Physics Colloquia

Searching for a Gravitational Wave Background with Pulsar Timing Arrays

Sarah Vigeland, Asst. Professor, Dept. of Physics, UW-Milwaukee
Pulsar timing arrays use observations of millisecond pulsars to detect nanohertz gravitational waves. The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) Collaboration has recently released their 15-year data set containing observations of 68 millisecond pulsars. These data contain evidence for Hellings-Downs correlations, which are characteristic of a gravitational wave background.

The Self-force on Static and Dynamic Charges in Schwarzschild Spacetime Using the Method of Images
Alan Wiseman, Assoc. Professor, Dept. of Physics, UW-Milwaukee
One of the most basic examples of a self-force phenomenon (sometimes called the radiation reaction force) is that of a small, charged particle near a large spherical mass such as a Schwarzschild black hole. If the particle is held stationary, there are novel electrostatic forces on the particle. If the particle is orbiting the mass, the fields created by the particle back-react on the particle and cause it to depart from its otherwise free-fall motion. There are many ways to solve for the forces and motion in these circumstances, but past solutions have involved considerable technical machinery, and the results are messy and "non-intuitive".

Professor Gabor Csathy, Department of Physics and Astronomy, Purdue University

Emergent Particles and Topology in Flat Landau Bands

Electronic systems with flat energy bands support a variety of topological phases of current interest. The two-dimensional electron gas in the fractional quantum Hall regime is such a system. Ground states of this system found an elegant description in terms of emergent particles called composite fermions.

Dr. Marcus Noack, Research Scientist, Lawrence Berkeley National Lab
Next-Generation Gaussian Processes for Function Approximation, Uncertainty Quantification, and Decision-Making
Gaussian processes (GPs) and Gaussian-related stochastic processes are powerful tools for function approximation, uncertainty quantification, global optimization, and autonomous data acquisition due to their robustness, analytical tractability, and natural inclusion of Bayesian uncertainty estimates. Even so, Gaussian processes are often criticized for poor approximation performance and neck-breaking computational costs in real-life applications. The reason for this gap, however, is not the methodology itself but rather a user-caused lack of flexibility and domain awareness of the underlying prior probability distribution.

Joel Nowitzke, PhD Candidate, UW-Milwaukee
Modeling and Measurements of Network Formation and Viscoelastic Behavior of Folded Protein-Based Hydrogels
Proteins are vital for various daily functions and are even used in creating biocompatible materials through chemical crosslinking. However, predicting the mechanical properties of these materials is challenging due to the random orientation of constituent molecules within the network. Bridging the gap between nanoscopic and macroscopic scales is essential for formulating predictable biomaterials.

Rob Pisarski, Distinguished Scientist, Department of Physics, Brookhaven National Laboratory

The Ugly Duckling and the Swan: The Quark-Gluon Plasma and Heavy Ion Collision

I give a pedagogical and historical overview of the search for the Quark-Gluon plasma (QGP) in the collisions of heavy ions. I begin with a brief review of why we expect a QGP to be formed at high temperature. In this, numerical simulations in lattice Quantum ChromoDynamics (QCD) form the bedrock of the field. In particular, they demonstrate the relationship between deconfinement and the restoration of chiral symmetry.

Segev BenZvi, Assoc. Professor, Department of Physics, University of Rochester

Measuring Cosmic Expansion with the Dark Energy Spectroscopic Instrument

Since the first observations of the accelerating expansion of the universe at the end of the 1990s, astronomers and physicists have struggled to understand dark energy, a mysterious repulsive force that drives the acceleration. A number of models of dark energy exist. The simplest (the cosmological constant), assumes dark energy is non-interacting and is the same everywhere in space and time. Different models predict subtely different features in the large-scale structure of the universe. We are now entering an era of new photometric and spectroscopic surveys which can discriminate different models of dark energy with unprecedented precision.

Hongbin Li, Professor, Department of Chemistry, The University of British Columbia

Rational Engineering of Protein-based Biomaterials: from single molecule traits to functional material properties

In their biological settings, elastomeric proteins function as molecular springs, thereby establishing elastic connections, plus providing mechanical strength and elasticity. With an ability to change their shape (evolving from simple, random coil-like structures to a more sophisticated beads-on-a string formation), they fulfill their biological function. These complex protein polymers exhibit distinct mechanical properties.

The development of single molecule force spectroscopy techniques has made it possible to directly probe these properties, at the single molecule level, allowing us to understand their molecular design principles. This knowledge has enabled us to engineer novel elastomeric proteins to achieve tailored and well-defined nanomechanical properties.

Catalin Picu, Dept. of Mechanical, Aerospace & Nuclear Engineering, Rensselaer Polytechnic Institute

Soft Network Materials: Structure-Properties Relations

Many materials have a stochastic network of filaments as their main structural component and are referred to collectively as ‘network materials.’ This class includes all biological connective tissue, the extracellular matrix, the intra-cellular cytoskeleton, paper and cellulose-based products, nonwovens, as well as various molecular networks such as rubber, gels and thermosets.

Dr. Joshua "Shua" Sanchez, Postdoctoral Fellow, Department of Physics, MIT

Quantum Criticality and Magnetic Field-Induced Superconductivity

When electrons have strong interactions with each other, new quantum phases of matter emerge, such as magnetism, nematicity, charge order, and superconductivity. In these “Quantum Materials”, the microscopic interactions can be very difficult to probe and understand, yet they give rise to macroscopic properties that are easier to study and can be harnessed for new technologies.