Sharif Digital Repository

Given a simple polygon P in the plane, we present a parallel algorithm for computing the visibility polygon of an observer point q inside P. We use chain visibility concept and a bottom-up merge method for constructing the visibility polygon of point q. The algorithm is simple and mainly designed for GPU architectures, where it runs in O(logn) time using O(n) processors. This is the first work on designing a GPU-based parallel algorithm for the visibility problem. To the best of our knowledge, the presented algorithm is also the first suboptimal parallel algorithm for the visibility problem that can be implemented on existing parallel architectures. We evaluated a sample implementation of... 

Abstract: In 1973 E.W. Dijkstra introduced the notion of self-stabilization in the context of mutual exclusion. Considering the same problem on an array, we present a game theoretic analysis of self-stabilizing systems with three- or four-state machines. We give a formalized definition of the problem as a game where each player’s strategy represents the state of its corresponding machine. For the three-state case, we prove the impossibility of any infinite self-stabilizing systems on an array. For the four-state case we consider two algorithms. For Ghosh’s solution [1] we prove the upper bound of (n – 1)(n – 3) steps and that this bound is tight. Also we present another four-state... 

This paper presents a novel approach for detection and recognition of multi-view faces whose location is unknown and the illumination conditions are varying. The detection of faces is accomplished after canceling the effect of the various illumination conditions by using a proposed filter. Because of the independency of the approach to skin color of face, the persons with every kind of skin colors are detected even in completely dark environments. Next, the detected faces are recognized. It is a well known technique to combine the feature based methods with the template based methods in face recognition. Our experiments show that we can combine some proposed aspects of the feature based... 

This paper presents a novel approach for detection and recognition of multi-view faces whose location is unknown and the illumination conditions are varying. The illumination is a big problem in the face detection and recognition aspects. Two completely different methods are proposed for face detection in this paper. Our proposed methods do not use the skin colour information for face detection. The detection of faces is accomplished after cancelling the effect of the various illumination conditions. Because of the independency of the approaches to the face's skin colour, persons with every kind of skin colours are detected even in completely dark environments. Next, the detected faces are... 

This paper presents a novel approach for detection and recognition of multi-view faces whose size and location is unknown and the illumination conditions are varying. The illumination is a big problem in face detection and recognition. In this paper, a new pre-processing method is proposed in order to cancel the effect of various illumination conditions on a face. Then, a binary face is obtained that its pixels are 0 or 1. Next, a fuzzy face model is produced from the distribution of zeros in the binary face. The model is used in order to detect faces in images by using a fuzzy approach. Because of the independency of the detection method to the skin color of face, persons with every kind of... 

Electrochemical activity of TiO2 nanotube arrays (NTAs) is restricted by a wide band gap of TiO2. To overcome this restriction, we considered systematic research on two effective methods of doping of TiO2 NTAs such as the N-doping and electrochemical reductive doping and predicting the proper application of them. Band gap narrowing was occurred from 3.16 eV for undoped TiO2 NTAs to 2.9 and 2.7 eV at N-doped and self-doped TiO2 ones respectively. The electrochemical responses of the TiO2 NTAs before and after doping were examined by cyclic Voltammetry (CV) curve. To understand the electrochemical behavior of the undoped and doped TiO2 NTAs, electrochemical impedance spectroscopy (EIS) was... 

Although morphological disorder of nanotube structure is further down than the nanoparticular electrode, its density of traps are the hindering effects in the charge transport. In this study, crack-free TiO2 nanotube membranes, which obtained through a re-anodizing process, are fixed on transparent fluorine–tin-oxide glass by applying a few drops of Titanium Isopropoxide without needing the TiO2 powder paste. Front-side illuminated dye sensitized solar cells fabricated by undoped, N-doped and blue TiO2 nanotube membranes are investigated. The electrical characteristics of TiO2 nanotube based dye sensitized solar cells are followed by theoretical analysis using simple one-diode model....