Sharif Digital Repository

In this article the interaction of branes at angles with respect to each other with non-zero internal gauge fields are calculated by construction of the boundary states in spacetime in which some of its directions are compact on tori. The interaction depends on both angle and fields. (C) 2000 Elsevier Science B.V  

A two-dimensional Boussinesq-type model is presented accurate to O(μ)6 , μ = h0/l0, in dispersion and all consequential order for non-linearity with arbitrary bottom boundary, where h0 is the water depth and l0 is the characteristic wave length. The mathematical formulation is an extension of (4,4) the Padé approximant to include varying bottom boundary in two horizontal dimensions. A higher order perturbation method is used for mathematical derivation of the presented model. A two horizontal dimension numerical model is developed based on derived equations using the Finite Difference Method in higher-order scheme for time and space. The numerical wave model is verified successfully in... 

In the current research, a comprehensive analytical technique is presented to evaluate the non-Fourier thermal behavior of a 3-D hollow sphere subjected to arbitrarily-chosen space and time dependent boundary conditions. The transient hyperbolic thermal diffusion equation is driven based upon the Cattaneo-Vernotte (C-V) model and nondimensionalized using proper dimensionless parameters. The conventional procedure of separation of variables is applied for solving the 3-D hyperbolic heat conduction equation with general boundary conditions. In order to handle the time dependency of the boundary conditions, Duhamel's theorem is employed. Furthermore, for the purpose of demonstrating the... 

In this paper, we consider the problem of computing the visibility polygon (VP) of a query point q (or VP(q)) in a scene consisting of some obstacles with total complexity of n. We show that the combinatorial representation of VP(q) can be computed in logarithmic time by preprocessing the scene in O( n4logn) time and using O( n4) space. We can also report the actual VP(q) in additional O(|VP(q)|) time. As a main result of this paper, we will prove that we can have a tradeoff between the query time and the preprocessing time/space. In other words, we will show that using O(m) space, we can obtain O( n2log(m/n)/m) query time, where m is a parameter satisfying n2≤m≤ n4. For example, when m= n3,... 

In this paper, harmonic sources in a BDFM are studied, and a method for specifying rotor and stator space harmonic components is established. A criterion for evaluating different rotor designs is introduced, based on space harmonics. Then the equivalent space and time harmonic circuits are obtained, using basic equivalent circuit. Finally, the effects of these harmonics on the torque-speed characteristic are studied  

Brushless Doubly fed machines have two stator windings and an especial cage rotor. The main advantage of the machine is higher reliability in compare with DFIGs. Cross coupling is the mechanism, which provides indirect coupling of the two stator windings. In this paper, time and space harmonics in a BDFM are studied to find a criterion for evaluating different rotor designs and better cross coupling, based on the space harmonics. Then the equivalent space and time harmonic circuits are established, using basic equivalent circuit. Finally, the effects of these harmonics on the torque-speed characteristic are studied  

Technical evolution of location technologies has augmented the development and growth of location-based services. With widespread adoption of these services, threats to location privacy are increasing, entailing more robust and sophisticated solutions. This paper proposes an intuitive obfuscation-based scheme, which uses vagueness in human perception of nearness to provide a flexible and robust location privacy scheme. Key to this work is the concept of vagueness degree, which aims to enhance its robustness against privacy attacks. Furthermore, our scheme is totally in line with human perception of privacy and provides a solution, which mostly suits proximity-based services, social... 

Due to the unprecedented speed and volume of generated raw data in most of applications, data stream mining has attracted a lot of attention recently. Methods for solving these problems should address challenges in this area such as infinite length, concept-drift, recurring concepts, and concept-evolution. Moreover, due to the speedy intrinsic of data streams, the time and space complexity of the methods are extremely important. This paper proposes a novel method based on multiple-kernels for classifying non-stationary data streams, which addresses the mentioned challenges with special attention to the space complexity. By learning multiple kernels and specifying the boundaries of classes in... 

Computing the visibility polygon, VP, of a point in a polygonal scene, is a classical problem that has been studied extensively. In this paper, we consider the problem of computing VP for any query point efficiently, with some additional preprocessing phase. The scene consists of a set of obstacles, of total complexity O(n). We show for a query point q, VP(q) can be computed in logarithmic time using O(n 4) space and O(n 4 logn) preprocessing time. Furthermore to decrease space usage and preprocessing time, we make a tradeoff between space usage and query time; so by spending O(m) space, we can achieve O(n 2 log √ m/n)/√ m)query time, where n 2≤m≤n 4. These results are also applied to... 

A general method for deriving electromagnetic particle in cell (EMPIC) algorithms has been given by Eastwood [Comput. Phys. Commun. 64, 252 (1991)]. This method devises variation of the action-integral to find discrete governing equations. The most important advantage of this method is automatic inclusion of the time coordinate via the action integral into the computational domain. This inclusion is inevitable because electromagnetic algorithms are based on time evolution of the system from its initial state. The drawback of this method is that it is rather abstract. This causes obscurity of particle-mesh interactions and makes it hard to analyze physical treatments of the computational... 

In this paper, the Nonlinear Normal Modes (NNMs) analysis for the case of three-to-one (3:1) internal resonance of a slender simply supported beam in presence of compressive axial load resting on a nonlinear elastic foundation is studied. Using the Euler- Bernoulli beam model, the governing nonlinear PDE of the beam's transverse vibration and also its associated boundary conditions are extracted. These nonlinear motion equation and boundary condition relations are solved simultaneously using four different approximate-analytical solution techniques, namely the method of Multiple Time Scales, the method of Normal Forms, the method of Shaw and Pierre, and the method of King and Vakakis. The... 

In this investigation, a reactor model for prediction of the deactivation behavior of MTO's porous catalyst in a fixed bed reactor is developed. Effect of coking on molecular transport in the porous structure of SAPO-34 has been simulated using the percolation theory. Thermal effects of the reaction were considered in the model and the temperature profile of the gas stream in the reactor was predicted. The predicted loss in catalyst activity with time-on-stream was in very good agreement with the experimental data. The resulting coke deposition and gas temperature profiles along the length of reactor suggested a reaction front moving toward the outlet of the fixed bed reactor at the... 

This paper presents how can teach complicated problems in electrical engineering subjects (electrical machines) by using simulators such as MATLAB/SIMULINK. Simulation of direct vector control of induction machine (IM) drive on the rotor flux direction with composite model flux observer can improve electrical machine teaching-learning procedure for graduated and under graduated levels. In the indirect vector control of IM, current reference values are used for estimation angle of the rotor flux space vector (ARFSV), however using current reference values instead of current real values can decrease accuracy of ARFSV. In the direct vector control, current real values (current feedback)... 

Mathematical simulation of non-isothermal multiphase flow in deformable unsaturated porous media is a complicated issue because of the need to employ multiple partial differential equations, the need to take into account mass and energy transfer between phases and because of the non-linear nature of the governing partial differential equations. In this paper, an analytical solution for analyzing a fully coupled problem is presented for the one-dimensional case where the coefficients of the system of equations are assumed to be constant for the entire domain. A major issue is the non-linearity of the governing equations, which is not considered in the analytical solution. In order to... 

The aim of this study is to develop iterative regularization algorithms based on parameter and function estimation techniques to solve two-dimensional/axisymmetric transient inverse heat conduction problems in curvilinear coordinate system. The multiblock method is used for geometric decomposition of the physical domain into regions with patched-overlapped interface grids. The central finite-difference version of the alternating-direction implicit technique together with structured body-fitted grids is implemented for numerical solution of the direct problem and other partial differential equations derived by inverse analysis. The approach of estimating unknown parameters and functions is...