Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session F08: Patterns and FlowsRecordings Available

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Sponsoring Units: GSNP Chair: Ming Han, University of Chicago Room: McCormick Place W179B 
Tuesday, March 15, 2022 8:00AM  8:12AM 
F08.00001: Probing rare events in emergent reaction diffusion processes Schuyler B Nicholson Chemical and Biological systems utilize complex chemistry to generate patterns and perform computations. Patterns often form away from equilibrium at system sizes where fluctuations are correlated and dominate dynamics, but not yet near the macroscopic limit. This intermediate far from equilibrium regime leads to order and structures not accessible at equilibrium. While we possess a strong understanding of Biological architecture, (eg. at the cellular level) it is the chemistry of reactiondiffusion that ultimately implements and builds order and structure. The lack of synthetic systems that rival biology illustrates how we still have far to go towards understanding emergence of patterns and information processing in reactiondiffusion dynamics. Tensor networks have allowed manybody quantum systems to be studied at system sizes and in detail that exceeds previous methods. In this talk we will show how adapting Tensor networks to classical reactiondiffusion processes yields access to timedependent joint distributions at system sizes that rival those of kinetic MonteCarlo schemes such as the Gillespie algorithm but with high fidelity statistics. These statistics will be used to quantify rare events. 
Tuesday, March 15, 2022 8:12AM  8:24AM 
F08.00002: A Unified Theoretical Framework for Describing Diffusion Andrew B Li, Andrew B Li, Leonid Miroshnik, Brian D Rummel, Ganesh Balakrishnan, Sang M Han, Talid Sinno We propose a unified theoretical framework for describing diffusion that naturally incorporates free energy (e.g., Gibbs free energy) and phase diagram information to generate a selfconsistent free energy functional. We establish the general conditions for the CahnHilliard free energy/approximation to hold, and recover the CahnHilliard equations rigorously in the regular solution limit. By studying binary interdiffusion processes, we demonstrate novel predictions near a tricritical point and discuss how the CahnHilliard model and the new theory predictions diverge in their predictions of spinodal decomposition and nucleation. Based on this theory, we discuss a new physical interpretation of the CahnHilliard gradient energy term and how the standard interpretation can break down. We further consider the applications of this theory with respect to semiconductor interdiffusion, demonstrating how an interplay between selfdiffusivity and chemical potential can amplify the driving force due to gradient contributions, which is relevant in the thermal annealing of nanoscopic semiconductor devices exhibiting sharp compositional interfaces. 
Tuesday, March 15, 2022 8:24AM  8:36AM 
F08.00003: Checkerboard phase dynamics in the parallel update Manna model Buming Guo, Stefano Martiniani, Paul M Chaikin We find a novel checkerboard phase of a parallel update Manna sandpile model with a conserved number of particles on square lattice. At high densities above the absorbingactive transition, instead of seeing a randomly diffusive active phase with the conventional random sequential update, the system spontaneously separates into two sets of alternating checkerboard phases when following the parallel update rule. We explore a variety of the checkerboard phase phenomena including the Model Alike coarsening dynamics, densitydependent domain wall thickness, and nucleationlike behavior at higher density. A meanfield description is also proposed to capture the properties of this discrete checkerboard Manna model. 
Tuesday, March 15, 2022 8:36AM  8:48AM 
F08.00004: Tempered Fractional Brownian Motion on Finite Intervals Zachary Miller A Miller Diffusive transport in many complex systems features a crossover between anomalous diffusion at short times and normal diffusion at long times. This behavior can be mathematically modeled by cutting off (tempering) beyond a mesoscopic correlation time the powerlaw correlations between the increments of fractional Brownian motion. Here, we have investigated tempered fractional Brownian motion confined to a finite interval by reflecting walls. Specifically, we have explored how the tempering of the longtime correlations affects the strong accumulation and depletion of particles near reflecting boundaries recently discovered for untempered fractional Brownian motion. We have found that exponential tempering introduces a characteristic size for the accumulation and depletion zones but does not affect the functional form of the probability density close to the wall. In contrast, powerlaw tempering leads to more complex behavior that differs between the superdiffusive and subdiffusive cases. 
Tuesday, March 15, 2022 8:48AM  9:00AM 
F08.00005: Continuous modeling of discontinuities in anisotropic rods Tian Yu, Francesco Marmo, Sigrid Adriaenssens Slender structures with kinks and creases are ubiquitous in engineering applications such as frames, origami, and stretchable electronics. Due to the discontinuity of local tangent, modeling the mechanics of creased structures often requires cutting the folds and including specific boundary conditions. This work presents a continuous description of discontinuities in anisotropic rods using the distributed Heavisidelike function. We first apply this framework to study the folding and bistable behaviors of creased annular strips and polygonal frames (C^0 continuity), with their stability determined by the classical conjugate point test. Experiments confirmed these stable configurations predicted by our framework. Then we study the large deformation and postbuckling of a serpentine rod (C^1 continuity). The predictions unveil rich bifurcations and stable branches that are also observed in tabletop models. Both examples demonstrated the efficiency and convenience of this novel framework, which could facilitate the mechanical design of rods/stripsbased deployable systems and morphable robots. 
Tuesday, March 15, 2022 9:00AM  9:12AM 
F08.00006: Wave Buckling of Thin Plates Under Nonuniform Inplane Loading Hyunsu kwak, Kanghyun Ki, Junsik Kim, Anna Lee Wave buckling of plates is ubiquitous in nature and our daily lives, such as leaves of plants having rippled edges, wetted paper, and wrinkles in human skin. Here, we combine a theory, finite element simulations, and experiments to analyze the relationship between the nonuniform stress distribution and the shape of wave buckling. First, we develop a theoretical model that predicts the formation of wave buckling based on the strain energy method of RitzGalerkin. Then, finite element analyses are conducted to validate theoretical results in good agreement for various inplane loading conditions. Experiments examine how a thin elastomeric strip undergoes buckling instability when nonuniform stress is induced by swelling due to the diffusion of silicone oil. We measure timedependent amplitude and wavelength of wave buckling and find good agreement with theoretical results. Finally, we conduct parametric exploration and find that the normalized amplitude and wavelength are governed by the aspect ratio of plates and the ratio of maximum compressive stress to the elastic modulus. 
Tuesday, March 15, 2022 9:12AM  9:24AM 
F08.00007: Crumple dynamics of localized elastic excitations: interactions, patterns, and mediation of global deformation Robert S Hutton, Eduardo Vitral, Sam Riddle, Tian Yu, Eugenio Hamm, James Hanna We report a variety of elastic localization phenomena in experiments on bent sheets, with aspect ratio ranging from narrow strips to long plates, subject to lateral displacements that induce hysteretic and multistable buckling. Snapthrough is mediated by the appearance and propagation of "dcone"esque localized regions of high elastic energy; one might be tempted to call these "defects" by analogy with dislocations in crystals, or perhaps "crumplons" ("crumples" and "wrinklons" have been proposed by others). We document internal and boundary nucleation and escape, pairwise and boundary interactions, something suggestive of curvature screening, and pattern formation both in the form of rapid transient deformation as well as sustained stable organization. The complex behaviors observed when probing this simple system are representative of those found in plate and shell structures under generic loading. 
Tuesday, March 15, 2022 9:24AM  9:36AM 
F08.00008: Wrinkling in Curved Films MEGHA EMERSE, LUCAS GOEHRING Wrinkling is a selforganizing process that can spontaneously generate periodic structures out of a uniform surface and represents a promising pathway for designing materials that naturally adopt a regular topography. Recently, intrinsic curvature has been explored as a means for driving wrinkling processes; this can be observed when one tries to wrap a flat map onto a globe, which leads to patterns of creases or folds on it. Using 3Dprinted moulds, we prepare elastic membranes with different curvatures, including cases of positive and negative Gaussian curvature, and shapes with two distinct principal curvatures. Through these, we experimentally investigate the means to control the appearance, amplitude, and wavelength of wrinkles that spontaneously form when a curved membrane is constrained by a flat fluid substrate, and how these properties change along the membrane. 
Tuesday, March 15, 2022 9:36AM  9:48AM 
F08.00009: Dynamic Wrinkling of Geometrically Templated Poly(vinyl alcohol) Soap Films during LiquidtoSolid Phase Transition Yuchong Gao, Eleni Katifori, Shu Yang Wrinkles generated from dynamic buckling instability, compared to static wrinkling from materials mechanical properties mismatch, can offer a broader selection of attainable patterns due to the tunable material elasticity by environmental conditions such as humidity, temperature, and mechanical load. However, such dynamic wrinkling is often transient due to its formation on ephemeral liquid films or thin polymer sheets at interfaces. Here, we report a new method to fabricate longlasting wrinkling patterns from the dynamic process of drying high molecular weight poly(vinyl alcohol) (PVA) soap films templated by 3D printed frames. The PVA soap films are highly stable on the frame without burst due to the extensive chain entanglement; the wrinkle patterns can survive the phase transition and remain stable after water evaporation. The correlations between wrinkle patterns generated and PVA molecular weight, concentrations, evaporation speed, and environmental humidity are studied. An analytical model is established and verified experimentally. Possibilities to locally control the winkle patterns on films of zero and negative Gaussian curvatures are demonstrated. This work may give insights to program patterns towards applications such as flexible electronics and biomedical devices. 
Tuesday, March 15, 2022 9:48AM  10:00AM 
F08.00010: Experimental Measurement of Decay Length for Azimuthal Pressure Gradients in the Viscous Fingering Instability Savannah D Gowen, Thomas E Videbaek, Sidney R Nagel Iconic viscous finger patterns form when a lower viscosity fluid penetrates a higher viscosity fluid within a confined geometry. Using a previously described technique [1], we experimentally measure fluid velocities as a function of radius, r, along the midplane of a radial HeleShaw cell during nonlinear pattern formation after the instability onset. We find a difference in the fluid velocity between fluid flowing behind a finger protrusion and that behind the adjacent valley even far behind the interface. This velocity difference, ΔV, decays exponentially with the distance behind the interface: ΔV∝ r^{1} Exp [(r_{inner}–r)/λ]. Here r_{inner} is the inner radius of the interface. We measure the dependence of the decay length, λ, on the length and width of the fingers and compare these measurements with prior model predictions which relate the velocity of the finger and valley interfaces to the the viscosity ratio of the fluids. 
Tuesday, March 15, 2022 10:00AM  10:12AM 
F08.00011: MicroFluidic Model and Experiments for Blood Drops on a Hyperhydrophilic, Rapid Solidification Device, InnovaStrip, for Fast, Accurate, Cheap, Comprehensive Small Volume Blood Diagnostics using a SmartPhone App Arjun Sekar, Aarush Thinakaran, Wesley Peng, Thilina Balasooriya, Nikhil Suresh, Aashi R Gurijala, Srivatsan J Swaminathan, Rianna N Rane, Ashwin Suresh, Mohammed Sahal, Robert J Culbertson, Eric J Culbertson, Nicole Herbots Accurate Blood Diagnostics (BD) require 810 mL of blood per vial, expensive laboratories, and take days for results. Such large blood volumes lead to Hospital Acquired Anemia in 74% of patients and 100% of preemies. Hyperhydrophilic coatings HemaDrop™ in a new handheld BD device, InnovaStrip™, yield cheap, fast, accurate BD by flattening and solidifying blood drops into Homogeneous Thin Solid Films (HTSF) in minutes without coagulation. HTSFs are reproducible unlike Dried Blood Spots. HTSFs are analyzed via handheld XRay Fluorescence and Ion Beam Analysis. Both yield electrolytes, trace elements, toxic metals, and radionuclides to +/10%. To analyze data quickly and accurately, an algorithm, Fast Accurate Blood Analysis (FABA), converts data in mg/dL, the unit for BD. InnovaStrip™ combined with FABA yields thus comprehensive BD. InnovaStrip™'s potential is significant for bringing fast, accurate, handheld, comprehensive BD to refugee camps and poor, underserved, and underprivileged areas with limited access to BD labs. In addition, rapid pathogen detection has also been developed in a parallel, handheld, inexpensive device, InnovaBug™ to be combined with InnovaStrip™. 
Tuesday, March 15, 2022 10:12AM  10:24AM 
F08.00012: Physics of gut motility impacts absorption and bacterial growth Agnese Codutti, Karen Alim, Jonas Cremer Malfunctioning of the small intestine contractility and the ensuing bacterial population therein are linked to a plethora of diseases. We here study how the small intestine's variety of contractility patterns impacts nutrient uptake and bacterial population. Our analytical derivations in agreement with simulations identify flow velocity as the key control parameter of the nutrients uptake efficiency and bacterial growth, independently of the specifics of contractility patterns. Selfregulating flow velocity in response to the number of nutrients and bacteria in the gut allows achieving 100\% efficiency in nutrient uptake. Instead of the specifics of intestine contractility, our work points to the flow velocity and its variation in time within the intestine to prevent malfunctioning. 
Tuesday, March 15, 2022 10:24AM  10:36AM 
F08.00013: Modeling the colloidal physics of lifeessential processes biological cells Roseanna N Zia, Drew Endy, Akshay Maheshwari, Emma del Carmen Gonzalez Gonzalez, Alp M Sunol The frontier in operational mastery of biological cells arguably resides at the interface between biology and colloid physics: cellular processes that operate over colloidal length scales, where continuum fluid mechanics and Brownian motion underlie wholecell scale behavior. It is at this scale that much of cell machinery operates and is where reconstitution and manipulation of cells is most challenging. This operational regime is centered between the two wellstudied limits of structural and systems biology: the former focuses on atomisticscale spatial resolution with little time evolution, and the latter on kinetic models that abstract space away. Colloidal hydrodynamics modeling bridges this divide by unifying the disparate length and timescales of solventmolecule and colloidal dynamics, and may hold a key to numerous open questions in biological cell function. I will discuss our physicsbased computational model of a bacterial cell, where biomolecules and their interactions are physically represented, individually and explicitly. With it, we tackle a fundamental open question in biology from a physicochemical perspective: why does protein synthesis speed up at faster growth rates? I will report our findings in answer to this question, and demonstrate the general applicability of our "biocolloidal" framework to other open questions in macromolecular and cellular biology, including the role of gel maturation in neurodegenerative disease inheritance. 
Tuesday, March 15, 2022 10:36AM  10:48AM 
F08.00014: Infinite families of fracton fluids with momentum conservation Andrew M Osborne, Andrew Lucas We construct infinite families of new universality classes of fracton hydrodynamics with momentum conservation, both with multipole conservation laws and/or subsystem symmetry. We explorethe effects of broken inversion and/or timereversal symmetry at the ideal fluid level, along withmomentum relaxation. In the case of onedimensional multipoleconserving models, we write downexplicit Hamiltonian systems realizing these new universality classes. Many of these hydrodynamicuniversality classes exhibit instabilities and will flow to new nonequilibrium fixed points. 
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