No description available.

Os radicais nitróxidos tem sido muito utilizados em estudos de sistemas biológicos através do método de marcagem de spin. Apesar do grande número de publicações sobre aplicações, o número de estudos das propriedades intrínsecas dos nitróxidos ê bem reduzido. A importância de tais estudos é grande uma vez que o estudo de um sistema simples permite avaliar e interpretar os resultados dos sistemas biológicos, geralmente mais complicados Assim no presente trabalho estudou-se o espectro do RPE do 4-hidroxi-2,2,6,6-tetrametil piperidina-1 oxil (I) introduzido como impureza na sua matriz diamagnética 4-hidroxi-2,2,6,6-tetrametilpiperidina (II). Este processo de dopagem muito utilizado em física do estado sólido permitiu a determinação dos tensores g e A. Os valores obtidos gxx = 2.0098, gyy = 2.0061, gzz = 2.0024, e A xx = 5.3 G, Ayy = 7.0 G, Azz = 35.0 G, encontram-se dentro do esperado sendo que o valor de go = 2.0061 e Ao = 15.8 G evidencia a interação do fragmento N-O com ponte de hidrogênio (de hidroxila na posição 4 de uma molécula vizinha). A existência de dois centros paramagnéticos inequivalentes é interpretada corno devido a presença de duas possíveis conformações do fragmento N-O. As larguras das linhas de RPE observadas são grandes e em certas orientações do campo magnético ocorre o desdobramento da transição eletrônica num dubleto devido a interação com o hidrogênio da hidroxiIa que faz ponte com o N-O. A temperatura de cerca de -140&#176C e observada uma mudança sensível nos espectros de RPE evidenciando a desaparição da estrutura hiperfina na região de Axx e Ayy. Esta mudança está relacionada com o congelamento da rotação dos grupos metila afetando assim a interação dos prótons destes grupos com o elétron do fragmento N-O. O sistema estudado parece ser extremamente interessante do ponto de vista do estudo de influência de prótons na relaxação eletrônica do radical nitroxido. É evidenciada a forte dependência das propriedades paramagnéticas do nitróxido em relação à estrutura da vizinhança do fragmento N-O. / Nitroxide radicals are being used in many studies of biological systems through the spin label method. Despite the great number of publications involving the application of nitroxides only a reduced number of work s about nitroxides themselves is known. These studies are important because the knowledge of the properties of simple systems could be used in the interpretation of results in biological systems, normally mare complicated. In the present work the EPR spectra of 4-hydraxy-2,2,6,6-tetramethyl piperidine-l oxyl (I) introduced as impurity in the diamagnetic matrix of 4-hidraxy-2,2,6,6-tetramethyl piperidine (II) were studied. This process commonly used in solid state physics made it possible the determination of the g and A tensors. The values obtained : gxx = 2.0098, gyy = 2.0061, gzz = 2.0024, and A xx = 5.3 G, Ayy = 7.0 G, Azz = 35.0 G are typical for nitroxides. The mean values go = 2.0061 and Ao 15.8G are consistent with the presence af hydrogen bond to the N-O fragment (this bond is made with the proton of a hydroxyl in position 4 of a neighbour molecule). The existence of two magnetically inequivalent centers is interpreted so that two different conformations for the N-O fragment are possible. The line widths of the EPR lines are quite great and for some orientations of the magnetic field a splitting of the electronic transition in to a dublet occur. This splitting is due to the interaction of the electron in the N-Q fragment with the hydroxyl hydrogen which is bonded to the nitroxide group. At a temperature around -140&#176C a change in the EPR spectra is observed, when the hyperfine nitrogen structure in the region of A and A disappear. This change x y is related to the freezing of the rotation of the methyl groups affecting the interaction of the protons of these groups with the electron in the N-O. The system studied in the present work seems to be very interesting from the point of view of the influence of the protons in the electronic relaxation in the nitroxide radical. ln this context the strong dependency of the properties of the nitroxide relative to the structure of the neighbouring of the N-O fragment become evident.

No description available.

published_or_final_version / Diagnostic Radiology / Master / Master of Philosophy

Magnetic resonance imaging (MRI) is a valuable imaging technique. It provides excellent soft tissue contrast and multi-parametric non-invasive imaging protocols. Among those various techniques, diffusion MRI measures the water diffusion properties of biological tissue. It is a useful tool in characterizing various brain tissue microstructures quantitatively. With its rapid development, it is emerging that subtle changes can be probed by diffusion tensor imaging (DTI) quantitation. The objectives of this doctoral work are to access the subtle microstructural alterations in rodent brains due to hemodynamic changes, fear conditioning and sleep deprivation using in vivo DTI. With the improved reproducibility and specificity achieved by using advanced post-processing and animal preparation procedures, in vivo DTI is expected to be useful to explore the underlying biological mechanisms for posttraumatic stress disorder and memory deficit following sleep loss in human. Firstly, as DTI could be influenced by the presence of water molecules in brain vasculature, for better understand the reproducibility and sensitivity of in vivo DTI measurements, conventional DTI protocol was applied to a well-controlled rat model of hypercapnia. Our data demonstrated that diffusivities increased in whole brain, gray and white matter regions in response to hypercapnia. These results indicate that in vivo DTI quantitation in brain can be interfered by vascular factors on the order of few percents. Cautions should be taken in designing and interpreting quantitative DTI studies as all DTI indices can be potentially confounded by physiologic conditions, cerebrovascular and hemodynamic characteristics. Secondly, recent DTI studies have shown detection of long-term neural plasticity weeks to months following relatively extensive periods of training in animals. However, rapid plasticity within a short period (24 hours) after learning is important for observing the time course of training-evoked changes and narrow down candidate mechanisms. Fear conditioning (FC), which typically occurs over a short timescale (in minutes), was selected as a paradigm for investigation. Using voxel-wise repeated measures analysis, FA was found to increase in amygdala and decrease in hippocampus 1-hour post-FC, and it reversed in both regions 1-day post-FC. Results indicate that DTI can detect rapid microstructural changes in brain regions known to mediate fear conditioning in vivo. DTI indices could be explored as a translational tool to capture potential early biological changes in individuals at risk for developing post-traumatic stress disorder. Thirdly, in vivo DTI was employed to access regional specific microstructural changes following rapid eye movement sleep deprivation (SD), and explore possible temporal differentiation of these changes. With voxel-base analysis, MD is found to decrease in post-SD time points in bilateral hippocampi and cerebral cortex. The distributions of these clusters exhibited differentiable layer specific patterns, which were pointing to dentate gyrus and CA1 layer in hippocampus, and parietal cortex and barrel field layers in cerebral cortex. Results indicate that in vivo DTI is capable to detect microstructural changes in specific layers and reveal temporal distinction between them. These specific layers are possibly more susceptible to sleep loss, and the temporal distinction of changes between these layers might underlie learning and memory decline after SD. / published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

A study was undertaken to evaluate an automated process to invert for seismic moment tensors from seismic data recorded in mining environments. The data for this study was recorded at Nickel Rim South mine, Sudbury, Ontario. The mine has a seismic monitoring system manufactured by ESG Solutions that performs continuous monitoring of seismicity. On average, approximately 400 seismic events are recorded each day. Currently, data are automatically processed by ESG Solution's software suite during acquisition. The automatic processors pick the P- and/or S-wave arrivals, locate the events and solve for certain source parameters, excluding the seismic moment tensor. In order to solve for the moment tensor, data must be manually processed, which is laborious and therefore seldom performed. This research evaluates an automatic seismic moment tensor inversion method and demonstrates some of the difficulties (through inversions of real and synthetic seismic data) of the inversion process. Results using the method are also compared to the inversion method currently available from ESG Solutions, which requires the manual picking of first-motion polarities for every event. As a result of the extensive synthetic testing of the automatic inversion program, as well as the inversion of real seismic data, it is apparent that there are key parameters requiring greater accuracy in order to increase the reliability of the automation. These parameters include the source time function definition, source location (in turn requiring more accurate and precise knowledge of the earth media), arrival time picks and an attenuation model to account for ray-path dependent filtering of the source time function. In order to improve the automatic method three key pieces of research are needed: (1) studying various location algorithms (and the effects of increasing earth model intricacy) and automatic time picking to improve source location methods, (2) studying how the source time pulse can be accurately extracted from the seismic records, as well as the validity of various source models, and (3) studying how attenuation can be modeled more accurately to account for the filtering of the seismic waves through the earth media (in particular distortion to the source time function). / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2012-08-17 23:08:32.198

In many applications that deal with high dimensional data, it is important to not store the high dimensional object itself, but its representation in a data sparse way. This aims to reduce the storage and computational complexity. There is a general scheme for representing tensors with the help of sums of elementary tensors, where the summation structure is defined by a graph/network. This scheme allows to generalize commonly used approaches in representing a large amount of numerical data (that can be interpreted as a high dimensional object) using sums of elementary tensors. The classification does not only distinguish between elementary tensors and non-elementary tensors, but also describes the number of terms that is needed to represent an object of the tensor space. This classification is referred to as tensor network (format). This work uses the tensor network based approach and describes non-linear block Gauss-Seidel methods (ALS and DMRG) in the context of the general tensor network framework. Another contribution of the thesis is the general conversion of different tensor formats. We are able to efficiently change the underlying graph topology of a given tensor representation while using the similarities (if present) of both the original and the desired structure. This is an important feature in case only minor structural changes are required. In all approximation cases involving iterative methods, it is crucial to find and use a proper initial guess. For linear iteration schemes, a good initial guess helps to decrease the number of iteration steps that are needed to reach a certain accuracy, but it does not change the approximation result. For non-linear iteration schemes, the approximation result may depend on the initial guess. This work introduces a method to successively create an initial guess that improves some approximation results. This algorithm is based on successive rank 1 increments for the r-term format. There are still open questions about how to find the optimal tensor format for a given general problem (e.g. storage, operations, etc.). For instance in the case where a physical background is given, it might be efficient to use this knowledge to create a good network structure. There is however, no guarantee that a better (with respect to the problem) representation structure does not exist.

Thesis (M. Phil.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 66-73) Also available in print.

Thesis (Ph. D.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 97-111). Also available in print.

Os radicais nitróxidos tem sido muito utilizados em estudos de sistemas biológicos através do método de marcagem de spin. Apesar do grande número de publicações sobre aplicações, o número de estudos das propriedades intrínsecas dos nitróxidos ê bem reduzido. A importância de tais estudos é grande uma vez que o estudo de um sistema simples permite avaliar e interpretar os resultados dos sistemas biológicos, geralmente mais complicados Assim no presente trabalho estudou-se o espectro do RPE do 4-hidroxi-2,2,6,6-tetrametil piperidina-1 oxil (I) introduzido como impureza na sua matriz diamagnética 4-hidroxi-2,2,6,6-tetrametilpiperidina (II). Este processo de dopagem muito utilizado em física do estado sólido permitiu a determinação dos tensores g e A. Os valores obtidos gxx = 2.0098, gyy = 2.0061, gzz = 2.0024, e A xx = 5.3 G, Ayy = 7.0 G, Azz = 35.0 G, encontram-se dentro do esperado sendo que o valor de go = 2.0061 e Ao = 15.8 G evidencia a interação do fragmento N-O com ponte de hidrogênio (de hidroxila na posição 4 de uma molécula vizinha). A existência de dois centros paramagnéticos inequivalentes é interpretada corno devido a presença de duas possíveis conformações do fragmento N-O. As larguras das linhas de RPE observadas são grandes e em certas orientações do campo magnético ocorre o desdobramento da transição eletrônica num dubleto devido a interação com o hidrogênio da hidroxiIa que faz ponte com o N-O. A temperatura de cerca de -140&#176C e observada uma mudança sensível nos espectros de RPE evidenciando a desaparição da estrutura hiperfina na região de Axx e Ayy. Esta mudança está relacionada com o congelamento da rotação dos grupos metila afetando assim a interação dos prótons destes grupos com o elétron do fragmento N-O. O sistema estudado parece ser extremamente interessante do ponto de vista do estudo de influência de prótons na relaxação eletrônica do radical nitroxido. É evidenciada a forte dependência das propriedades paramagnéticas do nitróxido em relação à estrutura da vizinhança do fragmento N-O. / Nitroxide radicals are being used in many studies of biological systems through the spin label method. Despite the great number of publications involving the application of nitroxides only a reduced number of work s about nitroxides themselves is known. These studies are important because the knowledge of the properties of simple systems could be used in the interpretation of results in biological systems, normally mare complicated. In the present work the EPR spectra of 4-hydraxy-2,2,6,6-tetramethyl piperidine-l oxyl (I) introduced as impurity in the diamagnetic matrix of 4-hidraxy-2,2,6,6-tetramethyl piperidine (II) were studied. This process commonly used in solid state physics made it possible the determination of the g and A tensors. The values obtained : gxx = 2.0098, gyy = 2.0061, gzz = 2.0024, and A xx = 5.3 G, Ayy = 7.0 G, Azz = 35.0 G are typical for nitroxides. The mean values go = 2.0061 and Ao 15.8G are consistent with the presence af hydrogen bond to the N-O fragment (this bond is made with the proton of a hydroxyl in position 4 of a neighbour molecule). The existence of two magnetically inequivalent centers is interpreted so that two different conformations for the N-O fragment are possible. The line widths of the EPR lines are quite great and for some orientations of the magnetic field a splitting of the electronic transition in to a dublet occur. This splitting is due to the interaction of the electron in the N-Q fragment with the hydroxyl hydrogen which is bonded to the nitroxide group. At a temperature around -140&#176C a change in the EPR spectra is observed, when the hyperfine nitrogen structure in the region of A and A disappear. This change x y is related to the freezing of the rotation of the methyl groups affecting the interaction of the protons of these groups with the electron in the N-O. The system studied in the present work seems to be very interesting from the point of view of the influence of the protons in the electronic relaxation in the nitroxide radical. ln this context the strong dependency of the properties of the nitroxide relative to the structure of the neighbouring of the N-O fragment become evident.