Sharif Digital Repository

Congestion is an important issue in the network environment. To keep stable the perfor-mance of the network, congestion control algorithms have been extensively studied. Queue management method employed by the routers is one of the important issues in the congestion control study. Active Queue Management (AQM) has been proposed for early detection of congestion inside the network. AQM mechanisms control the queue length in a router by dropping arriving packets. The Random Early Detection (RED) is the most popular AQM mechanism used in routers on the Intenet to allow network users to simultaneously achieve high throughput and low average delay. The RED algorithm may cause heavy oscillation of... 

A Mobile Ad hoc NETwork (MANET) is a set of wireless mobile nodes that form a self configured network. MANETs do not have infrastructure and are not currently deployed on large scales. So research in this area is simulation based. Mobility model in a mobile ad hoc network explains the movement pattern of mobile users and is designed to describe the change of their location, velocity and acceleration over time. One of the challenges in this field is the definition of a common mobility model that provides an accurate and realistic movement description of mobile nodes. In this thesis we want to study the mobility pattern of vehicles on Kish Island and compare it with different kinds of... 

Estimation of runoff in the ungauged basins is a challenge for hydrologists. The main objective of this research is to produce runoff coefficient map using SCS-CN (1972) and Kennessey (1930) as empirical models to for Urmia Lake basin between for 2006-2011.Both SCS-CN and Kennessey methods use slope, land use, and soil permeability data to estimate surface runoff. Accuracy of each model is tested along with the observed runoff using the Root Mean Square Error (RMSE).Urmia Lake basin includes about 400,000 hectares irrigated land, which constitutes around 10 percent of the entire basin area. To exclude the anthropological activities from the estimations, methods were applied only for 28... 

Objective: Accurate quantification in PET imaging is essential for proper evaluation and requires attenuation and scatter correction. Typically, this correction is performed using CT; however, the propagation of CT image errors to PET, the additional radiation dose in PET/CT, especially in pediatric cases and repeated scans, as well as challenges associated with standalone PET and PET/MRI, highlight the need for alternative approaches. This study investigates the capability of deep learning in jointly correcting attenuation and scatter for PET images with different radiotracers. Methods: Various neural network models, including ResNet, U-Net, and swin UNETR, were trained for direct... 

Resources management is essential duo to sustainable development and marine resources limitations. There are several ways to restore coastal damaged ecosystems, one of the best and most cost effective solution is establishment of artificial reefs. A popular type of artificial reef is named Reef ball, a hollow hemisphere. In some regions these habitats has also been used as submerged breakwater. These structures recover and protect endangered species ecosystem although they provide aesthetic view to a beach. Main application of these structures is to provide a safe environment for marine creature. In this study initially Transmission coefficient variation in two-dimensional model experiments... 

In static PET/CT imaging, the Standardized Uptake Value (SUV) parameter is used to evaluate diseases. The use of this parameter provides valuable information to physicians in many cases. However, this parameter has limitations and is not suitable for certain clinical applications, such as assessing treatment response and differentiating between benign and malignant tumors. In contrast, utilizing dynamic imaging systems can yield significant information through the extraction of kinetic features and quantitative analysis based on temporal data. However, the use of dynamic PET imaging in a clinical setting can be challenging due to factors such as prolonged scan times (> 60 minutes),... 

Positron Emission Tomography (PET) imaging is a modern sectional imaging technique widely used due to its advantages in visualizing the physiological functions of body tissues. In this method, a radiotracer is injected into the body, concentrating in the area of interest. As the positron-emitting radionuclide decays, positron annihilation occurs, resulting in the emission of two gamma rays in opposite directions. The PET scanner detects these gamma rays; however, scattering may occur during their journey from the patient’s body to the detector, which can introduce errors in tumor localization. To reconstruct images and correct for these scatter effects, various techniques such as iterative... 

Establishing an efficient free trade agreement (FTA) requires some conditions in both trading partners. The median voter approach insists on the direction of general interests (identified by the utility of a median voter) to explain how two countries may agree to sign an FTA. At the other side, lobbying approach emphasizes on the role of interest groups (groups with a large influence on the public decisions) in forming FTAs. Taking into account the theoretically based and empirically robust foundation of the median voter approach, we rely on it to investigate the major determinants of free trade agreements in the case of ECO countries besides all their main trade partners. The database... 

The goal of this master thesis is to develop a new accurate numerical algorithm for digital differential relay to protect a power transformer. This work employs specially developed software to simplify its input signal processing task which helps to quickly and accurately detect and clear the transformer internal faults. The available commercial transformer digital differential relays lack the required sensitivity to detect turn to turn faults when a few numbers of turns (less than 10% of the winding) are involved. This work presents a new equivalent circuit for transformer when a turn to turn fault occurs on either winding. This equivalent circuit helped to develop an accurate algorithm for... 

This thesis studied the definition of a green building and the elements associated with the construction of a green residential apartment in comparison with traditional buildings with respect to condition of Karaj city. The first step in green construction is preparing a guideline. For this, LEED (Leadership in Energy and Environmental Design) the most well-known code for green buildings is used and Adapted with Iran’s National Building Regulations. Creating a checklist to rate buildings is one of the most important parts of Green Building Regulations. To achieve the points, US LEED certification is analyzed in both qualitative and quantitative perspectives. A questioner is applied in... 

This study investigates the effect of commodity price shock, including oil and base metals prices, on Tehran exchange and industries stock returns. These industries have the largest market share in Tehran exchange and may heavily depend on global prices. Using weekly data from 1387 to 1396, Multifactor and VAR models are performed to analyze the variance decomposition and impulse response function of each industry to 1% price shock. In addition to global prices, some macroeconomic factors that are likely to affect stock returns are considered. The results show that commodities price shocks have dynamic and significant effects on stock returns  

Screw compressors are rotary positive displacement compressors that utilize a pair of helical lobed rotors in a casing. Part 3 of ISO 10816 does not include Positive displacement compressors. VDI 3836 has more vibration amplitude limitations for this compressor than industrial machines under ISO 10816-3. The screw compressor has no valves; therefore, the location of the suction and discharge ports determines the compressor cycle. This study focuses on the condition monitoring through vibration analysis of screw compressors. The purpose of this study is to investigate the reason for excluding of screw compressors by ISO standard and also to explain the vibration dependence of these... 

Polyethylene is one of the most widely used industrial materials for producing water and gas pipes due to low pricing and mechanical properties and high corrosion resistance. Various parameters such as molecular weight and the short chain branches distribution strongly affect the mechanical properties of these materials. PE100 grade of this material has been introduced with bimodal molecular weight distribution, has excellent mechanical properties and especially high creep resistance and today is used for pipe production in water distribution systems. In the first part of this study, the effect of 1-butene comonomers on different properties of three PE100 and two PE80 resins produced in... 

Vegetation can be used as a research solution at the cutting edge of knowledge, cost-effective, aesthetic, pleasing, and environmentally friendly in natural hazards. Understanding the hydraulic properties, including the permeability of vegetated soils, is very important for various environmental applications. Different and sometimes conflicting behaviors have been observed in literature. There has been no general consensus in the literature regarding permeability due to the influence of several factors. In addition, there are many uncertainties about the effect of plant cultivation and root system effects on anisotropic soil permeability. It is essential to address this issue because of the...