Global ETD Search
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 16 of 16 for “"Isotopic exchange"”.
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Structure sensitivity of H2/D2 Isotopic Exchange on Pt/Al2O3 catalysts
… to the activity of H2 activation in the H/D isotopic exchange reaction. In this work, the kinetics of H2 is studied by performing the H2-D2 isotopic exchange reaction on Pt-supported catalysts with different nuclearity to extract the activation barriers and pre-exponential factors for …
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Chromium and uranium isotopic exchange kinetics and isotope fractionation during oxidation of tetravalent uranium by dissolved oxygen
… studies. Correctly interpreting Cr and U isotopic compositions in groundwater and sed- imentary rock samples requires thorough understanding of relevant isotope fractionation mechanisms, many of which are still poorly understood. Isotopic exchange and oxidation reactions are two types of …
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Antimony isotopes as indicators of redox reactions in aqueous systems: fractionation during Sb(V) reduction by sulfide and isotope exchange kinetics between dissolved Sb(III) and Sb(V)
… of Sb. For other contaminant elements, stable isotopic ratio measurements have been useful for source tracing and detection of environmentally critical chemical reactions (e.g., Wiederhold 2015). We seek to develop Sb isotopic ratios as tools for detecting and quantifying Sb in the environment. …
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An experimental study of proton-exchanged lithium niobate optical waveguides
… origin of the problems associated with proton-exchanged waveguides, and to investigate possible solutions. Chapter 1 gives a brief introduction to the properties of lithium niobate, and discusses the methods available for fabricating optical waveguides in the bulk material, with particular …
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Use of stable isotopes to assess phytoremediation of soils contaminated with cadmium and zinc.
… being the most common. Another approach is the isotopic exchange method which has been regularly used for estimating the bioavailable P in soil. This technique relies on the assumption that isotopically exchangeable P is available to a growing plant and yields the so called E-value for a soil. …
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Hydrogen-deuterium exchange studies by mass spectrometry: A method for obtaining conformational structures of proteins in solution
Hydrogen-deuterium exchange (HDX) coupled with electrospray ionization (ESI) in mass spectrometry (MS) has become an important method in the study of protein structure and dynamics. It provides an opportunity for obtaining conformational structures of protein motions in physiological conditions and …
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Laboratory and field-based investigations of subsurface geochemical processes in seafloor hydrothermal systems
… of hydrocarbons under hydrothermal conditions. Isotopic exchange between low molecular weight n-alkanes and water is shown to be facilitated by metastable equilibrium reactions between alkanes and their corresponding alkenes, which are feasible in natural systems. In Chapter 5, the controls on …
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The hydrogeology of the Oman Mountains
… no statistically significant relationship. The isotopic composition of groundwater is strongly influenced by the rainfall amount (related to storm frequency), and not just by altitude/temperature. Storm events with long return periods are of disproportionate importance to recharge. Despite the …
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Laboratory and field-based investigations of subsurface geochemical processes in seafloor hydrothermal systems
… of hydrocarbons under hydrothermal conditions. Isotopic exchange between low molecular weight n-alkanes and water is shown to be facilitated by metastable equilibrium reactions between alkanes and their corresponding alkenes, which are feasible in natural systems. In Chapter 5, the controls on …
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Hydrogen-water isotope exchange in a trickle bed column by process simulation and 3D computational fluid dynamics modelling
… element in the universe and exists under three isotopic forms: protium, deuterium and tritium. Protium is commonly used in a variety of industries including electronics, metallurgy, chemistry and petrochemistry. Deuterium and tritium have taken more roles in both civil and defence nuclear …
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Geochemical and isotopic characteristics of palaeo-hydrothermal fluids related to granite magmatism, S W England
… fluids, together with geochemical and isotopic constraints from the characterisation of Palӕozoic metasedimentary country rocks, support the view that the fluids were genetically associated with the granites. Fluid interaction with the local metasedimentary rocks at a high level crustal …
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Experimental, geochemical and isotopic insights on melting and degassing behavior on Earth
… and degassing at high pressure, geochemical and isotopic fingerprints of the Earth’s oldest rocks, and kinetic processes associated with aqueous supercritical fluids. The main lines of investigation rely on the tools of experimental petrology (Chapters 2 and 3) and stable isotope geochemistry …
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Nitrogen cycling in oxygen deficient zones : insights from [delta]¹⁵N and [delta]¹⁸O of nitrite and nitrate
… must be known so that we can distinguish the isotopic signature of each process. One of the important processes to consider here is nitrification, the process by which ammonium is oxidized nitrite and then to nitrate. This thesis describes numerous experiments using both cultures of nitrifying …
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Mercury stable isotope geochemistry as a tool for tracing sources and chemical transformations in the environment
… two dissolved species. The results of these exchange experiments show that Hg(0) and Hg(II) have the ability to exchange isotopes very quickly, which will have implications for interpreting field isotope data.
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Pedogenic carbonates in loess formation rates, formation conditions and source apportionment assessed by isotopes and molecular proxies
… rates were successfully determined with the 14C isotopic exchange approach by exposing loess to artificially labeled 14CO2 and subsequent quantification of 14C incorporated in secondary (recrystallized) CaCO3. Within the range of natural soil CO2 concentrations, recrystallization rates increased …