Bulletin of the American Physical Society
Annual Meeting of the APS Four Corners Section
Volume 62, Number 17
Friday–Saturday, October 20–21, 2017; Fort Collins, CO
Session F1: Plenary II |
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Chair: David Dunlap, University of New Mexico Room: Lory Student Center Theatre |
Friday, October 20, 2017 3:00PM - 3:36PM |
F1.00001: Unexpected parallelisms: From swimming bacteria to wound healing and cancer metastasis Invited Speaker: Charles Wolgemuth Over 20 years ago, Neil Mendelson observed whirls and jets in dense colonies of \textit{Bacillus subtilis}. This organized collective motion has since been shown to arise whenever swimming bacteria are at sufficient density. Under appropriate conditions, hydrodynamic effects drive the alignment of nearby bacteria, but dipole-distributed forces from the bacteria destabilize the system and cause the formation of transient vortices and jets. When your skin gets cut, one of the first processes is re-epithelialization. The top living layer of your skin, the epithelium, heals itself via the crawling of cells over the wounded region. Experiments have shown that this process involves elaborate coordinated cell motions that include whirling vortices. Are the similarities in these two disparate systems coincidence? Or is similar physics driving these analogous motions? Here I will discuss our attempts to construct mathematical models for these two systems that are grounded in the basic behaviour of the single cells that generate the motions. An intriguing connection is that both swimming bacteria and crawling epithelial cells exert dipole-distributed forces on their surroundings. Using experiments to test these models has led to some unexpected results. For example, it has been shown that while confined suspensions of \textit{B. subtilis} form a single, stable, counter-rotating vortex, confined \textit{E. coli} instead forms micro-spin cycles, a persistent periodically reversing vortex. What defines the marked difference between the collective dynamics of these two flagellated swimmers? In addition, in epithelial cells, perturbations that slow isolated cells are found to dramatically increase collective migration. I will show that our models naturally predict these behaviours and can quantitatively match our experimental data. I will conclude by arguing for a biophysical examination of the transition to metastasis in cancer and discuss how our epithelial cell model may provide insights that are currently obscured by traditional genomic and proteomic methodologies. [Preview Abstract] |
Friday, October 20, 2017 3:36PM - 4:12PM |
F1.00002: Detecting the Highest Energy Photons from Extreme Astrophysical Sources Invited Speaker: Brenda Dingus The High Altitude Water Cherenkov (HAWC) gamma-ray observatory detects the highest energy photons from astrophysical sources. HAWC is located at 14000’ above sea level near Puebla, Mexico and has been fully operational since March 2015. HAWC observes ~2/3 of the sky each day and has produced a map with ~40 sources of which about one quarter were previously unknown. The sources detected by HAWC are due to particles accelerated in astrophysical sources to energies much higher than man-made accelerators can produce. These astrophysical particle accelerators include the shocks produced by the remnants of supernovae, the winds powered by rapidly spinning neutron stars, and the relativistic jets emitted from supermassive black holes in distant galaxies. We are also searching HAWC data for new types of high energy gamma-ray sources, such as coincidences with satellite-detected gamma-ray bursts, gravitational-wave detectors, and neutrino observatories. And HAWC observations of dark matter rich objects, such as dwarf spheroidal galaxies, place strong constraints on the annihilation or decay of dark matter into gamma-rays. In this talk, I will give an overview of HAWC and this exciting window on the universe. [Preview Abstract] |
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