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981.
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
982.
983.
Anthony M. Spencer Per Ivar Briskeby Lone Dyrmose Christensen Rune Foyn Marie KjФlleberg Erling Kvadsheim Ian Knight Morten Rye-Larsen John Williams 《《幕》》2008,31(1):115-124
Offshore exploration in Norway and Denmark-in the North Sea, the Norwegian Sea and the Barents Sea-has involved drilling about 850 wildcat wells, resulting in about 300 oil and gas finds, of which 84 are fields with production. The recoverable resources of all these finds total about 65 billion barrels of oil equivalent. Almost all these hydrocarbons come from a Jurassic source and the main reservoirs and traps are Jurassic sandstones in fault blocks and Paleocene sandstones or Cretaceous chalks in gentle domes. The article describes four major fields-Ekofisk, Gullfaks, Ormen Lange and SnФhvitto illustrate some of the many challenges in developing and producing the hydrocarbons.
Elsewhere in Norden, there has been much less exploration. Drilling results have mostly been negative in mainland Sweden, onshore Denmark, onshore Svalbard and on- and offshore West Greenland. Minor oil finds have been made in Palaeozoic rocks in the Baltic Sea. The first wells have recently been drilled off the Faroe Islands, resulting in one discovery. No drilling has taken place on- or offshore East Greenland.
As a result of the hydrocarbon activities in Norway and Denmark, petroleum geoscience there has flourished, with 2000 geoscientists currently employed in the industry, many technical innovations made, a wealth of publically available information and a great increase in the understanding of the geology. 相似文献
Elsewhere in Norden, there has been much less exploration. Drilling results have mostly been negative in mainland Sweden, onshore Denmark, onshore Svalbard and on- and offshore West Greenland. Minor oil finds have been made in Palaeozoic rocks in the Baltic Sea. The first wells have recently been drilled off the Faroe Islands, resulting in one discovery. No drilling has taken place on- or offshore East Greenland.
As a result of the hydrocarbon activities in Norway and Denmark, petroleum geoscience there has flourished, with 2000 geoscientists currently employed in the industry, many technical innovations made, a wealth of publically available information and a great increase in the understanding of the geology. 相似文献
984.
Andrea B. Rieser Yongjiang Liu Johann Genser Franz Neubauer Robert Handler Xiao‐Hong Ge 《地学学报》2006,18(1):79-87
New single‐grain 40Ar/39Ar detrital white‐mica ages from the Lulehe section at the eastern Qaidam Basin yield uniform Permian ages between 250 ± 3 and 279 ± 3 Ma throughout the whole Cenozoic sequence. This is inconsistent with the present hinterland, which is composed of early Palaeozoic metamorphic units with subordinate early Palaeozoic and few Permian granites. The new data indicate that Permian tectonic units are likely more widespread at the north‐eastern margin of the Tibetan plateau as known at present, particularly within the Qilian Mountains. The preferred explanation is that the Qaidam block represents a rigid indenter, which indented during late Tertiary times into early Palaeozoic orogenic units. This is consistent with recent findings of a NW‐trending sinistral Permian ductile shear zone and a dextral, NW‐trending Tertiary fault system close to the north‐eastern margin of the Qaidam Basin. 相似文献
985.
Matthew R. Bate Ian A. Bonnell 《Monthly notices of the Royal Astronomical Society》2005,356(4):1201-1221
We investigate the dependence of stellar properties on the mean thermal Jeans mass in molecular clouds. We compare the results from the two largest hydrodynamical simulations of star formation to resolve the fragmentation process down to the opacity limit, the first of which was reported by Bate, Bonnell & Bromm. The initial conditions of the two calculations are identical except for the radii of the clouds, which are chosen so that the mean densities and mean thermal Jeans masses of the clouds differ by factors of 9 and 3, respectively.
We find that the denser cloud, with the lower mean thermal Jeans mass, produces a higher proportion of brown dwarfs and has a lower characteristic (median) mass of the stars and brown dwarfs. This dependence of the initial mass function (IMF) on the density of the cloud may explain the observation that the Taurus star-forming region appears to be deficient in brown dwarfs when compared with the Orion Trapezium cluster. The new calculation also produces wide binaries (separations >20 au), one of which is a wide binary brown dwarf system.
Based on the hydrodynamical calculations, we develop a simple accretion/ejection model for the origin of the IMF. In the model, all stars and brown dwarfs begin with the same mass (set by the opacity limit for fragmentation) and grow in mass until their accretion is terminated stochastically by their ejection from the cloud through dynamically interactions. The model predicts that the main variation of the IMF in different star-forming environments should be in the location of the peak (due to variations in the mean thermal Jeans mass of the cloud) and in the substellar regime. However, the slope of the IMF at high masses may depend on the dispersion in the accretion rates of protostars. 相似文献
We find that the denser cloud, with the lower mean thermal Jeans mass, produces a higher proportion of brown dwarfs and has a lower characteristic (median) mass of the stars and brown dwarfs. This dependence of the initial mass function (IMF) on the density of the cloud may explain the observation that the Taurus star-forming region appears to be deficient in brown dwarfs when compared with the Orion Trapezium cluster. The new calculation also produces wide binaries (separations >20 au), one of which is a wide binary brown dwarf system.
Based on the hydrodynamical calculations, we develop a simple accretion/ejection model for the origin of the IMF. In the model, all stars and brown dwarfs begin with the same mass (set by the opacity limit for fragmentation) and grow in mass until their accretion is terminated stochastically by their ejection from the cloud through dynamically interactions. The model predicts that the main variation of the IMF in different star-forming environments should be in the location of the peak (due to variations in the mean thermal Jeans mass of the cloud) and in the substellar regime. However, the slope of the IMF at high masses may depend on the dispersion in the accretion rates of protostars. 相似文献
986.
987.
The Solar Radiation and Climate Experiment (SORCE) Mission for the NASA Earth Observing System (EOS) 总被引:1,自引:0,他引:1
The NASA Earth Observing System (EOS) is an advanced study of Earth's long-term global changes of solid Earth, its atmosphere,
and oceans and includes a coordinated collection of satellites, data systems, and modeling. The EOS program was conceived
in the 1980s as part of NASA's Earth System Enterprise (ESE). The Solar Radiation and Climate Experiment (SORCE) is one of
about 20 missions planned for the EOS program, and the SORCE measurement objectives include the total solar irradiance (TSI)
and solar spectral irradiance (SSI) that are two of the 24 key measurement parameters defined for the EOS program. The SORCE
satellite was launched in January 2003, and its observations are improving the understanding and generating new inquiry regarding
how and why solar variability occurs and how it affects Earth's energy balance, atmosphere, and long-term climate changes. 相似文献
988.
989.
Mutual Potential of Homogeneous Polyhedra 总被引:2,自引:0,他引:2
Robert A. Werner Daniel J. Scheeres 《Celestial Mechanics and Dynamical Astronomy》2005,91(3-4):337-349
The mutual gravitational potential between a pair of homogeneous polyhedra is expressed using an infinite series. The nested
volume integrals are evaluated analytically and result in simple tensor expressions containing no special functions. However,
complexity increases as O(6
n
), where n is the term degree. An alternate formulation due to Liebenthal is also presented. 相似文献
990.
Robert Connon Smith Otto Mehes Dave Vande Putte Nigel A. Hawkins 《Monthly notices of the Royal Astronomical Society》2005,360(1):364-374
Simultaneous spectroscopic and photometric observations of the Z Cam type dwarf nova SY Cancri were used to obtain absolute flux calibrations. A comparison of the photometric calibration with a wide-slit spectrophotometric calibration showed that either method is equally satisfactory. A radial velocity study of the secondary star, made using the far-red Na i doublet, yielded a semi-amplitude of K 2 = 127 ± 23 km s−1 . Taking the published value of 86 ± 9 km s−1 for K 1 gives a mass ratio of q = M 2 / M 1 = 0.68 ± 0.14 ; this is very different from the value of 1.13 ± 0.35 quoted in the literature. Using the new lower mass ratio, and constraining the mass of the white dwarf to be within reasonable limits, then leads to a mass for the secondary star that is substantially less than would be expected for its orbital period if it satisfied a main-sequence mass–radius relationship. We find a spectral type of M0 that is consistent with that expected for a main-sequence star of the low mass we have found. However, in order to fill its Roche lobe, the secondary must be significantly larger than a main-sequence star of that mass and spectral type. The secondary is definitely not a normal main-sequence star. 相似文献