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Colloquium

During the 2020 Fall semester, all Physics and Astronomy Colloquia will be presented remotely using Zoom on Thursdays at 4pm CT.  For details please contact Ashley E. Brammer by email (ashley.e.brammer@vanderbilt.edu) or phone (615-343-7389).

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Fall 2020

Thursday September 3rd 2020 4:00 PM

M. Shane Hutson, Professor and Chair, Department of Physics and Astronomy

State of the Physics and Astronomy Department - 2020   (show abstract)

It is of course an understatement to say that 2020 has been a year of disruption in academia. Our students went home; our classrooms went virtual; our labs and offices were shuttered. Nonetheless, if you look back at the 2019-20 academic year, our faculty, postdocs and students achieved great things – made possible with the help of our dedicated staff. I want to take our first colloquium of the fall to recognize those accomplishments and to talk about how we can maintain and build on our momentum. I will share my thoughts on how to do so under admittedly trying circumstances, beginning with a focus on our shared mission. Rather than thinking of the “research, teaching, service” mantra as simply a way to categorize all the tasks we complete each year, let’s take a step back and think about its implications for our priorities as a department. Then let those priorities shape our goals, and then let those goals shape how each of us – whether faculty, staff, postdoc or student – chooses to spend our finite energy and effort. I hope this generates plenty of discussion and is just the beginning of a robust and continuing conversation.

Thursday September 10th 2020 4:00 PM

Richard Haight, IBM TJ Watson Research Center

An Overview of Quantum Computing at IBM: IBM-Q From Fundamentals to Practice   (show abstract)

Quantum computing has developed from mathematical applications of fundamental quantum mechanics to the realization of an actual multiple qubit computational platform, called IBM-Q, that is accessible to external users. I will give an overview of quantum computing methodologies but focus more specifically on IBM’s approach utilizing Josephson Junctions imbedded in resonator structures that operate at 10 mK. In addition to discussing the mathematical basis of quantum computing, I’ll describe several key quantum gates and how they are implemented in a quantum computer. Qiskit, IBM’s platform that enables external users to write programs on IBM-Q will be discussed. I will finish by describing quantum transduction, a method that we are developing to enable blind computing and scaling using entangled photons for optical communication.

Host:L. Feldman

Thursday September 17th 2020 4:00 PM

Frank von Hippel, Professor and Co-Director of Program on Science and Global Security, Princeton University

Nuclear Threat Reduction   (show abstract)

"There is growing concern about the systematic elimination of US-Russian nuclear arms control agreements and an emerging three-way nuclear-arms race between the United States, Russia and China. At the same time, the public, including most physicists, assume that the actual danger of a nuclear war is negligible. The biggest danger, accidental nuclear war, as dramatized by a number of near misses during the Cold War, seems to have been forgotten. In fact, with the lack of high-level attention to nuclear-weapons dangers in any branch of the US government; continuing concerns about the vulnerabilities of US and Russian nuclear command and control systems and China’s nuclear forces to first strikes; US and Russian launch-on-warning postures with decision times of minutes; and the advent of ballistic missile defense, anti-satellite weapons, hacking, and hypersonic and other missiles with unpredictable trajectories, the danger may have increased. This talk will explain the current crisis in nuclear arms control, recall the past waves of constructive engagement of independent physicists with nuclear-weapons policy, and discuss the roles physicists can play in explaining crisis and arms-race instabilities to the public and Congress and in advocating remedies. The talk also will introduce the APS-sponsored Physicists Coalition for Nuclear Threat Reduction to facilitate the reengagement of more independent physicists with this issue. For those who might be interested, there will be a separate more detailed discussion of opportunities to get involved, including with the Coalition, the day after the colloquium."

Host: S. Hutson

Thursday September 24th 2020 4:00 PM

Jason Dexter, JILA, University of Colorado, Boulder

Imaging black holes: beyond the shadow   (show abstract)

In the past year, the longstanding goal of imaging a black hole has become reality. Two long baseline interferometry experiments operating at submillimeter and near-infrared wavelengths can now achieve microarcsecond scale angular resolution with sufficient sensitivity to detect synchrotron radiation from the Galactic center black hole, Sgr A*, and the supermassive black hole in M87. I will discuss the first results from each experiment, focusing on the opportunity to study accretion and jet physics in the immediate vicinity of an event horizon. I will outline the challenge of pushing towards tests aimed at determining whether black holes in the Universe are those predicted by General Relativity.

Host:J. Runnoe

Thursday October 1st 2020 4:00 PM

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Thursday October 8th 2020 4:00 PM

David Smith, Department of Radiology, Vanderbilt University

Alternative Pathways in Physics: My Journey from Astrophysics to Astrobiology to Medical Imaging and AI   (show abstract)

I trace my path from naive physics undergraduate obsessed with general relativity to faculty in a medical school doing cancer research. Along the way I will note points when a confluence of diverse expertise enabled my research contributions, from pure astronomy to astrobiology to radiation physics and on to my current work in artificial intelligence in medicine. I will discuss my experience in using a physics education as a foundation for interdisciplinary research and alternative careers

Host: J. Gore

Thursday October 15th 2020 4:00 PM

Joseph Simon, Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder

Merging Galaxies and Supermassive Black Hole Binaries: Multi-Messenger Astrophysics with Pulsar Timing Arrays   (show abstract)

Pulsar timing arrays (PTAs) are galactic-scale low-frequency (nHz - μHz) gravitational wave (GW) observatories, which aim to directly detect GWs from supermassive black hole (SMBH) binaries (≥ 107 M⊙). SMBH binaries are predicted products of galaxy mergers and are a crucial step in galaxy formation theories. The primary source of gravitational radiation in the nHz regime is expected to be a stochastic background, formed from the cosmic population of SMBH binaries. In this talk, I will discuss the current state-of-the-art detection approaches to searching for a gravitational wave background in pulsar timing data and present the results obtained by analyzing the 12.5-year data release from the North American Observatory for Gravitational Waves (NANOGrav). Understanding the link between SMBH binaries and the gravitational radiation detected by PTAs is crucial to our community's capability of making meaningful scientific statements using PTA observations. I will end my talk with a discussion of ongoing work which provides a direct translation between PTA data and the parameters of SMBH binary evolution in galactic cores, including the relation between the mass of the central supermassive black hole and the galactic bulge (the MBH − Mbulge relation) and the coupling between the binary and its galactic environment.

Host: S. T. Taylor

Thursday October 22nd 2020 4:00 PM

Julie Hogan, Bethel University

CMS Particle Flow: the LEGO tutorial and searches for new massive quark   (show abstract)

The Compact Muon Solenoid detector at CERN's Large Hadron Collider uses a method called "particle flow" to interpret electronic signals in detector elements as particles like electrons or muons. This critical software is rarely learned in detail by young CMS researchers. I will share an engaging new hands-on tool developed for summer tutorials at Fermilab: the Particle Flow LEGO Experience. Then I will present recent searches for new physics particles called "vector-like quarks", which decay to a variety of massive quarks and bosons. In these searches we connect the particle flow information from showers of quark-based particles with machine learning algorithms to probe for evidence of new physics.

Host: S. Starko and R. Scherrer

Thursday October 29th 2020 4:00 PM

Prof. Aviva Rothman, Department of History, Case Western University

Johannes Kepler on Perspective and Harmony   (show abstract)

Astronomer Johannes Kepler (1571-1630) understood harmony--a concept at the core of all of his work--in ways that relied heavily on the idea of perspective. In this talk, I will focus on how Kepler approached three forms of perspective--optical, cosmological, and historical. I will also consider how he incorporated those ideas when it came to the reform of the Julian calendar, hotly debated in his day. All this will shed further light on Kepler's conception of harmony, of truth, and of community. Prof. Rothman is the author of The Pursuit of Harmony: Kepler on Cosmos, Confession and Community (University of Chicago Press, 2017) and “Johannes Kepler’s pursuit of harmony,” Physics Today 73(1), 36 (2020).

Host: R. Haglund

Thursday November 5th 2020 4:00 PM

ALICE CLAIR HANKLA LECTURE

Dr. Jacklyn M. Gates, Lawrence Berkeley National Laboratory

Modern Day Alchemy: Making and Investigating the Heaviest Elements on Earth   (show abstract)

Over the last two decades, the chart of nuclides has been expanded to include six new elements and dozens of new isotopes in the heavy (Z>92) and superheavy (Z>103) region. These new nuclides must be formed one-atom-at-a-time in complete-fusion evaporation reaction. Once formed, the atoms typically exist for just seconds or less before they decay. While we have made great progress in expanding the number of known heavy and superheavy nuclei, we often known little about these nuclei beyond their production method and decay properties. Even basic information about their proton and neutron numbers, not to mention nuclear shapes, nuclear structure or chemical properties, is unknown. This can lead to some confusion when assigning nuclear and chemical properties to these nuclides. At the Lawrence Berkeley National Laboratory (LBNL), we have coupled the Berkeley Gas-filled Separator (BGS) to the FIONA mass analyzer. This allows us the simultaneous ability to determine mass numbers of heavy and superheavy nuclides while we either study their decay properties or investigate their chemical natures. Here we will discuss recent experiments at LBNL to investigate the masses of superheavy nuclei, clarify mass assignments of neutron-deficient actinides and to atom-at-a-time chemistry on heavy and superheavy nuclei.

Host: J. Hamilton

Thursday November 26th 2020 4:00 PM

Thanksgiving Holidays

Thursday December 3rd 2020 4:00 PM

Alberto Sesana, Dipartimento di Fisica G. Occhialini, Università di Milano Bicocca, Italy

Massive black hole binaries in the era of multimessenger astronomy   (show abstract)

Following detection by advanced LIGO, gravitational wave (GW) stocks are on the rise. Despite their enormous impact, ground based detectors are only sensitive to GW sources in the audio band. The low frequency GW Universe is still unexplored and future spaceborne interferometers such as LISA and ongoing and future pulsar timing arrays (PTAs) have the potential to probe this window from nHz to mHz, unveiling the gravitational universe and its sources, in particular massive black hole binaries (MBHBs). Forming in the aftermath of galaxy mergers, those sources are expected to be the loudest in the GW universe and possibly bright in the electromagnetic (EM) spectrum. I will discuss the expected joint GW and EM emission of MBHBs and future opportunities for multimessenger observations with LISA and PTA and future EM facilities such as LSST, SKA, Athena.

Host: S. T. Taylor

Spring 2021

Thursday January 28th 2021 4:00 PM

Andreas Berlind, Department of Physics and Astronomy, Vanderbilt University

Astrophysics and Data Science   (show abstract)

Data science is an interdisciplinary field whose goal is to extract knowledge and enable discovery from complex data using a fusion of computation and statistics. In this talk I will discuss how our research group uses machine learning, one of the central tools of data science, in our quest to understand how structure formed in the universe. I will present results from a set of student-led projects and use them to illustrate the types of questions that can be addressed with these powerful tools, as well as their limitations.

Host:S. Hutson

Thursday February 4th 2021 4:00 PM

Chung-Pei Ma, Department of Astronomy, University of California, Berkeley

Supermassive Black Holes in Nearby Galaxies   (show abstract)

Supermassive black holes are a fundamental component of galaxies. Residing at the centers of galaxies, these black holes have masses up to tens of billion suns and directly impact the evolution of their host galaxies. I will describe recent progress in discovering new populations of ultra-massive black holes, and how these results are revising our understanding of the symbiotic relationships between black holes and galaxies and the sources of low-frequency gravitational waves.

Host: S. Taylor

Thursday February 11th 2021 4:00 PM

GUY and REBECCA FORMAN LECTURE

Laurie E. McNeil, Bernard Gray Distinguished Professor, Department of Physics and Astronomy, University of North Carolina at Chapel Hill

No less than success: Pedagogy and curriculum in thriving physics departments   (show abstract)

What does it take for a physics department to thrive? How can it best accomplish its missions of creating new knowledge, transmitting knowledge to future scientists and the general population, and preparing the next generation to take up their roles in the profession and beyond? The climate for physics departments is changing as student demographics transform, new career opportunities (requiring new skills) become available, and funding agency priorities shift. Like any organism, a physics department needs to evolve to be successful in a new environment. In particular, thriving departments make use of the insights about how people learn that have emerged from physics and astronomy education research, to educate their students more effectively and enhance recruitment and retention. They also take heed of the recommendations about curriculum arrived at by the physics and astronomy community under the aegis of our professional societies, in order to best prepare all of their graduates for their future careers. With strategic initiatives, effective leadership, and collective action it is possible to achieve these goals while also maintaining excellence in research. I will share what I have learned about these matters both from my experience leading my department and as part of efforts at the national level, in hopes of starting a conversation about what the Vanderbilt Physics and Astronomy Department can do to assure that it continues to thrive for the foreseeable future.

Host: S. Hutson

Thursday February 18th 2021 4:00 PM

Neil Abernethy, Associate Professor of Biomedical Informatics and Medical Education, University of Washington

Epidemic models of COVID-19: Uses and abuses during the pandemic   (show abstract)

Mathematical models and simulations have become important tools to study the dynamics of infectious disease epidemics. In addition to understanding the theoretical behavior of epidemics, these models have increasingly been used for forecasting, policy evaluation, situational awareness, economic analysis, and decision making. Although the epidemiology of SARS-CoV-2 is typical in many ways, this pandemic has presented unique modeling challenges. In this talk I will review the pros and cons of different modeling approaches, address attempts to synthesize model findings, and discuss the implications of new developments such as the vaccine rollout and SARS-CoV-2 genetic variants. I will highlight some contributions to this body of work from the physics community including percolation theory and molecular dynamics. Finally I will preview some work in my lab to enable localized, replicated simulations at the scale of a global pandemic.

Host: S. Hutson

Thursday February 25th 2021 4:00 PM

Kerri Phillips and Sylvie DeLaHunt, Johns Hopkins Applied Physics Laboratory

Breaking Down Barriers to Diversity and Inclusion in STEM   (show abstract)

Collegiate STEM programs struggle with both the recruitment and retention of female students: women are less likely than men to enroll in STEM programs and more likely to leave those programs before graduation. From a young age, girls are exposed to social norms that can reduce their interest and confidence in STEM fields. These gendered experiences influence how collegiate women perceive and respond to institutional obstacles commonly associated with traditional STEM programs, including grading policies, lack of transparency, and classroom climate. With a focus on retention, this session will overview the individual and institutional obstacles that work together to disproportionately discourage female students. The authors will propose ways collegiate programs can adapt to promote the inclusion and success of all students and will discuss strategies for students and professionals to help cultivate an inclusive and supportive culture.

Host: S. Starko

Thursday March 4th 2021 4:00 PM

Alpha A. Lee, University of Cambridge, U.K.

From soft matter to hypothesis testing: Using machine learning to discover hidden structures in molecules and materials    (show abstract)

Many problems soft matter pertain to uncovering order amid fluctuations and noise. I will show how new insights can be gleaned by reframing those problems using the language of statistical hypothesis testing and machine learning. In the first part of my talk, I will discuss the application of random matrix theory to drug discovery. Having a rigorous null distribution of background noise due to having insufficient data leads to a fruitful way to uncover motifs that determine protein-ligand binding directly from data. In the second part of my talk, I will discuss the application of Bayesian machine learning to understand the structure of concentrated electrolytes. Our machine learning method reveals distinct ionic environments, and sheds light on anomalously long screening lengths that have been observed experimentally.

Host: S. Hutson

Thursday March 11th 2021 4:00 PM

Yusuke Toyama, Mechanobiology Institute, National University of Singapore

Mechanical wave propagation in a tissue upon cell death   (show abstract)

Apoptosis, or programmed cell death, is the most common mechanism of eliminating damaged or unnecessary cells during embryonic development, tissue homeostasis, and certain pathological conditions. When a cell undergoes apoptosis within a tissue, the apoptotic cell is extruded from its neighboring non- dying cells. It has been shown by many labs, including ours, that this mechanical process is driven by the formation and contraction of the actomyosin cables in the dying and the neighboring cells, and/or by the crawling of the neighboring cells. However, how the mechanical interaction between the apoptotic cell and neighboring non-dying cells feedbacks to cellular function and cell fate of the surrounding tissue is largely elusive. In this talk, I will present our latest findings of how mechanical tension is altered in the surrounding tissue in a wavelike fashion as a consequence of apoptosis, and how this force propagation triggers cell cycle progression and proliferation of the neighboring cells.

Host: S. Hutson

Thursday March 18th 2021 4:00 PM

Simon Elliot Wall, Department of Physics and Astronomy, Aarhus University, Denmark

Lighting up Quantum Materials   (show abstract)

Quantum materials exhibit exotic properties such as topological protection and high temperature superconductivity. They are also materials that often display rich phase diagrams in which phases with diametrically opposite properties sit in close proximity. Recently it has been found that femtosecond pulses of light can be used to manipulate the phase of these materials, and even induce phases that are not found in equilibrium, with the most exciting claim being the ability to use light to induce a superconducting-like phase [1]. This has opened up the possibility of controlling quantum materials “on demand” [2] However, how do observe these microscopic and transient changes in materials and how, specifically, does light allow us to manipulate them? In this talk, I will outline how femtosecond pulses of light interact with solids causing structural changes. I will show how X-ray techniques, enabled by free electron lasers, allows us to look beyond average atomic changes, and look directly at the pathway atoms take during a phase transition and our observation of light induced disorder [3]. Finally I will discuss our approach [4] to using femtosecond x-rays to image nucleation and growth of transient phases on the nanoscale with femtosecond time resolution. [1] D. Fausti et al. “Light induced superconductivity in a stripe-ordered cuprate” Science 331, 189 (2011) [2] D. N. Basov et al. “Towards properties on demand in quantum materials” Nature Materials 16, 1077 (2017) [3] S. Wall et al. “Ultrafast disordering of vanadium dimers in photoexcited VO2” Science 362, 572 (2018) [4] L. Vidas et al. “Imaging Nanometer Phase Coexistence at Defects During the Insulator–Metal Phase Transformation in VO2 Thin Films by Resonant Soft X-ray Holography” Nano Letters 18, 3449 (2018)

Host: R. Haglund

Thursday March 25th 2021 4:00 PM

FRANCIS G. SLACK LECTURE

Martin Rees, Institute of Astronomy, Cambridge University, U.K.

Real and Counterfactual Universes   (show abstract)

Over a timespan of 13.8 billion years the material emerging from the big bang has transformed into our complex cosmos. This talk will outline some highlights of recent progress, The emergence and properties of galaxies, stars, planets and life depend on a few key numbers: the 'constants' of micro-physics and the parameters that describe our expanding universe. According to some cosmologists and string theorists, domains may actually exist where these constants have different values: it is then interestingto explore what range of values would permit the emergence of complexity. But even those who are allergic to the concept of a multiverse may find their insight enhanced by exploring 'counterfactual' universes, just as some historians speculate about 'counterfactual' scenarios -- eg what would have happened to North America if the Brits had fought more effectively in 1776!

Host: S. Hutson

Thursday April 8th 2021 4:00 PM

Governor Phil Bredesen

Physics in the world of business and politics

Host:S. Hutson

Thursday April 15th 2021 4:00 PM

Paul Lasky, School of Physics and Astronomy, Monash University, Australia, and OzGrav Centre of Excellence for Gravitational Wave Discovery

The future of gravitational-wave astronomy   (show abstract)

Advanced LIGO and Virgo have now completed their third observing run, having detected more than 70 mergers of compact binary systems involving black holes and/or neutron stars. The future of this field is bright, with future prospects including tests of general relativity in the ultra-strong field regime, probing of bulk matter at supranuclear densities, and much more. I will recap what gravitational-wave astronomy has taught us about the Universe to date, and discuss some of the next major discoveries that we hope to see in the coming years. I will also discuss a proposed gravitational-wave observatory that targets neutron star physics, while also being a technology driver for the next generation of instruments.

Host: S. Taylor

Thursday April 22nd 2021 4:00 PM

Ole Molvig, Department of History, Vanderbilt University

AI Einstein: experiments at the intersection of the humanities, science, and emergent technology

Host: N. Tolk

Thursday April 29th 2021 4:00 PM

Reka Albert, Distinguished Professor of Physics and Biology, Pennsylvannia State University

Network-based dynamic modeling of biological systems: toward understanding and control   (show abstract)

My group is using network science and dynamic modeling to understand the emergent properties of biological systems. As an example, we think of cell types as attractors of a dynamic system of interacting (macro)molecules, and we aim to find the network patterns that determine these attractors. We collaborate with wet-bench biologists to develop and validate predictive dynamic models of specific systems. Over the years we found that network-based discrete dynamic modeling is very useful in synthesizing causal interaction information into a predictive, mechanistic model. We use the accumulated knowledge gained from specific models to draw general conclusions that connect a network's structure and dynamics. An example of such a general connection is our identification of stable motifs, which are self-sustaining cyclic structures that determine points of no return in the dynamics of the system. We have shown that control of stable motifs can guide the system into a desired attractor. We have recently translated the concept of stable motif to a broad class of continuous (ODE-based) models. I will use examples from our work to argue that stable motif - based attractor control can form the foundation of therapeutic strategies on a wide application domain.

Hosts: K. Varga and S. Hutson