Sharif Digital Repository

Throughout the history of science, mankind has always invented tools and methods to help him deal with complex problems, means that constitute the science. Systems theory and all the tools and methods introduced by it to analyze and judge simple to complex systems, although relatively recent, has left an enormous impact on current life style by being one those very important sciences that make dealing with complex systems easier. On the other hand, the importance of educational systems and their impact over the success of societies and large systems is close to obvious. In today’s world, having an effective educational system which can deliver required information to people and prepare them... 

Data envelopment Analysis is a non parametric technique which estimates the efficiency of a decision making unit in compare with others. In correspondent literature this unit’s Inputs and outputs are often assumed to be deterministic, but in recent years different approaches which viewing the data as non deterministic are presented. In this study we propose an algorithm for determining the stability region of a DMU while we assume other DMUs’ data are fixed. This algorithm is based on changing the reference set of the under investigation DMU. In fact applying these changes make the DMU move toward other DMUs’ efficient frontiers and by using this fact it is possible to determine the... 

Gene expression using microarrays technology has special importance in biology studies especially in cancer researches. Using this technology we can assess expression level of several thousand genes simultaneously. One of the major applications of this technology is diseases’ diagnosis which cancers are the most important types of them. The problem in classifying microarray data is its high dimension; although number of samples hardly exceeds a hundred. This severe asymmetry and high dimensionality, results in reduction of accuracy, speed, stability and generalization of classification methods. Thus, one of the most important issues in cancer diagnosis is selection of related and useful... 

Controlled islanding, also known as system splitting, can effectively prevent blackouts of power system by separating it into two or more islands. To make each island reach steady state point by available measures, each island must be observable. This paper proposes a new modified three phase method to find proper splitting strategy, considering observability as a new constraint, to minimize effect of system splitting on network observability. Some techniques about strategy searching are introduced to increase its speediness and related algorithms are described in detail in this thesis. The simulation results presented show efficiency of method in finding proper splitting strategies. In the... 

In this thesis, dynamic behavior of the Iran’s power grid has been analyzed and inter-area oscillations of this grid have been studied. Important results of this thesis are inter-area oscillation modes characteristics, regions and coherent generators and tie-lines in expose of high amplitude oscillations. These results could be used in different applications. It is time consuming and complicated to apply complete model for dynamic analyzing, therefore in most of researches an equivalent dynamic model should be prepared. First step for constructing this grid is identifying coherent generators. There are different methods to identify coherent ones, but it is not possible to apply all of them... 

Online voltage stability assessment is essential for preventing the failure in power systems. Voltage instability in power systems usually occurs in consequence of contingency situations or continuous load increasing or both of them. A new method for online voltage stability assessment using the data acquired from phasor measurement units (PMUs) and offline trained decision trees is presented in this thesis. The index of voltage stability margin (VSM) is used for security assessment and considering WSCC criterion, different operation points are divided in two classes: safe and unsafe. In order to obtain the voltage stability margin and generate the database, a new method which has been named... 

oltage stability is a dynamic phenomenon. The time frame of interest for voltage stability phenomenon may vary from a few seconds to tens of minutes. Therefore, voltage stability may be either a short-term or a long-term phenomenon. The past proposed voltage stability protection schemes have major drawbacks in both static and dynamic aspects. To mitigate the drawbacks of the previously proposed voltage stability protection schemes in both static and dynamic domains two system protection schemes are proposed. In static domain, the proximity to the collapse point(i.e. proximity is measured by a voltage stability indicator) as well as the instability mechanism (i.e. determination of the most... 

This thesis addresses the problem of dynamic security assessment in power sys-tems with an emphasis on its application in restructured power systems and issues arising in its applications. The new electric utility environment has an immedi-ate consequence of emphasis on reliability and secure operation of power systems. This requires faster and more precise methods to assess the dynamic aspect of se-curity. On the other hand, this issue is becoming challenging when the determined dispatch might not be accommodated due to violation of the limits.This thesis addresses the problem of dynamic security assessment in power sys-tems with an emphasis on its application in restructured power systems... 

Conjugation of proteins to nanoparticles has numerous applications in sensing, imaging, delivery, catalysis, therapy and control of protein structure and activity. Therefore, characterizing the nanoparticle–protein interface is of great importance. A variety of covalent and non-covalent linking chemistries have been reported for nanoparticle attachment. Typically, a specific protein residue is linked directly to the nanoparticle core or to the ligand. As conjugation often affects the protein structure and function, techniques to probe structure and activity are assessed Characterization studies of nanoparticle–protein complexes show that the structure and function are influenced by the... 

In the present study, design and manufacturing of a connected pipe liquid fuel ramjet test platform is implemented for performance investigation of a research liquid fuel ramjet burner in the thermodynamic flight conditions. Design and manufacturing of platform systems include: the hot air supply system, the liquid fuel system and the square cross-sectional combustion chamber with the v-gutter shape flame holder. In order to determine the performance range of subsystems, calibration process has been carried out. Calibration process of the hot air supply system includes: determining of the burner inlet velocity and temperature. Also, calibration of the liquid fuel system includes: determining... 

In this research, aluminum composite foams reinforced with silicon carbides were manufactured using melt direct foaming with gas. The density of produced foams changed from 0.1 to 0.35 g cm-3. At first, simulation of bubble configuration was carried out in order to specify the effective parameters on foaming process. As the result, parameters such as ceramic particle volume percentage and gas type were selected. Results showed that, to process foam with acceptable stability, there was a critical minimum of ceramic particles concentration above which, stability of the foam was enhanced. Gas type was also showed to have a significant effect on foam stability. Argon, carbon dioxide and air were... 

AZ91 alloy (Mg-9Al-1Zn-0.2Mn) is the most important Magnesium casting alloy and because of its high strength to weight ratio, is increasingly demanded in automobile and aerospace industry as the best alloy of the present century. Poor creep resistance of AZ91 alloy is attributed to poor elevated temperature properties of Mg17Al12, which has melting point of 437°C. The softening of the Mg17Al12 phase at elevated temperature is the main cause of grain boundary sliding. in this investigation, The effects of addition of Si element on the microstructure and mechanical properties of AZ91 alloy have been studied as a solution to produce high temperature resistant magnesium alloys. The results show... 

Concrete gravity dams are structures of much importance which their failure due to earthquakes results in a catastrophe. Therefore, precise stability analysis of these types of dams against sliding and overturning is essential. The common method of safety assessment of gravity dams is based on limit equilibrium method assuming that dam slides and overturns as a rigid structure. Although providing high safety factors is somehow acceptable to meet the safety requirements of dams, it should be considered that the whole system of dam body and foundation is flexible in reality and its performance should be studied in this case for stability analysis. In this investigation, first, stability... 

In this thesis, an extended nonlinear model of peripheral milling process (2D) is presented. For the first time, cutting forces are described through a complete third order polynomial function of the axial depth of cut. Also, cubic nonlinearity is considered for the structural stiffness as a function of tool tip displacement. To complete the model, process damping and tool wear effects are also considered. A set of experiments including modal tests to determine natural frequencies and structural damping ratios; and also cutting force measurements at different feed rates to determine nonlinear cutting force coefficients, are carried out. Also, measurement of critical axial depth of cut at... 

Releasing radioactive materials in atmosphere and their damages on human health via emitting radioactivity, show the necessity of investigations on their behavior. To simulate behavior of radioactive materials in atmosphere, we use Gaussian plume model. Gaussian model as a mathematical tool can simulate diffusion of Gaseous matters. This model also can be employed for radioactive materials. Radioactive materials vanish by decaying and can be produced via decaying of their mothers! Therefore, later effect must be considered in the Gaussian model via a factor. Many factors like wind speed and weather conditions also are involved in diffusion of radioactive materials. By considering all of... 

Bluff bodies are commonly used to stabilize flames in many high-speed flow applications. V-gutters are one of the most common bluff bodies that are mainly used in ramjet combustors and turbojet or turbofan afterburners for flameholding. Aerodynamic characteristics of flow behind V-gutter has crucial effect on mechanism of flame stabilization, therefore more experimental investigations still seem to be necessary in this area. Particle Image Velocimetry technique which has high temporal and spatial resolution has been used in this research in order to better investigate the structure and dynamics of this unsteady and complex flow filed. Experiments were done on a reference V-gutter in... 

In this thesis, two kind of Kirchhoff type equations are investigated. for each of them we prove existence and uniqueness of weak solution by letting hypothesizes on problems functions and initial conditions and using Faedo-Galerkin method and some theorems in functional analysis. It is should be mentioned that one of the problems has unique strong solution according to compactness theorems. In the nest step stability of these equations are investigated. for this purpose it is showed that total energy of systems will tend to zero as time goes to infinity. Furthermore at the end of each chapter numerical results are presented to illustrate accuracy of obtained theoretical results. Finally we... 

Low temperature cracking is the most important type of asphalt pavement distress that occurs in cold climates. Up until the development of performance grading (PG) based binder specification, there was no irect indication of low temperature suitability of asphalt binders. PG specification was mainly developed for and validated by neat binders.
With increased use of modified asphalt binders in recent years, some of the limitations and shortcomings of the original PG specifications have surfaced.Considering that low temperature cracking is a fracture failure, it was hypothesized that tests based on the fracture mechanics and fracture energy parameter can lead to better classification of... 

Poorly damped Low Frequency electromechanical Oscillations (LFOs) confine the capability of power system transmission lines. This phenomenon, which is the result of dynamic interactions among generator groups, may make the system prone to small- signal instability in some cases. Due to the use of some system controllers such as AVRs, these oscillations are inevitable.
Hence, electromechanical modes detection and assessing stability margin are important requirement in power system planning and operation, and can provide significant help to power system operators by preventing stability problems.
From the distant past, in order to monitor small-signal stability, power system operators... 

Various application of polyethylene material in different industries caused to modern techniques for controlling and measuring specifications of micro-particle suspension. Many industries try to increase stability of suspensions in front of their phase separation.
Because of the consequences of suspension homogeneity, at first, we measured this property. Then, the stability was tested by three different methods. In the first method, the transmitted laser light was measured to assay the suspensions stability. In the second, number of sediments of particles was counted. Sedimentation velocity of particles was measured directly by using a horizontal microscope as the third method. The...