A comparison of collisions of saltating grains with loose and consolidated silt surfaces
Bibliographic record
Abstract
A particle tracking velocimetry system was used to study the trajectories of saltating sand particles as they impacted either consolidated (solid) or unconsolidated (loose) silt surfaces in a wind tunnel. The tunnel friction velocity varied between 0.26 and 0.3 m s −1 . The average coefficient of restitution, defined as the ratio of postcollision velocity to precollision velocity, was found to be ε = 0.64 for the loose bed and ε = 0.79 for the solid bed, respectively. The average ratio of energy loss to impact energy was found to be E L / E 0 = 0.58 for the loose bed and E L / E 0 = 0.37 for the solid bed, respectively. These indices demonstrate that the loose bed absorbs more momentum and energy from the impacting sand particle. The average ejection angle was lower at 18° for the loose bed than 23° for the solid bed. In the loose surface, crater formations were observed to form with each impact. Surface profile measurements suggest an average crater volume of >0.1 mm 3 . For both beds, the coefficient of restitution decreases with the particle impact speed. In the case of the solid bed, the dependence on impact speed is in good agreement with a model of two colliding spheres with identical material properties. With regard to the loose bed, a model of the impacting particle motion as it plows through and plastically deforms the bed material is tested. If the ratio of the horizontal to vertical forces on the particle as it plows through the bed is taken as a linear function of impact speed, the model is in good agreement with measured data. This suggests that compaction of the surface may occur along with the plowing and displacement of loose bed material.
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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 | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".