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Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 110 for “"18O"”.
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A comprehensive global 3D model of delta-18O in atmospheric CO2
… comprehensive global 3D model to simulate delta-18O in atmospheric CO2. The aim is to disentangle this isotope signal which offers the potential to determine the CO2 gross fluxes of the terrestrial biosphere. Model surface processes have been validated against regional experiments while the …
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Estudo da influência da força de emparelhamento na transferência de dois nêutrons na reação 13C( 18O,16 O) 15C
… de dois nêutrons na reação direta 13C( 18O,16 O) 15C, a uma energia de bombardeamento de 84 MeV. Recentemente, foram encontrados indícios de que a correlação entre dois nêutrons no processo de transferência, na reação 12C( 18O,16 O) 14C [1], desempenha um papel crucial nesse processo, de …
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STABLE ISOTOPE RATIOS AS A PROXY FOR HUMAN GEOGRAPHIC PROVENANCE: BIOGEOGRAPHICAL EVIDENCE FROM THE 2H, 18O, AND 13C SIGNATURES IN MODERN HUMAN TEETH
… studies as well as forensic investigations. Both 18O and 2H stable isotope signatures are well established proxies as environmental indicators of climate (temperature) and source water and are therefore considered reliable indicators of geographic life trajectories of animals and humans. …
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Heavy-ion double charge exchange reactions as tools for 0bb decays. The 40Ca(18O,18Ne)40Ar reaction at 270 MeV by using MAGNEX
… angular and energy resolution. In particular (18O,18Ne) reaction at 270 MeV incident energy on 40Ca target was investigated. In order to estimate the contribution of the concurrent channels the 40Ca(18O,18F)40K single charge exchange intermediate channel and the competing processes …
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Studio dello scattering 18O + 48Ti a 275 MeV, simulazioni Monte Carlo e caratterizzazione sperimentale del rivelatore di piano focale di MAGNEX per il progetto NUMEN
… di tali canali nel caso della collisione 18O + 48Ti a 275 MeV di energia incidente è qui presentata per la prima volta. Sono descritte la procedura di riduzione dei dati e l’analisi teorica svolte durante il periodo del Dottorato di Ricerca. Il secondo pilastro di questa Tesi consiste …
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Why are there no low-δ18O magmas In convergent margins? A case of the Central Andes, Northern Chile
It has long been thought that low-δ 18O magmas (<5.7‰) are only found in extensional tectonic settings. Low-δ 18O magmas are rare, worldwide, especially in subduction zone settings. The main objective of this study was to conduct a search for low-δ 18O magmas in the Central Volcanic Zone (CVZ) of …
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Evaluation of Paleo-climate for the Boise Area, Idaho, from the last Glacial Maximum to the Present Based on delta 2H and delta 18O Groundwater Composition
… water lines (LMWL) using the delta 2H and delta 18O composition of the groundwater were defined for each system using linear regression techniques. LMWL had variable and defined single slopes of 6.94 and 8. Deuterium excess values (d) were found for each system for each linear regression method. …
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A multi-isotopic geochemical investigation of the Lower Zone, Bushveld Complex, South Africa: implications for a crustal component for parental magmas
… Layered Suite (RLS) such as elevated 18O values. These geochemical and isotopic systems include major elements, trace elements, highly siderophile elements, oxygen isotopes, 87Sr/86Sr, 143Nd/144Nd, and Os-Os isotopes. Samples come from the Nooitgedacht Borehole 2 (NG2) at Union Section …
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Petrogenesis of lavas from Volcano Azufre, Northern Chile: evidence for crustal input
… 87Sr/86Sr ratios of 0.7067 - 0.7075 and δ 18O values of 7.85 - 9.72 are high in comparison to those of other Central Andean lavas, however in comparison to other erupted lavas of the APVC they are low. A transition from the edges of the APVC towards the centre show an increase in 87Sr/86Sr …
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Oxygen isotopes as a tracer of biospheric CO2 gross fluxes : a local feasibility study
… CO2 mixing ratio or to temperature changes. The 18O/16O ratio of CO2 has the potential to separate respiration and assimilation fluxes because of their characteristic isotopic signatures derived from equilibration with respective water reservoirs (i.e. soil and leaf water). The associated …
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Temporal Variations of delta 2 H, delta 18 O and Deuterium Excess in Atmospheric Moisture and Improvements in the CO 2 -H 2 O Equilibration Technique for 18 O/ 16 O Isotope Ratio Analysis
… (1981-2000) of the stable isotope ratios D/H and 18O/16O in atmospheric water vapour collected at the Central European site Heidelberg (49° 25’ N and 8° 41’ E) is analysed. Its basic features, such as seasonal variations of D/H and 18O/16O, are discussed and compared with the isotope composition …
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Impact of Isotopic Heterogeneity in Shallow Systems on Modeling of Stormflow Generation
… average throughfall is enriched by 0.5% in 0^18O and 3.0% in 0D relative to rain; site-specific differences in canopy cause up to 1.2 % variation in 0^18O among collectors for the same storm; and throughfall ^18O enrichment takes place throughout the storm, not just at the beginning. …
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Isotopic Tracers as Evidence of Denitrification in the Karlsruhe Aquifer
… an increase in the heavy isotopes of 15N and 18O within the NO₃¯ ion. Such an increase is not evident in other nitrate attenuation processes. This dual isotope method may even be extended to identify the source of the contamination based upon isotopic signatures of specific nitrate sources. …
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Geochemical Approaches to Paleobiology, Paleoclimatology, and Chronostratigraphy of the Cretaceous Cloverly Formation
… Cloverly fossil assemblage by analyzing the 18O of biogenic phosphates from a large set of vertebrate fossils. This has resulted in the first quantitative surface-air temperature estimate (22.3 +/- ~ 5 °C) for the Cloverly, as well as insights into the water use ecology and hydroclimatic …
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Experimental and theoretical multi-channel study of direct nuclear reactions: a tool to provide data driven information on neutrino-less double-beta decay
… present thesis. They involve the cases of the 18O + 12C, 18O + 76Se and 20Ne + 76Ge networks of quasi-elastic nuclear reactions at 15.3 AMeV incident energy. The advantages of the newly proposed multi-channel approach are applied to the NUMEN nuclear reaction data analysis. Regarding the …
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The paleoceanography of the Bering Sea during the last glacial cycle
… minerals with very low 13C (-22.4%), high 18O (6.5%), and high [Mg]/[Ca], which seem associated with sulfate reduction of organic matter and possibly anaerobic oxidation of methane. The episodes lasted less than 1000 years and were spaced about 1000 years apart. During MIS3 at 55-20 ky BP …
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The oxygen isotope composition of the country rock of the Koegel Fontein igneous complex
… plug, and the quartz porphyry dykes have δ18O values as low as -4.1‰, and these are believed to be the result of selective dehydration and melting of previously 18O-depleted rock (Curtis et al., 2013; Olianti and Harris, 2018). This thesis investigates the oxygen isotope composition of the …
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Sulfoxide Catalyzed Dehydrative Glycosylation. Reaction Development and Mechanistic Analysis
… Successful determination of the proportion of 18O-incorporation in the glycosyl sulfonate as a function of its formation, via the technique of dynamic monitoring of 13C-16/18O isotopic chemical shift perturbations, provides strong evidence that hemiacetal activation proceeds through initial …
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First experimental evidence of the Giant Pairing Vibration in atomic nuclei
… the nuclear pairing field. In particular, the (18O,16O) reactions at 84 MeV incident energy on 12C and 13C targets are investigated. A vast literature is available on the subject of the pairing correlations and two-neutron transfer reactions, but some key questions need still to be answered. The …
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Chemical, isotopic, and temporal variations during crustal differentiation : insights from the Dariv Igneous Complex, Western Mongolia
… that large (1 to 1.8%o) increases in [delta]18O as a melt evolves from basaltic to granitic in composition due to the fractionation of low [delta]18O minerals. As such, the majority of [delta]180 values of upper crustal silicic plutonics can be explained through fractional crystallization of …
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