Events at Physics |
Events on Thursday, October 12th, 2017
- R. G. Herb Condensed Matter Seminar
- All-Dielectric Optical Metamaterials
- Time: 10:00 am
- Place: 5310 Chamberlin Hall
- Speaker: Jason Valentine , Vanderbilt University
- Abstract:
Optical metamaterials are man-made materials in which structuring is used to control the effective optical properties. Using the engineering freedom associated with structuring, researchers have utilized metamaterials for a number of exotic applications including sub-diffraction limit imaging and cloaking. However, absorption loss has been a major impediment to the adoption of metamaterials in practical applications. This absorption loss arises due to ohmic damping in the metals that traditionally comprise the unit cell. In this talk, I will discuss all-dielectric metamaterials in which metal, and the accompanying absorption, is completely avoided. As with their metallic counterparts, manipulation of the unit cell structure of all-dielectric metamaterials offers a means to engineer a wide variety of optical properties. Along these lines, I will discuss several implementations of all-dielectric metasurfaces with functionalities that include polarization control, wavefront tailoring, near-unity reflection, and sharp Fano resonances. The freedom to achieve a wide variety of optical properties, combined with the reduction in absorption loss, could lead to ultra-thin optical elements including lenses, waveplates and sensors as well as more complex assemblies of these elements in the form of metaoptics.
- Host: Brar
- NPAC (Nuclear/Particle/Astro/Cosmo) Forum
- Neutrino Quantum Kinetics and the Early Universe
- Time: 2:30 pm
- Place: 5280 Chamberlin Hall
- Speaker: Evan Grohs , University of Michigan
- Abstract: The laboratory of the early universe provides a setting for testing Beyond Standard Model (BSM) physics in the particle and cosmological sectors. Any BSM physics in operation at early times may produce slight deviations on the primordial element abundances and cosmic microwave background observables predicted within the standard cosmology. The identification and characterization of such BSM signatures require a precise treatment of the neutrino energy and flavor wave functions during the time of Big Bang Nucleosynthesis (BBN) using the Quantum Kinetic Equations (QKEs). I will review some of the work done on characterizing BBN with a Boltzmann-energy-transport approach, as well as ongoing work towards a full QKE treatment with neutrino oscillations and collisions. A QKE treatment of early-universe neutrino physics will greatly assist observers and theorists as the next generation cosmological experiments come on line in the near future.
- Host: Baha Balantekin
- Astronomy Colloquium
- Observing gas in the circumgalactic medium and the Cosmic Web
- Time: 3:30 pm - 5:00 pm
- Place: 4421 Sterling Hall, Coffee and Cookies 3:30 PM. Talk begins at 3:45 PM
- Speaker: Bart Wakker, UW Madison Astronomy Dept
- Abstract: Using HST spectra of AGN we study the gas inside and outside galaxy halos. We find that galaxies have extended (300 kpc radius) halos, which blend into the general intergalactic medium. We study properties of the gas as function of location in the galaxy halos. We also have constructed the first 3-D view of a 30x6 Mpc filament at cz~3500 km/s, This filamentis defined using a new catalogue of nearby galaxies, which is mostly complete down to a luminosity of about 0.05 L* and includes homogenized diameters and luminosities. The baryonic mass of the filament galaxies is 1.4x10^13 Msun, while the mass of filament gas outside galaxy halos is found to be 5.2x10^13 Msun. We find that simulations overpredict the detection rate of gas in the filament between 2.1 and 5 Mpc from the axis. The width of the Lya lines correlates with filament impact parameter and four BLAs in our sample all occur within 400 kpc of the filament axis, indicating increased temperature and/or turbulence. We further find that the recent Haardt & Madau (2012) extragalactic ionizing background predicts a factor 3-5 too few ionizing photons.
- Host: Astronomy Department