Sharif Digital Repository

Direct metal deposition (DMD) process is an additive manufacturing technology that is rapidly gaining laser importance due to its various capabilities in applications such as coating, repairing high-value damaged parts, rapid prototyping and even production in small quantities. Among the equipment needed for this process, nozzle is perhaps the most important component because its performance affect the efficiency of powders trapped in the molten pool, and is crucial to the quality of the deposited layer. The existing nozzle designs can be categorized in two groups; lateral and coaxial nozzles; and the coaxial ones are divided into continuous and discontinuous types. Coaxial nozzles have... 

The main purpose of this thesis is to propose effective meta-heuristic algorithms for solving the scheduling problems. We consider the problems that are associated with two areas: project scheduling and shop scheduling. In project scheduling area, only the resource constrained project scheduling problem (RCPSP) is considered. For solving this problem, a hybrid particle swarm optimization (PSO) algorithm is developed. The proposed algorithm outperforms other existing PSO algorithms for the problem. However, most of the contributions of this thesis are related to the second area. The shop scheduling problems of concern include: job shop, stage shop and partial job shop. We developed two... 

This project focuses on the design of fuel drop tanks for airplanes that add minimal drag and positive lift to the flying object. This will obviously effect the stability and dynamic performance of the airplane. To reduce adverse dynamic effects the tank was divided to several segment with a special emptying sequence. The add-on tank has to have no interference with the object existing systems and require minimum structural changes in the object. Several designs were proposed and the one gaining highest marks was selected. The flow field and the dynamic behavior of combined vehicle and drop tanks were studied using FE simulations. The result shows that adding a drop tank with optimized... 

Free and Open-Source Software (FOSS) is grown rapidly and many researches are conducted to study FOSS developments. The studies aim to help FOSS development by finding bugs, analyzing developers, modeling evolution of software and categorizing them. Finding proper developers or key developers of each group is essential in developing software, recommend developers and assigning bugs to proper developers. Community detection detects groups of nodes having dense connections. The groups represent developers which cooperate closely on developing FOSS. The thesis proposes a method based on evolutionary algorithms and topological analysis to detect communities in open-source software development... 

Complex networks have recently become a very noticeable subject because of their remarkable theory on real networks such as rumor spreading. This thesis contributes to a prevention strategy which uses a maximal clique algorithm to find overlapping communities and also uses inverse targeting immunization strategy to immune these communities. By the using maximal clique algorithm combined with inverse targeting strategy we have achieved that the TIK method (targeted immunization using k-clique percolation) obtains 10% of better immunization than HD (highest degree) method which is one of the best methods in targeted immunization strategies. The TIK also demonstrates that rumor spreading is... 

Open source software development is growing rapidly according to request of market. Different types of analysis have done on open source development networks to extract knowledge and help both developers and users to decide better. In this thesis, we try to extract data from one of the biggest open source development repositories GitHub and then a community detection algorithm will apply on these data for different time stamps. Then we propose an evolution tracking model and implement it to detect evolution of communities from 2013 until 2015. Then communities size evolution and changes in communities such as growth, dissolve, merge, split and formation will be discussed. After that we... 

Researching in the field of optimization of network immunizing and epidemic spreading is an active and important area. According to literature review, influential nodes are detected based on global graph metrics such as centrality measures. On the other hand, when a network infrastructure is not available and a direct or straight path between source and destination may not be accessible, one can use opportunistic networks routing protocols in Delay Tolerant Networks to recognize influential users is an appropriate approach. In this work, we use a real world three layer dataset which consists of digital data (social relations and Bluetooth contact traces) of individuals. We convert the real... 

In healthcare field to reduce costs, high availability, increasing reliability, access to data from multiple locations and manage distributed information between centers, doctors and patients; there is a certain need to a distributed system and cloud services are a good option to meet that need. In this thesis different models of service delivery in the healthcare were studied which included traditional and cloud models. Also from the survey, the metrics which we used to compare these models were extracted. These metrics include quantitative metrics such as cost, setup time, availability, multi-regional, elasticity, efficiency and qualitative metrics including integrity, privacy,... 

Complex network studies grow by the scientific community, thanks to the increasing availability of real-world network data. The importance of using analysis on this type of network algorithms and community structure is one of the most important problems in the field of complex networks. Community Detection in a multidimensional network is still under investigation in the research community. The aim of this research is to give an algorithm for community discovery. We have reviewed the basis for multidimensional network analysis and will present a solid repertoire of basic concepts and analytical measures, which take into account the general structure of multidimensional networks. Then, we... 

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... 

In drilling oil well with respect to depth of several thousand meters, knowing the physical conditions of down-hole well such as temperature, pressure and stress have particular importance in prevention of possible injuries such as breaking the drill bit or increasing temperature. If these data can transfer from down-hole to bore-hole of the well, the operators can prevent from critical conditions such as intertangle of the drill-string. Currently, because of this lack of information, there are irreparable damages in oil industry annually. Based on researches, because of down-hole conditions of the well, these data can’t transfer with electromagnetic telemetry. Currently one of the data... 

Drilling in oil industry, is an expensive process in produce and extract oil from well. Any mistake in drilling may cause many drawbacks for industry owners. Phisic’s quantities information at downhole like tempreture, pressure and force on bit synchronously can inform user from torrid conditions and prevent undesired events by actions like evoke bit from downhole or change at rotation velocity in drilling and finally stop operations. With attention to a lot of problems in data transport from long distance more than one kilometer from downhole, scientists believe that one of the methods to do this process is converting data gathered at the bottom hole to acoustic waves and transmit them to... 

Web servers and web applications are susceptible to different attacks. In order to detect web-based attacks Intrusion detection systems (IDS) should be equipped with a large number of signatures. Unfortunately various types of web threats are increasingly growing and so detection and prevention of all these new and old attacks is exhaustive and really difficult.This thesis represents a designed system for intrusion detection that uses different techniques to discover vulnerabilities with derived patterns and also some user behavior based attacks against web applications. This was done by using new dataset which was generated by new log file.The primary objective of this thesis shows the... 

Nowadays, deployment of peer-to-peer video streaming systems over wireless mesh networks has attained increasing popularity among a large number of users around the world. In this thesis, we present an efficient peer-to-peer live video streaming architecture over multi-hop wireless mesh networks. In our proposed architecture, we take the physical topology of the network into account and based on a distributed locality-aware neighbor selection algorithm in the overlay construction phase, we generate an efficient mesh-based overlay on top of wireless mesh networks. In locality-aware neighbor selection algorithm, instead of choosing randomly, peers find their best neighbors based on their... 

To make Wireless Multimedia Sensor Networks (WMSNs) more practical, researchers have tried to meet its challenges in the last decade. Some factors of WMSNs, such as low bandwidth and channel errors, cause a decrease in the video quality that is declared as distortion. On the other hand, one important requirement in the context of multimedia streaming is its quality. In this thesis, we first introduce and use an adaptive cross-layer error control in the link layer, and then we implement a new cross-layer source rate control Mechanism for efficient and reliable real-time multimedia streaming in wireless sensor networks. Our main objective is to minimize distortion. Some of the used cross-layer... 

Most of current the MAC protocols for Wireless Sensor Networks (WSNs) concern about energy efficiency rather than low latency. The main source of energy consumption in the MAC layer is idle listening, and most of these protocols use duty cycling for reducing energy consumption. But duty cycling method increases packet delivery latency. This problem is very critical in real time applications where packets should meet their deadline. There are some solutions for this problem. For example a node forwards data packets multi hop away instead of one hop in a single cycle. In this research, an efficient cross layer MAC protocol for real time applications is proposed. In this protocol multi hop... 

In this thesis, we propose a QoS-aware routing algorithm for multimedia streaming that uses cross-layer information (application layer and physical layer) in Wireless Multimedia Sensor Networks (WMSN). Our goal is to use cross-layer information to route video packets efficiently and deliver a higher quality video in streaming applications. Our QoS-Aware Multi-Path Selection (QAMPS) method is based on multi-path multi-priority selection algorithm that uses Two-Phase geographic Greedy Forwarding (TPGF) as a routing algorithm. The proposed method guarantees QoS by splitting video streams into I-frames, P-frames and B-frames in the application layer and passes them to the network layer for... 

Since the contribution bandwidth of each CDN (Content Delivery Network) node and also each peer are limited, optimal allocation of their bandwidth to their partners is an interesting issue. In this work, an efficient resource allocation algorithm in a hybrid CDN-P2P (Content Delivery Network- peer to peer) video streaming network has been designed and each peer will receive the video chunks with the bit rate according to the number of nodes that the peer supports. We have added this algorithm to Coolstreaming because it does not have a resource allocation mechanism. In Coolstreaming each peer when requests chunks from its neighbors, the neighbors will send the peer the requested chunks with... 

In the current study, shape-memory alloys are analysed analytically under mechanical loading. Due to the special properties of these materials, their usage in various applications is rapidly increasing. However, mostly, the numerical methods such as finite-elements methods are employed to model the thermo-mechanical behavior of these materials. Also, due to the complexity of their behavior, there are few analytical solutions for them in the literature. In this research, an analytical approach is proposed to investigate the response of these materials under mechanical loading using a fundamental model which is suitable for modelling their crystalline structure. Given the impact of multiple...