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    Development of an empirical model for catalyst lifetime in isobutane/ butene alkylation

    , Article Industrial and Engineering Chemistry Research ; Volume 42, Issue 17 , 2003 , Pages 3886-3892 ; 08885885 (ISSN) Kazemeini, M ; Sahebdelfar, S ; Khorasheh, F ; Badakhshan, A ; Sharif University of Technology
    American Chemical Society  2003
    Dimensional analysis of the governing equations in liquid-phase, solid-acid-catalyzed alkylation was used to develop an empirical model for the catalyst lifetime in terms of important operating variables. It was found that the dimensionless catalyst lifetime in a continuous stirred tank reactor was a function of four dimensionless groups, incorporating all important kinetic and operating variables. A power-law correlation was found to be adequate in representing the available experimental data. Because the alkylation reactions are highly diffusion-limited, it was shown that only three of the four exponents in the power-law correlation were independent. As such, the fourth exponent was... 

    Turbulent flow using a modified V2f turbulence model

    , Article 2004 ASME International Mechanical Engineering Congress and Exposition, IMECE 2004, Anaheim, CA, 13 November 2004 through 19 November 2004 ; Volume 260 , 2004 , Pages 587-594 ; 08888116 (ISSN) Montazeri, H ; Kazemzadeh Hannan, S ; Farhanieh, B ; Sharif University of Technology
    An improved version of the V2f turbulence model has been examined in this paper. The objective was to overcome the convergence problem encountered in the original V2f model. The convergence problem is due to the commonly-used wall boundary condition, which therefore has been modified in the proposed model. To test the soundness of the new model, several two-dimensional cases such as Poiseuille flow, channel flow, and backward-step flow has been analyzed and the results are compared with the standard k - ε model, DNS, and in case of the backward flow problem, also with the original V2f model. Based on the comparison, the new model presents a promising approach both with respect to convergence... 

    Predictions of some internal microstructural models for polymer melts and solutions in shear and elongational flows

    , Article Macromolecular Theory and Simulations ; Volume 13, Issue 7 , 2004 , Pages 655-664 ; 10221344 (ISSN) Eslami, H ; Ahmad Ramazani, S. A ; Ali Khonakdarl, H ; Sharif University of Technology
    In this work, the behavior of some internal microstructural models with different mobility tensors has been studied for polymer melts and solutions under steady and transient simple shear and elongational flows. The time evolution equations for conformation and stress tensors in the models reviewed have their root in the Generalized Poisson bracket formalism. Two different families of conformational models have been selected for this study. The first family is based on the Modified Finitely Extensible Nonlinear Elastic (FENE-P) energy while the second uses a Volume Preserving Conformational Rheological (VPCR) model based on the Hookean Helmholtz free energy function. Several expressions for... 

    Physiological and psychological neural system modeling for a key-pressing test

    , Article Proceedings of the IASTED International Conference on Biomedical Engineering, Salzburg, 25 June 2003 through 27 June 2003 ; 2003 , Pages 66-70 ; 0889863539 (ISBN) Mahmudi, H ; Shahdi, S. A ; Vahdat, B. V ; IASTED ; Sharif University of Technology
    The model introduced in this article for neural system describes both physiological and psychological concepts of neural system and is based on the models of individual elements of the system. This model includes psychological characteristics such as; perception, prediction, learning and response planning, and physiological features such as; sensory analysis, memory and motor execution. The model is designed in such a way that it describes the performance of the neural system for a key-pressing test. The key-pressing experiment consists of a screen with numbers from 1 to 9, which is shown to the operator where one of the numbers is specified by a special color and the operator is to push the... 

    Generative model selection using a scalable and size-independent complex network classifier

    , Article Chaos ; Volume 23, Issue 4 , 2013 ; 10541500 (ISSN) Motallebi, S ; Aliakbary, S ; Habibi, J ; Sharif University of Technology
    Real networks exhibit nontrivial topological features, such as heavy-tailed degree distribution, high clusteringsmall-worldness. Researchers have developed several generative models for synthesizing artificial networks that are structurally similar to real networks. An important research problem is to identify the generative model that best fits to a target network. In this paper, we investigate this problem and our goal is to select the model that is able to generate graphs similar to a given network instance. By the means of generating synthetic networks with seven outstanding generative models, we have utilized machine learning methods to develop a decision tree for model selection. Our... 

    Model checking in Rebeca

    , Article Proceedings of the International Conference on Parallel and Distributed Processing Techniques and Applications, Las Vegas, NV, 23 June 2003 through 26 June 2003 ; Volume 4 , 2003 , Pages 1819-1822 ; 1892512416 (ISBN) Sirjani, M ; Movaghar, A ; Iravanchi, H ; Jaghoori, M ; Shali, A ; Sharif University of Technology
    Rebeca is a recently introduced actor-based language, for modeling concurrent and distributed systems. In this paper, we present our work on model checking Rebeca code. Rebeca is a high level language, comparing to the most of languages used for modeling, in the existing model checker tools. So, we need specific abstraction techniques for model checking Rebeca code. Here, we show some of these abstraction techniques used and some case studies  

    Solidification of A356 Al alloy: Experimental study and modeling

    , Article Kovove Materialy ; Volume 49, Issue 4 , 2011 , Pages 253-258 ; 0023432X (ISSN) Shabani, M. O ; Mazahery, A ; Bahmani, A ; Davami, P ; Varahram, N ; Sharif University of Technology
    While it is well recognized that microstructure controls the physical and mechanical properties of a material, the complexity of the microstructure often makes it difficult to be simulated by analytical or numerical techniques. In this paper we present a suitable approach to compute microstructures within a casting using the finite element technique. This technique allows implementing microstructure data from experiments and equations that describe microstructure as function of local solidification parameters. The comparison of this model's predictions with the ones in the literature and also experimental measurements of secondary dendrite arm spacing, average length and diameter of silicon... 

    Grain size distribution after similar and dissimilar gas tungsten arc welding of a ferritic stainless steel

    , Article Journal of Mining and Metallurgy, Section B: Metallurgy ; Volume 51, Issue 1 , 2015 , Pages 61-66 ; 14505339 (ISSN) Ranjbarnodeh, E ; Serajzadeh, S ; Kokabi, A. H ; Fischer, A ; Sharif University of Technology
    Technical Faculty in Bor  2015
    In this study, gas tungsten arc welding of ferritic stainless steel and grain size distribution in heat affected zone of the welded samples were investigated. Both similar and dissimilar arc welding operations were considered where in dissimilar welding joining of stainless steel to mild steel was examined. In the first stage, a three-dimensional model was developed to evaluate temperature field during and after arc welding while the model was performed using finite element software, ANSYS. Then, the effects of welding heat input and dissimilarity of the joint on the weld pool shape and grain growth in HAZ of stainless steel was investigated by means of model predictions and experimental... 

    Concrete basic creep predi ction based on time-temperature equivalence relation and short-term tests

    , Article Arabian Journal for Science and Engineering ; Volume 35, Issue 2 A , 2010 , Pages 105-121 ; 13198025 (ISSN) Barani, O. R ; Mostofinejaad, D ; Saadatpour, M. M ; Shekarchi, M ; Sharif University of Technology
    Using temperature as an accelerator of reactions in short-term tests for the prediction of concrete creep is the main idea of this paper. The application of a time-temperature equivalence relation is examined with reference to creep in concrete under constant moisture conditions. A mathematical model is developed which uses short-term tests to predict long-term creep deformation of concrete under constant moisture conditions, taking into account aging of concrete and the influence of temperature. The thermal activation is assumed to be governed by the Arrhenius principle, and the activation energy of the viscosity of water is found to be applicable in the analysis of the experimental data.... 

    Development of a rheological model for polymeric fluids based on FENE model

    , Article Polyolefins Journal ; Volume 6, Issue 1 , 2019 , Pages 95-106 ; 23222212 (ISSN) Ebrahimi, H ; Ahmad Ramazani, S. A ; Davachi, S. M ; Sharif University of Technology
    Iran Polymer and Petrochemical Institute  2019
    Rheological models for polymer solutions and melts based on the finitely extensible non-linear elastic (FENE) dumbbell theory are reviewed in this study. The FENE-P model that is a well-known Peterlin approximation of the FENE model, indicates noticeable deviation from original FENE predictions and also experimental results, especially in the transient flow. In addition, both FENE and FENE-P models have some shortcomings from the point of view of theory. To overcome these shortcomings, a new approximation of the FENE spring force has been established. It has been used to develop a modified constitutive rheological model for polymeric fluids. In the procedure of modeling, the effect of... 

    An inhomogeneous model universe behaving homogeneously

    , Article General Relativity and Gravitation ; Volume 40, Issue 5 , 2008 , Pages 1047-1069 ; 00017701 (ISSN) Khosravi, Sh ; Kourkchi, E ; Mansouri, R ; Akrami, Y ; Sharif University of Technology
    We present a new model universe based on the junction of FRW to flat Lemaitre-Tolman-Bondi (LTB) solutions of Einstein equations along our past light cone, bringing structures within the FRW models. The model is assumed globally to be homogeneous, i.e. the cosmological principle is valid. Local inhomogeneities within the past light cone are modeled as a flat LTB, whereas those outside the light cone are assumed to be smoothed out and represented by a FRW model. The model is singularity free, always FRW far from the observer along the past light cone, gives way to a different luminosity distance relation as for the CDM/FRW models, a negative deceleration parameter near the observer, and... 

    Green's function approach to quantum criticality in the anisotropic Kondo necklace model

    , Article Physical Review B - Condensed Matter and Materials Physics ; Volume 77, Issue 9 , 2008 ; 10980121 (ISSN) Rezania, H ; Langari, A ; Thalmeier, P ; Sharif University of Technology
    We have studied the quantum phase transition between the antiferromagnetic and spin liquid phases for the two-dimensional anisotropic Kondo necklace model. The bond operator formalism has been implemented to transform the spin Hamiltonian to a bosonic one. We have used the Green's function approach including a hard core repulsion to find the low energy excitation spectrum of the model. The bosonic excitations become gapless at the quantum critical point where the phase transition from the Kondo singlet state to long range antiferromagnetic order takes place. We have studied the effect of both intersite (δ) and local (Δ) anisotropies on the critical point and on the critical exponent of the... 

    Constructing the critical curve for a symmetric two-layer Ising model

    , Article Journal of Theoretical and Computational Chemistry ; Volume 3, Issue 2 , 2004 , Pages 217-224 ; 02196336 (ISSN) Ghaemi, M ; Mirza, B ; Parsafar, G. A ; Sharif University of Technology
    A numerical method based on the transfer matrix method is developed to calculate the critical temperature of two-layer Ising ferromagnet with a weak inter-layer coupling. The reduced internal energy per site has been accurately calculated for symmetric ferromagnetic case, with the nearest neighbor coupling K1 = K2 = K (where K1 and K2 are the nearest neighbor interaction in the first and second layers, respectively) with inter-layer coupling J. The critical temperature as a function of the inter-layer coupling ξ = J/K, is obtained for very weak inter-layer interactions, ξ < 0.1. Also a different function is given for the case of the strong inter-layer interactions (ξ > 1). The importance of... 

    Analytical solution for the free vibration analysis of delaminated timoshenko beams

    , Article The Scientific World Journal ; Volume 2014 , 2014 ; ISSN: 1537744X Jafari Talookolaei, R. A ; Abedi, M ; Sharif University of Technology
    This work presents a method to find the exact solutions for the free vibration analysis of a delaminated beam based on the Timoshenko type with different boundary conditions. The solutions are obtained by the method of Lagrange multipliers in which the free vibration problem is posed as a constrained variational problem. The Legendre orthogonal polynomials are used as the beam eigenfunctions. Natural frequencies and mode shapes of various Timoshenko beams are presented to demonstrate the efficiency of the methodology  

    Biodegradation kinetics and interactions of styrene and ethylbenzene as single and dual substrates for a mixed bacterial culture

    , Article Journal of Environmental Health Science and Engineering ; 2015 ; 2052336X (ISSN) Hazrati, H ; Shayegan, J ; Seyedi, S. M ; Sharif University of Technology
    BioMed Central Ltd  2015
    This study examined biodegradation kinetics of styrene and ethylbenzene as representatives of alkenylbenzenes and mono-alkylbenzenes, respectively. The compounds were studied independently and as binary mixtures using a series of aerobic batch degradation experiments introduced by acclimatized mix culture. Initial concentration of styrene and ethylbenzene in the liquid phase vacillated from 0 to 220 mg/l. The Andrew model was applied for the biodegradation of individual substrates and the estimated constants of the equation for styrene and ethylbenzene were μmax = 0.1581, 0.2090 (1/h), KS =25.91, 37.77 (mg/L), KI =13.15, 62.62 (mg/L), respectively. The accomplished parameters from single... 

    An interruption in the highway: New approach to modeling the car-traffic

    , Article Electronic Journal of Theoretical Physics ; Volume 6, Issue 23 , 2009 , Pages 123-136 ; 17295254 (ISSN) Rezaeezadeh, A ; Sharif University of Technology
    A very common phenomena in car-traffic system is investigated in this article. The problem is one-dimensional. We try to find the wave equation of the traffic and then, we'll talk more about the simulation of the system using Matlab7.6  

    Axial-flow compressor performance prediction in design and off-design conditions through 1-D and 3-D modeling and experimental study

    , Article Journal of Applied Fluid Mechanics ; Volume 9, Issue 5 , 2016 , Pages 2149-2160 ; 17353572 (ISSN) Peyvan, A ; Hajilouy benisi, A ; Sharif University of Technology
    Isfahan University of Technology 
    In this study, the main objective is to develop a one dimensional model to predict design and off design performance of an operational axial flow compressor by considering the whole gas turbine assembly. The design and off-design performance of a single stage axial compressor are predicted through 1D and 3D modeling. In one dimensional model the mass, momentum and energy conservation equations and ideal gas equation of state are solved in mean line at three axial stations including rotor inlet, rotor outlet and stator outlet. The total to total efficiency and pressure ratio are forecasted using the compressor geometry, inlet stagnation temperature and stagnation pressure, the mass flow rate... 

    Development of kinetic model for xanthan production in a laboratory-scale batch fermentor

    , Article Iranian Journal of Science and Technology, Transaction A: Science ; Volume 42, Issue 1 , March , 2018 , Pages 261-266 ; 10286276 (ISSN) Zakeri, A ; Pazouki, M ; Vossougi, M ; Sharif University of Technology
    Springer International Publishing  2018
    The present study was undertaken to investigate a kinetic model for cell growth evaluation and biopolymer production by Xanthomonas campestris in a laboratory-scale batch fermentor. The optimum conditions selected for biopolymer production were 30 °C for media temperature, 500 rpm for agitation rate, 65 g/l for sugarcane concentration and 1.5 vvm for air flow rate. A detailed, unstructured, mathematical kinetic model is presented here for batch production of xanthan biopolymer from X. campestris. Set of ordinary differential equations were developed as logistic model for X. campestris growth and logistic incorporated Luedeking–Piret model for xanthan production. These models would offer more... 

    Impact of mobile source emission inventory adjustment on air pollution photochemical model performance

    , Article Urban Climate ; Volume 32 , 2020 Shahbazi, H ; Hosseini, V ; Sharif University of Technology
    Elsevier B.V  2020
    Coupled weather forecasting and chemical transport models are useful tools to evaluate air pollution episodes in big cities for the purpose of forecasting and air pollution abatement measures' evaluation. However, large set of accurate data of various sources and modeling calibrations are needed for such complex modeling system to be reliable. The problem becomes more obvious when the model is operated over a domain in which there is a general lack of accurate input data such as emission inventory data. The current study investigates the possibility of model tuning for more accurate prediction of air pollutant concentrations in the city of Tehran in an air pollution episode as a case study.... 

    Model checking, automated abstraction, and compositional verification of Rebeca models

    , Article Journal of Universal Computer Science ; Volume 11, Issue 6 , 2005 , Pages 1054-1082 ; 0958695X (ISSN) Sirjani, M ; Movaghar, A ; Shali, A ; De Boer, F. S ; Sharif University of Technology
    Actor-based modeling, with encapsulated active objects which communicate asynchronously, is generally recognized to be well-suited for representing concurrent and distributed systems. In this paper we discuss the actor-based language Rebeca which is based on a formal operational interpretation of the actor model. Its Java-like syntax and object-based style of modeling makes it easy to use for software engineers, and its independent objects as units of concurrency leads to natural abstraction techniques necessary for model checking. We present a front-end tool for translating Rebeca to the languages of existing model checkers in order to model check Rebeca models. Automated modular...