arXiv subjects

J. Cheraghalizadeh

Publications and source records attributed to J. Cheraghalizadeh.

17 recordsLinked to original sources

arXiv2024

Statistical analysis of the drying pattern of coffee

In this study, we experimentally study the dried pattern droplets of coffee with and without sugar. We statistically analyze the rough surface formed after the stain becomes dried. The amount of sugar is controlled by the mass $m$. Along with the formation of the coffee ring, we discuss the Marangoni effect, in the system, and also analyzed the statistics of the cracks. For large enough $m$ values, the exponents approach to the ones for the Gaussian free field (GFF) (the loop fractal dimension $\frac{3}{2}$, loop and gyration radius distribution exponents $τ_l=\frac{7}{3}$ and $τ_r=3$ respectively). Using the multifractal analysis (MA) for the mass configuration of the dried pattern, we numerically show that, the mass-fractal dimension is $1.76\pm 0.04$ for the case without sugar, which decreases increasing the sugar. This is explained by the fact that the droplet becomes more hydrophilic, resulting in more sparse spatial patterns, in agreement compatible with the contact angle analysis.

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arXiv2022

Simulating Cumulus Clouds based on Self-Organized Criticality

Recently it was shown that self-organized criticality is an important ingredient of the dynamics of cumulus clouds (Physical Review E, 103(5), p.052106, 2021). Here we introduce a new algorithm to simulate cumulus clouds in two-dimensional square lattices, based on two important facts: the cohesive energy of wet air parcels and a sandpile-type diffusion of cloud segments. The latter is realized by considering the evaporation/condensation of air parcels in various regions of the cloud, which enables them to diffuse to the neighboring regions. The results stemming from this model are in excellent agreement with the observational results reported in the above-cited paper, where the exponents have been obtained for the two-dimensional earth-to-sky RGB images of clouds. The exponents that are obtained at the lowest condensation level in our model are consistent with the observational exponents. We observed that the cloud fields that we obtain from our model are fractal, with the outer perimeter having a fractal dimension of $D_f = 1.25 \pm 0.01$. Furthermore, the distributions of the radius of gyration and the loop length follow a power-law function with exponents $τ_r = 2.3 \pm 0.1$ and $τ_l = 2.1 \pm 0.1$, respectively. The loop Green function is found to be logarithmic with the radius of gyration of the loops following the observational results. The winding angle statistic of the external perimeter of the cloud field is also analyzed, showing an exponent in agreement with the fractal dimension, which may serve as the conformal invariance of the system.

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arXiv2022

Sandpiles Subjected to Sinusoidal Drive

This paper considers a sandpile model subjected to a sinusoidal external drive with the time period $T$. We develop a theoretical model for the Green function in a large $T$ limit, which predicts that the avalanches are anisotropic and elongated in the oscillation direction. We track the problem numerically and show that the system shows additionally a regime where the avalanches are elongated in the perpendicular direction with respect to the oscillations. We find a transition point between these two regimes. The power spectrum of avalanche size and the grains wasted from the parallel and perpendicular directions are studied. These functions show power-law behaviour in terms of the frequency with exponents, which run with $T$.

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arXiv2022

Mapping cumulus clouds to scale invariant rough surfaces

Motivated by a recent observation on the self-organized criticality of cumulus clouds (Phys. Rev E 103, 052106, 2021) we study their connection to self-similar rough surfaces, in which $f\equiv \log I$ plays the role of the main field, where $I$ is the intensity of the received visible light. By simulating the light scattering based on a coarse-grained phenomenological model in a two-dimensional cloud, we argue the possible connection of $I$ to the actual cloud thickness. Although in the vertical incident light $f$ is proportional to the cloud thickness, in the general case it is complected. We study the statistical properties of observational data for $f$ with a focus on the conventional exponents of this scale-invariant rough surface. By calculating the roughness exponents, and comparing them with other exponents like the fractal dimension of loops, the distribution function of the radius of gyration and loop lengths, and the exponent of the green function, we prove that this surface is unconventional in the sense that it is the non-Gaussian self-affine random surface which violates the Kondev hyper-scaling relations.

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arXiv2021

Invasion percolation in short-range and long-range disorder background

In this paper, we investigate the invasion percolation (IP) in imperfect support in which the configuration of imperfections is considered to be correlated. Three lattice models were engaged to realize this pattern: site percolation, Ising model and random Coulomb potential (RCP). The first two models are short range interaction (SRI), whereas the last one includes coulomb like interactions which is pretty long range (long-range interactions, LRI). By examining various dynamical observables we show that the critical exponents of SRI IP are robust against the control parameters (temperature in the Ising model and occupation probability in site percolation), whereas its properties in the LRI (RCP) supports are completely different from the normal IP (i.e. on the regular lattice). Especially the fractal dimension of the external frontier of the largest hole converges to $1.099\pm 0.008$ for RCP IP, whereas it is nearly $\frac{4}{3}$ for SRI IP being compatible with normal IP. Additionally a novel dynamical crossover is seen in the RCP IP according to which the time dependence of all of the observables is divided to three parts: the power-law (small times), the logarithmic (mid time), and the linear (long time) regimes. The second crossover time is shown to go to infinity in the thermodynamic limit, whereas the first crossover time is nearly unchanged, signaling the dominance of the logarithmic regime. The observables become nearly constant in the thermodynamic limit for the long time, showing that it is a stationary phase.

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arXiv2021

Self-similar but not conformally invariant traces obtained by modified Loewner forces

The two-dimensional Loewner exploration process is generalized to the case where the random force is self-similar with positively correlated increments. We model this random force by a fractional Brownian motion with Hurst exponent $H\geq \frac{1}{2}\equiv H_{\text{BM}}$, where $H_{\text{BM}}$ stands for the one-dimensional Brownian motion. By manipulating the deterministic force, we design a scale-invariant equation describing self-similar traces which lack conformal invariance. The model is investigated in terms of the "input diffusivity parameter" $κ$, which coincides with the one of the ordinary Schramm-Loewner evolution (SLE) at $H=H_{\text{BM}}$. In our numerical investigation, we focus on the scaling properties of the traces generated for $κ=2,3$, $κ=4$ and $κ=6,8$ as the representatives, respectively, of the dilute phase, the transition point and the dense phase of the ordinary SLE. The resulting traces are shown to be scale-invariant. Using two equivalent schemes, we extract the fractal dimension, $D_f(H)$, of the traces which decrease monotonically with increasing $H$, reaching $D_f=1$ at $H=1$ for all $κ$ values. The left passage probability (LPP) test demonstrates that, for $H$ values not far from the uncorrelated case (small $ε_H\equiv \frac{H-H_{\text{BM}}}{H_{\text{BM}}}$) the prediction of the ordinary SLE is applicable with an effective diffusivity parameter $κ_{\text{eff}}$. Not surprisingly, the $κ_{\text{eff}}$'s do not fulfill the prediction of SLE for the relation between $D_f(H)$ and the diffusivity parameter.

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arXiv2020

Self-organized criticality in cumulus clouds

The shape of clouds has proven to be essential for classifying them. Our analysis of images from fair weather cumulus clouds reveals that, besides by turbulence they are driven by self-organized criticality (SOC). Our observations yield exponents that support the fact the clouds, when projected to two dimensions (2D), exhibit conformal symmetry compatible with $c=-2$ conformal field theory (CFT), in contrast to 2D turbulence which has $c=0$ CFT. By using a combination of the Navier-Stokes equation, diffusion equations and a coupled map lattice (CML) we successfully simulated cloud formation, and obtained the same exponents.

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arXiv2020

Some Properties of Sandpile Models as Prototype of Self-Organized Critical Systems

This paper is devoted to the recent advances in self-organized criticality (SOC), and the concepts. The paper contains three parts; in the first part we present some examples of SOC systems, in the second part we add some comments concerning its relation to logarithmic conformal field theory, and in the third part we report on the application of SOC concepts to various systems ranging from cumulus clouds to 2D electron gases.

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arXiv2020

Two temperature Ising Model

We introduce a two-temperature Ising model as a prototype of superstatistic critical phenomena. The model is described by two temperatures ($T_1,T_2$) in zero magnetic field. To predict the phase diagram and numerically estimate the exponents, we develop Metropolis and Swendsen-Wang Monte Carlo method. We observe that there is a non-trivial critical line, separating ordered and disordered phases. We propose an analytic equation for the critical line in the phase diagram. Our numerical estimation of the critical exponents illustrates that all points on the critical line belong to the ordinary Ising universality class.

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arXiv2020

The elastic backbone phase transition in the Ising model

The two-dimensional (zero magnetic field) Ising model is known to undergo a second order para-ferromagnetic phase transition, which is accompanied by a correlated percolation transition for the Fortuin-Kasteleyn (FK) clusters. In this paper we uncover that there exists also a second temperature $T_{\text{eb}}<T_c$ at which the elastic backbone of FK clusters undergoes a second order phase transition to a dense phase. The corresponding universality class, which is characterized by determining various percolation exponents, is shown to be completely different from directed percolation, proposing a new anisotropic universality class with $β=0.54\pm 0.02$, $ν_{||}=1.86\pm 0.01$, $ν_{\perp}=1.21\pm 0.04$ and $d_f=1.53\pm 0.03$. All tested hyper-scaling relations are shown to be valid.

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arXiv2020

Geometry-induced non-equilibrium phase transition in sandpiles

We study the sandpile model on three-dimensional spanning Ising clusters with the temperature $T$ treated as the control parameter. By analyzing the three dimensional avalanches and their two-dimensional projections (which show scale-invariant behavior for all temperatures), we uncover two universality classes with different exponents (an ordinary BTW class, and SOC$_{T=\infty}$), along with a tricritical point (at $T_c$, the critical temperature of the host) between them. The transition between these two criticalities is induced by the transition in the support. The SOC$_{T=\infty}$ universality class is characterized by the exponent of the avalanche size distribution $τ^{T=\infty}=1.27\pm 0.03$, consistent with the exponent of the size distribution of the Barkhausen avalanches in amorphous ferromagnets (Phys. Rev. L 84, 4705 (2000)). The tricritical point is characterized by its own critical exponents. In addition to the avalanche exponents, some other quantities like the average height, the spanning avalanche probability (SAP) and the average coordination number of the Ising clusters change significantly the behavior at this point, and also exhibit power-law behavior in terms of $ε\equiv \frac{T-T_c}{T_c}$, defining further critical exponents. Importantly the finite size analysis for the activity (number of topplings) per site shows the scaling behavior with exponents $β=0.19\pm 0.02$ and $ν=0.75\pm 0.05$. A similar behavior is also seen for the SAP and the average avalanche height. The fractal dimension of the external perimeter of the two-dimensional projections of avalanches is shown to be robust against $T$ with the numerical value $D_f=1.25\pm 0.01$.

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arXiv2018

Schramm-Loewner evolution in the random scatterer Henon-percolation landscapes

The Shcramm-Loewner evolution (SLE) is a correlated exploration process, in which for the chordal set up, the tip of the trace evolves in a self-avoiding manner towards the infinity. The resulting curves are named SLE$_κ$, emphasizing that the process is controlled by one parameter $κ$ which classifies the conformal invariant random curves. This process when experiences some environmental imperfections, or equivalently some scattering random points (which can be absorbing or repelling) results to some other effective scale-invariant curves, which are described by the other effective fractal dimensions and equivalently the other effective diffusivity parameters $κ_{\text{effective}}$. In this paper we use the classical Henon map to generate scattering (absorbing/repelling) points over the lattice in a random way, that realizes the percolation lattice with which the SLE trace interact. We find some meaningful power-law changes of the fractal dimension (and also the effective diffusivity parameter) in terms of the strength of the Henon coupling, namely the $z$ parameter. For this, we have tested the fractal dimension of the curves as well as the left passage probability. Our observations are in support of the fact that this deviation (or equivalently non-zero $z$s) breaks the conformal symmetry of the curves. Also the effective fractal dimension of the curves vary with the second power of $z$, i.e. $D_F(z)-D_F(z=0)\sim z^2$.

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arXiv2018

Correlation effects in the diluteness pattern in non-integral dimensional systems on $ν=\frac{4}{5}$ superdiffusion process

The effect of the correlations in the diluteness pattern in the systems with non-integral dimensionality, on $ν=\frac{4}{5}$ superdiffusion process is considered in this paper. These spatial correlations have proved to be very effective in the critical phenomena. To simulate the particles motion in this process, we employ the loop erased random walk (LERW). The spatial correlations between imperfections (site-diluteness) also have been modeled by the Ising model on a square lattice. It models the forbidden regions into which the particles are not allowed to enter. The correlations are controlled by an artificial temperature $T$. The trace of the walkers is shown to be self-similar, whose fingerprint is the power-law behaviors. The detailed analysis of the random walker's traces reveal that the (Ising-type) correlations affect their geometrical properties. At the critical artificial temperature $T_c$ we observe that the exponent of end-to-end distance $ν$ becomes $0.807\pm 0.002$. The fractal dimension of the walker's trace is the other geometrical quantity which scales inversely with the square root of the correlation length of the Ising model, i.e. $D_f(T)-D_f(T_c)\sim ζ^{-α}$ in which $α=0.43\pm 0.05$. The winding angle test also reveals that the traces are compatible with the Schramm-Loewner evolution theory, and the diffusivity parameter for $T=T_c$ is $κ=1.89\pm 0.05$.

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arXiv2018

Gaussian Free Field in the iso-height random islands tuned by percolation model

The Gaussian free field (GFF) is considered in the background of random iso-height islands which is modeled by the site percolation with the occupation probability $p$. To realize GFF, we consider the Poisson equation in the presence of normal distributed white-noise charges, as the stationary state of the Edwards-Wilkinson (EW) model. The iso-potential (metallic in the terminology of the electrostatic problem) sites are chosen over the lattice according to the percolation problem, giving rise to some metallic islands and some active (not metallic, nor surrounded by a metallic island) area. We see that the dilution of the system by incorporating metallic particles (or equivalently considering the iso-height islands) annihilates the spatial correlations and also the potential fluctuations. Some local and global critical exponents of the problem are reported in this work. The GFF, when simulated on the active area show a cross over between two regimes: small (UV) and large (IR) scales. Importantly, by analyzing the change of exponents (in and out of the critical occupation $p_c$) under changing the system size and the change of the cross-over points, we find two fixed points and propose that GFF$_{p=p_c}$ is unstable towards GFF$_{p=1}$.

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arXiv2018

Scaling properties of mono-layer graphene away from the Dirac point

The statistical properties of the carrier density profile of graphene in the ground state in the presence particle-particle interaction and random charged impurity in zero gate voltage has been recently obtained by Najafi \textit{et al.} (Phys. Rev E95, 032112 (2017)). The non-zero chemical potential ($μ$) in gated graphene has non-trivial effects on electron-hole puddles, since it generates mass in the Dirac action and destroys the scaling behaviors of the effective Thomas-Fermi-Dirac theory. We provide detailed analysis on the resulting spatially inhomogeneous system in the framework of the Thomas-Fermi-Dirac theory for the Gaussian (white noise) disorder potential. We show that, the chemical potential in this system as a random surface, destroys the self-similarity, and the charge field is non-Gaussian. We find that the two-body correlation functions are factorized to two terms: a pure function of the chemical potential and a pure function of the distance. The spatial dependence of these correlation functions is double-logarithmic, e.g. the two-point density correlation $D_2(r,μ)\propto μ^2\exp\left[-\left(-a_D\ln\ln r^{β_D}\right)^{α_D} \right]$ ($α_D=1.82$, $β_D=0.263$ and $a_D=0.955$). The Fourier power spectrum function behaves like $\ln(S(q))=-β_S^{-a_S}\left(\ln q \right)^{a_S}+2\ln μ$ ($a_S=3.0\pm 0.1$ and $β_S=2.08\pm 0.03$) in contrast to the ordinary Gaussian rough surfaces for which $a_S=1$ and $β_S=\frac{1}{2}(1+α)^{-1}$, ($α$ being the roughness exponent). The geometrical properties are however similar to the un-gated ($μ=0$) case, with the exponents that are reported in the text.

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arXiv2018

Gaussian Free Field in the background of correlated random clusters, formed by metallic nanoparticles

The effect of metallic nano-particles (MNPs) on the electrostatic potential of a disordered 2D dielectric media is considered. The disorder in the media is assumed to be white-noise Coulomb impurities with normal distribution. To realize the correlations between the MNPs we have used the Ising model with an artificial temperature $T$ that controls the number of MNPs as well as their correlations. In the $T\rightarrow 0$ limit, one retrieves the Gaussian free field (GFF), and in the finite temperature the problem is equivalent to a GFF in iso-potential islands. The problem is argued to be equivalent to a scale-invariant random surface with some critical exponents which vary with $T$ and correspondingly are correlation-dependent. Two type of observables have been considered: local and global quantities. We have observed that the MNPs soften the random potential and reduce its statistical fluctuations. This softening is observed in the local as well as the geometrical quantities. The correlation function of the electrostatic and its total variance are observed to be logarithmic just like the GFF, i.e. the roughness exponent remains zero for all temperatures, whereas the proportionality constants scale with $T-T_c$. The fractal dimension of iso-potential lines ($D_f$), the exponent of the distribution function of the gyration radius ($τ_r$), and the loop lengths ($τ_l$), and also the exponent of the loop Green function $x_l$ change in terms of $T-T_c$ in a power-law fashion, with some critical exponents reported in the text. Importantly we have observed that $D_f(T)-D_f(T_c)\sim\frac{1}{\sqrt{ξ(T)}}$, in which $ξ(T)$ is the spin correlation length in the Ising model.

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arXiv2018

Self-Avoiding Walk on the square site-diluted Ising-correlated lattice

The self-avoiding walk on the square site-diluted correlated percolation lattice is considered. The Ising model is employed to realize the spatial correlations of the metric space. As a well-accepted result, the (generalized) Flory's mean field relation is tested to measure the effect of correlation. After exploring a perturbative Fokker-Planck-like equation, we apply an enriched Rosenbluth Monte Carlo method to study the problem. To be more precise, the winding angel analysis is also performed from which the diffusivity parameter of Schramm-Loewner evolution (SLE) theory ($κ$) is extracted. We find that at the critical Ising (host) system the exponents are in agreement with the Flory's approximation. For the off-critical Ising system we find also a new behavior for the fractal dimension of the walker trace in terms of the correlation length of the Ising system $ξ(T)$, i.e. $D_F^{\text{SAW}}(T)-D_F^{\text{SAW}}(T_c)\sim \frac{1}{\sqrt{ξ(T)}}$.

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