Energy velocity of multiply scattered waves in strongly scattering media
Bibliographic record
Abstract
The important influence of the relative refractive index of scattering inclusions on energy transport of classical waves through disordered media is clearly demonstrated through ultrasonic experiments on monodisperse emulsions. Our ultrasonic techniques measure both the transmitted average wave field and the multiply scattered diffusive intensity, enabling a full characterization of wave transport through the media and the measurement of both the group and energy velocities over a wide range of frequencies. The emulsions were fabricated using microfluidic techniques that permit accurate control of droplet size and concentration, for droplet inclusions with very different acoustic properties relative to the yield stress fluids in which the droplets were immersed. Thus we have been able to investigate emulsions containing either ``slow'' fluorinated oil droplets (sound speed ${v}_{1}$ less than ${v}_{0}$ of the surrounding fluid) or ``fast'' liquid metallic droplets $({v}_{1}>{v}_{0})$. We find that the energy velocity that describes the transport of energy by the dominant diffusive waves is mainly governed by the sound speed within the scatterers, and can be either much slower or faster than any of the other wave velocities. The possibility that the energy velocity could be faster than any other wave velocity when ${n}_{\text{rel}}={v}_{0}/{v}_{1}<1$ was not anticipated in previous work. These observations are successfully explained by theories that are valid for scalar waves in media containing a low concentration of scatterers, and are directly applicable to our dilute ``all-fluid'' emulsions. The role of droplet resonances on the behavior of the energy velocity is also demonstrated, and the mechanism leading to the large differences in the energy velocity in the two emulsion systems is elucidated through calculations of the energy density inside the droplets relative to the incident energy density.
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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 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 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".