5,552 research outputs found
pSESYNTH project: Community mobilization for a multi-disciplinary paleo database of the Global South
How to enhance paleoscientific research, collaboration and application in the Global South? The INQUA-funded multi-year pSESYNTH project envisions the first multi-disciplinary Holocene paleo database through a collaborative vision for past human–environmental systems in the Global South, and their future sustainability
Lithium Production in Companions of Accreting X-Ray Binaries by Neutron Spallation of C,N,O Elements
We examine the processes which could lead to the observed enhancement of Li
and possibly other light elements (Be, B) in the companions of a number of
X-ray novae. We conclude that one of the most promising mechanisms is the
spallation of CNO elements on the surface of the companion induced by the
neutron flux produced in the hot accretion flow onto the compact object. Direct
production of the observed Li and its deposition onto the dwarf companion seem
less likely, mainly because of the possibility of its destruction in the
production region itself and difficulties in its deposition associated with the
configuration of the companion's magnetic field. We discuss other potential
observables of the above scenario.Comment: 23 pages Latex, of which 5 pages of tables, to appear in the
Astrophysical Journal, Vol 512, Feb 10 issu
Non-stationary Rayleigh-Taylor instability in supernovae ejecta
The Rayleigh-Taylor instability plays an important role in the dynamics of
several astronomical objects, in particular, in supernovae (SN) evolution. In
this paper we develop an analytical approach to study the stability analysis of
spherical expansion of the SN ejecta by using a special transformation in the
co-moving coordinate frame. We first study a non-stationary spherical expansion
of a gas shell under the pressure of a central source. Then we analyze its
stability with respect to a no radial, non spherically symmetric perturbation
of the of the shell. We consider the case where the polytropic constant of the
SN shell is and we examine the evolution of a arbitrary shell
perturbation. The dispersion relation is derived. The growth rate of the
perturbation is found and its temporal and spatial evolution is discussed. The
stability domain depends on the ejecta shell thickness, its acceleration, and
the perturbation wavelength.Comment: 16 page
A Possible Explanation of the Radio Afterglow of GRB980519: The Dense Medium Effect
GRB{980519} is characterized by its rapidly declining optical and X-ray
afterglows. Explanations of this behavior include models invoking a dense
medium environment which makes the shock wave evolve quickly into the
sub-relativistic phase, a jet-like outflow, and a wind-shaped circumburst
medium environment. Recently, Frail {et al}. (1999a) found that the latter two
cases are consistent with the radio afterglow of this burst. Here, by
considering the trans-relativistic shock hydrodynamics, we show that the dense
medium model can also account for the radio light curve quite well. The
potential virtue of the dense medium model for GRB{980519} is that it implies a
smaller angular size of the afterglow, which is essential for interpreting the
strong modulation of the radio light curve. Optical extinction due to the dense
medium is not important if the prompt optical-UV flash accompanying the
-ray emission can destroy dust by sublimation out to an appreciable
distance. Comparisons with some other radio afterglows are also discussed.Comment: 5 pages, 1 figure, a few minor changes made and references up dated,
MNRAS, in pres
Angular Momentum Conservation Law for Randall-Sundrum Models
In Randall-Sundrum models, by the use of general Noether theorem, the
covariant angular momentum conservation law is obtained with the respect to the
local Lorentz transformations. The angular momentum current has also
superpotential and is therefore identically conserved. The space-like
components of the angular momentum for Randall-Sundrum models are
zero. But the component is infinite.Comment: 10 pages, no figures, accepted by Mod. Phys. Lett.
Self-consistent stability analysis of spherical shocks.
In this paper, we study self-similar solutions, and their linear stability as well, describing the flow within a spherical shell with finite thickness, expanding according to a power law of time, t q , where q>0. The shell propagates in a medium with initially uniform density and it is bounded by a strong shock wave at its outer border while the inner face is submitted to a time-dependent uniform pressure. For q=2/5, the well-known Sedov–Taylor solution is recovered. In addition, although both accelerated and decelerated shells can be unstable against dynamic perturbations, they exhibit highly different behaviors. Finally, the dispersion relation derived earlier by Vishniac (Vishniac, E.T. in Astrophys. J. 274:152, 1983) for an infinitely thin shell is obtained in the limit of an isothermal shock wave
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