Sharif Digital Repository

In this project we focused on Simulation of two-phase (gas-oil) flow in 2D anisotropic porous medium on unstructured grids by finite volume method.Since the permeability assumes to be full tensor, common discretization methods for pressure and flux equations couldn’t satisfy continuity conditions then a new method of discretization named continuous flux approximation introduced.In this new method, cell center pressure calculated by directly applying flux continuity conditions to control volume boundaries. In this project a ninepoint scheme is used, it means that for making the flux continuity conditions over each control volume in two dimensions all neighboring cells are involved.The reason... 

Circular polarization (CP) is one of the common polarization types used in wireless systems for frequency identification (RFID), global positioning (GPS) and wireless local area networks (WLAN), since it can provide greater flexibility in orientation angle between transmitter and receiver, and better mobility and weather penetration than the linearly polarized antennas. Magnetic permeability in ferrites can be tuned by external magnetic field ; So ferrites can be good candidates for new reconfigurable CP antenna technology. In this project, we will consider circularly polarized slot antenna with a wide axial ratio beamwidth that consists of a normally magnetized ferrite substrate mounted... 

Continuous approximation of pressure and flux fields is one of main goals of simulating flow in porous media. To compute the pressure field in heterogeneous and anisotropic media using minimum memory and time, it is necessary to use a conservative flux-continuous scheme. Nowadays, one of the most efficient approaches to minimize the solving time of large-scale problems is parallel computing. In this research, a parallel algorithm for flux-continuous multi-point flux approximation (MPFA) scheme with full pressure support (FPS) is designed and implemented on unstructured triangular grids by cell-centered approach. In this work, 2D single phase flows are investigated. The results are presented... 

In wireless communication systems increasing the gain of antennas is seminal to increase in coverage and data transmission rate, and reducing the possible errors. One of the main factors for improving the antenna gain is matching the polarizations of the transmitter and the receiver antennas. Towards this end, both the transmitter and the receiver antennas should have the same axial ratio, specific direction and polarizations. As far as the flexibility of the direction angle between the transmitter and the receiver is concerned, the so-called circular polarization is preferred do the linear polarization. The antennas with circular polarizations are prominently utilized in satellites,... 

In this work, we evaluate differernt tensor decomposition methods in application of fECG extraction from abdominal ECG recordings. After selecting proper tensor decomposition tool (Tucker decomposition) we propose a linear source separation algorithm based on a measure of quasi-periodicity. The quasi-periodicity is attained through the use of a constraint on a matrix factorization problem. In practice, we form a three dimensional ”tensor” by stacking the observation matrix and rough estimates obtained by both linear and non-linear subspace reconstruction methods. The method is applied to a database of electrocardiography (ECG) recordings, where rough subspace estimates of maternal and fetal... 

Tensors are valuable tools to represent EEG data. Tucker decomposition is the most used tensor decomposition in multidimensional discriminant analysis and tensor extension of LDA (Higher Order Discriminant Analysis-HODA) is a popular tensor discriminant method used for data of ERP-based BCIs. In this Thesis we introduce a new tensor-based feature reduction technique, named Higher Order Spectral Regression Discriminant Analysis (HOSRDA), with application in P300-based BCIs. The proposed method (HOSRDA) is a tensor extension of Spectral Regression Discriminant Analysis (SRDA) and casts the eigenproblem of HODA to a regression problem and therefore overcome the probable issue of singularity of... 

In this paper a new multi-scale method is developed for modeling heterogeneous materials, this method is based on homogenization and it is classified as hierarchical multi-scale method. For simulating problems in continues media, finding the elastic tensor is necessity, in homogeneous material this tensor come down from Young’s modulus and poison’s ratio, however in Nano-scale problems specially in heterogeneous material, this solution does not work and need to revise. To deal with heterogeneity in these problems homogenization by a representative volume element is a novel method. The properties of material is imported from RVE in each step of solving problem to larger scale, and by... 

Determination of the elastic fields associated with a spherical multiply-coated inhomogeneous inclusion is a problem of great interest among researchers. In this work a set consisting of N+1 concentric spherical domains is considered. Each domain is either isotropic or spherically isotropic and is functionally graded (FG) in the radial direction. The outermost spherical surface is subjected to nonuniform loading and the constituent phases are subjected to some prescribed nonuniform body force and eigenstrain fields. When the outermost domain is an unbounded medium with zero eigenstrain and body force fields then an N-phase multi-inhomogeneous inclusion problem is realized for which the... 

In this essay we study the concepts of nuclearity in C-algebras, and amenability in Banach algebras. A proof on the "every amenable C-algebra is nuclear" is studied. A Banach algebra A is called amenable if every continous derivation D : A ! E , is inner i.e. there exists anif in this denition E is a dual Banach A-module and norm continuity replace by w-continuity then we have Connes-amenability; Connes-amenability was rst considered for von Neumann algebras in [J-K-R] (and thus should perhaps be called Johnson-Kadison-Ringrose amenability). The reason why this notion of amenability is usually associated with A. Connes are his papers [Conn 1] and [Conn 2] The name "Connes-amenability" seems... 

Fractured rock masses contain fractures facilitating the fluid movement and storage. Permeability and material behavior of this particular material is poorly understood. Hence, there would be a great need of determining the characteristics of such materials. In this paper, an equivalent approach has been implemented at first in order to equivalently determine the hydro-mechanical and geomechanical characteristics of the fractured rock masses in the form of anisotropic tensors. The equivalent permeability and compliance tensors are derived based upon fluid dissipation energy and linear elasticity, respectively. In addition, the effect of derived characteristics on a single-phase (solid... 

According to the AdS/CFT correspondance,Gravity in an asymptotically AdS spacetimes has a conformal field theory dual. One of the perplexing concepts in theoretical physics is obtaining a comprehensive understanding of holography. To this end, it is of interest to explore whether holography exists beyond the known example of the AdS/CFT correspondence and for spacetimes other than the AdS. asymptotically flat spacetimes are of great theoretical importance.A correspondence has recentlay been proposed,which is between asymptotically flat spacetimes and a field theory with Galilean conformal symmerty and it is known as BMS/GCA correspondance.In this thsis,we have reviewed this correspondence... 

Einstein's general theory of relativity is an admirable successful and unifier geometrical modeling among concepts of space, time and gravity. This theory along with special theory of relativity made a massive change in our physical view and this, especially in its historical context, has deep and interesting consequences in man's philosophical viewpoint which can be studied. Some parts of this thesis relates to these consequences. Some of these interesting consequences may be hidden by computional or mathematical viewpoint and often these equations do not contain enough intuition. in one part, we provide a formulizatin of Einstein's equaion that is intuitional which can be translated in... 

This thesis is about one of the newest attractive theories in mathematics and theoretical physics; Topological Quantum Field Theory (TQFT) has some basic algebraic requirements called tensor categories, after introducing them and describing axioms of the theory which has suggested by Atiyah in 1988, we will see that the category of 2d-TQFT is equivalent to the category of commutative frobenius algebras over an arbitrary field .In the last part we focus on some topological aspects of theory in dimension 3 and some invariants of 3d manifolds , we will see these invariants are the main tool for construction a 3d-TQFT  

Event related potentials (ERPs), are potentials that arise from the occurrence of an event in the electroencephalogram signals and have very small amplitude compared to the Electroencephalogram (EEG) signal. For that reason, to access ERPs, the experiment is repeated several times under similar conditions and then the are extracted by synchronized averaging, but in this way information such as Amplitude and Delay (Lag) which reflect Mental fatigue and Task habituation of subject is disappeared. Many methods for extracting the ERP components from the EEG signals have been presented as matrices. However, due to the twodimensional information (time and space) available, resource extraction is... 

The concept of generalized strains is a well-established subject in the classical continuum mechanics. The characteristics and various applications of the generalized strains have been the point of interest of many researchers in the classical continuum mechanics. The aim of this thesis is the introduction of generalized strains in the micropolar theory, as a non-classical continuum theory. A set of generalized strains is suggested for the deformation of macro-elements. Moreover, a set of generalized strains is proposed for the micro-structures. Since the rate of strains possesses a significant importance in the constitutive equations of nonlinear analysis of solids, expressions for the rate... 

The aim in the current thesis is to introduce a powerful method based on quantitative Acoustic Emission approach for structures health monitoring in a way that the proposed method can be used for industrial purposes. In order to do this, after presenting a survey on moment tensor concept and its relation to crack nucleation in solids, the equivalent forces of crack initiation are calculated. These forces are then applied on the meshed area of a 2D finite element model. The corresponding result is the propagation of acoustic waves which are modeled by using finite element analysis. After waveform data acquisition in the imaginary sensor positions and implying source location analysis, the... 

Diffusion Weighted Imaging (DWI) is a non-invasive method for investigating the brain white matter. Assuming the Gaussian model for diffusion process, diffusion tensor is constructed and Diffusion Tensor Images (DTI) are obtained. White matter is constructed from fiber bundles which have crossing in most of the regions. In the crossing regions, the Gaussian model cannot work. In this situation, DTI cannot reconstruct the fiber structures correctly. Therefore, High Angular Resolution Diffusion Imaging (HARDI) was proposed to solve this problem. Q-ball imaging is a new technique for HARDI reconstruction which is useful for estimating diffusion Orientation Distribution Function (ODF). ODF is a... 

One of the main subjects that has been vastly studied recently, is the final fate of Black holes with Hawking radiation. Radiation of a black hole changes the black hole, thus horizons of the black hole will also have dynamics. For a radiating black hole the inward flux of matter and the flux of radiation are two important factors for determining black hole energymomentum tensor that determine dynamics of different kinds of horizons. Quantum flux calculation needs choosing a proper quantum state as vacuum for calculating the expectation value of energy-momentum tensor. In this thesis we have attempted to write a useful reference and we hope it could help the reader to prepare for studying... 

In modelling of large deformations in deformable solids, rate type constitutive equations are of great importance. In order to fulfill the material objectivity conditions it is necessary to choose an objective rate of stress tensor. On the other hand, using corotational rates, because of their special properties (which are resulted of the fact that varaition of parameters are computed from an observer connected to a rotated triad), in rate type non-linear elastic constitutive equations (called hypo-elastic equations) are notable. In this thesis, the necessary conditions for a linear rate type isotropic tensor-valued function of a tensor argument and its rate to be integrable are driven. In... 

The brain electrical signal (EEG) has been widely used in clinical and academic research, due to its ease of recording, non-invasiveness and precision. One of the applications can be emotion recognition from the brain's electrical signal. Generally, two types of parameters (Valence and Arousal) are used to determine the type of emotion, which, in turn, indicate "positive or negative" and "level of extroversion or excitement" for a specific emotion. The significance of emotion is determined by the effects of this phenomenon on daily tasks, especially in cases where the person is confronted with activities that require careful attention and concentration.In the emotion recognition problem,...