Sharif Digital Repository

The purpose of study is the modeling and evaluation of the role of authorities in enhancing the effectiveness of seismic vulnerability reduction policies. Seismic vulnerability reduction of infrastructures depends on the measures that must be taken before a disaster occurrence. In addition to increasing disaster preparedness, an important part of the pre-disaster measures is taken to increase the robustness of the infrastructure. In some cases, measures to reduce the vulnerability of infrastructure, such as the resilience of residential buildings, require the coordinated role’s implementation of relevant organizations. Evidence shows that in many cases, policies to reduce the vulnerability... 

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),... 

Different molybdenum oxide nano/micro structure thin films were synthesized by thermal evaporation method under various growth conditions such as deposition time, temperature and evaporation source-substrate distance. Molybdenum oxide nanostructures grown on Si(100) such as nanowalls, nanostars and nanowires were characterized with scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), atomic force microscopy (AFM) and high resolution transmission electron microscopy (HRTEM). Shape and type of nanostructures were determined with SEM, AFM and HRTEM analysis. XPS analysis showed that the synthesized nanostructures contained Mo6+, Mo5+, Mo4+ and... 

Synthesis, characterization and photocatalytic applications of core-shell like ZnO@CdS nanorods have been studied in this research. The synthesis of core-shell like ZnO@CdS nanorods was carried out in three different steps. At first, ZnO seed layer was formed on glass substrate via sol-gel process under optimum conditions using absolute ethanol solution containing zinc acetate and a stabilizer ( either Monoethanolamine (MEA) or diethanolamine (DEA)). When MEA used as stabilizer, the optimum concentration of sol was found 0.2 M, while increasing the sol concentration caused the seed layer to be grown in a string-like structure. The RMS surface roughness of seed layer prepared by 0.2 M sol... 

Because of the working conditions of semiconductors at ambient temperature and pressure, degradation of organic pollutants through semiconductors photocatalysis has attracted the interest of many researchers. Because of its large exciton binding energy,high chemical and physical stability,high electron and hole mobility, and low cost; zinc oxide, an n-type semiconductor with 3.2 eV direct band gap, is widely used in applications such as photocatalysts, solar cells, and light-emitting diodes. Among various morphologies of ZnO, 1D nanostructures such as nanowires and nanorods have recieved much attention due to their high surface to volume ratio. However, the application of ZnO as a... 

Finding necessary and sufficient conditions for a sequence to be graphic or in more general setting existence of factor with predscribed degree sequence of a general graph and also existence of a polynomial algorithm for finding this factor are classical problems of graph theory. These problems were discussed and solved between 1952 to 1972 by prominent mathematicians such as Erdős, Tutte, Edmonds et al. In this thesis we initially discuss most generalized forms of this problems namely Tutte’s f-factor and Lovasz’ (g; f)-factor theorems. Then some simple generalization of the special cases like Erdős-Gallai and Gale-Ryser theorems are investigated. And by using a form of Lovasz’ (g;... 

ZnO is a wide and direct band gap (3.37 eV) semiconducting material with a large exciton binding energy (60 meV). It has been extensively studied in the last few years owing to its potential applications in various fields such as surface acoustic wave devices (SAW), transparent electrode, solar cell windows, photovoltaic devices, gas sensors and photoelectrochemical cells. Recently, much attention has been paid to rare-earth (RE) doped ZnO for possible applications in visible emitting phosphors in displays, high power lasers, and other optoelectronic devices. In this thesis, initially ZnO thin films were deposited on glass and ITO substrates using sol-gel dip-coating method. Optical and... 

hydrogen considered as one of clean energy carriers and is the most promising alternative to fossil fuels. The production of hydrogen from photoelectrochemical water splitting using titanium dioxide nanotubes arrays (TNA) as a photoanode has been of interest to many researchers in recent years. In this study, TNAs were fabricated with two-step anodic oxidation method at a constant applied voltage of 60 V DC. The fabrication process was performed for duration time of 1, 2, 3, 4 and 5 hours. Photoelectrochemical analysis for the fabricated samples shows that TNA prepared for 3 hours anodic oxidation time exhibited the highest current density of 1 mA.cm-2 at 0.5 V bias voltage (Optimized... 

In this research, two type of graphene quantum dots (GQDs) have synthesized including, normal GQDs and nitrogen-doped GQDs (N-GQDs). Then, each of GQDs were deposited on the 1 dimensional zinc oxide (ZnO) nanostructures namely nanowires (NWs) and branched hierarchical (BH) systems. Then, photocatalytic activity of the samples were studied in photodegradation of methylene blue (MB) and methylene orange (MO) under visible light. First, ZnO nanowires (ZnO NWs) were fabricated by anodization of zinc sheet possessing wurtzite crystal structure with their average length and diameter measured in the range of 50-60 μm and 170-300 nm, respectively. Then, normal GQDs were synthesized by... 

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...