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Refined microstructure of compo cast nanocomposites: the performance of combined neuro-computing, fuzzy logic and particle swarm techniques
, Article Neural Computing and Applications ; Volume 26, Issue 4 , May , 2015 , Pages 899-909 ; 09410643 (ISSN) ; Rahimipour, M. R ; Tofigh, A. A ; Davami, P ; Sharif University of Technology
Springer-Verlag London Ltd
2015
Abstract
Aluminum metal matrix composites (MMCs) reinforced with nanoceramics are ideal materials for the manufacture of lightweight automotive and other commercial parts. Adaptive neuro-fuzzy inference system combined with particle swarm optimization method is implemented in this research study in order to optimize the parameters in processing of aluminum MMCs. In order to solve the problems associated with poor wettability, agglomeration and gravity segregation of nanoparticles in the melt, a mixture of alumina and aluminum particles was used as the reinforcement instead of raw nanoalumina. Microstructural characterization shows dendritic microstructure for the sand cast and non-dendritic...
Understanding the occurrence of the surface turbulence in a nonpressurized bottom gating system: numerical simulation of the melt flow pattern
, Article Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications ; Volume 232, Issue 3 , March , 2018 , Pages 230-241 ; 14644207 (ISSN) ; Baghani, A ; Bahmani, A ; Tamizifar, M ; Davami, P ; Ostad Shabani, M ; Mazahery, A ; Sharif University of Technology
SAGE Publications Ltd
2018
Abstract
Surface turbulence during the filling of the mold triggers the entrainment of oxide films, which appears to be detrimental to the soundness of the final casting. Nonpressurized and bottom-gating systems have been employed in order to avoid such casting defects by reducing the surface velocity of the liquid metal. However, recent studies have shown that the melt front velocity in the mold entrance may exceed the critical value in the nonpressurized and bottom-gating systems. Therefore, a study was conducted on numerical simulation melt flow pattern in nonpressurized and bottom-gating systems. It was noted that the liquid metal enters the gate and then mold cavity with a higher velocity by...
Wear wear properties of rheo-squeeze cast aluminum matrix reinforced with nano particulates
, Article Protection of Metals and Physical Chemistry of Surfaces ; Volume 52, Issue 3 , 2016 , Pages 486-491 ; 20702051 (ISSN) ; Heydari, F ; Tofigh, A. A ; Rahimipour, M. R ; Razavi, M ; Mazahery, A ; Davami, P ; Sharif University of Technology
Maik Nauka Publishing / Springer SBM
2016
Abstract
There are many approaches to fabricate nanoparticles reinforced aluminum matrix composites. However, uniform distribution of nanoparticle within aluminum matrix remains a difficult challenge. In this study, a novel method is used by taking the advantages from squeeze casting of semi-solid aluminum slurry combined with electromagnetic field to refine the microstructure of the primary Al and eutectic Si phase, plus to obtain uniform distribution nano alumina particles in the aluminum matrix. It is noted that electromagnetic field plays an important role in the formation of non-dendritic primary α-Al particles and a great microstructure refinement occurs as a consequence of the pressure...
Simultaneous microwave chirped pulse generation and antenna beam steering
, Article Progress In Electromagnetics Research M ; Volume 22 , 2012 , Pages 137-148 ; 19378726 (ISSN) ; Akbari, M ; Sharif University of Technology
2012
Abstract
A new structure is suggested for simultaneous microwave chirped pulse generation and array antenna beam steering. It is based on using a multi-channel fiber Bragg grating in a photonic microwave delay-line filter. The paper presents a feasibility study of the idea, discussing the main performance parameters of both signal generation and beam steering functions. Specifically, it focuses on the effects of wavelength tuning, resolution and accuracy. The study shows that custom off-the-shelf components could be used to implement an all optical system capable of generating chirped pulses while steering the radiation pattern of a small sized antenna array. The advantages of the structure for...
Effects of group delay ripple on optical beam-formers for pulsed antenna arrays
, Article Optical and Quantum Electronics ; Volume 43, Issue 6-10 , November , 2012 , Pages 109-120 ; 03068919 (ISSN) ; Akbari, M ; Sharif University of Technology
Springer New York LLC
2012
Abstract
A semi-analytical formulation is presented to quantify the effects of group delay ripple on the performance of an optical beam-former. For delay elements, implemented with commercially available multi-channel fiber Bragg gratings, an impulse response is introduced and calculated for the group delay ripple. To do this, the transfer function of the fiber Bragg grating is parted into two dispersive and non-dispersive sections. This will also easethe demonstration of the fiber Bragg grating as a true time delay element. The formulation is applied to an ultra-wideband pulsed array of antennas. As an example the array factor and electric field patterns of a four element antenna array is derived,...
Non-linear effects of intensity-modulated and directly detected optical links on receiving a linear frequency-modulated waveform
, Article IET Optoelectronics ; Volume 5, Issue 6 , 2011 , Pages 255-260 ; 17518768 (ISSN) ; Akbari, M ; Sharif University of Technology
2011
Abstract
Limitations imposed by the non-linearity of optical links, in the front end of a receiving array antenna, on the performance of a pulse compression radar are studied. Particularly linear frequency-modulated waveforms backscattered from a pair of targets are inspected. Inter-modulation and gain compression by noise are presented as two remarkable phenomena. For an interconnection of two dual-drive Mach-Zehnder modulators, the sensitivity of the compressed echo at the output of a matched filter receiver to certain tunable parameters is studied numerically. Finally, certain values of DC bias and phase shift between the modulators' electrodes are recommended
Performance analysis of an optical beam-forming network with custom microwave CAD tools
, Article Proceedings - 2010 18th Iranian Conference on Electrical Engineering, ICEE 2010, 11 May 2010 through 13 May 2010, Isfahan ; 2010 , Pages 100-104 ; 9781424467600 (ISBN) ; Akbari, M ; Sharif University of Technology
2010
Abstract
Next generation wideband and ultra-wideband radar antenna arrays need efficient true-time delay networks for array control. Optical beam-forming networks have been considered as a promising solution in such arrays. Performance analysis of optical beam-formers is thus quiet necessary. In this paper signal to noise ratio and dynamic range of simple optical beam-forming structures are investigated with a custom microwave CAD tool. Two structures with optical and RF power combining methods are discussed. With the proposed devices' parameters, the optical combining method shows better performance for low and moderate optical powers
An investigation on the performance of receiving optical beam-forming networks
, Article Final Program and Book of Abstracts - iWAT 2010: 2010 International Workshop on Antenna Technology: Small Antennas, Innovative Structures and Materials, 1 March 2010 through 3 March 2010 ; March , 2010 ; 9781424448845 (ISBN) ; Akbari, M ; Sharif University of Technology
2010
Abstract
Next generation wideband and ultra-wideband radar antenna arrays need efficient true-time delay networks for array control. Following the great interest for optical control of antenna array beam steering, performance analysis of optical beam-formers is a must. In this paper signal to noise ratio and dynamic range of simple optical beamforming structures with components off the shelf are investigated theoretically. Especially the effects of certain power combining components such as arrayed wave guide gratings, broadband passive optical combiners and microwave combiners inspected. It turns up that an efficient microwave combiner would surpass the optical combiners in both SNR and dynamic...
Calculation of the Energy Release Rate of Nano-Cracks in FCC Materials Via the Many Body Atomic Scale FEM
, M.Sc. Thesis Sharif University of Technology ; Mohammadi Shodja, Hossein (Supervisor)
Abstract
Since the classical continuum theory fails to deal with the problems associated with defects, stress concentrators, and relevant deformation phenomena in solids, alternative approaches that can detect the atomistic nature of materials' fracture are required. The deficiency of the capture the size effect which yields delusively high values for some components of the stress field right on the edge of the stress concentrators, and its weakness in describing the complex interaction between small inhomogeneities, cracks and the like when they are only a few nanometers apart, are among some of the disadvantages of the classical approach. In recent years, however, atomistic methods are emerging to...
Investigating the Effects of DBS on Brain Connectivity by Causal Inference in Parkinson’s Disease
, M.Sc. Thesis Sharif University of Technology ; Rabiee, Hamid Reza (Supervisor)
Abstract
Parkinson’s disease (PD) is a progressive debilitating neurological disorder that causes motor and cognitive impairment. Administration of dopaminergic medication (Levodopa) has been reported to be effective in attenuating the excessive pathological synchronization in basal ganglia. However, long term levodopa therapy has its pitfalls. High frequency deep brain stimulation (DBS) has been suggested as an effective alternative for reducing motor symptoms in PD. In this method, distinct brain regions involved in the pathophysiology of the disease are stimulated electrically at high frequencies (i.e. at 130 Hz). While several studies have been carried out on the effects of DBS and its clinical...
Silicon morphology modelling during solidification process of A356 al alloy
, Article International Journal of Cast Metals Research ; Volume 25, Issue 1 , 2012 , Pages 53-58 ; 13640461 (ISSN) ; Mazahery, A ; Davami, P ; Razavi, M ; Sharif University of Technology
2012
Abstract
In this paper, an introduction of the finite element approach to microstructure based modelling is provided, and the primary and secondary dendrite arm spacings of A356 alloy in the solidification process are simulated. The simulated results of dendrite morphology and the experimental measurements are presented and compared with the investigations of other researchers, which confirmed the accuracy of this model in its ability to predict the dendrite arm spacing. Each of the length scales, including silicon rod diameter and spacing, is discussed in detail. Analytical equations are generated for the length scales and incorporated in the Sharif University Technology academic software for the...
A modified method for detection of interface and onset point in the asphaltenic fluids
, Article Energy Sources, Part A: Recovery, Utilization and Environmental Effects ; 2020 ; Bayat Shahparast, M ; Barzegar, F ; Sharif University of Technology
Taylor and Francis Inc
2020
Abstract
Asphaltene precipitation and deposition causes many serious problems to the petroleum industry from the reservoir to the surface facilities. Therefore, it is important to bring it under control by finding a method to accelerate or slow down its precipitation and deposition. For achieving this purpose two parameters play an important role; onset point of the precipitation and amount of the deposited phase. When asphaltene precipitates, it is capable of depositing in the solution. After the deposition, the solution split into two phases; asphaltene-rich and asphaltene-lean. Determining the amount of the deposited phase needs to distinguish the interface between two phases. In this study, a...
Laboratory detection methods for the human coronaviruses
, Article European Journal of Clinical Microbiology and Infectious Diseases ; 2020 ; Dowlatshahi, S ; Abdekhodaie, M. J ; Sharif University of Technology
Springer Science and Business Media Deutschland GmbH
2020
Abstract
Coronaviruses are a group of envelop viruses which lead to diseases in birds and mammals as well as human. Seven coronaviruses have been discovered in humans that can cause mild to lethal respiratory tract infections. HCoV-229E, HCoV-OC43, HCoV-NL63, and HCoV-HKU1 are the low-risk members of this family and the reason for some common colds. Besides, SARS-CoV, MERS-CoV, and newly identified SARS-CoV-2, which is also known as 2019-nCoV, are the more dangerous viruses. Due to the rapid spread of this novel coronavirus and its related disease, COVID-19, a reliable, simple, fast, and low-cost detection method is necessary for patient diagnosis and tracking worldwide. Human coronaviruses detection...
Laboratory detection methods for the human coronaviruses
, Article European Journal of Clinical Microbiology and Infectious Diseases ; Volume 40, Issue 2 , 2021 , Pages 225-246 ; 09349723 (ISSN) ; Dowlatshahi, S ; Abdekhodaie, M. J ; Sharif University of Technology
Springer Science and Business Media Deutschland GmbH
2021
Abstract
Coronaviruses are a group of envelop viruses which lead to diseases in birds and mammals as well as human. Seven coronaviruses have been discovered in humans that can cause mild to lethal respiratory tract infections. HCoV-229E, HCoV-OC43, HCoV-NL63, and HCoV-HKU1 are the low-risk members of this family and the reason for some common colds. Besides, SARS-CoV, MERS-CoV, and newly identified SARS-CoV-2, which is also known as 2019-nCoV, are the more dangerous viruses. Due to the rapid spread of this novel coronavirus and its related disease, COVID-19, a reliable, simple, fast, and low-cost detection method is necessary for patient diagnosis and tracking worldwide. Human coronaviruses detection...
Diffusive Holling type-II predator-prey system with harvesting of prey
, Article Journal of Mathematical Analysis and Applications ; Vol. 410, issue. 1 , 2014 , pp. 469-482 ; ISSN: 0022247X ; Sharif University of Technology
2014
Abstract
We study diffusive heterogeneous predator-prey system with Holling type-II functional response in the presence of harvesting in prey equation i.e.{-δu=λu-a(x)u2-buv1+mu-ch(x)in Ω,-δv=μv-v2+duv1+muin Ω,∂νu=∂νv=0on ∂Ω, where Ω is a smooth bounded region in RN and a(x) is a nonnegative continuous function on Ω, with Ω0 a region such that Ω⊂Ω and a(x)>0 on Ω\u03a90. We show that in the case of weak prey growth rate, i.e. λ less than the first eigenvalue of -δ in Ω0, the system has a positive solution for the values of μ in a bounded interval and c>0 sufficiently small. We also investigate the multiplicity of positive solutions in this case. When the prey growth rate is strong, we will show that...
Multivariate Process Variability Monitoring Improvements
, Ph.D. Dissertation Sharif University of Technology ; Akhavan Niaki, Taghi (Supervisor)
Abstract
We consider finding some efficient control schemes for multivariate variability monitoring with capability of working with individual observations. To do this, the existing efficient control charts for multivariate variability monitoring are studied first and it is determined that the and control statistics, defined by individual observations, estimate the covariance matrix quite well. However, the control method that is based on monitoring the trace of these matrices is not necessarily the best. Thus, by applying the first and the second norm on these two statistics, four new control schemes, namely MEWMSL1, MEWMVL1, MEWMVL1 and MEWMVL2are proposed. Performance comparison results show...
Production of net-shaped dense metal-carbide-based composites through an infiltration process at intermediate temperature
, Article International Journal of Refractory Metals and Hard Materials ; Volume 38 , 2013 , Pages 35-39 ; 02634368 (ISSN) ; Sani, M. A. F ; Shabani, K ; Bodaghi, M ; Sharif University of Technology
2013
Abstract
Tungsten composites are interesting materials for high temperature applications. These composites are conventionally produced by solid state reaction, where elevated temperatures and long sintering processes are inevitable, and generally produce volatile components that increase defects and impair the properties of the composites for high temperature applications. In the present paper, synthesis of dense near net-shaped transition metal-metal carbide by reaction casting is studied, which creates a potential application for the composite at 2000 C. Since the pores of the ceramic preform are filled with reaction products, this technique is referred to as displacive compensation porosity (DCP)....
Performance analysis and multi-objective optimization of an organic Rankine cycle with binary zeotropic working fluid employing modified artificial bee colony algorithm
, Article Journal of Thermal Analysis and Calorimetry ; 2018 ; 13886150 (ISSN) ; Maghsoudi, P ; Shabani, B ; Gorgani, H. H ; Shabani, N ; Sharif University of Technology
Springer Netherlands
2018
Abstract
From a thermal point of view, zeotropic mixtures are likely to be more efficient than azeotropic fluids in low-temperature power cycles for reduction in exergy destruction occurring during heat absorption/rejection processes due to their suitable boiling characteristics. In this study, comprehensive energetic and exergetic analyses are mathematically performed for an organic Rankine cycle (ORC) system employing a potential binary zeotropic working fluid, namely R717/water. For this purpose, initially mass, energy, and exergy balance equations are derived. With regard to the similarity in molar mass of R717 (17.03 g mol−1) and water (18.01 g mol−1), there is no need to alter the size of the...
Performance analysis and multi-objective optimization of an organic Rankine cycle with binary zeotropic working fluid employing modified artificial bee colony algorithm
, Article Journal of Thermal Analysis and Calorimetry ; Volume 136, Issue 4 , 2019 , Pages 1645-1665 ; 13886150 (ISSN) ; Maghsoudi, P ; Shabani, B ; Gorgani, H. H ; Shabani, N ; Sharif University of Technology
Springer Netherlands
2019
Abstract
From a thermal point of view, zeotropic mixtures are likely to be more efficient than azeotropic fluids in low-temperature power cycles for reduction in exergy destruction occurring during heat absorption/rejection processes due to their suitable boiling characteristics. In this study, comprehensive energetic and exergetic analyses are mathematically performed for an organic Rankine cycle (ORC) system employing a potential binary zeotropic working fluid, namely R717/water. For this purpose, initially mass, energy, and exergy balance equations are derived. With regard to the similarity in molar mass of R717 (17.03 g mol −1 ) and water (18.01 g mol −1 ), there is no need to alter the size of...
Fabrication of Al Based Nanocomposite with Al2O3 and Al3Ti Reinforcements by Mechanical Milling and Press and Sintering (In situ method) and Investigation of Its Wear Behavior
, M.Sc. Thesis Sharif University of Technology ; Seyed Reihani, M (Supervisor)
Abstract
In this study, Aluminium based nanocomposite with Al3Ti and Al2O3 nanoparticles have been elaborated by mechanical alloying. For this purpose, Al and TiO2 powders have been blended with weight ratios of 10, 20 and 30 percents and were milled using a planetary mill. Morphological variations in different timing periods of mechanical milling process was investigated by Scaning Electron Microscopy (SEM) and The optimal times for alloying were determined for each combination. The pure Aluminium and the powder with 10, 20 and 30%wt reinforcement had coax morphology after respectively for 44, 30, 24 and 14 hours. after studing phase transformations by XRD analysis, the final powders were cold...