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匹配条件： “Mohsen Saghafian” ，找到相关结果约2302条。
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Evaluation of the Capability of the Multigrid Method in Speeding Up the Convergence of Iterative Methods
Iman Harimi,Mohsen Saghafian
ISRN Computational Mathematics , 2012, DOI: 10.5402/2012/172687

Abstract:

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Abstract: The performance of the multigrid method and the effect of different grid levels on the convergence rate are evaluated. The two-, three-, and four-level V-cycle multigrid methods with the Gauss-Seidel iterative solver are employed for this purpose. The numerical solution of the one-dimensional Laplace equation with the Dirichlet boundary conditions is obtained using these methods. For the Laplace equation, a two-frequency function involving high- and low-frequency components is defined. It is observed that, however, the GS method can smooth out the high-frequency error components properly, but because the difference scheme for Laplace equation is remarkably concise, in the fine grids, a very large number of iterations are needed for extending the boundary conditions into the domain. Furthermore, the obtained results reveal that the number of necessary iterations for convergence is reduced considerably by employing the two-level multigrid algorithm. But increasing the number of levels of algorithm does not have any significant effect on the convergence rate in this study. 1. Introduction The standard iterative methods like Jacobi and Gauss-Seidel (GS) rapidly damp out the local errors (high-frequency errors) of the solution, but they are extremely slow to remove the global errors (low-frequency errors) [1, 2]. In fact, these methods have a local stencil and may require a large number of iterations to converge. The multigrid method (MG) is one of the most efficient methods for solving linear and nonlinear systems, which can speed up the rate of damping out low-frequency errors. In this method, the high-frequency components of the solution error are damped by an iterative solver, or smoother, on a fine grid, whereas the low-frequency components are transferred to the coarser grid. On the coarser grid, these low-frequency error components appear as high-frequency ones, which are iteratively solved by a smoother. The typical application of the multigrid method is the numerical solution of elliptic partial differential equations [3]. The multigrid methods have also been used successfully for problems in image processing and vision [4]. In the past decades, many researchers including Fedorenko, Bakhvalov, and Brandt have studied and developed the multigrid methods [5–10]. The multigrid idea was first introduced by Fedorenko in 1962 and 1964 [5, 6] and then generalized by Bakhvalov in 1966 [7]. The multigrid algorithms were developed to practical applicability by Brandt in 1973 [8]. In 1977, Brandt [9] introduced a multilevel adaptive technique (MLAT) for fast

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Multi-objective optimization for combined quality–quantity urban runoff control
S. Oraei Zare, B. Saghafian,A. Shamsai
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2012,

Abstract: Urban development affects the quantity and quality of urban surface runoff. In recent years, the best management practices (BMPs) concept has been widely promoted for control of both quality and quantity of urban floods. However, means to optimize the BMPs in a conjunctive quantity/quality framework are still under research. In this paper, three objective functions were considered: (1) minimization of the total flood damages, cost of BMP implementation and cost of land-use development; (2) reducing the amount of TSS (total suspended solid) and BOD5 (biological oxygen demand), representing the pollution characteristics, to below the threshold level; and (3) minimizing the total runoff volume. The biological oxygen demand and total suspended solid values were employed as two measures of urban runoff quality. The total surface runoff volume produced by sub-basins was representative of the runoff quantity. The construction and maintenance costs of the BMPs were also estimated based on the local price standards. Urban runoff quantity and quality in the case study watershed were simulated with the Storm Water Management Model (SWMM). The NSGA-II (Non-dominated Sorting Genetic Algorithm II) optimization technique was applied to derive the optimal trade off curve between various objectives. In the proposed structure for the NSGA-II algorithm, a continuous structure and intermediate crossover were used because they perform better as far as the optimization efficiency is concerned. Finally, urban runoff management scenarios were presented based on the optimal trade-off curve using the k-means method. Subsequently, a specific runoff control scenario was proposed to the urban managers.

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Multiple Periodic Solutions for Some Classes of First-Order Hamiltonian Systems [PDF]
Mohsen Timoumi
Applied Mathematics (AM) , 2011, DOI: 10.4236/am.2011.27114

Abstract: Considering a decomposition R²N=A⊕B of R²N , we prove in this work, the existence of at least (1+dimA) geometrically distinct periodic solutions for the first-order Hamiltonian system Jx'(t)+H'(t,x(t))+e(t)=0 when the Hamiltonian H(t,u+v) is periodic in (t,u) and its growth at infinity in v is at most like or faster than |v|^a, 0≤a<1 , and e is a forcing term. For the proof, we use the Least Action Principle and a Generalized Saddle Point Theorem.

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Corrosion effect on the flexural strength & micro-hardness of ips e-max ceramics [PDF]
Cherif Mohsen
Open Journal of Stomatology (OJST) , 2011, DOI: 10.4236/ojst.2011.12006

Abstract: Objectives: The effect of ceramics construction (press- able, machinable) and corrosion on flexural strength and micro-hardness was studied. Materials & Methods: Two types of ceramics were tested: IPS e-max Press and IPS e-max CAD. Forty samples were constructed and divided into 2 groups according to the type of ceramics. Each group was then subdivided into 2 subgroups. Subgroups 1 were not subjected to corrosion while subgroups 2 were subjected to corro-sion test. Finally each subgroup was divided into 2 classes according to the type of test: biaxial flexural strength, micro-hardness. Results: There was a sig-nificant difference between the two tested ceramics as regard weight loss as IPS e-max CAD recorded less weight loss than IPS e-max Press. As regard the flex-ural strength, IPS e-max CAD recorded significant higher strength than IPS e-max Press. Corroded sam- ples recorded significant lower flexural strength than non-corroded samples for the two tested ceramics. As regard the Vickers micro-hardness test, the results showed significant difference between the two tested ceramics. IPS e-max CAD recorded higher mi-cro-hardness values than IPS e-max Press. The results also showed that the corroded samples recorded no significant micro-hardness values than non- corroded samples for the two tested ceramics. Conclusions: IPS e-max CAD recorded less weight loss weight loss after being subjected to corrosion test than IPS e-max Press. The method of fabrication affected the flexural strength µ-hardness of ceramic as machinable ceramic (e-max CAD) recorded significant higher data than pressable ceramic (e-mas Press). Corrosion decreased the flexural strength of both tested ceramics but had no effect on micro- hardness.

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Using Intelligent Computational Methods for Optimizing Niching Method [PDF]
Mohsen Jahanshahi
International Journal of Intelligence Science (IJIS) , 2011, DOI: 10.4236/ijis.2011.11001

Abstract: Optimization implies the minimization or maximization of an objective function. Some problems have sev-eral optimum points which all, should be computed. Niching method is presented to do so. However, its efficiency can be improved via combining it with Memetic algorithm. Therefore, in this paper, Memetic method is used to improve this method in terms of convergence rate and diversity. In the proposed methods, genetic algorithm, PSO, and learning automata are used as a local search algorithm of Memetic method. The result of simulations demonstrates that proposed methods are more effective compared with Niching in terms of convergence and diversity.

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Vertical marginal gap & retention of ceramic full coverage & inlay retained ceramic fixed partial dentures [PDF]
Cherif Mohsen
Open Journal of Stomatology (OJST) , 2011, DOI: 10.4236/ojst.2011.14021

Abstract: Objectives: A comparison study between ceramic full coverage FPDs & 3 designs of ceramic inlay retained FPDs regarding vertical marginal gap & retention. Materials & Methods: Twenty samples were construc- ted and divided into 4 groups according to the type of restorations: full coverage, inlay-shaped (occluso-pro- ximal inlay + proximal box), tub-shaped (occluso-pro- ximal inlay), and proximal box-shaped FPDs. All samples were subjected to a vertical marginal gap measurements followed by a retention test. Results: The vertical marginal gap data showed no significant difference between full coverage FPDs, the tub-shap- ed inlay retained FPDs and the proximal box-shaped inlay retained FPDs. While there was a difference between these three designs and the inlay retained FPDs. Regarding retention, the full coverage FPDs recorded higher retentive strengths and was signifi-cant difference than all inlay retained FPDs designs tested. The inlay-shaped design was significant dif-ference than the other two inlay retained FPDs de-signs. Conclusions: There was no significant differ- ence between full coverage FPDs, tub-shaped & pro- ximal box shaped inlay retained FPDs as regard ver- tical marginal discrepancies. While, the inlay-haped design showed the highest vertical marginal discrep- ancies. The premolar & molar retainers for the same type of restorations showed no difference in vertical marginal discrepancies. All measured vertical mar- ginal discrepancies were in the range of clinical ac- ceptance. The full coverage FPDs recorded higher retentive strengths than all inlay retained FPDs de- signs tested. The inlay-shaped design recorded the highest retentive strengths among the three inlay re- tained FPDs designs. There was no difference as re- gard retentive strengths between tub-shaped & pro- ximal box shaped inlay retained FPDs.

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Electromagnetic Radiation Reaction and Stability of the Hydrogen-Like Atoms [PDF]
Mohsen Dehghani
Journal of Modern Physics (JMP) , 2011, DOI: 10.4236/jmp.2011.211174

Abstract: Based on a suitable linear combination of the physical and un-physical electromagnetic potentials, the radiation reaction potentials have been calculated. Through the near zone expansion of the potentials, it has been shown that in either of the relativistic and non-relativistic cases the outgoing (radiated) energy of the electrons orbiting the nucleus is substituted by incoming (electromagnetic radiation reaction) energy. This means that energy is conserved and the classical hydrogen-like atoms are stable.

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Optimal Redundancy Allocation in Hierarchical Series-Parallel Systems Using Mixed Integer Programming [PDF]
Mohsen Ziaee
Applied Mathematics (AM) , 2013, DOI: 10.4236/am.2013.41014

Abstract:

Reliability optimization plays an important role in design, operation and management of the industrial systems. System reliability can be easily enhanced by improving the reliability of unreliable components and/or by using redundant configuration with subsystems/components in parallel. Redundancy Allocation Problem (RAP) was studied in this research. A mixed integer programming model was proposed to solve the problem, which considers simultaneously two objectives under several resource constraints. The model is only for the hierarchical series-parallel systems in which the elements of any subset of subsystems or components are connected in series or parallel and constitute a larger subsystem or total system. At the end of the study, the performance of the proposed approach was evaluated by a numerical example.

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Additive Manufacturing: The Most Promising Technology to Alter the Supply Chain and Logistics [PDF]
Mohsen Attaran
Journal of Service Science and Management (JSSM) , 2017, DOI: 10.4236/jssm.2017.103017

Abstract:

To compete in a global economy, manufacturers are forced to move towards low volume production of innovative and customized products with high added value. Three-dimensional printing, also known as additive manufacturing (AM) or rapid prototyping enables and facilitates production of moderate to mass quantities of products that can be individually customized. The technology is truly innovative with endless product design possibilities and potential to enhance global supply chain capabilities. The technology improves efficiencies of the entire supply chain, from the cost of distribution to assembly and carry, all the way to the component itself. This article reviews evolution of new supply chain models, examines some of the potential benefits of AM in challenging traditional manufacturing constraints, explores its impact on the traditional and global supply chain and logistics, and investigates its transformative potential and its impact on various industry segments.

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