Physics & Astronomy Colloquium

Colloquium: Photoluminescence Spectra of Emeralds from Different Origins

Trace impurity ions Cr3+ and V3+ in emerald both absorb visible light in the red and blue-violet range, giving rise to the emerald's green color. The Cr3+ impurity can also luminesce in the visible red when illuminated with laser light. We have shown that peak positions and relative intensities of R lines appearing in the photoluminescence spectrum of emerald depend upon the emerald's origin. In particular the R1 line of lab created emeralds is positioned at the shortest wavelengths, while for natural emeralds with a non-schist origin this line is found at the same or longer wavelengths, and for natural schist origin emeralds this line peaks at even longer wavelengths.1 Recently we have learned that the R1 line's peak position depends upon concentrations of trace impurities Mg2+ and Na+ in the emerald, and that the less common shifts of the R2 line's peak arise from increased concentrations of the trace impurity Li1+.

 

Refreshments will be served in CP 179 at 3:15 PM

Date: 
Friday, March 25, 2016 - 3:30pm to 4:30pm
Location: 
CP155
Type of Event (for grouping events):

Colloquium: LHCb: Results, Prospects and Pentaquarks?

The LHCb experiment at CERN was designed to be, and has become, the world's premier lab for studying processes where the net quark content changes. Such studies permit potentially observing the effects of particles at very high mass scales, even those with masses that (greatly) exceed the energy of the LHC itself. I will summarize the constraints placed on new high-mass particles by LHCb to-date, and also highlight a few interesting anomalies that have been seen. The LHCb physics program expanded rapidly during LHC Run 1 to include searches for dark bosons, studies of exotic tetraquark and pentaquark states, and novel probes of proton structure. I will give an overview of the current status and future prospects for each of these topics. 
 
Refreshments will be served in CP 179 at 3:15 PM
Date: 
Friday, April 22, 2016 - 3:30pm to 4:30pm
Location: 
CP155
Type of Event (for grouping events):

Colloquium: Star Formation In All the Wrong Places, and Other Astronomical Puzzles, Revealed By the SOFIA Observatory

NASA's SOFIA (Stratospheric Observatory for Infrared Astronomy), an airborne observatory optimized for conducting astrophysical investigations across the infrared-to-sub-millimeter spectral range, is an international partnership between the U.S. and German space agencies. As an airborne telescope optimized for infrared data collection SOFIA offers the only regular access to the wide swath of infrared wavelengths obscured by Earth's lower atmosphere and unavailable to ground-based observatories.

The presentation will focus on scientific results, some surprise discoveries, and unique analysis techniques utilizing SOFIA data. One dominant theme is how stars are able to form in extreme environments such as in the Galactic Center, where energetic radiation fields and a hot, turbulent medium in the vicinity of a supermassive black hole would seemingly be unconducive to the observed prolific star production. SOFIA offers unique tools for such studies, such as the ability to reveal kinematic signatures showing the details of how a star forming cloud collapsed to its current state, as well as providing clocks capable of directly measuring the collapse timescales for comparison to theoretical predictions.

Refreshments will be served in CP 179 at 3:15 PM

Date: 
Friday, April 15, 2016 - 3:30pm to 4:30pm
Location: 
CP155
Type of Event (for grouping events):

Van Winter Memorial Lecture: Quantum Revivals and the Modular Group

If we start with a quantum system in a particular state and let it evolve undisturbed according to the rules of quantum mechanics, usually it will not return to its initial state. However, there are exceptions, for example a simple harmonic oscillator. More generally the existence of such quantum revivals is associated with an infinite-dimensional algebra which generates the spectrum of the hamiltonian. Important examples are rational conformal field theories in two and higher dimensions. I discuss these in detail and show how an action of the modular group implies a complicated time-dependence for the return amplitude, including incomplete revivals at all rational multiples of the fundamental frequency.

For more information on this and previous van Winter Memorial Lectures, please visit https://math.as.uky.edu/van-winter

 

Refreshments will be served in CP 179 at 3:45 PM

Date: 
Thursday, April 7, 2016 - 4:00pm to 5:00pm
Location: 
CP320

Colloquium: Quantum Quenches: a probe of non-equilibrium many-body physics

In a quantum quench, system is prepared in some initial state (usually the ground state of some hamiltonian) and then allowed evolve in isolation with a different hamiltonian, for example, by rapidly quenching a parameter. This is most interesting for many-body systems where one can ask questions such as whether subsystems reach a stationary state, whether this state appears thermal, and how quickly does it reach this state. Although an obvious set of problems, they have only recently come to the fore with possibility of performing such experiments in ultra-cold atoms and other systems. In this talk I will try to address these questions in the context of some simple, and not-so-simple exactly solvable models.
 

Refreshments will be served in CP 179 at 3:15 PM

Date: 
Friday, April 8, 2016 - 3:30pm to 4:30pm
Location: 
CP155
Type of Event (for grouping events):

Colloquium: Blue Skies, Rainbows, and Neutrons

When photons scatter, their angular distribution and energy shift reveal information about the structure of the scattering target. As a result, photon scattering has long been used to study materials at the atomic and molecular level. By substantially increasing the photon energy, experiments can also be used to measure electromagnetic properties of the proton and neutron -- properties which are sensitively related to the interactions among the constituent quarks and gluons. We will discuss experiments which measure the electric and magnetic polarizabilities of the nucleon, and present new results for the neutron.
 

Refreshments will be served in CP 179 at 3:15 PM

Date: 
Friday, April 1, 2016 - 3:30pm to 4:30pm
Location: 
CP155
Type of Event (for grouping events):

Physics Colloquium: Mapping the Chemistry of the Galaxy with SDSS/APOGEE

Details of the chemical composition of stars provide information about the formation and evolution of the galaxies in which they form. I will outline some of the connections and provide some results for our Milky Way Galaxy from the Sloan Digital Sky Survey (SDSS) Apache Point Observatory Galactic Evolution Experiment (APOGEE). APOGEE is providing maps of the abundances of stars across the Milky Way. These suggest different timescales for star formation in different locations, both radially and vertically within the disk of the Galaxy, and also suggest that movement of stars within the Galaxy, through a process knows as radial migration, is important.

Refreshments will be served in CP 179 at 3:15 PM

Date: 
Friday, March 4, 2016 - 3:30pm to 4:30pm
Location: 
CP155
Type of Event (for grouping events):

Andrew Chamblin Memorial Colloquium: Entanglement and Spacetime

In this colloquium, I would like to review a recently developed new interpretation of gravitational spacetime in terms of quantum entanglement. The AdS/CFT correspondence in string theory provides a simple holographic computation of entanglement entropy. This generalizes the well-known "Entropy=Area relation" of Bekenstein-Hawking and strongly suggests that a gravitational spacetime consists of infinitely many bits of quantum entanglement. Indeed, an explicit realization of this idea is provided by so called tensor networks, which is a geometrical way to describe a given wave function in quantum many-body systems. I would like to explain these recent developments. 

Date: 
Friday, October 16, 2015 - 3:30pm to 4:30pm
Location: 
CP179

Physics and Astronomy Colloquium: Neutrinos from Nuclear Reactors: Searches and Surprises

Nuclear reactors are very bright sources of neutrinos. The radioactive fission products are neutron rich, and beta decay back to the valley of stability while emitting (electron anti-)neutrinos along the way. This was how the neutrino was discovered, and how we verified that neutrino oscillations explained the Solar Neutrino Problem. More recently, the Daya Bay Reactor Neutrino Experiment discovered a new mode of neutrino oscillation, and the PROSPECT experiment is being planned to search for "sterile" neutrinos.

This talk will first review the basics of neutrinos, their detection, neutrino oscillations, and nuclear reactors as neutrino sources. We'll then take a tour of recent results and next steps, including some surprises in what we've learned about the reactor neutrino source itself.
 

Refreshments will be served in CP 179 at 3:15 PM

Date: 
Friday, September 18, 2015 - 3:30pm to 4:30pm
Location: 
CP155

The Structure and Evolution of Milky Way-Like Galaxies

Matthew Bershady University of Wisconsin

A small fraction of the universe's energy-density is comprised of normal matter. A still smaller fraction is bound into stars and gas that we can see and are responsible for life. This talk examines what we know about the baryon content of, and how stars assembled in, galaxies like the Milky Way (MW). Dynamical measurements from integral-field spectroscopy indicate the baryonic mass of spiral disks is small. Radiative-transfer modeling of dusty, edge-on galaxies reveals super-thin stellar disks previously missed. These findings yield a consistent picture of light disks with young luminosity-weighted stellar ages. A new census from the Sloan Digital Sky Survey-IV, now underway, will test how broadly these results apply to the galaxy population as a whole. This advance allows us to better place the MW in context of today's galaxy population, and to leverage the MW's unique archaeological record against observations of distant galaxies. A critical question that can be resolved is whether stellar age and abundance gradients in galaxy disks are the result of a settling process of decreasingly turbulent gas or dynamical heating.

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