February 5, 2016 3:30PM BPB-207. Rebekah Dawson. All Planets Great and Small.

Discoveries of exoplanets so different from those in our Solar System have called in question conventional theories for how planetary systems form and evolve. I will present recent progress in our understanding of the physical processes that drive the assembly of planetary systems and result in the surprising variety of orbital architectures we observe today. I will discuss orbital evolution in both the large and small planet regime and physical processes that link planetary orbits to their physical properties and properties of their host stars.

January 29, 2016 3:30PM BPB-207. Joseph M. Zaug. Ultrafast Shock Compression Experiments to Rapidly Test Extreme Condition Materials Predictions.

In this talk, we will discuss recent results from ultrafast tabletop laser compression experiments on fluids, polymers, and high energy density organic molecules including single crystals. Previous work on ultrafast shocked metals will be summarized and serve as an introduction to our technical approach. Extreme material theories benefit from this research through a growing understanding of how ultrahigh strain rate (10⁸ -10¹¹ s^-1) loading processes affect later-time high-strain rate (10⁴ -10⁶ s^-1) phenomena occurring on macroscale dimensions.

Larger scale gun-based compression platforms nominally generate 10⁶ s^-1 maximum equilibrated strain rate loads; however, initial rising transient strain rates —not measured— may actually reach ultrahigh values. At present, the ultrafast shock community currently utilizes diagnostics that measure hydrodynamic flow and UV/VIS absorption; however, these methods tell us nothing directly about structure or chemical states. (We can consider perspectives on the viability of potential solutions to this long-standing challenge.) Nonetheless, when we’ve matched —on identical temporal and spatial scales— hydrodynamic data with commensurate molecular dynamics or crystal mechanics simulation results, more comprehensive pictures materialize that further illuminate the progression of early-time shock induced phenomena, such as high-strain rate induced elastic to plastic wave transitions preceding chemical initiation. Definitive knowledge gaps are also discovered.

We will conclude this presentation with an example of how one may use ultrafast compression-quench experiments to freeze metastable intermediate products. Shockwave compression states normally release to high-temperature thermodynamic states governed by the heat capacity of the starting material; however, by stopping (at an early-stage) shock induced chemical decomposition, i.e., bond breaking, one can trap or even consider synthesizing previously inaccessible transient species. For example, diamond formation from shocked TATB (1,3,5-triamino-2,4,6-trinitrobenzene) had been predicted for decades and was finally proved correct using this novel experimental approach.

Dr. Joseph (Joe) Zaug - Founding member (1997) and leader of the High Pressure Chemistry Group within the Materials Sciences Division at Lawrence Livermore National Laboratory. (Ph.D. in Physical Chemistry, University of Washington, Seattle, 1994; B.S. in Chemistry, Illinois Institute of Technology, 1988) He has twenty-five years of experience developing tools that quasi-statically and/or dynamically compress materials and engineering new approaches to characterize extreme condition material response using primarily laser-based systems. Numerous grand-challenge science issues have been met by these innovations resulting in high-profile publications in disciplines such as geophysics, high-pressure physics and chemistry including chemical synthesis, and materials science. Joe and his group actively collaborate with international and U.S. collaborators. His current research focus is on measuring equations of state and physical or chemical phase transitions of single crystals, polymers, and composite materials subjected to quasi-static and ultrahigh strain rate loads. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344

January 22, 2016 3:30PM BPB-207. David Radice. Turbulent Lives: Tales of Neutron Stars.

Neutron stars live interesting and mysterious lives: from the moment they are created in core-collapse supernovae, to the moment some of them eventually collapse to black-holes. In this talk, I will cover some aspects of their lives. I will discuss their birth in core-collapse supernovae, focusing on the key role of hydrodynamic turbulence in triggering the explosion, and their death in neutron star mergers. Finally, I will present recent results on the outcome of the dynamical ejection of neutron-star matter that might take place during mergers.

January 6, 2016. Jason Steffen on NPR's Marketplace.

Jason Steffen (Physics and Astronomy) was a guest on NPR's Marketplace, talking about how to more efficiently board an airplane. He began researching the issue as a graduate student after being frustrated by slow boarding processes and flight delays.

The press release from UNLV:

Jason Steffen News Center