An article by by Elizabeth Landau, senior communications specialist with NASA summarizes Randall Dannen's recent work on the physics of active galactic nuclei in Daniel Proga's research group. Read the NASA website article here. and Randall's original paper here.
This work investigates the structural and chemical stability of technetium under extreme conditions using in situ synchrotron X-ray diffraction. Utilizing advanced pressure and laser heating techniques we are able to access different regimes of the energy landscapes unexplored by previous studies. There are two sets of study; both of which are fundamental to understanding the physical and chemical behavior of this radioactive transition element. The first, is the discovery and characterization of a new, high pressure high temperature allotrope of Tc. Through structural analysis, we are able to demonstrate the existence of magnetic ordering - only the second example in a 4d metal. The second, is the synthesis of a new family of nitride compounds whose physical properties are explored.
The defense presentation is open to the public via Webex conference meeting hosted by Dr. Ashkan Salamat.
Monday, May 11, 2020 1:00 pm | 1 hour | (UTC-07:00) Pacific Time (US & Canada)
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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.
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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Chao-Chin Yang, Zhaohuan Zhu, Stephen Lepp, and Xiao Hu just were awarded a $474,315 research grant by NASA through the Astrophysics Theory Program. They will conduct state-of-the-art computer simulations to model a circumstellar disk around a young star and study the dust-gas dynamics in the disk. The investigation will help us understand the variety of morphological features such as rings and gaps in nearby circumstellar disks detected recently by high-resolution, high-contrast observations. It will also improve the understanding of the process of planet formation. Zhu and Lepp are co-investigators on the project, and Hu is a collaborator.
The text courtesy an original announcement in UNLV Today.
Chao-Chin Yang, Zhaohuan Zhu and Stephen Lepp just were awarded a $456,315 research grant by NASA through the Emerging Worlds Program. They will investigate one of the most difficult stages in the course of planet formation, for example, how kilometer-scale planetesimals can be built from pebble-sized materials around a young star before a planet can be fully assembled. By conducting state-of-the-art computer simulations and comparing the results with the properties of the Kuiper Belt objects observed in our own solar system, they will be able to test the leading theory of planetesimal formation at unprecedentedly high resolutions. The investigation will further improve our understanding of the origins of the solar system as well as the thousands of the extrasolar planetary systems. Zhu and Lepp are co-investigators on the project.
The text courtesy an original announcement in UNLV Today.
UNLV physicist Ashkan Salamat was one of just 46 university professors nationwide – and the first from UNLV – to earn an Early Career Award from the U.S. Department of Energy’s (DOE) Office of Science.
Read the UNLV News and Publications article here.
