58,955 research outputs found
Non-breaking wave effects on buoyant particle distributions
© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in DiBenedetto, M. H. Non-breaking wave effects on buoyant particle distributions. Frontiers in Marine Science, 7, (2020): 148, doi:10.3389/fmars.2020.00148.The dispersal of buoyant particles in the ocean mixed layer is influenced by a variety of physical factors including wind, waves, and turbulence. Microplastics observations are often made at the free surface, which is strongly forced by surface gravity waves. Many studies have used numerical simulations to examine how turbulence and wave effects (e.g., breaking waves, Langmuir circulation) control buoyant particle dispersal at the ocean surface. However these simulations are not wave phase-resolving. Therefore, the effects of an unsteady free surface due to surface gravity waves remain unknown in this context. To address this, we develop an analytical model for the distribution of buoyant particles as a function of wave-phase under wind-wave conditions in deep-water. Using this analytical model and complementary numerical simulations, we quantify the effects of a nonbreaking, monochromatic, progressive wave train on the equilibrium vertical and horizontal distributions of buoyant particles. We find that waves result in non-uniform horizontal distributions of particles with more particles under the wave crests than the troughs. We also find that the waves can stretch or compress the equilibrium vertical distribution. Finally, we consider the effects of waves on the sampling of microplastics with a towed net, and we show that waves have the ability to lower the measured concentrations relative to nets sampling without the influence of waves.This work was supported by the Postdoctoral Scholar Program at the Woods Hole Oceanographic Institution, and by the US National Science Foundation under grant no. CBET-1706586
A public code for general relativistic, polarised radiative transfer around spinning black holes
Ray tracing radiative transfer is a powerful method for comparing theoretical
models of black hole accretion flows and jets with observations. We present a
public code, grtrans, for carrying out such calculations in the Kerr metric,
including the full treatment of polarised radiative transfer and parallel
transport along geodesics. The code is written in Fortran 90 and efficiently
parallelises with OpenMP, and the full code and several components have Python
interfaces. We describe several tests which are used for verifiying the code,
and we compare the results for polarised thin accretion disc and semi-analytic
jet problems with those from the literature as examples of its use. Along the
way, we provide accurate fitting functions for polarised synchrotron emission
and transfer coefficients from thermal and power law distribution functions,
and compare results from numerical integration and quadrature solutions of the
polarised radiative transfer equations. We also show that all transfer
coefficients can play an important role in predicted images and polarisation
maps of the Galactic center black hole, Sgr A*, at submillimetre wavelengths.Comment: 22 pages, 12 figures, submitted to MNRAS. code available at:
github.com/jadexter/grtran
Instability in Shocked Granular Gases
Shocks in granular media, such as vertically oscillated beds, have been shown
to develop instabilities. Similar jet formation has been observed in
explosively dispersed granular media. Our previous work addressed this
instability by performing discrete-particle simulations of inelastic media
undergoing shock compression. By allowing finite dissipation within the shock
wave, instability manifests itself as distinctive high density non-uniformities
and convective rolls within the shock structure. In the present study we have
extended this work to investigate this instability at the continuum level. We
modeled the Euler equations for granular gases with a modified cooling rate to
include an impact velocity threshold necessary for inelastic collisions. Our
results showed a fair agreement between the continuum and discrete-particle
models. Discrepancies, such as higher frequency instabilities in our continuum
results may be attributed to the absence of higher order effects.Comment: 6 pages, prepared for the proceedings of the APS Topical Group on
Shock Compression of Condensed Matter in Seattle, Washington, from July 7th
through July 12th, 201
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