Sharif Digital Repository

In this research ,Al-20Si-5Fe-3Cu-1Mg-XMn alloys were produced by gas atomizing and melt spinning processes. Microstructure and growth morphology of powder and ribbons were investigated using optical microscopy , scanning electron microscopy. powders were hot pressed at 400ºC/250Mpa and microstractural variations, mechanical properties were evaluated after consolidation. Results show that relatively high cooling rate in gas-atomized powders lead to refinement of microstructure and formation of semi-equilibrium δ intermetallic phase . As the powder particle size decrease , the growth morphology changes from primary silicon + euthectic to euthectic + primary dendritic aluminum . Mn changed the... 

Electrochemical water splitting which consists of two half-reactions, namely; the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), is an important process in electrochemical energy storage and sustainable production of energy. Therefore, the development of cost-effective and efficient electrocatalysts for water splitting has attracted a lot of interest. In this work, a new nanocomposite was prepared from cobalt diselenide and cerium (IV) oxide derived from calcination of a cerium-based metal-organic framework (Ce-MOF), via hydrothermal and electrodeposition methods. The structure and morphology of synthesized materials were investigated by XRD, FE-SEM, EDX, and BET... 

In the past few years, many research works on the controllable integration of metal nanoparticles and metal-organic frameworks were done, since the obtained composite material shows a synergism effect in catalysis and photocatalysis, drug delivery applications, gas, and energy storage, as well as sensing. For the first time, in this study, we employed template-assisted growth to synthesize Au-HKUST-1 Nanocomposite. XRD analysis entirely confirms that employing this strategy in synthesizing Au-HKUST-1 was wholly successful, and the plasmonic properties of this nanostructure were studied via UV-visible spectroscopy. In the course of synthesis, gold nanoparticles with 70nm diameter were... 

The human brain is the most sensitive and important human organ and surgery must be done with high precision and without risk. During surgery, brain tissue deform continuously due to gravity, out of the cerebrospinal fluid and the changing pressure of the cerebrospinal fluid and the surgical maneuvers. Because the surgeon has no direct view on brain internal, the ways to solve this problem is to pay attention. This method makes it possible to the surgeon see in the brain and the brain tissue deformation. This thesis method is based on biomechanical modeling. After forming finite element model from the pre-operative MRI, brain surface and volume datasets during surgery as a load, apply to the... 

Recently, the number of requests for multicast services through the wireless networks has increased. However, for successful deployment of these services, security and efficiency of content delivery must be provided at first. This thesis presents a new approach for secure multicast in wireless networks. This approach, CRAW (Combination of Re-keying and Authentication in Wireless networks) combines member authentication procedure with group key management protocol together to provide efficient re-keying. One-time password is proposed for member authentication and CKC (Code for Key Calculation) is suggested for group key management in wireless networks. In fact, the combination of... 

Recently, demand for using variant applications in distributed networks has been increased largely. Most of these applications are based on group communication.In distributed group communication, two important factors need to be considered, group construction, and Group Key Management (GKM). The group construction specifies the process of constructing a new group by cooperation between distributed users. As well, GKM ensures re-freshness of the group key after each join/leave operation. Both of these tasks must be done by collaboration between members. This leads to imposing complexity and communication overhead to the system.This thesis proposes efficient methods for group construction and... 

Spam mails are unwanted mails sent to large numbers of users. Such emails not only consume the network resources but also cause lots of security uncertainties. Based on our observation, the location where the spam filters operate in is an important parameter to save network resources. In this thesis, we introduce a new and effective approach to avoid spam emails from being transferred by relocating the filtering system in the sender mail server. Compared with previous methods in our method, the spam email is detected after spammer clicks on the send button. Here the sender mail server decides based on some pre-defined criteria. If the sender mail server determines that the email is not spam,... 

Retrofitting and strengthening existing structures is one of the most important concepts of structural and earthquake engineering. Strengthening of structures could be due to changes in application and applied load, errors in calculation, mistakes in construction, weakness of old codes, structural height increases and changes in environmental conditions. Different methods for increasing the flexural strength and ductility of reinforced concrete beams, as one of the major structural components, have been presented. This research presents an experimental study on the strengthening of reinforced concrete beams by reinforced concrete jackets (classical method) and Fiber Reinforced Polymer (FRP)... 

Rigid analytic geometry was developed by John Tate in 1971. Although it seems that a rigid analytic spaces on non-Archimedean field F, is like something called F-analytic manifold; however in general these two are distinct concepts.
In this thesis; we introduce rigid analytic spaces. It begins in chapter one by non-Archimedean fields. In this chapter also contains theorem 1-3-7; which there is no proof for it without usage of methods of this chapter; up to the present. Topics discussed in this chapter are interesting subjects of other applica¬tions of non-Archimedean fields. There is a visualization of the field Q_p; and an appendix includes some definitions and consequences of ordered... 

Reviewing the literature on air traffic flow management shows that reducing flight delay is one of the main challenges facing air transportation systems. This is due to the high cost of incurring delays. At the first stage, two mixed integer-programming model is presented here that aims to minimize delay cost of air traffic. The first presented model seeks to minimize flights delay costs by choosing an optimal airport configuration and balancing departure and arrival flights and the second presented model solve this problem with the new approach with categorizing the airplane by types and prioritizing them. Numerical examples are solved in CPLEX 12.6 to evaluate models performance. Numeric... 

Voltage Controlled Oscillator (VCO) is one of the essential blocks in communication transceivers. The important specifications of the VCOs like Phase Noise, always is a motivation for researchers in order to introduce novel approaches to conquer these challenges. By development of technology and appearance of new fabrication technologies, this issue take more attention that the past. Also the out of control parameters like process variation and temperature, affect that. So, according to the challenges ahead and the demand of transceiver systems for low phase noise and reasonable power consumption, solutions for overcome these challenges. Finally, a class-C VCO with the tuning range of 4.25-5... 

Traffic flow modeling on different levels was always the topic of many studies. In this regard, many researchers have tried to eliminate traffic problems by developing precise models. Therefore, in this study and in its two major parts, we developed two models: one macroscopic and one microscopic. Like previous studies, the main purpose here was the development of traffic flow models that have better precision and give more information about the mechanism behind the traffic phenomena. Our focus was on the free spaces in front of drivers which were considered in a macroscopic traffic flow model and resulting microscopic traffic flow model.First part, addresses the first-order extension of the...