Sharif Digital Repository

By an increase in demands for multimedia services of mobile, wireless networks shall provide Quality of Service (QoS) requirements for users moving in cells. Multimedia services such as voice, data and image own different features and every QoS are different from the other due to delay and demand for bandwidth.
This thesis presents a new model of call admission control which consists of a few key elements for protecting the network in different conditions of workload in a manner that calls blocking /dropping are kept under desired level. This model consists of two traffic classes of voice and data in order to give apriority to handoff call over new call, the parameters in this model are... 

In this thesis, the orbit determination of Low Earth Orbits (LEO) using the integrated magnetometer and horizon sensor data has been investigated. Orbit determination is an essential part of a space mission. Not only the modeling, guidance, navigation and control errors may results in error in injecting the satellite into its nominal orbit, the environmental disturbances deviate the satellite from its predicted orbit and from an operational perspective most satellites need continuous orbit determination. Traditionally, ground based orbit determination is used which are non-autonomous and expensive and just can be used for specific times which the satellite can be observed from the ground... 

The aquatic canopy areas such as wetlands play an important role in ecology of these area. The exchange flow between open water and vegetated area occurs due to sunlight and surface cooling. Wind also causes surface evaporation and create a cold layer at the surface of water. The creation of exchange flow and its magnitude depends on parameters like solid volume fraction and thermal gradient. In this thesis, the goal is to determine the effects of floating vegetation on the hydrodynamic characteristics of exchange flowas a result of surface cooling experimentally. In this research, the PIV method was used to measure velocity profiles. In the experiments, solid volume fraction, depth of... 

Clustering algorithms are developed to provide general attitudes on database, recognizing latent structures and their more effective accessibility. Recently, broad studies are conducted on clustering since it is recognized as an important tool to explore and analyze data. Clustering is a fundamental learning operation without monitoring in data exploration which divides data into groups of objects so that objects in one group have the most similarity to each other and lowest similarity to objects in other groups. Some clustering algorithms such fuzzy clustering model (FCM) are widely used in clustering problem solution although this technique addresses local optimized searches. Additionally,... 

Flameless combustion is among the newest combustion technologies that is used for reducing the pollutants in recent couple of decades. Within this combustion regime, diminution of super hot points throughout the combustion chamber along with decline in production of pollutant gases occur simultaneously. This kind of combustion often is created by applying two processes; first by preheating the fuel and/or oxydizer flows at the inlet to tempratures over the self-ignition level; and second with diluting the whole amount of fuel and oxidizer in the chamber. These two happen by using hot exhaust gas of the same chamber (via feedback) or of the previous section (in multi-section chambers).... 

The growing number of disasters in recent years has become a significant threat to hospital buildings' resilience and preparedness. Besides, the stochastic nature of these disasters and the complexity of the hospital building systems exacerbate the difficulty of making appropriate decisions during and after disasters. To address the issue, this research proposes a novel model that utilizes the capabilities of Bayesian Networks (BNs) and Building Information Modeling (BIM). This model helps decision-makers in hospitals and medical centers measure various effects of disasters on utility systems and analyze the consequences of their decisions. The capabilities of the proposed model are tested... 

In line with developments in the technology of integrated circuits, transistors are implemented in silicon. Although the price is reduced; design is more complicated, which causes the efficiency and power consumption to face some difficulties in such design. The reason why modern GDI-based circuit is the focus of attention is that in designing a digital circuit, less power is required while more efficiency is obtained. Lowering the complexity of the logic circuit can bring about reduction of power consumption and propagation delay and decrease the circuit space. GDI-based integrated circuits resemble MOSFET transistors but have fewer transistors and higher performance capability. This study... 

The growth of high voltage dc-dc switching power supplies in various applications such as medical, industrial and laboratory research is undeniable. Design of these power supplies, respect to their expectation have some restrictions. Among the main characteristics, appropriate output voltage regulation, high efficiency, fast dynamic response and low EMI problems, are expected. Transformers constraints as one of the key components of high voltage dc-dc switching power supplies, plays essential role in the selection of converter topology and its control algorithm. In this thesis, first, with regard to issues of high frequency and high voltage transformers, provides a good approximation model... 

Optimization of heat transfer in vehicle's underhood which contains radiator, cylidir block, cylinder head and … with minimum pressure loss on engine is one of the most important problems of the car companies in all over the world.To design some cooling parts like simple radiators which doesn’t have a effective cooling effect, we can use equations.but for more complicated geometries which is morte efficient we have many complicated solutions.So in this condition computationl analysis and laboratories play an important role.in this condition we should consider that producing a sample and the process of verifying the result of test is too expensive.So recently the car companies prefare... 

Raising number of vehicles and increasing tendency of people to possess their own cars have posed a lot of expenses on users. One of the most significant of them is the time it takes to travel between origin and destination. Several researches have been conducted so far in order to evenly distribute travel times among transportation network users. A variable that has been neglected in many of these studies is travel time variability. Users, obviously, need to know not only the travel time, but also the probability of varying this time. In this research, an analytical model has been developed on a geometrical basis that includes both traffic conditions and intersection characteristics to...