Sharif Digital Repository

This thesis studies the possible solution to the H0 tension via a dynamical systems approach. The early dark energy (IDE) scenario can somewhat alleviate the Hubble constant tension. On the other hand, postulating a new subdominant EDE in the pre – recombination Universe can also resolve the H0 tension. We introduce a novel model to interweave the early dark energy(EDE) and interacting dark energy-dark matter (IDE) scenarios. In this scenario, the early dark energy emerges naturally by changing the topological class of the phase portrait of the universe dynamics. In particular, an EDE component contributing only 10% of the matter density of the Universe—preferably in the vicinity of the... 

Temerature fluctuation of the Cosmic Microwave Background (CMB) is one of the key observebles of the modern cosmology. Today, it is widely believed that quantum fluctuation that are stretched to horizon scales during a period of acceleration expansion -- at the onset of evolution of the universe-- are responsible for these perturbations. In the simplest scenarios of the inflation, a scalar field is responsible for both nearly expansional expansion of the universe and the proimordial fluctuations. In this thesis, we investigate the models of inflation with an additional light degree of freedom. In particular, we employ the method of the Effective Field Theory to study the general structure... 

By studying of simulations, it can be seen that the linear point (LP), a point lies midway between the scales associated with the peak and the dip in the correlation function on BAO scales, is a useful window into cosmology and large scale structures rather than baryonic echo peak. Some fundamental features of the LP, been unaffected by redshift space distortions and gravitational non-linear effects, has made it important. I want to find evidences to stability of the LP by utilizing Standard Perturbation Theory through my thesis  

Austenitic stainless steels are the most common kinds of stainless steels. Although these alloys are generally very weldable, there are some problems in join- ing of them using fusion welding. Solidification and liquation cracking or corrosion at grain bound- aries in the heat-affected zone are examples of these problems. Transient liquid phase (TLP) bonding is an important variation of diffusion bonding that has the potential to overcome this problems. Two-step TLP bonding is an ingenious development to form non-planar interface. This method consists of a short-time high temperature heating to melt interlayer followed by isothermal solidification of liquid phase at a lower temperature. In... 

Sensor Observation Service (SOS) which is defined by Open Geospatial Consortium (OGC) Sensor Web Enablement group is a Web service specification in order to standardize the way sensors and sensor data are discovered and accessed on the Sensor Web. Multiple instances of this service can be implemented around the world, providing huge amount of data every moment. Each of these services operates in specific domain of knowledge (thematic), spatial and temporal dimensions. One way to reveal the underlying data over all of them is to provide an architecture for data integration to allow the user to query sensor data without the knowledge of the infrastructure components. In this research, a novel... 

In the last decade, Intrusion Detection Systems has attracted attention due to their importance in network security, but still they've shortcomings. Generating a lot of low level alerts is the main problem. Many of these alerts are actually false positives. One suggested solution is Alert Correlation Analysis. Because of false positives alert correlation techniques are not able to build accurate scenarios, but the accuracy of alerts can be verified with the aid of the information logged in the host systems. In this dissertation after surveying the current alert correlation techniques, a model will be introduced to effectively verify the generated alerts and to apply correlation techniques to... 

Recently, data stream has been popular in many contexts like click sequences in web pages, obtained data from sensor networks and satellite data. A data stream is an ordered list of points that should be used once. Clustering of these kinds of data is one of the most difficult issues in data mining. Due to the high amount of data, the traditional clustering algorithms are not suitable for this family of problems. Many data stream clustering algorithms have been proposed in recent years considered the scalability (largeness) of data, but most of them didn’t attend to the following issues. •The quality of clustering can be bad over the time. •Some of the algorithms cannot handle arbitrary... 

Nowadays the importance of ontologies in various domains such as semantic web and NLP is obvious. Manually construction of ontologies is a time-consuming, costly and error prone. The non-manual building of ontologies approaches are divided to the expand approach and the merge approach, each has pros and cons. The expand approach is preferred upon the merge approach for languages with few lingual resources. The most important thing in the expand approach, which is building an ontology from another existing ontology, is making distinction between the different meanings of polysemous words. This activity is called word sense disambiguation(WSD). The existing approaches usually give attention to... 

Semantic relation extraction is one of the challenging information extraction’s steps. The main task of relation extraction is finding of relationships in text corpus using Machine Learning methods. There are plenty of usage for relation extraction such as providing information for Question Answering systems, protein interaction detection in biomedical corpora and ontology population. There are many research take placed in this area in which relation extraction task is defined as a classification problem and in most of them, this problem is solved by SVM method. Results of recent research imply that current state of relation extraction methods are far from appropriate state that is... 

With the explosive increase in the amount of information in the today's world, the need for high-speed data transmission is felt more and more. According to Cisco's forecast, the traffic explosion in real wireless networks will continue. According to the forecast, the volume of data traffic on wireless networks will be about one hundred and ninety exabytes in the next two years, and in the next four years will reach over five hundred exabytes per year. On the other hand, the advent of new technologies, such as the Internet of Things and the Tactile Internet, pushes us to make it possible to transmit with very low delays and high reliability in future generation networks. In this project, we... 

Web service plays an important role in software development. Since Web service can be used in small scale and large scale environments, many different entities may participate in each interaction. Regarding situation, a lot of information is available around these entities. This kind of information is called context. In some cases, context information is used to provide outputs which are called context-aware systems.
The main challenging issue in producing a context-aware system is context modeling and sharing. Semantic Web and its ontology languages are the most promising solution to context modeling. In pervasive computing many ontologies are proposed for this purpose, but little... 

Protein multiple sequence alignment is one of important problems in biology which no polynomial time algorithms is known for it yet. Due to importance of this problem, several methods have been developed to find an approximate solution for it. Approximation algorithms, Evolutionary algorithms and Probabilistic methods are some of these methods. According to evolutionary nature of this problem, evolutionary algorithms and specifically genetic algorithms can be a potential good solution method for this problem. In this project we have a survey on using genetic algorithms for this problem and after mentioning benefits and draw backs of existing methods, we develop a method for improving one of... 

Today many applications produce data stream that grow continuously over time. Classification is an important task in mining this data. One of the major challenges in classification of data streams is that the underlying concept of data may change over time; this needs updating the classification model. Many of traditional classification algorithms are adapted for classifying data streams. Evolutionary algorithms are stochastic methods that have been successfully applied to a wide range of optimization problems. Harmony search is a new evolutionary algorithm that convergence to global optimum and can be applied to discrete and continuous data. The evolutionary nature of classifying data... 

Considering the wide applications of 304 stainless steel in various industries and the existing literature on transient liquid phase bonding of stainless steels with a variety of interlayers, the present work aimed to reduce the bonding time by using a two step bonding method. Faster bonding reduces both energy consumption during bonding and the base metal grain growth. It also leads to a lower reduction in the base metal and joint strength.Due to the melting point of the interlayer, different durations and a temperature of 1200°C were selected for the first step. This temperature was maintained for a specified period of time before it sharply dropped to and remained at 1180°C (the...