Sharif Digital Repository

With the ever-growing use of cloud computing by practitioners and also the emphasis placed by researchers from various backgrounds on this field, collaboration between various clouds has emerged as a new research area garnering a lot of attention in recent years. Cloud Federation, in which different clouds interact for purposes such as increased productivity and decreased costs, is one aspect of this new trend, which although faced with many challenges,has the potential to make cloud computing even more pervasive then before.In this thesis, by focusing on statistical multiplexing in the resource usage behavior of cloud requests, we evaluate the efficient and fair partitioning of requests in... 

Recently, biopolymers such as alginate, cellulose, chitosan, gelatine, starch and wool have been used as supports for catalytic applications. Several interesting features of the biopolymers for example, bio-degradable, environmentally safe, high sorption capacity, physical and chemical versatility make them attractive to use as supports. This study, the four functionalized biopolymer-based composites were designed and synthesized as well as heterogeneous catalysts used in the synthesis of 1,2,3-triazoles, oxidation of alcohol, reduction of nitroarenes and carbon-carbon coupling reactions.A novel cellulose supported copper NHC complex has been prepared by the reaction of cellulose supported... 

In recent years, the crude oil spills in the oceans and the excessive emission of electromagnetic waves in the living environment have threatened human health. Therefore, different methods have been considered to deal with each of these two threats. Recently, the use of polymeric boron nitride composites in the production of crude oil absorbents and electromagnetic wave shieldings has received attention due to its thermal conductivity, thermal and chemical stability. In the first step of this research, superhydrophobic composites of polyurethane sponges were prepared by boron nitride and electrically conductive nanomaterials that had photothermal and electrothermal properties. The results... 

Online Social Networks have become indispensable platforms to model social interactions and for the retrieval of knowledge based on economical, political, social and ... criteria. The importance of social networks for such uses stems from the vast amount of social data that it gathers for use by researchers. Aside from it’s impact on the field of social network analysis, the ever-growing use of social media by users has added even more importance to social network data as it contains a history of the users virtual life. Unfortunately research on proposals to support the management of this vast amount of data, whether for the conceptual modeling of social data or to provide a uniform modeling... 

In recent years horizontal Ground Heat Exchangers (GHEs) has attracted a growing interest as heat source/sink for ground source heat pump systems. Horizontal GHEs initial installation costs are lower than the vertical ones; however, they require larger land area and more pipes. Therefore, it is necessary to reduce their required land area and pipe length by improving their thermal performance. In this study, a numerical modal based on 3-D simulation of GHE with computational fluid dynamics methods is developed. The model is used to evaluate the thermal performance and initial installation cost of horizontal GHEs. Four different types of horizontal GHEs: linear, spiral, horizontal and... 

In this thesis, we study the treewidth of social networks. The importance of studding treewidth is for two reasons. The first is that for the graph with bounded treewidth, many optimization problems that are NP-hard in general, can be solved in polynomial or even linear time. The second is that the high value of treewidth in a graph, reflects some high degree of connectivity and robustness, which is an essential factor in designing many networks. But the problem is that determining the value of treewidth in a graph is NP-complete so, computing the treewidth of real complex networks is not feasible. We first review the related works and mention the weakness of the past works, then introduce a... 

In this thesis, first of all we introduce the Anderson model, Multifractality, and conformal field theory. Then we try to determine some critical and scaling quantities for the critical wave functions in the 2D systems with spin-orbit interactions We implement a correction-to-scaling analysis by introducing an irrelevant exponent which leads to a proper and sharp evaluation of the critical parameters including correlation exponent, rescaled localization length and the critical disorder. Then, we survey the multifractal properties of this model and obtain some multifractal exponent in the critical point. Finally, we will survey the existence of the conformal invariance symmetry in it. Our... 

Intelligent transportation systems (ITS) have been widely studied in recent years. One of the challenging problems in this field is routing on urban networks, which are largescale networks that are almost planar and sparse. In the routing problem, a person wants to journey from a known source to a known destination. He may have multiple choices as to the path to traverse, and wants to discover the best path, designated in terms of its travel time. The routing problem can itself be a subproblem of another larger problem, and so the running time of the routing algorithm is important. In addition, the existence of traffic flow on urban roads has great impact on travel times. The network is... 

A social network represents a set of entities and their relationships. Telecommunication networks, online social networks, and paper citation networks are some examples of networks in real world. Nowadays, analysis of social networks is an interesting research area with important applications. Particularly, managers of the social networks and the decision makers often require intelligent decision support for futures study in these social systems. The demanded decision support systems make it possible to define the desired social problem and to analyze the ”what-if scenarios.“ Computer simulation is an appropriate approach toward such decision support systems. In this approach, the desired... 

In recent years with the growth and development of emerging technologies, one of the main challenges in various organizations is the issue of Business-IT Alignment programs at different levels of strategic, tactical, and operational. Many managers and experts in the field of information technology recognize the importance of this issue because of its broad effects on the development and maturity of the organization. However, they face various difficulties in creating actionable plans to achieve high levels of alignment. The main problem is the inability to measure the alignment degree index. This index is affected by various sub-indicators in various fields of business and information... 

The solar-driven humidification-dehumidification desalination system with a geothermal dehumidifier (SD-HDH-GD) has been given special attention, for producing drinking water and subsurface irrigation applications. This contribution scrutinizes the performance of the geothermal dehumidifier of the SD-HDH-GD system. To this aim, a comprehensive three-dimensional transient computational fluid dynamics model of the geothermal dehumidifier and the surrounding soil is developed. An experimental setup is established to verify the developed numerical model. At first, the performance of the system in a short-term period of 12 hours is investigated, and the effect of several operation parameters is... 

Given an event O and a set of experts E, we describe a method for finding a subset of experts S whose aggregated opinions best predict the outcome of O. Therefor, the problem can be regarded as team formation for performing a prediction task. In order to estimate competency of each team we propose measure Sum Squared Error which uses experts’ records of predictions during past k days. For simplicity, opinion pooling is selected as the method of information aggregation. we prove in case of simple averaging of opinions,finding best team is NP-hard. we suggest some rounding and heuristic algorithms for finding near optimal solutions. Simulation results show that a variation of tabu search used... 

Creative play is both engaging and educational. Finger painting, building with blocks, drawing, or dressing up – all such activities intimately link imagination and self expression with exploration and problem solving. With creative play, children have fun while learning new skills and enhancing their understanding of the world. However, with the popularity and ubiquity of digital devices, an increasing amount of play time happens in the digital world, such as with video games where the link to creativity is sometimes questionable. Instead of creative play, children simply play. In this thesis, we describe the design, development and preliminary evaluation of a novel animation tool for... 

Knot theory is the study of ambient isotopy classes of compact 1–manifolds in a 3-manifold. In classical knot theory this 3-manifold is R3 or S3. This field has experienced a great transformative advances in recent years because of its strong connections with and a number of other mathematical disciplines including topology of 3-manifolds and 4-manifolds, gauge theory, representation theory, categorification, morse theory, symplectic geometry and the theory of pseudo-holomorphic curves. In this thesis we start with classical knot theory, introducing some of its (classical) invariants like unknotting number, Seifert genus and slice genus of a knot, knot group and finally Alexander Polynomial... 

According to the increase of interest in the internet of things, the importance of understanding the ongoing situation in an environment and acting upon them is largely considered. Due to the massive size of sensors used in a smart environment, there are plenty of data manufactured every second. Therefore, an interpretation of this data is mandatory to obtain valuable information to comprehend the situation ongoing in an environment. Situation recognition can bring a better understanding of the interaction between the smart actuators and sensors with the living agents in the environments.This will enable the system to help people do their routines, save energy, and accomplish more... 

People usually use trust and reputation when they encounter uncertainty in the nature. Graphs are good tools to model and analysis of trust’s problems. If we show human and computer agents by graph’s nodes and trust values by its edges, in literature, the output graph is so-called Web of Trust. Most recently, there are three major research areas in which trust is studied. First area is policy-based trust which uses policies, digital signature and authentication methods. Second area is reputation-based trust which uses reputation and social network tools to estimate trust where past interactions or performance for an entity are combined to assess its future behavior. Third area is trust... 

Peer-to-Peer networks are invented to enable participants (peers) to share their resources and find and use the shared resources of the others. So the main issue is the mechanism of finding granted resources of the other peers. In Peer-to-Peer networks, there is no central server to index shared resources of the peers. So peers should collaborate to provide a fully distributed mechanism for searching resources. Considering the huge size of peer-to-peer systems, it is apparent that efficiency of the search mechanism is very critical. In this thesis, to have efficient seach in Peer-to-Peer networks, we propose two approaches. Then based on these approaches, we propose the third approach to... 

With significant advances in software development technologies in recent years, it is possible to have complex software applications, wich include large number of heterogeneous software components distributed over a large network of computers with different computational capabilities. To run such applications, their components must be instantiated on proper hardware resources in their target environments so that all requirements and constraints are met and some quality of service parametesrs (e.g.,reliability, load balancing, etc) are also optimized. This process is called software deployment. For large, distributed ,component-based applications¬ with many constraints and requirements, it ... 

Today, peer to peer networks have become quite popular due to their ability to easy access to shared resources regardless of their location in World. In these systems files are stored at the end user machines which named peer, rather than at a central server, in contrast to the traditional client-server systems, files are transferred directly between peers. sending and receiving those data, occupy a large amount of the internet bandwidth. So, by improving the efficiency of these networks, the total efficiency of the internet will improved. These systems are usually constructed on the other networks such as TCP/IP as an underlay or physical networks. Despite of structure of peer to peer...