Sharif Digital Repository

Opportunistic spectrum access in cognitive radio networks has introduced multiple challenges in the realization of this technology. One of these key challenges is spectrum mobility, in which a secondary user (SU) must be able to vacate channels upon the appearance of a primary user (PU) and reestablish a communication link to avoid service termination, known as spectrum handoff. For a connection-based modeling, multiple interruptions can occur, which lead to multiple handoffs; hence, in a proactive approach, a sequence of target channels, rather than a single target channel must be determined. The first parts of this thesisis dedicated to the analysis of a time-slotted cognitive radio, in... 

While digital IC technology scales down, the impact of size effects in copper interconnects become more important because wire dimensions reach the same order of electron mean free path yielding increased resistivity of metal due to surface and grain boundary scatterings. Hence, because of their longer MFP, Carbon nanotubes are proposed as potential candidates for replacing copper interconnects. Furthermore, wires, especially power and ground lines, are becoming more and more vulnerable to electromigration because of rapid grows in current densities which increases the temperature of IC and interconnects as well. Sub-ambient cooling has long been suggested for improving the performance of... 

The Riemann- Hilbert correspondence theorem is a higher dimensional generalization of Hilbert’s 21st problem. The main problem was about existence of differential equations with regular singularities on Riemann sphere with a specific monodromy group. Deligne generalized the problem to algebraic connections with regular singularities. Kashiwara and Mebkhout independently generalized the theorem for derived category of D-modules. In this thesis, we will begin by studying this theorem in simple cases.In chapter 3 generalized version of the theorem by Deligne,will be introduced. At the end of the third chapter a proof of Riemann-Hilbert correspondence for the special case of projective curves... 

Graph Theory and Combinatorial Analysis like the other branches of science use the probability for solving their problems. At the first , we will introduce the most common tools from probability used in Discrete Mathematics, such as “The Lovasz Local Lemma”. Most of them are based on Linearity of Expectation, Concentration Theorems and some other innovative methods such as Deletation Method. We will present different examples for these techniques. Also we will introduce “Random Graphs” and their importance. Specially we will explain how to use “Threshold Functions” to obtain different properties about the majority of graphs. Rainbow Connection, is a natural and interesting quantifiable way... 

In this thesis, the behavior of proposed moment resisting precast beam-column concrete connection under cyclic and monotonic loads is investigated. In this study, the finite element models of precast and monolithic middle and corner connections are created. The results of finite element analysis under cyclic loading is verified with existing experimental results based on failure mode, ductility, energy dissipation capacity and flexural strength. Based on the results of nonlinear finite element analysis, the analytical behavior of samples is in good agreement with experimental results and finite element analysis of proposed precast connection can be replaced with supplementary tests. Then the... 

Iran requires basic changes in using construction materials and industrial system of house production due to its particular climatic conditions such as being located on the earthquake belt and social conditions such as lack of house. 3D panel is one of the best options for industrial construction and especially mass building.
In this thesis, different suggested designs for L & T shaped wall to wall connections of 3D panel under lateral-cyclic and gravity loading were modeled and analyzed by ANSYS software. Numerical analysis indicates that concrete perpendicular hank and welded wire mesh WWF 3/3/50/50 have positive effect on the ultimate strength and ductility of the connection. Hence,... 

Friction drilling or flow drilling is a method of making holes in metal sheets, in which the material is pushed with the aid of heat from friction. This procedure allows making holes in sheet metal, with a sleeve formed as the hole is created. This sleeve is then threaded and used as the nut, thus eliminating the need for access to the interior faces of hollow steel sections. On the other hand, with the development of advanced manufacturing techniques, larger and thicker hollow structural sections are becoming more popular in mid-rise and multistory structures. onsequently, flow drilling can be considered as a viable alternative for traditional drilling techniques, where the material is... 

Today steel tubular systems are used more than before, especially in recent years. A difficulty with this type of systems is making beam to column connections using bolts due to no access to holes of bolts from the inside of tube or hollow circular column. Reverse channel connection is devised and introduced to prevail this problem. Access to holes in this connection is from the inside of channel. In this connection, the web of the channel is connected to steel beam using bolts and the two legs of channel is welded to face of tube column.
This type of connection does include some innovations; not too many researchers work on different versions of this connection. This thesis provides an...