Physics and Astronomy Calendar

Week of Monday, February 20th 2017

Monday, February 20th 2017
10:00 am:
Thesis Defense in Keller Hall 4-178A
Speaker: Tao Qu, University of Minnesota
Subject: Ferromagnetic Material Properties and Performance in Spintronic Devices
This is the public portion of Ms. Qu's thesis defense. Her advisor is Randall H. Victora.
12:15 pm:
Speaker: Lilya Williams, UMN
Subject:  Interplay between dark and baryonic matter in galaxy centers: new constraints from dynamics and lensing

The central 5-10 kpc of elliptical galaxies, while in long term steady state, are not truly relaxed. The primary reason is that baryons and dark matter are not fully mixed. We demonstrate this by comparing observed and simulated galaxies to theoretically derived prediction for dynamically relaxed collisionless systems, and by examining the observed population of quadruply imaged lensed systems hosted by galaxies. The unrelaxed state can be used to our advantage, to extract information about the formation and evolution of the central regions of galaxies and hence all that they depend on: baryonic processes, central supermassive black hole, and especially dark matter properties. I will describe some ongoing work on this, and sketch future directions.

Tuesday, February 21st 2017
11:30 am:
Speaker: Rajan Gupta, Los Alamos National Laboratory
Subject: In a world with 10 billion people, what will 8 billion do?
Please note change of time, room and day for the seminar, this week only.

Rapid advances in automation, robotization, computerization are changing local and global job markets. Worldwide, the youth are struggling to understandand define a meaningful role for themselves and a promising future for their families. While the future for the innovators, leaders and entrepreneurs is brighter than ever before, a large majority are becoming pessimistic and losing hope. This talk will examine existing trends and correlate many of the current challenges---jobs, poverty, population, migration, climate change, environmental degradation, etc.--- to ask the question, is liberal democracy under threat.

4:30 pm:
There will be no seminar this week.

Wednesday, February 22nd 2017
1:25 pm:
Speaker: Ke Wang, Harvard University
Subject: Manipulating Charge Carriers for Quantum Transport in Van der Waals Materials Nanostructures
Candidate for the Condensed Matter Experimental Assistant Professor Position

Since the discovery of graphene via mechanical exfoliation, it has been shown that the electronic properties of solids can undergo dramatic change when the material thickness is reduced to the atomic limit. Recently, the quality of these 2-dimensional (2D) electronic systems has been significantly improved by hexagonal boron nitrides encapsulation, enabling the electron mean free path only limited by the size of the samples. However, mesoscopic transport studies in these systems are relatively unexplored due to the challenges in the device fabrication processes. Here we develop a robust procedure for making gated-defined nanostructures in 2D van der Waals materials without compromising their intrinsic 2DEG quality, providing versatile experimental platforms to explore various novel quantum phenomena in these systems. By confining and manipulating charge carriers [1][2], we demonstrate relativistic electron-optics, resonant quantum Hall (QH) tunneling spectroscopy, tunable optical trion lifetime and quantized mesoscopic transport in graphene and transition metal dichalcogenides [2]. Our results bode well for addressing many key problems in condensed matter physics, including Luttinger physics, high fidelity logic gates in Loss-DiVincenzo qubits, gate-controlled quantum optics, measurement of small fractional QH energy gaps, and functional quantum devices based on pseudospin manipulation and electron optics.

[1] Wang, et al, Phys. Rev. Lett. 111, 046801 (2013).
[2] Wang, et al, ArXiv:1610.02929 (2016).

Faculty Host: James Kakalios
Planning meeting
4:30 pm:
CM Journal Club in PAN 120
To be announced.

Thursday, February 23rd 2017
10:10 am:
Biophysics Seminar in 120 PAN
Speaker: Ragnar Stefansson, University of Minnesota
Subject: To be announced.
Speaker: Chris Nolting and Tom Jones
3:35 pm:
Speaker: Daniel Baker, University of Colorado
Subject: Economic and Societal Impacts of Severe Space Weather
Refreshments to be served outside Smith 100 after the colloquium.

This presentation describes extreme space weather impacts and their economic and societal costs. Modern technological society is characterized by a complex set of interdependencies among its critical infrastructures. These are vulnerable to the effects of intense geomagnetic storms and solar storms. Strong currents flowing in the ionosphere can disrupt and damage Earth-based electric power grids and contribute to the accelerated corrosion of oil and gas pipelines. Magnetic storm-driven ionospheric disturbances interfere with high-frequency radio communications and navigation signals from Global Positioning System (GPS) satellites. Exposure of spacecraft to solar particles and radiation belt enhancements can cause temporary operational anomalies, damage critical electronics, degrade solar arrays, and blind optical systems such as imagers and star trackers. Moreover, intense solar particle events present a significant radiation hazard for astronauts during the high-latitude segment of the International Space Station (ISS) orbit as well as for future human explorers of the Moon and Mars. In addition to such direct effects as spacecraft anomalies or power grid outages, a thorough assessment of the impact of space weather events on present-day society must include the collateral effects of space-weather-driven technology failures. For example, polar cap absorption events due to solar particles can degrade – and, during severe events, completely black out – radio communications along transpolar aviation routes. A complete picture of the socioeconomic impact of space weather must include both direct, as well as collateral, effects of space-weather-driven technology failures on dependent infrastructures and services. It is also imperative that we—as a technological society—develop a truly operational space weather observing and modeling system in which the benefits of accurate forecasts are clearly established.

Faculty Host: Roberta Humphreys

Friday, February 24th 2017
11:00 am:
Speaker: Daniel Baker
The seminar will be held on Friday, this week only.
11:15 am:
Speaker: Ming Li and Chris Plumberg, University of Minnesota
Subject: Quark Matter 2017 - Synopsis
11:15 am:
Speaker: Daniel Baker, University of Colorado
Subject: Studying Relativistic Particle Acceleration and Loss in Our Cosmic Backyard: Van Allen Probes Radiation Belt Exploration
Please note change of time, room and day for the seminar, this week only.

Early observations of the Earth’s radiation environment suggested that the Van Allen belts could be delineated into an inner zone dominated by high-energy protons and an outer zone dominated by high-energy electrons. Subsequent studies showed that electrons in the energy range 100 keV < E< 1 MeV often populated both the inner and outer zones with a pronounced “slot” region relatively devoid of energetic electrons existing between them. The energy distribution, spatial extent and particle species makeup of the Van Allen belts has been subsequently explored by several space missions. However, recent observations by the NASA dual-spacecraft Van Allen Probes mission have revealed wholly unexpected properties of the radiation belts, especially at highly relativistic (E > 2 MeV) and ultra-relativistic (E > 5 MeV) kinetic energies. In this talk we show using high spatial and temporal resolution data from the Relativistic Electron-Proton Telescope (REPT) experiment on board the Van Allen Probes that multiple belts can exist concurrently and that an exceedingly sharp inner boundary exists for ultra-relativistic electrons. Using additionally available Van Allen Probes data, we demonstrate that these remarkable features of energetic electrons are not due to a physical boundary within Earth’s intrinsic magnetic field. Rather it likely that human-generated electromagnetic transmitter wave fields produce such effects suggesting that human-made wave-particle scattering effects deep inside the Earth’s magnetosphere can contribute to an almost impenetrable barrier through which the most energetic Van Allen belt electrons cannot migrate

The seminar has been cancelled for this week. The speaker will be rescheduled for a future date.
Speaker: Yann Mambrini (CNRS, LPT of University Paris XI)
Subject: Historical Dark Matter Papers
Speaker: Patrick Kelly, University of California - Berkeley
Subject: Using Galaxy Cluster Lenses as Extreme Probes
Candidate for the MIfA Assistant Professor position

Galaxy clusters can highly magnify galaxies behind them, making cluster lenses powerful tools for studying the high-redshift universe. The James Webb Space Telescope, when pointed towards foreground cluster fields, will be sensitive to even low-luminosity galaxies at redshift z > 6 (~35th magnitude) thought to drive reionization. In regions of high magnification, however, cluster magnification maps show strong disagreements. I will describe the first-known multiply imaged, strongly lensed supernova (SN), which appeared in late 2014 in an Einstein cross configuration in the MACS1149 galaxy-cluster field. The timing of the reappearance of the SN, at an offset of ~8 arcseconds, in 2015 disagrees with most but not all predictions, and illustrates a promising approach for identifying the most accurate cluster-modeling techniques and magnification maps. I will next discuss observations of an individual star at high redshift, which acts as a new window into the nature of galaxy-cluster dark matter. Detections of hundreds of thousands of SNe and thousands of lensed transients by the Large Synoptic Survey Telescope and the Wide-Field Infrared Survey Telescope will allow new insights into star formation and stellar evolution beginning at z~15-20, as well as the nature of dark matter and dark energy.

Speaker: Robert Schulmann, The Einstein Papers Project
Subject: "Albert Einstein: Political Consistency in Volatile Times"
Refreshments served at 3:25 p.m.

There is a remarkable consistency in Einstein’s views on physics and politics, and in his personal relations. In concentrating on political aspects of the Einstein trajectory, I will stress the continuities, above all the moral consistencies that underpinned his political evolution and that explain at least in part the hold he still has on us. Ever the non-conformist, it is Einstein’s sensitivity to the plight of the underdog, to the weaker members of society, and to the outsider that serves as the major contributing factor. I plan to tease out some strands that have particular significance in the present political situation.

Speaker: Rafael Fernandes, University of Minnesota
4:40 pm:
There will be no seminar this week.

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