Sharif Digital Repository

Underbalanced drilling is a type of drilling operation in which the pressure of the drilling fluid is less than the pressure of the formation. This pressure difference has created advantages for this method. Less formation damage, reduction of pipe stuck, increasing rate of penetration and production during drilling are the advantages of this method compared to traditional methods. To reduce the pressure of the drilling fluid, very low density fluids should be used. One way to reduce density is to mix a compressible fluid such as gas into water. Due to the difference in density and surface tensile strength of water and gas, these two phases do not combine, so a stable combination of these... 

Image segmentation is a technique which divides an image into significant parts. The accuracy of this technique plays an important role when it applies on medical images. Among various image segmentation methods, clustering methods have been extensively investigated and used. Since it is an unsupervised method, the existence of a small amount of side-information which is extracted from a specific application (in this case, medical image) could improve its accuracy. Using this side-information in clustering methods introduces a new generation of clustering approaches called semi-supervised clustering. This information usually has a format of pair-wise constraints and can be prepared easily... 

Three distinct areas in linguistic studies are typically considered, namely, syntax, semantics and pragmatics. Each category has a specific realm and deals with special linguistic phenomena. Presenting exact definition and clarification of the corresponding boundaries of each area is considered in both linguistics and philosophy of language. In order to explain the “meaning” for sentences of a language, this issue turns out to be vital. Representing the definition and evaluating the domain of each area, is the objective of the first chapter. In chapter two, some important semantic theories have been investigated. Since at first one semantic theory ought to clear its position about reference,... 

Common Object Request Broker Architecture (CORBA) is a standard for hybrid applications that is designed and supported by Object Management Group (OMG). This standard defines protocols and Relational Data Model Objects / Services which can be connected into heterogeneous software (written in different languages). So we can use CORBA to share the distributed object platform, without worrying about where they are located or who has designed them. CORBA can package the codes (in some programming languages) and add the packaging information, such as the ability to execute the codes and how to implement them. So this package or object code can execute some other programs or CORBA objects that... 

In this study the concept of the origin of life, as an important question, is investigated and reviewed.Then the possibility of the beginning of life from an extraterrestrial origin is studied via spectroscopy methods to analyze the role of the cosmic waves.Moreover, by considering the similarity between the chirality of the essential amino acids and extraterrestrial amino acids, found in meteors the various methods for studying the structure of molecules, as well as the possibility of the transfer of the central elements of life from space to the earth are reviewed in details.Finally, we suggest how chirality might be emerged due to the interaction of the molecule with the environment,... 

The purpose of this dissertation is proposing a probabilistic model in transition systems of records. In these systems, two acceptance state of finite and infinite string have proposed which acceptance state of finite string is called probabilistic finite automata of records and acceptance state of infinite string is called probabilistic buchi automata of records. The buchi automata of records is an operational semantic for Reo coordination language. Reo is a coordination language to coordinate existing component of a component based system. Reo circuits with non-deterministic and probabilistic channel can be modeled by proposing probabilistic buchi automata of records. In this dissertation... 

The main goal of this thesis is to verify real-time properties of timed coordinated systems specified by timed-Reo circuits using the model checking techniqe. We use Timed Buchi Automata of Records (TBAR) as the semantics of timed-Reo. The model checking is done by converting Timed Buchi Automata of Records to an extension of Timed Automata that are usingas input of UPPAAL tool. We introduce a writer-automaton, which is synchronous with the desired Timed Automata, for initializing input ports. A tool that transforms Timed Buchi Automata of Records to UPPAAL Timed Automata has been implemented. Finally, two model checking case studies are examined by usingof our implemented tool over UPPAAL  

In this thesis the usage of probabilistic reasoning in collaborative filtering is investigated. The problem of predicting users' rating is formulated as a Bayesian decision problem and a generative probabilistic model is used in order to find the optimal decision. Two different probabilistic models are considered: user based model and rating based model. In user based model prediction of ratings is based on structural learning of Bayesian networks. In rating based model, we assume a predefined Bayesian network represents the joint distribution over model variables and rating prediction is carried out using McMc inference method. MovieLens dataset is chosen to evaluate and compare the results... 

Approximate Agreement (AA) is one of the most important issues in distributed networks in which non-faulty processes execute a voting algorithm to reach the values that are very close to each other. AA for Partially Connected Networks (PCNs) is very limited because a node may not have a complete view of the whole network which makes it difficult to reach the convergence. This research proposes a convergent Fuzzy algorithm for synchronous distributed networks in the presence of faulty or Byzantine processes. When each node receives a new value from its neighbors,it runs the convergent Fuzzy algorithm. If the received value is not in the expected range of values, the processor can discard the... 

In a distributed system, each solution for the problem of Byzantine Agreement requires that some of correct processes reach a common decision value from a set of proposed values while Byzantine processes may behave arbitrary. This problem is one of the most fundamental problems in the theory of distributed systems. While the problem has been widely studied in fully-connected fixed networks, few studies have been carried out in the context of self-organizing mobile networks such as Mobile Ad-Hoc Networks.
This research presents a randomized consensus protocol with three additional modules for the case of dynamic networks: Participant Detectors, Failure Detectors and Maintainer. We assume... 

The World Wide Web has been experiencing a massive growth regarding its content and users in recent years; therefore the need for effective means of accessing and processing available items has attracted a wide range of researchers and industries. Recommender systems has emerged to help both users to find what they may be interested in and the producers to sell their products more efficiently. As the number of these techniques grow, the need to evaluate them properly increases as well. However the proposed evaluation metrics are very diverse and often inconsistent with each other. Although there had been immense research in this field, there is no united and proper approach for evaluation of... 

Network Motifs are subgraphs that appear more frequently in real networks than randomize networks. Frequent replication of a subgraph could imply evolution, network performance or some other particular reasons. From algorithmic perspective, network motif discovery in a graph is a difficult problem. Since, at least it includes the whole graph isomorphism. Hence, for solving this problem in practice, we need computable graphs. The existing algorithms so far, have high running times and memory usages. In this thesis, we present a new algorithm called CGQ. Within this algorithm, we use both QuateXelero and G-Trie algorithms which respectively have better performance in census of real networks... 

Monitoring of activities of elderly and intelligent decisions about their living environment is a key challenge in smart environments. In the case of such challenges, correctness of system performance is highly dependent on how the model is designed. In the ambient intelligence (AMI) modeling, formal modeling is one of the best approaches because it supports certainty. In addition, time, location and mobility in AMI are crucial requirements, particularly in emergency treatment services. Ambient calculus is a formalism for describing mobility, process migration and message transfer, but it cannot express metric time duration. In this paper we propose an extension of ambient calculus with time... 

Security protocols assure the security of the communications in computer systems using techniques such as cryptographic primitives. However, the usage of such protocols is faced by the lack of fault tolerance, where a minor disruption could cause a destructive damage. Therefore, there is a requirement to assess the reliability of these protocols. In this thesis model checking of timed security protocols is done. Model checking process includes steps that will be modeling protocol with high level and human readable specification language named THLPSL and converting this specification to special kind of timed automata named XTA and model checking will be done with UPPAAL verification tool. We... 

By intertwining community daily life to electricity, high reliability and quality, safe, and low-cost services become among common expectations of electric energy customers. The substantial sources of fault events, however, lead to unexpected service interruptions. The exhaustion of existing devices, radial structure of current distribution networks, and lack of sufficient control and monitoring systems even worsen the situation. Therefore, investing in distribution systems in order to improve the service reliability and quality has been deemed as a proper strategy for electricity planners and operators. Various approaches have been proposed to achieve this aim. Among them, implementing... 

Paraphrases are sentences or phrases, which convey the same meaning using different words. There are different definitions for paraphrasing and most linguists believe that, paraphrases approximately equivalent in meaning. Paraphrase recognition is useful in different natural language processing areas such as question answering, information extraction, plagiarism recognition and machine translation. In this thesis, the purpose is to present a method for paraphrase recognition, using deep semantic analysis and meaning representation of sentences. To achieve this purpose first, meaning features were defined for every syntactic category and semantic analysis of sentences alongside mapping of... 

With long-term evolution of large scale software systems, the study and engineering of architectural evolution becomes more and more important. In order to manage high level changes, the architects should plan the architecture evolution in a series of releases. Planning and analysis of architectural evolution is a challenge and plays a significant role in evolution management. An assessment solution could promote overall accuracy and quality of the evolution process. Compliance checking with expert-defined rules is a well-known assessment solution and could be applied in the field of architectural evolution. In this thesis, a solution is proposed in order to compliance check these evolution...