Sharif Digital Repository

A set S of vertices of a graph G = (V, E) with no isolated vertex is a total dominating set if every vertex of V (G) is adjacent to some vertex in S. The total domination numberγt (G) is the minimum cardinality of a total dominating set of G. The total domination subdivision numbersdγt (G) is the minimum number of edges that must be subdivided in order to increase the total domination number. We consider graphs of order n ≥ 4, minimum degree δ and maximum degree Δ. We prove that if each component of G and over(G, -) has order at least 3 and G, over(G, -) ≠ C5, then γt (G) + γt (over(G, -)) ≤ frac(2 n, 3) + 2 and if each component of G and over(G, -) has order at least 2 and at least one... 

In this study, an accurate analytical solution for the nonlinear free vibration of a conservative oscillator with inertia and static type cubic nonlinearities is derived. This solution has been obtained using homotopy analysis method (HAM). Then, homotopy Pade technique is applied to accelerate the convergence rate of the series solution. This study shows that the HAM leads to an accurate analytical solution, which is valid for a wide range of considered system parameters. Unlike the other analytical methods, HAM can control and adjust the convergence region and rate of the approximation series solution. The excellent accuracy of the current results is demonstrated by comparing with the... 

Molecular structural mechanics approach is implemented to investigate vibrational behavior of single-layered graphene sheets. By using the atomistic modeling, mode shapes and natural frequencies are obtained. Vibration analysis is performed under different chirality and boundary conditions. Numerical results from the finite element technique are applied to develop empirical equations via a statistical multiple non-linear regression model. With the proposed empirical equations, fundamental frequencies of single-layered graphene sheets under considered boundary conditions can be predicted within 3 percent accuracy. Copyright © 2007 by ASME  

We propose a new coded cooperation scheme for wireless communications to obtain transmit diversity in the scenarios that agents such as mobile handsets, sensor network nodes and etc., due to size, power or other constraints, cannot utilize multiple antennas. New scheme supports more than two cooperative users with a relatively low cooperation level. We evaluate the performance of the proposed scheme in a frequency nonselective slow fading channel. For two cooperative users, we provide the exact analytical analysis. However, for more than two users, as the analytical analysis is very complicated, our performance evaluation is based on computer simulations. Our numerical results show that each... 

Arrays of N weakly coupled oscillators are considered in different configurations. The locking bandwidth for these arrays is defined statistically. Various factors affecting the locking bandwidth and the effect of the coupling network topology on locking bandwidth are studied by solving the dynamic equations of the array numerically. The analytical locking bandwidth for two configurations of arrays is computed and the results are compared with the numerical solution of dynamic equations. © The Institution of Engineering and Technology 2008  

In this paper, we propose a new modeling approach for analytical evaluation of normalized throughput and average backoff time for IEEE 802.11 MAC standard in non-saturation mode and with Poisson arrivals. To this end, we map different stages of distributed coordinated function (DCF) onto different components of a closed multi-class BCMP queueing network with arbitrary service time distribution. At the last part of the paper, we illustrate the applicability of the proposed approach by some numerical results in both saturation and non-saturation modes and obtain average backoff time for different arrival rates. © 2007 IEEE  

This paper presents a new approach to economic dispatch (ED) problem with non-continuous and non-smooth cost functions using a hybrid evolutionary programming (EP) algorithm. In the proposed method the concept of multi-agent (MA) systems and EP are integrated together to form a new multi-agent evolutionary programming (MAEP) approach. In MAEP, an agent represents a candidate solution to the optimization problem in hand, and all agents live together in a global environment. Each agent senses its local environment, competes with its neighbors, and also learns by using its own knowledge. MAEP uses these agent-agent interactions and the evolutionary mechanism of EP to obtain the optimal... 

In the present study, the presence of a baffle and its effect on the hydrodynamics of the flow in a primary settling tank has been investigated experimentally by ADV (Acoustic Doppler Velocimeter). On the other hand, the characteristics of this flow field were simulated by an unsteady two-phase finite volume method, and VOF (Volume of Fluid) model; and results were evaluated by the experimental data. The numerical calculation performed by using k - ε RNG model agrees well with experiments. It depicts the ability of this method in predicting the velocity profile and flow structure. In addition, the optimum position of the baffle to achieve the best performance of the tank was determined by... 

We have performed a numerical solution for band structure of an Abrikosov vortex lattice in type-II superconductors forming a periodic array in two dimensions for applications of incorporating the photonic crystals concept into superconducting materials with possibilities for optical electronics. The implemented numerical method is based on the extensive numerical solution of the Ginzburg-Landau equation for calculating the parameters of the two-fluid model and obtaining the band structure from the permittivity for both orthogonal polarizations, which depends on the above parameters and the frequency. This is while the characteristics of such crystals highly vary with an externally applied... 

The noise emission level associated with two types of speed reducers has been investigated numerically and experimentally for different dimensions and different speeds of vehicle (20, 40 and 60 km/h) and zero acceleration. Numerical analysis has been performed using an FEM method in the ANSYS environment. The experiments show that for a bump of height 0.04 m, the peak noise level is increased by between 1 and 14 dB (A) whereas, for bump of height 0.055 m, the peak noise level increases by between 1 and 19 dB (A). There is an excellent agreement between the numerical and experimental results. © 2006 Elsevier Ltd. All rights reserved  

Predictions of the gas temperature and pressure profiles are vital to the design and operation of gas transmission lines. Available analytical methods for the calculation of these profiles are evaluated and a numerical framework for the rigorous calculation has been developed. The predictions from both the analytical and numerical procedure have been compared to field data from the Iranian Gas Trunk-lines (IGAT). These comparisons showed that all the available methods were tuned using data obtained from small to medium diameter pipes extrapolated poorly to large diameter pipelines. In order to improve the predictions for large diameter pipelines, the effect of model parameters such as soil... 

In this paper, a new tool positioning strategy for five-axis machining, called the penetration-elimination method (PEM), is introduced. The PEM gains from two innovative techniques that can considerably improve the computational efficiency during the calculation of the optimal tool orientations. The first technique includes developing a quantitative definition for the gouging concept and using this definition in conjunction with powerful numerical root-finder algorithms to determine the optimized tool orientations. The second technique dynamically detects the ineffective grid points and drops them from calculations and consequently takes a great role in reducing the computational burden. The... 

In this paper, a new method is proposed for modal parameter estimation using time-frequency representations. Smoothed Pseudo Wigner-Ville distribution which is a member of the Cohen's class distributions is used to decouple vibration modes completely in order to study each mode separately. This distribution reduces cross-terms which are troublesome in Wigner-Ville distribution and retains the resolution as well. The method was applied to highly damped systems, and results were superior to those obtained via other conventional methods. © 2006 Elsevier Ltd. All rights reserved  

Torsional buckling of carbon nanopeapods (carbon nanotubes filled with fullerenes) is studied using a continuum-based multi-layered shell model. The model takes into account non-bonded van der Waals interactions between nested fullerenes and the innermost layer of host nanotube. For nanopeapods with linearly arranged nested fullerenes, equivalent pressure distribution is proposed to model these interactions. Deriving explicit equations governing the torsional stability, it is concluded that the critical torsional load of a carbon nanopeapod is less than that of a carbon nanotube under otherwise identical geometric and mechanical conditions. Performing numerical calculations, it is also shown... 

This article applies a novel non-Boussinesq numerical algorithm to solve the free-convection problem in a wide range of thin to thick vertical cavities subject to different side-wall temperatures. In this regard, the compressible flow equations are solved using a primitive incompressible method. No Boussinesq approximation and low Mach number consideration are included in the formulation. To implement the compressibility effect, the density field is calculated via the equation of state for gas. The temperature gradient is suitably varied to generate different low to high thermobuoyant fields, where the Boussinesq approximation may or may not be valid. Contrary to published works on the thin... 

In this paper, the Markov models, eigenvectors and eigenvalue concepts are used to propose a methodology for analyzing the transient reliability of a system with identical components and identical repairmen. The components of the systems under consideration can have two distinct configurations, namely; they can be arranged in series or in parallel. A third case is also considered, in which the system is up (good) if k-out-of-n components are good. For all three cases, a procedure is proposed for calculating the transient probability of the system availability and the duration of the system to reach the steady state. © Sharif University of Technology, February 2007  

The commuting graph of a ring R, denoted by Γ (R), is a graph whose vertices are all non-central elements of R and two distinct vertices x and y are adjacent if and only if xy = yx. Let D be a division ring and n ≥ 3. In this paper we investigate the diameters of Γ(Mn(D)) and determine the diameters of some induced subgraphs of Γ(Mn(D)), such as the induced subgraphs on the set of all non-scalar non-invertible, nilpotent, idempotent, and involution matrices in Mn(D). For every field F, it is shown that if Γ(Mn(F)) is a connected graph, then diam Γ(Mn(F)) ≤ 6. We conjecture that if Γ(Mn(F)) is a connected graph, then diam Γ(Mn(F)) ≤ 5. We show that if F is an algebraically closed field or n... 

This paper introduces adaptive consensus, a spatio-temporal adaptive method to improve convergence behavior of the current consensus fusion schemes. This is achieved by introducing a time adaptive weighting method for updating each sensor data in each iteration. Adaptive consensus method will improve node convergence rate, average convergence rate and the variance of error over the network. A mathematical formulation of the method according to the adaptive filter theory as well as derivation of the time adaptive weights and convergence conditions are presented. The analytical results are verified by simulation as well. ©2006 IEEE  

In this study, two methods for solving economic dispatch problems, namely Hopfield neural network and X iteration method are compared. Three sample of power system with 3, 6 and 20 units have been considered. The time required for CPU, for solving economic dispatch of these two systems has been calculated. It has been shown that for on-line economic dispatch, Hopfield neural network is more efficient and the time required for convergence is considerably smaller compared to classical methods. © 2006 IEEE  

In this paper a three-dimensional steady state incompressible turbulent air flow is considered in a large single room. The buoyancy affected turbulent air flow is simulated by solving governing equations numerically. The turbulence modeling includes both k - ε and zero-equation models and their results are compared to the experimental data. The paper reviews several aspects such as displacement of radiator system performance, temperature and flow field distribution and comfort. The results show that the best temperature distribution and comfort obtain when radiator is installed under the window and its height be equal to or greater than that of the window. Copyright © 2006 by ASME