Loading...
Search for:
shahryar-nejad--s
0.208 seconds
Total 11164 records
Investigation and modeling of the thermal conductivity of PP/clay nanocomposites and PP/MWCNT nanocomposites
, Article E-Polymers ; Dec , 2010 ; 16187229 (ISSN) ; Golzary, A ; Sharif University of Technology
2010
Abstract
In this study, polypropylene/clay nanocomposites were prepared by melt blending method and their thermal conductivity and the thermal conductivity of polypropylene/multi-wall carbon nanotube (MWCNT) nanocomposites were investigated and modeled. It is found that the thermal conductivity of the PP/Clay and PP/MWCNT nanocomposites is increased with increasing temperature. The thermal conductivity of the nanocomposites is improved due to incorporation of nanoclay and MWCNT compared with pure PP matrix
Design and Implement of an Ultra Low Ripple Power Supply for Cathode of Microwave Tube
, M.Sc. Thesis Sharif University of Technology ; Kaboli, Shahryar (Supervisor)
Abstract
The purpose of this Thesis is designing and constructing of high voltage power supply with very low ripple. Proposed method of this thesis is formed of two sections. In this proposed structure, in first section, structure is on basis of diodes rectifier that has been used for producing main portion of output load energy. Second section uses with aim of regulating of first stage voltage. In attention to existence of noises and available offsets in different sections of proposed circuits, model is basis of two stages structure. Sampling of output voltage by using of resistance divider for main loop of circuit has been done. So noises and offsets available in circuit act as prevented factor...
Analysis of the Challenges in the Design of High Power and High Frequency Inverters
, M.Sc. Thesis Sharif University of Technology ; Kaboli, Shahryar (Supervisor)
Abstract
Power Inverter or DC to AC voltage converter is one of the most important and widely discussed topics in the world of power electronics and systems such as DC/DC converters. Increasing the switching frequency of the inverter, in addition to its many advantages, also creates challenges that will be addressed in this dissertation. To build a high frequency yet reliable inverter, you need accurate and comprehensive information about the inverter circuitry, parasitic elements, switches and their behavior against fault conditions such as short circuit, protection requirements and etc.In this dissertation, several MOSFET transistors is shorted under various test conditions while parameters...
Improving the Performormance of an Ultra Narrow Pulse Generator based on Transmission Lines
, M.Sc. Thesis Sharif University of Technology ; Kaboli, Shahryar (Supervisor)
Abstract
The ultra-narrow pulse generator have being used for direct production of pulsed power. One of these structures is being used to make a bipolar pulse and its main feature is the utilization of the real transmission lines (not PFN) with an intricate structure that caused volume to be compressed. It is desired to reach an appropriate design by analyzing the output waveform and its relation to the transmission line parameters. A little piece of work has been done in the past but there were some differences from our anticipations in the waveforms, like pre-pulse, long rise and fall times and overshoot that caused by some non-idealities in the structure. What we have done in this project is to...
Analysis and Improvement of Output Voltage Ripple in High Voltage DC Power Supply
, M.Sc. Thesis Sharif University of Technology ; 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...
Design and Implement of Voltage Ripple Measuring System for Power Supply of Microwave Tubes
, M.Sc. Thesis Sharif University of Technology ; Kaboli, Shahryar (Supervisor)
Abstract
Mostly, the high voltage DC power supplies have output voltage ripple. In such an applications like power supply of microwave lamps in radar systems, low output voltage ripple is an important point of operational characteristics. On the other hand, measuring the low voltage ripple will be a challenge that can lead to recognize of its reasons and reduce its amplitude. In this thesis, different ways of ripple measurement constraints is described, then a method based on high pass filters for output voltage ripple measurement is implemented. The impact of components tolerance and their parasitic components like shunt parasitic resistance of a capacitor in filter operational characteristics is...
Toward a collaborative method for knowledge management of software architectural decisions based on trust
, Article 12th International Conference on Fuzzy Systems and Knowledge Discovery, 15 August 2015 through 17 August 2015 ; 2015 , Pages 828-834 ; 9781467376822 (ISBN) ; Moaven, S ; Habibi, J ; Alidousti, R
Institute of Electrical and Electronics Engineers Inc
2015
Abstract
Design and implementation of Architecture is a knowledge-driven process. Evaluation and verification the knowledge, in order to ensure its quality, have important role in improving overall design process. Furthermore, Architectural decision making is a complex and multi-criteria decision making problem in which multiple stakeholders make decisions from their perspectives causing overlaps and conflicts in the adopted decisions. Therefore, the requirement for strategies to manage these issues and also to improve coordination and cooperation among the various stakeholders to improve the overall process design is necessary. In this regard, there have been several activities that focus on...
Idiosyncratic return volatility and the role of firm fundamentals: A cross-country analysis
, Article Global Finance Journal ; Volume 50 , 2021 ; 10440283 (ISSN) ; Hoseinzade, S ; Sharif University of Technology
Elsevier B.V
2021
Abstract
We investigate the relation between fundamental idiosyncratic volatility and stock returns idiosyncratic volatility using data from 56 countries. We find a strong positive relation between fundamental idiosyncratic volatility and idiosyncratic volatility of returns. This association, however, seems to be entirely concentrated in the developed economies, and we find no effect in the emerging markets. Specifically, fundamental idiosyncratic volatility does not lead to more idiosyncratic return volatility in countries with poor legal institutions and weak shareholder protection laws. © 2021 Elsevier Inc
Biodegradation of synthetic dye using partially purified and characterized laccase and its proposed mechanism
, Article International Journal of Environmental Science and Technology ; Volume 16, Issue 12 , 2019 , Pages 7805-7816 ; 17351472 (ISSN) ; Borghei, S. M ; Yaghmaei, S ; Sharif University of Technology
Center for Environmental and Energy Research and Studies
2019
Abstract
The supernatant obtained from the extracellular laccase produced by Phanerochaete chrysosporium was used as the enzyme source to conduct a partial purification, characterization and dye decolorization study. The partially purified enzyme was stable in the pH range of 3–5 and showed an optimum activity at pH 4.0, using guaiacol as a substrate. Laccase stability of pH was determined and discovered to retain 100% of its activity at a pH of 4.0 after 2 h. The maximum enzyme activity was obtained between 30 and 50 °C. The maximum velocity and Michaelis constant were calculated as 3.171 µM−1·min and 1628.23 µM, respectively. The enzyme was activated by Fe2+, Zn2+, Ca2+ and Cu2+, while Hg2+, Mn2+,...
Kinetic studies of Bisphenol A in aqueous solutions by enzymatic treatment
, Article International Journal of Environmental Science and Technology ; Volume 16, Issue 2 , 2019 , Pages 821-832 ; 17351472 (ISSN) ; Borghei, S. M ; Yaghmaei, S ; Sharif University of Technology
Center for Environmental and Energy Research and Studies
2019
Abstract
Bisphenol A (BPA), which is a major component in the production of various consumer products, is one of the most significant endocrine-disrupting chemicals. In this research, the biocatalytic elimination of Bisphenol A using laccase produced by Phanerochaete chrysosporium was examined and optimized. The response surface methodology was used to study the effect of independent variables such as pH, temperature, initial laccase activity, initial Bisphenol A concentration, and the interactive effects of each variable on the removal of Bisphenol A and residual enzyme activity. Based on response surface plots, the maximum Bisphenol A removal (93%) was detected at a pH value of 8, temperature...
Kinetic studies of Bisphenol A in aqueous solutions by enzymatic treatment
, Article International Journal of Environmental Science and Technology ; Volume 16, Issue 2 , Febraury , 2018 , Pages 821–832 ; 17351472 (ISSN) ; Borghei, S. M ; Yaghmaei, S ; Sharif University of Technology
Center for Environmental and Energy Research and Studies
2018
Abstract
Bisphenol A (BPA), which is a major component in the production of various consumer products, is one of the most significant endocrine-disrupting chemicals. In this research, the biocatalytic elimination of Bisphenol A using laccase produced by Phanerochaete chrysosporium was examined and optimized. The response surface methodology was used to study the effect of independent variables such as pH, temperature, initial laccase activity, initial Bisphenol A concentration, and the interactive effects of each variable on the removal of Bisphenol A and residual enzyme activity. Based on response surface plots, the maximum Bisphenol A removal (93%) was detected at a pH value of 8, temperature 40...
Effects of loading modes on reliability of cracked structures using FORM and MCS
, Article International Journal of Precision Engineering and Manufacturing ; Volume 18, Issue 1 , 2017 , Pages 63-76 ; 22347593 (ISSN) ; Nazari, S. A ; Sharif University of Technology
SpringerOpen
2017
Abstract
Studying the reliability of cracked structures under different types of failure modes such as a mixture of Mode I and Mode II loadings has been of great importance in many applications. The purpose of this study is to evaluate the effects of different modes of loading, i.e. pure Mode I, pure Mode II and Mixed mode I/II loadings on the reliability of cracked structures via three typical case studies including 1st: through crack in a very wide plate, 2nd: cracked pressurized fuselage and 3rd: cracked fastener holes under actual geometries and loading conditions using the FORM, the fracture toughness and the equivalent SIF for Mixed mode I/II loading which is extracted by the Energy release...
Genetic algorithm-based pore network extraction from micro-computed tomography images
, Article Chemical Engineering Science ; Volume 92 , 2013 , Pages 157-166 ; 00092509 (ISSN) ; Jamshidi, S ; Iglauer, S ; Boozarjomehry, R ; Sharif University of Technology
2013
Abstract
A genetic-based pore network extraction method from micro-computed tomography (micro-CT) images is proposed in this paper. Several variables such as the number, radius and location of pores, the coordination number, as well as the radius and length of the throats are used herein as the optimization parameters. Two approaches to generate the pore network structure are presented. Unlike previous algorithms, the presented approaches are directly based on minimizing the error between the extracted network and the real porous medium. This leads to the generation of more accurate results while reducing required computational memories. Two different objective functions are used in building the...
Immobilization of laccase from trametes hirsuta onto CMC coated magnetic nanoparticles
, Article International Journal of Engineering, Transactions A: Basics ; Volume 33, Issue 4 , 2020 , Pages 513-519 ; Ghazvini, S ; Hejazi, S ; Yaghmaei, S ; Ghobadi Nejad, Z ; Sharif University of Technology
Materials and Energy Research Center
2020
Abstract
In this study Fe3O4/CMC magnetic nanoparticles were synthesized through co-precipitation method. Afterward, laccase from Trametes hirsuta was immobilized onto Carboxymethyl cellulose (CMC)-coated magnetic Fe3O4 nanoparticles by covalent bonding between carboxyl groups of carboxymethyl cellulose and amine group of laccases. Also, the resulted magnetic nanoparticles and immobilized laccase were characterized by Fourier-transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and dynamic light scattering (DLS) analysis. Moreover, the vital factors in enzyme immobilization, such as contact time, amount of N-hydroxysuccinimide (NHS), and the amount of nanoparticles were...
Descriptive epidemiology of traumatic injuries in 18890 adults: A 5-year-study in a tertiary trauma center in Iran
, Article Asian Journal of Sports Medicine ; Volume 6, Issue 1 , 2015 ; 2008000X (ISSN) ; Nabian, M. H ; Oryadi Zanjani, L ; Foroughmand Araabi, M. H ; Shahryar Kamrani, R ; Sharif University of Technology
2015
Abstract
Background: Basic epidemiological data can provide estimates when discussing disease burden and in the planning and provision of healthcare strategies. There is little quantitative information in the literature regarding prevalence of traumatic injuries from developing countries. Objectives: The aim of the current preliminary study was to reveal the prevalence and age and gender distribution of various traumatic injuries in a tertiary referral orthopedic hospital in Iran. Patients and Methods: In a prospective descriptive study, all traumatic injured patients attending the Orthopedic Trauma Unit of our center in a five year period were included. Demographic details, the cause of injury,...
Biodegradation of cyanide by a new isolated strain under alkaline conditions and optimization by response surface methodology (RSM)
, Article Journal of Environmental Health Science and Engineering ; Vol. 12, issue. 1 , 2014 ; Yaghmaei, S ; Nejad, Z. G ; Sharif University of Technology
2014
Abstract
Background: Biodegradation of free cyanide from industrial wastewaters has been proven as a viable and robust method for treatment of wastewaters containing cyanide. Results: Cyanide degrading bacteria were isolated from a wastewater treatment plant for coke-oven-gas condensate by enrichment culture technique. Five strains were able to use cyanide as the sole nitrogen source under alkaline conditions and among them; one strain (C2) was selected for further studies on the basis of the higher efficiency of cyanide degradation. The bacterium was able to tolerate free cyanide at concentrations of up to 500 ppm which makes it a good potentially candidate for the biological treatment of cyanide...
Optimization of supercritical carbon dioxide extraction of essential oil from Dracocephalum kotschyi Boiss: An endangered medicinal plant in Iran
, Article Journal of Chromatography A ; Volume 1422 , 2015 , Pages 73-81 ; 00219673 (ISSN) ; Taji, S ; Goodarznia, I ; Sharif University of Technology
Elsevier
2015
Abstract
Extraction of the essential oil from a medicinal plant called Dracocephalum kotschyi Boiss was performed by green technology of supercritical carbon dioxide (SC-CO2) extraction. A Taguchi orthogonal array design with an OA16 (45) matrix was used to evaluate the effects of five extraction variables: pressure of 150-310bar, temperature of 40-60°C, average particle size of 250-1000μm, CO2 flow rate of 2-10ml/s and dynamic extraction time of 30-100min. The optimal conditions to obtain the maximum extraction yield were at 240bar, 60°C, 500μm, 10ml/s and 100min. The extraction yield under the above conditions was 2.72% (w/w) which is more than two times the maximum extraction yield that has been...
Biodegradation of cyanide under alkaline conditions by a strain of pseudomonas putida isolated from gold mine soil and optimization of process variables through response surface methodology (RSM)
, Article Periodica Polytechnica Chemical Engineering ; Volume 62, Issue 3 , May , 2018 , Pages 265-273 ; 03245853 (ISSN) ; Yaghmaei, S ; Ghobadi Nejad, Z ; Sharif University of Technology
Budapest University of Technology and Economics
2018
Abstract
In regard to highly poisonous effects of cyanide ion, concerns have been focused recently on treatment of such compounds in different ways. Four bacterial strains (C1-C4) capable of using cyanide as nitrogen source were isolated from contaminated gold mine soil samples under alkaline conditions at 30 °C, pH 9.5-10.5, and agitation speed 150 rpm. The gram-negative bacterium C3 (identified as Pseudomonas parafulva NBRC 16636(T) by 16S rRNA gene sequencing) was able to tolerate cyanide up to 500 ppm besides removing 93.5% of 200 ppm cyanide in 13 days which was confirmed by microorganisms growth. The addition of basal salts enhanced the removal efficiency of C3 by 16%. Cyanide removal...
Iranian doctoral students’ shared experience of English-medium publication: the case of humanities and social sciences
, Article Higher Education ; Volume 80, Issue 2 , Desember , 2020 , Pages 255-271 ; Qaracholloo, M ; Rezaei, S ; Sharif University of Technology
Springer
2020
Abstract
The present study was an attempt to explore international English-medium publication in humanities and social sciences in Iran. In so doing, 50 PhD students from 8 humanities and social sciences disciplines, who had already published or attempted to publish in English-medium journals, were requested to write reflection guide accounts and to take part in follow-up semi-structured interviews. The reflection guide and interview data were analyzed based on the principles of grounded theory research yielding the four major themes of motivations, hurdles, strategies, and call for support. The results indicated that the Iranian PhD students in the fields of humanities and social sciences are...
An AHP-based multi-criteria model for assessment of the social sustainability of technology management process: A case study in banking industry
, Article Technology in Society ; Volume 65 , 2021 ; 0160791X (ISSN) ; Mansour, S ; Karamipour, A ; Sharif University of Technology
Elsevier Ltd
2021
Abstract
The abrupt development of technology has confronted different industries' managers with crucial decision points. The scope of their decisions' impact goes beyond their companies' borders. Sustainable assessment of technology investigates the economic, environmental, and social effects of technologies on firms and their environment. Nonetheless, the technology management process includes different steps (such as technology acquisition and exploitation) which need a comprehensive decision-making tool toward sustainable development targets. This paper aims to propose an integrated decision-making model to investigate the social sustainability of the technology management process. Considering...