Colloquium Schedule
Fall 2025
The Microlensing Planet Landscape on the Eve of Roman
Jennifer Yee '07, Harvard University
Friday, September 19, at 12:45
Microlensing has now detected hundreds of planets, in large part due to The Korea Microlensing Telescope Network (KMTNet). Using large, statistical analyses of the KMTNet events, we have measured the planet-star mass ratio function of planets into the super-Earth regime. We have also measured the mass function of free-floating planets. I will discuss these results, their connection to the broader planet population and observed disk substructures, and implications for planet formation theory.
Influence of Tiny Pins On The Dynamics of A Sheared Granular System
Katharina Vollmayr-Lee, Bucknell University
Friday, October 31, at 12:45
A granular system such as sand, M&Ms, or disks, can be behave like a fluid and when compressed and/or at higher density the system undergoes a "jamming transition" to behave like a solid. The here presented work is from a collaboration with A. Graves, C. Bester, and B. Utter. I will present computer simulations of a two dimensional 50:50 binary mixture of purely repulsive harmonic disks of radii 1:1.4. Via top and bottom walls of frozen particles we shear the system at constant shear rate. We investigate how the dynamics is influenced by the addition of fixed miniscule disks ("pins") of radius 0.004 placed on a square lattice. The average velocity profile, that is the velocity component in the direction of shear as function of the distance from the lower wall, strongly depends on the number of pins, but not on the distance from the jamming transition and not on the shear rate. The characteristic length of the velocity profile is set by the distance of the first layer of pins to the wall. When observing the velocity over time, there are huge fluctuations, which depend on the shear rate. We acknowledge the financial support from the National Science Foundation DMR-1905737 and DMR-1905474 and XSEDE/ACCESS allocations DMR-190064/PHY230003 and TRA100004.
Observations and Lessons Learned from a 47 Year Career in Physics (and Counting)
Dr. Robert E. Tench, RET and Associates LLC
Friday, November 7, at 12:45
Abstract:
Dr. Tench will present a narrative of his career and professional experiences as a physicist working in industry, academic laboratories, and government over the past 47 years. The talk will cover the following areas:
- Guidelines for Professional Technical Presentations
- Professional Guidance for Early Career Scientists and Engineers
- Historical Context in Physics: Newton, Gauss, Einstein
- Example of a Physics Career Progression
- A Look to the Future
Biography:
Dr. Robert E. Tench received a B.A. in Physics with High Honors from Swarthmore College in 1978 and a Ph.D. in Physics from MIT in 1985. The title of his dissertation was "Precision Studies of Atom-Field Interaction in Vapors"; and his thesis supervisor was Prof. Shaoul Ezekiel of EECS and AeroAstro. His photonics and fiber optics career has involved research, development, and manufacturing at AT&T and Lucent Bell Labs, Agere Systems, the National Security Agency, Johns Hopkins University Applied Physics Laboratory, Cybel LLC, and Fibertek. He is currently President and Chief Scientist at RET and Associates LLC (www.retandassociatesllc.com). He has placed over two dozen photonics and fiber optics products into manufacture, has twelve patents granted or pending, and has published over 115 journal and conference papers.
Stellar Capture of Primordial Black Holes: Gravitational-Wave Beats and Premature Stellar Collapse
Thomas Baumgarte, Bowdoin College
Friday, November 14, at 12:45
Primordial black holes (PBHs) - if they exist - interact with stars. PBHs with sufficiently large masses can be captured gravitationally and swallowed by stars. Once inside the star, PBHs orbit about the stellar center while slowly accreting stellar material and emitting gravitational radiation. In this talk, I will demonstrate that the pericenter advance of the PBH's orbit, which is sensitive to the stellar structure, leaves a characteristic "beat" signature in the emitted gravitational-wave signal. A future detection of such a signal, emitted by a PBH inside a neutron star, would therefore provide detailed information about the nuclear equation of state. I will also explore whether PBH capture by main-sequence stars could trigger a "premature collapse" and lead to the formation of black holes in the so-called upper and lower mass gaps
