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Colloquium

Unless otherwise noted, the physics colloquia are held in Room 307 of the Science and Engineering Research Facility. Refreshments are served at 3:00 p.m. with the talk following at 3:30.

Please note: since Fall 2017 colloquia are not webcast or recorded. Videos from Spring 2017 colloquia are available here. Earlier semesters are available in the Webcast archives.

Spring 2019 Schedule
Date
Speaker
Title
Host

January 14

Lee Riedinger
University of Tennessee

Reflections on a Long Career

Hanno Weitering

January 21

MLK Holiday

No Colloquium

NA

January 28

 

No Colloquium

NA

February 4

Sarah Tuttle
University of Washington

Tracing Galaxy Ecosystems - Galaxy Evolution and the Gas That Shapes It

Sowjana Gollapini

February 11

Ed Brown
Michigan State University

Accreting Neutron Stars and the Physics of Dense Matter

Andrew W. Steiner

February 18

Thia Keppel
Jefferson Lab

From Fundamental Nuclear Physics to Cancer Instrumentation: Science at Jefferson Lab

Nadia Fomin

February 25

Kipton Barros
Los Alamos National Laboratory

Machine Learning of Interatomic Potentials

Cristian Batista

March 4

Jon Link
Virginia Tech

Hunting the Sterile Neutrino

Yuri Efremenko

March 11

Andrew Puckett
University of Connecticut

Nucleon Imaging at the Femtoscale via Elastic Electron-Nucleon Scattering

Nadia Fomin

March 18

Spring Break

No Colloquium

NA

March 25

Magdalena Djordjevic
University of Belgrade

Dynamical Energy Loss Formalism and Comparison with Experimental Data

Christine Nattrass

April 1

Stephan Schlamminger
NIST

The Revised International System of Units

Geoff Greene

April 8

Paul Wiggins
University of Washington

Why Systems Biology Shouldn’t Work… but Does… and What Heat Capacity Can Explain about Learning

Jaan Mannik

April 15

Peter Armitage
Johns Hopkins University

On Ising's Model of Ferromagnetism

Jian Liu

April 22

Amy Slaton
Drexel University

HONORS DAY to follow/Check back for Exact April 22 Schedule

Identity and Diversity in the Science Classroom: What Good is Welcome?

Nadia Fomin


Abstracts
January 14
Lee Riedinger, University of Tennessee

Reflections on a Long Career

Joining the UT Physics faculty in 1971 was a career-defining step for me and led to many opportunities in the last 47 years. In this talk I will reflect on the various stages of my long career with emphasis on the things I learned at each step and the people that affected and guided me the most.


February 4
Sarah Tuttle, University of Washington

Tracing Galaxy Ecosystems - Galaxy Evolution and the Gas That Shapes it

Galaxy evolution is a crucial part of understanding how the baryons of our universe are distributed and transported. Galaxies are also difficult remote laboratories to work in because of the many interacting processes that govern their resulting morphology, because of their evolution through time, and because of their distance. I will present several sets of data we are using to pick apart processes that are shaping interactions between gas and galaxies, as well as the instruments I have built to study them. I will first show an unusual local (z < 0.05) sample of galaxies with blue bulges and red disks that are found in a variety of environments. These local galaxies are observed both with LRS2 at the HET and MaNGA (a part of SDSS-IV). I will also show early work with a collection of Lyman alpha emitters (LAEs) with extended emission highlighting likely gas reserves at higher redshifts (2 < z < 4). Both of these experiments highlight different ways we can pursue the full baryonic accounting for galaxy systems, and I will detail the upcoming SDSS-V projects that will add to our understanding of these galaxy ecosystems in the Milky Way and beyond. I will briefly highlight both integral field spectroscopy systems as well as the robotic fiber positioners we are taking part in building for SDSS-V.


February 11
Ed Brown, Michigan State University

Accreting Neutron Stars and the Physics of Dense Matter

Neutron stars are composed of the densest observable matter in nature and occupy the intellectual frontier between astrophysics, nuclear physics, and, now, gravitational physics. Current and planned nuclear experiments on heavy nuclei and observations of neutron stars in both electromagnetic and gravitational waves will be exploring the nature of dense matter from complimentary approaches. Many observed neutron stars accrete hydrogen- and helium-rich matter from a companion star. During the slow compression to nuclear density the accreted matter is transmuted from being proton-rich to being proton-poor. These reactions affect many observable phenomena — from energetic explosions on the neutron star's surface to cooling of the surface layers — that in turn inform us about the nature of the deep interior of the neutron star. In this talk, I shall describe what recent astronomical observations and nuclear physics experiments are telling us about the nature of matter at nuclear densities.


February 18
Cynthia (Thia) Keppel, Jefferson Lab

From Fundamental Nuclear Physics to Cancer Instrumentation: Science at Jefferson Lab

The Thomas Jefferson National Accelerator Facility (Jefferson Lab) underwent a major upgrade, doubling the beam energy to 12 GeV and substantially upgrading the associated experimental equipment. Experiments leveraging this upgrade have been underway for a couple years now, and many new results are on the near term horizon. An overview of this program and first data will be presented. In addition, some applications of detector technology from the fundamental nuclear physics program to medical instrumentation will be discussed.


February 25
Kipton Barros, Los Alamos National Laboratory

Machine Learning of Interatomic Potentials

Machine learning is emerging as a powerful tool to emulate electronic structure calculations. Deep neural networks can now predict atomic interactions with accuracies exceeding density functional theory, and approaching that of coupled cluster theory, at a tiny fraction of the computational cost. I will discuss recent methods for building interatomic potentials relevant to chemistry, materials science, and biophysics applications. A key idea is active learning, in which the training dataset is generated on-the-fly, to fill in gaps of the machine learning model, and to achieve a surprising level of transferability.


March 4
Jon Link, Virginia Tech

Hunting the Sterile Neutrino

It is well known that in the Standard Model of Particle Physics there are exactly three flavors, or types, of neutrinos. Still, for more than two decades there have been a persistent, yet unproven, hints of a fourth neutrino type: the so called “sterile neutrino”. This hypothetical sterile neutrino’s properties are truly bizarre. Like all neutrinos, it does not interact via the electromagnetic or nuclear strong forces, but, unlike common neutrinos, it also has no nuclear weak interaction. Instead, it interacts only through its mixing with the three common neutrinos in a phenomenon known as neutrino oscillation. This talk will explore the evidence both for and against the sterile neutrino, and discuss approaches to solving this sterile neutrino mystery through new experimental tests.


March 11
Andrew Puckett, University of Connecticut

Nucleon Imaging at the Femtoscale via Elastic Electron-Nucleon Scattering

Protons and neutrons, collectively known as nucleons, are the building blocks of the atomic nucleus, but are not elementary particles. Instead, nucleons are composite objects of finite, measurable size, with a rich and complicated internal structure. Approximately 99% (by mass) of all visible matter in the universe is dynamically generated by the strong interactions that bind the elementary quarks of the Standard Model together to form protons, neutrons, and nuclei. Understanding how the behavior of strongly interacting matter emerges from Quantum Chromodynamics (QCD), the theory of the strong interaction, is a central problem in nuclear physics. Much of what we know about the microscopic structure of nucleons and nuclei comes from electron scattering experiments, starting with the pioneering work of Hofstadter and collaborators at Stanford in the 1950s and continuing to the present day. Modern accelerators are capable of producing electron beams of high energy, intensity, duty cycle, and polarization, allowing the nucleon's quark structure to be resolved in ever finer detail in both coordinate and momentum space. Elastic electron-nucleon scattering, in which the nucleon remains intact and in its ground state after a "hard" collision, is sensitive to the spatial distributions of charge and magnetism in the nucleon via form factors describing the deviation of nucleon structure from point-like behavior as a function of the momentum transferred in the collision. The measurement of these form factors at "large" momentum transfers is presently a unique worldwide capability of Jefferson Lab's (JLab's) Continuous Electron Beam Accelerator Facility (CEBAF). The new Super BigBite Spectrometer (SBS), to be installed in JLab's Hall A in 2020, is designed to efficiently measure the nucleon form factors to the highest accessible momentum transfers following the recent 12 GeV energy upgrade of CEBAF. In this colloquium, I will give a brief overview of the historical development and modern understanding of nucleon structure, emphasizing the insights gained from elastic form factor measurements. Then, I will give a detailed overview of the SBS form factor program and its expected impact on our understanding of the nucleon.


March 25
Magdalena Djordjevic, University of Belgrade

Dynamical Energy Loss Formalism and Comparison with Experimental Data

Dynamical energy loss that we developed allows generating reliable predictions of high pt suppression. In this talk, I will provide an overview of the dynamical energy loss formalism, followed by comparison of our theoretical predictions with experiments data. I will also discuss how contribution of different steps in the suppression scheme contribute to complex suppression patterns at LHC and RHIC.


April 1
Stephan Schlamminger, National Institute of Standards and Technology

The Revised International System of Units

On world metrology day, May 20th, this year, a revision to the International System of Units will become effective. This revision is implementing a fundamental change. Up to this day, seven very different definitions for the base units were used. In the revised SI, all units trace back to seven fundamental constants. The numerical values of four constants, the Avogadro, Boltzmann, and Planck constant, and the elementary charge will be fixed on this day. Together with three constants whose numerical values have been fixed previously, the hyperfine transition frequency of an isotope of cesium, the speed of light in vacuum, and a specified luminous efficacy, the seven base units can be found (or realized as the metrologist would say). In this talk, I will explain the new SI, give reasons for the revisions and show some of the experiments that led to the redefinition and can be used in the future to realize some of the units.


April 8
Paul Wiggins, University of Washington

Why Systems Biology Shouldn’t Work… but Does… and What Heat Capacity Can Explain about Learning

Despite an intensifying interest in applications of machine learning to the analysis of big data, fundamental questions remain about the mechanisms of learning: (i) How can immensely complex models ever learn from small datasets? (ii) What is the physics of learning and (iii) are there universal properties in learning processes? In this talk, I will elaborate on a long-discussed analogy between Bayesian statistics and statistical mechanics. This correspondence reveals a surprisingly simple answer to these three questions by analogy, in the well known physics of the heat capacity. Finally, I will discuss how these insights can be used to design new learning algorithms.


April 15
Peter Armitage, Johns Hopkins University

On Ising's Model of Ferromagnetism

The 1D Ising model is a classical model of great historical significance for both classical and quantum statistical mechanics. Developments in the understanding of the Ising model have fundamentally impacted our knowledge of thermodynamics, critical phenomena, magnetism, conformal quantum field theories, particle physics, and emergence in many-body systems. Despite the theoretical impact of the Ising model there have been very few good 1D realizations of it in actual real material systems. However, it has been pointed out recently, that the material CoNb2O6, has a number of features that may make it the most ideal realization we have of the Ising model in one dimension. In this talk I will discuss the surprisingly complex physics resulting in this simple model and review the history of "Ising’s model” from both a scientific and human perspective. In the modern context I will review recent experiments by my group and others on CoNb2O6. I want to give some perspective about how those of interested in the physics of condensed matter can go searching for material systems that are realizations of particular Hamiltonians. And I will show how low frequency light in the THz range gives unique insight into the tremendous zoo of phenomena arising in this simple material system. It is remarkable that in a system as simple as this quasi-1D chain, analogies to phenomena and mathematical structures as diverse as quark confinement, quantum number fractionalization, Majorana fermions, Airy functions, and a 248 dimensional Lie algebra(!) can be found.


April 22
Amy Slaton, Drexel University

Identity and Diversity in the Science Classroom: What Good is Welcome?

Many STEM, Humanities, and other instructors today bring inclusive intentions to their teaching yet feel frustrated with conventional academic "diversity" programming for different reasons. Students, too, express a wide range of reactions to such initiatives. In the sciences, these responses can diverge especially strongly. For some science faculty and students, mandated attention to identity feels unneeded and like a distraction from the "real" teaching and learning. But for others, university diversity programs traffic in mere feel-good visions of tolerance, failing to address deep, systemic inequities or the lived trauma of racism, sexism, homophobia, or ablism. Surely our own, self-ascribed or experienced identities shape our reactions. But why, some 40 years after U.S. universities first introduced so-named projects, does the whole notion of "diversity" satisfy so few? Could the very nature of STEM Diversity’s good intentions, often pivoting on ideologies of tolerance and welcome, stand in the way of deeper reflection or change? We’ll consider the recent history of anti-discrimination efforts in the academic sciences and the conundrum of what could possibly be wrong with an earnest desire to include under-represented communities. We’ll also ask what might come next for our address of equity in the sciences, and who should decide.


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