Sharif Digital Repository

In recent years, the use of high specific strength aluminum alloys in automotive and aerospace industries is in progress due to their energy savings. On the other hand, the carbon nanotubes (CNTs), due to their ultra-high strength and modulus of elasticity, have been considered as an excellent reinforcement for the metal matrix composites used in these industries. For production of these materials, the severe plastic deformation (SPD) has been known as a method of grain refinement to increase the strength and ductility. In this research, the composites of AlMg6 reinforced with CNT were produced by accumulated roll bonding (ARB) known as a SPD technique and their properties were compared... 

Orbital angular momentum (OAM)and the radial quantum number (p) in infinite-dimensional Hilbert space are two degrees of freedom of light which are associated with the spatial distribution of the electromagnetic field. They are attracting a growing interest for their potential in communication applications ranging from classical communication to fundamental tests of quantum mechanics,quantum communication and quantum cryptography. However, a third party trying to eavesdrop information from communication channel and treat channel security , quantum cryptography or quantum key distribution (QKD) is the secure communication method which is based on the quantum mechanical principles can... 

Electromagnetic field modes have several degrees of freedom, including polarization, orbital angular momentum, and radial order, which can be described by orthogonal modes. By using all the degrees of freedom in communication, the channel capacity can be increased dramatically. With the aim of increasing the capacity and correcting the errors created along the optical fiber, two important issues have been addressed in this thesis. First, the states propagated in the fiber may be disrupted by many unwanted factors and may not be transmitted correctly. Therefore, measures should be taken to minimize the impact of these factors as much as possible or to compensate for their effects. In the... 

In this thesis, we review the proof to standardness of Einstein solvamanifolds which is based on some results from Geometric Invariant Theory and stratification of topological spaces. Standardness is a very simple and yet powerful algebraic condition on the lie algebra of a solvmanifold which yields to remarkable existence and uniqueness and obstruction results  

Galaxy clusters are the most massive virialized systems in the universe. Their studies provide crucial grasp on the galaxy formation and evolution, dark matter and its nature, cosmological parameters and large scale structure of the universe. Because of their significant role in cosmology, providing a catalogue of galaxy clusters in a wide range of spatial angle, mass and redshift seems vital. Galaxy cluster detection can be performed by various methods in a broad spectrum of electromagnetic radiation. Optical detection of galaxy clusters is of the most traditional and popular methods. Among optical algorithms, one of the most efficient is called Cluster Red Sequence (CRS) which applies the... 

The topic of operations research and optimization is widely used in various fields, from transportation industries to military industries. Researchers in these fields seek to improve answers to problems and methods. In computer science, optimization methods are widely used. One of the most important problems in computer science are NP-hard problems; These problems are inherently not solvable in polynomial time. Therefore, the use of innovative methods, despite not guaranteeing the optimality of the solution, provide a suitable solution to bring the result closer to the optimal solution. Integer linear programming problems are also considered as NP-hard problems. The branch-and-bound... 

The processing of brain signals, including the electrocorticogram (ECoG) signal, is widely used in the investigation of neurological diseases. Conventionally, the ECoG signal has frequency components up to the range of 80 Hz. Studies have proven that in some conditions, such as epilepsy, the brain signal includes frequency components higher than 80 Hz, which are called high-frequency oscillations (HFO). Therefore, HFOs are recognized as a biomarker for epilepsy. The aim of this thesis is to review the previous methods of detecting HFOs and to present new methods with greater efficiency in the direction of diagnosis or treatment of epileptic patients. For this purpose, we used the ECoG data... 

In the present study, an analytical solution is developed to calculate the interlaminar stresses in long generally cross-ply laminated composite plates subjected to bending. At first, upon the integration of the strain-displacement relations and using the existing patterns in deformation of the long laminate, the general displacement field is extracted and simplified to the final form. Presented solution is based on a combined method containing the equivalent single-layer (ESL) theories beside the Reddy’s layerwise theory. In this method, the equivalent single-layer theories are utilized because of their simplicity and low computational efforts rather than the layerwise theory in evaluation...