Loading...
Search for: parsa-delivand--ahmad-reza
0.129 seconds

    Investigation of the Starting Process of a Second Throat Exhaust Diffuser in a High-Altitude Test Stand

    , M.Sc. Thesis Sharif University of Technology Parsa Delivand, Ahmad Reza (Author) ; Farahani, Mohammad (Supervisor) ; Fouladi, Nematollah (Supervisor)
    Abstract
    In the present study, the effect of the diffuser inlet-to-nozzle exit area ratio (A_d/A_e ) on the gradual starting performance of a second throat exhaust diffuser has been investigated experimentally. Experiments have been carried out with four conical nozzles with different expansion ratios and considering two approaches of gradual increase and gradual decrease of nozzle chamber pressure by a high-pressure air tank. Investigations show that at high area ratios before starting the diffuser, oscillations in the pressure of the test chamber are created due to the instability of the flow at the diffuser inlet. By frequency analysis of the vacuum chamber pressure, it is observed that as A_d/A_e... 

    On the links of vertices in eimplicial d-complexes embeddable in the euclidean 2d-space

    , Article Discrete and Computational Geometry ; Volume 59, Issue 3 , 2018 , Pages 663-679 ; 01795376 (ISSN) Parsa, S ; Sharif University of Technology
    Springer New York LLC  2018
    Abstract
    We consider d-dimensional simplicial complexes which can be PL embedded in the 2d-dimensional Euclidean space. In short, we show that in any such complex, for any three vertices, the intersection of the link-complexes of the vertices is linklessly embeddable in the (2 d- 1 ) -dimensional Euclidean space. In addition, we use similar considerations on links of vertices to derive a new asymptotic upper bound on the total number of d-simplices in an (continuously) embeddable complex in 2d-space with n vertices, improving known upper bounds, for all d≥ 2. Moreover, we show that the same asymptotic bound also applies to the size of d-complexes linklessly embeddable in the (2 d+ 1 ) -dimensional... 

    On the links of vertices in simplicial d-complexes embeddable in the euclidean 2d-space

    , Article Discrete and Computational Geometry ; 2017 , Pages 1-17 ; 01795376 (ISSN) Parsa, S ; Sharif University of Technology
    2017
    Abstract
    We consider d-dimensional simplicial complexes which can be PL embedded in the 2d-dimensional Euclidean space. In short, we show that in any such complex, for any three vertices, the intersection of the link-complexes of the vertices is linklessly embeddable in the (Formula presented.)-dimensional Euclidean space. In addition, we use similar considerations on links of vertices to derive a new asymptotic upper bound on the total number of d-simplices in an (continuously) embeddable complex in 2d-space with n vertices, improving known upper bounds, for all (Formula presented.). Moreover, we show that the same asymptotic bound also applies to the size of d-complexes linklessly embeddable in the... 

    Scattering Theory on Locally symmetric Spaces

    , M.Sc. Thesis Sharif University of Technology Ehyaei, Ahmad Reza (Author) ; Razvan, Mohammad Reza (Supervisor)
    Abstract
    Scattering theory on locally symmetric space first was studied by Peter Lax and Ralph Phillips. They studied the and develop scattering theory on it. Without the Fourier analysis tools this theory was completed with a lot of computations. In this thesis first we try to construct Fourier analysis by definition Fourier transform then by means of new tools we prove very short version of scattering theory on locally symmetric space . In general case for studying scattering theory we need firs spectral decomposition of Hilbert space of square integrable functions locally symmetric spaces of rational rank one is achieved by quotient of symmetric space where G is Lie group and K is maximal... 

    Analysis and Improvement of QoS in Optical CDMA Networks Using Cross Layer Design Concepts

    , M.Sc. Thesis Sharif University of Technology Hosseini, Ahmad Reza (Author) ; Pakravan, Mohammad Reza (Supervisor)
    Abstract
    According to the rapid growing in communication devices, users need higher rates for their usages. Fiber optics is one the major choices to support such rates. One of the simplest and cheapest networks is Local Area Network (LAN) as a Passive Optical Network (PON). In these networks, some computers are locally connected to a passive optical device and communicate through it. Multiple access to a shared channel is an important task in such a network. In this thesis, Code Division Multiple Access (CDMA) is used and a new algorithm for Multiple Access Control Sublayer (MAC) based on scheduling will be developed to improve Quality of Service (QoS) and stabilize the network.
    In the scheduling... 

    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... 

    Design and fabrication of a new multi-loop saddle coil for 1.5 T MRI

    , Article Review of Scientific Instruments ; Volume 90, Issue 11 , 2019 ; 00346748 (ISSN) Parsa, J ; Mohammadzadeh, M ; Sharif University of Technology
    American Institute of Physics Inc  2019
    Abstract
    Radiofrequency coils provide high-resolution magnetic resonance (MR) imaging of human tissues. A small RF coil produces MR images with a higher resolution compared to the commercial volume MR coils from mass limited samples. Signal to noise ratio (SNR) plays a key role in the optimal design of receiver radiofrequency coils. In this work, we present a three-loop saddle coil suitable for MR imaging of digits of the human body. The geometry of the introduced coil is optimized to achieve the highest SNR. The coil performance is evaluated through comparing the measured SNR maps of the optimal coil derived from MR images of a saline phantom with the corresponding measured SNR maps of a commercial... 

    Measurement and control of nonlinear dynamic systems over the internet (IoT): Applications in remote control of autonomous vehicles

    , Article Automatica ; Volume 95 , 2018 , Pages 93-103 ; 00051098 (ISSN) Parsa, A ; Farhadi, A ; Sharif University of Technology
    Elsevier Ltd  2018
    Abstract
    This paper presents a new technique for almost sure asymptotic state tracking, stability and reference tracking of nonlinear dynamic systems by remote controller over the packet erasure channel, which is an abstract model for transmission via WiFi and the Internet. By implementing a suitable linearization method, a proper encoder and decoder are presented for tracking the state trajectory of nonlinear systems at the end of communication link when the measurements are sent through the packet erasure channel. Then, a controller for reference tracking of the system is designed. In the proposed technique linearization is applied when the error between the states and an estimate of these states... 

    Reference tracking of nonlinear dynamic systems over AWGN channel using the describing function

    , Article Scientia Iranica ; Volume 26, Issue 3 D , 2019 , Pages 1724-1735 ; 10263098 (ISSN) Parsa, A ; Farhadi, A ; Sharif University of Technology
    Sharif University of Technology  2019
    Abstract
    This paper presents a new technique for mean square asymptotic reference tracking of nonlinear dynamic systems over Additive White Gaussian Noise (AWGN) channel. The nonlinear dynamic system has periodic outputs and sinusoidal inputs and is cascaded with a bandpass filter acting as an encoder. By using the describing function method, the nonlinear dynamic system is represented by an equivalent linear dynamic system. Then, for this system, a mean square asymptotic reference tracking technique, including an encoder, a decoder, and a controller, is presented. It is shown that the proposed reference tracking technique results in mean square asymptotic reference tracking of nonlinear dynamic... 

    Reference tracking of nonlinear dynamic systems over AWGN channel using the describing function

    , Article Scientia Iranica ; Volume 26, Issue 3 D , 2019 , Pages 1724-1735 ; 10263098 (ISSN) Parsa, A ; Farhadi, A ; Sharif University of Technology
    Sharif University of Technology  2019
    Abstract
    This paper presents a new technique for mean square asymptotic reference tracking of nonlinear dynamic systems over Additive White Gaussian Noise (AWGN) channel. The nonlinear dynamic system has periodic outputs and sinusoidal inputs and is cascaded with a bandpass filter acting as an encoder. By using the describing function method, the nonlinear dynamic system is represented by an equivalent linear dynamic system. Then, for this system, a mean square asymptotic reference tracking technique, including an encoder, a decoder, and a controller, is presented. It is shown that the proposed reference tracking technique results in mean square asymptotic reference tracking of nonlinear dynamic... 

    Numerical Investigation of Parameters Affecting the Behavior of Backdraft Phenomena and Its Extinguishing

    , M.Sc. Thesis Sharif University of Technology Parsa, Sina (Author) ; Farhanieh, Bijan (Supervisor)
    Abstract
    Fires in buildings and closed environments are considered as the most important types of fires due to the possibility of the presence of people and the possibility of life-threatening. Understanding and predicting fire behavior is critical to preventing damage. Backdraft is a special phenomenon of fire that occurs in a chamber with limited ventilation. In a closed environment where there is fire, over time, due to the closed doors and windows, the oxygen required for combustion decreases and as a result, semi-combustible materials can be dangerously exposed to the environment with flammable vapors and gases. Fill and when sufficient air reaches this chamber, a sudden explosion or the same... 

    New coding scheme for the state estimation and reference tracking of nonlinear dynamic systems over the packet erasure channel (IoT): Applications in tele-operation of autonomous vehicles

    , Article European Journal of Control ; 2020 Parsa, A ; Farhadi, A ; Sharif University of Technology
    Elsevier Ltd  2020
    Abstract
    This paper presents a new technique for the state estimation and reference tracking of nonlinear dynamic systems over the packet erasure channel, which is an abstract model for transmission via the Internet, WiFi wireless network and ZigBee modules. A new encoder and decoder for real time state estimation of nonlinear dynamic systems at the end of communication link when the measurements are sent through the limited capacity erasure channel, are presented. Then, using the available results from control theory, a controller for reference tracking and hence the stability of the system is also designed. That is, for nonlinear systems, almost sure asymptotic state estimation and reference... 

    Tele-operation of autonomous vehicles over additive white Gaussian noise channel

    , Article Scientia Iranica ; Volume 28, Issue 3 , 2021 , Pages 1592-1605 ; 10263098 (ISSN) Parsa, A ; Farhadi, A ; Sharif University of Technology
    Sharif University of Technology  2021
    Abstract
    This paper is concerned with the tele-operation of autonomous vehicles over analog Additive White Gaussian Noise (AWGN) channel, which is subject to transmission noise and power constraint. The nonlinear dynamic of autonomous vehicles is described by the unicycle model and is cascaded with a bandpass filter acting as encoder. Using the describing function method, the nonlinear dynamic of autonomous vehicles is represented by an approximate linear system. Then, the available results for linear control over analog AWGN channel are extended to account for linear continuous time systems with non-real valued and multiple real valued eigenvalues and for tracking a non-zero reference signal.... 

    New coding scheme for the state estimation and reference tracking of nonlinear dynamic systems over the packet erasure channel (IoT): Applications in tele-operation of autonomous vehicles

    , Article European Journal of Control ; Volume 57 , 2021 , Pages 242-252 ; 09473580 (ISSN) Parsa, A ; Farhadi, A ; Sharif University of Technology
    Elsevier Ltd  2021
    Abstract
    This paper presents a new technique for the state estimation and reference tracking of nonlinear dynamic systems over the packet erasure channel, which is an abstract model for transmission via the Internet, WiFi wireless network and ZigBee modules. A new encoder and decoder for real time state estimation of nonlinear dynamic systems at the end of communication link when the measurements are sent through the limited capacity erasure channel, are presented. Then, using the available results from control theory, a controller for reference tracking and hence the stability of the system is also designed. That is, for nonlinear systems, almost sure asymptotic state estimation and reference... 

    Developing an Applied Model for Energy Management in Dairy Production Industry

    , M.Sc. Thesis Sharif University of Technology Bahmanpour khalesi, Ahmad Reza (Author) ; Mokhtar, Ali Reza (Supervisor) ; Miremadi, Ali Reza (Supervisor)
    Abstract
    Reviewing trends of energy consumption in the world reveals that sooner or later energy resources will be depleted. This concerning rate of consumption has brought about more greenhouse gases (GHG) emission influencing deleteriously on environment and climate. Human has continued energy consumption to maintain and improve the quality of his life through industrial production. Industry as a significant energy user owns considerable contribution to this consumption. Several attempts have been carried out to develop energy management systems in order to improve the energy efficiency of industrial sectors. Whilst they are comprehensive and could be applied to any sector, there is lack of... 

    Formability analysis of Tailor Welded Blank Pridaction with Friction Stret Weld

    , M.Sc. Thesis Sharif University of Technology Habibi, Mostafa (Author) ; Asempour, Ahmad (Supervisor) ; Naghdabadi, Reza (Supervisor)
    Abstract
    The Tilor welded blank (TWB) two or more sheets with different thickness or strength which are welded together. The automobile designer are searching for new methods to reduce the cars’ weight and producing cost in order to diminish fuel consumption so they can survive in the competitive market. One way to achieve to this seemingly Contradictory demands, is using TWB in cars’ body. One of the most applicable methods to investigate the formability of metals sheets, is Forming Limit Diagrams (FLD). Three ways to determine the FLD are: Analytical Method, Experimental Methods, and Numerical Method. The experimental method to determine FLD, require metal sheets to undergo in different strain... 

    Comparing the Performance of Centrifuge, Membrane Filter and Filter Press for Clarification of Lipase Enzyme

    , M.Sc. Thesis Sharif University of Technology Taheraslani, Ahmad Reza (Author) ; Rousta Azad, Reza (Supervisor)
    Abstract
    Lipases (Triacyl Glycerol Acyl Hydrolase, EC.3.1.1.3) are multidimensional biocatalysts which have many applications in food industrials, dairy, fats and oils processing, detergents, synthesis of pure chemical and pharmaceutical materials, paper industrial and cosmetics. Generally, industrial enzymes are produced extracellularly, so their separation from a low-cost complex medium (usually used for production) is one of the cost stages in their production process. Filtration is the most economical method of separation in the production of enzymes, but due to the small size of colloidal particles and cell masses present in the fermentation environment, its use is subject to limitations. In... 

    A queuing network model for minimizing the total makespan of computational grids

    , Article Computers and Electrical Engineering ; Volume 38, Issue 4 , 2012 , Pages 827-839 ; 00457906 (ISSN) Parsa, S ; Entezari Maleki, R ; Sharif University of Technology
    2012
    Abstract
    This paper offers a mathematical solution based on queuing theory and a generalized stochastic Petri net model to minimize the total makespan of the grid computing environments. A grid manager could minimize the total makespan through cautious distribution of subtasks to the grid resources. Subtask arrival rates depend on the arrival rate of the grid tasks submitted to the grid manager, local tasks directly submitted to the grid resources and the processing speed of the resources. Modeling the grid environment using queuing network, the steady state analysis of the network will result in the mean response time of the resources. Therefore, the total makespan could be minimized by minimizing... 

    A ray tracing acceleration technique for wave propagation modeling

    , Article APMC 2009 - Asia Pacific Microwave Conference 2009, 7 December 2009 through 10 December 2009, Singapore ; 2009 , Pages 1100-1103 ; 9781424428021 (ISBN) Parsa, S ; Shishegar, A. A ; Sharif University of Technology
    IEEE  2009
    Abstract
    In this paper we deal with ray tracing acceleration problem in wave propagation simulation as a separate problem from its computer graphical counterpart and try to review accelerating techniques with this point of view. We build a classical kd-tree adapted to the special geometry of the problem. Then we mention the main differences between these two problems and devise algorithms that use these differences for accelerating intersection test in this problem even further  

    Fluid Suspended Films in Present of Electric Field and Voltage

    , Ph.D. Dissertation Sharif University of Technology Shirsavar, Reza (Author) ; Amjadi, Ahmad (Supervisor) ; Ejtehadi, Mohammad Reza ($item.subfieldsMap.e)
    Abstract
    Scientists want to know how they can control fluids motion. They use electric fields for controlling the fluids in different dimensions. In small size, application of electric fields is very important because of biological applications. We use electric current and field for rotating freely suspended films. Here, we study soap, polar and non-polar liquids, MBBA liquid crystal and ferrofluids films. We show that the surface charge plays the crucial role in rotating the films.We study the correlation between rotation of a film and different physical quantities.Our experiments confirm that dipole moments of fluid molecules do not show a clear effect on the rotation. Increasing the dipole moment...