Fall 2007

August 31, 2007
"Conductive Barrier Josephson Junctions for 100 ghz+ Superconductive Circuit Applications" Speaker: Lei Yu, School of Materials, Arizona State University.
3:10 pm
Hayes Hall 109
Like transistors to CMOS technology, Josephson junctions are the fundamental devices of superconductive circuit technology. Despite the requirement of cryogenic cooling, rapid single flux quantum (RSFQ) logic based superconductive circuits promise high-speed, low power, and uncomplicated circuit design that can not be matched by any known semiconductor based circuits. RSFQ has strong potential for large-scale and high-performance applications operate at 100 GHz or beyond, such as microprocessors and communication systems. However, material and process related issues plagued the design of Josephson junctions that used in current industry. As a result, RSFQ technology is still far away from the speed and integration levels it promised to deliver. We predicted that junction with near metal-insulator transition material as barrier can have characteristics that are ideal for the next generation of RSFQ circuits. I will report on both experimental and theoretical investigations that aimed towards our goal of 1.) developing new junctions as drop-in replacements for tunnel junctions in the existing RSFQ circuit process. 2) understanding the fundamental physical principles regarding the transport properties of near metal-insulator transition barrier junctions, especially those related to high speed. Ideally, we intended to establish a set of principles governing the design of all conductive barrier Josephson junctions. Reception to follow in Hayes Hall Lobby.

September 7, 2007
"Sculpting the Universe" - Speaker: David H. Weinberg, Department of Astronomy, The Ohio State University
3:10 pm
Franklin Miller, Jr. Lecture Hall (Hayes Hall 109)
Over the last four years, Dr. Weinberg has been collaborating with artist Josiah McElheny on the design of cosmologically inspired sculptures, which represent the history of the expanding universe and the formation of structure within it. He will describe these sculptures and the astronomical concepts that underlie them, which include the nature of cosmic expansion, the transition from an opaque universe to a transparent universe, the formation and clustering of galaxies and quasars, the seeding of cosmic structure by primordial fluctuations in the early universe, and the possibility that our observable cosmos is only an "island" in a larger "multiverse."

September 14, 2007
"Fiber Bundle Models," by Dr. Prabasaj Paul, Department of Physics, Denison University
3:10 pm
Franklin Miller, Jr. Lecture Hall (Hayes Hall 109)
Fiber bundle models, introduced in 1926 to investigate the strength of cotton yarns, have since been used to study a wide range of systems, from earthquakes to traffic flow. These models are characterized by a few simple parameters, but often exhibit complex, interesting and realistic behavior. The talk will be an introduction to fiber bundle models and a look at some of their applications.

September 21, 2007
Disturbing Systems At Equilibrium: What Can We Learn From The Fluctuation-Dissipation Theorem? by Maxim Lavrentovich, '08
3:10 pm
Franklin Miller, Jr. Lecture Hall (Hayes Hall 109)
The fluctuation-dissipation theorem (FDT) is a cornerstone of modern statistical mechanics. First articulated by Callen and Welton in 1951, the FDT connects microscopic fluctuations in a system at equilibrium to that system's response to an external perturbation. This provides a fundamental connection between equilibrium and non-equilibrium behaviors of thermodynamic systems. The connection facilitates an understanding of many systems including plasmas, lasers, biological systems, and electrical circuits. This talk will highlight the general character of the FDT by presenting various expressions of the theorem. We will derive the FDT and apply it to a specific physical model. The talk will conclude with a proposal to study the FDT in the language of information theory. This new approach may shed light on the basic ideas behind the FDT and explain how information is stored and erased in systems driven out of equilibrium.

September 28, 2007
Actin' Pushy And Pulling Springs: Two Forms Of Biological Motion, by Dr. Arpita Upadhyaya, Department of Physics, Institute for Physical Science & Technology, University of Maryland
3:10 pm
Franklin Miller, Jr. Lecture Hall (Hayes Hall 109)
A fundamental attribute of living cells is their ability to move. Dr. Upadhyaya will talk about two forms of biological motion driven by different physical mechanisms. The polymerization of the protein, actin, appears to be the source of the propulsive force for eukaryotic cell motion. While the alphabet soup of proteins that initiate and control actin polymerization is being scrupulously characterized, it is not clear how this generates a force to push. Dr. Upadhyaya will describe experiments in which they have reconstructed motility using phospholipid vesicles as model cell membranes in order to probe the polymerization forces. Vorticella, one of the most powerful cellular machines, is a single celled organism with a cell body attached to a substrate by a slender stalk which contains a rod-like polymeric structure (i.e., spasmoneme). Vorticella motility is characterized by an extremely rapid contraction which is powered by the collapse of the spasmoneme. Using high-speed imaging experiments to study the dynamics of contraction, they show that the contraction process is power-limited.

October 12, 2007
"Optimization in Neutron Scattering," by David Lenkner '08
3:10 pm
Franklin Miller, Jr. Lecture Hall (Hayes Hall 109)
Abstract: In experimental physics, the tools used to arrive at a result are often just as interesting as the result itself. Especially when the length scale of interest is very small, the mere act of observation involves a wide array of physical principles, and demands a great deal of expertise and ingenuity. Add into the equation the ever-present constraints of time and expense, and we end up with a complex and fascinating challenge. Small Angle Neutron Scattering (SANS) is a unique approach to the problem, and has paved the way for a good deal of important condensed matter research. As a method of studying nanometer-scale structures, SANS utilizes both the particle and wave nature of neutrons to reveal the locations of different atoms in a sample. We will explore some of the principles and problems behind SANS, and analyze some of the solutions that are currently being developed at the Indiana University Low-Energy Neutron Source. *In Collaboration with the Indiana University Physics Program

October 19, 2007
"Contacts and Conductors: Converting Light to Energy and Energy to Light" - Speaker: Dr. Joseph J. Berry, National Renewable Energy Laboratory
3:10 pm
Franklin Miller, Jr. Lecture Hall (Hayes Hall 109)
Abstract: While numerous strategies/devices to transform photons into electricity and vice versa exist, increasing energy costs have accelerated efforts to improve the efficiency of this conversion process. In addition to overall efficiency of such devices the costs of materials and manufacturing are also important factors in the adoption of opto-electronic energy technologies. This talk will address these topics by providing an introduction to some of the ongoing research in the National Renewable Energy Laboratory's (NREL) National Center for Photovoltaics (NCPV). An overview of the motivation and research approach used in the manufacturing and advanced concepts group will also be presented. We will then focus on the research efforts to develop novel materials for use in photovoltaics and low cost high efficiency solid state lighting. Basic materials physics of traditional semiconductor light emitters and the challenges associated their with adoption will be presented as to a springboard to discussing novel organic devices. Results from organic device studies demonstrating the importance of the organic inorganic interface in developing inexpensive solar energy systems and low cost efficient lighting will be presented.

October 26, 2007
"Numerical Simulations of the Cahn-Hilliard Model of Phase Separation" - Speaker: Pushkar Dahal, '08
3:10 pm
Franklin Miller, Jr. Lecture Hall (Hayes Hall 109)
Abstract: When the enthalpy of the homogeneous state of two fluids is greater than the enthalpy of the separated state, a miscibility gap is said to exist. Under this condition, infinitesimal variations in the local composition of the mixture lower its free energy and lead to phase separation. Here we discuss the simulation results of the Cahn-Hilliard model to describe how the concentrations of the constituents diffuse through the system. One prediction is that characteristic domain size obeys the Lifshitz-Slyozov (LS) relation during the scaling regime. We discuss the methods for determining the scaling regime of the time evolution for various compositions of the mixtures. Extensive numerical simulations were carried out for a unit-less time step of 200,000. It was found that for some concentrations of the mixture, the scaling regime is not reached even at a very late time while for others the scaling regime is reached in an early time.

November 2, 2007
"Magnetic Resonance Force Microscopy -- Coarse Approach" --Speaker: Andrew Berger, '08
3:10 pm
Franklin Miller, Jr. Lecture Hall (Hayes Hall 109)
Abstract: Magnetic resonance force microscopy (MRFM) has been developed as a means to achieve higher sensitivity and greater resolution than was previously available through traditional induction-based magnetic resonance imaging. Through the use of an ultra-small mechanical cantilever, extremely small forces -- into the attonewton (10-18 N) range -- have been detected. Application of this technique is promising for both the 3D mapping of atomic-scale structures as well as quantum computing via the manipulation of spins. Because of the novelty of this technology, development of the experimental apparatus itself is largely a responsibility of the researcher. Some issues that must be dealt with include thermal contraction of materials, sources of noise, and measurement protocol. The design and implementation of the coarse approach mechanism, which is responsible for bringing the sample into proximity with the cantilever, will be discussed.

November 9, 2007
"Taking the Space Elevator from Science Fiction to Engineering," by Dr. Larry Bartoszek, Bartoszek Engineering
3:10 pm
Franklin Miller, Jr. Lecture Hall (Hayes Hall 109)
Dr. Bradley Edwards and Eric Westling have published what has to be the cheapest way to build a space elevator in their book "The Space Elevator--a revolutionary Earth-to-Space Transportation System". The only thing missing at the moment is a Carbon Nanotube fabric strong enough to satisfy the strength requirements of the elevator. There are many reasons why this fabric will become available within the next few years, and the initial cost estimate of the elevator puts it within the ability of a corporation (or individual) to build. Once the CNT fabric becomes available, there are many engineering, economic and regulatory hurdles to cross before the elevator becomes the cheapest way to transport cargo into space. This talk will cover the Edwards and Westling elevator design and construction scenario, and some conceptual design work by Bartoszek Engineering on the first construction climber.

November 30, 2007
Speaker: Joseph Konieczny, '08
3:10 pm
Franklin Miller, Jr. Lecture Hall (Hayes Hall 109)
Abstract: To Follow

November 30, 2007
"CCD Photometry at the Kenyon College," by Joey Konieczny '08
3:10 pm
Franklin Miller, Jr. Lecture Hall (RBH 109)
Abstract: When measuring astronomical objects there are certain systematic effects that need to be accounted for in order to obtain accurate scientific results. We will explore the causes and effects of vignetting from the optical assembly of telescopes, thermal noise produced by the measuring instrument, air mass extinction, and how to effectively correct for these by comparing different experimental methods. Then we will talk about applications and interpretations of data such as RGB imaging, and how to detect variable stars and transiting planets. We will conclude with results from the Kenyon College Miller Observatory summer science project from the summer of 2007.

December 7, 2007
"Supernovae Found in Gamma-Ray Bursts" -- Speaker: Professor Dean Richardson, Department of Physics, Denison University
3:10 pm
Franklin Miller, Jr., Lecture Hall (Hayes Hall 109)
Abstract: The connection between, at least some, gamma-ray bursts and supernovae was spectroscopically confirmed a few years ago. Due to observational difficulties, there have been very few gamma-ray bursts with a confirmed supernova association; although, it is thought to be common. A number of Gamma-Ray Burst afterglow light curves show a rebrightening after about 10-20 days. This rebrightening is likely due to an underlying supernova. Light curve data is much easier to obtain than spectra; especially for distant gamma-ray bursts. In analyzing these light curves Professor Richardson has extracted the supernova component and compared that resulting light curve to a supernova model. From this model Professor Richardson is able to get a good estimate of the supernova's peak brightness, the total kinetic energy in the explosion and the total mass ejected in the explosion.