Bibliographic record
Abstract
Terrestrial age of meteorites gives us important information to estimate the terrestrial history of the meteorites. With the advent of AMS, the required sample mass of meteorite for measurement has been reduced as small as 0.1g. As a result, many more ^<14>C measurements have been performed intensively by the Toronto AMS group, Canada, the Arizona AMS group, USA, and so on. In Japan, AMS ^<14>C measurements of meteorites have been scarcely performed, to our regret. We are now at the early stage of the program for studying ^<14>C activities in meteorites, and constructing a system to extract ^<14>C from meteorites, in a similar method used by the Arizona group. A meteorite powder sample mixed with pure iron chips is combusted in a RF furnace (Leco HF-10) in the presence of purified carbon-free oxygen in a closed vacuum-tight glass line system. The sample gases evolved are passed through MnO_2 and Pt/CuO traps, and then the CO_2 is separated in a liq.N_2 trap, by pumping out oxygen completely. The amount of ^<14>CO_2 is determined by a pressure transducer in a certain volume and diluted with a known amount of ^<14>C^free CO_2. The total CO_2 is graphitized by reducing with hydrogen in a Fe-powder catalyst and the produced graphite is measured of its ^<14>C concentration with a Tandetron accelerator mass spectrometer at the Dating and Materials Research Center, Nagoya University. Extraction yields of CO_2 using the above method which employs RF melting of steel standards of known carbon content were about 90%. The new extraction procedure gave higher extraction yields and older ^<14>C ages than those using the old extraction method. Carbon yields of two Antarctic meteorites (Y-75102 and ALH-77294), however, were significantly low, and the carbon-14 terrestrial ages for the meteorites were different from the reported values. The results might be caused by imperfect combustions of the meteorites and high blanks from the crucible with iron chips alone. Further studies are needed to improve analytical techniques.
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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) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.011 | 0.006 |
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".