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821.
The shielding effect of plasma on the electrostatic potential due to a central nucleus is studied. The potential is determined by the Poisson equation with Boltzmann factor for the charge density of ions. The aim of this work is to find approximated analytical solutions, without the usual linearization hypothesis, by means of the technique of quasifractional approximants in two points. In a previous work (Martín and Pérez, 1994) a quasifractional fractional approximation was obtained, but the coefficients were found by means of the numerical solution of the differential equation. Now we find a complete analytical expression. The approximant found is highly precise in the range of validity of the physical model used. 相似文献
822.
William S. Burgett Michael M. Vick David S. Davis Matthew Colless Roberto De Propris Ivan Baldry Carlton Baugh Joss Bland-Hawthorn Terry Bridges Russell Cannon Shaun Cole Chris Collins Warrick Couch Nicholas Cross Gavin Dalton Simon Driver George Efstathiou Richard Ellis Carlos S. Frenk Karl Glazebrook Edward Hawkins Carole Jackson Ofer Lahav Ian Lewis Stuart Lumsden Steve Maddox Darren Madgwick Peder Norberg John A. Peacock Will Percival Bruce Peterson Will Sutherland Keith Taylor 《Monthly notices of the Royal Astronomical Society》2004,352(2):605-654
823.
The presence of matter in its different forms in a hexadimensional space-time, where gravitation is coupled to a conformal field, generates a class of cosmological solutions with very peculiar features: the initial proper distance between any two points of the space-time is infinite, following successive contraction and expansion phases in the evolution of the Universe. This behaviour defines a Anti-Big Bang Singular Cosmology. In this article we analyze this primordial cosmological scenario considering different matter forms and the effects of a Conformal Transformation on the metric. 相似文献
824.
Carlos E. López 《Astrophysics and Space Science》2004,290(3-4):439-447
With the advent of virtual observatories, most astrometry-oriented projects being currently developed—and those to come in the near future—will be greatly enriched. Among these projects it is worth mentioning double stars and multiple systems, proper-motion detections, identification of lost high-proper-motion stars, a detailed census of open cluster members, and precovery of natural satellites, minor planets and comets. A brief discussion of some of these studies is presented. To accomplish the goals proposed by the virtual observatories concept, a massive amount of high-quality astrometric data is needed in advance. It is shown that today's astrometry is about to ready to face these new challenges. 相似文献
825.
826.
Carlos Osácar Jesús Palacián Manuel Palacios 《Celestial Mechanics and Dynamical Astronomy》1995,62(1):93-98
A numerical algorithm to evaluate the dilogarithmic function of a complex argument is proposed. The use of the dilogarithm in celestial mechanics appears in the exact Delaunay normalization of some functions involving the equation of the centre. 相似文献
827.
Ricardo Génova-Santos José Alberto Rubiño-Martín Rafael Rebolo † Kieran Cleary ‡ Rod D. Davies Richard J. Davis Clive Dickinson § Nelson Falcón ‡‡ Keith Grainge Carlos M. Gutiérrez Michael P. Hobson Michael E. Jones ¶ Rüdiger Kneissl Katy Lancaster Carmen P. Padilla-Torres Richard D. E. Saunders Paul F. Scott Angela C. Taylor ¶ Robert A. Watson †† 《Monthly notices of the Royal Astronomical Society》2005,363(1):79-92
828.
N. Rea G. L. Israel T. Oosterbroek S. Campana S. Zane R. Turolla V. Testa M. Méndez L. Stella 《Astrophysics and Space Science》2007,308(1-4):505-511
We report here on X-ray and IR observations of the Anomalous X-ray Pulsar (AXP) 1RXS J170849-400910. First, we report on new XMM-Newton, Swift-XRT and Chandra observations of this AXP, which confirm the intensity–hardness correlation observed in the long term X-ray monitoring of this source. These new X-ray observations show that the AXP flux is rising again, and the spectrum hardening. If the increase of the source intensity is indeed connected with the glitches and a possible bursting activity, we expect this source to enter in a bursting active phase around 2006–2007. Second, we report on deep IR observations of 1RXS J170849-400910, taken with the VLT-NACO adaptive optics, showing that there are many weak sources consistent with the AXP position. Neither star A or B, as previously proposed by different authors, might yet be conclusively recognised as the IR counterpart of 1RXS J170849-400910. Third, using Monte Carlo simulations, we re-address the calculation of the significance of the absorption line found in a phase-resolved spectrum of this source, and interpreted as a resonant scattering cyclotron feature. 相似文献
829.
Summary TheIAU Symposium No. 61 (Perth, 1973, “New Problems in Astrometry’) makes clear that radiosources will play an important role for astrometry
in view of the linkage of reference systems.
The purposes developed later were to link the various systems from the earth and the solar system to the most inertial possible
one.
Extragalactic radiosources are the most reliable objects but they are faint. So, intermediate objects are needed. Among them
the radiostars, optical objects having radioemission at a certain level and for given frequencies have a fundamental and key
position.
Most of such radiostars are double or multiple ‘binaries’ as it can be seen from the list of reference stars issued by the
Working Group of Commission 24, Working Group created in 1978. The last issue of the core list of radiostars was presented
by Ch. de Vegt (Chairman of the WG) on the occasion of the last General Assembly of the IAU (November 1985).
A recent study of the system α Scorpii (Antares) has shown that the data concerning the magnitude and the spectral type are
not accurate enough, according to the accuracy obtained for the astrometric position (±0
.
s
003 for an astrolabe campaign in right ascension).
There is also a need for better knowledge about the orbits. In the case of the astrolabe observations, if the distance between
the components in <3″ the astrometric position concerns the photocenter and accurate physical properties are needed for comparison
with the radio position.
Better astrophysical properties are strongly needed for all radiostars to be used as references, during the time the astrometrists
have to improve the accuracy of their measurements both in optical and radio fields.
Presented by S. Débarbat. 相似文献
830.
Bruce E. Frey J.Rubén Lara-Lara Lawrence F. Small 《Estuarine, Coastal and Shelf Science》1983,17(2):213-218
The eruption of Mt Saint Helens on 18 May 1980 resulted in a massive increase in suspended particulate material in the Columbia River Estuary, producing a substantial increase in light attenuation. Since photosynthesis in the estuarine water column is partly controlled by the depth of light penetration in the water, photosynthesis was reduced by about 75% during the period of increased turbidity. It took about five weeks for the estuary to clear. Although primary production within the estuarine water column was greatly diminished during this period, the flux of particulate carbon through the estuary was high, and the total production we estimate to have been lost amounted to only about 2% of the total particulate carbon flux just after the eruption. That the high levels of turbidity in the estuary did not induce a severe fall in the phytoplankton population is evidence that phytoplankton biomass concentrations in the Columbia River Estuary are mostly a function of import from the Columbia River, rather than a function of in situ production. 相似文献