968 resultados para Development and applications


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The objective of the research carried out in this report was to observe the first ever in-situ sonochemical reaction in the NMR Spectrometer in the megahertz region of ultrasound. Several reactions were investigated as potential systems for a sonochemical reaction followed by NMR spectroscopy. The primary problem to resolve when applying ultrasound to a chemical reaction is that of heating. Ultrasound causes the liquid to move and produces 'hot spots' resulting in an increase in sample temperature. The problem was confronted by producing a device that would counteract this effect and so remove the need to account for heating. However, the design of the device limited the length of time during which it would function. Longer reaction times were required to enable observations to be carried out in the NMR spectrometer. The fIrst and most obvious reactions attempted were those of the well-known ultrasonic dosimeter. Such a reaction would, theoretically, enable the author to simultaneously observe a reaction and determine the exact power entering the system for direct comparison of results. Unfortunately, in order to monitor the reactions in the NMR spectrometer the reactant concentrations had to be signifIcantly increased, which resulted in a notable increase in reaction time, making the experiment too lengthy to follow in the time allocated. The Diels-Alder Reaction is probably one of the most highly investigated reaction systems in the field of chemistry and it was this to which the author turned her attention. Previous authors have carried out ultrasonic investigations, with considerable success, for the reaction of anthracene with maleic anhydride. It was this reaction in particular that was next attempted. The first ever sonochemically enhanced reaction using a frequency of ultrasound in the megahertz (MHz) region was successfully carried out as bench experiments. Due to the complexity of the component reactants the product would precipitate from the solution and because the reaction could only be monitored by its formation, it was not possible to observe the reaction in the NMR spectrometer. The solvolysis of 2-chloro-2-methylpropane was examined in various solvent systems; the most suitable of which was determined to be aqueous 2-methylpropan-2-ol. The experiment was successfully enhanced by the application of ultrasound and monitored in-situ in the NMR spectrometer. The increase in product formation of an ultrasonic reaction over that of a traditional thermal reaction occurred. A range of 1.4 to 2.9 fold improvement was noted, dependent upon the reaction conditions investigated. An investigation into the effect of sonication upon a large biological molecule, in this case aqueous lysozyme, was carried out. An easily observed effect upon the sample was noted but no explanation for the observed effects could be established.

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Bio-impedance analysis (BIA) provides a rapid, non-invasive technique for body composition estimation. BIA offers a convenient alternative to standard techniques such as MRI, CT scan or DEXA scan for selected types of body composition analysis. The accuracy of BIA is limited because it is an indirect method of composition analysis. It relies on linear relationships between measured impedance and morphological parameters such as height and weight to derive estimates. To overcome these underlying limitations of BIA, a multi-frequency segmental bio-impedance device was constructed through a series of iterative enhancements and improvements of existing BIA instrumentation. Key features of the design included an easy to construct current-source and compact PCB design. The final device was trialled with 22 human volunteers and measured impedance was compared against body composition estimates obtained by DEXA scan. This enabled the development of newer techniques to make BIA predictions. To add a ‘visual aspect’ to BIA, volunteers were scanned in 3D using an inexpensive scattered light gadget (Xbox Kinect controller) and 3D volumes of their limbs were compared with BIA measurements to further improve BIA predictions. A three-stage digital filtering scheme was also implemented to enable extraction of heart-rate data from recorded bio-electrical signals. Additionally modifications have been introduced to measure change in bio-impedance with motion, this could be adapted to further improve accuracy and veracity for limb composition analysis. The findings in this thesis aim to give new direction to the prediction of body composition using BIA. The design development and refinement applied to BIA in this research programme suggest new opportunities to enhance the accuracy and clinical utility of BIA for the prediction of body composition analysis. In particular, the use of bio-impedance to predict limb volumes which would provide an additional metric for body composition measurement and help distinguish between fat and muscle content.