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    A Study On Nuclear C-Algebras

    , M.Sc. Thesis Sharif University of Technology Soleimani Malekan, Meisam (Author) ; Farhadi, Hamid Reza (Supervisor)
    Abstract
    In this essay we study the concepts of nuclearity in C-algebras, and amenability in Banach algebras. A proof on the "every amenable C-algebra is nuclear" is studied. A Banach algebra A is called amenable if every continous derivation D : A ! E , is inner i.e. there exists anif in this denition E is a dual Banach A-module and norm continuity replace by w-continuity then we have Connes-amenability; Connes-amenability was rst considered for von Neumann algebras in [J-K-R] (and thus should perhaps be called Johnson-Kadison-Ringrose amenability). The reason why this notion of amenability is usually associated with A. Connes are his papers [Conn 1] and [Conn 2] The name "Connes-amenability" seems... 

    Iteratively Constructing Preconditioners via the Conjugate Gradient Method

    , M.Sc. Thesis Sharif University of Technology Mousa Abadian, Mohammad (Author) ; Farhadi, Hamid Reza (Supervisor)
    Abstract
    The main goal of this work is solving system of linear equations Ax = b, where A is a n_n square matrix, b is a n_1 vector and x is the vector of unknowns. When n is large, using direct methods is not economical. Thus, the system is solved by iterative methods. At first, projection method onto subspace K _ Rn with dimension m _ n is described, and then this subspace K is equalized with the krylov subspace. Then,some samples of projection methods onto the krylov subspace, such as FOM, GMRES and CG (Conjugate Gradient), are considered. The preconditioning of the linear system is explained, that is, instead of solving system Ax = b, the system PAx = Pb (P nonsingular), is solved, such that the... 

    Fractional Brownian Motion and Application in Mathematical Finance

    , M.Sc. Thesis Sharif University of Technology Sabzikar, Farzad (Author) ; Zohuri Zangeneh, Bijan (Supervisor) ; Farhadi, Hamid Reza (Co-Advisor)
    Abstract
    Farctional Brownian motion (fBm) is a Gaussian Stochastic process B={B_t ∶t ≥0} With zero mean and Covariance function given by RH (t,s)=1/2 (t^2H+ S^2H-├|t-├ s┤|┤ 〖^2H〗) Where 0

    A Randomized Cache Policy for Network of Caches

    , M.Sc. Thesis Sharif University of Technology Farhadi, Pegah (Author) ; Sarbazi-Azad, Hamid (Supervisor) ; Seyed Rezaza Dalali, Mostafa (Co-Supervisor)
    Abstract
    In a network of caches, the precious cache space must be efficiently managed. A wasteful cache management algorithm might make redundant copies of the same content at several caches. Therefore, there must be an algorithm (a.k.a admission policy) to find a proper location in the network for every content to be cached. One way to locate different content at different caches is based on content popularity. Thus, popular content is closer to requesters. However, measuring content popularity at every router is not practical due to the high overhead the algorithm imposes on the routers. A more practical approach is to distribute different parts of the content to several caches along the path from... 

    Feedback channel in linear noiseless dynamic systems controlled over the packet erasure network

    , Article International Journal of Control ; Volume 88, Issue 8 , 2015 , Pages 1490-1503 ; 00207179 (ISSN) Farhadi, A ; Sharif University of Technology
    Taylor and Francis Ltd  2015
    Abstract
    This paper is concerned with tracking state trajectory at remote controller, stability and performance of linear time-invariant noiseless dynamic systems with multiple observations over the packet erasure network subject to random packet dropout and transmission delay that does not necessarily use feedback channel full time. Three cases are considered in this paper: (1) without feedback channel, (2) with feedback channel intermittently and (3) with full time availability of feedback channel. For all three cases, coding strategies that result in reliable tracking of state trajectory at remote controller with asymptotically zero mean absolute estimation error are presented. Asymptotic mean... 

    Stability of linear dynamic systems over the packet erasure channel: A co-design approach

    , Article International Journal of Control ; Volume 88, Issue 12 , May , 2015 , Pages 2488-2498 ; 00207179 (ISSN) Farhadi, A ; Sharif University of Technology
    Taylor and Francis Ltd  2015
    Abstract
    This paper is concerned with the stability of linear time-invariant dynamic systems over the packet erasure channel subject to minimum bit rate constraint when an encoder and a decoder are unaware of the control signal. This assumption results in co-designing the encoder, decoder and controller. The encoder, decoder, controller and conditions relating transmission rate to packet erasure probability and eigenvalues of the system matrix A are presented for almost sure asymptotic stability of linear time-invariant dynamic systems over the packet erasure channel with feedback acknowledgment. When the eigenvalues of the system matrix A are real valued, it is shown that the obtained condition for... 

    Stability of nonlinear uncertain Lipschitz systems over the digital noiseless channel

    , Article Scientia Iranica ; Volume 25, Issue 3D , 2018 , Pages 1523-1532 ; 10263098 (ISSN) Farhadi, A ; Sharif University of Technology
    Sharif University of Technology  2018
    Abstract
    This paper is concerned with the stability of nonlinear Lipschitz systems subject to bounded process and measurement noises when transmission from sensor to controller is subject to distortion due to quantization. A stabilizing technique and a sufficient condition relating transmission rate to Lipschitz coefficients are presented for almost sure asymptotic bounded stability of nonlinear uncertain Lipschitz systems. In the absence of process and measurement noises, it is shown that the proposed stabilizing technique results in almost sure asymptotic stability. Computer simulations illustrate the satisfactory performance of the proposed technique for almost sure asymptotic bounded stability... 

    Sub-optimal control over AWGN communication network

    , Article European Journal of Control ; Volume 37 , 2017 , Pages 27-33 ; 09473580 (ISSN) Farhadi, A ; Sharif University of Technology
    2017
    Abstract
    In this paper a sub-optimal control technique is proposed for a linear Gaussian system with a few distributed interacting sub-systems. Controller of each sub-system has only access to its own measurement and a noisy version of measurement and control vectors of other sub-systems that are communicated through an Additive White Gaussian Noise (AWGN) communication network. The power to be allocated to each transmitter antenna is calculated so that the received signal is the transmitted signal plus additive white Gaussian noise. Under some conditions it is shown that the proposed sub-optimal control technique results in bounded mean square stability. The satisfactory performance of the proposed... 

    Alert Correlation Analysis For Intrusion Detection

    , M.Sc. Thesis Sharif University of Technology Farhadi, Hamid (Author) ; Jalili, Rasool (Supervisor)
    Abstract
    While intrusion detection systems (IDSs) are widely used, large number of alerts as well as high rate of false positive events make such a security mechanism insufficient. Accordingly, a track of recent security research, focused on alert correlation. This thesis proposes a Hidden Markov Model (HMM) based correlation method of intrusion alerts which have been fired from different IDS sensors across an enterprise. We used HMM to predict the next attack class of the intruder that is also known as plan recognition. Our method has two advantages. Firstly, it does not require any usage or modeling of network topology, system vulnerabilities, and system configurations. Secondly, as we perform high... 

    Throughput enhancement of a random access WLAN by combination of digital and analog network coding

    , Article IEEE International Conference on Communications, 5 June 2011 through 9 June 2011 ; June , 2011 ; 05361486 (ISSN) ; 9781612842332 (ISBN) Farhadi, F ; Ashtiani, F ; Sharif University of Technology
    2011
    Abstract
    In this paper, we propose a new packet routing scheme, i.e., a combined digital and analog network coding scheme (DNC-ANC) suitable for multiple unicast scenario. In this respect, we consider a random access WLAN comprised of single and multi-hop unicast sessions. Then we modify the MAC scheme in order to enable ANC. In order to evaluate the effect of the proposed DNC-ANC scheme analytically, we employ an open queueing network and map the details of MAC as well as routing schemes onto its suitable parameters. By writing the corresponding traffic equations and applying the stability condition, we are able to find the maximum stable throughput for the considered scenario. Finally, we will show... 

    Distributed Optimal Control Based on an Efficient Method for Communication

    , M.Sc. Thesis Sharif University of Technology Karbasi, Ali (Author) ; Farhadi, Alireza (Supervisor)
    Abstract
    This thesis is concerned with an optimal trade-off between communication overhead and the number and size of neighborhoods in a distributed optimal control technique for large-scale systems that is based on the Jacobi iteration and two-layer architecture for communication. Although this method efficiently reduces computational overhead, continuous and proper data transfer between subsystems that are very often far from each other, is required to achieve an acceptable performance. However, limited transmission bandwidth and short communication range result in significant communication overhead. This causes significant time latency between measurement and applied calculated control actions,... 

    Model Predictive Control Based on Integer Programming

    , M.Sc. Thesis Sharif University of Technology Ahmadi, Vahid (Author) ; Farhadi, Alireza (Supervisor)
    Abstract
    Many industrial systems have on/off actuators. Traditionally, these systems are controlled using traditional control methods, like PID controller. The performance of this controller is not ideal for these systems, especially in term of transient response and power consumption. Due to the large number of constraints for these systems, to improve the performance of them, it is necessary to use the model predictive control technic. The decision variables of these systems are integer, hence it is necessary to develop the model predictive control method based on integer programming, which is the subject of this thesis. The main challenge in the development of this model predictive control method,... 

    CFD-Modeling and Simulation of Droplets Evaporation With a Size Distribution Function

    , M.Sc. Thesis Sharif University of Technology Pirhadi, Zahra (Author) ; Farhadi, Fatollah (Supervisor)
    Abstract
    Injecting several droplets with a known size distribution function in the hot gas environment makes droplets smaller because of evaporation or reaction. Droplets lifetime specification is important in vapor-liquid interactive processes such as chemical or process industries. In previous works, different approximate semi-empirical methods are developed to specify droplets lifetime without considering their size distribution. In this work, governing equations is studiedconsidering a size distribution function for droplets. There is not any analytical method for solving this set of equations, so numerical methods using CFD packages such as Fluent, are applicable in these cases. In this study,... 

    Distributed model predictive control with hierarchical architecture for communication: application in automated irrigation channels

    , Article International Journal of Control ; Volume 89, Issue 8 , 2016 , Pages 1725-1741 ; 00207179 (ISSN) Farhadi, A ; Khodabandehlou, A ; Sharif University of Technology
    Taylor and Francis Ltd  2016
    Abstract
    This paper is concerned with a distributed model predictive control (DMPC) method that is based on a distributed optimisation method with two-level architecture for communication. Feasibility (constraints satisfaction by the approximated solution), convergence and optimality of this distributed optimisation method are mathematically proved. For an automated irrigation channel, the satisfactory performance of the proposed DMPC method in attenuation of the undesired upstream transient error propagation and amplification phenomenon is illustrated and compared with the performance of another DMPC method that exploits a single-level architecture for communication. It is illustrated that the DMPC... 

    Design and Development of the Automated Irrigation Channel Pilot

    , M.Sc. Thesis Sharif University of Technology Bakhshi, Mahsa (Author) ; Farhadi, Alireza (Supervisor)
    Abstract
    The present thesis is concerned with design and development of automated irrigation system pilot. This system is obtained by equipping each regulating gate of irrigation network with a controlling hardware. This hardware is designed and developed in this project for Iran’s regulating gate, which are either slide gate or radial gate. This hardware consists of a) Ultrasonic sensor for measure gate upstream water level, b) Wireless modem for exchanging measurements between automated gates, c) controller, d) Electric motor and driver, e) shaft encoder and f) adaptor. The satisfactory performance of this hardware is shown via several experiments on the pilot  

    Control of Nonlinear Dynamic Systems over the Packet Erasure Channel: Applications in Remote Control of Autonomous Vehicles

    , Ph.D. Dissertation Sharif University of Technology Parsa, Ali (Author) ; Farhadi, Alireza (Supervisor)
    Abstract
    Abstract: In this dissertation, the problem of tracking and stabilization of nonlinear dynamic systems over the packet erasure channel is addressed. Using the idea of linearization of nonlinear system around current working point, and by the design of an encoder, decoder, and controller for the linearized system, state tracking and reference tracking of the nonlinear system are addressed. To prove the traking and stability of the system, the strong law of large numbers and the dwell time approach are used. By computer simulations, the theoretical development is applied on the nonlinear dynamic of the unicycle model, which is a suitable model for autonomous vehicles, such as drones, unmanned... 

    Involutions on the second duals of group algebras and a multiplier problem

    , Article Proceedings of the Edinburgh Mathematical Society ; Volume 50, Issue 1 , 2007 , Pages 153-161 ; 00130915 (ISSN) Farhadi, H ; Ghahramani, F ; Sharif University of Technology
    2007
    Abstract
    We show that if a locally compact group G is non-discrete or has an infinite amenable subgroup, then the second dual algebra L1(G) ** does not admit an involution extending the natural involution of L1(G). Thus, for the above classes of groups we answer in the negative a question raised by Duncan and Hosseiniun in 1979. We also find necessary and sufficient conditions for the dual of certain left-introverted subspaces of the space Cb(G) (of bounded continuous functions on G) to admit involutions. We show that the involution problem is related to a multiplier problem. Finally, we show that certain non-trivial quotients of L1(G)** admit involutions  

    Dynamic Simulation of the Ammonia Tank Failure at Pardis Petrochemical Company

    , M.Sc. Thesis Sharif University of Technology Farhadi, Zeinab (Author) ; Rashtchian, Davood (Supervisor)
    Abstract
    Liquid ammonia atmospheric tank (20000 ton) attached to Pardis Petrochemical Complex was ruptured on 8th August 2011 due to overpressure blast injury so that ammonia gas was spread throughout the complex. The current study was aimed to evaluate ammonia leakage and emission from the tank. For this purpose, in addition to evaluate ammonia emission into the air, pressure changes were investigated to simulate the rupture. First of all, ammonia tanks and urea stocks were simulated and then considering two aerial classes (D and B), the incident was stimulated. According to this model, up to 1000 m, was contaminated with 1000 ppm of ammonia. Since there was no experimental data for validating the... 

    A network coding-based packet forwarding scheme for unicast random access networks with exponential backoff

    , Article 2013 Iran Workshop on Communication and Information Theory ; May , 2013 , Page(s): 1 - 6 ; 9781467350235 (ISBN) Farhadi, F ; Ashtiani, F ; Sharif University of Technology
    2013
    Abstract
    Exponential backoff is an intrinsic feature of MAC-layer standards of most types of ad hoc networks. It leads to random access channels with memory. In this paper we propose a new network coding-based packet forwarding scheme suitable for multiple unicast scenarios in downlink direction of a wireless network. The wireless nodes as well as the access point attempt to access the channel, based on slotted Aloha with exponential backoff. In the proposed scheme we convert multiple unicast scenario to a combination of several anycast and a multicast scenarios. By proposing an open multiclass queueing network, we are able to derive the maximum stable download throughput of the network. The... 

    Network Coding-based Packet Relaying in Wireless Networks

    , M.Sc. Thesis Sharif University of Technology Farhadi, Farzaneh (Author) ; Ashtiani, Farid (Supervisor)
    Abstract
    In this thesis, we propose two new network coding-based packet relaying schemes suitable for multiple unicast scenarios in a random access network. In such networks the channels may have memory dependent upon the random access scheme. Thus, the optimal scheme for memoryless channels reported recently in the literature is not necessarily optimal in random access networks. In our proposed schemes, we convert a multiple unicast scenario to a combination of multiple anycast and a few multicast scenarios. By such an approach, we exploit the channels between relay node and the other nodes, instead of using only one channel at each packet transmission, for as many as possible. By simple analytical...