Sharif Digital Repository

The two central topics of information theory are the compression and the transmission of data. Shannon, in his seminal work, formalized both these problems and determined their fundamental limits. Since then the main goal of coding theory has been to find practical schemes that approach these limits.Polar codes, recently invented by Arıkan, are the first practical codes that are known to achieve the capacity for a large class of channels. Their code construction is based on a phenomenon called “channel polarization”.
Since the performance of polar code degrades when the block length is small, several kinds of Reed – Solomon concatenation is considered in order to improve the... 

In this thesis, a one-dimensional simulation, developed in previous studies, is utilized to study the stability phenomenon in axial compressors of gas turbine engines. The transient and dynamic operation of the axial compressor is determined by solving the conservation equations, expressed as one dimensional and time dependent Euler equations with related turbomachinery source terms. As known, stall and surge are one of the most destructive dynamic phenomenon in gas turbine engine compression systems starting with a flow separation. This occurrence is investigated in detail. In general, while choking phenomenon may occur during engine startup in the first stages, stall... 

Every day thousands of questions and answers are posted on CQA websites. Stack Overflow is known as one of the most famous CQA websites in the field of programming. Asking high-quality questions on this website is one of the significant challenges that users face, leading to negative experiences in some cases. In this research history of questions, answers, and post-edits are studied to get insights for predicting questions’ quality. There is a new approach proposed that takes both post scores, and their edits into account to predict their quality. The questions edits that are studied are the one that happened before getting an accepted answer. Furthermore, it is shown that predicting these... 

In this research, a new method is proposed for constructing concrete structures with complex geometry, including topology-optimized concrete dams on a small scale. According to global statistics, concrete is the most consumed material in the world after water, and its production process causes a lot of damage to the environment. One of the best ways to reduce concrete consumption is to use tools such as topology optimization to design concrete structures. Nevertheless, few research has been done in the field of topology optimization of concrete dams, one of the important reasons for which is the difficulty of building physical model to perform physical tests, validating numerical models, and... 

Little research has been conducted on the topic of water resources management in case of deep uncertainty. It is vital for the management method to be upgraded in order to accompany future changes. The purpose of this study is to inspect some viable scenarios and deriving proper reservoir management solutions in case of deep uncertainty. This is important due to the fact that future changes are often not considered when water resources structured are being designed. In the past, some researches in this field of study were done; For instance, the effects of climate change on reservoirs have been assessed. Also methods for coming up with scenarios have been proposed, most of which are based on... 

Ejtehadi, M. R. (Mohammad Reza)All cells store their hereditary information in the same linear chemical code, DNA molecule. These information organize all activities of the cell. Therefore, studying various properties of DNA is a big step toward understanding life. Physicists are interested in elastic properties of DNA molecule. DNA is somehow a chain of successive atoms that have been arranged in a helical ladder shape. DNA is a stiff polymer so one has to use a large amount of energy to bend it. Interestingly, in most of the natural cases, DNA is highly packed into spaces that are much smaller that its total length. Cell’s nucleus and viral capsids are some examples. Virus maybe the... 

Network design problem has been, and is, an important problem in transportation. Network design based on different objectives affects network's performance in different dimensions, so it is crucial to define a good objective for the network design problem that improves the network's performance in more than one aspect. The purpose of this study is to obtain the differences between the two network design problems, one based on resiliency, and the other based on consumer surplus.Network design problem based on consumer surplus minimizes the total travel time for the users in the network. Network design problem based on resiliency is defined as: (1) before the incident, (2) after the incident... 

The use of carbon nanotubes in Nano-switches is the new technology employed in NEMS. Nano-switches can also perform as a micro-switch where nano-switches have longer life time, consume lower power and have smaller size with respect to micro-switches. As the dimensions get smaller, continuous models lose their accuracy and molecular methods should be utilized. Non local theory, is attempting to change the responses of continuum models assuaging them to the molecular results. In the current project, non local theory is used to rewrite the governing equations of nano tubes motion and the results are compared with the classical results. In this modeling, the axial force and the mid-plane... 

Human action recognition is one of the computer vision branches. Video surveillance and human-computer interaction is among its modern applications. The main goal of this subject is to label RGB-D videos which are captured from acting human. Therefore, labeling the input videos among pre-learned action is called as action recognition.The action recognition problem consists of two primary parts. The first part is selecting a suitable descriptor to describe input videos, and the other part is the way that the system has been learned based on the learning action data. The main goal of this research title is to propose a method for recognizing each action video (that is acted by human and... 

In a solar central system plant about 40% of energy losses occurs in the heliostat field. Furtheremore, half of the investment costs for construction of the plant is related to the heliostat field. Therefore, an optimal design of the heliostat field is necessary for reduction of levelized cost of energy in solar tower power plants. In this study, in order to optimally design the heliostat field, first energy performance of the helistat field in one year is simulated. Solar power and sun’s position at each moment of the day is determined by mathematical relations. Then, loss factors in the field are modelled and heliostat field layout is designed by an algorithm. Finally, by using PSO... 

The power generation system of this type of power plants operates on the air flowing through the power plant’s chimney and colliding with the turbine blades within the chimney. When the solar collector warms the nearby air and thus expands the air by absorbing the sunlight, a difference is created in the density. Then, this difference in the density creates the phenomenon of buoyancy, making the air pass to the top of the chimney through the collector.This study simulated and optimized a solar chimney power plant. The simulation and optimization were performed based on the information of Manzanares Solar Chimney Power Plant in Spain (located in 150 km from the south of Madrid). It was... 

The issue under discussion in this paper is to optimize the fuel consumption of the Toyota Prius hybrid car. In order to solve this problem, the ADVISOR design model used by NREL in the Matlab / Simulink environment has been used. Various parts of this model are described. The optimization performed on this issue is based on the emotional controller. This controller works by simulating learning in animals based on encouraging and punishing them. With the introduction of the controller, the model and its inclusion in the fuel consumption control and its implementation have achieved good results. In the initial state and the controller in the model, the fuel consumption was 4.9 liters per 100... 

Today, due to the scarcity of fossil energy resources, security of energy supply, and increasing environmental concerns, we need to develop new technologies to promote energy-saving and reduce greenhouse gas emissions. One of the suitable options for this purpose is to use the simultaneous production of electric power, cooling, and heating. Meanwhile, trigeneration systems that provide part of their energy needs from the sun, due to the free solar energy source and low environmental impact, can be an ideal technology for clean and safe scattered production. The present study has suggested a trigeneration system of cooling, heating, and power generation based on the organic Rankin cycle and... 

Today, due to increasing electricity consumption and demand, the use of conventional systems such as thermal, hydro and nuclear power plants is not enough to convert energy. Over the past century, scientists have sought to discover new technologies for exploiting different forms of energy and converting them into high-efficiency electrical energy. One of these ways is to use the phenomenon of magnetohydrodynamics (magnetic fluid dynamics) to convert thermal energy directly into electrical energy. Magnetohydrodynamics is a theoretical field that studies the dynamics of fluids with electrical conductivity. Induction magneto-hydrodynamic generators use ionized hot plasma (a quasi-neutral gas of... 

The thesis attempts to investigate one of the factors influencing enterprise innovation, namely, innovation cooperation, its types and its diversity by using the data of about 2,500 companies in different fields of industry of national innovation survey that had been collected in 1395 hijri. In this research, firstly, by reviewing the literature on the field of innovative cooperation and the performance of enterprise innovation, the model of the association of colleagues with innovation performance has been extracted. In the following, it answers to this question is whether the cooperation with colleagues is essentially affecting the innovation performance of Iranian firms or not? The...