Sharif Digital Repository

Tipping points occur in diverse systems in various disciplines such as ecology, climate science, economy, sociology, and engineering. Critical thresholds in system parameters or state variables at which a tiny perturbation can lead to a qualitative change in the system exist in many subsystems in complex systems. These thresholds are called tipping points, and these subsystems are called tipping elements. Additionally, many systems with tipping points can be modeled as networks of coupled multistable subsystems. Domino-like tippings are called tipping cascades. Considering that these tipping cascades are primarily unprecedented, it is essential to study the dynamics and control of these... 

Oil pollutants are among the important sources of pollution in countries with oil and gas industries such as Iran. Soil pollution by these pollutants is one of the environmental issues and hazards. All kinds of organic and inorganic pollutants in the soil may penetrate the underground water or enter the atmosphere in the form of gas, which respectively enters the food chain through absorption by plants or enter the body of living organisms through breathing. They include humans, which are a threat to the health and life of living beings. For example, many of these pollutions cause diseases such as cancer, suppression of the body's immune system, or even obesity; therefore, it is necessary to... 

Cancer is a life-threatening group of diseases that arises from the uncontrolled growth and division of cells in the body. Treatment options for cancer include surgery, chemotherapy, radiation therapy, immunotherapy, targeted therapy, and hormone therapy. However, resistance to anticancer drugs can develop through a variety of mechanisms, such as the upregulation of drug efflux pumps and alterations in DNA repair mechanisms. One common mechanism of drug resistance is through changes in metabolism, where cancer cells switch to alternative metabolic pathways to survive and evade the effects of anticancer drugs. The development of new drugs targeting specific molecules and pathways involved in... 

Security for wireless communication networks has become a crucial issue because of the broadcast nature of wireless channels. On every cellular network Since it is possible for passive nodes to easily overhear the confidential information transmitted between transmitter and receiver, it is necessary to provide secure communication.When a cellular user wants to communicate with a node or base station on the cellular network, it expects that information will be transmitted and received without interference, with enough quality and without eavesdropping. On the other hand In practical scenarios, we know that cellular network nodes are not equipped with ideal equipment and some percent... 

In this thesis, we review recent advances on controlling of complex systems. We provide in details, the concepts of synchronizability and synchronization controllability.Then we will investigate synchronization controllability under different pinning schemes, and propose a new pinning strategy to increase controllability and consequently decrease the number of required pinned nodes (known as driver nodes) to assure a stable synchronized state. We also study the network characteristics of resulted sequence of driver nodes. Finally, we will employ our proposed schemes to study the controllability of complex networks of chaotic Rossler oscillators  

In recent decades the Due to development of coating techniques and the diversity of high organic matter, Discussion of organic coating materials being raised. Moreover, because of many applications of organic thin film in electronic and optical systems for example OTFTs and OLEDs Organic thin film growth topic is very interesting for scientists. Among these, some scientists study the theory and another bunch of scientists pay to practical aspects of this topic. In this thesis I pay to the theoretical level of Organic thin film growth and I simulate the system includes a collection of molecules, Went on to study some statistical properties of the system will be discussed and the dynamic... 

In this thesis we study the dispersion of one-dimensional scalar waves in a random media. We used the finite difference method to obtain the numerical solution of wave equation in this media. Then we were able to find wave signals for different disorder intensities and at different distances from the source. Using the Wavelet Transform, intresting features such as phase and group velocity can be studied. The Morlet function is used as the mother wavelet for decomposing the signals at different places. Cross-correlation functions of Wavlet transforms of the signals at different positions are used to obtain phase velocity and its dependence on frequency. We show how the phase velocity at the... 

Since recording first electroencephalogram (EEG) of human brain in 1929 until now it becomes as a powerful tool in neuroscience. At first information extraction was done by visionary approaches only. But because of some problems in the context of inaccuracy and also in analyzing data different methods were proposed in order to extract hidden information of EEG. Among these approaches Fourier transformation was suggested as a very useful method that could draw out so many characteristics of signal different frequency components. However this way had many faults that cause limitation in analyzing time series and as a result other methods have been considered. One method that later has been... 

The synchronization phenomena are abundant is science, nature, engineering, and social life. Systems as diverse as clocks, singing crickets, cardiac pacemakers, firing neurons, and applauding audiences exhibit a tendency to operate in synchrony. These phenomena are universal and can be understood within a common framework based on modern nonlinear dynamics. First chapter of this thesis describes the basic ideas of the synchronization in an intuitive way. The main physical concepts are presented with experimental examples.
One of the main effects of synchronization is the ability to infer the directionality of coupling for two time series. Uncovering the directionality of coupling is a... 

Pesticides are broadly applied in croplands, glasshouses, and orchards in order to increase agricultural products and their quality. Among the variety of pesticides, organophosphorus pesticides (OPs), possessing high insecticidal activity, acute toxicity and relatively short environmental persistence, have been widely used for pest control in agriculture. However, this effect might lead to adverse health impacts or death for mammals and humans. Thus, even at trace levels, it is of great importance to develop a simple, sensitive, inexpensive and real-time detection method for monitoring the levels of pesticides in the environment, foodstuffs and biological samples. The integration of metallic... 

In this thesis we would like to investigate structural disorder of Graphene and its effect on electronic properties. Graphene is a one-layer crystal of Carbon atoms which was the first two dimensional crystal observed experimentally. Low energy current carriers on Graphene behave like mass-less Dirac fermions and this interesting electronic property attracts much attention on studying Graphene. Structural disorder of Graphene highly affects its electronic properties. We study thermal fluctuations of Graphene sheet, disorder super lattice, and static ripples, as structural disorders of Graphene. Disorders due to thermal fluctuations of graphene induce a disordered gauge field on the graphene... 

In this thesis, we first briefly review the basic concepts of stochastic processes. After reviewing and studying the dynamic equation that can explain a stochastic process, we show how one can find on a data-driven basis, the first-, second- and higher-order interactions between different subunits of a complex system by disentangling the dynamics of multivariate time series into stochastic and deterministic parts. Our data-driven approach is to detect different degrees of interactions obtained using conditional moments of Kramers-Moyal coefficients from unconditioned correlation functions and statistical moments of multivariate N-dimensional multivariate time series. Finally, we study the... 

In this thesis the resilience of a neural network is examined under structural perturbation.The network consists of Spiking neurons with specific dynamics or they are binary neurons and the network is non-spiking. Neural network is a multi-dimensional and multi-stable system therefore we can map their dynamical equations to effective one-dimensional equation with one parameter which shows the environmental conditions.The resilience of the system is evaluated with respect to changes in weights and edges of the network and the the resilience pattern of the system is obtained.Finally, the recovery and control methods are briefly discussed  

Complex systems involve a large number of degrees of freedom and consist of many components. Interactions of these components with each other, or with an external force, play a significant role in the collective behavior of the complex system.We come across complex systems in many different fields of study including neuroscience, climatology, studying stock markets, etc. The non-linearity of the interactions between their components is what they have in common. Interesting macro-scale properties can be observed in a complex system, as a result of the collective behavior of the system components. We usually focus on studying a group of components in a system, rather than a single component,... 

According to the Pawula theorem, we know that stochastic processes with non-vanishing higher-order Kramers-Moyal coefficients cannot be described by the Fokker-Planck and Langevin equation. Using rotating Gaussian white noise, we define generalized Brownian motion of different orders, also known as fractional Brownian motion. Similar to the Langevin equation, which is used for the random behavior of a stochastic process using standard Brownian motion, we also use a set of generalized Brownian motions for the random behavior of a stochastic process that has non-vanishing higher-order Kramers-Moyal coefficients of higher orders. Given that these noises are complex-valued, we define the... 

In this thesis, we first provide a brief overview of the basic concepts of stochastic processes and the mathematical tools required to study these processes. Then, we demonstrate that by using a data-driven approach, one can obtain the corresponding coefficients for deterministic, diffusion, and jump components of the stochastic process. In this method, the conditional moments of Kramers–Moyal coefficients are calculated using statistical moments of N-dimensional time series. These coefficients enable us to determine different orders of interactions, diffusion and jump properties, and %relationships coupling coefficients between time series. Furthermore, to evaluate the accuracy of the... 

A complex system consists of a large number of subsystems that interact with each other and with the environment. These systems have collective behaviors that may are desired and undesired. Learning, intelligence and epilepsy are examples of desirable and undesirable collective behaviors. Control of these systems arises when they are out of the desired state or one wants to avoid approaching the system to its undesired state. For control of complex systems, we need external functions that apply to specific subsystems. These functions can be obtained from the numerical solution of Hamilton-Jacobi-Bellman equation. The Hamilton-Jacobi-Bellman equation is nonlinear and must be solved at very... 

Nowadays, applications of industrial robots are significantly increasing due to their flexibility, programmable, accuracy, rapidity and etc. Among these, machining robots play an important role at manufacturing industries. One of the main concerns of the researchers, is the tip vibrations of robot arms. In most times, these vibrations are self-excited, unpredictable and intolerable. Thus, finding a method for reducing vibration should be investigated. The purpose of vibration control is vibration suppression to enhance the reliability of the system. The aim of this project is the modeling of the machining robot arm in turning process and then application of robust control to reduce...