Events at Physics |
Events During the Week of March 11th through March 18th, 2018
Monday, March 12th, 2018
- Plasma Physics (Physics/ECE/NE 922) Seminar
- X-ray sources from laser-plasma acceleration: development and applications for high energy density sciences
- Time: 12:00 pm
- Place: 2241 Chamberlin Hall
- Speaker: Félicie Albert, Lawrence Livermore National Laboratory
- Abstract: Bright sources of x-rays, such as synchrotrons and x-ray free electron lasers (XFEL) are transformational
tools for many fields of science. They are used for biology, material science, medicine, or industry. Such
sources rely on conventional particle accelerators, where electrons are accelerated to gigaelectronvolts
(GeV) energies. The accelerating particles are also wiggled in magnetic structures to emit x-ray radiation
that is commonly used for molecular crystallography, fluorescence studies, chemical analysis, medical
imaging, and many other applications. One of the drawbacks of synchrotrons and XFELs is their size and
cost, because electric field gradients are limited to about a few 10s of MeV/M in conventional
accelerators.
This seminar will review particle acceleration in laser-driven plasmas as an alternative to generate x-rays.
A plasma is an ionized medium that can sustain electrical fields many orders of magnitude higher than
that in conventional radiofrequency accelerator structures. When short, intense laser pulses are focused
into a gas, it produces electron plasma waves in which electrons can be trapped and accelerated to GeV
energies. This process, laser-wakefield acceleration (LWFA), is analogous to a surfer being propelled by
an ocean wave. Betatron x-ray radiation, driven by electrons from laser-wakefield acceleration, has
unique properties that are analogous to synchrotron radiation, with a 1000-fold shorter pulse. This source
is produced when relativistic electrons oscillate during the LWFA process.
An important use of x-rays from laser plasma accelerators we will discuss is in High Energy Density
(HED) science. This field uses large laser and x-ray free electron laser facilities to create in the laboratory
extreme conditions of temperatures and pressures that are usually found in the interiors of stars and
planets. To diagnose such extreme states of matter, the development of efficient, versatile and fast (subpicosecond
scale) x-ray probes has become essential. In these experiments, x-ray photons can pass
through dense material, and absorption of the x-rays can be directly measured, via spectroscopy or
imaging, to inform scientists about the temperature and density of the targets being studied.
Work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory
under contract DE-AC52-07NA27344, supported by the LLNL LDRD program under tracking code 13-LW-076,
16-ERD-024, 16-ERD-041, supported by the DOE Office of Fusion Energy Sciences under SCW 1476 and SCW
1569, and by the DOE Office of Science Early Career Research Program under SCW 1575. Tuesday, March 13th, 2018
- Chaos & Complex Systems Seminar
- Speech as a dynamical system
- Time: 12:05 pm - 1:00 pm
- Place: 4274 Chamberlin (Refreshments will be served)
- Speaker: Ben Parrell, UW Department of Communication Sciences and Disorders
- Abstract: The act of speaking is one of the most complex motor behaviors humans produce: a set of over 100 muscles must be precisely coordinated in space and time to produce rapid movements (50-300 ms) at a high rate (roughly 40 unique sounds per second). How can we control such a complex system with enough precision to produce intelligible speech? This talk will present the view that speech is a hierarchical dynamical system, with control needed only at a high-level (of speech goals or tasks) rather than a system where all muscle activations are controlled centrally. I will explain how this approach can explain speech phenomena in various languages, and show a preliminary sketch of how such a system could be instantiated in the brain.
- Host: Clint Sprott
- "Physics Today" Undergrad Colloquium (Physics 301)
- Neutrino astronomy at the South Pole
- Time: 1:20 pm - 2:10 pm
- Place: 2241 Chamberlin Hall
- Speaker: Albrecht Karle, UW Madison Department of Physics
- Host: Wesley Smith
Wednesday, March 14th, 2018
- Department Meeting
- Time: 12:15 pm
- Place: 5310 Chamberlin Hall
Thursday, March 15th, 2018
- R. G. Herb Condensed Matter Seminar
- Correlated Nanoelectronics
- Time: 10:00 am
- Place: 5310 Chamerlin Hall
- Speaker: Jeremy Levy, University of Pittsburgh
- Abstract: The study of strongly correlated electronic systems and the development of quantum transport in nanoelectronic devices have followed distinct, mostly non-overlapping paths. Electronic correlations of complex materials lead to emergent properties such as superconductivity, magnetism, and Mott insulator phases. Nanoelectronics generally starts with far simpler materials (e.g., carbon-based or semiconductors) and derives functionality from doping and spatial confinement to two or fewer spatial dimensions. In the last decade, these two fields have begun to overlap. The development of new growth techniques for complex oxides have enabled new families of heterostructures which can be electrostatically gated between insulating, ferromagnetic, conducting and superconducting phases. In my own research, we use a scanning probe to “write” and “erase” conducting nanostructures at the LaAlO3/SrTiO3 interface. The process is similar to that of an Etch-a-Sketch toy, but with a precision of two nanometers. A wide variety of nanoscale devices have already been demonstrated, including nanowires, nanoscale photodetectors, THz emitters and detectors, tunnel junctions, diodes, field-effect transistors, single-electron transistors, superconducting nanostructures and ballistic electron waveguides. These building blocks may form the basis for novel technologies, including a platform for complex-oxide-based quantum computation and quantum simulation.
- Host: Eriksson
- Theory Seminar (High Energy/Cosmology)
- De Sitter from D3-branes?
- Time: 3:30 pm
- Place: 5280 Chamberlin Hall
- Speaker: Ander Retolaza, DESY Theory Group
- Abstract: If de Sitter vacua exist in string theory compacti cations is an unanswered question. All attempts to realize such vacua are based on 4D e effective field theory descriptions. The standard procedure to construct them first deals with moduli stabilization, generically leading to anti de Sitter space, and then adds a localized source which increases the vacuum energy while leaving the stabilization untouched, typically an anti-D3-brane on a warped throat. These 4D ideas conflict with higher dimensional results telling that
in warped compacti cations one needs to include some object that violates the strong energy condition to obtain 4D de Sitter.
In this talk I will provide a 10D description of a popular 4D construction to obtain de Sitter and show that the 4D eff ective field theory misses a crucial point when trying to uplift the vacuum energy above zero. Then, I will apply this knowledge to other models in the market. - Host: Vernon Barger
- Astronomy Colloquium
- Planet Formation in the Era of ALMA
- Time: 3:30 pm - 5:00 pm
- Place: 4421 Sterling Hall, Coffee and cookies 3:30 PM, Talk begins at 3:45 PM
- Speaker: Ke Zhang, University of Michigan
- Abstract: Planetary systems are common in the universe, and our solar system is just one outcome of a vast number of possibilities. This great diversity is largely rooted and developed in their birth environments--- gas-rich protoplanetary disks around several Myr-old young stars. Therefore, studying the structures and evolutions of solids and gaseous components in these disks are necessary for our understanding of the diversity and ultimately the chance of habitability of planetary systems. I will discuss recent results from The Atacama Large Millimeter/submillimeter Array (ALMA) in characterizing protoplanetary disks, and new insight/puzzles that these results add to our understanding of planet formatting processes. In particular, I will focus on three areas: (1) the commonality of substructures in disks and their links to planet(esimal) formation, (2) new approaches to probe the planet-forming mid-plane region and locations of critical chemical transitions such as snowlines, (3) direct determination of carbon and oxygen elemental abundances in disk atmospheres and their implication for the initial atmospheric composition of extra-solar gas giants.
Friday, March 16th, 2018
- No events scheduled