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    Energy-landscape networks of spin glasses

    , Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 77, Issue 3 , 2008 ; 15393755 (ISSN) Seyed Allaei, H ; Seyed Allaei, H ; Ejtehadi, M. R ; Sharif University of Technology
    2008
    Abstract
    We have studied the topology of the energy landscape of a spin-glass model and the effect of frustration on it by looking at the connectivity and disconnectivity graphs of the inherent structure. The connectivity network shows the adjacency of energy minima whereas the disconnectivity network tells us about the heights of the energy barriers. Both graphs are constructed by the exact enumeration of a two-dimensional square lattice of a frustrated spin glass with nearest-neighbor interactions up to the size of 27 spins. The enumeration of the energy-landscape minima as well as the analytical mean-field approximation show that these minima have a Gaussian distribution, and the connectivity... 

    Vortex with fourfold defect lines in a simple model of self-propelled particles

    , Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 93, Issue 3 , 2016 ; 15393755 (ISSN) Seyed Allaei, H ; Ejtehadi, M. R ; Sharif University of Technology
    American Physical Society  2016
    Abstract
    We study the formation of a vortex with fourfold symmetry in a minimal model of self-propelled particles, confined inside a squared box, using computer simulations and also theoretical analysis. In addition to the vortex pattern, we observe five other regimes in the system: a homogeneous gaseous phase, band structures, moving clumps, moving clusters, and vibrating rings. All six regimes emerge from controlling the strength of noise and from the contribution of repulsion and alignment interactions. We study the shape of the vortex and its symmetry in detail. The pattern shows exponential defect lines where incoming and outgoing flows of particles collide. We show that alignment and repulsion... 

    Topologic Properties Of The Energy Landscape Network In Frustrated Systems

    , M.Sc. Thesis Sharif University of Technology Allaei, Hamid (Author) ; Ejtehadi, Mohammad Reza (Supervisor)
    Abstract
    The study of Energy Landscape of physical systems has a key role in complex problems. In this project we have enumerated the energy landscape of a finite squared lattice spin glass with nearest neighbored interactions to study its behavior. We choose the coupling constants of this spin glass system with Heb rule. According to this rule the coupling constants are chosen in a way to make specific patterns of spin configuration as a local minimum. We have studied these spin glasses with different number of patterns. In our computation we saw a significant difference between spin glasses with odd and even number of patterns. We addressed this behavior to properties of coupling constant... 

    Gaussian theory for spatially distributed self-propelled particles

    , Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 94, Issue 6 , 2016 ; 15393755 (ISSN) Seyed Allaei, H ; Schimansky Geier, L ; Ejtehadi, M. R ; Sharif University of Technology
    American Physical Society  2016
    Abstract
    Obtaining a reduced description with particle and momentum flux densities outgoing from the microscopic equations of motion of the particles requires approximations. The usual method, we refer to as truncation method, is to zero Fourier modes of the orientation distribution starting from a given number. Here we propose another method to derive continuum equations for interacting self-propelled particles. The derivation is based on a Gaussian approximation (GA) of the distribution of the direction of particles. First, by means of simulation of the microscopic model, we justify that the distribution of individual directions fits well to a wrapped Gaussian distribution. Second, we numerically... 

    Simulation of droplet trains in microfluidic networks

    , Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 82, Issue 3 , September , 2010 ; 15393755 (ISSN) Djalali Behzad, M ; Seyed Allaei, H ; Ejtehadi, M. R ; Sharif University of Technology
    2010
    Abstract
    We show that in a microfluidic network with low Reynolds numbers, a system can be irreversible due to hysteresis effects. We simulated a network of pipes that was used in a recent experiment. The network consists of one loop connected to input and output pipes. A train of droplets enters the system at a uniform rate, but the droplets may leave the system in a periodic or even a chaotic pattern. The output pattern depends on the time interval between incoming droplets as well as the network geometry. For some parameters, the system is not reversible  

    Propagation of acoustic waves as a probe for distinguishing heterogeneous media with short-range and long-range correlations

    , Article Journal of Statistical Mechanics: Theory and Experiment ; Volume 2008, Issue 3 , 2008 ; 17425468 (ISSN) Vaez Allaei, S. M ; Sahimi, M ; Rahimi Tabar, M. R ; Sharif University of Technology
    2008
    Abstract
    The propagation of acoustic waves in strongly heterogeneous media is studied using direct numerical simulations. Two types of heterogeneous media are considered. In one type, the spatial distribution of the local elastic constants contain long-range correlations with a power law, nondecaying correlation function. The correlation length is, therefore, as large as the linear size of the system. In the second type of heterogeneous media the correlation length is decreased, up to the linear size of the blocks in the computational grid and, therefore, the distribution of the elastic constants is uncorrelated or white noise, but with the same mean and variance as that of the correlated media. We... 

    Gaussian Theory for Derivation of Continuum Equations of Self-propelled Particles

    , Ph.D. Dissertation Sharif University of Technology Allaei, Hamid (Author) ; Ejtehadi, Mohammad Reza (Supervisor) ; Moghimi, Saman (Co-Advisor)
    Abstract
    The collective behavior of active matters, e.g. colony of micro swimmers and flocks of birds is modeled with self-propelled particles. It is evident that a continuum description of such systems is useful in determining the collective behavior in large scales. One can make continuum equations in active matter with the help of symmetry arguments. However, the equation is in a phenomenological level with undetermined transport coefficients. It is possible to construct the continuum equations from microscopic rules to find the transport coefficients in terms of microscopic parameters with approximations. One of the usual approximations called truncation method is to truncate the Fourier series... 

    Diffusion and self-assembly of C60 molecules on monolayer graphyne sheets

    , Article Scientific Reports ; Volume 6 , 2016 ; 20452322 (ISSN) Ozmaian, M ; Fathizadeh, A ; Jalalvand, M ; Ejtehadi, M. R ; Vaez Allaei, S. M ; Sharif University of Technology
    Nature Publishing Group  2016
    Abstract
    The motion of a fullerene (C60) on 5 different types of graphyne is studied by all-atom molecular dynamics simulations and compared with former studies on the motion of C60 on graphene. The motion shows a diffusive behavior which consists of either a continuous motion or discrete movements between trapping sites depending on the type of the graphyne sheet. For graphyne-4 and graphyne-5, fullerenes could detach from the surface of the graphyne sheet at room temperature which was not reported for similar cases on graphene sheets. Collective motion of a group of fullerenes interacting with a graphyne studied and it is shown that fullerenes exhibit stable assemblies. Depending on the type of... 

    Height fluctuations and intermittency of V2O5 films by atomic force microscopy

    , Article Journal of Physics Condensed Matter ; Volume 15, Issue 12 , 2003 , Pages 1889-1898 ; 09538984 (ISSN) Iraji Zad, A ; Kavei, G ; Rahimi Tabar, M. R ; Vaez Allaei, S. M ; Sharif University of Technology
    2003
    Abstract
    The spatial scaling law and intermittency of the V2O5 surface roughness has been investigated by atomic force microscopy. The intermittency of the height fluctuations has been checked by two different methods, first, by measuring the scaling exponent of the qth moment of height-difference fluctuations i.e. Cq = <|h(x1) - h(x2)|q>, and second, by defining the generating function Z(q, N) and generalized multi-fractal dimension Dq. These methods predict that there is no intermittency in the height fluctuations. The observed roughness and dynamical exponents can be explained by numerical simulation on the basis of the forced Kuramoto-Sivashinsky equation  

    Propagation and localization of acoustic and elastic waves in heterogeneous materials: Renormalization group analysis and numerical simulations

    , Article Acta Mechanica ; Volume 205, Issue 1-4 , 2009 , Pages 197-222 ; 00015970 (ISSN) Sahimi, M ; Rahimi Tabar, M. R ; Bahraminasab, A ; Sepehrinia, R ; Vaez Allaei, S. M ; Sharif University of Technology
    2009
    Abstract
    We describe and discuss the recent progress in the study of propagation and localization of acoustic and elastic waves in heterogeneous media. The heterogeneity is represented by a spatial distribution of the local elastic moduli. Both randomly distributed elastic moduli as well as those with long-range correlations with a nondecaying power-law correlation function, are considered. The motivation for the study is twofold. One is that recent analysis of experimental data for the spatial distribution of the elastic moduli of rock indicated that the distribution is characterized by the type of long-range correlations that we consider in this study. The second motivation for the problem is to... 

    Localization of elastic waves in heterogeneous media with off-diagonal disorder and long-range correlations

    , Article Physical Review Letters ; Volume 94, Issue 16 , 2005 ; 00319007 (ISSN) Shahbazi, F ; Bahraminasab, A ; Vaez Allaei, S. M ; Sahimi, M ; Rahimi Tabar, M. R ; Sharif University of Technology
    2005
    Abstract
    Using the Martin-Siggia-Rose method, we study propagation of acoustic waves in strongly heterogeneous media which are characterized by a broad distribution of the elastic constants. Gaussian-white distributed elastic constants, as well as those with long-range correlations with nondecaying power-law correlation functions, are considered. The study is motivated in part by a recent discovery that the elastic moduli of rock at large length scales may be characterized by long-range power-law correlation functions. Depending on the disorder, the renormalization group (RG) flows exhibit a transition to localized regime in any dimension. We have numerically checked the RG results using the... 

    Reply to "comment on 'renormalization group analysis and numerical simulation of propagation and localization of acoustic waves in heterogeneous media'"

    , Article Physical Review B - Condensed Matter and Materials Physics ; Volume 77, Issue 21 , 2008 ; 10980121 (ISSN) Bahraminasab, A ; Esmailpour, A ; Vaez Allaei, S. M ; Shahbazi, F ; Sahimi, M ; Rahimi Tabar, M. R ; Sharif University of Technology
    2008
    Abstract
    Based on extensive new numerical simulations, we show that Chu's arguments and objections against our previous results are invalid. In addition, we explain the origin of the differences between our results and the previous ones, obtained based on a simple model of one-dimensional disordered materials. © 2008 The American Physical Society  

    Optimizing Transmisson from Distant Wind Farms

    , M.Sc. Thesis Sharif University of Technology Abdollahi Mansourkhani, Hamid Reza (Author) ; Hosseini, Hamid (Supervisor)
    Abstract
    Wind power is site dependent and is by nature partially dispatchable. Furthermore, good wind sites are far from grid. Due to these problems, and along with the existing limitations in the transmission networks, a comprehensive analysis over an extended time is needed to properly explore all potential wind sites for wind capacity allocation. This problem is computationally expensive and decomposition methods are required to break down this problem. Here Benders decomposition approach is used, which is a popular technique for solving large-scale problems, to decompose the original problem into a master and a subproblem. The master problem is a linear problem, which allocates wind capacity to... 

    Identification of the Set of Single Nucleotide Variants in Genome Responsible for the Differentiation of Expression of Genes

    , M.Sc. Thesis Sharif University of Technology Khatami, Mahshid (Author) ; Rabiee, Hamid Reza (Supervisor) ; Beigi, Hamid (Supervisor)
    Abstract
    Single nucleotide polymorphs, There are changes caused by a mutation in a nucleotide in the Dena sequence. Mononucleotide polymorphisms are the most common type of genetic variation. Some of these changes have little or no effect on cells, while others cause significant changes in the expression of cell genes that can lead to disease or resistance to certain diseases. Because of the importance of these changes and their effect on cell function, the relationships between these changes are also important. Over the past decade, thousands of single disease-related mononucleotide polymorphisms have been identified in genome-related studies. Studies in this field have shown that the expression of... 

    Synthesis & Characterization of Au-HKUST-1 Nanocomposite and Evaluation of Plasmonic Properties of Gold Nanoparticles in this Nanocomposite

    , M.Sc. Thesis Sharif University of Technology Moazzeni, Hamid Reza (Author) ; Madaah Hosseini, Hamid Reza (Supervisor)
    Abstract
    In the past few years, many research works on the controllable integration of metal nanoparticles and metal-organic frameworks were done, since the obtained composite material shows a synergism effect in catalysis and photocatalysis, drug delivery applications, gas, and energy storage, as well as sensing. For the first time, in this study, we employed template-assisted growth to synthesize Au-HKUST-1 Nanocomposite. XRD analysis entirely confirms that employing this strategy in synthesizing Au-HKUST-1 was wholly successful, and the plasmonic properties of this nanostructure were studied via UV-visible spectroscopy. In the course of synthesis, gold nanoparticles with 70nm diameter were... 

    Stochastic analysis and regeneration of rough surfaces

    , Article Physical Review Letters ; Volume 91, Issue 22 , 2003 ; 00319007 (ISSN) Jafari, G.R ; Fazeli, S. M ; Ghasemi, F ; Vaez Allaei, S. M ; Rahimi Tabar, M ; Iraji zad, A ; Kavei, G ; Sharif University of Technology
    2003
    Abstract
    We investigate the 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. © 2003 The American Physical Society  

    Synthesis of Magnetite (Fe3O4)-Avastin Nanocomposite as a Potential Drug for AMD Treatment

    , M.Sc. Thesis Sharif University of Technology Zargarzadeh, Mehrzad (Author) ; Maddah Hosseini, Hamid Reza (Supervisor) ; Delavary, Hamid (Co-Advisor)
    Abstract
    Age-related macular degeneration (AMD) is the most common cause of vision loss in those aged over 50. There are two main types of AMD, Wet and Dry form. Wet AMD is more severe though more treatable. There are three conventional treatments for AMD including laser therapy, surgery and intravitreal injection of anti-VEGF into the eye. Delivery of drugs to the posterior segment of the eye is still challenging and several implants and devices are currently under investigation for their ability to stimulate the retina, producing visual percepts. The application of intravitreal bevacizumab (Avastin) has expanded tremendously from the time of its introduction into ophthalmic care since 3 years ago.... 

    Detection of Central Nodes in Social Networks

    , Ph.D. Dissertation Sharif University of Technology Mahyar, Hamid Reza (Author) ; Movaghar, Ali (Supervisor) ; Rabiee, Hamid Reza (Supervisor)
    Abstract
    In analyzing the structural organization of many real-world networks, identifying important nodes has been a fundamental problem. The network centrality concept deals with the assessment of the relative importance of network nodes based on specific criteria. Central nodes can play significant roles on the spread of influence and idea in social networks, the user activity in mobile phone networks, the contagion process in biological networks, and the bottlenecks in communication networks. High computational cost and the requirement of full knowledge about the network topology are the most significant obstacles for applying the general concept of network centrality to large real-world social... 

    Cost-Sensitive Classifiers and Their Applications

    , M.Sc. Thesis Sharif University of Technology Ahmadi, Zahra (Author) ; Beigy, Hamid (Supervisor)
    Abstract
    Decision making often has different effects and results with unequal importance. Most of classifiers try to minimize the rate of misclassified instances. These classifiers assume equal costs for different misclassification types. However, this assumption is not true in many real world problems and different misclassification types have different costs. These differences can be applied by introducing the cost in the process of learning. In this manner, total cost of misclassification will be the evaluation metric of classification. In order to apply this metric to the problems, new learning algorithms are needed. Cost-sensitive learning is the related area of machine learning which deals with... 

    Data Stream Classification in Presence of Concept Drift Using Ensemble Learning

    , M.Sc. Thesis Sharif University of Technology Sobhani, Parinaz (Author) ; Beigy, Hamid (Supervisor)
    Abstract
    Traditional classification techniques of machine learning assume that data have stationary distributions. This assumption for recent challenges where tremendous amount of data are generated at unprecedented rates with evolving patterns, is not true anymore. Classification of data streams has become an important area of machine learning, as the number of applications facing these challenges increases. Examples of such data streams applications include text streams, surveillance video streams, credit card fraud detection, market basket analysis, information filtering, computer security, etc. An appropriate method for such problems should adapt to drifting concepts by revising and refining the...