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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

The Aristocratic Émigrés Of The French Revolution: Their Struggles, Travels and Search for National Identity

Thomas, Blair 01 January 2014 (has links)
An analysis of the noble émigés of the French Revolution from 1789-1814. This paper looks at their life in the ancien régime, their life abroad in Coblenz and London, and their return to France. It focuses on their struggle and accomplishments abroad and their search for a collective identity during a time of uncertainty.
22

Photoionization of Fullerens and Atoms Confined in Fullerenes

Hadigheh Javani, Mohammad 18 December 2014 (has links)
The photoionization cross sections of small fullerenes (C28, C32, C40, C44, and C50), and the outer and near-outer shells of atoms (noble gases, alkaline earth) confined endohedrally inside a C60 molecule are calculated employing a time-dependent local density approximation formulation. Plasmon and confinement resonances are found to be a general feature of these cross sections, and dramatic interchannel coupling effects, significantly increasing the atomic cross sections, are exhibited in all cases in the vicinity of the C60 plasmons. Hybridization effects, the mixing of the atomic and cage bound state wave functions, are also found, but no systematics of the hybridization present themselves. Also, in the case of Ar@C60, Inter-atomic Columbic decay (ICD) has been found and studied.
23

Unravelling the history of the lunar regolith

Curran, Natalie January 2017 (has links)
The lunar regolith is sensitive to the bombardment history of the Moon and contains a wealth of knowledge regarding the types of processes that have modified the lunar crust through time. Noble gases that are produced and trapped in the lunar regolith, as a result of this interaction with the space environment, can be used to determine the cosmic ray exposure age, maturity, shielding depth and antiquity age of lunar regolith samples. This thesis aims to probe this temporal archive to further understand the impact history of the Moon contained within the regolith. Initially, all the published noble gas literature data for the Apollo regolith breccias, drill cores and soils was compiled into a database where trapped and cosmogenic noble gas component were calculated. These data were used to summarise the history of the lunar regolith contained in the Apollo sample archive. A dichotomy between the "ancient" (determined by the antiquity indicator using the 40Ar/36Artr ratio) regolith samples and those formed in more recent times has been described previously (e.g., McKay et al., 1986).The ancient breccias and soils (&gt;~3.5 Ga) have typically experienced limited amounts of surface exposure (i.e., they are 'immature'). Whereas, regolith samples formed in more recent times ( < 3.5 Ga, << 2 Ga) show a range of maturities. It is likely that the difference in maturity between the ancient and younger breccias reflects the changing collisional conditions of the time i.e., impact flux and regolith turnover rates. Here, 12 lunar meteorite regolith breccias were analysed for their noble gas content (Ne, Ar, Xe isotopes) to determine if lunar meteorites show the same difference between (40Ar/36Ar)tr ratio and maturity. Lunar meteorites in this study and previously published data do show the same negative correlation between (40Ar/36Ar)tr ratio and maturity. Furthermore, many of the lunar meteorite samples have (40Ar/36Ar)tr ratio between 1 and 2.5 indicating antiquity ages of approximately 1-2 Ga. This potentially reflects a declining period of random intermediate impacts bracketing the period between the 'ancient' and 'recent' samples. The same techniques were applied to newly discovered lunar meteorite MIL 13317. This included a full petrology description, mineral chemistry, U-Pb and Pb-Pb ages, and analysis of noble gas content to decipher the regolith history of this new sample. The meteorite is a mixture of mare and highland components (including mare basalts, FAN, Mg-suite and KREEP) with ancient ages (~ 4.3Ga) and a complex regolith history (exposure age ~500 to 800 Ma, antiquity age ~1.92 Ga). MIL 13317 is an important addition to the lunar collection as it contains material from previously unsampled areas of the Moon which is interpreted here to be associated with the northern regions of the Procellarum KREEP Terrane. Work was also begun on Apollo 16 regolith breccias using the same analytical techniques. However, due to instrument issues and friable samples much of the work was not completed and will be continued after the PhD. Understanding the data collected here and the techniques used will feed forward to future missions to the Moon to understand noble gas concentrations in the lunar regolith.
24

The timing of volcano-ice interactions and deglaciation in Iceland

Street, Kathryn January 2017 (has links)
Iceland possesses numerous subglacial volcanoes (tuyas and tindars) that act as geological records of the thick ice sheets that once spanned across the country. Flat topped volcanic summits, which were able to penetrate through the covering ice, provide an estimate of the ice sheet's minimum thickness at the time the volcano was in its final eruptive stage. Iceland not only provides a large number of potential subglacial edifices to sample but is geologically interesting as it sits above a magmatic hotspot and spreading ridge, providing a long term record of volcanism during considerable climate variability. However, it is unknown exactly in which glacial cycle these volcanic edifices formed, due to the lack of accurate and reliable eruption ages. Helium isotopes are valuable tracers of the mantle source for the origin of volcanic rocks. Helium isotopes are comprised of a mixture of magmatic helium trapped whilst in the mantle, cosmogenic helium built up by interaction with cosmic rays during surface exposure and radiogenic helium produced from the in situ decay of U and Th. These helium components yield invaluable information on the mantle source, time of eruption and length of exposure respectively. The principle aim of this study is to determine whether reliable and accurate eruption ages of basaltic subglacial volcanoes in Iceland are possible, by applying a relatively new geochronological tool: U-Th/He dating. These eruption ages combined with cosmogenic derived 3He surface exposure ages of the summits helps to establish ice surface elevation and thickness fluctuations over time. Olivine bearing basalt samples were acquired from 14 tuyas, 4 tindars and 1 shield volcano across the Western and Northern Volcanic Zones in Iceland (WVZ and NVZ). Samples were collected from the base of each edifice for U-Th/He dating and the summits of 3 tuyas for cosmogenic 3He surface exposure dating. Olivine phenocrysts were hand-picked and analysed on two noble gas mass spectrometers (VG5400 and Helix-MC instruments). As part of the analytical procedure for these techniques, magmatic helium trapped in the olivine grains is also analysed. The mantle helium isotope ratios indicate that nearly all edifices sampled obtain a MORB-like source (1-18RA) except for an OIB-like (24RA) centrally located tuya, Bláfell. The helium ratios acquired in the NVZ are lower (4-11RA) than those in the WVZ (8-20RA). There are no significant differences seen in the mantle components between the different types of edifice sampled. Mantle helium isotope ratios confirm the heterogeneity of the mantle beneath Iceland. The cosmogenic 3He exposure ages of Hlöđufell and Bláfell in the WVZ and Gaesafjöll in the NVZ are determined as 0.5±7.4ka, 67±0.7ka and 108±46ka respectively. This study presents the first 3He cosmogenic exposure age determined to be over 20ka in Iceland. The low concentrations of U and Th observed in Icelandic olivines (0.002-0.04 nmol/g and 0.01-0.1 nmol/g respectively) prevent any reliable disequilibrium ages to be established. Minimum secular equilibrium U-Th/He ages are determined and provide a range of erroneously large eruption ages (0.4 - 80.4 Ma), due to potential helium implantation and under-detection of 3He released during sample analysis. Progress can be made towards determining accurate eruption ages for Icelandic basalts if certain factors are adhered to and various sources of helium are separated effectively.
25

Investigating the role of chemical and geochemical tracers for CO2 transport and storage

Kilgallon, Rachel January 2016 (has links)
Changes in the atmospheric concentration of greenhouse gases and aerosols alter the energy balance of the climate system. CO2 is the most significant anthropogenic greenhouse gas. The primary source of the increased atmospheric concentration of CO2 since the preindustrial period is from fossil fuel exploitation. As the global need for energy is currently met by combustion of fossil fuels it is imperative that a method of reducing the levels of CO2 being emitted is used. Carbon capture and storage (CCS) is the combination of CO2 capture from large point sources, with the transport of CO2 to a suitable geological storage site where it can safely be contained. Geological CCS technology has the potential to a make a significant contribution to a low carbon technology future. As with any technology, it is imperative to identify techniques that could be used to form part of the monitoring programme. In this thesis, the role of chemical and geochemical tracers are investigated during the transport and storage of CO2. For the first part of this research, a review of the natural gas and CO2 pipeline network in North America and United Kingdom has been compiled from published literature and historical experience. Using this information, research was carried out to determine why odourising has been suggested for CO2 pipeline transport and what benefit it would add. Based on experience from natural gas, it is concluded that high pressure pipelines of CO2 through sparsely populated areas could have odourant added, but will gain little safety benefit. However, adding odourant to CO2 gas phase pipes could aid detection of leaks as well improve public assurance and should be considered in more detail. For the second part of this research, a specially constructed flow cell was designed and built to investigate how noble gases could be used as effective early warning tracers for CO2 migration in storage sites. From this equipment, experimental breakthrough curves for noble gases and SF6 travelling through a sample of Fell sandstone in relation to CO2 over a pressure gradient range of 10,000 – 50,000 Pa were generated. Although noble gases are described as conservative tracers, comparing the breakthrough curves over a range of pressure gradients show that they do not behave as simply as previously assumed. These results were then modelled using a one dimensional advective dispersion transport equation to fit curves to the experimental outputs using two different modelling approaches. A statistical approach can derive the input parameters for an analytical approach, which is needed to understand the dispersivity behaviour of the tracers. A set of values for the dispersivity of noble gases, SF6 and CO2 through porous media is presented in this research. Using a baseline value approach, initial arrival times for krypton and xenon from this research suggest that they could be used as a means of detecting CO2 migration. While helium, neon and argon appear to be unsuitable as early warning tracers for initial detection of CO2, this suggests that they can be used as part of mixture to fingerprint individual CO2 storage sites that may be in close proximity to one another. Results from the experimental and modelling analysis, identify a system where preferential paths exist depending on the change in pressure gradient. The different transport channels progress from a Darcy linear flow regime to a non-linear laminar flow. These results propose an explanation for the patterns observed from tracers in large-scale reservoirs but the output values obtained are limited by scale-dependence and would not be suitable for direct upscaling.
26

NMR of small solutes in liquid crystals and molecular sieves

Ylihautala, M. (Mika) 27 May 1999 (has links)
Abstract The present thesis deals with the nuclear magnetic resonance (NMR) spectroscopy of small solutes applied to the studies of liquid crystals and molecular sieves. In this method, changes induced by the investigated environment to the static spectral parameters (i.e. nuclear shielding, indirect and direct spin-spin coupling and quadrupole coupling) of the solute are measured. The nuclear shielding of dissolved noble gases is utilized for the studies of thermotropic liquid crystals. The relation between the symmetry properties of mesophases and the nuclear shielding is described. The different interaction mechanisms perturbing the observed noble gas nuclear shielding are discussed, particularly, the role of long-range attractive van der Waals interactions is brought out. The suitability of the noble gas NMR spectroscopy to the studies of lyotropic liquid crystals is investigated in terms of nuclear shielding and quadrupole coupling interactions. In molecular sieve systems, the effect of inter- and intracrystalline motions of solutes on their NMR spectra is discussed. A novel method for the measurement of the intracrystalline motions is developed. The distinctions in the 13C shielding of methane adsorbed in AlPO4-11 and SAPO-11, two structurally similar molecular sieves differing in composition, are indicated.
27

Noble gases and halogens in Icelandic basalts

Weston, Bridget January 2013 (has links)
Noble gas and halogen data from a suite of Icelandic samples are presented. Iceland combines hotspot volcanism, a spreading ridge and abundant subglacially erupted samples. This combination allows for samples that erupted under high enough pressures to retain a measurable mantle volatile content, and also display signatures representing interaction between ocean island basalt (OIB) and mid-ocean ridge basalt (MORB) mantle sources.Erupted samples used to determine the mantle’s halogen and noble gas content have undergone a degassing process that can alter their volatile composition. An existing disequilibrium degassing model is developed with the modified model taking into account the evolution of the major volatiles over a multi-stage process and the different conditions present during magma ascent and quenching. The modified model allows substantially lower elemental noble gas ratios to be reached under disequilibrium conditions than allowed by the original model. Initial CO2 concentrations, pressure, diffusivity, ascent rate and degree of disequilibrium are shown to be critical parameters for this model. Final degassed noble gas concentrations are most affected by the surface quenching stage of an eruption, whereas noble gas elemental ratios can be primarily determined during magma ascent. In applying this model to MORB and OIB sample suites, the 3He/22Ne ratio of the MORB source mantle is constrained to be lower than 4.4, similar to estimates for the OIB source mantle. Additionally the most straightforward match between the degassing model and OIB helium and neon data suggest the OIB source mantle has 3He concentrations similar to or lower than the MORB source mantle. This finding requires a model for the OIB source mantle in which a high 3He/4He component is added to a helium-poor protolith.Noble gas studies are hampered by the large, isotopically atmospheric component typically found in Icelandic subglacial samples, which can swamp other signatures. Detailed analysis of a volatile rich sample from SW Iceland shows evidence for more than one ‘contaminant’ component and that two component fits used incorrectly can produce misleadingly precise source mantle noble gas ratios. Multi component best fits to noble gas elemental ratios find that four components are present in samples from this region. These components are unfractionated air, fractionated air and a mantle component which shows some variation due to degassing. Combining the disequilibrium degassing model with component resolution allows limits to be placed on the source mantle composition for this sample. The light noble gas source composition is compatible with mixing between a solar (‘direct nebula’) component and a MORB-like component. This direct nebula signature is at odds with an implanted signature seen in both Ne and Kr for the convecting mantle, and shows that both accretionary volatile origins must have contributed during the Earth’s formation. The heavy noble gases show an elemental abundance pattern which is distinct from air and solar patterns, and trends towards seawater. This confirms the presence of a recycled volatile signature in Iceland’s mantle but it is not possible to further constrain the origin of this signature.The Icelandic halogen data shows no evidence for significant fractionation during degassing or melt generation. Source estimates for the Br/Cl and I/Cl ratios for Iceland’s plume are found to be (1.56±0.03) x 10-3 and (3.1±0.3) x 10-5, compatible with estimates for the MORB source mantle. Halogen source concentrations in central Iceland are found to be approximately three times higher than estimates for the convecting mantle and correlate with the regions of Iceland that show high 3He/4He ratios and high source water contents. This may indicate a recycled halogen signature associated with Iceland’s proposed mantle plume.
28

Development of Non-Noble Metal Ni-Based Catalysts for Dehydrogenation of Methylcyclohexane

Shaikh Ali, Anaam 30 November 2016 (has links)
Liquid organic chemical hydride is a promising candidate for hydrogen storage and transport. Methylcyclohexane (MCH) to toluene (TOL) cycle has been considered as one of the feasible hydrogen carrier systems, but selective dehydrogenation of MCH to TOL has only been achieved using the noble Pt-based catalysts. The aim of this study is to develop non-noble, cost-effective metal catalysts that can show excellent catalytic performance, mainly maintaining high TOL selectivity achievable by Pt based catalysts. Mono-metallic Ni based catalyst is a well-known dehydrogenation catalyst, but the major drawback with Ni is its hydrogenolysis activity to cleave C-C bonds, which leads to inferior selectivity towards dehydrogenation of MCH to TOL. This study elucidate addition of the second metal to Ni based catalyst to improve the TOL selectivity. Herein, ubiquitous bi-metallic nanoparticles catalysts were investigated including (Ni–M, M: Ag, Zn, Sn or In) based catalysts. Among the catalysts investigated, the high TOL selectivity (> 99%) at low conversions was achieved effectively using the supported NiZn catalyst under flow of excess H2. In this work, a combined study of experimental and computational approaches was conducted to determine the main role of Zn over Ni based catalyst in promoting the TOL selectivity. A kinetic study using mono- and bimetallic Ni based catalysts was conducted to elucidate reaction mechanism and site requirement for MCH dehydrogenation reaction. The impact of different reaction conditions (feed compositions, temperature, space velocity and stability) and catalyst properties were evaluated. This study elucidates a distinctive mechanism of MCH dehydrogenation to TOL reaction over the Ni-based catalysts. Distinctive from Pt catalyst, a nearly positive half order with respect to H2 pressure was obtained for mono- and bi-metallic Ni based catalysts. This kinetic data was consistent with rate determining step as (somewhat paradoxically) hydrogenation of strongly chemisorbed intermediate originating from TOL. DFT calculation indicated that Zn metal prefers to occupy the step sites of Ni where unselective C–C bond breaking was considered to preferentially occur, explaining suppression of hydrogenolysis activity. Additionally, it confirmed that the H-deficient species at methyl position group (C6H5CH2) was stable on the surface, making its hydrogenation being rate determining step, consistent with positive order in H2 pressure on TOL formation rate. This may explain the conclusive role by H2 in facilitating desorption of the H-deficient surface species that was produced through further dehydrogenation of TOL.
29

Chaucer's Scatological Art in Three Fabliaux

Rutledge, William Brennan 13 May 2006 (has links)
Chaucer's fabliaux, particularly The Miller's Tale, The Merchant's Tale, and The Summoner's Tale, combine the crude humor associated with the genre with features of ?higher? genres, most notably the courtly romance tradition (for the first two tales), and the homiletic and scholarly debate traditions (for the last tale). The marriage of the scatology present in fabliaux with the characteristics of literary art is Chaucer's unique achievement and differentiates his tales from their analogues. This marriage occurs when characters of one class arrogate the types of discourse usually associated with another class. As a result of this discourse switching, the balancing of art and scatology in these three tales blurs the distinction between crudity and sophistication and makes the tales scatological art.
30

Structure of the electrical double layer at aqueous gold and silver interfaces for saline solutions

Hughes, Zak, Walsh, T.R. 13 March 2019 (has links)
No / We report the structure of the electrical double layer, determined from molecular dynamics simulations, for a range of saline solutions (NaCl, KCl, MgCl2 and CaCl2) at both 0.16 and 0.60 mol kg(-1) on different facets of the gold and silver aqueous interfaces. We consider the Au/Ag(111), native Au/Ag(100) and reconstructed Au(100)(5×1) facets. For a given combination of metallic surface and facet, some variations in density profile are apparent across the different cations in solution, with the corresponding chloride counterion profiles remaining broadly invariant. All density profiles at the higher concentration are predicted to be very similar to their low-concentration counterparts. We find that each electrolyte responds differently to the different metallic surface and facets, particularly those of the divalent metal ions. Our findings reveal marked differences in density profiles between facets for a given metallic interface for both Mg(2+) and Ca(2+), with Na(+) and K(+) showing much less distinction. Mg(2+) was the only ion for which we find evidence of materials-dependent differences in interfacial solution structuring between the Ag and Au. / Veski, Air Force Office for Scientific Research grant #FA9550-12-1-0226

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