Spring 2009

January 16, 2009
"Crystals, Polymers, Lithography, Oh My! -- Towards Integrating Optical Systems onto a Chip" by Dr. Martha (Marty) Baylor
3:10 pm
Franklin Miller, Jr. Lecture Hall (RBH 109)
Dr. Martha (Marty) Baylor is a candidate for a tenure-track position in the Department of Physics. Abstract: The cocktail party problem describes the human ability to separate one voice from a mixture of voices. Solving the cocktail party problem is very important to signal processing applications such a ... I will present data from an optical system capable of separating signal with bandwidths orders of greater than what has been achieved in algorithmic approaches. Unfortunately, this optical processor is physically too big to be used in real-world applications. I will discuss how photolithography techniques in photopolymers could one day enable the miniaturization of optical systems to the size of a computer chip. Warning: People in the front row may get illuminated.

January 23, 2009
"Winds of Change: Galactic Outflows and the Structure of our Milky Way Galaxy" by Dr. John Everett
3:10 pm
Franklin Miller, Jr. Lecture Hall (RBH 109)

Dr. John Everett is a candidate for a tenure-track position in Physics.
Abstract: In the past decade, astronomers have made great strides in understanding the structure and evolution of galaxies over cosmic time. I will start by outlining our understanding of galactic structure, and by introducing some of the major processes at work in shaping our Milky Way Galaxy. Along the way, I will show how our apparently cool, calm, and collected Milky Way still presents us with some striking puzzles. One of these mysteries is a large swath of T = 3x106 K ionized gas, spanning an area of the sky thousands of times larger than the full moon, surrounding the center of our Galaxy. Working on a model that combines many of the Milky Way's components, we have found that our Galaxy can launch an outflow of ionized gas, covering a large fraction of the Galaxy, and that this model does indeed match the observed X-ray emission. I will close by talking about further tests, the important ramifications of this outflow for the Milky Way (which now seems neither very cool, calm, nor collected!), and applications to other galaxies.

January 26, 2009
"Lasers, Discharges and the Fingerprints of Molecules" by Dr. Robert Ekey
4:10 pm
Franklin Miller, Jr. Lecture Hall (RBH 109)

Dr. Robert Ekey is a candidate for a tenure-track position in Physics.
Abstract: Each molecule or atom is uniquely defined by its fingerprint, i.e. spectroscopic, dynamic and chemical properties. Understanding these properties allows us to identify the chemical makeup of many things, from a galaxy far, far away to the aurora of the Northern Lights. We use lasers to excite molecular hydrogen to highly exotic states whose protons are stretched to almost seven times their normal separation. These rarely observed states are stable, even though the total energy of the molecule is greater than the energy needed to expel an electron from the molecule. We also use a high voltage discharge source to excite gaseous molecular nitrogen into states that are not accessible in the laboratory using lasers. Following the discharge pulse, light is emitted from the gas, which is similar to the afterglow seen in the Northern Lights. By looking at the spectral makeup of the light, we can determine the effect of the discharge on the populations of the observed states. Warning: People in the front row may get illuminated.

January 30, 2009
"Gravitational Waves: A New View of the Universe" by Dr. John T. Giblin, Jr.
3:10 pm
Franklin Miller, Jr. Lecture Hall (RBH 109)

Dr. John T. Giblin, Jr. (Tom) is a candidate for a tenure-track position in Physics.
Abstract: Since the first Astronomers viewed the night sky, science has relied on the observation of electromagnetic radiation, light, to learn about the Universe outside our solar system. Such observations led to the discovery of the expansion of the Universe, the relative abundances of matter, radiation, and dark energy in the current Universe as well as a wealth of information pertaining to the physics of stars, galaxies, clusters, etc. Just as light is associated with the electromagnetic force, the gravitational radiation is believed to be associated with gravity. In this talk, I will introduce gravitational radiation, and discuss how it is created and how it propagates. I will briefly outline scenarios in the early universe that may have created these waves and describe precision calculations of the corresponding gravitational wave signatures.

February 6, 2009
"2D Melting is Different" by Dr. Terry Sheridan, Department of Physics, Ohio Northern University
3:10 pm
Franklin Miller, Jr. Lecture Hall (RBH 109)

Abstract: When a three-dimensional system like a snowman melts, the change in entropy is discontinuous. This is called a "first-order" phase transition. In a "second-order" or "continuous" transition, the change in entropy is continuous. Melting in two-dimensional systems is predicted to occur as two distinct continuous phase transitions. In the first transition, the system loses bond-orientational order, leading to a hexatic phase. In the second transition, the system loses translational order to become a liquid.
The melting transition in a two-dimensional dusty plasma has recently been studied using the DONUT (Dusty ONU experimenT) experiment. A two-dimensional crystal consisting of about 4000 microscopic dust particles was heated by jiggling the particles up and down. The shaking motion couples to an in-plane acoustic instability, thereby raising the dusty plasma's effective temperature. The "thermodynamic" phase of the system was characterized for increasing temperature using the Lindemann ratio, defect density, bond-orientational correlation function, and pair correlation function. A melting transition showing evidence for a hexatic phase was observed.

February 20, 2009
CANCELLED -- "Electron Interferometers or Stock Market Predictors: The Curious Story of Negative Ions" by Dr. N. Daniel Gibson, Professor of Physics & Astronomy, Denison University
3:10 pm
Franklin Miller, Jr. Lecture Hall (RBH 109)
DUE TO UNFORESEEN CIRCUMSTANCES, THE PHYSICS COLLOQUIUM IS CANCELLED FOR FRIDAY, FEBRUARY 20.
Abstract: Negative ions are found in stellar atmospheres, industrial plasmas and lighting discharges to give just a few examples. In spite of their frequently low densities, negative ions often play key roles as either strategic information probes or as the prevailing catalysts in complex systems and reactions. As such, these ions are also of great interest to those investigating effects on biological systems including the human body. Due to the dominant nature of the electron correlations in negative ions, these inherently many-body systems present tremendous challenges for theoretical and calculational atomic physicists. We have used negative ions as a source of ultralow energy electrons to perform a quantum interference experiment in an electric field. Photodetachment from negative S ions has been studied in external electric fields up to 400 V/cm. We compare the cross sections for the field free case of photodetachment and the case of photodetachment in an electric field. A number of quantum mechanical effects including below threshold tunneling and cross section oscillations are predicted and observed. These results have implications for high precision electron affinity measurements, for understanding resonance effects in negative ion photodetachment experiments and possibly for predicting the Dow Jones Industrial Average.

March 20, 2009
"Dose Distributions in Photon and Proton Radiotherapy " Senior Exercise Talk by Austin Faught, '09
3:10 pm
Franklin Miller, Jr. Lecture Hall (RBH 109)

Abstract: One of the most commonly prescribed treatments for cancerous tumors is ionizing radiation. With the help of physicists, physicians look to minimize exposure of healthy tissue while delivering the appropriate dose to the planned treatment volume. Advances in the use of Gamma rays, X-rays, and heavy ions such as protons have allowed for more complex treatment plans that yield better dose distributions. This talk will examine how radiation interacts with matter and how dose is defined. The physics of both photon and proton radiotherapy will be discussed before concluding with a brief modality comparison.

March 27, 2009
"Why Microscopic Organisms Can't Move Like Scallops " Senior Exercise Talk by Dustin Schneider, '09
3:10 pm
Franklin Miller, Jr. Lecture Hall (RBH 109)
Abstract: The world in which we live in is not the same as the world in which microscopic organisms live in. Motion in these two worlds are governed by two slightly different forces. This talk begins by exploring how motion in any fluid medium works. The motion of a microscopic organism will be analyzed in depth for the special case of when the Reynolds Number is very small. This analysis will account for why microscopic organisms cannot move like scallops and how these organisms get around this restriction. Reception to follow.

April 3, 2009
"Physics and Baseball" by Dr. Alan Nathan, Department of Physics, University of Illinois at Urbana-Champaign
3:10 pm
Franklin Miller, Jr. Lecture Hall (RBH 109)
Abstract: I have been a physicist for all my professional life. I have been a baseball fan even longer. And in recent years, I have figured out that I can do both physics and baseball at the same time. It is truly like having your cake and eating it too. In this talk, I will tell some of the ways that a physicist analyzes the game of baseball. In the course of doing so, I will address some interesting and practical questions from a physics perspective, such as: How does a baseball bat work? Why do aluminum bats outperform wood bats? Does corking the bat help? How much did that curve ball break? Can a curveball be hit farther than a fastball? Why are towering popups difficult to catch? And the very topical, can steroid usage increase homerun production? My goal is that all will enjoy this talk, whether your interest is physics, baseball, or the intersection between them.

April 10, 2009
"Kenyon 20000 Leagues Under the Sea" by Lieutenant AJ Franz, USN, Kenyon '04
3:10 pm
Franklin Miller, Jr. Lecture Hall (RBH 109)
Lieutenant Franz is a Special Operations Forces (SOF) and Tomahawk Strike Officer, USS Ohio, SSGN-726 (Blue) Abstract: The US submarine force is the most modern and mighty in the world, able to traverse the oceans and seas of the world untethered by the supply lines that hamper conventional warships. The submarine force takes great pride in safely operating nuclear power plants in the hostile undersea environment without outside regulation and is able to do so because of highly trained operators and strict procedural compliance. This presentation introduces all aspects of the submarine force's mission, focusing on the new SSGN platform (USS OHIO, SSGN-726), and introduces the basics of nuclear power to produce propulsion and electricity.

April 17, 2009
"Growing a Universe in your Aquarium: A Fish-Eye View" Senior Exercise Talk by Thomas Linz, '09
3:10 pm
Franklin Miller, Jr. Lecture Hall (RBH 109)
Abstract: While current observations reveal our current universe to be a homogenous mix of matter and dark energy, standard cosmological models suggest that there were periods during which our universe underwent phase transitions, changing the dominant form of energy. During these transitions, the universe would not be homogenous, leading to what is known as the "Swiss-Cheese Universe." This inhomogeneous cosmology is still an open research question today. My research involves the first step towards building this inhomogeneous cosmology, considering the dynamics of a bubble universe in an otherwise empty spacetime. In this talk, I describe my research and point out some of its properties which had been previously ignored. Reception to follow.

April 24, 2009
"Sync City: Exploring Collective Behavior in Hodgkin-Huxley Neurons" Senior Honors Talk by Gilad Barlev, '09
3:10 pm
Franklin Miller, Jr. Lecture Hall (RBH 109)
Abstract: The neuron is believed to be the fundamental unit of brain function. Relatively simple cells, they act in an essentially binary fashion, firing discretely at given intervals, based on the stimuli they are presented. Yet out of the interactions of billions upon billions of these cells arise all brain function, from performing autonomous regulation to performing Puccini. But alongside these amazing feats of emergent behavior, the neuronal society has a seedy underworld: when neurons decide to get together and act in synchrony, mayhem ensues in the form of disorders such as epilepsy. In this talk, we spend a day (or, rather, a second) in the life of a single simulated neuron, following it as it moves through its dynamical regimes, from quiescent to single-spiking to oscillatory to over-spiking, and then move on to study the collective behavior of neural networks, specifically synchrony, in hopes of answering the question: how can we best keep our neurons out of trouble? Reception to follow.

May 1, 2009
"Physics and Art" by Thomas Greenslade, Jr., Professor Emeritus of Physics
3:10 pm
Franklin Miller, Jr. Lecture Hall (RBH 109)
Abstract: Do you wonder how the Irish plan to revive their economy? How do you build a cathedral without those annoying buttresses and flying buttresses? What is the best place to eavesdrop on your friends? How does a spider add color to its web? How do you put a spectre into a play? These and many other questions will be answered in the latest installment of the Greenslade end-of-the-year lectures. For next year, look forward to seeing how a thread of water can hold you up and how music can be transmitted on a beam of light.