# This Week at Physics

## Events at Physics |
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### Events During the Week of September 30th through October 7th, 2018

### Monday, October 1st, 2018

**Plasma Physics (Physics/ECE/NE 922) Seminar****Understanding Heavy Ion Impurity Transport in Tokamaks****Time:**12:05 pm**Place:**2241 Chamberlin Hall**Speaker:**Dr. Emily Belli, General Atomics**Abstract:**In a fusion reactor, the transport of heavy impurities, such as tungsten from material surfaces, into the high-temperature core must be minimized since accumulation can lead to fuel dilution and radiation losses, ultimately degrading the energy confinement and fusion performance. Assessing the level of core accumulation requires sophisticated transport models beyond those typically use for studying the main ions and plasmas with low-Z impurities. In particular, centrifugal effects due to sonic rotation, which arises in tokamaks from torque due to neutral beam injection for plasma heating, can lead to significant modifications to the simulated transport of heavy impurities. The lack of sonic rotation effects in most theoretical models means that widely-used reduced models are inadequate for studying heavy impurities and thus computationally-intensive advanced kinetic codes are needed. In this work, we use state-of-the art gyrokinetic (turbulent) and neoclassical (collision) codes to develop an understanding of the physical mechanisms driving the particle transport of tungsten in tokamaks and how tungsten accumulation can be avoided

Cosponsored by a generous grant from the Women in Science & Engineering Leadership Institute ( WISELI)### Tuesday, October 2nd, 2018

**Chaos & Complex Systems Seminar****Some half-baked philosophy of mathematics****Time:**12:05 pm**Place:**4274 Chamberlin (refreshments will be served)**Speaker:**Moe Hirsch, UW Department of Mathematics**Abstract:**I'll discuss what I think are the basic philosophical questions:

(1) What makes math universal? Its results seem independent of time and place. No one doubts Euclid's or Pythagoras' theorems of thousands of years ago, even if we think some of the proofs aren't correct. No one since Hitler and Stalin thinks its correctness depends on race, religion or nationality. But will the same math be found wherever there's life in the universe?

(2) Why is math so useful? Try spending a day without thinking about numbers.

(3) Its results seem absolutely true. But are they? If they are, how can we prove it? And if we can prove it, how do we know our proof is correct?

Readings:

Essays in Humanistic Mathematics: Mathematical Association of America

What is Mathematics Really? R. Hersh, Oxford University Press

Where Mathematics Comes from: G. Lakoff & R Nunez, Basic Books

The Math Gene: K. Devlin, Basic Books**Host:**Clint Sprott### Wednesday, October 3rd, 2018

**No events scheduled**### Thursday, October 4th, 2018

**R. G. Herb Condensed Matter Seminar****Topological quantum computation with Majorana zero modes****Time:**10:00 am**Place:**5310 Chamberlin Hall**Speaker:**Roman Lutchyn, Microsoft Station Q**Abstract:**Research in quantum computing has offered many new physical insights as well as the potential of exponentially increasing the computational power that can be harnessed to solve important problems in science and technology. The largest fundamental barrier to building a scalable quantum computer is errors caused by decoherence. Topological quantum computing overcomes this barrier by exploiting topological materials which, by their nature, limit errors. In this talk, I will discuss how to engineer topological superconductors at the interface of a conventional superconductor and a semiconductor with spin-orbit interaction. I will review recent experiments aiming to detect Majorana zero-energy modes at the ends of the proximitized nanowires. Finally, I will present designs for scalable quantum computers composed of qubits involving superconducting islands in a Coulomb blockade regime hosting aggregates of four or more Majorana zero modes.**Host:**Levchenko**Cosmology Journal Club****Time:**12:00 pm**Place:**5242 Chamberlin Hall**Abstract:**Please visit the following link for more details:

http://cmb.physics.wisc.edu/journal/index.html

Feel free to bring your lunch!

If you have questions or comments about this journal club, would like to propose a topic or volunteer to introduce a paper, please email Ross Cawthon (cawthon@wisc.edu) and Santanu Das (sdas33@wisc.edu).**Astronomy Colloquium****Diermeier Visiting Professor****"Chemical Cartography of the Milky Way Disk with SDSS/APOGEE"****Time:**3:30 pm**Place:**4421 Sterling Hall, Coffee and cookies 3:30 PM. Talk Begins at 3:45 PM**Speaker:**Jon Holtzman, Department Head, Astronomy, New Mexico State University**Abstract:**The SDSS Apache Point Observatory Galactic Evolution Experiment (APOGEE) has collected high resolution near-IR spectra of several hundred thousand stars across the Milky Way. I'll describe some observational results about the spatial variation of chemical abundances as a function of Galactocentric radius and distance from the midplane, discussing mean abundances, metallicity distribution function, and the variation of abundance ratios of multiple elements. Additional information related to stellar ages can be obtained from [C/N] for red giant stars. Several lines of evidence suggest that radial migration has had a significant impact on the Galactic disk.**Host:**Professor Matt Bershady### Friday, October 5th, 2018

**Theory Seminar (High Energy/Cosmology)****The Effective Description of Stringy de Sitter****Time:**2:00 pm**Place:**5280 Chamberlin Hall**Speaker:**Lars Aalsma, University of Amsterdam**Abstract:**If de Sitter vacua in string theory exist, they should break supersymmetry spontaneously. In the context of the KKLT construction, anti-D3-branes are used to break supersymmetry and are claimed to give rise to metastable de Sitter vacua. In this talk, I will present recent progress made in understanding how anti-D3-branes break supersymmetry spontaneously and discuss its implications on the effective description of stringy de Sitter space.**Physics Department Colloquium****Special Event: Julian E. Mack Lecture****The changing flow of energy through the Earth's Climate System****Time:**3:30 pm**Place:**2241 Chamberlin Hall**Speaker:**Kevin Trenberth, NCAR**Abstract:**Radiant energy from the sun is unevenly absorbed in the Earth system because of the sun-Earth geometry, and the annual and diurnal cycles. The energy is transformed into internal energy (temperature-related sensible heat), latent energy (associated with phase changes of water), potential energy (associated with height and gravity), and kinetic energy (associated with motion). The energy may be stored in atmospheric, ocean, cryosphere and land heat reservoirs and moved around mainly by the atmosphere and ocean, which give rise to our weather and climate. Ultimately it is radiated back to space as infrared radiation, and for a stable climate the global mean outgoing and incoming radiation must balance. However, there is an energy imbalance caused by increasing greenhouse gases in the atmosphere, and most of the imbalance, over 90%, goes into the ocean. Accordingly, ocean heat content (OHC) provides a primary indicator of climate change, along with sea level rise. Regional energy and water imbalances drive heat transports in the atmosphere and ocean currents, and through evaporation, precipitation, and runoff. Natural variability, especially El Niño, plays a small role globally, but can be significant locally. By adopting a holistic approach that includes top-of-atmosphere (TOA) radiation, vertically-integrated atmospheric transports, surface energy fluxes, and ocean heat transports, closure of the energy and water cycles on regional scales can be achieved. A new formulation of the energetics of the atmosphere and the climate system is used to refine estimates of the surface energy fluxes as a residual of TOA and atmospheric energetics. When the surface flux is combined with OHC estimates, ocean heat transports can be computed and validated with in situ observations. Understanding the disposition of the energy imbalance is essential for determining how climate change is manifested.**Host:**Alex Levchenko