Physics & Astronomy Colloquia, Vanderbilt University, 2006-2007
Much Ado About Nothing
Lawrence Krauss, Case Western Reserve University
Thursday, August 31, 2006 - 4:00-5:00 pm in Stevenson Center 4327 (Reception at 3:30 pm in SC 6333)
The realization that empty space probably contains most of the energy in our observable universe has dramatically changed not only our current picture of cosmology, but also our thinking about a wide variety of topics ranging from the future of the computation in the universe, to the nature of fundamental physical laws and the anthropic principle. I will describe the growing evidence, from a wide variety of astronomical and cosmological data, that the energy of empty space is constant, and then discuss some of the implications (both good and bad) of this possibility for physics.
Breaking Away, Selective Withdrawal and Islets in the Stream: The Role of Singularities in Fluid Flow
Sid Nagel, University of Chicago
Thursday, September 7, 2006 - 4:00-5:00 pm in Stevenson Center 4327 (Reception at 3:30 pm in SC 6333)
The exhilarating spray from waves crashing into the shore, the distressing sound of a faucet leaking in the night, and the indispensable role of bubbles dissolving gas into the oceans are but a few examples of the ubiquitous presence and profound importance of drop formation and splashing in our lives. During fission, a fluid forms a neck that becomes vanishingly thin at the point of breakup. This topological transition is accompanied by a dynamic singularity in which physical properties such as pressure diverge. Singularities of this sort often organize the overall dynamical evolution of nonlinear systems.
I will first discuss the role of singularities in the breakup of droplets. I will then present a second experiment, selective withdrawal, in which we study the steady-state shape of a liquid as it is withdrawn by a nozzle through a surrounding fluid. Here, a change in topology may again be accompanied by a singularity. Applications of this geometry that rely on singular dynamical behavior, are relevant for the coating of biological particles that may be of particular use in medical transplantation technologies.
Stellar Winds and the Angular Momentum Problem
Sean Matt, University of Virginia
Thursday, September 21, 2006 - 4:00-5:00 pm in Stevenson Center 4327 (Reception at 3:30 pm in SC 6333)
Due to the Sun's proximity, the magnetized solar wind keeps the Earth within its clutches, occasionally influencing our lives. The Sun's magnetic field is generated by rotation, and the magnetic field spins-down the Sun, ungratefully biting the hand that feeds it. I will demonstrate, very generally, how magnetic fields influence winds, and how they transport angular momentum. The current spin rate of the Sun and other stars cannot be understood without a comprehensive theory of their winds during their past. This necessarily takes us back to the early stages of star formation, when the stars are thought to be too young for winds to be important. Here, the range of spin rates observed has not been satisfactorily explained. I will point out some major problems with the most common model and argue instead that high-powered stellar winds provide the most likely solution.
The Midlife Crisis of the Cosmos
Amy Barger, University of Wisconsin
Thursday, September 28, 2006 - 4:00-5:00 pm in Stevenson Center 4327 (Reception at 3:30 pm in SC 6333)
With the advent of new space observatories and new instruments on ground-based telescopes, astronomers have now mapped much of the star formation and the super-massive black hole accretion that produces the light of the universe. The emerging consensus is that the early universe was dominated by a small number of giant galaxies containing colossal black holes and prodigious bursts of star formation, while the more recent universe is surprisingly active in a more dispersed mode---the creation of stars and the accretion of material into black holes is being carried out in a large number of medium-size and small galaxies. I will discuss the observations at many different wavelengths that have led astronomers to accept that there has been a vast downsizing that is redistributing cosmic activity from the large to the small.
Seeing Dark Energy with SNAP
Larry Gladney, University of Pennsylvania
Thursday, October 5, 2006 - 4:00-5:00 pm in Stevenson Center 4327 (Reception at 3:30 pm in SC 6333)
Our current cosmological model is compelling and simple, but puzzling in that two-thirds of the universe seems to be composed of a new form of energy, termed dark energy, which reveals itself only because it causes accelerated expansion of the universe. Several promising methods exist for exploring the source of this acceleration, and thereby determining fundamental aspects of dark energy and dark matter. Due to the central importance of understanding dark energy for both cosmology and particle physics, defining the optimal mission for examining its nature may be among the most important astro/particle physics tasks of the next decade. In this talk I will introduce the subject of dark energy from a particle physicist's perspective, explain why it is important as an ``energy frontier'' topic, then present a concise summary of the ways we might study it.
The role of ion channel clustering for calcium signaling
Peter Jung, Ohio University
Thursday, October 12, 2006 - 4:00-5:00 pm in Stevenson Center 4327 (Reception at 3:30 pm in SC 6333)
Calcium signaling is one of the most important and universal intracellular signaling mechanisms. Calcium signals regulate the contraction of the heart muscle, the production of digestive enzymes in the liver, synaptic transmission, and start the developmental process of eggs after fertilization - to name only a few. The specificity of the signal is determined by the spatial and temporal shape of the calcium transients. To signal de-arrest of the cell cycle of egg cells, for example, a sustained calcium transient for minutes is required presumably to protect the egg from "stochastic" onset of development. An important but not well understood problem is the relation between calcium signal specificity and the spatial distribution of calcium signaling effectors. Since it is experimentally impossible to move signaling effectors to generate an ensemble of desired distributions, computational modeling and quantitative analsysis offers an alternate route. I will review the basic elements of calcium signaling and the modeling of them. I will then proceed to show how clustering of the release channels can have a dramatic impact on the cellular calcium signal. If time permits I will report on a study that explores how the signaling specificity of the fertilization signal is reached during maturation of the egg cell.
Hydrodynamics and soft physics: from complex fluids to living cells
M. Cristina Marchetti, Syracuse University
Thursday, October 19, 2006 - 4:00-5:00 pm in Stevenson Center 4327 (Reception at 3:30 pm in SC 6333)
Historically the term hydrodynamics was synonymous with fluid mechanics and referred to the study of the dynamics of fluids in motion under specified boundary conditions. Today hydrodynamics denotes the description of the collective large-scale dynamics of a wide class of systems, from magnets to crystalline solids, in terms of a small number of conserved and broken symmetry variables. After introducing some of the general ideas behind modern hydrodynamics, I will discuss its application to soft condensed matter and biological systems. I will introduce a new class of soft active complex matter to which energy is continuously supplied by internal and external sources. As an important example of active matter I will describe the structure and mechanical properties of the cell cytoskeleton. This is a complex network of long biopolymers crosslinked by motor proteins that act like nanomachines, supplying energy to the filament network and controlling its structure and function.
Dark Energy, Or Worse?
Sean Carroll, California Institute of Technology
Thursday, October 26, 2006 - 4:00-5:00 pm in Stevenson Center 4327 (Reception at 3:30 pm in SC 6333)
Our universe is accelerating and we don't know why. Together, ordinary matter and ordinary gravity are unable to account for this phenomenon. The simplest explanation invokes "dark energy," a smooth and persistent component of the universe's energy budget, which could be a cosmological constant or a slowly-varying field. Alternatively, Einstein's theory of general relativity could be breaking down on cosmological scales. I will discuss the basic evidence for the accelerating universe, some of the theoretical proposals that have been put forward to account for it, and future observational tests that will help us distinguish between the possibilities.
Hidden Noncommutative Geometric Structure of Space-Time
Ali Chamseddine, American University of Beirut
Thursday, November 2, 2006 - 4:00-5:00 pm in Stevenson Center 4327 (Reception at 3:30 pm in SC 6333)
Hosted jointly with the Department of Mathematics
The geometry of space-time is reconstructed from the low-energy spectrum defined by the quarks and leptons. I show that there is a hidden noncommutative structure and that the dynamics of the unified geometrical theory is governed by the "Spectral Action Principle".
When Obsessions Collide: Golf and Physics - Wendell G. Holladay Lecture
Robert Grober, Frederick Phineas Rose Professor of Applied Physics and Professor of Physics, Yale University
Thursday, November 9, 2006 - 4:00-5:00 pm in Stevenson Center 4327 (Reception at 3:30 pm in SC 6333)
The revolution in low power microelectronics has enabled the development of electronically enabled golf clubs. These intelligent sensor systems allow for quantitative studies of the golf swing with unprecedented detail. This talk summarizes some of the interesting physics and biomechanics that have been learned about the golf swing through the use of this technology.
Bio: Prof. Grober's scientific expertise is in materials physics, high spatial resolution optical imaging and spectroscopy, and general scientific instrumentation. Prof. Grober earned his undergraduate degree from Vanderbilt University, received M.S. and Ph.D. degrees from the University of Maryland College Park, and was a postdoc at AT&T Bell Labs in Murray Hill, NJ. Prof. Grober joined the Yale faculty in 1994. He serves the federal government as a scientific consultant on issues of National Security and National Defense and is the founder of Sonic Golf LLC., a company specializing in electronically enabled, intelligent golf clubs.
Minimal Energy Problems and Best-Packing
Ed Saff and Doug Hardin, Vanderbilt University
Thursday, November 16, 2006 - 4:00-5:00 pm in Stevenson Center 4327 (Reception at 3:30 pm in SC 6333)
If a large number of point charges (of like charge) are constrained to a bounded surface in 3-dimensional space and repel each other according to an inverse distance potential law (1/r)^s, where r is the distance between particles (s=1 corresponds to Coulomb potential), we investigate which potential laws (which values of s) ensure that equilibrium configurations are uniformly distributed over the surface.
Science and Science Fiction
Robert Scherrer, Vanderbilt University
Thursday, November 30, 2006 - 4:00-5:00 pm in Stevenson Center 4327 (Reception at 3:30 pm in SC 6333)
I will explore the similarities and differences between the process of writing science fiction and the process of “producing” science, specifically theoretical physics. What are the ground rules for introducing unproven new ideas in science fiction, and how do they differ from the corresponding rules in physics? How predictive is science fiction? (For that matter, how predictive is theoretical physics?) I will also contrast the way in which information is presented in science fiction, as opposed to its presentation in scientific papers, and I will examine the relative importance of ideas (as opposed to the importance of the way in which these ideas are presented). Finally, I will discuss whether a background as a research scientist provides any advantage in writing science fiction.
Women in Science: Why so Few?
Meg Urry, Yale University
Thursday, December 7, 2006 - 4:00-5:00 pm in Stevenson Center 4327 (Reception at 3:30 pm in SC 6333)
Recent years have seen much discussion about why there are so few women in science, particularly in the academy. Despite mostly steady increases in the number of women in science, the attrition of women at every level of advancement remanins higher than that of men. Some have suggested this is because women lack the intrinsic aptitude of men for science and technology, but abundant research by sociologists and psychologists indicates cultural and societal factors are the dominant reason. These studies offer persuasive evidence that the playing field is not yet level. The just-released report from the National Academy of Sciences, "Beyond Bias and Barriers: Fulfilling the Potential of Women in Academic Science and Engineering," summarizes the statistics and the research, and offers recommendations for change.
Web Search: How does it Work?
Jan Pedersen, Yahoo! Chief Scientist, Search
Joint Colloquium with ACCRE (Advanced Computing Center for Research & Education) and with the Department of Electrical Engineering & Computer Science
Thursday, January 11, 2007 - 4:00-5:00 pm in Stevenson Center 4327 (Reception at 3:30 pm in SC 6333)
Web Search is a modern marvel. Daily, millions of people search billions of documents in milliseconds through a deceptively simple user interface that delivers the world's knowledge. Yet most consumers have only the vaguest notion as to how it all works. I will survey the key concepts in web search and provide a quick introduction into search algorithmics, search architecture and evaluation. In addition, I will touch briefly on what we can expect from this marvel in the next few years.
Continuous Quantum Measurement of Solid-state Qubits
Alexander Korotkov, University of California - Riverside
Thursday, January 18, 2007 - 4:00-5:00 pm in Stevenson Center 4327 (Reception at 3:30 pm in SC 6333)
The starting point of the talk is a simple question: what happens to a solid-state qubit in the process of its continuous measurement by a detector? (Particular realization is a “charge” qubit measured by a quantum point contact or a single-electron transistor.) While for ensemble of qubits the measurement simply leads to decoherence, the evolution of a single qubit is significantly different: it depends on the noisy detector output and may be fully coherent, though non-unitary. The theory describing such evolution has been developed relatively recently and provides a number of experimentally testable predictions. As an example, we will discuss how to maintain nondecaying Rabi oscillations in a qubit by using a quantum feedback loop. Other experimental proposals include qubit entanglement by measurement, quantum nondemolition squeezing of a nanoresonator, and undoing of a weak quantum measurement of a qubit. The first experiment verifying the coherent non-unitary evolution of a superconducting qubit due to continuous measurement has been recently realized.
Bringing Black Holes Together: An N-body Mechanic's Collision Report
Kelly Holley-Bockelmann, Penn State University
Thursday, January 25, 2007 - 4:00-5:00 pm in Stevenson Center 4327 (Reception at 3:30 pm in SC 6333)
Astronomers now know that supermassive black holes are a natural part of nearly every galaxy, but how these black holes form, grow, and interact within the galactic center is still a mystery. I will discuss how we can use N-body simulations to track the interplay between galaxies and supermassive black holes. We have discovered that the shape of the galaxy influences the black hole, but the effect is not entirely one-sided. Supermassive black holes leave an imprint on the galaxy structure as well, and surprisingly, can even change the structure and kinematics of the intracluster medium where galaxies live. There is more work to be done to uncover how supermassive black holes and galaxies co-exist, and I will talk about what important questions remain.
Neutron Stars in Globular Clusters
Natalia Ivanova, Canadian Institute for Theoretical Astrophysics
Tuesday, January 30, 2007 - 4:00-5:00 pm in Stevenson Center 4327 (Reception at 3:30 pm in SC 6333)
In dense stellar systems, dynamical interactions between objects lead to the frequent formation of exotic stellar objects, unusual binaries and systems of higher multiplicity. This is particularly important for the question of formation of X-ray binaries. As only a very small fraction of the formed neutron stars is retained by globular clusters, this study inevitably becomes a million-body problem that demands the use of special numerical tools.
I will discuss how neutron stars are produced and retained in globular clusters, outlining the most important dynamical channels and evolutionary events that affect the population of mass-transferring binaries with neutron stars and result in the formation of recycled pulsars. Other questions to be discussed are whether we can put constraints on the stellar evolution by comparing the observed millisecond pulsar population and theoretical results, as well as the nature of statistically significant overproduction of low-mass X-ray binaries in the metal-rich globular clusters.
Cosmological Probes of Dark Energy
Dragan Huterer, University of Chicago
Thursday, February 1, 2007 - 4:00-5:00 pm in Stevenson Center 4327 (Reception at 3:30 pm in SC 6333)
One of the great mysteries of modern cosmology is the origin and nature of dark energy - a smooth component that contributes about 70% of the total energy density in the universe and causes its accelerated expansion. Although discovered less than a decade ago, dark energy domination has recently been confirmed via several independent cosmological probes; nevertheless, there are no good theoretical leads as to its physical provenance. In this talk I examine critically various approaches to measure the macroscopic properties of dark energy, and describe accurate yet general methods to model the expansion history of the universe in the presence of dark energy. I discuss the importance of controlling the systematic errors in upcoming surveys, and show examples from recent work applied to weak gravitational lensing. Finally, I talk about the SNAP space telescope and its prospects to help us understand the nature of dark energy.
Chiral Condensate, Parity Violation and Extra Dimensions at Femto- and Nano-Scales
Dmitry Kharzeev, Brookhaven National Lab
Thursday, February 8, 2007 - 4:00-5:00 pm in Stevenson Center 4327 (Reception at 3:30 pm in SC 6333)
Chiral symmetry - the symmetry between left and right - is one of the most fundamental concepts of Nature. At femto-meter scales, it manifests itself as an approximate symmetry of the modern theory of strong interactions - Quantum Chromo-Dynamics, where the fundamental constituents of protons and neutrons, quarks, are almost massless. Nevertheless, this symmetry is broken in the physical world spontaneously due to the formation of chiral
condensate which is thus responsible for the large masses of baryons as observed in Nature. The chiral condensate melts under extreme conditions of high temperature and density which are achieved in the current experiments at Relativistic Heavy Ion Collider at BNL; these studies will soon be extended at the Large Hadron Collider at CERN. Under such extreme conditions, encountered previously in the Big Bang, the vacuum changes its properties and may contain domains with broken parity, with interesting impications for heavy ion collisions and for the cosmology of the Early Universe.
At nano-scales, chiral symmetry governs the dynamics of quasi-particles in fascinating new materials, such as graphene - a single atom layer of carbon atoms arranged in a honeycomb lattice. I will discuss the formation of chiral (excitonic) condensate in graphene in the external magnetic field and other implications of chiral symmetry in this material, which may have important practical applications in nano-electronics. The spin density waves propagating in the chiral condensate in graphene allow an interesting mathematical interpretation in terms of a dynamics of 2-dimensional membrane in a space-time with extra spatial dimensions.
From Galaxy Clustering Measurements to Cosmology and Galaxy Formation Physics
Andreas Berlind, New York University
Tuesday, February 6, 2007 - 4:00-5:00 pm in Stevenson Center 4327 (Reception at 3:30 pm in SC 6333)
Measurements of the universe on large scales (most notably using Cosmic Microwave Background and supernovae data) have led to a dominant cosmological model (Lambda-CDM) that is highly successful in predicting the large-scale structure of the universe. Much of the focus of testing this model has thus shifted to the small scales of galaxies and clusters of galaxies, where large astronomical surveys have recently produced measurements with unprecedented precision. I will discuss how we can harness the power of these large surveys to learn about cosmology and galaxy formation physics. Along the way, I will present results from galaxy clustering measurements in the Sloan Digital Sky Survey.
DEEP2 and Beyond: Studying the Universe with Surveys
Jeffrey Newman, University of California - Berkeley
Tuesday, February 13, 2007 - 4:00-5:00 pm in Stevenson Center 4327 (Reception at 3:30 pm in SC 6333)
In this talk I will describe tests of fundamental physics from the DEEP2 Galaxy Redshift Survey, the current state of the art in studies of the distant Universe, and also explore what sorts of future redshift surveys will be needed to calibrate future dark energy probes such as LSST or SNAP. DEEP2 is the first project to study the distant Universe with a dataset comparable in size and nature to recent generations of local surveys. It was designed to measure both the properties of galaxies and their distribution in space at redshift z~1, looking back over more than half the age of the Universe. In this talk, I will first describe this recently-completed survey, along with tests for both temporal and spatial variation in the value of the fine structure constant using DEEP2 data. Next, I will describe a new method which can empirically calibrate photometric redshift measurements to the accuracy required by SNAP or LSST, even using incomplete surveys of only the brightest galaxies at a given redshift. This is in contrast to conventional techniques, which require that spectroscopic samples be similar to the objects calibrated; that limitation may be avoided by exploiting the large-scale clustering of galaxies.
Finally, I will describe one example of the power of surveys: their ability to find new classes of astrophysical object, such as a double active galactic nucleus discovered in DEEP2 data.
Quasar Feedback in Structure Formation
Evan Scannapieco, University of California - Santa Barbara
Thursday, February 15, 2007 - 4:00-5:00 pm in Stevenson Center 4327 (Reception at 3:30 pm in SC 6333)
For the past 10 billion years, the typical mass of star-forming galaxies has been decreasing, seemingly in direct conflict with the prevailing model of cosmological structure formation. Using analytic arguments and reviewing recent observations, I will demonstrate that the solution to this mystery is likely to lie in the formation of supermassive black holes, which exert strong feedback on their environments as they pass through an active phase, known as a quasar. Next, I will present the results of one of the largest cosmological smooth particle hydrodynamic simulations every carried out, which includes this feedback process and can be used to make detailed observational comparisons. In particular, our modeling places us in a unique position to interpret joint measurements of the distributions of quasars, galaxies, and small-scale distortions in the microwave background. Finally, I will summarize other aspects of my ongoing research, focusing on studies that constrain the properties of the first stars.
The Charm and Beauty of RHIC
Ralf Averbeck, Stony Brook University
Thursday, February 22, 2007 - 4:00-5:00 pm in Stevenson Center 4327 (Reception at 3:30 pm in SC 6333)
Ultra relativistic collisions of heavy ions are investigated at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. These collisions heat nuclear matter to energy densities achieved before only within the first few microseconds after the big bang. The experiments at RHIC have shown that under these conditions nuclear matter melts into a strongly interacting low viscosity fluid of quarks and gluons which is opaque to energetic quarks and gluons. Particles carrying heavy quarks, i.e. charm or bottom quarks, are among the most interesting probes utilized to study the properties of this so-called strongly interacting Quark Gluon Pasma (sQGP). The measurement of heavy quark production in ultra relativistic heavy ion collisions is an experimental challenge and, at the same time, rich in terms of physics information. A selection of current results, which hint at exciting and novel physics, will be discussed.
Giant Telescopes, Ancient Skies: New Views of the Universe - Carl K. Seyfert Lecture in Astronomy
Caty Pilachowski, Indiana University
Wednesday, March 14, 2007 - 4:00-5:00 pm in Stevenson Center 4327 (Reception at 3:30 pm in SC 6333)
The decade of the 1990's saw the construction of more than a dozen telescopes that dwarf the 200" behemoth at Palomar, telescopes with apertures more than twice its size. With these new telescopes, astronomers have discovered the acceleration of the Universe and changed forever our perception of cosmology. We now know that the stars and galaxies we see in the sky make up less than 5% of the content of the universe - and the remaining 95% we have yet to identify or understand. These giant new telescopes have revealed the presence of more than 200 new planets circling other stars, and shown us that these planets are stranger than anything we imagined. These new instruments have also given us a peek into stellar nurseries where stars - and planets - are born. Now astronomers are planning even larger telescopes that will allow us to see almost to the beginning of time and space, and to witness the formation of the first stars and galaxies after the Big Bang. These telescopes, with apertures of 20 or 30 meters, will challenge not only our technology, but our imaginations.
New Horizons in Particle Physics - Francis G. Slack Lecture
Jerome Friedman, Massachusetts Institute of Technology
Thursday, March 15, 2007 - 4:00-5:00 pm in Stevenson Center 4327 (Reception at 3:30 pm in SC 6333)
Great progress was made in particle physics in the second half of the 20th Century, driven by the development of new types of accelerators and particle detectors. The combination of extensive experimental results and new theoretical insights led to the quark model, Quantum Chromodynamics, and Electroweak Unification. These form the basis of a remarkably successful theory of elementary particles, called the Standard Model. Although its predictions have been confirmed with good precision at present accelerator energies, this theory has raised a number of deep questions that need to be addressed in the TeV energy region. Experimental programs to search for answers to these questions are being prepared at the Large Hadron Collider, a 14 TeV proton-proton collider at CERN, which will be commissioned at the end of this year. Plans are also being developed internationally to propose the construction of a complementary facility, the International Linear e+e- Collider.
Professor Friedman will give a second talk on Friday, March 16:
Are We Really Made of Quarks?
The answer to the question, "Are we really made of quarks?" is yes; but physicists did not arrive at this answer easily. The quark model, which embodied a radically new conceptual view of the structure of matter, was fiercely debated and generally rejected by the physics community. Its ultimate acceptance took well over a decade and occurred only after inescapable and compelling experimental evidence, but free quarks have never been observed. This talk will describe how physicists came to this seemingly strange conclusion and discuss the implications of such a picture on our concept of matter.
Oxide-Semiconductor Materials for Quantum Computation
Jeremy Levy, University of Pittsburgh
Thursday, March 22, 2007 - 4:00-5:00 pm in Stevenson Center 4327 (Reception at 3:30 pm in SC 6333)
Quantum computers, as yet undeveloped, are believed to be able to efficiently solve strategically important problems like number factorization, database search, and the Schroedinger equation itself. The staggering potential of these and other applications has led to a worldwide race to develop scalable equantum information technology. Compared to ordinary computers, the state of experimental quantum computation is primitive--neither quantum bits (qubits) nor quantum gates (qugates) have been demonstrated in a scalable form. In this talk I will focus on a proposal to create a quantum information processor using ferroelectrically coupled electron spins in silicon. Progress toward these goals, pursued within the Center for Oxide-Semiconductor Materials for Quantum Computation (COSMQC), will be described.
Enhancing the emission efficiency of a single molecule with a particle antenna. (a) Fluorescence enhancement as a function of distance. (b) Fluorescence imaging of single molecules.
Nanoscale Spectroscopy with Optical Antennas
Lukas Novotny, Institute of Optics, University of Rochester
Thursday, March 29, 2007 - 4:00-5:00 pm in Stevenson Center 4327 (Reception at 3:30 pm in SC 6333)
Antennas are devices that efficiently convert localized energy to free propagating radiation, and vice versa. They are a key enabling technology in the microwave and radiowave regime but their optical counterpart is greatly unexplored.
In order to understand antenna-coupled light emission and absorption we use a single molecule as an elementary light emitting device. With an optical antenna in the form of a simple gold particle we are able to increase the emission efficiency by more than a factor of 10. However, for very short distances between particle and molecule the fluorescence yield drops drastically because of nonradiative energy transfer. A simple gold particle is not an efficient optical antenna and it can be expected that favorably designed nanoplasmonic structures will yield much higher enhancement.
Optical antennas can be employed as light sources for high-resolution optical microscopy and spectroscopy. We demonstrate vibrational (Raman scattering) and nonlinear imaging with spatial resolutions down to 10nm.
Contemporary Introductory Physics - Guy & Rebecca Forman Lecture
Ruth Chabay, North Carolina State University
Friday, April 6, 2007 - 4:00-5:00 pm in Stevenson Center 4327 (Reception at 3:30 pm in SC 6333)
The goal of the contemporary physics enterprise is to explain a broad range of phenomena by using only a very small number of powerful fundamental principles. Matter & Interactions is a modern, calculus-based introductory physics curriculum for engineering and science students, which places a strong emphasis on making and using physical models, and on starting from fundamentals in analyzing physical systems. Computational modeling is an integral part of the course. An emphasis on microscopic models and on the atomic nature of matter makes possible the unification of topics that are traditionally taught as disconnected, and allows deeper exploration of the predictive power of fundamental principles. A collaborative project involving Purdue, Georgia Tech, and NC State is focused on institutionalizing this reform curriculum in large universities. For additional information, see http://www4.ncsu.edu/~rwchabay/mi.
Aberration Corrected STEM - an Atomic Scale Window to the World of Catalysis and Beyond
Albina Y. Borisevich, Oak Ridge National Laboratory
Tuesday, April 10, 2007 - 4:00-5:00 pm in Stevenson Center 4327 (Reception at 3:30 pm in SC 6333)
Aberration-corrected scanning transmission electron microscopy (STEM) is fast becoming the definitive tool for studies of the nanoworld, providing sub-Ångström resolution and single-atom sensitivity. Several examples will be given from the field of heterogeneous catalysis. Single-atom imaging and spectroscopy reveal real-space atomic structure and, in combination with theory, uncover physical mechanisms of catalysis. Aberration correction also enables unprecedented 3D sensitivity by STEM with nm-scale depth resolution in addition to sub-Ångström lateral resolution. Complete structure of nanomaterials can be examined and objects down to a single atom can be located in 3D. New advances and the future of the field will also be discussed.
Is the Universe Out of Tune?
Glenn Starkman, Case Western Reserve University
Thursday, April 12, 2007 - 4:00-5:00 pm in Stevenson Center 4327 (Reception at 3:30 pm in SC 6333)
The Cosmic Microwave Background Radiation is our most important source of information about the early universe. Many of its features are in good agreement with the predictions of the so-called standard model of cosmology -- the Lambda Cold Dark Matter Inflationary Big Bang. However, the large-angle correlations in the microwave background exhibit several statistically significant anomalies compared to the predictions of the standard model. Not only is there a lack of large angle correlations, but the lowest multipoles seem to be correlated with each other, rather than statistically independent. Indeed, they also seem to be correlated with the geometry of the solar system, suggesting that what little power there is on large scales is locally not cosmologically produced.
This Week's Colloquia:
The Hunt for the Snark: From Physics of Information Technology to Molecular Electromechanical Machines
Sergei Kalinin, Oak Ridge National Laboratory
Tuesday, April 17, 2007 - 4:00-5:00 pm in Stevenson Center 4327 (Reception at 3:30 pm in SC 6333)
Progress in information technology requires novel computational state variables such as spin or electric dipoles, materials systems, and coupling phenomena as a fundamental basis of data storage, processing, and control. Coupling between permanent polarization and electric field in ferroelectric and multiferroic materials suggest exciting novel strategies for non-volatile memory and data storage applications. In this talk, I will present recent results on the Scanning Probe Microscopy studies of fundamental polarization reversal mechanisms in ferroelectrics, multiferroics, and multiferroic heterostructures. In the second part of the talk, I will discuss applications of SPM for energy dissipation imaging using a novel approach based on excitation and detection of signal having finite amplitude density in a selected region in Fourier domain. The applications of this band excitation method are illustrated for electromechanical, magnetic, and mechanical imaging. Ultimately, these studies provide enabling fundamental science for molecular electromechanical machines - the complementary element to molecular electronics that will allow not only computation, but also motion on molecular scales.
Research was supported by the U.S. Department of Energy Office of Basic Energy Sciences Division of Materials Sciences and Engineering and was performed at Oak Ridge National Laboratory which is operated by UT-Battelle, LLC.
Cool Stars and Magnetic Activity in the Sloan Digital Sky Survey
Suzanne Hawley, University of Washington
Thursday, April 19, 2007 - 4:00-5:00 pm in Stevenson Center 4327 (Reception at 3:30 pm in SC 6333)
I will briefly describe the Sloan Digital Sky Survey, an ongoing experiment to observe the northern sky from Apache Point Observatory in southern New Mexico. I will then discuss a project to investigate the properties of surface magnetic activity in cool, low mass stars, using an SDSS sample comprising nearly 50,000 stars. Our results show that the lifetime and strength of magnetic activity in low mass stars differs markedly from solar-type stars, and that these parameters depend strongly on the mass and surface temperature of the star. We calibrate for the first time an age-activity relation for the M dwarf sequence. These data provide constraints on the formation and evolution of magnetic fields in fully convective stars.