arXiv subjects

S. M. S. Movahed

Publications and source records attributed to S. M. S. Movahed.

33 records · Page 2Linked to original sources

arXiv2019

Long-range temporal correlation in Auditory Brainstem Responses to Spoken Syllable /da/

The speech auditory brainstem response (sABR) is an objective clinical tool to diagnose particular impairments along the auditory brainstem pathways. We explore the scaling behavior of the brainstem in response to synthetic /da/ stimuli using a proposed pipeline including Multifractal Detrended Moving Average Analysis (MFDMA) modified by Singular Value Decomposition. The scaling exponent confirms that all normal sABR are classified into the non-stationary process. The average Hurst exponent is $H=0.77\pm0.12$ at 68\% confidence interval indicating long-range correlation which shows the first universality behavior of sABR. Our findings exhibit that fluctuations in the sABR series are dictated by a mechanism associated with long-term memory of the dynamic of the auditory system in the brainstem level. The $q-$dependency of $h(q)$ demonstrates that underlying data sets have multifractal nature revealing the second universality behavior of the normal sABR samples. Comparing Hurst exponent of original sABR with the results of the corresponding shuffled and surrogate series, we conclude that its multifractality is almost due to the long-range temporal correlations which are devoted to the third universality. Finally, the presence of long-range correlation which is related to the slow timescales in the subcortical level and integration of information in the brainstem network is confirmed.

q-bio.QM↗

arXiv2018

Identification of Defective Two Dimensional Semiconductors by Multifractal Analysis: The Single-layer ${\rm MoS_2}$ Case Study

Two dimensional semiconductor such as single-layer transition metal dichalcogenides (SL-TMD) have attracted most attentions as an atomically thin layer semiconductor materials. Typically, lattice point defects (sulfur vacancy) created by physical/chemical method during growth stages, have disadvantages on electronic properties. However, photoluminescence (PL) spectroscopy is conventionally used to characterize single-layer films but until now it has not been used to show the presence of defects or estimate their population due to overall similarity of general feature PL spectra. To find a feasible and robust method to determine the presence of point defects on single layer ${\rm MoS_2}$ without changing the experimental setup, Multifractal Detrended Fluctuation Analysis (MF-DFA) and Multifractal Detrended Moving Average Analysis (MF-DMA) are applied on the PL spectrum of single layer ${\rm MoS_2}$. We compare the scaling behavior of PL spectrum of pristine and defective single layer ${\rm MoS_2}$ determined by MF-DFA and MF-DMA. Our results reveal that PL spectrum has multifractal nature and different various population of point defects (sulfur vacancy) on single layer ${\rm MoS_2}$ change dramatically multifractality characteristics (Hurst, Hölder exponents) of photoluminescence spectrum. It is exhibited creating more lattice point leads to smaller fluctuations in luminescent light that it can help to design special defect structure for light emitted devices. The relative populations of point defects are almost elucidated without utilizing expensive characterization instruments such as scanning tunneling microscopy (STM) and high resolution transmission electron microscopy (HR-TEM).

cond-mat.mtrl-sci↗

arXiv2018

The Integrated Sachs-Wolfe Effect in the Bulk Viscous Dark Energy Model

We examine linear perturbation theory to evaluate the contribution of viscosity coefficient in the growing of dark matter perturbations in the context of the bulk viscous dark energy model inspired by thermodynamical dissipative phenomena proposed by [B. Mostaghel et al., 2017, The European Physical Journal C, 77, 541]. As the cosmological implementations, we investigate the {\it Integrated Sachs-Wolfe} (ISW) auto-power spectrum, the ISW-galaxy cross-power spectrum and derive limits on $fσ_8$. The dimensionless bulk viscosity coefficient ($γ$) in the absence of interaction between dark sectors, modifies the Hubble parameter and the growth function, while the Poisson equation remains unchanged. Increasing $γ$ reduces the dark matter growing mode at the early epoch while a considerable enhancement will be achieved at the late time. This behavior imposes non-monotonic variation in the time evolution of gravitational potential generating a unique signature on the CMB photons. The bulk viscous dark energy model leads to almost a decreasing in ISW source function at the late time. Implementation of the Redshift Space Distortion (RSD) observations based on "Gold-2017" catalogue, shows $Ω^0_{\rm m} =0.303^{+0.044}_{-0.038}$, $γ=0.033^{+0.098}_{-0.033}$ and $σ_8= 0.769^{+0.080}_{-0.089}$ at $1σ$ level of confidence. Finally, tension in the $σ_8$ is alleviated in our viscous dark energy model.

astro-ph.CO↗

arXiv2018

Crossing statistics of laser light scattered through a nanofluid

In this paper, we investigate the crossing statistics of speckle patterns formed in Fresnel diffraction region by a laser beam scattering through a nanofluid. We extend $zero-crossing$ statistics to assess dynamical properties of nanofluid. According to joint probability density function of laser beam fluctuation and its time derivative, theoretical framework for Gaussian and non-Gaussian regimes are revisited. We count number of crossings not only at {\it zero} level but also for all available thresholds to determine the average speed of moving particles. Using probabilistic framework in determining crossing statistics, {\it a priori} Gaussianity is not essentially considered, therefore even in presence of deviation from Gaussian fluctuation, this modified approach is capable to compute relevant quantities such as mean value of speed more precisely. Generalized total crossing which represents the weighted summation of crossings for all thresholds to quantify small deviation from Gaussian statistics is introduced. This criterion can also manipulate the contribution of noises and trends to infer reliable physical quantities. The characteristic time scale for having successive crossings at a given threshold is defined. In our experimental setup, we find that increasing sample temperature leads to more consistency between Gaussian and perturbative non-Gaussian predictions. The maximum number of crossing does not necessarily occur at mean level indicating that we should take into account other levels in addition to {\it zero} level to achieve more accurate assessments.

cond-mat.stat-mech↗

arXiv2018

Multifractal Analysis of Pulsar Timing Residuals: Assessment of Gravitational Wave Detection

We introduce a pipeline including multifractal detrended cross-correlation analysis (MF-DXA) modified by either singular value decomposition or the adaptive method to examine the statistical properties of the pulsar timing residual ($PTR$) induced by a gravitational wave (GW) signal. We propose a new algorithm, the so-called irregular-MF-DXA, to deal with irregular data sampling. Inspired by the quadrupolar nature of the spatial cross-correlation function of a gravitational wave background, a new cross-correlation function, $\barσ_{\times}$, derived from irregular-MF-DXA will be introduced. We show that, this measure reveals the quadrupolar signature in the $PTRs$ induced by stochastic GWB. We propose four strategies based on the $y$-intercept of fluctuation functions, the generalized Hurst exponent, and the width of the singularity spectrum to determine the dimensionless amplitude and power-law exponent of the characteristic strain spectrum as $\mathcal{H}_c(f)\sim\mathcal{A}_{yr}(f/f_{yr})^ζ$ for stochastic GWB. Using the value of Hurst exponent, one can clarify the type of GWs. We apply our pipeline to explore 20 millisecond pulsars observed by Parkes Pulsar Timing Array. The computed scaling exponents confirm that all data are classified into a nonstationary class implying the universality feature. The value of the Hurst exponent is in the range $H\in [0.56,0.87]$. The $q$-dependency of the generalized Hurst exponent demonstrates that the observed $PTRs$ have multifractal behavior, and the source of this multifractality is mainly attributed to the correlation of data which is another universality of the observed datasets. Multifractal analysis of available $PTRs$ datasets reveals an upper bound on the dimensionless amplitude of the GWB, $\mathcal{A}_{yr}< 2.0\times 10^{-15}$.

astro-ph.SR↗

arXiv2018

Cosmic String Detection with Tree-Based Machine Learning

We explore the use of random forest and gradient boosting, two powerful tree-based machine learning algorithms, for the detection of cosmic strings in maps of the cosmic microwave background (CMB), through their unique Gott-Kaiser-Stebbins effect on the temperature anisotropies.The information in the maps is compressed into feature vectors before being passed to the learning units. The feature vectors contain various statistical measures of processed CMB maps that boost the cosmic string detectability. Our proposed classifiers, after training, give results improved over or similar to the claimed detectability levels of the existing methods for string tension, $Gμ$. They can make $3σ$ detection of strings with $Gμ\gtrsim 2.1\times 10^{-10}$ for noise-free, $0.9'$-resolution CMB observations. The minimum detectable tension increases to $Gμ\gtrsim 3.0\times 10^{-8}$ for a more realistic, CMB S4-like (II) strategy, still a significant improvement over the previous results.

astro-ph.CO↗

arXiv2017

Multi-Scale Pipeline for the Search of String-Induced CMB Anisotropies

We propose a multi-scale edge-detection algorithm to search for the Gott-Kaiser-Stebbins imprints of a cosmic string (CS) network on the Cosmic Microwave Background (CMB) anisotropies. Curvelet decomposition and extended Canny algorithm are used to enhance the string detectability. Various statistical tools are then applied to quantify the deviation of CMB maps having a cosmic string contribution with respect to pure Gaussian anisotropies of inflationary origin. These statistical measures include the one-point probability density function, the weighted two-point correlation function (TPCF) of the anisotropies, the unweighted TPCF of the peaks and of the up-crossing map, as well as their cross-correlation. We use this algorithm on a hundred of simulated Nambu-Goto CMB flat sky maps, covering approximately $10\%$ of the sky, and for different string tensions $Gμ$. On noiseless sky maps with an angular resolution of $0.9'$, we show that our pipeline detects CSs with $Gμ$ as low as $Gμ\gtrsim 4.3\times 10^{-10}$. At the same resolution, but with a noise level typical to a CMB-S4 phase II experiment, the detection threshold would be to $Gμ\gtrsim 1.2 \times 10^{-7}$.

astro-ph.CO↗

arXiv2017

Assessment of 48 Stock markets using adaptive multifractal approach

Stock market comovements are examined using cointegration, Granger causality tests and nonlinear approaches in context of mutual information and correlations. Underlying data sets are affected by non-stationarities and trends, we also apply AMF-DFA and AMF-DXA. We find only 170 pair of Stock markets cointegrated, and according to the Granger causality and mutual information, we realize that the strongest relations lies between emerging markets, and between emerging and frontier markets. According to scaling exponent given by AMF-DFA, $h(q=2)>1$, we find that all underlying data sets belong to non-stationary process. According to EMH, only 8 markets are classified in uncorrelated processes at $2σ$ confidence interval. 6 Stock markets belong to anti-correlated class and dominant part of markets has memory in corresponding daily index prices during January 1995 to February 2014. New-Zealand with $H=0.457\pm0.004$ and Jordan with $H=0.602\pm 0.006$ are far from EMH. The nature of cross-correlation exponents based on AMF-DXA is almost multifractal for all pair of Stock markets. The empirical relation, $H_{xy}\le [H_{xx}+H_{yy}]/2$, is confirmed. Mentioned relation for $q>0$ is also satisfied while for $q<0$ there is a deviation from this relation confirming behavior of markets for small fluctuations is affected by contribution of major pair. For larger fluctuations, the cross-correlation contains information from both local and global conditions. Width of singularity spectrum for auto-correlation and cross-correlation are $Δα_{xx}\in [0.304,0.905]$ and $Δα_{xy}\in [0.246,1.178]$, respectively. The wide range of singularity spectrum for cross-correlation confirms that the bilateral relation between Stock markets is more complex. The value of $σ_{DCCA}$ indicates that all pairs of stock market studied in this time interval belong to cross-correlated processes.

q-fin.ST↗

arXiv2017

Consistency of nonlinear interacting ghost dark energy with recent observations

In this paper we investigate ghost dark energy model in the presence of non-linear interaction between dark energy and dark matter. We also extend the analysis to the so called generalized ghost dark energy (GGDE) which $ρ_D=αH+βH^2$. The model contains three free parameters as $Ω_D, ζ(=\frac{8πG β}{3})$ and $b^2$ (the coupling coefficient of interactions). We propose three kinds of non-linear interaction terms and discuss the behavior of equation of state, deceleration and dark energy density parameters of the model. We also find the squared sound speed and search for signs of stability of the model. To compare the interacting GGDE model with observational data sets, we use more recent observational outcomes, namely SNIa from JLA catalog, Hubble parameter, baryonic acoustic oscillation and the most relevant CMB parameters including, the position of acoustic peaks, shift parameters and redshift to recombination. For GGDE with the first non-linear interaction, the joint analysis indicates that $Ω_D=0.7192\pm0.0062$, $b^2=0.146^{+0.030}_{-0.026}$ and $ζ=0.104\pm0.047$ at 1 optimal variance error. For the second interaction, the best fit values at $1σ$ confidence are $Ω_D=0.72091\pm0.0065$, $b^2=0.0395\pm0.0080$ and $ζ\le0.0173$. According to combination of all observational data sets considered in this paper the best fit values for third non-linearly interacting model are $Ω_D=0.7287\pm0.0062$, $b^2=0.0109\pm0.0023$ and $ζ\le0.00764$ at $1σ$ confidence interval. Finally we found that the presence of interaction is compatible in mentioned models via current observational data sets.

astro-ph.CO↗

arXiv2017

Non-minimal Derivative Coupling Scalar Field and Bulk Viscous Dark Energy

Inspired by thermodynamical dissipative phenomena, we consider bulk viscosity for dark fluid in a spatially flat two-component Universe. Our viscous dark energy model represents Phantom crossing avoiding Big-Rip singularity. We propose a non-minimal derivative coupling scalar field with zero potential leading to accelerated expansion of Universe in the framework of bulk viscous dark energy model. In this approach, coupling constant ($κ$) is related to viscosity coefficient ($γ$) and energy density of dark energy at the present time ($Ω_{\rm DE}^0$). This coupling is bounded as $κ\in [-1/9H_0^2(1-Ω_{\rm DE}^0), 0]$ and for $γ=0$ leads to $κ=0$. To perform robust analysis, we implement recent observational data sets including Joint Light-curve Analysis (JLA) for SNIa, Gamma Ray Bursts (GRBs) for most luminous astrophysical objects at high redshifts, Baryon Acoustic Oscillations (BAO) from different surveys, Hubble parameter from HST project, {\it Planck} data for CMB power spectrum and CMB Lensing. Joint analysis of JLA$+$GRBs$+$BAO$+$HST shows that $Ω_{\rm DE}^0=0.696\pm 0.010$, $γ=0.1404\pm0.0014$ and $H_0=68.1\pm1.3$ at $1σ$ confidence interval. {\it Planck} TT observation provides $γ=0.32^{+0.31}_{-0.26}$ at $68\%$ confidence limit for viscosity coefficient. Tension in Hubble parameter is alleviated in this model. Cosmographic distance ratio indicates that current observed data prefer to increase bulk viscosity. Finally, the competition between Phantom and Quintessence behavior of viscous dark energy model can accommodate cosmological old objects reported as a sign of age crisis in $Λ$CDM model.

astro-ph.CO↗

arXiv2017

Spin Hall effect originated from fractal surface

Spin hall effect (SHE) in thin films is inherited by surface roughness. Although roughness effect on SHE has been studied in thin films, but roughness is not only parameter in rough surfaces. Our results show that how other statistical parameters of rough surface play important role in SHE. In this paper we investigate theoretically the effects of correlated surface roughness in the SHE with self affine fractal surface in non-heavy metallic thin films in the frame work of the Born approximation. The surface roughness is described by the k-correlation model and is characterized by the roughness exponent H (0 <= H <= 1), the in plane correlation length kesi and the rms roughness amplitude delta. We show that the spin Hall angle can increase by one order of magnitude when H decreasing from H = 1 to H = 0. We also demonstrate the SHE for surface roughness with distribution function of the Gaussian profile is mainly contributed by the side jump scattering while for that with a non-Gaussian profile, both side jump and skew scattering are present. our achievements demonstrate the important role of roughness texture profile for SHE in non-heavy metals.

cond-mat.mes-hall↗

arXiv2016

Dynamics of magnetic nano-flake vortices in Newtonian fluids

We study the rotational motion of nano-flake ferromagnetic discs 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 discs 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 stored in the discs. Our approach can be implemented in many practical applications including biotechnology and multi-functional fluidics.

cond-mat.stat-mech↗

arXiv2016

Crossing Statistics of Anisotropic Stochastic Surface

In this paper, we propose crossing statistics and its generalization, as a new framework to characterize the anisotropy in a 2D field, e.g. height on a surface, extendable to higher dimensions. By measuring $ν^+$, the number of up-crossing (crossing points with positive slope at a given threshold of height ($α$)), and $N_{tot}$ (the generalized roughness function), it is possible to distinguish the nature of anisotropy, rotational invariance and Gaussianity of any given surface. For the case of anisotropic correlated self- or multi-affine surfaces (even with different correlation lengths in various directions and/or directional scaling exponents), we analytically derive some relations between $ν^+$ and $N_{tot}$ with corresponding scaling parameters. The method systematically distinguishes the directions of anisotropy, at $3σ$ confidence interval using P-value statistics. After applying a typical method in determining the corresponding scaling exponents in identified anisotropic directions, we are able to determine the kind and ratio of correlation length anisotropy. To demonstrate capability and accuracy of the method, as well validity of analytical relations, our proposed measures are calculated on synthetic stochastic rough interfaces and rough interfaces generated from simulation of ion etching. There are good consistencies between analytical and numerical computations. The proposed algorithm can be mounted with a simple software on various instruments for surface analysis and characterization, such as AFM, STM and etc.

physics.comp-ph↗

arXiv2015

Coupled uncertainty provided by a multifractal random walker

The aim here is to study the concept of pairing multifractality between time series possessing non-Gaussian distributions. The increasing number of rare events creates "criticality". We show how the pairing between two series is affected by rare events, which we call "coupled criticality". A method is proposed for studying the coupled criticality born out of the interaction between two series, using the bivariate multifractal random walk (BiMRW). This method allows studying dependence of the coupled criticality on the criticality of each individual system. This approach is applied to data sets of gold and oil markets, and inflation and unemployment.

physics.data-an↗

arXiv2015

Assessment of petrophysical quantities inspired by joint multifractal approach

In this paper joint multifractal random walk approach is carried out to analyze some petrophysical quantities for characterizing the petroleum reservoir. These quantities include Gamma emission (GR), sonic transient time (DT) and Neutron porosity (NPHI) which are collected from four wells of a reservoir. To quantify mutual interaction of petrophysical quantities, joint multifractal random walk is implemented. This approach is based on the mutual multiplicative cascade notion in the multifractal formalism and in this approach $L_0$ represents a benchmark to describe the nature of cross-correlation between two series. The analysis of the petrophysical quantities revealed that GR for all wells has strongly multifractal nature due to the considerable abundance of large fluctuations in various scales. The variance of probability distribution function, $λ_{\ell}^2$, at scale $\ell$ and its intercept determine the multifractal properties of the data sets sourced by probability density function. The value of $λ_0 ^2$ for NPHI data set is less than GR's, however, DT shows a nearly monofractal behavior, namely $λ_0 ^2\rightarrow 0$, so we find that $λ_0^2({\rm GR})>λ_0^2({\rm NPHI})\ggλ_0^2({\rm DT})$. While, the value of Hurst exponents can not discriminate between series GR, NPHI and DT. Joint analysis of the petrophysical quantities for considered wells demonstrates that $L_0$ has negative value for GR-NPHI confirming that finding shaly layers is in competition with finding porous medium while it takes positive value for GR-DT determining that continuum medium can be detectable by evaluating the statistical properties of GR and its cross-correlation to DT signal.

physics.comp-ph↗