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momeni--saman
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Critical Behavior of Neuronal Systems: an Information Theory Viewpoint
, M.Sc. Thesis Sharif University of Technology ; Moghimi, Saman (Supervisor)
Abstract
Experiments conducted in recent two decades indicated critical behavior in neural activity at different scales. Theoretically occurrences of these critical and power-law behavior can significantly facilitate brain activities correspondent to computation and memory tasks, but attaining the critical point essentially demands externally fine-tuning which has not been established yet. This fine-tuning often lies with placing system at transition point. Recent studies of group showed that a transition from synchronous to asynchronous phase could be achievable by a change in external parameters. At the very transition point, neuronal avalanches statistically demonstrate a power-law behavior which...
A Botnet Detection Technique
, M.Sc. Thesis Sharif University of Technology ; Kharrazi, Mehdi (Supervisor)
Abstract
A set of infected computers which are coordinated in some manner by one’s willingness and can perform malicious activities and provide threats in the cyberspace forms a network of bots, namely botnet. Botnet threats are more important and significant than other malwares due to their huge scale. A lot of computers coming together in a network obeying one’s commands allows their controller to conduct, for example, DoS attacks larger than ever seen incidents. This thesis, introduces botnets, their various threats, and an effective technique for detecting them. For this reason, different probable states of bots will be studied and modeled as a coherent bot life-cycle. The bot life-cycle allows...
Introducing structural approximation method for modeling nanostructures
, Article Journal of Computational and Theoretical Nanoscience ; Vol. 7, Issue 2 , 2010 , p. 423-428 ; ISSN: 15461955 ; Alasty, A ; Sharif University of Technology
2010
Abstract
In this work a new method for analyzing nanostructured materials has been proposed to accelerate the simulations for solid crystalline materials. The proposed Structural Approximation Method (SAM) is based on Molecular Dynamics (MD) and the accuracy of the results can also be improved in a systematic manner by sacrificing the simulation speed. In this method a virtual material is used instead of the real one, which has less number of atoms and therefore fewer degrees of freedom, compared to the real material. The number of differential equations that must be integrated in order to specify the state of the system will decrease significantly, and the simulation speed increases. To generalize...
Improving a computer networks course using the Partov simulation engine
, Article IEEE Transactions on Education ; Volume 55, Issue 3 , 2012 , Pages 436-443 ; 00189359 (ISSN) ; Kharrazi, M ; Sharif University of Technology
2012
Abstract
Computer networks courses are hard to teach as there are many details in the protocols and techniques involved that are difficult to grasp. Employing programming assignments as part of the course helps students to obtain a better understanding and gain further insight into the theoretical lectures. In this paper, the Partov simulation engine and experience using this engine in a computer networks course are discussed. Since 2009, various programming assignments based on the Partov system have been set to help students in their learning process. Student feedback has been very good; this has been quantified in two surveys in which a majority of students expressed their satisfaction with this...
Partov: A network simulation and emulation tool
, Article Journal of Simulation ; Volume 10, Issue 4 , 2016 , Pages 237-250 ; 17477778 (ISSN) ; Kharrazi, M ; Sharif University of Technology
Palgrave Macmillan Ltd
2016
Abstract
Network protocol design and evaluation requires either full implementation of the considered protocol and evaluation in a real network, or a simulation based on a model. There is also a middle approach in which both simulation and emulation are used to evaluate a protocol. In this article the Partov engine, which provides both simulation and emulation capabilities simultaneously, is presented. Partov benefits from a layered and platform-independent architecture. As a pure simulator, it provides an extensible plugin-based platform that can be configured to perform both real-time and non-real-time discrete-event simulations. It also acts as an emulator, making interaction with real networks...
Introducing structural approximation method for modeling nanostructures
, Article Journal of Computational and Theoretical Nanoscience ; Volume 7, Issue 2 , February , 2010 , Pages 423-428 ; 15461955 (ISSN) ; Alasty, A ; Sharif University of Technology
2010
Abstract
In this work a new method for analyzing nanostructured materials has been proposed to accelerate the simulations for solid crystalline materials. The proposed Structural Approximation Method (SAM) is based on Molecular Dynamics (MD) and the accuracy of the results can also be improved in a systematic manner by sacrificing the simulation speed. In this method a virtual material is used instead of the real one, which has less number of atoms and therefore fewer degrees of freedom, compared to the real material. The number of differential equations that must be integrated in order to specify the state of the system will decrease significantly, and the simulation speed increases. To generalize...
Exact solution for the massless cylindrically symmetric scalar field in general relativity, with cosmological constant
, Article International Journal of Modern Physics A ; Volume 24, Issue 31 , 2009 , Pages 5991-6000 ; 0217751X (ISSN) ; Miraghaei, H ; Sharif University of Technology
2009
Abstract
In this paper we present a new exact solution for scalar field with cosmological constant in cylindrical symmetry Associated cosmological models including a model that describes a cyclic universe are discussed
Software De-Obfuscation and its Applications to Malware Analysis
, Ph.D. Dissertation Sharif University of Technology ; Kharrazi, Mehdi (Supervisor)
Abstract
Obfuscation transformations complicate a software and make it incomprehensible via syntactical changes. This provides high incentive for malware authors to employ different obfuscation techniques. The practical nature of this problem and lack of common definitions in this area have limited the encountering fronts. Whenever a new obfuscation method becomes known in the wild, ad-hoc deobfuscation solutions follow it, trying to recognize it in details and reverse it step by step. As more obfuscation transformations become readily available for malware developers, this approach becomes more costly and impractical. This rises the perceived need for automated deobfuscation. For example, the...
LDMBL: An architecture for reducing code duplication in heavyweight binary instrumentations
, Article Software - Practice and Experience ; Volume 48, Issue 9 , 2018 , Pages 1642-1659 ; 00380644 (ISSN) ; Kharrazi, M ; Sharif University of Technology
John Wiley and Sons Ltd
2018
Abstract
Emergence of instrumentation frameworks has vastly contributed to the software engineering practices. As the instrumentation use cases become more complex, complexity of instrumenting programs also increases, leading to a higher risk of software defects, increased development time, and decreased maintainability. In security applications such as symbolic execution and taint analysis, which need to instrument a large number of instruction types, this complexity is prominent. This paper presents an architecture based on the Pin binary instrumentation framework to abstract the low-level OS and hardware-dependent implementation details, facilitate code reuse in heavyweight instrumentation use...
Designing an intelligent controller for a molecular valve
, Article 2008 Proceedings of the ASME - 2nd International Conference on Integration and Commercialization of Micro and Nanosystems, MicroNano 2008, 3 June 2008 through 5 June 2008, Kowloon ; 2008 , Pages 195-201 ; 0791842940 (ISBN); 9780791842942 (ISBN) ; Alasty, A ; Sharif University of Technology
2008
Abstract
Too much effort has been done for manipulating individual atoms, using nano-manipulators and Scanning Tunneling Microscopes (STM). On the other hand, characterization and manipulation of nano-flows is of great concern. In the current work a molecular valve has been considered, which is made up of six atoms placed on the circumstance of a circle. A fuzzy controller has been designed for controlling the diameter of this molecular valve. The designed fuzzy controller used singleton fuzzifier, Mamdani inference engine, center average defuzzifier and exponential membership functions. A model based on the classical Molecular Dynamics (MD) is used for modeling the nano-system and passing the states...
Stress distribtuion on open-ended carbon nanotubes
, Article 2008 Proceedings of the ASME - 2nd International Conference on Integration and Commercialization of Micro and Nanosystems, MicroNano 2008, 3 June 2008 through 5 June 2008, Kowloon ; 2008 , Pages 343-351 ; 0791842940 (ISBN); 9780791842942 (ISBN) ; Alasty, A ; Sharif University of Technology
2008
Abstract
The stress distribution on open-ended Carbon Nanotubes (CNTs) embedded in a composite material is considered in this work and an analytical solution for the stress distribution has been obtained. The effects of CNT's thickness and CNT's length on the distribution of stress have been investigated. To find the governing relations, continuity equations of the axisymmetric problem in cylindrical coordinate (r,o,z) are used. Under some assumptions, the governing equations are solved and by using constitutive equations and applying the boundary conditions, an equation which relates the stress applied to the representative volume element with the stress distribution on the CNT, has been found. The...
Pure coupled mode analysis of diffraction by isotropic transmission volume gratings
, Article IEEE Transactions on Antennas and Propagation ; Volume 52, Issue 12 , 2004 , Pages 3304-3311 ; 0018926X (ISSN) ; Rashidian, B ; Sharif University of Technology
2004
Abstract
The idea of pure coupled mode approach is extended to the analysis of volume grating structures. In this approach, diffraction orders inside the grating are expanded over TE and TM components and unperturbed wavevectors are used instead of Floquet wavevectors of conventional coupled wave approach. Coupling between these orders are considered to model the diffraction. Three-dimensional grating structures are analyzed, and comparisons with rigorous coupled wave analysis are made to verify the accuracy and determine the range of applicability of the proposed method. © 2004 IEEE
Improved coupled wave analysis of two-dimensional planar multiple gratings
, Article IEEE Transactions on Antennas and Propagation ; Volume 52, Issue 1 , 2004 , Pages 165-171 ; 0018926X (ISSN) ; Rashidian, B ; Sharif University of Technology
2004
Abstract
An improved coupled wave approach is presented for the analysis of diffraction behavior of a two-dimensional spatially periodic or almost periodic dielectric layer illuminated by TE polarized plane waves. This method applies to any simultaneous composition of arbitrarily modulated planar transmission gratings with any permittivity in neighboring regions. Two major improvements have been made. In the first part, the eigenvalues and eigenvectors of coupled wave system of equations are first-order corrected to reduce the inherent errors generated by neglecting second-order derivatives. In the second part, a scattering matrix method is used to model the effect of boundaries. Using this method,...
Chaos in Sandpile Models With and Without Bulk Dissipation
, M.Sc. Thesis Sharif University of Technology ; Moghimi-Araghi, Saman (Supervisor)
Abstract
A complte set of characteristic parameters of the sandpile models is still unknown. We have studied the existence of ”weak chaos” critical exponent in different sandpile models and we have shown that it is a characteristic exponent of deterministic models. We have shown that BTW and Zhang models do not belong to the same universality class (contrary to Zhang’s previous conjecture and contrary to Ben-Hur & Biham’s results.) Also we have shown that directed models, specificly Ramaswamy-Dhar’s directed model form a different universality class. ”Weak chaos” exponent in also studied in massive models and we have shown that by increase of dissipation, the exponent decreases rapidly to an...
Sandpiles and Surface Growth
, M.Sc. Thesis Sharif University of Technology ; Moghimi Araghi, Saman (Supervisor)
Abstract
We study the Abelian Sandpile Model and its relation with surface growth. ese two models are related through their field theories and equations of motion. It has been shown that the different features of different sandpile models can be expressed in terms of the noise term in the surface growth equation. A mapping between the simplest sandpile model, the BTW model, and a surface growth has already been introduced. is surface growth has not been studied in details so far. In this thesis we study different features of this surface growth corresponding to the BTW model, continuous sandpile model and also massive abelian sandpile model. We also consider different boundary conditions
The Abelian Sand-pile Model (ASM) and Generalization to the Continuous State
, M.Sc. Thesis Sharif University of Technology ; Moghimi Araghi, Saman (Supervisor)
Abstract
The four-page article by Bak, Tang and Wiesenfeld in 1987 was a beginning to a new wave of physicists’ efforts to explain and describe the concept of complexity; a not-so-well-defined concept that resists against the reductionist tools and methods of physics. The Self-organized Criticality theory presented in that article via a simple model, known as sandpile model, was first of all an effort to explain the numerous occurrence of power law distribution in nature. SOC was introduced to tell us why so many natural phenomena like Earthquakes, landslides, forest fires, extinction and other seemingly non-related catastrophic events, more or less obey the scale-less power law distribution; A...
Transition from Abelian Sandpile Model to Manna Model
, M.Sc. Thesis Sharif University of Technology ; Moghimi-Araghi, Saman (Supervisor)
Abstract
In this research, we want to address the question of universality classes in BTW and Manna sandpile models. So far, number of works has been devoted to this issue but the the answer remained unsolved. We will try another approach to study this question by perturbing the original models. To this end, we introduce three models that have evolution rules between BTW model and Manna model. By simulating this models, we observe that in the presence of perturbation, the probability dis- tribution has two regimes of behaviour which are separated by a new characteristic scale. The regime of small avalanches is described by the exponent of BTW model and the regime of large avalanches by the exponent...
Generalized Growth Models
, M.Sc. Thesis Sharif University of Technology ; Moghimi-Araghi, Saman (Supervisor)
Abstract
Edwards-Wilkinson’s equation can be achieved from a Hamiltonian. When we have the Hamiltonian for the system, there are common approaches that makes it out of critical. In other words,the ”mass” should be added to the system. In this study we have tried to simulate and solve analytically these models that are involved mass term. We try to onstruct these mass terms in a way that have a minimum impact on the system and we study the quantities that characterize the out of critical behaviors
Percolation on Small World Networks
, M.Sc. Thesis Sharif University of Technology ; Moghimi Araghi, Saman (Supervisor)
Abstract
Percolation is a phenomenon that can be found in many physical problems. Additionally, as a statistical model, it has a very rich physics, since many fundamental concepts in the context of critical phenomena and complex systems-such as phase transition, scaling laws etc can be found in the model. Percolation phenomenon can be defined on different lattices. In this thesis we study percolation on small-world networks. In small-world networks, in addition to local bonds that connects the neighbouring sites, there exist some long-ranged bonds that connect cites far from each other. Social networks, some networks of internet or the gene networks are examples of such networks. Therefore, to study...
Simulation of the Self-organized Critical Models on the
Human’s Brain Network
,
M.Sc. Thesis
Sharif University of Technology
;
Moghimi Araghi, Saman
(Supervisor)
Abstract
Self-organized critical phenomena are interesting phenomena which are ubiquitous in nature. Examples include mountain ranges , coastlines and also activities in the hu-man's brain. In these processes, without fine-tuning of any external parameter such as the temperature, the system exhibits critical behavior. In other words, the dynamics of the system, drives it towards an state in which long range correlations in space and scaling behaviors can be seen.The first successful model which could characterize such systems was BTW model, introduced by Bak , Tang and Wiesenfeld in 1987. This model, later named Abelian sandpile model, was very simple and because of this simplicity, a large amount of...