Search for: models--theoretical
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    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... 

    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  

    Methods to Derive the Differential Equation of the Free Surface Boundary

    , Article Ground Water ; Volume 49, Issue 2 , 2011 , Pages 133-143 ; 0017467X (ISSN) Wang, X. S ; Neuman, S. P ; Strack, O. D. L ; Verruijt, A ; Jamali, M ; Seymour, B ; Bear, J ; Cheng, A. H. D ; Chen, C ; Kuang, X ; Jiao, J. J ; Sharif University of Technology

    Multi-item multiperiodic inventory control problem with variable demand and discounts: A particle swarm optimization algorithm

    , Article Scientific World Journal ; Vol. 2014 , 2014 ; ISSN: 23566140 Mousavi, S. M ; Niaki, S. T. A ; Bahreininejad, A ; Musa, S. N ; Sharif University of Technology
    A multi-item multiperiod inventory control model is developed for known-deterministic variable demands under limited available budget. Assuming the order quantity is more than the shortage quantity in each period, the shortage in combination of backorder and lost sale is considered. The orders are placed in batch sizes and the decision variables are assumed integer. Moreover, all unit discounts for a number of products and incremental quantity discount for some other items are considered. While the objectives are to minimize both the total inventory cost and the required storage space, the model is formulated into a fuzzy multicriteria decision making (FMCDM) framework and is shown to be a... 

    Extension of weighted sum of gray gas data to mathematical simulation of radiative heat transfer in a boiler with gas-soot media

    , Article The Scientific World Journal ; Vol. 2014 , 2014 ; ISSN: 1537744X Gharehkhani, S ; Nouri-Borujerdi, A ; Kazi, S. N ; Yarmand, H ; Sharif University of Technology
    In this study an expression for soot absorption coefficient is introduced to extend the weighted-sum-of-gray gases data to the furnace medium containing gas-soot mixture in a utility boiler 150 MWe. Heat transfer and temperature distribution of walls and within the furnace space are predicted by zone method technique. Analyses have been done considering both cases of presence and absence of soot particles at 100% load. To validate the proposed soot absorption coefficient, the expression is coupled with the Taylor and Foster's data as well as Truelove's data for CO2-H2O mixture and the total emissivities are calculated and compared with the Truelove's parameters for 3-term and 4-term gray... 

    Analytical relations for long-droplet breakup in asymmetric T junctions

    , Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 91, Issue 5 , May , 2015 ; 15393755 (ISSN) Bedram, A ; Moosavi, A ; Hannani, S. K ; Sharif University of Technology
    American Physical Society  2015
    We develop accurate analytical relations for the droplet volume ratio, droplet length during breakup process, and pressure drop of asymmetric T junctions with a valve in each of the branches for producing unequal-sized droplets. An important advantage of this system is that after manufacturing the system, the size of the generated droplets can be changed simply by adjusting the valves. The results indicate that if the valve ratio is smaller than 0.65, the system enters a nonbreakup regime. Also the pressure drop does not depend on the time and decreases by increasing the valve ratio, namely, opening the degree of valve 1 to valve 2. In addition, the results reveal that by decreasing... 

    Quartic balance theory: Global minimum with imbalanced triangles

    , Article Physical Review E ; Volume 102, Issue 1 , 2020 Kargaran, A ; Ebrahimi, M ; Riazi, M ; Hosseiny, A ; Jafari, G. R ; Sharif University of Technology
    American Physical Society  2020
    Balance theory proposed by Heider for the first time modeled triplet interaction in a signed network, stating that relationships between two people, friendship or enmity, is dependent on a third person. The Hamiltonian of this model has an implicit assumption that all triads are independent, meaning that the type of each triad, being balanced or imbalanced, determined apart from the state of other triads. This independence forces the network to have completely balanced final states. However, there exists evidence indicating that real networks are partially balanced, raising the question of what is the mechanism preventing the system to be perfectly balanced. Our suggestion is to consider a... 

    Nonlinear analysis of anesthesia dynamics by fractal scaling exponent

    , Article 28th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, EMBS'06, New York, NY, 30 August 2006 through 3 September 2006 ; 2006 , Pages 6225-6228 ; 05891019 (ISSN); 1424400325 (ISBN); 9781424400324 (ISBN) Gifani, P ; Rabiee, H. R ; Hashemi, M. R ; Taslimi, P ; Ghanbari, M ; Sharif University of Technology
    The depth of anesthesia estimation has been one of the most research interests in the field of EEG signal processing in recent decades. In this paper we present a new methodology to quantify the depth of anesthesia by quantifying the dynamic fluctuation of the EEG signal. Extraction of useful information about the nonlinear dynamic of the brain during anesthesia has been proposed with the optimum Fractal Scaling Exponent. This optimum solution is based on the best box sizes in the Detrended Fluctuation Analysis (DFA) algorithm which have meaningful changes at different depth of anesthesia. The Fractal Scaling Exponent (FSE) Index as a new criterion has been proposed. The experimental results... 

    Adversarial orthogonal regression: Two non-linear regressions for causal inference

    , Article Neural Networks ; Volume 143 , 2021 , Pages 66-73 ; 08936080 (ISSN) Heydari, M. R ; Salehkaleybar, S ; Zhang, K ; Sharif University of Technology
    Elsevier Ltd  2021
    We propose two nonlinear regression methods, namely, Adversarial Orthogonal Regression (AdOR) for additive noise models and Adversarial Orthogonal Structural Equation Model (AdOSE) for the general case of structural equation models. Both methods try to make the residual of regression independent from regressors, while putting no assumption on noise distribution. In both methods, two adversarial networks are trained simultaneously where a regression network outputs predictions and a loss network that estimates mutual information (in AdOR) and KL-divergence (in AdOSE). These methods can be formulated as a minimax two-player game; at equilibrium, AdOR finds a deterministic map between inputs... 

    Experimental design in analytical chemistry -Part I: Theory

    , Article Journal of AOAC International ; Vol. 97, issue. 1 , 2014 , pp. 3-11 ; ISSN: 10603271 Ebrahimi-Najafabadi, H ; Leardi, R ; Jalali-Heravi, M ; Sharif University of Technology
    This paper reviews the main concepts of experimental design applicable to the optimization of analytical chemistry techniques. The critical steps and tools for screening, including Plackett-Burman, factorial and fractional factorial designs, and response surface methodology such as central composite, Box-Behnken, and Doehlert designs, are discussed. Some useful routines are also presented for performing the procedures  

    Theoretical modeling and simulation of higher order FWM crosstalks in multichannel WDM optical communication systems

    , Article Advanced Materials Research, Xiamen ; Volume 660 , 2013 , Pages 130-134 ; 10226680 (ISSN) ; 9783037856413 (ISBN) Yazdani, A ; Noshad, M ; Farrokhi, A ; Sharif University of Technology
    In this paper, we derive a theoretical model for the higher order FWM power in WDM networks with NZDSF fibers for the first time. We have investigated the higher order FWM power theoretically and by numerical simulations. Dividing the fiber into finite number of elements and applying the boundary conditions, allow us derive an expression for second order power penalty. At the end of each element we derive the first order FWM power for all wavelengths and use these values to calculate the second order FWM power in the next element. Consequently, for each channel we can compute the total second order FWM power penalty at the end of the fiber  

    Fractional order model reduction approach based on retention of the dominant dynamics: Application in IMC based tuning of FOPI and FOPID controllers

    , Article ISA Transactions ; Volume 50, Issue 3 , July , 2011 , Pages 432-442 ; 00190578 (ISSN) Tavakoli Kakhki, M ; Haeri, M ; Sharif University of Technology
    Fractional order PI and PID controllers are the most common fractional order controllers used in practice. In this paper, a simple analytical method is proposed for tuning the parameters of these controllers. The proposed method is useful in designing fractional order PI and PID controllers for control of complicated fractional order systems. To achieve the goal, at first a reduction technique is presented for approximating complicated fractional order models. Then, based on the obtained reduced models some analytical rules are suggested to determine the parameters of fractional order PI and PID controllers. Finally, numerical results are given to show the efficiency of the proposed tuning... 

    Simulation of DNA electrophoresis through microstructures

    , Article Electrophoresis ; Volume 28, Issue 3 , 2007 , Pages 301-308 ; 01730835 (ISSN) Maleki Jirsaraei, N ; Sarbolouki, M. N ; Rouhani, S ; Sharif University of Technology
    The dependence of the mobility of DNA molecules through an hexagonal array of micropillars on their length and the applied electric field was investigated and it was found that mobility is a nonmonotonic function of their length. Results also revealed that the size dependence of the DNA mobility depends on the applied electric field and there is a crossover around E ≈ 25 V/cm for the mobility of λ-DNA and T4-DNA. These observations are explained in terms of the diffusion process inside the structure affected by the solvent and are modeled using the Langevin and its corresponding Fokker-Planck equations. The phenomenon is generalized under three regimes in a phase diagram relating the... 

    An optimization based approach embedded in a fuzzy connectivity algorithm for airway tree segmentation

    , Article Proceedings of the 30th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, EMBS'08 - "Personalized Healthcare through Technology", 20 August 2008 through 25 August 2008, Vancouver, BC ; 2008 , Pages 4011-4014 ; 9781424418152 (ISBN) Yousefi Rizi, F ; Ahmadian, A. R ; Fatemizadeh, E ; Alirezaie, J ; Sharif University of Technology
    The main problem with airway segmentation methods which significantly influences their accuracy is leakage into the extra-luminal regions due to thinness of the airway wall during the process of segmentation. This phenomenon potentially makes large regions of lungparenchyma to be wrongly identified as airways. A solution to this problem in the previous methods was based on leak detection followed by reducing leakage during the segmentation process. This has been dealt with adjusting the segmentation parameters and performing the re-segmentation process on the pre-segmented area. This makes the algorithm very exhaustive and more dependent on the user interaction. The method presented here is... 

    A heuristic method for finding the optimal number of clusters with application In medical data

    , Article 30th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, EMBS'08, Vancouver, BC, 20 August 2008 through 25 August 2008 ; 2008 , Pages 4684-4687 ; 9781424418152 (ISBN) Bayati, H ; Davoudi, H ; Fatemizadeh, E ; Sharif University of Technology
    IEEE Computer Society  2008
    In this paper, a heuristic method for determining the optimal number of clusters is proposed. Four clustering algorithms, namely K-means, Growing Neural Gas, Simulated Annealing based technique, and Fuzzy C-means in conjunction with three well known cluster validity indices, namely Davies-Bouldin index, Calinski-Harabasz index, Maulik-Bandyopadhyay index, in addition to the proposed index are used. Our simulations evaluate capability of mentioned indices in some artificial and medical datasets. © 2008 IEEE  

    Symmetric bursting behaviors in the generalized FitzHugh-Nagumo model

    , Article Biological Cybernetics ; Volume 107, Issue 4 , 2013 , Pages 465-476 ; 03401200 (ISSN) Abbasian, A. H ; Fallah, H ; Razvan, M. R ; Sharif University of Technology
    In the current paper, we have investigated the generalized FitzHugh-Nagumo model. We have shown that symmetric bursting behaviors of different types could be observed in this model with an appropriate recovery term. A modified version of this system is used to construct bursting activities. Furthermore, we have shown some numerical examples of delayed Hopf bifurcation and canard phenomenon in the symmetric bursting of super-Hopf/homoclinic type near its super-Hopf and homoclinic bifurcations, respectively  

    Theoretical investigation on antioxidant activity of bromophenols from the marine red alga Rhodomela confervoides: H-atom vs electron transfer mechanism

    , Article Journal of Agricultural and Food Chemistry ; Volume 61, Issue 7 , 2013 , Pages 1534-1541 ; 00218561 (ISSN) Javan, A. J ; Javan, M. J ; Tehrani, Z. A ; Sharif University of Technology
    Bromophenols are known as antioxidant radical scavengers for some biomolecules such as those in marine red alga. Full understanding of the role played by bromophenols requires detailed knowledge of the radical scavenging activities in probable pathways, a focus of ongoing research. To gain detailed insight into two suggested pathways, H-atom transfer and electron transfer, theoretical studies employing first principle quantum mechanical calculations have been carried out on selected bromophenols. Detailed investigation of the aforementioned routes revealed that upon H-atom abstraction or the electron transfer process, bromophenols cause an increase in radical species in which the unpaired... 

    Coarsening dynamics of nanodroplets on topographically structured substrates

    , Article Journal of Physics Condensed Matter ; Volume 25, Issue 4 , 2013 ; 09538984 (ISSN) Asgari, M ; Moosavi, A ; Sharif University of Technology
    Employing a biharmonic boundary integral method with linear elements, coarsening dynamics of nanodroplets on topographical step heterogeneity is investigated. It is shown that the step height and droplet configuration have an influential effect on the dynamics. Increasing the step height slows down the process while locating the droplets close to the step boosts the coarsening rate. Considering a slip boundary condition enhances the dynamics and reveals a transition in the droplet migration direction. Our results reveal that increasing the surface wettability weakens the dynamics. Various types of the disjoining pressure over the step are also considered and their effects on the coarsening... 

    Influence of ridge filter material on the beam efficiency and secondary neutron production in a proton therapy system

    , Article Zeitschrift fur Medizinische Physik ; Volume 22, Issue 3 , September , 2012 , Pages 231-240 ; 09393889 (ISSN) Riazi, Z ; Afarideh, H ; Sadighi-Bonabi, R ; Sharif University of Technology
    Elsevier  2012
    In this work, the 3D proton dose profile is calculated in a homogenous water phantom using a Monte Carlo application developed with the Geant4 toolkit. The effect of the ridge filter material (for SOBP widths of 6, 9 and 12 cm) on the homogeneity of the dose distribution, secondary neutron production and beam efficiency are investigated in a single ring wobbling irradiation system. The energy spectrum of secondary neutrons per primary proton at various locations around the phantom surface is calculated. The simulation revealed that most of the produced neutrons are released at slight angles which enable them to reach the patient and consequently to be hazardous. Also, the homogeneity of the... 

    Continuous-time state-space unsteady aerodynamic modeling based on boundary element method

    , Article Engineering Analysis with Boundary Elements ; Volume 36, Issue 5 , 2012 , Pages 789-798 ; 09557997 (ISSN) Mohammadi Amin, M ; Ghadiri, B ; Abdalla, M. M ; Haddadpour, H ; De Breuker, R ; Sharif University of Technology
    In this paper a continuous-time state-space aerodynamic model is developed based on the boundary element method. Boundary integral equations governing the unsteady potential flow around lifting bodies are presented and modified for thin wing configurations. Next, the BEM discretized problem of unsteady flow around flat wing equivalent to the original geometry is recast into the standard form of a continuous-time state-space model considering some auxiliary assumptions. The system inputs are time derivative of the instantaneous effective angle of attack and thickness/camber correction terms while the outputs are unsteady aerodynamic coefficients. To validate the model, its predictions for...