Loading...
Search for: razzaghi--masoumeh
0.168 seconds

    Study of the triple-mass tethered satellite system under aerodynamic drag and J2 perturbations

    , Article Advances in Space Research ; Volume 56, Issue 10 , November , 2015 , Pages 2141-2150 ; 02731177 (ISSN) Razzaghi, P ; Assadian, N ; Sharif University of Technology
    Elsevier Ltd  2015
    Abstract
    The dynamics of multi-tethered satellite formations consisting of three masses are studied in this paper. The triple-mass triple-tethered satellite system is modeled under the low Earth orbit perturbations of drag and Earth's oblateness and its equilibrium conditions are derived. It is modeled as three equal end-masses connected by a uniform-mass straight tether. The lengths of tethers are supposed to be constant and in this manner the angles of the plane consisting the masses are taken as the state variables of the system. The governing equations of motion are derived using Lagrangian approach. The aerodynamic drag perturbation is expressed as an external nonconservative force and the Earth... 

    Transport Properties in Heterostructures of 2D Layers of Graphene with WS2 and hBN Quantum Dots

    , M.Sc. Thesis Sharif University of Technology Razzaghi, Zahra (Author) ; Simchi, Abdolreza (Supervisor)
    Abstract
    Graphene based photodetectors which are modified with quantum dots, are the new generation of detectors. In these supplies an integration of graphene’s unique characteristics like high conductivity and mobility and the high light absorption of quantum dots, are used.In this research graphene by chemical vapor deposition in centimetric large scales, tungsten disulfide quantum dots, boron nitride and graphene quantum dots and 2D tungsten disulfide have been synthesized. In the next step each of them were characterized to modify the quality of used layers in heterostructure.Based on the characteristic tests, quantum dots aspect ratios were 1 to 5 nanometers. Also tungsten disulfide was obtained... 

    Brandom’s Conception of Trust

    , M.Sc. Thesis Sharif University of Technology Razzaghi, Ashkan (Author) ; Abazari, Arash (Supervisor)
    Abstract
    A Spirit of Trust results from Brandom's thirty-year effort to give a pragmatistic reading of Hegel's Phenomenology of Spirit. In A Spirit of Trust, Brandom reformulates Hegel's arguments in the language of contemporary Analytical Philosophy and gives a unique interpretation of Hegel's key concepts. In this Thesis, we will examine one of its key concepts, namely, Trust; We will pursue the following questions: First, What is Trust? And what is its connection to other aspects of Brandom's philosophy? Second, How does Trust help us in overcoming Alienation? Third, Are Confession and Forgiveness, which are the constitutive concepts of Trust, psychologistic or normative? Fourth, What is the... 

    Linear decoupled space-time codes

    , Article 14th IEEE 2003 International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC2003, Beijing, 7 September 2003 through 10 September 2003 ; Volume 3 , 2003 , Pages 2862-2867 ; 0780378229 (ISBN); 9780780378223 (ISBN) Razzaghi, P ; Khalaj, B. H ; Sharif University of Technology
    2003
    Abstract
    In this paper, we will introduce a new constraint on linear space-time block codes that will result in a novel decoupled symbol-by-symbol detection scheme. Based on the new framework, a quasi-decoupled space-time code that is applicable to any number of transmit and receive antennas will be proposed. We will also solve a more general case and show that all other known solutions to this problem such as orthogonal designs and Clifford algebra representations, represent special cases of such general solution which will provide an easier framework, to deal with such codes. It is noticeable that the new framework not only provides better understanding of earlier solutions but may also help in... 

    Cross-cultural Perceptions of Impoliteness by Native English Speakers and EFL Learners: The Case of Apology Speech Act

    , Article Journal of Intercultural Communication Research ; Vol. 43, issue. 4 , Sep , 2014 , pp. 304-326 ; ISSN: 17475759 Tajeddin, Z ; Alemi, M ; Razzaghi, S ; Sharif University of Technology
    2014
    Abstract
    This study investigated native English speakers’ and English as a foreign language (EFL) learners’ perception of (im)politeness. Seventy-five native speakers and 177 EFL learners were administered a discourse completion task for the speech act of apology accompanied by responses violating politeness by various degrees. Participants were asked to assess the degree of (im)politeness embedded in each response and to write down their assessment comments. Content analysis of respondents’ comments indicated that both groups mentioned similar (im)politeness criteria. However, the analysis of frequency counts displayed significant differences between the two groups in their degree of preference for... 

    Optimal Retrieval Trajectory of Tethered System of Space Debris for Maximize the Aerodynamic Heating

    , M.Sc. Thesis Sharif University of Technology Razzaghi, Pourya (Author) ; Malaek, Mohammad Bagher (Supervisor)
    Abstract
    In this study, a model for the optimal routes for the recovery of space debris is expressed. The dynamic model using a binary system consisting of satellites and orbital debris containment space is extracted. Trastrhay available on satellite and aerodynamic drag on the system circuit changes the whole system and the entry of debris into the thick atmosphere began to burn.This circuit must be optimized. The thrusters are assumed as variable optimization problem. After simulation of optimization, it follows that by changing the initial value thrusters, Trastrhay the optimal cost function changes. Also, indicating the final height of system affects on parameters, thrusters and the cost... 

    Design and test of an astigmatism compensated dynamical stable ring resonator for a subjoule class Nd:YAG laser without external elements

    , Article Optical Engineering ; Volume 58, Issue 2 , 2019 ; 00913286 (ISSN) Razzaghi, D ; Rezanejad, M ; Shayganmanesh, M ; Gohari, N ; Sharif University of Technology
    SPIE  2019
    Abstract
    An astigmatism compensated isosceles triangular ring resonator is designed and tested for a subjoule class Nd:YAG laser, considering the thermal lensing effects. The ABCD approach is used and the laser rod is considered as a lens like media whose optical power is induced by dissipated heat in the rod. The beam spot size, divergence angle, and some other parameters were studied for both sagittal and tangential planes and a minimal astigmatic configuration is designed applying dynamic stability condition. It is shown practically that the designed resonator emits a circular TEM00 Gaussian beam (using an aperture). Comparative studies were also done considering a linear resonator especially for... 

    Feasibility study of auto ignition in in-situ combustion process

    , Article Journal of the Japan Petroleum Institute ; Volume 51, Issue 5 , 2008 , Pages 287-297 ; 13468804 (ISSN) Razzaghi, S ; Kharrat, R ; Vossoughi, S ; Rashtchian, D ; Sharif University of Technology
    2008
    Abstract
    Air injection, and the resulting in-situ combustion process, utilizes an inexpensive injectant, air, to accelerate oil recovery and increase reserves. The potential of auto ignition of heavy oil during in situ combustion process was studied in KEM reservoir. The risk of carbonate decomposition due to high temperature was examined. The carbonate rock decomposition was taken at 650°C. The peak of low temperature combustion by producing CO was initiated at 275°C when air was injected. There was no risk of decomposition of the carbonate Sarvak formation due to high temperatures of the process. Enrichment of the injecting fluid by oxygen increased the possibility of ignition. Ignition occurred... 

    (IM)Politeness in Speech Act Production: Native Speaker's and EFL Learners' Perceptions and Criteria

    , M.Sc. Thesis Sharif University of Technology Razzaghi, Masoumeh (Author) ; Tajeddin, Ziaeddin (Supervisor) ; Alemi, Minoo (Co-Advisor)
    Abstract
    Scholars in the field of pragmatics consistently argue about the inadequacy of research on the concept of impoliteness. Compared to politeness, which was the focus of most investigations, the phenomenon of impoliteness has been greatly neglected. It is a truism that learning a language involves both politeness and impoliteness concepts of that language. Regarding this fact, researchers must pay greater attention to alleviate the imbalance between politeness and impoliteness studies. The current study is an attempt to investigate the criteria of (im)politeness as they were specified by two groups of English native speakers and Iranian EFL learners. Seventy-five native English speakers and 177... 

    Investigation of auto ignition condition under different parameters

    , Article Iranian Journal of Chemistry and Chemical Engineering ; Volume 27, Issue 2 , 2008 , Pages 93-101 ; 10219986 (ISSN) Razzaghi, S ; Kharrat, R ; Rashtchian, D ; Vossoughi, S ; Saraji, S ; Sharif University of Technology
    2008
    Abstract
    In this work, the potential of auto-ignition of heavy oil during in-situ combustion (ISC) process was studied. Kinetic studies were carried out using Thermo Gravimetric Analyzer (TGA), Differential Scanning Calorimetry (DSC) and Accelerating Rate Calorimetric (ARC) techniques. Effects of oxygen partial pressure, reservoir pressure and clay on auto ignition condition were investigated on a number of different heavy oil samples from south west Iran mixed with silica sand or crushed carbonate rock and clay. Based on the experimental results obtained by TGA runs, the kinetic equation was derived for different oil samples in the presence of different sands. Effect of partial pressure of oxygen in... 

    Differentially Detection in UWB Communicatio Systems without Reference Transmission

    , M.Sc. Thesis Sharif University of Technology Rahmati, Mojtaba (Author) ; Nasiri Kenari, Masoumeh (Supervisor)
    Abstract
    In recent years, UWB multiple access communication systems have received a great attention due to its many advantages. The most important advantages of a UWB system can be summarized as its high data rates, low power consumption, fading immunity and high precision routing. One of the important problems in a UWB system implementation is in its receiver part in which in order to use a coherent RAKE receiver, the channel coefficients have to be estimated. Since UWB channel is a dense multipath fading channel with a very high number of resolvable paths, the channel coefficient estimation based on using training sequence is very complicated. To resolve this problem, transmit reference (TR)... 

    Spectrum Sensing in Cognitive Radio Networks

    , Ph.D. Dissertation Sharif University of Technology Taherpour, Abbas (Author) ; Nasiri Kenari, Masoumeh (Supervisor)
    Abstract
    In this thesis, we consider the problem of spectrum sensing in cognitive radio networks. First, the collaborative energy detectors based spectrum sensing are investigated in the case of known noise variance for two models of primary user (PU) signal, i.e. random and unknown deterministic signals. Since the derived optimum collaborative energy detector requires the signal-to-noise ratio (SNR) of secondary users (SU) and it has complex structure, the generalized likelihood ratio (GLR) detector is proposed for both models of PU signal which leads to the same decision rules for both models. Simulation results show that the performance of the proposed GLR detector is near to that of optimal... 

    Cooperative Communications in Free-Space Optical Networks

    , Ph.D. Dissertation Sharif University of Technology Karimi, Mehdi (Author) ; Nasiri Kenari, Masoumeh (Supervisor)
    Abstract
    With recent successes in laboratory tests, and in atmosphere and space demonstrations, there is no doubt that the free-space optical (FSO) communications is ready for operational deployment. Large bandwidth, unlicensed spectrum, excellent security, and quick and inexpensive setup are among its most attractive features. Despite their attractive features, FSO communications suffer from several challenges in practical deployment; the major of them is fading or scintillation and path loss. To overcome such limitations, Channel Coding along with MIMO and Cooperative techniques have been proposed. Although the promising effects of cooperative transmissions in RF communications have greatly been... 

    Multiple-Access Techniques for Wireless Indooor Infrared Communication with Dispersive Link

    , Ph.D. Dissertation Sharif University of Technology Hamdi, Mazda (Author) ; Nasiri-Kenari, Masoumeh (Supervisor)
    Abstract
    Infrared wireless local area networks are a suitable choice for a fast and cheap wireless network, providing rates over 10 Mbps with access to unregulated bandwidth. Among multiple-access techniques for infrared wireless networks, CDMA1 has attracted the most interest, due to its simple structure and power ecency. However, spreading the spectrum in CDMA prohibits exploiting the low-rate strong channel codes. The other limiting factor in infrared networks is the channel dispersion. In this thesis, these two issues are considered and an internally coded scheme for time-hopping CDMA, suitable for wireless infrared communication is proposed and with accurate modelling of infrared dispersive... 

    Harnessing Interference in Cooperative Communication Networks

    , Ph.D. Dissertation Sharif University of Technology Hejazi, Mohsen (Author) ; Nasiri-Kenari, Masoumeh (Supervisor)
    Abstract
    The compute-and-forward (CMF) method has shown a great promise as an innovative approach to exploit interference towards achieving higher network throughput. Here, instead of recovering single messages, the relays attempt to reliably decode (compute) and pass an integer linear combination of the transmitted messages, referred to as an equation, to the destination. By receiving sufficient equations,the destination can solve the linear equation system to recover the desired messages.Two main challenges of the CMF methods are the computational complexity and the rank failure problem at the destination. In this thesis, to decrease the implementation as well as the computational complexity of the... 

    Analysis of Cache-aided Wireless Communications Systems in the Presence of IRS

    , M.Sc. Thesis Sharif University of Technology Changizi, Abolfazl (Author) ; Nasiri Kenari, Masoumeh (Supervisor)
    Abstract
    Future mobile networks are expected to not only bring more wireless connectivity and higher data rates, but also to support several high-quality services including low-latency, ultra-reliable, and energy-efficient communications. To support these needs, intelligent reflecting surfaces (IRSs) have recently attracted a lot of attention due to their potential for reconfiguring the wireless channel and are considered as a promising solution for future mobile generations. On the other hand, the exponential growth of network traffic, and its non-uniform distribution result in network congestion during peak-traffic times and network underutilization during off-peak times. Caching or content... 

    Efficient Transmission and Reception in Wireless Communication Systems based on NOMA

    , Ph.D. Dissertation Sharif University of Technology Mokhtari, Fatemeh (Author) ; Nasiri Kenari, Masoumeh (Supervisor)
    Abstract
    Multiple access technologies are one of the key features of different generations of wireless communication. From the first generation to the fourth generation, orthogonal multiple access (OMA) schemes have been utilized to serve multiple users in different orthogonal resource blocks in time, frequency or code domain. However, the new application scenarios for the fifth generation impose the requirements of higher system throughput, massive connectivity, and low latency, which can not be fulfilled with OMA schemes. Therefore, non-orthogonal multiple access (NOMA) schemes have attracted increasing attention in both industry and academia. In NOMA, multiple users may occupy the same resource... 

    Non-coherent Detection and Analysis of Ultra-Wideband (UWB) Communication Systems

    , M.Sc. Thesis Sharif University of Technology Manaffam, Saeed (Author) ; Nasiri Kenari, Masoumeh (Supervisor)
    Abstract
    In this thesis, we investigate the previously introduced Code-Shifted Reference (CSR) time hopping (TH) ultra-wideband (UWB) communication systems as a potential transmitted scheme reference technique. In this system, the orthogonality between the reference and data bearing signals is acquired in code domain. Also, we consider a simple scheme to clean to obtain a clean template to be used in the correlator receiver for the CSR –UWB, this method was used in UWB system before. In this method, which we call as averaged (Ave.) CSR-UWB, the template for each symbol is obtained by taking the average over all the frames of the symbol interval. It is shown that Ave-CSR system achieves higher... 

    Cooperative Communications Based on Jointly Network Coding and Rateless Coding Approach and Their Analysis

    , M.Sc. Thesis Sharif University of Technology Mansourifard, Parisa (Author) ; Nasiri Kenari, Masoumeh (Supervisor)
    Abstract
    In recent years, coded cooperation has been considered as one of the best methods to cope with fading and at the same time to achieve channel coding gain. On the other hand, the idea of network coding has been introduced for increasing the efficiency of cooperative networks. In addition, it has been shown that only by jointly designing of network coding and channel coding, the capacity will be achievable. Also, to adjust the rate to the channel capacity without requiring the channel state information at the transmitter, Rateless coding has been proposed. In this thesis above techniques are combined to gain their advantages and to improve system performance. To this end, first we consider a... 

    Spectrum Handover in Cognitive Radio Networks

    , M.Sc. Thesis Sharif University of Technology Shokri, Hossein (Author) ; Nasiri-Kenari, Masoumeh (Supervisor)
    Abstract
    Powerful spectrum sensing and access strategies enable cognitive radios to find transmission opportunity in spectral resources dedicated exclusively to the incumbent/primary users (PUs). One of the key effecting factors on cognitive radio network (CRN) throughput is the spectrum sensing sequence used by each secondary user (SU). In this thesis, modeling, performance evaluation, and throughput maximization of a CRN are investigated. More specifically, firstly we evaluate the performance of sequential method for handovers regarding a SU’s average throughput and consumed energy, and an optimization problem is formulated to maximize the throughput through selecting optimal channel sensing time....