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A Deep Recurrent Neural Network Model for Supervised Labeling of Variable Length Sequences
, M.Sc. Thesis Sharif University of Technology ; Rabiee, Hamid Reza (Supervisor)
Abstract
In recent years, machine learning has been widely used to solve various computational problems. One of the most fundamental and integral type of these issues is the problem of classification, in which the data samples of different types such as image, voice, or video are classified into different categories. Since these data types are inherently sequential, the problem of classifying sequential data, is of great importance. This problem has a wide range of applications, including but not restricted to, handwriting recognition, voice recognition, malware detection, and fraud detection in financial transactions. Regarding the fact that in many cases, the length of the sequence (which could be...
Experimental Investigation of Cooling Hot Surfaces By Electrospray
, M.Sc. Thesis Sharif University of Technology ; Morad, Mohammad Reza (Supervisor)
Abstract
The electrospray technique involves the production of small charged droplets through the application of electrohydrodynamic forces. Under well-defined operating conditions, multiple flow modes can be observed, among which the stable jet-cone mode has received significant attention from the research community. This mode is desirable due to its uniform droplet diameter, reduction in droplet rebound when impacting hot surfaces, and potential for utilizing two-phase heat transfer for cooling purposes. In this study, a comprehensive experimental investigation was conducted to evaluate the cooling of hot surfaces through the use of electrospray in the steady cone-jet mode. The fundamental...
Synthesis and Characterization of TiO2 and WO3 Thin Film Photoanodes Containing Noble Metal Nanoparticles and (TiO2)x-(ZnO)1-x Nanocomposite Photanodes for H2 Production
, Ph.D. Dissertation Sharif University of Technology ; Moshfegh, Ali Reza (Supervisor)
Abstract
Growing demand on energy and limitation and consequence of fossil fuels have caused to utilize the clean and renewable energy sources. Hydrogen is a clean energy carrier which produced just water vapor during combustion. Today, methods which are usually used to produce this fuel are based on using fossil fuel compounds. Therefore, utilizing new production methods is unavoidable. One of these methods is using semiconductors such as TiO2 to spilt water and produce H2 by solar irradiation. Reducing the energy gap of these semiconductors to match the solar spectrum, specially in its visible range, modification of their structures, surfaces and stability are the main challenges in hydrogen...
Modeling of Large Deformation Frictional Contact Using the Augmented-Lagrange Method
, M.Sc. Thesis Sharif University of Technology ; Khoei, Amir Reza (Supervisor)
Abstract
The numerical modeling of engineering contact problems is one of the most difficult and demanding tasks in computational mechanics. Frictional contact can be observed in many problems; such as: crack propagation, metal forming operation, drilling pile etc. In metal forming operations the required shape changes are obtained by either of forming process, such as pressing, hammering, rolling or extruding the material between the tools which are much stiffer than shaped material. Because of large difference between deformability of the tool and material, relative movements occur in contact area. These relative movements produce the normal and tangential stresses, which have important role on...
Two Dimensional Elastic Wave Propagation Analysis in Functionally Graded Materials using Finite Element Method in both Time and Frequency Domain
, M.Sc. Thesis Sharif University of Technology ; Naghdabadi, Reza (Supervisor) ; Sohrabpour, Saeed (Supervisor)
Abstract
In this thesis the tow-dimensional wave propagation in a functionally graded elastic medium is considered. It is assumed that the stiffness and density of the medium vary continuously in one direction. This work presents analysis in both time and frequency domain. In time domain, a graded element is presented for static and dynamic analyses in FGMs. This element clearly simulates wave propagation in inhomogeneous materials. The most important property which an element must have to be reasonable in wave propagation analyses in FGMs is simulating reflection only from boundaries. In frequency domain a dynamic stiffness matrix is generated using stiffness and mass matrix used in time domain...
Simulation of SO2 absorption in a venturi scrubber
, Article Chemical Engineering Communications ; Volume 197, Issue 7 , Feb , 2010 , Pages 934-952 ; 00986445 (ISSN) ; Mohebbi, A ; Taheri, A ; Sharif University of Technology
2010
Abstract
In this study, a three-dimensional mathematical model, based on a nonuniform droplet concentration distribution, has been developed to simulate gas absorption in a venturi scrubber. The mass transfer process was illustrated by assuming the liquid phase as a combination of droplets and film. The flow, just as the annular two-phase flow, includes a flow of liquid film layer on the walls and a flow of gas and liquid drops in the core. Peclet number was determined using experimental data reported by Viswanathan et al. (1984) for distribution of droplets across the cross section of the scrubber. The mathematical model for gas absorption was justified by comparing the theoretical predictions with...
Modeling, Design, and the Application of Humanoid Robots in the Treatment of Children with Autism
, Ph.D. Dissertation Sharif University of Technology ; Meghdari, Ali (Supervisor) ; Pouretemad, Hamid Reza (Co-Advisor) ; Alemi, Minoo (Co-Advisor)
Abstract
Statistics have shown an endemic worldwide increase of Autistic Spectrum Disorders (ASD) since the 1960s, Iran also faces the same problem. Autistic disorders are characterized by three major behavioral disorders: impaired social interaction, impaired communication, and impaired imagination and social creativity. The usage of robots in autism diagnosis and treatment has been increasing in recent years. In this study, our objective (as one of the pioneers in Iran) is to explore the clinical application of two interactive social humanoid robots (NAO and ALICE with the Iranian names of NIMA and MINA) as medical assistants in the treatment and education of children with autism in order to...
The effect of prestrain temperature on kinetics of static recrystallization, microstructure evolution, and mechanical properties of low carbon steel
, Article Journal of Materials Engineering and Performance ; Volume 27, Issue 5 , 2018 , Pages 2049-2059 ; 10599495 (ISSN) ; Karimi Taheri, K ; Karimi Taheri, A ; Sharif University of Technology
Springer New York LLC
2018
Abstract
In this research, the samples of a low carbon steel sheet were rolled up to a thickness prestrain of 67% at three different temperatures consisted of room, blue brittleness, and subzero temperature. Microhardness, SEM, and tensile tests were carried out to evaluate the static recrystallization kinetics defined by the Avrami equation, microstructural evolution, and mechanical properties. It was found that the Avrami exponent is altered with change in prestrain temperature and it achieves the value of 1 to 1. 5. Moreover, it was indicated that prestraining at subzero temperature followed by annealing at 600 °C leads to considerable enhancement in tensile properties and kinetics of static...
An investigation on tensile properties of coiled carbon nanotubes using molecular dynamics simulation
, Article Diamond and Related Materials ; Volume 74 , 2017 , Pages 154-163 ; 09259635 (ISSN) ; Karimi Taheri, K ; Karimi Taheri, A ; Sharif University of Technology
Elsevier Ltd
2017
Abstract
A coiled carbon nanotube (CCNT) can be formed from the distortion of parent toroidal carbon nanotube with a uniform pitch length and a uniform spring rise angle. In this research molecular dynamics simulation was carried out to assess the tensile properties of three CCNT having indexes of (3,3), (4,4), and (5,5). The results indicated that Stone-Wales defects are necessary for thermodynamic stability of the CCNTs. The stress-strain curves showed that the yield stress, yield strain, and failure strain are decreased with increase in temperature. The force-displacement curves revealed that the spring constant of these materials is highly depended on the tube diameter and rising angle, while it...
Microstructural evolution, mechanical properties, and corrosion resistance of a heat-treated Mg alloy for the bio-medical application
, Article Journal of Magnesium and Alloys ; Volume 7, Issue 1 , 2019 , Pages 80-89 ; 22139567 (ISSN) ; Karimi Taheri, K ; Karimi Taheri, A ; Sharif University of Technology
National Engg. Reaserch Center for Magnesium Alloys
2019
Abstract
During the recent years, some Mg based alloys have extensively been considered as a new generation of degradable and absorbable bio-medical materials. In this work, the Mg–2Zn–1Gd–1Ca (wt%) alloy as a new metallic bio-material was produced by the casting process followed by the heat treatment. The samples of the alloy were solution treated at temperatures of 500, 550, and 600 °C and then quench aged at temperatures of 125, 150, and 175 °C. The results of SEM-EDS examinations indicated that the alloy microstructure consists of α-Mg matrix and the Ca2Mg6Zn3 and Mg3Gd2Zn3 secondary phases. With regard to the results of Vickers hardness test, the temperatures of 500 °C and 150 °C were selected...
A study of hyperelastic models for predicting the mechanical behavior of extensor apparatus
, Article Biomechanics and Modeling in Mechanobiology ; Volume 16, Issue 3 , 2017 , Pages 1077-1093 ; 16177959 (ISSN) ; Karimi Taheri, K ; Narooei, K ; Karimi Taheri, A ; Sharif University of Technology
Springer Verlag
2017
Abstract
In this research, the nonlinear elastic behavior of human extensor apparatus was investigated. To this goal, firstly the best material parameters of hyperelastic strain energy density functions consisting of the Mooney–Rivlin, Ogden, invariants, and general exponential models were derived for the simple tension experimental data. Due to the significance of stress response in other deformation modes of nonlinear models, the calculated parameters were used to study the pure shear and balance biaxial tension behavior of the extensor apparatus. The results indicated that the Mooney–Rivlin model predicts an unstable behavior in the balance biaxial deformation of the extensor apparatus, while the...
Impacts of socially assistive robots on improving the quality of life in children with autism
, Article Encyclopedia of Child and Adolescent Health, First Edition ; Volume 1 , 2023 , Pages 99-125 ; 978-012818873-6 (ISBN); 978-012818872-9 (ISBN) ; Sharif University of Technology
Elsevier
2023
Abstract
Statistics have shown an endemic worldwide increase of Autistic Spectrum Disorders (ASD) since the 1960s. Autistic disorders are characterized by three major behavioral disorders: impaired social interaction, impaired communication, and impaired imagination and social creativity. The usage of Socially Assistive Robots (SAR) in autism screening and treatment has been increasing in recent years. In this chapter, after reviewing the most important findings of using SAR in autism area, I present some of our recent findings on the clinical application of two interactive social humanoid robots (i.e., NAO and ALICE with the Iranian names of Nima and Mina) as medical assistants in the treatment and...
An investigation on microstructure evolution, mechanical properties, and strain aging of Mg-1.8Zn-0.7Si-0.4Ca biomedical alloy processed by equal channel angular pressing
, Article Journal of Materials Engineering and Performance ; Volume 28, Issue 8 , 2019 , Pages 5207-5219 ; 10599495 (ISSN) ; Karimi Taheri, K ; Karimi Taheri, A ; Shaeri, M. H ; Sharif University of Technology
Springer New York LLC
2019
Abstract
The influence of equal channel angular pressing (ECAP) on microstructure and mechanical behavior, as well as, strain aging during ECAP and post-ECAP of Mg-1.8Zn-0.7Si-0.4Ca biomedical alloy was examined. The alloy in solid solution heat-treated condition was processed by ECAP with route BC at 350 and 400 °C. The specimens ECAPed at 350 °C were aged at 125 and 150 °C for different times. The hardness and shear punch test results indicated that performing ECAP at 350 °C for 4 passes increases the hardness and shear strength of the alloy from 48 HV and 110 MPa to 71 HV and 188 MPa, respectively. It was revealed that the average grain size of the alloy decreases from 78 µm to about 3 µm after 4...
The effect of deformation heating on restoration and constitutive equation of a wrought equiatomic NiTi alloy
, Article Journal of Materials Engineering and Performance ; Volume 21, Issue 4 , April , 2012 , Pages 516-523 ; 10599495 (ISSN) ; Karimi Taheri, A ; Karimi Taheri, K ; Sarraf, I. S ; Abbasi, S. M ; Sharif University of Technology
2012
Abstract
In this study, a set of constitutive equation corrected for deformation heating is proposed for a near equiatomic NiTi shape memory alloy using isothermal hot compression tests in temperature range of 700 to 1000 °C and strain rate of 0.001 to 1 s -1. In order to determine the temperature rise due to deformation heating, Abaqus simulation was employed and varied thermal properties were considered in the simulation. The results of hot compression tests showed that at low pre-set temperatures and high strain rates the flow curves exhibit a softening, while after correction of deformation heating the softening is vanished. Using the corrected flow curves, the power-law constitutive equation of...
Blade shape optimization of marine propeller via genetic algorithm for efficiency improvement
, Article Proceedings of the ASME Turbo Expo ; Volume 5 , 2012 , Pages 235-242 ; 9780791844717 (ISBN) ; Mazaheri, K ; Sharif University of Technology
2012
Abstract
In this paper, a numerical optimization method has been carried out to optimize the shape and efficiency of a propeller. For analysis of the hydrodynamic performance parameters, an extended vortex lattice method was used by implementing an open-source code which is called OpenProp. The method of optimization is a non-gradient based algorithm. After a trade-off between a few gradient-based and non-gradient based algorithms, it is found that the problem of being trapped in local optimum solutions can be easily solved by choosing nongradient based ones. Hence, modified Genetic algorithm is used to implement the so-called hydrodynamic performance analyzer code. The objective function is to...
Hydrodynamic optimization of marine propeller using gradient and non-gradientbased algorithms
, Article Acta Polytechnica Hungarica ; Volume 10, Issue 3 , 2013 , Pages 221-237 ; 17858860 (ISSN) ; Mazaheri, K ; Sharif University of Technology
2013
Abstract
Here a propeller design method based on a vortex lattice algorithm is developed, and two gradient-based and non-gradient-based optimization algorithms are implemented to optimize the shape and efficiency of two propellers. For the analysis of the hydrodynamic performance parameters, a vortex lattice method was used by implementing a computer code. In the first problem, one of the Sequential Unconstraint Minimization Techniques (SUMT) is employed to minimize the torque coefficient as an objective function, while keeping the thrust coefficient constant as a constraint. Also, chord distribution is considered as a design variable, namely 11 design variables. In the second problem, a modified...
Byzantine consensus for unknown dynamic networks
, Article Journal of Supercomputing ; Volume 71, Issue 4 , April , 2015 , Pages 1587-1603 ; 09208542 (ISSN) ; Izadi, M ; Sharif University of Technology
Kluwer Academic Publishers
2015
Abstract
In a distributed system, each solution for the problem of Byzantine agreement requires that some of the correct processes reach a common decision value from a set of proposed values while Byzantine processes may behave arbitrarily. While the problem has been widely studied in fully connected fixed networks, few studies have been carried out in the context of self-organizing mobile networks such as mobile ad hoc networks. We present a randomized consensus protocol with three additional modules for the case of dynamic networks: participant detectors, failure detectors and maintainer. We assume an asynchronous network with unknown participants where processes can be fixed or move continuously...
Dynamic-programming-based failure-tolerant control for satellite with thrusters in 6-DOF motion
, Article Advances in Space Research ; Volume 65, Issue 12 , 2020 , Pages 2857-2877 ; Assadian, N ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
In this paper, a dynamic-programming approach to the coupled translational and rotational control of thruster-driven spacecraft is studied. To reduce the complexity of the problem, dynamic-programming-based optimal policies are calculated using decoupled position and attitude dynamics with generalized forces and torques as controls. A quadratic-programming-based control allocation is then used to map the controls to actuator commands. To control the spacecraft in the event of thruster failure, both the dynamic programming policies and control allocation are reconfigured to cope with the losses in controls. The control allocation parameters are adjusted dynamically to ensure the satellite...
Tariff-aware power management for reducing the break-even time of on-site solar power installation in data center
, Article Renewable Energy Focus ; Volume 32 , 2020 , Pages 55-62 ; Goudarzi, M ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
The global energy crisis and harmful effects of fossil fuel usage as well as the rapid rate of electricity price growth forces Data Centers (DCs) providers to install on-site Renewable Energy (RE). However, the huge installation investment, as well as fluctuating characteristic, impedes the widespread usage of RE. Reducing the break-even time of the required investment is a reinforcing economic incentive that complements the environmental incentive to further encourage DC Providers to use more RE. This paper takes advantages of an economic opportunity, namely the electricity pricing models, as well as a technological opportunity, namely the distributed Uninterruptable Power Supply (UPS)...
New methods of reducing the phase quantization error effects on beam pointing and parasitic side lobe level of the phased array antennas
, Article 2006 Asia-Pacific Microwave Conference, APMC, Yokohama, 12 December 2006 through 15 December 2006 ; Volume 3 , 2006 , Pages 2114-2117 ; 4902339102 (ISBN); 9784902339109 (ISBN) ; Farzaneh, F ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2006
Abstract
Usually the digital phase shifters are used to steer the beam of a phased array antenna, and the accuracy of beam steering and other properties of the radiation pattern is dependent on the number of bits of the phase shifter and its resolution. In this paper the results of simulations, accomplished using a number of phase feeding methods in order to reduce the phase quantization error effects are presented and three new methods are introduced and compared with the previous works. Copyright 2006 IEICE