The X-ray and extreme-ultraviolet flux evolution of SS Cygni throughout outburst     

Peter J. Wheatley  Christopher W. Mauche  Janet A. Mattei 《Monthly notices of the Royal Astronomical Society》2003,345(1):49-61

We present the most complete multiwavelength coverage of any dwarf nova outburst: simultaneous optical, Extreme Ultraviolet Explorer and Rossi X-ray Timing Explorer observations of SS Cygni throughout a narrow asymmetric outburst. Our data show that the high-energy outburst begins in the X-ray waveband 0.9–1.4 d after the beginning of the optical rise and 0.6 d before the extreme-ultraviolet rise. The X-ray flux drops suddenly, immediately before the extreme-ultraviolet flux rise, supporting the view that both components arise in the boundary layer between the accretion disc and white dwarf surface. The early rise of the X-ray flux shows that the propagation time of the outburst heating wave may have been previously overestimated.
The transitions between X-ray and extreme-ultraviolet dominated emission are accompanied by intense variability in the X-ray flux, with time-scales of minutes. As detailed by Mauche & Robinson, dwarf nova oscillations are detected throughout the extreme-ultraviolet outburst, but we find they are absent from the X-ray light curve.
X-ray and extreme-ultraviolet luminosities imply accretion rates of  3 × 10¹⁵ g s⁻¹  in quiescence,  1 × 10¹⁶ g s⁻¹  when the boundary layer becomes optically thick, and  ∼10¹⁸ g s⁻¹  at the peak of the outburst. The quiescent accretion rate is two and a half orders of magnitude higher than predicted by the standard disc instability model, and we suggest this may be because the inner accretion disc in SS Cyg is in a permanent outburst state.  相似文献   

居民收入与通信网络市场经济效益研究--以河北省通信网络为实例     

刘江林  李应良  石宏宇 《成都信息工程学院学报》2005,20(6):662-666

利用Logisitic曲线模型和扩展支撑模型对居民可支配收入预测和单项消费预测，以河北省居民的收入及其消费支出为实例，研究了城镇居民和农民的可支配收入分配和单项边际消费倾向，合理建立了预测模型，并理论计算了1999～2003年的通信消费方面的边际消费倾向、预测了2004～2008年通信消费情况。最后，根据预测结果对通信网络建设提出了一些有价值的建议。  相似文献   

Correcting systematic effects in a large set of photometric light curves     

O. Tamuz  T. Mazeh  S. Zucker † 《Monthly notices of the Royal Astronomical Society》2005,356(4):1466-1470

We suggest a new algorithm to remove systematic effects in a large set of light curves obtained by a photometric survey. The algorithm can remove systematic effects, such as those associated with atmospheric extinction, detector efficiency, or point spread function changes over the detector. The algorithm works without any prior knowledge of the effects, as long as they linearly appear in many stars of the sample. The approach, which was originally developed to remove atmospheric extinction effects, is based on a lower rank approximation of matrices, an approach which has already been suggested and used in chemometrics, for example. The proposed algorithm is especially useful in cases where the uncertainties of the measurements are unequal. For equal uncertainties, the algorithm reduces to the Principal Component Analysis (PCA) algorithm. We present a simulation to demonstrate the effectiveness of the proposed algorithm and we point out its potential, in the search for transit candidates in particular.  相似文献   

Nonlinear impact monitoring: line of variation searches for impactors     

Andrea Milani  Steven R. Chesley  Giacomo Tommei 《Icarus》2005,173(2):362-384

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The nature of Europa's dark non-ice surface material: Spatially-resolved high spectral resolution spectroscopy from the Keck telescope     

John R. Spencer  William M. Grundy  Robert W. Carlson  Gary B. Hansen 《Icarus》2006,182(1):202-210

We present new 1.45-1.75 μm spectra of Europa's dark non-ice material with a spectral resolution (λ/δλ) of 1200, obtained by using adaptive optics on the Keck telescope to spatially separate the spectrum of the non-ice material from that of the surrounding ice-rich regions. Despite the great increase in spectral resolution over the previous best spectra of the non-ice material, taken with Galileo's near-infrared mapping spectrometer (NIMS) with λ/δλ=66, no new fine-scale spectral structure is revealed. The smoothness of the spectra is inconsistent with available laboratory spectra of crystalline hydrated salts at Europa temperatures, but is more consistent with various combinations of non-crystalline hydrated salts and/or hydrated sulfuric acid, as have been matched to the lower-resolution NIMS spectra.  相似文献   

WR 143: a Wolf–Rayet binary     

Watson P. Varricatt  Nagarhalli M. Ashok 《Monthly notices of the Royal Astronomical Society》2006,365(1):127-133

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蛤蜊科3种贝类16SrRNA基因片段及ITS2核苷酸序列分析   总被引：4，自引：0，他引：4  

孟学平高如承  董志国阎斌伦程汉良  李艳杰陈建安 《广东海洋大学学报》2006,26(4):8-13

利用PCR技术分别扩增连云港及启东沿海蛤蜊科的西施舌（Coelomactra antiquata）、中国蛤蜊（Mactra chinensis）和四角蛤蜊（Mactra veneriformis）3种双壳贝的16SrRNA基因片段和ITS2核苷酸序列．测序后用DNAstar软件分析了核苷酸差异。结果显示：三种贝类16SrRNA基因片段长度相同，均为306bp（去除引物）．核苷酸存在多态性。共有45个变异位点，54个核苷酸发生了变异。全部为碱基置换。西施舌与中国蛤蜊此片段核苷酸的同源性为88．9％．与四角蛤蜊的同源性为88．6％．中国蛤蜊与四角蛤蜊的同源性为90．6％。三种蛤蜊ITS2序列分别为390bp（西施舌）、441bp（四角蛤蜊）和466bp（中国蛤蜊）。存在长度多态性．ITS2核苷酸差异分析结果显示．西施舌与中国蛤蜊的同源性为70．9％-71．1％，西施舌与四角蛤蜊的为70．5％-71．0％。中国蛤蜊与四角蛤蜊的同源性为88．1％-88．8％。ITS2序列分析结果与16SrRNA基因片段分析结果一致．2种分子分析法均显示中国蛤蜊与四角蛤蜊的亲缘关系近。  相似文献   

The Faint Sky Variability Survey – I. Goals and data reduction process     

P. J. Groot  P. M. Vreeswijk  M. E. Huber  M. E. Everett  S. B. Howell  G. Nelemans  J. van Paradijs  E. P. J. van den Heuvel  T. Augusteijn  E. Kuulkers  R. G. M. Rutten  J. Storm 《Monthly notices of the Royal Astronomical Society》2003,339(2):427-434

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Hydrated sulphuric acid in dense molecular clouds     

Flavio Scappini  Cesare Cecchi-Pestellini  Harvey Smith  William Klemperer  Alexander Dalgarno 《Monthly notices of the Royal Astronomical Society》2003,341(2):657-661

We consider sulphur depletion in dense molecular clouds, and suggest hydrated sulphuric acid, H₂SO₄ ·  n H₂O, as a component of interstellar dust in icy mantles. We discuss the formation of hydrated sulphuric acid in collapsing clouds and its instability in heated regions in terms of the existing hot core models and observations. We also show that some features of the infrared spectrum of hydrated sulphuric acid have correspondence in the observed spectra of young stellar objects.  相似文献   

The NAIAD experiment for WIMP searches at Boulby mine and recent results     

B. Ahmed  G. J. Alner  H. Araujo  J. C. Barton  A. Bewick  M. J. Carson  D. Davidge  J. V. Dawson  T. Gamble  S. P. Hart  R. Hollingworth  A. S. Howard  W. G. Jones  M. K. Joshi  V. A. Kudryavtsev  T. B. Lawson  V. Lebedenko  M. J. Lehner  J. D. Lewin  P. K. Lightfoot  I. Liubarsky  R. Lüscher  J. E. McMillan  B. Morgan  G. Nicklin  S. M. Paling  R. M. Preece  J. J. Quenby  J. W. Roberts  M. Robinson  N. J. T. Smith  P. F. Smith  N. J. C. Spooner  T. J. Sumner  D. R. Tovey 《Astroparticle Physics》2003,19(6):691-702

The NAIAD experiment (NaI Advanced Detector) for weakly interacting massive particle (WIMP) dark matter searches at Boulby mine (UK) is described. The detector consists of an array of encapsulated and unencapsulated NaI(Tl) crystals with high light yield. Six crystals are collecting data at present. Data accumulated by four of them (10.6 kg × year exposure) have been used to set upper limits on the WIMP–nucleon spin-independent and WIMP–proton spin-dependent cross-sections. Pulse shape analysis has been applied to discriminate between nuclear recoils, as may be caused by WIMP interactions, and electron recoils due to gamma background. Various calibrations of crystals are presented.  相似文献