Sharif Digital Repository

In this project, we prepared two new tetranuclear clusters with linear Pt2Ag2 and Pt2Au2 metal cores. First, The tetranuclear cluster [Ag2Pt2(Cl2)(bhq2)(μ-(PPh2)2py)2](OTf)2, 1, from the reaction of 1 equivalent of Pt(bhq)Cl(SMe2), with 1 equivalent of AgOTf and μ-(PPh2)2py ligand has been prepared. Secondly, the tetranuclear cluster [Au2Pt2 (μ-(PPh2)2py)2(Cl2)(bhq2)]( PF6 )2, 3, by the reaction of 1 equivalent of the mononuclear complex [Au(μ-(PPh2)2py)2]PF6 with 1 equivalent of PtbhqClSMe2 and μ-(PPh2)2py ligand has been prepared. Structure of complexes has been fully characterized in solution, solid and gas states using multinuclear NMR spectroscopy, X-ray crystallography and ESI-MS... 

Energy Harvesting is one of the techniques which can be utilized in Green Communications and increase the wireless networks lifetime. In an EH system, each resource is supplied with the energy harvested from the environment. When we confront with a situation that the users of one channel want to increase their rates and this action negatively affects the other user’s rates, the user’s cooperation problem for obtaining a fair rate will be created. In this study, at first we consider a Multiple Access Channel and we assume that the energy resources of transmitters are harvested according to a known probability. In addition, we assume that the transmitters do not know the instantaneous amount... 

Massive MIMO systems are systems, where the base station has many number of antenna so each user’s channel is orthogonal to one another.These systems have some valuable advantages such as reduction of energy needed for transmission and significant improvement in spectral efficiency, which makes them be suitable for next generation of wireless communication systems. Another advantage of Massive MIMO systems is inherent resistance against passive eavsdroppers due to having a directed power radiation in direction of the desired user. However another physical layer attack threat these systems: attacking in pilot phase then eavsdropping in downlink phase which must taken care of in physical... 

The increasing expansion of wireless communications and the increase in information traffic and the number of communication users, and on the other hand, the frequency and energy frequency limitations have led to the emergence of new generation communications. In the fifth generation of communications, one of the solutions to ensure the optimal use of bandwidth is the use of the non-orthogonal multiple access (NOMA) schema, which of course, the use of such a scheme in the system naturally increases the complexity of the receivers. Unlike most access methods in previous generations of communications, the goal of NOMA is the simultaneous use of multiple users from a frequency band for data... 

The problem of distributed binary hypothesis testing in the Gray-Wyner network with side information is studied in this dissertation. An observer agent has access to a discrete memoryless and stationary source and describes its observation to two detecting agents via one common and two private channels. The channels are considered error-free but rate-limited. Each detecting agent also has access to its own discrete memoryless and stationary source, i.e., the side information. The goal is to perform two distinct binary hypothesis testings on the joint distribution of observations at detecting agents. Additionally, the observing agent aims to keep a correlated latent source private against the... 

FGM sheets with component or grain size gradient in their thickness direction provide mechanical and physical gradient properties through ND direction. FGMs are fabricated by various methods including centrifugal casting, powder metallurgy, PVD and CVD,all of which suffer from some shortcomings such as porosity of the products, low rate and high cost of production and restrictions on mass production. In this study, 2 and 4 layered Al matrix FGM sheets containing SiC and Al2O3 powders were fabricated by laminating method of Accumulative Roll Bonding(ARB). Two approaches of stacking were chosen as accumulative coupled roll bonding (ACRB) and (ASRB) for initial roll bonding and subsequent... 

Collaborative edge computing (CEC) is a recently popular paradigm enabling sharing of computation resources among different edge devices. In CEC, multiple stakeholders (mobile users, mobile edge computing servers, cloud servers,...) collaborate to provide new computation capacity in order to perform computation-intensive tasks efficiently in the edge. In the thesis, each task, the data that should be computed in the cloud or edge, was modeled as a graph of dependent sub-tasks. Resource allocation for task offloading is an important problem to address in CEC as we need to decide when and where each subtask is executed. In this work, we mathematically formulate the problem of resource... 

The increase in mobile data traffic adversely affects the quality of service experienced by mobile users. Moreover, the cost incurred by developing infrastructure exceeds its profit. Therefore, there is a trend toward finding cost effective schemes to cope with increase in mobile data traffic. One of the recent elegant solutions is mobile data offloading based on D2D communications. In this thesis, we propose a new offloading scheme using D2D communications for delay-tolerant services. In this regard, we assume a common file is demanded by a subset of users in different time instances and we accumulate demands to serve them in a scheme where devices are divided into non-overlapping... 

Energy crisis has always been a crucial issue faced by the development of wireless communication techniques. As a more energy-efficient network architecture, green communications and networks (GCNs) have recently attracted significant attention from academia and industry. In order to enable the technical and economical GCNs, several emerging techniques have been proposed including energy-efficient and energy harvesting techniques. Although these emerging techniques have drawn considerable attention and have been studied recently, there are still many open theoretical and practical problems to be addressed. Energy harvesting (EH) is a key technology to achieve the objectives of GCNs. This... 

In the next generation of wireless networks, wireless network virtualization is considered as an efficient technology to enhance the network capacity. This technology enables the separation between wireless network infrastructure and the services it provides that enhances some of the existing capabilities and make new capabilities in the network. Spectrum sharing,infrastructure sharing, network sharing, resource slicing are some of these capabilities.Furthermore, the mentioned separation causes the lower entry barriers for small beneficiary entities. The increment in the number of beneficiary entities makes intense competitions among them leading to lower costs for different services. Also,... 

With the increasing use of wireless communications, the need for optimal utilization of bandwidth and energy has become undeniable. Reconfigurable Intelligent Surfaces (RIS) have emerged as a promising technology for the efficient use of telecommunications resources. One proposed model of these surfaces is the Simultaneously Transmitting and Reflecting RIS (STAR-RIS), which, unlike conventional reflective surfaces, can simultaneously reflect part of the incoming waves and transmit part of them. This study examines the potential use of these surfaces in simultaneous wireless information and power transfer networks. In the defined problem, energy receivers are not reliable, and there is a... 

Particle reinforced aluminum matrix composites have considerable attraction in automotive and aerospace industries due to their special properties as light weight, high ratio of strength/density, improved elastic modulus, low coefficient of thermal expansion and high wear and corrosion resistance. Among the production processes of metal matrix composites, accumulative roll bonding process has particular importance due to producing ultrafine grained composite sheets. However, uncontrolled and undesired agglomeration of particles is the main problem in producing these composites. In this research, the Al2O3 and SiC nanoparticles were electrostatically stabilized against agglomeration by... 

Splitting in ingot cast structures and transverse cracks in continuous cast structures are the main problems of hot rolling of low carbon resulfurized free-cutting (LCRF) steels. Presence of high volume fraction of manganese sulfide inclusions in cast structure increases the risk of alligatoring in hot rolling. Because of high sulfur content of these steels and probability of formation of low melting point phases, minimum level of manganese and maximum level of copper and tin is necessary. Morphology of manganese sulfide is another important factor in hot forming of these steels, which can be controlled by level of deoxidation in steel making. In fact, MnS2 is present in fully killed... 

Dependence of some magnetic properties such as core loss and permeability on temper rolling was studied in this thesis. It is shown that with a proper temper rolling sharper textures are obtained in the electrical steel and the magnetic properties in the longitudinal and traverse directions are improved. By texture analysis, it is shown that because of temper rolling, shear strain on the surface of the sheet is the main factor for abnormal grain growth and shear texture formation on the surface. The result of formation of this texture is enhancement of the {100} intensity and reduction of the {111} intensity, leading to the improvement of the permeability. Temper rolling is always... 

Due to increased mortality from Coronary Heart Disease, it is important to work on ways to treat this disease. An effective method of treatment on this disease is the coronary stent implantation. There are nearly two decades passed since implanting the first heart stent. The main objective of this research is design and manufacturing of the medical stents of stainless steel 316 L. Stent materials should have excellent corrosion resistance and biocompatibility. Various materials such as stainless steel 316 L, platinum alloys, niobium alloys, cobalt alloys are used for manufacturing the stents. In this project, at the first stage seam tube was prodected with laser welding of a tube with... 

New materials as hybrid materials or laminate composites, due to combination of many properties, can be used in many industries. The aim of this research is bonding of three-layered St/AZ31/St composite by roll-bonding process. The roll-bonding process was performed at three preheating temperatures, 340, 400 and 450 ⁰C, with thickness reduction of 30 to 68% and different thicknesses of intermediate layer (AZ31). In order to improve the bonding strength, the as-rolled specimens were annealed at constant temperature of 375 ⁰C. For evaluation of bond strength and investigating the formation of a diffusion layer, the results of peel test and microscopic images were studied. Tensile specimens... 

Metal matrix composites (MMC) and metal foams (MF) have been the topic of numerous researches during the last decades. The appropriate mechanical and physical properties of these materials make them useful in various industries. In this research, a unique approach is introduced for producing MMCs and MFs in which accumulative roll bonding (ARB) is employed in order to achieve a homogeneous distribution of ceramic particles in the metal matrix. Also, foamed structures can be made by subjecting Al/TiH2 composite to an appropriate annealing heat treatment where TiH2 particles decompose to hydrogen and titanium. In this work, the effect of number of ARB cycles on the size and distribution of...