55 research outputs found
Interacting viscous ghost tachyon, K-essence and dilaton scalar field models of dark energy
We study the correspondence between the interacting viscous ghost dark energy
model with the tachyon, K-essence and dilaton scalar field models in the
framework of Einstein gravity. We consider a spatially non-flat FRW universe
filled with interacting viscous ghost dark energy and dark matter. We
reconstruct both the dynamics and potential of these scalar field models
according to the evolutionary behavior of the interacting viscous ghost dark
energy model, which can describe the accelerated expansion of the universe. Our
numerical results show that the interaction and viscosity have opposite effects
on the evolutionary properties of the ghost scalar filed models.Comment: 16 pages, 17 figure
Revised spherically symmetric solutions of gravity
We study spherically symmetric static empty space solutions in
model of gravity. We show that the Schwarzschild
metric is an exact solution of the resulted field equations and consequently
there are general solutions which {are perturbed Schwarzschild metric and
viable for solar system. Our results for large scale contains a logarithmic
term with a coefficient producing a repulsive gravity force which is in
agreement with the positive acceleration of the universe.Comment: 8 page
L’Amélioration de la Sécurité du Chiffrement Algébrique Modulaire par les Générateurs de Fibonacci
Le Chiffre de Hill est l'un des algorithmes à clés symétriques qui a montré des avantages pour le cryptage de données. Cependant l'algorithme original est vulnérable aux «Attaque à Texte Clair Choisi». Un autre revers pour le Cryptage des images est qu’il révèle certaines tendances et ne cache pas toutes les caractéristiques de l'image (images avec des fonds homogènes). Pour surmonter ces problèmes, dans cet article, nous proposons une modification de l’algorithme de Hill en incluant une translation et en introduisant à chaque étape du processus du Cryptage des clés dynamiques Pseudo-Aléatoirement. La partie expérimentale de cet article prouve que la variante proposée donne un meilleur cryptage pour tous types d'images et montre bien une amélioration par rapport à l’algorithme conventionnel
Reconstructing f(R) model from Holographic DE: Using the observational evidence
We investigate the corresponding relation between gravity and an
interacting holographic dark energy. By obtaining conditions needed for some
observational evidence such as, positive acceleration expansion of universe,
crossing the phantom divide line and validity of thermodynamics second law in
an interacting HDE model and corresponding it with mode of gravity we
find a viable model which can explain the present universe. We also
obtain the explicit evolutionary forms of the corresponding scalar field,
potential and scale factor of universe.Comment: 11page. phys. Scr (2012
Etude comparative de deux cryptosystèmes: L’AES versus l’attracteur Chaotique
Le transfert croissant de données multimédias engendre des besoins en termes de sécurité d’informations. Pour répondre aux normes de confidentialité, plusieurs algorithmes de cryptage ont été développés ces dernières années. En raison de l’utilisation massive des données images dans divers domaines (médicale, industrielle, …), il est nécessaire d’utiliser et d’adapter ces techniques de sécurité à ce type de données. Dans ce contexte, une étude comparative de deux algorithmes de cryptage appliqués aux images est réalisée. Le premier est le cryptosystème classique dit Advanced Encryption Standard (AES) et le deuxième issu des signaux chaotiques basés sur une carte logistique afin d’évaluer leurs robustesse en termes de sécurité
Modified gravity in a viscous and non-isotropic background
We study the dynamical evolution of an model of gravity in a viscous
and anisotropic background which is given by a Bianchi type-I model of the
Universe. We find viable forms of gravity in which one is exactly the
Einsteinian model of gravity with a cosmological constant and other two are
power law models. We show that these two power law models are stable
with a suitable choice of parameters. We also examine three potentials which
exhibit the potential effect of models in the context of scalar tensor
theory. By solving different aspects of the model and finding the physical
quantities in the Jordan frame, we show that the equation of state parameter
satisfy the dominant energy condition. At last we show that the two power law
models behave like quintessence model at late times and also the shear
coefficient viscosity tends to zero at late times.Comment: 7 pages, 2 figure
Interacting New Agegraphic Dark Energy in a Cyclic Universe
The main goal of this work is investigation of NADE in the cyclic universe
scenario. Since, cyclic universe is explained by a phantom phase (),
it is shown when there is no interaction between matter and dark energy, ADE
and NADE do not produce a phantom phase, then can not describe cyclic universe.
Therefore, we study interacting models of ADE and NADE in the modified
Friedmann equation. We find out that, in the high energy regime, which it is a
necessary part of cyclic universe evolution, only NADE can describe this
phantom phase era for cyclic universe. Considering deceleration parameter tells
us that the universe has a deceleration phase after an acceleration phase, and
NADE is able to produce a cyclic universe. Also it is found valuable to study
generalized second law of thermodynamics. Since the loop quantum correction is
taken account in high energy regime, it may not be suitable to use standard
treatment of thermodynamics, so we turn our attention to the result of
\citep{29}, which the authors have studied thermodynamics in loop quantum
gravity, and we show that which condition can satisfy generalized second law of
thermodynamics.Comment: 8 pages, 3 figure
Reconstruction of the equation of state for the cyclic universes in homogeneous and isotropic cosmology
We study the cosmological evolutions of the equation of state (EoS) for the
universe in the homogeneous and isotropic
Friedmann-Lema\^{i}tre-Robertson-Walker (FLRW) space-time. In particular, we
reconstruct the cyclic universes by using the Weierstrass and Jacobian elliptic
functions. It is explicitly illustrated that in several models the universe
always stays in the non-phantom (quintessence) phase, whereas there also exist
models in which the crossing of the phantom divide can be realized in the
reconstructed cyclic universes.Comment: 29 pages, 8 figures, version accepted for publication in Central
European Journal of Physic
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