast的中文翻译： adj. 辽阔的；巨大的；庞大的；大量的 词形变化：形容词比较级：vaster，vastest；副词：vastly；名词：vastness。 同义词：huge，immense，brobdingnagian； 。单词分析：这些形容词均有“巨大的，庞大的”之意。 huge：含义广，强调体积或容积的庞大。也可用于引申意义。enormous：指体积、数量或程度远远超过一般标准。 immense：正式用词，侧重空间的广阔，也指面积或分量的巨大。giant：非正式用词，多为褒义。指如巨人般的庞大体积。 gigantic：指面积或体积的巨大，但多用于引申意义。 colossal：侧重尺寸、规模和体积的无比巨大。 vast：多指空间、面积、范围的巨大，不涉及重量。 massive：指大的体积、数量和重量，侧重庞大而笨重。 tremendous：指某物很大，大得惊人；也可用作引申意义。 vast的英语解释： unusually great in size or amount or degree or especially extent or scope 相关短语： vast population and limited farmland 人多地少 vast scale 大量的 vast stretches of paddy fields 成片的稻田 vast sums 大笔金钱 vast的例句：

and the vast extent of America would insure him impunity and safety 美洲大陆那么大，他当然更有把握能够逍遥法外了。 From her ruptured tanks poured a reddish-brown gusher of oil that roiled and boiled and gradually spread a vast slick over the greyblue waters 从破裂的油轮里，喷涌出一股股红棕色的原油，汹涌澎湃，渐渐地在蔚蓝色海面上形成了一层巨大的油膜。 They are war- horses. Either could face ten thousand. They make the white silk stretch away into a vast desert. 此皆骑战一敌万,缟素漠漠开风沙。 He inherited vast estates on his accession to the throne. 他即位后继承了大片领地。 Love is closer anyway and warmer than adoration of some vast unknowable cloud 爱情，比起对巨大而不可捉摸的云雾的崇拜来说，毕竟更加亲切，更加温暖。

FindWindow函数详解

C#中使用FindWindow函数详解 FindWindow 用来根据类名和窗口名来得到窗口句柄的。但是这个函数不能查找子窗口，也不区分大小写。 如果要从一个窗口的子窗口中查找需要使用FindWindowEX。 1.在C#中使用方法如下： [DllImport("User32.dll", EntryPoint = "FindWindow")] private static extern IntPtr FindWindow(string lpClassName,string lpWindowName); [DllImport("User32.dll", EntryPoint = "FindWindowEx")] private static extern IntPtr FindWindowEx(IntPtr hwndParent, IntPtr hwndChildAfter, string lpClassName, string lpWindowName); [DllImport("User32.dll", EntryPoint = "FindWindow")] private static extern IntPtr FindWindow(string lpClassName,string lpWindowName); [DllImport("User32.dll", EntryPoint = "FindWindowEx")] private static extern IntPtr FindWindowEx(IntPtr hwndParent, IntPtr hwndChildAfter, string lpClassName, string lpWindowName); 2. 实例参考： IntPtr hWnd = FindWindow(null, "test Demo"); 这样会查找所有title是"test Demo"的窗口。 参考下面的资料解释 3. FindWindow参数详解： Parameters lpClassName [in] Pointer to a null-terminated string that specifies the class name or a class atom created by a previous call to the RegisterClass or RegisterClassEx function. The atom must be in the low-order word of lpClassName; the high-order word must be zero. If lpClassName points to a string, it specifies the window class name. The class name can be any name registered with RegisterClass or RegisterClassEx, or any of the predefined control-class names.

标志及其含义

1 中国银行(Bank Of China)，行标从总体上看是古钱形状代表银行，“中”字代表中国；外圆表明中国银行是面向全球的国际性大银行。 2 工商银行(Industrial and Commercial Bank of China Limited)，整体标志是以一个隐性的方孔圆币，体现金融业的行业特征，标志的中心是经过变形的“工”字，中间断开，使工字更加突出，表达了深层含义。两边对称，体现出银行与客户之间平等互信的依存关系。以“断”强化“续”，以“分”形成“合”，是银行与客户的共存基础。设计手法的巧应用，强化了标志的语言表达力，中国汉字与古钱币形的运用充分体现了现代气息。 3 建设银行（China Construction Bank），以古铜钱为基础的内方外圆图形,有着明确的银行属性,着重体现建设银行的"方圆"特性,方,代表着严格、规范、认真；圆，象征着饱满、亲和、融通。图形右上角的变化，形成重叠立体的效果，代表着“中国”与“建筑”英文缩写，即：两个C字母的重叠，寓意积累，象征建设银行在资金的积累过程中发展壮大，为中国经济建设提供服务。图形突破了封闭的圆形，象征古老文化与现代经营观念的融会贯通，寓意中国建设银行在全新的现代经济建设中，植根中国，面向世界。标准色为海蓝色，象征理性、包容、祥和、稳定，体现国有商业银行的大家风范，寓意中国建设银行象大海一样吸收容纳各方人才和资金。 4

交通银行（BANK OF COMMUNICATIONS),交通银行行徽将英文译名BANK OF COMMUNICATIONS词首的小写字母“b”和“c”组合起来，构成了一个立体面，表示企业的实力和业务的综合性。整个图案具有延伸感，体现交通银行不断发展、壮大、日益繁荣的趋势。标准色为深蓝色，象征交通银行像大海一样博大精深，寓意稳重，踏实而可靠！交通银行是由晚清著名改革派政治家和书法家郑孝胥题写的。 5 农业银行（Agricultural Bank of China），中国农业银行标志图为圆形，由中国古钱和麦穗构成。古钱寓意货币、银行；麦穗寓意农业，它们构成农业银行的名称要素。整个图案成外圆内方，象征中国农业银行作为国有商业银行经营的规范化。麦穗中部构成一个“田”字，阴纹又明显地形成半形，直接了当地表达出农业银行的特征。麦穗芒刺指向上方，使外圆开口，给人以突破感，象征中国农业银行事业不断开拓前进。行徽标准色为绿色。绿色的心理特性是：自然、新鲜、平静、安逸、有保障、有安全感、信任、可靠、公平、理智、理想、纯朴，让人联想到自然、生命、生长；绿色是生命的本原色，象征生机、发展、永恒、稳健，表示农业银行诚信高效，寓意农业银行事业蓬勃发展。中国农业银行标志的原作者是陈汉民先生。 6 整个标志为字母“A”的字型体，由四段半径不同的圆弧线交汇而声成。整体构图简洁大方，富于动感。图形鲜红的色彩代表了安踏的活力与进取精神。圆弧构造出的空间感展现了安踏人开拓创业的无限发展前景，变型的“A”则抽象出一只升腾而起的飞行形象，以极其简约，

Findbugs使用简介

Findbugs使用简介 Findbugs是一个在java程序中查找bug的程序，它查找bug模式的实例，也就是可能出错的代码实例，注意Findbugs是检查java字节码，也就是*.class文件。其实准确的说，它是寻找代码缺陷的，很多我们写的不好的地方，可以优化的地方，它都能检查出来。例如：未关闭的数据库连接，缺少必要的null check，多余的null check，多余的if后置条件，相同的条件分支，重复的代码块，错误的使用了"=="，建议使用StringBuffer代替字符串连加等等。而且我们还可以自己配置检查规则(做哪些检查,不做哪些检查)，也可以自己来实现独有的校验规则(用户自定义特定的bug模式需要继承它的接口,编写自己的校验类,属于高级技巧)。 Findbugs是一个静态分析工具，它检查类或者JAR 文件，将字节码与一组缺陷模式进行对比以发现可能的问题。Findbugs自带检测器，其中有60余种Bad practice，80余种Correctness，1种Internationalization，12种Malicious code vulnerability，27种Multithreaded correctness，23种Performance，43种Dodgy。 Bad practice 坏的实践 一些不好的实践，下面列举几个： HE：类定义了equals()，却没有hashCode()；或类定义了equals()，却使用 Object.hashCode()；或类定义了hashCode()，却没有equals()；或类定义了hashCode()，却使用Object.equals()；类继承了equals()，却使用Object.hashCode()。 SQL：Statement 的execute方法调用了非常量的字符串；或Prepared Statement是由一个非常量的字符串产生。 DE：方法终止或不处理异常，一般情况下，异常应该被处理或报告，或被方法抛出。 Correctness 一般的正确性问题 可能导致错误的代码，下面列举几个：

随机森林原理解释及其中各个参数的含义中文解释 (2)

一、RF原理解释： 首先，从给定的训练集通过多次随机的可重复的采样得到多个bootstrap 数据集。接着，对每个 bootstrap 数据集构造一棵决策树，构造是通过迭代的将数据点分到左右两个子集中实现的，这个分割过程是一个搜索分割函数的参数空间以寻求最大信息增量意义下最佳参数的过程。然后，在每个叶节点处通过统计训练集中达到此叶节点的分类标签的直方图经验的估计此叶节点上的类分布。这样的迭代训练过程一直执行到用户设定的最大树深度（随机森林提出者Breiman采用的是ntree=500）或者直到不能通过继续分割获取更大的信息增益为止，网上的代码中作者都是对树的最大深度设置了最大值。 二、函数，参数的中文解释 function model = classRF_train(X,Y,ntree,mtry, extra_options)随机森林中模型的训练 X,表示输入的数据矩阵 Y输出 Ntree 设置的树的数目 Mtry的默认值为 floor(sqrt(size(X,2))，表示不超过矩阵X列数的二次开根值的整数。extra_options 包含很多控制RF的项 取值为1或0，默认值为1，表示是否做变量替换 表示预先知道的类，函数首先得到一个升序排列的标签然后给先前的类同样的排序。

只在分类器中使用的一个向量，长度等于类的数目。对类的观察值是取对cutoff投票占的的最大比例的一个。 用于分层抽样 样本的长度 表示终端节点的最小值，这个参数设置得越大会使更小的树生长，耗时更少。 判断是否需要对预测器的importance进行评估 决定是否对casewise的重要性度量进行计算 判别是否计算行之间的距离 判断是否计算out-of-bag 如果设定为TRUE，当随机森林运行的时候输出更多冗长的数据。如果设置为一些整数，输出每个追踪树。 通过树的数目矩阵跟踪每个样本在树上的in-bag。 norm_votes 统计每一类的投票数 importance 对于分类器来说是一个列数等于类别数加二，第一列计算精度下降值。在ncalss+1列表示所有类平均精度减少值。最后一列表示Gini指数平均减小值。在随机森林用于回归的应用中importance 表示的含义又不一样，我们只用到分类的作用，所以对回归的含义不做介绍。 importanceSD 标准差 localImp 包含importance标准化残差测量值的矩阵 ntree 生长的树的数目

(完整版)英语宾语补足语用法详解

Contents 英语宾语补足语用法详解 (2) 一、概念 (2) 二、何时用现在分词、何时用过去分词作主语(宾语)补足语 (2) 三、可以用分词作主语或宾语补足语的动词 (3) 典例精析： (4)

英语宾语补足语用法详解 一、概念 分词作主语补足语和宾语补足语其实是同一成分用于两种不同的句式中。具体地说，主动态句子中的宾语补足语就是被动态句子中的主语补足语。先了解宾语补足语，则很容易了解主语补足语。 宾语补足语：在英语中，某些及物动词不仅需要宾语，而且还要求某个词或词组来补充说明宾语，即表示宾语代表的人或物所发出的动作或所处的状态，这个词或短语称为宾语补足语。有些语法书把宾语和补足语称为复合宾语。 句型：及物动词+宾语(n./pron.)+宾语补足语(n./adj./adv./to do/-ing/-ed/介词短语共7种表示法) 该句型若变成被动语态，即将宾语提到句首作主语，原主动语态中的宾语补足语此时在被动语态中起到补充说明主语的作用，所以改称主语补足语。例如： A cook will be immediately fired if he is found smoking in the kitchen. 此句中smoking是主语he的补足语，所以称为主语补足语。 二、何时用现在分词、何时用过去分词作主语(宾语)补足语 分词作主语(宾语)补足语时，若主语(宾语)与分词之间是主动关系，则用现在分词表示主动； 如果主语(宾语)与分词之间是被动关系，则用过去分词表示被动。例如： He was heard singing in the next room. He was singing.主语he与补足语“唱歌”之间是主动关系，故用现在分词singing。 One of the glasses was found broken. One of the glasses was broken.主语one of the glasses与补足语“打破”之间是被动关系，故用过去分词broken。 Don‘t leave the water running while you brush your teeth.

汉字偏旁部首的含义

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一根丝线绞丝旁，绫罗绸缎细裁量。偏旁部首歌（下）》 斜玉旁，王字旁，环佩玲珑响叮当； 正文反写反文旁，收放自如好文章； 衣少一点示字旁，福禄禧寿添吉祥； 高头大马马字旁，骆驼背上驮两箱； 一撇一捺人字头，三人从命来会合； 一二三四四字头，赏罚分明无疏漏； 春日无光春字头，春加两虫变蠢头； 去尾留头病字头，病痛缠身人消瘦； 秃尾老虎虎字头，子虚乌有别犯愁；多一点，宝盖头，一扇牢门两人守；少一点，秃宝盖，冠军桂冠头上戴；两根草，草字头，花草芳菲蝶儿游；一竿青竹竹字头，提篮背筐挖笋头；一片屋顶户字头，层层房间一座楼；一座山，山字头，清风微岚绕山岗；点点滴滴雨字头，雨雪霏霏乌云走；一横一撇片厂头，人在东厢马在厩；像四非四皿字底，碟盏盆盘收柜里；一颗红心心字底，忐忑不安心焦急；四条边，是方框，囝囝囡囡编圆筐

Linux find命令常见用法汇总

Linux find命令常见用法汇总 导读:Linux系统中查找文件的命令式find，find命令具有强大的功能，能够提供多种查找条件，下面小编就给大家带来Linux中find命令的常见用法汇总，一起来学习下吧。 ·find path -option ［-print ］［-exec -ok command ］{} \; find命令的参数； pathname：find命令所查找的目录路径。例如用。来表示当前目录，用/来表示系统根目录。 -print：find命令将匹配的文件输出到标准输出。 -exec：find命令对匹配的文件执行该参数所给出的shell命令。相应命令的形式为‘command’ { } \;，注意{ }和\；之间的空格。 -ok：和-exec的作用相同，只不过以一种更为安全的模式来执行该参数所给出的shell命令，在执行每一个命令之前，都会给出提示，让用户来确定是否执行。 #-print 将查找到的文件输出到标准输出 #-exec command {} \; —–将查到的文件执行command操作，{} 和\;之间有空格 #-ok 和-exec相同，只不过在操作前要询用户 例：find 。-name .svn | xargs rm -rf ==================================================== -name filename #查找名为filename的文件 -perm #按执行权限来查找 -user username #按文件属主来查找

-group groupname #按组来查找 -mtime -n +n #按文件更改时间来查找文件，-n指n天以内，+n指n天以前-atime -n +n #按文件访问时间来查GIN：0px“》 -ctime -n +n #按文件创建时间来查找文件，-n指n天以内，+n指n天以前-nogroup #查无有效属组的文件，即文件的属组在/etc/groups中不存在 -nouser #查无有效属主的文件，即文件的属主在/etc/passwd中不存 -newer f1 ！f2 找文件，-n指n天以内，+n指n天以前 -ctime -n +n #按文件创建时间来查找文件，-n指n天以内，+n指n天以前-nogroup #查无有效属组的文件，即文件的属组在/etc/groups中不存在 -nouser #查无有效属主的文件，即文件的属主在/etc/passwd中不存 -newer f1 ！f2 #查更改时间比f1新但比f2旧的文件 -type b/d/c/p/l/f #查是块设备、目录、字符设备、管道、符号链接、普通文件 -size n［c］#查长度为n块［或n字节］的文件 -depth #使查找在进入子目录前先行查找完本目录 -fstype #查更改时间比f1新但比f2旧的文件 -type b/d/c/p/l/f #查是块设备、目录、字符设备、管道、符号链接、普通文件 -size n［c］#查长度为n块［或n字节］的文件 -depth #使查找在进入子目录前先行查找完本目录 -fstype #查位于某一类型文件系统中的文件，这些文件系统类型通常可在/etc/fstab中找到 -mount #查文件时不跨越文件系统mount点 -follow #如果遇到符号链接文件，就跟踪链接所指的文件 -cpio %; #查位于某一类型文件系统中的文件，这些文件系统类型通常可在/etc/fstab中找到 -mount #查文件时不跨越文件系统mount点 -follow #如果遇到符号链接文件，就跟踪链接所指的文件 -cpio #对匹配的文件使用cpio命令，将他们备份到磁带设备中 -prune #忽略某个目录 ===================================================== $find ~ -name ”*.txt“ -print #在$HOME中查.txt文件并显示 $find 。-name ”*.txt“ -print $find 。-name ”［A-Z］*“ -print #查以大写字母开头的文件 $find /etc -name ”host*“ -print #查以host开头的文件 $find 。-name ”［a-z］［a-z］［0–9］［0–9］.txt“ -print #查以两个小写字母和两个数字开头的txt文件 $find 。-perm 755 -print $find 。-perm -007 -exec ls -l {} \; #查所有用户都可读写执行的文件同-perm 777 $find 。-type d -print $find 。！-type d -print $find 。-type l -print $find 。-size +1000000c -print #查长度大于1Mb的文件

find和xargs的组合用法

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俄语名字的中文含义(引申义)

Мужские имена: Александр 亚历山大(希) 保卫者 Алексей 阿历克赛(希) 保卫 Анатолий 阿纳托利(希) 日出 Андрей 安德烈(希) 勇敢的 Антон 安东(希) 投入战斗 Борис 鲍里斯(俄，保) 为荣誉而斗争 Валентин 瓦连京(拉) 健康的 Валерий 瓦列里(拉) 强壮的 Василий 瓦西里(希) 统治的 Виктор 维克多(拉) 胜利者 Владимир 弗拉基米尔(斯) 拥有世界 Геннадий 根纳季(希) 高尚的 Евгений 叶夫根尼(希) 高尚的 Егор 叶戈尔(希) 农民 Ефим 叶菲姆(希) 好心肠的 Иван 伊万(古犹) 上帝珍爱 Игорь 伊戈尔(俄) 富裕之神保护 Илья 伊利亚(古犹) 我的上帝耶和华 Лев 列夫(希) 狮子 Леонид 列昂尼德(希) 狮子 Максим 马克西姆(拉) 最大的 Матвей 马特维(古犹) 上帝耶和华的礼物Михаил 米哈依尔(古犹) 如上帝一样 Никита 尼基塔(希) 胜利 Николай 尼古拉(希) 人民胜利 Олег 奥列格(斯堪的纳维亚) 神圣的 П?тр 彼得(希) 石头

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15个极好的Linux find命令示例

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