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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Deployment and evaluation of an aerosol time-of-flight mass spectrometer

Freney, Evelyn J. January 2006 (has links)
This thesis presents research using a commercial aerosol time-of-flight mass spectrometer (ATOFMS TSI 3800), which was deployed in the laboratory to determine fundamental aspects of ion formation as well as to develop scaling factors to improve the number and chemical quantification of the ATOFMS instrument and to characterise pharmaceutical drug products. Additionally, data from field campaigns both in Ireland and Scotland were evaluated. Data from the deployment of the ATOFMS instrument at Mace Head, Galway, Ireland were used to determine the size and chemical composition of individual particles in the atmosphere as part of the North Atlantic Marine Boundary Layer Experiment (NAMBLEX) during August 2002. A total of 191,504 particles were detected. Rapid changes in number density, size and chemical composition of the atmospheric aerosol were observed. These data were analysed using a combination of statistical clustering procedures and manual classification, yielding three broad categories of particles; sea salt, dust and carbon-containing. The ATOFMS instrument has been used to assess the level of co-association of individual drug components present in different pharmaceutical products. Different efficiencies for different aerosolised pharmaceutical asthma drug products are reported.
22

Image segmentation for automatic target recognition : an investigation of a method of applying post-segmentation derived information to a secondary segmentation process

Reavy, Richard Wilson January 1999 (has links)
A fundamental automatic target recognition (ATR) system can be composed of an object segmentation stage, followed by feature extraction from those objects produced by segmentation, and finally classification of these object features. The capability of such a system in terms of classification success is therefore limited not only by the quality of the feature extraction and classification methods used, but also by the quality of the initial object segmentation. In this thesis, a novel architecture is described which uses two stages of segmentation. This allows image features derived after a primary segmentation stage to influence the parameters of a secondary segmentation stage which is applied to the same image area. This is aimed at allowing improved, and locally optimised, segmentation of those objects which were poorly segmented by the primary segmentation stage. To enable the implementation of the system, a probability density estimate function is used as a method of detecting novelty in objects presented for classification. This is found to be a non-ideal solution, although useful in the context of the application concerned. The development of all the system components, and ultimately the full ATR system, is described with experimental results derived from real-world infrared imagery. From this work, conclusions are drawn as to the usefulness of a such a two-stage segmentation architecture; specifically, the clutter rejection flexibility and the potential ability for the system to locally optimise segmentation on a per object basis are highlighted.
23

Laser desorption laser photoionisation time-of-flight mass spectrometry

Dale, Michael John January 1994 (has links)
The work described in this thesis is concerned with the development and application of laser desorption laser photoionisation time-of-flight mass spectrometry (L<SUP>2</SUP>TOFMS). This technique has been used to enable photoionisation mass spectra of a very wide variety of involatile and thermally labile molecules to be recorded. The instrument used for this work is described along with an overview of the fundamental principles behind this methodology. A number of specific classes of molecules have been studied using the L<SUP>2</SUP>TOFMS. These include polyaromatic hydrocarbons, porphyrins, dyestuffs and a variety of analytically important staining agents. The advantages of this approach for analysing complex mixtures, which yield relatively simple mass spectra, have been demonstrated for both environmental systems and commercially important mixtures. It has also been shown that L<SUP>2</SUP>TOFMS can be used for the direct interrogation of target systems adsorbed onto organic substrates. L<SUP>2</SUP>TOFMS has been used to probe the photophysics of both porphyrin molecules and a series of azo dyes. Ionising wavelength dependent fragmentation was observed for a number of metallotetraphenylprophyrins and metallo- octaethylporphyrins. Using 193 nm laser photoionisation, molecular dissociation, involving loss of the macrocycle side groups, was shown to be similar to that obtained by electron impact ionisation. Whereas, at 266 nm, fragmentation via a neutral intermediate state, resulting in the loss of the metal from the macrocycle, competes with further photon absorption. Characteristic azo-bond photoreductive cleavage has been observed for azo molecules when using 266 nm laser photoionisation. This behaviour is linked to the cis-trans photoiosomerisation of the azo bond.
24

Capability of MLS instruments in the observations of atmospheric gravity waves

Dasananda, Songkot January 2001 (has links)
We found that the temperature response functions of both UARS MLS and EOS MLS instrument for waves with typical vertical wavelength of 1-20 km are sharply peaked at certain horizontal wavelengths but their amplitudes are always less than ~60% in case of UARS MLS and 80% for EOS MLS. The responses at vertical wavelength of 10-20 km, in particular, are considerably high to waves with horizontal wavelength of scales ~200-500 km which are propagating away from the satellite position with respect to the line-of-sight direction. These are waves that should be most detectable with both of the MLS instruments in the real observations in terms of the amplitude response. The variance response functions in the 32-measurement limb-tracking mode of UARS MLS and 150-measurment limb-tracking mode of EOS MLS have also peaked at some certain horizontal wavelengths for waves of vertical wavelength 1-20 km but their amplitudes never exceeds ~20% for UARS MLS and 30% for EOS MLS. Like the temperature response, the variance responses at vertical wavelengths of 10-20 km are maximum to waves with horizontal wavelength of scales ~200-500 km which are propagating away from the satellite position with respect to the LOS. In the contrary, gravity waves with vertical wavelength of few kilometers are unlikely to be much visible to the MLS instruments due to the very low response regardless of their horizontal wavelength scales or directions of propagation.
25

The effect of surface waves on buoyant jets

Shawcross, Alistair Charles January 2002 (has links)
A Laser Induced Fluorescence (LIF) technique has been used to measure the effect of surface waves on the dilution of a line plume produced by the merging of buoyant jets discharged from a model outfall. Full-field, time averaged concentration maps were produced of plumes both in wave and still conditions. From these an increase in dilution was found comparable with published values for wave effects on round plumes. The full field nature of the technique also allowed the region of the plume in which the increase in dilution takes place to be clearly identified. LIF and Particle Image Velocimetry (PIV) measurements were also made of a single round buoyant jet discharged into quiescent and simulated wave conditions. Again full-field, time averaged concentration and also velocity maps of the plume were produced and increases in dilution due to wave effects were found to be in line with previously published data. The apparatus allowed LIF measurements to be taken under simulated wave conditions that could be used to produce three dimensional concentration maps of the plume.
26

Charge transfer across liquid/liquid interfaces : theory and applications

Beattie, Paul Daniel January 1995 (has links)
This thesis is concerned with charge transfer processes at the interface between two immiscible electrolyte solutions (ITIES), from both a kinetic and analytical viewpoint. Microholes, formed by ultra-violet excimer laser photoablation of polyester films, and micropipettes, fabricated from borosilicate glass capillaries by means of a pipette puller, are both used to support the ITIES for the study of ion and assisted ion transfer reactions respectively. Using the techniques of steady-state voltammetry and a.c. impedance, both processes are found to be dependent on diffusion of the participating species to the interface only. Electron transfer reactions at the ITIES are studied using cyclic voltammetry. Transfer between the hexacyanoferrate redox couple ([Fe(CN)<SUB>6</SUB>]<SUP>3-/4-</SUP>) in the aqueous phase, and ferrocene and 1,1'-dimethylferrocene, respectively, in the organic (1,2-DCE) phase, is investigated. Results obtained for transfer between copper (II) ions in the aqueous phase and ferrocene in 1,2-DCE are also presented. An investigation is made into the inhibition of the enzyme butyrylcholinesterase by the organophosphate compound paraoxon (diethyl <I>p</I>-nitrophenyl phosphate), using butyrylcholine chloride as the substrate. Experimental measurement is based on the transfer of the butyrylcholine cation across the ITIES. By this method it is possible to determine the rate constants for both the inhibition of the enzyme and the hydrolysis of butyrylcholine.
27

Production, isolation and characterisation of fullerenes and related species

McQuillan, Robert James January 1997 (has links)
This thesis describes the development and application of techniques for the production, isolation and characterisation of fullerenes and carbon nanotubes, and the attempted production of endohedral fullerenes. A benchtop carbon arc reactor for the macroscopic production of these species was built. The construction and characterisation of this carbon are reactor is described. Experiments aimed at optimising the productivity of the reactor by varying the operating conditions are described in relation to possible fullerene formation schemes. These included the effect of experimental variables such as reactor buffer gas pressure, discharge current, internal dimensions, and graphite electrode size on fullerene formation. The use of graphite electrodes packed with a possible fullerene precursor molecule, tri-indane, was also investigated as a means of probing fullerene formation mechanisms and increasing the quantity of fullerenes produced. A wide range of techniques for the extraction of fullerene rich soot and for chromatographic separation and mass spectrometric characterisation of the resulting fullerenes have been investigated. A high yield extraction protocol is described involving preliminary large scale separation of fullerenes by competitive complexation with AlCl<SUB>3</SUB>. Chromatographic studies led to the development of a novel stationary phase for separation of fullerenes using high performance liquid chromatography (HPLC).The characterisation of this stationary phase using on-line particle beam mass spectrometry is described. The change in enthalpy for adsorption of C<SUB>60</SUB> and C<SUB>70</SUB> on this stationary phase have been experimentally determined. A linear relationship between molecular weight and chromatographic retention time has also been established for fullerenes eluting from such a column.
28

In situ molecular analysis using two-step laser mass spectrometry

Wright, Scott Jason January 1997 (has links)
The work described in this thesis is concerned with the development of laser desorption laser photoionisation mass spectrometry (L2MS) towards spatially resolved analysis of real complex molecular systems. A broad overview of the main elements of the technique is presented. In addition, the experimental procedures and equipment used to carry out this work are described in some detail. Photoionisation mass spectra recorded for a series of azo dyes and porphyrin pigments revealed a marked wavelength dependence in their ionisation and fragmentation channels. The relationship between this behaviour and the known photochemical and photophysical properties of these molecules is discussed. The photochemistry of these molecules has been exploited to aid the differentiation between isomeric species. The selectivity inherent in the L2MS technique has been exploited for <I>in situ</I> studies of a number of real systems. Polymer additives, such as antioxidants and ultraviolet stabilisers, have been successfully detected directly from their host polymer matrices without recourse to extraction, separation or pre-concentration. The technique has been shown to be surface specific, suggesting that the long-term goal of spatially resolved analysis to monitor, for example, additive aggregation and migration to the surface are feasible. In further <I>in situ</I> studies, polycyclic aromatic hydrocarbons, an important class of priority pollutants, adsorbed onto aerosol particulates have been detected. Electrochemically polymerised indoles, known to form conducting films, have also been identified directly from the electrode surface. Finally, current limitations of the L2MS technique are discussed. It is suggested that many of the problems identified are inextricably linked to the laser desorption process. It is shown that energy imparted to neutral molecules during the desorption event can lead to fragmentation. This has implications for both the ionisation of high mass molecules and for quantitative studies. Possible ways of circumventing these problems are discussed. The future outlook for the technique, both for fundamental studies, and as an analytical tool, is also discussed.
29

Metal photodissolution effect in As-S glasses and its application in IR grating fabrication

Zakery, A. January 1991 (has links)
This work investigates the feasibility of using the metal photodissolution effect peculiar to chalcogenide glasses as a means for producing grating structures for use at infrared wavelengths. The material properties and characteristics of the effect relevant to grating fabrication and performance has been examined, the study dealing exclusively with Ag photodissolution in As-S glasses. Different fabrication techniques have been investigated and the performance of the gratings produced has been compared with theoretical predictions. A technique based on simultaneous reflectivity and transmissivity measurements has been developed and used to probe the kinetics of photodissolution, in particular its dependence on wavelength and intensity of illumination. A composition around As<SUB>30</SUB>S<SUB>70</SUB> was found to be optimum for applications since it had maximum sensitivity and also exhibited negligible photodarkening. A model has also been proposed for photodissolution which explains the spectral dependence and the intensity dependence of the photodissolution rate and suggests that the actinic radiation is absorbed in the photodoped layer. Gratings were produced both holographically and by mask exposure and suitable etchants identified for removal of the undoped material and the residual Ag layer. A coupled-wave model has been developed which predicts that diffraction efficiencies of up to 90% can be achieved in the multiwave regime at 10.6 μm. Diffraction efficiencies of up to 20% have been measured for both the zero and ± 1 orders at 632.8 nm which are in good agreement with the results of the theoretical model. Optical constants of both the undoped and Ag-doped As-S films have been measured over the wavelength range 0.5-12 μm to enable the analysis of kinetics measurements and also the development of the theoretical model. The results of these measurements show that there is a significant change in the refractive index (by up to 0.5, depending on Ag content) and also in the optical gap of the As-S films upon incorporation of silver, although the absorption coefficient of the Ag-doped As-S films remains small in the IR. The results of a secondary ion mass spectroscopy analysis showed that the composition of the As-S films varies very little with depth while the silver concentration may vary by up to 20% in the Ag-doped As-S films.
30

A new magnetometer for the neutron EDM experiment

Chibane, Yacine January 1990 (has links)
A new magnetic field monitoring technique has been develloped to measure the average magnetic field seen by neutrons stored in a 40 litre cavity for times of the order 150 seconds. The precessing frequency of polarised Mercury atoms stored with the neutrons is measured by an optical technique and we expect to determine the magnetic field averaged over the storage time to 2 parts in 101•

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