UNLV Department of Physics and Astronomy

Forum Schedule:  Fridays 3:45pm - 4:45pm

DateSpeakerTitle & Abstract
Feb 3Dr. Dusan Keres
(UC Berkeley/ UCSD)
(host: Nagamine)
"Galaxy Formation: Physics and Numerics"
I will discuss recent progress in understanding of galaxy evolution based on cosmological hydrodynamic simulations. Both theory and observations suggest that galaxies are not closed boxes but they accrete material from their surroundings expel mass, metals, energy and momentum into circum-galactic and inter-galactic media. While galactic outflows are frequently observed using absorption lines form background sources, direct detection of infalling material is more difficult owing to its modest covering factor, lower metallicity and complexity of disentangling its emission from other sources and uncertainties in modeling. Future progress in quantitative predictions for baryon circulation in and out of galaxies will need significant advances in modeling of relevant physical processes, dramatic increase in resolution and, most importantly, more accurate treatment of hydrodynamics. New moving-mesh technique was recently successfully implemented in AREPO code that combines strengths of previous methods and avoids many of the weaknesses. We have used this code for simulations of galaxy formation in a cosmological context and found that higher accuracy, when compared to standard implementation of smoothed particle hydrodynamics, leads to more extended gaseous disks of galaxies and more efficient cooling of hot gas in halos. These preliminary results show promise in solving some of the outstanding issues in galaxy formation and evolution.
Feb 6
(Special talk 1pm)
Dr. Nitya Kallivayalil
(Yale University)
(host: Nagamine)
"The Magellanic Clouds and Stream: Galactic Accretion in Action"
I present proper motions (tangential velocities) for the Large & Small Magellanic Clouds (LMC & SMC) based on three epochs of Hubble Space Telescope data, spanning a 7 year baseline, and centered on background quasars. The Magellanic Clouds are two of the largest and most prominent dwarf galaxies associated with the Milky Way. The high quality of the data has allowed us to measure their velocities to unprecedented precision, leading to some unexpected results. I will discuss the consequences of these new measurements for our understanding of the global dynamics of the Milky Way-LMC-SMC system. I will also show how we have been able to measure the rotation curve of the LMC purely from our proper motion data, without the need to rely on other studies of the LMC's geometry. This is the first time that this has been done for an external galaxy using only optical proper motion techniques, and shows the power of upcoming time-domain surveys such as LSST. This work is part of a larger effort towards 6-D mapping of the Milky Way.
Feb 17Dr. Sean Shieh
(Univ. of Western Ontario)
(host: HiPSEC)
Feb 24
(Special talk 1:30pm)
Dr. Frank Garner
(Radiation Effects Consulting)
(host: Farley)
"Radiation Damage Resistance in Steel Alloys : Void Swelling and Irradiation Creep of Ferritic-Martensitic Alloys at Very High Radiation Doses"
In a nuclear reactor, the steel making up the reactor is subject to intense radiation for long exposure times. The doses are measured in displacements per atoms (dpa). Doses in present reactors may be 100 dpa, and future reactor concepts envision doses as high as 600 dpa. In order to achieve high burn-up of fast reactor fuel it is necessary to contain the fuel in cladding that resists void swelling and irradiation creep more effectively than is achieved using austenitic steels. The current first-generation candidate swelling-resistant alloys are ferritic and ferritic-martensitic steels, with second-generation alloys being oxide dispersion-hardened variants of these steels. It is well known that ferritic alloys as a class swell and creep less than do austenitic alloys. Whereas current maximum fuel burn-ups of 10-11% are attained in fast reactors for doses of ~100-150 dpa using swelling-prone austenitic steels, higher burn-ups require 250-300 dpa, while some other reactor concepts envision doses of 400-600 dpa. The question arises whether acceptable levels of swelling and irradiation creep of ferritic-martensitic steels at such high doses are achievable. A review is presented of recent high-dose irradiation studies on HT9 and EP-450 conducted in FFTF and BOR-60 with maximum doses of 200 and 163 dpa, respectively, and also on EP-450, EP-823 and EP-852 irradiated side-by side in BN-350 to doses of 61 dpa.
Feb 24Dr. Enge Wang
(Peking University)
(host: Chen)
"What controls the evolution of surface-based nanostructures? Insights from computer simulations"
Pattern formation and decay in early stages of growth is fundamental to many materials in physics and chemistry. Understanding the complex interplay between the factors that influence the evolution of surface-based nanostructures can be challenging. Computer simulations play an important role in providing key insights. In this talk, I will first introduce the one-, two-, and three-dimensional Ehrlich-Schwoebel (ES) barrier in the kinetics-driven growth process. Within this framework, I will show how to control efficiently the island shape, the island instability, and the film roughness. Furthermore, I will discuss a novel concept: a truly upward adatom diffusion on metal surfaces, which is beyond the traditional ES barrier model. This process offers new indications on how to use ab initio kinetic Monte Carlo simulations to uncover some of the building regulations on the evolution mechanism down to the atomic scale.
Mar 1
(Special Talk, 1pm)
Dr. Julie Comerford
(UT Austin)
(host: Rhee)
"Dual Supermassive Black Holes as New Observational Tracers of Galaxy Evolution"
In recent years dual supermassive black holes (SMBHs), which are kpc-scale separation SMBHs in merger-remnant galaxies, have emerged as a new testing ground for theories of galaxy evolution. Dual SMBHs are direct observational tracers of galaxy mergers and SMBH mass growth during mergers, and, because they are the smallest that are resolvable, provide the tightest observational constraints on SMBH mergers. However, the full potential of dual SMBHs for studies of these topics has not yet been realized, due to the small number of known dual SMBHs. I will describe the first systematic search for dual SMBHs. This search employs a combination of large spectroscopic surveys of galaxies, longslit spectroscopy, imaging, and X-ray and radio observations to identify and characterize dual SMBHs that power active galactic nuclei. I will present te first batch of dual SMBHs that have been discovered with these techniques. This systematic survey will produce the first large catalog of dual SMBHs, which will enable measurements of the galaxy merger rate, SMBH growth via gas accretion during mergers, and the SMBH merger rate of interest to future gravitational-wave experiments.
Mar 2
(Special Joint Chemistry-Physics Forum; CHE-101, 3:30pm)
Prof. John Bohn
(host: Naduvalath)
"Ultracold Molecules as Quantum Molecular Beams"
For decades, experiments involving carefully controlled molecular beams have opened up the physical chemistry of small molecules in tremendous detail, limited, however, by the distribution of translational velocities within the beam. Nowadays, new technologies are emerging, capable of producing gaseous samples that are "ultracold," i.e., that have translational temperatures of order microKelvin. In this unique environment, scattering and reactions are strongly influenced by both quantum mechanics and easily-controlled laboratory circumstances. The first such experiment has recently obtained a modicum of information on a simple reaction. I will discuss the ideas behind this experiment, and speculate on future elaborations that may impact on physical chemistry.
Mar 9No ForumHiPSEC event
Mar 23Prof. Yangzhang Ma
(Texas Tech Univ.)
(host: Tschauner/Zhao)
"Materials under pressure and shear"
Mar 30Dr. Alex Lacerta
(host: Zhao)
Apr 6NO FORUMSpring Break
Apr 12
(Special Talk, Thu 12pm)
Prof. Andrew Smith
(host: Zhang)
"CTA and the Future of Ground Based Gamma-ray Astronomy"
Following on the successes of the current generation of ground-based TeV gamma-ray observatories such as VERITAS, MAGIC, and HESS, the Cherenkov Telescope Array (CTA) represents the next step forward in measuring the TeV universe. While the current generation of Imaging Atmospheric Cherenkov Telescope arrays (IACTs) are based around designs consisting of several 12-17m class telescopes, CTA will consist of an array of over 35 telescopes ranging in size from 7-30m with arrays located in both the Southern and Northern hemispheres. In this talk I will review the technique behind ground-based gamma-ray astronomy as well as the key results from current IACTs. I will describe the design of CTA as well as the predictions for what CTA will accomplish. I will also discuss the activities of the CTA site selection committee; this group has identified several ideal candidates for the northern CTA array near Flagstaff, AZ. This location would make CTA-North the next great Southwestern observatory, rivaling such iconic astronomical installations as the VLA and Kitt Peak.
Apr 20Prof. Mark Krumholz
(UC Santa Cruz)
(host: Nagamine)
"The Origin of the Initial Mass Function"
Star-forming environments vary by orders of magnitude in density, pressure, metallicity, and other properties, yet the initial mass function (IMF) of the stars they produce remains stubbornly unchanged. Explaining the origin and universality of the IMF is one of the oldest problems in theoretical astrophysics, but in the last few years advances in understanding how gas fragments, together with algorithmic advances that have allowed simulations to include improved physics such as radiative transfer, have produced significant progress. I describe these advances, and lay out the beginnings of a theoretical model capable of explaining the IMF.
Apr 27Dr. Juan Perez-Mercador
(Harvard University)
(host: Zygelman)
"Life and the Evolution of the Universe"
During the last decades we have put together a picture of the Evolution of the Universe where on the basis of a few basic principles we understand how it has changed through its history and evolved into the morphologies we observe today: we even have sets of equations that encapsulate the above. In addition we know that chemical evolution takes place in the Interstellar Medium, and are beginning to understand many details of the formation of planetary systems and their planets. During this period we have also developed a deep understanding of the Co-Evolution of Life in our planet and understood an extraordinary number of the many features and properties of extant and extinct living systems. Biology today is still a lot about detail, and our understanding of Life and Living Systems is still far from the more simplicity-based that we have for the Universe. Notwithstanding this, efforts are on their way to build a Bridge Between the Big-bang and Biology in order to pin down the accidental from the regular in Biology and, eventually, engineer living systems from scratch. This involves observational, experimental and phenomenological work in areas such as Interstellar Chemistry, Planetary Exploration, Origin of Life, Evolution of Life, Genomics, Synthetic Life or the Search for Life beyond the Earth. In this talk we will give a brief review of this exciting area and discuss some selected contributions coming from Physics and Information Theory applied to Life.

Past forums: Fall '08   Spring '09   Fall '09   Spring '10   Fall '10   Spring '11   Fall '11