Loading...
Search for: hashemi--homayoun
0.157 seconds

    Information-Theoretic Analysis of Coognitive Radio Networks

    , Ph.D. Dissertation Sharif University of Technology Charmmchi, Hosseein (Author) ; Hashemi, Homayoun (Supervisor) ; Nasiri Kenari, Masoumeh (Supervisor)
    Abstract
    In this thesis, the effect of cognition in wireless networks is studied. In a wireless communica-tion network, cognition is the ability of a device to sense the transmissions of neighboring nodes and adapt its own transmission to the sensed environment. Cognitive radios are very attractive be-cause of the increasing need for more efficient use of frequency spectrum. The goal of this thesis is the analysis of cognitive radio networks from an information theoretic perspective and to this end statistical models of the wireless medium with a limited and tractable number of devices are uti-lized. We consider three different models in three parts of the thesis. First, we consider a new... 

    Application of Damage Indices In Seismic Analysis of Concrete Frames Using Endurance Time Method

    , M.Sc. Thesis Sharif University of Technology Baniassadi, Arash (Author) ; Esmaeil Pourestekanchi, Homayoun (Supervisor)
    Abstract
    In most places in the world as it is in our country, structural vibration caused by earthquakes are among the most destructive menaces for the building. For this reason one of the main goals for civil engineers is constructing structures that can perform properly in an earthquake-exposed situation. For moving toward this goal it is necessary to estimate structural responses considering probable earthquake excitation and use these data for design of new structures or retrofitting of existing ones. In this research, the capability of a new method named Endurance Time analysis in seismic assessment of concrete moment frame is investigated in nonlinear range. ET is a new dynamic time history... 

    Performance-Based Design of Steel Structures with Metallic damper Using Endurance Time Method

    , M.Sc. Thesis Sharif University of Technology Yousefian Moghadam, Sina (Author) ; Esmaeil Pourestekanchi, Homayoun (Supervisor)
    Abstract
    Preventing critical damages to structures and hence saving the lives and money is an inevitable work which a designer has to do. During the earthquake, huge amount of energy applies to the structure and finding a way to reduce transfer of this energy to main structure is crucial. For this purpose, Structural Control systems may be used. Metallic Dampers are one of those systems which absorb the earthquake input energy by having nonlinear deformations. In this Thesis, one type of this dampers which is innovated by Estekanchi, have been studied .Indeed, this damper is a connection between bracing and main frame. In this damper a U shape part acts as a sacrificing portion and absorbs energy by... 

    Seismic Performance and Cost Assessment of Concrete Bridges Designed by Iranian Bridge Code

    , M.Sc. Thesis Sharif University of Technology Haghani Baei, Ali (Author) ; Esmaeil Purestekanchi, Homayoun (Supervisor)
    Abstract
    The purpose of this study is to evaluate the performance and seismic costs for pre-designed bridges according to the Iranian Bridge Code, which maps and details are available in Code 294. In order to evaluate performance, seismic costs of a structures are determined over its life cycle and these costs are compared eventually. Seismic costs are divided into two parts of the initial cost and life cycle cost of the structure. The initial costs depend on the cost of constructing the bridge, but life cycle costs are depends on seismic damage for structure and its users over the useful life of the bridge. These damages include the cost of maintenance of the bridge over its useful life and the... 

    Seismic Analysis of Elevated Concrete Tanks with Endurance Time Method

    , M.Sc. Thesis Sharif University of Technology Ghasemi Khalafloo, Pouya (Author) ; Esmaeil Poorestekanchi, Homayoun (Supervisor)
    Abstract
    Elevated concrete tanks have a wide range of applications in storing drinking water, firefighting, sewage, oil, toxic chemicals, and similar fluids. Therefore, due to their usage, these tanks are usually placed in the category of very important structures and vital arteries. Consequently, their design against seismic loads and their proper performance during earthquakes are of great importance. The endeavor time Analysis is a seismic analysis method in which the structure is subjected to an increasing dynamic excitation whose intensity gradually increases over time. The structure's response over time is examined, and based on the corresponding response to various levels of excitation... 

    A Front-End for an Integrated UHF RFID Reader

    , M.Sc. Thesis Sharif University of Technology Homayoun, Aliakbar (Author) ; Sharif Bakhtiar, Mehrdad (Supervisor) ; Atarodi, Mojtaba (Supervisor)
    Abstract
    The use of Radio Frequency Identification is increasing rapidly. The reason is the capability to transfer data wirelessly without line-of-sight necessity, high data rate and long read range. The main advantage of barcode is its lower cost which has ensured its existence for many years. The applications and materials that are identified by RFID increase as the price of RFID tags decrease. This Project deals with the front-end of an Integrated RFID Reader for the UHF band. The bottleneck of the design is the presence of a large interferer just hundreds of kilohertz apart from the desired signal which is at about 900 MHz. The key idea of the design is utilizing feedback in order to cancel... 

    Dynamics of a Viscoelastic Plate on a Viscoelastic Foundation Subjected to a Moving Mass

    , Ph.D. Dissertation Sharif University of Technology Foyouzat, Mohammad Ali (Author) ; Esmaeil Purestekanchi, Homayoun (Supervisor) ; Mofid, Masoud (Co-Advisor)
    Abstract
    This thesis investigates the dynamic response of a viscoelastic plate resting on a viscoelastic Winkler foundation subjected to the excitation of a moving mass. Through application of the Laplace transform, the governing equation of the problem is derived for a general viscoelastic material. Thereafter, an analytical-numerical method is proposed in order to determine the dynamic response of the viscoelastic plate. The method is based on transforming the governing partial differential equation into a new solvable system of linear ordinary differential equations. To that extent, the proposed solution proves to be applicable to plates made of any viscoelastic material and with various boundary... 

    ALR detector for coherent radar detection of rapid fluctuating signals

    , Article IEICE Transactions on Communications ; Volume E83-B, Issue 11 , 2000 , Pages 2519-2525 ; 09168516 (ISSN) Modarres Hashemi, M ; Sharif University of Technology
    Institute of Electronics, Information and Communication, Engineers, IEICE  2000
    Abstract
    In this paper, we consider the coherent radar detection of rapid fluctuating signals in the Gaussian noise. This problem has been previously solved by employing the GLR technique, but we use the ALR to improve the detection performance. So, after deriving an approximate ALR detector, we compare the new detector with the GLR and ' Square-law detectors and we show its superiority  

    Coronary artery lipid accumulation prevention through vibrating piezo electric nano plates embedded in smart stent

    , Article Medical Engineering and Physics ; Volume 118 , 2023 ; 13504533 (ISSN) Ahmadi Arpanahi, R ; Hosseini Hashemi, K ; Ahmadian, M. T ; Mohammadi, B ; Hosseini Hashemi, S ; Sharif University of Technology
    Elsevier Ltd  2023
    Abstract
    Considering the lipid concentration and side effects regarding the stents used by surgeons, a new heart stent model is proposed. In the new stent, a few piezo plates are designed and attached to the stents by which release of the lipids can take place due to the applied alternative voltages. Due to the vibrations of small-scale piezoelectric plates, the deposition of low-density-lipoproteins (LDL) floating in the blood flow in the coronary arteries is prevented. Small-scale effects are considered using nonlocal elasticity theory, and the interaction between fluid and solid is modeled using the Navier-Stokes equation. The effect of fluid parameters as well as applied voltage and geometry... 

    Empirical comparison of sliding friction and wear behaviors of gray and white cast iron

    , Article ASME 2010 10th Biennial Conference on Engineering Systems Design and Analysis, ESDA2010, 12 July 2010 through 14 July 2010, Istanbul ; Volume 1 , 2010 , Pages 489-493 ; 9780791849156 (ISBN) Hashemi, M ; Ghajar, R ; Sharif University of Technology
    2010
    Abstract
    In this paper, sliding friction and wear behaviors of gray cast iron A35 and white cast iron manufactured by quenching from the same cast iron in water were studied and compared by employing pin-on-disk wear tests. Microstructure of the worn surfaces before and after the wear tests were investigated by optical microscope observations. These images show that flakes separated from the surface in gray cast iron due to delamination process, while in white cast iron, the separation of materials from its surface is in the form of powder. In addition, the gray cast iron had higher graphite volume fraction with Type-A graphite flake morphology. The results show that white cast iron has less rate of... 

    Investigation of the small-scale effects on the three-dimensional flexural vibration characteristics of a basic model for micro-engines

    , Article Acta Mechanica ; Volume 226, Issue 9 , September , 2015 , Pages 3085-3096 ; 00015970 (ISSN) Hashemi, M ; Asghari, M ; Sharif University of Technology
    Springer-Verlag Wien  2015
    Abstract
    The coupled three-dimensional flexural vibrations of a micro-rotating shaft–disk system, as a basic model for micro-engines, are investigated in this paper by considering small-scale effects utilizing the modified couple stress theory. Governing equations of motion are derived by the use of Hamilton’s principle. Then, implementing the Galerkin approach, an infinite set of ordinary differential equations is obtained for the system. With truncated two-term equations, expressions for the first two natural frequencies are written, and for the two corresponding modes, the maximum rotational speed up to which the system will be stable is analytically determined. Parametric studies on the results... 

    Analytical study of three-dimensional flexural vibration of micro-rotating shafts with eccentricity utilizing the strain gradient theory

    , Article Meccanica ; Volume 51, Issue 6 , 2016 , Pages 1435-1444 ; 00256455 (ISSN) Hashemi, M ; Asghari, M ; Sharif University of Technology
    Springer Netherlands  2016
    Abstract
    In this work, some vibrational response parameters of strain gradient based micro-spinning Rayleigh beams with mass eccentricity distribution are investigated within infinitesimal deformation conditions. Governing equations of motion are derived utilizing the Hamilton’s principle. The gyroscopic effects and rotary inertia are both included in the formulation. By applying the Galerkin method, analytical expressions for natural frequencies of the micro beam in forward and backward whirl motions are obtained. In addition, an expression for the vibrational amplitude of the micro-beam due to mass eccentricity distribution is determined. Some numerical results are presented to study the effect of... 

    Size-dependent vibrational behavior of a Jeffcott model for micro-rotor systems

    , Article Journal of Mechanical Science and Technology ; Volume 30, Issue 1 , 2016 , Pages 35-41 ; 1738494X (ISSN) Hashemi, M ; Asghari, M ; Sharif University of Technology
    Korean Society of Mechanical Engineers  2016
    Abstract
    In this study, several analytical expressions are obtained for the vibrational characteristics of a Jeffcott model for micro-rotor systems based on the strain gradient theory to investigate the small-scale effects on the model. The Jeffcott model consists of a massless microrotating shaft and a disk as a rotor with eccentricity. The disk is mounted on the middle of the shaft. Two second-order differential equations associated with the oscillating motion of the rotor in the plane perpendicular to the longitudinal axis are presented and transformed into a complex form. The stiffness of the system is determined by obtaining the deflection of a strain-gradient-based nonrotating microbeam... 

    On the size-dependent flexural vibration characteristics of unbalanced couple stress-based micro-spinning beams

    , Article Mechanics Based Design of Structures and Machines ; Volume 45, Issue 1 , 2017 , Pages 1-11 ; 15397734 (ISSN) Hashemi, M ; Asghari, M ; Sharif University of Technology
    2017
    Abstract
    On the basis of the modified couple stress theory, some analytical results are obtained for vibrational parameters of micro-spinning Rayleigh beams with an axial mass-eccentricity distribution. The modified couple stress theory is a nonclassical continuum theory capable to capture the size effects in small-scale structures. After writing the governing equations of motion, they are transformed to the complex form. Then by utilizing the Galerkin method, analytical expressions for natural frequencies of the micro-spinning beam in forward and backward whirl motions are obtained. Critical speeds are also analytically presented in the two whirl motions for different modes. Moreover, the... 

    Morphology development and mechanical properties of unsaturated polyester resin containing nanodiamonds

    , Article Polymer International ; Volume 66, Issue 6 , 2017 , Pages 950-959 ; 09598103 (ISSN) Hashemi, M ; Shojaei, A ; Sharif University of Technology
    2017
    Abstract
    Unsaturated polyester/styrene (UP) resin was filled with nanodiamonds (NDs) containing carboxyl and methacrylate functionalities using mechanical mixing. Field emission SEM exhibited a uniform dispersion of tightly bound aggregates of nanosized spherical NDs with good interfacial interaction. Rheological measurements exhibited a step increment in the shear viscosity of a UP/ND suspension at 0.6 wt% ND resembling a percolation state at this loading. Shear viscosity data supported by dynamic mechanical analysis results suggested the development of effective ND particles in which ND aggregates were covered by only polyester macromolecules. Accordingly, the morphology of UP/ND composites... 

    Analysis of H-plane waveguide discontinuities using hybrid multimode contour integral and mode matching techniques

    , Article 2007 SBMO/IEEE MTT-S International Microwave and Optoelectronics Conference, IMOC, Salvador, 29 January 2007 through 1 November 2007 ; December , 2007 , Pages 840-843 ; 1424406617 (ISBN); 9781424406616 (ISBN) Hashemi, A ; Banai, A ; Sharif University of Technology
    2007
    Abstract
    A new hybrid method based on multimode contour integral and mode matching techniques will be introduced. It is capable of analyzing any H-plane discontinuity in a rectangular waveguide. The process is based on segmentation and dividing the structure into key building blocks. We use the multimode contour integral method to analyze the blocks including irregular shape H-plane discontinuities. In opposite to traditional contour integral method, which considers only the effect of dominant mode (TE10) on wave ports, multimode contour integral considers the effect of higher order modes (TE n0) excited by discontinuities on these ports. The mode matching technique will be used to analyze the... 

    Biometric identification through hand geometry

    , Article EUROCON 2005 - The International Conference on Computer as a Tool, Belgrade, 21 November 2005 through 24 November 2005 ; Volume II , 2005 , Pages 1011-1014 ; 142440049X (ISBN); 9781424400492 (ISBN) Hashemi, J ; Fatemizadeh, E ; Sharif University of Technology
    IEEE Computer Society  2005
    Abstract
    A new approach for person identification based on hand geometry is presented. After preprocessing hand features are extracted from a photograph taken while user has placed his/her hand (either left or right) on the platform of a document scanner with no limits or fixation. Different pattern recognition techniques like Gaussian mixture modeling (GMM), Radial basis function neural networks (RBF), Multi layer perceptron (MLP), k-Nearest Neighbor (k-NN), Bayes method and mahalanobis/Hamming distance have been used in classification section. Experimental results show a rate of success above 90%. © 2005 IEEE  

    Expert Finding in Bibliographic Network

    , M.Sc. Thesis Sharif University of Technology Hashemi, Hadi (Author) ; Beigy, Hamid (Supervisor)
    Abstract
    Expert finding in bibliographic networks has received increasing attention in recent years. This task concerns with finding relevant researchers for a given topic. In this thesis, we propose a model to determine authority of authors who have participated in the Communities. This model has a little improvement over community based baseline model. However, due to the low performance of community based models, the proposed authority based model cannot improve the document based baseline models either. Therefore, we try to improve document based models, instead of community based models and have proposed two other models which are based on authors’ topic dominance for expert finding. Document... 

    Optimized Fabrication of Spinel Nanao Powder Mn1.5Co1.5O4 Through Sol-Gel Method Applicable to Solid Oxid Fuel Cell

    , M.Sc. Thesis Sharif University of Technology Hashemi, Tahereh (Author) ; Askari, Masoud (Supervisor)
    Abstract
    Nowadays, too much attention has been paid to Solid Oxide Fuel Cells (SOFC). One of the key components in SOFC is interconnect which plays an important role in SOFC performance. Interconnect can be either a metallic or ceramic layer that sits between each individual cell. The reduction in operating temperature of SOFC resulted in interests in using metallic interconnectors. However, the oxidation of these metallic materials is big challenge. Chromium (Cr), Nickel (Ni) and Iron (Fe) alloys have been employed to overcome this deficiency. However, these alloys bring another difficulty which is the presence of active elements such as Cr which reduces the performance of interconnects by forming... 

    Synthesis and Electrochemical Study of Endohedral Fullerenes Prepared by Arc Vaporizing Method

    , M.Sc. Thesis Sharif University of Technology Hashemi, Ali (Author) ; Ghanbari, Bahram (Supervisor)
    Abstract
    Fullerenes are molecular solid materials which are composed of 3D closed shell carbon-only structure. As soon as mass production of fullerenes was performed, the synthesis and characterization of endohedral fullerenes having at least one non-carbon element in the hollow fullerene cage, was started (in which about 30 atoms inserted in it so far). Furthermore, because of low efficiency and purity of these nano-particles, nowadays characterization of fullerenes is one of the most important research fields. In this project, we firstly optimized the fullerene production parameters in an arc discharge reactor to reach convenient efficiency. Then, the synthesis of endohedral fullerene by vaporizing...