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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

MOLECULAR DYNAMICS SIMULATION OF HYDROGEN ISOTOPES TRAPPING ON TUNGSTEN: THE EFFECT OF PRE-IRRADIATION

Enes Ercikan (8053514) 29 November 2019 (has links)
<p>To achieving successfully commercial nuclear fusion energy, fully understanding of the interaction between plasma particles and plasma facing components is one of the essential issues. Tungsten, due to good thermal and mechanical properties such as high thermal conductivity and melting temperature, is one of the most promising candidates. However, the plasma facing components interacting with the extreme environmental conditions such as high temperature and radiation may lead to nanostructure formation, sputtering and erosion that will lead to material degradation. And these deformations may influence not only properties of plasma facing components but also might affect the plasma itself. For example, the contamination of plasma with a few amounts of tungsten, a high Z element, as a result of erosion or sputtering may cause core plasma cooling that results in loss of plasma confinement. Additionally, the retention of hydrogen isotopes, especially tritium, in tungsten is essential issue because of its radioactivity and market value.</p> In this study, deuterium trapping in tungsten is analyzed by molecular dynamics method and the effect of pre-irradiation on trapping is studied. Non-cumulative studies show that the increase in the energy of hydrogen isotopes rises the absorption rate, the initial implantation depth, and the average resting time for initial implantation. Additionally, the effect of implanted deuterium due to pre-irradiation on the hydrogen isotopes trapping is analyzed by combining both cumulative and non-cumulative simulations, and results indicate that while the increase in the pre-irradiation time raises the absorption rate of deuterium with higher energy than 80 eV, it causes a decrease the initial implantation depth and the average resting time for initial implantation because of deuterium-deuterium interactions. Additionally, the deuterium-deuterium interactions may transfer enough energy to implanted deuterium to start a motion which may lead to deeper implantation or escaping from the surface of tungsten. The escaping from surface as a result of deuterium-deuterium interaction could explain the decrease in accumulation rate of deuterium while absorption rate rises.
22

Advancing lacustrine proxies for paleohydrology studies

Corcoran, Megan 02 June 2023 (has links)
No description available.
23

Hydrogen and Muonium behaviour in diamond

Joseph, Sithole Makgamathe 31 March 2005 (has links)
This work is aimed at the understanding of the dynamical behavior of hydrogen in diamond. The investigation was carried out using Transverse Field muon Spin Rotation (TF-SR) and the Longitudinal Field muon Spin Relaxation (LF-SR) techniques. The chemical analogy between hydrogen (p+e-) and muonium (u+e-) enabled the study of the indirect dynamical behavior of hydrogen in diamond. The TF-SR and LF-SR measurements were carried out in an isotopically pure 13C diamond in the temperature ranges 11 mK - 320 K and 10 K - 400 K, respectively. In the TF-SR results, the Prompt Absolute Fraction (PAF) of both diamagnetic and the paramagnetic states are temperature independent. The spin relaxation rate for the state is non-zero and temperature independent, while that of the Mux state is non-zero and temperature dependent. The behavior of indicates that the u+d is immobile, while that of MuT indicates the mobility in diamond. The LF-SR results provide hop rate and associated nuclear hyperfine interaction parameters of the Mut state in diamond. / Physics / M.Sc. (Physics)
24

Coadsorption de l’hydrogène et du deutérium sur zéolithes à températures cryogéniques : effet des propriétés de l’adsorbant sur la sélectivité / Coadsorption of hydrogen and deuterium on zeolites at cryogenic temperatures : influence of the sorbent’s properties on selectivity

Giraudet, Maxence 11 April 2019 (has links)
L’adsorption de l’hydrogène et du deutérium purs ou en mélanges a été étudiée sur une série de zéolithes en faisant varier différents paramètres (taille et géométrie des pores, rapport Si/Al, nature du cation compensateur de charge).Les sélectivités d’adsorption ont été déterminées dans un large domaine de pression (0,1 – 1000 hPa) et de température (45 – 100 K) à l’aide une technique originale basée sur le couplage de la manométrie et de la spectrométrie de masse conçue et mise au point au laboratoire. En accord avec les données de la littérature, pour tous les matériaux et toutes les conditions expérimentales étudiées, le processus de coadsorption est toujours en faveur du deutérium. En revanche, la sélectivité varie en fonction du taux de remplissage, des propriétés des matériaux et de la température. La cinétique de coadsorption joue un rôle très important sur la sélectivité d’adsorption et ce tout particulièrement dans le domaine de fort remplissage.Ces travaux ont permis d’identifier les paramètres de l’adsorbant et les conditions opératoires qui permettront le développement d’un procédé de séparation efficace des isotopes de l’hydrogène par adsorption sélective. / The adsorption of hydrogen and deuterium (single gases and mixtures) was studied on a series of zeolites with varied parameters (Si/Al ratio, nature of the charge-compensating cation, pore geometry and diameter of pore aperture). Thermodynamic adsorption selectivities towards deuterium with respect to hydrogen were measured in a large pressure range (0.1 – 1000 hPa) and for several temperatures (45 – 100 K). The adsorption selectivity was assessed using direct coadsorption measurements performed by manometry coupled with mass spectrometry. For all studied zeolites and experimental conditions, the coadsorption process is selective towards deuterium, in agreement with the literature. However, the adsorption selectivity depends on the loading, the sorbent’s properties and the temperature. We have found that the coadsorption kinetics strongly influences the adsorption selectivity, especially at high loading. This work gives the guidelines for the choice of the formulation of materials and the optimal operating conditions for having an efficient separation of hydrogen isotopes using zeolite-based adsorbents.
25

Geochemical assessment of gaseous hydrocarbons: mixing of bacterial and thermogenic methane in the deep subsurface petroleum system, Gulf of Mexico continental slope

Ozgul, Ercin 30 September 2004 (has links)
Mixtures of bacterial and thermogenic methane are found both at vents at the seafloor and in reservoirs in the deep subsurface of the Gulf of Mexico continental slope. The C1-C5 gas that most recently charged reservoirs of Jolliet (GC 184), Genesis (GC 160/161) and Petronius (VK 786) fields is estimated to include 17%-28%, 31%-51%, 31%-49% bacterial methane, respectively. Geochemical assessment of the reservoir gas in the fields show that the gas may be the product of thermal cracking of Upper Jurassic crude oil before final migration to the reservoirs. The gas from three different fields is of similar thermal maturity levels. In contrast to oil in reservoirs in the fields, which shows biodegradation effects, the C1-C5 reservoir gas is unaltered by biodegradation. Late gas migration may have occurred at or near present burial depth and flushed the reservoir system of previously biodegraded hydrocarbon gas to include any previous bacterial methane. Molecular and isotopic properties of reservoir gas and oil suggest that bacterial methane mixed with thermogenic hydrocarbon gas before entering the reservoirs. Thus the source of the bacterial methane is logically deeper than the present depth (>~4 km) and temperatures of the reservoirs. High sedimentation rate and low geothermal gradient may offer conditions favorable for generation and preservation of bacterial methane in deep subsurface petroleum system of the Gulf slope. Bacterial methane dispersed across the large drainage areas of the deep subsurface petroleum system may have been swept by migrating fluids at >4 km, and then charged both vents (GC 185, GC 233 and GC 286) at the seafloor and reservoirs in the deep subsurface. The volume of bacterial methane from geologically significant depth in rapidly subsiding basins may be underestimated.
26

Hydrogen and Muonium behaviour in diamond

Joseph, Sithole Makgamathe 31 March 2005 (has links)
This work is aimed at the understanding of the dynamical behavior of hydrogen in diamond. The investigation was carried out using Transverse Field muon Spin Rotation (TF-SR) and the Longitudinal Field muon Spin Relaxation (LF-SR) techniques. The chemical analogy between hydrogen (p+e-) and muonium (u+e-) enabled the study of the indirect dynamical behavior of hydrogen in diamond. The TF-SR and LF-SR measurements were carried out in an isotopically pure 13C diamond in the temperature ranges 11 mK - 320 K and 10 K - 400 K, respectively. In the TF-SR results, the Prompt Absolute Fraction (PAF) of both diamagnetic and the paramagnetic states are temperature independent. The spin relaxation rate for the state is non-zero and temperature independent, while that of the Mux state is non-zero and temperature dependent. The behavior of indicates that the u+d is immobile, while that of MuT indicates the mobility in diamond. The LF-SR results provide hop rate and associated nuclear hyperfine interaction parameters of the Mut state in diamond. / Physics / M.Sc. (Physics)
27

Análise compartimental e aspectos dosimétricos aplicados ao colesterol marcado com sup(3)H / Compartimental analysis and dosimetric aspects applied to cholesterol with sup(3)H labeled

OLIVEIRA, ADRIANO dos S. 03 February 2016 (has links)
Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2016-02-03T11:46:20Z No. of bitstreams: 0 / Made available in DSpace on 2016-02-03T11:46:20Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
28

Análise compartimental e aspectos dosimétricos aplicados ao colesterol marcado com sup(3)H / Compartimental analysis and dosimetric aspects applied to cholesterol with sup(3)H labeled

OLIVEIRA, ADRIANO dos S. 03 February 2016 (has links)
Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2016-02-03T11:46:20Z No. of bitstreams: 0 / Made available in DSpace on 2016-02-03T11:46:20Z (GMT). No. of bitstreams: 0 / Doenças cardiovasculares (DCVs) são uma das maiores causas de morte ao redor do mundo, de acordo com a Organização Mundial da Saúde (OMS). Sabe-se que, alterações do nível das lipoproteínas plasmáticas, que são responsáveis pelo transporte do colesterol pela corrente sanguínea, estão relacionadas com o desenvolvimento de doenças cardiovasculares. Por essa razão conhecer os parâmetros biocinéticos das lipoproteínas plasmáticas e quantificá-los é importante para corrigir e aprofundar estudos relacionados às doenças associadas a alterações no nível das lipoproteínas. O objetivo principal deste trabalho é fornecer um modelo biocinético e estimar as doses radiométricas para o 3H-Colesterol, um traçador radioativo empregado em estudos fisiológicos e metabólicos. O modelo utilizado neste trabalho foi baseado em [SCHWARTZ e col., 2004] quanto à distribuição do colesterol pelas lipoproteínas e no modelo gastrointestinal do [ICRP 30, 1979]. As doses distribuídas nos compartimentos do modelo e nos órgãos e tecidos de um adulto padrão descritos no [ICRP 106, 2008] foram calculadas utilizando a metodologia MIRD (Medical Internal Radiation Dose) e a análise compartimental realizada pelo programa computacional Matlab®. Os coeficientes de doses foram estimados para um phantom de um homem padrão (73 kg) descrito no [ICRP 60, 1991]. As doses estimadas tanto para o modelo quanto as estimadas para outros órgãos foram baixas e não ultrapassaram a maior dose obtida que foi no intestino grosso superior, como sendo 46,8 &mu;Gy. Esses parâmetros poderão ser utilizados como auxilio em trabalhos que necessitem de pareceres dos comitês de ética, quanto ao uso do 3H-Colesterol como traçador radioativo. / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
29

Advancements in Isotopic Geolocation Tools for Insect Migration Research

Reich, Megan 18 January 2024 (has links)
Migratory insects are vital components of global ecosystems and provide important ecosystem services, yet the migration phenomenon is understudied in insects compared to vertebrates. In this thesis, I aim to deepen our understanding of insect migration, using the monarch butterfly Danaus plexippus (L.) and the painted lady butterfly Vanessa cardui (L.) as model systems. Studying insect migration is notoriously difficult given the small size, high abundance, and short lifespans of insects. Isotope geolocation has shown promise for overcoming these obstacles. Here, I develop and apply metals and metal isotopes, specifically strontium isotope ratios (⁸⁷Sr/⁸⁶Sr), to increase the spatial precision of isotope geolocation and demonstrate how isotopic geolocation tools can advance our understanding of insect migration at the population level. In the first chapter, I test the validity of using ⁸⁷Sr/⁸⁶Sr, lead isotopes, and a suite of 23 metals and metalloids to estimate the natal origins of migratory insects, by investigating the pathways of metal incorporation into butterfly wing tissues. Using an 8-week diet-switching experiment, I show that the concentrations of many metals in insect wings can be altered through the adult diet or dust deposition, making them poor candidates for geolocation but potentially interesting tools to study insect physiology, diet, or toxicology. For example, lead was found to accumulate on butterfly wings from external sources, and lead isotopes could potentially be used to quantify the exposure of migratory insects to metal pollution. Some metals, including Ba, Cs, Mg, Na, Rb, Sr, Ti, Tl, and U, are good candidates for developing geolocation tools. I focused on ⁸⁷Sr/⁸⁶Sr and demonstrated that, despite some caveats, this tool is valid for isotope geolocation. In the second chapter, I outline the steps required to use ⁸⁷Sr/⁸⁶Sr for the geolocation of insects, including the calibration of a spatial model of isotopic variation (i.e., an isoscape) using random forest regression. I then combine hydrogen isotope values (δ²H) and ⁸⁷Sr/⁸⁶Sr into a dual assignment framework to estimate the natal origins of a single generation of monarch butterflies in eastern North America. I demonstrate that combining these two isotopes provides a more spatially constrained estimate of natal origin than using either isotope alone. In the third chapter, I apply this framework to characterize the migratory patterns and migratory connectivity of an insect species across a geographical barrier, the Sahara. Painted ladies journeying northwards across the Sahara appear to do so in a gradual progression, although spatiotemporal sampling limitations prevented a complete characterization of this movement. In contrast, painted ladies migrating southwards appear to journey in a broad front, parallel migration pattern with little longitudinal movement. Evidence for a leapfrog migration pattern was found in the western region, wherein butterflies of northernmost origin journey farther south than butterflies bred in more southerly regions. This leapfrog migration pattern suggests distinct migratory behaviours within painted lady butterflies wherein some individuals migrate longer distances than others. In the fourth chapter, I apply isotope geolocation to characterize the migration distances of multiple individuals and assess the potential genetic differentiation of butterflies migrating distinct distances. I use δ²H and ⁸⁷Sr/⁸⁶Sr-based geographic assignment to confirm that some painted ladies migrate up to 4,000 km from Europe to sub-Saharan Africa, while others migrate shorter distances from Europe to the circum-Mediterranean region. Despite these differences in migration distance, genome-wide analysis revealed a lack of adaptive variation between short- and long-distance migrants. Instead, variation in migration distance in painted lady butterflies is likely the result of a plastic response to environmental conditions. Overall, the methodological developments presented in this thesis are a step forward in studying insect migration. The development and application of metals and metal isotopes for insect geolocation opens new avenues to study the migration phenomenon at different scales with widespread relevance for conservation and pest management.

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