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physics-astronomy

Physics and Astronomy Colloquium, 2013-2014

Colloquia are held on Thursdays at 3PM 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 2:30pm in Stevenson 6333.

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Fall 2013

Thursday, September 5

Dennis Zaritsky, Department of Astronomy, University of Arizona

Faint Matter in Galaxies   (show abstract)

The focus of dark matter studies must now be on galactic scales. First, this is the final domain where potential conflicts with the standard paradigm have been identified. Second, galaxies are the environment in which we expect to eventually have indirect or direct detection(s) of dark matter. Unfortunately, in this sense, the central regions of galaxies (including the region of the Milky Way that we inhabit) are dominated by baryons. Any conflict with the standard paradigm or dark matter detection/limit must be understood within the context of the baryonic physics and the baryonic contribution to the mass density. This requires a far greater understanding of the baryonic components than what we currently have. In this talk I will focus on two aspects of this challenge, the stellar initial mass function and the search for a complete accounting of stellar baryons in galaxies.

Host: A. Berlind

Thursday, September 19

Kelly Holley-Bockelmann, Department of Physics and Astronomy, Vanderbilt University

Building the Black Hole in Our Own Backyard   (show abstract)

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. In theory, gas-rich major galaxy mergers can easily generate the central stockpile of fuel needed for a low mass central black hole 'seed' to grow quickly and efficiently into a supermassive one. Because of the clear theoretical link between gas-rich major mergers and supermassive black hole growth, this major merger paradigm has become a well-accepted way to form the billion solar mass black holes that power bright quasars in the early universe. It's much less clear, though, how well this paradigm works for growing the 'lightest' supermassive black holes; these million solar mass black holes tend to lie in galaxies like our own Milky Way, where the supermassive black hole is currently quiescent and major mergers were few and far between. This talk will touch on some current and ongoing work on refining our theories of black hole growth for this lightest supermassive class, and will feature the work of Fisk and Vanderbilt graduate students and postdocs.

Host: R. Scherrer

Thursday, September 26

Joel Kastner, Rochester Institute of Technology

Observing Star and Planet Formation at Close Range   (show abstract)

The past decade has seen an explosion in our knowledge of young stars near Earth. This development is generating rapid progress in the study of star and planet formation and, in particular, is driving recent and forthcoming direct imaging searches for young, warm exoplanets and proto-exoplanets. We are exploiting the recent availability of all-sky ultraviolet and infrared photometric data to compile a comprehensive list of candidate young age, 100 Myr, low-mass stars within 300 light years of Earth. Followup spectroscopy and space motion measurements are yielding the ages and distances of these candidates. In parallel, we are conducting comprehensive, multiwavelength (radio to X-ray) investigations of specific nearby, young, Sun-like stars that are orbited by dusty, gaseous ("protoplanetary") disks. These observations are yielding, among other things, insight into the effects of intense high­-energy radiation from young, hyperactive host stars on the molecular chemistries within protoplanetary disks, as well as evidence for ongoing planet building.

Host: D. Weintraub

Thursday, October 3

Andreas Berlind, Department of Physics and Astronomy, Vanderbilt University

From Dark Matter to Galaxies: Probing the Spatial Structure of the Universe and Testing our Cosmological Models   (show abstract)

The last decade has seen an explosion of high precision measurements of the structure of the universe, courtesy of large galaxy surveys such as the Sloan Digital Sky Survey (SDSS). Galaxy clustering measurements encode information about the nature and abundance of dark matter and dark energy, as well as the complex physical process of galaxy formation. However, harnessing the full constraining power of the data is very challenging since it requires a detailed understanding of the statistical and systematic uncertainties in both data and models, which in turn demands significant computational effort. I will discuss my onging research program to analyze SDSS data and model it with the help of cosmological N-body simulations, highlighting several results from both recent and current ongoing projects.

Host: R. Scherrer

Thursday, October 10---Fall Break

Thursday, October 17

Robert Scherrer, Department of Physics and Astronomy, Vanderbilt University

Could Dark Matter be Electromagnetic?   (show abstract)

One of the leading candidates for dark matter is a weakly-interacting massive particle (WIMP), with an annihilation cross section typical of the weak interaction. However, recent years have also seen a growth of interest in the possibility that dark matter interacts electromagnetically. While charged dark matter is largely ruled out, recent papers have explored the possibility of dark matter with a magnetic dipole moment, an electric dipole moment, or an anapole moment. I will review the calculation that determines the relic abundance of a given dark matter particle, and show why charged dark matter is ruled out, while higher order multipoles are not. I will then discuss the signatures of electromagnetic dark matter in direct detection experiments, and show why the anapole is favored over dipole dark matter for particles with masses greater than 10 GeV. Directions for future investigation will be outlined.

Host: T. Weiler

Thursday, October 24

Bernardo Mendoza, Centro de Investigaciones en Optica, Leon, Mexico

Optical properties of nanostructured metamaterials   (show abstract)

We present a very efficient recursive method to calculate the effective optical response of nanostructured metamaterials made up of particles with arbitrarily shaped cross sections arranged in periodic two-dimensional arrays. We consider dielectric particles embedded in a metal matrix with a lattice constant much smaller than the wavelength. Neglecting retardation our formalism allows factoring the geometrical properties from the properties of the materials. If the conducting phase is continuous the low frequency behavior is metallic. If the conducting paths are nearly bloqued by the dielectric particles, the high frequency behavior is dielectric. Thus, extraordinary-reflectance bands may develop at intermediate frequencies, where the macroscopic response matches vacuum. The optical properties of these systems may be tuned by adjusting the geometry.

Host: N. Tolk

Thursday, October 31

Vaughan Jones, Department of Mathematics, Vanderbilt University

Do all subfactors come from physics?   (show abstract)

A subfactor is a mathematical object connected to analysis, algebra, topology, geometry, combinatorics. There is a lot of circumstantial evidence that subfactors are deeply connected with physics, especially in one and two dimensions. For instance the transfer matrices of 2-D statistical mechanical methods define subfactors of some interest, the braiding of n-point functions in conformal field theory produces subfactors in a similar way and algebras of local observables in superselection sectors "are" subfactors. Many new and apparently "exotic" subfactors have been discovered recently and understood using planar algebra methods. It is tempting to speculate that a subfactor itself may produce a lattice model or conformal field theory. I will try to explain these objects, which generalize the notion of group, in an accessible way and give a crazy idea, Halloween appropriate, of taking a continuum limit what mathematicians call the "Thompson group" are the local scale transformations on a 1-dimensional lattice with sites at every dyadic rational.

Host: R. Scherrer

Thursday, November 7---HOLLADAY LECTURE

Vernita Gordon, University of Texas, Austin

Spatial structure in multicellular bacterial systems: how it develops, and why it matters   (show abstract)

Microbial biofilms are communities of interacting single-celled organisms that are bound to a surface and to each other by extracellular polymers. (1) These extracellular polymers give the biofilm its structural and mechanical properties. We have recently found that extracellular polymers also influence the behavior of single cells attached to surfaces, before a biofilm has formed. This suggests that single-celled measurables could serve as a predictive readout for biofilm structure and mechanics. This would be convenient, because biofilm mechanics is important for biofilm removal yet tricky to measure. (2) Extracellular polymers also control intracellular associations, which is important for consortial interactions. We study one such interaction that depends on the population density and spatial arrangement of bacteria: in the presence of a front-line antibiotic, bacterial cells can protect each other at short range and inhibit each other at long range. This suggests ways in which co-culture with unicellular eukaryotes could benefit bacteria, and also presents a model system with which to study spatially-dependent intercellular interactions. (3) Finally, we have recently developed a method for controlling the spatial arrangement of bacteria so that the effects of spatial structure can be studied. We arrange bacteria on surfaces with single-cell resolution using laser trapping, so that native motility and the signalling effects of surface attachment are preserved unhindered. We demonstrate that this approach can be used to study spatially-dependent group behaviors of bacteria.

Host: E. Rericha

Thursday, November 14

Kang Wang, Department of Electrical Engineering, UCLA

Energy Scaling of Spintronics – A new paradigm for nanoelectronics - From spin based memory to low dissipation intelligent systems    (show abstract)

The talk will describe the physics of collective spins or nanomagnetic and the engineering of spin-orbit interaction at the interface. First, I will give a brief overview of the energy challenge of today's CMOS scaling. Then I will describe the advantages and impact of magnetic devices in terms of its low switching energy, high speed, high endurance, and scalability. The physics of spin transfer torque (STT) will be described for its application of spintronic memory. Next, we will describe in addition the physics of spin-orbit interaction and spin Hall to improve energy efficient switching via polarized spins. Only recently, it was shown to possibly use electric field to control magnetic properties of metallic ferromagnetic layers. For the latter, we will describe a couple of fundamental mechanisms of voltage control of magnetic moment and direction at the metallic surface. I will specifically describe a new concept of electric field control of metallic magnetism, that is, the use of electric field to manipulate magnetic field via engineering of the spin-orbit interactions at the metallic interface. This will lead to electric-field or voltage controlled magneto-electric (ME) memory (Me-RAM) , resulting in much reduced energy dissipation for switching. The dynamics of the switching as well as additional physical processes in improving the switching process will be outlined. The integration of such magnetic devices with CMOS will reduce the standby leakage of CMOS circuits and thus enable further scaling of CMOS with improved performance. Energy scaling will be addressed. Further advances are possible by adopting the spin wave bus concept -- the use of spin waves for logic and interconnect . With low energy, high density memory and spin wave bus, it may be possible to construct a new type of neuromorphic information processing electronics. These types of devices may be integrated directly on top of front-end processed CMOS to enable new generations of nonvolatile instant-on electronics and other systems. A potential new paradigm of intelligent nano-systems may emerge. 1. J. G. Alzate, P. Khalili Amiri, P. Upadhyaya, S.S. Cherepov, J. Zhu2, M. Lewis, J. A. Katine, J. Langer, K. Galatsis, I. Krivorotov, and K. L. Wang, "Voltage-Induced Switching of Nanoscale Magnetic Tunnel Junctions", IEDM. 2012. 2. Khitun, A., Bao, M., Lee, J.-Y., Wang, K.L., Lee, D.W., Wang, S. X. and Roshchin, I.V., "Inductively Coupled Circuits with Spin Wave Bus for Information Processing", Journal of Nanoelectronics and Optoelectronics, 3(1): 24-34. (March 2008) 3. K. L. Wang and P. Khalili Amiri, "Nonvolatile Spintronics: Perspectives on Instant-on Nonvolatile Nanoelectronics Systems", J Spin, Vol. 2, No. 2 (2012) 1250009

Host: K. Varga

Thursday, November 21

Philip Kim, Department of Physics, Columbia University

Bloch, Landau, and Dirac: Hofstadter's Butterfly in Graphene   (show abstract)

Electrons moving in a periodic electric potential form Bloch energy bands where the mass of electrons are effectively changed. In a strong magnetic field, the cyclotron orbits of free electrons are quantized and Landau levels forms with a massive degeneracy within. In 1976, Hofstadter showed that for 2-dimensional electronic system, the intriguing interplay between these two quantization effects can lead into a self-similar fractal set of energy spectrum known as "Hofstadter's Butterfly." Experimental efforts to demonstrate this fascinating electron energy spectrum have continued ever since. Recent advent of graphene, where its Bloch electrons can be described by Dirac feremions, provides a new opportunity to investigate this half century old problem experimentally. In this presentation, I will discuss the experimental realization Hofstadter's Butterfly via substrate engineered graphene under extremely high magnetic fields controlling two competing length scales governing Dirac-Bloch states and Landau orbits, respectively.

Host: K. Bolotin

Thursday, November 28, Thanksgiving Break

Thursday, December 5

James Butler, Smithsonian National Museum of Natural History

Mysteries Hidden in Diamond: Blue and Pink Diamonds    (show abstract)

Diamond is a fascinating material to Gemologists, Geologists, and materials scientists. Now we can grow diamond of higher purity and quality than found in nature by synthetic techniques (Chemical Vapor Deposition and High Pressure High Temp. presses), there is a resurgence of interest in diamond materials for technological applications. In most cases, impurities and defects (intentional or unintentional) control the desired properties. In this talk I will explore some of these defects in natural diamonds which impact color, electrical properties, etc. examining two rare types of natural diamonds, blue and pink.

Host: N. Tolk

Spring 2014

Thursday, January 9

Mike Downer, University of Texas, Austin

Plasma-Based Particle Accelerators: There's Plenty of Room at the Bottom   (show abstract)

Over the past few years, compact plasma-based particle accelerators have advanced sufficiently that it is no longer a pipe dream to imagine a tabletop x-ray free-electron laser in every major university in the world [1], or proton cancer therapy on a scale that many hospitals could afford. I will survey recent experimental highlights in the field that make these hopes more realistic than even a few years ago. These include a milestone achieved recently using the Texas Petawatt Laser: nearly mono-energetic acceleration of plasma electrons to 2 GeV with unprecedented sub-milliradian beam divergence [2]. I will discuss near-term prospects for improving plasma-based accelerators further. Finally I will describe new holographic techniques that enable experimenters to visualize the electron density waves that lie at the heart of plasma-based accelerators [3,4]. Such 4D visualization, previously available only from intensive computer simulations, helps physicists understand how plasma-based particle accelerators work, and how to make them work better. [1] K. Nakajima, "Towards a table-top free electron laser," Nature Physics 4, 92 (2008). [2] X. Wang et al., "Quasi-monoenergetic laser-plasma acceleration of electrons to 2 GeV," Nature Communications 4, 1988 (2013). [3] N. H. Matlis et al., "Snapshots of laser wakefields," Nature Physics 2, 749 (2006). [4] Z. Li et al., "Single-shot tomographic movies of light-velocity objects," Nature Communications, in press (2014).

Host: N. Tolk

Thursday, January 16

John Gore, Department of Physics and Astronomy, Vanderbilt University

Contrast mechanisms in NMR imaging   (show abstract)

Magnetic resonance imaging (MRI) relies on recording the nuclear magnetic resonance (NMR) signals from mobile hydrogen nuclei in (mainly) water. Images may portray a range of different properties of cellular media because NMR signals can be made sensitive to different aspects of the local environment in which water is found - these include the nature and concentrations of macromolecules, physico-chemical properties such as pH, compartmentation effects, transport rates and so forth. Variations in these properties gives rise to useful image contrast that can be used to characterize tissues. Two specific types of contrast will be highlighted, which loosely share a similar conceptual origin viz. the effects of a magnetic field gradient. When applied deliberately, field gradients may be used to encode and quantify molecular diffusion effects and novel techniques have been developed that enable diffusion-based MRI to probe tissue microstructure and detect intracellular changes in e.g. cancer. Similarly, intrinsic field gradients may be generated when the magnetic susceptibility of a region varies, and diffusion effects may then give rise to signal changes that reflect the presence and character of microscopic inhomogeneities such as caused by microvasculature. This provides the basis for functional MRI, which is widely used now for assessing functional connectivity between brain regions. The applications of these simple physical phenomena include studies of tumor biology as well as neural function.

Host: E. Rericha

Thursday, January 23

Yoav Kallus, Princeton Center for Theoretical Science, Princeton University

Signatures of non-equilibrium dynamics in self-organized disordered structures   (show abstract)

The study of random close-packed (RCP) structures of hard spheres has brought unexpected unity to the study of granular materials and structural glasses. RCP is one example of a wide variety of self-organized disordered structures observed in systems that evolve from a region of instability (or under-constraint) to the margin of stability (or over-constraint), whereupon their evolution stops. In RCP, this marginal stability has long been associated with the notion of isostaticity, equality between number of constraints and number of degrees of freedom, but new characteristics of marginal stability, which epitomize the approach to stability have been recently identified. These characteristics are manifested in critical (power-law) distributions of weak contacts and near-contacts. I will discuss the implications of these signatures to the study of self-organized disordered structures in general, using RCP and random Bravais lattice sphere packings as the main sources of numerical data.

Host: R. Scherrer

Thursday, January 30

Sunghwan Jung, Department of Engineering Science and Mechanics, Virginia Tech

Drinking, Diving, and Bouncing fluids   (show abstract)

I will discuss three fluid-mechanics problems: fluid motions related to drinking, diving, and bouncing, which you might have experienced or observed once during daily activities. Drinking: Drinking is defined as the animal action of taking water into the mouth, but to fluid mechanists, is simply one kind of fluid transport phenomena. Classical fluid mechanics show that fluid transport can be achieved by either pressure-driven or inertia-driven processes. In a similar fashion, animals drink water using pressure-driven or inertia-driven mechanisms. For example, domestic cats and dogs lap water by moving the tongue fast, thereby developing the inertia-driven mechanism. We will investigate how cats and dogs drink water differently and discuss the underlying fluid mechanics. Diving: We investigate how a soft elastic body responds to water-entry impact analogous to a bird diving into water to catch prey. Dumbbell shaped objects made of two acrylic spheres connected by an elastic rod are dropped into water. A buckling threshold was found by varying impact force and elastic rod stiffness. This threshold may have implication as to how birds are able to safely dive into water at high speeds and avoid any neck-injury. Bouncing: When two fluid jets collide, they can bounce off each other, due to a thin film of air which keeps them separated. We describe the stable non-coalescence phenomenon between two jets of the same fluid, colliding obliquely with each other. Using a simple experimental setup, we carry out a parametric study of the bouncing jets by varying the jet diameter, velocity, collision angle, and fluid viscosity, which suggests a scaling relation that captures the transition of colliding jets from bouncing to coalescence. This parameter draws parallels between jet coalescence and droplet splashing (crown-splash), indicating that the transition is governed by a surface instability. Upon time permitted, I will discuss other current on-going projects in my research group.

Host: E. Rericha

Thursday, February 6

Raju Venugopalan, Brookhaven National Laboratory

How does the violence of a heavy ion collision settle to the calm of a (nearly) perfect quark-gluon fluid?    (show abstract)

Hydrodynamics is "unreasonably effective" in describing bulk features of ultra relativistic heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) and at the Large Hadron Collider (LHC). The quark-gluon fluid that is produced is nearly perfect-- it flows about 10 times more smoothly than liquid Helium. We examine how the violent collision of ultra relativistic heavy ions at 0.9999997 the speed of light could produce such a perfect fluid on time scales of 10^{-23} seconds. We suggest that weak wave turbulence, observed in a variety of physical systems across wide energy scales, may be playing a bigger role in the thermalization process than previously understood.

Host: J. Velkovska

Thursday, February 13

Nadya Mason, Department of Physics, University of Illinois at Urbana-Champaign

In proximity to novel physics: Topological Insulators coupled to Superconductors   (show abstract)

Topological insulators (TI's) are materials that are insulators in their interiors, but have unique conducting states on their surfaces. They have attracted significant interest as fundamentally new electronic phases having potential applications from dissipationless interconnects to quantum computing. In particular, coupling the surface state of a TI to an s-wave superconductor is predicted to produce the long-sought Majorana quasiparticle excitations, which could play a role in solid-state implementations of a quantum computer. A requisite step in the search for Majorana fermions is to understand the nature and origin of the supercurrent generated between superconducting contacts and a TI. In this talk, I will discuss TI-superconductor junctions, focusing on transport measurements taken as the chemical potential is moved from the bulk bands into the band gap, or through the true topological regime characterized by the presence of only surface currents.

Host: K. Holley-Bockelman

Thursday, February 20

Junichiro Kono, Department of Electrical and Computer Engineering and Department of Physics and Astronomy, Rice University

Superfluorescence from a Quantum-Degenerate Electron-Hole Gas    (show abstract)

Quantum particles sometimes cooperate to develop an ordered state, where macroscopic coherence appears spontaneously. Here, we demonstrate that such spontaneous appearance of coherence occurs in an optically excited semiconductor quantum well in a high magnetic field [1-3]. When we create a dense electron-hole (e-h) plasma with an intense laser pulse, after a certain delay, an ultrashort burst of coherent radiation emerges. We interpret this striking phenomenon as a manifestation of superfluorescence (SF), in which a macroscopic polarization spontaneously builds up from an initially incoherent ensemble of excited quantum oscillators and then decays abruptly, producing giant pulses of coherent radiation. SF has been observed in atomic gases, but the present work represents the first observation of SF in a semiconductor, where not only real-photon exchange but also virtual-photon exchange (Coulomb interactions) is responsible for the formation of macroscopic coherence. We found that Coulomb interactions dramatically enhance and modify the collective superradiant decay of the e-h plasma. Unlike typical spontaneous emission from semiconductors, which occurs at the band edge, the observed SF occurs at the quasi-Fermi energy of the highly degenerate carrier distribution, up to 150 meV above the band edge. As the carriers are consumed by ultrafast radiative recombination, the quasi-Fermi energy goes down, and we observe a continuously red-shifting streak of SF at zero magnetic field and a series of sequential SF bursts from higher to lower Landau levels in a magnetic field. This Coulomb enhancement allows the magnitude of the giant dipole to exceed even the maximum possible value for ordinary SF (i.e., the total sum of in-phase oscillations of individual dipoles), making e-h SF even more "super" than atomic SF. 1. G. T. Noe et al., Nature Physics 8, 219 (2012). 2. G. T. Noe et al., Fortschritte der Physik 61, 393 (2013). 3. J.-H. Kim et al., Physical Review B 87, 045304 (2013).

Host: N. Tolk

Thursday, February 27---Jointly sponsored by EECS

RDML Timothy J. White, Tailored Access Operations, National Security Agency

Cybersecurity: dependency, consequence, and future (your) opportunity   (show abstract)

SUMMARY: An hour-long (or so) conversation about Cybersecurity placed in the context of national security. Increasingly interconnected, growing dependencies and commensurate vulnerabilities, cyberspace presents both consequence and opportunity for any nation. Some thoughts on why we should be concerned and ideas on what you can do. Assertions should be challenged and questions welcome.

Host: R. Scherrer

Thursday, March 6, Spring Break

Thursday, March 13

Maura McLaughlin, Department of Physics and Astronomy, West Virginia University

Building a Galactic Scale Gravitational Wave Observatory   (show abstract)

Timing an array of pulsars could result in the detection of a stochastic gravitational wave background, most likely resulting from an ensemble of supermassive black hole binaries, and is already constraining models for galaxy formation and the tension of cosmic strings. Pulsar timing arrays are also sensitive to continuous and burst gravitational wave sources. I will give an overview of the observational strategies and detection algorithms used for these various source classes. I will then describe the efforts of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), a collaboration which monitors an array of over 40 millisecond pulsars with the Green Bank Telescope and Arecibo Observatory. I will describe the dramatic gains in sensitivity that are expected from discoveries of many new millisecond pulsars, more sensitive instrumentation, improved detection algorithms, and international collaboration and discuss the likely time to gravitational wave detection using pulsar timing under various scenarios.

Host: K. Holley-bockelmann

Thursday, March 20

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Host:

Thursday, March 27---SLACK LECTURE

Freeman Dyson, Institute for Advanced Studies, Princeton, New Jersey

Four Revolutions and More to Come   (show abstract)

I was lucky to be a student just at the beginning of four revolutions that happened at the same time: space, nuclear energy, the genome, and computing. Space was the V2 rockets that Werner von Braun was dropping on our heads in London. Nuclear energy was the bombs in Hiroshima and Nagasaki. The genome was the experiment done by Oswald Avery at the Rockefeller Institute in New York, proving that DNA was the chemical basis of heredity. Computing was the ENIAC, the first electronic computer, built at the University of Pennsylvania to compute the trajectories of artillery shells. For the next sixty-five years I had a front seat, watching these four revolutions change the world and taking a minor part in each of them. I believe you students today have the same kind of opportunities that we had. The four revolutions are not finished. Space and nuclear may be slowing down, but the genome and computing are still speeding up. I see two new scientific revolutions coming in neurology and paleontology, the understanding of the brain, and the understanding of the evolution of human nature. Each of them will have profound effects and will open big opportunities. There are other revolutions beginning in technology. The shale gas revolution, distributing wealth and health more equitably over the planet,liberating us from excessive dependence on coal and oil. The manufacturing revolution that will begin when your generation has mastered the language of the genome, so that all kinds of industrial and consumer goods can be grown rather than made. It is up to your generation to make these things happen. My advice to you is, take chances and do not be afraid of failure. You are doing well if your fourth job is a success. Good luck to all of you!

Host: R. Scherrer

Thursday, April 3

John C. Angus, Department of Chemical Engineering, Case Western Reserve University

Diamond Synthesis: Then and Now   (show abstract)

Diamond synthesis by chemical vapor deposition has been a major advance in materials science. In this talk the birth pains, current status, and unanswered questions surrounding this technology are discussed. Following World War II there was a great surge of interest in high-pressure diamond synthesis in the United States, Sweden, and the former Soviet Union, which culminated with the announcement of success by General Electric in 1955. During this time period major efforts were also made in low-pressure, metastable synthesis. These efforts were characterized by great secrecy and a considerable lack of transparency. The first public reports of diamond syntheses at low pressure appeared in the 1960's. In addition to great scepticism about the veracity of these claims, a common view was that, even if true, growth rates were far too slow to be of interest. Also, many claimed that the process violated fundamental thermodynamic laws. These attitudes changed dramatically in 1984 when a Japanese group announced growth rates in the micron per hour range. Diamond grown by chemical vapor deposition is now a well-established technology with many diverse applications. Despite this major progress, significant unresolved issues and opportunities remain.

Host: N. Tolk

Thursday, April 10---FORMAN LECTURE

Wilton Virgo, Massachusetts Institute of Technology

Six Easy Bytes: Learning Physics Through Technology   (show abstract)

The globally connected science classroom has become mobile, interactive and cloud-based. MOOCs, apps, ebooks and scientific visualization have flipped the classroom and gamified academia, to the point where education and technology are now inseparable when it comes to pedagogy. How can the the great theory of quantum mechanics be brought to vibrant life by making connections to cutting-edge research, or to the ubiquitous devices that we interact with every day? In what ways do the use and understanding of technology enhance our capacity to wonder and effectively learn about the physical world? The lecture will move beyond the edubabble to construct an understanding of how technology has transformed STEM learning in our culture of science.

Host: N. Tolk

Thursday, April 17---SEYFERT LECTURE

Peter F. Michelson, Stanford University

The High-Energy Universe revealed by the Fermi Gamma-Ray Space Telescope   (show abstract)

The Fermi Gamma-ray Space Telescope images the entire sky every three hours. It has been doing this for more than 5 years and has revealed thousands of previously unknown high-energy gamma-ray sources both within the Milky Way galaxy and at cosmological distances that vary on timescales from milliseconds to years. These sources include active galaxies containing super massive black holes, rapidly spinning neutron stars (pulsars), supernova remnants, and high-energy gamma ray bursts. Fermi has revealed not only new sources and source classes, but has taught us unexpected new things about well-studied objects such as the Crab nebula. This talk begins with a brief reminiscence of how Fermi (then known as GLAST) was conceived of, then surveys the time-variable high-energy sky that Fermi has revealed, and concludes with a summary of unanswered questions (such as What is the nature of Dark Matter?) that future observations with the Fermi Observatory may answer.

Host: K. Holley-bockelmann

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