Sharif Digital Repository

Chaotic behavior takes place in different physical systems such as chemical reactors. In this thesis, dynamical behavior of chemical reactors in which polymerization or series reactions take place has been considered. It has been shown that these reactors have chaotic dynamics under special condition. Two reactors of the second type (with series reactions) for cases of known and unknown parameters have been synchronized by a control method and stability of the proposed scheme has been established by the Lyapunov stability theorem. Simulation results show the effectiveness of proposed method. Since concentration measurement is difficult and expensive, an observer has been used for... 

One way to increase the power and efficiency of the gas turbines is to cool their incoming air. There are different methods to cool down the inlet air. One of the most widely used and suitable method is spraying or fogging the water droplets into the air at the gas turbine air inlet. In this research and for the first time, the effect of fogging system on the performance of a combined cycle incorporated with a J-class gas turbine (M-501J) is investigated using the computational fluid dynamics (CFD). There are so many parameters, which affect the amount of achieved efficiency. A few of them includes the average temperature and humidity at the outlet, the evaporation efficiency of the water... 

The dynamic behavior of networks largely depends on their structural properties. The information or failures can spread through the links of complex networks constructed by people or agents, and their physical and informational contacts. In this research, the process of network diffusion was investigated in different model and real networks. In particular, we focused on ”cascaded failure” and ”viral marketing” which are among the major topics that have attracted much attention in this context. Firstly, we investigated the robustness of modular complex networks against random and systematic component failures. Many real-world networks have modular structure and they may undergo random errors... 

Although many aspects of helical strand have been carried out, there are still some situations which need more studies. Based on previous studies of wire rope the constitutive equations regarding the rope tension and torque to the rope deformations are carried out. In which constitutive constants depend on both the rope material and geometry of the rope. Equations of motion for straghit rope loaded simultaneously in tension and torque are derived, and with using extensional-torsional deformations in both side of the rope, dynamic stiffness matrix is derived. Some experimental results and currently models are compared with my research model numerically. Finally, mechanic response of helically... 

This dissertation investigates the detection of false data injection attacks in largescale residential energy grids. A typical multi-micro-grid framework is investigated by considering the geographical dispersion of equivalent models, wherein each microgrid is assumed as an agent and managed by a local aggregator. Furthermore, a fully distributed Nash equilibrium seeking algorithm in the partial-decision information scenario is proposed, where each microgrid estimates the actions of all the microgrids by relying only on the information exchanged with some neighbors over a communication network. To effectively reduce unnecessary signal transmission among the agents, an adaptive algorithm,... 

Access to a reduced and fast mathematical model that can predict the input-output behavior of interconnected systems with acceptable accuracy and in a short time is crucial. The purpose of this project is to provide an object-oriented platform for identifying a model based on input-output data of interconnected systems in real-time. On this basis, in the case of developing fast estimation algorithms and updating the model quickly (in case of extensive changes in the system), good predictions of the model can be used for various applications. In this research, machine learning and data analysis methods are used to extract useful features and relations from data. Then, taken advantage of this... 

User cooperation is an important concept in wireless networks to achieve best performance subject to low cost. Dynamic and broadcast natures of wireless networks are two indispensable characteristics of these networks. Therefore, when a user transmits his signal to the receiver, other users in his neighborhood may receive the signal as well. Hence, these neighbors can decide to cooperate with each other in transmitting their messages to the receiver. On the other hand, due to the dynamic nature of the wireless networks, one can assume that each user has some knowledge about the interference signals or the fading coefficient that are not known to the other users. Therefore by utilizing user... 

Reliable and secure communication requires low error probability and low information leakage, respectively. But there are different metrics for error probability and information leakage. Two important reliability metrics are ϵ or zero probability of error. An ϵ-error criterion requires the (average or maximal) error probability to vanish as the blocklength increases, while a zero-error criterion, demands the error to be exactly zero for every given bloklength. Three important security metrics are weak, strong, or perfect secrecy. A weak notion of secrecy requires the percentage of the message that is leaked to vanish as the code blocklength increases, while a strong notion of secrecy... 

The rapid evolution of artificial intelligence (AI) technologies has led to the widespread adoption of AI systems in diverse research and industrial fields. Deep neural networks, at the forefront of AI's power, demonstrate high performance by leveraging large volumes of training data. However, acquiring such vast amounts of data requires collaboration among individual data owners, who may have concerns about privacy. To address these concerns, various privacy-preserving methodologies have been proposed. These methodologies share a common goal of striking a balance between preserving privacy and maintaining data utility. This study aims to explore and analyze these privacy protection... 

Regarding to the emergence of quantum computers and advances in the large scale implementation of them, exploiting hard problems of coding theory is of great importance.This family of problems, like those of lattices, has an acceptable resistance against classic and quantum attacks. Thus, they can be replaced with hard problems in number theory and algebra. Increasing dominance of cyberspace made us highly dependent to it. Consequently, preparing tools and methods to mitigate future threats is necessary. Digital signatures constitute an important family of cryptographic primitives. Code-based digital signatures are mostly suffering from two main drawbacks: large public key and long time of... 

Two new frameworks for achievability proof in network information theory (NIT) are introduced . The first framework which we call it OSRB (Output Statistics of Random Binning) framework, uses random binning arguments and is based on a duality between channel and source coding problems. Furthermore, the OSRB framework uses pmf approximation arguments instead of counting and typicality which are used widely in conventional achievability proofs in NIT. This allows for proving coordination and strong secrecy problems, where certain statistical conditions on the distribution of random variables need to be satisfied. These statistical conditions include independence between messages and... 

Two new frameworks for achievability proof in network information theory (NIT) are introduced . The first framework which we call it OSRB (Output Statistics of Random Binning) framework, uses random binning arguments and is based on a duality between channel and source coding problems. Furthermore, the OSRB framework uses pmf approximation arguments instead of counting and typicality which are used widely in conventional achievability proofs in NIT. This allows for proving coordination and strong secrecy problems, where certain statistical conditions on the
distribution of random variables need to be satisfied. These statistical conditions include independence between messages and... 

“Decode and Forward” is one of coding strategies used in relay channel and networks in which each relay in the network decodes the transmitted message by the sender and other relays in the network and then re-encode and transmit it to the other relays and the receiver in the network. This process results in the cooperation between the relays and the sender to remove the uncertainty of the receiver about the transmitted message. “irregular encoding-successive decoding”, “regular encoding-backward decoding” and “regular encoding-sliding window decoding” are different methods usually used in “Decode and Forward” strategy. “partial decode and forward” is a generalized form of “decode and... 

In this thesis the problem of simultaneously generating multiple keys among multiple terminals is investigated. After providing a survey on the related works and exploiting the problem of sharing a common secret key and a private key among three terminals, we introduce a new source model which we call it the Four-Terminal model. We consider the problem of generating three kinds of keys among legitimate terminals and investigate the problem under two different scenarios, Backward and Forward scenarios, which depend on the kind of restrictions imposed on the usage of the public channel. We derive an achievable region for the backward scenario, using the combination of superposition coding and... 

In order to utilize cooperative resources of a network, we have to investigate cooperative networks and strategies. Information theory, by introducing different concepts such as coordination and common information, gives us a suitable tool to study cooperative networks and using their resources. In this thesis, we investigate coordination and secret key agreement in cooperative networks. Our study consists of two parts. In the first part, we consider coordination and its applications in cooperative networks. For this purpose, we introduce the triangular multiterminal network as a proper model for studying empirical coordination in multiterminal networks and establish an inner and outer... 

In this thesis, the problem of secret key agreement in the channel model with side information is studiedx. In order to investigate the problem, we consider three models according to the different ways of side information availability which are the state-dependent broadcast channel; the state-dependent broadcast channel in presence of public channel and the state-dependent wiretap channel with degraded versions of the channel state information.For the problem of secret key agreement in broadcast channels, two models, the state-dependent wiretap channel and state-dependent three receivers broadcast channel, are considered. We obtain inner and outer bounds of the secret key capacity region for... 

Interference management is one of the key issues in wireless networks wherein multiple source-destination pairs share the same medium and frequency band and interfere with each other. The exponentially growth in the number of wireless systems and services results in the spectrum shortage which has emerged the technologies that increase the spectral efficiency. Providing the users with cognition equipments in these networks enables them to sense the medium and use the obtained data to adapt their transmissions to cooperate with other users and improve their own rates as well as the others which results in the cognitive radio technology. In order to access the full potential of this technology,... 

Due to the remarkable growth in using communication networks such as ad-hoc, wireless and sensor networks, studying the building blocks of these networks (e.g., relay channel and interference channel) from information theoretic viewpoint and investigating cooperative strategies have recently received considerable attention. Also, owing to wide range of applications, state-dependent channels have been widely studied. In this dissertation, at first, we consider a state-dependent relay channel (SD-RC). For the cases wherein channel states are available causally or non-causally at different nodes, we propose new achievable rates for this channel using compress-and-forward strategy. Also we... 

This research aims to establish a novel approach to meet the capacity utilization challenge of the freight forwarders in order to maximize the expected revenue in a cargo network. The two-dimensional cargo capacities are assumed to be stochastic and limited in each leg. A stochastic dynamic programming model is developed to demonstrate the maximization of expected revenue over a finite planning horizon, in which each fare class request is to be either accepted or rejected. Although the main problem is computationally intractable due to multidimensional state variable, it can be decomposed into one-dimensional capacity control sub-problems for each leg. A heuristic algorithm is developed to...