Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session F24: NoiseDriven Dynamics in FarFromEquilibrium Systems IFocus

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Sponsoring Units: GSNP DBIO Chair: Stephen Teitsworth, Duke University Room: 401 
Tuesday, March 3, 2020 8:00AM  8:36AM 
F24.00001: Climate variability: a manifestation of fluctuations in a nonequilibrium steady state Invited Speaker: Jeffrey B. Weiss The climate system is forced by incoming solar radiation, is damped by outgoing longwave radiation, and is, apart from timedependent natural and anthropogenic forcing, approximately in a nonequilibrium steady state. The natural variability about the timemean climate state takes the form of coherent, preferred, spatiotemporal patterns with names such as the ElNiño Southern Oscillation, the MaddenJulien Oscillation, the Atlantic Multidecadal Oscillation, and the Pacific Decadal Oscillation. These climate oscillations have large human impacts and their response to anthropogenic climate change is uncertain. Nonequilibrium steady states can be characterized by persistent currents in phase space and we interpret climate oscillations as the physical space manifestation of those phase space currents. We describe a new diagnostic for phase space currents, the phase space angular momentum, which describes the rotational flow of trajectories in phase space by analogy to the mass angular momentum of a fluid rotating in physical space. One advantage of the phase space angular momentum is that it can be readily calculated from an observed time series with no assumptions about an underlying model. We find that the phase space angular momenta in simple stochastic models of the ElNiño Southern Oscillation and the MaddenJulien Oscillation agree surprisingly well with that seen in observations of the climate system. We propose that the phase space angular momentum might be a useful general metric to describe fluctuations in nonequilibrium steady states. 
Tuesday, March 3, 2020 8:36AM  8:48AM 
F24.00002: Critical Dynamics of Anisotropic Antiferromagnets in an External Field Uwe Claus Tauber, Riya Nandi We numerically investigate the nonequilibrium critical dynamics in threedimensionalanisotropic antiferromagnetsin the presence of an external magnetic field. The phase space of this system exhibits two critical lines which meet at a bicritical point. In this system, the nonconserved components of staggered magnetization order parameter couple dynamically to the conserved component of the magnetization density along the direction of the external field. By employing a hybrid computational algorithm that combines reversible spin precession with relaxational Monte Carlo updates, we study the aging scaling dynamics for the model C critical line, identifying the critical initial slip, decay and aging collapse exponents, thus also verifying the dynamic critical exponent. We also probe the dynamic exponent of the model F critical line by investigating the systemsize dependence of the characteristic spin wave frequencies near criticality. Furthermore, we investigate the aging scaling behavior of the slow order parameter and conserved field near the bicritical point. 
Tuesday, March 3, 2020 8:48AM  9:00AM 
F24.00003: Current fluctuations in presence of timeperiodic metabolic conditions Danilo Forastiere, Gianmaria Falasco, Massimiliano Esposito We address the current response to periodic driving of a crucial biochemical reaction network, namely, substrate inhibition. We focus on the conversion rate of substrate into product under timevarying metabolic conditions, modelled by a periodic modulation of the product concentration. Coarsegraining the original model to a minimal solvable one by means of a projection technique, we study the leading behavior of the time averaged current and its fluctuations using a large deviations approach. We show that there exist different regimes, depending on the kinetic rates, in which positive and negative amplitude resonant effects take place, and we provide interpretations for the role that these nonequilibrium effects can play in the metabolic network. 
Tuesday, March 3, 2020 9:00AM  9:12AM 
F24.00004: Large scale kinetic modeling of metabolic networks YongCong CHEN, Xiaomei Zhu, Ping Ao, Minjuan Xu Problems: 
Tuesday, March 3, 2020 9:12AM  9:24AM 
F24.00005: Temperature interfaces in the KatzLebowitzSpohn driven lattice gas Ruslan Mukhamadiarov, Priyanka ., Uwe Claus Tauber We explore the intriguing spatial patterns that emerge in a twotemperature KatzLebowitzSpohn (KLS) model in two dimensions, a driven lattice gas with attractive nearestneighbor interactions and periodic boundary conditions.The domain is split into two regions with hopping rates governed by different temperatures T > Tc and Tc, respectively, where Tc indicates the critical temperature for phase ordering. When the temperature boundaries are oriented transverse to the drive, the hotter region experiences an unexpected phase separation caused by the lower sustained current in the cooler region. The resulting density profiles in both hot and cold subsystems are similar to the wellcharacterized coexistence and maximalcurrent phases in (T)ASEP models with open boundary conditions, yet display marked fluctuation corrections. In contrast, when the temperature boundaries are oriented along the drive, the KLS dynamics is crucially determined by the choice of hopping rates across the temperature interfaces. In particular, when the latter break particlehole symmetry, we observe particle influx from the cooler into the hotter region. 
Tuesday, March 3, 2020 9:24AM  9:36AM 
F24.00006: Anomalous heating in a colloidal system: Observation of the inverse Mpemba effect Avinash Kumar, John Bechhoefer We present the first experimental observation of anomalous heating in colloidal systems, a phenomenon known as the inverse Mpemba effect. In particular, under certain conditions, we observe that an initially cold system heats up faster than an identical warm system when coupled to the same thermal bath. We study the effect in a system consisting of a Brownian particle in a tilted doublewell potential set in an asymmetric domain. We also study the forward Mpemba effect, where an initially hot system cools faster than an identical warm system. We observe the forward effect for a wide range of temperatures and domain sizes (region in space explored by the particle). By controlling the relative sizes of the basins of attraction of the stable and metastable potential wells, we can provide a direct kinetic path between the hot initial state and the cold equilibrium. We then observe exponentially faster cooling. This is the first experimental evidence for the strong Mpemba effect. 
Tuesday, March 3, 2020 9:36AM  9:48AM 
F24.00007: Decomposition of anomalous diffusion in generalized Lévy walks into its constitutive effects Vidushi Adlakha, Philipp G. Meyer, Erez Aghion, Holger Kantz, Kevin E. Bassler Anomalous diffusion is observed in a variety of physical and social systems, including blinking quantum dots, animal locomotion, intraday trades in financial markets and cold atoms in dissipative optical lattices. Generalized Lévy walks can be used to model their dynamics. We show that the anomalous diffusive behavior found in these systems can be decomposed into three fundamental constitutive causes. These causes, or effects, are related to ways that the Central Limit Theorem fails. The increments generated through the stochastic process can have either longtime correlations, infinite variance, or be nonstationary. Each of these properties can cause anomalous diffusion and is characterized by what is known as the Joseph, Noah and Moses effects, respectively. In generalized Lévy walks, a complex combination of these effects leads to the observed sub and superdiffusive behaviors. We analytically calculate the scaling exponents determining each of the three constitutive effects and confirm the results with numerical simulations. The results satisfy a fundamental scaling relation between the exponents. 
Tuesday, March 3, 2020 9:48AM  10:00AM 
F24.00008: A coupled twospecies model for the pair contact process with diffusion Shengfeng Deng, Uwe Claus Tauber The contact process with diffusion (PCPD) defined by the pair reactions 2B→3B, 2B→0 and diffusive particle spreading exhibits an unusual active to absorbing phase transition whose universality class has long been disputed. Multiple studies indicated that further coarsegraining of the model may be needed for its effective longtime, largescale description. We introduce a coarsegrained twospecies representation for the PCPD in which single particles B and particle pairs A are coupled according to the processes 2B→A, A→A+B, A→0, A→2B, with each type of particles diffusing independently. We employ Monte Carlo simulations in one, two, and three dimensions to demonstrate that this model consistently captures the pertinent features of the PCPD. In the inactive phase, A particles die out rapidly, effectively leaving the B species to undergo pure pair annihilation kinetics. At criticality, both A and B densities decay with similar exponents to those measured for the PCPD and display meanfield scaling above the critical dimension d_{c}=2. In one dimension, exponents for the B species obtained from seed simulations also agree well with previously reported ranges. 
Tuesday, March 3, 2020 10:00AM  10:12AM 
F24.00009: Anomalous Diffusion with an Absorbing Wall Alex Warhover, Thomas Vojta Fractional Brownian Motion and the Fractional Langevin Equation, random processes characterized by longtime power law correlations in the noise, are prototypical models for anomalous diffusion. We employ large scale Monte Carlo simulations to investigate these models in the presence of an absorbing wall. In the limit of vanishing correlations, our findings reproduce the wellknown results for normal diffusion. In contrast, the interplay between the absorbing wall and the longrange power correlations leads to a singular probability density close to the wall. We compare our results to those of Fractional Brownian Motion [1] as well as the Fractional Langevin Equation [2] in the presence of a reflecting wall, and we discuss implications of our results. 
Tuesday, March 3, 2020 10:12AM  10:24AM 
F24.00010: Diffusion in dynamic crowded spaces David Yllanes, Harry Bendekgey, Greg Huber, Le Yan Brownian motion in disordered media is now well understood in the case of immobile hard obstacles. In many practical applications, however, the space itself can be dynamic. An important example is transport inside the cell, a very crowded environment with obstacles of varying sizes and complicated shapes that are constantly being rearranged. This situation has received comparatively little attention. With the everincreasing quality of microscopy techniques, allowing for the tracking of particles inside living cells, the need for a quantitative model is clear. 
Tuesday, March 3, 2020 10:24AM  10:36AM 
F24.00011: Trajectories and transport characteristics of a Brownian particle in a 1D potential subject to bias. Trey Jiron, Jarrod Schiffbauer We investigate onedimensional driven, diffusive motion of a single Brownian particle moving through a periodic lattice potential and subject to a constant, uniform bias using a Langevin equation of motion. The model yields explicit trajectories with biasdependent trapping, hopping, and linear response regimes at sufficiently low temperatures and the statistical behavior generated by an ensemble of trajectories are essentially those of an asymmetric simple exclusion process. Moreover, we find that, at low bias, the system exhibits a negative differential mobility, decreasing with applied bias, to a distinct local minimum in the hopping transport regime. In the context of the dynamical model, we argue the nonmonotonic behavior of the transport coefficient can be explained by the role of friction as the particle passes through the minima in each well. Such a model may be employed to describe a wide variety of intriguing transport behaviors. As an example, we show that experimental data on the transition from static to kinetic friction through a plastic regime can be described by such a model. 
Tuesday, March 3, 2020 10:36AM  10:48AM 
F24.00012: Fluctuation theorem for geometric pumping processes Hisao Hayakawa We derive an extended fluctuation theorem for an open quantum system coupled with two reservoirs under onecycle modulation. We confirm that the geometric phase caused by the BerrySintisynNemenman curvature in the parameter space generates nonGaussian fluctuations. This nonGaussianity is enhanced for the instantaneous fluctuation relation when the bias between the two reservoirs disappears. 
Tuesday, March 3, 2020 10:48AM  11:00AM 
F24.00013: Stochastic Line Integrals as Metrics of Irreversibility and Heat Transfer Stephen Teitsworth, John Neu Stochastic line integrals provide a powerful tool for quantitatively characterizing irreversibility and detailed balance violation in noisedriven dynamical systems. A particular realization of such integrals, the stochastic area, was recently introduced for linear systems and has been tested experimentally in coupled linear electrical circuits [1,2]. In this talk, we provide a framework for understanding general properties of stochastic line integrals and clarify their implementation for experiments and simulations as well as their utility as metrics for quantifying nonequilibrium behavior. Theoretical results are supported by numerical studies of an overdamped, twodimensional massspring system driven out of equilibrium. In this case, the stochastic area can be concisely expressed in terms of a streamfunction the sign of which determines the orientation of probability current loops. Furthermore, the stream function allows one to analytically understand the dependence of stochastic area on key parameters such as the noise strength (equivalently temperature) for both nonlinear and linear springs. 
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