Sharif Digital Repository

Wireless sensor networks (WSNs) are tiny devices with limited computation and power supply. For such devices, data transmission is a very energy-consuming operation. Data aggregation eliminates redundancy and minimizes the number of transmissions in order to save energy. This research explores the efficiency of data aggregation by focusing on different aspects of the problem such as energy efficiency, latency and accuracy. To achieve this goal, we first investigate data aggregation efficiency with constraint on delay, which can be compatible with other important system properties such as energy consumption and accuracy. By simulation, we will show that, depending on the application, we can... 

Post-tensioning is the most versatile form of prestressing, a technique which enables engineers to make the most effective use of the material properties of concrete, and so to design structural elements which are strong, slender, and efficient. Design of post-tensioned concrete structures is not difficult and, if done properly can contribute significantly to the economy and the aesthetic qualities of a structure. Post-tensioned building floors and bridge girders have found widespread use in office buildings, parking structures and bridges. They are also frequently employed in warehouses and public buildings. Now a days bridges and other type of structures, in many countries are designed... 

The primary aim of this research is to test the weak form of Efficient Market Hypothesis in Iran’s Housing Market. Average price of one square meter of residential property is provided by The Ministry of Housing and Urban Development in urban areas of Iran with different frequencies. The data is available in the form of quarterly time series for the metropolitan districts of capital of Tehran, semi-annual time series for five major mega cities and annual time series for a group of eighteen cities. The econometric tests performed to evaluate the market efficiency can be grouped to two main categories i.e. tests performed on time series data and tests performed on panel data. Three alternative... 

The Use of peer-to-peer architectures instead of traditional client-server architecture can be beneficial in many aspects such as increasing scalability of the systems, enhancing fault tolerance in critical situations, extending the system resources and various other advantages. Nowadays, many applications are based on peer-to-peer architectures and as a result, a large portion of the internet traffic is produced by these applications. This has been a motivation to many researchers to focus on reducing the amount of this traffic while satisfying the content distribution demands. One of the main problems that can result in generating large amount of traffic and also long response times for... 

Due to increase of industrial plants and development of cities in the world, there is an increase in demand for all types of energy, especially fossil fuels.Consequently, energy related decisions have become an important factor in national and international political decision makings. Regarding to remarkable effects of energy decisions on economical, industrial, political, social and environmental aspects of our country and considering the importance of energy management in our country as an energy-based country, we have focused in this research on studying several energy management systems (national and international systems) and made an assessment on their applicability and effectiveness.... 

Today, peer to peer networks have become quite popular due to their ability to easy access to shared resources regardless of their location in World. In these systems files are stored at the end user machines which named peer, rather than at a central server, in contrast to the traditional client-server systems, files are transferred directly between peers. sending and receiving those data, occupy a large amount of the internet bandwidth. So, by improving the efficiency of these networks, the total efficiency of the internet will improved. These systems are usually constructed on the other networks such as TCP/IP as an underlay or physical networks. Despite of structure of peer to peer... 

In the present research, the weak level efficiency of securitise market is reviewed and examined .Therefore the “Random Walk Hypothesis” has been examined on the time series of daily efficiency index of TEHRAN SECURITISE MARKET. The main difference between this research and the previous researches which have been performed previously in Iran, is the method of Hypothesis Test. The” Variance Ratio Test” has been used as a method of Hypothesis’ Test. In the second chapter, the theoretical and experimental literatures of this research has been described in detail. In parallel with the ” Variance Ratio Test”, the impact of the Day of week and the “HETROSCEDASITY TEST” also has been... 

Evolving Informational Efficiency in financial markets is of a significant role in the financial economic development. The present research is an endeavour to test the efficiency improvement in Tehran stock exchange by a GARCH-M model which is estimated by Kalman Filter technique. To conduct the estimation and tests, we have used daily data (over 1384-1388) on the return of Bank and Financial intermediaries, Metal groups and the main index of TSE. The findings show that the information inefficiency hypothesis can not be rejected, although any noticeable improvements are not observed in the inefficiency trend of the financial time series, the level of inefficiency trends are rather different... 

In the ongoing research project on tall buildings, the study of wind-induced demands is categorized as: along-wind and crosswind responses. These demands are caused by different mechanisms. Moving along the wind-induced is due to the effects of turbulence impact while the perpendicular component is related to the effects of windstorm. Along-wind response may be of special importance with respect to the comfort criteria. The loading condition on skyscrapers may differ from low-rise buildings due to the number of stories, on structures due to the high number of stories, and the importance of dynamic effects of current loading (wind). On the other hand the effect of wind load on tall structures... 

These days, according to increasing requirement to the applications of clean rooms in industries in and within the developing industry of computer, positive indicators that show a real need to a compere comprehensive study and research about the Clean rooms, in oder to predict the distribution and dispersal of the particles. Correct determination of indoor airflow and particle concentration distribution results in new standard development for Clean rooms. As computational fluid dynamics has become a powerful tool for indoor airflow studies, in this research, influence of effective parameters on the flow and concentration distribution in clean rooms has been... 

In this study different models of an aerodynamic particle sizer and aerodynamic focusing lens were introduced and governing equations for an aerodynamic focusing lens for flow fields and particle motions were discussed. An aerodynamic focusing lens was simulated for analyzing particle motions and flow fields. Two kinds of models are considered; One was Ahmadi`s model and the other one was Wang`s model and both models are axisymmetric. The results show that for small particles (sub 30 nanometers), Brownian motions were highly effective on transmission efficiency and producing particle beams. The two models are compared and the results show that Ahmadi`s model produce narrower particle beams... 

Nanofluids are new engineering materials with great potential for application in process industries. Their enhanced heat-transfer properties are reported in recent literatures. However, with respect to the influence of nanoparticles on mass transfer characteristics, limited number of studies available in the literature, deal primarily with gas-liquid systems. In this work, mass transfer performance and droplet behavior along a pulsed liquid-liquid extraction column, is studied where SiO2 nanoparticles with concentrations of 0.01, 0.05 and 0.1 vol% and different hydrophobicities are applied to the dispersed phase. Using ultrasonication, nanoparticles were dispersed in kerosene as the base... 

Entrepreneurship is a process that requires high motivation for success. Self-efficacy is to believe the person's ability to organize and carry out certain types of activities to produce specific outcomes. Thus helping to increase self-efficacy beliefs in people who have attempted to entrepreneurship can increase their chances of success. On the other hand Self-leadership has been defined as “the process” of influencing oneself to establish the self-direction and self-motivation needed to perform. And include three major strategies named Behavioral focused strategies, Intrinsic motivation (Natural Reward) strategies, Constructive thought pattern strategies and some specific behaviors in each... 

A lot of efforts to make CMOS integrated wireless systems have been made in the past few years. One of the most challengeable parts of wireless systems is power amplifier designing with high output power (Watt Level). Power amplifier linearization and efficiency are the most important parameters. Today, high linear and efficiency power amplifier designing is one of the most important designer challenge of integrated circuits in wireless networks. Generally, there is one inverse relation between linearization and power efficiency. So, circuit and system solutions have been suggested that high efficiency nonlinear switching power amplifier with linearization techniques and linear power... 

The economic activities in a country involved with depletion of natural resources and emission of pollutants and gases to the environment. Depletion of exhaustible resources and environmental pollutions are two determinants of sustainability of development. The present research work is aimed at studying the sustainability of Iranian economy in 2009. The analysis of sustainable development of economy is based the concept of exergy, exergy efficiency and ecological exergy efficiency. Exergy efficiency is the ratio of the exergy of a product in economic activity to the exergy of input streams to that section of economy. Ecological exergy efficiency is defined as the ratio of exergy of product... 

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... 

With increasing rate of digital information in the world, design, configuration, and networking of enterprise storage systems has become an essential part in designing data centers. The performance of data storage systems in serving incoming requests is one of the major parameters of such systems. A major metric to measure performance is response time. This parameter is, in particular, crucial in enterprise applications such as financial, credit, multimedia, and real-time applications. A common approach to enhance the performance of enterprise storage systems is improving the hit ratio of the system global memory using prefetching technique. Using prefetching technique, a data block is... 

Centrifugal compressors have wide applications in the turbochargers, aircraft propulsion and petrochemical industry. Therefore it is important to design high efficiency centrifugal compressor. Knowledge of compressor performance at different conditions, energy losses and the contribution of each component of compressor in efficiency losses have of great importance.
In this research, different loss models of the centrifugal compressor were reviewed and investigated. Then 1D codes were developed based on the loss models, and performance characteristics of S2B Schweitzer and GT4082 Garret compressors at different conditions were achieved. In order to evaluate the modeling results,... 

In this thesis, the goal is to improve the efficiency of quantum and solar cell. The effect of quantum wells was simulated by Silvaco. Initially, the quantum well has been adjusted to a cell junction GaAs. Then, using quantum wells in cell junction towing and three, improving short-circuit, the returns will be 53.79% and 54.33%. This efficiency is about 10% more than the triple-junction solar cells. To improve the efficiency effects of layer thicknesses, parameters, and the number of quantum wells were studied.Tandem cell is 〖In〗_0.51 〖Ga〗_0.49 P/GaAs, and triple is 〖In〗_0.51 〖Ga〗_0.49 P/GaAs/〖In〗_0.28 〖Ga〗_0.72 As. By adjusting the quantum well and sandwiching the well layers staggered by... 

In this essay, by putting in the framework of linear-quadratic optimal control (LQ),we study and solve the mean-variance portfolio selection problem. Two models will be studied in our work; in one we assume that the price process satisfies a diffusion stochastic differential equation, while in the second model, we assume it to satisfy a jump-diffusion stochastic differential equation. In both models, a formula for the efficient frontier is obtained. This essay is mainly obtained from the works of the following articles and books:
1)X.Y. Zhou and D. Li, Continuous-Time Mean-Variance Portfolio Selection:A Stochastic LQ Framework. Applied Mathematics and Optimization. 42(2000),...