Sharif Digital Repository

We study the effect of a phenomenological parameterized quintessence model on low, intermediate and high redshift observations. At low and intermediate redshifts, we use the Gold sample of supernova Type Ia (SNIa) data and recently observed size of baryonic acoustic peak from Sloan Digital Sky Survey (SDSS), to put constraint on the parameters of the quintessence model. At the high redshift, the same fitting procedure is done using WAMP data, comparing the location of acoustic peak with that obtain from the dark energy model. As a complementary analysis in a flat universe, we combine the results from the SNIa, CMB and SDSS. The best fit values for the model parameters are Ωm=0.27-0.02+0.02... 

In this work we study the dynamics of the Universe in f(R)=R2-R02 modified gravity with the Palatini formalism. We use data from recent observations, such as the supernova type Ia Gold sample and Supernova Legacy Survey data, the size of the baryonic acoustic peak from the Sloan Digital Sky Survey, the position of the acoustic peak from the cosmic microwave background observations, and large-scale structure formation from the 2dFGRS survey, to put constraints on the parameters of the model. To check the consistency of this action, we compare the age of old cosmological objects with the age of the Universe. In the combined analysis with all the observations, we find the parameters of the... 

We study one of the simplest covariant modified-gravity models based on the Dvali-Gabadadze-Porrati (DGP) brane cosmology, a self-accelerating universe. In this model gravitational leakage into extra dimensions is responsible of late-time acceleration. We mainly focus on the effects of the model parameters on the geometry and the age of universe. Also we investigate the evolution of matter density perturbations in the modified gravity model, and obtain an analytical expression for the growth index, f. We show that increasing Ωrcleads to less growth of the density contrast δ, and also decreases the growth index. We give a fitting formula for the growth index at the present time and indicate... 

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. © 2009 IOP Publishing Ltd. and SISSA  

We investigate the statistical anisotropy and Gaussianity of temperature fluctuations of Cosmic Microwave Background (CMB) radiation data from the Wilkinson Microwave Anisotropy Probe survey, using the Multifractal Detrended Fluctuation Analysis, Rescaled Range, and Scaled Windowed Variance methods. Multifractal Detrended Fluctuation Analysis shows that CMB fluctuations has a long-range correlation function with a multifractal behavior. By comparing the shuffled and surrogate series of CMB data, we conclude that the multifractality nature of the temperature fluctuation of CMB radiation is mainly due to the long-range correlations, and the map is consistent with a Gaussian distribution  

We study the rotational motion of nano-flake ferromagnetic disks suspended in a Newtonian fluid, as a potential material owing the vortex-like magnetic configuration. Using analytical expressions for hydrodynamic, magnetic and Brownian torques, the stochastic angular momentum equation is determined in the dilute limit conditions under applied magnetic field. Results are compared against experimental ones and excellent agreement is observed. We also estimate the uncertainty in the orientation of the disks due to the Brownian torque when an external magnetic field aligns them. Interestingly, this uncertainty is roughly proportional to the ratio of thermal energy of fluid to the magnetic energy... 

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  

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... 

We investigate the stochasticity in temperature fluctuations in the cosmic microwave background (CMB) radiation data from the Wilkinson Microwave Anisotropy Probe. We show that the angular fluctuation of the temperature is a Markov process with a Markov angular scale, ΘMarkov = 1.01 -0.07+0.09. We characterize the complexity of the CMB fluctuations by means of a Fokker-Planck or Langevin equation and measure the associated Kramers-Moyal coefficients for the fluctuating temperature field T (n̂)and its increment, ∇ T = T(n̂2). Through this method we show that temperature fluctuations in the CMB have fat tails compared to a Gaussian distribution. © 2006 IOP Publishing Ltd and SISSA  

Authentication schemes play vital roles in computer and communication security. In order to authenticate the remote users, password based schemes have been widely used. In this paper we introduce a secure remote user authentication scheme based on bilinear pairing that satisfies all security requirements which are mentioned for password based authentication schemes using smart card  

We use multifractal detrended fluctuation analysis (MF-DFA), to study sunspot number fluctuations. The result of the MF-DFA shows that there are three crossover timescales in the fluctuation function. We discuss how the existence of the crossover timescales is related to a sinusoidal trend. Using Fourier detrended fluctuation analysis, the sinusoidal trend is eliminated. The Hurst exponent of the time series without the sinusoidal trend is 0.12 ± 0.01. Also we find that these fluctuations have multifractal nature. Comparing the MF-DFA results for the remaining data set to those for shuffled and surrogate series, we conclude that its multifractal nature is almost entirely due to long range... 

We consider the O (n) theory in the n → 0 limit. We show that the theory is described by logarithmic conformal field theory, and that the correlation functions have logarithmic singularities. The explicit forms of the two-, three- and four-point correlation functions of the scaling fields and the corresponding logarithmic partners are derived. © 2004 Elsevier B.V. All rights reserved  

The aim of this paper is to investigate the feasibility of a combined cooling, heating, and power generation system with a micro turbine using biogas as the fuel to supply the heat and electricity demands in a real wastewater treatment plant. The plant is optimized using the system's total cost rate and the amount of the produced biogas as objective functions. The anaerobic digester is modeled using the ADM1 model. The optimization variables include digester hydraulic retention time, compressor pressure ratio, isentropic compressor efficiency, recuperator pinch time temperature, turbine isentropic efficiency, turbine input temperature, and the number of micro turbines. In the first scenario... 

We investigate the average frequency of positive slope ν +α, crossing the velocity field in the Burgers equation. The level crossing analysis in the inviscid limit and the total number of positive crossings of the velocity field before the creation of singularities are given. The main goal of this paper is to show that this quantity, ν+α, is a good measure for the fluctuations of velocity fields in the Burgers turbulence. © 2006 IOP Publishing Ltd  

An effective approach for the synthesis of 2-(alkylthio)thiazol-4(5H)-ones from alkyl dithiocarbamates and chloroacetyl chloride in the presence of NaHCO3 has been developed. Good to excellent yields of products, simple reaction conditions and general applicability are the most important advantages of this protocol  

Synthesis and characterization of metal dithiocarbamate complexes of N 1 ,N 3 -dicinnamylpropane-1,3-diamine, N 1 ,N 4 -dicinnamylbutane-1,4-diamine and N 1 ,N 6 -dicinnamylhexane-1,6-diamine are reported. The ligands are prepared using cinnamaldehyde and primary diamines to provide the corresponding diimines, followed by reduction with NaBH 4 to afford the corresponding secondary diamines. Diamines react with carbon disulfide in basic medium to furnish the corresponding bis(dithiocarbamate) salts, which underwent complexation with metals. The prepared complexes were characterized by IR, 1 H and 13 C NMR, TGA and elemental analyses. Although the dinuclear metal dithiocarbamate macrocyclic...