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This Week at Physics

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Events During the Week of April 22nd through April 29th, 2018

Monday, April 23rd, 2018

Plasma Physics (Physics/ECE/NE 922) Seminar
Helicons, Whistlers, Lower Hybrid Waves: Physics of Wave Propagation and Absorption for Current Drive Via Landau Damping
Time: 12:05 pm
Place: 2241 Chamberlin Hall
Speaker: Robert I. Pinsker, General Atomics
Abstract: In this seminar, I present the application of plasma waves in the lower hybrid range of frequencies (LHRF) for current drive in tokamaks. Wave damping mechanisms in a nearly collisionless hot magnetized plasma are briefly described, and the connections between the properties of the damping mechanisms and the optimal choices of wave properties (mode, frequency, wavelength) are explored. The two wave modes available for current drive in the LHRF are described and compared. The terms applied to these waves in different applications of plasma physics are elucidated. The character of the ray paths of these waves in the LHRF is illustrated in slab and toroidal geometries. Applications of these ideas to experiments in the DIII-D tokamak are discussed. Experiments are already underway using the 'helicon' wave (fast wave in the lower hybrid range of frequencies) at 0.5 GHz. The antenna/plasma coupling in the linear (very low power) regime of a 12-element 'comb-line' traveling wave antenna has been measured in tokamak discharges; a high-power system at ~1 MW power with a 30-element comb-line is in preparation. Experiments at a similar power level using the lower hybrid (slow) wave at 4.6 GHz are planned; the key feature of these experiments will be the location of the 'grill' wave-launcher on the high-field (small major radius) side of the torus to obtain much better wave accessibility to the core than would be possible using the conventional placement of the launcher on the low-field (large major radius) side at the outboard mid-plane.
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Tuesday, April 24th, 2018

Chaos & Complex Systems Seminar
Postgenomic complexity
Time: 12:05 pm
Place: 4274 Chamberlin (Refreshments will be served)
Speaker: Joan Fujimura, UW Department of Sociology
Abstract: The postgenomic era has been ongoing for some time, depending on whom one asks. This talk will discuss several fields that developed with the aim to complexify the reductionism of genetics. I earlier wrote about systems biology and developmental systems theory. Developmental Systems Theory (DST) developed in negative response to the genetic reductionism of early genetics rhetoric and theoretical approaches. Systems biology developed in positive response to the vast territories of information produced by the genome sequencing projects, what we now call “big data.” Sociologists have studied systems biology and epigenetics as hoped-for avenues to operationalize DST and complexity. Epigenetics has recently been proclaimed to be the solution to difficulties met by genetics and genomics in the search for health and disease mechanisms and potential therapies. However, epigenetics as DNA methylation at and around the genome differs vastly from “epigenetic inheritance.” Some scholars have argued that epigenetics is producing reductive explanations such as “blame the mother,” that emulate genetic reductive explanations. This talk will discuss these in the context of our current research on epigenetics and systems biology.
Host: Clint Sprott
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"Physics Today" Undergrad Colloquium (Physics 301)
Chaos
Time: 1:20 pm
Place: 2241 Chamberlin Hall
Speaker: Clint Sprott, UW Madison Department of Physics
Host: Wesley Smith
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Council Meeting
Council Meeting
Time: 4:00 pm
Place: 2314 Chamberlin Hall
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Wednesday, April 25th, 2018

Department Meeting
Department Meeting
Time: 12:15 pm
Place: 5310 Chamberlin Hall
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Thursday, April 26th, 2018

R. G. Herb Condensed Matter Seminar
Quantum field theory of nematic transitions in spin orbit coupled spin-1 polar bosons
Time: 10:00 am
Place: 5310 Chamberlin Hall
Speaker: Elio König , Rutgers University
Abstract: We theoretically study an ultra-cold gas of spin-1 polar bosons in one spatial dimension which are subject to a quadratic Zeeman field and a Raman induced spin-orbit coupling. Concentrating on the regime in which the background fields can be treated perturbatively we analytically solve the model in its low-energy sector, i.e. we characterize the relevant phases and the quantum phase transitions between them. Depending on the sign of the effective quadratic Zeeman field ε, two superfluid phases with distinct nematic order appear. In addition, we uncover a spin-disordered superfluid phase at strong coupling. We employ a combination of renormalization group calculations and duality transformations to access the nature of the phase transitions. At ε = 0, a line of spin-charge separated pairs of Luttinger liquids divides the two nematic phases and the transition to the spin disordered state at strong coupling is of the Berezinskii-Kosterlitz-Thouless type. In contrast, at ε ≠ 0, the quantum critical theory separating nematic and strong coupling spin disordered phases contains a Luttinger liquid in the charge sector that is coupled to a Majorana fermion in the spin sector (i.e. the critical theory at finite ε maps to a quantum critical Ising model that is coupled to the charge Luttinger liquid). Due to an emergent Lorentz symmetry, both have the same, logarithmically diverging velocity. We discuss the experimental signatures of our findings that are relevant to ongoing experiments in ultra-cold atomic gases of 23Na.
Host: Alex Levchenko
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Observation of the highest-energy gamma rays with the HAWC Observatory
Time: 2:30 pm
Place: 5310 Chamberlin Hall
Speaker: Kelly Malone, Penn State
Abstract: Galactic sources that accelerate particles to PeV energies (“PeVatrons”) are expected to exist, but to date only the Galactic Center has been identified as such. One of the signatures of a PeVatron is a hard gamma-ray spectrum that extends without any apparent spectral cutoff to at least tens of TeV. High-energy (> 50 TeV) gamma-ray observations are therefore essential in identifying PeVatron candidates. The High Altitude Water Cherenkov Observatory (HAWC) has sensitivity to gamma rays in this previously largely unexplored energy regime. HAWC is well suited to performing all-sky surveys due to its large instantaneous field of view (~2 sr) and high duty cycle (> 95%). I will discuss candidate sources seen above 50 TeV in the first 1000 days of HAWC data and discuss potential connections to the IceCube neutrinos. I will also briefly discuss the energy estimation method used by HAWC.
Host: Stefan Westerhoff
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Astronomy Colloquium
Star formation, polarization, and magnetic fields in the ALMA era
Time: 3:30 pm
Place: 4421 Sterling Hall, Coffee and cookies 3:30 PM. Talk starts at 3:45 PM
Speaker: Chat Hull, NAOJ Fellow, NAO of Japan, NAPJ Chile Observatory, Joint Alma Observatory
Abstract:
The results from the ALMA polarization system have begun both to expand and to confound our understanding of the role of the magnetic field in low-mass star formation. After a brief motivation via CARMA, SMA, and other polarization observations from the prior decade, I will discuss new ALMA results, including the highest resolution and highest sensitivity polarization images made to date of two very young, Class 0 protostellar sources. These new observations achieve ~140 AU resolution, allowing us to probe polarization -- and thus magnetic field orientation -- in the innermost regions surrounding the protostars. First is a Class 0 protostellar source in Serpens known as Ser-emb 8, where a comparison with cutting-edge, moving-mesh AREPO simulations suggests that cloud-scale turbulence -- not a large-scale magnetic field preserved from the source's natal cloud -- is dictating the magnetic field morphology immediately surrounding the protostar. In contrast, in the second source, known as Serpens SMM1, the magnetic field has clearly been shaped by the bipolar outflow emanating from the central source -- a situation that is quite different from the turbulence-dominated morphology of Ser-emb 8. Finally, I will show recent observations of polarization toward IM Lup, a much more evolved, Class II protoplanetary disk. In the case of IM Lup, consistent with previous observations of other disks, the polarization appears to be due to scattering by dust grains, thus complicating the search for magnetic fields in disks, but opening up a new window into dust grain growth and evolution.
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Can a tool developed for hurricane prediction be taken to predict neutrino flavor evolution?
Time: 4:00 pm
Place: 5280 Chamberlin Hall
Speaker: Eve Armstrong, University of Pennsylvania
Abstract: We assess the utility of an optimization-based data assimilation (D.A.)
technique for treating the problem of nonlinear neutrino flavor
transformation in core-collapse supernovae. D.A. was invented for
numerical weather prediction, and it shares some features of machine
learning for the purposes of predictive power. Within the D.A. framework,
one uses measurements obtained from a physical system to estimate the
state variable evolution and parameter values of the associated model.
Formulated as an optimization procedure, D.A. can offer an
integration-blind approach to predicting model evolution, which offers an
advantage for models that thwart solution via traditional numerical
integration techniques. Further, D.A. performs most optimally for models
whose equations of motion are nonlinearly coupled. In this exploratory
work, we consider a simple steady-state model with two mono-energetic
neutrino beams coherently interacting with each other and a background
medium. As this model can be solved via numerical integration, we have an
independent consistency check for D.A. solutions.

We find that the procedure can capture key features of flavor evolution
over the entire trajectory, even given measurements of neutrino flavor
only at the endpoint, and with an assumed known initial flavor
distribution. Further, the procedure permits an examination of the
sensitivity of flavor evolution to estimates of unknown model parameters,
locates degeneracies in parameter space, and can identify the specific
measurements required to break those degeneracies.
Host: Baha Balantekin
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WIPAC at Women in STEM outreach event
WIPAC at Women in STEM outreach event
Time: 4:30 pm
Place: Kromery Middle School, 7009 Donna Dr. Middleton, WI 53562
Speaker: WIPAC researchers, WIPAC
Abstract: WIPAC will have a outreach booth at the Women in STEM night hosted by 2 Middleton high school clubs. The purpose of the event is to encourage young girls to pursue STEM and show them real-life examples of what they can do with their knowledge. We will be bringing our cosmic messenger bean bag toss game, DOM, South Pole gear and talk to the participants about IceCube Neutrino Observatory.
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Friday, April 27th, 2018

Physics Department Colloquium
When the Universe was one second old
Time: 3:30 pm
Place: 2241 Chamberlin Hall
Speaker: George Fuller , UC San Diego
Abstract: The imminent advent of 30-m class telescopes and Stage-4 cosmic microwave
background observatories promises to give us precision measurements of key
parameters which are set in the very early universe. For example, we may
soon know to fair precision the amount of relic relativistic energy and
the deuterium and helium abundances set during the time when the neutrinos
fall out of thermal and chemical equilibrium. Given the excitement and
ferment right now surrounding new ideas in dark matter and other beyond
standard model (BSM) physics, we would very much like to leverage these
coming measurements into deeper insights into this epoch, in effect
turning the early universe into a precision BSM physics laboratory. Doing
so, however, requires theorists to "raise their game" in modeling the
neutrino decoupling epoch. We will discuss these issues and reveal some
surprising features of the universe when it was roughly one second in age.
Host: Baha Balantekin
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