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    Probabilistic Output-Only Identification of Soil-Structure Systems Using Shear Beam Model

    , M.Sc. Thesis Sharif University of Technology Masoudifar, Mohsen (Author) ; Mahsuli, Mojtaba (Supervisor) ; Ghahari, Farid (Co-Supervisor)
    Abstract
    This paper proposes a novel probabilistic framework for output-only identification of a soil-structure system. The system is modeled by a vertical shear beam resting on the soil representative springs. The proposed framework estimates the unknown parameters of the system and the foundation input motion time history simultaneously, using sparsely measured responses of the structure. The unknown parameters of the system include stiffness of the sway and rocking springs, shear modulus of the beam, and the modal damping ratios of the system. These parameters are modeled as random variables whose joint probability distribution is updated in a Bayesian scheme using the observations of structural... 

    Probabilistic Identification of Soil-foundation Impedance Function Using Kalman Filter

    , M.Sc. Thesis Sharif University of Technology Jabini, Amin (Author) ; Mahsouli, Mojtaba (Supervisor) ; Ghahari, Farid (Co-Supervisor)
    Abstract
    This paper puts forward a probabilistic approach for simultaneous identification of the dynamic stiffnesses of the soil-foundation and the foundation input motion of soil-structure systems from sparsely-measured structural responses. The soil-structure system in this approach is represented by a shear building resting on sway- and rocking-representative springs and dashpots. The proposed approach employs unknown-input extended Kalman filtering in time domain. This method is built upon Bayesian updating and accounts for two major sources of uncertainty in the problem: the process noise that account for the modeling errors and the measurement noise. In the proposed method, the state vector of... 

    Effects of soil-structure interaction on response of structures subjected to near-fault earthquake records

    , Article 2008 Seismic Engineering International Conference Commemorating the 1908 Messina and Reggio Calabria Earthquake, MERCEA 2008, Reggio Calabria, 8 July 2008 through 11 July 2008 ; Volume 1020, Issue PART 1 , 2008 , Pages 642-649 ; 0094243X (ISSN); 9780735405424 (ISBN) Ghannad, M. A ; Amiri, A ; Farid Ghahari, S ; Sharif University of Technology
    2008
    Abstract
    Near-fault ground motions have notable characteristics such as velocity time histories containing large-amplitude and long-period pulses caused by forward directivity effects and acceleration time histories with high frequency content. These specifications of near-fault earthquake records make structural responses to be different from those expected in far-fault earthquakes. In this paper, using moving average filtering, a set of near-fault earthquake records containing forward directivity pulses are decomposed into two parts having different frequency content: a Pulse-Type Record (PTR) that possesses long period pulses, and a relatively high-frequency Background Record (BGR). Studying the... 

    Rapid Seismic Damage Estimation using Bayesian System Identification

    , Ph.D. Dissertation Sharif University of Technology Rostami, Parisa (Author) ; Mahsuli, Mojtaba (Supervisor) ; Ghahari, Farid (Co-Supervisor)
    Abstract
    This dissertation presents a comprehensive probabilistic framework based on system identification for rapid seismic damage assessment of buildings at regional scale. Given the large number of buildings within a region and the need for rapid damage detection, this research uses simplified models with low computational cost to model each building. For this purpose, stochastic filters are employed as system identification tools. In the first step, a continuous linear model consisting of a Timoshenko beam in combination with the extended Kalman filter is utilized. This model is subjected to joint state-parameter identification under both fixed- and flexible-base conditions. Additionally, the... 

    Towards MPEG4 compatible face representation via hierarchical clustering-based facial feature extraction

    , Article ISCI 2011 - 2011 IEEE Symposium on Computers and Informatics ; 2011 , Pages 436-441 ; 9781612846903 (ISBN) Ghahari, A ; Mosleh, M ; Sharif University of Technology
    2011
    Abstract
    Multi-view imaging and display systems has taken a divide and conquer approach to 3D sensing and visualization. We aim to make more reliable and robust automatic feature extraction and natural 3D feature construction from 2D features detected on a pair of frontal and profile view face images. We propose several heuristic algorithms to minimize possible errors introduced by prevalent imperfect orthogonal condition and non-coherent luminance trying to address the problems incurred with illumination discrepancies on common surface points in accommodation of multi-views. In our approach, we first extract the 2D features that are visible to both cameras in both views. Then, we estimate the... 

    Hybrid clustering-based 3D face modeling upon non-perfect orthogonality of frontal and profile views

    , Article 2010 International Conference on Computer Information Systems and Industrial Management Applications, CISIM 2010, 8 October 2010 through 10 October 2010, Krackow ; 2010 , Pages 578-584 ; 9781424478170 (ISBN) Ghahari, A ; Mosleh, M ; Sharif University of Technology
    2010
    Abstract
    Multi view imaging has attracted increasing attention recently and has become one of the potential avenues in future video systems. We aim to make more reliable and robust automatic feature extraction and natural 3D feature construction from 2D features detected on a pair of frontal and profile view face images. We propose several heuristic algorithms to minimize possible errors introduced by prevalent non-perfect orthogonal condition and non-coherent luminance. In our approach, we first extract the 2D features that are visible to both cameras in both views. Then, we estimate the coordinates of the features in the hidden profile view based on the visible features extracted in the two... 

    Automatic MPEG4 compatible face representation using clustering-based modeling schemes

    , Article 2010 International Conference on Computer Information Systems and Industrial Management Applications, CISIM 2010, 8 October 2010 through 10 October 2010, Krackow ; 2010 , Pages 96-102 ; 9781424478170 (ISBN) Ghahari, A ; Mosleh, M ; Sharif University of Technology
    2010
    Abstract
    Multi view imaging has attracted increasing attention recently and has become one of the potential avenues in future video systems. We aim to make more reliable and robust automatic feature extraction and natural 3D feature construction from 2D features detected on a pair of frontal and profile view face images. We propose several heuristic algorithms to minimize possible errors introduced by prevalent non-perfect orthogonal condition and non-coherent luminance. In our approach, we first extract the 2D features that are visible to both cameras in both views. Then, we estimate the coordinates of the features in the hidden profile view based on the visible features extracted in the two... 

    Considering rupture directivity effects, which structures should be named 'long-period buildings'?

    , Article Structural Design of Tall and Special Buildings ; Volume 22, Issue 2 , 2013 , Pages 165-178 ; 15417794 (ISSN) Ghahari, S. F ; Khaloo, A. R ; Sharif University of Technology
    2013
    Abstract
    Recorded accelerograms in the regions near active faults may have specific characteristics that inclusion of their effects on the response of structures is necessary. Of particular importance are permanent displacement, i.e. fling-step, rupture directivity pulses and high-frequency content. Several researchers have focused on the effects of rupture directivity pulses on response of structures. They have shown that long-period structures are severely affected by these types of excitations. However, in near-fault regions, the question 'which building structures are long period?' has not been clearly and quantitatively answered. In this paper, responses of 10-, 20-, 30- and 40-story steel... 

    Dynamics of entanglement of bosonic modes on symmetric graphs

    , Article Physics Letters, Section A: General, Atomic and Solid State Physics ; Volume 363, Issue 4 , 2007 , Pages 271-276 ; 03759601 (ISSN) Ghahari, F ; Karimipour, V ; Shahrokhshahi, R ; Sharif University of Technology
    Elsevier  2007
    Abstract
    We investigate the dynamics of an initially disentangled Gaussian state on a general finite symmetric graph. As concrete examples we obtain properties of this dynamics on mean field graphs (also called fully connected or complete graphs) of arbitrary sizes. In the same way that chains can be used for transmitting entanglement by their natural dynamics, these graphs can be used to store entanglement. We also consider two kinds of regular polyhedron which show interesting features of entanglement sharing. © 2006 Elsevier B.V. All rights reserved  

    Blind identification of soil-structure systems

    , Article Soil Dynamics and Earthquake Engineering ; Volume 45 , February , 2013 , Pages 56-69 ; 02677261 (ISSN) Ghahari, S. F ; Ghannad, M. A ; Taciroglu, E ; Sharif University of Technology
    2013
    Abstract
    Surrounding soil can drastically influence the dynamic response of buildings during strong ground shaking. Soil's flexibility decreases the natural frequencies of the system; and in most cases, soil provides additional damping due to material hysteresis and radiation. The additional damping forces, which are in non-classical form, render the mode shapes of the soil-structure system complex-valued. The response of a soil-foundation system can be compactly represented through impedance functions that have real and imaginary parts representing the stiffness and damping of the system, respectively. These impedance functions are frequency-dependent, and their determination for different... 

    Study on elastic response of structures to near-fault ground motions through record decomposition

    , Article Soil Dynamics and Earthquake Engineering ; Volume 30, Issue 7 , Jan , 2010 , Pages 536-546 ; 02677261 (ISSN) Ghahari, S. F ; Jahankhah, H ; Ali Ghannad, M ; Sharif University of Technology
    2010
    Abstract
    Accelerograms recorded near active faults have some important characteristics that make them different from those recorded in far-fault regions. High-frequency components in acceleration records and long-period velocity pulses are among notable specifications of such ground motions. In this paper, a moving average filtering with appropriate cut-off frequency has been used to decompose the near-fault ground motions into two components having different frequency contents: first, Pulse-Type Record (PTR) that possesses long-period pulses; second, the relatively high-frequency BackGround Record (BGR), which does not include large velocity pulses. Comparing the results with those extracted through... 

    Throughput Analysis in Multi Hop Cellular Networks

    , M.Sc. Thesis Sharif University of Technology Vaezi, Kaveh (Author) ; Ashtiani, Farid (Supervisor)
    Abstract
    OFDMA multi-hop cellular network (MCN) is the topic of a wide range of research today. In this thesis, we analyse this type of networks, regarding shadowing status, mobility patterns and different service requirements. In the multi-hop (MH) scenario, six fixed relays are set up in each cell, which split the cell into seven subcells. For mobility modeling, each subcell is split into several sub-regions. Mobile nodes are able to maintain at each sub-region with a random time distribution and migrate from it to one of its neighboring sub-regions. We also consider three types of services requiring specific number of subcarriers with specific BERs. The set of subcarriers is distributed among... 

    Throughput Analysis of a Cognitive Multi-hop Wireless Network Overlaid on a Cellular Network

    , M.Sc. Thesis Sharif University of Technology Soleimani, Hosein (Author) ; Ashtiani, Farid (Supervisor)
    Abstract
    In this thesis, we evaluate the maximum stable throughput of a cognitive multi-hop IEEE 802.11-based WLAN overlaid on a cellular network. In the considered scenario, the secondary users operate in the downlink or uplink frequency band of primary network and transmit their data in free primary channels using OFDM technique. The activity of primary nodes is modeled independently by ON-OFF alternating states. To model the scenario, each secondary user is modeled with an open queueing network. The queueing network can model the transmission of data as well as the effect of primary users. By writing the traffic equations of the queueing network and applying the stability conditions, we are able... 

    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... 

    Analysis of the Effect of Frame Aggregation in IEEE 802.11 Standard

    , M.Sc. Thesis Sharif University of Technology Soleimani, Mohammad (Author) ; Ashtiyani, Farid (Supervisor)
    Abstract
    In this thesis the effect of frame aggregation mechanism in maximizing throughput in Wireless Local Area Networks (WLANs) have been investigated. Frame aggregation has become a part of the IEEE 802.11 standard as the amendment IEEE 802.11n. First, we have a quick review on access control layer in IEEE 802.11 standard then illustrate the necessity of frame aggregation. Afterwards, we propose an analytical model for the analysis of an IEEE 802.11n network comprised of an Access Point (AP) and several conventional nodes, all in the coverage area of each other. This analytical model focuses on downlink throughput; therefore only AP uses frame aggregation and the other nodes use basic IEEE 802.11... 

    Performance Analysis of Cognitive Radio Networks With Capability of Spectrum Mobility

    , M.Sc. Thesis Sharif University of Technology Bayat, Mozhgan (Author) ; Ashtinani, Farid (Supervisor)
    Abstract
    In cognitive radio networks, secondary users try to use empty channels that primary users provide for transmitting data. First, the secondary users sense the target channels. If the selected channel is empty, they send their data. When the primary user returns, the secondary user has to find another empty channel for transmitting data. The process of changing channel is called hand off. In recent years, there are challenges in the spectrum mobility of for reducing delay time of secondary users packet. In this thesis, we assume that the secondary users network is an ad-hoc network. We use contestation based method for reducing collision between secondary users. In this thesis, we present an... 

    Content Distribution Service Analysis in Vehicular Ad-Hoc Networks

    , M.Sc. Thesis Sharif University of Technology Kananian, Borna (Author) ; Ashtiani, Farid (Supervisor)
    Abstract
    Car accident damages take about 7 percent of GPD of Iran every year. As a result of car accidents, the economy of the country is damaging irreparably. The amount of road casualties equals casualties in a complete war. Considering the aforementioned conditions, the researchers are thinking about new technologies to reduce the cost of the accidents. So the use of Vehicular ad-hoc Networks (VANET) is inevitable in the near future. Content distribution service is one of the emerging services of VANETs. This service is used in both safety and comfort related applications. Content distribution describes delivery of media content such as Video, Audio, Image, Text, Software, and Video Games over... 

    Energy Harvesting in Wireless Communication Networks

    , Ph.D. Dissertation Sharif University of Technology Moradian, Masoumeh (Author) ; Ashtiani, Farid (Supervisor)
    Abstract
    In this dissertation, we focus on two types of EH cooperative networks. In the first type, the source and relay nodes access a shared channel according to a random access protocol. Also, they harvest energy from non-RF environmental resources. The relay node has data and energy buffers to store the packets of the source and the harvested energy, respectively. Our main goal is to find the optimal relaying protocol at the relay node. In this regard, the first type of the EH cooperative networks are investigated in two different scenarios. In the first one, the MAC channels of the nodes are independent of the applied policy at the relay node, and thus the throughput of the network is fixed.... 

    Cooperative Networks from the MAC Layer Viewpoint

    , Ph.D. Dissertation Sharif University of Technology Vaezi, Kaveh (Author) ; Ashtiani, Farid (Supervisor)
    Abstract
    Cooperative networks have attracted much attention in the last decade. Being introduced to mitigate the inefficiencies in the physical layer, cooperation can also be beneficial in upper layers, such as MAC layer. Using cooperative communications is specifically more challenging in the random access networks, where collision is a main concern. Delay, as one of the main performance metrics in random access networks, can decrease significantly by using cooperative communications. Transmission delay, i.e., the required time for delivering one packet form its source to destination, is an important metric in many communication networks, such as the networks in which each node generates and... 

    Analysis of Age of Information in Multisource Communication Networks

    , M.Sc. Thesis Sharif University of Technology Asavdi, Sepehr (Author) ; Ashtiani, Farid (Supervisor)
    Abstract
    In this thesis, we investigate the age of information in multisource networks. To this end, in the first phase of this thesis, we evaluate the Age of Information (AoI) in slotted ALOHA network. Regarding the interactions among the nodes in such a network, we model the memory of this network with a Trellis and find the peak Age of Information (PAoI) by using this Trellis. Then, we evaluate Age of Information-constrained regions and achievable throughput regions in the slotted ALOHA network and optimize Age of information in a symmetric case. In the second phase, we propose an efficient prioritizing scheme from AoI point of view and find the distribution of AoI and PAoI in such a scheme with...