Student Poster Abstracts

Please note that while there is not one required or mandatory size, all posters should fit in a space no longer than 36” (91 cm) wide and preferably be no more than about 48” (122 cm) in height. Arrangements can be made for other sizes as necessary.

If you are not able to get your poster printed before you leave home (or are unable to easily transport), you may get posters printed at FedEx Office (http://local.fedex.com/co/boulder/office-0402/).

Select a session to see all posters scheduled for that session

Session #1


Madhuvanthi Guruprasad Athani
mathani1@jh.edu
Johns Hopkins University


Srivatsa Badariprasad
srivatsa.badariprasad@ncl.ac.uk
University of Newcastle upon Tyne

Vortex Lattice Nucleation in Dipolar Bose-Einstein Condensates


Degenerate quantum gases with strong permanent dipole moments are a robust platform for studying anisotropic and long-ranged phenomena in strongly correlated quantum systems. When subjected to a rotating magnetic field, the resulting precession of the dipole moments of a magnetic dipolar Bose-Einstein condensate (dBEC) imparts angular momentum to the system. Due to the superfluidity of an interacting BEC, this has the consequence of quantum vortices forming in a hitherto vorticity-free fluid. Our recent work focusses on theoretically tracking the evolution of a dBEC as the magnetic field rotation frequency is slowly accelerated from zero until the vortices have formed, and then observing the relaxation of the system to its final state at a fixed rotation frequency. We find that the dBEC closely follows pre-existing semi-analytical predictions until the onset of vorticity, and that the vortex-filled states are characterised by background density striping and tilting. After sufficiently long hold durations, the vortices relax into an Abrikosov lattice with the lattice and background dBEC density profile approaching our predictions of the expected ground state.


Christopher Browne
christopher.a.browne4@gmail.com
Princeton University

Elastic turbulence in 3D porous media


Many energy, environmental, industrial, and microfluidic processes rely on the flow of polymer solutions through porous media. Unexpectedly, the macroscopic flow resistance often increases above a threshold flow rate in a porous medium—but not in bulk solution. The reason why has been a puzzle for over half a century. Here, by directly visualizing flow in a transparent 3D porous medium, we demonstrate that this anomalous increase is due to the onset of an elastic instability in which the flow exhibits strong spatio-temporal fluctuations reminiscent of inertial turbulence, despite the small Reynolds number. Our measurements enable us to quantitatively establish that the energy dissipated by pore-scale fluctuations generates the anomalous increase in the overall flow resistance. Because the macroscopic resistance is one of the most fundamental descriptors of fluid flow, our results both help deepen understanding of complex fluid flows, and provide guidelines to inform a broad range of applications.


Freya Bull
freya.bull@ed.ac.uk
University of Edinburgh

A model for the infection dynamics of a urinary catheter


Catheter associated urinary tract infections (CAUTI) constitute up to 40% of hospital acquired infections, yet there is still limited understanding of how CAUTI develops. By combining population dynamics and fluid dynamics, I construct a mathematical model to find new insight. Within this model, bacteria spread as a wave on the external surface of the catheter. On reaching the bladder they proliferate within the urine, before being swept down the inside of the catheter by the urine flow. Some bacteria stick to the inside surface of the catheter, where they grow just as on the outside. From this model, the rate of urine production by the kidneys emerges as a critical parameter, governing a pseudo second-order phase transition. Low urine production rates give rise to an infected bladder state, transitioning, as the rate increases, into a washed-out state where the catheter can still be infected but there is no detectable growth within the urine.


Pulkit Kumar Dubey
pkd1005@wildcats.unh.edu
University of New Hampshire


Kirsten Daniela Endresen
kendres3@jhu.edu
Johns Hopkins University

Inducing Topological Defects in Cell Monolayers Using Topography


We investigate the effects of the long-range orientational order that arrises from anisotropically-shaped cells aligning with their neighbors, as a nematic liquid crystal. A consequence of their liquid crystal order is the presence of highly disordered regions known as topological defects, where stresses are concentrated. There is growing evidence that in living systems, the presence of topological defects impacts the behavior of cells. We induce the formation of topological defects with +1 and -1 topological charges in monolayers of 3T6 fibroblasts and EpH-4 epithelial cells using topographically patterned substrates. We study the density and dynamics of the cells in these regions, and we examine the effects of varying the height of ridges, which breaks up the monolayer by creating barriers between groups of cells.


Aaron Hui
hui.122@osu.edu
Ohio State University

Noise thermometry in electron hydrodynamics


Johnson noise thermometry, based on the Johnson-Nyquist theorem, offers a powerful primary thermometry technique to access the electron temperature at the nanoscale. In practical situations, one needs to generalize the Johnson-Nyquist theorem to handle spatially inhomogenous temperature profiles. This was previously done for Wiedemann-Franz-obeying ohmic devices, where it was found that Joule heating leads to a geometry-independent increase in Johnson noise. However, there has been great recent interest in strongly-interacting electron hydrodynamic systems which do not admit a local conductivity nor obey the Wiedemann-Franz law, signatures of which have even been observed in previous thermometry experiments. In this paper, we study low-frequency Johnson noise in the hydrodynamic setting for a rectangular geometry. As opposed to the ohmic setting, we find that the Johnson noise is no longer geometry-independent due to non-local viscous gradients. Despite this, ignoring the geometric correction only leads to an error of at most 40% as compared to naively using the ohmic result.


Egor Kiselev
j.kiselev@gmail.com
Technion

Floquet Hydrodynamics


Chloe Lindeman
cwlindeman@uchicago.edu
University of Chicago

How does a material make memories?


Jammed systems which are cyclically sheared will often find periodic orbits after just a few cycles, thus encoding a memory of their drive amplitude. Aspects of these periodic orbits can be captured by models of interacting hysteretic regions (“hysterons”) that represent particle rearrangements in the jammed packings. However, there remains a gap between hysterons as a model and the rearrangements they aim to describe. Here, we study small jammed systems — on the order of 10 particles — to probe the nature of rearrangements. For packings with one pair of rearrangements (one hysteron) in their periodic orbit, we examine the two-state nature of the strain region between the rearrangements and begin to paint a more robust picture of the extent to which these systems behave like model hysterons.


Pawel Matus
matus@pks.mpg.de
Max Planck Institute for the Physics of Complex Systems

Anomaly-induced transport regime in Weyl semimetals


We study propagation of an oscillatory electromagnetic field inside a Weyl semimetal. In conventional conductors, the motion of the charge carriers in the skin layer near the surface can be diffusive, ballistic, or hydrodynamic. We show that the presence of chiral anomalies, intrinsic to the massless Weyl particles, leads to a hitherto neglected transport regime, in which the relation between the current and the electric field becomes nonlocal as a result of the diffusion of the valley charge imbalance into the bulk of the material. We propose to use this novel regime as a diagnostic of the presence of chiral anomalies in optical conductivity measurements. These results are obtained from a generalized kinetic theory which includes various relaxation mechanisms, allowing us to investigate different transport regimes of Weyl semimetals.


Calvin Pozderac
pozderac.16@osu.edu
Ohio State University

Exact solution for the thermalization transition in a model fracton system


We consider the thermalization transition of a model fracton system with respect to average filling. In our 1D lattice model, which conserves particle number and dipole, we consider the application of random z-site gates that obey our dipole constraint. In the limit of infinite system size and fixed average filling, we calculate the critical filling above which the fracton system thermalizes. Through number theoretic analogies and numerical corroboration, we find a critical filling, n_c, of 1/(z-2). Further, we determine the both the correlation length and dynamical critical exponents.


Shikhar Rai
shikhar.rai@rochester.edu
University of Rochester

Scale of oceanic eddy killing by wind from global satellite observations


Wind provides net energy to the ocean at the surface but not all lengthscales receive energy from the winds. The mesoscale and smaller scales are damped by the wind by the process known as eddy killing. We investigate the lengthscale below which the winds effectively kill eddy, it’s variability and their causes and its importance. We find in the global average eddies of below 260km are killed by wind at the rate of ~50GW, eddy killing has seasonality because of the wind speed and the magnitude of eddy killing is comparable to the magnitude of inverse cascades, PE to KE conversion, in the energetic regions like western boundary currents and Antarctic Circumpolar Current.


Jonas Rønning
jonas.ronning@fys.uio.no
University of Oslo

Flow around topological defects in active nematic films


Jonas Rønning1, M. Cristina Marchetti2, Mark J. Bowick3 and Luiza Angheluta1

  1. Njord Centre, Department of Physics, University of Oslo, P. O. Box 1048, 0316 Oslo, Norway
  2. Department of Physics, University of California Santa Barbara , Santa Barbara, CA 93106, USA
  3. Kavli Institute for Theoretical Physics, University of California Santa Barbara, Santa Barbara, CA 93106, USA

The hydrodynamics of active nematics is characterized by an active turbulence regime whereby topological defects proliferate and interact with each other. The nematic state corresponds to orientational order, which is punctuated by half integer disclinations, as lowest energy defects. We study the flow induced by the active stress around isolated ±1/2 defects in an active nematic film in the presence of both viscous dissipation (η) and friction with the substrate (Γ). The interplay between the two dissipation mechanisms gives rise to a length scale〖 l〗_d^2=η/Γ, which sets the scale of the self-propulsion velocity for the +1/2 defect, and the scale for the decay of flow velocity and vorticity. Spanning vortices with alternating vorticity are formed around the defect in an active nematic film confined to a disk. The shape of these vortices, in addition to the self-propulsion of the positive defect, is determined by the relation between the discs radius R and〖 l〗_d. For small systems, in units of l_d, the velocity is proportional to the radius. As the size become larger the velocity become set by the dissipation length and the vortices become elongated. In the limit of R→∞ the vortices closes at infinity.


Daniel William Swartz
dswartz@mit.edu
Massachusetts Institute of Technology

Both colonization and competition abilities determine the fitness at the frontier of an expanding population


Bacteria colonize new territory in a process known as range expansion. This expansion is driven by the division of bacteria, allowing for the expanding population to accrue mutations resulting in evolution at the expansion front. In most cases, evolution will select for a faster expansion rate. However, there have been reported cases where a mutant evolves which expands slower than the wildtype and yet is able to out-compete the wildtype strain in coculture. This competition between fast and slow expanders generates dented fronts which we study in this work. We present a theory describing the competition at the boundary of a growing front between two populations. In typical one-dimensional competition, invasion generates a travelling wave which can be either ”pulled” or ”pushed”. We generalize these cases to competition on a growing front in both pulled and pushed regimes. We then demonstrate how coupling competition to the morphology of the expansion can have large effects on both the invasion velocity and the outcome of competition.


Adrian van Kan
avankan@berkeley.edu
University of California, Berkeley


Jiarong Wu
jiarongw@princeton.edu
Princeton University

How does the wind amplify ocean surface waves?


Wind excites and amplifies ocean surface waves. These wind waves modulate the mass, momentum and energy transfer between the ocean and the atmosphere. There are still vigorous discussions about the mechanism of wind wave growth despite decades of theoretical, experimental, and numerical studies. We conducted fully-coupled direct numerical simulation to better understand the physics of wind-wave interaction, and to quantify the wind energy input for various wind wave conditions. We verified the pressure forcing assumption with detailed flow field outputs. We also obtained reasonable wave growth rates for different wave ages and wave steepness, and identified potential reasons for discrepancies in previous results.


Weixuan (Rosa) Xu
weixuan_xu@brown.edu
Brown University

Topological Signature of Stratospheric Poincare -- Gravity Waves


The rotation of the earth breaks time-reversal and parity symmetries in an opposite sense north and south of the equator, leading to a topological origin for certain atmospheric and oceanic equatorial waves. Away from the equator the shallow water and stably-stratified primitive equations show that Poincaré-gravity waves have nontrivial topology as evidenced by a phase singularity in frequency-wavevector space.  This non-trivial topology then predicts, via the principle of bulk-boundary correspondence, the existence of two equatorial waves, the Kelvin and Yanai waves.  To verify the existence of these topological properties, we examine ERA5 reanalysis data to study cross-correlations between the wind velocity and geopotential height in the mid-latitude stratosphere at the 50 hPa level, and find the expected vortex and anti-vortex in the phase of the correlations at the frequencies of the Poincaré-gravity waves. These results demonstrate a new way to deepen understanding of waves in the stratosphere, and this approach provides a new tool for investigating waves in other components of the climate system.


Houssam Yassin
hyassin@princeton.edu
Princeton University

Surface Quasigeostrophic Turbulence in Variable Stratification


Traditional surface quasigeostrophic theory assumes a vertically uniform stratification, and, as a consequence, the theory is only valid at horizontal scales smaller than 10 km (in the wintertime mid-latitude open ocean). At larger horizontal scales, the vertical structure of the ocean’s stratification becomes important. We present a generalization of surface quasigeostrophic theory that accounts for arbitrary vertical stratification. We find that the seasonality of upper ocean stratification (in particular, the seasonality in mixed-layer depth) implies a seasonality in surface quasigeostrophic turbulence. Deep wintertime mixed-layers lead to a non-local surface quasigeostrophic turbulence characterized by thin buoyancy fronts and vortices spanning a wide range of scales. In contrast, shallow summertime mixed-layers lead to a more local surface quasigeostrophic turbulence where the surface buoyancy appears spatially diffuse. The variable stratification theory also predicts a seasonal kinetic energy spectrum. If the submesoscales (1-100 km) are in the forward cascade of buoyancy variance, the theory predicts a wintertime spectrum proportional to k−7/3. In contrast, the lack of scale invariance across the submesoscales in summer causes the cascade theory to fail but simulations generally suggest a kinetic energy spectrum that is flatter in summertime than in wintertime. We conclude by suggesting that submesoscale interior quasigeostrophic turbulence may be seasonal as well because it also depends on the vertical structure of ocean stratification.