Sharif Digital Repository

The problem studied in this research is the online stochastic bipartite matching. In this problem the vertices of one side of the given graph arrive in an online manner, with respect to a probability distribution. Also the edges of the graph exist according to a given probability distribution and one should perform queries from an oracle to know about the existence of an edge. The given graph shall be weighted or unweighted. The goal here is to find a maximum matching in the graph that is as close to the omniscient optimum as possible, while the number of queries performed per vertex is limited. In the general case of the problem, there are no specific conditions, but in other versions,... 

When a crack is subjected to a compression field, it will close and its edges will get into contact with each other. Depending on the direction and magnitude of the loads and also the coefficient of friction, ‘stick’ or ‘slip’ situationsbetween the edges will occur. This type of crack is known as ‘frictional crack.’ In this project, first these cracks are studied analytically and the order of singularity is derived using asymptotic analysis and also the analytical fields are determined for both ‘isotropic’ and ‘orthotropic’ materials. Then, numerical simulations are carried out using extended finite element method which is considered as the most powerful means for analyzing the problems... 

Electromagnetic levitation gas condensation (ELGC) method was used to synthesize silver nanoparticles. Silver droplets were melted and levitated stably at about 1130 °C with appropriate flat coils in a 10 mm OD silica tube. High purity argon, nitrogen and helium were employed as carrier gases and cooling media. Morphology and particle size of the products were investigated by scanning and transmission electron microscopy (SEM and TEM), X-ray diffraction (XRD) energy dispersive X-ray analysis (EDAX) and dynamic light scattering (DLS). The DLS, SEM and TEM studies demonstrated narrow size distribution of spherical shape Ag nanoparticles with particle size of about 60, 45 and 35 nm synthesized... 

Icing is a prominent and consequently a primitive parameter in aeronautic accidents.This has promoted the aerospace and aeronautical companies to work on that very seriously since four decades ago. There are several systems to confront with ice accumulation over the airplane surface; such as pneumatic, weeping, electrical, and heating systems. Of course, each of them has its own advantages and disadvantages. At the first step of our study, we need to determine the criteriaaffecting the customer needs, airplane constraints, and the specified missions. At the second stage, it requires selectinga preferred system and we should have taken our decision based on the facts that a good choice can... 

In this thesis, we establish a fixed point result of Krasnoselskii type for the sum A+B, where A and B are continuous maps acting on locally convex spaces. We apply such results to obtain strong solutions for some quasi-linear elliptic equations with lack of compactness. We also provide an application to the existence and regularity theory of solutions to a nonlinear integral equation modeled in a Banach space. Finally, we develop a sequentially weak continuity result for a class of operators acting on vector-valued Lebesgue spaces. Such a result is used together with a geometric condition as the main tool to provide an existence theory for nonlinear integral equations in Lp(E)  

In this study, silver nanoparticles (Ag NPs) with different morphologies were synthesize by physical and chemical methods. Spherical silver nanoparticles were synthesized by electro magnetic levitation melting approach, while silver nanoplates and nanorods were prepared by chemical reduction route. Ag NPs were then coated with thin porous silica shell. The dissolution behavior of synthesized Ag@SiO2 was investigated in PBS at 25, 37 and 55 °C. Spherical and triangular Ag@SiO2 were conjugated by Penicillin G molecules. The silver and penicillin contents of the synthesized nano-antibiotics were determined by ICP-OES and TGA analyses. The nanoparticles were characterized by X-ray diffraction... 

Particulate porous mateials have always been of interest in terms of reducing shock waves effects in different protective applications. Therefore, the physics governing the flow in porous media is especially significant for which different models have been presented by the researchers. The complexities of these media have caused many existing models to be unable to properly predict the behavior of granular media under shock loadings. On the other hand, the complexity of the equations makes the numerical solution of them cumbersome and costly in a way that many researchers do not solve the whole coupled equations and reduce their number. In addition, current high-resolution TVD solutions of... 

Almost half of all cancer patients receive radiation therapy as main or part of the treatment process. Before performing radiation therapy, first it is necessary to determine the patient’s treatment plan and estimate the outcome of it based on the dose distribution. The quality of treatment is dependent on the accuracy of dosimetry calculations that lies in Monte Carlo algorithms. Unfortunately, most of the computation time is long and not suitable for clinical applications. On the other hand, a real treatment planning will be possible if all aspects of radiation therapy should be considered. The radiation source that is obtained from a medical linear accelerator head is one of these... 

Transmission-mode ultrasound computed tomography (USCT) has emerged as a novel, safe, and cost-effective method for quantitative imaging of biological tissues, especially in breast screening. Despite technological advancements, challenges such as reduced accuracy in heterogeneous media, incomplete acoustic field coverage, sensitivity to initial conditions, and phenomena like cycle skipping still limit image quality and reconstruction speed in these systems. In this thesis, aiming to improve the speed and performance of USCT imaging, three reconstruction algorithms have been designed, implemented, and evaluated: a travel-time-based Gauss-Newton method, frequency-domain full waveform inversion... 

Interactions in social networks consist of positive relations, such as friendship, trust, like, and negative relations, such as antagonism, distrust, dislike. “Signed networks” are utilized to model these networks. These networks are presented by “signed graphs” in which nodes are the people and relations are modeled by sign of edges. One of the challenging problem in signed networks is link sign prediction, i.e., specifying unknown edge sign along with evolution of the network given sign of some edges and further information about remainder of network. Two approaches are used to answer this problem. The first approach is proposing computing models for sign prediction. In this assertion we... 

Purpose of this research is an investigation on the effect of soil behavior on fatigue life of steel catenary risers in touch down zone. Steel catenary risers are a part of pipeline installed between the seabed and the offshore platform on the sea level, and its application is to transfer the gas or oil from the seabed to the sea level. Steel catenary risers for their resilience against buckling, easy installation, lower cost comparing other conductors are preferred to other means of conducting oil in recent years. The most challenging issue in the design of this kind of riser is the fatigue problem. The characteristic of the wave loadings we are facing in this environment is cyclic;... 

Nowadays, ultra-high bandwidths and speed are essential for information processing and transmission. Also, we know optical systems have these properties. Therefore, we use optical systems to provide these essentials. We need optical devices to obtain all optical systems. Optical buffers and memories are examples of optical devices which realization of them is still an unsolved challenge. The slow light is suitable method to realize optical buffers. To realize slow light, different methods have been introduced. One of these methods is slowing down of the group velocity of light pulses in a medium which we use that in this thesis. To realize these, many different methods and material systems... 

In this study, different stages of biodiesel production from microalgae were investigated, specifically the extraction step.Various cultivation methods were also studied among which cultivation under stress was the best. Different carbon sources were also investigated to achieve highest growth. Sodium acetate with complete growth was achieved after 8 days with 6.22% fatty acid recovery. Different mixtures of solvents were compared with Blye and Dier method. Results showed that the mixture of hexane and methanol with crude lipid extraction of 15% and fatty acid recovery of 3.97% were chosen as the solvent mixture of equilibria experiments.Organic solvent composed of hexane (non-polar... 

In recent years, industrial robots have been greatly used as orienting devices in industry, especially in the automotive, shipbuilding and aerospace manufacturing industries. Industrial robots are gradually finding their niche in manufacturing, replacing less universal and more expensive CNC-machines. Application area of robots is constantly growing; they begin to be used for the assembly, pick-and-place operations, machining operations and etc. The use of robots for machining operations is growing because of their flexibility to perform a broad spectrum of tasks at a lower cost when compared with machine tools. Recently, parallel robots have attracted more and more researchers’ attention in...