排序方式: 共有22条查询结果,搜索用时 31 毫秒
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Douglas S. Hall Gregory W. Henry Dietmar Böhme Peter A. Brooks Sandy Chang Ales Dolzan George L. Fortier Robert E. Fried Russell M. Genet Bruce S. Grim James Hannon Darrel B. Hoff Kevin Krisciunas Howard J. Landis Howard P. Louth Larry P. Lovell Paul Nielsen Bobby E. Powell Harry D. Powell Don Pray Thomas R. Renner Charles W. Rogers Stephen Shervais Douglas M. Slauson Samuel Slote Harold J. Stelzer Arthur J. Stokes Jack C. Troeger Louis C. Turner Norman F. Wasson Kenneth W. Zeigler 《Journal of Astrophysics and Astronomy》1991,12(4):281-287
We present photoelectric photometry of λ And never before published, obtained between February 1982 and December 1990 at 29
different observatories. Then we combine it with all other photometry available to us (previously published, contained in
the I.A.U. Commission 27 Archives, and obtained with the Vanderbilt 16-inch automatic telescope but not yet published), to
yield a 14.8-year data base. Analysis reveals a long-term cycle in mean brightness, with a full range of 0m.15 and a period of 11.4 ± 0.4 years. Because most of our new photometry was concentrated in the 1983-84 observing season,
we analyze that one well-defined light curve with a two-spot model. Spot A keeps a 0m.04 amplitude throughout four rotation cycles whereas the amplitude of spot B diminishes from 0m.09 down almost to 0m.03. The spot rotation periods were 55d.9 ± 0d.6 and 520d.8 ± 1d.0, respectively. 相似文献
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Butonat, Trichlorfon und Dichlorvos sind für Escherichia coli und Enterobacter aerogenes erst in relativ hohen Konzentrationen akut toxisch. Eine negative Beeinflussung der Wachstunisrate tritt im Konzentrationsbereich ≧1000 mg 1−1 (Butonat, Trichloifon) bzw. ≧250 mg 1−1 (Dichlorvos) ein. Bis zu diesen Konzentrationsbereichen werden die Wirkstoffe durch die Bakterien inaktiviert bzw. metabolisiert. Die Bestimmung der Wachstunisrate erfolgt über den Sauerstoffverbrauch der Kultur im SAPROMAT AP 12. Die Wirkstoffkonzentrationen werden dünnschichtchromatographisch analysiert. 相似文献
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Zaid Bahaeldeen Vollert Florian Gibmeier Jens Mengel Lena Stelzer Oliver Schneider Achim 《Acta Geotechnica》2023,18(2):865-876
Acta Geotechnica - The hole erosion test (HET) was developed to simulate piping erosion and to study the erosion parameters of cohesive soils. The erosion rate in the HET is evaluated by the... 相似文献
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J. A. Eaton D. S. Hall G. W. Henry J. L. Hopkins K. Krisciunas H. J. Landis H. Louth E. H. Olsen T. R. Renner H. J. Stelzer 《Astrophysics and Space Science》1983,93(2):271-276
Photoelectric photometry obtained in 1971 and 1972 is compared with that obtained in 1980–81 and 1981–82 to derive a photometric period of 77 d .65. JD 2444636.0 is an epoch of minimum light. The full amplitude has been as large as 0 m .18 inV. Curiously, the mean light level has dropped by almost 0 m .2 over the last ten years. This binary is additionally interesting because of the recently discovered white dwarf secondary component and because unpublished radial velocity measures of Fekel show a large (0.1) eccentricity and an orbital period (57 d .1) very different from our photometric period. 相似文献
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Assessing the importance of seepage and springs to nitrate flux in a stream network in the Wisconsin sand plains
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Evaluating the flow paths that contribute to solute flux in stream networks can lead to greater understanding of the linkages between biogeochemistry and hydrology. We compared the contributions of groundwater in spring brooks and in seepage through the streambed to nitrate flux in the Emmons Creek network in the Wisconsin sand plains. We predicted that spring brooks would contribute disproportionately to nitrate flux due to the presumed higher advection rates in springs and less opportunity for nitrate removal relative to seeps. Nitrate flux was measured in 15 spring brooks that entered Emmons Creek. Nitrate flux from seepage was measured at the locations of 30 piezometers, based on Darcy's Law, and by a reach‐scale injection of Rhodamine water tracing (RWT). When seepage discharge was estimated from the RWT release, groundwater inputs from seepage and springs accounted for the discharge gain in the Emmons Creek channel. Springs brooks and seepage (based on the RWT release) contributed 37% and 63%, respectively, to nitrate flux inputs in the study reach. Contrary to our prediction, seeps contributed disproportionately to nitrate flux relative to their discharge. Relatively high rates of seepage discharge and higher than anticipated nitrate concentrations in the shallow pore water at seepage locations contributed to the unanticipated result. 相似文献
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P. Bonifacio E. Caffau P. Franois L. Sbordone H.‐G. Ludwig M. Spite P. Molaro F. Spite R. Cayrel F. Hammer V. Hill M. Nonino S. Randich B. Stelzer S. Zaggia 《Astronomische Nachrichten》2011,332(3):251-257
Some insight on the first generation of stars can be obtained from the chemical composition of their direct descendants, extremely metal‐poor stars (EMP), with metallicity less than or equal to 1/1000 of the solar metallicity. Such stars are exceedingly rare, the most successful surveys, for this purpose, have so far provided only about 100 stars with 1/1000 the solar metallicity and 4 stars with about 1/10000 of the solar metallicity. The Sloan Digital Sky Survey has the potential to provide a large number of candidates of extremely low metallicity. X‐shooter has the unique capability of performing the necessary follow‐up spectroscopy providing accurate metallicities and abundance ratios for several elements (Mg, Al, Ca, Ti, Cr, Sr,...) for EMP candidates. We here report on the results for the first two stars observed in the course of our Franco‐Italian X‐shooter GTO. The two stars were targeted to be of metallicity around –3.0, the analysis of the X‐shooter spectra showed them to be of metallicity around –2.0, but with a low α to iron ratio, which explains the underestimate of the metallicity from the SDSS spectra. The efficiency of X‐shooter allows an in situ study of the outer halo, for the two stars studied here we estimate distances of 3.9 and 9.1 kpc, these are likely the most distant dwarf stars studied in detail to date (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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M.A. Pogodin S. Hubrig R.V. Yudin M. Schller J.F. Gonzlez B. Stelzer 《Astronomische Nachrichten》2012,333(7):594-612
We present the results of our observations of eight magnetic Herbig Ae/Be stars obtained with the X‐shooter spectrograph mounted on UT2 at the VLT. X‐shooter provides a simultaneous, medium‐resolution and high‐sensitivity spectrum over the entire wavelength range from 300 to 2500 nm. We estimate the mass accretion rates (Ṁacc) of the targets from 13 different spectral diagnostics using empiric calibrations derived previously for T Tauri‐type stars and brown dwarfs. We have estimated the mass accretion rates of our targets, which range from 2 × 10–9 to 2 × 10–7 M⊙ yr–1. Furthermore, we have found accretion rate variability with amplitudes of 0.10–0.40 dex taking place on time scales from one day to tens of days. Additional future night‐to‐night observations need to be carried out to investigate the character of Ṁacc variability in details. Our study shows that the majority of the calibration relations can be applied to Herbig Ae/Be stars, but several of them need to be re‐calibrated on the basis of new spectral data for a larger number of Herbig Ae/Be stars (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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Katalin Olah Joel A. Eaton Douglas S. Hall Gregory W. Henry Edward W. Burke Jr. Carlson R. Chambliss Robert E. Fried Howard J. Landis Howard Louth Thomas R. Renner Harold J. Stelzer Richard P. Wasatonic 《Astrophysics and Space Science》1985,108(1):137-152
Investigating more than 270 nightly mean magnitudes of the long-period RS CVn binary HK Lac, we can draw some conclusions about the nature of its complicated light variations. The mean brightness, the apparent photometric period, and the shape of the light curve all show strong variations. Analysis with a starspot model, assuming two large spots and a general uniform spottedness, indicates two comparably large spots which appear to have maintained their separate identities for the last 15 yr and drifted in longitude separation from each other smoothly by only about 45°. The phase of the two spots indicates both are rotating very nearly synchronously with the orbital motion, one slightly (0.025%) faster and the other slightly (0.080%) slower. the latitudes of the two spots, one farther above the equator and one closer to the equator, are consistent with solar-type differential rotation and yield an estimate of 25±12° for the co-rotating latitude. A correlation between mean spot latitude and instantaneous photometric period yields another estimate of 31±2°, in agreement with the first. 相似文献