Sharif Digital Repository

Considerable increase in speed and decrease in size of electronic devices results in increase of heat flux, so there is a need to enhance efficiency of cooling electronic devices. In the present research two sets of OLPHPs with five turns for two different magnetic nano-fluids were fabricated and the effects of working fluid (water, and two types of magnetic nano-fluids), working pressure, concentration, magnetic field, magnets location, and inclination angle on the thermal performance of OLPHPs have been considered in both startup and steady thermal conditions.
Experimental results show that magnetic nano-fluids can improve thermal performance of the OLPHPs. Application of magnetic... 

Since critical and defining sets have been examined in various fields of combinatorics, including Latin squares and different branches of graph theory, we aim to present a portion of the obtained results con-cerning defining sets in diverse fields of graph theory, and provide a survey on them.In the present dissertation, we examine defining sets of vertex coloring,edge coloring, total coloring and forcing sets of orientation of graphs,perfect matching, hull and geodetic sets. Since complete graphs’ col-oring defining sets and Latin squares’ critical sets are closely related,we shall discuss them in a coloring framework. Furthermore, for dif-ferent graph families, including regular graphs,... 

Finding necessary and sufficient conditions for a sequence to be graphic or in more general setting existence of factor with predscribed degree sequence of a general graph and also existence of a polynomial algorithm for finding this factor are classical problems of graph theory. These problems were discussed and solved between 1952 to 1972 by prominent mathematicians such as Erdős, Tutte, Edmonds et al. In this thesis we initially discuss most generalized forms of this problems namely Tutte’s f-factor and Lovasz’ (g; f)-factor theorems. Then some simple generalization of the special cases like Erdős-Gallai and Gale-Ryser theorems are investigated. And by using a form of Lovasz’ (g;... 

Let G be a graph and F : V (G) ...! 2N be a function. The graph G is said to be F-avoiding if there exists an orientation O of G such that d+ O(v) =2 F(v) for every v 2 V (G), where d+O(v) denotes the out-degree of v in the directed graph G with respect to O. In this thesis it is shown that if G is bipartite and jF(v)j dG(v) 2 for every v 2 V (G), then G is F-avoiding. The bound jF(v)j dG(v) 2 is best possible. For every graph G, we conjecture that if jF(v)j dG(v) 1 2 for every v 2 V (G), then G is F-avoiding. We also argue this conjecture; the best possibility and some partial solutions, e.g. for the complete graphs. For graph G, we say the set f(d+ i ; d i ); i = 1; : : : ; ng of... 

Despite the great work done in the field of the engine mount system to reduce vibrations transmitted from the vehicle to the body, an efficient process is still needed to achieve the optimal response to the design of the engine mount system.The goal of the project is to provide an ideal model for optimizing the stiffness, position, and orientation of the vehicle's engine mount system. In this regard, the activities carried out consist of three parts of the modeling, optimization, and verification of the response. In the modeling section, a linear model of 13 degrees of freedom has been proposed for the engine, mount and vehicle assembly, which also has the ability to model the rigidity of... 

Nowadays dielectric substrates are widely used in Microwave Integrated Circuits. These substrates are made layer by layer in order to have favorable mechanical and thermal properties. The materials of the layers are usually different from each other and often each layer is a combination of different materials. This difference in material type and manufacturing method causes the substrate to have a different permitivity coefficient in two major directions, namely parallel and perpendicular direction. In fact, the electric field observes a different permitivity coefficient in each direction. This causes a problem in circuits that have both perpendicular and parallel electric field...