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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.
61

Time resolved anomalous small angle X-ray scattering of the sol-gel process

Barnardo, Twilight January 2010 (has links)
This investigation employs Anomalous Small Angle X-ray Scattering (ASAXS), and further expands the technique for conducting time resolved experiments within synchrotron facilities. ASAXS utilises the absorption effects of a given element as photon energies approach an absorption edge, and is used to extract partial scattering functions of the individual species within a composite material. In situ ASAXS is used to explore and understand the complex reactions in sol gel processing. The gelation process for zirconia, yttria stabilised zirconia (YSZ), YSZ and zirconia in silica, and zinc-silica systems are observed using in situ ASAXS across the zirconia and zinc absorption edges respectively. A new technique of high temperature time resolved double ASAXS, which explores two absorption edges in a single experiment, has also been employed to investigate phase changes during the sintering of YSZ and YSZ in silica. A computational model for ASAXS is also proposed, which can be used as a tool for data analysis. It is shown that monochromator resolution induces an uncertainty into the correct values of the coefficients - used to extract scattering information from individual species within a composite material. The model suggests methods to reduce this uncertainty in order to converge on the correct solution. New techniques for future time resolved ASAXS experiments are also presented. Time resolved ASAXS of the gelation process reveals contrast in the resonant term for sol-gels containing zirconia. The profile of which is independent of the relative concentrations of yttria and silica. It is proposed that the zirconia is being fully integrated into the gel network to form zirconia-silica chains. In comparison, the zinc systems did not reveal this effect, and instead display contrast in both the resonant and cross terms, implying a gel network is forming at the exclusion of zinc. High temperature in situ double ASAXS of the YSZ materials reveals the nucleation of nano zirconia at temperatures close to 400ºC. The nano crystals grow to eventually incorporate yttria, preserving the zirconia in the cubic and tetragonal phases. Inhomogeneities are revealed during crystal growth; caused by the mixed phase states of zirconia and YSZ present in the material. It is also shown that the presence of a silica matrix delays the growth of these crystals until a temperature of 780 ºC is reached. Samples with high concentrations of yttria also reveal an additional feature beyond 900ºC indicating a saturation point for cubic YSZ formation.
62

The effect of adsorbent heterogeneity on pure-gas and multicomponent adsorption equilibrium, especially at low pressures, and accurate prediction adsorption equilibrium

Yufeng, H. January 2005 (has links)
A Tian-Calvet type microcalorimeter has been constructed and used to measure the adsorption isotherms and the isosteric heat of adsorption of pure methane, ethane and CO<sub>2</sub>, and the binary mixtures of the above-mentioned three adsorptives in three pure-silica MCM-41 samples with different pore diameters at room temperature and at pressures up to 1 bar. Ideal Adsorption Solution Theory (IAST) was applied to predict the binary adsorption isotherms and isosteric heats for individual components in the mixture. It is found that all the three binary mixtures behave ideally in MCM-41 at room temperature and at low pressures. The adsorption isotherms of binary ethane/CO<sub>2</sub> mixtures in the three MCM-41 samples was measured using a high-pressure volumetric apparatus at 264.6 K and at pressures up to 30 bar. IAST was used to study the adsorption system, and it gives quite accurate predictions of multicomponent adsorption equilibrium at low pressures and shows some deviations at moderate and high pressures, presumably due to the chemical dissimilarity of the two adsorptives. Grand canonical Monte Carlo simulations have been carried out to study the same adsorption system. The simulations were carried out using three different models for MCM-41 with different degrees of surface heterogeneity. The model that has an amorphous structure, generated by an energy-minimization procedure, gives the best predictions for ethane adsorption, especially at low pressures, suggesting that this model incorporates a good representation of the heterogeneity of the real MCM-41 material. Excellent predictions of the adsorption of pure CO<sub>2</sub> and binary mixtures of ethane and CO<sub>2</sub> in MCM-41 are obtained with the model, further confirming the realism of this model Long-ranged electrostatic interactions are included for the simulation of CO<sub>2</sub>, these interactions, which play an important role, are treated by a simple one-dimension summation method, which gives an accurate calculation of the potential.
63

Differential Zernike filter for phasing of segmented mirror and image processing

Huang, Tao January 2009 (has links)
The major objective of this thesis is to study the differential Zernike filter and its applications in phasing segmented mirror and image processing. In terms of phasing, we provide both theoretical analysis and simulation for a differential Zernike filter based phasing technique, and find that the differential Zernike filter perform consistently better than its counterpart, traditional Zernike filter. We also combine the differential Zernike filter with a feedback loop, to represent a gradient-flow optimization dynamic system. This system is shown to be capable of separating (static) misalignment errors of segmented mirrors from (dynamical) atmospheric turbulence, and therefore compress the effects of atmospheric turbulence. Except for segmented mirror phasing, we also apply the Zernike feedback system in image processing. For the same system dynamics as well as in segment phasing, the Zernike filter feedback system is capable of compress the static noisy background, and makes the single particle tracking algorithm even working in case of very low signal-to-noise ratio. Finally, we apply an efficient multiple-particle tracking algorithm on a living cell image sequence. This algorithm is shown to be able to deal with higher particle density, while the single particle tracking methods are not working under this condition.
64

Extending the measurement range of high-speed speckle pattern interferometry

Wu, Tao January 2009 (has links)
A digital speckle pattern interferometer based on a complementary metal-oxide semiconductor (CMOS) camera was developed. The temporal evolution of dynamic deformation was measured using inter-frame phase stepping. A numerical and analytical investigation showed that the maximum surface velocity that can be reliably measured with inter-frame phase stepping corresponds to ±0.3 times the surface velocity at which the interferogram is sampled at the Nyquist limit (vNyq). The flexibility of the CMOS detector readout was used to identify regions of interest with full-field time-averaged measurements and then to interrogate those regions with time-resolved measurements sampled at up to 70 kHz. To increase the surface velocity measurement range, spatial phase stepping was introduced to the high-speed CMOS system. A pair of binary phase gratings introduced double-channel sensing with a fixed phase step between the two channels. The maximum surface velocity was increased to ±1.0vNyq. Sub-Nyquist theory was implemented for the dynamic measurements and the measurement range with a continuous-wave laser illumination was increased by an order of magnitude with respect to inter-frame phase stepping to ±3.0vNyq. A numerical and analytical investigation showed that with a reduced exposure, for example from pulsed laser illumination, the maximum surface velocity that can be reliably measured is ±15.9vNyq and the surface acceleration is ±253.3vNyq with the current set-up. Due to spatial variations in speckle intensity, some low-modulating and saturated pixels within the small regions of interest interrogated at up to 70 kHz could not be analysed. The nonlinear LinlogTM response of the CMOS camera was used to increase the valid measurement area on the object surface by incorporating pixels that would be below a modulation threshold or saturated if recorded with a linear CCD detector.
65

The construction and use of a novel ion translational energy spectrometer

Singh, S. January 1985 (has links)
No description available.
66

The effect of humidity and pressure on space charge growth in high voltage air discharges

Turri, R. January 1988 (has links)
In this thesis the effect of humidity and gas density on discharge development and breakdown characteristics in a short sphere/plane gap subject to positive switching impulses has been investigated. The experiment was carried out in a sealed ionization chamber using laboratory air for pressures in the range 0.7 to 1.4 bar and absolute humidity levels from 2 to 15 g m<SUP>-3</SUP>. Both pressure and humidity could be closely controlled and measured. The impulse shape was = 100/2500 μs and the test gap consisted of a 5 cm diameter sphere 20 cm above an earthed plane. An improved version of biased field-filter and a newly designed composite field/charge probes have been developed, which enabled time-resolved measurements of the electric field distribution at the cathode in the presence of space charge to be made together with a quantitative measurement of the conducted charge in the central region of the cathode. Statistical flashover tests and measurements of apparent charge injection were made and both sets of data were analyzed using a Generalized Liklihood Method, which has been developed during this work and is recommended to be considered for possible adoption as a standard procedure. The breakdown probabilities were found to satisfy a cumulative normal distribution and the charge measurements provided significant additional information at low probability levels. The measured values of V_50 were found to depend linearly upon absolute humidity with a slope of 1.5 kV per g m^-3 at all pressures. The withstand voltages, on the other hand, were only weakly dependent upon absolute humidity. The humidity correction factors found in the present work agree well with the IEC Standards at 1.2 and 1.4 bar, but they depart appreciably at low pressures. In a second series of measurements, simultaneous time-resolved measurements of the light output from the discharge, the apparent charge injection at the HV electrode, the electric field distribution and transfer charge at the cathode, have been made. The results have greatly clarified the mechanism of the space-charge growth in the transition regime from uniform-field to non-uniform-field breakdown, and should enable predictive models of the discharge development and breakdown voltage to be made.
67

Investigation into the factors controlling the sensitivity of oxygen optical sensors

Thomas, M. D. January 1998 (has links)
The main objective of this thesis is to establish the main factors which control the sensitivity of thin-film oxygen optical sensors. In Chapter 1 the main sensing principles and the main classes of oxygen-sensitive lumophores are described. Numerous examples are given describing the major developments in oxygen sensors. Finally, research areas of interest are outlined. Chapter 2 describes the experimental methods and the chemicals used in this work. In Chapter 3 the incorporation of the lumophore tris (4,7-diphenyl-1,10-phenanthroline) ruthenium (II) ditetraphenylborate, [Ru(dpp)<SUB>3</SUB><SUP>2+</SUP> (Ph<SUB>4</SUB>B<SUP>-</SUP>)<SUB>2</SUB>], in different polymer-plasticizer matrices is described. The sensitivity of the sensor depends upon the nature of the polymer matrix and plasticizer. A detailed study of a highly plasticized system utilising the polymer poly(methyl methancrylate), PMMA, is reported. In Chapter 4, the properties of two highly plasticized oxygen sensors are investigated using [Ru(dpp)<SUB>3</SUB><SUP>2+</SUP> (Ph<SUB>4</SUB>B<SUP>-</SUP>)<SUB>2</SUB>], and dichlorobis (4,7-diphenyl-1, 10-phenanthroline) iridium (III) tetraphenylborate, [Ir(dpp)<SUB>2</SUB>Cl<SUB>2</SUB><SUP>+</SUP> (Ph<SUB>4</SUB>B<SUP>-</SUP>)] in the most sensitive polymer and plasticizer combination reported in Chapter 3, <I>i.e.</I> cellulose acetate butyrate polymer-tri-n-butyl phosphate plasticizer (CAB-TBP). In Chapter 5 the oxygen quenching and natural lifetime of tris (2,2'-bipyridyl) ruthenium (II) ditetraphenylborate, [Ru(bpy)<SUB>3</SUB><SUP>2+</SUP>(Ph<SUB>4</SUB>B<SUP>-</SUP>)<SUB>2</SUB>], is studied in a variety of neat plasticizers, in unplasticized and TBP plasticized CAB and PMMA oxygen sensors. The compatibility of the polymer and plasticizer is considered in relation to the oxygen sensitivity of the sensors. In Chapter 6, a pyrene lumophore is used as a polarity probe and as an oxygen sensor. The polarity of the encapsulating medium and the sensitivity of the sensors is studied. Reasons for the lack of correlation between the increase in sensitivity and the polarity of the encapsulating medium, measured using pyrene as the probe, are discussed.
68

Experiments into Quantum Turbulence and the Demagnetisation of Kaptonand Aerogel in Superfluid 3He-B

Whitehead, Rebecca January 2006 (has links)
This thesis describes the findings of two experiments carried ~ut in 3He-B at ultra low temperatures. The princip,le tool used for thermometry in both experiments is vibrating wire resonators. Vibrating wire resonators are used at Lancaster as thermometers and heaters and they can be used to produce turbulence in superfluid 3He-B. Turbulence in 3He-B is created using a vibrating wire resonator and a black body radiator is used to create a beam of quasi-particles which are retro-reflected off the turbulence. The properties of a black body radiator are used to create a model to investigate the vortex line density. The vortex line density is shown to be dependent on the temperature of the bulk superfluid. The properties of two different substrates immersed in 3He-B are studied. It has been found that when a proprietary material, Kapton, is subjected to a changing magnetic field, a large amount of heating and cooling is observed. When a different substrate, aerogel, is used the same effects are observed. We show that when aerogel that is immersed in 3He-B is subjected to a changing magnetic field the surrounding helium cools from rv 200 JLK to rv 115 JLK. It is thought that the effects are caused by the solid helium that coats the strands. Several models have been developed to calculate the heat capacity and some interesting features have been observed. We identify the fact that aerogel in 3He-B would make an excellent second cooling stage for many ultra low temperature experiments.
69

Quantum Transport in Nanowires and Molecular Structures

Sirichantaropass, Skon January 2008 (has links)
No description available.
70

An analysis and applications of a Bayesian inference technique for dynamical systems

Duggento, Andrea January 2009 (has links)
No description available.

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