Physics and Astronomy Calendar

All future

Tuesday, April 23rd 2019
1:25 pm:
Space Physics Seminar in Tate 301-20
Speaker: Sheng Tian
Subject: The azimuthal propagation of dipolarization in the inner-magnetosphere
Speaker: Jarvis Haupt and Mike Garwood
Subject: Bringing Compact High-Field MRI Systems to Life through Novel Methods that Tolerate Extreme Field Inhomogeneity

MRI is critically important for understanding the human brain and for diagnosing neurological disease, yet is currently inaccessible to ~90% of the world’s population. One way to increase the accessibility of MRI is to decrease the size of the magnet, making it lighter and transportable, but this comes at the cost of greatly diminished uniformity of the main magnetic field, B0. Thus, the main obstacle to making a small MRI scanner comes down to the question: Is it possible to make high quality MR images with a highly inhomogeneous B0? To accomplish this, the basic approach to performing MRI must change; specifically, how spatial information is encoded, and then, how the resulting MRI signals can be reconstructed into high resolution images. In this talk we will discuss the unique challenges and opportunities that arise within our approach, which uses spatiotemporal, frequency-swept pulses to excite MRI signals over broad frequency ranges and a model-based image reconstruction algorithm that deciphers the spatiotemporal information in the MRI signals.

Faculty Host: Vuk Mandic

Wednesday, April 24th 2019
1:25 pm:
Speaker: Ming Yi, Rice University
Subject: Role of Orbital Physics in Iron Chalcogenide Superconductors

Electron correlation effects give rise to a variety of emergent phenomena in quantum materials—high temperature superconductivity, electronic nematicity, Mott insulating phase, magnetism. The family of Fe(Se,Te) superconductors plays a remarkable host to all of these phenomena in different parameter regimes. In this talk, I will present angle-resolved photoemission results on two aspects of electron correlation effects in this material family—i) orbital-selective Mott insulating behaviors towards the FeTe end of the phase diagram, and ii) electronic nematicity in completely detwinned FeSe. Both examples showcase the phenomenal way that correlation effects rewrite the low energy electronic states of a material system, and reveal the exceptional role the orbital degree of freedom plays in composing the fundamental physics in iron chalcogenide superconductors.

Faculty Host: Rafael Fernandes
Speaker: Chris White, Higgs Centre for Theoretical Physics, University of Edinburgh
Subject: Reactor Neutrino Physics from the PROSPECT Experiment

PROSPECT, the Precision Oscillation and Spectrum Experiment, is a reactor antineutrino experiment designed to search for eV-scale sterile neutrinos and measure the spectrum of antineutrinos from highly-enriched 235U at the High Flux Isotope Reactor (HFIR). PROSPECT uses a 4-ton, segmented 6Li-doped liquid scintillator detector to make a high-resolution measurement of the prompt energy spectrum from inverse beta decay on protons. An optical and radioactive source calibration system integrated into the active detector volume is used to characterize the optical and energy response of all detector segments. I will discuss the construction and characterization of the PROSPECT detector and report on PROSPECT’s first measurement of the energy spectrum associated with reactor antineutrinos.

Thursday, April 25th 2019
10:10 am:
Biophysics Seminar in 120 PAN
Speaker: Siddarth Karuka, PhD student in Jochen Mueller’s lab, School of Physics and Astronomy
Subject:  Progress Report: Axial Super-Resolution with Two-Photon Microscopy

The Nuclear Envelope (NE) is a ~40 nm space enclosed by the Outer and Inner Nuclear Membrane (ONM and INM), that separates the nucleus from the cytoplasm. Although recent research has identified the NE as a critical signaling hub for a cell, it remains difficult to study with current fluorescence microscopy techniques that are limited to 50 nm axial resolution. To study systems like these, we have developed the dual color z-scan (DC Z-Scan) technique that can achieve axial resolution on the order of a nanometer. We first demonstrate the technique on a supported lipid bilayer, and then use it to measure the thickness of NE, distinguish proteins that reside on the ONM vs INM and study the translocation kinetics of these proteins.

12:10 pm:
Speaker: Trevor Knuth and Evan Skillman
3:35 pm:
Physics and Astronomy Colloquium in Physics Tate B50
Speaker: Sanjay Reddy, University of Washington
Subject: Neutron stars come of age

About 50 years after their discovery, neutron stars are poised to take center stage in this era of multi-messenger astrophysics. In the not-so-distant-future (10-20 years) it is likely that next generation gravitational wave observatories will detect gravitational waves from hundreds of mergers involving neutron stars every year. I will highlight advances in theory and mention some key observations that have already provided fundamental new insights about neutron star properties and their central role in nuclear astrophysics. I will discuss how neutron stars, and extreme phenomena involving them, can serve as laboratories to study phase transitions in dense matter, nucleosynthesis, and dark matter in the coming decades.

Faculty Host: Joseph Kapusta

Friday, April 26th 2019
11:00 am:
Nuclear Physics Seminar in Physics Tate 301-20
Speaker: Sanjay Reddy, University of Washington
Subject: “Hunting for dark matter with neutron stars”

I will discuss new strategies to discover or constrain dark matter using neutron stars and gravitational waves.

12:20 pm:
Speaker: Fei Chen
Subject: Signatures of Superconducting Fluctuations on the Nonlinear Susceptibility of Layered Superconductors
12:30 pm:
Speaker: Grant Remmen (UC Berkeley)
Subject: Entropy Bounds on Effective Field Theory from Rotating Dyonic Black Holes
2:30 pm:
Speaker: There will be no colloquium today
Faculty Host: Charles E. Woodward
Speaker: Olivia Weisser, History - University of Massachusetts
Subject: Republic of Venus: Shopping for Venereal Cures in Early Modern London
Refreshments served at 3:15 p.m.
3:35 pm:
Speaker: Autumn Brower, University of Minnesota
Subject: How computer coaches impact math anxiety in introductory physics students
Note the change of location for this seminar, this week only.

Math anxiety is a multidimensional construct that can
manifest at cognitive, affective, behavioral and physiological levels.
With the increased use of technology in our society, there has been an
increased need for more technology in educational settings. This
presentation looks at the role of technology—in the form of online
physics computer coaches—to better understand math anxiety patterns in
introductory physics students. It considers the limitations of the
data collected on the coaches in the context of math anxiety. It also
looks at how math anxiety can be turned into a positive quality
through the use of a model on human performance and how that can be
applied to learning, teaching, and education.

Speaker: Career Advisory Board Visit + Meet, no seminar this week.

Monday, April 29th 2019
12:15 pm:
Speaker: Patrick Kelly, UMN

Tuesday, April 30th 2019
Speaker: TBD
Subject: TBD
Faculty Host: Vuk Mandic

Wednesday, May 1st 2019
1:25 pm:
Speaker: Jack Harris, Yale University
Subject: A pedagogical introduction to the emergence of topology in non-Hermitian dynamics

A collection of coupled linear oscillators is widely regarded as a trivial physical system. Nevertheless, in recent years it has become evident that weak loss (or gain) in these systems can result in a variety of qualitative surprises - even in the purely linear regime. Effects that have attracted considerable attention include: PT symmetry breaking, exceptional points, non reciprocity, and topological control. I will describe a simple framework that unites these "non-Hermitian" effects and explains why topology emerges generically in damped coupled linear oscillators. I will discuss the application of these concepts in classical systems and in quantum systems. Lastly, I will describe an optomechanical experiment that offers a natural way to realize generic non-Hermiticity.

Faculty Host: Paul Crowell

Thursday, May 2nd 2019
10:10 am:
Biophysics Seminar in 120 PAN
Speaker: TBD
12:10 pm:
Speaker: Tom Jones and Jamie Cheshire
3:35 pm:
Speaker: Jack Harris (Yale University)
Subject: Quantum optomechanics with superfluid helium
Note change of room for this week only. Refreshments in atrium after the Colloquium.

To observe quantum effects in the motion of macroscopic objects typically requires high-precision readout, low temperature, and low optical and mechanical loss. Superfluid helium offers many advantages in these regards. I will describe two optomechanics experiments based on superfluid helium. In the first, the superfluid fills a Fabry-Perot optical cavity. The cavity is used to monitor the quantum fluctuations of the superfluid's acoustic modes. This system is amenable to single photon/phonon detection schemes, and so may provide a route to more exotic quantum effects in massive objects. The second experiment uses magnetic levitation to suspend a mm-scale drop of superfluid in vacuum. I will describe preliminary measurements of the drop's formation, trapping, and evaporative cooling, and of the drop's mechanical resonances and optical resonances.

Faculty Host: Paul Crowell
4:00 pm:
A.O.C. Nier Lecture in B50 Tate
Speaker: Kenneth A. Farley, W.M. Keck Foundation Professor of Geochemistry
Subject:  The geologic record of asteroid collisions and comet showers from cosmic dust 3He in marine sediments

Friday, May 3rd 2019
11:00 am:
Nuclear Physics Seminar in Physics Tate 301-20
Speaker: Samuel Giuliani, NSCL/FRIB Laboratory, Michigan State University
Subject: r process, kilonova and nucleosynthesis of superheavy elements: The role of fission

The rapid neutron capture process (r process) is responsible for the production of half of the elements heavier than iron that we observe in the Universe. The quest to identify its actual astrophysical site is still ongoing, but there are strong indications, including the recent observation of the GW170817 electromagnetic counterpart, that make neutron star mergers (NSM) a likely candidate. Reliable estimates of nucleosynthesis yields on NSM require an accurate description of the relevant nuclear physics inputs including nuclear masses, neutron capture rates, β- and α-decay rates and, for fissioning nuclei, fission rates and fission fragments distributions. Several of these quantities can be computed from a consistent theoretical framework using the energy density functional (EDF) approach.
In this talk I will revise how uncertainties in the nuclear physics properties of neutron-rich nuclei impact nucleosynthesis calculations, with a focus in the fission properties of (super)heavy nuclei. I will present a new set of fission rates obtained from microscopic nuclear many-body calculations, which are used as a nuclear input in r-process nucleosynthesis calculations in NSM. The possible formation of superheavy elements during the r-process nucleosynthesis as well as the impact on kilonova light curve, a quasithermal transient powered by freshly synthesized r-process nuclei, will be discussed. Finally, I will introduce recent developments in the estimation of fission yields and the possible extension to r-process nuclei.

12:20 pm:
Speaker: Saumitran Kastirurangan
Subject: Effect of disorder on boundary modes in nodal topological materials
12:30 pm:
Speaker: Sergei Dubovsky (NYU)
2:30 pm:
There will be no colloquium this week

Tuesday, May 7th 2019
1:25 pm:
Space Physics Seminar in Tate 301-20
Speaker: Prof. Mark Engebretson
Subject: MMS, Van Allen Probes, GOES 13, and Ground Based Magnetometer Observations of EMIC Wave Events Before, During, and After a Modest Interplanetary Shock
Speaker: Stefano Gonella and Bojan Guzina
Subject: What Lies Beneath: inverse scattering with sparse data (Guzina), and Learning the Sparse Code of Solids with Anomalies: A Model-Agnostic Approach to Wave-Based Diagnostics (Gonella)

Guzina: Waveform tomography and in particular inverse obstacle scattering are essential to a broad spectrum of scientific and technological disciplines, including sonar and radar imaging, geophysics, oceanography, optics, medical diagnosis, and non-destructive material testing. In general, any relationship between the wavefield scattered by an obstacle and its geometry (or physical characteristics) is nonlinear, which invites two overt solution strategies: (i) linearization via e.g. Born approximation and ray theory, or (ii) pursuit of the nonlinear minimization approach. Over the past two decades, however, a number of sampling methods have emerged that both consider the nonlinear nature of the inverse scattering problem and dispense with iterations. Commonly, these techniques deploy an indicator functional that varies with spatial coordinates of the trial i.e. sampling point, and projects the sensory data (namely observations of the scattered field) onto a functional space reflecting the ‘baseline’ wave motion in a background domain. This indicator functional, designed to reach extreme values when the sampling point strikes the anomaly, can be formulated from either a mathematical or a physical standpoint. An example of the latter methodology is perhaps best exemplified via the topological sensitivity (TS) approach. This talk will cover the idea and experimental validation of the TS methodology in the context of acoustic and elastic waves, including a recent backing of the approach within the framework of catastrophe theory.

Gonella: In this work we illustrate an approach to structural and materials diagnostics revolving around the mechanistic reinterpretation of concepts and methods originated in the fields of signal and image processing and machine learning. Anomalies and defects manifest in the dynamic response of a solid medium as a collection of salient and spatially localized events, which are reflected in the data structure of the response in the form of a set of behaviorally or topologically sparse features. We introduce a model-agnostic and baseline-free methodology that requires virtually no a priori knowledge of the medium’s material properties and forsakes the need for any knowledge of the system's behavior in its pristine state. This agnostic attribute makes the methodology powerful in dealing with media with heterogeneous or unknown property distribution, for which a material model is unsuitable or unreliable. The method revolves around the construction of sparse representations of the dynamic response, which are obtained by learning instructive dictionaries that form a suitable basis for the response data. The resulting sparse coding problem is recast as a modified dictionary-learning task with additional sparsity constraints enforced on the atoms of the dictionaries, which provides them with a prescribed spatial topology designed to unveil potential anomalous regions in the physical domain. The method is validated using synthetically generated data as well as experimental data acquired using a scanning laser Doppler vibrometer.

Faculty Host: Vuk Mandic

Wednesday, May 8th 2019
Speaker: Turab Lookman
Faculty Host: Martin Greven

Thursday, May 9th 2019
3:35 pm:
Physics and Astronomy Colloquium in Physics Tate B50
Speaker: David Weinberg, The Ohio State University
Subject: Decoding Chemical Evolution and Nucleosynthesis

I will discuss insights from analytic and numerical models of
galactic chemical evolution and observations of Milky Way
elemental abundances from the SDSS APOGEE survey. Under
generic model assumptions, abundances and abundance ratios
approach an equilibrium in which element production from
nucleosynthesis is balanced by element depletion from star
formation and outflows. Reproducing solar abundances requires
outflows with mass-loading factors of 1-3, but one can evade
this conclusion by assuming low stellar yields or metal-enhanced
winds; the high observed deuterium abundance of the local ISM
argues against these alternatives and in favor of outflows.
Starbursts or other sudden transitions can produce temporary
boosts in alpha-to-iron ratios, and other surprising behavior
such as backward evolution of a stellar population from high
metallicity to low metallicity. APOGEE observations show
that the distributions of stars in (alpha,iron,age)-space change
steadily across the Milky Way disk. Given these distributions,
the behavior of other APOGEE abundance ratios can be explained
by changes in the ratio of core collapse to Type Ia supernova
enrichment. The separability of "multi-element cartography"
offers a route to empirically constraining supernova yields
in a way that is insensitive to uncertainties in other aspects
of chemical evolution.

Faculty Host: Evan Skillman

Friday, May 10th 2019
12:20 pm:
Speaker: Robert Sponsel
Subject: TBA

Monday, May 13th 2019
10:00 am:
Faculty Host: Boris Shklovskii

Tuesday, May 14th 2019
1:00 pm:
Faculty Host: Boris Shklovskii

Wednesday, September 25th 2019
1:25 pm:
Speaker: Scott Crooker, Los Alamos National Lab
Subject: TBD
Faculty Host: Paul Crowell

Wednesday, October 16th 2019
7:00 pm:
14th Annual Misel Family Lecture in McNamara Alumni Center 
Speaker: Professor Charles M. Marcus, Niels Bohr Institute

Thursday, October 17th 2019
3:35 pm:
14th Annual Misel Colloquium in Tate Hall B50
Speaker: Professor Charles M. Marcus, Niels Bohr Institute

Wednesday, November 13th 2019
1:25 pm:
Speaker: Ana Maria Rey, University of Colorado - Boulder
Subject: TBD

Thursday, November 14th 2019
3:35 pm:
Physics and Astronomy Colloquium in Physics Tate B50
Speaker: Ana Maria Rey, University of Colorado - Boulder
Subject: TBD
Faculty Host: Rafael Fernandes

Wednesday, January 1st 2020

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