Sharif Digital Repository

Geometric Spanner is a well-known problem aiming to add some edges between given points to build a graph in which the distance of each two nodes is at most their euclidean distance multiplied by t. One answer for this question can be the complete graph. But we like to use a smaller graph and minimize total edge weights, number of edges, or maximum degree of the graph. We study this problem in the Massively Parallel Computation model. In this model, each machine has not enough space to save all input data. We should divide input into multiple machines and run our algorithm in multiple steps. In each step, each machine computes with only a partition of data. After that, machines share their... 

Ground subsidence refers to the gradual downward movement of the ground’s surface, often occurring on a large scale due to excessive extraction from aquifers. Nowadays, climatic changes and global warming are fundamental phenomena that can lead to the drying of surface layers of the soil. From a geomechanical and environmental geotechnics perspective, this phenomenon can pose risks such as cracking and increased intensity of ground subsidence. Ground subsidence in cracked soils does not occur uniformly. The rate of subsidence in cracked parts differs from that in uncracked parts. The presence of pathways for increased energy and moisture exchange between the soil and the atmosphere through... 

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... 

Today in many industrial sectors, technology has made significant progress. Investing in advanced manufacturing technologies, especially computer integrated manufacturing systems is essential in order to survive in a competitive environment, improve performance, response to demand fluctuations and increase customer satisfaction. With available technologies and systems in computer integrated manufacturing (CIM) and its related technologies, the application of CIM in manufacturing enterprises is a reality and can meet the need of complicated manufacturing environment. Implementation of these systems brings many tangible and intangible benefits. But, according to several factors that must be... 

Since early civilizations underground water pipes have played a major role on promoting human being life style. Today, centuries after designing water mains equipment, utilizing a water distribution and sewage collection system is matter of great necessity in modern metropolises. In current research the pilot area is located in the city center .the major motivation for opting such area was extraordinary breakage rate which was unseen on other city areas and nearby cities. Data pertaining to four commonly used pipe material were collected. Preliminary data quality analysis was conducted to detect distinct contradictions. On basis of collected data, breakage rate plots were depicted for each... 

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... 

Many processes in the petroleum engineering industry involve particle transport in oil and gas reservoirs including sand production, fines migration, and nanoparticle injection. In these processes it is important to understand where the particles are travelling in the reservoir and the impact that they have on the formation properties. Large particles can damage the formation and decrease permeability which reduces the productive capacity of the reservoir. During nanoparticle injection, forces at the pore level can cause retention of particles and prevent their recovery. In addition, due to the heterogeneity of typical reservoirs, it is difficult to predict how particles will spread across... 

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),...