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Application of Rosin-Rammler model for analysis of CSD in sugar crystallization
, Article Crystal Research and Technology ; Volume 50, Issue 11 , 2015 , Pages 873-878 ; 02321300 (ISSN) ; Alamolhoda, A. A ; Matloubi Moghaddam, F ; Nayeri, S ; Sharif University of Technology
Wiley-VCH Verlag
2015
Abstract
Crystal-size distribution (CSD) is one of the most important parameters in sugar production. The objective is to grow crystals of uniform sizes or narrow CSD. CSD appears to be determined by the growth-rate history of the crystals and the relative supersaturation (SS) of the solution from which crystals growth takes place. Three methods for preparation of nucleation seeds were described and used for industrial crystallization of raw and white sugars; these are wet milling filtered sugar (ML), agitating saturated solution (AS) and powdered sugars (PD). Rosin-Rammler (RR) and mathematical models were adopted to investigate CSD and the uniformity of the produced crystals. Higher uniformity...
A kinetic study of facile fabrication of MIL-101(Cr) metal-organic framework: effect of synthetic method
, Article Inorganica Chimica Acta ; Volume 471 , 2018 , Pages 513-520 ; 00201693 (ISSN) ; Kazemeini, M ; Sharif University of Technology
Elsevier S.A
2018
Abstract
MIL-101(Cr) metal–organic framework samples were successfully synthesized through the conventional electrical heating (CE), ultrasound (US), and microwave (MW) synthetic methods at three different temperatures and various synthesis times. These were done with the aim of understudying the crystallization kinetics of these complex MIL's structures. The nucleation and crystal growth steps were thus, quantified through measuring the relative crystallinity of the prepared MIL-101(Cr) utilizing the PXRD and FESEM analysis under various synthesis conditions. In addition, the textural properties of the fully crystallized samples measured through the N2 adsorption–desorption isotherms at 77 K. The...
Diffusive logistic equations with harvesting and heterogeneity under strong growth rate
, Article Advances in Nonlinear Analysis ; Volume 8, Issue 1 , 2019 , Pages 455-467 ; 21919496 (ISSN) ; Torabi Tehrani, H ; Sharif University of Technology
De Gruyter
2019
Abstract
We consider the equation (equation presented) where Ω is a smooth bounded domain in ℝ N , b(x) and h(x) are nonnegative functions, and there exists Ω 0 ⊃ Ω such that {x : b(x) = 0} = Ω0. We investigate the existence of positive solutions of this equation for c large under the strong growth rate assumption a ≥ λ 1 (Ω0), where λ 1 (Ω0) is the first eigenvalue of the δ in Ω0 with Dirichlet boundary condition. We show that if h = 0 in Ω\u03a90, then our equation has a unique positive solution for all c large, provided that a is in a right neighborhood of λ 1 (Ω0). For this purpose, we prove and utilize some new results on the positive solution set of this equation in the weak growth rate case
High resolution simulations of unstable modes in a collisionless disc
, Article Astronomy and Astrophysics ; Volume 473, Issue 1 , 2007 , Pages 31-40 ; 00046361 (ISSN) ; Just, A ; Korchagin, V. I ; Jalali, M. A ; Sharif University of Technology
2007
Abstract
We present N-body simulations of unstable spiral modes in a dynamically cool collisionless disc. We show that spiral modes grow in a thin collisionless disk in accordance with the analytical perturbation theory. We use the particle-mesh code SUPERBOX with nested grids to follow the evolution of unstable spirals that emerge from an unstable equilibrium state. We use a large number of particles (up to N = 40 & 106) and high-resolution spatial grids in our simulations (1283 cells). These allow us to trace the dynamics of the unstable spiral modes until their wave amplitudes are saturated due to nonlinear effects. In general, the results of our simulations are in agreement with the analytical...
Effects of Laser Peening with Different Coverage Areas on Residual Stress and Fatigue Crack Growth
, M.Sc. Thesis Sharif University of Technology ; Farrahi, Gholamhossein (Supervisor) ; Mehmanparast, Ali (Co-Advisor)
Abstract
Failure due to fatigue loading is one of the main reasons for the wear out of parts in the industry. Prevention of failure and improving the fatigue life of materials have been studied by many researchers. Desirable compressive residual stress have important effect on improving the lifetime of materials. Laser peenning leads to increase fatigue life of metals by creating compressive residual stress at the surface of the pieces.This study investigates the effect of different laser coverage areas on residual stresses using finite element method and also investigates the fatigue crack growth experimentally.Simulation results show that increasing the laser peening rows impart the residual...
A diffusion-controlled kinetic model for growth of Au-catalyzed ZnO nanorods: Theory and experiment
, Article Journal of Crystal Growth ; Volume 309, Issue 1 , 2007 , Pages 70-75 ; 00220248 (ISSN) ; Madaah Hosseini, H. R ; Sharif University of Technology
2007
Abstract
A kinetic model for growth of ZnO nanorods via vapor-liquid-solid (VLS) mechanism based on the bulk diffusion of Zn atoms through the Au-Zn droplet is presented. The dependences of the growth rate on size are given quantitatively. A general expression for the growth rate of nanorods during VLS process is derived. The derived formula shows the dependences of growth rate on lateral size of nanorods, concentration and supersaturation of Zn atoms in the liquid droplet. Based on the presented kinetic model the smaller nanorods have faster growth rate. Au-catalyzed ZnO nanorods are grown by chemical vapor transport and condensation (CVTC) process experimentally. Theoretical and experimental...
Effect of Grinding and Shot Peening on Fatigue Life of Welded Joints
, M.Sc. Thesis Sharif University of Technology ; Farrahi, Gholamhossein (Supervisor)
Abstract
Metallurgical initial defects, stress concentration due to change in geometry and induced tensile residual stress during welding create an extraordinary high possibility of fatigue cracks nucleation and propagation in the weld toe region. Despite this, the ever increasing use of welding in offshore, aerospace and automotive industries, as the most applied mechanical joint, has occasioned a very extensive attempt to achieve an in-depth understanding of failure mechanisms and fatigue life improvement techniques of welded joints. Generally, these techniques could be classified into two broad categories. The first consists of methods that modify the geometry and the other is related to the...
Numerical and Experimental Study on Optimization of Overload arameters for Fatigue Life Increase
, M.Sc. Thesis Sharif University of Technology ; Saadat Foumani, Mahmoud (Supervisor)
Abstract
Fatigue life and crack growth retardation due to periodic tensile overload that superposed on constant amplitude cycles has been investigated. The tests were performed using C(T) specimens made of 7075 aluminium. All periodic overload tests were carried out at the same spacing between overloads and the effect of overload ratio on fatigue life has been investigated. Results of experiments revealed that the at low and high overload ratios, crack growth rate is relatively high and there is an optimum OLR that maximize interaction and thus minimize FCGR. Whit OCR-1=50, overload ratio of 1.85 led to maximum interaction and resulted in 219% increase in specimen's life relative to CA loading. Also...
Optimization of operating parameters and rate of uranium bioleaching from a low-grade ore
, Article Journal of Radioanalytical and Nuclear Chemistry ; Vol. 301, issue. 2 , 2014 , pp. 341-350 ; ISSN: 02365731 ; Roosta-Azad, R ; Safdari, S. J ; Sharif University of Technology
Abstract
In this study the bioleaching of a low-grade uranium ore containing 480 ppm uranium has been reported. The studies involved extraction of uranium using Acidithiobacillus ferrooxidans derived from the uranium mine samples. The maximum specific growth rate (μ max) and doubling time (t d) were obtained 0.08 h-1 and 8.66 h, respectively. Parameters such as Fe2+ concentration, particle size, temperature and pH were optimized. The effect of pulp density (PD) was also studied. Maximum uranium bio-dissolution of 100 ± 5 % was achieved under the conditions of pH 2.0, 5 % PD and 35 °C in 48 h with the particles of d 80 = 100 μm. The optimum concentration of supplementary Fe2+ was dependent to the PD....
Enhancing bioleaching and iron oxidation efficiency of native strain of acidithiobacillus ferrooxidans, by optimizing the ambient growth conditions
, Article Pollution Research ; Volume 28, Issue 3 , 2009 , Pages 329-336 ; 02578050 (ISSN) ; Nemati, F ; Roostaazad, R ; Shitole, M. G ; Gade, W. N ; Sharif University of Technology
Abstract
In this study, we have investigated the bioleaching potential of a native strain of Acidithiobacillus ferrooxidans isolated from zinc and lead sulfide mines under varied ambient conditions of growth and substrate consumption. In the process of standardizing growth conditions to improve iron oxidation, bioleaching of zinc and lead is also found to be enhanced. The effects of pH, temperature, initial inoculum, Fe2+ and ammonium sulphate concentration on growth and bio-oxidation efficiency of the bacteria have been evaluated. The results indicate that the optimum pH required for the growth of the bacterium is 1.8; however, the same for maximum efficiency is 1.5. It is also found that pH has a...
A heterogeneous diffusive logistic model of a single species population dynamics with predation and harvesting terms
, Article Nonlinear Analysis, Theory, Methods and Applications ; Volume 156 , 2017 , Pages 1-16 ; 0362546X (ISSN) ; Torabi Tehrani, H ; Sharif University of Technology
Abstract
We study existence and multiplicity of positive solutions of a heterogeneous diffusive logistic equation with predation and harvesting terms, −Δu=au−b(x)u2−c, where a,c,m and d are positive constants, Ω a bounded smooth domain in RN, and b(x) is a nonnegative function on Ω¯, with Ω0 a region such that Ω¯0⊂Ω and Ω¯0={x∈Ω:b(x)=0}. Under the strong growth rate assumption, that is, when a is greater than the first eigenvalue of −Δ in Ω0 with Dirichlet boundary condition, we show that the equation has at least one positive solution for 0≤d0. In addition, in case c
Microstructural and failure analysis of welded primary reformer furnace tube made of HP-Nb micro alloyed heat resistant steel
, Article Engineering Failure Analysis ; Volume 68 , 2016 , Pages 32-51 ; 13506307 (ISSN) ; Karimi Taheri, A ; Jalilvand, S ; Habibi, A ; Sharif University of Technology
Elsevier Ltd
2016
Abstract
In this paper, the failure of the reformer furnace tube, made of HP-Nb micro alloyed heat resistant steel is investigated. The failure was due to a longitudinal crack developing in the circumferential weld joint close to the outlet end of the tube, where the mean wall temperature had reached the highest value during service. According to the temperature records during the period of 7 years of being in service, the tube had experienced temperatures higher than the tubes designed temperature. This situation besides the occurrence of several sudden shutdowns caused the mechanical properties degradation.Macroscopic and microscopic examinations revealed that the failure had occurred due to the...
Assessing operational flexibility of microgrids considering electrical and thermal energy resources
, Article 2019 Smart Gird Conference, SGC 2019, 18 December 2019 through 19 December 2019 ; 2019 ; 9781728158945 (ISBN) ; Moeini Aghtaie, M ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2019
Abstract
With high growth rate of demand for energy in different societies, the need for energy resources has been increased significantly. This has resulted in introduction of new energy resources, i. e. renewable energy resources in generation sector of energy systems. However, the intrinsic features of these energy resources call for higher flexibility in different sectors of energy systems. Flexibility in a comprehensive sense tries to cover the amount of imbalance between production and demand in energy systems. This paper has attempted to introduce the concept of operational flexibility in microgrids and it also has presented a step-by-step algorithm to assess this operational index based on a...
Residual Stress Determination of Multi-pass Welding Process, Stress Relieving Procedures and Its Effect on Crack Propagation
, M.Sc. Thesis Sharif University of Technology ; Farahi, Gholamhossein (Supervisor)
Abstract
One of the most important issues in welding is residual stresses. It is desirable to produce less residual stresses when possible and to reduce them which remain in the structure. At the present, various methods have been developed to reduce the residual stresses. The most important methods are heat treatment, shot peening, and grinding. The main problem in using these methods is cost, and for large structures these methods are often impractical. In recent decades, a technique called vibratory stress relief has been developed. It is used for large structures without limitation of size and weight; besides, the cost of this process is much less in comparison with other conventional methods...
A Numerical Comparison between Ring Indentation, Punching and Shot Peening on Fatigue Crack Retardation of Al-A356.0
, M.Sc. Thesis Sharif University of Technology ; Farrahi, Gholam Hossein (Supervisor)
Abstract
Most engineering components must be manufactured so they are safe to use and are ‘‘fit for purpose’’. However despite all the efforts, cracking of the engineering components is inevitable. Residual stresses play an important role in either increasing or decreasing the possibility of failure. For instance, enhancement in apparent toughness following pre-loading arises principally because of the creation of local crack tip compressive residual stresses. Introducing compressive residual stresses can also slow the fatigue crack growth. Yet, the dilemma is choosing an efficient method growth to introduce such stresses for retardation of fatigue crack growth. There are many methods available in...
Prediction of Stable Fatigue Crack Growth in Laser Peened 316L SS with Variable Beam Diameter and Pre-crack Length Using Artificial Neural Network
, M.Sc. Thesis Sharif University of Technology ; Farrahi, Gholamhossein (Supervisor)
Abstract
Processing an alloy can enhance its mechanical properties. Based on repeated radiation of high-power pulsed laser beam, laser shock peening (LSP) is one way to impart favorable residual stress in an alloy and to enhance its damage tolerance property. Study of overlapping LSP is possible through the simulation of limited laser shots. Still, its computational cost is higher than that of a single shot. This research, primarily, is aimed at improving a methodology for reduction of computations in the study of an overlapping LSP and its impacts on fatigue crack growth. Addressing research gaps by utilizing the methodology is the secondary goal. The methodology consists of plastic strain...
Rapid growth of hydroxyapatite nanoparticles using ultrasonic irradiation
, Article Ultrasonics Sonochemistry ; Volume 17, Issue 5 , Jun , 2010 , Pages 853-856 ; 13504177 (ISSN) ; Taghavinia, N ; Rouhani, S ; Sharif University of Technology
2010
Abstract
A rapid, environmental friendly and low-cost method to prepare hydroxyapatite nanoparticles is proposed. In this method, hydroxyapatite is produced in a sonicated pseudo-body solution. The sonication time was found effective in the formation of the crystalline phase of nanoparticles. In our experimental condition, 15 min sonication resulted in the most pure hydroxyapatite phase. Also it was shown that growth temperature is a crucial factor and hydroxyapatite crystallizes only at 37 °C. The particles formed by sonication were generally smaller and more spherical than those obtained without sonication. Sonication increased the hydroxyapatite crystal growth rate up to 5.5 times compared to...
Electrophoretic deposition of chitosan
, Article Materials Letters ; Volume 63, Issue 26 , 2009 , Pages 2253-2256 ; 0167577X (ISSN) ; Pishbin, F ; Boccaccini, A. R ; Sharif University of Technology
2009
Abstract
The electrophoretic deposition (EPD) of chitosan on metallic substrates was investigated. The electrophoretic mobility of the natural biopolymer in aqueous solution as a function of pH was studied. Because the protonation/deporotonation of chitosan is pH-dependent, the electrophoretic mobility and deposition rate is shown to increase with increasing pH from 2.9 to 4.1. The film growth rate is estimated to vary in the range 0.02-0.08 μm/s depending on the pH value. At high growth rates (> 0.05 μm/s), a porous film is obtained due to hydrogen entrapment. The EPD method developed here is applicable for the surface modification of metal implants by chitosan to develop novel bioactive coatings. ©...
Electrocrystallization of Ni nanocones from chloride-based bath using crystal modifier by electrochemical methods
, Article Journal of Alloys and Compounds ; Volume 818 , 2020 ; Aliofkhazraei, M ; Dolati, A ; Rouhaghdam, A. S ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
The early stages of nucleation and growth of nanostructures can control the shape and final size of the fabricated nanostructure. Therefore, the study of the nucleation and growth mechanism of nanostructures is of great importance. The purpose of this study is to investigate the nucleation and growth mechanism of nickel nanocones from a chloride-based bath containing ethylene ammonium dichloride as a crystal modifier. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry tests were employed to investigate the nucleation and growth mechanism and also the mechanism of crystal modifier performance on the growth of nanocones. Electrochemical studies revealed...
Micro-structural aspects of fatigue crack propagation in atomistic-scale via the molecular dynamics analysis
, Article Engineering Fracture Mechanics ; Volume 226 , 2020 ; Khoei, A. R ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
In this paper, the fatigue crack propagation is modeled using the Molecular Dynamics (MD) analysis based on the Embedded Atom Method (EAM). The crack growth simulation is performed for the single-crystal and poly-crystalline specimens subjected to cyclic loading/unloading conditions, and the crack growth rate is investigated at the atomistic level. The MD simulations are carried out under different model parameters, including the load pattern, maximum applied strain, temperature, loading frequency, and percentage of defects by employing more than 4000 molecular dynamics analyses to study the sensitivity of crack propagation process to the simulation parameters. The threshold values of...