2021-01-19T22:12:05Z
http://ijaa.du.ac.ir/?_action=export&rf=summon&issue=23
Iranian Journal of Astronomy and Astrophysics
IJAA
2322-4924
2322-4924
2017
4
1
Noether Symmetry in f(T) Theory at the anisotropic universe
A.
Aghamohammadi
As it is well known, symmetry plays a crucial role in the theoretical physics. On other hand, the Noether symmetry is a useful procedure to select models motivated at a fundamental level, and to discover the exact solution to the given lagrangian. In this work, Noether symmetry in f(T) theory on a spatially homogeneous and anisotropic Bianchi type I universe is considered. We discuss the Lagrangian formalism of f(T ) theory in anisotropic universe. The point-like Lagrangian is clearly constructed.The explicit form of f(T) theory and the corresponding exact solution are found by requirement of Noether symmetry and Noether charge. A power-law f(T), the same as the FRW universe, can satisfy the required Noether symmetry in the anisotropic universe with power- law scale factor. It is regarded that positive expansion is satisfied by a constrain between parameters.
Noether symmetry
anisotropic Bianchi type I universe
modified theories of gravity
f(T) gravity
2017
04
01
1
8
http://ijaa.du.ac.ir/article_84_3d11a75bdbcbb1c17f437303622835b1.pdf
Iranian Journal of Astronomy and Astrophysics
IJAA
2322-4924
2322-4924
2017
4
1
Effect of random telegraph noise on entanglement and nonlocality of a qubit-qutrit system
Hakimeh
Jaghouri
Samira
Nazifkar
We study the evolution of entanglement and nonlocality of a non-interacting qubit-qutrit system under the eﬀect of random telegraph noise (RTN) in independent and common environments in Markovian and non-Markovian regimes. We investigate the dynamics of qubit-qutrit system for diﬀerent initial states. These systems could be existed in far astronomical objects. A monotone decay of the nonlocality (entanglement) is found in the Markov regime, while for non-Markovian noise, phenomena of sudden change (death) and revival occurs. We ﬁnd that the preserving nonlocality (entanglement) depends on initial state of the system in common and independent environments; so, we can not strictly conclude that independent or common environments are more robust against the noise.
keyword
2017
04
01
9
17
http://ijaa.du.ac.ir/article_91_b5bee8f95aabb0536aa0909083a32fc5.pdf
Iranian Journal of Astronomy and Astrophysics
IJAA
2322-4924
2322-4924
2017
4
1
Pulsating red giant and supergiant stars in the Local Group dwarf galaxy Andromeda I
Elham
Saremi
Abbas
Abedi
Atefeh
Javadi
Jacco
van Loon
Habib
Khosroshahi
We have conducted an optical long-term monitoring survey of the majority of dwarf galaxies in the Local Group, with the Isaac Newton Telescope (INT), to identify the long period variable (LPV) stars. LPV stars vary on timescales of months to years, and reach the largest amplitudes of their brightness variations at optical wavelengths, due to the changing temperature. They trace stellar populations as young as ~ 30 Myr to as old as ~ 10 Gyr whose identification is one of the best ways to reconstruct the star formation history.<br /> The system of galactic satellites of the large Andromeda spiral galaxy (M31) forms one of the key targets of our monitoring survey. In this first paper in the series, we present the first results from the survey in the form of a census of LPV stars in Andromeda I (And I) dwarf galaxy.<br /> Photometry was obtained for 10585 stars in a 0.07 square degree field, of which 116 stars<br /> were found to be variable, most of which are Asymptotic Giant Branch (AGB) stars.<br /> Our data were matched to mid-infrared photometry from the Spitzer Space Telescope, and to optical catalogues of variable stars from the Hubble Space Telescope.
stars: evolution
stars: red giants
supergiants
stars: mass-loss
stars: oscillations
galaxies: individual: Andromeda I
galaxies: stellar content
2017
04
01
19
36
http://ijaa.du.ac.ir/article_92_bc6ca8daf6e604a9634da5dde859f833.pdf
Iranian Journal of Astronomy and Astrophysics
IJAA
2322-4924
2322-4924
2017
4
1
A Simplified Solution for Advection Dominated Accretion Flows with Outflow
Seyede Tahere
Kashfi
Shahram
Abbassi
The existence of outflow in the advection dominated accretion flows has been confirmed by both numerical simulations and observations. The outow models for ADAF have been investigated by several groups with a simple self similar solution. But this solution is inaccurate at the inner regions and can not explain the emitted spectrum of the flow; so, it is necessary to obtain a global solution for ADAFs with outflow. In this paper, we use a simplified global solution to study the structure of ADAF in the presence of outflow. In this method which is proposed by Yuan et al (2008, hereafter YMN08), the radial momentum equation is replaced by a simple algebraic relation between angular velocity and Keplerian angular velocity to avoid the difficulty of the calculation of global solution. We consider the radial dependence for mass accretion rate <em>M</em> =<em>M</em> <em><sub>out</sub></em>(<em>r/r</em><em><sub>out</sub></em>)<em><sup>s</sup></em>where <em>s </em>is a constant and we do not change the other dynamical equations. We investigate the variation of physical quantity of accretion flow which is caused by outflow. The results that we obtained comply with our expectations from the influence of outflow on the structure of accretion flow.
accretion
accretion disks
black hole
global solution
outflow
2017
04
01
37
43
http://ijaa.du.ac.ir/article_105_a49a64c684d30c77c4e2f0be27a74ba2.pdf
Iranian Journal of Astronomy and Astrophysics
IJAA
2322-4924
2322-4924
2017
4
1
Modeling Magnetic Field in Heavy ion Collisions Using Two Diﬀerent Nuclear Charge Density Distributions
Susan
Abbas Nejad
Supervisor: Dr. Umut
Gursoy
By studying the properties of matter during heavy-ion collisions, a better understanding of the Quark-Gluon plasma is possible. One of the main areas of this study is the calculation of the magnetic ﬁeld, particularly how the values of conductivity aﬀects this ﬁeld and how the ﬁeld strength changes with proper time. In matching the theoretical calculations with results obtained in lab, two diﬀerent models for charge density distribution inside ions is used. In this study, after explanation of some theoretical background, the magnetic ﬁeld contribution of the spectators and participants in Pb-Pb ion collision is calculated in a conductive medium and vacuum. Results are compared using two diﬀerent nuclear charge density models.
Quark-Gluon Plasma
QCD
Heavy Ion Collisions
Electromagnetic ﬁeld
Nuclear density distributions
2017
04
01
45
56
http://ijaa.du.ac.ir/article_106_c8c2df32ce5297813a9d26aa61bd9df9.pdf
Iranian Journal of Astronomy and Astrophysics
IJAA
2322-4924
2322-4924
2017
4
1
Soliton-like Solutions of the Complex Non-linear Klein-Gordon Systems in 1 + 1 Dimensions
Mohammad
mohammadi
Ali Reza
Olamaei
In this paper, we present soliton-like solutions of the non-linear complex Klein-Gordon systems in 1+1 dimensions. We will use polar representation to introduce three different soliton-like solutions including, complex kinks (anti-kinks), radiative profiles, and localized wave-packets. Complex kinks (anti-kinks) are topological objects with zero electrical charges. Radiative profiles are objects that move at the speed of light and therefore, have a zero rest mass. They can be created in kink-anti-kink collisions and vice versa. Localized wave packet solutions are non-topological objects for which wave and particle behavior are reconciled in a classical way. For localized wave packet solutions, the trivial initial phase imposes an uncertainty on the collision fates.
complex
non-linear
Klein-Gordon
soliton
uncertainty
kink
radiative-profile
wave-packet
2017
04
01
57
68
http://ijaa.du.ac.ir/article_108_1dac6703cd70c6208c97d18ea09f4ff9.pdf