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951.
M. Anna Lakshmi S. Umapathy O. Prakash V. Vasanth 《Astrophysics and Space Science》2011,332(2):373-378
The paper investigates the effects of thermal conductivity and non-uniform magnetic field on the gravitational instability
of a non-uniformly rotating infinitely extending axisymmetric cylinder in a homogeneous heat conducting medium. The non-uniform
rotation and magnetic field are supposed to act along θ and z directions of the cylinder. It is found that the gravitational instability of this general problem is determined by the same
criterion as obtained by Dhiman and Dadwal (Astrophys. Space Sci. 325(2):195–200, 2010) for the self-gravitating isothermal medium in the presence of non-uniform rotation and magnetic field with the only difference
that adiabatic sound velocity is now replaced by the isothermal sound velocity. It is found that the thermal conductivity
has stabilizing effect on the onset of gravitational instability. Further, the stabilizing/destabilizing effect of the non-uniform
magnetic field on the gravitational instability of heat conducting medium has been discussed and is illustrated by considering
some special forms of the basic magnetic fields. 相似文献
952.
Lorenzo Iorio Herbert I. M. Lichtenegger Matteo Luca Ruggiero Christian Corda 《Astrophysics and Space Science》2011,331(2):351-395
Recent years have seen increasing efforts to directly measure some aspects of the general relativistic gravitomagnetic interaction
in several astronomical scenarios in the solar system. After briefly overviewing the concept of gravitomagnetism from a theoretical
point of view, we review the performed or proposed attempts to detect the Lense-Thirring effect affecting the orbital motions
of natural and artificial bodies in the gravitational fields of the Sun, Earth, Mars and Jupiter. In particular, we will focus
on the evaluation of the impact of several sources of systematic uncertainties of dynamical origin to realistically elucidate
the present and future perspectives in directly measuring such an elusive relativistic effect. 相似文献
953.
K. A. Firoz J. Hwang I. Dorotovič T. Pintér Subhash C. Kaushik 《Astrophysics and Space Science》2011,331(2):469-484
Cosmic rays registered by Neutron Monitor on the surface of the Earth are believed to originate from outer space, and sometimes
also from the exotic objects of the Sun. Whilst the intensities of the cosmic rays are observed to be enhanced with sudden,
sharp and short-lived increases, they are termed as ground level enhancements (GLEs). They are the occurrences in solar cosmic
ray intensity variations on short-term basis, so different solar factors erupted from the Sun can be responsible for causing
them. In this context, an attempt has been made to determine quantitative relationships of the GLEs having peak increase >5%
with simultaneous solar, interplanetary and geophysical factors from 1997 through 2006, thereby searching the responsible
factors which seem to cause the enhancements. Results suggest that GLE peaks might be caused by solar energetic particle fluxes
and solar flares. The proton fluxes which seemed to cause GLE peaks were also supported by their corresponding fluences. For
most of the flares, the time integrated rising portion of the flare emission refers to the strong portion of X-ray fluxes
which might be the concern to GLE peak. On an average, GLE peak associated X-ray flux (0.71×10−4 w/m2) is much stronger than GLE background associated X-ray flux (0.11×10−6 w/m2). It gives a general consent that the GLE peak is presumably caused by the solar flare. Coronal mass ejection alone does
not seem to cause GLE. Coronal mass ejection presumably causes geomagnetic disturbances characterized by geomagnetic indices
and polarities of interplanetary magnetic fields. 相似文献
954.
Jérôme Pétri 《Astrophysics and Space Science》2011,331(2):555-563
Neutron stars are the densest objects known in the Universe. Being the final product of stellar evolution, their internal
composition and structure is rather poorly constrained by measurements. 相似文献
955.
Ahmad Rami El-Nabulsi 《Astrophysics and Space Science》2011,332(1):37-42
We investigate the late-time dynamics of a four-dimensional universe based on the effective action of a Brans-Dicke scalar
field in the presence of the matter source term, conformal coupling of the scalar curvature to the scalar field, a dynamical
cosmological constant and Gauss-Bonnet higher-order terms in the scalar curvature. Many new interesting features are revealed
and discussed in some details. 相似文献
956.
Jakob Walcher Brent Groves Tamás Budavári Daniel Dale 《Astrophysics and Space Science》2011,331(1):1-51
Fitting the spectral energy distributions (SEDs) of galaxies is an almost universally used technique that has matured significantly
in the last decade. Model predictions and fitting procedures have improved significantly over this time, attempting to keep
up with the vastly increased volume and quality of available data. We review here the field of SED fitting, describing the
modelling of ultraviolet to infrared galaxy SEDs, the creation of multiwavelength data sets, and the methods used to fit model
SEDs to observed galaxy data sets. We touch upon the achievements and challenges in the major ingredients of SED fitting,
with a special emphasis on describing the interplay between the quality of the available data, the quality of the available
models, and the best fitting technique to use in order to obtain a realistic measurement as well as realistic uncertainties.
We conclude that SED fitting can be used effectively to derive a range of physical properties of galaxies, such as redshift,
stellar masses, star formation rates, dust masses, and metallicities, with care taken not to over-interpret the available
data. Yet there still exist many issues such as estimating the age of the oldest stars in a galaxy, finer details of dust
properties and dust-star geometry, and the influences of poorly understood, luminous stellar types and phases. The challenge
for the coming years will be to improve both the models and the observational data sets to resolve these uncertainties. The
present review will be made available on an interactive, moderated web page (), where the community can access and change the text. The intention is to expand the text and keep it up to date over the
coming years. 相似文献
957.
We investigate the background dynamics when dark energy is coupled to dark matter in the universe described by loop quantum
cosmology. We consider dark energy of the form modified Chaplygin gas. The dynamical system of equations is solved numerically
and a stable scaling solution is obtained. It henceforth resolves the famous cosmic coincidence problem in modern cosmology.
The statefinder parameters are also calculated to classify this dark energy model. 相似文献
958.
Einar Tandberg-Hanssen 《Solar physics》2011,269(2):237-251
The article starts with an autobiographical account, where the author relates how his several study-trips abroad gradually
led him to the study of solar physics in general, and prominences particularly. 相似文献
959.
We explore the hard X-ray source distributions of an C1.1 flare occurred on 14 December 2007. Both Hinode/EIS and RHESSI observations are used. One of EIS rasters perfectly covers the double hard X-ray footpoints, where the EUV
emission appears strong from the cool line of He ii (log T=4.7) to the hot line of Fe xvi (log T=6.4). We analyze RHESSI X-ray images at different energies and different times before the hard X-ray maximum. The results
show a similar topology for the time-dependent source distribution (i.e. at 14:14:35 UT) as that for energy-dependent source distribution (i.e. at a given energy band of 6 – 9 keV) overlapped on EUV bright kernels, which seems to be consistent with the evaporation
model. 相似文献
960.
Similarity model of feed support system for FAST 总被引:1,自引:0,他引:1
A new design of feed support system for Five hundred meter Aperture Spherical Telescope (FAST) is proposed in this paper.
According to the similarity theory, a 1:15 scale model of feed support system has been built to make systemic research on
the feasibility of the system. Then the control system and hardware structure of the feed support system are illustrated.
A complete astronomical observation track is run by the scale model and the experiments results demonstrate that the new feed
support system can satisfy the observation accuracy requirement of FAST. 相似文献