Showing papers by "Amirkabir University of Technology published in 2008"
TL;DR: A numerical scheme to solve the two-dimensional damped/undamped sine-Gordon equation is proposed based on using collocation points and approximating the solution employing the thin plate splines radial basis function (RBF).
363 citations
TL;DR: In this paper, a hybrid harmony search algorithm (HHSA) is proposed to solve engineering optimization problems with continuous design variables, where sequential quadratic programming (SQP) is employed to speed up local search and improve precision of the HSA solutions.
319 citations
TL;DR: In this paper, a ZSM-5 zeolite crystal with different Si/Al molar ratios in the range of 10-50 was synthesized using sodium silicate, aluminum sulfate and tetrapropylammonium bromide as the organic template.
Abstract: ZSM-5 zeolite crystal with different Si/Al molar ratios in the range of 10-50 was synthesized using sodium silicate, aluminum sulfate and tetrapropylammonium bromide (TPA-Br) as the organic template. The produced samples were characterized using XRD, FT-IR, SEM and EDX techniques. All synthesized samples were found to be ZSM-5 zeolite as confirmed by XRD and supported by FT-IR. SEM results showed that ZSM-5 synthesized with different Si/Al molar ratios had different morphologies and particle sizes. It was found that the average ZSM-5 crystal size increased as Si/Al molar ratio increased. Thermogravimetric-difference thermal analysis (TG-DTA) technique was also used to measure the amount of template occluded inside the crystal pore. The synthesized Na-ZSM-5 was transformed into its acidic form, i.e., H-ZSM-5 using ion exchange method with ammonium nitrate solution. The H-ZSM-5 acidity was determined by NH3-TPD. These results showed that different Si/Al molar ratios have effect on surface acidity of samples. The surface areas of the H-ZSM-5 were measured using BET method and the results showed that, decrease in Si/Al ratio, decreased the surface area. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
318 citations
TL;DR: The solution of a delay differential equation is presented by means of a homotopy perturbation method and then some numerical illustrations are given to reveal that the proposed method is very effective and simple to perform.
281 citations
TL;DR: A powerful optimal coordination method based on GA is introduced to solve the problems of miscoordination and continuous or discrete time setting multiplier (TSM) or time dial setting (TDS).
274 citations
TL;DR: In this paper, the chromium adsorption from aqueous solution by wheat bran was investigated, and the influence of contact time, pH, adsorbent dose and initial chromium concentration on the performance of the process was investigated.
Abstract: In this research, adsorption of chromium (VI) ions on wheat bran has been studied through using batch adsorption techniques. The main objectives of this study are to 1) investigate the chromium adsorption from aqueous solution by wheat bran, 2) study the influence of contact time, pH, adsorbent dose and initial chromium concentration on adsorption process performance and 3) determine appropriate adsorption isotherm and kinetics parameters of chromium (VI) adsorption on wheat bran. The results of this study showed that adsorption of chromium by wheat bran reached to equilibrium after 60 min and after that a little change of chromium removal efficiency was observed. Higher chromium adsorption was observed at lower pHs, and maximum chromium removal (87.8 %) obtained at pH of 2. The adsorption of chromium by wheat bran decreased at the higher initial chromium concentration and lower adsorbent doses. The obtained results showed that the adsorption of chromium (VI) by wheat bran follows Langmuir isotherm equation with a correlation coefficient equal to 0.997. In addition, the kinetics of the adsorption process follows the pseudo second-order kinetics model with a rate constant value of 0.131 g/mg.min The results indicate that wheat bran can be employed as a low cost alternative to commercial adsorbents in the removal of chromium (VI) from water and wastewater.
215 citations
TL;DR: A bi-objective model is set up for the distribution network of a three-echelon supply chain, with two objective functions: minimizing costs, and minimizing the sum of backorders and surpluses of products in all periods.
213 citations
TL;DR: In this article, a variational iteration method was used to solve the Lane-Emden equation for a self-gravitating, spherically symmetric polytropic fluid.
206 citations
TL;DR: In this article, a numerical scheme to solve the one-dimensional hyperbolic telegraph equation using collocation points and approximating the solution using thin plate splines radial basis function was proposed.
Abstract: Recently, it is found that telegraph equation is more suitable than ordinary diffusion equation in modelling reaction diffusion for such branches of sciences. In this article, we propose a numerical scheme to solve the one-dimensional hyperbolic telegraph equation using collocation points and approximating the solution using thin plate splines radial basis function. The scheme works in a similar fashion as finite difference methods. The results of numerical experiments are presented, and are compared with analytical solutions to confirm the good accuracy of the presented scheme. © 2007 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2008
197 citations
TL;DR: In this paper, a new method, based on linear prediction, is proposed for wind speed forecasting, which utilizes the "linear prediction" method in conjunction with "filtering" of the wind speed waveform.
186 citations
TL;DR: A new approach to DFR at the distribution networks considering DGs is presented, which applies the particle swarm optimization (PSO) approach to solve the DFR, which is a nonlinear optimization problem.
15 May 2008-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the relationship between failure mode and weld fusion zone characteristics (size and microstructure) was studied and it was found that spot weld strength in the pullout failure mode is controlled by the strength and fusion zone size of the galvanized steel side.
Abstract: Resistance spot welding was used to join austenitic stainless steel and galvanized low carbon steel. The relationship between failure mode and weld fusion zone characteristics (size and microstructure) was studied. It was found that spot weld strength in the pullout failure mode is controlled by the strength and fusion zone size of the galvanized steel side. The hardness of the fusion zone which is governed by the dilution between two base metals, and fusion zone size of galvanized carbon steel side are dominant factors in determining the failure mode.
TL;DR: In this article, a new two-parameter lifetime distribution with decreasing failure rate is introduced, and the estimation of the parameters attained by the EM algorithm and their asymptotic variances and covariances are obtained.
TL;DR: The proposed approach, based on a Bayesian classifier, utilizes the adaptive mixtures method and Markov random field model to obtain and upgrade the class conditional probability density function (CCPDF) and the a priori probability of each class.
TL;DR: In this paper, a rod-shaped nano-hydroxyapatite (nHAP) and poly( l -lactide acid) composite scaffold was used for bone tissue engineering applications.
Abstract: The aims of this work were synthesis of rod shaped nano-hydroxyapatite (nHAP) and fabrication of novel nano-hydroxyapatite/poly( l -lactide acid) (nHAP/PLLA) composite scaffold. In the first step, the identification and morphology of chemically synthesized nHAP particles were determined by XRD, EDX, FTIR and SEM analyses. The rod shaped nHAP particles with an average size of approximately 37–65 nm in width and 100–400 nm in length were found similar to natural bone apatite in terms of chemical composition and structural morphology. In the second step, nHAP and micro sized HAP (mHAP) particles were used to fabricate HAP filled PLLA (HAP/PLLA) composites scaffolds using thermally induced phase separation method. The porosity of scaffolds was up to 85.06% and their average macropore diameter was in the range of 64–175 μm. FTIR and XRD analyses showed some molecular interactions and chemical linkages between HAP particles and PLLA matrix. The compressive strength of nanocomposite scaffolds could high up to 14.9 MPa while those of pure PLLA and microcomposite scaffolds were 1.79 and 13.68 MPa, respectively. The cell affinity and biocompatibility of the nanocomposite scaffold were found to be higher than those of pure PLLA and microcomposite scaffolds. Following the results, the newly developed nHAP/PLLA composite scaffold is comparable with cancellous bone in terms of microstructure and mechanical strength, so it may be considered for bone tissue engineering applications.
TL;DR: In this paper, the adsorption of acid red 14 (AR14) and acid blue 92 (AB92) onto the microporous and mesoporous egg shell membrane (ESM) was investigated in aqueous solution in a batch system with respect to initial dye concentration, pH, contact time, particle size and biosorbent doses at 20 ± 1 °C.
TL;DR: Hard shell of apricot stones was selected from agricultural solid wastes to prepare effective and low cost adsorbent for the gold separation from gold-plating wastewater and showed that under the optimum operating conditions, more than 98% of gold was adsorbed onto activated carbon after only 3h.
TL;DR: A survey of coupling agents used in composites can be found in this paper, where the authors present a comparison of different functional groups of a coupling agent with respect to polymeric composites.
Abstract: Fibril or particulate fillers used to reinforce polymeric composites are often inorganic, so, as two dissimilar materials cannot compatibilize with each other, the problem of adherence always exists. To solve this problem a third material can help as a coupling agent. A coupling agent should have the ability to adhere to both surfaces by means of different functional groups. Silane coupling agents are frequently used because of several outstanding aspects they have. This review is a survey on these coupling agents used in composites.
TL;DR: The simulation results show that the proposed multiscale nonlinear thresholding methods for ultrasound speckle suppression outperforms several recently and the state-of-the-art techniques qualitatively and quantitatively.
Abstract: Speckle noise is an inherent nature of ultrasound images, which may have negative effect on image interpretation and diagnostic tasks. In this paper, we propose several multiscale nonlinear thresholding methods for ultrasound speckle suppression. The wavelet coefficients of the logarithm of image are modeled as the sum of a noise-free component plus an independent noise. Assuming that the noise-free component has some local mixture distribution (MD), and the noise is either Gaussian or Rayleigh, we derive the minimum mean squared error (MMSE) and the averaged maximum (AMAP) estimators for noise reduction. We use Gaussian and Laplacian MD for each noise-free wavelet coefficient to characterize their heavy-tailed property. Since we estimate the parameters of the MD using the expectation maximization (EM) algorithm and local neighbors, the proposed MD incorporates some information about the intrascale dependency of the wavelet coefficients. To evaluate our spatially adaptive despeckling methods, we use both real medical ultrasound and synthetically introduced speckle images for speckle suppression. The simulation results show that our method outperforms several recently and the state-of-the-art techniques qualitatively and quantitatively.
TL;DR: This work constructs an iterative algorithm to solve the generalized coupled Sylvester matrix equations over reflexive matrices Y, Z and obtains the optimal approximation reflexive solution pair to a given matrix pair.
25 Nov 2008
TL;DR: This paper proposes Fractional-order Hopfield Neural Networks (FHNN), a network mainly based on the classic well-known Hopfield net in which fractance components with fractional order derivatives, replace capacitors.
Abstract: This paper proposes Fractional-order Hopfield Neural Networks (FHNN). This network is mainly based on the classic well-known Hopfield net in which fractance components with fractional order derivatives, replace capacitors. Stability of FHNN is fully investigated through energy-like function analysis. To show how effective the FHNN network is, an illustrative example for parameter estimation problem of the second-order system is finally considered in the paper. The results of simulation are very promising.
TL;DR: In this paper, the authors show that there are two approaches for dealing with long-term production planning problems: (1) deterministic and (2) uncertainty-based approaches.
Abstract: Long-term production planning (LTPP) is a large-scale optimization problem that aims to find the block extraction sequence that produces the maximum possible net present value (NPV) whilst satisfying a variety of physical and economical constraints. The economic feasibility of a mine is highly dependent upon careful LTPP. As the mining industries extract deeper and lower grade ores, LTPP is becoming a key item that can result in ceasing operations or continuing the project. Mathematical programming models are well suited to optimizing LTPP of open pit mines. These mathematical models have been studied extensively in the literature since the 1960s. The result of this study shows that there are two approaches for dealing with LTPP problems: (1) deterministic and (2) uncertainty-based approaches. This paper first discusses the deterministic algorithms and then, after an introduction to uncertainty associated with mining projects, reviews uncertainty-based algorithms. The advantages and disadvantages of these...
TL;DR: In this paper, the authors considered the scenario of supply chain with multiple products and multiple suppliers, all of which have limited capacity, and they used a genetic algorithm (GA) to solve the model.
TL;DR: Investigation of the scheduling problem of parallel identical batch processing machines in which each machine can process a group of jobs simultaneously as a batch finds a hybrid genetic heuristic (HGH) to minimize makespan objective.
TL;DR: In this paper, the authors proposed a feature selection method based on ant colony optimization (ACO), which is inspired of ant's social behavior in their search for the shortest paths to food sources.
TL;DR: In this paper, the photocatalytic degradation of azo dye acid red 114 in water was studied and a model was proposed for photodegradation of dyes using immobilized [TiO2/clinoptilololite (SSD)].
TL;DR: In this paper, the effect of welding sequence on welding deformations in pipe-pipe joints of AISI stainless-steel type was investigated using three-dimensional thermo-mechanical analysis.
TL;DR: Two new methods to solve optimal chiller loading (OCL) problem are employed, continuous genetic algorithm (GA) and particle swarm optimization (PSO), which easily overcome deficiencies in other conventional optimization methods.
TL;DR: In this paper, the thermal and mechanical instability of truncated conical shells made of functionally graded material (FGM) is studied and the governing equations are based on the first-order shell theory and the Sanders nonlinear kinematics equations.
Abstract: Thermal and mechanical instability of truncated conical shells made of functionally graded material (FGM) is studied in this paper. It is assumed that the shell is a mixture of metal and ceramic that its properties changes as a function of the shell thickness. The governing equations are based on the first-order shell theory and the Sanders nonlinear kinematics equations. The results are obtained for a number of thermal and mechanical loads and are validated with the known data in the literature.