Sharif Digital Repository

Polar codes were introduced by Arikan in 2009. These codes are the first family of codes that with low encoding complexity and successive cancellation decoder, can achieve the channel capacity. Polar codes, at first were implemented for channel coding, but in 2010 performance of these codes in binary and q-ary alphabet source was studied. It is shown that these codes can perform efficiently in channel coding and source coding. On the other hand, one of the most important continuous sources are Gaussian sources. Due to the importance of Gaussian sources and good performance of polar codes, we try to evaluate the performance of these codes in Gaussian sources. Note that, these codes have... 

Crack nucleation and growth is unfavorable in many industrial and every day-life cases. designers’ effort is to prevent or delay it by taking into account safety and maintenance considerations; but in some industrial operations, the main target is to form a crack in a part to achieve a particular shape; and designers’ duty is to control the way it happens. so numerical modeling of this phenomena has many useful applications in preventing the structures’ failure and designing the production processes for industrial goods; and because of this, a great attention has been paid to it in the last two decades. a situation usually encountered in every day-life is the earthquake excitation which... 

Additive manufacturing (AM) has gained significant attention in recent years as a novel approach to fabricate three-dimensional parts. Its advantages, including high speed, low-cost production for small-scale batches, and greater design freedom, have made it a competitive alternative to traditional manufacturing methods. However, the application of AM for components subjected to fretting fatigue requires careful evaluation. Fretting fatigue is a major cause of failure in turbines, particularly at the contact interface between turbine blade roots and disk. In this study, the influence of AM and post-processing treatments on the fretting fatigue life of Ti-6Al-4V alloy was investigated. Five... 

In thi¬s thesis we studied 3d reconstruction of synchronized multi-view videos containing dynamic scenes of complicated deformable surfaces and fast motions, such as soccer scenes. Our pupose is to extract shape and motion of scene simultaneousely via a spacio-temporal framework. To this end, we translate our problem to a registration problem both in stereo and temporal pairs. We review 3D reconstruction methods and their related concepts like stereo correspondence and scene flow. This review is necessary to choose the best solution.In proposed solution we formulate 3d recnstruction problem as an optimization problem.Using variational framework we integrate error functional over image planes... 

Previous studies and field evidences show that creating appropriate interactions between sales and marketing departments is a challenge for many organizations. The main objective of this research is to develop and elaborate a conceptual framework in which "cooperation mechanisms" between sales and marketing and it’s "consequences" determined and provide an explanation that shows how configuration of sales and marketing relationship affects its consequences. The results show that "organizational ambidexterity" is the core consequence in proper architecture of the relationship between sales and marketing. In the strategy literature, combination of the dual capabilities of exploration and... 

Fired heaters are large and complex items used in process plants. Tubular furnaces used mainly in chemical, petrochemical, and refinery process plants. For many process plants, the fired heater performance will determine process unit run-length. High tube metal temperature and coking in the process-fired heaters is one of the serious problems of process plants. Coke forms because the oil in tubes is no longer thermally stable at the operating conditions. Oil film temperature in the inside wall of tube somewhere that, process fluid has highest temperature and lowest velocity. Therefore, process fluid peak film temperature will determined rate of coke formation. This temperature is dependent... 

Today, the increase in greenhouse gases and the accumulation of thesegases in the atmosphere has caused a destructive environmental impact. Transportation systems in the country consume 25 % of the energy, which isalso the main cause of air pollution in addition to the imposition of fuelconsumption and fuel imports this has led to the design and deployment of vehicles with new technologies, necessity and importance that hybridvehicles is one of the new technologies. Considering that the average speedin road traffic is low and internal combustion engines have lower efficiencyand higher emissions, the hybrid vehicle reduces the current costs (fuelconsumption) and external costs (air pollution)... 

One of the most important problems in machine learning is investigating the performance of the learning algorithms, and especially deep neural networks, on adversarial examples, which are generated by imperceptibly perturbing input images, so that cause the model make a wrong prediction. Not only this line of research is important for making deep neural networks dependable, but also can help with understanding the fundamental limitations of deep neural networks, and the nature of their operation, which can in turn provide researchers with valuable insights into artificial intelligence. In this research work, we have tried to approach the topic with a mainly theoretical mindset. The method we... 

Existing face forgery detection methods mainly focus on certain features of images, such as features related to image noise, local textures or frequency statistics of images for forgery detection. This makes the extracted representations and the final decision depend on the data in the database and makes it difficult to detect forgery with unknown manipulation methods. Solving this challenge, which is called the generalization challenge in artificial intelligence literature, has become the main goal of researchers in this field. In this thesis, the focus is on extracting effective features for success in forgery detection and preventing the performance of the forgery detection network from... 

Free access to large-scale public datasets, together with the rapid advancement of deep learning techniques and networks, particularly generative models, has led to the production of forged content whose distinction from authentic content has become impossible for humans and many classical forgery detection methods. The well-known term deepfake refers to a deep learning–based technique capable of generating forged images and videos by manipulating their content. A common example of deepfake forgery is identity manipulation in images and videos through facial alteration. In this research, three main objectives related to deepfake methods are considered. First, deepfake generation techniques... 

Structural changes in the energy sector, including the need to diversify sources of energy supply, security of supply, energy consumption growth in developing countries, rising oil prices and the exhaustibility of fossil fuel reserves, environmental issues, increased consumption of petrochemical products etc., has led to increased share of natural gas in primary energy supply. Iran has a wide range of options to use natural gas endowment. The present research aims to develop a model for optimal allocation of natural gas to various applications.The gas distribution system is modeled in the present study. Technical onstraints together with economic characteristics are considered in the model.... 

The advent of maturing fuel cell technologies presents an opportunity to achieve significant improvements in energy conversion efficiencies at different scales and environmental conservation simultaneously. This work deals with modeling, simulation and control of planar solid oxide fuel cell with internal reformer. The presented model is based on conservation laws (mass, energy, and momentum), besides an electrochemical model with all sorts of voltage losses (ohmic losses, activation overpotentials, and concentration overpotentials). Methane steam reforming, water-gas shift reaction, and hydrogen oxidation are the main reactions in this modeling scheme. The obtained governing equations lead... 

In recent years, deep learning has experienced rapid and remarkable advancements, demonstrating exceptional performance in various applications such as computer vision, natural language processing, and autonomous vehicles. These models are continually evolving and expanding, yet they harbor inherent vulnerabilities that prevent complete trust in their reliability. One of the most critical issues is their susceptibility to adversarial attacks, where a clean image is subtly manipulated to create an adversarial example. Adversarial examples, generated by adding imperceptible perturbations to input data, can easily mislead deep learning models into making highly confident yet incorrect...