Bulletin of the American Physical Society
APS March Meeting 2021
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session A16: Control of Noisy NonLinear Dynamical SystemsFocus Live

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Sponsoring Units: GSNP DBIO Chair: Uwe Tauber, Virginia Tech 
Monday, March 15, 2021 8:00AM  8:12AM Live 
A16.00001: Curvaturemediated feedback leads to turbulence of growing interfaces Laeschkir Würthner, Erwin Frey The cytoplasmic membrane of cells is a complex object which dynamically undergoes shape transitions during many cellular processes. One important aspect is the generation and maintenance of curvature, which defines the morphology of cells. Recently, it has been shown that cytoskeletal motor proteins induce membrane deformations via highly cooperative interactions between motor proteins and lipids which depend on membrane morphology [1]. Motivated by this work, we have studied the dynamics of a growing interface driven by the local density of membrane proteins. A key feature of our model is a coupling between interface morphology and attachment kinetics of proteins. For the deterministic case, we find that morphological coupling results in chaotic dynamics, reminiscent of the KuramotoShivashinsky equation. The emergence of chaos is quantitatively confirmed by numerically determining the spectrum of Lyapunov exponents. We find that our model is similar to the KPZ model with nonuniform growth velocity along the interface. Our results further show that the growth kinetics do not fall into the KPZ universality class. 
Monday, March 15, 2021 8:12AM  8:24AM Live 
A16.00002: Phase Diagram and Interfacial Instabilities in the Driven WidomRowlinson Lattice Gas Ronald Dickman, Royce Zia, Maxim Lavrentovich, Hugues Chate The WidomRowlinson lattice gas is a twospecies model exhibiting phase 
Monday, March 15, 2021 8:24AM  8:36AM Live 
A16.00003: Microemulsions in the driven WidomRowlinson lattice gas Maxim Lavrentovich, Ronald Dickman, Royce Zia The driven WidomRowlinson lattice gas exhibits a remarkable nonequilibrium steady state in which uniform stripes form perpendicular to the drive direction. We study this model at low particle densities in two and threedimensions, where we find a disordered phase with a characteristic length scale (similar to a “microemulsion”). We develop a continuum theory of this disordered phase and derive a coarsegrained fieldtheoretic action for the nonequilibrium dynamics, making predictions for the dynamic structure factors. The system may be described via two coupled fields, a "charge" and overall particle density field, which have structure factors with different characteristic velocities, generated by an interplay between the nearest neighbor exclusion rule and the drive. We then show how fluctuation corrections may generate the "microemulsion" phase and speculate on the origin of a characteristic linear cusp in the static structure factor. This work lays the foundation for understanding the stripe phenomenon more generally and points toward a new kind of nonequilibrium patternforming phase transition. 
Monday, March 15, 2021 8:36AM  8:48AM Live 
A16.00004: Strong current response to slow modulation: A metabolic casestudy Danilo Forastiere, Gianmaria Falasco, Massimiliano Esposito We study 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, modeled by a periodic modulation of the product concentration. We find that the system exhibits a strong nonlinear response to small driving frequencies both for the mean timeaveraged current and for the fluctuations. For the first, we obtain an analytic formula by coarsegraining the original model to a solvable one. The result is nonperturbative in the modulation amplitude and frequency. We then refine the picture by studying the stochastic dynamics of the full system using a large deviation approach that allows us to show the resonant effect at the level of the timeaveraged variance and signaltonoise ratio. Finally, we discuss how this nonequilibrium effect may play a role in metabolic and synthetic networks. 
Monday, March 15, 2021 8:48AM  9:00AM Live 
A16.00005: Controlling the velocity of DNA base in nanopores using flossing Jyoti Mahalik, Murugappan Muthukumar One of the challenging problems associated with the ionic current based DNA sequencing methods is the control of DNA base motion inside nanopores. For accurate base calling, the velocity of the DNA base inside the nanopore needs to be slow enough to be detected and the fluctuations associated with its motion needs to be small. We propose a DNA flossing technique for controlling the DNA base motion inside the nanopore and we demonstrate this using Langevin dynamics simulation. In this proposed technique, the single stranded DNA is covalently linked to symmetric flexible polycations at both ends. Such a chain can be captured by the nanopore using high bias. Once captured, the DNA is electrophoretically moved back and forth indefinite number of times. Using square wave alternating voltage the velocity of the DNA base is demonstrated to slow down by an order of magnitude at high frequencies of the alternating voltage. By varying the polycation length, magnitude and frequency of the applied alternating voltage, individual DNA base motion has been monitored while translocating through the nanopore. DNA base dynamics inside the nanopore as a function of these parameters helps us to understand the physics and practicality of flossing technique for genome sequencing applications. 
Monday, March 15, 2021 9:00AM  9:12AM 
A16.00006: Combining Statistical Thermodynamics, Control Theory and Reinforement Learning to Predict Regulation and Posttranslational Control of Metabolism Samuel Britton, William Cannon, Mark Alber Metabolic regulation is mostly known only for wellstudied reactions of central metabolism in model organisms. We use two approaches to predict enzyme regulation policies and investigate the hypothesis that regulation is driven by the need to maintain the solvent capacity in the cell. The first predictive method uses a statistical thermodynamics and metabolic control theory framework while the second method is performed using a hybrid optimization–reinforcement learning approach. As previously hypothesized, regulation is herein shown to control the concentrations of both immediate and downstream product concentrations at physiological levels. Model predictions provide the following two novel general principles: (1) the regulation itself causes the reactions to be much further from equilibrium instead of the common assumption that highly nonequilibrium reactions are the targets for regulation; and (2) the minimal regulation needed to maintain metabolite levels at physiological concentrations maximizes the free energy dissipation rate instead of preserving a specific energy charge. The resulting energy dissipation rate is an emergent property of regulation which may be represented by a high value of the adenylate energy charge. 
Monday, March 15, 2021 9:12AM  9:24AM Live 
A16.00007: No synchronization for coupled oscillators on smallworld networks Kevin Liu Rodrigues, Ronald Dickman The synchronization of oscillators is seen in many different systems, such as fireflies and cold atom clouds. Nonetheless, there's a limit on how simple a model can be and still be capable of synchronizing. In most models, an oscillator requires at least three levels (or phase values) in order to display a synchronized solution. Therefore, much of the fundamental investigations around synchronization have been performed on such threestate models due to their relative simplicity (as opposed to continuous or models with many phase values). In this work, we show that one such model may fail to achieve synchronization even when the dynamics occur on networks with nonlocal coupling and even longrange interactions. Failure to synchronize happens through a longlived metastable traveling wave solution and is dependent on initial conditions and fluctuations. 
Monday, March 15, 2021 9:24AM  9:36AM Live 
A16.00008: Recent Advances in the Understanding of Dynamic Phase Transitions in Ferromagnetic Thin Films Mikel Quintana, Juan Marcos Marín Ramírez, Andreas Berger The magnetization dynamics of ferromagnetic thin films can exhibit abrupt changes in its trajectory if one alters the period P or amplitude H_{0} of the dynamics generating external magnetic field. Such changes impact the period averaged magnetization vector Q, which is the dynamic order parameter, and its behavior can be explored by means of nonequilibrium phase diagrams. The fundamental behavior of Q exhibits significant similarities with the equilibrium phase properties of ferromagnets, which makes its understanding crucially relevant in the field of nonequilibrium physics [1]. Only recent progress in magnetooptical Kerr effect detection have allowed for detailed experimental explorations of the complete dynamic phase space. Here, we present some of our most recent experimental results, specifically related to our studies of the vector nature of Q in thin films with uniaxial anisotropy, as well as work on the general definition of the conjugate field of Q. 
Monday, March 15, 2021 9:36AM  9:48AM Live 
A16.00009: BarrierControlled NonEquilibrium Criticality in Random Organization Qunli Lei, Hao Hu, Ran Ni Random organization is a generic phenomenon found in many nonequilibrium systems, while the mechanism of the nonequilibrium criticality in these systems remains elusive. Here, by using computer simulation and theoretical analysis, we study the role of activation barrier on the criticality of nonequilibrium phase transitions in a randomorganizing hardsphere model. We find that at zero thermal noise, with increasing the activation barrier, the type of transition changes from a continuous conserved directed percolation into a discontinuous dynamic transition by crossing a tricritical point. A meanfield theory is proposed to explain this phenomenon, which suggests that the transition at finite thermal noise belongs to the Ising universality. Moreover, we obtain the tricritical exponents in the system which quantitatively agree with field theory simulations. This mechanism of the barriercontrolled criticality has many implications in dynamics of amorphous materials, chemical reactions and epidemic spreading. 
Monday, March 15, 2021 9:48AM  10:24AM Live 
A16.00010: Control of the surface roughness during a growth process described by the KardarParisiZhang equation Invited Speaker: Priyanka Priyanka Control theory is a widely used tool in engineering to develop controlled, stable models of dynamical systems. The control of deterministic models has been extensively studied; however, investigations of the control of nonequilibrium systems are less explored due to combined nonlinearity and noise. I will focus on understanding the effect of both linear and nonlinear control processes on the intrinsic dynamics and stationary properties of nonequilibrium systems. In particular, I will discuss how to achieve the saturation of the mean surface roughness to a prescribed value in a stochastic growth process described by the (1+1)dimensional KardarParisiZhang (KPZ) equation, by means of a nonlinear feedback control scheme that manipulates a subset of Fourier modes. The control process limits the time and length scales within which the system behaves according to its intrinsic stochastic dynamics. These time and length scales show scaling behavior with the control parameter, and the associated scaling exponents are related to those of the unperturbed KPZ model. 
Monday, March 15, 2021 10:24AM  10:36AM Live 
A16.00011: Ensemble reservoir equivalence in driven lattice gases Leonardo Calazans, Ronald Dickman For stochastic lattice models in spatially uniform nonequilibrium steady states (NESS), temperature and chemical potential can be defined via coexistence with heat and particle reservoirs. We consider NESS in the driven lattice gas with nearestneighbor exclusion. In weak contact with a particle reservoir, it attains a NESS with a fluctuating particle number, analogous to the grand canonical ensemble in equilibrium. Are the properties of this NESS equivalent to those found with fixed particle number? We report numerical evidence for such an ensemble equivalence between NESS in the limit of large system sizes. Additionally, we ask if the macroscopic properties depend on the nature of the exchange between system and reservoir. For example, although the stochastic interaction between system and reservoir usually involves exchange of a single particle, one may also consider a reservoir that inserts or removes pairs of particles. In equilibrium, equivalence of pair and singleparticle reservoirs is guaranteed by the canonical form of the probability distribution on configuration space. We find that out of equilibrium, this equivalence no longer holds. 
Monday, March 15, 2021 10:36AM  10:48AM Live 
A16.00012: Dynamical Transitions in Aperiodically Kicked Tight Binding Models Vikram Ravindranath, Santhanam M. S. Generally, upon the introduction of noise, coherence in a quantum system is quickly lost and the dynamics of a localised state becomes diffusive. However, we have found that the AubryAndréHarper model, a tightbinding model with kicked, quasiperiodic onsite disorder is robust to the effects of noise in the periodicity and amplitude of the kick. Moreover, under a protocol which delivers kicks at random intervals, we have been able to engineer a sharp, dynamical, ballistictodiffusive transition, with the break time decided by the characteristics of the noise. Such behaviour even takes place for translationally invariant systems. Considering a 2band model, we have found that this behaviour is related to the existence of flat bands, and the mechanism for asymptotic diffusion is similar to that of a classical random walk. 
Monday, March 15, 2021 10:48AM  11:00AM Live 
A16.00013: Fieldtheoretic approach to study a class of reactiondiffusion models Prashant Sharma We present a fieldtheoretic derivation of a class of models of reactiondiffusion systems of which the GrayScott model is a special case. Numerical studies of some of these models have shown the phenomena of self replicating spots and stripes [1,2]. More recently, a fieldtheoretic approach was used to study the noise driven phase transitions in GrayScott model. [3] We use our field theory approach to analytically study the dynamics of the spots for a general class of models and compare analytics with numerical results. 
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