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This Week at Physics

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Events During the Week of November 20th through November 26th, 2011

Monday, November 21st, 2011

Plasma Physics (Physics/ECE/NE 922) Seminar
TBD
Time: 12:05 pm
Place: 2317 Engineering Hall
Speaker: John Canik, ORNL
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Condensed Matter Theory Group Seminar
Spin resonance in Fe-based superconductors
Time: 4:30 pm
Place: 5310 Chamberlin
Speaker: Saurabh Maiti, UW-Madison
Abstract: Fe-based superconductors(FeSCs) and cuprates are often held as prime candidates for study that can lead to the understanding of the unconventional high Tc superconductivity. In this talk, I will briefly mention the motivation behind looking for spin resonance in unconventional superconductors. I will mention some the similarities and differences that are seen in experiments in these two family of compounds. Unlike in the cuprates where people agree on the d-wave symmetry, FeSCs are much more interesting. Different symmetries and structures are possible for the gap structure in these materials. Observation of a spin resonance indicates presence of on order parameter that needs to flip its sign in some parts of the Fermi-surface. Experiments in FeSC actually see a relatively broad peak (unlike in cuprates) and this has been argued by some groups to be due to a 'sign preserving' order parameter contrary to the popular 'sign-flipping' order parameter in FeSCs. In this talk I will present our resolution of the conflict and explain how the experimental observations can be understood by accounting for nodes in the gap, impurity scattering and Fermi-surface geometry.
Host: Perkins
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Tuesday, November 22nd, 2011

Chaos & Complex Systems Seminar
Sleep: A global or a local process?
Time: 12:05 pm
Place: 4274 Chamberlin
Speaker: Vladyslav Vyazovskiy, UW Department of Psychiatry
Abstract: Sleep is usually thought of as a global behavior and a global brain state. However, recent evidence indicates that sleep intensity, measured as electroencephalogram (EEG) slow-wave activity, is not uniformly distributed across cortical areas. Some brain regions appear to need more sleep (or more "intense" sleep) than others, and such local sleep regulation occurs in a use-dependent manner. When the brain is awake, neurons in the cerebral cortex fire irregularly and the EEG displays low-amplitude, high-frequency oscillations. After falling asleep, neurons start oscillating between ON periods, when they fire as during wake, and OFF periods, when they stop firing altogether, and the EEG displays high amplitude slow waves. However, after sleep deprivation, cortical neurons can go briefly "OFF line" as they do in sleep, accompanied by slower waves in the local EEG. Strikingly, neurons often go OFF line in one cortical area and not in another. During these periods of "local sleep", whose incidence increases with wake duration, rats appear awake, active, and display a wake EEG. Thus, in sleep-deprived rats, though both the EEG and behavior indicate wakefulness, local populations of neurons in the cortex may be falling asleep.
Host: Clint Sprott
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Wednesday, November 23rd, 2011

No events scheduled

Thursday, November 24th, 2011

Thanksgiving Break

Friday, November 25th, 2011

Thanksgiving Break

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