Sharif Digital Repository

In this thesis, we first review MOdified Gravity (MOG) theory as an alternative to dark matter models and then investigate some of the phenomena related to galaxy dynamics and gravitational lensing within the framework of this theory. In the last step, we present a model for the interaction of the fifth force field and the electromagnetic field. This model is based on the definition of a current density of matter using the energy momentum tensor in which the Lorentz symmetry is broken. This is due to the existence of a constant coefficient in the interaction, which can be considered as a fixed background field or observer 4-velocity that couples to energy momentum tensor. After introducing... 

In this thesis the capacity and flow assignment problems in worldwide webs is considered in order to minimize the total cost of networks and delays in network links. The main result of this problem is increasing the speed of message transmission and providing better quality of service delivery for network users. For pursuing these goals, Recursive Artificial Neural Networks is proposed for solving the problem and because of their high power and accuracy in reaching optimal solutions, they are convergent to optimal solutions very well. The method is tested on four different topologies and the results show that Recursive Artificial Neural Networks have high efficiency to reach optimal... 

David Hilbert posed a list of mathematical problems in 1900. Hilbert's tenth problem was "Is there an algorithm to determine whether a given Diophantine equation, has a solution with all unknowns taking integer values." Although Matiyasevich Showed that the answer to this problem is negative in the general case; the answer of this problem for a specific diophantine equation $f(x,y) $ that has rational coefficients, is unknown. Thue-Mahler equation is a diophantine equation of the form: $$F(x,y)=c\cdot p_1^{z_1}\cdots p_v^{z_v}$$ where $F$ is homogeneous with integer coefficients, degree $n\geq3$ and $p_1,\ldots p_v$ are distinct rational primes ($v\geq1$). All the unknowns are... 

The Nurse Scheduling Problem (NSP), is one of the most complicated problem in health care management systems. The problem is to determine a work schedule by considering some requirements such as governmental policies, staff and their managers satisfaction, etc. Nowadays, while the demand of treatment centers for nurses has increased especially in hospitals, the population of qualified nurses has decreased. In such a fuzzy situation, the managers of the treatment centers want a better nurse scheduling in order to increase the quality of giving services to their patients and consequently increase their income. In this thesis, a two-stage nurse scheduling problem with uncertainties in... 

In this dissertation, the buckling and postbuckling analysis of lattice conical shells are presented. The outer skins of the shell may be reinforced by cross-ply laminated composites. The shell is subjected to uniform axial compression and the boundary conditions are simply supported. This problem is solved using two different approaches. At first approach, the main priority is high speed calculations, which is investigated in static and dynamic types of loadings. In the case of static loads, the equilibrium equations are formulated based on the classical theory and von Karman type of nonlinearity. The equations are solved by Galerkin method and a closed-form relation is derived. In the case...