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 A16: From Grains to Complex Flows to Sustainable Materials: Soft Matter Meets Climate ChangeFocus
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Sponsoring Units: DSOFT GSNP Chair: Vinutha H.A., Georgetown University Room: Room 208 |
Monday, March 6, 2023 8:00AM - 8:36AM |
A16.00001: Electrifying granular flows: probing the interior dynamics of volcanic plumes and pyrocumulonimbus clouds using electrostatics Invited Speaker: Joshua Mendez Harper The electrification of volcanic plumes and wildfire-driven thunderstorms has been described intermittently for centuries, if not longer. For instance, Pliny the Younger noted dazzling lightning displays during the 79 AD eruption of Vesuvius. Although sometimes dismissed as secondary effects, recent work suggests that the electrical properties of ash and smoke clouds may reveal intrinsic properties of a flow that would otherwise be opaque to observation. Evidence for this hypothesis has steadily accumulated in the context of volcanic eruptions. Over the last decade, field studies across the world have shown that electrification in ash-laden plumes is ubiquitous. Paired with numerical models and focused laboratory experiments, these observations describe the microphysical mechanisms which link charge generation and electrical activity to the physical, chemical, and dynamic processes underpinning an eruption itself. Because lightning and associated electric fields may be measured remotely, understanding these relationships offers new opportunities to detect and monitor eruptions from afar, while safeguarding vulnerable populations. Recently, there has been substantial interest in applying these same principles to smoke plumes associated with mega-fires. The risk of devastating wildfires has increased in both historically-prone regions and areas where blazes were rare. Violent pyroconvection may generate wildfire-augmented thunderstorms, or pyrocumulonimbus clouds (pyroCb). These electrified storms act as "smoke stacks," efficiently transporting enormous amounts of particles from the surface to the lower stratosphere. More locally, pyroCbs may modify the course of a wildfire by increasing rate of fuel consumption, enhancing downwind ignition by wind-blown embers, and generating pyrogenic lightning. Like volcanic plumes, the internal dynamics and structure of pyroCbs are only marginally understood and the study of pyrogenic lightning is in its infancy. Monitoring extreme granular flows with electrostatic sensors requires an interdisciplinary approach at the intersection of soft matter, atmospheric science, electrostatics, and engineering. This talk summarizes the rapid and exciting progress toward this goal and provides a vision for future developments. |
Monday, March 6, 2023 8:36AM - 8:48AM |
A16.00002: Avalanches in 2D granular media Florent Pollet, Adel A Djellouli, Anne S Meeussen, Gabriele Albertini, Ilya Svetlizky, Arthur Young, Chris Rycroft, Shmuel Rubistein, Katia Bertoldi Granular systems are ubiquitous in nature, ranging from sand and colloids to planetary bodies and popcorn and present a very rich behavior. In this work, we focus on a single layer of mono-disperse beads that are shaken horizontally with an orbital motion (no out-of-plane oscillations). We find that a critical velocity exists above which a nucleation phenomenon is triggered: one bead leaves the plane and goes up. This event then triggers the ascension of other beads and ultimately leads to a steady state with two layers (one on the plate and one up in the air) and a permanent flow between them. We investigate this phenomenon using a combination of experiments, state-of-the-art machine learning algorithms and numerical simulations and identify a scaling law to describe it. Since our experiments can be easily visualized, we envisage that they could serve as a platform to gain insight into avalanches and phase transitions in more complex and less accessible systems. |
Monday, March 6, 2023 8:48AM - 9:00AM |
A16.00003: Rheological state diagrams for model earth suspensions under shear flow Shravan Pradeep, Paulo E Arratia, Eric Sigg, Douglas J Jerolmack Wildfire followed by intense rain on hillslopes causes debris flow. These fast-slowing, dense slurries of earth materials pose threat to human life and infrastructure. These events have been recently exacerbated due the rapidly increasing threat under climate change and associated extreme weather conditions. Recently, we have examined post-wildfire debris from 2018 Montecito mudslides and developed a simple Bingham-type viscoplastic model that could help improve debris flow prediction models in the future. These mixtures were highly heterogenous in nature and as such the interplay between various components in the the debris suspension mixture and their flow mechanics are not completely understood. In this study, we examine model earth mixtures to understand the minimum number of ingredients required to generate complex behavior observed for natural debris flows. We use model mud mixture which contains two components - silica sand and kaolinite clay. An order of magnitude difference in particle sizes coupled with particle shape effects of the constituents create complexity in interparticle interactions. Interplay between frictional (from sand) and attractive interactions (from clay) generate a rich rheological behavior in these model earth mixtures. In pure clay suspensions, yield stress values diverge as concentrations approach the respective jamming point. Increasing the sand content breaks the yield stress divergence and beyond a threshold sand concentration, the yield stress no longer changes with increasing suspension volume fraction. We believe that this non-monotonic behavior in the yield stress with increasing sand concentration is a signature of the change in interactions and associated microstructural changes in the suspension. With increasing sand content, the cohesive contacts between kaolinite particles are lubricated. This reduces the number of average stress-bearing contacts in the suspension and thereby lowering the overall yield stress. Using the steady shear flow curves, we map stress-shear rate state diagrams for suspensions with increasing solid sand content. We anticipate that the framework created for model earth suspensions can be extended to understand the flow regimes in heterogeneous real earth mixtures under steady shear flow. |
Monday, March 6, 2023 9:00AM - 9:12AM |
A16.00004: Those sinking moments: measuring sedimentation dynamics of marine snow Rahul Chajwa, Eliott M Flaum, Manu Prakash Ecosystems on our planet are driven out of equilibrium with energy input from the sun resulting in a flux of matter across food chains, contributing to the global carbon cycle. This flux is remarkably vivid in the biological pump of our oceans, with gravity driving the downward flux of carbon in the form of marine snow. Using a newly invented hydrodynamic levitation based microscopy [Nature Methods vol. 17, 1040–1051 (2020)], we measure the sedimentation dynamics of marine snow aggregates in the Gulf of Maine; highlighting the dynamic nature of marine snow aggregates. Drawing on the insights from field observations, we construct a minimal model based on far-field Stokesian hydrodynamics with inter-particle stickiness, and numerically explore the formation of these aggregates from an initially homogeneous sedimenting suspension. Our experimental observations and theoretical model paves the way for understanding the structure and dynamics of marine snow; thus offering a new window into the physics of Carbon transport in the ocean. |
Monday, March 6, 2023 9:12AM - 9:24AM |
A16.00005: Bacteria bioluminesce in response to fluid shear Sumit Kumar Birwa, Raymond E Goldstein, Nuno M Oliveira Bioluminescence by marine microorganisms is generally characterized by either pulse-like or continuous light production. Large eukaryotic organisms such as dinoflagellates exhibit a brief burst of light when mechanically stimulated, while bacteria can produce light continuously for long periods of time. An interesting open question is whether, like dinoflagellates which respond to fluid shear, bacteria exhibit any direct response to such stimulation. We have developed a method of investigating this possibility using an optical rheometer, and have studied the response of 5 separate species of marine bacteria under a range of shear rates. For all species, we find that the intensity of bioluminescence is a sigmoidal function of the applied shear rate and that the light production exhibits hysteresis under cycles of increasing and decreasing shear. Since oxygen consumption is a necessity for bacterial bioluminescence, I will discuss how the interpretation of such experimental observations requires a careful analysis of the possible competing effects of direct response to fluid dynamical shear and the effects of shear-induced mixing on oxygen availability. |
Monday, March 6, 2023 9:24AM - 9:36AM |
A16.00006: Ice mélange and the rheology of floating granular materials Justin C Burton, Kavinda Nissanka, Nandish Vora, Ayushi Rajpoot, Alexander A Robel, Jason Amundson Between the boundaries of tidewater glaciers and the ocean sits ice mélange, the worlds largest granular material. Created by glacial calving events in narrow straits or fjords, the dynamics and physical properties of ice mélange are important for determining variability in calving rates and meltwater release. We explore ice mélange with experiments that study its rheology, transverse velocity profile, and thickness profile. Polypropylene is used as a substitute for comminuted ice, due to their similar densities. We explored a variety of shapes in a narrow water tank with rough walls to simulate a fjord. A suspended acrylic plate acts as our glacier terminus. It is attached to two force sensors, allowing us to measure the force imparted by the mélange. Cameras mounted above and on the side of the chamber allow us to track surface velocity fields (using PIV) and depth profiles respectively. By comparing our results to simple, depth-averaged models of granular fluids, the thickness profile provides the friction coefficient between the mélange and the walls. Additionally, velocity profiles transverse to the flow direction allow us to test the accuracy of different granular rheologies. Finally, our experimental setup allows for rapid perturbations to the mélange (i.e. calving events), whereby the transient force and recovery to equilibrium can be measured. |
Monday, March 6, 2023 9:36AM - 9:48AM |
A16.00007: Modelling Seasonal Sea-Ice Dynamics within the Nares Strait Using a Lagrangian Discrete Element Approach Svetoslav Nikolov, Kara Peterson, Adrian Turner, Dan S Bolintineanu, Joel T Clemmer, Devin O'Conner The cryosphere is a critical components of Earth’s climate system, storing over two-thirds of the Earth’s freshwater supply and helping regulate radiative heat transfer between the Earth and the Sun. Sea-ice is perhaps the most dynamical piece of the cryosphere, experiencing large seasonal fluctuations, that have strong impacts on both marine biogeochemistry and animal migration patterns. In this regard, the ability to offer high-fidelity regional predictions of sea-ice/floe distributions is highly desirable. In the past elastic/visco-plastic continuum models have been successfully used to model large scale Arctic/Antartic seasonal sea-ice fluctuations. However, in smaller regional studies (1km resolution and lower), the discontinuous and nonlinear response of sea-ice, becomes difficult to resolve with continuum models. At these smaller length scales, Lagrangian models, like the discrete-element method (DEM), where each ice floe can be treated explicitly, can represent the underlying sea-ice dynamics more naturally. To this end, we utilize the Hopkins contact model within the Discrete Element Method for Sea-Ice (DEMSI) to examine seasonal sea-ice changes within the Kane Basin of the Nares Strait. Within this study we test the role that different sea-ice distributions have on the initial sea-ice fracture and breakup during the spring season. To test the robustness of the Hopkins contact model we also carry out both Sobol and Delta sensitivity analyses which examine how different contact parameters impact sea-ice dynamics. |
Monday, March 6, 2023 9:48AM - 10:00AM |
A16.00008: A gravity driven inverse cascade controls the size distribution of raindrops Florian Poydenot In the last century, scientists have failed to explain the drop-size distribution of natural rain and in particular the increase of the mean raindrop diameter with the rain intensity. This robust dependence implies a control of raindrops polydispersity by collective effects, and not by the instability nor by the stochastic evolution of individual drops. Here we show from first hydrodynamics principles that gravity driven drop coalescence controls the size distribution of raindrops. Our theory adapts the concept of energy cascade across scales in turbulence to the distribution of drop mass. We derive the steady state distribution reached when drops nucleate at a constant rate by solving the condition of a constant water mass flux across scales and compare it to existing experimental data. A key aspect of the model is the collision efficiency of gravity settling drops — large droplets fall faster than small ones and coalesce with them in their path. We compute the collision efficiency, including the lubrication pressure between drops, whose divergence as the air gap vanishes is regularized by both non-continuum effects in the air film, and flow inside the drops. It opens the possibility to improve the description of cloud micro-physics in atmospheric simulations. |
Monday, March 6, 2023 10:00AM - 10:12AM |
A16.00009: Mechanical stability of lipid monolayers and bilayers in the presence of pollutants Marina Pasquet, Joelle Frechette The environmental threat of plastic pollution is becoming increasingly important, with millions of tons of plastic debris being dumped into aquatic ecosystems each year. As a result, tiny fragments of plastic, called microplastics (particles < 5 mm, including nanosized plastics < 1 µm), are now found everywhere: freshwater, oceans and beaches, seabeds, rain, air and even in areas such as deserts and mountains. The small size of these plastics makes them particularly dangerous and ingestible by aquatic biota or directly by humans. Even more alarming, poly- and perfluoroalkyl substances (PFAS) coined forever chemicals, which have been found to pose a serious human health risk and linked to cancer, are omnipresent and persistent over long time scales in the environment, where they are in contact with microplastics. |
Monday, March 6, 2023 10:12AM - 10:24AM |
A16.00010: Using hydrogels to reach advection-limited atmospheric water capture H. Jeremy J Cho, Yiwei Gao, Ryan A Phung Atmospheric water harvesting is a way to tap into the water vapor around us as a new water resource to combat water scarcity. Existing studies often focus on the thermodynamic limits of water absorption in new water-absorptive materials exposed to different humidity environments. However, we believe that a water harvesting approach based on mass transfer principles can provide favorable water capture performance. Thus, we explore the role of hydrogel polymer structure, functionalization, crosslinking, poroelastic diffusion, advective boundary layers, and environmental conditions on water capture performance. We perform a combination of lab tests and outdoor tests in the hot, arid Las Vegas environment. The results of this work can inform better design of atmospheric water harvesting and related applications such as dehumidification and water recycling. |
Monday, March 6, 2023 10:24AM - 10:36AM |
A16.00011: Quick Release Anti-Fouling Hydrogels for Solar-Driven Water Purification Xiaohui Xu, Rodney Priestley, Sujit S Datta Hydrogels are promising soft materials for energy and environmental applications, including sustainable and off-grid water purification and harvesting. A current impediment to technology translation is the low water production rate well below daily human demand. To overcome this challenge, we designed a rapid-response, antifouling, loofah-inspired solar absorber gel (LSAG) capable of producing potable water from various contaminated sources at a rate of ~ 26 kg m-2 h-1, which is sufficient to meet daily water demand. The LSAG—produced at room temperature via aqueous processing using an ethylene glycol (EG)-water mixture—uniquely integrates the attributes of poly(N-isopropyl acrylamide) (PNIPAm), polydopamine (PDA), and poly (sulfobetaine methacrylate) (PSBMA) to enable off-grid water purification with enhanced photothermal response and the capacity to prevent oil- and bio-fouling. The use of the EG-water mixture was critical to forming the loofah-like structure with enhanced water transport. Remarkably, under various sunlight irradiations of 1 and 0.5 sun, LSAG required only 10 to 20 min to release ~ 70 % of its stored liquid water, respectively. Equally important, we demonstrate the ability of LSAG to purify water from various harmful sources, including those containing small molecules, oils, metals, and microplastics. |
Monday, March 6, 2023 10:36AM - 10:48AM |
A16.00012: The Fixed Tropopause Temperature Hypothesis: FiTT for Purpose? Brett McKim The Fixed Tropopause Temperature (FiTT) hypothesis says that Earth's radiative tropopause, the top of the troposphere, remains at a fixed temperature even as the surface warms. FiTT currently lacks a physical explanation and evidence across models. Here, we derive the tropopause temperature from first principles and find that the tropopause temperature should be fixed because it depends on water vapor's atmospheric distribution and its spectroscopy. We then show that a fixed tropopuase temperature is a robust feature of Earth's atmosphere by testing FiTT across a hierarchy of climate models. Our work gives a renewed appreciation for the role of thermodynamics and spectroscopy in determining a major feature of Earth's general circulation. |
Monday, March 6, 2023 10:48AM - 11:00AM |
A16.00013: Comparing Surface and Column-integrated Aerosol Loadings with Relative Humidity as a Correction Factor Jeevan Regmi, Rudra Aryal, Khem N Poudyal, Amod Pokhrel, Nabin Malakar, Madhu Gyawali The comparison of concentration of surface PM 2.5 with Aerosol Optical Depth (AOD) retrieved from MODIS was made in Kathmandu in the year 2020. The hourly and seasonal averaged PM 2.5 was correlated with temporal AOD and corrected using relative humidity, which improved their correlation significantly. It was found that the correlation was comparatively low for the months with higher average temperature. |
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