Sharif Digital Repository

In this thesis, we considered several types of the visibility problem. These problems include computing the visibility polygon of a point observer inside a polygonal domain, maintaining visibility polygon of a moving point observer, visibility coherence in space, maintaining visibility polygon of a moving segment observer and visibility dependent simplification. Furthermore, we considered these problems in both offline and streaming settings. These problems arise in different practical areas, such as computer graphics, machine vision, robotics, motion planning, geographic information systems (GIS) and computational geometry. We obtained effective theoretical results as well as superior... 

The ever-increasing volume of data and calculations has caused a noticeable increase in the importance of computer processing speed. Therefore, topics related to parallel processing as an effective solution in increasing the speed of calculations have been specially investigated and studied. Systolic computing is a powerful approach to parallelize data and perform concurrent computations. Systolic arrays fulfill the goals of the algorithm by directing data flow among different processors and performing minor calculations on them. The slowness and limitations of processors compatible with these arrays, such as FPGAs, have faced many challenges in applying and using their capacities. These... 

Nowadays the evaluation startups has been difficult and this problem increases the likelihood of misunderstanding price of company's stock. Companies need precise evaluation in different steps of their development. during fund-raising, To make the investors’ share determine, the value of companies should be calculated because the investors’ share equals the ratio of new investment to the value of company after investment. Besides, during the merge or possession of a company, to determine the value of the deal or the share of the dealers, we need to evaluate value of the company. to evaluate the Intrinsic value of company, we need to know potential revenue streams, financial statements, the... 

Telecommunication Company of Iran (TCI), as a government owned company that provides fixed, mobile and Internet services. It is in the process of privatization. In order to be survived in competitive environment, it is required to be an agile and dynamic organization. Also it should be seriously sensitive in profit margin. To be a dynamic company, the management of the company is expecting to introduce a new and modern service named Advanced Communication Services (ACS). This service consists of Video on Demand (VOD), live and archive television programs, tell-learning and e- shopping. For TCI, it's crucial to find a right and precise answer to the challenging question "Will ACS be a... 

The visibility is one of the most important problems in computational geometry. Two points are said to be visible to each other, if the line segment that joins them does not intersect any obstacles. The art gallery problem is a well-studied visibility problem in computational geometry. It originates from a real-world problem of guarding an art gallery with the minimum number of guards who together can observe the whole gallery. In many of applications, the “guards” are “landmarks” deployed in an environment to help provide navigation and localization service to mobile robots. The mobile device communicates with these landmarks through wireless, or other “line-of-sight” signaling... 

With the advancement of technologies such as the Internet of Things the number of devices that are connected to the Internet are increasing rapidly and they continuously generate data that is increasing day by day. Data generation rate in these devices can be so large that practically the existing hardware has not the ability to store and process all information related to that data in appropriate way. In this situation, streaming models become more important. In the stream computing models, online processing of these data are implemented with memory complexity of O(1) . Stream algorithms refers to algorithms that input data is in the form of streams. Data appear and are removed from the... 

The blood supply chain faces substantial challenges due to fluctuations in donation and demand, as well as the perishability of blood products. Consequently, decision makers require an integrated analytical framework to ensure resilient and efficient operations. This study develops a multi-product, bi-objective robust optimization model for designing a blood supply chain capable of withstanding demand variability. From the perspective of blood bank managers, the model simultaneously minimizes operational costs and transportation time while satisfying hospital demand. The decision scope includes locating and configuring permanent and temporary facilities, determining shipment policies, and... 

Finding a path between two specified points is one of the most common problem in computational geometry. The minimum-link path problem is in this category. The minimum-link path between two points is the path between these points with the minimum number of segments. Minimum-link paths have application in areas such as computer graphic, geographic information systems, robotics, image processing, cryptography and VLSI.In this thesis we study variations of the minimum link path problem. Specifically we consider the constrained minimum-link paths in which the path must passes through some given
regions. We detected a flaw in a previously presented algorithm and propose a method to fix this... 

Ising model. It means that the partition function of each lattice model is equal to the partition function of 2D Ising model. This completeness is proved by using concepts and techniques from quantum information theory and is based on the universality of cluster states. We have now proved this important result, by using independent and general concepts and methods which are accessible to a wide audience of researchers across many disciplines. Furthermore, our method has the advantage of eing algorithmic in nature so that, by following a set of simple graphical transformations, one is able to transform any discrete lattice model to an Ising model defined on a (polynomially) larger 2D... 

Structural efficiency is a primary concern in today’s aerospace and aircraft industries. This brings about the need for strong and light weight structures. To increase the strength of a panel without considerable increase in its weight, we may use a lattice of stiffeners which may have shells connected to one side of the lattice or both sides of it. These structures are usually called grid stiffened structures. Aircraft fuselage and launch vehicle fuel tanks are some of the many applications of these structures in aerospace and aircraft industries. These structures include two major groups; isogrids (grid stiffened structures with equivalent isotropic properties) and orthogrids (grid... 

With the advancement of technology, the volume of network traffic has also increased dramatically. The optical network, as the main part of the backbone communication system, plays a significant role in the transmission of network traffic. Due to the limited network resources, an efficient resource allocation in optical networks is required to increase network performance and reduce costs. To solve resource allocation optimization problems, an effective tool is needed to provide a suitable solution in a reasonable time. Resource allocation problems are usually developed on a graph, which is derived from network topology or other properties of the network. As a result, graph-based tools seem to... 

Membrane bioreactor (MBR) is a combination of conventional activated sludge (CAS) and membrane filtration which owing to its advantages such as high quality effluent and low excess sludge production, has gained increasing application in wastewater treatment. The major drawback of a MBR is the membrane fouling that reduces the permeate flux, which in turn increases the overall operational costs due to high energy requirements. In existing study, the combination of sludge oxidation and coagulation/flocculation addition was investigated for mitigation of membrane fouling in a membrane bioreactor. Oxidation can facilitate sludge flocculation and hence improve the properties of mixed liquor. The... 

Dead Reckoning navigation, as an infrastructure-independent approach, plays a key role in scenarios where access to the Global Navigation Satellite System (GNSS) is unavailable; however, its performance is consistently affected by the accumulation of errors in inertial measurement unit (IMU) sensors. In this research, a novel approach is proposed to enhance the accuracy of this method. In the first stage, sensor noise modeling is performed using three innovative approaches. The first approach involves a static tuning based on an adaptive Extended Kalman Filter (AEKF). In this method, the discrete process noise covariance matrix is adaptively estimated, and the continuous-time process noise... 

To provide a safe environment for space equipments and infrastructures in addition to managing the role of hazardous objects that are known as space debris, the presented thesis describes a new robust technique to estimate the dynamic states and inertial parameters of Uncooperative Space Objects (USO) with uncertain dynamics in the cluttered orbits. The prescribed method is especially effective to capture stray objects, capture and servicing of the satellites, rendezvous and collision avoidance maneuvers, space explorations as well as Actrive Debris Removal (ADR) missions. Such missions call for high degree of precision and reliable estimation methods. The proposed estimation architecture... 

Pipe freezing has become well established in industry as a method of short-termisolation in order to carry out maintenance or repairs. It is often necessary to repair system components without plant shutdown or drainage of system having many piping structures which may have hazardous or expensive fluid. Therefore, a series of tests has been arranged to investigate the ice plug formation in two standard pipes with different diameter size. The freeze zone on the pipe has been created by means of an aluminum jacket which liquid nitrogen flows in it. In the tests the freezing time, amount of liquid nitrogen usage andthe pressure tolerance of ice plug have been determined. Moreover, the numerical... 

In recent years, the area of research on micro flying robots has been developed due to the development in micro manufacturing technologies. Due to extra advantages of these flying robots, they are implemented in military and civilian missions such as identifying, espionage, aerial relays, traffic surveillance, rescue, aid, etc. Ability to fly in specified areas, without human injuries, low manufacturing and energy costs, easy and fast implementation, Easy Maintenance, etc, which are some advantages of these robots. We can control these robots manually by remote controllers (RC) or by Auto guidance systems. On the other hand, these robots are used in research laboratories for testing new... 

Range Profile (RP) is known as one of the most important tools for radar target recognition. The main problem with range profile for radar target recognition is its sensitivity to aspect angle. To overcome this problem, range profiles are assumed to have the same statistical characteristics in small frames of aspect angles or context dependent models such as HMM may be used. All methods presented, seems to have some shortcomings to offer a model based on physical circumstances of target maneuver. For example in such models, consecutive samples of RPs in an aspect frame are assumed to be statistically independent with the same distribution (IID). Here we propose dynamic system (DS) for... 

The present thesis aims at investigating the dynamic interaction of slosh and aeroelasticity in the fuel contained aero vehicles. The main approach in this research is to develop reduced order models for description of the coupled system. In this regard, boundary element method is used to develop slosh dynamic model. Axisymmetric boundary element method with non-symmetric boundary conditions is used to develop slosh dynamic model for axisymmetric containers. Zoning method is used to develop slosh dynamic model for the multi-baffled tanks and based on it, slosh equivalent mechanical model is developed for multi-baffled tanks. Finite element method along with modal technique is used to develop... 

There are numerous ways available to achieve low temperatures that cryocoolers might be among the most important of them. In the meantime, the pulse tube refrigerator has a special place due to its simple geometry and not be using any moving parts. This simple property make the pulse tube refrigerator one of the most popular methods to achieve low temperatures. Nowadays, a pulse tube refrigerator is used for cooling in the range of 4 to 123 Kelvin in two form of one-stage and two-stage and up to an approximate power of 1 KW. Today, due to the temperature and the amount of power required for cooling, as well as the time it takes to reach that temperature, this chiller is used in medical,...