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 (firstname.lastname@example.org) or phone (615-343-7389).
Thursday August 26th 2021 12:00 AM
James Bullock, University of California - Irvine
Dark Matter and Dwarf Galaxies
Over the past five years, new data from automated sky surveys have more than doubled the number of known satellite galaxies orbiting around the Milky Way disk, revealing a population of ultra-faint systems with total light output barely reaching ~1000 times that of the Sun. These newly-discovered dwarf galaxies represent galaxy formation in the extreme: massive balls of dark matter that happen to host enough stars for us to find them. Kinematics studies have revealed that they are the most dark matter dominated objects in the known universe. Many of these galaxies could not have been discovered if they were slightly farther away, suggesting that new, deeper surveys will discover hundreds more as they cover more sky with bigger telescopes. I discuss how dark matter dominated dwarfs of this kind offer a particularly useful target for dark matter indirect detection experiments.
Host: A. Berlind
Thursday September 2nd 2021 12:00 AM
James Dickerson, Vanderbilt University
Nanoparticle Deposition via Electrophoresis
Semiconducting, insulating, and metallic nanoparticles have attracted considerable interest recently due to their size-dependent, quantum confinement characteristics, which make them attractive for a broad platform of optical, magnetic, and electronic devices. Proposed commercial applications include solid state lighting devices, magnetic recording media, ultra-light video displays, and bio-imaging reagents.
For nanoparticles to be employed in an array of commercial and industrial applications, a technique for the facile, rapid, and site-selective assembly of homogeneous, densely packed, defect-free thin films must be realized. The most widely used methods for casting nanoparticle (NP) constituents into densely packed, thermally stable films, such as evaporation-driven self assembly and Langmuir-Blodgett casting, have some recognized limitations, including the inability to achieve both large-scale ordering of the nanoparticles as well as robust chemical and structural properties. NP deposition schemes also require an understanding of both the NP dynamics in solution and the interactions that govern nanoparticle-substrate and nanoparticle-nanoparticle binding. Further, these procedures require knowledge of the intrinsic and collective properties of NPs that arise from of electrostatic, magnetic, and fluctuating electric dipole effects. The organization and stability of colloidal NP assemblies are markedly affected by the surface charge state of the constituents. Although much research has been done on the assembly of nanoparticles with a distribution of surface charge states, little has been done on the assembly of like-charged nanoparticles. In this case, repulsive Coulomb interactions, as well as van der Waals, dipole-dipole, and steric interactions govern the types of assemblies that can form. The only nanoparticle deposition scheme that considers the primary physical characteristics of the NPs in the film formation and incorporates the most favorable attributes of NP deposition is electrophoretic deposition.
Recent progress in the electrophoretic deposition of nanoparticles and other nanoscale materials will be the emphasis of this presentation. Highlighted are the recent discoveries of the fabrication of free-standing nanoparticle thin films, comprised solely of electrophoretically deposited iron oxide nanocrystals, cadmium selenide nanocrystals, and carbon nanotubes, as well as transparent films of europium and gadolinium sesquioxide nanoparticles.
Host: R. Scherrer
Thursday September 9th 2021 12:00 AM
Will Happer, Princeton University
Carbon Dioxide, Friend or Foe?
In this talk I will review the physics of global warming due to increased levels of CO2. The current CO2 levels are still low compared to values that have been the norm since the Cambrian, 550 million years ago. Because of the large positive feedback factors assumed from water vapor and clouds, the warming predicted by climate models may well be exaggerated. Increasing atmospheric levels of CO2 may actually be a net benefit to the planet because of increased crop yields and other advantages of a warmer climate and more atmospheric CO2.
Host: N. Tolk
Thursday September 16th 2021 12:00 AM
David Lubensky, University of Michigan
Self-Organization in Animal Development
Developmental biology presents some of the most amazing examples of self-organization found in nature: Starting from a single-celled egg, an animal is able, largely without outside help, to construct an entire, incredibly intricate organism, with cells of different types taking on myriad shapes and arranged in complex patterns to create a viable adult. Many of the individual steps in this maturation bear at least a superficial resemblance to examples of pattern formation or self-assembly in simpler physical systems, and there is a long tradition of using physically-inspired models to try to understand developmental processes. Only relatively recently, however, have experimental techniques reached the point where it is possible to subject these models to stringent tests. While confirming some classical ideas, such experiments have also begun to reveal how specifically biological controls interact with more generic physical effects to lead to reliable and robust development. Using examples from my own research on eye development in fruit flies and in fish, I will show how it is becoming possible to dissect the mechanisms of self-organization during development and illustrate some of the surprising new physical ideas that can result from such investigations.
Host: S. Hutson
Thursday September 23rd 2021 12:00 AM
Charles Townes, University of California - Berkeley
How Do New Things Happen? Origins of the Laser
The many ways by which new inventions, discoveries, and ideas arise will be outlined with examples. The particular case of the laser will be discussed in detail, from its origins to its present development,from a personal point of view.
Host: N. Tolk
Thursday September 30th 2021 12:00 AM
David Cobden, University of Washington
Phase transitions in nanostructures
Because of the change in structure, the latent heat, and the need for nucleation, first-order phase transitions involving a solid phase tend to very sensitive to inhomogeneities and to be difficult to study in bulk material. For solid-solid transitions the situation is particularly bad, with random domain formation, high strain, and fracture being almost unavoidable. I will discuss how working with nanoscale systems, which are small compared with the scale of inhomogeneities and domains, allows much improved control of such transitions. It also opens up possibilities to investigate phase transitions in reduced dimensionality, where the physics may be qualitatively different from that in three dimensions and may be more theoretically tractable as well. These advantages will be illustrated in two systems: a solid-solid transition driven by electron-electron correlations in a vanadium dioxide nanobeam; and vapor-liquid-solid transitions occurring in a monolayer of gas atoms adsorbed on a carbon nanotube.
Host: J. Nag and R. Haglund
Thursday October 7th 2021 12:00 AM
Jeff Hughes, Boston University
Space Weather: Understanding how the Sun affects what we do
Space weather is a term used to describe the variable conditions in the earth’s space environment that can damage or disrupt satellite systems, radio communications, GPS navigation, and even the electrical power grid. The sun is a relatively benign magnetic star, but not completely benign. Solar flares and coronal mass ejections launch X-rays, energetic charged particles, and clouds of hot magnetized plasma that can impact Earth causing ionospheric disturbances and severe geomagnetic storms. Predicting these events and their outcomes – space weather forecasting – presents a considerable challenge. We are creating a suite of physics-based numerical models that simulate the space environment from the sun to the earth’s upper atmosphere with the aim of both better understanding the complex coupling between the sun, the solar wind and the earth’s magnetosphere and ionosphere (geospace), and developing tools to help the space weather forecasters in the National Weather Service and the Air Force. As an illustration of the use of models in an observational science, I will focus on how these models have helped us distinguish three distinct sources of solar wind plasma at the sun.
Host: K. Stassun
Thursday October 14th 2021 12:00 AM
Timothy Wei, Rensselaer Polytechnic Institute
Fundamental Fluid Dynamics and the Olympic Swimming Movement
The world of competitive swimming is dynamic. Swimmers today are bigger, stronger and faster than they ever have been. The training regimen of an elite athlete includes not only endless practice of his or her skills, but also a carefully planned diet, strength and endurance training, and hours of mental preparation. Within this framework, we have teamed with USA Swimming to develop advanced, fluid dynamics based training and analysis tools for current and future Olympic swimmers. The focus of this presentation will be on the objectives, methodologies and outcomes of measurements of flow around swimmers. Movies of PIV flow measurements and time resolved force measurements around swimmers, including Beth Botsford and Megan Jendrick, 1996 and 2000 Gold Medalists in the 100 meter back and 100 meter breast, respectively, will be presented. Work with Ariana Kukors, 2009 World Championships gold medalist and world record holder in the 200 IM. In addition, the measurement technique has recently been applied to dolphins. Data from those experiments will be shown as well.
Host: S. Hutson
Thursday October 21st 2021 12:00 AM
Samuel H. Dworetsky PhD, formerly General Attorney in the IP-Law group of AT&T
The Laser Patent Battles – The Intersection of Science and the Law
The patent system was established by the Founders to act as a major incentive for innovation. However, the aspects of an innovation that are protected by a patent often differ from the scientific view of the significance of the innovation. In this talk, the battle between the Schalow/Townes laser patent and the patent on the same subject sought by one of Townes’ graduate students will be presented as a case study in the difference in perspective between the scientific community and the patent community. The goal of the presentation will be to introduce you to the idiosyncrasies of the patent system from the perspective of a research physicist who mutated into a patent attorney. Along the way, you will learn about the history of the laser as well as about patent law and alternative career opportunities – while all the time having a good time and laughing more often than you would expect!
Host: N. Tolk
Thursday October 28th 2021 12:00 AM
Tao Han, University of Wisconsin
High Energy Physics: The Next Two Decades
With a brief review of the historical development in high energy physics, we appreciate the extraordinary achievements thus far, formulated as the "Standard Model", in understanding Nature at the highest energy scales (or the shortest distances) currently experimentally accessible. Yet, theoretical arguments and indirect experimental observations indicate the existence of new physics at the TeV scale, the "terascale". The precise form of the new physics is unknown, but may have far-reaching implications in cosmology, astroparticle physics, and nuclear physics. The CERN Large Hadron Collider (LHC) has just begun its historical mission to explore the physics at this energy frontier. Exciting new discovery is highly anticipated. Future high energy colliders such as the International Linear Collider (ILC) will further help to reveal the true nature of the elementary particles. The "terascale" physics will dominate in the next two decades to come.
Host: T. Weiler
Herschel Rabitz, Princeton University
Controlling Quantum Dynamics Phenomena with Photonic Reagents and Beyond
Controlling quantum dynamics phenomena with tailored radiation has a long history with many successes appearing in the recent literature. These studies encompass both theoretical simulations as well as laboratory experiments, especially using shaped laser pulses acting as a class of “photonic reagents” for directing the dynamics. Successful illustrations include manipulation of rotational, vibrational, electronic and reactive processes both in gaseous and condensed phases. Optimal control techniques are providing the means to obtain the best possible control yields under the specified conditions.
Given the latter very encouraging positive control outcomes, a basic question is why the simulations and laboratory experiments are working out well. A number of rational arguments suggest that controlling quantum dynamics phenomena should be a difficult and delicate process, which is sensitive to noise and possibly a number of other factors. Theoretical analyses will be presented to provide a foundation to begin to understand the many control successes. Most importantly, the control landscape (i.e., the search space for effective controls) generally has remarkably simple topology, permitting easy and rapid searches for effective controls. Material will be presented considering the systematic nature of controlling quantum phenomena based on viewing the Hamiltonian structure and applied field as collectively forming sets of controls. These overall results indicate the rich nature of controlling quantum phenomena and provide some hints at what might lie ahead.
Hosts: N. Tolk and S. Rosenthal
R.B. Piercey, Eastern Kentucky University
Human Consciousness and Quantum Mechanics
Some of the most important contributions classical science has made to the evolution of modern thought are the notions that the external world is real; that it is governed by causal determinism; and that it can be considered as separate from the human minds that experience and observe it. These assumptions are central to our notions of "deterministic laws"; of "isolated systems", of "instantaneous states" and of a world that is coherent and knowable.
Since the early part of the twentieth century, however, the theory of quantum mechanics has pointed out weaknesses of such epistemological assumptions and a fresh consideration of the role of the human mind in understanding the "external world" is in order. Common interpretations of quantum mechanics argue that physical systems can manifest very different properties depending on the the kinds of observations that an observer chooses to make. They argue further that the system's properties are actually created by the observation at the time of observation instead of pre-existing as intrinsic, un-observed properties of the system. In these interpretations, the free choice of the observer can cause the system to be in a particular state. If the interpretations are accurate and free will exists in any normal sense, then observers are able to not only cause the current state of the system to be what is observed, but also to select the history for the system that makes the current state possible. With no intrinsic properties and with the suggestion of backward causation, these interpretations conflict with our pedestrian understanding of causal determinism and time.
We explore the nature and role of the human brain and what it can – and probably cannot – do. We review the science of intentional action to better understand the status of free will in science. Finally, we consider whether quantum mechanics provides a new perspective on the nature of human consciousness.
Host: A. Ramayya
Thursday November 25th 2021 12:00 AM
Thanksgiving Holidays, no colloquium
Mercedes Richards, Penn State University
The Observational and Computational Challenges of Imaging Accretion Disks and Streams in Interacting Binary Star Systems
Direct images of interacting binary stars are difficult to obtain because the separation between the stars is in the milli-arcsecond regime. Modern optical interferometers have now produced the first resolved optical images of the brightest and nearest eclipsing binary in the sky, however these direct images do not contain enough detail to show how the gas moves between the stars. The technique of Doppler tomography has been used effectively to create two-dimensional and three-dimensional images of the gas flows in interacting binaries. These results were achieved through multiple steps including the systematic collection of time-resolved spectra of binary systems, the use of image processing software similar to medical tomography codes, hydrodynamic simulations of the gas flows, and the creation and application of a spectrum synthesis code to model the spectrum of the accretion disk and gas stream.
Host: K. Stassun
Thursday December 9th 2021 12:00 AM
Mark Riley, Florida State University
The Fascinating Gamma-Ray World of the Atomic Nucleus: The Revolution Continues
It was Niels Bohr who first suggested looking at gamma-ray emission spectra in order to characterize the properties of the unique quantal system we call the atomic nucleus. Much progress has been made since this pioneering suggestion and in the last few decades a revolution has taken place in our ability to create and observe the intricate emission patterns from nuclei under extreme conditions. A remarkable diversity of phenomena have been discovered as increasingly sensitive instrumentation have revealed unexpected properties and exotic behavior. This talk aims to give an introduction to this field, a taste of some of these recent discoveries while also charting exciting possibilities for the future.
Host: J. Hamilton
Diola Babayoko, Southern University
Systemic Mentoring for Competitiveness: The Model of the Timbuktu Academy
This presentation succinctly describes the paradigm, programs, activities, and results of the implementation of the ten-strand systemic mentoring model of the Timbuktu Academy at Southern University and A&M College in Baton Rouge, Louisiana. Accompanying articles and documents, it is hoped, will stimulate a replication that seems warranted by unquestionable results over 20 years. As per the title of the presentation, systemic mentoring is shown to effect the integration of education and research for contemporary competitiveness. Superior learning, significant research participation, on-time graduation, and admission and success in top graduate schools are some of the results not only for the Physics Scholars of the Academy, but also for those in Chemistry, Engineering and other disciplines. Trends at the federal and other levels indicate that systemic mentoring is not just good for the students (undergraduate and graduate), but also for the scholar mentors themselves – as far as grant funding is concerned. A few disappointments that may occur to a mentor are explained away with the Central Limit Theorem (so that they may not become serious discouragements.) The Academy’s nationally recognized, positive impacts on the participation of minorities in the scientific and technological enterprise of this country point to the relevance of mentoring to the effective promotion of diversity.
Host: D. Ernst
Thursday January 28th 2021 12:00 AM
Gregor Neuert, MIT
Dynamic Information Processing in Individual Cells: a Single-Molecule Approach in Systems Biology
Understanding and predicting how cells sense and respond to their environments is a key goal of systems biology. New experimental and computational methodologies have helped elucidate many signal transduction pathways and gene regulation mechanisms, but it remains difficult to predict the phenotypic diversity of cellular dynamics. To better understand and predict these complex networks, we propose a comprehensive approach for the identification of gene regulation systems. First, we developed a quantitative assay to measure single-molecule expression of endogenous mRNA at fast temporal resolution in individual cells. Second, we developed an efficient and flexible computational approach to analyze data from such experiments. Third, we integrated these experimental and computational approaches within a novel hierarchical network identification framework, which involves several clearly defined rounds of analysis, prediction, experiment design, and validation. Finally, we show that our semi-automated hierarchical approach can select a single, predictive gene regulatory model from out of several thousand automatically-generated hypotheses. In addition the identified model provides accurate predictions at diverse environmental and genetic conditions, which extend well beyond its training data. Since our approach is not specific to any gene, pathway or organism, it can lead to new insight into complex cellular networks from yeast to human.
Host: R. Scherrer
Thursday February 4th 2021 12:00 AM
Josh Milstein, University of Michigan
Switching Genes On and Off by Bending and Stretching DNA
Our current understanding of how genes function is dominated by cellular biochemistry. DNA, however, is a polymer and as such displays a variety of biomechanical properties that may directly influence the regulation and expression of genes. I will discuss some of the experiments our group has conducted that show how cells could modulate the expression of particular genes by applying very small amounts of tension to the chromosome. These experiments were performed in vitro; however, in order to assess the true relevance of DNA mechanics to gene expression, we must observe similar results within actual living cells. Toward this end, I will also present a new technique that our group has devised for driving our work into the in vivo realm.
Host: R. Scherrer
Erin Rericha, University of Maryland
Host: R. Scherrer
Thursday February 11th 2021 12:00 AM
Junhua Yuan, Harvard University
Host: R. Scherrer
Thursday February 18th 2021 12:00 AM
Jaan Mannik, Delft University of Technology
Host: R. Scherrer
Thursday February 25th 2021 12:00 AM
Anders Carlsson, Washington University
Nonlinear Protein Waves in Biological Cells
Nonlinear waves based on chemical reactions and diffusion are a startling example of the ways in which simple laws of motion can lead to complex behaviors in physical systems. In this talk, I will discuss an example of such waves involving the protein actin in biological cells. Actin can exist either as an isolated protein in solution, or in the form of filaments which have mechanical rigidity. Recent experiments have shown that filamentous actin forms spontaneous waves which are correlated with protrusion of the cell membrane. I will present a theoretical model of such waves based on the three-dimensional structure of the gel formed by actin filaments, interacting with catalytic proteins in the cell membrane. Implementation of this model via simulation shows that the actin system displays characteristic transitions between dynamic behaviors including traveling waves and patches, as the intracellular protein concentrations are varied. The connections between this behavior and the ability of biological cells to spontaneously explore their environment will be discussed.
Host: S. Hutson
Thursday March 4th 2021 12:00 AM
Sergei Voloshin, Wayne State University
Host: V. Greene
Thursday March 11th 2021 12:00 AM
Spring Break, no colloquium
Paul J. Steinhardt, Princeton University
Host: D. Weintraub
Alan Guth, MIT
Host: R. Scherrer
Thursday April 1st 2021 12:00 AM
Paul Kalas, University of California - Berkeley
Host: K. Stassun
Thursday April 8th 2021 12:00 AM
Kevin Stenson, University of Colorado
Host: P. Sheldon
Thursday April 15th 2021 12:00 AM
Deirdre Shoemaker, Penn State University
Host: K. Holley-Bockelmann
Thursday April 22nd 2021 12:00 AM
John Harris, Yale University
Host: V. Greene