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Relative intensity noise study in two mode quantum dot laser
, Article Optica Applicata ; Volume 41, Issue 4 , 2011 , Pages 961-970 ; 00785466 (ISSN) ; Mirmoeini, S. Z ; Faez, R ; Sharif University of Technology
2011
Abstract
In this paper, for the first time, we present a semiclassical noise model for InAs/GaAs quantum dot (QD) laser considering two photon modes, i.e., ground and first excited states lasing. This model is based on the five level rate equations. By using this model, the effect of temperature variations on relative intensity noise (RIN) of QD laser is investigated. We find that the RIN significantly degrades when excited state (ES) lasing emerges at high temperature. Furthermore, we investigate the influence of the quantum dot numbers on the RIN properties
Simulation And Analysis of Terahertz Laser Based on Graphene
, M.Sc. Thesis Sharif University of Technology ; Faez, Rahim (Supervisor)
Abstract
Graphene, a monolayer carbon-atomic honeycomb lattice crystal, has attracted attention due to its peculiar carrier transport properties owing to the gapless energy spectrum. Due to lack of applicable light source in terahertz (THz) band, further researches to finding materials that are suitable for semiconductor lasers in this band to be continued. In this thesis, the population inversion possibility that is the first provision of laser operation, was analyzed in graphene optical pumping situation. The analysis was done by numerical solving of carrier concentration and energy density relations.As a result of this analysis population inversion is obtained when the stimulation square pulse has...
Effect of Al antioxidant on the rate of oxidation of carbon in MgO-C refractory
, Article Journal of the American Ceramic Society ; Volume 90, Issue 2 , 2007 , Pages 509-515 ; 00027820 (ISSN) ; Nemati, Z. A ; Mahshid, S ; Hosseini, S ; Hashemi, B ; Sharif University of Technology
2007
Abstract
Kinetics of air oxidation of MgO-C-Al refractory at 600°-1300°C were investigated using the software based on the modifled shrinking core model (KDA). Commercial bricks containing 88.5% MgO, 10% residual carbon, and 1.5% aluminum anti-oxidant were oxidized isothermally with air. Combination of experimental data with model calculations indicated gas diffusion through solid material and pores as a major controlling step. Previously observed chemisorption process was eliminated from the rate-controlling mechanism with addition of aluminum antioxidant. Comprehensive rate equations were devised for MgO-C-Al and MgO-C oxidation reactions. Overall activation energies of Q id (internal diffusion) =...
Numerical modeling of ureagenesis in a microfluidic channel mimicking a liver lobule
, Article 2015 22nd Iranian Conference on Biomedical Engineering, ICBME 2015, 25 November 2015 through 28 November 2015 ; 2015 , Pages 54-59 ; 9781467393515 (ISBN) ; Firoozabadi, B ; Saidi, M. S ; Firoozbakhsh, K ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2015
Abstract
Ammonia detoxification is one of the main functions of the liver results in production of urea. In this study ammonia elimination and urea production was simulated in a microchannel mimicking the hepatic porto central axis. Navier- Stockes equations along with convection equations were solved for the related species in the entire domain. Since the Reynolds number was small (~1) the fluid flow regime was laminar. Urea cycle was modeled regarding its four main enzymes. Twelve rate equations were also solved in order to obtain the concentration of each metabolites participating in urea cycle. Concentration of the urea reached its maximum ca. 1.2e-5 M at the end of the channel which is in good...
An energy-based approach for analysis of dynamic plastic deformation of metals
, Article International Journal of Mechanical Sciences ; Volume 66 , January , 2013 , Pages 94-100 ; 00207403 (ISSN) ; Naghdabadi, R ; Arghavani, J ; Sharif University of Technology
2013
Abstract
An energy-based ordinary differential equation is derived for a plastic wave propagating through a Taylor impact test specimen. Using the definition of true strain, an analytical equation is presented to calculate the strain rate across the plastic wave front. Having considered a Johnson-Cook plasticity model for the projectile material, the derived energy equation accompanied by a governing kinematics relation and the strain rate equation is numerically integrated to obtain the final deformed profile of the specimen. The results of the energy based model are then compared with those of the commonly used momentum-based approach as well as the existing experimental data in literature for...
The leaching kinetics of an oxide gold ore with iodide/iodine solutions
, Article Hydrometallurgy ; Volume 113-114 , 2012 , Pages 42-50 ; 0304386X (ISSN) ; Sharif University of Technology
2012
Abstract
Two types of gold ores were subjected to iodide/iodine leaching at room temperature. The effects of three factors, including ore type (a carbonaceous and an oxide gold ores), iodide/iodine concentration, and the presence of oxygen in solution on gold leaching performance were investigated. The carbonaceous ore showed only 20% gold extraction, since gold-iodide complexes readily adsorb on organic matter. In contrast, gold extraction from the oxide ore in a solution containing 20 g/L iodide and 4 g/L iodine reached 77% in 6 h and 89% in 24 h. With iodate as the oxidant, no gold could be leached in 48 h. When the iodate was partially converted to iodine by adding HCl to the solution, gold...
Mathematical modeling of human blood clotting formation
, Article 6th International Special Topic Conference on ITAB, 2007, Tokyo, 8 November 2007 through 11 November 2007 ; 2007 , Pages 273-276 ; 9781424418688 (ISBN) ; Jahed, M ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2007
Abstract
Over the last two decades, mathematical modeling has become a popular tool in study of blood coagulation. This paper describes the coagulation pathway and presents a mathematical model for the generation of blood clot in human vasculature. Parameters of interest in this study include procoagulants and anticoagulants whose activity may be enhanced by various activator enzymes. The process of human blood clotting involves a complex interaction between these parameters and continuous time and state processes. In this work, we propose to model these highly inter-relational processes by a set of nonlinear chemical rate equations. We have modeled this process as a dynamical system, as chemical...
Laser-induced photo transmutation of 126Sn - A hazardous nuclear waste product-into short-lived nuclear medicine of 125Sn
, Article Energy Conversion and Management ; Volume 64 , 2012 , Pages 466-472 ; 01968904 (ISSN) ; Sadighi, S. K ; Zare, S ; Sadighi Bonabi, R ; Sharif University of Technology
2012
Abstract
Relativistic electrons, generated in the interaction of an ultra-intense laser pulse with plasma in front of a high-Z solid target, when passing near the nuclei of the solid target produce several MeV highly collimated Bremsstrahlung gamma beam, which can be used to induce photo-nuclear reactions. In this work the possibility of photo-induced transmutation (γn) of a nuclear waste of 126Sn with a half-life of 100,000 years into 125Sn with a half-life of 9.64 days was investigated for the first time. Calculations based on the available experimental data show that the Bremsstrahlung γ beam generated by irradiating a 2 mm thick tantalum target as a converter with 1020Wcm-2μm2 and 10 Hz table-top...
Reaction kinetics determination and neural networks modeling of methanol dehydration over nano γ-Al 2O 3 catalyst
, Article Journal of Industrial and Engineering Chemistry ; Volume 18, Issue 6 , 2012 , Pages 2059-2068 ; 1226086X (ISSN) ; Kazemeini, M ; Zaherian, A ; Zakerinasab, M. R ; Sharif University of Technology
2012
Abstract
In this research nano γ-Al 2O 3 catalyst was synthesized through precipitation process then characterized and utilized for methanol dehydration reaction in a slurry batch reactor in route to the indirect synthesis of the dimethyl ether (DME). In this venue, effects of the key parameters on methanol conversion and catalyst stability were investigated. Moreover, the internal and external mass transfer resistances were eliminated; hence the intrinsic kinetics controlled the reaction. Therefore, the optimum conditions for temperature, methanol concentration, catalyst mass and stirrer speed were determined to be 300°C, 1.18mol/l, 1.5g and 1100rpm, respectively. Next, different reaction rate...
An experimental design approach to determine effects of the operating parameters on the rate of Ru promoted Ir carbonylation of methanol
, Article World Academy of Science, Engineering and Technology ; Volume 73 , March , 2011 , Pages 598-603 ; 2010376X (ISSN) ; Kazemini, M ; Mohammadrezaee, A ; Sharif University of Technology
Abstract
carbonylation of methanol in homogenous phase is one of the major routesfor production of acetic acid. Amongst group VIII metal catalysts used in this process iridium has displayed the best capabilities. To investigate effect of operating parameters like: temperature, pressure, methyl iodide, methyl acetate, iridium, ruthenium, and water concentrations on the reaction rate, experimental design for this system based upon central composite design (CCD) was utilized. Statistical rate equation developed by this method contained individual, interactions and curvature effects of parameters on the reaction rate. The model with p-value less than 0.0001 and R 2 values greater than 0.9; confirmeda...
Simulation of softening kinetics and microstructural events in aluminum alloy subjected to single and multi-pass rolling operations
, Article Applied Mathematical Modelling ; Volume 40, Issue 17-18 , 2016 , Pages 7571-7582 ; 0307904X (ISSN) ; Serajzadeh, S ; Sharif University of Technology
Elsevier Inc
Abstract
In this study, a multi-scale model is proposed to assess softening kinetics and microstructural changes during isothermal annealing within an aluminum alloy. In the first stage, an elastic-plastic finite element analysis is performed for computing the distributions of effective plastic strain and stress while the stored energy after cold rolling is defined based on the predicted data and then utilized for generation of the initial conditions in the microstructural analysis. In the next stage, an algorithm based on cellular automata coupled with a first order rate equation is used to determine the progress of softening behavior at elevated temperatures while both recrystallization and...
An inhomogeneous theoretical model for analysis of PbSe quantum-dot-doped fiber amplifier
, Article Optics Communications ; Volume 282, Issue 22 , 2009 , Pages 4449-4454 ; 00304018 (ISSN) ; Rooholamini, H ; Rahimi, L ; Askari, A. A ; Sharif University of Technology
2009
Abstract
Optical fiber doped with lead salts quantum dots (QDs) of different radii, has previously been proposed as a wide-band amplifier in the optical communication range. The emission and absorption spectra of QDs are size-dependent. Optical fiber amplifier doped with QDs of different sizes is an inhomogeneous gain medium. This inhomogeneity is the principle of operation of wide-band quantum-dot-doped fiber amplifiers (QDFAs). To study the effects of inhomogeneity such as spectral hole burning on the amplifier behavior, a fiber amplifier with an arbitrary size distribution of QDs is taken into consideration. The light propagation equations and rate equations for the inhomogeneous medium are...
Long-term deactivation of a commercial CoMo-Al2O3 catalyst in hydrodesulfurization of a naphtha stream
, Article Industrial and Engineering Chemistry Research ; Volume 48, Issue 7 , 2009 , Pages 3331-3340 ; 08885885 (ISSN) ; Hoseini, M ; Sharif University of Technology
2009
Abstract
Long-term deactivation of a commercial CoMoγ-Al2O3 catalyst used in the hydrodesulfurization of a naphtha stream was studied using 35 months of operating data of an industrial HDS fixed bed reactor. The major sulfur-containing species of the naphtha feed was identified as 2-ethyl-4-methylthiophene (2E4MT) based on GC-MS analysis. The characterization of the industrial catalysts was performed by BET, XRD, XRF, and HCN Leco analyses. The reaction rate constant of the gas-phase hydrodesulfurization reaction was calculated by fitting the industrial reactor conversion data to the Hougen-Watson rate equation, assuming that the surface reaction between the sulfur-containing species and adsorbed...
A numerical model for predicting hepatocytes ureagenesis and its related inborn enzyme deficiencies: case studies
, Article Scientia Iranica ; Volume 26, Issue 1B , 2019 , Pages 408-420 ; 10263098 (ISSN) ; Firoozabadi, B ; Saidi, M. S ; Firoozbakhsh, K ; Sharif University of Technology
Sharif University of Technology
2019
Abstract
One important functionality of liver cells is ammonia detoxification and urea production. In this study, a numerical model of the urea cycle in hepatocytes was developed. Navier Stokes and convection equations were employed to study the process of ammonia elimination and urea production using a microfluidic channel. The concentration of urea and ammonia throughout the channel was obtained. Furthermore, the urea cycle was modelled with respect to its four main enzymes. This resulted in twelve rate equations that were solved to determine the concentration of each metabolite participating in the urea cycle. Application of results implied common disorders such as hyperammonemia types I and II...
A numerical model for predicting hepatocytes ureagenesis and its related inborn enzyme deficiencies: Case studies
, Article Scientia Iranica ; Volume 26, Issue 1B , 2019 , Pages 408-420 ; 10263098 (ISSN) ; Firoozabadi, B ; Saidi, M. S ; Firoozbakhsh, K ; Sharif University of Technology
Sharif University of Technology
2019
Abstract
One important functionality of liver cells is ammonia detoxification and urea production. In this study, a numerical model of the urea cycle in hepatocytes was developed. Navier Stokes and convection equations were employed to study the process of ammonia elimination and urea production using a microfluidic channel. The concentration of urea and ammonia throughout the channel was obtained. Furthermore, the urea cycle was modelled with respect to its four main enzymes. This resulted in twelve rate equations that were solved to determine the concentration of each metabolite participating in the urea cycle. Application of results implied common disorders such as hyperammonemia types I and II...
Harmonic content and relaxation resonant frequency of a modulated laser diode
, Article Scientia Iranica ; Volume 16, Issue 2 D , 2009 , Pages 145-156 ; 10263098 (ISSN) ; Bavafa, M ; Chamanzar, M. R ; Khorasani, S ; Sharif University of Technology
2009
Abstract
In this paper, an analysis of the harmonic contents of the optical output power for an in-plane single mode laser diode is performed, and the results are described in detail. In the first step, the absolute value of power for each harmonic is obtained in terms of various laser diode parameters, and the variations of external parameters, such as modulation current, bias current and frequency, are discussed. The analysis is done by direct solution of the rate equations of an arbitrary laser diode for carrier and photon densities. It is known that the optical power has a nonlinear dependence on frequency, and the maximum optical power of each harmonic is attained in its resonance frequency. The...
Theory of optimal mixing in directly modulated laser diodes
, Article Scientia Iranica ; Volume 16, Issue 2 D , 2009 , Pages 157-162 ; 10263098 (ISSN) ; Cabon, B ; Sharif University of Technology
2009
Abstract
Using a simple nonlinear model based on rate equations, and by employing a harmonic balance method, we develop a theory of optimal mixing in directly modulated semiconductor laser diodes. We perform a consistent numerical solution to the mixing in laser diodes to the arbitrary accuracy and intermodulation index (m, n). Through numerical computations we demonstrate that there is an optimal bias in mixing, corresponding to a relaxation frequency, fr, coinciding with the subcarrier frequency, f1, at which the mixing power is maximized nearly simultaneously for all intermodulation products, fmn. In terms of increasing the signal's current amplitude, it will be shown that it would result in a...
Kinetics of platinum extraction from spent reforming catalysts in aqua-regia solutions
, Article Hydrometallurgy ; Volume 95, Issue 3-4 , 2009 , Pages 247-253 ; 0304386X (ISSN) ; Khosravian Gh., H ; Mortaheb, H. R ; Sharif University of Technology
2009
Abstract
Platinum content of two commercial spent reforming catalysts were extracted in aqua-regia solutions under atmospheric pressure and at temperatures up to 100 °C. Three factors, including presence of coke, catalyst particle size, and impeller agitation speed were first tested to study the relative importance of mass-transfer resistances during Pt extraction reaction. Catalyst particle sizes < 100 μm and agitation speeds > 700 rpm eliminated the internal and external mass-transfer resistances, respectively. The effect of other factors, including HNO3-to-HCl volume ratio, liquid-to-solid mass ratio, and the reaction temperature on the extraction rate of platinum were then examined. Pt extraction...
An inhomogeneous theoretical model for analyzing the temporal response of high concentration erbium-doped fiber laser
, Article Solid State Lasers and Amplifiers III, Strasbourg, 8 April 2008 through 10 April 2008 ; Volume 6998 , 2008 ; 0277786X (ISSN); 9780819471963 (ISBN) ; Karvar, M ; Bahrampour, A ; Sharif University of Technology
2008
Abstract
In this paper the gain dynamics of an erbium-doped fiber laser (EDFL) with an inhomogeneous active medium in the presence of ion pairs is modeled. A two-level model for single ions and a three-level model for ion pairs are employed to write the propagation and rate equations of inhomogeneous laser medium. The governing equations are an uncountable system of partial differential equations (PDEs). By employing the moment method, the system of PDEs is converted to a finite system of ordinary differential equations (ODEs). The Solution of the system of ODEs is used to analyze the output power of a high concentration EDFL. As it expected, theoretical results show that the threshold pumping power...