Sharif Digital Repository

Transcranial direct current stimulation (tDCS) over the different brain regions has been documented in clinical and laboratory experiments. Anodal tDCS on the dorsolateral prefrontal cortex (DLPFC) has shown promising effects in enhancing cognition. Furthermore, such stimulations have been proposed in treatment of several neurological and psychological disorders. Investigations have verified the positive effect of such stimulations on drug addicts by diminishing their drug craving after stimulation. In spite of the extended research in this field, the effect of tDCS on different brain region and brain networks has yet not been studied through computational models. In this study, we evaluated... 

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... 

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... 

Quantum Information Processing (QIP) is one of the active areas of research in both theoretical and experimental physics. Any experimental technique that is used for a scalable implementation of QIP must satisfy DiVincenzo’s criteria [17]. Nuclear Magnetic Resonance (NMR) satisfies many of these conditions, but it is not scalable and cannot initialize the qubits to pure state [28]. NMR can be a great platform for studying the fundamentals of QIP. In this project, for a two­qubit system, we prepare pseudo pure states from the initial mixed states by using unitary operations and implement CNOT gates. According to the results of our experiments, we can apply all the gates with high fidelity.... 

This is common for organizations to don't move in their specified mission statement direction, because of pressures for saving themselves in reaction to environment changes. This problem can be addressed as conflict between survival and identity. In this thesis we approach this problem by synthesizing "Viable System Model" and "System Dynamics". Basic of this model shaped on viable system model structure and system dynamics modeling. In literature there is only two such models. But they are not detailed enough for providing mathematical analysis. In this research, law of requisite variety (one of the key principles in cybernetics) has been quantified. In this synthetic model, appropriate... 

Space debris have increasing importance for space missions. The towing removal scheme is one of the most promising ways for active removal of these debris from LEO orbits. In this approach, an active propelled satellite captures the debris via a space tether and a tethered net which by producing a force opposite to its velocity, it will cause deorbiting and burning the debris in the dense atmosphere. One of the issues with this technique is the danger of tether rupture which for solving that two tethers instead of one can be used. In this research study of active removal of flexible space debris via double tethered towing system has been done. Dynamic modeling has been done with Newton’s and...