Weekly Colloquium

Most weeks during the semester, we host a scholar for a one-day visit. The visit culminates with a public talk on a topic of contemporary physics or astronomy. Students are welcome to these talks, and seniors are required to attend at least nine over the course of a year. Near the end of each semester, honors thesis students give public lectures on their work.   

Our Astronomy program is part of the Five College Astronomy Department, which hosts its own colloquium series Thursdays at 3:45 pm at UMass. 

  • Contact colloquium organizer Alice Simmoneau with any questions about colloquia, or being added to our mailing list.

October 2020

Tue, Oct 6, 2020

Assistant Professor of Physics Candice Etson, Wesleyan University: "Using Single-Molecule Imaging to Investigate Protein-DNA Interactions"

Proteins and DNA constantly interact with one another and are inextricably linked by both the central dogma of molecular biology and the critical need for maintenance and faithful transfer of genomic information from mother to daughter cells. However, many important protein-DNA interactions are transient and dynamic, which makes them particularly challenging to observe and characterize. Technological advances in fluorescence microscopy, including total internal reflection fluorescence (TIRF) microscopy, have made it possible to observe these processes in real time at the single-molecule level. These types of studies can reveal interactions and dynamics that would normally be obscured by the ensemble averaging that occurs in other approaches. Molecular processes are stochastic at the single-molecule level, and they often involve multiple intermediate steps. Therefore, careful statistical analysis of single-molecule data can provide key insights into the mechanistic details of these processes.

In this talk, I will describe how my research group is using single-molecule TIRF microscopy to directly observe the activity of restriction endonucleases. This class of enzymes includes numerous members that bind to DNA and mediate double strand breaks at specific sites based on the DNA sequence. I will describe how we collect data on individual cleavage events, and how we analyze the data to extract information about how these enzymes work. In addition, I will describe how TIRF microscopy can be used to collect single-molecule Förster Resonance Energy Transfer (FRET) data. This approach can provide even more detailed information about dynamic protein-DNA interactions.

Tue, Oct 13, 2020

Professor Amy Connolly, Ohio State University: "High-Energy Neutrino Astrophysics with Radio Techniques"

Multimessenger astronomy has entered an exciting new era with the recent discovery of both gravitational waves and cosmic neutrinos. I will focus on extremely energetic neutrinos as particles that can uniquely probe the most extreme astrophysics sources at cosmic distances, as well as fundamental physics in an unexplored energy regime. While optical Cerenkov radiation remains the most powerful strategy for neutrino detection over a broad energy range, the radio Cerenkov technique has emerged in the last two decades as the most promising for a long-term program to push the neutrino frontier by over a factor of 1,000 in energy. I will present the latest results from the field of high-energy neutrino astrophysics, with a focus on the balloon-borne ANITA experiment and the in-ice South Pole array ARA. I will also give an overview of the many exciting projects in this field that are on the horizon, and their anticipated impact in terms of the astrophysics and particle physics questions that we seek to answer.

Tue, Oct 20, 2020

Professor Philip Bucksbaum, Stanford University: "Ultrafast Strong Field AMO Physics"

Electron-electron and electron-ion forces drive all processes in chemistry, yet for many years these interactions were difficult to capture in experiments because of the ultra-short time scales and distances involved.

Two advances in laser technology led to methods that overcome these problems. The first was the development 30 years ago of powerful ultrafast lasers with focused optical fields comparable to the binding fields in chemical bonds, exceeding one volt per Angstrom. These lasers led to new ways to control the interactions of electrons in atoms on their natural time scales.

The second advance was the development in the last decade of ultrafast x-ray lasers with Angstrom-wavelengths and even higher focused fields. These can be used to produce movies of molecules as they undergo bond rearrangements in tens to hundreds of femtoseconds (millionth-billionths of a second). Recent improvements in the x-ray source will soon enable measurements that can resolve attosecond-scale (billionth-billionth of a second) electron motion in x-ray-atom interactions.

Tue, Oct 27, 2020

Research Assistant in Physics Abigail Plummer, Harvard: "Instability, Frustration and Phase Transitions in Thin Elastic Sheets"

Thin sheets, such as plant leaves, cell membranes and atomically thin materials, can show complex and surprising behaviors when allowed to grow and deform in three dimensions. One such behavior is the purely elastic shape memory found in disordered spring networks and, to a good approximation, crumpled paper. In this talk, I will introduce a simplified model for this effect, in which we locally swell a periodic array of points on an elastic sheet. When the local expansion is sufficiently large, or the sheet is sufficiently flexible, the regions of dilation will prefer to buckle out of the plane. We find that we can understand the ground state as well as the finite temperature behavior of this system if we assume that the buckled dilations behave like spins in an Ising model, a simple model for magnetism and phase transitions.