Sharif Digital Repository

In this thesis NJL and quark-meson models, as effective models for quantum chro-modynamics in low energies, are studied mainly. After reviewing models and phe-nomena related to the strong interaction in zero and non-zero temperature, firstly the critical coupling of NJL model for non-zero temperature and chemical potential is calculated. Then, the contribution of ring diagrams in the effective potential of quark-meson model is presented. Finaly, the effect of ring diagrams of quark-meson model on chiral phase transition is investigated. For NJL model, it is shown that the chemical potential lowers the critical coupling for chiral phase transition. Also for quark-meson model, it is shown that... 

By definition, Mobile Clouds are networks of mobile nodes, which are connected together using short-range communication links, and at the same time keep their connection with the long-range cellular networks. Short-range communication links in Mobile Clouds provide the opportunity of Resource Sharing, which can result in new services for end-users. These services are beyond the boundaries of traditional networks.
In the following report, we aim at focusing on some problems related to Mobile Clouds. First, we present a centralized model for managing the mobility of the nodes; then we try to propose algorithms for efficient data update and processing; and finally, we introduce a novel... 

In this research, we have studied the effect of coding techniques, as well as partial data placement in cache memories throughout the network. Cache memories play an important role in information centric networks. As content delivery account for the major part of data transfers in current IP-based data networks, these network structures have gained much attention recently and hence optimizing cache performance in their structure is of great importance.Throughout this research, we first analyze the effect of simultaneous data delivery from multiple cache memories on the network performance. We consider two basic models for the network graph; and show there exists a fundamental trade-off among... 

As fossil fuels are still the world's most important source of energy, as well as the maturity of most of the world's oil reservoirs, there is a need for enhanced oil recovery methods to meet the world's increasing oil demands. MEOR methods are new and promising methods that are still in the research and development stage. One of the MEOR methods is the use of biosurfactants, which increase the oil recovery by two mechanisms: 1) reducing the interfacial tension between water and oil and 2) changing the wettability of the rock. In this study, the performance of two glycolipid biosurfactants, rhamnolipid and sophorolipid, in increasing oil recovery has been investigated. Initially, surface... 

The methods of Enhanced Oil Recovery (EOR) from reservoirs have been taken into consideration recently due to the decline in oil reserves and the rise in energy demand. Studies and investigations indicate the tremendous potential of chemical approaches based on injecting ionic liquids into the porous media with the goal of improving oil recovery. Additionally, hydrogels and polymers, which are two of the process' primary materials, are thought to be good alternatives. In the current study, a hydrogel based on carboxymethyl cellulose was first created and synthesized. Ionic liquids based on imidazolium and triflate anion were then added, and their effectiveness in enhancing the properties... 

The following dissertation discusses Ionic Liquids (ILs) as an alternative to commercial surfactants for use in the Enhanced Oil Recovery process. Ionic Liquids came to researchers’ attention due to their environmental nature and their tolerance for high temperatures and salinity. In this work, firstly, an extensive literature review is carried out, and then, experiments are designed and performed to evaluate ILs’ surface activity and performance in a lab-scale EOR set-up. The Ionic Liquids used in this work consist of three types of methylimidazolium nitrate, [MIM]+[NO3]-, with three different alkyl chain lengths. This combination, and specifically the effect of nitrate anions on EOR and... 

Petrophysical properties of reservoir rocks are of the most important parameters in fluid flow simulation and reservoir characterization. Although in core laboratories some well-known procedures for determination of these parameters are applied, in almost all of them the rocks are assumed to be homogeneous and their properties are taken up as identical in all directions. To eliminate these unrealistic assumptions, an accurate, non-destructive technique with appropriate degree of resolution is required for recognition of internal heterogeneity of cores. Medical “CT Scanner” is one of these techniques whose information in conjunction of conventional experiments could reduce their limitations... 

The main purpose of this study is to evaluate the linkage between two constructs about teamwork activities. One of them is "self-leadership in teamwork", the extent to which a person could control and manage his thoughts and activities in teamwork. The other is "shared leadership orientation", which is about orientation of people to contribute in leadership processes. This linkage evaluated with consideration of "self-efficacy in shared leadership" as a moderator.
Questionnaires of self-leadership in teamwork and self-efficacy in shared leadership elicited from literature with a little change and shared leadership questionnaire developed in another study by the author.Questionnaires... 

Women are going to play more important roles in the economy of most countries including Iran. Hence, since the number of entrepreneurs among women is increasing, identifying characteristics and other factors that cause these group to be successful, is a critical issue. Studies show that entrepreneurs, especially women entrepreneurs, face numerous problems in their career. These problems are especially more demanding in societies with unique cultural attributes. Therefore, applying personal and managerial solutions in order to overcome these problems are necessary. On the other hand, researchers believe that one of the most effective and beneficial concepts helping entrepreneurs in their... 

The present study was performed aiming to identify the ethical dilemmas human resource managers confront with in Iranian project-based organizations as well as to trace out the underlying causes. “Ethical dilemma” refers to a decision making situation in which ethical considerations render all the alternatives inapt, thence making the decision making process ethically complex. First of all, a theoretical framework was developed based on the preceding research; then, the study was further conducted utilizing a qualitative research method with an exploratory approach. The data were collected using in-depth interviews and analysed using the theme analysis method. The corresponding interviewees... 

Using Distributed leadership framework while studying the leadership phenomena in teams, especially in educational environment, has received more attention by scholars in these years. Although the results of these researches indicated positive consequences mostly, the need for exploratory studies to identify situational and contextual factors in distributed leadership effectiveness has been mentioned. In other words, it has been suggested that the effectiveness of distributed leadership in teams may be affected by situational and contextual factors. In the current multiple case study, after the initial study of leadership and its functions in some schools of Sharif University of Technology,...