Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session Y62: Interfaces and Mixing - Non-equilibrium Transport Across the ScalesInvited
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Sponsoring Units: DCMP Chair: Snezhana Abarzhi, Univ of Western Australia Room: BCEC 258C |
Friday, March 8, 2019 11:15AM - 11:51AM |
Y62.00001: First Principles Based Multiscale Atomistic Methods for Non-Equilibrium Transport Across Interfaces Invited Speaker: William Goddard This symposium is focused on Non-equilibrium transport and mixing across interfaces, with papers describing non-equilibrium coupling of transport at interfaces, including mesoscopic and macroscopic dynamics in fluids, plasmas, and other materials over scales from microns to celestial. Most such descriptions deal with the materials in terms of density and equations of state rather than specific atomistic structures and chemical processes. At interfacial boundaries, such atomistic information can be quite relevant, but it is not yet practical to couple phenomena at celestial scales with the atomistic descriptions of chemistry. The starting point for including such information is quantum mechanics (QM). But practical QM calculations are limited to 100’s of atoms for 10’s of picoseconds, far from the scales required to properly inform the continuum level about the atomistics. To bridge this enormous gap, we are developing practical methods to extend the scale of the atomistic simulation by several orders of magnitude while retaining QM accuracy for describing chemical processes. These developments are aimed toward including the relevant chemistry for systems with millions of atoms. We will describe the progress in accomplishing these extensions of first-principles-based atomistic simulations to larger scales while dramatically decreasing computational efforts. |
Friday, March 8, 2019 11:51AM - 12:27PM |
Y62.00002: Interface dynamics: New mechanisms of stabilization and destabilization and structure of flow fields Invited Speaker: Snezhana Abarzhi Interfacial mixing and transport are nonequilibrium processes coupling kinetic to macroscopic scales. They occur in fluids, |
Friday, March 8, 2019 12:27PM - 1:03PM |
Y62.00003: Nanoscale view of assisted ion transport through the liquid-liquid interface Invited Speaker: Mark Schlossman During solvent extraction, amphiphilic extractants assist the transport of metal ions across the liquid–liquid interface between an aqueous ionic solution and an organic solvent. Investigations of the role of the interface in ion transport challenge our ability to probe fast molecular processes at liquid–liquid interfaces on nanometer-length scales. Recent development of a thermal switch for solvent extraction has addressed this challenge, which has led to the characterization by X-ray surface scattering of interfacial intermediate states in the extraction process. We find that trivalent rare earth ions, Y(III) and Er(III), combine with bis(hexadecyl) phosphoric acid (DHDP) extractants to form inverted bilayer structures at the interface; these appear to be condensed phases of small ion–extractant complexes. The stability of this unconventional interfacial structure is verified by molecular dynamics simulations. The ion–extractant complexes at the interface are an intermediate state in the extraction process, characterizing the moment at which ions have been transported across the aqueous–organic interface, but have not yet been dispersed in the organic phase. In contrast, divalent Sr(II) forms an ion–extractant complex with DHDP that leaves it exposed to the water phase; this result implies that a second process that transports Sr(II) across the interface has yet to be observed. Calculations demonstrate that the budding of reverse micelles formed from interfacial Sr(II) ion–extractant complexes could transport Sr(II) across the interface. Our results suggest a connection between the observed interfacial structures and the extraction mechanism, which ultimately affects the extraction selectivity and kinetics. |
Friday, March 8, 2019 1:03PM - 1:39PM |
Y62.00004: Spiky Electric and Magnetic Field Structures in Flux Rope Experiments Invited Speaker: Walter Gekelman Magnetic flux ropes are bundles of twisted magnetic fields and their associated currents. They are common on the surface of the sun (and presumably all other stars) and are observed to have a large range of sizes and lifetimes. One or more flux ropes are routinely generated in the Large Plasma Device at UCLA. The ropes are kink unstable and when they collide fully 3D magnetic reconnection occurs. The time dependent magnetic field, plasma flow, electron temperature, plasma density, and the space charge and inductive electric fields were measured at over 42,000 spatial positions throughout the plasma volume over several million rope collisions. Magnetic field lines are followed and used to derive quasi-seperatrix layers, locations where reconnection occurs. The complete data set was used to evaluate all the terms in Ohm’s law, which resulted in unphysical plasma resistivity. It was then determined that in this situation Ohm’s law is non-local. The resistively was properly evaluated using the fluctuation dissipation theorem (Kubo resistivity). Time domain structures (TDS) , sharp pulses in potential and magnetic field are generated during reconnection events and subsequent move from the reconnection region into the rope currents. The probability distribution function of the spike amplitudes is log-normal, the same as the fold of crumpled paper. A amplitude counting method is used to create a vector map of the magnetic field of the spikes. TDS observed by satellites are ubiquitous in the plasma surrounding the earth. |
Friday, March 8, 2019 1:39PM - 2:15PM |
Y62.00005: Subdiffusive and superdiffusive transport in plane steady viscous flows Invited Speaker: Alexander Nepomnyashchy Dispersion of particles in chaotic, turbulent or random flows has been studied for a long time. It is known that the action of advection on large spatial and temporal sales typically can be described as an (anisotropic) normal diffusion process. However, as found by Kraichnan in 1970, that is not the case for steady two-dimensional flows of incompressible viscous fluids. We show that the deterministic transport of particles through lattices of solid bodies or arrays of steady vortices can be anomalous. Motion along regular patterns of streamlines is typically aperiodic. Repeated slow passages near stagnation points and/or solid surfaces serve for eventual decorrelation. Singularities of passage times near the obstacles, determined by the boundary conditions, affect the character of transport anomalies. Flows past regular arrays of vorticies are subdiffusive; the temporal evolution of MSD displays some nontrivial similarity properties. Tracers advected through lattices of solid obstacles can feature superdiffusion. The particle transport in spatially irregular flows is also considered. The analytical predictions match the results of numerical simulations. |
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