Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session T36: DCOMP & GSNP Prize SymposiumInvited Undergrad Friendly
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Sponsoring Units: GSNP DCOMP Chair: Cynthia Reichhardt, Los Alamos National Laboratory; Talat Rahman, University of Central Florida Room: Room 236 |
Thursday, March 9, 2023 11:30AM - 12:06PM |
T36.00001: Leo P. Kadanoff Prize Winner: Itamar Procaccia Invited Speaker: Itamar Procaccia In this lecture I will review recent work in which we developed a screening theory for describing the effect of plastic events in amorphous solids on their emergent mechanics. The suggested theory uncovered an anomalous mechanical response of amorphous solids where plastic events collectively induce distributed dipoles that are analogous to dislocations in crystalline solids. The theory was tested against various examples of amorphous solids in two- and three dimensions, including frictional and friction-less granular media and numerical models of amorphous glass. It was shown that for generic amorphous solids classical elasticity theory needs to be re-consdiered, to allow for the fundamental changes in mechamical responses, including the appearance of energent scales that modify the theory in a substantial way. We conclude by interpreting the mechanical response as the formation of non-topological distributed dipoles that have no analogue in the crystalline defects literature. Having in mind that the onset of dipole screening is reminiscent of Kosterlitz-Thouless and Hexatic transitions, the finding of dipole screening in three-dimensions is particularly novel. |
Thursday, March 9, 2023 12:06PM - 12:42PM |
T36.00002: GSNP Dissertation Award: Critical Transitions in Turbulence Invited Speaker: Adrian van Kan Turbulence is ubiquitous in the universe, and comprises a wide range of space and time scales. In three dimensions (3D), energy is transferred from large to small scales (direct cascade). In two dimensions (2D), the opposite is true (inverse cascade). Here I present results from direct numerical simulations (DNS) of the Navier-Stokes equations, modelling, asymptotics and methods from statistical physics pertaining to different scenarios where the largest scales in a turbulent flow change their properties abruptly at a critical parameter value. In each case, the physics close to the critical point is characterised in detail. First, rotating turbulence in an elongated domain is studied using an asymptotic expansion, with a single parameter combining layer height and rotation rate. At a critical parameter value, energy begins to be transferred inversely. Density stratification is found to impact the energy cascades nontrivially. The second scenario concerns turbulence in a thin layer of variable depth, forming large-scale vortices (LSV) below a critical height. The flow is studied numerically and a mean field model is proposed, explaining observed scaling laws. The transition to LSVs is shown to be subcritical. Third, a simplified model of 3D perturbations on 2D flow is presented. The model facilitates a stability analysis of LSV at a reduced cost, reproducing intermittent growth in perturbation amplitude recently observed in DNS. The perturbation growth rate fluctuates following a heavy-tailed distribution. The mathematical structure of the model is studied in detail using a Langevin equation with Lévy noise. Finally, exact results on the microcanonical statistical mechanics of truncated 2D Euler flows are presented. By evaluating phase space integrals, we compute the reversal statistics for the largest-scale mode in a square domain with free-slip boundaries. We validate the microcanonical results numerically by using a minimal model, in contrast with the canonical ensemble, which is shown to fail in this example. |
Thursday, March 9, 2023 12:42PM - 1:18PM |
T36.00003: Aneesur Rahman Prize for Computational Physics Winner: Pablo G. DebenedettiA Computational Perspective on the Physics of Supercooled Water Invited Speaker: Pablo G Debenedetti There has been uninterrupted interest in the physics of supercooled water since pioneering experiments by Speedy and Angell [1] first revealed pronounced increases in water’s response functions upon cooling. The preponderance of experimental evidence [2, 3] is consistent with the existence of a metastable critical point at deeply supercooled conditions. This point marks the termination of a locus of metastable liquid-liquid coexistence [4]. Free energy calculations [5], molecular dynamics simulations [6], and a combination of machine learning, computational chemistry, and advanced sampling [7, 8] support the existence of a second critical point in supercooled water, and illustrate the essential role that computer simulations have played in defining the frontiers of knowledge in this area. |
Thursday, March 9, 2023 1:18PM - 1:54PM |
T36.00004: Metropolis Dissertation Award Winner: Nonradiative Transitions at Defects in Solids Invited Speaker: Mark E Turiansky Point defects and impurities in solids provide a means for carriers to recombine nonradiatively, which has important implications for the performance of electronic devices. These nonradiative transitions are driven by the electron-phonon interaction, where excess energy is given to lattice vibrations. First-principles calculations are a powerful tool to assess and predict the impact of defect-mediated nonradiative recombination. I will discuss the development of and recent improvements to the Nonrad code, which implements a first-principles formalism to evaluate the nonradiative transition rate. I will then overview several examples of its application to solve outstanding research problems. In hexagonal boron nitride, single-photon emitters have been observed, which are promising for applications in quantum information science. I will describe how nonradiative transitions can help to rationalize the optical dynamics of these emitters and suggest that the microscopic origin of the emission is a boron dangling bond. Halide perovskite solar cells have achieved remarkable efficiencies, but defect-mediated nonradiative recombination still poses a problem. I will discuss how our studies of nonradiative recombination in the perovskites provide potential routes for improving device efficiency. |
Thursday, March 9, 2023 1:54PM - 2:30PM |
T36.00005: Julius Edgar Lilienfeld Prize Winner: Albert-László BarabásiNetwork Science: From Abstract to Physical Networks Invited Speaker: Albert-Laszlo Barabasi The architecture of a wide range of real systems, from the cell to the brain and communication systems, is best described as networks with complex topologies. Network science has led to the realization that despite the diversity of these systems, the underlying networks emerge and evolve following simple but generic laws, that are best unveiled using the toolset of statistical physics. As a result of these advances, today network science is an indispensable tool from physics to medicine, and its applications, ranging from epidemic control during COVID to medical diagnostic tools affecting patients, directly impact our lives. I will also explore the applications of the network science toolset to physical networks, like the brain or metamaterials, which are networks whose links are physical entities that cannot cross each other. Link physicality affects both the evolution and the structure of a network, in a way that is not captured by current graph-based approaches. Yet, the existence of an exact mapping between physical networks and independent sets allows us to derive the onset of physical effects and the emergence of a jamming transition, demonstrating that physicality impacts the network structure even when the total volume of the links is negligible. |
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