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This Week at Physics

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Events During the Week of September 17th through September 24th, 2017

Monday, September 18th, 2017

Graduate Introductory Seminar
Atomic, Molecular, and Optical Physics
Time: 12:00 pm
Place: 4274 Chamberlin Hall
Speaker: Kolkowitz, Lawler, Saffman, Walker, Yavuz
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Plasma Physics (Physics/ECE/NE 922) Seminar
Turbulent dynamo in a partially ionized medium
Time: 12:00 pm
Place: Chamberlin 2241
Speaker: Dr. Siyao Xu, Hubble Fellow, UW Madison
Host: Stanislav Boldyrev
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Council Meeting
Council Meeting
Time: 4:00 pm
Place: 2314 Chamberlin Hall
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Tuesday, September 19th, 2017

Chaos & Complex Systems Seminar
Nonlinear normal modes for analysis of geometrically nonlinear structures
Time: 12:05 pm
Place: 4274 Chamberlin (refreshments will be served)
Speaker: Matthew Allen, UW Department of Mechanical Engineering
Abstract: Geometric nonlinearity is an important consideration when designing many structures, for example the skin panels for future hypersonic cruise vehicles where intense pressures and aerodynamic heating can cause the panels to vibrate in and out of buckled states. Highly flexible joined-wing aircraft, which are being sought for station keeping at high altitude, can also exhibit nonlinear dynamic phenomena. It may also be possible to add a nonlinear element to an otherwise linear structure in order to reduce vibration levels and increase its life, leading to quieter automobiles or more durable spacecraft. All of these applications are challenging because numerical response predictions are expensive and these nonlinear systems exhibit a large range of phenomena, each of which may require a specialized analysis technique. This work shows that tremendous insight can be gained into the dynamics of these types of nonlinear structures using undamped nonlinear modal analysis.

This presentation highlights advances in modeling for geometrically nonlinear structures and discusses how nonlinear modes can be used in analysis, design and testing. While academics have used simplified Galerkin/Ritz models for years to qualitatively study the geometrically nonlinear response of plates and beams, those methods often do not scale to industrial practice where the geometry is far more complicated and many degrees of freedom must be considered. The work focuses on structures that are modeled in commercial finite element software and uses a non-intrusive approach in which a series of static loads are applied to the structure and a nonlinear Reduced Order Model (ROM) is fit to the load-displacement behavior. Nonlinear modes prove to be effective in discerning whether the reduced basis contains the fidelity needed to capture the dynamics of interest and in assuring that the loads are large enough to allow the ROM to be accurately computed. Nonlinear modes are also found to be intimately connected to the response of the structure to random loading, such as the pressure fields experienced by many aircraft. These concepts are demonstrated by applying them to a variety of finite element models, showing that the nonlinear modes provide tremendous insight into the dynamics of the structure.
Host: Clint Sprott
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Wednesday, September 20th, 2017

Department Meeting
Department Meeting
Time: 12:15 pm
Place: 5310 Chamberlin Hall
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Thursday, September 21st, 2017

R. G. Herb Condensed Matter Seminar
TBD
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Jerry Hunter, UW: Director of Facilities, College of Engineering
Abstract: TBD
Host: Eriksson
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Astronomy Colloquium
Magnetic Fields and the Early Stages of Star Formation
Time: 3:30 pm
Place: 4421 Sterling Hall, Coffee and cookies 3:30 PM , Talk begins at 3:45 PM
Speaker: Dick Crutcher, University of IL
Abstract: The role and importance of magnetic fields in star formation has been uncertain ever since their initial detection in the interstellar medium almost 70 years ago. I will discuss techniques for measuring interstellar magnetic fields in molecular clouds, briefly describe some of the principal theories for the formation and evolution of molecular clouds, and discuss the current status and future possibilities of observational testing of the theoretical predictions of star formation theories.
Host: Astronomy Department
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Friday, September 22nd, 2017

Physics Department Colloquium
Laboratory cosmology
Time: 3:30 pm
Place: 2241 Chamberlin Hall
Speaker: Andrei Derevianko, University of Nevada-reno
Abstract: Laboratory cosmology is a nascent field offering an intriguing potential for exacting the nature of dark matter and dark energy with small-scale experiments. The searches involve precision measurement devices and rely on detecting predicted dark sector signatures. I will review such signatures with an emphasis on atomic clocks, atom interferometers, and their networks. I will illustrate these ideas using our dark matter search with atomic clocks on board Global Positioning System satellites.
Host: Mark Saffmann
Presentation: WallCrossing.pdf
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