Tuesday, April 21, 2020

Randall Dannen published in Astrophysical Journal Letters.

PhD student Randall Dannen (College of Sciences, CoS) has recently demonstrated a novel method to create clouds around black holes. To appear in May as a Letter in the prestigious Astrophysical Journal, this work, led by Dannen, was co-authored with Prof. Daniel Proga (Dannen’s PhD adviser), Drs. Tim Waters (CoS) and Sergei Dyda (the University of Cambridge). It combines methodology from both observational and theoretical disciplines to address an outstanding problem in the field of Active Galactic Nuclei (AGN).

At the center of every massive galaxy, there exists a supermassive black hole (SMBH). When the gas around these SMBHs starts to fall in, it shines exceptionally bright. In fact, AGN are the most energetic long-lived objects in the universe. As a consequence of this immense release of energy, some material that is falling onto SMBHs can be ejected, forming AGN winds. These winds can extend all the way out to galactic scales, where astronomers see that rather than the flow being smooth, there exist discrete clumps. However, it has been challenging to form these clouds in state of the art computational models. Thus, this discovery of how to form clouds in numerical simulations is a major development.

Here is a link to the paper Clumpy AGN Outflows due to Thermal Instability and to the project website http://www.physics.unlv.edu/astro/clumpywindsims.html.

Wednesday, April 15, 2020

April 17, 2020 11:00AM PDT. Christian Childs dissertation defense: Development of CO2 laser-heating for the study of wide band gap oxide materials.

Development of CO2 laser-heating for the study of wide band gap oxide materials
Christian Childs
Ph.D. Candidate, Department of Physics and Astronomy

The ability to access a vast region of the pressure-temperature landscape using energy density tuning enables exotic states of matter to be probed. A well documented method for such exploration, under static conditions, is the use of the laser-heated diamond anvil cell (LH-DAC), utilizing a combination of high pressure (> 300 GPa) and high temperature (> 5000 K). Combining the LH-DAC with in situ synchrotron techniques utilizes characterization methods to measure structural and electronic responses at these extreme conditions.

The wavelength of the laser source defines the type of interaction with the sample that occurs, with metals typically being heated using near-IR light through an inverse-Bremsstrahlung process, while insulators are transparent at these wavelengths and must be coupled with mid-IR light through anharmonic polariton-phonon scattering processes. This technique of directly heating insulators is under developed and poorly understood.

I will present our development of CO2 laser heating techniques to directly heat a series of wide band gap insulators, La2Sn2O7, ZrO2, and CeO2, under high pressure conditions. As the emissivity of insulators are poorly constrained under extreme conditions, limiting optical pyrometry techniques, I will present a series of new, powerful tools for determining the absolute temperature of such systems. In addition to demonstrating the design of instrumentation here at UNLV I will present two dedicated laser heatings systems at Argonne National Laboratory's Advanced Photon Source at sector 16-IDB for in-situ x-ray diffraction and at sector 16-BMD for in-situ x-ray absorption spectroscopy. Both of these instruments are the first of their kind, permitting the direct probing of warm dense matter and providing the scientific community with the tools of tomorrow.

Committee Members:
Dr. Ashkan Salamat, Advisory Committee Chair
Dr. David Shelton, Advisory Committee Member
Dr. Andrew Cornelius, Advisory Committee Member
Dr. Paul Forster, Graduate College Representative

The defense presentation is open to the public via Webex conference meeting hosted by Dr. Ashkan Salamat

Friday, Apr 17, 2020 11:00 am | 1 hour | (UTC-07:00) Pacific Time (US & Canada)
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