Non-invasive electrical imaging of the heart aims to quantitatively reconstruct information about the electrical activity of the heart from multiple thoracic ECG signals. The computational framework required to produce such electrical images of the heart from non-invasive torso surface signals is presented. It is shown reliable electrical images of the heart can be obtained under a controlled environment. This has been demonstrated using an anatomically realistic boundary element porcine torso model. The procedures required to create a subject specific model using a small number of control points and to create a specific heart model from three-dimensional ultrasound images using a linear fitting procedure are presented. From discrete ECG electrodes a continuous representation of the potential field over the entire torso surface can also be produced using this linear fitting procedure. The construction of the transfer matrices for the two predominant electrocardiographic sources (epicardial potentials and myocardial activation times) are described in detail. The transfer matrices are used to compute activation times within the heart and epicardial potentials on the heart surface. Myocardial activation times are computed using an algorithm based on the Critical Point Theorem while epicardial potentials are computed using standard Tikhonov and Truncated SVD spatially regularised methods as well as Greensite's spatial and temporal regularisation method. The regularisation parameters for the epicardial potentials are determined using a variety of methods (e.g., CRESO criterion, L-curve, zero-crossing). The potential and activation based formulations are compared in a comprehensive inverse simulation study. To try and capture the dynamic and variable nature of cardiac electrical activity, the study is performed with three different types of cardiac sources with a realistic porcine model. These simulations investigate the effect on the computed solutions of individual and combinations of modelling errors. These errors include corruption in the torso surface signals, changes in material properties and geometric distortion. In general, the activation based formulation is preferred over the epicardial potential formulations, with Greensite's method found to be the best method for reconstructing epicardial potentials. Under optimal conditions, the activation approach could reconstruct the activation times to within RMS. Both potential and activation based formulations were found to be relatively insensitive to changes in material properties such as lung conductivities and activation function shapes. When examining individual errors, the geometry and positions of the torso and heart had the greatest effects on the inverse solutions. The relative heart position needed to be determined to within to obtain results within of the solutions obtained under control conditions. When the modelling errors are combined to produce errors which can be expected in a clinical or experimental situation the activation based solutions were consistently more accurate than potential based solutions. The next necessary step in this project is the detailed validation of the results against in-vivo data. This step is necessary before such algorithms can be reliably used to aid in the assessment of heart function in a clinical environment.

Non-invasive electrical imaging of the heart aims to quantitatively reconstruct information about the electrical activity of the heart from multiple thoracic ECG signals. The computational framework required to produce such electrical images of the heart from non-invasive torso surface signals is presented. It is shown reliable electrical images of the heart can be obtained under a controlled environment. This has been demonstrated using an anatomically realistic boundary element porcine torso model. The procedures required to create a subject specific model using a small number of control points and to create a specific heart model from three-dimensional ultrasound images using a linear fitting procedure are presented. From discrete ECG electrodes a continuous representation of the potential field over the entire torso surface can also be produced using this linear fitting procedure. The construction of the transfer matrices for the two predominant electrocardiographic sources (epicardial potentials and myocardial activation times) are described in detail. The transfer matrices are used to compute activation times within the heart and epicardial potentials on the heart surface. Myocardial activation times are computed using an algorithm based on the Critical Point Theorem while epicardial potentials are computed using standard Tikhonov and Truncated SVD spatially regularised methods as well as Greensite's spatial and temporal regularisation method. The regularisation parameters for the epicardial potentials are determined using a variety of methods (e.g., CRESO criterion, L-curve, zero-crossing). The potential and activation based formulations are compared in a comprehensive inverse simulation study. To try and capture the dynamic and variable nature of cardiac electrical activity, the study is performed with three different types of cardiac sources with a realistic porcine model. These simulations investigate the effect on the computed solutions of individual and combinations of modelling errors. These errors include corruption in the torso surface signals, changes in material properties and geometric distortion. In general, the activation based formulation is preferred over the epicardial potential formulations, with Greensite's method found to be the best method for reconstructing epicardial potentials. Under optimal conditions, the activation approach could reconstruct the activation times to within RMS. Both potential and activation based formulations were found to be relatively insensitive to changes in material properties such as lung conductivities and activation function shapes. When examining individual errors, the geometry and positions of the torso and heart had the greatest effects on the inverse solutions. The relative heart position needed to be determined to within to obtain results within of the solutions obtained under control conditions. When the modelling errors are combined to produce errors which can be expected in a clinical or experimental situation the activation based solutions were consistently more accurate than potential based solutions. The next necessary step in this project is the detailed validation of the results against in-vivo data. This step is necessary before such algorithms can be reliably used to aid in the assessment of heart function in a clinical environment.

Thesis (M. S.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Tentzeris, Emmanouil; Committee Member: Andrew Peterson; Committee Member: Laskar, Joy; Committee Member: Papapolymerou, Ioannis. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Non-invasive electrical imaging of the heart aims to quantitatively reconstruct information about the electrical activity of the heart from multiple thoracic ECG signals. The computational framework required to produce such electrical images of the heart from non-invasive torso surface signals is presented. It is shown reliable electrical images of the heart can be obtained under a controlled environment. This has been demonstrated using an anatomically realistic boundary element porcine torso model. The procedures required to create a subject specific model using a small number of control points and to create a specific heart model from three-dimensional ultrasound images using a linear fitting procedure are presented. From discrete ECG electrodes a continuous representation of the potential field over the entire torso surface can also be produced using this linear fitting procedure. The construction of the transfer matrices for the two predominant electrocardiographic sources (epicardial potentials and myocardial activation times) are described in detail. The transfer matrices are used to compute activation times within the heart and epicardial potentials on the heart surface. Myocardial activation times are computed using an algorithm based on the Critical Point Theorem while epicardial potentials are computed using standard Tikhonov and Truncated SVD spatially regularised methods as well as Greensite's spatial and temporal regularisation method. The regularisation parameters for the epicardial potentials are determined using a variety of methods (e.g., CRESO criterion, L-curve, zero-crossing). The potential and activation based formulations are compared in a comprehensive inverse simulation study. To try and capture the dynamic and variable nature of cardiac electrical activity, the study is performed with three different types of cardiac sources with a realistic porcine model. These simulations investigate the effect on the computed solutions of individual and combinations of modelling errors. These errors include corruption in the torso surface signals, changes in material properties and geometric distortion. In general, the activation based formulation is preferred over the epicardial potential formulations, with Greensite's method found to be the best method for reconstructing epicardial potentials. Under optimal conditions, the activation approach could reconstruct the activation times to within RMS. Both potential and activation based formulations were found to be relatively insensitive to changes in material properties such as lung conductivities and activation function shapes. When examining individual errors, the geometry and positions of the torso and heart had the greatest effects on the inverse solutions. The relative heart position needed to be determined to within to obtain results within of the solutions obtained under control conditions. When the modelling errors are combined to produce errors which can be expected in a clinical or experimental situation the activation based solutions were consistently more accurate than potential based solutions. The next necessary step in this project is the detailed validation of the results against in-vivo data. This step is necessary before such algorithms can be reliably used to aid in the assessment of heart function in a clinical environment.

In the past few years, “green technologies and touch screen technologies for portable devices has came to hot topic in consumer market. The demand for transparent conducting oxides (TCO) is increasing continuously. Therefore, the potential replacement of indium tin oxide (ITO), which is the most widely used TCO in industry, by aluminum zinc oxide (AZO) draws much attention in order to solve the problem of shortage of ITO one day due to the consisting of rare-earth element. In this work, electrical and optical properties of AZO had been characterized according to different sputtering parameters such as oxygen contents, working pressures and gas flow ratios. Physics of electrical conduction and optical transparency of AZO films were revealed and analyzed in order to set up a more complete relationship between mechanism and performance. Meanwhile, a comparison of sensitivity between AZO and zinc oxide (ZnO) to sputtering environment had been made and behaviors of AZO at low temperature had been presented. Optimum sputtering conditions for AZO had been established as a function of sputtering time and the film resistivity reached down to 7 x 10-4 Ω·cm while film transmittance was above 85% when t = 140 mins having film thickness about 610 nm. Degradation of AZO had been investigated. Application of AZO in OLED fabrication had been carried out after film refinement and device performance had been given. Finally, simulation of OLED structure was done for better device performance

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O objetivo deste trabalho é o de caracterizar o processo de condução do EPDM e de formulações deste material quando nele se incorpora diferentes concentrações de trihidróxido de alumínio (alumina trihidratada). Dois procedimentos experimentais foram utilizados para se obter os resultados: o primeiro utilizando medidas de corrente no estado estacionário variando-se a espessura das amostras, o potencial, o material do eletrodo e a temperatura e o segundo através de medidas da distribuição de cargas elétricas no interior do material empregando o método de propagação de um pulso de pressão. Na análise dos resultados experimentais encontrou-se presença de polarização elétrica e de condução, a qual apresenta dependência linear do logaritmo da condutividade com a raiz do campo, na região de altos campos elétricos. Estudo comparativo de alguns modelos foi realizado sem que nenhum deles explicasse os nossos resultados. Propusemos tentativamente a combinação de efeitos de superfície e de volume. Para o material com crescente concentração de alumina também se encontrou dependência da condutividade com a raiz do campo, mas a interpretação dos resultados ficou mais incerta. Além disto, um efeito quadrático com a concentração de alumina foi encontrado para a polarização e para a condução um efeito linear / This work attempts to characterize the processes of electric conduction in the EPDM copolymer and its composites with several contents of alumina trihydrate filler. Two different experimental procedures were employed: (i) measurements of the steady state electric current for several sample thicknesses, applied voltages, temperatures, and different types of electrode (ii) charge distribution measurements using the pressure wave propagation method. The results showed that there is an electric polarization superimposed to an electric conduction. For high electric fields a linear dependence of the log of the conductivity versus the square root of the electric field was found. Several theoretical models were employed aimed at explaining the experimental results but none gave satisfactory results. It seems that the most adequate model is one in which both surface and bulk processes are considered. When the content of alumina trihydrate filler was increased, a linear dependence between the logs of conductivity against the square root of the electric field was again observed, though the results could not be readily interpreted. It was also found that the electric polarization and the electric conductivity show a quadratic and a linear dependence on the alumina trihydrate content, respectively

Ph.D. (Theoretical Physics) / In this thesis the thermodynamic and magnetic properties of the non-degenerate Hubbard model are investigated. The underlying lattice is the bcc-lattice. The results obtained will therefore be especially applicable to systems with a single, narrow conduction band. As a check the thermodynamic properties of the model system are first calculated in two limiting cases, namely the free electron 'gas and the strong coupling limit. In this process, use is made of results related to Wick's Theorem, which are developed in an appendix. Another check is provided by the calculation of the ground state spectrum of a finite, fourpoint system. These results are obtained using standard group theory techniques. The ground state for the non-degenerate Hubbard model is solved approximatively by a variational method. Once again the necessary version of Wick's theorem is developed in an appendix. The ,results for the neutral case (i.e. a half-filled band) is in agreement with other studies on AB-lattices: It is found that the system is anti ferromagnetic for all values of the coupling constant. The quarter and three-quarter filled cases, hitherto not studied because of numerical complexity, yield a completely different picture. For increasing values of the coupling constant second order phase transitions are found, first from the para- to the ferromagnetic phase and then from the ferro- to the anti ferromagnetic phase. The only results available in the literature related to this case were obtained for an almost half-filled band in the strong-coupling limit and qualitatively support the findings of the present study. It is proposed that the simple theory used in this study be extended for use in physical systems such as Cr.

M.Sc. / The efficiency of commercial polycrystalline silicon solar cells is currently 12% and 15% in the case of single crystalline cells. It is possible to lose about half of the open circuit voltage due to inferior contacts on the cell. It is thus clear that inferior contacts can seriously impede the relative low efficiency and care should be taken to make good ohmic contacts. Experiments were done to evaluate the influence of several factors on the quality and stability of the contacts. 1 C2•cm p-type polycrystalline silicon and 3 52.cm n-type single crystalline silicon were primarily used for these experiments. Results of molybdenum contacts on n-type silicon are also presented and the problems with silver epoxy contacts are discussed. It was found that aluminium contacts on p-type polycrystaline silicon improve with temperature and time, while those on single crystaline n-type degrade with temperature and time. These changes are already present at room temperature and are attributed to solid state diffusion of the aluminium into the silicon. This results in a p + layer. In the case of contacts on p-type, the behaviour is that of a Schottky diode. After the solid state diffusion, it becomes possible for the charges to quantum mechanically tunnel through the p+ layer. This results in an improvement of the contact. The contacts on n-type however, are ohmic just after evaporation. Similar to the p-material, the p+ layer causes a p+-n-junction with the depletion layer primarily in the n-type material. This causes a degradation in the contact quality. It is possible to achieve good quality contacts on polycrystaline p-type material, by annealing the contacts above 500°C for one minute. These contacts however, are non-ideal. SEM photographs show that the silicon surface is crated by pits due to solid state diffusion. It is only at these pits that conduction through the Schottkybarrier is possible. Since the area of the pits constitutes only a portion of the total area, only a portion of the surface will partake in conduction. Contact resistance is always present. For pm sized contacts on integrated circuits, the spesific resistance is of the order of 10 -6 Q.cm2. Contacts on solar cells, however, are of millimetre dimensions and the spesific resistance can be four orders of magnitude larger. The conduction through the surface can be modelled as conduction through a surface that is constituted of a mixture of minute ohmic and diode surfaces.

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