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#### Structure formation in a variable dark energy model and observational constraints

, Article ESO Astrophysics Symposia ; Volume 2008 , 2008 , Pages 3-7 ; 14312433 (ISSN); 3540747125 (ISBN); 9783540747123 (ISBN) ; Movahed, M. S ; Sharif University of Technology
2008

Abstract

The interpretation of a vast number of cosmological observations in the framework of FRW models suggests that the major part of the energy density of the universe is in form of dark energy with still unknown physical nature. In some models for dark energy, which are motivated by particle physics theory, the equation of state and the contribution of dark energy to the energy density of the universe can be variable. Here we study structure formation in a parameterized dark energy model, and compare its predictions with recent observational data, from the Supernova Ia gold sample and the parameters of large scale structure determined by the 2-degree Field Galaxy Redshift Survey (2dFGRS), and...

#### Power-law parametrized quintessence model

, Article Physical Review D - Particles, Fields, Gravitation and Cosmology ; Volume 75, Issue 2 , 2007 ; 15507998 (ISSN) ; Movahed, M. S ; Sharif University of Technology
2007

Abstract

We propose a simple power-law parametrized quintessence model with time-varying equation of state and obtain corresponding quintessence potential of this model. This model is compared with Supernova Type Ia (SNIa) Gold sample data, size of baryonic acoustic peak from Sloan Digital Sky Survey (SDSS), the position of the acoustic peak from the CMB observations and structure formation from the 2dFGRS survey and put constrain on the parameters of model. The parameters from the best fit indicates that the equation of state of this model at the present time is w0=-1.40-0.65+0.40 at 1σ confidence level. Finally we calculate the age of universe in this model and compare it with the age of old...

#### Discrimination of Sol and Gel states in an aging clay suspension

, Article Chemical Physics ; Volume 423 , September , 2013 , Pages 167-172 ; 03010104 (ISSN) ; Movahed, M. S ; Jafari, G. R ; Sharif University of Technology
2013

Abstract

The dynamical scattered light intensity and multiplicative cascade model was employed to characterize the anisotropic charged colloidal particles suspension during the so-called Sol-Gel transition. Generally we looked for finding a criterion to distinguish the properties of Sol and Gel states systematically. The probability density function (PDF) of the light scattering intensity shows an obvious change with proceeding of the sample aging process (during of gelation state). Our results confirmed that in the so-called Sol state, the value of non-Gaussian parameter, kW, as a function of time is larger than that of for weak-Gel or in coexistence Sol-Gel state. The number of cascades in the...

#### Observational tests of a two parameter power-law class modified gravity in Palatini formalism

, Article Physical Review D - Particles, Fields, Gravitation and Cosmology ; Volume 80, Issue 6 , 2009 ; 15507998 (ISSN) ; Movahed, M. S ; Rahvar, S ; Sharif University of Technology
2009

Abstract

In this work we propose a modified gravity action f(R)=(Rn-R0n)1/n with two free parameters of n and R0 and derive the dynamics of a universe for this action in the Palatini formalism. AIM: We do a cosmological comparison of this model with observed data to find the best parameters of a model in a flat universe. METHOD: To constrain the free parameters of model we use SNIa type Ia data in two sets of gold and union samples, CMB-shift parameter, baryon acoustic oscillation, gas mass fraction in cluster of galaxies, and large-scale structure data. RESULT: The best fit from the observational data results in the parameters of model in the range of n=0.98-0.08+0.08 and ΩM=0.25+0.1-0.1 with one...

#### A parametrized variable dark energy model: Structure formation and observational constraints

, Article International Journal of Modern Physics D ; Volume 15, Issue 9 , 2006 , Pages 1455-1472 ; 02182718 (ISSN) ; Movahed, M. S ; Rahvar, S ; Sharif University of Technology
2006

Abstract

In this paper we investigate a simple parametrization scheme of the quintessence model given by Wetterich [Phys. Lett. B 594, 17 (2004)]. The crucial parameter of this model is the bending parameter b, which is related to the amount of dark energy in the early universe. Using the linear perturbation and the spherical infall approximations, we investigate the evolution of matter density perturbations in the variable dark energy model, and obtain an analytical expression for the growth index f. We show that increasing b leads to less growth of the density contrast δ, and also decreases the growth index. Giving a fitting formula for the growth index at the present time, we verify that the...

#### Markov properties of electrical discharge current fluctuations in plasma

, Article Journal of Statistical Physics ; Volume 143, Issue 1 , 2011 , Pages 148-167 ; 00224715 (ISSN) ; Movahed, M. S ; Khorram, S ; Rahimi Tabar, M. R ; Sharif University of Technology
Abstract

Using the Markovian method, we study the stochastic nature of electrical discharge current fluctuations in the Helium plasma. Sinusoidal trends are extracted from the data set by the Fourier-Detrended Fluctuation analysis and consequently cleaned data is retrieved. We determine the Markov time scale of the detrended data set by using likelihood analysis. We also estimate the Kramers-Moyal's coefficients of the discharge current fluctuations and derive the corresponding Fokker-Planck equation. In addition, the obtained Langevin equation enables us to reconstruct discharge time series with similar statistical properties compared with the observed in the experiment. We also provide an exact...

#### Stochastic qualifier of gel and glass transitions in laponite suspensions

, Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 81, Issue 6 , Jun , 2010 ; 15393755 (ISSN) ; Jabbari Farouji, S ; Movahed, M. S ; Jafari, G. R ; Rahimi Tabar, M. R ; Sharif University of Technology
2010

Abstract

The existence of the important similarities between gelation and glass transition makes it hard to distinguish between the two types of nonergodic states experimentally. Here, we report on a stochastic analysis of the scattered light intensity through a colloidal particles suspension during the gel and glass formation. In this analysis, we exploit the methods developed for complex hierarchical systems, such as turbulence. Using the multiplicative log-normal cascade models, we provide a criterion to distinguish gels from glasses

#### Multifractal analysis of light scattering-intensity fluctuations

, Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 80, Issue 6 , 2009 ; 15393755 (ISSN) ; Jabbari Farouji, S ; Movahed, M. S ; Jafari, G. R ; Rahimi Tabar, M. R ; Sharif University of Technology
Abstract

We provide a simple interpretation of non-Gaussian nature of the light scattering-intensity fluctuations from an aging colloidal suspension of Laponite using the multiplicative cascade model, Markovian method, and volatility correlations. The cascade model and Markovian method enable us to reproduce most of recent empirical findings: long-range volatility correlations and non-Gaussian statistics of intensity fluctuations. We provide evidence that the intensity increments Δx (τ) =I (t+τ) -I (t), upon different delay time scales τ, can be described as a Markovian process evolving in τ. Thus, the τ dependence of the probability density function p (Δx,τ) on the delay time scale τ can be...

#### Fractal properties of plasma discharge current fluctuations

, Article 36th EPS Conference on Plasma Physics 2009, EPS 2009 - Europhysics Conference Abstracts, 29 June 2009 through 3 July 2009, Sofia ; Volume 33 E1 , 2009 , Pages 645-648 ; 9781622763368 (ISBN) ; Movahed, M. S ; Rahimi Tabar, M. R ; Sobhanian, S ; Khorram, S ; Sharif University of Technology
Abstract

We use multifractal detrended fluctuation analysis (MF-DFA) to study the electrical discharge current fluctuations in plasma and show that it has multifractal properties and behaves as a weak anti-correlated process. Comparison of the MF-DFA results for the original series with those for the shuffled and surrogate series shows that correlation of the fluctuations is responsible for the multifractal nature of the electrical discharge current

#### Uncertainty in the fluctuations of the price of stocks

, Article International Journal of Modern Physics C ; Volume 18, Issue 11 , 2007 , Pages 1689-1697 ; 01291831 (ISSN) ; Movahed, M. S ; Norouzzadeh, P ; Bahraminasab, A ; Sahimi, M ; Ghasemi, F ; Rahimi Tabar, M. R ; Sharif University of Technology
2007

Abstract

We report on a study of the Tehran Price Index (TEPIX) from 2001 to 2006 as an emerging market that has been affected by several political crises during the recent years, and analyze the non-Gaussian probability density function (PDF) of the log returns of the stock prices. We show that while the average of the index did not fall very much over the time period of the study, its day-to-day fluctuations strongly increased due to the crises. Using an approach based on multiplicative processes with a detrending procedure, we study the scale-dependence of the non-Gaussian PDFs, and show that the temporal dependence of their tails indicates a gradual and systematic increase in the probabilityof...

#### Exact analysis of level-crossing statistics for (d+1)-dimensional fluctuating surfaces

, Article Journal of Statistical Physics ; Volume 124, Issue 6 , 2006 , Pages 1471-1490 ; 00224715 (ISSN) ; Movahed, M. S ; Nasiri, S. D ; Masoudi, A. A ; Sahimi, M ; Sharif University of Technology
2006

Abstract

We carry out an exact analysis of the average frequency ν+ αxi in the direction x i of positiveslope crossing of a given level α such that, h(x, t) h = α, of growing surfaces in spatial dimension d. Here, h(x, t) is the surface height at time t, and h is its mean value. We analyze the problem when the surface growth dynamics is governed by the Kardar-Parisi-Zhang (KPZ) equation without surface tension, in the time regime prior to appearance of cusp singularities (sharp valleys), as well as in the random deposition (RD) model. The total number N + of such level-crossings with positive slope in all the directions is then shown to scale with time as t d/2 for both the KPZ equation and the RD...

#### Level crossing analysis of the stock markets

, Article Journal of Statistical Mechanics: Theory and Experiment ; Issue 6 , 2006 ; 17425468 (ISSN) ; Movahed, M. S ; Fazeli, S. M ; Rahimi Tabar, M. R ; Masoudi, S. F ; Sharif University of Technology
2006

Abstract

We investigate the average frequency of positive slope ν α+ crossing for the returns of market prices. The method is based on stochastic processes in which no scaling feature is explicitly required. Using this method we define a new quantity to quantify the stage of development and activity of stock exchanges. We compare the Tehran and western stock markets and show that some, such as the Tehran (TEPIX) and New Zealand (NZX) stock exchanges, are emerging, and also that TEPIX is a non-active market and is financially motivated to absorb capital. © 2006 IOP Publishing Ltd. and SISSA