Fall 2018 Seminar
Talks are 12:00 noon on Thursdays in Olin Science 268, unless
otherwise noted.
August 30, 2018
Reaction fronts and swimming microbes in fluid flows
Abstract:
We present experiments on the effects of laminar flows on the spreading of the excitable Belousov-Zhabotinsky chemical reaction and on the motion of swimming bacteria. The results of these experiments have applications for a wide range of systems including microfluidic chemical reactors, cellular-scale processes in biological systems, and blooms of phytoplankton in the oceans. To predict the behavior of reaction fronts, we adapt tools used to describe chaotic fluid mixing in laminar flows.In particular, we propose "burning invariant manifolds" (BIMs) that act as one-way barriers that locally block the motion of reaction fronts. These barriers are measured experimentally in a range of vortex-dominated 2- and 3-dimensional fluid flows. A similar theoretical approach predicts "swimming invariant manifolds" (SwIMs) that are one-way barriers the impede the motion of microbes in a flow. We are conducting experiments to test the existence of SwIMs for both wild-type and smooth swimming bacillus subtilus in hyperbolic and vortex-dominated fluid flow.
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September 13, 2018
Detecting Gravitational Waves with a Pulsar Timing Array
Paul Baker,
Center for Gravitational Waves and Cosmology, West Virginia University
Abstract:
The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) expects to directly detect a stochastic gravitational wave background (GWB) from super massive black hole binaries in the near future. This will be accomplished by monitoring many stable millisecond radio pulsars and looking differences in the expected and actual time of arrival of pulses. We will review the sources of nanohertz gravitational waves that are detectable with pulsar timing arrays, like NANOGrav. Then we will discuss the fundamental techniques used by pulsar timing arrays to time pulsars and identify the GWB signature in data.
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September 27, 2018
Compositions of Extrasolar Planets: What Will We Learn from Our Next Planet Hunter?
Abstract: Thousands of extrasolar planets have been discovered, yet our quest to understand what they are like and how they formed is just beginning. A crucial aspect of this effort is to assess the possible compositions of these planets - that is, are they more rocky like Earth, or do they have significant layers of gas like Neptune or Uranus? A new planet hunter called the Transiting Exoplanet Survey Satellite (TESS) is designed to address this question by discovering hundreds of sub-Neptune-sized planets that orbit stars relatively close to our Sun, and subsequently measuring precise masses for at least 50 of them. In this talk I will discuss how we determine exoplanet compositions, what we know about them so far, and how our understanding may evolve thanks to TESS.
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