Sharif Digital Repository

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 presents a recursive approach for solving kinematic and dynamic problems in snake-like robots using Kane's equations. An n-link model with n-nonholonomic constraints is used as the snake robot model in our analysis. The proposed algorithm which is used to derive kinematic and dynamic equations recursively, enhances the computational efficiency of our analysis. Using this method we can determine the number of additions and multiplications as a function of n. The proposed method is compared with the Lagrange and Newton-Euler's method in three different aspects: Number of operations, CPU time and error in the computational procedures. © 2006 Cambridge University Press  

A parallel manipulator is a closed loop mechanism in which a moving platform is connected to the base by at least two serial kinematic chains. The main problem engaged in these mechanisms, is their restricted working space as a result of singularities. In order to tackle these problems, many methods have been introduced by scholars. However, most of the mentioned methods are too much time consuming and need a great amount of computations. They also in most cases do not provide a good insight to the existence of singularity for the designer. In this paper a novel approach is introduced and utilized to identify singularities in parallel manipulators. By applying the new method, one could get a... 

This paper proposed a new curvature based path-description method for path-generation of planar mechanism, in which the position vector of a point on coupler, which follows most closely a predefined path, is directly calculated as a function of coupler motion properties. In addition this curvature based method makes it possible to define an objective function independent of rotation and translation transformations. Therefore, in this method, initial position, orientation, and coupler point vector parameters are not the optimization variable. These five parameters could be calculated as a function of other design parameters and they are found when these optimal values are obtained. Reducing... 

In this paper, AC Optimal Power Flow combined with UPFC has been used to manage the congestion of transmission lines in a restructured power system with pool market model. The modeling of Unified Power Flow Controller (UPFC) has been adopted based on bipolar model and power injection method. To determine an appropriate location for UPFC as well as to set its parameters, an approach based on genetic algorithm has been suggested. The modified IEEE 14-bus system is used to determine the effectiveness and applicability of the proposed method and results are discussed. ©2006 IEEE  

This paper presents a feature-based license plate localization algorithm that copes with multi-object problem in different image capturing conditions. The proposed algorithm is robust against illumination, shadow, scale, rotation, and weather condition. It extracts license plate candidates using edge statistics and morphological operations and removes the incorrect candidates according to the determined features of license plates. We have formed a rather complete database of 269 images in different conditions. The proposed algorithm successfully detecteds the accurate location of the license plates in 96.5% cases, which outperforms the other available approaches in the literature. © 2006... 

Transit assignment is an important problem in the literature of transportation. Almost all competitive algorithms in this area are strategy based. For uncongested transit networks, the problem may be formulated into an optimization problem for which good solution algorithms exist. A variational inequality formulation of the problem with several solution methods is also presented in the literature for congested networks. This paper is devoted to solving a transit assignment problem based on complementarity formulation using path flows. The solution algorithm exploits the three concepts of decomposition, path generation, and linearization. The procedure has been applied on a large-scale... 

A new reduced-order modeling approach is presented. This approach is based on fluid eigenmodes and without using the static correction. The vortex lattice method is used to analyze unsteady flows over two-dimensional airfoils and three-dimensional wings. Eigenanalysis and reduced-order modeling are performed using a conventional method with and without the static correction technique. In addition to the conventional method, eigenanalysis and reduced-order modeling are also performed using the new proposed method, that is, without static correction requirement. Numerical examples are presented to demonstrate the accuracy and computational efficiency of the proposed method. Based on the... 

An analytical procedure for supersonic flutter analysis of two-dimensional panels was developed using unsteady potential flow aerodynamic theory. The local spatial influence was considered as an integral over the plate area. The U-g method was used for flutter prediction. Results indicate a stabilizing effect of the unsteady potential flow aerodynamics theory compared to the quasi-steady first-order piston theory  

The method of unity bond index-quadratic exponential potential (UBI-QEP) and the computer simulation of the temperature programmed desorption (TPD) patterns are employed to derive the kinetic and thermodynamic parameters associated with the steps of the pathway we propose for the catalytic decomposition of methyl iodide on the Cu(111) surface. Assuming a highly reactive `hot methyl' surface intermediate and on the basis of our calculations it is concluded that the desorption of a part of this species is responsible for the reported methyl radical TPD peak at 140 K, while a part of this surface species is trapped in the three-fold sites of the Cu(111) surface and desorbs to form the reported... 

Quantum dots cellular automata is a new computing method in the nanotechnology that has considerable features such as low power, small dimension and high speed switch. A QCA device stores logic based on the position of individual electrons. The fundamental logic elements in QCA are the majority (Fig.1 (a)) and inverter gates (Fig.1 (b)) that operate based on the Coulomb repulsion between electrons [1]  

Almost all of the existing domain adaptation methods assume that all test data belong to a single stationary target distribution. However, in many real world applications, data arrive sequentially and the data distribution is continuously evolving. In this paper, we tackle the problem of adaptation to a continuously evolving target domain that has been recently introduced. We assume that the available data for the source domain are labeled but the examples of the target domain can be unlabeled and arrive sequentially. Moreover, the distribution of the target domain can evolve continuously over time. We propose the Evolving Domain Adaptation (EDA) method that first finds a new feature space... 

Optical computing has emerged as a promising candidate for real-time and parallel continuous data processing. Motivated by recent progresses in metamaterial-based analog computing [Science 343, 160 (2014)], we theoretically investigate the realization of two-dimensional complex mathematical operations using rotated configurations, recently reported in [Opt. Lett. 39, 1278 (2014)]. Breaking the reflection symmetry, such configurations could realize both even and odd Green's functions associated with spatial operators. Based on such an appealing theory and by using the Brewster effect, we demonstrate realization of a firstorder differentiator. Such an efficient wave-based computation method... 

The Minimum Maximum Outdegree Problem (MMO) is to assign a direction to every edge in an input undirected, edge-weighted graph so that the maximum weighted outdegree taken over all vertices becomes as small as possible. In this paper, we introduce a new variant of MMO called the p-Split Minimum Maximum Outdegree Problem (p-Split-MMO) in which one is allowed to perform a sequence of p split operations on the vertices before orienting the edges, for some specified non-negative integer p, and study its computational complexity. © 2020 Elsevier B.V  

Nowadays the Internet users are from different ages and groups. The disabled people also use the Internet. Some websites are especially created for disabled people. Many Internet sites offers services for human users, but unfortunately some computer programs are designed to abuse these services. To solve this problem, some systems named CAPTCHA (Completely Automated Public Turing test to tell Computers and Human Apart) have been introduced to distinguish between human users and computer programs. CAPTCHA methods are mainly based on the weaknesses of OCR systems while using them is undesirable for human users, especially for disabled people. Therefore some CAPTCHA methods are designed... 

We aim to propose a novel fiber Raman amplifier modeling based on the moment method, which is previously introduced for modeling the inhomogeneous Erbium doped fiber amplifiers and recently employed to analyze the fiber Raman amplifier with continuous pump spectrum. In this model, the number of governing equations is independent of the number of signals and according to the degree of accuracy it is proportional to the number of pumps. This method is employed to analyze the Raman fiber amplifiers with an arbitrary input signal line shape and to minimize the gain ripple of the fiber Raman amplifier with respect to the pump powers and pump frequencies. © 2008 Elsevier B.V. All rights reserved  

In recent years by growing computer applications, new technologies are also invented. Meanwhile new issues are faced such as security. One of the security areas is hidden exchange of information which contains methods such as cryptography and steganography. Steganography is the art of hiding data in a cover media such as image or sound. In this paper a new method for Steganography in Persian and Arabic texts is presented. In this method pseudo-space character is used for hiding the data. This character prevents the Persian and Arabic letters from joining but without adding a space between the two and keeps the words closer together. Its code is 200C in Unicode hex notation. This character... 

In this work, hydrodynamic effects of multiple squared cross-section cold jets inclined normally into a hot cross flow were computationally simulated using large eddy simulation (LES) approach. The finite volume method and the SIMPLE algorithm on a multi-block non-uniform staggered grid were applied. The jet into cross flow velocity ratio and the jet Reynolds number were 0.5 and 4,700, respectively. Simulations were performed for three different jets into cross flow temperature ratios, namely, 2, 1, and 0.5, corresponding to density ratios of 0.5, 1, and 2. The experimental and numerical results of Ajersch et al. (J. Turbomachinery 119(2), 330-342, 1997) at unit density ratio were used for...