Sharif Digital Repository

Todays we do not have the traditional hardware speed acceleration anymore. We have reached to the highest possible speed of single core processors. Thus, in order to run an algorithm faster we need either to improve the algorithm and make it more efficient, or to use a more powerful hardware to run it. For algorithms which we have reached to their lower bounds, we can not improve their efficiency. Furthermore, we can not have any faster traditional processor, so the only way is to use the power of parallel computation. With the advent of multicore processors the software industry has faced a new challenge, to adapt the softwares to use the power of these new processors. There are a lot of... 

Laser-assisted machining is nowadays considered as an alternative to conventional machining processes including ceramics grinding, which has provided the basis for extensive experimental and numerical studies in this field. Since the main difference between laser-assisted machining and conventional machining is in the presence of lasers, the main purpose of this study was to investigate the effects of laser on the laser assisted machining process. In this regard, in the first step the process of laser heating to the ceramic workpiece has been studied experimentally and numerically by finite element method. The material used in this research is a slip cast fused silica ceramic. The... 

With the development of technology and growing interest in using high performance and low price products, Wireless Sensor Networks (WSNs) are being dramatically deployed as an emerging technology. The main concern in WSNs is energy consumption that has an effect on sensor’s life time. In order to minimize the energy consumption, Data aggregation, which obtains aggregated values from WSNs, is an important functionality but yet time consuming. On the other hands, Emerging applications of Wireless Sensor Networks (WSNs) such as real-time detection of events need high-rate data collection, which is now an important challenge in WSNs. Multi-channel communication is one of the efficient methods to... 

Estimation of distribution algorithms (EDA) are optimization methods that search the solution space by building and sampling probabilistic models. The linkage tree genetic algorithm (LTGA), which can be considered an estimation of distribution algorithm, uses hierarchical clustering to build a hierarchical linkage model called the linkage tree, and gene-pool optimal mixing algorithm to generate new solutions. While the LTGA performs very well on problems with separable sub-problems, its performance deteriorates on ones with overlapping sub-problems. This thesis presents a comparison of the effect of different pre-constructed models in the LTGA's performance. Several important factors that... 

Multi-camera vehicle tracking is a necessary part of any video-based intelligent transportation systems (ITS) for extracting different traffic parameters such as link travel times and Origin/Destination (O/D) counts efficiently. In many applications it is needed to place traffic cameras disjoint from each other to cover wide areas. In this work we present a system for tracking vehicles in such network of cameras. The proposed system includes new ideas for handling inter-object occlusion as the most challenging part of single camera tracking phase. This approach is based on coding silhouette of moving objects before and after occlusion and separating occluded vehicles by finding longest... 

According to increase of multimedia applications such as video surveillance and environment monitoring in Wireless Multimedia Sensor Networks (WMSN), energy conservation and prolonging network lifetime become increasingly important. Therefore, energy conservation and maximization of system lifetime are commonly recognized as a key challenge in the design and implementation of WMSNs. In these networks, nodes sense the area with high degree of correlation due to the overlapping Field Of Views (FoVs) and causes wasting network energy. We present “overlapped region detection clustering” as a new clustering method to reduce redundant video streams and overcome waste of the energy. We apply scene... 

A finite volume algorithm to assess hydrodynamic aspects of a rigid and up to three degrees of freedom marine structure in the context of transient two-phase flow o viscous incompressible fluids is presented. Different components of the algorithm are selected just after a complete review of all probable choices. Using a collocated arrangement to save data, a fractional step method is applied to satisfy Navier-Stokes and continuity equations, as an appropriate choice in transient flows. Also, a volume fraction transport equation is solved to capture large and complex deformations of the interface between two phases. So, an effective fluid is introduced by combining two immiscible phases in... 

Nowadays, many entities and the relationships between them create different types of networks. Graphs are appropriate tools to model these networks. In a graph, nodes show individuals and edges show the relations between them. One of the most important research problems in the field of network analysis is community detection. In a network, a community is a group of nodes that has a lot of connections to the nodes inside the same group and a few to the ones which are outside. Community detection has many real world applications. Recommending items in recommender systems, detecting spy and terrorist groups and predicting future links between members in a social network are some examples where... 

Permeability is an essential parameter used for reservoir evaluation, simulation and management to optimize oil recovery. The conventional approach to estimate reservoir connectivity, conductivity, sweep efficiency and other critical information for decision-making is to build detailed geological models, which are then upscaled to a coarser grid where flow simulations are run. However, this takes many hours to be carried out even for a single realization practically. In practice, a very small number of realizations are considered and consequently the true uncertainty in the results is very poorly estimated. In this study, a statistical model of isotropic overlying sandbodies is used to... 

The increasing demand for high speed communications has made the optical fiber a favorite choice for different networks ranging from Local Area Networks (LANs) to Wide Area Networks (WANs). In this research we focus on the analysis and design of improved optical communication techniques with a focus on LAN applications.Noting the advantages of Optical Code Division Multiple Access (OCDMA), we have selected this method as the base of data transmission. Different modulation schemes can be implemented in an OCDMA system. Among these, Pulse Position Modulation (PPM) schemes can improve the system performance. We have evaluated Overlapping PPM (OPPM) in an OCDMA system employing Generalized... 

In this thesis, we would consentraite in the topic of irregular overlapped subarrays. In general, it would be a combination of topics overlapped and irregual arrays. In phased array topics, one of the important issues is cost. Main cost of array is consist of its phase shifter cost at all. Duo to the cost of phase shofters, overlapped subarray structure might be used. Philosophy of using overlapped subarrays returned to similar phase required for elements adjust together. But this emphasis is true just in limited field of view fields. But grating lobes could be seen even without beam steering. For solving grating lobes problem, overlapped structured has been presented. In overlapped... 

Statistical parametric speech synthesis (SPSS) has dominated speech synthesis research area over the last decade, due to its remarkable advantages such as high intelligibility and flexibility. Decision tree-clustered context-dependent hidden semi-Markov models are typically used in SPSS to represent probability densities of acoustic features given contextual factors. This research addresses four major limitations of this decision tree-based structure: (a) The decision tree structure lacks adequate context generalization; (b) It is unable to express complex context dependencies; (c) Parameters generated from this structure represent sudden transitions between adjacent states; (e) This... 

The major objectives of this study are to analytically and experimentally investigate the rheological behavior of polymers in the fractured carbonate medium based on the polymer solution properties and operational conditions. The intrinsic and apparent viscosity of high molecular weight-partially hydrolyzed poly (acrylamide) which is mainly used in enhanced oil recovery (EOR) processes hasbeen investigated in reservoir conditions. Since, the EOR efficiency of hydrolyzed poly (acrylamide) is very sensitive to the temperature and salinity of petroleumreservoirs; investigations have been carried out at different possible reservoirtemperatures using high saline polymer solutions. The parameters... 

Obtaining the exact elastic response of composite systems to externally applied stresses is thought to be the most important way for predicting the mechanical behavior and tailoring the properties of composites. Over the past few decades, a variety of analytical models has been developed to investigate different stress transfer mechanisms in fiber composites. Although 2-D analytical model is still highly desired. So in present research a modified analytical model is developed for 2-D elastic stress field distribution in short fiber composites in plain strain for overlapping fibers subjected to an applied axial load . Two sets of exact displacement solutions for the matrix and fiber derived... 

In aerospace applications, the weight of structures is considered as a major performance parameter. One of the most effective ways for weight reduction is then attributed to the structurally continuous manufacturing of mechanical components. In this way, not only the weight, but also the stress concentration, the cost, joints and fasteners applications, and the time of manufacturing are noticeably reduced. With this method, components with complicated shapes could be formed in a single manufacturing step. Special specification of whisker reinforced Metal Matrix Composites (MMC’s) has made these materials very attractive for the aerospace applications.That is why the superplastic forming of... 

Non-overlapping Cameras in multi-camera systems have become prevalent in robotics and computer vision research; therefore, it is possible to cover the wide field of view, and researches have been done for computing extrinsic parameters of cameras. These cameras do not have any overlap in their views, so obtaining the corresponding point in their images is somehow impossible. Light and shadow geometry is analogous to Structure from Motion problem. In this thesis,we study Structure from Motion problem and have tried to propose an approach for estimating extrinsic parameters of non-overlapping cameras in Multi-camera systems. We formulate the problem by using light and shadow geometry and...