310 research outputs found
Computation of Neutron Star Structure Using Modern Equation of State
Using the modern equations of state derived from microscopic calculations, we
have calculated the neutron star structure. For the neutron star, we have
obtained a minimum mass about which is nearly independent
of the equation of state, and a maximum mass between and
which is strongly dependent on the equation of state. It
is shown that among the equations of state of neutron star matter which we have
used, the stiffest one leads to higher maximum mass and radius and lower
central density. It is seen that the given maximum mass for the Reid-93
equation of state shows a good consistency with the accurate observations of
radio pulsars. We have indicated that the thickness of neutron star crust is
very small compared to the predicted neutron star radius.Comment: 16 pages, 6 figure
Contraction of cold neutron star due to in the presence a quark core
Motivated by importance of the existence of quark matter on structure of
neutron star. For this purpose, we use a suitable equation of state (EoS) which
include three different parts: i) a layer of hadronic matter, ii) a mixed phase
of quarks and hadrons, and, iii) a strange quark matter in the core. For this
system, in order to do more investigation of the EoS, we evaluate energy, Le
Chatelier's principle and stability conditions. Our results show that the EoS
satisfies these conditions. Considering this EoS, we study the effect of quark
matter on the structure of neutron stars such as maximum mass and the
corresponding radius, average density, compactness, Kretschmann scalar,
Schwarzschild radius, gravitational redshift and dynamical stability. Also,
considering the mentioned EoS in this paper, we find that the maximum mass of
hybrid stars is a little smaller than that of the corresponding pure neutron
star. Indeed the maximum mass of hybrid stars can be quite close to the pure
neutron stars. Our calculations about the dynamical stability show that these
stars are stable against the radial adiabatic infinitesimal perturbations. In
addition, our analyze indicates that neutron stars are under a contraction due
to the existence of quark core.Comment: 10 pages, 3 figures, 4 table
Investigation of the field-induced ferromagnetic phase transition in spin polarized neutron matter: a lowest order constrained variational approach
In this paper, the lowest order constrained variational (LOCV) method has
been used to investigate the magnetic properties of spin polarized neutron
matter in the presence of strong magnetic field at zero temperature employing
potential. Our results indicate that a ferromagnetic phase transition
is induced by a strong magnetic field with strength greater than ,
leading to a partial spin polarization of the neutron matter. It is also shown
that the equation of state of neutron matter in the presence of magnetic field
is stiffer than the case in absence of magnetic field.Comment: 23 pages, 9 figures Phys. Rev. C (2011) in pres
Model interoperability via model driven development
It is widely recognised that software development is a complex process. Among the factors that contribute to its inherent complexity is the gap between the design and the formal analysis domains. Software design is often considered a human oriented task while the analysis phase draws on formal representation and mathematical foundations. An example of this dichotomy is the use of UML for the software design phase and Petri Nets for the analysis; a separation of concerns that leads to the creation of heterogeneous models. Although UML is widely accepted as a language that can be used to model the structural and behavioural aspects of a system, its lack of mathematical foundations is seen as a serious impediment to rigorous analysis. Petri Nets on the other hand have a strong mathematical basis that is well suited for formal analysis; they lack however the appeal and the easeof-use of UML. A pressing concern for software developers is how to bridge the gap between these domains and allow for model interoperability and the integration of different toolsets across them, and thus reduce the complexity of the software development process. The aim of this paper is to present a Model Driven Development (MDD) model transformation which supports a seamless transition between UML and Petri Nets. This is achieved by model interoperability between UML Sequenc
File management in a mobile DHT-based P2P environment
The emergence of mobile P2P systems is largely due to the evolution of mobile devices into powerful information processing units. The relatively structured context that results from the mapping of mobile patterns of behaviour onto P2P models is however constrained by the vulnerabilities of P2P networks and the inherent limitations of mobile devices. Whilst the implementation of P2P models gives rise to security and reliability issues, the deployment of mobile devices is subject to efficiency constraints. This paper presents the development and deployment of a mobile P2P system based on distributed hash tables (DHT). The secure, reliable and efficient dispersal of files is taken as an application. Reliability was addressed by providing two methods for file dispersal: replication and erasure coding. Security constraints were catered for by incorporating an authentication mechanism and three encryption schemes. Lightweight versions of various algorithms were selected in order to attend to efficiency requirements
Effect of massive graviton on dark energy star structure
The presence of massive gravitons in the field of massive gravity is
considered as an important factor in investigating the structure of compact
objects. Hence, we are encouraged to study the dark energy star structure in
the Vegh's massive gravity. We consider that the equation of state governing
the inner spacetime of the star is the extended Chaplygin gas, and then using
this equation of state, we numerically solve the Tolman-Oppenheimer-Volkoff
(TOV) equation in massive gravity. In the following, assuming different values
of free parameters defined in massive gravity, we calculate the properties of
dark energy star such as radial pressure, transverse pressure, anisotropy
parameter, and other characteristics. Then, after obtaining the maximum mass
and its corresponding radius, we compute redshift and compactness. The obtained
results show that for this model of dark energy star, the maximum mass and its
corresponding radius depend on the massive gravity's free parameters and
anisotropy parameter. These results are consistent with the observational data,
and cover the lower mass gap. We also demonstrate that all energy conditions
are satisfied for this model, and in the presence of anisotropy, the dark
energy star is potentially unstable.Comment: 17 pages, 10 figures, 4 table
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