Physics Colloquia

Gravitational Waves from Galactic Nuclei
Nicholas Stone, Assistant Professor
Department of Astronomy, University of Wisconsin-Madison

The discovery of GW150914 inaugurated the era of gravitational wave (GW) astronomy, opening a new window to study our Universe's compact objects and through which to test general relativity. Now, a decade later, the LIGO-Virgo-KAGRA (LVK) collaboration has seen hundreds of GW signals, overwhelmingly from mergers of binary stellar mass black holes. Despite the many successes of GW astronomy, a zeroth-order astrophysical question remains unanswered: what astrophysical environments produce the LVK binary black holes, and by what process are they assembled? Although many formation channels have been proposed, one uniquely testable solution is the "AGN channel:" a scenario in which individual black holes pair up and merge in the dissipative gaseous environment of an active galactic nucleus.

Novel Imaging Techniques for Studying Interactions of Membrane Receptors Among Themselves and with Downstream Signaling Partners
Thomas D. Killeen, PhD Candidate
University of Wisconsin-Milwaukee Department of Physics & Astronomy

Cells rely on complex signaling networks to sense and respond to environmental stimuli, but the bigger picture of how molecular assembly leads to robust cellular signaling is only beginning to emerge. A major challenge in characterizing cellular signaling is the ability to directly observe the dynamic interactions between membrane receptors and intracellular signaling partners in living cells. To address this challenge, this work presents the development of advanced fluorescence imaging and computational analysis tools designed to improve the precision and quantitative power of live-cell micro-spectroscopy for studying protein dynamics in real time.

This week's Physics Colloquium has been cancelled.

Superconductors Investigated by High-Energy Particle Irradiation
Dr. Kyuil Cho, Assistant Professor
Department of Physics, Hope College

Superconductor is a material that shows zero resistivity and Meissner effect below its critical temperature. This material has been used for various applications such as superconducting wires, medical device MRI, superconducting magnets for particle accelerators, quantum computing circuits, and many more. The superconductivity research group at Hope College conducts unique research on novel superconductors by using high energy particles. High energy particle irradiation is a useful method to generate homogeneous artificial defects on superconductors. By investigating how the defects affect the properties of superconductors, one can uncover the fundamental mechanism of superconductivity.

Titin-based Molecular Underpinnings of Skeletal and Cardiac Muscle Function
Jorge Alegre-Cebollada, PhD
Associate Professor & Group Leader, CNIC (Spanish National Center for Cardiovascular Research)

Titin is the largest protein in the human body. The function of the protein is not any smaller: it is critical for the contractile activity of muscles in the skeletal system and in the heart. In my presentation, I will introduce fundamental concepts that link titin nanomechanics with the macroscopic mechanical function of muscle. I will focus on our recent data demonstrating dysregulation of titin nanomechanics that can contribute to increased risk of heart failure in diabetic patients.

How to Give a Talk
Dr. Jean Creighton
Director of the UWM Manfred Olson Planetarium

Giving an engaging talk takes more than just knowing your material.

In this talk, I’ll outline key steps for preparing and delivering a compelling presentation for a variety of audiences. We’ll explore how to understand your listeners, define the purpose of your talk, clarify your message with visuals and explanations, rehearse effectively, engage your audience, and market your talk to generate interest. These strategies will help make your presentation more impactful and enjoyable for everyone involved.

Altermagnets: A New Technologically Relevant Class of Quantum Magnets
Daniel Agterberg
Professor, University of Wisconsin-Milwaukee

Magnetism underpins much of our current information technology. It also derives purely from quantum mechanics. Traditionally, discussion emphasizes two classes of magnets: usual ferromagnets, which underly data storage devices, and antiferromagnets, in which magnetic moments adopt an up-down structural motif. Recently, a new class of magnets, altermagnets, has generated tremendous interest. This class mixes properties of ferromagnets and antiferromagnets in a way that is promising for future applications.

From Extreme Binary Stars to Self-Driving Cars
Dr. Tony Rodriguez
Data Scientist, Waymo LLC (formerly Harvard CfA)

Compact objects -- white dwarfs (WDs), neutron stars, and black holes -- are laboratories for studying extreme physics under conditions unable to be replicated on Earth. When located in binaries, it becomes possible to measure properties of compact objects such as magnetic field strength, temperature, and the effects of mass transfer from a companion. In this talk, I will describe recent advancements in our understanding of WD magnetism.

Solving Atomic Structures of Molecules and Nanoclusters Using Superfluid Helium Droplet Cooling and Laser Alignment
Wei Kong
Department Head & Professor, Department of Chemistry - Oregon State University

We are building a prototype experimental apparatus to determine the atomic structures of molecules and nanoclusters using electron diffraction. We use superfluid helium droplets for cooling, thereby achieving effective field-induced orientation and alignment of the sample species. Electron diffraction patterns from the chosen orientation can then be accumulated until a satisfactory signal-to-noise ratio can be obtained.

How Dark is Space?
Tod R. Lauer
Astronomer, NOIRLab

We used NASA’s New Horizons spacecraft to measure the cosmic optical background (COB) intensity integrated over 0.4 ≲ λ ≲ 0.9 μm. The survey comprises 16 high Galactic-latitude fields. Images were obtained with the LORRI camera when New Horizons was 57 AU distant from the Sun. As such, the sky intensity measurements were unaffected by zodiacal light, which strongly interferes with COB measurements attempted from the inner solar system. T he survey yields a highly significant detection (6.8σ) of the COB at 11.16 ± 1.65 (1.47 sys, 0.75 ran) nW m−2 sr−1 at the LORRI pivot wavelength of 0.608 μm. The estimated integrated intensity from background galaxies, 8.17 ± 1.18 nW m−2 sr−1, can account for the great majority of this signal. The rest of the COB signal is formally classified as anomalous intensity but is not significantly different from zero. The simplest interpretation is that the COB is completely due to galaxies.