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This Week at Physics

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Events During the Week of March 10th through March 17th, 2019

Monday, March 11th, 2019

Plasma Physics (Physics/ECE/NE 922) Seminar
Numerical modeling of magnetic self-organization at the top of the solar convection zone
Time: 12:05 pm
Place: 2241 Chamberlin Hall
Speaker: John O'Bryan, University of Washington-Seattle
Abstract: Nonlinear, numerical computation with the NIMROD code is used to explore magnetic self-organization near the narrow, convectively unstable super-adiabatic layer at the top of the solar convection zone. The convective turbulence produced by the super-adiabatic rapidly saturates with kinetic and magnetic energy fluctuations in equipartition. Magnetic self-organization produces a radially-localized, latitudinally-elongated magnetic structure. The convective turbulence drive is stabilized by magnetic field, which limits the achievable magnetic field from localized turbulence alone. Differential rotation of the sun creates an inductive electric field which also causes growth of the magnetic field within the structure, the rate of which scales with its magnitude. The saturated small-scale turbulence can also drive a large-scale dynamo through the magnetic shear-current effect. When considered together, the localized convective turbulence and rotational flow shear create a robust mechanism for magnetic field generation, regardless of its magnitude. The nonlinear evolution of such a shallow magnetic structure may provide insight into the evolution of surface magnetic features.
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Astronomy Colloquium
Monday special talk
Decoding the Magnetic Universe
Time: 3:30 pm
Place: 4421 Sterling Hall, 3:30 PM Coffee and cookies, 3:45 PM Talk Begins
Speaker: Ann Mao , Max Planck Institute for Radioastronomy
Abstract: Dynamically important magnetic fields have been shown to play pivotal roles in processes that are closely linked to galaxy evolution, such as disk-halo interaction, gas accretion and galactic-scale outflows in local galaxies. However, how galaxies and their magnetic fields have co-evolved since the early Universe remains an unsolved fundamental question in astro-plasma physics and cosmology due to the lack of galactic magnetic field measurements beyond the local Universe.

In this talk, I will first describe how the advent of broadband radio polarimetry is revolutionizing the field of cosmic magnetism by enabling unambiguous and precise polarization measurements. Moreover, these broadband polarization data allow one to derive magnetized gas properties that were impossible to obtain in the past with narrowband data and these new data are now shedding new light on galactic magnetic fields near and far.

I will then demonstrate how broadband polarimetry, in combination with innovative observational methods can allow us to, for the first time, robustly measure magnetic fields in galaxies in previously uncharted redshift regimes. I will present the first results from our campaign, including our record-holder detection of coherent magnetic fields in a disk galaxy as seen 4.6 Gyrs ago, with similar field strength and geometry to local galaxies. This is the most distant galaxy to-date with a robust magnetic field measurement and it is consistent with mean-field dynamo generated fields already in place when the Universe was 2/3 of its current age. I will describe our efforts to interpret the observed magnetic fields in distant galaxies by producing synthetic polarimetric observations from dynamo theories and cosmological magneto-hydrodynamics simulations.

To conclude, I will discuss exciting prospects of decoding the origin and evolution of galactic magnetic fields with Square Kilometre Array pathfinders and the next generation radio telescopes.
Host: Professor Ellen Zweifel
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Tuesday, March 12th, 2019

Chaos & Complex Systems Seminar
Big data ecology: Advancing the study of the natural world through citizen science
Time: 12:05 pm
Place: 4274 Chamberlin (refreshments will be served)
Speaker: Ben Zuckerberg, UW Department of Forest and Wildlife Ecology
Abstract: For more than a hundred years, ecology relied on carefully planned field studies focusing on a few species for a few years on a few parcels of land. These studies advanced numerous theories on how species interact with their environment, but the early 21st century ushered in a new era in the use of "big data" in ecology. Big data broadly describes large complex datasets arising from advancements in information technology and data acquisition. For ecologists, the most important stream of big data comes from citizen science programs that enlist the public in collecting observations of the natural world. Citizen scientists, equipped with both old tools (binoculars) and new technologies (smartphones), regularly collect data on where species occur across the world and are essential for documenting the ecological impacts of environmental change. I will present our recent work on the use of citizen science for studying impacts of urbanization and climate change on bird communities, and discuss the successes and challenges of big data ecology.
Host: Clint Sprott
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
gFEX: A Level 1 Calorimeter Trigger for ATLAS at the Run3 LHC (and beyond)
Time: 2:15 pm
Place: 5280 Chamberlin Hall
Speaker: Sabine Lammers , University of Indiana-Bloomington
Abstract: The Global Feature Extractor (gFEX) subsystem of the ATLAS Level 1 Calorimeter trigger is intended to enhance the selectivity of the L1 trigger and increase sensitivity to key physics channels. The gFEX identifies large-radius jets, typical of Lorentz-boosted objects, by means of wide-area jet algorithms refined with subjet information. The architecture of the gFEX permits event-by-event local pileup suppression for these jets using baseline subtraction techniques comparable to those developed for offline analyses. The gFEX architecture is also suitable for other global event algorithms such as missing Et and centrality-related variables.
Host: Kevin Black
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Council Meeting
Time: 3:30 pm
Place: 2314 Chamberlin Hall
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Wednesday, March 13th, 2019

Department Meeting
Time: 12:15 pm
Place: B343 Sterling Hall
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Thursday, March 14th, 2019

NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Measure what is measurable and make measurable what is not so — Uncover new physics with bosons at the LHC and upgrades of the CMS detector to maximize the discovery potential
Time: 2:00 pm
Place: 5280 Chamberlin Hall
Speaker: Miaoyuan Liu, Fermilab
Abstract: The Standard Model describes the building blocks of matter and their
interactions. It has been tested extensively with experimental data and
found to be incredibly successful in describing nature. Discovering the
Higgs boson in 2012 at the LHC completed the picture of the SM. The LHC
is at the forefront of directly searching for new physics which is
Beyond-Standard-Model (BSM), and I will discuss searches for
supersymmetric partners of the electroweak bosons, as well as
measurement of an extremely rare process with three WWW bosons as
stringent tests of the SM. I will also discuss the instrumentation which
enables such studies. The discussion includes the recently completed CMS
Phase-1 pixel upgrade, as well as the R&D studies towards solving the
future trigger and computing challenges using innovative machine
learning approaches in future high energy experiments.
Host: Tulika Bose
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Astronomy Colloquium
Building a Gravitational Wave Detector with Millisecond Pulsars
Time: 3:30 pm
Place: 4421 Sterling Hall, Coffee and cookies 3:30 PM, Talk begins 3:45 PM
Speaker: Joseph Swiggum, NANOGrav Postdoctoral Fellow Center for Gravitation, Cosmology, & Astrophysics University of Wisconsin-Milwaukee
Abstract: The Green Bank North Celestial Cap (GBNCC) pulsar survey aims to cover the full sky north of -40 degrees declination at 350 MHz using the Green Bank Telescope. One of the main science goals of the survey is to find new millisecond pulsars (MSPs) and rapidly assess their suitability for inclusion in pulsar timing arrays (PTAs). The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) currently monitors about 75 MSPs with sub-microsecond RMS residuals in an effort to detect low-frequency gravitational waves from merging supermassive black hole binaries. The best way to improve our sensitivity to the stochastic gravitational wave background is to add high-caliber MSPs to PTAs and this is also an essential strategy for long-term characterization of the gravitational wave signal. Over the past two years, ten MSPs have been discovered in the GBNCC pulsar survey. Several have already been added to NANOGrav and released to the International Pulsar Timing Array (IPTA) collaboration. I will discuss GBNCC survey sensitivity, search procedures, and assessments of new MSP discoveries for PTA inclusion, as well as how current yields inform our future strategies for gravitational wave detection and signal characterization.
Host: Robert Benjamin
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Friday, March 15th, 2019

Physics Department Colloquium
Special Event: Kerst Lecture
The long way to steady state fusion plasmas - the superconducting stellarator device Wendelstein 7-X
Time: 3:30 pm
Place: 2241 Chamberlin Hall
Speaker: Thomas Klinger, Max-Planck-Institut für Plasmaphysik and Greifswald University
Abstract: Stellarators are disruption-free and inherently capable to operate in steady-state. The optimized superconducting stellarator device Wendelstein 7-X (major radius 5.5 m, minor radius 0.5 m, 30m3 plasma volume) restarted operation after the assembly of a graphite heat shield and 10 inertially cooled island divertor modules. With 2.5 T magnetic field on axis and 8 MW micro wave heating power, high performance divertor plasmas are generated that allow one to establish the scientific basis for the extrapolation to a next step device. Wendelstein 7-X was designed for steady-state high-power operation, more specifically for 1800 s at 10 MW input power. This talk summarizes the physics results obtained during the recent first operation phases, notably high density and performance discharges, stellarator physics optimization, and island divertor operation. We also discuss the key physics subjects for optimized stellarators and briefly review the construction of such a first-of-a-kind device.
Host: Cary Forest
Video: https://vod.physics.wisc.edu/media/2019_03_15.m4v
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