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hesari--abdolaziz
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Chern–Weil Theory Extended to a Class of Infinite Dimensional Bundles
, M.Sc. Thesis Sharif University of Technology ; Esfahani Zadeh, Mostafa (Supervisor)
Abstract
Given a principal bundle a characteristic class is an element of the cohomology al- gebra of the classifying space of structure group of the bundle with coefficients in a commutative ring with unit ,which have a functorial property .When the structure groupe of the bundle is a Lie group and the coefficient ring is the real or complex num- bers , the Chern–Weil approach provides a geometric construction of char-acteristic classes. Classical Chern–Weil formalism relates geometry to topology, assigning to the cur- vature of a connection, de Rham cohomology classes of the underlying manifold.This theory developped in the 40’s by Shiing-ShenChern and Andre Weil which can be seen as a generalisation...
Towards a general framework for evaluating software development methodologies
, Article Proceedings - International Computer Software and Applications Conference, 19 July 2010 through 23 July 2020 ; July , 2010 , Pages 208-217 ; 07303157 (ISSN) ; 9780769540856 (ISBN) ; Mashayekhi, H ; Ramsin, R ; Sharif University of Technology
2010
Abstract
It has become essential to scrutinize and evaluate software development methodologies, mainly because of their increasing number and variety. Evaluation is required to gain a better understanding of the features, strengths, and weaknesses of the methodologies. The results of such evaluations can be leveraged to identify the methodology most appropriate for a specific context. Moreover, methodology improvement and evolution can be accelerated using these results. However, despite extensive research, there is still a need for a feature/criterion set that is general enough to allow methodologies to be evaluated regardless of their types. We propose a general evaluation framework which addresses...
Advanced nonlinear dynamic analysis of arch dams considering joints effects
, Article Advances in Mechanical Engineering ; Volume 201 , 2014 ; ISSN: 16878132 ; Ghaemian, M ; Shamsai, A ; Sharif University of Technology
2014
Abstract
Influence of joints behavior on arch dams operation during the earthquakes is investigated. The case study is the Karun-1 double curvature arch dam with the height of 200 meters. The arch dam-foundation-reservoir systems are modeled with and without joints and estimate the effects of contraction and lift joints on stresses and displacements response histories for assessing the earthquake performance. According to nolinear dynamical analysis results, inclusion of the contraction and lift joints considerably influenced the dam response
A comparative study of two cavitation modeling strategies for simulation of inviscid cavitating flows
, Article Ocean Engineering ; Volume 108 , November , 2015 , Pages 257-275 ; 00298018 (ISSN) ; Ezzatneshan, E ; Fattah Hesari, K ; Sharif University of Technology
Elsevier Ltd
2015
Abstract
In the present work, two cavitation modeling strategies, namely the barotropic cavitation model and the transport equation-based model are applied and assessed for the numerical simulation of inviscid cavitating flows over two-dimensional and axisymmetric geometries. The algorithm uses the preconditioned Euler equations employing the interface capturing method for both the cavitation models. A same numerical solution procedure is used herein for discretizing the governing equations resulting from these two cavitation modeling strategies for the assessment to be valid and reliable. A central difference finite-volume scheme employing the suitable dissipation terms to account for density jumps...
Configuration Design of Mechanical Structure Coupled with MSMA in Energy Harvesting
, M.Sc. Thesis Sharif University of Technology ; Sayyadi, Hassan (Supervisor)
Abstract
In recent years, energy harvesting from ambient sources in order to use for low-powered electronics has been considered by many researchers. Wind energy, solar energy, water energy, mechanical energy from vibrations, etc are common sources of ambient energy. In this thesis, optimization of energy harvesting from ambient vibration using magnetic shape memory alloy is presented. To this end, a clamped-clamped beam coupled with MSMA units is considered. A shock load is applied to a proof mass which is attached to the middle of the beam. As a result of beam vibration a longitudinal strain is produced in the MSMA. This strain changes magnetic flux inside the coil connected to MSMA and as a...
Synthesis and characterization of (2E,2 E)-3,3-((9,9-diocyl-9H-flourene-2,7-diyl)bis(4,1-phenylene))bis(2-cyanoacylic acid) as a symmetrical metal-free organic dye
, Article Journal of the Chinese Chemical Society ; Volume 62, Issue 5 , May , 2015 , Pages 393–397 ; 00094536 (ISSN) ; Hadavand, B. S ; Hashemi, M. M ; Sharif University of Technology
Chinese Chemical Society Taiwan
2015
Abstract
In this study a novel symmetrical metal-free organic dye for applications in dye-sensitized solar cells (DSSCs) was synthesized. This dye (D) was designed with A-π-D-π-A framework and synthesized with 9,9-dioctylfluorene as electron donor, phenylene as π-spacer and cyanoacetic acid as electron acceptor. The chemical structure of product was determined using UV-Vis, FT-IR, CNMR, HNMR spectroscopy techniques. The presence of a phenylene π-bridge between the donor and the acceptor units and the di-anchoring moieties in this structure led to enhancement of conjugation lengths and molar extinction coefficient (ε) that is promising for further improvement of the conversion efficiency of DSSCs
Synthesis and characterization of (2E,2 E)-3,3-((9,9-diocyl-9H-flourene-2,7-diyl)bis(4,1-phenylene))bis(2-cyanoacylic acid) as a symmetrical metal-free organic Dye
, Article Journal of the Chinese Chemical Society ; Volume 62, Issue 5 , 2015 , Pages 393-397 ; 00094536 (ISSN) ; Hadavand, B. S ; Hashemi, M. M ; Sharif University of Technology
Chinese Chemical Society Taiwan
2015
Abstract
In this study a novel symmetrical metal-free organic dye for applications in dye-sensitized solar cells (DSSCs) was synthesized. This dye (D) was designed with A-π-D-π-A framework and synthesized with 9,9-dioctylfluorene as electron donor, phenylene as π-spacer and cyanoacetic acid as electron acceptor. The chemical structure of product was determined using UV-Vis, FT-IR, CNMR, HNMR spectroscopy techniques. The presence of a phenylene π-bridge between the donor and the acceptor units and the di-anchoring moieties in this structure led to enhancement of conjugation lengths and molar extinction coefficient (ε) that is promising for further improvement of the conversion efficiency of DSSCs....
Online Algorithms for Fair Allocation of Goods
, M.Sc. Thesis Sharif University of Technology ; Zarrabi Zadeh, Hamid (Supervisor)
Abstract
In this thesis, we study the max-min fair allocation of goods which represents one of the most basic problems in scheduling theory. Here we consider the online problem of allocating a set of indivisible items among agents whom each has her own preference list over the items. The goal is to maximize the minimum happiness (profit) of the agents.We present an algorithm with competitive ratio n 2 and prove that this competitive ratio is tight. We also consider this problem when each agent has a type and the number of types is constant and solve the problem where the number of types is 2 or 3. Furthermore, we study the problem with resource augmentation. We focus on doubling the number of items...
Modeling and active control of chatter vibrations of piezoelectric stacked machining arm in micro-turning process
, Article Meccanica ; Volume 55, Issue 9 , 18 July , 2020 , Pages 1707-1731 ; Moradi, H ; Movahhedy, M. R ; Sharif University of Technology
Springer
2020
Abstract
Self-excited vibrations known as chatter are considered as the most detrimental issue in micro-turning processes. Occurring unpredictably, they adversely affect the tool life, productivity rate and surface quality of the machining processes. In this paper, a novel machining arm is modeled as a piezoelectric stacked rod which is subjected to a chatter force in the orthogonal micro-turning process. Due to the fact that machining processes are affected by various sources of uncertainties, H∞ robust control approach is used to suppress the chatter vibrations of the machining arm in the presence of tool wear and dynamic model parameter variations. Also, input control force of the system is...
Fabrication, characterization and mechanical properties of hybrid composites of copper using the nanoparticulates of SiC and carbon nanotubes [electronic resource]
, Article Journal of Materials Science and Engineering: A ; 10 June 2013, Volume 572, P.83–90 ; Salahi, E ; Alikhani Hesari, F ; Simchi, A. (Abdolreza) ; Kim, H. S ; Sharif University of Technology
Abstract
Copper based hybrid composites containing nano-sized silicon carbide and carbon nanotubes reinforcements with minimal porosity were fabricated via mechanical milling followed by hot pressing technique. Microstructures of the powders and consolidated materials were studied using scanning electron microscope, X-ray diffraction, Raman spectroscopy, and scanning transmission electron microscope. Microstructural characterization of the materials revealed that the addition of nanosized silicon carbide reinforcement lowered the grain growth rate and enhanced the homogenization during mechanical milling. Microhardness measurements and compression test showed considerable improvements in mechanical...
Effect of nanoparticle content on the microstructural and mechanical properties of nano-SiC dispersed bulk ultrafine-grained Cu matrix composites [electronic resource]
, Article Journal of Materials & Design ; December 2013, Volume 52, Pages 881–887 ; Salahi, E ; Alikhani Hesari, F ; Kim, H. S ; Simchi, A. (Abdolreza) ; Sharif University of Technology
Abstract
In this study, the microstructural and mechanical features of monolithic pure Cu and Cu matrix nanocomposites reinforced with three different fractions (2, 4, and 6 vol%) of SiC nanoparticles (n-SiC) fabricated via a combination of high energy mechanical milling and hot pressing techniques were investigated. The fabricated composites exhibited homogeneous distribution of the n-SiC with few porosities. It was found that the grain refinement, the planar features within the grains, and the lattice strains increase with increase in the n-SiC content. The yield and compressive strengths of the nanocomposites were significantly improved with increases in the n-SiC content up to 4 vol%; then they...
A novel configuration for low-grade heat-driven desalination based on cascade MED
, Article Energy ; Volume 229 , 2021 ; 03605442 (ISSN) ; Salimnezhad, F ; Khoshgoftar Manesh, M. H ; Morad, M. R ; Sharif University of Technology
Elsevier Ltd
2021
Abstract
A novel MED-based desalination system for low-grade heat sources with a temperature between 65 °C and 90 °C has been proposed. Low-grade heat-driven desalination systems are of the most important methods for increasing energy efficiency and assisting the environment along with alleviating the water scarcity problem. The new proposed system is known as cascade multi-effect distillation (CMED). It is designed based on multi-step heat extraction from the heat source fluid (HSF). Multi-step heat absorption helps to form two arrays of MED effects and to utilize two boosters to achieve better performance. The advantage of this system is less complexity (for example, lower vapor injection), and...
Microstructure and compressibility of SiC nanoparticles reinforced Cu nanocomposite powders processed by high energy mechanical milling [electronic resource]
, Article Ceramics International ; Volume 40, Issue 1, Part A, January 2014, Pages 951–960 ; Salahi, E ; Alikhani Hesari, F ; Simchi, A ; Kim, H. S ; Sharif University of Technology
Abstract
Cu/SiC nanocomposite powders with homogeneously distributed nanosize SiC particles were produced by high energy mechanical milling (MM). Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and micro-hardness and density measurements were performed to understand the effects of microstructure and hardness on compaction behavior during MM. The effects of SiC nanoparticle content and mechanical milling time on apparent density (AD) and tap density (TD) of the nanocomposite powders were systematically investigated. The Hausner ratio (HR), defined as TD to AD, were estimated to evaluate friction between the particles. Increasing MM duration and SiC content resulted...
Robust Control of Self-Excited Vibration in Machining Arm
, M.Sc. Thesis Sharif University of Technology ; Moradi, Hamed (Supervisor) ; Movahhedi, Mohammad Reza (Supervisor)
Abstract
Nowadays, applications of industrial robots are significantly increasing due to their flexibility, programmable, accuracy, rapidity and etc. Among these, machining robots play an important role at manufacturing industries. One of the main concerns of the researchers, is the tip vibrations of robot arms. In most times, these vibrations are self-excited, unpredictable and intolerable. Thus, finding a method for reducing vibration should be investigated. The purpose of vibration control is vibration suppression to enhance the reliability of the system. The aim of this project is the modeling of the machining robot arm in turning process and then application of robust control to reduce...
Microstructural development and mechanical properties of nanostructured copper reinforced with SiC nanoparticles [electronic resource]
, Article Journal of Materials Science and Engineering: A (Elsevier) ; 15 April 2013, Volume 568, Pages 33–39 ; Salahi, E ; Hesari, F. A ; Yoon, E.Y ; Kim, H.S ; Simchi, A. (Abdolreza) ; Sharif University of Technnology
Abstract
Nanostructured Cu and Cu-2 vol% SiC nanocomposite were produced by high energy mechanical milling and hot pressing technique. Microstructure development during fabrication process was investigated by X-ray diffraction, scanning electron microscope, scanning transmission electron microscope, and electron backscatter diffraction techniques. The results showed that the microstructure of copper and copper-based nanocomposite composed of a mixture of equiaxed nanograins with bimodal and non-random misorientation distribution. The presence of SiC nanoparticles refined the grain structure of the copper matrix while the fraction of low angle grain boundaries was increased. Evaluation of mechanical...
Microstructure and compressibility of SiC nanoparticles reinforced Cu nanocomposite powders processed by high energy mechanical milling
, Article Ceramics International ; Volume 40, Issue 1 PART A , January , 2014 , Pages 951-960 ; ISSN: 02728842 ; Salahi, E ; Alikhani Hesari, F ; Simchi, A ; Kim, H. S ; Sharif University of Technology
2014
Abstract
Cu/SiC nanocomposite powders with homogeneously distributed nanosize SiC particles were produced by high energy mechanical milling (MM). Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and micro-hardness and density measurements were performed to understand the effects of microstructure and hardness on compaction behavior during MM. The effects of SiC nanoparticle content and mechanical milling time on apparent density (AD) and tap density (TD) of the nanocomposite powders were systematically investigated. The Hausner ratio (HR), defined as TD to AD, were estimated to evaluate friction between the particles. Increasing MM duration and SiC content resulted...
Effect of nanoparticle content on the microstructural and mechanical properties of nano-SiC dispersed bulk ultrafine-grained Cu matrix composites
, Article Materials and Design ; Volume 52 , 2013 , Pages 881-887 ; 02641275 (ISSN) ; Salahi, E ; Alikhani Hesari, F ; Kim, H. S ; Simchi, A ; Sharif University of Technology
Elsevier Ltd
2013
Abstract
In this study, the microstructural and mechanical features of monolithic pure Cu and Cu matrix nanocomposites reinforced with three different fractions (2, 4, and 6. vol%) of SiC nanoparticles (n-SiC) fabricated via a combination of high energy mechanical milling and hot pressing techniques were investigated. The fabricated composites exhibited homogeneous distribution of the n-SiC with few porosities. It was found that the grain refinement, the planar features within the grains, and the lattice strains increase with increase in the n-SiC content. The yield and compressive strengths of the nanocomposites were significantly improved with increases in the n-SiC content up to 4. vol%; then they...
Fabrication, characterization and mechanical properties of hybrid composites of copper using the nanoparticulates of SiC and carbon nanotubes
, Article Materials Science and Engineering A ; Volume 572 , 2013 , Pages 83-90 ; 09215093 (ISSN) ; Salahi, E ; Alikhani Hesari, F ; Simchi, A ; Kim, H. S ; Sharif University of Technology
2013
Abstract
Copper based hybrid composites containing nano-sized silicon carbide and carbon nanotubes reinforcements with minimal porosity were fabricated via mechanical milling followed by hot pressing technique. Microstructures of the powders and consolidated materials were studied using scanning electron microscope, X-ray diffraction, Raman spectroscopy, and scanning transmission electron microscope. Microstructural characterization of the materials revealed that the addition of nanosized silicon carbide reinforcement lowered the grain growth rate and enhanced the homogenization during mechanical milling. Microhardness measurements and compression test showed considerable improvements in mechanical...
Microstructural development and mechanical properties of nanostructured copper reinforced with SiC nanoparticles
, Article Materials Science and Engineering A ; Volume 568 , 2013 , Pages 33-39 ; 09215093 (ISSN) ; Salahi, E ; Hesari, F. A ; Yoon, E. Y ; Kim, H. S ; Simchi, A ; Sharif University of Technology
2013
Abstract
Nanostructured Cu and Cu-2. vol% SiC nanocomposite were produced by high energy mechanical milling and hot pressing technique. Microstructure development during fabrication process was investigated by X-ray diffraction, scanning electron microscope, scanning transmission electron microscope, and electron backscatter diffraction techniques. The results showed that the microstructure of copper and copper-based nanoco mposite composed of a mixture of equiaxed nanograins with bimodal and non-random misorientation distribution. The presence of SiC nanoparticles refined the grain structure of the copper matrix while the fraction of low angle grain boundaries was increased. Evaluation of mechanical...