76,329 research outputs found
Analytical models for quark stars
We find two new classes of exact solutions to the Einstein-Maxwell system of
equations. The matter content satisfies a linear equation of state consistent
with quark matter; a particular form of one of the gravitational potentials is
specified to generate solutions. The exact solutions can be written in terms of
elementary functions, and these can be related to quark matter in the presence
of an electromagnetic field. The first class of solutions generalises the Mak
and Harko model. The second class of solutions does not admit any singularities
in the matter and gravitational potentials at the centre.Comment: 10 pages, To appear in Int. J. Mod. Phys.
Constrained semi-analytical models of Galactic outflows
We present semi-analytic models of galactic outflows, constrained by
available observations on high redshift star formation and reionization.
Galactic outflows are modeled in a manner akin to models of stellar wind blown
bubbles. Large scale outflows can generically escape from low mass halos
(M<10^9 M_sun) for a wide range of model parameters but not from high mass
halos (M> 10^{11} M_sun). The gas phase metallicity of the outflow and within
the galaxy are computed. Ionization states of different metal species are
calculated and used to examine the detectability of metal lines from the
outflows. The global influence of galactic outflows is also investigated.
Models with only atomic cooled halos significantly fill the IGM at z~3 with
metals (with -2.5>[Z/Z_sun]>-3.7), the actual extent depending on the
efficiency of winds, the IMF, the fractional mass that goes through star
formation and the reionization history of the universe. In these models, a
large fraction of outflows at z~3 are supersonic, hot (T> 10^5 K) and have low
density, making metal lines difficult to detect. They may also result in
significant perturbations in the IGM gas on scales probed by the Lyman-alpha
forest. On the contrary, models including molecular cooled halos with a normal
mode of star formation can potentially volume fill the universe at z> 8 without
drastic dynamic effects on the IGM, thereby setting up a possible metallicity
floor (-4.0<[Z/Z_sun]<-3.6). Interestingly, molecular cooled halos with a
``top-heavy'' mode of star formation are not very successful in establishing
the metallicity floor because of the additional radiative feedback, that they
induce. (Abridged)Comment: 27 pages, 31 figures, 2 tables, pdflatex. Accepted for publication in
MNRA
Some analytical models of radiating collapsing spheres
We present some analytical solutions to the Einstein equations, describing
radiating collapsing spheres in the diffusion approximation. Solutions allow
for modeling physical reasonable situations. The temperature is calculated for
each solution, using a hyperbolic transport equation, which permits to exhibit
the influence of relaxational effects on the dynamics of the system.Comment: 17 pages Late
Generalized Semi-Analytical Models of Supernova Light Curves
We present generalized supernova (SN) light curve (LC) models for a variety
of power inputs. We provide an expression for the power input that is produced
by self-similar forward and reverse shocks in SN ejecta - circumstellar matter
(CSM) interaction. We find that this ejecta-CSM interaction luminosity is in
agreement with results from multi-dimensional radiation hydrodynamics
simulations in the optically-thin case. We develop a model for the case of an
optically-thick CSM by invoking an approximation for the effects of radiative
diffusion. In the context of this model, we provide predictions for the time of
forward shock break-out from the optically-thick part of the CSM envelope. We
also introduce a hybrid LC model that incorporates ejecta-CSM interaction plus
Ni-56 and Co-56 radioactive decay input. We fit this hybrid model to the LC of
the Super-Luminous Supernova (SLSN) 2006gy. We find that this model provides a
better fit to the LC of this event than previously presented models. We also
address the relation between Type IIL and Type IIn SN with ejecta-CSM
interaction models. Forward and reverse shock power input due to CSM
interaction can produce the LCs of Type IIn SNe in terms of duration, shape and
decline rate. This model can also produce LCs that are symmetric in shape
around peak luminosity. We conclude that the observed LC variety of SNe Type
IIn and of the SLSNe is likely to be a byproduct of the large range of
conditions relevant to significant ejecta-CSM interaction as a power source.Comment: 48 pages, 13 figure
Expansion-Free Cavity Evolution: Some exact Analytical Models
We consider spherically symmetric distributions of anisotropic fluids with a
central vacuum cavity, evolving under the condition of vanishing expansion
scalar. Some analytical solutions are found satisfying Darmois junction
conditions on both delimiting boundary surfaces, while some others require the
presence of thin shells on either (or both) boundary surfaces. The solutions
here obtained model the evolution of the vacuum cavity and the surrounding
fluid distribution, emerging after a central explosion. This study complements
a previously published work where modeling of the evolution of such kind of
systems was achieved through a different kinematical condition.Comment: 9 pages, Revtex. Typos corrected. Published in Int. J. Mod. Phys.
Analytical Models for Valence Fermions in Isotropic Traps
For isotropic confining Ioffe-Pritchard or TOP potentials, a valence fermion
trapped with a closed core of other fermions can be described by an analytical
effective one-particle model with a physical eigenspectrum. Related
constructions exist for Paul and Penning traps. The analytical models arise
from quantum-mechanical supersymmetry.Comment: accepted for publication in Physics Letters
Correlation of ground tests and analyses of a dynamically scaled Space Station model configuration
Verification of analytical models through correlation with ground test results of a complex space truss structure is demonstrated. A multi-component, dynamically scaled space station model configuration is the focus structure for this work. Previously established test/analysis correlation procedures are used to develop improved component analytical models. Integrated system analytical models, consisting of updated component analytical models, are compared with modal test results to establish the accuracy of system-level dynamic predictions. Design sensitivity model updating methods are shown to be effective for providing improved component analytical models. Also, the effects of component model accuracy and interface modeling fidelity on the accuracy of integrated model predictions is examined
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