Search for: models
Total 7968 records
Article Chaos ; Volume 23, Issue 4 , 2013 ; 10541500 (ISSN) ; 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...
Article Kovove Materialy ; Volume 49, Issue 4 , 2011 , Pages 253-258 ; 0023432X (ISSN) ; 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) ; 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) ; 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....
Article Polyolefins Journal ; Volume 6, Issue 1 , 2019 , Pages 95-106 ; 23222212 (ISSN) ; 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...
Article General Relativity and Gravitation ; Volume 40, Issue 5 , 2008 , Pages 1047-1069 ; 00017701 (ISSN) ; 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...
Article Physical Review B - Condensed Matter and Materials Physics ; Volume 77, Issue 9 , 2008 ; 10980121 (ISSN) ; 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...
Article The Scientific World Journal ; Volume 2014 , 2014 ; ISSN: 1537744X ; 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) ; 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...
Article Electronic Journal of Theoretical Physics ; Volume 6, Issue 23 , 2009 , Pages 123-136 ; 17295254 (ISSN) ; 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) ; 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...
Article Iranian Journal of Science and Technology, Transaction A: Science ; Volume 42, Issue 1 , March , 2018 , Pages 261-266 ; 10286276 (ISSN) ; 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 ; 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....
Control effectiveness investigation of a ducted-fan aerial vehicle using model predictive controller, Article International Conference on Advanced Mechatronic Systems, ICAMechS ; 2014 , pp. 532-537 ; Emami, S. A ; Sharif University of Technology
Special attention is given to vertical takeoff and landing air vehicles due to their unique capabilities and versatile missions. The main problem here is control effectiveness at low flight speeds and transition maneuvers because of the inherent instability. RMIT is a small sized tail-sitter ducted fan air vehicle with a particular configuration layout, multiple control surfaces, low weight, and high-speed flight capability. In the current study, a comprehensive nonlinear model is firstly developed for RMIT, followed by a validation process. This model consists of all parts including aerodynamic forces and moments, control surfaces term together with the gravity and driving fan forces....
Prediction of methane uptake on different adsorbents in adsorbed natural gas technology using a rigorous model, Article Energy and Fuels ; Vol. 28, issue. 10 , September , 2014 , p. 6299-6314 ; Mesbah, M ; Shokrollahi, A ; Bahadori, A ; Ghazanfari, M. H ; Sharif University of Technology
One of the most promising methods for transporting natural gas and overcoming its low energy density is adsorbed natural gas (ANG) technology. ANG technology is highly dependent on the perfect conception of adsorption isotherms in different operational conditions and on different adsorbents. In this study, the utilization of a novel mathematical model of least squares support vector machine (LSSVM) for accurate prediction of adsorption isotherm has been examined. The considered variables were temperature, pressure and type of adsorbents. A data set containing 670 experimental data points of methane adsorption on 10 different adsorbents in a broad range of temperature and pressure were used...
Article Journal of Statistical Mechanics: Theory and Experiment ; Volume 2012, Issue 2 , Feb , 2012 ; 17425468 (ISSN) ; Aghamohammadi, C ; Khorrami, M ; Sharif University of Technology
A one-dimensional kinetic Ising model at a finite temperature on a semi-infinite lattice with time varying boundary spins is considered. Exact expressions for the expectation values of the spin at each site are obtained, in terms of the time dependent boundary condition and the initial conditions. The solution consists of a transient part which is due to the initial conditions, and a part driven by the boundary. The latter is an evanescent wave when the boundary spin is oscillating harmonically. Low-and high-frequency limits are investigated in greater detail. The total magnetization of the lattice is also obtained. It is seen that for any arbitrary rapidly varying boundary conditions, this...
Article International Journal of Modern Physics B ; Volume 25, Issue 32 , 2011 , Pages 4709-4720 ; 02179792 (ISSN) ; Lotfi, E ; Moghimi Araghi, S ; Sharif University of Technology
We investigate a new version of sandpile model which is very similar to Abelian Sandpile Model (ASM), but the height variables are continuous ones. With the toppling rule we define in our model, we show that the model can be mapped to ASM, so the general properties of the two models are identical. Yet the new model allows us to investigate some problems such as the effect of very small mass on the height probabilities, different boundary conditions
Article PLOS ONE ; Volume 11, Issue 11 , 2016 ; 19326203 (ISSN) ; Motahari, S. A ; Hosseinkhalaj, B ; Sharif University of Technology
Public Library of Science
Lander-Waterman's coverage bound establishes the total number of reads required to cover the whole genome of size G bases. In fact, their bound is a direct consequence of the well-known solution to the coupon collector's problem which proves that for such genome, the total number of bases to be sequenced should be O(G ln G). Although the result leads to a tight bound, it is based on a tacit assumption that the set of reads are first collected through a sequencing process and then are processed through a computation process, i.e., there are two different machines: one for sequencing and one for processing. In this paper, we present a significant improvement compared to Lander-Waterman's...
Article Brodogradnja ; Volume 67, Issue 1 , 2016 , Pages 85-100 ; 0007215X (ISSN) ; Seif, M.S ; Mehdigholi, H ; Sharif University of Technology
Brodarski Institute 2016
Ship transportation is increasing globally as is the risk of collision especially in congested areas. Numerical modeling method is a major simulation method to predict ship maneuverability. Ship maneuvering in calm water is an important topic to avoid collisions and leads to safe navigation. Therefore, reliable ship maneuvering simulations are required for incident analysis and prevention. In recent time within the research community orientated towards ship hydrodynamics an increasing attention has been paid to simultaneous solution of the planing ship maneuvering problem. The maneuverability of planing craft has been the subject of many research projects during the last few decades. To...
Developing a mathematical model for Ibuprofen's controlled release accounting for solubility and diffusion effects, Article Computer Aided Chemical Engineering ; Volume 26 , 2009 , Pages 737-742 ; 15707946 (ISSN); 9780444534330 (ISBN) ; Kazemeini, M ; Baroodi, P ; Jezowski J ; Thullie J ; Sharif University of Technology
In this research a mathematical model for controlled drug delivery of Ibuprofen has been developed which accounts for physical kinetics based upon variations of the drug concentration, size and release time for a spherical drug pill. Through this model, the drug release for three sizes of the active ingredient including; 213nm (representing existence of only diffusion limitations), 515nm (representing existence of only solubility limitations) and 367nm (representing both diffusion and solubility limitations) was calculated. Theoretical amounts of the drug after two hours of release are calculated to be 95.3, 99.5 and 95.5 percent, respectively. Comparison of theoretical and experimental data...