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    Design and optimization of a heat driven thermoacoustic refrigerator

    , Article Applied Thermal Engineering ; Volume 62, Issue 2 , 25 January 2014 , Pages 653–661 Ghorbanian, K ; Karimi, M ; Sharif University of Technology
    Abstract
    The present paper deals with the design and optimization of a heat driven thermoacoustic refrigerator. A simplified model is developed which enables to pinpoint and examine the most important physical characteristics of a compact traveling wave thermoacoustic refrigerator driven by a traveling wave thermoacoustic engine. The model can explain the so-called traveling standing wave effect in thermoacoustics very well. The position, length and hydraulic radius of the refrigerator are optimized for the maximum total COP. The prime mover efficiency, refrigerator COP and dimensionless dissipation and their impacts on total COP are investigated and discussed. The results indicate that a COP of... 

    Signal and noise improvement of travelling wave fet mixers

    , Article 2nd International Conference on Microwave and Millimeter Wave Technology, ICMMT 2000, 14 September 2000 through 16 September 2000 ; 2000 , Pages 76-79 ; 0780357434 (ISBN); 9780780357433 (ISBN) Moradi, G ; Abdipour, A ; Farzaneh, F ; Ghorbani, A ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2000
    Abstract
    The influence of the loading of the FET electrodes, on signal and noise performances of the device in mixer application is studied. It is shown that exciting the input signal from one end of the gate and extracting the output signal from the opposite ends of the gate can improve the device characteristics, provided that the two remaining ends of the gate and the drain are properly loaded. This structure makes the lines (i.e. the gate and the drain electrodes) to be matched with the loads. Therefore it leads to a travelling wave FET mixer, which is a good candidate for high power mm-wave application. © 2000 IEEE  

    Detonatlve travelling waves for combustions

    , Article Applicable Analysis ; Volume 77, Issue 3-4 , 2001 , Pages 405-418 ; 00036811 (ISSN) Hesaaraki, M ; Razani, A ; Sharif University of Technology
    2001
    Abstract
    The existence of travelling wave solution to equations of a viscous heat conducting combustible fluid is proved. The reactions are assumed to be one step exothermic reactions with a natural discontinuous reaction rate function. The problem is studied for a general gas. Instead of assuming the ideal gas conditions we consider a general thermodynamics which is described by a fairly mild set of hypotheses. Travelling waves for detonations reduce to specific heteroclinic orbits of a discontinuous system of ODE's. The existence proof for heteroclinic orbits corresponding to weak and strong detonation waves is carried out by some general topological arguments in ODE. The uniqueness and... 

    Rigorous derivation of temporal coupled mode theory expressions for travelling and standing wave resonators coupled to optical waveguides

    , Article 7th International Conference on Photonics, Optics and Laser Technology, PHOTOPTICS 2019, 25 February 2019 through 27 February 2019 ; 2019 , Pages 201-208 ; 9789897583643 (ISBN) Zarif, A ; Memarian, M ; Mehrany, K ; Ribeiro P ; Raposo M ; Andrews D ; Institute for Systems and Technologies of Information, Control and Communication (INSTICC) ; Sharif University of Technology
    SciTePress  2019
    Abstract
    Temporal coupled mode theory (CMT) has so far been applied phenomenologically in the analysis of optical cavity-waveguide structures, and relies on a priori knowledge of the to-be-excited resonator mode. Thus a rigorous derivation from Maxwell's equations, and without any prior knowledge of the resonator type is needed. In this paper we derive temporal CMT of optical cavities coupled to waveguides. Starting from Maxwell's equations and considering a proper expansion of the modes of the waveguide and resonator, and using mode orthogonality, the temporal CMT for this structure is obtained. We show that this formulation is general and can be applied to both traveling wave and standing wave type... 

    Rigorous derivation of temporal coupled mode theory expressions for travelling and standing wave resonators coupled to optical waveguides

    , Article 7th International Conference on Photonics, Optics and Laser Technology, PHOTOPTICS 2019, 25 February 2019 through 27 February 2019 ; 2019 , Pages 201-208 ; 9789897583643 (ISBN) Zarif, A ; Memarian, M ; Mehrany, K ; Sharif University of Technology
    SciTePress  2019
    Abstract
    Temporal coupled mode theory (CMT) has so far been applied phenomenologically in the analysis of optical cavity-waveguide structures, and relies on a priori knowledge of the to-be-excited resonator mode. Thus a rigorous derivation from Maxwell's equations, and without any prior knowledge of the resonator type is needed. In this paper we derive temporal CMT of optical cavities coupled to waveguides. Starting from Maxwell's equations and considering a proper expansion of the modes of the waveguide and resonator, and using mode orthogonality, the temporal CMT for this structure is obtained. We show that this formulation is general and can be applied to both traveling wave and standing wave type... 

    Analysis of in-plane vibration and critical speeds of the functionally graded rotating disks

    , Article International Journal of Applied Mechanics ; Volume 11, Issue 2 , 2019 ; 17588251 (ISSN) Bagheri, E ; Jahangiri, M ; Sharif University of Technology
    World Scientific Publishing Co. Pte Ltd  2019
    Abstract
    In this paper, the in-plane free vibration analysis of the functionally graded rotating disks with variable thickness is presented utilizing DQM. It is assumed that the rotational velocity of the disk is constant and the thickness and material properties including modulus of elasticity and density vary along the radial coordinate. The distribution of the forward and backward traveling waves versus the angular velocity is demonstrated for several modal circles and nodal diameters with respect to the fixed and rotating coordinate systems. After presenting the accuracy and convergence of the numerical method, the derived formulation and the solution method are validated by comparing the results... 

    Numerical investigation of the forward and backward travelling waves through an undulating propulsor: performance and wake pattern

    , Article Ships and Offshore Structures ; Apr , 2015 ; 17445302 (ISSN) Ebrahimi, M ; Abbaspour, M ; Sharif University of Technology
    Taylor and Francis Ltd  2015
    Abstract
    Recently, the mechanisms of natural undulatory locomotion of aquatic animal swimming have become one of the most significant issues for the researchers, swimmers and engineers. This study aims to elucidate and compare the propulsive vortical signature and performance of backward (negative undulation) and forward (positive undulation) travelling waves through a typical fishlike propulsor by a systematic numerical study. The numerical approach uses a pressure-based finite volume method solver to solve Navier–Stokes equations in an arbitrary Lagrangian–Eulerian framework domain containing a two-dimensional NACA 0012 foil moving with prescribed kinematics. Some of the important findings are: (1)... 

    Numerical investigation of the forward and backward travelling waves through an undulating propulsor: performance and wake pattern

    , Article Ships and Offshore Structures ; Volume 11, Issue 5 , 2016 , Pages 517-539 ; 17445302 (ISSN) Ebrahimi, M ; Abbaspour, M ; Sharif University of Technology
    Taylor and Francis Ltd  2016
    Abstract
    Recently, the mechanisms of natural undulatory locomotion of aquatic animal swimming have become one of the most significant issues for the researchers, swimmers and engineers. This study aims to elucidate and compare the propulsive vortical signature and performance of backward (negative undulation) and forward (positive undulation) travelling waves through a typical fishlike propulsor by a systematic numerical study. The numerical approach uses a pressure-based finite volume method solver to solve Navier–Stokes equations in an arbitrary Lagrangian–Eulerian framework domain containing a two-dimensional NACA 0012 foil moving with prescribed kinematics. Some of the important findings are: (1)... 

    Non-Reciprocity in Transmission Line Resonator with Time Varying Boundary Condition

    , M.Sc. Thesis Sharif University of Technology Shams, Raheleh (Author) ; Mehrany, Khashayar (Supervisor) ; Memarian, Mohammad (Supervisor)
    Abstract
    Structures with time-varying electromagnetic properties can potentially yield non-reciprocity, amplification, harmonic generation, and other interesting wave propagation phenomena. To date, some studies have dealt with time-varying media and circuits, including time-varying optical ring resonators having degenerate travelling wave resonances. In time-varying ring resonators, the clockwise and counter clockwise resonances lose their degeneracy, and non-reciprocity is observed. One of the main challenges of such research is the need to induce time-variations in the entirety of the resonator or structure, which makes their implementation very limited or impossible in practice. The purpose of... 

    The Existence and Stability of Classical Solutions in the Neural Fields Equations

    , M.Sc. Thesis Sharif University of Technology Shafiee, Ahmad (Author) ; Fotouhi Firouzabadi, Morteza (Supervisor)
    Abstract
    In this thesis, first, the modeling method of neural fields is precisely presented. Then, Existence and Stability of different solutions of one dimensional neural fields like Standing Pulses, Traveling Waves and ... are investigated in three different models of neural fields. In order for proving Existence and Stability of the solutions the mathematical tools like Fourier transform and Evans function are applied. All the models which analysed in this thesis have the following Integro-Differential Equation form:
    τ
    ∂u(x, t)
    ∂t
    = −u(x, t) +
    ∫ +∞
    −∞
    w(x, y)f[u(y, t)]dy + I(x, t) + s(x, t)
    and also in some models the parameters might be changed  

    Design and optimization of a heat driven thermoacoustic refrigerator

    , Article Applied Thermal Engineering ; Volume 61, Issue 2 , 2013 , Pages 653-661 ; 13594311 (ISSN) Ghorbanian, K ; Karimi, M ; Sharif University of Technology
    2013
    Abstract
    The present paper deals with the design and optimization of a heat driven thermoacoustic refrigerator. A simplified model is developed which enables to pinpoint and examine the most important physical characteristics of a compact traveling wave thermoacoustic refrigerator driven by a traveling wave thermoacoustic engine. The model can explain the so-called traveling standing wave effect in thermoacoustics very well. The position, length and hydraulic radius of the refrigerator are optimized for the maximum total COP. The prime mover efficiency, refrigerator COP and dimensionless dissipation and their impacts on total COP are investigated and discussed. The results indicate that a COP of... 

    Neural fields with fast learning dynamic kernel

    , Article Biological Cybernetics ; Volume 106, Issue 1 , January , 2012 , Pages 15-26 ; 03401200 (ISSN) Abbassian, A. H ; Fotouhi, M ; Heidari, M ; Sharif University of Technology
    Abstract
    We introduce a modified-firing-rate model based on Hebbian-type changing synaptic connections. The existence and stability of solutions such as rest state, bumps, and traveling waves are shown for this type of model. Three types of kernels, namely exponential, Mexican hat, and periodic synaptic connections, are considered. In the former two cases, the existence of a rest state solution is proved and the conditions for their stability are found. Bump solutions are shown for two kinds of synaptic kernels, and their stability is investigated by constructing a corresponding Evans function that holds for a specific range of values of the kernel coefficient strength (KCS). Applying a similar... 

    Travelling-wave Ka-band frequency scanning Antennas for millimeter-wave imaging applications

    , Article 2016 8th International Symposium on Telecommunications, IST 2016, 27 September 2016 through 29 September 2016 ; 2017 , Pages 591-595 ; 9781509034345 (ISBN) Ranjbar Naeini, M ; Fakharzadeh, M ; Farzaneh, F ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2017
    Abstract
    In this paper, a novel travelling-wave printed Frequency Scanning Antenna (FSA), which can be used for imaging purposes, is proposed. All sample designs scan the space symmetrically about the broadside direction. For different scanning ranges, two low profile antennas are designed on a 6.6 mils thick Rogers 4350 board substrate layer. Impedance bandwidth of the first one covers 6.5GHz, from 29.5GHz to 36GHz, and this antenna scans 56° in angular space. The second antenna has 5.6GHz bandwidth from 30.6GHz to 36.2GHz, and scans 98° in angular space by means of switching the input port. The average gain and the Side-lobe level (SLL) of the first and the second antennas are 11.46dBi, 12.8dB, and... 

    The Impact of Non-reciprocal One-way Propagation on the Coupling between Electromagnetic Resonators and Waveguides

    , M.Sc. Thesis Sharif University of Technology Zarif, Arezoo (Author) ; Mehrany, Khashayar (Supervisor) ; Rajaei, Behzad (Co-Advisor)
    Abstract
    Subwavelength localization of electromagnetic energy with intense local fields, also known as electromagnetic hotspots, has received significant attention over the past few decades. In most cases the hotspot is achieved through the resonant concentration of electromagnetic fields. One way recently considered to get hotspot is through reflection of electromagnetic waves in nonreciprocal one-way structures, in plasmonics and via magneto optic effect.However these hotspots are less confined compared to hotspots caused by resonances. So combining nonreciprocal structures with resonance can provide better hotspots.Our aim in this thesis is to study nonreciprocal resonant structures using coupled... 

    Analysis and Improvement of Output Voltage Ripple in High Voltage DC Power Supply

    , M.Sc. Thesis Sharif University of Technology Ziaoddini, Mojtaba (Author) ; Kaboli, Shahryar (Supervisor)
    Abstract
    The TWT is highly sensitive to the ripple amplitude of its power supply output voltage. If the amplitude of the output voltage's ripple exceeds a certain limit, the amplitude of the undesired harmonics in the power spectrum of the TWT is greatly increased. Increasing the amplitude of undesired harmonics in the TWT output power spectrum reduces the accuracy and performance of the TWT. Therefore, for optimum TWT performance, a low-ripple power supply is essential. Typically, a low-frequency rectifier or high-frequency switching structure is used to build a high-voltage DC power supply. In this thesis, the different structures of high voltage DC power supplies are studied. Next, by focusing on... 

    Numerical Investigation of Jet Pump Performance in Traveling Wave Thermoacoustic Engine

    , M.Sc. Thesis Sharif University of Technology Barzegari, Ali (Author) ; Ghorbanian, Kaveh (Supervisor)
    Abstract
    Thermoacoustic engines are a promising alternative to the conventional heat engines due to the absence of moving parts in the hot region and the small temperature difference required for operation. However, the traveling wave thermoacoustic engine configuration has a relatively lower efficiency due to a phenomenon called Gedeon streaming. In this regard, a jet pump might be used to lower the negative effects of Gedeon streaming. The jet pump, which is simply an element consisting of one or more tapered holes, induces an oscillating flow through the asymmetric device and hence resulting in a time-averaged pressure drop across it. As a result, by balancing this time averaged pressure drop with... 

    Stability and Traveling Waves of a Stage–structured (Predator-rey)Model with Holing Type-II Functional Response and Harvesting

    , M.Sc. Thesis Sharif University of Technology Keyhani Shayeste, Mozhgan (Author) ; Hesaaraki, Mahmoud (Supervisor)
    Abstract
    IN this upper ,we consider a reaction –diffusion predator-prey model with stage –structure, holling type –ll functional response. Nonlocal spatial impacat and harvesting The stability of the equilibria is investigated. Furthermore, by the cross-iteration schauder fixed point theorem, we deduce the existence of traveling wave solution which connects the zero solution and the positive constant eguilibrium  

    Design of a Coupled Thermoacoustic Refrigerator System based on Heat Absorption of Piston Engines of Power Plants

    , M.Sc. Thesis Sharif University of Technology Dehghani, Ali (Author) ; Mazaheri, Karim (Supervisor)
    Abstract
    Design and parametric study of a coupled thermoacoustic refrigerator system has been carried out based on thermoacoustic theories. The purpose of coupled thermoacoustic refrigerator design is to cool a container with small dimensions for use in cold storage above zero. The application of this refrigerator is where the waste heat of piston engines of distributed generation (DG) plants can be used as energy input. The design is based on the simplicity and low cost of the refrigerator. Therefore, the engine and refrigerator part of the coupled thermoacoustic refrigerator is enclosed in a resonator with a fixed diameter, which is closed on both sides of the resonator. Two standing-wave... 

    Analysis of a Mathematical Model Describing the Geographical Spread of Dengue Disease

    , Ph.D. Dissertation Sharif University of Technology Gazori, Fereshteh (Author) ; Hesaaraki, Mahmoud (Supervisor)
    Abstract
    Dengue is one of the most important infectious diseases in the world. This disease is a viral infection that is transmitted to humans through the bite of a mosquito called Aedes aegypti. For this reason, geographical regions infected with this type of mosquito are at risk of Dengue outbreak. In this thesis, we first present a mathematical model describing the geographical spread of Dengue disease, which includes the movement of both the human population and the winged mosquito population. This model is derived from a mixed system of partial and ordinary differential equations. Our proposed model has the ability to consider the possibility of asymptomatic infection, so that the presence of... 

    Closed form formula for longitudinal slot of LWAs with minimum side lobe level

    , Article 2017 25th Iranian Conference on Electrical Engineering, ICEE 2017, 2 May 2017 through 4 May 2017 ; 2017 , Pages 1820-1824 ; 9781509059638 (ISBN) Boozari, M ; Bayderkhani, R ; Alijani, M. G ; Neshati, M. H ; Sharif University of Technology
    Abstract
    In this paper a closed-form expression is introduced to calculate slot shape of long slot leaky wave waveguide antennas at its fundamental mode of operation with minimum side lobe level (SLL). The derived equation is a function of geometrical parameters of the structure. This is an advantage because they show a clear relationship between geometrical parameters of the antenna and radiated field that allows intelligent modification of the pattern. The Gaussian slot is used to obtain the best radiation pattern with lowest SLL. The results obtained by introduced formula are compared with the full wave commercial simulator such as HFSS software which confirms the accuracy of the introduced...