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ghasemi--mahdi
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Dyes Adsorption and Removal of Aqueous Solutions with Novel Adsorbents Based on Graphene Oxide
, M.Sc. Thesis Sharif University of Technology ; Borghei, Mahdi (Supervisor) ; Ghasemi, Shahnaz (Co-Supervisor)
Abstract
Nowadays, water pollution and water sources decreasion, is one of the important issues of our world. Treatment of polluted water and wastewater and recycling of those to industries and common uses, is very necessary. Dyes, is one of the biggest parts of water pollutants, especially, in textile plants. There are some ways for dye removal, in the industries; including biological, chemical and physical methods. Among of these methods, physical removal of dyes through adsorption (with Activated Carbon or other adsorbents), is very popular. Hydrogels are three-dimensional hydrophilic polymer networks, introducing very good swelling rate, mechanical properties and pollutants adsorption. In this...
Improvement of Communication Cost and Waiting Time Trade off in Content Delivery Networks
, M.Sc. Thesis Sharif University of Technology ; Jafari Siavoshani, Mahdi (Supervisor)
Abstract
By increasing the use of Internet and sharing information in this platform, servers are equipped with more robust hardware and a wider bandwidth network. But the growth of data and services is such that a server, no matter how powerful, does not have the ability to respond all users! Several servers are used to solve this problem. Data centers, content delivery networks, and so on are emerged depending on types of service. One of the important issues in these systems is how to distribute loads between servers in a proportional manner. In this thesis, we first examine the relationship between cost and response time on user requests. Cost can be considered as a communication cost or financial...
Photocatalytic Reactor Design for Degradation of Bisphenol A
, M.Sc. Thesis Sharif University of Technology ; Borghei, Mahdi (Supervisor) ; Ghasemi, Shahnaz (Co-Supervisor)
Abstract
One of the Advanced Oxidation Process (AOP) is Photocatalyst method. Structure of this method is according to three foundation: 1. Catalyst, 2. Source of energy, 3. Wastewater. Progress of human activity around variety of fields such as pharmaceutical, plastic industry, and medical science has produced some micro pollutants such as Bisphenol A (BPA) that has aroused the public concerns in recent years. The half-life of this components in water, air and soil is too long, so typical methods such as biological method, activated sludge and carbon adsorption are inefficient in removing BPA. This work describes a visible light responsive Carbon Quantum Dots(CQDs) embedded on TiO_2 nanoparticles...
Parallelized numerical modeling of the interaction of a solid object with immiscible incompressible two-phase fluid flow
, Article Engineering Computations (Swansea, Wales) ; Volume 34, Issue 3 , 2017 , Pages 709-724 ; 02644401 (ISSN) ; Nikbakhti, R ; Ghasemi, A ; Hedayati, F ; Malvandi, A ; Sharif University of Technology
2017
Abstract
Purpose - A numerical method is developed to capture the interaction of solid object with two-phase flow with high density ratios. The current computational tool would be the first step of accurate modeling of wave energy converters in which the immense energy of the ocean can be extracted at low cost. Design/methodology/approach - The full two-dimensional Navier-Stokes equations are discretized on a regular structured grid, and the two-step projection method along with multi-processing (OpenMP) is used to efficiently solve the flow equations. The level set and the immersed boundary methods are used to capture the free surface of a fluid and a solid object, respectively. The full...
Oscillating pipe flow: High-resolution simulation of nonlinear mechanisms
, Article 2006 ASME Joint U.S.- European Fluids Engineering Division Summer Meeting, FEDSM2006, Miami, FL, 17 July 2006 through 20 July 2006 ; Volume 1 SYMPOSIA , 2006 , Pages 1-10 ; 0791847500 (ISBN); 9780791847503 (ISBN) ; Sharif University of Technology
American Society of Mechanical Engineers
2006
Abstract
A new perspective suitable for understanding the details of nonlinear pumping (formation of traveling shocks) inside a pressurized cavity is constructed in this paper. Full compressible axisymmetric three-dimensional Navier-Stokes equations are used as the starting point to cover all complexities of the problem that exceedingly increase for particular ranges of Mach, Reynolds and Prandtl numbers. Then a very high-order numerical method is introduced to preserve the user-defined order of accuracy for practical simulations. For removal of spurious waves, higher-order compact filters are derived. All equations are marched in time using the classical Runge-Kutta algorithm which is appropriate...
An optimized large-stencil approach for capturing near-PI frequencies
, Article 12th AIAA/CEAS Aeroacoustics Conference, Cambridge, MA, 8 May 2006 through 10 May 2006 ; Volume 5 , 2006 , Pages 3010-3022 ; 1563478099 (ISBN); 9781563478093 (ISBN) ; Sharif University of Technology
American Institute of Aeronautics and Astronautics Inc
2006
Abstract
Large-stencil schemes which their spectral properties are acceptable in the vicinity of ω = π are analyzed for the first time. A machine independent model for evaluating the efficiency of generalized time-marching finite-difference algorithms over periodic domains is developed. This model which is based on operation count reveals that for small values of Total Computational Cost(TCC), the previous low-order small-stencil schemes are more efficient while for moderate TCC, the efficiency of optimized large-stencil schemes abruptly increases. This important result is the motivation for developing optimized large-stencil schemes. The current schemes are successfully implemented in a full...
Numerical solution of high-frequency oscillations of a gas column using a modified lax-wendroff scheme
, Article International Conference on Noise and Vibration Engineering 2006, ISMA 2006, Heverlee, 18 September 2006 through 20 September 2006 ; Volume 4 , 2006 , Pages 2191-2199 ; Sharif University of Technology
Katholieke Universiteit Leuven
2006
Abstract
Recently, several high-order accurate methods have been developed for solving nonlinear equations governing in the high-frequency oscillations of a fluid column. If we assume that the value of Reynolds and Prandtl numbers are high enough then it is possible to neglect the effect of Stokes Layer and it has been previously shown that the calculated pressure profile obtained by solving three-dimensional axisymmetric compressible NS (Navier-Stokes) equations is in good agreement with one-dimensional adiabatic model of Ilinskii. For this particular flow which is the typical of engineering flows inside acoustical compressors, it is clear that high-resolution simulation of NS equations in higher...
Oscillating pipe flow: high-resolution simulation of nonlinear mechanisms
, Article 2006 2nd ASME Joint U.S.-European Fluids Engineering Summer Meeting, FEDSM 2006, Miami, FL, 17 July 2006 through 20 July 2006 ; Volume 2006 , 2006 ; 0791837831 (ISBN); 9780791837832 (ISBN) ; Sharif University of Technology
2006
Abstract
A new perspective suitable for understanding the details of nonlinear pumping (formation of traveling shocks) inside a pressurized cavity is constructed in this paper. Full compressible axisymmetric three-dimensional Navier-Stokes equations are used as the starting point to cover all complexities of the problem that exceedingly increase for particular ranges of Mach, Reynolds and Prandtl numbers. Then a very high-order numerical method is introduced to preserve the user-defined order of accuracy for practical simulations. For removal of spurious waves, higher-order compact filters are derived. All equations are marched in time using the classical Runge-Kutta algorithm which is appropriate...
Facile synthesis and simulation of MnO2 nanoflakes on vertically aligned carbon nanotubes, as a high-performance electrode for Li-ion battery and supercapacitor
, Article Electrochimica Acta ; Volume 390 , 2021 ; 00134686 (ISSN) ; Abnavi, A ; Ghasemi, F ; Ghasemi, S ; Sanaee, Z ; Mohajerzadeh, S ; Sharif University of Technology
Elsevier Ltd
2021
Abstract
This study reports the successful fabrication of high-performance flexible binder-free lithium-ion battery anode and supercapacitor based on the synthesis of 3D hierarchical MnO2 nanoflakes (NFs) on vertically aligned carbon nanotubes (VACNTs) grown upon stainless steel (SS). The experimental results revealed that the prepared electrodes were well served as supercapacitors with a tremendous specific capacitance of MnO2 NFs VACNT/SS 1131 F/g at 0.25 A/g in 0.5 mol.L−1 Na2SO4, 518.8% more than VACNT/SS (218 F/g). Compared to other MnO2 NFs/CNT composites, as-fabricated binder-free MnO2 NFs/VACNTs electrode achieves outstanding performance with high initial discharge and charge capacities of...
Facile synthesis and simulation of MnO2 nanoflakes on vertically aligned carbon nanotubes, as a high-performance electrode for Li-ion battery and supercapacitor
, Article Electrochimica Acta ; Volume 390 , 2021 ; 00134686 (ISSN) ; Abnavi, A ; Ghasemi, F ; Ghasemi, S ; Sanaee, Z ; Mohajerzadeh, S ; Sharif University of Technology
Elsevier Ltd
2021
Abstract
This study reports the successful fabrication of high-performance flexible binder-free lithium-ion battery anode and supercapacitor based on the synthesis of 3D hierarchical MnO2 nanoflakes (NFs) on vertically aligned carbon nanotubes (VACNTs) grown upon stainless steel (SS). The experimental results revealed that the prepared electrodes were well served as supercapacitors with a tremendous specific capacitance of MnO2 NFs VACNT/SS 1131 F/g at 0.25 A/g in 0.5 mol.L−1 Na2SO4, 518.8% more than VACNT/SS (218 F/g). Compared to other MnO2 NFs/CNT composites, as-fabricated binder-free MnO2 NFs/VACNTs electrode achieves outstanding performance with high initial discharge and charge capacities of...
MBBR and MBR Reactor Configuration for Better Performance
, M.Sc. Thesis Sharif University of Technology ; Borgheei, Mahdi (Supervisor)
Abstract
Membrane bioreactors (MBRs) which are commonly understood as the combination of membrane filtration and biological treatment using activated sludge have several advantages, but membrane fouling reduces the membrane efficiency, permeability and lifetime. An alternative is replacing a moving bed biofilm reactor (MBBR) with the activated sludge system which may reduce the effect of membrane fouling. The sludge produced in MBBRs has poor settling characteristics, therefore, their efficiency is limited by the sedimentation tank performance and they require a larger settling surface. The combination of moving bed biofilm reactors and membrane bioreactors can compensate for the drawbacks of both of...
Equipment failure rate in electric power distribution networks: An overview of concepts, estimation, and modeling methods
, Article Engineering Failure Analysis ; Volume 145 , 2023 ; 13506307 (ISSN) ; Shahrabi Farahani, E ; Fotuhi Firuzabad, M ; Dehghanian, P ; Ghasemi, A ; Wang, F ; Sharif University of Technology
Elsevier Ltd
2023
Abstract
The evolution of the organizational attitudes regarding strategic management of system physical assets and the emergence of new technologies call for special attention to maintenance and reliability. State-of-the-art literature suggested a number of techniques and strategies for estimating the equipment failure rates; however, paralyzed by lack of real-world data, existing literature mostly relied on simplifications that may bring about unique challenges and result in low-accuracy estimations. This paper reviews the existing literature in estimating and modeling the failure rate of power system equipment. The review includes the existing models and the ongoing research on degradation,...
Forecasting the effects of a Canada-US currency union on output and prices: A counterfactual analysis
, Article Journal of Forecasting ; Volume 32, Issue 7 , 2013 , Pages 639-653 ; 02776693 (ISSN) ; Sharif University of Technology
2013
Abstract
This paper is a counterfactual analysis investigating the consequences of the formation of a currency union for Canada and the USA: whether outputs increase and prices decrease if these countries form a currency union. We use a two-country cointegrated model to conduct the counterfactual analysis, where the conditional forecasts are generated based on the Gaussian assumption. To deal with structural breaks and model uncertainty, conditional forecasts are generated from different models/estimation windows and the model-averaging technique is used to combine the forecasts. We also examine the robustness of our results to parameter uncertainty using the wild bootstrap method. The results show...
Optimum waist of localized basis functions in truncated series employed in some optical applications
, Article Applied Optics ; Volume 49, Issue 8 , 2010 , Pages 1210-1218 ; 1559128X (ISSN) ; Mehrany, K ; Sharif University of Technology
2010
Abstract
The waist parameter is a particularly important factor for functional expansion in terms of localized orthogonal basis functions. We present a systematic approach to evaluate an asymptotic trend for the optimum waist parameter in truncated orthogonal localized bases satisfying several general conditions. This asymptotic behavior is fully introduced and verified for Hermite - Gauss and Laguerre-Gauss bases. As a special case of importance, a good estimate for the optimum waist in projection of discontinuous profiles on localized basis functions is proposed. The importance and application of the proposed estimation is demonstrated via several optical applications
Microstructural evolution mechanism during brazing of Hastelloy X superalloy using Ni–Si–B filler metal
, Article Science and Technology of Welding and Joining ; 2017 , Pages 1-7 ; 13621718 (ISSN) ; Pouranvari, M ; Sharif University of Technology
2017
Abstract
The paper aims at understanding solidification phenomena and solid state precipitations during diffusion brazing of Hastelloy X nickel base superalloy using a ternary Ni–4.5Si–3.2 B (in wt-%) filler metal. The joint is featured by the formation of Ni-rich solid solution in an isothermal solidification zone, borides/silicide formation during eutectic-type solidification in an athermal solidification zone, on-cooling precipitation of fine nickel silicides in the joint centerline, in situ precipitation of Mo–Cr-rich borides in the diffusion affected zone and grain growth in the heat affected zone. The implication of the phase transformations on the joint properties is discussed. It is shown...
A quantum mechanical approach towards the calculation of transition probabilities between DNA codons
, Article BioSystems ; Volume 184 , 2019 ; 03032647 (ISSN) ; Shafiee, A ; Sharif University of Technology
Elsevier Ireland Ltd
2019
Abstract
The role of quantum tunneling in altering the structure of nucleotides to each other and causing a mutational event in DNA has been a topic of debate for years. Here, we introduce a new quantum mechanical approach for analyzing a typical point-mutation in DNA strands. Assuming each codon as a base state, a superposition of codon states could provide a physical description for a set of codons encoding the same amino acid and there are transition amplitudes between them. We choose the amino acids Phe and Ile as our understudy bio-systems which are encoded by two and three codons, respectively. We treat them as large quantum systems and use double- and triple-well potential models to study the...
A new approach to study the Zeno effect for a macroscopic quantum system under frequent interactions with a harmonic environment
, Article Scientific Reports ; Volume 9, Issue 1 , 2019 ; 20452322 (ISSN) ; Shafiee, A ; Sharif University of Technology
Nature Publishing Group
2019
Abstract
Quantum Zeno and anti-Zeno behaviors of a two-level macroscopic quantum system in interaction with a harmonic environment are studied using the perturbation theory. The system-environment interactions are applied in a successive and step-by-step way. A new expression for the probability of surviving the macrosystem in its initial state, after the Nth interaction step, is derived through a different method of calculation. It is shown that multiple transitions between Zeno and anti-Zeno behaviors can be found in our approach. We have shown that in addition to the environmental parameters like the Ohmicity, the macroscopic trait of the system also has a notable effect on the decay rate Γ(τ)....
Thermal processing strategies enabling boride dissolution and gamma prime precipitation in dissimilar nickel-based superalloys transient liquid phase bond
, Article Materials and Design ; Volume 182 , 2019 ; 02641275 (ISSN) ; Pouranvari, M ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
The microstructure of dissimilar transient liquid phase bond between Hastelloy X and IN792 nickel-based superalloys is featured by lack of sufficient formation of γ′ precipitates in the bond-centerline and extensive in-situ precipitation of boride second phases in the diffusion affected zones (DAZ). This paper investigates the impact of two thermal processing strategies, using standard solution treatment and aging of IN792 (STA strategy) and using solution treatment of IN792 followed by a post-bond heat treatment utilizing solution treatment of Hastelloy X and aging treatment of IN792 (SPTA strategy) on the joint microstructure and mechanical properties. The boride precipitates in the DAZ of...
Fast isothermal solidification during transient liquid phase bonding of a nickel alloy using pure copper filler metal: solubility vs diffusivity
, Article Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science ; Volume 50, Issue 5 , 2019 , Pages 2235-2245 ; 10735623 (ISSN) ; Pouranvari, M ; Sharif University of Technology
Springer Boston
2019
Abstract
This investigation aims at understanding the underlying fundamentals of the isothermal solidification phenomenon during the transient liquid phase (TLP) bonding process. The isothermal solidification is governed by solid-state diffusion of the melting point depressant (MPD) into the base material, which, in turn, is controlled by both kinetic and thermodynamic parameters; however, the latter factor is generally ignored. In this work, the competition between kinetics and thermodynamics of diffusion were considered in TLP bonding of a nickel alloy, Monel 400, using two distinct filler metals including pure copper (Cu) and Ni-Si-B filler metal. The joint generated by Ni-Si-B filler metal...
Intermetallic phase formation during brazing of a nickel alloy using a Ni–Cr–Si–Fe–B quinary filler alloy
, Article Science and Technology of Welding and Joining ; Volume 24, Issue 4 , 2019 , Pages 342-351 ; 13621718 (ISSN) ; Pouranvari, M ; Sharif University of Technology
Taylor and Francis Ltd
2019
Abstract
Fundamental understanding of the intermetallic phase formation is the key for enhancing the robustness and reliability of the brazed joints. The paper addresses the phase transformations during brazing of the Hastelloy X nickel-base superalloy using the quinary Ni–13Cr–4.5Si–4.2Fe–2.8B (wt-%) braze alloy. The mechanisms of intermetallic formation via solidification and solid-state precipitation are discussed. The athermal solidification zone (ASZ) is featured by the formation of brittle and hard borides and boro-silicides that are formed via eutectic reactions. However, in contrast to other commercial B-bearing Ni-based filler alloys, it was identified that the presence of a high-volume...