1,721,036 research outputs found
Statistical-Analysis of a Mixed-Layer X-Ray-Diffraction Peak
Get PDFFil: Rebollo-Neira, Laura. Department of Mathematics. Aston University. Birmingham; United KingdomFil: Constantinides, Anthony G.. Imperial College London. Department of Electrical and Electronic Engineering. London; United KingdomFil: Plastino, Ángel Luis. CONICET; ArgentinaFil: Alvarez, Alberto Guillermo. Departamento de Química. Universidad de Los Andes; ColombiaFil: Bonetto, Rita D.. Centro de Investigación y Desarrollo en Ciencias Aplicadas Dr. Jorge J. Ronco. CINDECA. Facultad de Ingeniería y de Ciencias Exactas. Universidad Nacional de La Plata; ArgentinaFil: Iñíguez Rodríguez, Adrián Mario. Centro de Investigaciones Geológicas (CIG). Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; Argentin
Sparse image approximation
Get PDFThis thesis addresses the problem associated with the approximation of signals as linear superposition of elementary components often called 'atoms'. `After highlighting the limitations of using only orthogonal elements, approximation technique is extended to consider the selection of atoms from a large redundant set, called a `dictionary'. In particular, a highly correlated `mixed dictionary' is considered, from which the atoms are selected through highly non-linear techniques known as Matching Pursuit Strategies. These techniques evolve by stepwise selection of dictionary atoms. In particular, a relatively new strategy named Block wise Orthogonal Matching Pursuit is considered. This technique operates on images divided into blocks and extends the stepwise selection of dictionary atoms to also select the blocks be approximated at each iteration step. The implementation of block selection introduces extra requirements, which has motivated the Macro Processing Scheme proposed in this thesis. The project also focuses on effectiveness of the approach with regards to processing time. In this respect, a C++ implementation of the Block wise Orthogonal Matching Pursuit technique has been developed to operate in MATLAB environment. Using the developed tools a number of comparative tests, with respect to sparse image representation, have been performed and analysed
Sparse image representation with encryption
Get PDFIn this thesis we present an overview of sparse approximations of grey level images. The sparse representations are realized by classic, Matching Pursuit (MP) based, greedy selection strategies. One such technique, termed Orthogonal Matching Pursuit (OMP), is shown to be suitable for producing sparse approximations of images, if they are processed in small blocks. When the blocks are enlarged, the proposed Self Projected Matching Pursuit (SPMP) algorithm, successfully renders equivalent results to OMP. A simple coding algorithm is then proposed to store these sparse approximations. This is shown, under certain conditions, to be competitive with JPEG2000 image compression standard. An application termed image folding, which partially secures the approximated images is then proposed. This is extended to produce a self contained folded image, containing all the information required to perform image recovery. Finally a modified OMP selection technique is applied to produce sparse approximations of Red Green Blue (RGB) images. These RGB approximations are then folded with the self contained approach
Dipole Dynamics in the Point Vortex Model
Get PDFPresented here is a thorough theoretical and numerical investigation into the dynamics of vortex dipoles in point vortex and point vortex adjacent systems. We begin by reviewing the basic laws of fluid flow and thus standard hydrodynamic turbulence after which, motivated by the vortex filament description of fluid flow, we introduce the intriguing phenomenon of quantum turbulence. From this quantum turbulence we motivate study of the point vortex model, including a description of the basic theory of point vortex systems. Using Kirchoff’s Hamiltonian formulation of the 2D point vortex model in the infinite domain, we consider work done into dipole-vortex collisions, as well as extending this to consider the dipole-dipole collisions in both the integrable and non-integrable cases. Here we solve for important dynamical quantities such as the scattering angle, of great importance to the mixing of turbulent systems, and also the vortex separations at the dipole periapsis, as well as the extremum values of dipole separation, and we discuss the possibility of dipole creation in such systems. We consider this as a numerical analysis but also analyse each interaction regime theoretically where possible, finding perfect agreement between theoretical predictions and numerical results where this is done. The study then continues by considering the collisions of dipoles with same-signed rotating vortex clusters, and also analysing the possibility of approximating the dynamics of a dipole colliding with large vortex clusters by the dynamics of a dipole colliding with equivalently strong single point vortices, we find such an approximation is even more effective than may first be considered, with the dipole-vortex simulations often faithfully reproducing the dynamical quantities of the dipole-clusters. We also consider the scattering angles and dipole creation possibility as before, noting the highly chaotic behaviour found at impact parameters close to zero. We then move from the 2D infinite domain point vortex model in the strict sense in order to consider how point vortex systems may capture behaviour of standard turbulent systems; by considering large N periodic point vortex systems we realise the 2D turbulent phenomenon of the inverse energy cascade through additional forcing and dampening mechanisms. Finally, we give a study on the effect of the interaction of sound waves with a vortex dipole. Investigating the notion that sound will lead to an eventual vortex collapse, we find this is highly dependent upon the initial conditions present, more specifically the initial sound distribution, as this behaviour although realised in Gaussian distributed sound is not realised in Rayleigh-Jean distributed sound. Therefore, it is speculated that the shrinkage and annihilation processes occur not due to the presence of sound alone but instead through the out-of-equilibrium motion as the system relaxes towards the eventual statistical equilibrium of vortex annihilation
Measurements design and phenomena discrimination
Get PDFThe construction of measurements suitable for discriminating signal components produced by phenomena of different types is considered. The required measurements should be capable of cancelling out those signal components which are to be ignored when focusing on a phenomenon of interest. Under the hypothesis that the subspaces hosting the signal components produced by each phenomenon are complementary, their discrimination is accomplished by measurements giving rise to the appropriate oblique projector operator. The subspace onto which the operator should project is selected by nonlinear techniques in line with adaptive pursuit strategies
Effective high compression of ECG signals at low level distortion
Get PDFAn effective method for compression of ECG signals, which falls within the transform lossy compression category, is proposed. The transformation is realized by a fast wavelet transform. The effectiveness of the approach, in relation to the simplicity and speed of its implementation, is a consequence of the efficient storage of the outputs of the algorithm which is realized in compressed Hierarchical Data Format. The compression performance is tested on the MIT-BIH Arrhythmia database producing compression results which largely improve upon recently reported benchmarks on the same database. For a distortion corresponding to a percentage root-mean-square difference (PRD) of 0.53, in mean value, the achieved average compression ratio is 23.17 with quality score of 43.93. For a mean value of PRD up to 1.71 the compression ratio increases up to 62.5. The compression of a 30 min record is realized in an average time of 0.14 s. The insignificant delay for the compression process, together with the high compression ratio achieved at low level distortion and the negligible time for the signal recovery, uphold the suitability of the technique for supporting distant clinical health care
Constructive updating/downdating of oblique projectors:a generalization of the Gram-Schmidt process
Get PDFA generalization of the Gram-Schmidt procedure is achieved by providing equations for updating and downdating oblique projectors. The work is motivated by the problem of adaptive signal representation outside the orthogonal basis setting. The proposed techniques are shown to be relevant to the problem of discriminating signals produced by different phenomena when the order of the signal model needs to be adjusted
Análisis de señales e inferencia estadística
Get PDFLa propiedad común a todas las señales que analizaremos, es que cualquiera de ellas admite una representación positiva en alguna base. El interés por el análisis de este tipo de señales, se debe a que en su representación está contenida la estadística del sistema.
Puesto que intentar dar la representación de una señal, a partir de un número finito de medidas sobre la misma, es un problema que en general admite más de una solución, adoptaremos el criterio que provee la Teoría de la Información para elegir una de las posibles soluciones.
Aceptando el postulado de la teoría, a tal solución la presentamos como la mejor que podemos dar en base a la información conocida. Comprobamos la validez de tal afirmación a través del propio conjunto de medidas disponibles.
En la primera parte de este trabajo, supondremos conocida la base donde una señal admite representación positiva. Para tratar estos casos, presentamos un formalismo y desarrollamos una metodología que permite instrumentar el criterio que adoptamos. Ejemplificaremos la bondad del método aplicándolo a la resolución de ejemplos numéricos y situaciones realistas.
A partir del capítulo IV, discutiremos la forma de elegir una base adecuada, en término del tipo de información que contiene una representación. De todas las señales pertenecientes al conjunto Srp, seleccionaremos aquellas que contienen información acerca de la distribución de estados de un sistema y las llamaremos "señales estadísticas". Por medio del método previamente presentado, encontraremos la distribución de estados, partiendo de medidas sobre estas señales estadísticas. Ilustraremos el procedimiento propuesto, estudiando sistemas de arcillas interestratificadas, por medio del diagrama de difracción de rayos X que produce.Tesis digitalizada en SEDICI gracias a la Biblioteca de Física de la Facultad de Ciencias Exactas (UNLP).Doctor en FísicaUniversidad Nacional de La PlataFacultad de Ciencias Exacta
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