An HLLC Riemann solver for relativistic flows – II. Magnetohydrodynamics     

A. Mignone  G. Bodo 《Monthly notices of the Royal Astronomical Society》2006,368(3):1040-1054

An approximate Riemann solver for the equations of relativistic magnetohydrodynamics (RMHD) is derived. The Harten–Lax–van Leer contact wave (HLLC) solver, originally developed by Toro, Spruce and Spears, generalizes the algorithm described in a previous paper to the case where magnetic fields are present. The solution to the Riemann problem is approximated by two constant states bounded by two fast shocks and separated by a tangential wave. The scheme is Jacobian-free, in the sense that it avoids the expensive characteristic decomposition of the RMHD equations and it improves over the HLL scheme by restoring the missing contact wave.
Multidimensional integration proceeds via the single step, corner transport upwind (CTU) method of Colella, combined with the constrained transport (CT) algorithm to preserve divergence-free magnetic fields. The resulting numerical scheme is simple to implement, efficient and suitable for a general equation of state. The robustness of the new algorithm is validated against one- and two-dimensional numerical test problems.  相似文献   

Statistical description of the radiation field in a homogeneous medium of finite optical thickness     

A. G. Nikoghossian 《Astrophysics》2006,49(2):228-239

The problem of finding statistical averages which characterize the radiation field in a semi-infinite atmosphere has been discussed by the author in a series of papers. In this paper some of the results obtained there are generalized to media of finite optical thickness. The average number of scattering events undergone by a photon during its random walk in an atmosphere and the average time required for this are determined. Three different types of averages are considered, depending on the photon characteristics over which the averages are taken. Special attention is devoted to the asymptotic behavior of these quantities for media with large optical depths taking the influence of continuum absorption into account. __________ Translated from Astrofizika, Vol. 49, No. 2, pp. 263–275 (May 2006).  相似文献   

High-resolution observations of a complete sample of 27 FR II radio galaxies and quasars with 0.3 < z < 0.6     

G. M. Gilbert  J. M. Riley  M. J. Hardcastle  J. H. Croston  G. G. Pooley  P. Alexander 《Monthly notices of the Royal Astronomical Society》2004,351(3):845-890

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Radiation exposure and Mission Strategies for Interplanetary Manned Missions (REMSIM)   总被引：1，自引：0，他引：1  

C. Cougnet  N. B. Crosby  S. Eckersley  C. Foullon  V. Guarnieri  S. Guatelli  D. Heynderickx  A. Holmes-Siedle  C. Lobascio  S. Masiello  P. Nieminen  G. Parisi  P. Parodi  M. A. Perino  M. G. Pia  R. Rampini  P. Spillantini  V. Tamburini  E. Tracino 《Earth, Moon, and Planets》2004,94(3-4):279-285

Cosmic radiation is an important problem for human interplanetary missions. The “Radiation Exposure and Mission Strategies for Interplanetary Manned Missions–REMSIM” study is summarised here. They are related to current strategies and countermeasures to ensure the protection of astronauts from radiation during interplanetary missions, with specific reference to: radiation environment and its variability; radiation effects on the crew; transfer trajectories and associated fluences; vehicle and surface habitat concepts; passive and active shielding concepts; space weather monitoring and warning systems.  相似文献   

Radiative Transfer in Inhomogeneous Atmospheres. III     

A. G. Nikoghossian 《Astrophysics》2004,47(3):412-421

The approach proposed in the previous parts of this series of papers is used to solve the radiative transfer problem in scattering and absorbing multicomponent atmospheres. Linear recurrence relations are obtained for both the reflectance and transmittance of these kinds of atmospheres, as well as for the emerging intensities when the atmosphere contains energy sources. Spectral line formation in a one-dimensional inhomogeneous atmosphere is examined as an illustration of the possibility of generalizing our approach to the matrix case. It is shown that, in this case as well, the question reduces to solving an initial value problem for linear differential equations. Some numerical calculations are presented.  相似文献   

Magnetic Reconnection Solutions Based on a Generalized Ohm's law     

Craig  I.J.D.  Watson  P.G. 《Solar physics》2003,214(1):131-150

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Opposition polarimetry and photometry of S- and E-type asteroids     

Irina N Belskaya  Vasilij G Shevchenko  Yurij N Krugly  Yurij S Efimov  Alberto Cellino 《Icarus》2003,166(2):276-284

The first results of the observational program devoted to simultaneous investigation of asteroid polarimetric and photometric opposition phenomena are presented. UBVRI polarimetric and V-band photometric observations of the S-type Asteroid 20 Massalia and the E-type Asteroids 214 Aschera and 620 Drakonia were carried out in 1996-1999 down to phase angles of 0.08°, 0.7°, and 1.2°, correspondingly. The S-type Asteroid 20 Massalia is characterized by the pronounced brightness opposition surge with an amplitude larger than that observed for the E-type asteroids. A sharp peak of negative polarization at small phase angles was not observed for this asteroid. The value of polarization degree at phase angle α<1° is less than 0.5% for both S and E types. The negative polarization branches of S and especially E-asteroids have an asymmetrical shape. The phase angle at which the polarization minimum occurs is close to the angle at which non-linear increase begins in the asteroid magnitude phase curves. A relation of the observed effects to the mechanism of coherent backscattering is discussed.  相似文献   

Building blocks in hierarchical clustering scenarios and their connection with damped Lyα systems     

Sofía A. Cora  Patricia B. Tissera †  Diego G. Lambas ‡  Mirta B. Mosconi 《Monthly notices of the Royal Astronomical Society》2003,343(3):959-970

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Asteroseismological studies of three β Cephei stars: IL Vel, V433 Car and KZ Mus     

G. Handler  R. R. Shobbrook  F. F. Vuthela  L. A. Balona  F. Rodler  T. Tshenye 《Monthly notices of the Royal Astronomical Society》2003,341(3):1005-1019

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Ion Irradiation of Asphaltite: Optical Effects and Implications for Trans-Neptunian Objects and Centaurs     

Moroz  L. V.  Baratta  G.  Distefano  E.  Strazzulla  G.  Starukhina  L. V.  Dotto  E.  Barucci  M. A. 《Earth, Moon, and Planets》2003,92(1-4):279-289

Trans-Neptunian Objects (TNOs) and Centaurs show remarkable colour variationsin the visual and near-infrared spectral regions. Surface alteration processes such asspace weathering (e.g., bombardment with ions) and impact resurfacingmay play an important role in the colour diversity of such bodies. Ion irradiation ofhydrocarbon ices and their mixtures with water ice transforms neutral (grey) surfacecolours of ices to red and further to grey. Along with the ices, TNOs and Centaursprobably contain complex carbonaceous compounds, in particular, complexhydrocarbons. Unlike ices, such refractory organic materials have originally lowvisual albedos and red colours in the visible and near-infrared ranges. Here wepresent the first results of ion irradiation experiments on asphaltite. Asphaltite isa natural complex hydrocarbon material. The reflectance spectra of asphaltite inthe 0.4–0.8 μm range have been recorded before irradiation and after eachirradiation step. We demonstrate that irradiation of this red dark material with30 keV H⁺ and 15 keV N⁺ ions gradually transforms its colour from redto grey as a result of carbonization. A moderate increase in the visual albedo hasbeen observed. These results may imply that the surfaces of primitive red objectsoptically dominated by complex refractory organics may show a similar spaceweathering trend. Our laboratory results were compared with published coloursof TNOs and Centaurs. A broad variety of spectral colours observed for TNOs andCentaurs may be reproduced by various spectra of irradiated organics correspondingto different ion fluences. However, such objects probably also contain ices and silicatecomponents which show different space weathering trends. This fact, together with alack of information about albedos, may explain difficulties to reveal correlations between surface colours within TNO and Centaur populations and their other properties, such as absolute magnitudes and orbital parameters.  相似文献