|Date||Host||Speaker||Title of the talk||Abstract|
|Feb. 7||Hor||Dr. Haskell Taub
University of Missouri - Columbia
Study of water diffusion on single-supported bilayer lipid membranes by neutron scattering
Neutron scattering and molecular dynamics simulations have been used to elucidate the diffusion of water molecules associated with single bilayer lipid membranes supported on a silicon substrate. This system serves as a physicist's model of biological membranes that surround all living cells. Knowledge of the water motion is important for understanding the membrane function. We first characterize the structure of our supported membranes as a function of temperature using Atomic Force Microscopy. We then perform high-energy-resolution quasielastic neutron scattering experiments at the NIST Center for Neutron Research and the Spallation Neutron Source at Oak Ridge National Laboratory on similarly prepared samples. By varying both membrane temperature and level of hydration, we find evidence of three different types of water motion: bulk-like, confined, and bound. The motion of bulk-like and confined water molecules is fast compared to those bound to the head groups of the lipid molecules, which move on the same nanosecond time scale as H atoms in the lipid molecules.
Bio: Dr. Taub is a member of the Department of Physics & Astronomy at the University of Missouri, Columbia. He received his B.S. from Stanford, his Ph.D. from Cornell, and did postdoc work at New York University. While working at Brookhaven National Laboratory, Dr. Taub was introduced to neutron scattering research and has since been conducting experiments to study the structure, phase transitions, and dynamics of adsorbed films. Currently, he is leading a large NSF-funded project aimed at training the next generation of scientists and engineers in neutron scattering research.
|A Hammett correlation for design of polymer-particle dielectric interfaces||
Polymer-ceramic nanocomposites are promising dielectrics for electronic and power devices, which in theory combine the high dielectric constant of ceramic particles with high dielectric breakdown strength (DBS) of polymer. Self-assembled monolayers (SAM) of electron-rich or -poor organophosphate coupling groups were applied to ferroelectric nanoparticles to investigate the role of functionalized interfaces on composite behavior, in particular the leakage current and DBS. The composite films synthesized from the modified filler particles dispersed into an epoxy polymer matrix were analyzed by dielectric spectroscopy, DBS, and leakage current measurements. The analysis results indicated that significant reductions in leakage current and dielectric loss and improvement in DBS resulted only when electropositive, electron-scavenging functional groups were located at the polymer-particle interface. The electronic effect of the organophosphate SAM at the polymer-particle interface was correlated through a Hammett relationship to leakage current and DBS. The Hammett relationship indicated surface group polarity and/or electron delocalization contribution(s) affected dielectric properties. The correlation of only polarity Hammett substituent constants suggested that only polarity, i.e. the electron density of the substituent affected dielectric properties. Correlations were not observed for either combined para- or resonance-effect Hammett substituent constants. A Hammett correlation may provide useful guidance in design of interfaces to improve electrical properties and future generation electrostatic capacitors, piezo or pyroelectric devices, etc.
|Feb. 21||Hor||Dr. Weida Wu
Topological defects in hexagonal manganites: from multiferroics to cosmology
Topological defects, such as domain walls and vortices, are pervasive in complex matter such as superfluids, liquid crystals, the earth’s atmosphere, and the early universe [1, 2]. Topological defects have been fruitful playgrounds for emergent phenomena [3, 4]. Recently, vortex-like topological defects, called magnetic skyrmions, were observed in helical magnets with broken inversion symmetry . The interplay between the topological spin texture of skyrmions and the spins of conduction electrons may lead to novel spintronic applications . Multiferroics are materials with coexisting magnetic and ferroelectric orders, where inversion symmetry is also broken. The cross-coupling between two ferroic orders can result in strong magnetoelectric coupling. Therefore, it is of both fundamental and technological interest to visualize cross-coupled topological defects in multiferroics. Indeed, topological defects with six interlocked structural antiphase and ferroelectric domains merging into a vortex core were revealed in multiferroic hexagonal manganites [8, 9]. Numerous vortices are found to form an intriguing self-organized network, and may be used to test Kibble-Zurek model of early universe . Many emergent phenomena, such as conduction and piezoelectric properties, were observed in charged ferroelectric domain walls protected by these topological defects [11-13]. More interestingly, unprecedented alternating uncompensated magnetic moments were discovered at coupled antiferromagnetic-ferroelectric domain walls in hexagonal manganites, which paves the way for potential multifunctional applications of cross-coupled domain walls .
1. Chaikin, P.M. and T.C. Lubensky, Principles of Condensed Matter Physics. 2000, Cambridge, UK: Cambridge University Press.
2. Fraisse, A.A., C. Ringeval, D.N. Spergel, and F.R. Bouchet, Small-angle CMB temperature anisotropies induced by cosmic strings. Phys. Rev. D, 78, 043535, (2008).
3. Seidel, J., et al., Conduction at domain walls in oxide multiferroics. Nat. Mater., 8, 229 - 234, (2009).
4. Mesaros, A., et al., Topological Defects Coupling Smectic Modulations to Intra-Unit-Cell Nematicity in Cuprates. Science, 333, 426-430, (2011).
5. Yu, X.Z., et al., Real-space observation of a two-dimensional skyrmion crystal. Nature, 465, 901-904, (2010).
6. Pfleiderer, C. and A. Rosch, Nature, 465, 880-881, (2010).
7. Cheong, S.W. and M. Mostovoy, Multiferroics: a magnetic twist for ferroelectricity. Nat. Mater., 6, 13-20, (2007).
8. Choi, T., et al., Insulating interlocked ferroelectric and structural antiphase domain walls in multiferroic YMnO3. Nature Materials, 9, 253, (2010).
9. Jungk, T., Á. Hoffmann, M. Fiebig, and E. Soergel, Electrostatic topology of ferroelectric domains in YMnO3. Appl. Phys. Lett., 97, 012904, (2010).
10. Griffin, S.M., et al., From multiferroics to cosmology: Scaling behaviour and beyond in the hexagonal manganites. arXiv:1204.3785, (2012).
11. Lochocki, E.B., et al., Piezoresponse force microscopy of domains and walls in multiferroic HoMnO3. Appl. Phys. Lett., 99, 232901, (2011).
12. Meier, D., et al., Anisotropic conductance at improper ferroelectric domain walls. Nature Materials, 11, 284–288, (2012).
13. Wu, W., et al., Conduction of topologically-protected charged ferroelectric domain walls. Phys. Rev. Lett., 108, 077203, (2012).
14. Geng, Y., et al., Collective Magnetism at Multiferroic Vortex Domain Walls. Nano Letters, 12, 6055−6059, (2012).
|Feb. 28||Bieniek||Dr. Annick Suzor-Weiner
French Embassy, Washington, DC.
Higher Education and Research in Science and Technology : a tool for Diplomacy and facing together Global Challenges
As the challenges we are all facing (e.g. health, environment and climate change, energy, cyber-security…) become more and more global, Science and Technology become more international and try to offer global solutions. Universities are the main actors of this common endeavor, and of the new "Science Diplomacy" which can help in many ways the progress towards peace and development.
With the example of the Office for Science and Technology at the Embassy of France, these new trends will be illustrated and the most efficient ways to help creating a global network of young "science diplomats" will be explored.
|Mar. 7||Vojta||Dr. Nandini Trivedi
Ohio State University
Cold Atoms Meets Condensed Matter Physics
Cold atoms in optical lattices are emerging as emulators of model Hamiltonians that describe complex materials. It is possible to tune the interactions, dimensionality, spin, statistics and a host of other variables in a completely disorder free environment. This has opened up unique possibilities of mapping out phase diagrams of quantum models and observing quantum phase transitions for the very first time. I will address several challenges such as: How do we probe the cold atoms? How do we measure their temperature? How do we characterize the phases?
||Hor||Dr. Craig Fennie
|Apr. 11||Jentschura||Dr. Robert Ehrlich
George Mason University
Climate for Energy Change: the urgent need to transition away from fossil fuels [+ 15 min on new evidence for tachyonic neutrinos]
Although the consensus of climate scientists is that a significant fraction of global warming is human-caused, there is a rising level of public polarization about the matter. Here I will discuss several reasons for this divide, and how clean energy can be the bridge across the political chasm to deal with the matter in a way that is sound both politically and technologically. We will also discuss other reasons besides climate change to move away from fossil fuels, and the advantages and drawbacks of renewable energy. Finally, we address some comments to students why they should consider entering the field and to faculty so as to promote support for an undergraduate minor in renewable energy. [In a separate 15 min segment I discuss some new evidence for tachyonic neutrinos from cosmology.]
* Please view Dr. Robert Ehrlich's video about tachyonic neutrinos.
|Apr. 18||Schulz||Dr. William McComas
University of Arkansas - Fayetteville
|The Nature of Biology: A View of the Life Sciences through a Philosophical Lens||This talk will address the science of biology as a special case within the larger domain of the philosophy of science. Such an examination is enlightening as a case study because the focus on biology will reveal that, although there are shared principles that cut across all the science, each scientific discipline exemplifies these shared principles in distinct and unique ways. To investigate the nature of biology we will explore questions such as: Is biology an autonomous and independent science? What is the philosophical status of biology as compared with physical science, for instance? What is unique about the philosophy of science as applied to biology? What are the big issues in the philosophy of biology, and why educators should care about the philosophy of science?|
|Apr. 25||Yamilov||Dr. Allard Mosk
University of Twente
|Imaging and focusing through strongly scattering layers||
 J. Bertolotti, E. G. van Putten, C. Blum, A. Lagendijk, W. L. Vos, and A. P. Mosk, “Non-invasive imaging through opaque scattering layers,” Nature491, 232–234 (2012).
Random scattering of light, such as one can observe in paper, paint and biological tissue, is a phenomenon of basic physical interest as well as of great relevance for applications. From a theoretical point of view, light scattering allows the study of interference effects such as Anderson localization . In applications, scattering is an obstacle to high-resolution imaging and focusing of light.
The propagation of laser light in scattering media can be controlled by shaping the incident wavefront . This control is based on the realization that scattering by stationary randomness performs a random linear transformation on the incident light modes. Wave front shaping methods effectively invert this transform and have given rise to a surge of fundamental studies of light propagation and new modalities of imaging and focusing through as well as inside turbid media , and in media such as scattering optical fibers . These methods need a calibration measurement, such as the measurement of a transmission matrix , to characterize the scattering medium. Very recently we demonstrated the use of speckle correlations for fluorescence imaging through strongly scattering layers without any invasive calibration . This is the first high-resolution imaging method that uses only scattered light. We scan the angle of incidence of the light on the scattering layer, and record the diffuse fluorescence from the object. As a result of fluctuations in the overlap between the scattered speckle and the object this fluorescent signal fluctuates. These fluctuations contain enough information to yield a high-resolution image of a small object. I will discuss the rapid progress that is being made in the development of practical imaging methods.
Fig. 1. Laser light that impinges on a strongly scattering screen is transmitted as a random speckled interference pattern. Speckle correlations can be used to focus light and retrieve image information .
* I will present results obtained in collaboration with E.G. van Putten, J. Bertolotti, D. Akbulut, S.A. Goorden, H. Yilmaz, C. Blum, W.L. Vos and A. Lagendijk.
 A. Lagendijk, B. van Tiggelen, and D. S. Wiersma, “Fifty years of Anderson localization,” Phys. Today 62, 24 (2009).
 I.M. Vellekoop and A.P. Mosk, “Focusing coherent light through opaque strongly scattering media,” Opt. Lett. 32 2309-2311 (2007).
 A. P. Mosk, A. Lagendijk, G. Lerosey, and M. Fink, “Controlling waves in space and time for imaging and focusing in complex media,” Nature Photon. 6, 283-292 (2012).
 S. M. Popoff, G. Lerosey, R. Carminati, M. Fink, A. C. Boccara, and S. Gigan, “Measuring the Transmission Matrix in Optics: An Approach to the Study and Control of Light Propagation in Disordered Media,” Phys. Rev. Lett. 104, 100601 (2010).
 N. P. Puente, E.I. Chaikina, S. Herath and A. Yamilov, “Fabrication, characterization and theoretical analysis of controlled disorder in the core of the optical fibers”, Appl. Opt. 50, 802 (2011)
|May 2||Hor||42nd Annual Harold Q. Fuller Prize Colloquium|