Colloquium Schedule

Spring 2014


Manipulating Magnetic States in Nanorings: The Future of Data Storage?

Katherine Aidala, Mt. Holyoke College
Fri., Feb. 7, 2014, 12:30 PM

Magnetic random access memory (MRAM) would combine the benefits of the hard drive (non-volatile, cheap, high density of bits) with the benefits of RAM (fast, mechanically robust). One proposal for MRAM involves the vortex state of nanorings, a state in which the magnetic moments align circumferentially in the clockwise or counterclockwise direction. For a symmetric ring in a uniform field, these states are energetically degenerate and cannot be selected experimentally. A circular field allows us to study the switching behavior between these vortex states. We have developed an experimental technique to apply a local circular field by passing current through the tip of an atomic force microscope. I will discuss how the atomic force microscope works, our experimental results demonstrating switching between the vortex states, and our understanding of the evolution of these states based on our simulations. We predict novel states that arise from both energy minimization and topological constraints.

See Prof. Aidala's website for more information about her research.


Positronium: The Simplest Exotic Atom

Gregory Adkins, Franklin and Marshall College
Fri., Mar. 28, 2014, 12:30 PM

Positronium is the exotic atom composed of an electron bound to its own antiparticle, the positron. Positronium is like other atoms, such as hydrogen, in being bound by the Coulombic attraction between particles of unlike charge. It is simpler than hydrogen or other atoms because its constituents are, so far as we know, point-like particles with no internal structure. Positronium is accessible both to high-precision measurements (of energy levels, decay rates, etc.) and to precise calculations based on current theory, so that positronium provides an important test of bound-state methods in Quantum Electrodynamics and a possible window onto new physics.

In this talk I will describe the dominant features of positronium physics in terms of basic quantum mechanics and relativity and will then discuss both refinements in the theory and also the ongoing experimental tests and challenges.


Fall 2013


Applications of Diffuse Optics in Non-Invasive Clinical Measurements of Tissue Metabolism

David Busch, University of Pennsylvania
Fri., Sep. 13, 2013, 12:30 PM

Tissue oxygen delivery is intimately dependent on blood flow, concentration, and oxygen saturation. However, these important physiological parameters are currently difficult or impossible to measure non-invasively in critically ill patients. Diffuse optical techniques utilize near infra-red light to provide a window into tissue hemodynamics. These tools can be integrated into intensive care units and applied to fragile patients. Our current studies include serial measurements of hemodynamics in patients following pediatric stroke and corrective surgery for congenital heart defects. Ultimately, we seek to provide tools to permit physicians measure the effects of their interventions on cerebral oxygen perfusion.

See Dr. Busch's website for more information about his research.   


Order From Disorder: Identifying 'Structure' in Disordered Proteins

Elizabeth Rhoades, Yale University
Fri., Oct. 4, 2013, 12:30 PM

In contrast to globular proteins, intrinsically disordered proteins do not form stable, compact structures under physiological conditions.  Rather, often their functions are derived from their properties as extended, flexible polymers.  It has recently been recognized that intrinsically disordered proteins are involved in a range of functional roles in the cell, as well as being associated with a number of diverse diseases, including cancers, neurodegenerative disorders, and cardiac myopathies.  We use single molecule fluorescence approaches to characterize both the 'structures' and dynamics of disordered proteins implicated in the progression of Parkinson's and Alzheimer's diseases. Our goal is to understand how disease-associated modifications to these proteins alter their conformational and dynamic properties and to relate these changes to disease pathology.

See Prof. Rhoades' website for more information about her research.   


Why Does Nature Like the Square Root of Negative One?

William Wootters, Williams College
Fri., Nov. 8, 2013, 12:30 PM

Quantum mechanics is a probabilistic theory, but the way we compute probabilities in quantum mechanics is quite different from what one would expect from, say, rolling dice or tossing coins.  To get a quantum probability, we first compute a complex-valued probability amplitude and then square its magnitude.  I begin this talk by looking for a deeper explanation of the appearance of probability amplitudes, or "square roots of probability," in the physical world.  It turns out that one can find a potential explanation-it is based on a principle of optimal information transfer-but the argument works only if the square roots are real rather than complex.  I then explore a particular theoretical model in which the probability amplitudes are taken to be real and the usual complex phase factor is replaced by a binary quantum variable.  One finds that the model leads to a one-parameter generalization of standard quantum theory.    

See Prof. Wootters' website for more information about his research.


Water-Based Liquid Crystals: Lessons from the World of LCDs

Peter Collings, Swarthmore College
Fri., Nov. 15, 2013, 12:30 PM

The huge liquid crystal display (LCD) industry relies on oil-based liquid crystals to produce the impressive displays that we use every day.  As a result, the properties and behavior of oil-based liquid crystals are well understood.  Much less is known about water-based liquid crystals, yet they are being investigated due to novel applications in biology and medicine.  One can start to understand the properties and behavior of water-based liquid crystals by exploiting the same conditions used to fabricate liquid crystal displays, but use water-based liquid crystals instead.  This has led to new knowledge of how water-based liquid crystals interact with surfaces and how they respond to the addition of twist-inducing agents.

See Prof. Collings' website for more information about his research.

A Place Like Home?: Revealing the Atmospheres of Super-Earths Orbiting Distant Stars

Eliza Kempton, Grinnell College
Fri., Dec. 6, 2013, 12:30 PM

Astronomers currently know of close to 1,000 planets orbiting distant stars beyond the confines of our solar system. Of these "extrasolar" planets, most are large gas-rich planets, similar to Jupiter or Saturn. However, more recently, due to improvements in discovery techniques and instrumentation, astronomers have started to discover much smaller extrasolar planets, which are only slightly larger (or more massive) than the Earth. This new class of planets, which have masses of 1-10 times that of the Earth, have come to be known as super-Earths. Super-Earths are particularly interesting because planets in this mass range are not present in our solar system, and they therefore represent a fundamentally new class of planets for astronomers to study. Recently, the first observations of a super-Earth atmosphere were obtained. They reveal a unique planet that does not seem to resemble anything found in our own solar system. In this talk I will begin by presenting an overview of extrasolar planet research, focusing in on what we know about super-Earths and their atmospheres. I will finish by presenting the first observational constraints on super-Earth atmospheric composition and structure, and I will explain some of the challenges to interpreting the available data.

See Prof. Kempton's website for more information about her research.