Sharif Digital Repository

Increasing in social communication via electronic ways has been made social network analysis of these communications more important each day. One of the most important aspects in social network analysis is community detection in such networks. There are many different ways to extract communities from social graph structure which in some of them the content of communication between actors has been noticed in community extraction algorithm. In this thesis after a short survey over advantages and disadvantages of existing methods for community detection, a new method for extracting communities from social networks has been suggested which in addition to streaming property of data it spot the... 

The classical approaches of drought analysis are performed using historical records and univariate statistical methods. In the use of historical records it is assumed that statistical characteristics of droughts will be exactly repeated in the future (the assumption of stationarity) and in the use of univariate methods it is assumed that drought variables (e.g. duration and severity) are independent; while on the contrary, global warming changes long-term climate patterns, which is called climate change, and also drought variables have significant correlation. Thus, results of classical approaches of drought analysis have uncertainties.The primary objective of this thesis is to propose an... 

The standard model of Cosmology (SM), based on Einstein’s theory of general relativity (GR), is the best model in describing the cosmic-scale observations. In galactic scales, however, galactic dynamics show a discrepancy between the observed luminous mass and the predicted value from the theory. Two approaches are suggested to eliminate this inconsistency: assuming the existence of dark matter within the context of GR, or modifying the theory of gravity in galactic scales, like MOND or MOG. In this thesis, we study the spherical collapse and the formation of shell galaxies in MOG, in comparison with SM. We introduce the action and the field equations of MOG and the equation of motion of a... 

The objective of this dissertation is to develop a model to monitor and project the long-term changes in meteorological drought under climate change at watershed scale. In this model, drought is defined based on joint precipitation-temperature values since negative correlation between precipitation and temperature implies that drier periods are often warmer, and therefore, the consequences of drought are more severe compared to low-precipitation periods with mild temperature. This is of particular importance considering global warming. To quantify drought, an indicator called precipitation-temperature deciles index, which is an extension of precipitation deciles index, is introduced. Copula... 

Strongly Rayleigh measures are an important class of negatively dependent (repulsive) probability measures. These measures are defined via a geometric condition, called “real stability”, on their generating polynomials, and have interesting probabilistic properties. On one important property of negatively dependent measures is their rigid dependence structure. In other words, the it is impossible for these measures to have strong overall dependencies. In this thesis, we study two manifestations if this phenomenon: (1) paving property and (2) tail triviality. Informally, the paving property states that it is possible to partition the set of the components of every strongly Rayleigh random... 

Traditional assumptions about assessment and learning have been challenged in higher education. Alternative types of assessment have been introduced to align to the students’ learning aims. Although, the growing body of literature of alternative types of assessment such as peer-assessment and self-assessment shed light on the advantages and benefits of embedding assessment in classroom activities, there is not absolute agreement on the consistency and accuracy of these types of assessment. To this aim, this study attempted to investigate the reliability and validity of self-assessment and peer-assessment of Iranian EFL learners’ written and oral production. The data was obtained from 32... 

In developing countries, one of the structural systems used for many buildings is the masonry system, and there are also many existing buildings worldwide with different uses constructed with this system, some of these buildings may have a major historical value and because of that, study of behavior of these buildings to find effective ways to improve their behavior is very important. In this study, the use of Textile Reinforced Concrete (TRC) for retrofit masonry walls is examined. For this purpose, seven scaled brick walls is used, including a test model, a model coated with plane concrete on one side of the wall, a model coated with plane concrete on both sides of the wall, a model... 

In this thesis, consider three important questions in the Iranian Wholesale Electricity Market (IWEM) and answer its. The first one is whether the bidding behavior of the firms in the IWEM has been ex-post optimal? The results of the research show that, on average, the firm’s bidding behavior didn’t optimal in the IWEM, and therefore the bidding strategy of them could be improved. This issue is importance from the regulatory viewpoint in terms of assessing market efficiency and market power of firms, as well as from the firm’s point of view to improve the bidding strategy and increase its profits. The second issue is the assessment of the firm’s ability to exercise unilateral market power by... 

Multi-part rotating parts are used in various industries with very high revolutions. Therefore, the method of assembling each part and keeping the axis of rotation of each part close to the axis passing through two supports (bearings) is important. In this research, three main steps are followed, the development of the differential equations governing the multi-part rotating system and the calculation of the range of oscillations created at the critical points, and then the calculation of the optimal assembly angles with the aim of reducing the introduced oscillations, and finally the discussion of crossing the speeds A crisis is being investigated. The method of obtaining the system of... 

MQTT (Message Queuing Telemetry Transport) is one of the essential and widely used protocols in the Internet of Things (IoT) networks. It operates at the application layer (Layer 7) for data transmission. As IoT applications using this protocol for communication have grown, securing such systems against security attacks has become a significant challenge. One of the important attacks implementable by IoT networks is Distributed Denial of Service (DDoS) attacks. In this thesis, we initially provide a general overview of IoT security and demonstrate how DDoS attacks disrupt the availability feature in these networks. We then examine known types of DDoS attacks to gain a better understanding of... 

Pistachio trade in Iran is of great importance in non-oil exports, and this country has been the main producer of this product for many years. In recent years, unfortunately, pistachio products have fallen sharply in the country, and on the other hand, the United States has been able to take a large share of the global market. The researchers have presented numerous reviews about the causes of this problem, most notably drought and water scarcity, inefficient agriculture, and the lack of comprehensive and efficient management of the pistachio supply chain. In this research, to address these problems, attention has been paid to sustainable supply chain management that addresses three... 

There are several methods for measuring thin film thickness, however, for the analysis of liquid film motors [1] we need a method which is capable of measuring the thickness using a single image of the film. In this work, we use the colors that appear on thin films, such as soup bubbles, which is a result of light interference to calculate the thickness of the layer  

One of the most elusive problems in quantum mechanics is the transition between classical and quantum physics. This problem can be traced back to the Schrodinger's cat. A key element that lies at the center of this problem is the lack of a clear understanding and characterization of macroscopic quantum states. Our understanding of Macroscopic Quantumness relies on states such as the Greenberger-Horne-Zeilinger(GHZ) or the NOON state. Here we take a first principle approach to this problem. We start from coherence as the key quantity that captures the notion of quantumness and demand the quantumness to be collective and macroscopic. To this end, we introduce macroscopic coherence which is the... 

With confidence in the recorded observations, the RLS method no longer estimates the recorded measurements by sensors, i.e. the displacement and speed of the floors, and only estimates the parameters. In contrast, in the EKF method, in addition to estimating the structure's parameters, a more precise estimation of the observations recorded by the sensors has been done by accepting the noise in the recorded observations. These methods, which are based on the Bayesian updating, investigate the two primary sources of uncertainty in a problem: a) measurement noise or observation noise, and b) process noise, which includes modeling errors. In these methodologies, the unknown system parameters,... 

Entanglement is one of the key resources of quantum information science which makes identification of entangled states essential to a wide range of quantum technologies and phenomena.This problem is however both computationally and experimentally challenging.Here we use autoencoder neural networks to find semi-optimal measurements for detection of entangled states. We show that it is possible to find high-performance entanglement detectors with as few as three measurements. Also, with the complete information of the state, we develop a neural network that can identify all two-qubits entangled states almost perfectly.This result paves the way for automatic development of efficient... 

The vortex tube is a simple device that injects compressed gas (air) tangentially into the vortex chamber through one or more injection nozzles. After entering, the flow becomes rotational and an axial cold flow goes towards the cold outlet and a peripheral hot flow goes towards the hot outlet. Besides all the different applications of the vortex tube, the main application of this device is cooling. Here, the goal is to optimize the geometry and physical conditions to improve the performance, which is done by using a commercial software and numerical analysis of a vortex tube to understand the flow physics and optimization. In this research, we use experimental and numerical data for...