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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 2009

Thursday September 2nd 2021 12:00 AM

Enectali Figueroa-Feliciano, MIT

Towards Direct Detection of Dark Matter with the Cryogenic Dark Matter Search   (show abstract)

After 20 years of hard work, we've come to the realization that we don't know what 96% of the universe is made of. About 23% of the universe is made up of dark matter, a mysterious substance that has played the dominant role in the formation of structure in our universe. The Cryogenic Dark Matter Search has attained world-leading sensitivity in the race to directly detect dark matter in the laboratory. I will review dark matter science, our experiment, our current results, and the next steps in the hunt to solve one of the most pressing questions in physics today.

Host: A. Berlind

Wolfgang Christian, Davidson College

Implementing A Computer Rich Modeling-Cycle Pedagogy    (show abstract)

Over the past dozen years the Davidson College Physics Department has produced some of the most widely used interactive computer-based curricular materials for the teaching of introductory and advanced physics courses. These materials are based on Java applets called Physlets and on new Open Source Physics programs and authoring tools. This talk outlines the pedagogical and technical features of our material and describes our current effort to create new material using the Easy Java Simulations modeling tool and to distribute it via the comPADRE National Science Digital Library. The Open Source Physics collection is available on the comPADRE website at http://www.compadre.org/osp/. Partial funding for this work was obtained through NSF grant DUE-0442581

Host: R. Scherrer

Thursday September 23rd 2021 12:00 AM

Shane Hutson, Vanderbilt University

How does a fly make itself? Dissecting morphogenesis with laser-microsurgery   (show abstract)

During the development of an organism, sheets of epithelial cells dynamically expand, contract and bend. These movements generate organismal form in a process known as morphogenesis – a process driven by cell-generated forces. The generation, distribution and regulation of these forces have been explored in multiple mathematical and computational models; however, few attempts have been made to test the validity of these models in vivo. I will present a method for probing morphogenetic forces in vivo using laser microsurgery. My group currently focuses on laser hole-drilling – a quantitative method borrowed from the engineer’s toolbox for residual stress analysis – in which a single laser pulse is used to rapidly ablate a subcellular hole clean through a one-cell thick epithelium. The surrounding cells recoil away from this hole, relaxing the pre-ablation, morphogenetic stresses. By carefully tracking the recoils (on ms time scales, with sub-µm precision and for dozens of embryos), one can estimate how stress is distributed. By staging the embryos, one can infer how this stress distribution changes during development. I will present results from fruit fly (Drosophila) embryos during two stages of embryonic development – germband retraction and dorsal closure. I will also discuss finite-element models that reproduce the observed recoil behavior and their implications for the microscopic construction and dynamic maintenance of an embryonic epithelium.

Host: R. Scherrer

Thursday October 21st 2021 12:00 AM

Tom Rogers

Bad Movie Physics from the Perspective of Art and Science   (show abstract)

A discussion of the bad physics portrayed in Hollywood movies. How it detracts from the art of moviemaking while reinforcing physics misconceptions and how to turn it around as an effective teaching tool. To see some examples of Insultingly Stupid Movie Physics, visit http://www.intuitor.com/moviephysics/

Host: R. Scherrer

Thursday October 28th 2021 12:00 AM

October Break, no colloquium

Thursday November 4th 2021 12:00 AM

Duco Jansen, Biomedical Engineering, Vanderbilt University

Stimulating neurons with light: current state and future challenges   (show abstract)

A novel method that employs infrared laser pulses to induce electrical activity (EP/AP) in neurons will be presented. This method has been shown to have several fundamental advantages over traditional electrical stimulation, including the spatial precision of stimulation that can be achieved in a non-contact fashion, and the lack of a stimulation artifact on the recording electrodes in classic stimulation-recording experiments. In this seminar I will present an overview of the concepts and applications of optical nerve stimulation. Characterization of optical stimulation and physiological validation will be shown. The underlying biophysical mechanisms of optical stimulations appear to be thermally mediated. I will present our work on mechanistic studies as well as on the applications in the peripheral nervous system (stimulation of motor neurons and stimulation of sensory nerves in the cochlea), stimulation in the CNS, and the development of a stand-alone optical nerve stimulator.

Host: S. Hutson

Thursday November 11th 2021 12:00 AM

Charles Ahn, Yale University

The Materials Physics of Complex Oxides   (show abstract)

Complex oxide materials exhibit a tremendous diversity of behavior encompassing a broad range of functional properties, such as magnetism, ferroelectricity, and superconductivity. As diverse as this behavior is, an even richer spectrum of possibilities becomes available if one starts to combine different complex oxides together with atomic-scale precision to create new artificially structured, heterogeneous systems. In these nanostructured materials, cross-coupling between the functionalities of the individual component materials allows one material to modify the properties of the other constituent. This talk describes experiments on the electrostatic modulation of magnetism and superconductivity using intense electric fields in these materials, along with applications of this approach to address current challenges in the modern electronics industry.

Host: R. Scherrer

Thursday November 18th 2021 12:00 AM

Teresa Montaruli, University of Wisconsin

In Search of Extraterrestrial High Energy Neutrinos   (show abstract)

I will review the search for astrophysical neutrinos and the status and results of neutrino telescopes in operation and decommissioned. I will describe the methods used for data analysis, and background discrimination. I will give emphasis to recent results of IceCube and ANTARES. I will interpret these results and consider their impact on theoretical predictions of neutrino fluxes correlated with measurements using other messengers, specifically gammas and ultra-high energy cosmic rays.

Host: T. Weiler

Thursday November 25th 2021 12:00 AM

Craig Hogan, Fermilab

Holographic Noise in Michelson Interferometers: a Direct Experimental Probe of Unification at the Planck Scale   (show abstract)

Classical spacetime and quantum mass-energy form the basis of all of physics. They become inconsistent with each other at the Planck scale, 5.4 times 10^{-44} seconds, which may signify a need for reconciliation in a unified theory. Although proposals for unified theories exist, a direct experimental probe of this scale, 16 orders of magnitude above Tevatron energy, has seemed hopelessly out of reach. However in a particular interpretation of holographic unified theories, derived from black hole evaporation physics, a world assembled out of Planck-scale waves displays effects of unification with a new kind of uncertainty in position at the Planck diffraction scale, the geometric mean of the Planck length and the apparatus size. In this case a new phenomenon may measurable, an indeterminacy of spacetime position that appears as noise in interferometers. The colloquium will discuss the theory of the effect, and our plans to build a holographic interferometer at Fermilab to measure it.

Host: R. Scherrer

Thursday December 2nd 2021 12:00 AM

Thanksgiving Holidays, no colloquium

Thursday December 9th 2021 12:00 AM

Anna Roe, Psychology, Vanderbilt University

Perception and the brain: from physics to psychophysics   (show abstract)

Physicists deal with measurements of the physical world. The accuracy of these measurements are subject to the fidelity and accuracy of their experimental instruments. Theories are developed to explain these measurements in a parsimonious and elegant fashion. Psychophysicists deal with measurements of the physical world as perceived through the brain. Their purpose is to understand and characterize mental representations. Currently, there are no theories to explain how internal mental representations are generated. As a neuroscientist, I strive towards understanding the circuitry in the brain which gives rise to the mental representations. Currently, what is known is that there are multiple stages of cortical processing that lead to what we know as perception. My research focuses on identifying what these stages are and, within each stage, what the elemental units of function are. The methods I use include optical imaging, electrophysiological, and behavioral methods in awake, trained animals. These studies have identified cortical elements representing simple object features, higher order complex objects, and mechanisms underlying visual attention and short-term working memory. My hope is that some day we will have an algorithm in hand that transforms the world of physics into the world of psychophysics.

Host: S. Hutson

Thursday December 16th 2021 12:00 AM

Chris Mihos, Case Western Reserve University

Using Intracluster Light to Probe Galaxy Clusters   (show abstract)

The life of a cluster galaxy is a violent one. As galaxy clusters form and evolve, their member galaxies frequently collide and interact both with other galaxies and galaxy groups, and with the cluster as a whole. Over time, gravitational tides strip stars from their host galaxies and spread them throughout the cluster to form a diffuse "intracluster light" (ICL). Using numerical simulations, we can explore the formation and structure of the ICL, and use it as a tracer of the dynamical evolution of galaxy clusters. We are using deep wide-field imaging to search for this extremely faint light in galaxy clusters, and have discovered a remarkably complex web of ICL in the nearby Virgo cluster.

Host: A. Berlind