Eric Sembrat's Test Bonanza

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The dawn of gravitational wave astronomy is upon us as Advanced LIGO and Advanced Virgo begin to come on line later this year. With the first detection of gravitational waves, the cosmic cacophony of the gravitational universe will be open to us, allowing us to probe some of the densest regions in the universe as well as some of the most energetic astronomical phenomena (eg. gamma-ray bursts). In order to perform gravitational wave astronomy, one must decipher the astrophysical information encoded in the detected gravitational wave signals. This seminar will give a brief overview of the methods for performing gravitational wave astronomy, based on Bayesian inference, and highlight some examples of gravitational wave astronomy for "unmodelled" burst gravitational wave signals and other transients signals.

I will try to explain, in elementary terms, the deep connection between space-time geometry and quantum entropy, uncovered in the work of Bekenstein, Hawking, 't Hooft, Gibbons Jacobson, Fischler, Susskind and Bousso. This leads to the conclusion that many of the fundamental degrees of freedom, which describe our world, are inaccessible to direct local measurement. Indeed, local excitations are constrained low entropy states of the fundamental degrees of freedom. These insights give us clues to the nature of a fundamental theory of quantum gravity, and have implications for early universe cosmology, inflation, and the particle physics at the TeV scale (I won't have time to discuss the last of these claims, which is highly speculative).

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In frustrated magnetic materials, geometry and magnetic interactions combine to suppress conventional magnetic order. Instead, disordered "spin liquid" states can host exotic magnetic phenomena which persist to the lowest measurable temperatures. Neutron scattering is an ideal experimental technique to understand spin-liquid states, but the absence of conventional magnetic order means that standard data-analysis methods cannot be used. Two limitations have traditionally restricted our understanding spin liquids at the atomic scale: (i) the magnetic interactions must be anticipated, and (ii) single-crystal samples must be available.

In my presentation, I will show how neutron-scattering data can be converted robustly into a three-dimensional model of the spin-liquid state. Using an atomistic refinement approach, I show that it is possible to recover accurate three-dimensional information from powder-averaged data, without making any assumptions about the underlying magnetic interactions. I will present experimental results for two materials. First, I present evidence for a "hidden order" state in the canonical frustrated magnet Gd3Ga5O12. Second, I use single-crystal neutron-scattering data to understand the origin of magnetic disorder in beta-Mn and its alloys. Finally, I will discuss the implications of these results for understanding disorder in other materials.

We present studies of the effects of vortex-dominated fluid flows on the dynamics of the oscillatory or excitable Belousov-Zhabotinsky reaction. The results of these experiments have applications for advection-reaction-diffusion dynamics in a wide range of systems including microfluidic chemical reactors, cellular-scale processes in biological systems, and blooms of phytoplankton in the oceans. Much of our work is focused on understanding how reaction fronts propagate in fluid flows. To analyze and predict the behavior of the fronts, we generalize tools developed to describe passive mixing. In particular, the concept of an invariant manifold is extended to account for reactive burning. These ``burning invariant manifolds'' (BIMs) are barriers that locally block the motion of reaction fronts. Unlike invariant manifolds for passive transport, however, the BIMs are barriers for front propagation in one direction only. These ideas are tested and illustrated experimentally in two-dimensional flows composed of a chain of alternating vortices, a spatially-random flow, and vortex flows with imposed winds. We are also extending these studies to three-dimensional flows.

We use recent constraints on the star formation rate---halo mass---redshift relation to model the host halo environments where short Gamma-Ray Burst (sGRB) progenitors are created.  These halo environments set minimum energy requirements for sGRB progenitors to leave the vicinity of their original galaxy.  We find that the fraction of sGRBs which are hostless is a robust probe of the underlying velocity kick distribution for sGRB progenitors, regardless of uncertainties in the sGRB time-delay distribution and observational systematics.  We use observed constraints on the hostless fraction of sGRBs to rule out several sGRB progenitor classes which cannot supply the necessary velocity kicks.  Finally, we discuss the ability of sGRB galaxy host properties (e.g., stellar mass and morphology) to further constrain model uncertainties.

One of the frontiers in modern cosmology is understanding the end of cosmic dark ages, when the first stars, supernovae, and galaxies transformed the simple early Universe into a state of ever-increasing complexity. I will talk about the possible physics behind the formation of these first luminous objects by presenting the results from our simulations. I will also discuss the possible observational signatures of the cosmic dawn that will be the prime targets for the future telescopes such as the James Webb Space Telescope (JWST).