Résumé: Understanding the rheological behavior of rapid granular flows is crucial for understanding various geological processes, such as fast fault slip and rapid motion of landslides. In this study, we conducted rotary shear experiments on different granular materials, spanning a range of shear velocities from slow to rapid and under varying normal stresses, to investigate the evolution of mechanical behavior under different flow conditions. The experimental results showed that steady-state shear resistance varied with normal stress and material composition at shear velocities below 1 m/s. A consistent velocity-dependent trend was observed. The steady-state shear resistance of the sample experienced a transition from velocity-strengthening behavior at low shear velocities (below 0.1 m/s) to velocity-weakening behavior at higher shear velocities (above 0.1 m/s). Interestingly, at shear velocities exceeding 1 m/s, the steady-state shear resistance became independent of normal stress and material composition, converging to a similar steady-state value for both crushable and uncrushable materials. Although normal stress and mineral composition had a limited influence on steady-state shear resistance at high shear rates, they significantly affected the weakening rate (the transition from peak strength to steady-state shear resistance), which was strongly correlated with the material's crushing ability, as characterized by the Weibull modulus. These findings provide insights into the mechanisms governing the hypermobility of mega-landslides and the rapid dynamics of geological flows.

Résumé: The transition to 5G and beyond has highlighted the need for efficient devices that operate at mm-wave frequencies, which require new structures and pose fabrication challenges. This paper proposes a novel non-linear antenna that combines the well-established substrate-integrated cavity (SIC) radiators and time-varying graphene for generating harmonic frequencies in the mm-wave spectrum. Graphene is represented as having a dispersive surface conductivity, while time modulation of the conductivity is introduced by varying the applied bias electric field. A modified FDTD algorithm is, additionally, used to simulate the time-varying graphene behaviour under different modulation schemes. The final antenna design involves an SIC resonator with a graphene-covered slot aperture for radiation. The numerical study highlights the effective generation of harmonics using the modulated graphene at the mm-wave regime. Finally, different modulation schemes are applied to enhance certain higher-order harmonics, demonstrating the potential of this non-linear antenna design for future mm-wave and THz frequency applications.

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.