UNLV Department of Physics and Astronomy

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

DateSpeakerTitle & Abstract
Aug 30
(Special Talk 11:45am-1pm)
Dr. Maohai Huang
(NAOC, China)
(host: Zhang)
"Dust component of the ISM: Numerical Modeling and Observation Results from Herschel"
After some introductory basics of interstellar dust I will discuss how the dust component of the interstellar media (ISM) is modeled with CLOUDY to produce observables in photodissociation regions (PDRs) and HII regions. Since its launch in May 2009 European Space Agency's Herschel Infrared Space Observatory has observed Galactic and extragalactic dust with unprecedented sensitivity and efficiency. I will discuss some of the observational results.
Sep 2
Sep 9
Sep 16
Sep 23Prof. Edo Berger
(Harvard University)
(host: Zhang)
"Short GRBs: Environments, Afterglows, and Prospects for Gravitational Wave Detections"
The bimodality of GRB durations points to distinct progenitor classes. While the progenitors of long GRBs are now known to be massive stars, the progenitors of short GRBs remain unidentified. In this talk I will discuss the discovery of short GRB afterglow and host galaxies, detailed studies of their environments from parsec to galactic scales, and initial studies of their afterglows. Taken together, these observations point to NS-NS binary mergers as the likely progenitors. With the upcoming Advanced LIGO it is therefore possible that short GRBs will be the first detected sources, and I will discuss approaches to make this connection.
Sep 30Dr. Ken-ichi Nishikawa
(Univ. of Alabama, Huntsville)
(host: Zhang)
"Radiation from accelerated particles in shocks and reconnections"
Plasma instabilities are responsible not only for the onset and mediation of collisionless shocks but also for the associated acceleration of particles. We have investigated particle acceleration and shock structure associated with an unmagnetized relativistic electron-positron jet propagating into an unmagnetized electron-positron plasma. Cold jet electrons are thermalized and slowed while the ambient electrons are swept up to create a partially developed hydrodynamic-like shock structure. In the leading shock, electron density increases by a factor of about 3.5 in the simulation frame. Strong electromagnetic fields are generated in the trailing shock and provide an emission site. These magnetic fields contribute to the electrons transverse deflection and, more generally, relativistic acceleration behind the shock. We have calculated, self-consistently, the radiation from electrons accelerated in the turbulent magnetic fields. We found that the synthetic spectra depend on the Lorentz factor of the jet, its thermal temperature and strength of the generated magnetic fields. We are currently investigating the specific case of a jet colliding with an anti-parallel magnetized ambient medium. The properties of the radiation may be important for understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets in general, and supernova remnants.
Oct 7Dr. Haozhe Liu
(Harbin Institute of Technology, China)
(host: Zhao)
"Synchrotron X-ray Diffraction Studies for Phase Transitions under High Pressure Conditions"
In this presentation, the joint effort from multiple institutions for HIT (Harbin Institute of Technology) Oversea Collaborative Base Program at Argonne National Laboratory (ANL) and Brookhaven National Laboratory (BNL) will be introduced. This program offers great opportunity for training young faculty and students in HIT as exchanging scholar in synchrotron facilities of ANL and BNL, and brings new projects and new insight for deeper understanding on phase transition behaviors of materials under high pressure extreme conditions. Several projects with fresh data and results will be presented, including a new type of disordered substitution alloy structural model for the puzzling high pressure phase of topological insulator Sb2Te3, phase diagram for superconducting material EuFe2As2 under high pressure and low temperature domain, and diffraction tomography development in diamond anvil cell environment for phase transitions researches.
Oct 14Prof. Surendra Saxena
(Florida International Univ.)
(host: Kumar)
"Materials at Extreme Conditions: Experiments and Thermodynamic Modeling"
The results of several experiments on laser heating of solids, particularly iron, will be discussed in this talk along with thermodynamic modeling of solid properties at extreme conditions. CeSMEC facilities will be briefly described. Problems with thermodynamic modeling of solids at extreme conditions arise due to lack of a suitable EoS for solids and melts. While several theory based models such as the Birch Murnaghan or the Vinet can be used for the pressure-volume data, the effect of temperature on volume presents difficulties. Pressure-volume-temperature data on several solids will be used to discuss the problem and some possible solutions which will permit us to obtain complete thermodynamic data (heat capacity and entropy) at extreme conditions.
Oct 19
(Special Talk: Wed 11:45a-1pm)
Dr. Ivan Hubeny
(Univ. of Arizona)
(host: Nagamine)
"From stars to quasars: Modeling radiation-dominated objects in astrophysics"
There is a whole class of astronomical objects for which radiation is not only a probe of the physical state, but is in fact an important energy balance agent. In these objects, radiative transfer plays a crucial role. Typical examples of such a situation are stellar atmospheres, interstellar matter and various structures within, and accretion disks. I concentrate on three types of objects - stellar atmospheres and black hole accretion disks, both around supermassive holes (quasars) and stellar-mass holes (X-ray binaries), and show that since they have many similarities they can be modeled using an analogous approach. I will give a brief overview of recent progress in their modeling. On the stellar atmospheres side, very sophisticated models including millions of lines are now being constructed without the approximation of Local Thermodynamic Equilibrium - the so-called non-LTE line-blanketed models. It is shown that they provide an excellent match to high-quality ground- and space-based spectra. In accretion disk modeling, we have constructed several grids of non-LTE disk models for a wide range of parameters, and used then to analyze various observed data.
Oct 21Dr. Weidong Li
(UC Berkeley)
(host: Zhang)
"The Lick Observatory Supernova Search (LOSS) and SN 2011fe in M101"
The Lick Observatory Supernova Search (LOSS), using the robotic 30-inch Katzman Automatic Imaging Telescope (KAIT), has discovered over 800 SNe in the past decade, and is one of the most successful nearby SN searches. There are two parts in this talk. (I) a brief summary of LOSS and its scientific results. In particular, I will focus on our recently published series of papers on the derivation of the nearby SN rates from our search. I will talk about the properties of our sample galaxies, the derivation of the luminosity functions of SNe from a complete sample, and the correlations between SN rates and their host galaxy properties. (II) a report on the constraints on the progenitor system of the bright SN Ia 2011fe in M101, a SN not discovered by LOSS. The deep archival HST data, together with our decade-long monitoring history of M101, favor a scenario where the exploding white dwarf of SN 2011fe accreted matter either from another white dwarf, or by Roche-lobe overflow from a subgiant or main-sequence star.
Oct 25
(Special Talk: Tue 2pm)
Dr. Bruce Normand
(Renming University, China)
(host: Chen)
"Quantum Magnets under Pressure"
Recent inelastic neutron scattering measurements have followed the evolution of the elementary excitations of the quantum antiferromagnet TlCuCl_3 through the pressure-induced quantum phase transition (QPT), which separates a dimer-based quantum disordered phase from a phase of long-ranged magnetic order. These experiments demonstrate the continuous emergence of a clearly defined, massive amplitude mode, or longitudinal excitation of the magnetic moment, in the ordered phase. In this presentation, the pressure-induced magnetic QPT is first compared with its field-induced counterpart. A complete theoretical description is introduced, in which the longitudinal mode emerges naturally, with no additional parameters. Linewidth measurements indicate that the longitudinal mode is critically damped, as expected for a system at its upper critical dimension. Finite-temperature experiments probe the quantum critical regime, where thermal and quantum fluctuations are combined: the behavior of the mode energies is universal, but the damping of the longitudinal mode diverges.
Nov 4Dr. Michele Trenti
(Univ. of Colorado)
(host: Nagamine)
"From the First Stars to the First Galaxies"
The first billion years after the Big Bang are characterized by a complex interplay between formation of the first stars (metal-free) and the first galaxies (metal-enriched). These first light sources start illuminating the Universe and ionizing hydrogen atoms, defining the initial conditions for the formation of today's stars, galaxies and black holes. The Wide Field Camera 3 on board the Hubble Space Telescope is providing us with a new view on this epoch, previously accessible only through numerical simulations. I will present an overview of the most recent results in the field, focusing on the comparison of Hubble's observations at redshift z>6 from the HUDF and BoRG surveys with theoretical/numerical models of galaxy formation and evolution.
Nov 15
(Special Talk: Tue 11:45a-1pm)
Dr. Ding-Xiong Wang
(Huazhong Univ. of Science & Technology)
(host: Zhang)
"Magnetic Extraction of Energy from Black Hole Systems"
Magnetic extraction of energy from black hole (BH) systems is presented, in which three main energy mechanisms, i.e., the Blandford-Payne process, Blandford-Znajek process, and magnetic coupling process, are introduced based on BH accretion. Application of these energy mechanisms to high-energy astrophysics such as GRBs, AGNs and BHXB is briefly discussed.
Nov 18
(Special talk, Fri 10am)
Dr. Kohta Murase
(Ohio State Univ.)
(host: Zhang)
"Multi-Messenger Signatures of Ultra-High-Energy Cosmic Rays"
The origin of ultra-high-energy cosmic rays (UHECRs), has been one of the biggest mysteries in physics and astronomy. The multi-messenger approach, using neutrinos and gamma rays as well as cosmic rays, is necessary in order to reveal the sources. Recently a Gton neutrino detector, IceCube, was completed, and several Cherenkov gamma-ray telescopes as well as the gamma-ray satellite Fermi are now operating, so that the era of the multi-messenger observations is coming. The importance the multi-messenger approach is even greater if cosmic rays are transiently produced by bursts and flares and/or they are heavy nuclei rather protons, since cosmic rays experience long time delays and/or significant deflections due to cosmic magnetic fields. In this talk, we discuss characteristic signals from extragalactic astrophysical sources, which are crucial for identifying the accelerators of UHECRs.
Nov 18Dr. Paul Kent
(Oak Ridge National Lab)
(host: Chen)
"Lithium ion batteries: Challenges and opportunities for quantum mechanics based simulations"
Advances in rechargeable lithium ion batteries have led to their near ubiquitous use in mobile devices. However, significant improvements in energy density, power density, lifetime, and overall cost are desired for widespread use in new applications such as in the automotive industry. This will require the modification and adoption of new cathode, anode, and electrolyte materials, as well as insights into lifetime altering mechanisms such as solid-electrolyte interphase formation. In this talk I will provide a gentle introduction to the fundamental physical principles of these energy storage devices, outline the challenging scientific problems that remain, and describe how quantum mechanics based simulations will be able to address some of these problems. I will also describe some of the fundamental problems with current modeling approaches and recent attempts to improve simulation capability on supercomputers.
Nov 22
(Special Talk, Tue 11:45am-12:45pm)
Dr. Junhwan Choi
(Univ. of Kentucky)
(host: Nagamine)
"Simulating very high-z galaxy"
The advent of the Wide Field Camera 3 on board the Hubble Space Telescope has dramatically improved our ability to measure the rest-frame UV light from galaxies at z > 6. We use cosmological N-body/Hydrodynamics simulation to study the formation and evolution of these galaxies. First, I summarize recent improvement in the numerical simulation. Second, I present the galaxy properties in the simulations and compare them with recent observation. From this study, we find the large population of low-mass galaxies at high-z that drive a rapid galaxy evolution. We also report that massive galaxies at z~10 are mostly a gas-rich disk.
Dec 1
Dr. Jonathan Gardner
(NASA Goddard)
(host: Rhee)
Barrick Auditorium 7:30pm; "A Scientific Revolution: the Hubble and James Webb Space Telescopes"
Astronomy is going through a scientific revolution, responding to a flood of data from the Hubble Space Telescope, other space missions, and large telescopes on the ground. In this talk, I will discuss some of the most important astronomical discoveries of the last 10 years, and the role that space telescopes have played in those discoveries. The next decade looks equally bright with the newly refurbished Hubble and the promise of its successor, the James Webb Space Telescope. I will describe how Hubble was upgraded and how and why we are building Webb.
Dec 2
(Special talk Fri 10am)
Dr. Jun Luo
(Huazhong Univ. of Science & Technology)
(host: Zhang)
"Progress on Laboratory Gravitational Experiments in HUST Group"
Many theoretical physicists are trying to find a universal unified theory to cover the four fundamental interactions, but up to now they can not answer the question why gravitation is so weak compared with the other forces. Therefore, experimental research on the essential nature of gravitation is still relevant to some of the most profound questions in fundamental physics. During the past thirty years, our group, center for gravitational experiments in Huazhong University of Science and Technology (HUST), has devoted on such fundamental gravitational experiments, and has reached some interesting results, which include determination of the Newtonian gravitational constant G, testing the Newtonian inverse square law in short ranges, and testing the weak equivalence principle. This talk gives a general introduction of our work in the field of laboratory gravitational experiments.
Dec 2Dr. Jonathan Gardner
(NASA Goddard)
(host: Rhee)
"The James Webb Space Telescope"
"The James Webb Space Telescope is the scientific successor to the Hubble and Spitzer Space Telescopes, and is currently the largest scientific project under construction in the United States. It will be a large (6.6m) cold (50K) telescope launched into orbit around the second Earth-Sun Lagrange point. It is a partnership of NASA with the European and Canadian Space Agencies. Science with the James Webb Space Telescope falls into four themes. The End of the Dark Ages: First Light and Reionization theme seeks to identify the first luminous sources to form and to determine the ionization history of the universe. The Assembly of Galaxies theme seeks to determine how galaxies and the dark matter, gas, stars, metals, morphological structures, and black holes within them evolved from the epoch of reionization to the present. The Birth of Stars and Protoplanetary Systems theme seeks to unravel the birth and early evolution of stars, from infall onto dust-enshrouded protostars, to the genesis of planetary systems. The Planetary Systems and the Origins of Life theme seeks to determine the physical and chemical properties of planetary systems around nearby stars and of our own, and investigate the potential for life in those systems. To enable these scientific objectives, Webb will have four instruments: The Near-Infrared Camera, the Near-Infrared multi-object Spectrograph, and the Near-Infrared Imager and Slitless Spectrograph will cover the wavelength range 0.6 to 5 microns, while the Mid-Infrared Instrument will do both imaging and spectroscopy from 5 to 28.5 microns. I will conclude the talk with a description of recent technical progress in the construction of the observatory."
Dec 9Prof. Matthew Baring
(Rice University)
(host: Zhang)
"The Quiescent and Flaring Emission of Magnetars"
Magnetars are the most powerful compact objects in the stellar mass range observed in the Milky Way. The initial spikes of giant flares seen in three soft gamma repeaters (SGRs) dwarf the fluxes of the brightest cosmological gamma-ray bursts. Periodicity seen in magnetar quiescent and outburst emission, and distinctive "spin-down" lengthening of the period have driven the paradigm that strongly-magnetized neutron stars constitute these fascinating sources. This talk summarizes properties of both quiescent and outburst emission in magnetars, and some dissipative processes in their magnetospheres, including Comptonization. It discusses the action and characteristics of resonant Compton upscattering in generating hard X-ray tails of magnetars, and also possible signatures of exotic mechanisms like photon splitting. The recent suggestion of possible photospheric radius expansion in the newly-discovered magnetar SGR 0501+4516 as an interpretation of Fermi-GBM light curves will also be briefly addressed.

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