Colloquia are held Monday afternoons in 265 Phillips Hall at 4:00pm. Tea and coffee are served at the speaker’s reception in the Chapman meeting area, 3:30pm. The student Questions and Answers will be held in Phillips 277 after the colloquium from 5:15-6:00pm.

Aug 28
“Electronic Stopping in Condensed Matter: Ab Initio Understanding of Electronic Excitation Dynamics under Proton Irradiation”

Yosuke Kanai, University of North Carolina

Transfer of the kinetic energy from a highly-energetic ion to electrons in condensed matter is described by the so-called electronic stopping. The projectile ions bear highly localized electric field that is quite heterogeneous at the atomistic scale, and massive electronic excitations are produced in the electronic stopping process. Understanding this phenomenon= in condensed matter systems under proton and other ion irradiation has implications in various modern technologies, ranging from nuclear fission/fusion reactors, to semiconductor devices for aerospace missions, to cancer therapy based on proton beam radiation. Electronic stopping has been long studied within linear response theory framework (e.g. Bethe theory), but recent advances in high-performance computers allow us to study the phenomena beyond such simplified treatment through the use of numerical simulations. In this talk, I will discuss how non-equilibrium dynamics simulations based on our recently-developed large-scale real-time time-dependent density functional theory enable us to study this electronic excitation process, using an important case of liquid water under proton irradiation as an example. In addition to determining the energy transfer rate (i.e. electronic stopping power), our work reveals several key features in the excitation dynamics at the mesoscopic and molecular levels for deciphering water radiolysis mechanism under proton irradiation.

Sept 11
“The Cosmological Quest for Evidence of the Birth of the Universe out of the Multiverse Landscape”

Grant Mathews, Notre Dame University

One expects that the universe was born out of a complicated string-theory landscape near the Planck epoch. Although the energy scale of the birth of the universe is not accessible in terrestrial experiments, the energy scale of such trans-Plankian physics might have been obtained during the early instants of accelerated chaotic inflation. This talk will summarize the quest for cosmological evidence of this birth of space-time out of the string-theory landscape. We will explore the possibility that a set of superstring excitations may have made itself known via their coupling to the field of inflation. This may have left an imprint of “dips” in the power spectrum of temperature fluctuations in the cosmic microwave background. The identification of this as due to a superstring is possible because there may be evidence for different oscillator states of the same superstring that appear on different scales on the sky. Similarly, as the universe emerged it is possible that the interaction with other nascent universes led to the formation of cold spots and/or large-scale curvature in the cosmic microwave background. Such curvature might appear as a cosmic “dark flow” with respect to the frame of the big bang. This talk will summarize current constraints on the existence of such dark flow and prospects for its identification in the future. The existence of extra dimensions during inflation can also impact impact the cosmic expansion after the inflation epoch through the projection of curvature and/or mass-energy from a higher dimension. This can be constrained by the ratio of tensor to scalar fluctuations in the cosmic microwave background and via the effects of modified expansion on the light elements produced during big bang nucleosynthesis.

Sept 18
“Title to be Announced”

Thomas Schaefer, North Carolina State University

Abstract to be announced.

Sept 25
“The Maps Inside Your Head”

Vijay Balasubramanian, University of Pennsylvania

Abstract: How do our brains make sense of a complex and unpredictable world? In this talk, I will discuss a physicist’s approach to the neural topography of information processing in the brain. First I will review the brain’s architecture, and how neural circuits map out the sensory and cognitive worlds. Then I will describe how highly complex sensory and cognitive tasks are carried out by the cooperative action of many specialized neurons and circuits, each of which has a simple function. I will illustrate my remarks with one sensory example and one cognitive example. For the sensory example, I will consider the sense of smell (“olfaction”), whereby humans and other animals distinguish vast arrays of odor mixtures using very limited neural resources. For the cognitive example, I will consider the “sense of place”, that is, how animals mentally represent their physical location. Both examples demonstrate that brains have evolved neural circuits that exploit sophisticated principles of mathematics – principles that scientists have only recently discovered.

Oct 2
“Title to be Announced”

Rachel Kuzio de Naray, Georgia State University

Abstract to be announced.

Oct 9
“Title to be Announced”

David Nelson, Harvard University

Abstract to be announced.

Oct 16
“Title to be Announced”

Matt Rosen, Athinoula A. Martinos Center for Biomedical Imaging

Abstract to be announced.

Oct 23
“Title to be Announced”

Paulo Bedaque, University of Maryland

Abstract to be announced.

Oct 30
“Title to be Announced”

Raphael Buosso, University of California, Berkeley

Abstract to be announced.

Nov 6
“Title to be Announced”

Lindley Winslow, Massachusetts Institute of Technology

Abstract to be announced.

Nov 13
“Earth’s Field NMR to Detect Spilled Oil Trapped under Arctic Ice”

Mark Conradi, ABQMR, Albuquerque, New Mexico

Oil production from wells in the arctic sea must face the possibility of leakage.  Spilled oil would try to rise to the surface, but would be blocked by the 1-2 meters of ice coverage.  ExxonMobil wants a detection method in-place before drilling or production begins.

Nuclear magnetic resonance can detect the abundant hydrogen nuclear spins of oil (and, unfortunately, water).  The device uses a detection coil large enough to reach through the ice, 6 meters in diameter.  The apparatus is flown by helicopter and then set onto the ice for detection.

Three physics issues arose in implementing the NMR solution.  (1) Pre-polarization is used to align the nuclear spins to a greater extent than the earth’s field can. This field must be intense and the stored energy must be removed rapidly, leading to innovative switching circuitry.  (2) The resonant pulses are frequency swept and must be adiabatic.  Pulses were designed that avoid interference from the counter-rotating field component.  (3) The signal of the oil must be distinguished from the much greater signal from sea water; this relies on the differences in the oil relaxation times compared to water.

 

Nov 20
“Title to be Announced”

Speaker to be Announced

Abstract to be announced.

Nov 27
“Title to be Announced”

Doug Edmonds, Penn State Hazleton

Abstract to be announced.

Dec 3
“Title to be Announced”

Hailin Wang, Oregon State University

Abstract to be announced.