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

Title: The Mathematics of Cloaking and Invisibility

Abstract:  Cloaking and invisibility are staples of popular fiction, especially science fiction.  The pseudo-explanation usually given is that "the selective bending of light rays" (to quote Mr. Spock) around the object to be cloaked can render the object invisible.  But with the laws of physics in the real world, is this really possible, even in theory?  Scientists and mathematicians have recently found that the answer to this question is a qualified "yes."  In this talk I'll give a quantitative, but accessible account of the essential mathematical idea behind one approach to cloaking, in the context of an electromagnetic imaging technique called ``impedance imaging.''

There will be a reception at 4:30 p.m. in 745 Patterson Office Tower.

I will discuss a model of asymmetric Dark Matter that is alternative to the standard thermal WIMP paradigm. In this model the Ordinary and Dark Matters are made of the same particles with the Standard Model interactions in both sectors, except two sectors do not interact with each other by the Standard Model forces. They only interact gravitationally and by some BSM mechanisms that mix neutral components from both sectors. Thus, for example, neutrinos can oscillate into sterile neutrinos and the neutrons into sterile neutrons. Sterile neutrino search has motivated proposals of several experiments, e.g. PROSPECT at HFIR/ORNL and short baseline at Fermilab. Recently some indications have appeared that neutrons might be transformed into sterile neutron states, so-called "mirror neutrons". I will review these indications and will discuss a new possible small, easy, and not-expensive experiment where transformations of neutron to mirror neutron can be detected by reappearance of neutrons from behind the absorption wall in regeneration mode. Such an experiment can be performed, for example, at SNS. A possible layout for SNS and estimates of the sensitivity will be presented.

The University of Notre Dame Nuclear Science Laboratory (NSL) is home to 2 electrostatic accelerators that are used for a variety of studies in nuclear physics. A major focus of these studies is to understand the properties and reactions of nuclei in astrophysical environments. This seminar will focus on these measurements with an emphasis on the direct measurements of reaction cross sections using the St. George Recoil Separator, the precision determination of resonance properties via elastic scattering measurements, and the investigation of reactions on radioactive nuclei using the TwinSol separator. Finally, future plans including the expansion of the NSL and the installation of an underground accelerator will also be discussed.

UKy alumnus Aaron Maschinot will present an informal discussion about his career transitioning from nuclear physics to the technology industry, and his experiences along the way. The seminar is targeted for graduate students.

The spectra resulting from observations of unresolved galaxies undergoing vigorous star formation originates from the emission given off by a large collection of H II regions within each galaxy. This gives rise to powerful selection effects: the emission lines we observe come from clouds with the physical conditions necessary to optimally emit them. Current modeling of star forming galaxies assumes a small range of conditions typically seen in local H II regions. Using spectral synthesis simulations that cover a vast parameter space, we have compiled an atlas of starburst galaxy emission line equivalent widths ranging from the UV to IR in order to assist observers in understanding the conditions present within their galaxy sample. With our own galaxy sample that spans a large range of ionization, we used this atlas to fit emission line ratios much better than when using previous modeling methodologies, revealing that the distribution of ionizing flux within a star forming galaxy, instead of its metallicity, is the primary physical parameter controlling the ionization level.

THz spectroscopy has sprung to the forefront of the study of quantum materials in recent years. With these recent advances, we can now bridge the gap between the capabilities of photonics in the infrared and visible range, and those of electronics in the microwave.

I will describe our recent explorations into the physics of topological insulator Bi2Se3 thin films, and of a multiferroic quantum magnet Sr2FeSi2O7 single crystals using terahertz spectroscopy.