Considering ice-premelting on a quartz rock surface (i.e. silica) we calculate the Lifshitz excess pressures in a four layer system with rock–ice–water–air.

Dispersion forces such as van der Waals forces between two microscopic particles, the Casimir-Polder forces between a particle and a macroscopic object or the Casimir force between two dielectric objects are well studied in vacuum. However, in realistic situations the interacting objects are often embedded in an environmental medium. Such a solvent influences the induced dipole interaction. With the framework of macroscopic quantum electrodynamics, these interactions are mediated via A PREPRINT -JUNE 5, 2019Figure 1: Sketch of the considered setups for the spherical problem and the one dimensional analogon: a) Two particles embedded in a medium creating an Onsager's real cavity with inhomogeneous dielectric profile; b) one-dimensional analogon with planarly inhomogeneous profile; c) Two spherical nano-particles embedded in a medium with an inhomogeneous cavity; d) the corresponding one-dimensional problem with two dielectric plates of finite thickness embedded in a medium with inhomogeneous profile.an exchange of virtual photons. Via this method the impact of a homogeneous solvent medium can be expressed as local-field corrections leading to excess polarisabilities which have previously been derived for hard boundary conditions. In order to develop a more realistic description, we investigate on a one-dimensional analog system illustrating the influence of a continuous dielectric profile.

In the study of dispersion forces, nonretarded, retarded and thermal asymptotes with their distinct scaling laws are regarded as cornerstone results governing interactions at different separations. Here, we show that when particles interact in a medium, the influence of retardation is qualitatively different, making it necessary to consider the non-monotonous potential in full. We discuss different regimes for several cases and find an anomalous behaviour of the retarded asymptote. It can change sign, and lead to a trapping potential.

Abstract. We devise an optimised bi-component multi-layered dielectric stack design to enhance the local irradiance for efficient photovoltaic upconversion materials. The field intensity profile throughout the photonic structure is numerically optimized by appropriate tuning of the individual layers' thicknesses. The optimality of the thus inferred structure is demonstrated by comparison with an analytically derived upper bound. The optimized local irradiance is found to increase exponentially with the number of layers, its rate determined by the permittivity ratio of the two material components. Manufacturing errors which induce deviations from the optimised design are accounted for statistically, and set a finite limit to the achievable enhancement. Notwithstanding, realistic assumptions on manufacturing errors still suggest achievable irradiances which are significantly larger than those obtained with the recently proposed Bragg stack structures.

This paper describes a numerical wall function method for RANS simulations of isothermal incompressible flows with separation and reattachment using an unstructured flow solver. The method is studied for the Spalart-Allmaras one-equation model and is implemented in OpenFOAM . For each wall node, a one-dimensional boundary-layer problem is integrated numerically on an embedded sub-grid in the near-wall region. The method is applied to the flow over a backward facing step, over a smoothly contoured ramp and over a NACA4412 airfoil to show the improvement of the results compared to universal wall functions.