Influence of Normal Stress, Shear Velocity and Materials on Steady-State Shear Resistance and Viscosity of Rapid Dry Granular Flows Hu, W., Y. Li, H. Gou, X. Jia, L. Zhou, and C. Chang Journal of Geophysical Research Solid Earth 130, no. 6 (2025)
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.
|
|
Enhanced mm-Wave Frequency Up-Conversion via a Time-Varying Graphene Aperture on a Cavity Resonator Amanatiadis, S., T. Karamanos, F. Lemoult, and N. V. Kantartzis Micromachines 16, no. 6, 679 (2025)
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.
|
|
Nonmonotonic Radiative Heat Transfer in the Transition from Far Field to Near Field Guillemot, V., R. Messina, V. Krachmalnicoff, R. Carminati, P. Ben-Abdallah, W. Poirier, and Y. De Wilde Physical Review Letters 134, no. 19 (2025)
Résumé: We present high precision measurements of the radiative heat transfer of a glass microsphere immersed in a thermal bath in vacuum facing three different planar substrates (SiO2, SiC, and Au), which exhibit very different optical behaviors in the infrared region. Using a thermoresistive probe on a cantilever, we show the nonmonotonic behavior of the radiative flux between the microsphere and its environment when the microsphere is brought closer to the substrate in the far-field to near-field transition regime. We demonstrate that this unexpected behavior is related to the singularities of dressed emission mechanisms in this three-body system sphere-substrate bath with respect to the separation distance.
|
|
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.
|
|