Sharif Digital Repository

Arvand is the name of robots specially designed and con-structed by sharif CE team for playing soccer according to RoboCup rules and regulations for the middle size robots. Two different types of robots are made, players and the goal keeper. A player robot consists of three main parts: mechanics (motion mechanism and kicker), hard-ware (image acquisition, processing unit and control unit) and software (image processing, wireless communication, motion control and decision making). The motion mechanism is based on two drive unit, two steer units and a castor wheel. We designed a special control board which uses two microcontrollers to carry out the software system decisions and transfers them... 

A comprehensive model for pervaporation in thin membrane channels was developed to study the effect of changing temperature and concentration on mass flux. This model consists of momentum, energy and species mass balances along and across the membrane in the flow channel. A computational fluid dynamics (CFD) code was written in C++ programming language to solve the coupled non-linear transport equations in the channel by finite volume method. The Semi-Implicit Pressure Link Equation (SIMPLE) CFD algorithm is used to modify the dependent variables in each of the iterations. The effect of variation of temperature and concentration on transport and thermodynamic properties were considered by... 

Partially adaptive routing algorithms are a useful category of routing algorithms due to their simple router logic and restricted adaptivity in selecting the next output channel towards the destination. Several partially adaptive routing algorithms on mesh and hypercube networks have been presented in the literature. But there is no study on evaluating the performance of these algorithms. This paper tries to compare the most important partially adaptive routing algorithms on the mesh and hypercube networks as the most popular topologies for multicomputers. The evaluation has been performed by the use of event driven simulator coded by C++ compiler. © 2006 IEEE  

Given a set of n segments and a query shape Q, the windowing length query asks for finding the sum of the lengths of the parts of the segments that lie inside Q. The popular places problem of a set of curves asks for the subset of the plane where each query shape centered at a point of that region intersects with at least f distinct curves. For square queries, an optimal O(n2) time algorithm and a matching lower bound exist. We solve the length query problem for convex polygons and disks as query shapes, with O(log n+ k) query time and polynomial preprocessing time that depends on the complexity of the query shape. We define a new version of the problem of finding popular places in a set of... 

Given a set of n segments and a query shape Q, the windowing length query asks for finding the sum of the lengths of the parts of the segments that lie inside Q. The popular places problem of a set of curves asks for the subset of the plane where each query shape centered at a point of that region intersects with at least f distinct curves. For square queries, an optimal O(n2) time algorithm and a matching lower bound exist. We solve the length query problem for convex polygons and disks as query shapes, with O(log n+ k) query time and polynomial preprocessing time that depends on the complexity of the query shape. We define a new version of the problem of finding popular places in a set of... 

In the present work, co-sintering of various powder injection molding (PIM) feedstocks including iron, low-alloy steels, high-alloy steels, and hardmetals was investigated. Dilatometric analysis was used to evaluate the sintering behaviour of co-injection moulded feedstocks after debinding. An approach based on the data of dimensional change versus time and temperature was proposed to determine the compatibility of two materials system for the two component powder injection molding (2C-PIM) process. The similarity of sintering behaviour of the twobody parts produced by 2C-PIM was quantified trough definition of a parameter termed as Apparent Co-Sintering Index (ACSI). The results determined... 

Progressive conversion/shrinking core (PC-SC) models of constant-size cylinders were exploited to interpret the decarburization reactions of MgO-C-Si bricks heated up under blown air. Chemical adsorption/solid (or pore) diffusion mechanisms governed the reaction rate. With 5% silicon, chemical adsorption vanished at 1000 and 1100°C. The oxidation rate lowered then with temperature. This was due apparently to the blocking of the pore-end gorges by the voluminous compounds (like Forstrite). Arrhenius plots of the specific rates yielded the activation energies of the prevailing steps. Without Si antioxidant, three steps were appreciated having activation energies of 51.65 (for chemical... 

To solve neutron transport equation in multigroup approach, in addition to weighting function and number of energy groups, proper selection of the group boundaries have high importance for the accuracy of the calculations. In the current paper, the bilinear combination of forward and adjoint neutron spectra is used for the optimization of 69 energy group structure of WIMSD5 lattice physics code. To remedy the energy self-shielding effect, homogeneous adjoint and forward BN equations on an ultrafine energy group structure have been solved to obtain the ultrafine forward and adjoint spectra. The coarse group intervals are selected to have equal values of bilinear function in each... 

This paper presents analysis of electric field distribution and optimization of C-type corona rings for 400 kV V-insulator strings composed of ceramic insulator units which are the most common configuration of overhead transmission lines. These strings are equipped with corona rings to enhance the insulation performance regarding to the effect of these rings on the insulation function and potential and electric field distribution. 3D field simulations are performed for the C-type of corona rings with different dimensions by software based on FEM analysis  

Given a set of n segments and a query shape Q, the windowing length query asks for finding the sum of the lengths of the parts of the segments that lie inside Q. The popular places problem of a set of curves asks for the subset of the plane where each query shape centered at a point of that region intersects with at least f distinct curves. For square queries, an optimal O(n2) time algorithm and a matching lower bound exist. We solve the length query problem for convex polygons and disks as query shapes, with O(log n+ k) query time and polynomial preprocessing time that depends on the complexity of the query shape. We define a new version of the problem of finding popular places in a set of... 

The k-means is the most popular clustering algorithm, but, as it needs too many distance computations, its speed is dramatically fall down against high-dimensional data. Although, there are some quite fast variants proposed in literature, but, there is still much room for improvement against high-dimensional large-scale datasets. What proposed here, k-means-g*, is based on a simple geometric concept. For four distinct points, if distance between all pairs except one pair are known, then, a lower bound can be determined for the unknown distance. Utilizing this technique in the assignment step of the k-means, many high-dimensional distance computations can be easily ignored, where small amount... 

The effect of pressure has been studied on structural and electronic properties of LaOFeAs high-T c superconductor by ab initio density functional theory by using pseudopotential Quantum Espresso code. The lattice parameters and ionic positions in the ambient pressure and some high pressure up to 20 GPa have been calculated. The obtained data versus the simple scaling relation for the ionic positions and distances for mechanical pressures have been discussed. The results of band structure and magnetic moment calculations of this compound versus the applied pressure are presented in this paper. The results are compared with the other experimental and computational data in the literature  

The bonding temperature is an important parameter for optimization of the Transient Liquid Phase (TLP) bonding process in order to achieve a sound joint with good mechanical properties. However, the bonding temperature used can also be restricted by the microstructural stability of the base metal. In this study, the effect of bonding temperature (1050-1200 °C) on the joint microstructure and mechanical properties was studied for TLP bonding of FSX-414 superalloy using MBF-80 interlayer with thickness of 50 μm. Increasing bonding temperature from 1050 to 1150 °C caused reduction in the time required for complete isothermal solidification in agreement with models based on the diffusion induced... 

This article describes a study on WC-10Co cemented carbides with different percent of grain growth inhibitors. Samples were prepared by the conventional powder metallurgy method, using WC and Co powder and different concentrations of VC and (Ta, Nb)C powder. All samples were processed using a hot isostatic press (HIP) and the effect of grain growth inhibitors on the microstructure and mechanical properties were investigated. Additionally, microstructure and powder particle morphology were examined using scanning electron microscopy (SEM) and electron dispersive spectroscopy (EDS). The specimen's microstructure proved that the addition of VC is more effective at suppressing grain growth than... 

This paper deals with the collision-free path planning of planar parallel robot by avoiding mechanical interferences and obstacle within the workspace. For this purpose, an Artificial Potential Field approach is developed. As the main contribution of this paper, In order to circumvent the local minima problem of the potential fields, a novel approach is proposed which is a combination of Potential Field approach, Fuzzy Logic and also a novel algorithm consisting of Following Obstacle as well as Virtual Obstacle methods, as a hybrid method. Moreover, the inverse kinematic problem of the 3-RRR parallel robot is analyzed and then the aforementioned hybrid method is applied to this mechanism in... 

Permeability of porous materials is an important characteristic which is extensively used in various engineering disciplines. There are a number of issues that influence the permeability coefficient among which the porosity, size of particles, pore shape, tortuosity, and particle size distribution are of great importance. In this paper a C++ GPU code based on three-dimensional lattice Boltzmann method (LBM) has been developed and used for investigating the effects of the above mentioned factors on the permeability coefficient of granular materials. Multirelaxation time collision scheme of the LBM equations is used in the simulator, which is capable of modeling the exact position of the... 

This paper presents the theoretical introduction and experimental validation of the "Class-J2 Mode Power Amplifier," which provides higher efficiency and output power compared with conventional class-J mode counterpart. This mode of operation is realized by injection of the second-harmonic current to drain node of a class-J power amplifier (PA) to reduce the 45° phase shift between drain current and voltage signals. Similar to class-J PAs, the second-harmonic impedance of class-J2 PAs is purely reactive to simplify the design of the output matching network. The auxiliary second-harmonic injection circuit comprises a transistor biased in class-B mode followed by a class-C biased amplifier to...