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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 13 of 13 for “"oxygen-18"”.
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Radiation-enhanced diffusion of oxygen-18 in uranium dioxide thin films
… (RED) and thermal diffusion of a buried 18O tracer layer in thin film UO2 was measured using Secondary-Ion Mass Spectroscopy (SIMS). Thin films were grown using a dedicated magnetron sputtering chamber. Samples were irradiated with 1.8 MeV Kr+ over a temperature range from 295 K to 623 K. …
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Substrate Cleavage Points of Some Carbohydrases as Determined by Oxygen-18 Studies
… 1 0025249.pdf: 2008667 bytes, checksum: f021809bf9b455b85bb8099a3d1bd6bd (MD5) Previous issue date: 1957
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Alpha-Oxygenation by Acylation-Rearrangement of Nitrones
… affords a new method for the (alpha)-oxygenation of aldehydes and cyclic ketones via (alpha)-acyloxy imines. The reaction apparently proceeds by initial acylation of the nitrone oxygen, proton removal, and {3,3}-sigmatropic rearrangement of the resulting N-vinyl-O-acylhydroxylamine. …
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Oxidation Mechanisms of Tetrahydrofolic Acid, Tetrahydrobiopterin and Related Compounds
… of zero- and first order dependence on oxygen, the relative contributions of which are affected by the exclusion of visible light. There is a linear dependence of rate on percentage ionisation of the 3,4-amide group and the reaction is retarded by protonation of N(5), suggesting that …
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Groundwater/surface water interaction in the Raisin River watershed, near Cornwall, Ontario.
… were collected for environmental isotopes (oxygen-18 and deuterium). Raisin River discharge data were also analysed. Seepage measurements and hydraulic conductivities exhibit significant variability. The coefficients of variation for seepage measurements ranged from 20.3 to 392%, and for …
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Modeling nonlinear, nonstationary, vector time series : methods and applications.
… layers, the ratios of carbon-13 isotopes and of oxygen-18 isotopes provide information on the types of vegetation, which in turn, gives information into the climate at the time that vegetation lived. We apply a momentum threshold vector autoregressive model (VMTAR) to the 3- dimensional series. …
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Seepage of Groundwater into the St. Clair River Near Sarnia, Ontario, Canada
… halides (TOX), chloride, and natural isotopes (oxygen-18, deuterium, and tritium). The average observed seepage rate of l. u x 10-8 m 3/s/m2 suggests higher chan expected hydraulic conductivity or hydraulic gradients in the streambed, 2 to 4 orders of magnitude greater than those determined in …
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Holocene Palynology of the Gulf of Papua, Papua New Guinea: Using Modern Palynomorph Distribution to Better Constrain Paleoenvironmental Changes
… between 5 to 6 kyr BP Palynomorph data and oxygen-18 isotopes from MD-50 also indicate an increase in El Niño Southern Oscillation (ENSO) activity at approximately 5 kyr BP.
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In-situ investigation and mitigation of carbon support corrosion of cathode catalyst in PEM fuel cells
… to the Pt redox reactions and Pt-catalyzed oxygen reduction reaction (ORR) by the differential electrochemical mass spectrometry (DEMS) spectra of cathode exhaust gases, CO₂, H₂ and O₂, from a PEMFC fed with humidified H₂ and He to the anode and cathode respectively. Furthermore, the …
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Old and subsurface water contributions to storm runoff generation in flat, fractured, clayey terrain.
… and surface runoff collecting systems. Isotopic (oxygen-18 "$\sp{18}O'')$ and chemical (electrical conductivity "EC", chloride "Cl$\sp-''$ and dissolved silica "SiO$\sb2'')$ parameters were utilized in a two-component mixing model or the trial-error separating method developed in this study to …
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Solute Chemistry and Isotopic Investigation of the Groundwater Flow Paths in Honey Lake Basin, Lassen County, California and Washoe County, Nevada
… water and mixing ratios are presented. δ<sup>18</sup>O and δD data show that deep groundwater was recharged by cooler, more humid precipitation from the last ice age, whereas shallow groundwaters reflect current meteoric conditions and show extensive evaporation trends. The two thermal flow …
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Theory and Utility of the Three Isotope Fractionation Relationship
… of isotope geochemistry began with the study of oxygen isotope geothermometry, most famously for carbonates. Traditionally oxygen isotope studies are only concerned with the relationship between one rare isotope, oxygen-18, and the common isotope, oxygen-16. In these cases, the abundance of the …