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Events: Departmental Colloquia

  • Joseph Lade Pawsey-Foundation of Australian Radio Astronomy in the 20thCentury-Sydney Australia

    Guest: W.M. Goss, Astronomer Emeritus, Former Director Very Large Array and the Very Long Baseline Array
    Thursday, March 22, 2018 3:30 pm - 4:30 pm
    Location: Physics Auditorium (202)

    In 1960 there were only 10 million people living in Australia, 45th in the world. Surprisingly, there were more radio astronomers (and associated engineers) than any other country. How was this possible? I will attempt to answer this remarkable achievement and show the impact that the Australians and British had in the decade 1945 to 1955, before the US began a massive program in radio astronomy. The Australians made numerous discoveries that changed the course of astronomy: the radio detection of the million degree solar corona, classification of the types of solar bursts, the invention of aperture synthesis (1945), the first earth rotation image (the quiet sun at 20 cm) and the identification of the first non-solar system objects with optical objects. Examples of the latter are the Crab Nebula, Virgo A and Centaurus A- NGC 5128 (in 1949). In addition, the first reliable all sky survey of a few thousand radio sources (at a wavelength of 3.5 m) by Mills and the elucidation of the spiral structure of the Milky Way using the newly discovered 21 cm hyperfine transition of HI (along with colleagues in the Netherlands). The major rivals of the Australians were the two groups in the United Kingdom at Cambridge and Manchester. The major cosmological conflicts between Ryle at Cambridge, a proponent of an evolving universe, and the steady state universe proposed by Hoyle, Bondi and Gold originated in 1954-1955; Mills in Sydney asserted that his source counts favoured a steady state universe.

    The founder of the Australian group was Joe Pawsey (1908-1962). Along with Prof Ron Ekers (past President of the International Union) and Dr Claire Hooker (historian of science at the University of Sydney), we are completing a book From the Sun to the Cosmos, J.L. Pawsey, Founder of Australian Radio Astronomy– to be published in 2020 and now 2/3 complete. Pawsey is one of the “big three” of radio astronomy in the post-war era: Sir Martin Ryle of the Cavendish Laboratory Cambridge (Nobel Prize Physics 1974), Sir Bernard Lovell of Jodrell Bank, University of Manchester. These three became the first radio astronomy Fellows of the Royal Society of London (Ryle-1951, Pawsey-1954 and Lovell-1955).

    I will also describe briefly three books about the history of Australian radio astronomy: two books about the first woman radio astronomer – Ruby Payne- Scott-in 2009 and 2013, and Four Pillars of Radio Astronomy: Mills, Christiansen, Wild, Bracewell in 2018. All are available via university library web sites on SPRINGERLINK for no cost. Numerous web sites about Ruby Payne-Scott are available on line.

    I became fascinated with the history of Australian radio astronomy when I moved to Australia as a postdoc over 50 years ago.

  • Dancing with Single Molecules; Single Molecules at Action under the Microscope

    Guest: Prof. Bingqian Xu, UGA College of Engineering
    Thursday, March 8, 2018 3:30 pm - 4:30 pm
    Location: Physics Auditorium (202)

    Single molecule studies, where science and engineering meet, apply the tools and measurement techniques of nanoscale physics and chemistry to generate remarkable new insights into how physical, chemical, and biological systems function. It permits direct observation of molecular behavior that can be obscured by ensemble averaging and enables the study of important problems ranging from the fundamental physics of electronic transport in single molecule junctions and biophysics of single molecule interactions, such as the energetics and non-equilibrium transport mechanisms in single molecule junctions and the energy landscape of biomolecular reactions, associated lifetimes, and free energy, to the study and design of single molecules as devices-molecular wires, rectifiers and transistors and high‐affinity, and anti‐cancer drugs. We have developed a Scanning Probe Microscopy (SPM) based nanotechnology toolbox to capture single molecules and tackle some of the thorniest problems that cannot be achieved otherwise. I will describe our studies using our pioneered highly integrated SPM-based approaches to (1) simultaneously fabricate, control, modulate, and monitor the electronic and mechanical properties of molecular junction devices at the single-molecule level. (2) Probe the biophysical mechanism of single‐molecule interactions, including the binding affinity and specificity. Our recent research examples will be used in the discussions.

  • The Road to Exascale Computing: Perspectives from a Computational Physicist

    Guest: Dr. Ying Wai Li, Oak Ridge National Laboratory
    Thursday, February 15, 2018 3:30 pm - 4:30 pm
    Location: Physics Auditorium (202)

    The next generation leadership-class high performance computer, Summit, will arrive at Oak Ridge National Laboratory by the end of the year of 2018. Summit is expected to deliver more than five times the computational performance of our current supercomputer, Titan. It will have a hybrid architecture, with each compute node containing multiple IBM POWER9 CPUs and NVIDIA Volta GPUs. As Summit brings us one step closer to Exascale computing, it will enable scientists to solve increasingly complex problems more efficiently. It will also provide opportunities to pioneer programming strategies and practices for high performance computing software development. What do these emerging technologies mean to physics and materials science research? What are the considerations when designing computer algorithms and developing scientific software to unleash the power of a gigantic computer like Summit? In this colloquium, I will share my experiences and insights on these questions, demonstrated through a few frontier research problems in computational physics and materials science.
  • Current Advances in Spinterface and Spin Transport in Organic Spin Valves

    Guest: Professor Tho Nguyen, UGA Physics and Astronomy
    Thursday, January 11, 2018 3:30 pm - 4:30 pm
    Location: Physics Auditorium (202)

    Organic spin valves (OSVs), which are comprised of an organic spacer sandwiched between two ferromagnetic (FM) electrodes, have attracted great attention from scientific community in the past 16 years. Such spin valve structures using inorganic spacers have revolutionized magnetic memory and sensor application. Magnetoresistance (MR) response in OSVs generally relies on the spin injection/detection at the FM/organic interface (dubbed spinterface), and the spin diffusion length in the organic spacer. Organic semiconductors (OSEC) possess weak hyperfine interaction and spin-orbit coupling, and hence long spin lifetime. The spin transport is due to π-orbital electrons in OSECs which are comprised of light-weight elements such as hydrogen and carbon. Therefore, they have been thought to possess considerably long spin diffusion length, suitable for obtaining larger MR in OSVs. However, in conventional OSVs, the interface between the organic and FM electrodes, and the structural order of the organic interlayer are poorly controlled because epitaxial growth is not possible for OSECs. Therefore, the spinterface effect and spin transport in these devices are complicated, and their complete understanding has remained elusive. In this talk, I will discuss the current advanced studies in our group for understanding and manipulating the spinterface effect and spin transport in OSVs. In particular, for the spin transport, we will show the statistical origin of the hyperfine interaction strength and the existence of curvature induced spin-orbit coupling in OSECs. For the spin injection/detection, we will present several methods to manipulate the spinterface effect. These include the use of self-assembled monolayers (SAM) at the interface, an organic ferroelectric insulator for the spacer, and organic/FM/organic triple layers for the spacer.

  • Interpretation and Misinterpretation of Newton’s Second Law for Variable Mass Systems

    Guest: Prof. Kanzo Nakayama, Department of Physics and Astronomy, UGA
    Thursday, November 16, 2017 3:30 pm - 4:30 pm
    Location: Physics Auditorium (202)

    Misinterpretation of Newton’s Second Law for variable mass systems currently found in the literature is addressed. In particular, it is shown that Newton’s Second law in the form F = dp/dt is valid for variable mass systems in general, contrary to the claims by some authors that it is not.
  • The Arcus Soft X-ray Grating Explorer

    Guest: Dr. Randall Smith, Smithsonian Astrophysical Observatory, Harvard
    Thursday, November 2, 2017 3:30 pm - 4:30 pm
    Location: Physics Auditorium (202)

    The Large Scale Structure (LSS) of the Universe grew via the gravitational collapse of dark matter, but the visible components that trace the LSS-galaxies, groups and clusters-have a more complex history. Their baryons experience shock heating, radiative cooling and feedback from black holes and star formation, which leave faint signatures of hot (T~10^5-10^8 K), metal-enriched gas in the interstellar and intergalactic media (ISM and IGM). While recent Planck and X-ray studies support this scenario, no current mission possesses the instrumentation necessary to provide direct observational evidence for these “missing baryons.” Arcus leverages recent advances in critical- angle transmission (CAT) gratings and silicon pore optics (SPOs), using CCDs with strong Suzaku heritage and electronics based on the Swift mission; both the spacecraft and mission operations reuse highly successful designs. Currently in a competitive Phase A and with a potential launch in 2023, Arcus will be the only observatory capable of studying, in detail, the hot galactic and intergalactic gas-the dominant baryonic component in the present-day Universe and ultimate reservoir of entropy, metals and the output from cosmic feedback. Its superior soft X-ray sensitivity will complement the forthcoming post-Hitomi and Athena calorimeters, which will have comparably high spectral resolution above 2 keV but poorer spectral resolution than XMM or Chandra in the Arcus bandpass.

  • Metal Chalcogenide Materials and Applications

    Guest: Professor Tina T. Salguero, Department of Chemistry, UGA
    Thursday, October 19, 2017 3:30 pm - 4:30 pm
    Location: Physics Auditorium (202)

    Metal chalcogenide materials have extraordinarily diverse structural and electronic properties. This talk will focus on our recent work with metal dichalcogenide and trichalcogenide compositions that exhibit metallic properties and charge density wave behavior, including TaSe2, TaSsub2, TaSe3, and NbS3. These materials can be exfoliated into nanosheets or nanoribbons, which can form the basis of nanostructured devices with special applications in the area of radiation-resilient electronics.
  • ITER: The Next Step Towards Realizing Fusion

    Guest: Dr. Mark Henderson, ITER, St. Paul-Les-Durrance, France
    Monday, September 11, 2017 3:30 pm - 4:30 pm
    Location: Physics Auditorium (202)

    The International Thermonuclear Experimental Reactor, or ITER, is being built in the south of France by an international collaboration of seven countries (US, EU, Japan, South Korea, India, China and Russia). ITER is a culmination of over 50 years of research in fusion and aims at producing a 10 fold gain in energy output, which will provide the necessary physics basis to then design and build demonstration reactors targeting a >40 fold gain. This talk will cover the basics of fusion energy and an overview of the ITER project. In addition, a brief description will be provided of the heating and current drive systems used to generate the 150 million degree temperatures required for sustaining the fusion reaction.
  • Stochasticity and Synchronization of Single-Cell Biological Clocks

    Guest: Prof. Bernd Schuttler, UGA Department of Physics and Astronomy, Institute of Bioinformatics, CSP
    Thursday, August 31, 2017 3:30 pm - 4:30 pm
    Location: Physics Auditorium (202)

    Oscillators, by virtue of their periodic dynamics, provide a way to tell time, as illustrated by the periodic movement of a clock’s pendulum. The study of coupled oscillators and their mutual synchronization has remained a problem central to physics for centuries, but has also captured the imagination of biologists in recent times. One example of synchronized oscillators are the circadian biological clocks found in the living cells of many organisms. Biological clocks are pervasive in their effects from genes to ecosystems. Biological clocks affect the health of animals and plants and they are being engineered for timed delivery of therapeutics, algal bioreactors for biofuel production, and crop improvement. The clock, through its light entrainment feature, impacts the genetic dynamics of bacterial assemblages in the world’s oceans and hence may affect carbon cycling in marine ecosystems. Understanding how cell populations synchronize their clock oscillations, to give rise to a fully functional “biological clock”, is therefore of substantial interest in current systems biology research. In this lecture, I will review our past experimental and modeling studies of the gene regulatory system dynamics of the biological clock in the filamentous fungus Neurospora crassa at the level of macroscopic cell populations. I will then discuss recent micro-fluidics-based experiments on the N. crassa biological clock, and its stochastic modeling, at the single-cell and few-cell level. In these experiments, one or a few cells are isolated inside small water droplets immersed in oil. Time series of fluorescent signals from clock-controlled (CCG) gene products are recorded for each individual cell. Detailed noise propagation analyses of these time series reveal that the biological clock module of single, isolated cells is strongly stochastic, with a broad power spectrum (periodogram) peaked at near-circadian (~22h) oscillation periods. At the few-cell level, statistical analysis of observations from 2-cell to 15-cell droplets demonstrate that the clocks become highly correlated when confined in close spatial proximity within the same aqueous droplet, suggesting that these correlations may be the precursor to the fully developed coherent clock oscillations observed in large cell populations. Ensemble network simulations (ENS) are performed on stochastic chemical reaction network models of single- and multiple-cell systems. The ENS results show that clock models with Gillespie-type stochastic reaction kinetics and a quorum sensing inter-cell communications are generally consistent with the experimental single- and few-cell data. Experimental searches are currently under way to identify possible diffusible exo-metabolites which could mediate such quorum-sensing inter-cell communications. Lastly, I will also discuss the light entrainment effects observed in single cells subjected to periodic on-off-illumination and their relation to the light entrainment seen in macroscopic cell populations.
  • Cusp Catastrophes and Neural Computing

    Guest: Prof. Andrew Sornborger, Department of Mathematics, UC Davis
    Thursday, April 27, 2017 3:30 pm - 4:30 pm
    Location: Physics Auditorium (202)

    The literature on information processing in neural systems is dominated by a focus on learning. Recent results have shown amazing computational abilities, in many cases with superhuman performance. Computers have been able to learn to play Atari games and Go better than we can. These successes have been based on so-called deep networks, caricatures of real, spiking neuronal networks. The work that I will present will focus on a different, but important topic in neural information processing: how the brain dynamically routes information from process to process. This ability may be seen in our ability to rapidly switch between different lines of thought. Line attractors in neural networks have been suggested to be the basis of many brain functions involving the propagation of spiking rate amplitudes, such as working memory, oculomotor control, head direction, locomotion, and sensory processing. I will discuss how, by incorporating pulse gating into feedforward neuronal networks, the propagation of information may be controlled and dynamically routed. I will show that spiking rate amplitude transmission in pulse-gated networks is associated with the existence of a cusp catastrophe, and that the slow (ghost) dynamics near the fold of the cusp underlies the robustness of an approximate line attractor that enables faithful amplitude propagation. Finally, I will demonstrate how pulse gating in combination with Hebbian learning can be used to construct predictive neural circuits and how such circuits generate oscillations with a characteristic frequency spectrum.
  • Cusp Catastrophes and Neural Computing

    Guest: Prof. Andrew Sornborger, Department of Mathematics, UC Davis
    Thursday, April 6, 2017 3:30 pm - 4:30 pm
    Location: Physics Auditorium (202)

    The literature on information processing in neural systems is dominated by a focus on learning. Recent results have shown amazing computational abilities, in many cases with superhuman performance. Computers have been able to learn to play Atari games and Go better than we can. These successes have been based on so-called deep networks, caricatures of real, spiking neuronal networks. The work that I will present will focus on a different, but important topic in neural information processing: how the brain dynamically routes information from process to process. This ability may be seen in our ability to rapidly switch between different lines of thought. Line attractors in neural networks have been suggested to be the basis of many brain functions involving the propagation of spiking rate amplitudes, such as working memory, oculomotor control, head direction, locomotion, and sensory processing. I will discuss how, by incorporating pulse gating into feedforward neuronal networks, the propagation of information may be controlled and dynamically routed. I will show that spiking rate amplitude transmission in pulse-gated networks is associated with the existence of a cusp catastrophe, and that the slow (ghost) dynamics near the fold of the cusp underlies the robustness of an approximate line attractor that enables faithful amplitude propagation. Finally, I will demonstrate how pulse gating in combination with Hebbian learning can be used to construct predictive neural circuits and how such circuits generate oscillations with a characteristic frequency spectrum.
  • Thank God for Nonlinearity. A 30,000 Feet View of the Nonlinear Dynamics of Many Particle Systems.

    Guest: Prof. Surajit Sen, Department of Physics, State University of New York at Buffalo
    Thursday, March 30, 2017 3:30 pm - 4:30 pm
    Location: Physics Auditorium (202)

    Nonlinear dynamics is about 400 some years old. European monarchs of the time cared about their ships surviving the rough Atlantic waves and thus Euler, Lagrange, Newton, Cauchy and many others worked on nonlinear wave equations (which presumably predate the linear wave equation!). In the nineteenth and twentieth centuries, nonlinear systems have been worked on in terms of continuum equations and we know that many of these (integrable) equations admit so-called soliton solutions where solitons are traveling, non-dispersive lumps of energy (almost like quanta but classical). In 1955, Fermi-Pasta-Ulam-Tsingou studied a nonlinear mass-spring chain and showed that the system has great trouble equilibrating. In 1983, Nesterenko first examined impulse propagation through an alignment of elastic grains and showed these systems too support solitons/solitary waves. Does the perturbed granular chain system equilibrate? What does it physically mean to have a non-integrable system? And why do we even care? The talk will touch upon the history and the current state of nonlinear physics of many particle systems and what all this physics can give us in terms of new scientific insights and novel technology.

    Parts of this work has been supported over time by the National Science Foundation and the Army Research Office. Many of the calculations have been done on the supercomputers at the Center for Computational Research at SUNY Buffalo.

  • Laboratory Astrophysics at Tokyo Metropolitan University

    Guest: Prof. Hajime Tanuma, Department of Physics, Tokyo Metropolitan University
    Thursday, March 23, 2017 3:30 pm - 4:30 pm
    Location: CSP Conference Room (322)

    At Tokyo Metropolitan University, three distinct experimental techniques are being deployed to study ionic and molecular processes relevant to astrophysics.

    A facility for multiply charged ion beam experiments with a 14.25 GHz electron cyclotron resonance ion source is used to measure charge exchange cross sections in collisions of multiply charged ions with neutral gases and to observe photon emission spectra under soft X-ray, extreme ultraviolet, and UV-visible irradiation. Currently we are interested in both solar wind charge exchange phenomena and spectroscopic data needed for the fusion reactor ITER.

    Our electrostatic ion storage ring, which was constructed in 2004 as the world’s third such device, is a facility that has become popular among atomic and molecular physicists. Using this ring, we have studied cooling processes of hot (around 3000 K) molecular and cluster ions, produced in an ion source. We have also performed experiments for C6H-, which is found in interstellar clouds, and small carbon anions.

    In a low temperature ion drift tube mass spectrometer, which can be operated at 4.3 K by using liquid helium, the mobility of atomic and small molecular ions in helium gas has been measured and the formation of helium cluster ions has been observed. We have observed elastic cross sections between molecular ions and He larger than the Langevin limit at very low energies. This phenomena might contribute to chemical evolution in interstellar clouds.

  • The Stratospheric Observatory For Infrared Astronomy (SOFIA): Studying the Universe while Traveling at Mach 0.85

    Guest: Dr. James De Buizer, Stratospheric Observatory For Infrared Astronomy, NASA Ames Research Center
    Thursday, March 2, 2017 3:30 pm - 4:30 pm
    Location: Physics Auditorium (202)

    SOFIA is an airborne observatory that consists of a 2.7m telescope mounted in a heavily modified Boeing 747 aircraft. Flying at altitudes up to 45000 feet, SOFIA can get above enough of the atmosphere to open up a broad swath of infrared wavelengths for scientific investigation which are completely unobservable from the ground. SOFIA has a large suite of science instruments covering a broad range of wavelengths and spectral resolutions, which make the observatory capable of performing a huge breadth of astronomical science from the optical to far-infrared. SOFIA is just beginning its 5th annual observing cycle, and has already produced a host of interesting science results. In this talk, I will discuss what makes this such a unique observatory in both form and function, and will highlight some of the more interesting science results obtained so far.
  • Nanoscopy of Anisotropic Black Phosphorous

    Guest: Prof. Y. Abate, Center for Nano-Optics (CeNO), Department of Physics and Astronomy, Georgia State University
    Thursday, February 16, 2017 3:30 pm - 4:30 pm
    Location: Physics Auditorium (202)

    Nanolayered and two-dimensional materials such as graphene, boron nitride, transition metal dichalcogenides, and black phosphorus have intriguing physical properties and bear promise of important applications. Of them, black phosphorus has unique electronic properties due to its anisotropic structure and highly tunable band gap both by number of monolayers and by surface doping. I will discuss our recent experimental investigation and theoretically interpretation of anisotropic near-field properties of a few-atomic monolayer nanoflakes of black phosphorus. We have discovered near-field patterns of outside bright fringes and high surface polarizability of nanofilm black phosphorus consistent with its surface-metallic behavior at mid-infrared frequencies. The major impediment to research and prospective application of single/few-layer black phosphorus is its chemical degradation under ambient conditions. I will present our experimental quantification of geometric properties and theoretical modeling of the chemical degradation process of black phosphorus as well as investigation of the effectiveness of passivation coatings using infrared nanoscopy.
  • The World’s Smallest Extreme Laboratories: Probing QED with Highly Charged Ions

    Guest: Prof. Joan Marler, Department of Physics and Astronomy, Clemson University
    Thursday, February 9, 2017 3:30 pm - 4:30 pm
    Location: Physics Auditorium (202)

    Highly charged ions (HCIs) are atoms in which all or most of the electrons have been stripped off. The remaining few (or one) electrons exist in the presence of the strong electric field generated from the nucleus. In the case of fully stripped Uranium this field is 1016 V cm-1, orders of magnitude stronger than any external field available in a laboratory. These ultra strong fields make HCIs ideal mini laboratories in which to test physical theories in extreme conditions.

    Quantum Electrodynamics (QED) is an extremely powerful and predictive theory describing the interaction of matter and light especially at low energy. However, in the instances where experimental and theoretical results differ there is an opportunity to study non-standard model physics. HCIs are also promising candidates for next generation atomic clocks and searches for time variation in the fundamental "constants". Additionally, while HCIs are rare on Earth, they are commonplace in the universe, in particularly in the high temperature and pressure environments of stars and solar winds. Understanding how to read the photon signature from interactions of HCIs with neutral gases in the universe gives information on the density, temperature and constituents of both.

  • Molecular Astrophysics: Cool Stars and Exoplanets

    Guest: Prof. Peter Bernath, Department of Chemistry and Biochemistry, Old Dominion University, Norfolk, VA
    Thursday, January 26, 2017 3:30 pm - 4:30 pm
    Location: Physics Auditorium (202)

    The spectra of "cool" astronomical objects such as low mass stars, brown dwarfs and exoplanets are dominated by molecular absorption features. Of particular interest are methane, water, ammonia and diatomic hydrides at high temperatures. An overview of this area of molecular astronomy will be presented from a spectroscopic perspective. The talk will include emission and absorption laboratory measurements of hot molecules by Fourier transform spectroscopy as related to exoplanets.
  • The Dark Side of H<sup>2</sup> in the Galaxy:  The Empire Strikes Back

    Guest: Prof. Loris Magnani, Department of Physics and Astronomy, The University of Georgia
    Thursday, January 19, 2017 3:30 pm - 4:30 pm
    Location: Physics Auditorium (202)

    The idea that substantial molecular gas is present in the interstellar medium but is not detectable by the CO(1-0) emission line has become fairly prevalent in the last decade. This component hasbecome known as "dark gas", a term first suggested in a paper describing its properties and extent by Grenier, Casandjian and Terrier (2005). Their main conclusion is that the dark gas mass in the Milky Way is comparable to the molecular mass detected by CO(1-0) emission. More recent studies seem to corroborate this conclusion. A key element in deciding whether molecular gas may be dark or not depends on thesensitivity of the CO observations. Here we present very sensitive CO, OH, and CH observations of the outer regions of diffuse molecular gas which show that most of the dark molecular gas can be spectroscopically detected with sensitive enough observations.
  • High Quality Computation of Selective Atomic and Molecular Processes

    Guest: Brendan M. McLaughlin, Centre for Theoretical Atomic, Molecular and Optical Physics, Queen’s University of Belfast
    Thursday, December 1, 2016 3:30 pm - 4:30 pm
    Location: CSP Conference Room (322)

    Photoionization of atomic and molecular species is an important process in determining the ionization balance and hence the abundances of elements in astrophysical nebulae. It has recently become possible to detect neutron-capture elements (atomic number Z>30) in a large number of ionized nebulae. Accurate assessment of elemental abundances in astrophysical nebulae can be made from the direct comparison of the observed spectra with synthetic non-local thermodynamic equilibrium (NLTE) spectra, if the atomic data for electron and photon interaction processes are known with sufficient accuracy. Experiments on light systems, trans-Fe elements and molecules at third generation synchrotron radiation source, such the Advanced Light Source (ALS) in Berkeley, California, USA, SOLEIL in Saint-Aubin, France, ASTRID II in Aarhus, Denmark and PETRA III, in Hamburg, Germany, require high quality theoretical studies to interpret experimental results. Results will be presented from recently developed ab initio R-matrix methods for atomic and molecular systems using parallel computing architectures. Photoionization cross sections will be presented for a variety of atomic species; Se, Kr, Ar, Xe, W, Si, S, Cl, C, N, and O, in neutral or low stages of ionization. Comparison of our theoretical results with experiments performed at leading synchrotron light sources serve as the ultimate benchmark for theory, in order to have confidence in the atomic and molecular data being incorporated into astrophysical modelling codes such as CLOUDY, XSTAR, CHIANTI and ATOMDB.
  • Unlocking the Potential of Multiply-Charged Ions

    Guest: Prof. Chad E. Sosolik, Department of Physics and Astronomy, Clemson University
    Thursday, October 6, 2016 3:30 pm - 4:30 pm
    Location: Physics Auditorium (202)

    In this talk I will discuss multi- to highly charged ions, and the broad range of physical problems, both fundamental and applied, where they appear. This will include an introduction to the Clemson University Electron Beam Ion Trap (EBIT) laboratory, where you can gain local access (less than 120 km from Athens-to-Clemson) to multiply charged ions, an otherwise unique form of matter common to the universe at large but extremely rare on Earth. As a historical tool, EBITs were designed for ground-based spectroscopy, as they provide one of the few ways of controllably testing astrophysical models in a tunable environment while probing atomic structure along the way. This interest in terrestrial astrophysics has led to the development hybrid EBITs as ion sources where extracted “beams” of ions are used to study gas, dust and ice interactions and provide data for modelling charge exchange and hollow atom decay processes. While EBITs owe their design to this astrophysical connection-to-reality, they have also opened the door for curiosity driven materials studies that have revealed unique "hillock" structures formed by ion impacts and they have led to new technology areas in modified materials, surface cleaning, self-guiding capillaries, and single ion implantation.
  • A Golden Lesson from Nature: The Origin of Nonequilibrium Surface Roughening in Thin Film Growth

    Guest: Professor Fereydoon Family, Department of Physics, Emory University, Atlanta
    Thursday, September 29, 2016 4:00 pm - 5:00 pm
    Location:

    Nature has given us tremendous inspirations since the beginning of the human civilization. Scientific progress has resulted often when new experiments have directly contradicted a well-established and verified theory. In this talk I will discuss an example of how progress was made in understanding the growth of thin films by molecular beam epitaxy when a seemingly paradoxical challenge was presented to existing theories that had been developed over a period of more than three decades. I will present an overview of the problem and how theory, simulation and experiments all played an important role in resolving this challenging problem.
  • Quantum Computing with Trapped Ions

    Guest: Prof. Kenneth Brown, Georgia Institute of Technology
    Thursday, September 22, 2016 3:30 pm - 4:30 pm
    Location: Physics Auditorium (202)

    Quantum computation promises an exponential algorithmic speed up over classical computation. Currently quantum computing hardware is limited by errors in the control and unwanted interactions with the environment. I will present our theoretical and experimental work on removing both control and algorithmic errors in ion trap quantum processors. I will also discuss proposals for scaling ion trap quantum computers from 10's to 100's of qubits.
  • Stark and Zeeman Spectroscopy of Open Shell Molecular Complexes in Helium Nanodroplets

    Guest: Prof. Gary E. Douberly, University of Georgia, Department of Chemistry
    Thursday, September 1, 2016 3:30 pm - 4:30 pm
    Location: Physics Auditorium (202)

    Pyrolytic decomposition of tert-butyl hydrogen peroxide has proven to be an efficient source for doping helium droplets with the hydroxyl radical (OH). Several OH containing molecular complexes have been stabilized in helium droplets following the sequential pick-up of OH and a closed shell molecular species. We have probed the geometric and electronic structures of these systems with infrared laser Stark and Zeeman spectroscopy, employing homogenous DC electric and magnetic fields applied to the laser-droplet beam interaction zone. For example, the T-Shaped OH—C2H2 complex has been probed via excitation of the OH and antisymmetric CH stretch modes. Partial quenching of orbital angular momentum upon complex formation results in parity splitting of rotational levels, which is fully resolved in the helium droplet spectra. A model Hamiltonian for the Stark effect for systems exhibiting partially quenched electronic angular momentum is employed to extract from experimental Stark spectra the permanent electric dipole moment for this system. Moreover, a model Zeeman Hamiltonian is derived, which allows for an analysis of coupling of the partially quenched electronic angular momentum to the external magnetic field and the associated gL and gS factors, which are apparently unaffected by the helium solvation environment. An IR-IR double resonance experiment with picosecond time resolution is proposed that will allow for an investigation of vibrational energy flow, vibrational pre-dissociation, and vibrational excitation-induced reaction in systems of this type.
  • Revisiting Decades-Old Physics to Improve Modern Molecular Imaging

    Guest: Prof. Warren S. Warren, Duke University
    Thursday, March 24, 2016 3:30 pm - 4:30 pm
    Location: Physics Auditorium (202)

    Molecular imaging-the use of chemical signatures to image function instead of merely structure-promises to enable a new generation of clinical modalities that can revolutionize both diagnosis and treatment. I will focus on two specific modalities-magnetic resonance and optical imaging-and discuss how a close coupling between basic physics on the one hand, and focused clinical questions on the other hand, enable new and important applications. In magnetic resonance, one of the most startling results of the last few decades was our work that showed coherences survive at room temperature between pairs of nuclear spins separated by many microns or millimeters. This gives insight into fundamental questions in quantum mechanics, such as the differences between coherence, correlation and entanglement; it also lets us image temperature in vivo, measure local anisotropy, and detect tissue activation. We have used fundamental symmetries in spin physics to populate states which are immune to most relaxation mechanisms (and thus persist for minutes to hours). Coupled with a new catalytic approach to enhance molecular magnetization by about a factor of 100,000 over thermal values, this can improve the molecular information in clinical imaging. In optics, our lab developed femtosecond pulse shaping technologies two decades ago. Today we know that the "killer application" is to access intrinsic nonlinear signatures at exceedingly low powers (less average power than a laser pointer). This makes it possible to gain image contrast from effects that were not previously observable in soft matter, such as excited state absorption, ground state depletion, and cross phase modulation. Applications to imaging hemoglobins and melanins in tissue to detect and assess cancer will be highlighted; I will also present work on nonlinear imaging of historical pigments in Renaissance paintings to infer the artist’s original colors and intent.
  • The Baryon Spectroscopy Program at JLAB

    Guest: Prof. Michael Doering, George Washington University
    Thursday, March 17, 2016 3:30 pm - 4:30 pm
    Location: Physics Auditorium (202)

    The strong interaction still provides mysteries to us, like the generation of mass and the fact that the most elementary particles --quarks and gluons-- cannot be directly observed. Measuring so-called baryonic resonances to shed light on these 40-years old problems, is a large-scale experimental effort at the Jefferson National Accelerator Facility (JLab). An overview of present and future JLab activities will be given, focused on the question of how to connect observations to theory. In particular, first results and their analysis from the Frozen Spin Target (FroST) Lab will be discussed.

    Conclusive answers in baryon spectroscopy are a long-sought goal. Necessary steps towards this goal will be discussed, such as statistical criteria, the need for hadron beams, and the need for a suitable amplitude parameterization to make the connection to (ab-initio) lattice QCD approaches. The material will be presented for a broader audience.

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