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M. Reza Rahimi Tabar

Publications and source records attributed to M. Reza Rahimi Tabar.

50 records · Page 3Linked to original sources
arXiv2005

Two-Scale Kirchhoff Theory: Comparison of Experimental Observations With Theoretical Prediction

We introduce a non-perturbative two scale Kirchhoff theory, in the context of light scattering by a rough surface. This is a two scale theory which considers the roughness both in the wavelength scale (small scale) and in the scales much larger than the wavelength of the incident light (large scale). The theory can precisely explain the small peaks which appear at certain scattering angles. These peaks can not be explained by one scale theories. The theory was assessed by calculating the light scattering profiles using the Atomic Force Microscope (AFM) images, as well as surface profilometer scans of a rough surface, and comparing the results with experiments. The theory is in good agreement with the experimental results.

physics.data-an↗
arXiv2004

Mid-Infrared Radiation as a Short-Term Earthquake Precursor

Recently it has been found by F. Freund that the granite under high pressure undergoes a phase transition from insulator to a p-type semiconductor. This phase transition is a key concept to understanding pre-earthquake phenomena. This effect accompanies with the radiation of the granite in the mid-infrared region. we were able to predict the recent earthquake in the south of Iran by monitoring this radiation.

physics.geo-ph↗
arXiv2003

Stochastic Analysis and Regeneration of Rough Surfaces

We investigate Markov property of rough surfaces. Using stochastic analysis we characterize the complexity of the surface roughness by means of a Fokker-Planck or Langevin equation. The obtained Langevin equation enables us to regenerate surfaces with similar statistical properties compared with the observed morphology by atomic force microscopy.

cond-mat.stat-mech↗
arXiv2003

Height Fluctuations and Intermittency of $V_2 O_5$ Films by Atomic Force Microscopy

The spatial scaling law and intermittency of the $V_2 O_5$ surface roughness by atomic force microscopy has been investigated. The intermittency of the height fluctuations has been checked by two different methods, first, by measuring scaling exponent of q-th moment of height-difference fluctuations i.e. $C_q = < |h(x_1) - h(x_2)|^{q} >$ and the second, by defining generating function $Z(q,N)$ and generalized multi-fractal dimension $D_q$. These methods predict that there is no intermittency in the height fluctuations. The observed roughness and dynamical exponents can be explained by the numerical simulation on the basis of forced Kuramoto-Sivashinsky equation.

cond-mat.stat-mech↗
arXiv2003

Disordered Systems and Logarithmic Conformal Field Theory

We review a recent development in theoretical understanding of the quenched averaged correlation functions of disordered systems and the logarithmic conformal field theory (LCFT) in d-dimensions. The logarithmic conformal field theory is the generalization of the conformal field theory when the dilatation operator is not diagonal and has the Jordan form. It is discussed that at the random fixed point the disordered systems such as random-bond Ising model, Polymer chain, etc. are described by LCFT and their correlation functions have logarithmic singularities. As an example we will discuss in detail the application of LCFT to the problem of random-bond Ising model in $ 2 \leq d \leq 4$.

cond-mat↗
arXiv2002

Discrete scale invariance, and its logarithmic extension

It is known that discrete scale invariance leads to log-periodic corrections to scaling. We investigate the correlations of a system with discrete scale symmetry, discuss in detail possible extension of this symmetry such as translation and inversion, and find general forms for correlation functions.

cond-mat↗
arXiv2002

Level Crossing Analysis of Growing surfaces

We investigate the average frequency of positive slope $ν_α^{+} $, crossing the height $α= h- \bar h$ in the surface growing processes. The exact level crossing analysis of the random deposition model and the Kardar-Parisi-Zhang equation in the strong coupling limit before creation of singularities are given.

cond-mat↗
arXiv2002

Strong Coupling Limit of the Kardar-Parisi-Zhang Equation in 2+1 Dimensions

A master equation for the Kardar-Parisi-Zhang (KPZ) equation in 2+1 dimensions is developed. In the fully nonlinear regime we derive the finite time scale of the singularity formation in terms of the characteristics of forcing. The exact probability density function of the one point height field is obtained correspondingly.

cond-mat↗
arXiv2001

Statistical Theory for the Kardar-Parisi-Zhang Equation in 1+1 Dimension

The Kardar-Parisi-Zhang (KPZ) equation in 1+1 dimension dynamically develops sharply connected valley structures within which the height derivative {\it is not} continuous. There are two different regimes before and after creation of the sharp valleys. We develop a statistical theory for the KPZ equation in 1+1 dimension driven with a random forcing which is white in time and Gaussian correlated in space. A master equation is derived for the joint probability density function of height difference and height gradient $P(h-\bar h,\partial_{x}h,t)$ when the forcing correlation length is much smaller than the system size and much bigger than the typical sharp valley width. In the time scales before the creation of the sharp valleys we find the exact generating function of $h-\bar h$ and $\partial_x h$. Then we express the time scale when the sharp valleys develop, in terms of the forcing characteristics. In the stationary state, when the sharp valleys are fully developed, finite size corrections to the scaling laws of the structure functions $<(h-\bar h)^n (\partial_x h)^m>$ are also obtained.

cond-mat.stat-mech↗
arXiv2000

Quenched Averaged Correlation Functions of the Random Magnets

It is shown that the ratios of the quenched averaged three and four-point correlation functions of the local energy density operator to the connected ones in the random-bond Ising model approach asymptotically to some $universal$ functions. We derive the explicit expressions of these universal functions. Moreover it is shown that the individual logarithmic operators have not any contribution to the connected correlation functions of the disordered Ising model.

cond-mat↗
arXiv1999

Multi-scale Correlation Functions in Strong Turbulence

Under the framework of V. Yakhot [Phys.Rev.E, {\bf57}, 1737 (1998)] modelling of intermittent structure functions in fully developed turbulence and based on the experimentally supported Markovian nature of turbulence cascades [R.Friedrich and J.Peinke, Phys.Rev.Lett, {\bf 78}, 863 (1997)], we calculate the multiscaling correlation functions. Fusion rules [V.S.L'vov and I. Procaccia, Phys.Rev.Lett. {\bf 76}, 2898 (1996)] which are experimentally tested [R. Benzi, L. Biferale, and F. Toschi, Phys.Rev.Lett. {\bf 80}, 3244 (1998)] to be compatible with almost uncorrelated multiplicative process can analyticaly be supported by direct calculations.

cond-mat↗
arXiv1999

Theoretical Model for the Kramers-Moyal Description of Turbulence Cascades

We derive the Kramers-Moyal equation for the conditional probability density of velocity increments from the theoretical model recently proposed by V.Yakhot [Phys.Rev.E {\bf 57}, 1737 (1998)] in the limit of high Reynolds number limit. We show that the higher order (n>=3) Kramers-Moyal coefficients tends to zero and the velocity increments are evolved by the Fokker-Planck operator. Our result is compatible with the phenomenological descriptions by R.Friedrich and J.Peinke [Phys.Rev.Lett. {\bf 78}, 863 (1997)].

cond-mat↗
arXiv1998

Phase Transition in a Self--Gravitating Planar Gas

We consider a gas of Newtonian self-gravitating particles in two-dimensional space, finding a phase transition, with a high temperature homogeneous phase and a low temperature clumped one. We argue that the system is described in terms of a gas with fractal behaviour.

hep-th↗