Directing Cherenkov photons with spatial nonlocality

Cherenkov radiation in natural transparent materials is generally forward-propagating, owing to the positive group index of radiation modes. While negative-index metamaterials enable reversed Cherenkov radiation, the forward photon emission from a swift charged particle is prohibited. In this work, we theoretically investigate emission behaviours of a swift charged particle in the nanometallic layered structure. Our results show that Cherenkov photons are significantly enhanced by longitudinal plasmon modes resulting from the spatial nonlocality in metamaterials. More importantly, longitudinal Cherenkov photons can be directed either forward or backward, stringently depending on the particle velocity. The enhanced flexibility to route Cherenkov photons holds promise for many practical applications of Cherenkov radiation, such as novel free-electron radiation sources and new types of Cherenkov detectors.

Анализ влияния нелокальности на характеристики ближнего поля слоистой частицы на подложке

The problem of electromagnetic plane wave scattering by a layered nanoparticle with a metal plasmon shell deposited on the surface of a transparent substrate is considered. Using the Discrete Source Method, the influence of spatial nonlocality in a metal layer on the near-field intensity and absorption cross section is investigated. The particle excitation by both a propagating and evanescent wave are considered. It is shown that the substrate has a more significant effect on the optical characteristics of the near field than on the intensity in the far zone. It was found that taking into account the nonlocal effect in the metal leads to a significant decrease in the plasmon resonance amplitude with a small blue shift.

Minimal wave speed of a diffusive SIR epidemic model with nonlocal delay

This paper is concerned with the minimal wave speed in a diffusive epidemic model with nonlocal delays. We define a threshold. By presenting the existence and the nonexistence of traveling wave solutions for all positive wave speed, we confirm that the threshold is the minimal wave speed of traveling wave solutions, which models that the infective invades the habitat of the susceptible. For some cases, it is proven that spatial nonlocality may increase the propagation threshold while time delay decreases the threshold.

Attenuation of waves in a viscoelastic peridynamic medium

The effect of spatial nonlocality on the decay of waves in a dissipative material is investigated. The propagation and decay of waves in a one-dimensional, viscoelastic peridynamic medium is analyzed. Both the elastic and damping terms in the material model are nonlocal. Waves produced by a source with constant amplitude applied at one end of a semi-infinite bar decay exponentially with distance from the source. The model predicts a cutoff frequency that is influenced by the nonlocal parameters. A method for computing the attenuation coefficient explicitly as a function of material properties and source frequency is presented. The theoretical results are compared with direct numerical simulations in the time domain. The relationship between the attenuation coefficient and the group velocity is derived. It is shown that in the limit of long waves (or small peridynamic horizon), Stokes’ law of sound attenuation is recovered.

Discrete Fractional Derivative Based Computational Model to Describe Dynamics of Bed-Load Transport

Bed-load transport in natural rivers exhibits nonlinear dynamics with strong temporal memory (i.e., retention due to burial) and/or spatial memory (i.e., fast displacement driven by turbulence). Nonlinear bed-load transport is discrete in nature due to the discontinuity in the sediment mass density and the intermittent motion of sediment along river beds. To describe the discrete bed-load dynamics, we propose a discrete spatiotemporal fractional advection-dispersion equation (D-FADE) without relying on the debatable assumption of a continuous sediment distribution. The new model is then applied to explore nonlinear dynamics of bed-load transport in flumes. Results show that, first, the D-FADE model can capture the temporal memory and spatial dependency characteristics of bed-load transport for sediment with different sizes. Second, fine sediment particles exhibit stronger super-diffusive features, while coarse particles exhibit significant subdiffusive properties, likely due to the size-selective memory impact. Third, sediment transport with an instantaneous source exhibits stronger history memory and weaker spatial nonlocality, compared to that with a continuous source (since a smaller number of particles might be blocked or buried relatively easier). Hence, the D-FADE provides a strict computational model to quantify discrete bed-load transport, whose nonlinear dynamics can be sensitive to particle sizes and source injection modes, both common in applications.