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Ultra slow acoustic energy transport in dense fish aggregates.

ABSTRACT: A dramatic slowing down of acoustic wave transport in dense fish shoals is observed in open-sea fish cages. By employing a multi-beam ultrasonic antenna, we observe the coherent backscattering phenomenon. We extract key parameters of wave transport such as the transport mean free path and the energy transport velocity of diffusive waves from diffusion theory fits to the experimental data. The energy transport velocity is found to be about 10 times smaller than the speed of sound in water, a value that is exceptionally low compared with most observations in acoustics. By studying different models of the fish body, we explain the basic mechanism responsible for the observed very slow transport of ultrasonic waves in dense fish shoals. Our results show that, while the fish swim bladder plays an important role in wave scattering, other organs have to be considered to explain ultra-low energy transport velocities.

SUBMITTER: Tallon B

PROVIDER: S-EPMC8413328 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BACKGROUND/OBJECTIVE:Although reducing energy density (ED) enhances weight loss, it is unclear whether all dietary strategies that reduce ED are comparable, hindering effective ED guidelines for obesity treatment. This study examined how changes in number of low-energy-dense (LED) (<4.186?kJ/1.0?kcal?g-1) and high-energy-dense (HED) (>12.56?kJ/3.0?kcal?g-1) foods consumed affected dietary ED and weight loss within an 18-month weight loss trial. METHODS:This secondary analysis examined data from participants randomized to an energy-restricted lifestyle intervention or lifestyle intervention plus limited non-nutrient dense, energy-dense food variety (n=183). Number of daily LED and HED foods consumed was calculated from three, 24-h dietary recalls and anthropometrics were measured at 0, 6 and 18 months. Multivariable-adjusted generalized linear models and repeated-measures mixed linear models examined associations between 6-month changes in number of LED and HED foods and changes in ED, body mass index (BMI), and percent weight loss at 6 and 18 months. RESULTS:Among mostly female (58%), White (92%) participants aged 51.9 years following an energy-restricted diet, increasing number of LED foods or decreasing number of HED foods consumed was associated with 6- and 18-month reductions in ED (?=-0.25 to -0.38?kJ?g-1 (-0.06 to -0.09?kcal?g-1), P<0.001). Only increasing number of LED foods consumed was associated with 6- and 18-month reductions in BMI (?=-0.16 to -0.2?kg?m-2, P<0.05) and 6-month reductions in percent weight loss (?=-0.5%, P<0.05). Participants consuming ?2 HED foods per day and ?6.6 LED foods per day experienced better weight loss outcomes at 6- and 18-month than participants only consuming ?2 HED foods per day. CONCLUSION:Despite similar reductions in ED from reducing number of HED foods or increasing number of LED foods consumed, only increasing number of LED foods related to weight loss. This provides preliminary evidence that methods used to reduce dietary ED may differentially influence weight loss trajectories. Randomized controlled trials are needed to inform ED recommendations for weight loss.

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Ultra slow acoustic energy transport in dense fish aggregates.

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