Department Colloquium

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Physics & Astronomy Department
Vanderbilt University
PMB 401807
2401 Vanderbilt Place
Nashville, TN 37240-1807

(615) 322-2828
(615) 343-7263

Physics and Astronomy Colloquium, 2010-2011

Colloquia are held on Thursdays at 4pm in room 4327 (building 4) of the Stevenson Science Center unless otherwise noted. Click here for directions, or phone the department. A reception with the speaker is held at 3:30pm in Stevenson 6333.

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Fall 2010

Thursday, August 26

James Bullock, University of California - Irvine

Dark Matter and Dwarf Galaxies   (show abstract)

Over the past five years, new data from automated sky surveys have more than doubled the number of known satellite galaxies orbiting around the Milky Way disk, revealing a population of ultra-faint systems with total light output barely reaching ~1000 times that of the Sun. These newly-discovered dwarf galaxies represent galaxy formation in the extreme: massive balls of dark matter that happen to host enough stars for us to find them. Kinematics studies have revealed that they are the most dark matter dominated objects in the known universe. Many of these galaxies could not have been discovered if they were slightly farther away, suggesting that new, deeper surveys will discover hundreds more as they cover more sky with bigger telescopes. I discuss how dark matter dominated dwarfs of this kind offer a particularly useful target for dark matter indirect detection experiments.

Host: A. Berlind

Thursday, September 2

James Dickerson, Vanderbilt University

Nanoparticle Deposition via Electrophoresis   (show abstract)

Semiconducting, insulating, and metallic nanoparticles have attracted considerable interest recently due to their size-dependent, quantum confinement characteristics, which make them attractive for a broad platform of optical, magnetic, and electronic devices. Proposed commercial applications include solid state lighting devices, magnetic recording media, ultra-light video displays, and bio-imaging reagents.

For nanoparticles to be employed in an array of commercial and industrial applications, a technique for the facile, rapid, and site-selective assembly of homogeneous, densely packed, defect-free thin films must be realized. The most widely used methods for casting nanoparticle (NP) constituents into densely packed, thermally stable films, such as evaporation-driven self assembly and Langmuir-Blodgett casting, have some recognized limitations, including the inability to achieve both large-scale ordering of the nanoparticles as well as robust chemical and structural properties. NP deposition schemes also require an understanding of both the NP dynamics in solution and the interactions that govern nanoparticle-substrate and nanoparticle-nanoparticle binding. Further, these procedures require knowledge of the intrinsic and collective properties of NPs that arise from of electrostatic, magnetic, and fluctuating electric dipole effects. The organization and stability of colloidal NP assemblies are markedly affected by the surface charge state of the constituents. Although much research has been done on the assembly of nanoparticles with a distribution of surface charge states, little has been done on the assembly of like-charged nanoparticles. In this case, repulsive Coulomb interactions, as well as van der Waals, dipole-dipole, and steric interactions govern the types of assemblies that can form. The only nanoparticle deposition scheme that considers the primary physical characteristics of the NPs in the film formation and incorporates the most favorable attributes of NP deposition is electrophoretic deposition.

Recent progress in the electrophoretic deposition of nanoparticles and other nanoscale materials will be the emphasis of this presentation. Highlighted are the recent discoveries of the fabrication of free-standing nanoparticle thin films, comprised solely of electrophoretically deposited iron oxide nanocrystals, cadmium selenide nanocrystals, and carbon nanotubes, as well as transparent films of europium and gadolinium sesquioxide nanoparticles.

Host: R. Scherrer

Thursday, September 9

Will Happer, Princeton University

Carbon Dioxide, Friend or Foe?   (show abstract)

In this talk I will review the physics of global warming due to increased levels of CO2. The current CO2 levels are still low compared to values that have been the norm since the Cambrian, 550 million years ago. Because of the large positive feedback factors assumed from water vapor and clouds, the warming predicted by climate models may well be exaggerated. Increasing atmospheric levels of CO2 may actually be a net benefit to the planet because of increased crop yields and other advantages of a warmer climate and more atmospheric CO2.

Host: N. Tolk

Thursday, September 16

David Lubensky, University of Michigan

Self-Organization in Animal Development   (show abstract)

Developmental biology presents some of the most amazing examples of self-organization found in nature: Starting from a single-celled egg, an animal is able, largely without outside help, to construct an entire, incredibly intricate organism, with cells of different types taking on myriad shapes and arranged in complex patterns to create a viable adult. Many of the individual steps in this maturation bear at least a superficial resemblance to examples of pattern formation or self-assembly in simpler physical systems, and there is a long tradition of using physically-inspired models to try to understand developmental processes. Only relatively recently, however, have experimental techniques reached the point where it is possible to subject these models to stringent tests. While confirming some classical ideas, such experiments have also begun to reveal how specifically biological controls interact with more generic physical effects to lead to reliable and robust development. Using examples from my own research on eye development in fruit flies and in fish, I will show how it is becoming possible to dissect the mechanisms of self-organization during development and illustrate some of the surprising new physical ideas that can result from such investigations.

Host: S. Hutson

Thursday, September 23

Charles Townes, University of California - Berkeley

How Do New Things Happen? Origins of the Laser   (show abstract)

The many ways by which new inventions, discoveries, and ideas arise will be outlined with examples. The particular case of the laser will be discussed in detail, from its origins to its present development,from a personal point of view.

Host: N. Tolk

Thursday, September 30

David Cobden, University of Washington

Phase transitions in nanostructures   (show abstract)

Because of the change in structure, the latent heat, and the need for nucleation, first-order phase transitions involving a solid phase tend to very sensitive to inhomogeneities and to be difficult to study in bulk material. For solid-solid transitions the situation is particularly bad, with random domain formation, high strain, and fracture being almost unavoidable. I will discuss how working with nanoscale systems, which are small compared with the scale of inhomogeneities and domains, allows much improved control of such transitions. It also opens up possibilities to investigate phase transitions in reduced dimensionality, where the physics may be qualitatively different from that in three dimensions and may be more theoretically tractable as well. These advantages will be illustrated in two systems: a solid-solid transition driven by electron-electron correlations in a vanadium dioxide nanobeam; and vapor-liquid-solid transitions occurring in a monolayer of gas atoms adsorbed on a carbon nanotube.

Host: J. Nag and R. Haglund

Thursday, October 7

Jeff Hughes, Boston University

Space Weather: Understanding how the Sun affects what we do   (show abstract)

Space weather is a term used to describe the variable conditions in the earth’s space environment that can damage or disrupt satellite systems, radio communications, GPS navigation, and even the electrical power grid. The sun is a relatively benign magnetic star, but not completely benign. Solar flares and coronal mass ejections launch X-rays, energetic charged particles, and clouds of hot magnetized plasma that can impact Earth causing ionospheric disturbances and severe geomagnetic storms. Predicting these events and their outcomes – space weather forecasting – presents a considerable challenge. We are creating a suite of physics-based numerical models that simulate the space environment from the sun to the earth’s upper atmosphere with the aim of both better understanding the complex coupling between the sun, the solar wind and the earth’s magnetosphere and ionosphere (geospace), and developing tools to help the space weather forecasters in the National Weather Service and the Air Force. As an illustration of the use of models in an observational science, I will focus on how these models have helped us distinguish three distinct sources of solar wind plasma at the sun.

Host: K. Stassun

Thursday, October 14

Timothy Wei, Rensselaer Polytechnic Institute

Fundamental Fluid Dynamics and the Olympic Swimming Movement    (show abstract)

The world of competitive swimming is dynamic. Swimmers today are bigger, stronger and faster than they ever have been. The training regimen of an elite athlete includes not only endless practice of his or her skills, but also a carefully planned diet, strength and endurance training, and hours of mental preparation. Within this framework, we have teamed with USA Swimming to develop advanced, fluid dynamics based training and analysis tools for current and future Olympic swimmers. The focus of this presentation will be on the objectives, methodologies and outcomes of measurements of flow around swimmers. Movies of PIV flow measurements and time resolved force measurements around swimmers, including Beth Botsford and Megan Jendrick, 1996 and 2000 Gold Medalists in the 100 meter back and 100 meter breast, respectively, will be presented. Work with Ariana Kukors, 2009 World Championships gold medalist and world record holder in the 200 IM. In addition, the measurement technique has recently been applied to dolphins. Data from those experiments will be shown as well.

Host: S. Hutson

Thursday, October 21

Samuel H. Dworetsky PhD, formerly General Attorney in the IP-Law group of AT&T

The Laser Patent Battles – The Intersection of Science and the Law   (show abstract)

The patent system was established by the Founders to act as a major incentive for innovation. However, the aspects of an innovation that are protected by a patent often differ from the scientific view of the significance of the innovation. In this talk, the battle between the Schalow/Townes laser patent and the patent on the same subject sought by one of Townes’ graduate students will be presented as a case study in the difference in perspective between the scientific community and the patent community. The goal of the presentation will be to introduce you to the idiosyncrasies of the patent system from the perspective of a research physicist who mutated into a patent attorney. Along the way, you will learn about the history of the laser as well as about patent law and alternative career opportunities – while all the time having a good time and laughing more often than you would expect!

Host: N. Tolk

Thursday, October 28

Tao Han, University of Wisconsin

High Energy Physics: The Next Two Decades   (show abstract)

With a brief review of the historical development in high energy physics, we appreciate the extraordinary achievements thus far, formulated as the "Standard Model", in understanding Nature at the highest energy scales (or the shortest distances) currently experimentally accessible. Yet, theoretical arguments and indirect experimental observations indicate the existence of new physics at the TeV scale, the "terascale". The precise form of the new physics is unknown, but may have far-reaching implications in cosmology, astroparticle physics, and nuclear physics. The CERN Large Hadron Collider (LHC) has just begun its historical mission to explore the physics at this energy frontier. Exciting new discovery is highly anticipated. Future high energy colliders such as the International Linear Collider (ILC) will further help to reveal the true nature of the elementary particles. The "terascale" physics will dominate in the next two decades to come.

Host: T. Weiler

Thursday, November 4, Joint Physics-Chemistry Colloquium

Herschel Rabitz, Princeton University

Controlling Quantum Dynamics Phenomena with Photonic Reagents and Beyond   (show abstract)

Controlling quantum dynamics phenomena with tailored radiation has a long history with many successes appearing in the recent literature. These studies encompass both theoretical simulations as well as laboratory experiments, especially using shaped laser pulses acting as a class of “photonic reagents” for directing the dynamics. Successful illustrations include manipulation of rotational, vibrational, electronic and reactive processes both in gaseous and condensed phases. Optimal control techniques are providing the means to obtain the best possible control yields under the specified conditions.

Given the latter very encouraging positive control outcomes, a basic question is why the simulations and laboratory experiments are working out well. A number of rational arguments suggest that controlling quantum dynamics phenomena should be a difficult and delicate process, which is sensitive to noise and possibly a number of other factors. Theoretical analyses will be presented to provide a foundation to begin to understand the many control successes. Most importantly, the control landscape (i.e., the search space for effective controls) generally has remarkably simple topology, permitting easy and rapid searches for effective controls. Material will be presented considering the systematic nature of controlling quantum phenomena based on viewing the Hamiltonian structure and applied field as collectively forming sets of controls. These overall results indicate the rich nature of controlling quantum phenomena and provide some hints at what might lie ahead.

Hosts: N. Tolk and S. Rosenthal

Thursday, November 11, Wendell Holladay Lecture

R.B. Piercey, Eastern Kentucky University

Human Consciousness and Quantum Mechanics   (show abstract)

Some of the most important contributions classical science has made to the evolution of modern thought are the notions that the external world is real; that it is governed by causal determinism; and that it can be considered as separate from the human minds that experience and observe it. These assumptions are central to our notions of "deterministic laws"; of "isolated systems", of "instantaneous states" and of a world that is coherent and knowable.

Since the early part of the twentieth century, however, the theory of quantum mechanics has pointed out weaknesses of such epistemological assumptions and a fresh consideration of the role of the human mind in understanding the "external world" is in order. Common interpretations of quantum mechanics argue that physical systems can manifest very different properties depending on the the kinds of observations that an observer chooses to make. They argue further that the system's properties are actually created by the observation at the time of observation instead of pre-existing as intrinsic, un-observed properties of the system. In these interpretations, the free choice of the observer can cause the system to be in a particular state. If the interpretations are accurate and free will exists in any normal sense, then observers are able to not only cause the current state of the system to be what is observed, but also to select the history for the system that makes the current state possible. With no intrinsic properties and with the suggestion of backward causation, these interpretations conflict with our pedestrian understanding of causal determinism and time.

We explore the nature and role of the human brain and what it can – and probably cannot – do. We review the science of intentional action to better understand the status of free will in science. Finally, we consider whether quantum mechanics provides a new perspective on the nature of human consciousness.

Host: A. Ramayya

Thursday, November 25

Thanksgiving Holidays, no colloquium

Thursday, December 2
Special time and location: 3:00 pm in SC 4309

Mercedes Richards, Penn State University

The Observational and Computational Challenges of Imaging Accretion Disks and Streams in Interacting Binary Star Systems    (show abstract)

Direct images of interacting binary stars are difficult to obtain because the separation between the stars is in the milli-arcsecond regime. Modern optical interferometers have now produced the first resolved optical images of the brightest and nearest eclipsing binary in the sky, however these direct images do not contain enough detail to show how the gas moves between the stars. The technique of Doppler tomography has been used effectively to create two-dimensional and three-dimensional images of the gas flows in interacting binaries. These results were achieved through multiple steps including the systematic collection of time-resolved spectra of binary systems, the use of image processing software similar to medical tomography codes, hydrodynamic simulations of the gas flows, and the creation and application of a spectrum synthesis code to model the spectrum of the accretion disk and gas stream.

Host: K. Stassun

Thursday, December 9

Mark Riley, Florida State University

The Fascinating Gamma-Ray World of the Atomic Nucleus: The Revolution Continues   (show abstract)

It was Niels Bohr who first suggested looking at gamma-ray emission spectra in order to characterize the properties of the unique quantal system we call the atomic nucleus. Much progress has been made since this pioneering suggestion and in the last few decades a revolution has taken place in our ability to create and observe the intricate emission patterns from nuclei under extreme conditions. A remarkable diversity of phenomena have been discovered as increasingly sensitive instrumentation have revealed unexpected properties and exotic behavior. This talk aims to give an introduction to this field, a taste of some of these recent discoveries while also charting exciting possibilities for the future.

Host: J. Hamilton

Spring 2011

Thursday, January 20, Guy & Rebecca Forman Lecture

Diola Babayoko, Southern University

Systemic Mentoring for Competitiveness: The Model of the Timbuktu Academy   (show abstract)

This presentation succinctly describes the paradigm, programs, activities, and results of the implementation of the ten-strand systemic mentoring model of the Timbuktu Academy at Southern University and A&M College in Baton Rouge, Louisiana. Accompanying articles and documents, it is hoped, will stimulate a replication that seems warranted by unquestionable results over 20 years. As per the title of the presentation, systemic mentoring is shown to effect the integration of education and research for contemporary competitiveness. Superior learning, significant research participation, on-time graduation, and admission and success in top graduate schools are some of the results not only for the Physics Scholars of the Academy, but also for those in Chemistry, Engineering and other disciplines. Trends at the federal and other levels indicate that systemic mentoring is not just good for the students (undergraduate and graduate), but also for the scholar mentors themselves – as far as grant funding is concerned. A few disappointments that may occur to a mentor are explained away with the Central Limit Theorem (so that they may not become serious discouragements.) The Academy’s nationally recognized, positive impacts on the participation of minorities in the scientific and technological enterprise of this country point to the relevance of mentoring to the effective promotion of diversity.

Host: D. Ernst

Thursday, January 27

Gregor Neuert, MIT

Dynamic Information Processing in Individual Cells: a Single-Molecule Approach in Systems Biology   (show abstract)

Understanding and predicting how cells sense and respond to their environments is a key goal of systems biology. New experimental and computational methodologies have helped elucidate many signal transduction pathways and gene regulation mechanisms, but it remains difficult to predict the phenotypic diversity of cellular dynamics. To better understand and predict these complex networks, we propose a comprehensive approach for the identification of gene regulation systems. First, we developed a quantitative assay to measure single-molecule expression of endogenous mRNA at fast temporal resolution in individual cells. Second, we developed an efficient and flexible computational approach to analyze data from such experiments. Third, we integrated these experimental and computational approaches within a novel hierarchical network identification framework, which involves several clearly defined rounds of analysis, prediction, experiment design, and validation. Finally, we show that our semi-automated hierarchical approach can select a single, predictive gene regulatory model from out of several thousand automatically-generated hypotheses. In addition the identified model provides accurate predictions at diverse environmental and genetic conditions, which extend well beyond its training data. Since our approach is not specific to any gene, pathway or organism, it can lead to new insight into complex cellular networks from yeast to human.

Host: R. Scherrer

Thursday, February 3

Josh Milstein, University of Michigan

Switching Genes On and Off by Bending and Stretching DNA   (show abstract)

Our current understanding of how genes function is dominated by cellular biochemistry. DNA, however, is a polymer and as such displays a variety of biomechanical properties that may directly influence the regulation and expression of genes. I will discuss some of the experiments our group has conducted that show how cells could modulate the expression of particular genes by applying very small amounts of tension to the chromosome. These experiments were performed in vitro; however, in order to assess the true relevance of DNA mechanics to gene expression, we must observe similar results within actual living cells. Toward this end, I will also present a new technique that our group has devised for driving our work into the in vivo realm.

Host: R. Scherrer

Monday, February 7
Special date and time

Erin Rericha, University of Maryland

Directed Cell Migration and Signal Relay   (show abstract)

Directed Migration of cells is vital to a wide array of biological processes: from the coordinated migration of cells during embryo development to the uncontrollable migration of a metastatic cancer. We investigate directed cell migration in the model organism Dictyostelium aiming to understand the underlying biophysics of their motion, their direction, and the coordination among cell groups. The problem of directed cell migration is often broken into three independent modules: a compass, propulsion, and cell-to-cell signaling. Applying principles from nonlinear dynamics, we explore the cross coordination of these modules by perturbing one and finding impact on the others. Our results indicate that the modules are closely linked: Changes in signal relay can lead to a dramatic increase in cell speed, and cell-surface adhesion affects group behavior. Considering all modules together allows us to utilize more information and move toward quantitative descriptions of key aspects of the cell-cell signaling and propulsion modules.

Host: R. Scherrer

Thursday, February 10

Junhua Yuan, Harvard University

Dynamics of bacterial propulsion: Behavior of the flagellar rotary motor near zero load    (show abstract)

Flagellated bacteria swim by rotating thin helical filaments, each driven at its base by a reversible rotary motor, powered by an ion flux. Studies of the physiology of the bacterial flagellar rotary motor have been limited to the regime of relatively high load due to technical limitations. Here, we developed a new technique that allows systematic study of the motor near zero load. Sixty-nanometer-diameter gold spheres were attached to motors lacking flagellar filaments, and a novel laser darkfield setup was used to monitor the sphere rotation. Resurrection experiments were carried out near zero load: paralyzed motors without torque generating units were resurrected by adding torque generating units to the motor one at a time. In contrast to the incremental increase in rotation rate during resurrection at high load, the rotation rate for motors near zero load jumped to the maximum value upon addition of the first torque-generating unit. Switching properties of the flagellar motor near zero load also were investigated, and the switching rates showed a linear dependence on motor torque. Rotation in either direction (clockwise: CW or counterclockwise: CCW) has been thought to be symmetric, exhibiting the same torques and speeds. Here, we measured the torque-speed relationship across all load regimes for CW rotation, and found that the torque decreases linearly with speed, a result remarkably different from that for CCW rotation. This work provides further insights into the torque-generating mechanism, helps to better understand the motor switching mechanism, and places tighter constraints on possible motor models.

Host: R. Scherrer

Thursday, February 17

Jaan Mannik, Delft University of Technology

Chromosome distribution and membrane curvature localize cell division machinery in Escherichia coli   (show abstract)

Micro- and nanofluidic devices combined with high-resolution quantitative imaging offer a variety of new possibilities to study single cells down to a nanometer-scale resolution. Here, I describe a study where we rely much on these new technological advances in elucidating the molecular mechanisms of bacterial cell division. We investigate how Escherichia coli bacteria are able reliably and accurately position their cell division proteins, i.e. the divisome, in normal and in irregularly shaped phenotypes. We use squeezed E. coli in shallow nanofabricated channels (J. Männik et al., Proc. Natl. Acad. Sci. U.S.A. 106 (2009) 14861) as an irregularly shaped phenotype and compare these cells to their normal rod-shaped counterparts. We study the roles of two molecular systems in this process - one consisting of MinCDE proteins and the other of the bacterial chromosome. We find that while Min proteins are effective in excluding cell division at the poles of rod-shaped bacteria, this inhibitory system becomes chaotic in more complicated cell shapes. Instead, we observe that localization of the divisome is highly anticorrelated with the complex pattern of chromosome distribution in squeezed E. coli cells. We also show that in addition to chromosomal distribution the curvature of a cell’s plasma membrane is instrumental in the fine scale positioning of the divisome. We find that linear divisome complexes form on the circumference of the squeezed cells so that their line curvature is maximized.

Host: R. Scherrer

Thursday, February 24

Anders Carlsson, Washington University

Nonlinear Protein Waves in Biological Cells   (show abstract)

Nonlinear waves based on chemical reactions and diffusion are a startling example of the ways in which simple laws of motion can lead to complex behaviors in physical systems. In this talk, I will discuss an example of such waves involving the protein actin in biological cells. Actin can exist either as an isolated protein in solution, or in the form of filaments which have mechanical rigidity. Recent experiments have shown that filamentous actin forms spontaneous waves which are correlated with protrusion of the cell membrane. I will present a theoretical model of such waves based on the three-dimensional structure of the gel formed by actin filaments, interacting with catalytic proteins in the cell membrane. Implementation of this model via simulation shows that the actin system displays characteristic transitions between dynamic behaviors including traveling waves and patches, as the intracellular protein concentrations are varied. The connections between this behavior and the ability of biological cells to spontaneously explore their environment will be discussed.

Host: S. Hutson

Thursday, March 3

Sergei Voloshin, Wayne State University

QCD in extreme: ultrarelativistic nuclear collisions   (show abstract)

Quantum Chromo Dynamics (QCD) is the theory of strong interactions. At present, perturbative QCD is firmly established and thoroughly tested experimentally. In the so called "soft sector", where the perturbation theory is not applicable, the theoretical calculations are very difficult, and the role of experiment becomes even more important . Ultrarelativistic heavy ion collisions provide invaluable information for our understanding of the strongly interacting matter at extreme conditions. In this talk, after short introduction to the heavy ion physics and presenting highlights from the previous years, I discuss in more detail recent exciting results on the anisotropic flow and correlations testing the chiral magnetic effect (CME). I discuss what anisotropic flow results teach us about the initial conditions and properties of the system created in ultrarelativistic heavy ion collisions. The CME, which manifests strong parity violation, is related in QCD to the existence of topologically non-trivial field configurations, such as instantons and sphalerons. Quark interactions with such gluonic fields are P-odd, and are predicted to lead to the charge separation along the strong magnetic field of non-central nuclear collisions, which can be tested experimentally.

Host: V. Greene

Thursday, March 10

Spring Break, no colloquium

Thursday, March 17, Carl Seyfert Lecture

Paul J. Steinhardt, Princeton University

Inflationary Cosmology on Trial   (show abstract)

This talk will be an unconventional perspective on the inflationary universe theory, the cornerstone of the current standard model of cosmology.

Host: D. Weintraub

Thursday, March 24, Francis G. Slack Lecture

Alan Guth, MIT

Inflationary Cosmology: Is Our Universe Part of a Multiverse?   (show abstract)

After a quick review of how inflation works, I will discuss some of the key features of our universe that suggest that it emerged from a period of inflation: its uniformity, its near-critical mass density, and the spectrum of density perturbations that is now observed in the cosmic microwave background. An interesting feature of inflation is that almost all versions of it lead to eternal inflation: inflation goes on forever, producing a "multiverse" of "pocket universes". I will then turn to the biggest outstanding mystery in cosmology: the value of the cosmological constant, or equivalently the energy density of the vacuum. Theories suggest that the vacuum energy density should be many orders of magnitude larger than what is observed. One controversial explanation starts with the premise that string theory offers a colossal number of vacuum-like states, with varying energy densities. If inflation can populate these vacua, and if life evolves mainly in vacua with small energy densities, then the mystery might be solved. I will argue that this explanation is logically sound, and even plausible.

Host: R. Scherrer

Thursday, March 31

Paul Kalas, University of California - Berkeley

HST Imaging of Fomalhaut: Direct detection of an exosolar planet and Kuiper Belt around a nearby star   (show abstract)

Advances in high-contrast imaging have produced a new sample of spatially resolved debris disks with morphologies attributed to the dynamical effects of planets. Chief among these is the case for a planetary system around the nearby A star Fomalhaut. Optical coronagraphic observations using the Advanced Camera for Surveys aboard HST shows a vast dusty debris belt offset from the star and cleanly sculpted at its inside border. Follow-up HST images have further revealed a co-moving point source with apparent orbital motion 18 AU interior to the dust belt. I will discuss both the observational and theoretical evidence that the point source is a planet with less than 3 Jupiter masses, making Fomalhaut b the lowest mass planet candidate detected via direct imaging. I will give alternate explanations and discuss future plans for the detailed mapping of Fomalhaut's planetary system.

Host: K. Stassun

Thursday, April 7

Kevin Stenson, University of Colorado

Results from the first year of LHC data   (show abstract)

The Large Hadron Collider had its first physics run in 2010 where the products of proton-proton collisions at a world-record energy of 7 TeV were recorded by four experiments at CERN. I will present a selection of results, based on this data set, from the CMS experiment. These results range from measurements of strange and beauty particle production to searches for new physics such as supersymmetry, extra dimensions, and microscopic black holes. I will also provide an outlook of the physics still to come from the LHC as the luminosity and energy increase.

Host: P. Sheldon

Thursday, April 14

Deirdre Shoemaker, Georgia Tech

Frontiers of Numerical Relativity   (show abstract)

The breakthroughs in numerical relativity of late 2005, early 2006 lead to the development of computational tools that allow us to explore where and how strong-field gravity can inform our understanding of gravitational waves and astrophysical phenomena. I will review these latest developments, focusing on binary black hole simulations and the role these simulations play in expanding the frontiers of numerical relativity into gravitational wave astronomy and computational astrophysics. I will summarize the collaborative efforts of the numerical relativity and data analysis communities working to capitalize on our improved understanding of merging black holes to enhance the likelihood of detection -- an urgent undertaking with advanced ground-based gravitational wave detectors expected to be taking science data in 2015. I will also discuss the growing body of work in numerical relativity simulating the late inspiral and merger of supermassive black holes in galactic centers using newly developed general relativistic, hydrodynamic codes. The last stages of coalescence are central to understanding the accretion processes onto the black hole and the conditions under which electromagnetic emission accompanies gravitational waves.

Host: K. Holley-Bockelmann

Thursday, April 21

John Harris, Yale University

Recreating the Primordial Quark-Gluon Soup   (show abstract)

Ultra-relativistic collisions of heavy ions at the Relativistic Heavy Ion Collider (RHIC) and at the Large Hadron Collider (LHC) create an extremely hot system at temperatures (T) expected only within the first microseconds after the Big Bang. At these temperatures (T ∼ 2 x 10^12 K), several hundred thousand times hotter than the sun’s core, normal hadrons cannot exist and nuclear matter “melts” to form a “soup” of quarks and gluons. At RHIC the soup flows easily, with extremely low viscosity, suggesting a nearly-perfect hot liquid of quarks and gluons. Furthermore, the liquid is opaque to very energetic quark and gluon probes, providing evidence that it is dense and highly interacting. I will present a motivation for physics in the field, an overview and interpretation of the RHIC results, highlight the first results from heavy ions at the LHC and discuss them in relation to the RHIC results.

Host: V. Greene

Wednesday, April 27

Gustavo Medina-Tanco, Universidad Nacional Autónoma de México

Probing the universe with extreme energy cosmic rays   (show abstract)

Cosmic rays (CR) with energies in excess of 100 EeV impinge the upper Earth atmosphere at a rate of ~1/(yr x 10^3 km^2). Such a small flux is at the root of the slow development of this area, which almost 50 yr after the pioneer observation of John Linsley at Volcano Ranch is still permeated by fundamental unknowns. The experimental challenge is only increased by the fact that the primary CR are only indirectly observed through the extensive air showers that they produce upon hitting atmospheric nuclei. Moreover, this negatively combines with current uncertainties in hadronic interactions at the high center of mass energies involved in the process. Thus, at present we do not know for sure the identity of the primary particles, where do they originate in the universe or what are the acceleration mechanisms operating at their sources. Despite these unknowns, considerable progress has been made during the last decade from measurements by the HiRes and Pierre Auger experiments. Furthermore, a large step forward is expected in the near future with the launch of the first space observatory devoted to extreme energy cosmic rays, JEM-EUSO, whose large exposure at the highest energies (each year of operation of JEM-EUSO is roughly equivalent to 5 yrs of Auger) opens the possibility of a charged particle astronomy. During the colloquium, the current state of the art of the field, JEM-EUSO’s scientific potential, and the main challenges for data analysis will be discussed.

Host: T. Weiler

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