Theoretical Study of Tellurium Isotope Fractionations in Ore-Forming Systems, and Studies of Doubly Substituted Isotopologues of Methane
Bibliographic record
Abstract
This thesis encompasses three research projects on the stable isotopes of tellurium and multiply substituted isotopologues of methane. In the first project (Chapter 2), I used theoretical techniques to predict tellurium isotope signatures of ore formation processes. In this study, equilibrium mass-dependent isotopic fractionation among Te-bearing species relevant to the formation of precious-metal ores is estimated with first-principles thermodynamic calculations. This work is the first theoretical study on the isotope fractionation of tellurium in ore-forming systems. In the second project (Chapter3), I investigated the potential of 13CH3D and 12CH2D2, the doubly substituted mass-18 isotopologues of methane, as tools for tracking atmospheric methane sources and sinks. Methane is the most abundant organic chemical and the second most important long-lived greenhouse gas in the atmosphere. It also has a significant impact on the chemistry of the troposphere and stratosphere. However, there are large uncertainties in the sources and sinks of methane to the atmosphere, as well as in their variability in time and space. I used electronic structure methods and initial isotopologue abundance measurements, from the UCLA Nu Panorama and other laboratories [Stolper et al., 2015; Wang et al., 2015; Young et al., 2017], to estimate kinetic and equilibrium isotope signatures for 13CH3D and 12CH2D2. Then I predicted the abundances of singly and doubly substituted methane species in atmosphere in different scenarios using a whole-atmosphere box model. This study is the first model ever to describe the atmospheric methane budget that includes both doubly substituted isotopologues, 13CH3D and 12CH2D2.The third project (Chapter 4) focused on measuring 13CH3D and 12CH2D2 in methane samples from natural boreal lakes, collected in Alaska, Canada, and Siberia. Wetlands are among the largest methane sources, and they will need to be characterized as part of the construction of any realistic global budget of 13CH3D and 12CH2D2. In this project all measurements were performed using gas chromatography and a high-resolution gas-source multiple-collector mass spectrometer (the UCLA Nu Panorama). Finally, these data are combined with recent predictions of future emissions growth to model the likely impacts of boreal lakes on the future atmospheric CH4 isotopologue budget up to year 2100. In addition to testing our model atmospheric budget, doubly substituted isotopologue measurements of CH4 appear to provide information about the likely production mechanism for natural CH4 samples.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.001 | 0.002 |
| Scholarly communication | 0.001 | 0.002 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".