Floquet scattering of shallow water waves by a vertically oscillating plate
Koukouraki, M., P. Petitjeans, A. Maurel, and V. Pagneux
Wave Motion 136, 103530 (2025)
Résumé: We report on the scattering of a plane wave from a vertically oscillating plate in the low frequency approximation by means of Floquet theory. In the case of a static plate, the scattering coefficients are evaluated via mode matching method for the full two-dimensional linearized water wave problem and are compared with the coefficients obtained from a reduced one-dimensional model in the shallow water approximation. The main part of the analysis is the extension of this 1D shallow water approximation to the case of a vertically oscillating plate, where time modulation is only encapsulated in the blockage coefficient. We show that the incident wave is scattered into Floquet sidebands and extract the scattering coefficients for each harmonic using a Floquet scattering formalism. Finally, considering a slowly oscillating plate, we propose a quasistatic approximation which appears to be particularly accurate.
|
|
Intraoceanic active rifting revealed by deep seismic reflection imaging in the southern Bay of Bengal, northeastern Indian Ocean
Shang, L., G. Hu, T. P. Ferrand, J. Pan, and C. Yang
Earth and Planetary Science Letters 658, 119328 (2025)
Résumé: Oceanic domains form via the break-up of the continental lithosphere resulting from extensional tectonic processes that eventually create passive margins. Whether active rifting and subsequent volcanic break-up occur within the oceanic lithosphere remains ambiguous. New seismic reflection data from the southern Bay of Bengal, where multiple mantle plumes were active during the late Cretaceous, provide visual evidence for resolving this issue. The studied seismic profile reveals an ∼300-km-wide anomalous crustal domain characterized by basement highs, irregular Moho depth fluctuations, and a thick pile of well-organized upper crustal dipping reflections. These features resemble those of volcanic passive margins, i.e., stacked volcanoclastic layers, seaward-dipping reflectors, underplating and failed rifting centers. Here, we document a similar setting within an intraoceanic domain, which is consistent with the active rifting model, with an excess magma supply presumably associated with active mantle upwelling. The structures described in the present study require a multistage dynamic process during local impingement of the northward-drifting Indian oceanic lithosphere by mantle upwelling, with a transition from thermal doming, intense volcanic eruptions and magmatic underplating, to lithospheric extension and necking, and finally to an incipient but failed rift. The volcanism initiated at ∼84–85 Ma, and volcanics were emplaced on young oceanic lithosphere with an age of ∼7–8 Ma. The active mantle upwelling that promoted the intraoceanic rifting was likely driven by a weak or pulsed branch of the Kerguelen Plume, which is also involved in producing the Ninety-East Ridge. These findings help further understand the processes dominating lithospheric breakup and extend some concepts seaward from passive margins to the interior of the oceanic lithospheric domain.
|
|
Sensitivity of Lamb waves in viscoelastic polymer plates to surface contamination
Spytek, J., D. A. Kiefer, R. K. Ing, C. Prada, J. Grando, and J. De Rosny
Ultrasonics 149, 107571 (2025)
Résumé: Detecting surface contamination on thin thermoformed polymer plates is a critical issue for various industrial applications. Lamb waves offer a promising solution, though their effectiveness is challenged by the strong attenuation and anisotropy of the polymer plates. This issue is addressed in the context of a calcium carbonate (CaCO3) layer deposited on a polypropylene (PP) plate. First, the viscoelastic properties of the PP material are determined using a genetic algorithm inversion of data measured with a scanning laser vibrometer. Second, using a bi-layer plate model, the elastic properties and thickness of the CaCO3 layer are estimated. Based on the model, the sensitivity analysis is performed, demonstrating considerable effectiveness of the A1 Lamb mode in detecting thin layers of CaCO3 compared to Lamb modes A0 and S0. Finally, a direct application of this work is illustrated through in-situ monitoring of CaCO3 contaminants using a straightforward inter-transducer measurement.
|
|
Submacular Choroidal Arteries: A Laser Doppler Holography and OCT Study
Paques, M., Z. Bratasz, L. Puyo, C. Chaumette, D. Castro Farias, M. Atlan, and S. Mrejen
Ophthalmology Science 5, no. 3, 100709 (2025)
Résumé: Objective: To document the aspect, topography and morphometry of normal human choroidal arteries in the posterior pole by laser Doppler holography (LDH) and OCT. Design: Cross-sectional study. Subjects: Fifty-four eyes of 27 healthy subjects. Methods: A prototypic LDH system captured the laser Doppler shift of the choroidal circulation within the central 20°. Doppler shifts were filtered to extract high velocity vessels. Images of choroidal arteries identified by LDH were subsequently registered with en face and cross-sectional OCT images. Subsequently, the diameters of macular choroidal arteries and their correlation to central choroidal thickness was measured on OCT B-scans. Main Outcome Measures: Spatial disposition, distribution, and diameters of choroidal arteries. Results: Choroidal arteries were identified by LDH and OCT from their emergence from short posterior ciliary arteries (sPCAs), and could be traced to second and third divisions. In the 8 eyes that underwent LDH, 7 of 8 (88%) showed a horizontal first-order artery within 0.5 disc diameter from the fovea. OCT B-scans showed that first-order arteries were located along the sclera-choroid interface; around arteries, the choroidal tissue formed a pyramid-shaped avascular structure with a posterior base contiguous and isoreflective to the sclera. In a cohort of 49 eyes, the diameter of horizontal submacular arteries (average [± standard deviation] 136.3 μm [±47]; range, 70–209 μm) was weakly correlated to central choroidal thickness (P = 0.09). Conclusions: First-order choroidal arteries emerging from sPCAs are located along the sclerochoroidal interface and are surrounded by a pyramid-shaped avascular space, which contributes to differentiate them from veins. The majority of normal eye show a submacular first-order artery running horizontally toward the temporal periphery. These results will pave the way for a better knowledge of diseases affecting the choroidal circulation. Financial Disclosure(s): Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.
|
|
Universal properties of Wigner delay times and resonance widths of tight-binding random graphs
Hidalgo-Castro, K. B., L. A. Razo-López, A. M. Martínez-Argüello, and J. A. Méndez-Bermúdez
Physical Review E 111, no. 4 (2025)
Résumé: The delay experienced by a probe due to interactions with a scattering media is highly related to the internal dynamics inside that media. This property is well captured by the Wigner delay time and the resonance widths. By the use of the equivalence between the adjacency matrix of a random graph and the tight-binding Hamiltonian of the corresponding electronic media, the scattering matrix approach to electronic transport is used to compute Wigner delay times and resonance widths of Erdos-Rényi graphs and random geometric graphs, including bipartite random geometric graphs. In particular, the situation when a single-channel lead attached to the graphs is considered. Our results show a smooth crossover towards universality as the graphs become complete. We also introduce a parameter ζ, depending on the graph average degree (k) and graph size N, that scales the distributions of both Wigner delay times and resonance widths, highlighting the universal character of both distributions. Specifically, ζ=(k)N-α where α is graph-model dependent.
|
|
Output control of dissipative nonlinear multimode amplifiers using spacetime symmetry mapping
Chen, C. W., K. Wisal, M. Fink, A. D. Stone, and H. Cao
Nature Physics (2025)
Résumé: In many linear and nonlinear systems, time-reversal symmetry makes it possible to control the output waves by appropriately shaping the input waves. However, time-reversal symmetry is broken in systems with energy dissipation, necessitating a different approach for relating the input and output fields. We theoretically consider a saturated multimode fibre amplifier in which light generates a heat flow and suffers thermo-optical nonlinearity, thus breaking time-reversal symmetry. We identify a spacetime symmetry that maps the target output back to an input field. This spacetime symmetry mapping applies phase conjugation, gain and absorption substitution but not time reversal, and it holds in a steady state and for slowly varying inputs. Our approach enables coherent wavefront control of nonlinear dissipative systems.
|
|
