Sharif Digital Repository

The most important researchers’ purposes in superconductivity are achievement of the room temperature superconductivity and to understand the high temperature superconductivity mechanism. Researchers’ goal in to increase the transition temperature by applying pressure, changing oxygen content, different doping, and changing stoichiometry in the families of the high temperature superconductors. In this research, which has been carried out in the Magnet Research Laboratary of Sharif University of Technology, samples of Y3Ba5Cu8O18, Gd3Ba5Cu8O18, and Pr3Ba5Cu8O18 have been synthesized by the standard solid-state reaction technique, the structure, electrical and magnetic properties of the... 

In communications systems, coding is used to combat channel errors. The redundancy introduced by coding enables the detection and/or correction of errors occurring in the channel. In addition to communications systems, coding is also beneficial in various other systems such as distributed storage systems and blockchain systems to cope with node failures, data erasures, and adversarial behaviors attempting to modify information. In existing applications of coding, it is generally assumed that the encoding operation is performed correctly and without errors, and errors are applied to the encoded data. In recent years, applications have emerged where the assumption of error-free encoding is not... 

Simulation optimization has been one of the most important topics in recent years. It is especially useful when the objective function cannot be computed directly or some of the parameters are stochastic. Buffer allocation problem is one of the important problems related to production lines. In this problem the objective is to determine the buffers between workstations so that the throughput is maximized. Non-linear and combinatorial nature of the problem, stochastic factors like machine breakdown or processing times and most importantly lack of a distinct relation for the objective function are the reasons of using simulation ... 

How is it possible for mind to be directed to the world? Or for it to be opened to the world? This question – formulated as the problem of knowledge - has been the central question of the modern philosophy. Rediscovering of the concept of "intentionality" as the mark of the mental by Franz Brentano, Contemporary philosophy succeeded in addressing this central question in a more direct and explicit a way. Intentional character of mind is more obvious in sensory experiences. Perception seems to be the minds openness to the world. But the possibility of having illusory or hallucinatory experiences challenges that very conception of perceptual experiences as openness. In analytic philosophy... 

In the last years, we have seen a rapid growth of data generation that leads to an increasing need for data analysis and big data technologies. Meanwhile, cloud computing witnessed great popularity and has become one of the best platforms for big data analytics due to its flexibility and scalability. However, there is not an obvious method for choosing the right cluster configuration for running big data jobs in clouds. Because different big data applications, workloads and cloud configurations can lead to different costs. Moreover, a heterogeneous cluster can use the benefits of distinguished properties of each machine to reduce the cost and execution time of the big data application. The... 

Given an event O and a set of experts E, we describe a method for finding a subset of experts S whose aggregated opinions best predict the outcome of O. Therefor, the problem can be regarded as team formation for performing a prediction task. In order to estimate competency of each team we propose measure Sum Squared Error which uses experts’ records of predictions during past k days. For simplicity, opinion pooling is selected as the method of information aggregation. we prove in case of simple averaging of opinions,finding best team is NP-hard. we suggest some rounding and heuristic algorithms for finding near optimal solutions. Simulation results show that a variation of tabu search used... 

In the last decade, the developement of Quantum Information theory have created new concepts and methods in the study of quantum many-body systems, that previously weren’t available to physicist involved in areas such as condensed matter and field theory. One of the most important steps is the insight provided by structure of the many body system’s Hilbert space. Although, it is not completed, it leads us to deep results.In fact, we have found out that with high probability, the state of a many-body system is located in a very small corner of the Hilbert space, which requires only a small number of parameteres to describe it, that with respect to the number of particles, it grows linearly... 

The major objectives of this study are to analytically and experimentally investigate the rheological behavior of polymers in the fractured carbonate medium based on the polymer solution properties and operational conditions. The intrinsic and apparent viscosity of high molecular weight-partially hydrolyzed poly (acrylamide) which is mainly used in enhanced oil recovery (EOR) processes hasbeen investigated in reservoir conditions. Since, the EOR efficiency of hydrolyzed poly (acrylamide) is very sensitive to the temperature and salinity of petroleumreservoirs; investigations have been carried out at different possible reservoirtemperatures using high saline polymer solutions. The parameters... 

The abstract is the most important section of the thesis because many readers limit most of their reading to abstracts, saving in-depth reading for specific theses. It should give the reader a "preview" of what's to come. The abstract should emphasize new and important aspects of the study or observations. The purpose of the abstract is to allow researchers to decide whether or not to read the whole thesis. The abstract is what researchers read first to decide if the thesis is important, interesting, and it allows them to assess the relevance of a thesis to their own research, without having to read the entire thesis. Thus, it is crucial that the abstract both summarize succinctly the key... 

Emission of CO2 and its diffusion into atmosphere is associated with negative effects on the environmental such as Green House Gases effect. Various techniques of CO2 Capture in energy conversion and processing plant are investigated. A method of CO2 Capture could be based on utilization of solar energy for producing methanol. Basic design of such a system and feasibility analysis of developing that system has been considered on the subject of the present research work. Basic design and commercial feasibility of the system producing methanol through capturing CO2 from exhaust gases of a power plant and hydrogen produced by using solar energy have done such an integrated system. The main... 

Wireless networks with the shared media require Medium Access Control (MAC) protocol that provides contention resolution mechanism. The design of MAC protocol is a challenging issue because of limited energy source and high propagation delay in UnderWater Acoustic Sensor Networks (UWASNs). The most important goal of the MAC design for underwater sensor networks is to resolve data packet collision efficiently with respect to energy consumption. So, selection of MAC protocol is an important task because it has significant impact on the system efficiency. A suitable MAC protocol must consider some factors such as fairness, energy consumption, latency and throughput based on various... 

In this study, the effect of green coffee extract powder, as a green corrosion inhibitor of steel in a concrete simulation environment was investigated. In this study, the green coffee extract was obtained by the Maceration method and its performance was investigated by weight loss method, electrochemical methods including Polarization, Electrochemical Impedance Spectroscopy. Scanning Electron Microscopy images were also used to visualize the corroded areas. The results of the polarization test showed that 450 mg/lit of coffee extract powder at 25 °C has the corrosion inhibiting efficiency of about 82% and the corrosion rate of the bare sample reduced from 6 to 1.16 mpy. The dosage of 550...