244,773 research outputs found

    How Saturated are Absorption Lines in the Broad Absorption Line Quasar PG 1411+442 ?

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    Recently, convincing evidence was found for extremely large X-ray absorption by column densities >1023cm−2> 10^{23} cm^{-2} in broad absorption line quasars. One consequence of this is that any soft X-ray emission from these QSOs would be the scattered light or leaked light from partially covering absorbing material. A detection of the unabsorbed soft X-ray and absorbed hard X-ray compo nent will allow to determine the total column density as well as the effective covering factor of the absorbing material, which can be hardly obtained from the UV absorption lines. Brinkmann et al. (1999) showed that both the unabsorbed and absorbed components are detected in the nearby very bright broad absorption line quasar PG 1411+442. In this letter, we make a further analysis of the broad band X-ray spectrum and the UV spectrum from HST, and demonstrate that broad absorption lines are completely saturated at the bottom of absorption troughs.Comment: 6 pages, 3 postscript figures. to appear in Astrophy. J. Letter

    Relationships of the Genera \u3ci\u3eAcanthametropus, Analetris,\u3c/i\u3e and \u3ci\u3eSiphluriscus\u3c/i\u3e, and Re-Evaluation of Their Higher Classification (Ephemeroptera: Pisciforma)

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    The historical higher classification of the genera Acanthametropus Tshernova, Analetris Edmunds, and Siphluriscus Ulmer is reviewed. The first comprehensive generic description of Siphluriscus is given, and first figures of wings are provided. A cladistic analysis of adult and larval characters of Acanthametropus and Analetris. and adult characters of Siphluriscus reveal a close relationship between the former two genera, which represent a well-defined clade based on five identified synapomorphies; however, Siphluriscus, which has been classified with them in the past, does not share any apomorphies with them but instead shares apomorphies with the genera of Siphlonuridae sensu stricto. Acanthametropus and Analetris are recombined in the family Acanthametropodidae, suppressing Analetrididae; and Siphluriscus is reassigned to the family Siphlonuridae sensu stricto, although taxon rank for both of these clades is still tentative and awaits comparative cladistic analysis of the entire suborder Pisciforma. The relationship to each other of these clades also remains in doubt. Stackelbergisca Tshernova, a fossil genus formerly classified with the three extant genera apparently does not share any of the 11 apomorphies used in this study, and is placed as family incertae within the Pisciforma

    Heat transfer and fluid mechanics measurements in transitional boundary layer flows

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    Experimental results are presented to document hydrodynamic and thermal development of flat-plate boundary layers undergoing natural transition. Local heat transfer coefficients, skin friction coefficients and profiles of velocity, temperature and Reynolds normal and shear stresses are presented. A case with no transition and transitional cases with 0.68% and 2.0% free-stream disturbance intensities were investigated. The locations of transition are consistent with earlier data. A late-laminar state with significant levels of turbulence is documented. In late-transitional and early-turbulent flows, turbulent Prandtl number and conduction layer thickness values exceed, and the Reynolds analogy factor is less than, values previously measured in fully turbulent flows

    Atmospheric turbulence simulation techniques with application to flight analysis

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    Statistical modeling of atmospheric turbulence is discussed. The statistical properties of atmospheric turbulence, in particular the probability distribution, the spectra, and the coherence are reviewed. Different atmospheric turbulence simulation models are investigated, and appropriate statistical analyses are carried out to verify their validity. The models for simulation are incorporated into a computer model of aircraft flight dynamics. Statistical results of computer simulated landings for an aircraft having characteristics of a DC-8 are reported for the different turbulence simulation techniques. The significance of various degrees of sophistication in the turbulence simulation techniques on the landing performance of the aircraft is discussed
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