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Linear Hardening in FCC Alloys
, Ph.D. Dissertation Sharif University of Technology ; Asgari, Sirous (Supervisor)
Abstract
Previous observation and models on the origin of linear hardening behavior in FCC polycrystals are critically reviewed. To reveal the draw backs of the previous models, selected results of an investigation on the evolution of microstructure during simple compression testing of two FCC polycrystals, Inconel 625 superalloy and AISI 316L stainless steel are reported. It is found that while a number of FCC polycrystals show linear hardening behavior, the evolution of the underlying microstructure may be quite different. It is argued that, in contrast to the current belief, deformation twinning may not be the sole cause of linear hardening in low SFE FCC polycrystals. It is suggested that only...
Influence of stacking fault energy and short-range ordering on dynamic recovery and work hardening behavior of copper alloys
, Article Scripta Materialia ; Volume 62, Issue 9 , May , 2010 , Pages 693-696 ; 13596462 (ISSN) ; Asgari, S ; Sharif University of Technology
2010
Abstract
True stress vs. true strain responses of Cu-6 wt.% Al and Cu-12 wt.% Mn alloys are presented. While Cu-6 wt.% Al alloy shows the typical mechanical response of low stacking fault energy alloys, the Cu-12 wt.% Mn alloy behaved similarly to medium to high stacking fault energy alloys. These findings clearly show that while short-range ordering triggers slip planarity, it has a minor effect on total dynamic recovery of these copper alloys
Evaluation of the role of deformation twinning in work hardening behavior of face-centered-cubic polycrystals
, Article Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science ; Volume 39, Issue 2 , 2008 , Pages 294-303 ; 10735623 (ISSN) ; Asgari, S ; Sharif University of Technology
2008
Abstract
Results of an investigation on the evolution of microstructure during simple compression testing of two face-centered-cubic (fcc) polycrystals, IN625 superalloy and 316L stainless steel, are reported and a review on the existing data related to the uniaxial deformation of fcc polycrystals is presented. It is found that while a number of fcc polycrystals show linear hardening behavior, the evolution of the underlying microstructure may be quite different. It is argued that, in contrast to the current belief, deformation twinning may not be the sole cause of linear hardening in low stacking fault energy (SFE) fcc polycrystals. It is suggested that, due to the requirement of slip system change...
Performance analysis of a new coded TH-CDMA scheme in dispersive infrared channel with additive gaussian noise
, Article Journal of Optical Communications ; Volume 34, Issue 2 , 2013 , Pages 107-120 ; 01734911 (ISSN) ; Kenari, M. N ; Sharif University of Technology
2013
Abstract
We consider a time-hopping based multiple access scheme introduced in [1] for communication over dispersive infrared links, and evaluate its performance for correlator and matched filter receivers. In the investigated time-hopping code division multiple access (TH-CDMA) method, the transmitter benefits a low rate convolutional encoder. In this method, the bit interval is divided into Nc chips and the output of the encoder along with a PN sequence assigned to the user determines the position of the chip in which the optical pulse is transmitted. We evaluate the multiple access performance of the system for correlation receiver considering background noise which is modeled as White Gaussian...
A new TH-CDMA scheme for dispersive infrared channel and its performance evaluation
, Article Journal of Optical Communications ; Volume 32, Issue 1 , 2011 , Pages 21-36 ; 01734911 (ISSN) ; Nasiri Kenari, M ; Sharif University of Technology
2011
Abstract
Infrared indoor wireless communications using nondirected links are subject to severe multipath distortion which causes intersymbol interference (ISI). To lessen multipath distortion effect and thereby to improve the system performance, in this paper, we consider a new time-hopping based multiple access scheme for this channel, in which one pulse is transmitted in each bit interval. The position of the pulse is determined based on the output of a low rate error correcting code along with the user's dedicated PN code. We evaluate the multiple access performance of the system for correlation receiver considering background noise, dark current, and thermal noise. We compare the performance of...
Multiple-Access Techniques for Wireless Indooor Infrared Communication with Dispersive Link
, Ph.D. Dissertation Sharif University of Technology ; Nasiri-Kenari, Masoumeh (Supervisor)
Abstract
Infrared wireless local area networks are a suitable choice for a fast and cheap wireless network, providing rates over 10 Mbps with access to unregulated bandwidth. Among multiple-access techniques for infrared wireless networks, CDMA1 has attracted the most interest, due to its simple structure and power ecency. However, spreading the spectrum in CDMA prohibits exploiting the low-rate strong channel codes. The other limiting factor in infrared networks is the channel dispersion. In this thesis, these two issues are considered and an internally coded scheme for time-hopping CDMA, suitable for wireless infrared communication is proposed and with accurate modelling of infrared dispersive...
Manufacturing And Investigation Of Microstructure, Precipitation Hardening And Tarnishing Of Ag-Cu-Ge Argentium® Alloy
, M.Sc. Thesis Sharif University of Technology ; Abbachi, Parvin (Supervisor) ; Hamdi, Farzad (Supervisor)
Abstract
In this study melting and casting process of Ag-6.3%wt Cu-1.2%wt Ge alloy with NaBH4 additive for grain refining was investigated. ICP and XRF chemical analysis was used for calculating of Boron and Germanium lost in the processing section then an appropriate route for manufacturing of this alloy was suggested. With SEM and EDS chemical analysis which was installed on SEM sample’s microstructures after cold work and heat treatment was investigated. Solidification’s phases were identified with using DTA, XRD and EDS. To introduce a mechanism for increasing of tarnishing resistance in Argentium alloy, XPS analysis were employed. Optical microscope images reveals that casting samples with grain...
Mobility modeling, spatial traffic distribution, and probability of connectivity for sparse and dense vehicular ad hoc networks
, Article IEEE Transactions on Vehicular Technology ; Volume 58, Issue 4 , 2009 , Pages 1998-2007 ; 00189545 (ISSN) ; Ashtiani, F ; Javanmard, A ; Hamdi, M ; Sharif University of Technology
2009
Abstract
The mobility pattern of users is one of the distinct features of vehicular ad hoc networks (VANETs) compared with other types of mobile ad hoc networks (MANETs). This is due to the higher speed and the roadmap-restricted movement of vehicles. In this paper, we propose a new analytical mobility model for VANETs based on product-form queueing networks. In this model, we map the topology of the streets and the behavior of vehicles at both intersections and different parts of the streets onto different parameters of a BCMP1 open queueing network comprising M/G/nodes. This model represents a sparse situation for VANETs. To include the effect of dense situation on the mobility model, we modify the...
How to increase energy efficiency in cognitive radio networks
, Article IEEE Transactions on Communications ; Volume 64, Issue 5 , 2016 , Pages 1829-1843 ; 00906778 (ISSN) ; Musavian, L ; Hamdi, K. A ; Marvasti, F ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2016
Abstract
In this paper, we investigate the achievable energy efficiency of cognitive radio networks where two main modes are of interest, namely, spectrum sharing (known as underlay paradigm) and spectrum sensing (or interweave paradigm). In order to improve the energy efficiency, we formulate a new multiobjective optimization problem that jointly maximizes the ergodic capacity and minimizes the average transmission power of the secondary user network while limiting the average interference power imposed on the primary user receiver. The multiobjective optimization will be solved by first transferring it into a single objective problem (SOP), namely, a power minimization problem, by using the...
Nonlinear dynamic analysis of a new antibacklash gear mechanism design for reducing dynamic transmission error
, Article Journal of Mechanical Design, Transactions of the ASME ; Volume 137, Issue 5 , 2015 ; 10500472 (ISSN) ; Dabbagh, V ; Amini, H ; Sarhan, A. A ; Akbari, J ; Hamdi, M ; Sharif University of Technology
American Society of Mechanical Engineers (ASME)
2015
Abstract
In this study, a new antibacklash gear mechanism design comprising three pinions and a rack is introduced. This mechanism offers several advantages compared to conventional antibacklash mechanisms, such as lower transmission error as well as lower required preload. Nonlinear dynamic modeling of this mechanism is developed to acquire insight into its dynamic behavior. It is observed that the amount of preload required to diminish the backlash depends on the applied input torque and nature of periodic mesh stiffness. Then, an attempt is made to obtain an approximate relation to find the minimum requiring preload to preserve the system's antibacklash property and reduce friction and wear on the...
Multi-objective selection and structural optimization of the gantry in a gantry machine tool for improving static, dynamic, and weight and cost performance
, Article Concurrent Engineering Research and Applications ; Volume 24, Issue 1 , 2016 , Pages 83-93 ; 1063293X (ISSN) ; Dabbagh, V ; Amini, H ; Sarhan, A. A. D ; Akbari, J ; Hamdi, M ; Ong, Z. C ; Sharif University of Technology
SAGE Publications Ltd
2016
Abstract
In this investigation, the multi-objective selection and optimization of a gantry machine tool is achieved by analytic hierarchy process, multi-objective genetic algorithm, and Pareto-Edgeworth-Grierson-multi-criteria decision-making method. The objectives include maximum static deformation, the first four natural frequencies, mass, and fabrication cost of the gantry. Further structural optimization of the best configuration was accomplished using multi-objective genetic algorithm to improve all objectives except cost. The result of sensitivity analysis reveals the major contribution of columns of gantry with respect to the crossbeam's contribution. After determining the most effective...
Optimal scheduling of demand side load management of smart grid considering energy efficiency
, Article Frontiers in Energy Research ; Volume 10 , 2022 ; 2296598X (ISSN) ; Abrar, M ; Abdul Muqeet, H ; Shahzad, M ; Jamil, H ; Hamdi, M ; Malik, A. S ; Hamam, H ; Sharif University of Technology
Frontiers Media S.A
2022
Abstract
The purpose of this research is to provide power grid energy efficiency solutions. In this paper, a comprehensive review and its optimal solution is proposed considering the various challenges of smart grid demand-side management. The main technique is based on a novel idea in the Smart Grid—demand response optimization which enables autonomous energy management on the demand side for a wide variety of customers. The first section of this research examines the smart grid issue and evaluates the state-of-the-art load management techniques in terms of the work’s scope. The demand-side load management architecture consists of three primary levels, two of them in line planning and low-cost...