Science.gov

Sample records for direct real-space observation

  1. Direct real-space observation of nearly stochastic behavior in magnetization reversal process on a nanoscale

    SciTech Connect

    Im, M.-Y.; Kim, D.-H.; Lee, K.-D.; Fischer, P.; Shin, S.-C.

    2007-06-01

    We report a non-deterministic nature in the magnetization reversal of nanograins of CoCrPt alloy film. Magnetization reversal process of CoCrPt alloy film is investigated using high resolution soft X-ray microscopy which provides real space images with a spatial resolution of 15 nm. Domain nucleation sites mostly appear stochastically distributed within repeated hysteretic cycles, where the correlation increases as the strength of the applied magnetic field increases in the descending and ascending branches of the major hysteresis loop. In addition, domain configuration is mostly asymmetric with inversion of an applied magnetic field in the hysteretic cycle. Nanomagnetic simulation considering thermal fluctuations of the magnetic moments of the grains explains the nearly stochastic nature of the domain nucleation behavior observed in CoCrPt alloy film. With the bit size in high-density magnetic recording media approaching nanometer length scale, one of the fundamental and crucial issues is whether the domain nucleation during magnetization reversal process exhibits a deterministic behavior. Repeatability of local domain nucleation and deterministic switching behavior are basic and essential factors for achieving high performance in high-density magnetic recording [1-3]. Most experimental studies on this issue reported so far have been mainly performed by indirect probes through macroscopic hysteresis loop and Barkhausen pattern measurements, which provide the ensemble-average magnetization. Thus, they are inadequate to gain insight into the domain-nucleation behavior on a nanometer length scale during the magnetization reversal process [4-6]. Very recently, coherent X-ray speckle metrology, where the speckle pattern observed in reciprocal space acts as a fingerprint of the domain configurations, was adopted to investigate stochastic behavior in the magnetization reversal of a Co/Pt multilayer film [7,8]. However, no direct observation on the stochastic behavior of

  2. Real-space observation of strong metal-support interaction: state-of-the-art and what's the next.

    PubMed

    Shi, X Y; Zhang, W; Zhang, C; Zheng, W T; Chen, H; Qi, J G

    2016-06-01

    The real-space resolving of the encapsulated overlayer in the well-known model and industry catalysts, ascribed to the advent of dedicated transmission electron microscopy, enables us to probe novel nano/micro architecture chemistry for better application, revisiting our understanding of this key issue in heterogeneous catalysis. In this review, we summarize the latest progress of real-space observation of SMSI in several well-known systems mainly covered from the metal catalysts (mostly Pt) supported by the TiO2 , CeO2 and Fe3 O4 . As a comparison with the model catalyst Pt/Fe3 O4 , the industrial catalyst Cu/ZnO is also listed, followed with the suggested ongoing directions in the field.

  3. Real-space observation of spectral degeneracy breaking in a waveguide-coupled disk microresonator.

    PubMed

    Blaize, Sylvain; Gesuele, Felice; Stefanon, Ilan; Bruyant, Aurélien; Lérondel, Gilles; Royer, Pascal; Martin, Bruno; Morand, Alain; Benech, Pierre; Fedeli, Jean-Marc

    2010-10-01

    We report on the real-space observation of resonant frequency splitting in a high-Q waveguide-coupled silicon-on-insulator microdisk resonator. Phase sensitive near-field analysis reveals the stationary nature of the two resonant states, and spectral investigations clearly show their orthogonality. These measurements emphasize the role of the coupling waveguide in this splitting phenomenon. The symmetry of the two stationary whispering gallery modes is clearly observed and is found to follow the axial symmetry of the waveguide-coupled microdisk as it has been reported by earlier theoretical predictions.

  4. An atomic model of brome mosaic virus using direct electron detection and real-space optimization.

    PubMed

    Wang, Zhao; Hryc, Corey F; Bammes, Benjamin; Afonine, Pavel V; Jakana, Joanita; Chen, Dong-Hua; Liu, Xiangan; Baker, Matthew L; Kao, Cheng; Ludtke, Steven J; Schmid, Michael F; Adams, Paul D; Chiu, Wah

    2014-09-04

    Advances in electron cryo-microscopy have enabled structure determination of macromolecules at near-atomic resolution. However, structure determination, even using de novo methods, remains susceptible to model bias and overfitting. Here we describe a complete workflow for data acquisition, image processing, all-atom modelling and validation of brome mosaic virus, an RNA virus. Data were collected with a direct electron detector in integrating mode and an exposure beyond the traditional radiation damage limit. The final density map has a resolution of 3.8 Å as assessed by two independent data sets and maps. We used the map to derive an all-atom model with a newly implemented real-space optimization protocol. The validity of the model was verified by its match with the density map and a previous model from X-ray crystallography, as well as the internal consistency of models from independent maps. This study demonstrates a practical approach to obtain a rigorously validated atomic resolution electron cryo-microscopy structure.

  5. An atomic model of brome mosaic virus using direct electron detection and real-space optimization.

    PubMed

    Wang, Zhao; Hryc, Corey F; Bammes, Benjamin; Afonine, Pavel V; Jakana, Joanita; Chen, Dong-Hua; Liu, Xiangan; Baker, Matthew L; Kao, Cheng; Ludtke, Steven J; Schmid, Michael F; Adams, Paul D; Chiu, Wah

    2014-01-01

    Advances in electron cryo-microscopy have enabled structure determination of macromolecules at near-atomic resolution. However, structure determination, even using de novo methods, remains susceptible to model bias and overfitting. Here we describe a complete workflow for data acquisition, image processing, all-atom modelling and validation of brome mosaic virus, an RNA virus. Data were collected with a direct electron detector in integrating mode and an exposure beyond the traditional radiation damage limit. The final density map has a resolution of 3.8 Å as assessed by two independent data sets and maps. We used the map to derive an all-atom model with a newly implemented real-space optimization protocol. The validity of the model was verified by its match with the density map and a previous model from X-ray crystallography, as well as the internal consistency of models from independent maps. This study demonstrates a practical approach to obtain a rigorously validated atomic resolution electron cryo-microscopy structure. PMID:25185801

  6. Direct real space observation of magneto-electronic inhomogeneity in ultra-thin film La{sub 0.5}Sr{sub 0.5}CoO{sub 3−δ} on SrTiO{sub 3}(001)

    SciTech Connect

    Kelly, S.; Galli, F.; Aarts, J. E-mail: aarts@physics.leidenuniv.nl; Bose, Shameek; Sharma, M.; Leighton, C. E-mail: aarts@physics.leidenuniv.nl

    2014-09-15

    Recent magnetotransport and neutron scattering measurements implicate interfacial magneto-electronic phase separation as the origin of the degradation in transport and magnetism in ultra-thin film La{sub 1−x}Sr{sub x}CoO{sub 3} on SrTiO{sub 3}(001). Here, using low temperature scanning tunneling microscopy and spectroscopy the first direct, real space observation of this nanoscopic electronic inhomogeneity is provided. Films of thickness 12.4 nm (32 unit cells) are found to exhibit spatially uniform conductance, in stark contrast to 4.7 nm (12 unit cell) films that display rich variations in conductance, and thus local density of states. The electronic heterogeneity occurs across a hierarchy of length scales (5–50 nm), with complex correlations with both topography and applied magnetic fields. These results thus provide a direct observation of magneto-electronic inhomogeneity in SrTiO{sub 3}(001)/La{sub 0.5}Sr{sub 0.5}CoO{sub 3} at thicknesses below 6–7 nm, in good agreement with less direct techniques.

  7. Real-space observation of unbalanced charge distribution inside a perovskite-sensitized solar cell.

    PubMed

    Bergmann, Victor W; Weber, Stefan A L; Javier Ramos, F; Nazeeruddin, Mohammad Khaja; Grätzel, Michael; Li, Dan; Domanski, Anna L; Lieberwirth, Ingo; Ahmad, Shahzada; Berger, Rüdiger

    2014-01-01

    Perovskite-sensitized solar cells have reached power conversion efficiencies comparable to commercially available solar cells used for example in solar farms. In contrast to silicon solar cells, perovskite-sensitized solar cells can be made by solution processes from inexpensive materials. The power conversion efficiency of these cells depends substantially on the charge transfer at interfaces. Here we use Kelvin probe force microscopy to study the real-space cross-sectional distribution of the internal potential within high efficiency mesoscopic methylammonium lead tri-iodide solar cells. We show that the electric field is homogeneous through these devices, similar to that of a p-i-n type junction. On illumination under short-circuit conditions, holes accumulate in front of the hole-transport layer as a consequence of unbalanced charge transport in the device. After light illumination, we find that trapped charges remain inside the active device layers. Removing these traps and the unbalanced charge injection could enable further improvements in performance of perovskite-sensitized solar cells. PMID:25242041

  8. Real-space observation of unbalanced charge distribution inside a perovskite-sensitized solar cell.

    PubMed

    Bergmann, Victor W; Weber, Stefan A L; Javier Ramos, F; Nazeeruddin, Mohammad Khaja; Grätzel, Michael; Li, Dan; Domanski, Anna L; Lieberwirth, Ingo; Ahmad, Shahzada; Berger, Rüdiger

    2014-09-22

    Perovskite-sensitized solar cells have reached power conversion efficiencies comparable to commercially available solar cells used for example in solar farms. In contrast to silicon solar cells, perovskite-sensitized solar cells can be made by solution processes from inexpensive materials. The power conversion efficiency of these cells depends substantially on the charge transfer at interfaces. Here we use Kelvin probe force microscopy to study the real-space cross-sectional distribution of the internal potential within high efficiency mesoscopic methylammonium lead tri-iodide solar cells. We show that the electric field is homogeneous through these devices, similar to that of a p-i-n type junction. On illumination under short-circuit conditions, holes accumulate in front of the hole-transport layer as a consequence of unbalanced charge transport in the device. After light illumination, we find that trapped charges remain inside the active device layers. Removing these traps and the unbalanced charge injection could enable further improvements in performance of perovskite-sensitized solar cells.

  9. Real-space observation of magnetic excitations and avalanche behavior in artificial quasicrystal lattices

    NASA Astrophysics Data System (ADS)

    Brajuskovic, V.; Barrows, F.; Phatak, C.; Petford-Long, A. K.

    2016-10-01

    Artificial spin ice lattices have emerged as model systems for studying magnetic frustration in recent years. Most work to date has looked at periodic artificial spin ice lattices. In this paper, we observe frustration effects in quasicrystal artificial spin ice lattices that lack translational symmetry and contain vertices with different numbers of interacting elements. We find that as the lattice state changes following demagnetizing and annealing, specific vertex motifs retain low-energy configurations, which excites other motifs into higher energy configurations. Additionally, we find that unlike the magnetization reversal process for periodic artificial spin ice lattices, which occurs through 1D avalanches, quasicrystal lattices undergo reversal through a dendritic 2D avalanche mechanism.

  10. Real-space observation of magnetic excitations and avalanche behavior in artificial quasicrystal lattices

    PubMed Central

    Brajuskovic, V.; Barrows, F.; Phatak, C.; Petford-Long, A. K.

    2016-01-01

    Artificial spin ice lattices have emerged as model systems for studying magnetic frustration in recent years. Most work to date has looked at periodic artificial spin ice lattices. In this paper, we observe frustration effects in quasicrystal artificial spin ice lattices that lack translational symmetry and contain vertices with different numbers of interacting elements. We find that as the lattice state changes following demagnetizing and annealing, specific vertex motifs retain low-energy configurations, which excites other motifs into higher energy configurations. Additionally, we find that unlike the magnetization reversal process for periodic artificial spin ice lattices, which occurs through 1D avalanches, quasicrystal lattices undergo reversal through a dendritic 2D avalanche mechanism. PMID:27694973

  11. Real-space finite-difference approach for multi-body systems: path-integral renormalization group method and direct energy minimization method.

    PubMed

    Sasaki, Akira; Kojo, Masashi; Hirose, Kikuji; Goto, Hidekazu

    2011-11-01

    The path-integral renormalization group and direct energy minimization method of practical first-principles electronic structure calculations for multi-body systems within the framework of the real-space finite-difference scheme are introduced. These two methods can handle higher dimensional systems with consideration of the correlation effect. Furthermore, they can be easily extended to the multicomponent quantum systems which contain more than two kinds of quantum particles. The key to the present methods is employing linear combinations of nonorthogonal Slater determinants (SDs) as multi-body wavefunctions. As one of the noticeable results, the same accuracy as the variational Monte Carlo method is achieved with a few SDs. This enables us to study the entire ground state consisting of electrons and nuclei without the need to use the Born-Oppenheimer approximation. Recent activities on methodological developments aiming towards practical calculations such as the implementation of auxiliary field for Coulombic interaction, the treatment of the kinetic operator in imaginary-time evolutions, the time-saving double-grid technique for bare-Coulomb atomic potentials and the optimization scheme for minimizing the total-energy functional are also introduced. As test examples, the total energy of the hydrogen molecule, the atomic configuration of the methylene and the electronic structures of two-dimensional quantum dots are calculated, and the accuracy, availability and possibility of the present methods are demonstrated.

  12. Supramolecular clusters and chains of 2,6-dimethylpyridine on Cu(110): Observation of dynamic configuration change with real-space surface science techniques and DFT calculations

    NASA Astrophysics Data System (ADS)

    Lee, Junseok; Sorescu, Dan C.; Lee, Jae-Gook; Dougherty, Dan

    2016-10-01

    The adsorption of 2,6-dimethylpyridine (2,6-DMP) on Cu(110) has been studied using low temperature scanning tunneling microscopy (LT-STM), time-of-flight electron stimulated desorption ion angular distribution (TOF-ESDIAD), and density functional theory (DFT) calculations. At low temperatures (T < ~ 150 K), the 2,6-DMP adsorbs in a flat configuration on Cu(110) producing clusters and extended domains via weak hydrogen bonding (C-H···N) with the molecular symmetry axis aligned along the < 001 > surface direction. At near-saturation coverage, a c(6 × 2) long-range ordered structure was observed. Upon annealing to T = 200 K, the 2,6-DMP molecules adopt an upright configuration with their pyridine ring plane oriented parallel to the < 1 1 ̅ 0 > azimuth. These upright 2,6-DMP molecules produce extended molecular chains where the repulsive interactions between the molecular chains give rise to coverage-dependent interchain distances.

  13. Real-space Berry phases: Skyrmion soccer (invited)

    SciTech Connect

    Everschor-Sitte, Karin Sitte, Matthias

    2014-05-07

    Berry phases occur when a system adiabatically evolves along a closed curve in parameter space. This tutorial-like article focuses on Berry phases accumulated in real space. In particular, we consider the situation where an electron traverses a smooth magnetic structure, while its magnetic moment adjusts to the local magnetization direction. Mapping the adiabatic physics to an effective problem in terms of emergent fields reveals that certain magnetic textures, skyrmions, are tailormade to study these Berry phase effects.

  14. Real-space Berry phases: Skyrmion soccer (invited)

    NASA Astrophysics Data System (ADS)

    Everschor-Sitte, Karin; Sitte, Matthias

    2014-05-01

    Berry phases occur when a system adiabatically evolves along a closed curve in parameter space. This tutorial-like article focuses on Berry phases accumulated in real space. In particular, we consider the situation where an electron traverses a smooth magnetic structure, while its magnetic moment adjusts to the local magnetization direction. Mapping the adiabatic physics to an effective problem in terms of emergent fields reveals that certain magnetic textures, skyrmions, are tailormade to study these Berry phase effects.

  15. Exciton-polariton oscillations in real space

    NASA Astrophysics Data System (ADS)

    Liew, T. C. H.; Rubo, Y. G.; Kavokin, A. V.

    2014-12-01

    We introduce and model spin-Rabi oscillations based on exciton-polaritons in semiconductor microcavities. The phase and polarization of oscillations can be controlled by resonant coherent pulses and the propagation of oscillating domains gives rise to phase-dependent interference patterns in real space. We show that interbranch polariton-polariton scattering controls the propagation of oscillating domains, which can be used to realize logic gates based on an analog variable phase.

  16. Visualizing coherent intermolecular dipole–dipole coupling in real space

    NASA Astrophysics Data System (ADS)

    Zhang, Yang; Luo, Yang; Zhang, Yao; Yu, Yun-Jie; Kuang, Yan-Min; Zhang, Li; Meng, Qiu-Shi; Luo, Yi; Yang, Jin-Long; Dong, Zhen-Chao; Hou, J. G.

    2016-03-01

    Many important energy-transfer and optical processes, in both biological and artificial systems, depend crucially on excitonic coupling that spans several chromophores. Such coupling can in principle be described in a straightforward manner by considering the coherent intermolecular dipole–dipole interactions involved. However, in practice, it is challenging to directly observe in real space the coherent dipole coupling and the related exciton delocalizations, owing to the diffraction limit in conventional optics. Here we demonstrate that the highly localized excitations that are produced by electrons tunnelling from the tip of a scanning tunnelling microscope, in conjunction with imaging of the resultant luminescence, can be used to map the spatial distribution of the excitonic coupling in well-defined arrangements of a few zinc-phthalocyanine molecules. The luminescence patterns obtained for excitons in a dimer, which are recorded for different energy states and found to resemble σ and π molecular orbitals, reveal the local optical response of the system and the dependence of the local optical response on the relative orientation and phase of the transition dipoles of the individual molecules in the dimer. We generate an in-line arrangement up to four zinc-phthalocyanine molecules, with a larger total transition dipole, and show that this results in enhanced ‘single-molecule’ superradiance from the oligomer upon site-selective excitation. These findings demonstrate that our experimental approach provides detailed spatial information about coherent dipole–dipole coupling in molecular systems, which should enable a greater understanding and rational engineering of light-harvesting structures and quantum light sources.

  17. Visualizing coherent intermolecular dipole-dipole coupling in real space

    NASA Astrophysics Data System (ADS)

    Zhang, Yang; Luo, Yang; Zhang, Yao; Yu, Yun-Jie; Kuang, Yan-Min; Zhang, Li; Meng, Qiu-Shi; Luo, Yi; Yang, Jin-Long; Dong, Zhen-Chao; Hou, J. G.

    2016-03-01

    Many important energy-transfer and optical processes, in both biological and artificial systems, depend crucially on excitonic coupling that spans several chromophores. Such coupling can in principle be described in a straightforward manner by considering the coherent intermolecular dipole-dipole interactions involved. However, in practice, it is challenging to directly observe in real space the coherent dipole coupling and the related exciton delocalizations, owing to the diffraction limit in conventional optics. Here we demonstrate that the highly localized excitations that are produced by electrons tunnelling from the tip of a scanning tunnelling microscope, in conjunction with imaging of the resultant luminescence, can be used to map the spatial distribution of the excitonic coupling in well-defined arrangements of a few zinc-phthalocyanine molecules. The luminescence patterns obtained for excitons in a dimer, which are recorded for different energy states and found to resemble σ and π molecular orbitals, reveal the local optical response of the system and the dependence of the local optical response on the relative orientation and phase of the transition dipoles of the individual molecules in the dimer. We generate an in-line arrangement up to four zinc-phthalocyanine molecules, with a larger total transition dipole, and show that this results in enhanced ‘single-molecule’ superradiance from the oligomer upon site-selective excitation. These findings demonstrate that our experimental approach provides detailed spatial information about coherent dipole-dipole coupling in molecular systems, which should enable a greater understanding and rational engineering of light-harvesting structures and quantum light sources.

  18. Real-space renormalized dynamical mean field theory

    NASA Astrophysics Data System (ADS)

    Kubota, Dai; Sakai, Shiro; Imada, Masatoshi

    2016-05-01

    We propose real-space renormalized dynamical mean field theory (rr-DMFT) to deal with large clusters in the framework of a cluster extension of the DMFT. In the rr-DMFT, large clusters are decomposed into multiple smaller clusters through a real-space renormalization. In this work, the renormalization effect is taken into account only at the lowest order with respect to the intercluster coupling, which nonetheless reproduces exactly both the noninteracting and atomic limits. Our method allows us large cluster-size calculations which are intractable with the conventional cluster extensions of the DMFT with impurity solvers, such as the continuous-time quantum Monte Carlo and exact diagonalization methods. We benchmark the rr-DMFT for the two-dimensional Hubbard model on a square lattice at and away from half filling, where the spatial correlations play important roles. Our results on the spin structure factor indicate that the growth of the antiferromagnetic spin correlation is taken into account beyond the decomposed cluster size. We also show that the self-energy obtained from the large-cluster solver is reproduced by our method better than the solution obtained directly for the smaller cluster. When applied to the Mott metal-insulator transition, the rr-DMFT is able to reproduce the reduced critical value for the Coulomb interaction comparable to the large cluster result.

  19. Real-space renormalization in statistical mechanics

    NASA Astrophysics Data System (ADS)

    Efrati, Efi; Wang, Zhe; Kolan, Amy; Kadanoff, Leo P.

    2014-04-01

    This review compares the conceptualization and practice of early real-space renormalization group methods with the conceptualization of more recent real-space transformations based on tensor networks. For specificity, it focuses upon two basic methods: the "potential-moving" approach most used in the period 1975-1980 and the "rewiring method" as it has been developed in the last five years. The newer method, part of a development called the tensor renormalization group, was originally based on principles of quantum entanglement. It is specialized for computing approximations for tensor products constituting, for example, the free energy or the ground state energy of a large system. It can attack a wide variety of problems, including quantum problems, which would otherwise be intractable. The older method is formulated in terms of spin variables and permits a straightforward construction and analysis of fixed points in rather transparent terms. However, in the form described here it is unsystematic, offers no path for improvement, and of unknown reliability. The new method is formulated in terms of index variables which may be considered as linear combinations of the statistical variables. Free energies emerge naturally, but fixed points are more subtle. Further, physical interpretations of the index variables are often elusive due to a gauge symmetry which allows only selected combinations of tensor entries to have physical significance. In applications, both methods employ analyses with varying degrees of complexity. The complexity is parametrized by an integer called χ (or D in the recent literature). Both methods are examined in action by using them to compute fixed points related to Ising models for small values of the complexity parameter. They behave quite differently. The old method gives a reasonably good picture of the fixed point, as measured, for example, by the accuracy of the measured critical indices. This happens at low values of χ, but there is no

  20. Real-space imaging of fractional quantum Hall liquids.

    PubMed

    Hayakawa, Junichiro; Muraki, Koji; Yusa, Go

    2013-01-01

    Electrons in semiconductors usually behave like a gas--as independent particles. However, when confined to two dimensions under a perpendicular magnetic field at low temperatures, they condense into an incompressible quantum liquid. This phenomenon, known as the fractional quantum Hall (FQH) effect, is a quantum-mechanical manifestation of the macroscopic behaviour of correlated electrons that arises when the Landau-level filling factor is a rational fraction. However, the diverse microscopic interactions responsible for its emergence have been hidden by its universality and macroscopic nature. Here, we report real-space imaging of FQH liquids, achieved with polarization-sensitive scanning optical microscopy using trions (charged excitons) as a local probe for electron spin polarization. When the FQH ground state is spin-polarized, the triplet/singlet intensity map exhibits a spatial pattern that mirrors the intrinsic disorder potential, which is interpreted as a mapping of compressible and incompressible electron liquids. In contrast, when FQH ground states with different spin polarization coexist, domain structures with spontaneous quasi-long-range order emerge, which can be reproduced remarkably well from the disorder patterns using a two-dimensional random-field Ising model. Our results constitute the first reported real-space observation of quantum liquids in a class of broken symmetry state known as the quantum Hall ferromagnet.

  1. Real-space collapse of a polariton condensate

    PubMed Central

    Dominici, L.; Petrov, M.; Matuszewski, M.; Ballarini, D.; De Giorgi, M.; Colas, D.; Cancellieri, E.; Silva Fernández, B.; Bramati, A.; Gigli, G.; Kavokin, A.; Laussy, F.; Sanvitto, D.

    2015-01-01

    Microcavity polaritons are two-dimensional bosonic fluids with strong nonlinearities, composed of coupled photonic and electronic excitations. In their condensed form, they display quantum hydrodynamic features similar to atomic Bose–Einstein condensates, such as long-range coherence, superfluidity and quantized vorticity. Here we report the unique phenomenology that is observed when a pulse of light impacts the polariton vacuum: the fluid which is suddenly created does not splash but instead coheres into a very bright spot. The real-space collapse into a sharp peak is at odd with the repulsive interactions of polaritons and their positive mass, suggesting that an unconventional mechanism is at play. Our modelling devises a possible explanation in the self-trapping due to a local heating of the crystal lattice, that can be described as a collective polaron formed by a polariton condensate. These observations hint at the polariton fluid dynamics in conditions of extreme intensities and ultrafast times. PMID:26634817

  2. Real-space collapse of a polariton condensate.

    PubMed

    Dominici, L; Petrov, M; Matuszewski, M; Ballarini, D; De Giorgi, M; Colas, D; Cancellieri, E; Silva Fernández, B; Bramati, A; Gigli, G; Kavokin, A; Laussy, F; Sanvitto, D

    2015-01-01

    Microcavity polaritons are two-dimensional bosonic fluids with strong nonlinearities, composed of coupled photonic and electronic excitations. In their condensed form, they display quantum hydrodynamic features similar to atomic Bose-Einstein condensates, such as long-range coherence, superfluidity and quantized vorticity. Here we report the unique phenomenology that is observed when a pulse of light impacts the polariton vacuum: the fluid which is suddenly created does not splash but instead coheres into a very bright spot. The real-space collapse into a sharp peak is at odd with the repulsive interactions of polaritons and their positive mass, suggesting that an unconventional mechanism is at play. Our modelling devises a possible explanation in the self-trapping due to a local heating of the crystal lattice, that can be described as a collective polaron formed by a polariton condensate. These observations hint at the polariton fluid dynamics in conditions of extreme intensities and ultrafast times. PMID:26634817

  3. A brief comparison between grid based real space algorithms andspectrum algorithms for electronic structure calculations

    SciTech Connect

    Wang, Lin-Wang

    2006-12-01

    Quantum mechanical ab initio calculation constitutes the biggest portion of the computer time in material science and chemical science simulations. As a computer center like NERSC, to better serve these communities, it will be very useful to have a prediction for the future trends of ab initio calculations in these areas. Such prediction can help us to decide what future computer architecture can be most useful for these communities, and what should be emphasized on in future supercomputer procurement. As the size of the computer and the size of the simulated physical systems increase, there is a renewed interest in using the real space grid method in electronic structure calculations. This is fueled by two factors. First, it is generally assumed that the real space grid method is more suitable for parallel computation for its limited communication requirement, compared with spectrum method where a global FFT is required. Second, as the size N of the calculated system increases together with the computer power, O(N) scaling approaches become more favorable than the traditional direct O(N{sup 3}) scaling methods. These O(N) methods are usually based on localized orbital in real space, which can be described more naturally by the real space basis. In this report, the author compares the real space methods versus the traditional plane wave (PW) spectrum methods, for their technical pros and cons, and the possible of future trends. For the real space method, the author focuses on the regular grid finite different (FD) method and the finite element (FE) method. These are the methods used mostly in material science simulation. As for chemical science, the predominant methods are still Gaussian basis method, and sometime the atomic orbital basis method. These two basis sets are localized in real space, and there is no indication that their roles in quantum chemical simulation will change anytime soon. The author focuses on the density functional theory (DFT), which is the

  4. RESCU: A real space electronic structure method

    NASA Astrophysics Data System (ADS)

    Michaud-Rioux, Vincent; Zhang, Lei; Guo, Hong

    2016-02-01

    In this work we present RESCU, a powerful MATLAB-based Kohn-Sham density functional theory (KS-DFT) solver. We demonstrate that RESCU can compute the electronic structure properties of systems comprising many thousands of atoms using modest computer resources, e.g. 16 to 256 cores. Its computational efficiency is achieved from exploiting four routes. First, we use numerical atomic orbital (NAO) techniques to efficiently generate a good quality initial subspace which is crucially required by Chebyshev filtering methods. Second, we exploit the fact that only a subspace spanning the occupied Kohn-Sham states is required, and solving accurately the KS equation using eigensolvers can generally be avoided. Third, by judiciously analyzing and optimizing various parts of the procedure in RESCU, we delay the O (N3) scaling to large N, and our tests show that RESCU scales consistently as O (N2.3) from a few hundred atoms to more than 5000 atoms when using a real space grid discretization. The scaling is better or comparable in a NAO basis up to the 14,000 atoms level. Fourth, we exploit various numerical algorithms and, in particular, we introduce a partial Rayleigh-Ritz algorithm to achieve efficiency gains for systems comprising more than 10,000 electrons. We demonstrate the power of RESCU in solving KS-DFT problems using many examples running on 16, 64 and/or 256 cores: a 5832 Si atoms supercell; a 8788 Al atoms supercell; a 5324 Cu atoms supercell and a small DNA molecule submerged in 1713 water molecules for a total 5399 atoms. The KS-DFT is entirely converged in a few hours in all cases. Our results suggest that the RESCU method has reached a milestone of solving thousands of atoms by KS-DFT on a modest computer cluster.

  5. Collisionless high energy particle losses in optimized stellarators calculated in real-space coordinates

    SciTech Connect

    Nemov, V. V.; Kasilov, S. V.; Kernbichler, W.

    2014-06-15

    An approach for the direct computation of collisionless losses of high energy charged particles is developed for stellarator magnetic fields given in real space coordinates. With this approach, the corresponding computations can be performed for magnetic fields with three-dimensional inhomogeneities in the presence of stochastic regions as well as magnetic islands. A code, which is based on this approach, is applied to various stellarator configurations. It is found that the life time of fast particles obtained in real-space coordinates can be smaller than that obtained in magnetic coordinates.

  6. Colloidal Suspensions in Shear Flow : a Real Space Study

    NASA Astrophysics Data System (ADS)

    Derks, D.

    2006-09-01

    We investigate the effect of shear flow on the microstructure of colloidal suspensions by means of microscopy. Systems of nearly equally sized particles are used, whose interactions and phase behavior are predominantly determined by their size and shape, and can further be tuned by the addition of polymers. Recently, a new type of shear cell was developed to study flowing suspensions in real space. The key property of this setup is the counter-rotating principle of the cone and plate, opening up the possibility to create a stationary layer in the bulk of the cell. In Chapter 2, we elaborate on the details of this setup and its performance. Fluorescence confocal microscopy is used to visualize the sheared suspension, and allows imaging of individual particles in the bulk in the stationary plane for a prolonged time. This way, the particle positions in a layer of, for example, a sheared colloidal crystal can be tracked. The particle dynamics in colloidal crystals in shear flow are the subject of Chapter 3. Here, the particles interact through a (nearly) hard sphere potential. Apart from the alignment of the crystal in the shear field and the collective zigzag motion, which had also been deduced from early scattering experiments, we find that random particle displacements increase with shear rate. Those increased fluctuations result in shear induced melting when their mean square displacement has reached about 13 % of the particle separation. Apart from hard spheres, we investigate mixtures of colloids and polymers in shear flow. The polymers cause an effective attraction between the spheres, leading to phase separation into a colloid rich (polymer poor) and a colloid poor (polymer rich) phase at sufficiently high colloid and polymer concentration. In Chapter 4, we study the demixing process in the (spinodal) two-phase region of the phase diagram. The system is quenched from an initially almost homogeneous state at very high shear rate to a low shear rate. A spinodal

  7. Real Space DFT by Locally Optimal Block Preconditioned Conjugate Gradient Method

    NASA Astrophysics Data System (ADS)

    Michaud, Vincent; Guo, Hong

    2012-02-01

    Real space approaches solve the Kohn-Sham (KS) DFT problem as a system of partial differential equations (PDE) in real space numerical grids. In such techniques, the Hamiltonian matrix is typically much larger but sparser than the matrix arising in state-of-the-art DFT codes which are often based on directly minimizing the total energy functional. Evidence of good performance of real space methods - by Chebyshev filtered subspace iteration (CFSI) - was reported by Zhou, Saad, Tiago and Chelikowsky [1]. We found that the performance of the locally optimal block preconditioned conjugate gradient method (LOGPCG) introduced by Knyazev [2], when used in conjunction with CFSI, generally exceeds that of CFSI for solving the KS equations. We will present our implementation of the LOGPCG based real space electronic structure calculator. [4pt] [1] Y. Zhou, Y. Saad, M. L. Tiago, and J. R. Chelikowsky, ``Self-consistent-field calculations using Chebyshev-filtered subspace iteration,'' J. Comput. Phys., vol. 219,pp. 172-184, November 2006. [0pt] [2] A. V. Knyazev, ``Toward the optimal preconditioned eigensolver: Locally optimal block preconditioned conjugate gradient method,'' SIAM J. Sci. Comput, vol. 23, pp. 517-541, 2001.

  8. Cosmological ensemble and directional averages of observables

    SciTech Connect

    Bonvin, Camille; Clarkson, Chris; Durrer, Ruth; Maartens, Roy; Umeh, Obinna E-mail: chris.clarkson@gmail.com E-mail: roy.maartens@gmail.com

    2015-07-01

    We show that at second order, ensemble averages of observables and directional averages do not commute due to gravitational lensing—observing the same thing in many directions over the sky is not the same as taking an ensemble average. In principle this non-commutativity is significant for a variety of quantities that we often use as observables and can lead to a bias in parameter estimation. We derive the relation between the ensemble average and the directional average of an observable, at second order in perturbation theory. We discuss the relevance of these two types of averages for making predictions of cosmological observables, focusing on observables related to distances and magnitudes. In particular, we show that the ensemble average of the distance in a given observed direction is increased by gravitational lensing, whereas the directional average of the distance is decreased. For a generic observable, there exists a particular function of the observable that is not affected by second-order lensing perturbations. We also show that standard areas have an advantage over standard rulers, and we discuss the subtleties involved in averaging in the case of supernova observations.

  9. Real-Space Holon Pairing in Underdoped Cuprates

    NASA Astrophysics Data System (ADS)

    Lovorn, Timothy; Sarker, Sanjoy

    2013-03-01

    We examine the behavior of a recently developed model for underdoped cuprates in the fluctuation regime above Tc. It is characterized by a spin gap and describes sublattice preserving hopping by holons and holon pairs, accompanied by a backflow of spin singlets. The singlets form a short-range valence-bond state which is continuously connected to the correct spin state at half filling. The theory, thus constrained, leads to the correct phase diagram and also explains the two-dimensionality of the metallic states. Superconductivity is due to pair hopping, as holons form real-space pairs at low densities and undergo a Bose-Einstein condensation below Tc. The pairs exist up to a temperature Tp >Tc , which is consistent with the observed Nernst effect and diamagnetism above Tc. The pair spectrum is calculated by identifying poles of the pair Green's function. Here we show that the specific heat of this system is in qualitative agreement with recent measurements. Work of Timothy Lovorn is supported by University of Alabama National Alumni Association License Tag Graduate Fellowship

  10. Direct observation and imaging of a spin-wave soliton with p-like symmetry.

    PubMed

    Bonetti, S; Kukreja, R; Chen, Z; Macià, F; Hernàndez, J M; Eklund, A; Backes, D; Frisch, J; Katine, J; Malm, G; Urazhdin, S; Kent, A D; Stöhr, J; Ohldag, H; Dürr, H A

    2015-01-01

    Spin waves, the collective excitations of spins, can emerge as nonlinear solitons at the nanoscale when excited by an electrical current from a nanocontact. These solitons are expected to have essentially cylindrical symmetry (that is, s-like), but no direct experimental observation exists to confirm this picture. Using a high-sensitivity time-resolved magnetic X-ray microscopy with 50 ps temporal resolution and 35 nm spatial resolution, we are able to create a real-space spin-wave movie and observe the emergence of a localized soliton with a nodal line, that is, with p-like symmetry. Micromagnetic simulations explain the measurements and reveal that the symmetry of the soliton can be controlled by magnetic fields. Our results broaden the understanding of spin-wave dynamics at the nanoscale, with implications for the design of magnetic nanodevices. PMID:26567699

  11. Direct observation and imaging of a spin-wave soliton with p-like symmetry

    DOE PAGESBeta

    Bonetti, S.; Kukreja, R.; Chen, Z.; Macià, F.; Hernàndez, J. M.; Eklund, A.; Backes, D.; Frisch, J.; Katine, J.; Malm, G.; et al

    2015-11-16

    Spin waves, the collective excitations of spins, can emerge as nonlinear solitons at the nanoscale when excited by an electrical current from a nanocontact. These solitons are expected to have essentially cylindrical symmetry (that is, s-like), but no direct experimental observation exists to confirm this picture. Using a high-sensitivity time-resolved magnetic X-ray microscopy with 50 ps temporal resolution and 35 nm spatial resolution, we are able to create a real-space spin-wave movie and observe the emergence of a localized soliton with a nodal line, that is, with p-like symmetry. Moreover, micromagnetic simulations explain the measurements and reveal that the symmetrymore » of the soliton can be controlled by magnetic fields. Our results broaden the understanding of spin-wave dynamics at the nanoscale, with implications for the design of magnetic nanodevices.« less

  12. Direct observation and imaging of a spin-wave soliton with p-like symmetry

    SciTech Connect

    Bonetti, S.; Kukreja, R.; Chen, Z.; Macià, F.; Hernàndez, J. M.; Eklund, A.; Backes, D.; Frisch, J.; Katine, J.; Malm, G.; Urazhdin, S.; Kent, A. D.; Stöhr, J.; Ohldag, H.; Dürr, H. A.

    2015-11-16

    Spin waves, the collective excitations of spins, can emerge as nonlinear solitons at the nanoscale when excited by an electrical current from a nanocontact. These solitons are expected to have essentially cylindrical symmetry (that is, s-like), but no direct experimental observation exists to confirm this picture. Using a high-sensitivity time-resolved magnetic X-ray microscopy with 50 ps temporal resolution and 35 nm spatial resolution, we are able to create a real-space spin-wave movie and observe the emergence of a localized soliton with a nodal line, that is, with p-like symmetry. Moreover, micromagnetic simulations explain the measurements and reveal that the symmetry of the soliton can be controlled by magnetic fields. Our results broaden the understanding of spin-wave dynamics at the nanoscale, with implications for the design of magnetic nanodevices.

  13. Direct observation and imaging of a spin-wave soliton with p-like symmetry

    NASA Astrophysics Data System (ADS)

    Bonetti, S.; Kukreja, R.; Chen, Z.; Macià, F.; Hernàndez, J. M.; Eklund, A.; Backes, D.; Frisch, J.; Katine, J.; Malm, G.; Urazhdin, S.; Kent, A. D.; Stöhr, J.; Ohldag, H.; Dürr, H. A.

    2015-11-01

    Spin waves, the collective excitations of spins, can emerge as nonlinear solitons at the nanoscale when excited by an electrical current from a nanocontact. These solitons are expected to have essentially cylindrical symmetry (that is, s-like), but no direct experimental observation exists to confirm this picture. Using a high-sensitivity time-resolved magnetic X-ray microscopy with 50 ps temporal resolution and 35 nm spatial resolution, we are able to create a real-space spin-wave movie and observe the emergence of a localized soliton with a nodal line, that is, with p-like symmetry. Micromagnetic simulations explain the measurements and reveal that the symmetry of the soliton can be controlled by magnetic fields. Our results broaden the understanding of spin-wave dynamics at the nanoscale, with implications for the design of magnetic nanodevices.

  14. Direct observation and imaging of a spin-wave soliton with p-like symmetry

    PubMed Central

    Bonetti, S.; Kukreja, R.; Chen, Z.; Macià, F.; Hernàndez, J. M.; Eklund, A.; Backes, D.; Frisch, J.; Katine, J.; Malm, G.; Urazhdin, S.; Kent, A. D.; Stöhr, J.; Ohldag, H.; Dürr, H. A.

    2015-01-01

    Spin waves, the collective excitations of spins, can emerge as nonlinear solitons at the nanoscale when excited by an electrical current from a nanocontact. These solitons are expected to have essentially cylindrical symmetry (that is, s-like), but no direct experimental observation exists to confirm this picture. Using a high-sensitivity time-resolved magnetic X-ray microscopy with 50 ps temporal resolution and 35 nm spatial resolution, we are able to create a real-space spin-wave movie and observe the emergence of a localized soliton with a nodal line, that is, with p-like symmetry. Micromagnetic simulations explain the measurements and reveal that the symmetry of the soliton can be controlled by magnetic fields. Our results broaden the understanding of spin-wave dynamics at the nanoscale, with implications for the design of magnetic nanodevices. PMID:26567699

  15. Local Analysis via the Real Space GREEN’S Function Method

    NASA Astrophysics Data System (ADS)

    Wu, Shi-Yu; Jayanthi, Chakram S.

    A complete account of the development of the method of real space Green’s function is given in this review. The emphasis is placed on the calculation of the local Green’s function in a real space representation. The discussion is centered on a list of issues particularly relevant to the study of properties of complex systems with reduced symmetry.They include: (i) the convergence procedure for calculating the local Green’s function of infinite systems without any boundary effects associated with an arbitrary truncation of the system; (ii) a general recursive relation which streamlines the calculation of the local Green’s function; (iii) the calculation of the eigenvector of selected eigenvalues directly from the Green’s function. An example of the application of the method to carry out a local analysis of dynamics of the Au(511) surface is also presented.

  16. EDITORIAL: From reciprocal space to real space in surface science From reciprocal space to real space in surface science

    NASA Astrophysics Data System (ADS)

    Bartels, Ludwig; Ernst, Karl-Heinz

    2012-09-01

    This issue is dedicated to Karl-Heinz Rieder on the occasion of his 70th birthday. It contains contributions written by his former students and colleagues from all over the world. Experimental techniques based on free electrons, such as photoelectron spectroscopy, electron microscopy and low energy electron diffraction (LEED), were foundational to surface science. While the first revealed the band structures of materials, the second provided nanometer scale imagery and the latter elucidated the atomic scale periodicity of surfaces. All required an (ultra-)high vacuum, and LEED illustrated impressively that adsorbates, such as carbon monoxide, hydrogen or oxygen, can markedly and periodically restructure surfaces from their bulk termination, even at pressures ten orders of magnitude or more below atmospheric. Yet these techniques were not generally able to reveal atomic scale surface defects, nor could they faithfully show adsorption of light atoms such as hydrogen. Although a complete atom, helium can also be regarded as a wave with a de Broglie wavelength that allows the study of surface atomic periodicities at a delicateness and sensitivity exceeding that of electrons-based techniques. In combination, these and other techniques generated insight into the periodicity of surfaces and their vibrational properties, yet were limited to simple and periodic surface setups. All that changed with the advent of scanning tunneling microscopy (STM) roughly 30 years ago, allowing real space access to surface defects and individual adsorbates. Applied at low temperatures, not only can STM establish a height profile of surfaces, but can also perform spectroscopy and serve as an actuator capable of rearranging individual species at atomic scale resolution. The direct and intuitive manner in which STM provided access as a spectator and as an actor to the atomic scale was foundational to today's surface science and to the development of the concepts of nanoscience in general. The

  17. Direct observation of time reversal violation

    SciTech Connect

    Bernabeu, J.

    2013-06-12

    A direct evidence for Time Reversal Violation (TRV) means an experiment that, considered by itself, clearly shows TRV independent of, and unconnected to, the results for CP Violation. No existing result before the recent BABAR experiment with entangled neutral B mesons had demonstrated TRV in this sense. There is a unique opportunity for a search of TRV with unstable particles thanks to the Einstein-Podolsky-Rosen (EPR) Entanglement between the two neutral mesons in B, and PHI, Factories. The two quantum effects of the first decay as a filtering measurement and the transfer of information to the still living partner allow performing a genuine TRV asymmetry with the exchange of 'in' and 'out' states. With four independent TRV asymmetries, BABAR observes a large deviation of T-invariance with a statistical significance of 14 standard deviations, far more than needed to declare the result as a discovery. This is the first direct observation of TRV in the time evolution of any system.

  18. A real-space stochastic density matrix approach for density functional electronic structure.

    PubMed

    Beck, Thomas L

    2015-12-21

    The recent development of real-space grid methods has led to more efficient, accurate, and adaptable approaches for large-scale electrostatics and density functional electronic structure modeling. With the incorporation of multiscale techniques, linear-scaling real-space solvers are possible for density functional problems if localized orbitals are used to represent the Kohn-Sham energy functional. These methods still suffer from high computational and storage overheads, however, due to extensive matrix operations related to the underlying wave function grid representation. In this paper, an alternative stochastic method is outlined that aims to solve directly for the one-electron density matrix in real space. In order to illustrate aspects of the method, model calculations are performed for simple one-dimensional problems that display some features of the more general problem, such as spatial nodes in the density matrix. This orbital-free approach may prove helpful considering a future involving increasingly parallel computing architectures. Its primary advantage is the near-locality of the random walks, allowing for simultaneous updates of the density matrix in different regions of space partitioned across the processors. In addition, it allows for testing and enforcement of the particle number and idempotency constraints through stabilization of a Feynman-Kac functional integral as opposed to the extensive matrix operations in traditional approaches. PMID:25969148

  19. Real-space density profile reconstruction of stacked voids

    NASA Astrophysics Data System (ADS)

    Pisani, Alice; Sutter, P.; Lavaux, G.; Wandelt, B.

    2016-10-01

    Modern surveys allow us to access to high quality large scale structure measurements. In this framework, cosmic voids appear as a new potential probe of Cosmology. We discuss the use of cosmic voids as standard spheres and their capacity to constrain new physics, dark energy and cosmological models. We introduce the Alcock-Paczyński test and its use with voids. We discuss the main difficulties in treating with cosmic voids: redshift-space distortions, the sparsity of data, and peculiar velocities. We present a method to reconstruct the spherical density profiles of void stacks in real space, without redshift-space distortions. We show its application to a toy model and a dark matter simulation; as well as a first application to reconstruct real cosmic void stacks density profiles in real space from the Sloan Digital Sky Survey.

  20. Real space electrostatics for multipoles. III. Dielectric properties

    NASA Astrophysics Data System (ADS)

    Lamichhane, Madan; Parsons, Thomas; Newman, Kathie E.; Gezelter, J. Daniel

    2016-08-01

    In Papers I and II, we developed new shifted potential, gradient shifted force, and Taylor shifted force real-space methods for multipole interactions in condensed phase simulations. Here, we discuss the dielectric properties of fluids that emerge from simulations using these methods. Most electrostatic methods (including the Ewald sum) require correction to the conducting boundary fluctuation formula for the static dielectric constants, and we discuss the derivation of these corrections for the new real space methods. For quadrupolar fluids, the analogous material property is the quadrupolar susceptibility. As in the dipolar case, the fluctuation formula for the quadrupolar susceptibility has corrections that depend on the electrostatic method being utilized. One of the most important effects measured by both the static dielectric and quadrupolar susceptibility is the ability to screen charges embedded in the fluid. We use potentials of mean force between solvated ions to discuss how geometric factors can lead to distance-dependent screening in both quadrupolar and dipolar fluids.

  1. Atomically resolved real-space imaging of hot electron dynamics

    PubMed Central

    Lock, D.; Rusimova, K. R.; Pan, T. L.; Palmer, R. E.; Sloan, P. A.

    2015-01-01

    The dynamics of hot electrons are central to understanding the properties of many electronic devices. But their ultra-short lifetime, typically 100 fs or less, and correspondingly short transport length-scale in the nanometre range constrain real-space investigations. Here we report variable temperature and voltage measurements of the nonlocal manipulation of adsorbed molecules on the Si(111)-7 × 7 surface in the scanning tunnelling microscope. The range of the nonlocal effect increases with temperature and, at constant temperature, is invariant over a wide range of electron energies. The measurements probe, in real space, the underlying hot electron dynamics on the 10 nm scale and are well described by a two-dimensional diffusive model with a single decay channel, consistent with 2-photon photo-emission (2PPE) measurements of the real time dynamics. PMID:26387703

  2. Atomically resolved real-space imaging of hot electron dynamics.

    PubMed

    Lock, D; Rusimova, K R; Pan, T L; Palmer, R E; Sloan, P A

    2015-09-21

    The dynamics of hot electrons are central to understanding the properties of many electronic devices. But their ultra-short lifetime, typically 100 fs or less, and correspondingly short transport length-scale in the nanometre range constrain real-space investigations. Here we report variable temperature and voltage measurements of the nonlocal manipulation of adsorbed molecules on the Si(111)-7 × 7 surface in the scanning tunnelling microscope. The range of the nonlocal effect increases with temperature and, at constant temperature, is invariant over a wide range of electron energies. The measurements probe, in real space, the underlying hot electron dynamics on the 10 nm scale and are well described by a two-dimensional diffusive model with a single decay channel, consistent with 2-photon photo-emission (2PPE) measurements of the real time dynamics.

  3. Real-space grids and the Octopus code as tools for the development of new simulation approaches for electronic systems.

    PubMed

    Andrade, Xavier; Strubbe, David; De Giovannini, Umberto; Larsen, Ask Hjorth; Oliveira, Micael J T; Alberdi-Rodriguez, Joseba; Varas, Alejandro; Theophilou, Iris; Helbig, Nicole; Verstraete, Matthieu J; Stella, Lorenzo; Nogueira, Fernando; Aspuru-Guzik, Alán; Castro, Alberto; Marques, Miguel A L; Rubio, Angel

    2015-12-21

    Real-space grids are a powerful alternative for the simulation of electronic systems. One of the main advantages of the approach is the flexibility and simplicity of working directly in real space where the different fields are discretized on a grid, combined with competitive numerical performance and great potential for parallelization. These properties constitute a great advantage at the time of implementing and testing new physical models. Based on our experience with the Octopus code, in this article we discuss how the real-space approach has allowed for the recent development of new ideas for the simulation of electronic systems. Among these applications are approaches to calculate response properties, modeling of photoemission, optimal control of quantum systems, simulation of plasmonic systems, and the exact solution of the Schrödinger equation for low-dimensionality systems.

  4. Real-space grids and the Octopus code as tools for the development of new simulation approaches for electronic systems

    NASA Astrophysics Data System (ADS)

    Andrade, Xavier; Strubbe, David; De Giovannini, Umberto; Larsen, Ask Hjorth; Oliveira, Micael J. T.; Alberdi-Rodriguez, Joseba; Varas, Alejandro; Theophilou, Iris; Helbig, Nicole; Verstraete, Matthieu J.; Stella, Lorenzo; Nogueira, Fernando; Aspuru-Guzik, Alán; Castro, Alberto; Marques, Miguel A. L.; Rubio, Angel

    Real-space grids are a powerful alternative for the simulation of electronic systems. One of the main advantages of the approach is the flexibility and simplicity of working directly in real space where the different fields are discretized on a grid, combined with competitive numerical performance and great potential for parallelization. These properties constitute a great advantage at the time of implementing and testing new physical models. Based on our experience with the Octopus code, in this article we discuss how the real-space approach has allowed for the recent development of new ideas for the simulation of electronic systems. Among these applications are approaches to calculate response properties, modeling of photoemission, optimal control of quantum systems, simulation of plasmonic systems, and the exact solution of the Schr\\"odinger equation for low-dimensionality systems.

  5. Real-space grids and the Octopus code as tools for the development of new simulation approaches for electronic systems.

    PubMed

    Andrade, Xavier; Strubbe, David; De Giovannini, Umberto; Larsen, Ask Hjorth; Oliveira, Micael J T; Alberdi-Rodriguez, Joseba; Varas, Alejandro; Theophilou, Iris; Helbig, Nicole; Verstraete, Matthieu J; Stella, Lorenzo; Nogueira, Fernando; Aspuru-Guzik, Alán; Castro, Alberto; Marques, Miguel A L; Rubio, Angel

    2015-12-21

    Real-space grids are a powerful alternative for the simulation of electronic systems. One of the main advantages of the approach is the flexibility and simplicity of working directly in real space where the different fields are discretized on a grid, combined with competitive numerical performance and great potential for parallelization. These properties constitute a great advantage at the time of implementing and testing new physical models. Based on our experience with the Octopus code, in this article we discuss how the real-space approach has allowed for the recent development of new ideas for the simulation of electronic systems. Among these applications are approaches to calculate response properties, modeling of photoemission, optimal control of quantum systems, simulation of plasmonic systems, and the exact solution of the Schrödinger equation for low-dimensionality systems. PMID:25721500

  6. Direct observation limits on antimatter gravitation

    SciTech Connect

    Fischler, Mark; Lykken, Joe; Roberts, Tom; /Fermilab

    2008-06-01

    The proposed Antihydrogen Gravity experiment at Fermilab (P981) will directly measure the gravitational attraction g between antihydrogen and the Earth, with an accuracy of 1% or better. The following key question has been asked by the PAC: Is a possible 1% difference between g and g already ruled out by other evidence? This memo presents the key points of existing evidence, to answer whether such a difference is ruled out (a) on the basis of direct observational evidence; and/or (b) on the basis of indirect evidence, combined with reasoning based on strongly held theoretical assumptions. The bottom line is that there are no direct observations or measurements of gravitational asymmetry which address the antimatter sector. There is evidence which by indirect reasoning can be taken to rule out such a difference, but the analysis needed to draw that conclusion rests on models and assumptions which are in question for other reasons and are thus worth testing. There is no compelling evidence or theoretical reason to rule out such a difference at the 1% level.

  7. Direct observations of atmospheric aerosol nucleation.

    PubMed

    Kulmala, Markku; Kontkanen, Jenni; Junninen, Heikki; Lehtipalo, Katrianne; Manninen, Hanna E; Nieminen, Tuomo; Petäjä, Tuukka; Sipilä, Mikko; Schobesberger, Siegfried; Rantala, Pekka; Franchin, Alessandro; Jokinen, Tuija; Järvinen, Emma; Äijälä, Mikko; Kangasluoma, Juha; Hakala, Jani; Aalto, Pasi P; Paasonen, Pauli; Mikkilä, Jyri; Vanhanen, Joonas; Aalto, Juho; Hakola, Hannele; Makkonen, Ulla; Ruuskanen, Taina; Mauldin, Roy L; Duplissy, Jonathan; Vehkamäki, Hanna; Bäck, Jaana; Kortelainen, Aki; Riipinen, Ilona; Kurtén, Theo; Johnston, Murray V; Smith, James N; Ehn, Mikael; Mentel, Thomas F; Lehtinen, Kari E J; Laaksonen, Ari; Kerminen, Veli-Matti; Worsnop, Douglas R

    2013-02-22

    Atmospheric nucleation is the dominant source of aerosol particles in the global atmosphere and an important player in aerosol climatic effects. The key steps of this process occur in the sub-2-nanometer (nm) size range, in which direct size-segregated observations have not been possible until very recently. Here, we present detailed observations of atmospheric nanoparticles and clusters down to 1-nm mobility diameter. We identified three separate size regimes below 2-nm diameter that build up a physically, chemically, and dynamically consistent framework on atmospheric nucleation--more specifically, aerosol formation via neutral pathways. Our findings emphasize the important role of organic compounds in atmospheric aerosol formation, subsequent aerosol growth, radiative forcing and associated feedbacks between biogenic emissions, clouds, and climate.

  8. Direct observation of laser guided corona discharges.

    PubMed

    Wang, Tie-Jun; Wei, Yingxia; Liu, Yaoxiang; Chen, Na; Liu, Yonghong; Ju, Jingjing; Sun, Haiyi; Wang, Cheng; Lu, Haihe; Liu, Jiansheng; Chin, See Leang; Li, Ruxin; Xu, Zhizhan

    2015-01-01

    Laser based lightning control holds a promising way to solve the problem of the long standing disaster of lightning strikes. But it is a challenging project due to insufficient understanding of the interaction between laser plasma channel and high voltage electric filed. In this work, a direct observation of laser guided corona discharge is reported. Laser filament guided streamer and leader types of corona discharges were observed. An enhanced ionization took place in the leader (filament) through the interaction with the high voltage discharging field. The fluorescence lifetime of laser filament guided corona discharge was measured to be several microseconds, which is 3 orders of magnitude longer than the fluorescence lifetime of laser filaments. This work could be advantageous towards a better understanding of laser assisted leader development in the atmosphere. PMID:26679271

  9. Direct observation of laser guided corona discharges

    PubMed Central

    Wang, Tie-Jun; Wei, Yingxia; Liu, Yaoxiang; Chen, Na; Liu, Yonghong; Ju, Jingjing; Sun, Haiyi; Wang, Cheng; Lu, Haihe; Liu, Jiansheng; Chin, See Leang; Li, Ruxin; Xu, Zhizhan

    2015-01-01

    Laser based lightning control holds a promising way to solve the problem of the long standing disaster of lightning strikes. But it is a challenging project due to insufficient understanding of the interaction between laser plasma channel and high voltage electric filed. In this work, a direct observation of laser guided corona discharge is reported. Laser filament guided streamer and leader types of corona discharges were observed. An enhanced ionization took place in the leader (filament) through the interaction with the high voltage discharging field. The fluorescence lifetime of laser filament guided corona discharge was measured to be several microseconds, which is 3 orders of magnitude longer than the fluorescence lifetime of laser filaments. This work could be advantageous towards a better understanding of laser assisted leader development in the atmosphere. PMID:26679271

  10. Direct observation of sub-binomial light.

    PubMed

    Bartley, Tim J; Donati, Gaia; Jin, Xian-Min; Datta, Animesh; Barbieri, Marco; Walmsley, Ian A

    2013-04-26

    Nonclassical states of light are necessary resources for quantum technologies such as cryptography, computation and the definition of metrological standards. Observing signatures of nonclassicality generally requires inferring either the photon number distribution or a quasiprobability distribution indirectly from a set of measurements. Here, we report an experiment in which the nonclassical character of families of quantum states is assessed by direct inspection of the outcomes from a multiplexed photon counter. This scheme does not register the actual photon number distribution; the statistics of the detector clicks alone serve as a witness of nonclassicality, as proposed by Sperling et al. [Phys. Rev. Lett. 109, 093601 (2012)]. Our work paves a way for the practical characterization of increasingly sophisticated states and detectors. PMID:23679726

  11. Reconstructing interaction potentials in thin films from real-space images

    NASA Astrophysics Data System (ADS)

    Gienger, Jonas; Severin, Nikolai; Rabe, Jürgen P.; Sokolov, Igor M.

    2016-04-01

    We demonstrate that an inverse Monte Carlo approach allows one to reconstruct effective interaction potentials from real-space images. The method is exemplified on monomolecular ethanol-water films imaged with scanning force microscopy, which provides the spatial distribution of the molecules. Direct Monte Carlo simulations with the reconstructed potential allow for obtaining characteristics of the system which are unavailable in the experiment, such as the heat capacity of the monomolecularly thin film, and for a prediction of the critical temperature of the demixing transition.

  12. EDITORIAL: From reciprocal space to real space in surface science From reciprocal space to real space in surface science

    NASA Astrophysics Data System (ADS)

    Bartels, Ludwig; Ernst, Karl-Heinz

    2012-09-01

    This issue is dedicated to Karl-Heinz Rieder on the occasion of his 70th birthday. It contains contributions written by his former students and colleagues from all over the world. Experimental techniques based on free electrons, such as photoelectron spectroscopy, electron microscopy and low energy electron diffraction (LEED), were foundational to surface science. While the first revealed the band structures of materials, the second provided nanometer scale imagery and the latter elucidated the atomic scale periodicity of surfaces. All required an (ultra-)high vacuum, and LEED illustrated impressively that adsorbates, such as carbon monoxide, hydrogen or oxygen, can markedly and periodically restructure surfaces from their bulk termination, even at pressures ten orders of magnitude or more below atmospheric. Yet these techniques were not generally able to reveal atomic scale surface defects, nor could they faithfully show adsorption of light atoms such as hydrogen. Although a complete atom, helium can also be regarded as a wave with a de Broglie wavelength that allows the study of surface atomic periodicities at a delicateness and sensitivity exceeding that of electrons-based techniques. In combination, these and other techniques generated insight into the periodicity of surfaces and their vibrational properties, yet were limited to simple and periodic surface setups. All that changed with the advent of scanning tunneling microscopy (STM) roughly 30 years ago, allowing real space access to surface defects and individual adsorbates. Applied at low temperatures, not only can STM establish a height profile of surfaces, but can also perform spectroscopy and serve as an actuator capable of rearranging individual species at atomic scale resolution. The direct and intuitive manner in which STM provided access as a spectator and as an actor to the atomic scale was foundational to today's surface science and to the development of the concepts of nanoscience in general. The

  13. Real space electrostatics for multipoles. III. Dielectric properties.

    PubMed

    Lamichhane, Madan; Parsons, Thomas; Newman, Kathie E; Gezelter, J Daniel

    2016-08-21

    In Papers I and II, we developed new shifted potential, gradient shifted force, and Taylor shifted force real-space methods for multipole interactions in condensed phase simulations. Here, we discuss the dielectric properties of fluids that emerge from simulations using these methods. Most electrostatic methods (including the Ewald sum) require correction to the conducting boundary fluctuation formula for the static dielectric constants, and we discuss the derivation of these corrections for the new real space methods. For quadrupolar fluids, the analogous material property is the quadrupolar susceptibility. As in the dipolar case, the fluctuation formula for the quadrupolar susceptibility has corrections that depend on the electrostatic method being utilized. One of the most important effects measured by both the static dielectric and quadrupolar susceptibility is the ability to screen charges embedded in the fluid. We use potentials of mean force between solvated ions to discuss how geometric factors can lead to distance-dependent screening in both quadrupolar and dipolar fluids. PMID:27544088

  14. Study on the mapping of dark matter clustering from real space to redshift space

    NASA Astrophysics Data System (ADS)

    Zheng, Yi; Song, Yong-Seon

    2016-08-01

    The mapping of dark matter clustering from real space to redshift space introduces the anisotropic property to the measured density power spectrum in redshift space, known as the redshift space distortion effect. The mapping formula is intrinsically non-linear, which is complicated by the higher order polynomials due to indefinite cross correlations between the density and velocity fields, and the Finger-of-God effect due to the randomness of the peculiar velocity field. Whilst the full higher order polynomials remain unknown, the other systematics can be controlled consistently within the same order truncation in the expansion of the mapping formula, as shown in this paper. The systematic due to the unknown non-linear density and velocity fields is removed by separately measuring all terms in the expansion directly using simulations. The uncertainty caused by the velocity randomness is controlled by splitting the FoG term into two pieces, 1) the ``one-point" FoG term being independent of the separation vector between two different points, and 2) the ``correlated" FoG term appearing as an indefinite polynomials which is expanded in the same order as all other perturbative polynomials. Using 100 realizations of simulations, we find that the Gaussian FoG function with only one scale-independent free parameter works quite well, and that our new mapping formulation accurately reproduces the observed 2-dimensional density power spectrum in redshift space at the smallest scales by far, up to k~ 0.2 Mpc‑1, considering the resolution of future experiments.

  15. Study on the mapping of dark matter clustering from real space to redshift space

    NASA Astrophysics Data System (ADS)

    Zheng, Yi; Song, Yong-Seon

    2016-08-01

    The mapping of dark matter clustering from real space to redshift space introduces the anisotropic property to the measured density power spectrum in redshift space, known as the redshift space distortion effect. The mapping formula is intrinsically non-linear, which is complicated by the higher order polynomials due to indefinite cross correlations between the density and velocity fields, and the Finger-of-God effect due to the randomness of the peculiar velocity field. Whilst the full higher order polynomials remain unknown, the other systematics can be controlled consistently within the same order truncation in the expansion of the mapping formula, as shown in this paper. The systematic due to the unknown non-linear density and velocity fields is removed by separately measuring all terms in the expansion directly using simulations. The uncertainty caused by the velocity randomness is controlled by splitting the FoG term into two pieces, 1) the ``one-point" FoG term being independent of the separation vector between two different points, and 2) the ``correlated" FoG term appearing as an indefinite polynomials which is expanded in the same order as all other perturbative polynomials. Using 100 realizations of simulations, we find that the Gaussian FoG function with only one scale-independent free parameter works quite well, and that our new mapping formulation accurately reproduces the observed 2-dimensional density power spectrum in redshift space at the smallest scales by far, up to k~ 0.2 Mpc-1, considering the resolution of future experiments.

  16. A real-space approach to the X-ray phase problem

    NASA Astrophysics Data System (ADS)

    Liu, Xiangan

    Over the past few decades, the phase problem of X-ray crystallography has been explored in reciprocal space in the so called direct methods . Here we investigate the problem using a real-space approach that bypasses the laborious procedure of frequent Fourier synthesis and peak picking. Starting from a completely random structure, we move the atoms around in real space to minimize a cost function. A Monte Carlo method named simulated annealing (SA) is employed to search the global minimum of the cost function which could be constructed in either real space or reciprocal space. In the hybrid minimal principle, we combine the dual space costs together. One part of the cost function monitors the probability distribution of the phase triplets, while the other is a real space cost function which represents the discrepancy between measured and calculated intensities. Compared to the single space cost functions, the dual space cost function has a greatly improved landscape and therefore could prevent the system from being trapped in metastable states. Thus, the structures of large molecules such as virginiamycin (C43H 49N7O10 · 3CH0OH), isoleucinomycin (C60H102N 6O18) and hexadecaisoleucinomycin (HEXIL) (C80H136 N8O24) can now be solved, whereas it would not be possible using the single cost function. When a molecule gets larger, the configurational space becomes larger, and the requirement of CPU time increases exponentially. The method of improved Monte Carlo sampling has demonstrated its capability to solve large molecular structures. The atoms are encouraged to sample the high density regions in space determined by an approximate density map which in turn is updated and modified by averaging and Fourier synthesis. This type of biased sampling has led to considerable reduction of the configurational space. It greatly improves the algorithm compared to the previous uniform sampling. Hence, for instance, 90% of computer run time could be cut in solving the complex

  17. Wind direction modelling using multiple observation points.

    PubMed

    Hirata, Yoshito; Mandic, Danilo P; Suzuki, Hideyuki; Aihara, Kazuyuki

    2008-02-28

    The prediction of wind direction is a prerequisite for the intelligent and efficient operation of wind turbines. This is a complex task, due to the intermittent behaviour of wind, its non-Gaussian and nonlinear nature, and the coupling between the wind speed and direction. To provide improved wind direction forecasting, we propose a nonlinear model with augmented information from an additional measurement point. This is further enhanced by making use of both the speed and direction components of the wind field vector. The analysis and a comprehensive set of simulations demonstrate that the proposed approach achieves improved prediction performance over the standard and persistent model. The potential of the proposed approach is justified by the fact that even relatively small improvements in the forecasts result in large gains in the produced output power.

  18. Bias deconstructed: unravelling the scale dependence of halo bias using real-space measurements

    NASA Astrophysics Data System (ADS)

    Paranjape, Aseem; Sefusatti, Emiliano; Chan, Kwan Chuen; Desjacques, Vincent; Monaco, Pierluigi; Sheth, Ravi K.

    2013-11-01

    We explore the scale dependence of halo bias using real-space cross-correlation measurements in N-body simulations and in PINOCCHIO, an algorithm based on Lagrangian Perturbation Theory. Recent work has shown how to interpret such real-space measurements in terms of k-dependent bias in Fourier space, and how to remove the k-dependence to reconstruct the k-independent peak-background split halo bias parameters. We compare our reconstruction of the linear bias, which requires no free parameters, with previous estimates from N-body simulations which were obtained directly in Fourier space at large scales, and find very good agreement. Our reconstruction of the quadratic bias is similarly parameter-free, although in this case there are no previous Fourier space measurements to compare with. Our analysis of N-body simulations explicitly tests the predictions of the excursion set peaks (ESP) formalism of Paranjape et al. for the scale dependence of bias; we find that the ESP predictions accurately describe our measurements. In addition, our measurements in PINOCCHIO serve as a useful, successful consistency check between PINOCCHIO and N-body simulations that is not accessible to traditional measurements.

  19. ATLAS: A real-space finite-difference implementation of orbital-free density functional theory

    NASA Astrophysics Data System (ADS)

    Mi, Wenhui; Shao, Xuecheng; Su, Chuanxun; Zhou, Yuanyuan; Zhang, Shoutao; Li, Quan; Wang, Hui; Zhang, Lijun; Miao, Maosheng; Wang, Yanchao; Ma, Yanming

    2016-03-01

    Orbital-free density functional theory (OF-DFT) is a promising method for large-scale quantum mechanics simulation as it provides a good balance of accuracy and computational cost. Its applicability to large-scale simulations has been aided by progress in constructing kinetic energy functionals and local pseudopotentials. However, the widespread adoption of OF-DFT requires further improvement in its efficiency and robustly implemented software. Here we develop a real-space finite-difference (FD) method for the numerical solution of OF-DFT in periodic systems. Instead of the traditional self-consistent method, a powerful scheme for energy minimization is introduced to solve the Euler-Lagrange equation. Our approach engages both the real-space finite-difference method and a direct energy-minimization scheme for the OF-DFT calculations. The method is coded into the ATLAS software package and benchmarked using periodic systems of solid Mg, Al, and Al3Mg. The test results show that our implementation can achieve high accuracy, efficiency, and numerical stability for large-scale simulations.

  20. Real-space formulation of the electrostatic potential and total energy of solids

    SciTech Connect

    Pask, J E; Sterne, P A

    2004-05-12

    We develop expressions for the electrostatic potential and total energy of crystalline solids which are amenable to direct evaluation in real space. Unlike conventional reciprocal space formulations, no Fourier transforms or reciprocal lattice summations are required, and the formulation is well suited for large-scale, parallel computations. The need for reciprocal space expressions is eliminated by replacing long-range potentials by equivalent localized charge distributions and incorporating long-range interactions into boundary conditions on the unit cell. In so doing, a simplification of the conventional reciprocal space formalism is obtained. The equivalence of the real- and reciprocal space formalisms is demonstrated by direct comparison in self-consistent density-functional calculations.

  1. Direct Observation of Spin- and Charge-Density Waves in a Luttinger Liquid

    NASA Astrophysics Data System (ADS)

    Cao, Chenglin; Marcum, Andrew; Mawardi Ismail, Arif; Fonta, Francisco; O'Hara, Kenneth

    2016-05-01

    At low energy, interacting fermions in one dimension (e.g. electrons in quantum wires or fermionic atoms in 1D waveguides) should behave as Luttinger liquids. In stark contrast to Fermi liquids, the low-energy elementary excitations in Luttinger liquids are collective sound-like modes that propagate independently as spin-density and/or charge-density (i.e. particle-density) waves with generally unequal, and interaction-dependent, velocities. Here we aim to unambiguously confirm this hallmark feature of the Luttinger liquid - the phenomenon of spin-charge separation - by directly observing in real space the dynamics of spin-density and ``charge''-density waves excited in an ultracold gas of spin-1/2 fermions confined in an array of 1D optical waveguides. Starting from a two-component mixture of 6 Li atoms harmonically confined along each of the 1D waveguides, we excite low lying normal modes of the trapped system - namely the spin dipole and density dipole and quadrupole modes - and measure their frequency as a function of interaction strength. Luttinger liquid theory predicts that the spin dipole frequency is strongly dependent on interaction strength whereas the density dipole and quadrupole mode frequencies are relatively insensitive. We will also discuss extending our approach to exciting localized spin density and particle density wavepackets which should propagate at different velocities. Supported by AFOSR and NSF.

  2. Direct Observation of Paramagnons in Palladium

    SciTech Connect

    Doubble, R.; Hayden, S M.; Dai, Pengcheng; Mook Jr, Herbert A; Thompson, James R; Frost, C.

    2010-01-01

    We report an inelastic neutron scattering study of the spin fluctuations in the nearly ferromagnetic element palladium. Dispersive over-damped collective magnetic excitations or 'paramagnons' are observed up to 128 meV. We analyze our results in terms of a Moriya-Lonzarich-type spin-fluctuation model and estimate the contribution of the spin fluctuations to the low-temperature heat capacity. In spite of the paramagnon excitations being relatively strong, their relaxation rates are large. This leads to a small contribution to the low-temperature electronic specific heat.

  3. Direct observation of ballistic Andreev reflection

    SciTech Connect

    Klapwijk, T. M.; Ryabchun, S. A.

    2014-12-15

    An overview is presented of experiments on ballistic electrical transport in inhomogeneous superconducting systems which are controlled by the process of Andreev reflection. The initial experiments based on the coexistence of a normal phase and a superconducting phase in the intermediate state led to the concept itself. It was followed by a focus on geometrically inhomogeneous systems like point contacts, which provided a very clear manifestation of the energy and direction dependence of the Andreev reflection process. The point contacts have recently evolved towards the atomic scale owing to the use of mechanical break-junctions, revealing a very detailed dependence of Andreev reflection on the macroscopic phase of the superconducting state. In present-day research, the superconducting in homogeneity is constructed by clean room technology and combines superconducting materials, for example, with low-dimensional materials and topological insulators. Alternatively, the superconductor is combined with nano-objects, such as graphene, carbon nanotubes, or semiconducting nanowires. Each of these “inhomogeneous systems” provides a very interesting range of properties, all rooted in some manifestation of Andreev reflection.

  4. Real-space imaging of a topologically protected edge state with ultracold atoms in an amplitude-chirped optical lattice

    PubMed Central

    Leder, Martin; Grossert, Christopher; Sitta, Lukas; Genske, Maximilian; Rosch, Achim; Weitz, Martin

    2016-01-01

    To describe a mobile defect in polyacetylene chains, Su, Schrieffer and Heeger formulated a model assuming two degenerate energy configurations that are characterized by two different topological phases. An immediate consequence was the emergence of a soliton-type edge state located at the boundary between two regions of different configurations. Besides giving first insights in the electrical properties of polyacetylene materials, interest in this effect also stems from its close connection to states with fractional charge from relativistic field theory. Here, using a one-dimensional optical lattice for cold rubidium atoms with a spatially chirped amplitude, we experimentally realize an interface between two spatial regions of different topological order in an atomic physics system. We directly observe atoms confined in the edge state at the intersection by optical real-space imaging and characterize the state as well as the size of the associated energy gap. Our findings hold prospects for the spectroscopy of surface states in topological matter and for the quantum simulation of interacting Dirac systems. PMID:27767054

  5. Real-space refinement of single-crystal electron diffuse scattering and its application to Bi2Ru2O7-δ

    NASA Astrophysics Data System (ADS)

    Goodwin, A. L.; Withers, R. L.; Nguyen, H.-B.

    2007-08-01

    A real-space atomistic refinement approach to the analysis of experimental electron diffraction patterns is described. The method employs the reverse Monte Carlo algorithm to produce atomistic configurations capable of qualitatively reproducing diffuse electron scattering patterns. Its implementation in the program EDRMC is described in detail, together with a number of additional constraints/restraints that can be used to guide the refinement process. In particular, appropriate restraints ensure the individual atomic displacements introduced to model the diffuse scattering patterns are simultaneously consistent with the known average structure. The approach is then used to interpret electron diffraction patterns measured for Bi2Ru2O7-δ. The diffuse scattering patterns observed are shown to arise primarily from concerted translations of Bi atoms. These translations can be interpreted in terms of rotations of [O'Bi4 ] tetrahedra correlated along the \\langle 110\\rangle crystal axes and uncorrelated along orthogonal directions.

  6. Simulation of Latex Film Formation Using a Cell Model in Real Space: Vertical Drying.

    PubMed

    Gromer, A; Nassar, M; Thalmann, F; Hébraud, P; Holl, Y

    2015-10-13

    This paper presents a simulation tool applied to latex film formation by drying, a hybrid between a classical numerical resolution method using finite differences and cellular automata, and making use of object-oriented programming. It consists of dividing real space into cells and applying local physical laws to simulate the exchange of matter between neighboring cells. In a first step, the simulation was applied to the simple case of vertical drying of a latex containing only one population of monodisperse particles and water. Our results show how the distribution of latex particles evolves through the different drying stages due to a combination of diffusion, convection, and particle deformation. While repulsive interactions between the particles tend to favor homogeneous distributions in the first drying stage, concentration gradients that develop in opposite ways can be observed depending on the drying regime. The distributions, calculated in various cases, reproduce and extend several theoretical results and are in qualitative agreement with some experimental findings. PMID:26378376

  7. Keeping it real: revisiting a real-space approach to running ensembles of cosmological N-body simulations

    NASA Astrophysics Data System (ADS)

    Orban, Chris

    2013-05-01

    In setting up initial conditions for ensembles of cosmological N-body simulations there are, fundamentally, two choices: either maximizing the correspondence of the initial density field to the assumed fourier-space clustering or, instead, matching to real-space statistics and allowing the DC mode (i.e. overdensity) to vary from box to box as it would in the real universe. As a stringent test of both approaches, I perform ensembles of simulations using power law and a ``powerlaw times a bump'' model inspired by baryon acoustic oscillations (BAO), exploiting the self-similarity of these initial conditions to quantify the accuracy of the matter-matter two-point correlation results. The real-space method, which was originally proposed by Pen 1997 [1] and implemented by Sirko 2005 [2], performed well in producing the expected self-similar behavior and corroborated the non-linear evolution of the BAO feature observed in conventional simulations, even in the strongly-clustered regime (σ8gtrsim1). In revisiting the real-space method championed by [2], it was also noticed that this earlier study overlooked an important integral constraint correction to the correlation function in results from the conventional approach that can be important in ΛCDM simulations with Lboxlesssim1 h-1Gpc and on scales rgtrsimLbox/10. Rectifying this issue shows that the fourier space and real space methods are about equally accurate and efficient for modeling the evolution and growth of the correlation function, contrary to previous claims. An appendix provides a useful independent-of-epoch analytic formula for estimating the importance of the integral constraint bias on correlation function measurements in ΛCDM simulations.

  8. Keeping it real: revisiting a real-space approach to running ensembles of cosmological N-body simulations

    SciTech Connect

    Orban, Chris

    2013-05-01

    In setting up initial conditions for ensembles of cosmological N-body simulations there are, fundamentally, two choices: either maximizing the correspondence of the initial density field to the assumed fourier-space clustering or, instead, matching to real-space statistics and allowing the DC mode (i.e. overdensity) to vary from box to box as it would in the real universe. As a stringent test of both approaches, I perform ensembles of simulations using power law and a ''powerlaw times a bump'' model inspired by baryon acoustic oscillations (BAO), exploiting the self-similarity of these initial conditions to quantify the accuracy of the matter-matter two-point correlation results. The real-space method, which was originally proposed by Pen 1997 [1] and implemented by Sirko 2005 [2], performed well in producing the expected self-similar behavior and corroborated the non-linear evolution of the BAO feature observed in conventional simulations, even in the strongly-clustered regime (σ{sub 8}∼>1). In revisiting the real-space method championed by [2], it was also noticed that this earlier study overlooked an important integral constraint correction to the correlation function in results from the conventional approach that can be important in ΛCDM simulations with L{sub box}∼<1 h{sup −1}Gpc and on scales r∼>L{sub box}/10. Rectifying this issue shows that the fourier space and real space methods are about equally accurate and efficient for modeling the evolution and growth of the correlation function, contrary to previous claims. An appendix provides a useful independent-of-epoch analytic formula for estimating the importance of the integral constraint bias on correlation function measurements in ΛCDM simulations.

  9. Direct observation of electron propagation and dielectric screening on the atomic length scale.

    PubMed

    Neppl, S; Ernstorfer, R; Cavalieri, A L; Lemell, C; Wachter, G; Magerl, E; Bothschafter, E M; Jobst, M; Hofstetter, M; Kleineberg, U; Barth, J V; Menzel, D; Burgdörfer, J; Feulner, P; Krausz, F; Kienberger, R

    2015-01-15

    The propagation and transport of electrons in crystals is a fundamental process pertaining to the functioning of most electronic devices. Microscopic theories describe this phenomenon as being based on the motion of Bloch wave packets. These wave packets are superpositions of individual Bloch states with the group velocity determined by the dispersion of the electronic band structure near the central wavevector in momentum space. This concept has been verified experimentally in artificial superlattices by the observation of Bloch oscillations--periodic oscillations of electrons in real and momentum space. Here we present a direct observation of electron wave packet motion in a real-space and real-time experiment, on length and time scales shorter than the Bloch oscillation amplitude and period. We show that attosecond metrology (1 as = 10(-18) seconds) now enables quantitative insight into weakly disturbed electron wave packet propagation on the atomic length scale without being hampered by scattering effects, which inevitably occur over macroscopic propagation length scales. We use sub-femtosecond (less than 10(-15) seconds) extreme-ultraviolet light pulses to launch photoelectron wave packets inside a tungsten crystal that is covered by magnesium films of varied, well-defined thicknesses of a few ångströms. Probing the moment of arrival of the wave packets at the surface with attosecond precision reveals free-electron-like, ballistic propagation behaviour inside the magnesium adlayer--constituting the semi-classical limit of Bloch wave packet motion. Real-time access to electron transport through atomic layers and interfaces promises unprecedented insight into phenomena that may enable the scaling of electronic and photonic circuits to atomic dimensions. In addition, this experiment allows us to determine the penetration depth of electrical fields at optical frequencies at solid interfaces on the atomic scale. PMID:25592539

  10. Direct Behavioral Observation in School Settings: Bringing Science to Practice

    ERIC Educational Resources Information Center

    Nock, Matthew K.; Kurtz, Steven M. S.

    2005-01-01

    Schools provide a useful, controlled setting for evaluating child behavior problems, yet direct observational coding procedures evaluated by child researchers have not been widely incorporated by practicing clinicians. This article provides a summary of procedures useful to clinicians performing direct behavioral observation in school settings. We…

  11. Real Space Imaging of Spin Polarons in Zn-Doped SrCu2(BO3)2

    NASA Astrophysics Data System (ADS)

    Yoshida, M.; Kobayashi, H.; Yamauchi, I.; Takigawa, M.; Capponi, S.; Poilblanc, D.; Mila, F.; Kudo, K.; Koike, Y.; Kobayashi, N.

    2015-02-01

    We report on the real space profile of spin polarons in the quasi-two-dimensional frustrated dimer spin system SrCu2(BO3)2 doped with 0.16% of Zn. The 11B nuclear magnetic resonance spectrum exhibits 15 additional boron sites near nonmagnetic Zn impurities. With the help of exact diagonalizations of finite clusters, we have deduced from the boron spectrum, the distribution of local magnetizations at the Cu sites with fine spatial resolution, providing direct evidence for an extended spin polaron. The results are confronted with those of other experiments performed on doped and undoped samples of SrCu2(BO3)2.

  12. Real-space representation of electron correlation in π-conjugated systems

    SciTech Connect

    Wang, Jian E-mail: e.j.baerends@vu.nl; Baerends, Evert Jan E-mail: e.j.baerends@vu.nl

    2015-05-28

    π-electron conjugation and aromaticity are commonly associated with delocalization and especially high mobility of the π electrons. We investigate if also the electron correlation (pair density) exhibits signatures of the special electronic structure of conjugated systems. To that end the shape and extent of the pair density and derived quantities (exchange-correlation hole, Coulomb hole, and conditional density) are investigated for the prototype systems ethylene, hexatriene, and benzene. The answer is that the effects of π electron conjugation are hardly discernible in the real space representations of the electron correlation. We find the xc hole to be as localized (confined to atomic or diatomic regions) in conjugated systems as in small molecules. This result is relevant for density functional theory (DFT). The potential of the electron exchange-correlation hole is the largest part of v{sub xc}, the exchange-correlation Kohn-Sham potential. So the extent of the hole directly affects the orbital energies of both occupied and unoccupied Kohn-Sham orbitals and therefore has direct relevance for the excitation spectrum as calculated with time-dependent DFT calculations. The potential of the localized xc hole is comparatively more attractive than the actual hole left behind by an electron excited from a delocalized molecular orbital of a conjugated system.

  13. Plasmon Surface Polariton Dispersion by Direct Optical Observation.

    ERIC Educational Resources Information Center

    Swalen, J. D.; And Others

    1980-01-01

    Describes several simple experiments that can be used to observe directly the dispersion curve of plasmon surface polaritons (PSP) on flat metal surfaces. A method is described of observing the increonental change in the wave vector of the PSP due to coatings that differ in thickness by a few nanometers. (Author/CS)

  14. Evaluation of Handheld Computers for Direct Systematic Classroom Observation

    ERIC Educational Resources Information Center

    Bahr, Michael W.; Gouwens, Donald A.; Schuh, Genevieve

    2012-01-01

    Through this study the authors evaluate outcomes associated with the use of handheld computers by interventionists in improving the efficiency of direct systematic classroom observation. Information from observations is used by interventionists for treatment planning and evaluation. In this study, interventionists were trained to use personal…

  15. Stochastic, real-space, imaginary-time evaluation of third-order Feynman-Goldstone diagrams.

    PubMed

    Willow, Soohaeng Yoo; Hirata, So

    2014-01-14

    A new, alternative set of interpretation rules of Feynman-Goldstone diagrams for many-body perturbation theory is proposed, which translates diagrams into algebraic expressions suitable for direct Monte Carlo integrations. A vertex of a diagram is associated with a Coulomb interaction (rather than a two-electron integral) and an edge with the trace of a Green's function in real space and imaginary time. With these, 12 diagrams of third-order many-body perturbation (MP3) theory are converted into 20-dimensional integrals, which are then evaluated by a Monte Carlo method. It uses redundant walkers for convergence acceleration and a weight function for importance sampling in conjunction with the Metropolis algorithm. The resulting Monte Carlo MP3 method has low-rank polynomial size dependence of the operation cost, a negligible memory cost, and a naturally parallel computational kernel, while reproducing the correct correlation energies of small molecules within a few mEh after 10(6) Monte Carlo steps.

  16. Stochastic, real-space, imaginary-time evaluation of third-order Feynman–Goldstone diagrams

    SciTech Connect

    Willow, Soohaeng Yoo; Hirata, So

    2014-01-14

    A new, alternative set of interpretation rules of Feynman–Goldstone diagrams for many-body perturbation theory is proposed, which translates diagrams into algebraic expressions suitable for direct Monte Carlo integrations. A vertex of a diagram is associated with a Coulomb interaction (rather than a two-electron integral) and an edge with the trace of a Green's function in real space and imaginary time. With these, 12 diagrams of third-order many-body perturbation (MP3) theory are converted into 20-dimensional integrals, which are then evaluated by a Monte Carlo method. It uses redundant walkers for convergence acceleration and a weight function for importance sampling in conjunction with the Metropolis algorithm. The resulting Monte Carlo MP3 method has low-rank polynomial size dependence of the operation cost, a negligible memory cost, and a naturally parallel computational kernel, while reproducing the correct correlation energies of small molecules within a few mE{sub h} after 10{sup 6} Monte Carlo steps.

  17. Stochastic, real-space, imaginary-time evaluation of third-order Feynman-Goldstone diagrams.

    PubMed

    Willow, Soohaeng Yoo; Hirata, So

    2014-01-14

    A new, alternative set of interpretation rules of Feynman-Goldstone diagrams for many-body perturbation theory is proposed, which translates diagrams into algebraic expressions suitable for direct Monte Carlo integrations. A vertex of a diagram is associated with a Coulomb interaction (rather than a two-electron integral) and an edge with the trace of a Green's function in real space and imaginary time. With these, 12 diagrams of third-order many-body perturbation (MP3) theory are converted into 20-dimensional integrals, which are then evaluated by a Monte Carlo method. It uses redundant walkers for convergence acceleration and a weight function for importance sampling in conjunction with the Metropolis algorithm. The resulting Monte Carlo MP3 method has low-rank polynomial size dependence of the operation cost, a negligible memory cost, and a naturally parallel computational kernel, while reproducing the correct correlation energies of small molecules within a few mEh after 10(6) Monte Carlo steps. PMID:24437869

  18. First-principles transport calculation method based on real-space finite-difference nonequilibrium Green's function scheme

    NASA Astrophysics Data System (ADS)

    Ono, Tomoya; Egami, Yoshiyuki; Hirose, Kikuji

    2012-11-01

    We demonstrate an efficient nonequilibrium Green's function transport calculation procedure based on the real-space finite-difference method. The direct inversion of matrices for obtaining the self-energy terms of electrodes is computationally demanding in the real-space method because the matrix dimension corresponds to the number of grid points in the unit cell of electrodes, which is much larger than that of sites in the tight-binding approach. The procedure using the ratio matrices of the overbridging boundary-matching technique [Y. Fujimoto and K. Hirose, Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.67.195315 67, 195315 (2003)], which is related to the wave functions of a couple of grid planes in the matching regions, greatly reduces the computational effort to calculate self-energy terms without losing mathematical strictness. In addition, the present procedure saves computational time to obtain the Green's function of the semi-infinite system required in the Landauer-Büttiker formula. Moreover, the compact expression to relate Green's functions and scattering wave functions, which provide a real-space picture of the scattering process, is introduced. An example of the calculated results is given for the transport property of the BN ring connected to (9,0) carbon nanotubes. The wave-function matching at the interface reveals that the rotational symmetry of wave functions with respect to the tube axis plays an important role in electron transport. Since the states coming from and going to electrodes show threefold rotational symmetry, the states in the vicinity of the Fermi level, the wave function of which exhibits fivefold symmetry, do not contribute to the electron transport through the BN ring.

  19. Applying direct observation to model workflow and assess adoption.

    PubMed

    Unertl, Kim M; Weinger, Matthew B; Johnson, Kevin B

    2006-01-01

    Lack of understanding about workflow can impair health IT system adoption. Observational techniques can provide valuable information about clinical workflow. A pilot study using direct observation was conducted in an outpatient chronic disease clinic. The goals of the study were to assess workflow and information flow and to develop a general model of workflow and information behavior. Over 55 hours of direct observation showed that the pilot site utilized many of the features of the informatics systems available to them, but also employed multiple non-electronic artifacts and workarounds. Gaps existed between clinic workflow and informatics tool workflow, as well as between institutional expectations of informatics tool use and actual use. Concurrent use of both paper-based and electronic systems resulted in duplication of effort and inefficiencies. A relatively short period of direct observation revealed important information about workflow and informatics tool adoption.

  20. Direct observation of isolated Damon-Eshbach and backward volume spin-wave packets in ferromagnetic microstripes

    NASA Astrophysics Data System (ADS)

    Wessels, Philipp; Vogel, Andreas; Tödt, Jan-Niklas; Wieland, Marek; Meier, Guido; Drescher, Markus

    2016-02-01

    The analysis of isolated spin-wave packets is crucial for the understanding of magnetic transport phenomena and is particularly interesting for applications in spintronic and magnonic devices, where isolated spin-wave packets implement an information processing scheme with negligible residual heat loss. We have captured microscale magnetization dynamics of single spin-wave packets in metallic ferromagnets in space and time. Using an optically driven high-current picosecond pulse source in combination with time-resolved scanning Kerr microscopy probed by femtosecond laser pulses, we demonstrate phase-sensitive real-space observation of spin-wave packets in confined permalloy (Ni80Fe20) microstripes. Impulsive excitation permits extraction of the dynamical parameters, i.e. phase- and group velocities, frequencies and wave vectors. In addition to well-established Damon-Eshbach modes our study reveals waves with counterpropagating group- and phase-velocities. Such unusual spin-wave motion is expected for backward volume modes where the phase fronts approach the excitation volume rather than emerging out of it due to the negative slope of the dispersion relation. These modes are difficult to excite and observe directly but feature analogies to negative refractive index materials, thus enabling model studies of wave propagation inside metamaterials.

  1. Direct observation of isolated Damon-Eshbach and backward volume spin-wave packets in ferromagnetic microstripes

    PubMed Central

    Wessels, Philipp; Vogel, Andreas; Tödt, Jan-Niklas; Wieland, Marek; Meier, Guido; Drescher, Markus

    2016-01-01

    The analysis of isolated spin-wave packets is crucial for the understanding of magnetic transport phenomena and is particularly interesting for applications in spintronic and magnonic devices, where isolated spin-wave packets implement an information processing scheme with negligible residual heat loss. We have captured microscale magnetization dynamics of single spin-wave packets in metallic ferromagnets in space and time. Using an optically driven high-current picosecond pulse source in combination with time-resolved scanning Kerr microscopy probed by femtosecond laser pulses, we demonstrate phase-sensitive real-space observation of spin-wave packets in confined permalloy (Ni80Fe20) microstripes. Impulsive excitation permits extraction of the dynamical parameters, i.e. phase- and group velocities, frequencies and wave vectors. In addition to well-established Damon-Eshbach modes our study reveals waves with counterpropagating group- and phase-velocities. Such unusual spin-wave motion is expected for backward volume modes where the phase fronts approach the excitation volume rather than emerging out of it due to the negative slope of the dispersion relation. These modes are difficult to excite and observe directly but feature analogies to negative refractive index materials, thus enabling model studies of wave propagation inside metamaterials. PMID:26906113

  2. Real-Space Imaging of the Atomic Structure of Organic-Inorganic Perovskite.

    PubMed

    Ohmann, Robin; Ono, Luis K; Kim, Hui-Seon; Lin, Haiping; Lee, Michael V; Li, Youyong; Park, Nam-Gyu; Qi, Yabing

    2015-12-30

    Organic-inorganic perovskite is a promising class of materials for photovoltaic applications and light emitting diodes. However, so far commercialization is still impeded by several drawbacks. Atomic-scale effects have been suggested to be possible causes, but an unequivocal experimental view at the atomic level is missing. Here, we present a low-temperature scanning tunneling microscopy study of single crystal methylammonium lead bromide CH3NH3PbBr3. Topographic images of the in situ cleaved perovskite surface reveal the real-space atomic structure. Compared to the bulk we observe modified arrangements of atoms and molecules on the surface. With the support of density functional theory we explain these by surface reconstruction and a substantial interplay of the orientation of the polar organic cations (CH3NH3)(+) with the position of the hosting anions. This leads to structurally and electronically distinct domains with ferroelectric and antiferroelectric character. We further demonstrate local probing of defects, which may also impact device performance.

  3. External occulters for direct observation of exoplanets: an overview

    NASA Astrophysics Data System (ADS)

    Cash, W.; Schindhelm, E.; Arenberg, J.; Lo, A.; Polidan, R.; Kasdin, J.; Vanderbei, R.; Kilston, S.; Noecker, C.

    2007-09-01

    Perhaps the most compelling piece of science and exploration now under discussion for future space missions is the direct study of planets circling other stars. Indirect means have established planets as common in the universe but have given us a limited view of their actual characteristics. Direct observation holds the potential to map entire planetary systems, view newly forming planets, find Earth-like planets and perform photometry to search for major surface features. Direct observations will also enable spectroscopy of exoplanets and the search for evidence of simple life in the universe. Recent advances in the design of external occulters - starshades that block the light from the star while passing exoplanet light - have lowered their cost and improved their performance to the point where we can now envision a New Worlds Observer that is both buildable and affordable with today's technology. We will summarize recent studies of such missions and show they provide a very attractive alternative near term mission.

  4. Retinex Image Processing: Improved Fidelity To Direct Visual Observation

    NASA Technical Reports Server (NTRS)

    Jobson, Daniel J.; Rahman, Zia-Ur; Woodell, Glenn A.

    1996-01-01

    Recorded color images differ from direct human viewing by the lack of dynamic range compression and color constancy. Research is summarized which develops the center/surround retinex concept originated by Edwin Land through a single scale design to a multi-scale design with color restoration (MSRCR). The MSRCR synthesizes dynamic range compression, color constancy, and color rendition and, thereby, approaches fidelity to direct observation.

  5. Routine hand hygiene audit by direct observation: has nemesis arrived?

    PubMed

    Gould, D J; Drey, N S; Creedon, S

    2011-04-01

    Infection prevention and control experts have expended valuable health service time developing and implementing tools to audit health workers' hand hygiene compliance by direct observation. Although described as the 'gold standard' approach to hand hygiene audit, this method is labour intensive and may be inaccurate unless performed by trained personnel who are regularly monitored to ensure quality control. New technological devices have been developed to generate 'real time' data, but the cost of installing them and using them during routine patient care has not been evaluated. Moreover, they do not provide as much information about the hand hygiene episode or the context in which hand hygiene has been performed as direct observation. Uptake of hand hygiene products offers an inexpensive alternative to direct observation. Although product uptake would not provide detailed information about the hand hygiene episode or local barriers to compliance, it could be used as a continuous monitoring tool. Regular inspection of the data by infection prevention and control teams and clinical staff would indicate when and where direct investigation of practice by direct observation and questioning of staff should be targeted by highly trained personnel to identify local problems and improve practice.

  6. Direct observation of molecular orbitals in an individual single-molecule magnet Mn12 on Bi(111).

    PubMed

    Sun, Kai; Park, Kyungwha; Xie, Jiale; Luo, Jiyong; Yuan, Hongkuan; Xiong, Zuhong; Wang, Junzhong; Xue, Qikun

    2013-08-27

    Single-molecule nanomagnets have unique quantum properties, and their potential applications require characterization and accessibility of individual single-molecule magnets on various substrates. We develop a gentle tip-deposition method to bring individual prototype single-molecule magnets, manganese-12-acetate (Mn12) molecules, onto the semimetallic Bi(111) surface without linker molecules, using low-temperature scanning tunneling microscopy. We are able to identify both the almost flat-lying and side-lying orientations of Mn12 molecules at 4.5 K. Energy-resolved spectroscopic mapping enables the first observation of several molecular orbitals of individual Mn12 molecules in real space, which is consistent with density functional theory calculations. Both experimental and theoretical results suggest that an energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the almost flat-lying Mn12 is only 40% of such a gap for an isolated (free) Mn12 molecule, which is caused by charge transfer from the metallic surface states of Bi to the Mn12. Despite the reduction of this gap, STM images show that the local lattices of Bi(111) covered with Mn12 remain essentially intact, indicating that Mn12-Bi interactions are not strong. Our findings open an avenue to address directly the local structural and electronic properties of individual single-molecule magnets on solid substrates.

  7. Direct Observation: Assessing Orthopaedic Trainee Competence in the Ambulatory Setting.

    PubMed

    Phillips, Donna P; Zuckerman, Joseph D; Kalet, Adina; Egol, Kenneth A

    2016-09-01

    The Accreditation Council of Graduate Medical Education requires that residency programs teach and assess trainees in six core competencies. Assessments are imperative to determine trainee competence and to ensure that excellent care is provided to all patients. A structured, direct observation program is feasible for assessing nontechnical core competencies and providing trainees with immediate constructive feedback. Direct observation of residents in the outpatient setting by trained faculty allows assessment of each core competency. Checklists are used to document residents' basic communication skills, clinical reasoning, physical examination methods, and medical record keeping. Faculty concerns regarding residents' professionalism, medical knowledge, fatigue, or ability to self-assess are tracked. Serial observations allow for the reinforcement and/or monitoring of skills and attitudes identified as needing improvement. Residents who require additional coaching are identified early in training. Progress in educational milestones is recorded, allowing an individualized educational program that ensures that future orthopaedic surgeons excel across all domains of medical and surgical competence. PMID:27479831

  8. Pain behavior observation: current status and future directions.

    PubMed

    Keefe, F J

    2000-01-01

    Individuals who have pain engage in certain pain-related behaviors that tend to communicate their pain to others. There is growing recognition that the careful observation of such pain behaviors is an important component of a comprehensive pain assessment. This article provides an overview of the current status of behavioral observation methods used to assess pain behavior. The first half of this article describes and evaluates the most commonly used pain behavior observation methods. These include self-observation methods such as activity diaries, and direct observation methods such as the use of standard behavior sampling methods and naturalistic observation methods. The second half of the article discusses several important future clinical and research applications of pain behavior observation methods. The need to develop practical, clinical methods for incorporating pain behavior observation methods into practice settings is emphasized. Important future research topics include studying the social context of pain behavior (eg, by examining how spouses respond to displays of pain behavior), examining the predictive validity of pain behavior (ie, how observed pain behaviors predict future disability and impairment), and identifying pain behavior subgroups within heterogeneous chronic pain populations. Further development and refinement of pain behavior observation methods is likely to increase our understanding of the varied ways that patients adapt to persistent pain.

  9. Kohn–Sham approach to quantum electrodynamical density-functional theory: Exact time-dependent effective potentials in real space

    PubMed Central

    Flick, Johannes; Ruggenthaler, Michael; Appel, Heiko; Rubio, Angel

    2015-01-01

    The density-functional approach to quantum electrodynamics extends traditional density-functional theory and opens the possibility to describe electron–photon interactions in terms of effective Kohn–Sham potentials. In this work, we numerically construct the exact electron–photon Kohn–Sham potentials for a prototype system that consists of a trapped electron coupled to a quantized electromagnetic mode in an optical high-Q cavity. Although the effective current that acts on the photons is known explicitly, the exact effective potential that describes the forces exerted by the photons on the electrons is obtained from a fixed-point inversion scheme. This procedure allows us to uncover important beyond-mean-field features of the effective potential that mark the breakdown of classical light–matter interactions. We observe peak and step structures in the effective potentials, which can be attributed solely to the quantum nature of light; i.e., they are real-space signatures of the photons. Our findings show how the ubiquitous dipole interaction with a classical electromagnetic field has to be modified in real space to take the quantum nature of the electromagnetic field fully into account. PMID:26627715

  10. Kohn-Sham approach to quantum electrodynamical density-functional theory: Exact time-dependent effective potentials in real space.

    PubMed

    Flick, Johannes; Ruggenthaler, Michael; Appel, Heiko; Rubio, Angel

    2015-12-15

    The density-functional approach to quantum electrodynamics extends traditional density-functional theory and opens the possibility to describe electron-photon interactions in terms of effective Kohn-Sham potentials. In this work, we numerically construct the exact electron-photon Kohn-Sham potentials for a prototype system that consists of a trapped electron coupled to a quantized electromagnetic mode in an optical high-Q cavity. Although the effective current that acts on the photons is known explicitly, the exact effective potential that describes the forces exerted by the photons on the electrons is obtained from a fixed-point inversion scheme. This procedure allows us to uncover important beyond-mean-field features of the effective potential that mark the breakdown of classical light-matter interactions. We observe peak and step structures in the effective potentials, which can be attributed solely to the quantum nature of light; i.e., they are real-space signatures of the photons. Our findings show how the ubiquitous dipole interaction with a classical electromagnetic field has to be modified in real space to take the quantum nature of the electromagnetic field fully into account. PMID:26627715

  11. Kohn-Sham approach to quantum electrodynamical density-functional theory: Exact time-dependent effective potentials in real space.

    PubMed

    Flick, Johannes; Ruggenthaler, Michael; Appel, Heiko; Rubio, Angel

    2015-12-15

    The density-functional approach to quantum electrodynamics extends traditional density-functional theory and opens the possibility to describe electron-photon interactions in terms of effective Kohn-Sham potentials. In this work, we numerically construct the exact electron-photon Kohn-Sham potentials for a prototype system that consists of a trapped electron coupled to a quantized electromagnetic mode in an optical high-Q cavity. Although the effective current that acts on the photons is known explicitly, the exact effective potential that describes the forces exerted by the photons on the electrons is obtained from a fixed-point inversion scheme. This procedure allows us to uncover important beyond-mean-field features of the effective potential that mark the breakdown of classical light-matter interactions. We observe peak and step structures in the effective potentials, which can be attributed solely to the quantum nature of light; i.e., they are real-space signatures of the photons. Our findings show how the ubiquitous dipole interaction with a classical electromagnetic field has to be modified in real space to take the quantum nature of the electromagnetic field fully into account.

  12. New Directions: Emerging Satellite Observations of Above-cloud Aerosols and Direct Radiative Forcing

    NASA Technical Reports Server (NTRS)

    Yu, Hongbin; Zhang, Zhibo

    2013-01-01

    Spaceborne lidar and passive sensors with multi-wavelength and polarization capabilities onboard the A-Train provide unprecedented opportunities of observing above-cloud aerosols and direct radiative forcing. Significant progress has been made in recent years in exploring these new aerosol remote sensing capabilities and generating unique datasets. The emerging observations will advance the understanding of aerosol climate forcing.

  13. Survival of Bacillus pumilus spores for a prolonged period of time in real space conditions.

    PubMed

    Vaishampayan, Parag A; Rabbow, Elke; Horneck, Gerda; Venkateswaran, Kasthuri J

    2012-05-01

    To prevent forward contamination and maintain the scientific integrity of future life-detection missions, it is important to characterize and attempt to eliminate terrestrial microorganisms associated with exploratory spacecraft and landing vehicles. Among the organisms isolated from spacecraft-associated surfaces, spores of Bacillus pumilus SAFR-032 exhibited unusually high resistance to decontamination techniques such as UV radiation and peroxide treatment. Subsequently, B. pumilus SAFR-032 was flown to the International Space Station (ISS) and exposed to a variety of space conditions via the European Technology Exposure Facility (EuTEF). After 18 months of exposure in the EXPOSE facility of the European Space Agency (ESA) on EuTEF under dark space conditions, SAFR-032 spores showed 10-40% survivability, whereas a survival rate of 85-100% was observed when these spores were kept aboard the ISS under dark simulated martian atmospheric conditions. In contrast, when UV (>110 nm) was applied on SAFR-032 spores for the same time period and under the same conditions used in EXPOSE, a ∼7-log reduction in viability was observed. A parallel experiment was conducted on Earth with identical samples under simulated space conditions. Spores exposed to ground simulations showed less of a reduction in viability when compared with the "real space" exposed spores (∼3-log reduction in viability for "UV-Mars," and ∼4-log reduction in viability for "UV-Space"). A comparative proteomics analysis indicated that proteins conferring resistant traits (superoxide dismutase) were present in higher concentration in space-exposed spores when compared to controls. Also, the first-generation cells and spores derived from space-exposed samples exhibited elevated UVC resistance when compared with their ground control counterparts. The data generated are important for calculating the probability and mechanisms of microbial survival in space conditions and assessing microbial contaminants

  14. SPICA Coronagraph for the Direct Observation of Exo-Planets

    NASA Astrophysics Data System (ADS)

    Enya, K.; S. W. Group

    2011-12-01

    We present a mid-infrared coronagraph which targets the direct observation of exo-planets for the Space Infrared telescope for Cosmology and Astrophysics (SPICA). Study and experiment are ongoing for an coronagraph for SPICA, and this coronagraph is currently regarded as an option of the focal plane instruments. The primary target of the SPICA coronagraph is the direct imaging and spectroscopy of exo-planets in infrared. The SPICA mission gives us a unique opportunity for high-contrast observations, because of its large telescope aperture (3.5 m), the clean point-spread function provided by the monolithic telescope mirrors, and the capability for infrared observations from space. Laboratory experiments were performed with a visible laser to demonstrate the principles of the coronagraph. In an experiment using a binary-shaped pupil coronagraph, it was demonstrated that the contrast exceeded the requirement of SPICA, 10×10-6. A coronagraph obtained using a binary-shaped pupil mask is a baseline solution for SPICA because of its feasibility and robustness, while the use of a phase-induced amplitude apodization/binary-mask hybrid coronagraph is also considered as an option. Further developments are ongoing in order to realize a mid-infrared coronagraph for SPICA. Considering SPICA to be an essential platform for coronagraphic studies, and taking into account the progress of key technologies, we propose to develop a mid-infrared coronagraph instrument for SPICA and to perform the direct observation of exo-planets by using it.

  15. Enhanced Optoelectronic Performance of a Passivated Nanowire-Based Device: Key Information from Real-Space Imaging Using 4D Electron Microscopy.

    PubMed

    Khan, Jafar I; Adhikari, Aniruddha; Sun, Jingya; Priante, Davide; Bose, Riya; Shaheen, Basamat S; Ng, Tien Khee; Zhao, Chao; Bakr, Osman M; Ooi, Boon S; Mohammed, Omar F

    2016-05-01

    Managing trap states and understanding their role in ultrafast charge-carrier dynamics, particularly at surface and interfaces, remains a major bottleneck preventing further advancements and commercial exploitation of nanowire (NW)-based devices. A key challenge is to selectively map such ultrafast dynamical processes on the surfaces of NWs, a capability so far out of reach of time-resolved laser techniques. Selective mapping of surface dynamics in real space and time can only be achieved by applying four-dimensional scanning ultrafast electron microscopy (4D S-UEM). Charge carrier dynamics are spatially and temporally visualized on the surface of InGaN NW arrays before and after surface passivation with octadecylthiol (ODT). The time-resolved secondary electron images clearly demonstrate that carrier recombination on the NW surface is significantly slowed down after ODT treatment. This observation is fully supported by enhancement of the performance of the light emitting device. Direct observation of surface dynamics provides a profound understanding of the photophysical mechanisms on materials' surfaces and enables the formulation of effective surface trap state management strategies for the next generation of high-performance NW-based optoelectronic devices. PMID:26938476

  16. Thermal effects on EXAFS: Ensemble averages and real-space approach

    SciTech Connect

    Vaccari, M.; Fornasini, P.

    2005-09-01

    Thermal effects on EXAFS are considered from a general perspective. The equivalence between canonical average and real space average is demonstrated without approximations in both classical and quantum regimes. The link between distribution of interatomic distances and the Hamiltonian of the system is clarified. The role of the one-dimensional effective potential is critically discussed.

  17. Hiding and Searching Strategies of Adult Humans in a Virtual and a Real-Space Room

    ERIC Educational Resources Information Center

    Talbot, Katherine J.; Legge, Eric L. G.; Bulitko, Vadim; Spetch, Marcia L.

    2009-01-01

    Adults searched for or cached three objects in nine hiding locations in a virtual room or a real-space room. In both rooms, the locations selected by participants differed systematically between searching and hiding. Specifically, participants moved farther from origin and dispersed their choices more when hiding objects than when searching for…

  18. Direct Observations of the Evolution of Polar Cap Ionization Patches

    NASA Astrophysics Data System (ADS)

    Zhang, Q.; Zhang, B.; Lockwood, M. M.; Hu, H.; Moen, J. I.; Ruohoniemi, J.; Thomas, E. G.; Zhang, S.; Yang, H.; Liu, R.; McWilliams, K. A.; Baker, J. B.

    2013-12-01

    Patches of ionization are common in the polar ionosphere where their motion and associated density gradients give variable disturbances to High Frequency (HF) radio communications, over-the-horizon radar location errors, and disruption and errors to satellite navigation and communication. Their formation and evolution are poorly understood, particularly under disturbed space weather conditions. We report direct observations of the full evolution of patches during a geomagnetic storm, including formation, polar cap entry, transpolar evolution, polar cap exit, and sunward return flow. Our observations show that modulation of nightside reconnection in the substorm cycle of the magnetosphere helps form the gaps between patches where steady convection would give a 'tongue' of ionization (TOI).

  19. Incorporating photometric redshift probability density information into real-space clustering measurements

    NASA Astrophysics Data System (ADS)

    Myers, Adam D.; White, Martin; Ball, Nicholas M.

    2009-11-01

    The use of photometric redshifts in cosmology is increasing. Often, however these photo-z are treated like spectroscopic observations, in that the peak of the photometric redshift, rather than the full probability density function (PDF), is used. This overlooks useful information inherent in the full PDF. We introduce a new real-space estimator for one of the most used cosmological statistics, the two-point correlation function, that weights by the PDF of individual photometric objects in a manner that is optimal when Poisson statistics dominate. As our estimator does not bin based on the PDF peak, it substantially enhances the clustering signal by usefully incorporating information from all photometric objects that overlap the redshift bin of interest. As a real-world application, we measure quasi-stellar object (QSO) clustering in the Sloan Digital Sky Survey (SDSS). We find that our simplest binned estimator improves the clustering signal by a factor equivalent to increasing the survey size by a factor of 2-3. We also introduce a new implementation that fully weights between pairs of objects in constructing the cross-correlation and find that this pair-weighted estimator improves clustering signal in a manner equivalent to increasing the survey size by a factor of 4-5. Our technique uses spectroscopic data to anchor the distance scale and it will be particularly useful where spectroscopic data (e.g. from BOSS) overlap deeper photometry (e.g. from Pan-STARRS, DES or the LSST). We additionally provide simple, informative expressions to determine when our estimator will be competitive with the autocorrelation of spectroscopic objects. Although we use QSOs as an example population, our estimator can and should be applied to any clustering estimate that uses photometric objects.

  20. Microcrack closure in rocks under stress - Direct observation

    NASA Technical Reports Server (NTRS)

    Batzle, M. L.; Simmons, G.; Siegfried, R. W.

    1980-01-01

    Direct observations of the closure of microcracks in rocks under increasing stress are reported. Uniaxial stresses up to 300 bars were applied to untreated and previously heated samples of Westerly granite and Frederick diabase by a small hydraulic press which fit entirely within a scanning electron microscope. Crack closure characteristics are found to depend on crack orientation, with cracks perpendicular to the applied stress closing and those parallel tending to open, as well as crack aspect ratio, crack intersection properties, stress concentrations and surface roughness. Uniaxial and hydrostatic stress measurements are found to be strongly dependent on fracture content as observed by SEM, and the observed hysteresis in strain measurements in the first stress cycles is also related to microscopic processes

  1. Real space imaging of spin polarons in Zn-doped SrCu(2)(BO(3))(2).

    PubMed

    Yoshida, M; Kobayashi, H; Yamauchi, I; Takigawa, M; Capponi, S; Poilblanc, D; Mila, F; Kudo, K; Koike, Y; Kobayashi, N

    2015-02-01

    We report on the real space profile of spin polarons in the quasi-two-dimensional frustrated dimer spin system SrCu(2)(BO(3))(2) doped with 0.16% of Zn. The (11)B nuclear magnetic resonance spectrum exhibits 15 additional boron sites near nonmagnetic Zn impurities. With the help of exact diagonalizations of finite clusters, we have deduced from the boron spectrum, the distribution of local magnetizations at the Cu sites with fine spatial resolution, providing direct evidence for an extended spin polaron. The results are confronted with those of other experiments performed on doped and undoped samples of SrCu(2)(BO(3))(2). PMID:25699459

  2. A partitioned shift-without-invert algorithm to improve parallel eigensolution efficiency in real-space electronic transport

    NASA Astrophysics Data System (ADS)

    Feldman, Baruch; Zhou, Yunkai

    2016-10-01

    We present an eigenspectrum partitioning scheme without inversion for the recently described real-space electronic transport code, TRANSEC. The primary advantage of TRANSEC is its highly parallel algorithm, which enables studying conductance in large systems. The present scheme adds a new source of parallelization, significantly enhancing TRANSEC's parallel scalability, especially for systems with many electrons. In principle, partitioning could enable super-linear parallel speedup, as we demonstrate in calculations within TRANSEC. In practical cases, we report better than five-fold improvement in CPU time and similar improvements in wall time, compared to previously-published large calculations. Importantly, the suggested scheme is relatively simple to implement. It can be useful for general large Hermitian or weakly non-Hermitian eigenvalue problems, whenever relatively accurate inversion via direct or iterative linear solvers is impractical.

  3. Direct observation of intermolecular interactions mediated by hydrogen bonding

    NASA Astrophysics Data System (ADS)

    De Marco, Luigi; Thämer, Martin; Reppert, Mike; Tokmakoff, Andrei

    2014-07-01

    Although intermolecular interactions are ubiquitous in physicochemical phenomena, their dynamics have proven difficult to observe directly, and most experiments rely on indirect measurements. Using broadband two-dimensional infrared spectroscopy (2DIR), we have measured the influence of hydrogen bonding on the intermolecular vibrational coupling between dimerized N-methylacetamide molecules. In addition to strong intramolecular coupling between N-H and C=O oscillators, cross-peaks in the broadband 2DIR spectrum appearing upon dimerization reveal strong intermolecular coupling that changes the character of the vibrations. In addition, dimerization changes the effects of intramolecular coupling, resulting in Fermi resonances between high and low-frequency modes. These results illustrate how hydrogen bonding influences the interplay of inter- and intramolecular vibrations, giving rise to correlated nuclear motions and significant changes in the vibrational structure of the amide group. These observations have direct impact on modeling and interpreting the IR spectra of proteins. In addition, they illustrate a general approach to direct molecular characterization of intermolecular interactions.

  4. Direct observation of intermolecular interactions mediated by hydrogen bonding

    SciTech Connect

    De Marco, Luigi; Reppert, Mike; Thämer, Martin; Tokmakoff, Andrei

    2014-07-21

    Although intermolecular interactions are ubiquitous in physicochemical phenomena, their dynamics have proven difficult to observe directly, and most experiments rely on indirect measurements. Using broadband two-dimensional infrared spectroscopy (2DIR), we have measured the influence of hydrogen bonding on the intermolecular vibrational coupling between dimerized N-methylacetamide molecules. In addition to strong intramolecular coupling between N–H and C=O oscillators, cross-peaks in the broadband 2DIR spectrum appearing upon dimerization reveal strong intermolecular coupling that changes the character of the vibrations. In addition, dimerization changes the effects of intramolecular coupling, resulting in Fermi resonances between high and low-frequency modes. These results illustrate how hydrogen bonding influences the interplay of inter- and intramolecular vibrations, giving rise to correlated nuclear motions and significant changes in the vibrational structure of the amide group. These observations have direct impact on modeling and interpreting the IR spectra of proteins. In addition, they illustrate a general approach to direct molecular characterization of intermolecular interactions.

  5. Direct Observation of Luminescent Silver Clusters Confined in Faujasite Zeolites.

    PubMed

    Altantzis, Thomas; Coutino-Gonzalez, Eduardo; Baekelant, Wouter; Martinez, Gerardo T; Abakumov, Artem M; Tendeloo, Gustaaf Van; Roeffaers, Maarten B J; Bals, Sara; Hofkens, Johan

    2016-08-23

    One of the ultimate goals in the study of metal clusters is the correlation between the atomic-scale organization and their physicochemical properties. However, direct observation of the atomic organization of such minuscule metal clusters is heavily hindered by radiation damage imposed by the different characterization techniques. We present direct evidence of the structural arrangement, at an atomic level, of luminescent silver species stabilized in faujasite (FAU) zeolites using aberration-corrected scanning transmission electron microscopy. Two different silver clusters were identified in Ag-FAU zeolites, a trinuclear silver species associated with green emission and a tetranuclear silver species related to yellow emission. By combining direct imaging with complementary information obtained from X-ray powder diffraction and Rietveld analysis, we were able to elucidate the main differences at an atomic scale between luminescent (heat-treated) and nonluminescent (cation-exchanged) Ag-FAU zeolites. It is expected that such insights will trigger the directed synthesis of functional metal nanocluster-zeolite composites with tailored luminescent properties. PMID:27391548

  6. Direct observation of lubricant additives using tomography techniques

    NASA Astrophysics Data System (ADS)

    Chen, Yunyun; Sanchez, Carlos; Parkinson, Dilworth Y.; Liang, Hong

    2016-07-01

    Lubricants play important roles in daily activities such as driving, walking, and cooking. The current understanding of mechanisms of lubrication, particularly in mechanical systems, has been limited by the lack of capability in direct observation. Here, we report an in situ approach to directly observe the motion of additive particles in grease under the influence of shear. Using the K-edge tomography technique, it is possible to detect particular additives in a grease and observe their distribution through 3D visualization. A commercial grease as a reference was studied with and without an inorganic additive of Fe3O4 microparticles. The results showed that it was possible to identify these particles and track their movement. Under a shear stress, Fe3O4 particles were found to adhere to the edge of calcium complex thickeners commonly used in grease. Due to sliding, the grease formed a film with increased density. This approach enables in-line monitoring of a lubricant and future investigation in mechanisms of lubrication.

  7. Direct observation of stepwise movement of a synthetic molecular transporter

    NASA Astrophysics Data System (ADS)

    Wickham, Shelley F. J.; Endo, Masayuki; Katsuda, Yousuke; Hidaka, Kumi; Bath, Jonathan; Sugiyama, Hiroshi; Turberfield, Andrew J.

    2011-03-01

    Controlled motion at the nanoscale can be achieved by using Watson-Crick base-pairing to direct the assembly and operation of a molecular transport system consisting of a track, a motor and fuel, all made from DNA. Here, we assemble a 100-nm-long DNA track on a two-dimensional scaffold, and show that a DNA motor loaded at one end of the track moves autonomously and at a constant average speed along the full length of the track, a journey comprising 16 consecutive steps for the motor. Real-time atomic force microscopy allows direct observation of individual steps of a single motor, revealing mechanistic details of its operation. This precisely controlled, long-range transport could lead to the development of systems that could be programmed and routed by instructions encoded in the nucleotide sequences of the track and motor. Such systems might be used to create molecular assembly lines modelled on the ribosome.

  8. Direct observation of negative-index microwave surface waves.

    PubMed

    Dockrey, J A; Horsley, S A R; Hooper, I R; Sambles, J R; Hibbins, A P

    2016-01-01

    Waves propagating in a negative-index material have wave-front propagation (wavevector, k) opposite in direction to that of energy flow (Poynting vector, S). Here we present an experimental realisation at microwave frequencies of an analogous surface wave phenomenon whereby a metasurface supports a surface mode that has two possible wavevector eigenstates within a narrow band of frequencies: one that supports surface waves with positive mode index, and another that supports surface waves with negative mode index. Phase sensitive measurements of the near-field of surface waves across the metasurface show the contrasting spatial evolution of the two eigenstates, providing a unique opportunity to directly observe the negative-index phenomenon. PMID:26903284

  9. Direct state reconstruction with coupling-deformed pointer observables

    NASA Astrophysics Data System (ADS)

    Zhu, Xuanmin; Zhang, Yu-Xiang; Wu, Shengjun

    2016-06-01

    Direct state tomography (DST) using weak measurements has received wide attention. Based on the concept of coupling-deformed pointer observables presented by Zhang et al. [Y.-X. Zhang, S. Wu, and Z.-B. Chen, Phys. Rev. A 93, 032128 (2016), 10.1103/PhysRevA.93.032128], a modified direct state tomography (MDST) is proposed, examined, and compared with other typical state tomography schemes. MDST has exact validity for measurements of any strength. We identify the strength needed to attain the highest efficiency level of MDST by using statistical theory. MDST is much more efficient than DST in the sense that far fewer samples are needed to reach DST's level of reconstruction accuracy. Moreover, MDST has no inherent bias when compared to DST.

  10. Direct observation of negative-index microwave surface waves

    PubMed Central

    Dockrey, J. A.; Horsley, S. A. R.; Hooper, I. R.; Sambles, J. R.; Hibbins, A. P.

    2016-01-01

    Waves propagating in a negative-index material have wave-front propagation (wavevector, k) opposite in direction to that of energy flow (Poynting vector, S). Here we present an experimental realisation at microwave frequencies of an analogous surface wave phenomenon whereby a metasurface supports a surface mode that has two possible wavevector eigenstates within a narrow band of frequencies: one that supports surface waves with positive mode index, and another that supports surface waves with negative mode index. Phase sensitive measurements of the near-field of surface waves across the metasurface show the contrasting spatial evolution of the two eigenstates, providing a unique opportunity to directly observe the negative-index phenomenon. PMID:26903284

  11. Method for observing phase objects without halos or directional shadows.

    PubMed

    Suzuki, Yoshimasa; Kajitani, Kazuo; Ohde, Hisashi

    2015-03-01

    A new microscopy method for observing phase objects without halos or directional shadows is proposed. The method is based on transformation of the surface profile of phase objects into a light intensity pattern. The key optical element is an annular aperture at the front focal plane of a condenser. The light flux passing through the annular aperture is changed by the specimen's surface profile and then passes through an objective and contributes to image formation. Theory and experimental results are presented. Phase images of induced pluripotent stem (iPS) cells with clear outlines were obtained with this method.

  12. Direct observation of Kelvin waves excited by quantized vortex reconnection.

    PubMed

    Fonda, Enrico; Meichle, David P; Ouellette, Nicholas T; Hormoz, Sahand; Lathrop, Daniel P

    2014-03-25

    Quantized vortices are key features of quantum fluids such as superfluid helium and Bose-Einstein condensates. The reconnection of quantized vortices and subsequent emission of Kelvin waves along the vortices are thought to be central to dissipation in such systems. By visualizing the motion of submicron particles dispersed in superfluid (4)He, we have directly observed the emission of Kelvin waves from quantized vortex reconnection. We characterize one event in detail, using dimensionless similarity coordinates, and compare it with several theories. Finally, we give evidence for other examples of wavelike behavior in our system.

  13. Direct Observation of Correlated Interdomain Motion in Alcohol Dehydrogenase

    SciTech Connect

    Biehl, Ralf; Monkenbusch, Michael; Richter, Dieter; Hoffmann, Bernd; Merkel, Rudolf; Falus, Peter; Preost, Sylvain

    2008-09-26

    Interdomain motions in proteins are essential to enable or promote biochemical function. Neutron spin-echo spectroscopy is used to directly observe the domain dynamics of the protein alcohol dehydrogenase. The collective motion of domains as revealed by their coherent form factor relates to the cleft opening dynamics between the binding and the catalytic domains enabling binding and release of the functional important cofactor. The cleft opening mode hardens as a result of an overall stiffening of the domain complex due to the binding of the cofactor.

  14. Direct observation of thermal relaxation in artificial spin ice.

    PubMed

    Farhan, A; Derlet, P M; Kleibert, A; Balan, A; Chopdekar, R V; Wyss, M; Perron, J; Scholl, A; Nolting, F; Heyderman, L J

    2013-08-01

    We study the thermal relaxation of artificial spin ice with photoemission electron microscopy, and are able to directly observe how such a system finds its way from an energetically excited state to the ground state. On plotting vertex-type populations as a function of time, we can characterize the relaxation, which occurs in two stages, namely a string and a domain regime. Kinetic Monte Carlo simulations agree well with the temporal evolution of the magnetic state when including disorder, and the experimental results can be explained by considering the effective interaction energy associated with the separation of pairs of vertex excitations. PMID:23952441

  15. Direct observation of Kelvin waves excited by quantized vortex reconnection

    PubMed Central

    Fonda, Enrico; Meichle, David P.; Ouellette, Nicholas T.; Hormoz, Sahand; Lathrop, Daniel P.

    2014-01-01

    Quantized vortices are key features of quantum fluids such as superfluid helium and Bose–Einstein condensates. The reconnection of quantized vortices and subsequent emission of Kelvin waves along the vortices are thought to be central to dissipation in such systems. By visualizing the motion of submicron particles dispersed in superfluid 4He, we have directly observed the emission of Kelvin waves from quantized vortex reconnection. We characterize one event in detail, using dimensionless similarity coordinates, and compare it with several theories. Finally, we give evidence for other examples of wavelike behavior in our system. PMID:24704878

  16. Direct observation of thitherto unobservable quantum phenomena by using electrons.

    PubMed

    Tonomura, Akira

    2005-10-18

    Fundamental aspects of quantum mechanics, which were discussed only theoretically as "thought experiments" in the 1920s and 1930s, have begun to frequently show up in nanoscopic regions owing to recent rapid progress in advanced technologies. Quantum phenomena were once regarded as the ultimate factors limiting further miniaturization trends of microstructured electronic devices, but now they have begun to be actively used as the principles for new devices such as quantum computers. To directly observe what had been unobservable quantum phenomena, we have tried to develop bright and monochromatic electron beams for the last 35 years. Every time the brightness of an electron beam improved, fundamental experiments in quantum mechanics became possible, and quantum phenomena became observable by using the wave nature of electrons.

  17. Direct Observations of PMC Local Time Variations by Aura OMI

    NASA Technical Reports Server (NTRS)

    DeLand, Matthew T.; Shettle, Eric P.; Thomas, Gary E.; Olivero, John J.

    2010-01-01

    The Ozone Monitoring Instrument (OMI) on the Aura satellite obtains unique measurements for polar mesospheric cloud (PMC) analysis. Its wide cross-track viewing swath and high along-track spatial resolution makes it possible to directly evaluate PMC occurrence frequency and brightness variations between 6S" and 8S' latitude as a function of local time over a 12-14 h continuous period. OMI PMC local time variations are closely coupled to concurrent variations in measurement scattering angle, so that ice phase function effects must be considered when interpreting the observations. Two different phase functions corresponding to bright and faint clouds are examined in this analysis. OMI observations show maximum frequency and albedo values at 8-10 h local time in the Northern Hemisphere, with decreasing amplitude at higher latitudes. Southern Hemisphere values reach a minimum at 18-20 h LT. Larger variations are seen in Northern Hemisphere data. No statistically significant longitudinal dependence was seen.

  18. Direct observations of the evolution of polar cap ionization patches.

    PubMed

    Zhang, Qing-He; Zhang, Bei-Chen; Lockwood, Michael; Hu, Hong-Qiao; Moen, Jøran; Ruohoniemi, J Michael; Thomas, Evan G; Zhang, Shun-Rong; Yang, Hui-Gen; Liu, Rui-Yuan; McWilliams, Kathryn A; Baker, Joseph B H

    2013-03-29

    Patches of ionization are common in the polar ionosphere, where their motion and associated density gradients give variable disturbances to high-frequency (HF) radio communications, over-the-horizon radar location errors, and disruption and errors to satellite navigation and communication. Their formation and evolution are poorly understood, particularly under disturbed space weather conditions. We report direct observations of the full evolution of patches during a geomagnetic storm, including formation, polar cap entry, transpolar evolution, polar cap exit, and sunward return flow. Our observations show that modulation of nightside reconnection in the substorm cycle of the magnetosphere helps form the gaps between patches where steady convection would give a "tongue" of ionization (TOI). PMID:23539601

  19. Direct observation of local atomic order in a metallic glass.

    PubMed

    Hirata, Akihiko; Guan, Pengfei; Fujita, Takeshi; Hirotsu, Yoshihiko; Inoue, Akihisa; Yavari, Alain Reza; Sakurai, Toshio; Chen, Mingwei

    2011-01-01

    The determination of the atomic configuration of metallic glasses is a long-standing problem in materials science and solid-state physics. So far, only average structural information derived from diffraction and spectroscopic methods has been obtained. Although various atomic models have been proposed in the past fifty years, a direct observation of the local atomic structure in disordered materials has not been achieved. Here we report local atomic configurations of a metallic glass investigated by nanobeam electron diffraction combined with ab initio molecular dynamics simulation. Distinct diffraction patterns from individual atomic clusters and their assemblies, which have been theoretically predicted as short- and medium-range order, can be experimentally observed. This study provides compelling evidence of the local atomic order in the disordered material and has important implications in understanding the atomic mechanisms of metallic-glass formation and properties.

  20. Direct observation of thitherto unobservable quantum phenomena by using electrons

    PubMed Central

    Tonomura, Akira

    2005-01-01

    Fundamental aspects of quantum mechanics, which were discussed only theoretically as “thought experiments” in the 1920s and 1930s, have begun to frequently show up in nanoscopic regions owing to recent rapid progress in advanced technologies. Quantum phenomena were once regarded as the ultimate factors limiting further miniaturization trends of microstructured electronic devices, but now they have begun to be actively used as the principles for new devices such as quantum computers. To directly observe what had been unobservable quantum phenomena, we have tried to develop bright and monochromatic electron beams for the last 35 years. Every time the brightness of an electron beam improved, fundamental experiments in quantum mechanics became possible, and quantum phenomena became observable by using the wave nature of electrons. PMID:16150719

  1. Large-scale real-space density-functional calculations: Moiré-induced electron localization in graphene

    SciTech Connect

    Oshiyama, Atsushi Iwata, Jun-Ichi; Uchida, Kazuyuki; Matsushita, Yu-Ichiro

    2015-03-21

    We show that our real-space finite-difference scheme allows us to perform density-functional calculations for nanometer-scale targets containing more than 100 000 atoms. This real-space scheme is applied to twisted bilayer graphene, clarifying that Moiré pattern induced in the slightly twisted bilayer graphene drastically modifies the atomic and electronic structures.

  2. Directly observable optical properties of sprites in Central Europe

    NASA Astrophysics Data System (ADS)

    Bór, József

    2013-04-01

    Luminous optical emissions accompanying streamer-based natural electric breakdown processes initiating in the mesosphere are called sprites. 489 sprite events have been observed with a TV frame rate video system in Central Europe from Sopron (47.68N, 16.58E, 230 m MSL), Hungary between 2007 and 2009. On the basis of these observations, characteristic morphological properties of sprites, i.e. basic forms (e.g. column, carrot, angel, etc.) as well as common morphological features (e.g. tendrils, glows, puffs, beads, etc.), have been identified. Probable time sequences of streamer propagation directions were associated with each of the basic sprite forms. It is speculated that different sequences of streamer propagation directions can result in very similar final sprite shapes. The number and type variety of sprite elements appearing in an event as well as the total optical duration of an event was analyzed statistically. Jellyfish and dancing sprite events were considered as special subsets of sprite clusters. It was found that more than 90% of the recorded sprite elements appeared in clusters rather than alone and more than half of the clusters contained more than one basic sprite forms. The analysis showed that jellyfish sprites and clusters of column sprites featuring glows and tendrils do not tend to have optical lifetimes longer than 80 ms. Such very long optical lifetimes have not been observed in sprite clusters containing more than 25 elements of any type, either. In contrast to clusters containing sprite entities of only one form, sprite events showing more sprite forms seem to have extended optical durations more likely. The need for further investigation and for finding theoretical concepts to link these observations to electric conditions ambient for sprite formation is emphasized.

  3. Direct observation of photoinduced bent nitrosyl excited-state complexes

    SciTech Connect

    Sawyer, Karma R.; Steele, Ryan P.; Glascoe, Elizabeth A.; Cahoon, James F.; Schlegel, Jacob P.; Head-Gordon, Martin; Harris, Charles B.

    2008-06-28

    Ground state structures with side-on nitrosyl ({eta}{sup 2}-NO) and isonitrosyl (ON) ligands have been observed in a variety of transition-metal complexes. In contrast, excited state structures with bent-NO ligands have been proposed for years but never directly observed. Here we use picosecond time-resolved infrared spectroscopy and density functional theory (DFT) modeling to study the photochemistry of Co(CO){sub 3}(NO), a model transition-metal-NO compound. Surprisingly, we have observed no evidence for ON and {eta}{sup 2}-NO structural isomers, but have observed two bent-NO complexes. DFT modeling of the ground and excited state potentials indicates that the bent-NO complexes correspond to triplet excited states. Photolysis of Co(CO){sub 3}(NO) with a 400-nm pump pulse leads to population of a manifold of excited states which decay to form an excited state triplet bent-NO complex within 1 ps. This structure relaxes to the ground triplet state in ca. 350 ps to form a second bent-NO structure.

  4. Cylindrical 3D video display observable from all directions

    NASA Astrophysics Data System (ADS)

    Endo, Tomohiro; Kajiki, Yoshihiro; Honda, Toshio; Sato, Makoto

    2000-05-01

    We propose a 3D video displaying technique that multiple viewers can observe 3D images from 360 degrees of arc horizontally without 3D glasses. This technique uses a cylindrical parallax barrier and 1D light source array. We have developed an experimental display using this technique and have demonstrated 3D images observable form 360 degrees of arc horizontally without 3D glasses. Since this technique is based on the parallax panoramagram, the parallax number and resolution are limited by the diffraction at the parallax barrier. To avoid these limits, we improved the technique by revolving the parallax barrier. We have been developing a new experimental display using this improved technique. The display is capable of displaying cylindrical 3D video images within the diameter of 100 mm and the height of 128 mm. Images are described with the resolution of 1254 pixels circularly and 128 pixels vertically, and refreshed at 30Hz. Each pixel has the viewing angle of 60 degrees and that is divided into 70 views, therefore the angular parallax interval of each pixel is less than 1 degree. In such a case, observers may barely perceive parallax discretely. The pixels are arranged on a cylinder surface, therefore produced 3D images can be observed from all directions.

  5. Direct microscopic observation of forward osmosis membrane fouling.

    PubMed

    Wang, Yining; Wicaksana, Filicia; Tang, Chuyang Y; Fane, Anthony G

    2010-09-15

    This study describes the application of a noninvasive direct microscopic observation method for characterizing fouling of a forward osmosis (FO) membrane. The effect of the draw solution concentration, membrane orientation, and feed spacer on FO fouling was systematically investigated in a cross-flow setup using latex particles as model foulant in the feedwater. Higher draw solution (DS) concentrations (and thus increased flux levels) resulted in dramatic increase in the surface coverage by latex particles, suggesting that the critical flux concept might be applicable even for the osmotically driven FO process. Under identical draw solution concentrations, the active-layer-facing-the-feed-solution orientation (AL-FS) experienced significantly less fouling compared to the alternative orientation. This may be explained by the lower water flux in AL-FS, which is consistent with the critical flux concept. The use of a feed spacer not only dramatically enhanced the initial flux of the FO membrane, but also significantly improved the flux stability during FO fouling. Despite such beneficial effects of using the feed spacer, a significant amount of particle accumulation was found near the spacer filament, suggesting further opportunities for improved spacer design. To the best of the authors' knowledge, this is the first direct microscopic observation study on FO fouling.

  6. Direct Observation Assessment of Milestones: Problems with Reliability

    PubMed Central

    Schott, Meghan; Kedia, Raashee; Promes, Susan B.; Swoboda, Thomas; O’Rourke, Kevin; Green, Walter; Liu, Rachel; Stansfield, Brent; Santen, Sally A.

    2015-01-01

    Introduction Emergency medicine (EM) milestones are used to assess residents’ progress. While some milestone validity evidence exists, there is a lack of standardized tools available to reliably assess residents. Inherent to this is a concern that we may not be truly measuring what we intend to assess. The purpose of this study was to design a direct observation milestone assessment instrument supported by validity and reliability evidence. In addition, such a tool would further lend validity evidence to the EM milestones by demonstrating their accurate measurement. Methods This was a multi-center, prospective, observational validity study conducted at eight institutions. The Critical Care Direct Observation Tool (CDOT) was created to assess EM residents during resuscitations. This tool was designed using a modified Delphi method focused on content, response process, and internal structure validity. Paying special attention to content validity, the CDOT was developed by an expert panel, maintaining the use of the EM milestone wording. We built response process and internal consistency by piloting and revising the instrument. Raters were faculty who routinely assess residents on the milestones. A brief training video on utilization of the instrument was completed by all. Raters used the CDOT to assess simulated videos of three residents at different stages of training in a critical care scenario. We measured reliability using Fleiss’ kappa and interclass correlations. Results Two versions of the CDOT were used: one used the milestone levels as global rating scales with anchors, and the second reflected a current trend of a checklist response system. Although the raters who used the CDOT routinely rate residents in their practice, they did not score the residents’ performances in the videos comparably, which led to poor reliability. The Fleiss’ kappa of each of the items measured on both versions of the CDOT was near zero. Conclusion The validity and

  7. Determining the structure of the real-space entanglement spectrum from approximate conditional independence

    NASA Astrophysics Data System (ADS)

    Kim, Isaac H.

    2013-04-01

    We study the ground state of a gapped quantum many-body system whose entanglement entropy SA can be expressed as SA=a|∂A|-γ, where a,γ are some constants and |∂A| is an area of the subsystem A. By using a recently proved operator extension of strong subadditivity of entropy [I. H. Kim, J. Math. Phys.JMAPAQ0022-248810.1063/1.4769176 53, 122204 (2012)], we show that a certain linear combination of the real-space entanglement spectrum has a small correlation with almost any local operator. Our result implies that there exists a structure relating the real-space entanglement spectrum over different subsystems. Further, this structure is inherited from the generic property of the ground state alone, suggesting that the locality of the entanglement spectrum may be attributed to the area law of entanglement entropy.

  8. Numerical Real Space Renormalization of a 2D Random Boson Model

    NASA Astrophysics Data System (ADS)

    Iyer, Shankar; Refael, Gil

    2011-03-01

    Interest in the random boson problem originated in experiments on Helium adsorbed in Vycor, but the problem arises in many contexts, including Josephson junction arrays and disordered cold atom systems. Recently, Altman, Kafri, Polkovnikov, and Refael have studied a rotor model description of interacting bosons subjected to quenched disorder in one dimension. Using a real space renormalization approach, they have identified a random fixed point that marks the transition between superfluid and Mott-glass phases. Here, we describe work that numerically extends their approach to the random boson problem in two dimensions. We first test the validity of the real space renormalization by comparison to exact diagonalization of small systems. Then, we move to larger systems and explore what the renormalization scheme can tell us about the nature of the insulating and superfluid phases.

  9. Excited calculations of large scale multiwalled nanotubes using real-space pseudopotential methods

    NASA Astrophysics Data System (ADS)

    Lena, Charles; Chelikowsky, James; Deslippe, Jack; Saad, Yousef; Yang, Chao; Louie, Steven G.

    2015-03-01

    One method for calculating excited states is the GW method. The GW method has many computational requirements. One of the bottlenecks is the calculation of numerous empty states. Within density functional theory, we use a real-space pseudopotential method (PARSEC) to calculate these empty states for multiwalled nanotubes. We illustrate the use of these empty states for calculating excited states using the GW method (BerkeleyGW). We demonstrate why using real-space density functional theory is advantageous for calculating empty states. Support provided by the SciDAC program, Department of Energy, Office of Science, Advanced Scientific Computing Research and Basic Energy Sciences. Grant Numbers DE-SC0008877 (Austin) and DE-FG02-12ER4 (Berkeley)

  10. Thermal expansion of a glassy alloy studied using a real-space pair distribution function

    SciTech Connect

    Louzguine-Luzgin, Dmitri V.; Inoue, Akihisa; Yavari, Alain R.; Vaughan, Gavin

    2006-03-20

    Thermal expansion of a glassy Cu{sub 55}Hf{sub 25}Ti{sub 15}Pd{sub 5} alloy studied by using reciprocal space functions is verified using a real-space pair distribution function. The experimental results obtained by real-time diffraction during heating in a synchrotron beam and their Fourier transformation processing to derive radial distribution functions indicate that both reciprocal and real-space distribution functions give good agreement in the calculation of thermal expansion data. In addition to providing structural information, these findings indicate that the change in the average atomic nearest-neighbor distance evaluated from the variation of the position of the main broad diffraction maximum can provide good thermal expansion data for metallic glasses.

  11. Direct observation of the strange b baryon Xib-.

    PubMed

    Abazov, V M; Abbott, B; Abolins, M; Acharya, B S; Adams, M; Adams, T; Aguilo, E; Ahn, S H; Ahsan, M; Alexeev, G D; Alkhazov, G; Alton, A; Alverson, G; Alves, G A; Anastasoaie, M; Ancu, L S; Andeen, T; Anderson, S; Andrieu, B; Anzelc, M S; Arnoud, Y; Arov, M; Arthaud, M; Askew, A; Asman, B; Assis Jesus, A C S; Atramentov, O; Autermann, C; Avila, C; Ay, C; Badaud, F; Baden, A; Bagby, L; Baldin, B; Bandurin, D V; Banerjee, S; Banerjee, P; Barberis, E; Barfuss, A-F; Bargassa, P; Baringer, P; Barreto, J; Bartlett, J F; Bassler, U; Bauer, D; Beale, S; Bean, A; Begalli, M; Begel, M; Belanger-Champagne, C; Bellantoni, L; Bellavance, A; Benitez, J A; Beri, S B; Bernardi, G; Bernhard, R; Berntzon, L; Bertram, I; Besançon, M; Beuselinck, R; Bezzubov, V A; Bhat, P C; Bhatnagar, V; Biscarat, C; Blazey, G; Blekman, F; Blessing, S; Bloch, D; Bloom, K; Boehnlein, A; Boline, D; Bolton, T A; Borissov, G; Bos, K; Bose, T; Brandt, A; Brock, R; Brooijmans, G; Bross, A; Brown, D; Buchanan, N J; Buchholz, D; Buehler, M; Buescher, V; Burdin, S; Burke, S; Burnett, T H; Buszello, C P; Butler, J M; Calfayan, P; Calvet, S; Cammin, J; Caron, S; Carvalho, W; Casey, B C K; Cason, N M; Castilla-Valdez, H; Chakrabarti, S; Chakraborty, D; Chan, K M; Chan, K; Chandra, A; Charles, F; Cheu, E; Chevallier, F; Cho, D K; Choi, S; Choudhary, B; Christofek, L; Christoudias, T; Cihangir, S; Claes, D; Clément, C; Clément, B; Coadou, Y; Cooke, M; Cooper, W E; Corcoran, M; Couderc, F; Cousinou, M-C; Crépé-Renaudin, S; Cutts, D; Cwiok, M; da Motta, H; Das, A; Davies, G; De, K; de Jong, S J; de Jong, P; De La Cruz-Burelo, E; De Oliveira Martins, C; Degenhardt, J D; Déliot, F; Demarteau, M; Demina, R; Denisov, D; Denisov, S P; Desai, S; Diehl, H T; Diesburg, M; Dominguez, A; Dong, H; Dudko, L V; Duflot, L; Dugad, S R; Duggan, D; Duperrin, A; Dyer, J; Dyshkant, A; Eads, M; Edmunds, D; Ellison, J; Elvira, V D; Enari, Y; Eno, S; Ermolov, P; Evans, H; Evdokimov, A; Evdokimov, V N; Ferapontov, A V; Ferbel, T; Fiedler, F; Filthaut, F; Fisher, W; Fisk, H E; Ford, M; Fortner, M; Fox, H; Fu, S; Fuess, S; Gadfort, T; Galea, C F; Gallas, E; Galyaev, E; Garcia, C; Garcia-Bellido, A; Gavrilov, V; Gay, P; Geist, W; Gelé, D; Gerber, C E; Gershtein, Y; Gillberg, D; Ginther, G; Gollub, N; Gómez, B; Goussiou, A; Grannis, P D; Greenlee, H; Greenwood, Z D; Gregores, E M; Grenier, G; Gris, Ph; Grivaz, J-F; Grohsjean, A; Grünendahl, S; Grünewald, M W; Guo, J; Guo, F; Gutierrez, P; Gutierrez, G; Haas, A; Hadley, N J; Haefner, P; Hagopian, S; Haley, J; Hall, I; Hall, R E; Han, L; Hanagaki, K; Hansson, P; Harder, K; Harel, A; Harrington, R; Hauptman, J M; Hauser, R; Hays, J; Hebbeker, T; Hedin, D; Hegeman, J G; Heinmiller, J M; Heinson, A P; Heintz, U; Hensel, C; Herner, K; Hesketh, G; Hildreth, M D; Hirosky, R; Hobbs, J D; Hoeneisen, B; Hoeth, H; Hohlfeld, M; Hong, S J; Hooper, R; Hossain, S; Houben, P; Hu, Y; Hubacek, Z; Hynek, V; Iashvili, I; Illingworth, R; Ito, A S; Jabeen, S; Jaffré, M; Jain, S; Jakobs, K; Jarvis, C; Jesik, R; Johns, K; Johnson, C; Johnson, M; Jonckheere, A; Jonsson, P; Juste, A; Käfer, D; Kahn, S; Kajfasz, E; Kalinin, A M; Kalk, J R; Kalk, J M; Kappler, S; Karmanov, D; Kasper, J; Kasper, P; Katsanos, I; Kau, D; Kaur, R; Kaushik, V; Kehoe, R; Kermiche, S; Khalatyan, N; Khanov, A; Kharchilava, A; Kharzheev, Y M; Khatidze, D; Kim, H; Kim, T J; Kirby, M H; Kirsch, M; Klima, B; Kohli, J M; Konrath, J-P; Kopal, M; Korablev, V M; Kothari, B; Kozelov, A V; Krop, D; Kryemadhi, A; Kuhl, T; Kumar, A; Kunori, S; Kupco, A; Kurca, T; Kvita, J; Lacroix, F; Lam, D; Lammers, S; Landsberg, G; Lazoflores, J; Lebrun, P; Lee, W M; Leflat, A; Lehner, F; Lellouch, J; Lesne, V; Leveque, J; Lewis, P; Li, J; Li, Q Z; Li, L; Lietti, S M; Lima, J G R; Lincoln, D; Linnemann, J; Lipaev, V V; Lipton, R; Liu, Y; Liu, Z; Lobo, L; Lobodenko, A; Lokajicek, M; Lounis, A; Love, P; Lubatti, H J; Lyon, A L; Maciel, A K A; Mackin, D; Madaras, R J; Mättig, P; Magass, C; Magerkurth, A; Makovec, N; Mal, P K; Malbouisson, H B; Malik, S; Malyshev, V L; Mao, H S; Maravin, Y; Martin, B; McCarthy, R; Melnitchouk, A; Mendes, A; Mendoza, L; Mercadante, P G; Merekov, Y P; Merkin, M; Merritt, K W; Meyer, J; Meyer, A; Michaut, M; Millet, T; Mitrevski, J; Molina, J; Mommsen, R K; Mondal, N K; Moore, R W; Moulik, T; Muanza, G S; Mulders, M; Mulhearn, M; Mundal, O; Mundim, L; Nagy, E; Naimuddin, M; Narain, M; Naumann, N A; Neal, H A; Negret, J P; Neustroev, P; Nilsen, H; Nomerotski, A; Novaes, S F; Nunnemann, T; O'Dell, V; O'Neil, D C; Obrant, G; Ochando, C; Onoprienko, D; Oshima, N; Osta, J; Otec, R; Otero y Garzón, G J; Owen, M; Padley, P; Pangilinan, M; Panov, G; Parashar, N; Park, S-J; Park, S K; Parsons, J; Partridge, R; Parua, N; Patwa, A; Pawloski, G; Penning, B; Perea, P M; Peters, K; Peters, Y; Pétroff, P; Petteni, M; Piegaia, R; Piper, J; Pleier, M-A; Podesta-Lerma, P L M; Podstavkov, V M; Pogorelov, Y; Pol, M-E; Polozov, P; Pompos, A; Pope, B G; Popov, A V; Potter, C; Prado da Silva, W L; Prosper, H B; Protopopescu, S; Qian, J; Quadt, A; Quinn, B; Rakitine, A; Rangel, M S; Rani, K J; Ranjan, K; Ratoff, P N; Renkel, P; Reucroft, S; Rich, P; Rijssenbeek, M; Ripp-Baudot, I; Rizatdinova, F; Robinson, S; Rodrigues, R F; Royon, C; Rozhdestvenski, A; Rubinov, P; Ruchti, R; Safronov, G; Sajot, G; Sánchez-Hernández, A; Sanders, M P; Santoro, A; Savage, G; Sawyer, L; Scanlon, T; Schaile, D; Schamberger, R D; Scheglov, Y; Schellman, H; Schieferdecker, P; Schliephake, T; Schmitt, C; Schwanenberger, C; Schwartzman, A; Schwienhorst, R; Sekaric, J; Sengupta, S; Severini, H; Shabalina, E; Shamim, M; Shary, V; Shchukin, A A; Shivpuri, R K; Shpakov, D; Siccardi, V; Simak, V; Sirotenko, V; Skubic, P; Slattery, P; Smirnov, D; Smith, R P; Snow, J; Snow, G R; Snyder, S; Söldner-Rembold, S; Sonnenschein, L; Sopczak, A; Sosebee, M; Soustruznik, K; Souza, M; Spurlock, B; Stark, J; Steele, J; Stolin, V; Stone, A; Stoyanova, D A; Strandberg, J; Strandberg, S; Strang, M A; Strauss, M; Strauss, E; Ströhmer, R; Strom, D; Strovink, M; Stutte, L; Sumowidagdo, S; Svoisky, P; Sznajder, A; Talby, M; Tamburello, P; Tanasijczuk, A; Taylor, W; Telford, P; Temple, J; Tiller, B; Tissandier, F; Titov, M; Tokmenin, V V; Tomoto, M; Toole, T; Torchiani, I; Trefzger, T; Tsybychev, D; Tuchming, B; Tully, C; Tuts, P M; Unalan, R; Uvarov, S; Uvarov, L; Uzunyan, S; Vachon, B; van den Berg, P J; van Eijk, B; Van Kooten, R; van Leeuwen, W M; Varelas, N; Varnes, E W; Vartapetian, A; Vasilyev, I A; Vaupel, M; Verdier, P; Vertogradov, L S; Vertogradova, Y; Verzocchi, M; Villeneuve-Seguier, F; Vint, P; Vokac, P; Von Toerne, E; Voutilainen, M; Vreeswijk, M; Wagner, R; Wahl, H D; Wang, L; Wang, M H L S; Warchol, J; Watts, G; Wayne, M; Weber, M; Weber, G; Weerts, H; Wenger, A; Wermes, N; Wetstein, M; White, A; Wicke, D; Wilson, G W; Wimpenny, S J; Wobisch, M; Wood, D R; Wyatt, T R; Xie, Y; Yacoob, S; Yamada, R; Yan, M; Yasuda, T; Yatsunenko, Y A; Yip, K; Yoo, H D; Youn, S W; Yu, J; Yu, C; Yurkewicz, A; Zatserklyaniy, A; Zeitnitz, C; Zhang, D; Zhao, T; Zhou, B; Zhu, J; Zielinski, M; Zieminska, D; Zieminski, A; Zivkovic, L; Zutshi, V; Zverev, E G

    2007-08-01

    We report the first direct observation of the strange b baryon Xi(b)- (Xi(b)+). We reconstruct the decay Xi(b)- -->J/psiXi-, with J/psi-->mu+mu-, and Xi--->Lambdapi--->ppi-pi- in pp collisions at square root of s =1.96 TeV. Using 1.3 fb(-1) of data collected by the D0 detector, we observe 15.2 +/- 4.4(stat)(-0.4)(+1.9)(syst) Xi(b)- candidates at a mass of 5.774 +/- 0.011(stat) +/- 0.015(syst) GeV. The significance of the observed signal is 5.5 sigma, equivalent to a probability of 3.3 x 10(-8) of it arising from a background fluctuation. Normalizing to the decay Lambda(b)-->J/psiLambda, we measure the relative rate sigma(Xi(b-) x B(Xi)b})- -->J/psiXi-)/sigma(Lambda(b)) x B(Lambda(b)-->J/psiLambda) = 0.28+/-0.09(stat)(-0.08)(+0.09)(syst). PMID:17930744

  12. Direct molecular dynamics observation of protein folding transition state ensemble.

    PubMed Central

    Ding, Feng; Dokholyan, Nikolay V; Buldyrev, Sergey V; Stanley, H Eugene; Shakhnovich, Eugene I

    2002-01-01

    The concept of the protein transition state ensemble (TSE), a collection of the conformations that have 50% probability to convert rapidly to the folded state and 50% chance to rapidly unfold, constitutes the basis of the modern interpretation of protein engineering experiments. It has been conjectured that conformations constituting the TSE in many proteins are the expanded and distorted forms of the native state built around a specific folding nucleus. This view has been supported by a number of on-lattice and off-lattice simulations. Here we report a direct observation and characterization of the TSE by molecular dynamic folding simulations of the C-Src SH3 domain, a small protein that has been extensively studied experimentally. Our analysis reveals a set of key interactions between residues, conserved by evolution, that must be formed to enter the kinetic basin of attraction of the native state. PMID:12496119

  13. Direct observation of acoustic oscillations in InAs nanowires.

    PubMed

    Mariager, Simon O; Khakhulin, Dmitry; Lemke, Henrik T; Kjaer, Kasper S; Guerin, Laurent; Nuccio, Laura; Sørensen, Claus B; Nielsen, Martin M; Feidenhans'l, Robert

    2010-07-14

    Time-resolved X-ray diffraction and optical reflectivity are used to directly measure three different acoustic oscillations of InAs nanowires. The oscillations are excited by a femtosecond laser pulse and evolve at three different time scales. We measure the absolute scale of the initial radial expansion of the fundamental breathing eigenmode and determine the frequency by transient optical reflectivity. For the extensional eigenmode we measure the oscillations of the average radial and axial lattice constants and determine the amplitude of oscillations and the average extension. Finally we observe a bending motion of the nanowires. The frequencies of the eigenmodes are in good agreements with predictions made by continuum elasticity theory and we find no difference in the speed of sound between the wurtzite nanowires and cubic bulk crystals, but the measured strain is influenced by the interaction between different modes. The wurtzite crystal structure of the nanowires however has an anisotropic thermal expansion.

  14. Dust resuspension under weak wind conditions: direct observations and model

    NASA Astrophysics Data System (ADS)

    Chkhetiani, O. G.; Gledzer, E. B.; Artamonova, M. S.; Iordanskii, M. A.

    2011-11-01

    Here we report the results of the direct observations of fine scale mineral dust aerosol carried out over extensive sand areas in desertificated lands of Kalmykia in 2007, 2009 and 2010 under conditions of weak wind and strong heating of the surface with near absence of saltation processes. Measurements show that the fine mineral dust aerosol in the chosen region constitutes a considerable fraction of the entire air aerosol in the atmospheric surface layer (in terms of both the number of particles and their mass). Data of fine aerosol mass concentrations are treated on the basis of physical model estimates obtained for fluid dynamic parameters in the viscous thermal boundary layer near the ground surface. The deviations of mass concentrations from background are linked to temperature drop in the thermal layer near the surface and the value of friction velocity.

  15. Direct observation of smectic layers in thermotropic liquid crystals.

    PubMed

    Zhang, C; Gao, M; Diorio, N; Weissflog, W; Baumeister, U; Sprunt, S; Gleeson, J T; Jákli, A

    2012-09-01

    We demonstrate subnanometer resolution cryo-TEM imaging of smectic layers in the smectic and nematic phases of two bent-core liquid crystals. Our results show perfect periodicity over several hundred layers in the smectic phase and also provide the first direct evidence of smectic clusters on length scales of 30-50 nm in a nematic liquid crystal. The results are corroborated with small angle x-ray scattering measurements. The observation of smectic clusters in the nematic phase is of special interest in bent-core liquid crystals, where the smectic clusters are stable over wide temperature ranges, in contrast to the well-known pretransitional "cybotactic" clusters that appear only in the vicinity of a bulk smectic phase. The means to characterize and manipulate this nanoscale molecular order could open up completely new liquid crystal-based technologies.

  16. Direct observation of the CRAND proton radiation belt source

    NASA Astrophysics Data System (ADS)

    Selesnick, R. S.; Hudson, M. K.; Kress, B. T.

    2013-12-01

    Observations of geomagnetically trapped 27-45 MeV protons following the November 2003 magnetic storm show a gradual intensity rise that is interpreted as a direct measurement of the cosmic ray albedo neutron decay (CRAND) source strength. The intensity rise is simulated by combining the detector response function with a model CRAND source, obtained by drift-averaging neutron intensity from Monte Carlo simulation of cosmic ray interactions in the atmosphere. The simulation, for 2.4

  17. Direct observations of field-induced assemblies in magnetite ferrofluids

    NASA Astrophysics Data System (ADS)

    Mousavi, N. S. Susan; Khapli, Sachin D.; Kumar, Sunil

    2015-03-01

    Evolution of microstructures in magnetite-based ferrofluids with weak dipolar moments (particle size ≤ 10 nm) is studied with an emphasis on examining the effects of particle concentration (ϕ) and magnetic field strength (H) on the structures. Nanoparticles are dispersed in water at three different concentrations, ϕ = 0.15%, 0.48%, and 0.59% (w/v) [g/ml%] and exposed to uniform magnetic fields in the range of H = 0.05-0.42 T. Cryogenic transmission electron microscopy is employed to provide in-situ observations of the field-induced assemblies in such systems. As the magnetic field increases, the Brownian colloids are observed to form randomly distributed chains aligned in the field direction, followed by head-to-tail chain aggregation and then lateral aggregation of chains termed as zippering. By increasing the field in low concentration samples, the number of chains increases, though their length does not change dramatically. Increasing concentration increases the length of the linear particle assemblies in the presence of a fixed external magnetic field. Thickening of the chains due to zippering is observed at relatively high fields. Through a systematic variation of concentration and magnetic field strength, this study shows that both magnetic field strength and change in concentration can strongly influence formation of microstructures even in weak dipolar systems. Additionally, the results of two commonly used support films on electron microscopy grids, continuous carbon and holey carbon films, are compared. Holey carbon film allows us to create local regions of high concentrations that further assist the development of field-induced assemblies. The experimental observations provide a validation of the zippering effect and can be utilized in the development of models for thermophysical properties such as thermal conductivity.

  18. Direct observations of field-induced assemblies in magnetite ferrofluids

    SciTech Connect

    Mousavi, N. S. Susan; Khapli, Sachin D.; Kumar, Sunil

    2015-03-14

    Evolution of microstructures in magnetite-based ferrofluids with weak dipolar moments (particle size ≤ 10 nm) is studied with an emphasis on examining the effects of particle concentration (ϕ) and magnetic field strength (H) on the structures. Nanoparticles are dispersed in water at three different concentrations, ϕ = 0.15%, 0.48%, and 0.59% (w/v) [g/ml%] and exposed to uniform magnetic fields in the range of H = 0.05–0.42 T. Cryogenic transmission electron microscopy is employed to provide in-situ observations of the field-induced assemblies in such systems. As the magnetic field increases, the Brownian colloids are observed to form randomly distributed chains aligned in the field direction, followed by head-to-tail chain aggregation and then lateral aggregation of chains termed as zippering. By increasing the field in low concentration samples, the number of chains increases, though their length does not change dramatically. Increasing concentration increases the length of the linear particle assemblies in the presence of a fixed external magnetic field. Thickening of the chains due to zippering is observed at relatively high fields. Through a systematic variation of concentration and magnetic field strength, this study shows that both magnetic field strength and change in concentration can strongly influence formation of microstructures even in weak dipolar systems. Additionally, the results of two commonly used support films on electron microscopy grids, continuous carbon and holey carbon films, are compared. Holey carbon film allows us to create local regions of high concentrations that further assist the development of field-induced assemblies. The experimental observations provide a validation of the zippering effect and can be utilized in the development of models for thermophysical properties such as thermal conductivity.

  19. Direct observations of field-induced assemblies in magnetite ferrofluids

    PubMed Central

    Mousavi, N. S. Susan

    2015-01-01

    Evolution of microstructures in magnetite-based ferrofluids with weak dipolar moments (particle size ≤ 10 nm) is studied with an emphasis on examining the effects of particle concentration (ϕ) and magnetic field strength (H) on the structures. Nanoparticles are dispersed in water at three different concentrations, ϕ = 0.15%, 0.48%, and 0.59% (w/v) [g/ml%] and exposed to uniform magnetic fields in the range of H = 0.05–0.42 T. Cryogenic transmission electron microscopy is employed to provide in-situ observations of the field-induced assemblies in such systems. As the magnetic field increases, the Brownian colloids are observed to form randomly distributed chains aligned in the field direction, followed by head-to-tail chain aggregation and then lateral aggregation of chains termed as zippering. By increasing the field in low concentration samples, the number of chains increases, though their length does not change dramatically. Increasing concentration increases the length of the linear particle assemblies in the presence of a fixed external magnetic field. Thickening of the chains due to zippering is observed at relatively high fields. Through a systematic variation of concentration and magnetic field strength, this study shows that both magnetic field strength and change in concentration can strongly influence formation of microstructures even in weak dipolar systems. Additionally, the results of two commonly used support films on electron microscopy grids, continuous carbon and holey carbon films, are compared. Holey carbon film allows us to create local regions of high concentrations that further assist the development of field-induced assemblies. The experimental observations provide a validation of the zippering effect and can be utilized in the development of models for thermophysical properties such as thermal conductivity. PMID:25829566

  20. Enabling direct nanoscale observations of biological reactions with dynamic TEM.

    PubMed

    Evans, James E; Browning, Nigel D

    2013-02-01

    Biological processes occur on a wide range of spatial and temporal scales: from femtoseconds to hours and from angstroms to meters. Many new biological insights can be expected from a better understanding of the processes that occur on these very fast and very small scales. In this regard, new instruments that use fast X-ray or electron pulses are expected to reveal novel mechanistic details for macromolecular protein dynamics. To ensure that any observed conformational change is physiologically relevant and not constrained by 3D crystal packing, it would be preferable for experiments to utilize small protein samples such as single particles or 2D crystals that mimic the target protein's native environment. These samples are not typically amenable to X-ray analysis, but transmission electron microscopy has imaged such sample geometries for over 40 years using both direct imaging and diffraction modes. While conventional transmission electron microscopes (TEM) have visualized biological samples with atomic resolution in an arrested or frozen state, the recent development of the dynamic TEM (DTEM) extends electron microscopy into a dynamic regime using pump-probe imaging. A new second-generation DTEM, which is currently being constructed, has the potential to observe live biological processes with unprecedented spatiotemporal resolution by using pulsed electron packets to probe the sample on micro- and nanosecond timescales. This article reviews the experimental parameters necessary for coupling DTEM with in situ liquid microscopy to enable direct imaging of protein conformational dynamics in a fully hydrated environment and visualize reactions propagating in real time. PMID:23315566

  1. Enabling direct nanoscale observations of biological reactions with dynamic TEM

    SciTech Connect

    Evans, James E.; Browning, Nigel D.

    2013-02-18

    Biological processes can occur over a wide range of spatial and temporal scales; from femtoseconds to hours and from angstroms to meters. Although no single experimental method can fully cover this entire phase space, many new biological insights can be expected from a better understanding of the processes that occur on the very fast timescales and very small length scales. In this regard, new instruments that use fast x-ray or electron pulses are now available that are expected to reveal new mechanistic insights for macromolecular protein dynamics. To ensure that any observed conformational change is physiologically relevant and not constrained by three-dimensional crystal packing, it would be preferable for experiments to utilize smaller protein samples such as single particles or two-dimensional crystals that mimic the target protein’s native environment. These samples aren’t typically amenable to x-ray analysis, but transmission electron microscopy has successfully imaged such sample geometries for over 40 years and permits data acquisition using both direct imaging and diffraction modes. While conventional transmission electron microscopes (TEM) have only visualized biological samples with atomic resolution in an arrested or frozen state, the recent development of the dynamic TEM (DTEM) extends electron microscopy capabilities into dynamics. A new 2nd generation DTEM that is currently being constructed has the potential to observe live biological processes with unprecedented spatiotemporal resolution by using pulsed electron packets to probe the sample on the micro- and nanosecond timescale. In addition to the enhanced temporal resolution, the DTEM also operates in the pump-probe regime that can permit visualizing reactions propagating in real-time. This article reviews the experimental parameters necessary for coupling DTEM with in situ liquid microscopy to allow direct imaging of protein conformational dynamics in a fully hydrated environment.

  2. Direct Observation of Tropomyosin Binding to Actin Filaments

    PubMed Central

    Schmidt, William M.; Lehman, William; Moore, Jeffrey R.

    2015-01-01

    Tropomyosin is an elongated α-helical coiled-coil that binds to seven consecutive actin subunits along the long-pitch helix of actin filaments. Once bound, tropomyosin polymerizes end-to-end and both stabilizes F-actin and regulates access of various actin binding proteins including myosin in muscle and non-muscle cells. Single tropomyosin molecules bind weakly to F-actin with millimolar Kd, whereas the end-to-end linked tropomyosin associates with about a one thousand-fold greater affinity. Despite years of study, the assembly mechanism of tropomyosin onto actin filaments remains unclear. In the current study, we used total internal reflection fluorescence (TIRF) microscopy to directly monitor the cooperative binding of fluorescently labeled tropomyosin molecules to phalloidin-stabilized actin filaments. We find that tropomyosin molecules assemble from multiple growth sites following random low affinity binding of single molecules to actin. As the length of the tropomyosin chain increases, the probability of detachment decreases, which leads to further chain growth. Tropomyosin chain extension is linearly dependent on tropomyosin concentration, occurring at approximately 100 monomers/(μM*s). The random tropomyosin binding to F-actin leads to discontinuous end-to-end association where gaps in the chain continuity smaller than the required seven sequential actin monomers are available. Direct observation of tropomyosin detachment revealed the number of gaps in actin-bound tropomyosin, the time course of gap annealing, and the eventual filament saturation process. PMID:26033920

  3. Microcrack closure in rocks under stress: direct observation

    SciTech Connect

    Batzle, M.L.; Simmons, G.; Siegfried, R.W.

    1980-12-10

    Microcrack closure in rocks under increasing stress was observed directly with a scanning electron microscope. Uniaxial stresses to 300 bars were applied with a small hydraulic press to specimens of Westerly (RI) granite, both unheated and previously heat cycled to 500/sup 0/C, and of Frederick (MD) diabase, heat cycled to 700/sup 0/C. Closure characteristics (rate, final closure pressure, etc.) depend on crack orientation, shape, surface roughness, and on the nature of fracture intersections and interactions. Cracks perpendicular to the applied stress closed while those parallel to the stress tended to open. Long, narrow cracks (low aspect ratio) closed at relatively low pressures. At some intersections, one fracture would open while another simultaneously closed, depending upon their orientations. Many fractures closed uniformly even though offset by other fractures. Local stress concentrations often caused new fracturing at low applied stress. Some fractures were propped open until material lodged inside was crushed. Significant irreversible damage occurred during the first stress cycle. Closure characteristics varied significantly among the samples. The unheated granite has cracks with rough, pitted, and mismatched walls. Only partial closure occurred under stress with many sections remaining open. Crack porosity is reduced but continues to be interconnected. Fractures in the preheated granite and diabase are also irregular, but the walls are well-matched and closure is nearly complete. The cracks in the heated granite closed at lower stresses than in the diabase. As the maximum stress was approached for the heated granite, new transgranular cracks formed and preexisting cracks were enlarged. The variations in closure rate and character were also observed in strain measurements.

  4. Method for observing phase objects without halos and directional shadows

    NASA Astrophysics Data System (ADS)

    Suzuki, Yoshimasa; Kajitani, Kazuo; Ohde, Hisashi

    2015-03-01

    A new microscopy method for observing phase objects without halos and directional shadows is proposed. The key optical element is an annular aperture at the front focal plane of a condenser with a larger diameter than those used in standard phase contrast microscopy. The light flux passing through the annular aperture is changed by the specimen's surface profile and then passes through an objective and contributes to image formation. This paper presents essential conditions for realizing the method. In this paper, images of colonies formed by induced pluripotent stem (iPS) cells using this method are compared with the conventional phase contrast method and the bright-field method when the NA of the illumination is small to identify differences among these techniques. The outlines of the iPS cells are clearly visible with this method, whereas they are not clearly visible due to halos when using the phase contrast method or due to weak contrast when using the bright-field method. Other images using this method are also presented to demonstrate a capacity of this method: a mouse ovum and superimposition of several different images of mouse iPS cells.

  5. Dust resuspension under weak wind conditions: direct observations and model

    NASA Astrophysics Data System (ADS)

    Chkhetiani, O. G.; Gledzer, E. B.; Artamonova, M. S.; Iordanskii, M. A.

    2012-06-01

    The results of direct observations of fine mineral dust aerosol (0.15-15 μm) were carried out on extensive sand areas in desertificated lands of Kalmykia in 2007, 2009, and 2010 under conditions of weak wind and strong heating of the surface, almost in the absence of saltation processes. These results show that the fine mineral dust aerosol (0.15-0.5 μm) in the region under consideration contributes considerably to the total aerosol content of the atmospheric surface layer. Data on the mass concentrations of fine aerosol are treated on the basis of physical model estimates obtained for fluid dynamic parameters in the viscous thermal boundary layer near the ground surface. Deviations of these mass concentrations from their background values are related to a temperature drop in the thermal layer at the surface and from the values of friction velocity. For small and moderate values of friction velocity, these mass concentrations increase proportionally to a temperature drop with an exponent of about 0.5, and, for high friction velocities, this exponent becomes negative (~-0.5), which implies a decrease in these concentrations with an increase in a temperature drop.

  6. Direct observation of interface instability during crystal growth

    NASA Technical Reports Server (NTRS)

    Tiller, W. A.; Feigelson, R. S.; Elwell, D.

    1982-01-01

    The general aim of this investigation was to study interface stability and solute segregation phenomena during crystallization of a model system. Emphasis was to be placed on direct observational studies partly because this offered the possibility at a later stage of performing related experiments under substantially convection-free conditions in the space shuttle. The major achievements described in this report are: (1) the development of a new model system for fundamental studies of crystal growth from the melt and the measurement of a range of material parameters necessary for comparison of experiment with theory. (2) The introduction of a new method of measuring segregation coefficient using absorption of a laser beam by the liquid phase. (3) The comparison of segregation in crystals grown by gradient freezing and by pulling from the melt. (4) The introduction into the theory of solute segregation of an interface field term and comparison with experiment. (5) The introduction of the interface field term into the theories of constitutional supercooling and morphological stability and assessment of its importance.

  7. Modelling 1-minute directional observations of the global irradiance.

    NASA Astrophysics Data System (ADS)

    Thejll, Peter; Pagh Nielsen, Kristian; Andersen, Elsa; Furbo, Simon

    2016-04-01

    Direct and diffuse irradiances from the sky has been collected at 1-minute intervals for about a year from the experimental station at the Technical University of Denmark for the IEA project "Solar Resource Assessment and Forecasting". These data were gathered by pyrheliometers tracking the Sun, as well as with apertured pyranometers gathering 1/8th and 1/16th of the light from the sky in 45 degree azimuthal ranges pointed around the compass. The data are gathered in order to develop detailed models of the potentially available solar energy and its variations at high temporal resolution in order to gain a more detailed understanding of the solar resource. This is important for a better understanding of the sub-grid scale cloud variation that cannot be resolved with climate and weather models. It is also important for optimizing the operation of active solar energy systems such as photovoltaic plants and thermal solar collector arrays, and for passive solar energy and lighting to buildings. We present regression-based modelling of the observed data, and focus, here, on the statistical properties of the model fits. Using models based on the one hand on what is found in the literature and on physical expectations, and on the other hand on purely statistical models, we find solutions that can explain up to 90% of the variance in global radiation. The models leaning on physical insights include terms for the direct solar radiation, a term for the circum-solar radiation, a diffuse term and a term for the horizon brightening/darkening. The purely statistical model is found using data- and formula-validation approaches picking model expressions from a general catalogue of possible formulae. The method allows nesting of expressions, and the results found are dependent on and heavily constrained by the cross-validation carried out on statistically independent testing and training data-sets. Slightly better fits -- in terms of variance explained -- is found using the purely

  8. Real space renormalization group and totalitarian paradox of majority rule voting

    NASA Astrophysics Data System (ADS)

    Galam, Serge

    2000-09-01

    The effect of majority rule voting in hierarchical structures is studied using the basic concepts from real space renormalization group. It shows in particular that a huge majority can be self-eliminated while climbing up the hierarchy levels. This majority democratic self-elimination articulates around the existence of fixed points in the voting flow. An unstable fixed point determines the critical threshold to full and total power. It can be varied from 50% up to 77% of initial support. Our model could shed new light on the last century eastern European communist collapse.

  9. Tunable Real Space Transfer Oscillator by Delayed Feedback Control of Chaos

    NASA Astrophysics Data System (ADS)

    Cooper, D. P.; Schöll, E.

    1995-03-01

    It is demonstrated numerically that by using Pyragas' method of chaos self-control a stable semiconductor oscillator can be designed based on driven real-space transfer oscillations in a modulation-doped heterostructure. By application of a small time-continuous delayed feedback voltage control signal, different unstable periodic orbits embedded in the chaotic attractor can be stabilized. Thus different modes of self-generated periodic voltage oscillations can be selected by choosing an appropriate delay time. This provides tunability to different discrete frequencies.

  10. Direct observation of optical precursors in a cold potassium gas

    NASA Astrophysics Data System (ADS)

    Jeong, Heejeong

    This thesis considers how an electromagnetic field propagates through a dispersive linear dielectric in the case when the field is turned on suddenly. It has been predicted nearly 100 years ago that the point in the waveform where the field first turns on (the front) propagates precisely at the speed of light in vacuum. Furthermore, it is predicted that distinct wave-packets develop after the front, but before the arrival of the main part of the field (the main signal). These wave-packets are known as optical precursors. It was believed that precursors are an ultra-fast phenomena, persisting only for a few optical cycles, and that they have an exceedingly small amplitude. I describe a method to increase the duration of optical precursors into the nanosecond range using a dielectric with a narrow resonance. I also show how to increase the precursor amplitude by tuning the carrier frequency of the field near the resonance frequency of the oscillators making up the dielectric medium. The field emerging from the dielectric consists of a several-nanosecond-long spike occurring immediately after the front with near 100% transmission, which subsequently decays to a constant value expected from Beer's Law of absorption. I demonstrate, using a modern asymptotic theory, that the spike consists of both the Sommerfeld and Brillouin precursors. Thus, my measurement is the first direct observation of optical precursors. The precursor research might be useful for imaging applications requiring penetrating optical radiation, such as in biological systems, or in optical communication systems. While the asymptotic theory explains qualitatively my observations, I find that there are large quantitative disagreements. I hypothesize that these errors are due to the fact that I use a weakly-dispersive narrow-resonance medium for which this theory has never been tested. I suggest empirical fixes to the theory by comparison to my data. I also compare the asymptotic theory and data to a

  11. Direct Observation of Two Proton Radioactivity Using Digital Photography

    SciTech Connect

    Rykaczewski, Krzysztof Piotr; Pfutzner, M.; Dominik, Wojciech; Janas, Z.; Miernik, K.; Bingham, C. R.; Czyrkowski, Henryk; Cwiok, Mikolaj; Darby, Iain; Dabrowski, Ryszard; Ginter, T. N.; Grzywacz, Robert Kazimierz; Karny, M.; Korgul, A.; Kusmierz, Waldemar; Liddick, Sean; Rajabali, Mustafa; Stolz, A.

    2007-01-01

    Recently the observation of a new type of spontaneous radioactive decay has been claimed in which two protons are simultaneously ejected by an atomic nucleus from the ground state1,2,3. Experimental data obtained for the extremely neutron-deficient nuclei 45Fe and 54Zn, were interpreted as the first evidence of such a decay mode which has been sought since 1960.4 However, the technique applied in those studies allowed only measurements of the decay time and the total energy released. Particles emitted in the decay were not identified and the conclusions had to be supported by theoretical arguments. Here we show for the first time, directly and unambiguously, that 45Fe indeed disintegrates by two-proton decay. Furthermore, we demonstrate that the decay branch of this isotope leads to various particle emission channels including two-proton and three-proton emission. To achieve this result we have developed a new type of detector V the Optical Time Projection Chamber (OTPC) in which digital photography is applied to nuclear physics for the first time. The detector records images of tracks from charged particles, allowing for their unambiguous identification and the reconstruction of decay events in three dimensions. This new and simple technique provides a powerful method to identify exotic decay channels involving emission of charged particles. It is expected that further studies with the OTPC device will yield important information on nuclei located at and beyond the proton drip-line, thus providing new material for testing and improving models of very unstable atomic nuclei.

  12. Direct Observations Of Microbial Activity At Extreme Pressures

    NASA Astrophysics Data System (ADS)

    Sharma, A.; Scott, J. H.; Cody, G. D.; Fogel, M.; Hazen, R. M.; Hemley, R. J.; Huntress, W. T.

    2002-12-01

    Microbial communities adapt to a wide range of pressures, temperatures, salinities, pH, and oxidation states. Although, significant attention has been focused on the effects of high and low temperature on physiology, there is some evidence that elevated pressure may also manifest interesting effects on cellular physiology, such as enzyme inactivation, cell-membrane breach, and suppression of protein interactions with various substrates. However, exactly how these factors affect intact cells is not well understood. In this study, we have adapted diamond anvil cells to explore the effects of high pressure on microbial life. We used the rate of microbial formate oxidation as a probe of metabolic viability. The utilization of formate by microorganisms is a fundamental metabolic process in anaerobic environments. We monitored in-situ microbial formate oxidation via molecular spectroscopy for Shewanella oneidensis strain MR1 and Escherichia coli strain MG1655 at high pressures (68 to 1060 MPa). At pressures of 1200 to 1600 MPa, living bacteria resided in fluid inclusions in ice-VI crystals and continued to be viable upon subsequent release to ambient pressures (0.1 MPa). Furthermore, direct microscopic observations indicate that these cells maintain their ability for cellular division upon decompression from such high pressures. Evidence of microbial viability and activity at these extreme pressures expands by an order of magnitude the range of conditions representing the habitable zone in the solar system. These results imply that pressure may not be a significant impediment to life. The maximum pressure explored in this work is equivalent to a depth of ~ 50 km below Earth's crust, or ~ 160 km in a hypothetical ocean. The pressures encountered at the depths of thick ice caps and deep crustal subsurface may not be a limiting factor for the existence of life. This suggests that deep (water/ice) layers of Europa, Callisto, or Ganymede, subduction zones on Earth, and the

  13. Modeling solvation effects in real-space and real-time within density functional approaches

    SciTech Connect

    Delgado, Alain; Corni, Stefano; Pittalis, Stefano; Rozzi, Carlo Andrea

    2015-10-14

    The Polarizable Continuum Model (PCM) can be used in conjunction with Density Functional Theory (DFT) and its time-dependent extension (TDDFT) to simulate the electronic and optical properties of molecules and nanoparticles immersed in a dielectric environment, typically liquid solvents. In this contribution, we develop a methodology to account for solvation effects in real-space (and real-time) (TD)DFT calculations. The boundary elements method is used to calculate the solvent reaction potential in terms of the apparent charges that spread over the van der Waals solute surface. In a real-space representation, this potential may exhibit a Coulomb singularity at grid points that are close to the cavity surface. We propose a simple approach to regularize such singularity by using a set of spherical Gaussian functions to distribute the apparent charges. We have implemented the proposed method in the OCTOPUS code and present results for the solvation free energies and solvatochromic shifts for a representative set of organic molecules in water.

  14. Modeling solvation effects in real-space and real-time within density functional approaches

    NASA Astrophysics Data System (ADS)

    Delgado, Alain; Corni, Stefano; Pittalis, Stefano; Rozzi, Carlo Andrea

    2015-10-01

    The Polarizable Continuum Model (PCM) can be used in conjunction with Density Functional Theory (DFT) and its time-dependent extension (TDDFT) to simulate the electronic and optical properties of molecules and nanoparticles immersed in a dielectric environment, typically liquid solvents. In this contribution, we develop a methodology to account for solvation effects in real-space (and real-time) (TD)DFT calculations. The boundary elements method is used to calculate the solvent reaction potential in terms of the apparent charges that spread over the van der Waals solute surface. In a real-space representation, this potential may exhibit a Coulomb singularity at grid points that are close to the cavity surface. We propose a simple approach to regularize such singularity by using a set of spherical Gaussian functions to distribute the apparent charges. We have implemented the proposed method in the Octopus code and present results for the solvation free energies and solvatochromic shifts for a representative set of organic molecules in water.

  15. Modeling solvation effects in real-space and real-time within density functional approaches.

    PubMed

    Delgado, Alain; Corni, Stefano; Pittalis, Stefano; Rozzi, Carlo Andrea

    2015-10-14

    The Polarizable Continuum Model (PCM) can be used in conjunction with Density Functional Theory (DFT) and its time-dependent extension (TDDFT) to simulate the electronic and optical properties of molecules and nanoparticles immersed in a dielectric environment, typically liquid solvents. In this contribution, we develop a methodology to account for solvation effects in real-space (and real-time) (TD)DFT calculations. The boundary elements method is used to calculate the solvent reaction potential in terms of the apparent charges that spread over the van der Waals solute surface. In a real-space representation, this potential may exhibit a Coulomb singularity at grid points that are close to the cavity surface. We propose a simple approach to regularize such singularity by using a set of spherical Gaussian functions to distribute the apparent charges. We have implemented the proposed method in the Octopus code and present results for the solvation free energies and solvatochromic shifts for a representative set of organic molecules in water. PMID:26472367

  16. A new parallel plate shear cell for in situ real-space measurements of complex fluids under shear flow.

    PubMed

    Wu, Yu Ling; Brand, Joost H J; van Gemert, Josephus L A; Verkerk, Jaap; Wisman, Hans; van Blaaderen, Alfons; Imhof, Arnout

    2007-10-01

    We developed and tested a parallel plate shear cell that can be mounted on top of an inverted microscope to perform confocal real-space measurements on complex fluids under shear. To follow structural changes in time, a plane of zero velocity is created by letting the plates move in opposite directions. The location of this plane is varied by changing the relative velocities of the plates. The gap width is variable between 20 and 200 microm with parallelism better than 1 microm. Such a small gap width enables us to examine the total sample thickness using high numerical aperture objective lenses. The achieved shear rates cover the range of 0.02-10(3) s(-1). This shear cell can apply an oscillatory shear with adjustable amplitude and frequency. The maximum travel of each plate equals 1 cm, so that strains up to 500 can be applied. For most complex fluids, an oscillatory shear with such a large amplitude can be regarded as a continuous shear. We measured the flow profile of a suspension of silica colloids in this shear cell. It was linear except for a small deviation caused by sedimentation. To demonstrate the excellent performance and capabilities of this new setup we examined shear induced crystallization and melting of concentrated suspensions of 1 microm diameter silica colloids.

  17. Conformational disorder of proteins assessed by real-space molecular dynamics refinement.

    PubMed Central

    Chen, Z; Chapman, M S

    2001-01-01

    Motion is critical to the function of many proteins, but much more difficult to study than structure. Due to lack of easy alternatives, although there are inherent limitations, there have been several prior attempts to extract some information from the Bragg scattering in conventional diffraction patterns. Bragg diffraction reflects only a small proportion of a protein's motion and disorder, so fitted values likely underestimate reality. However, this work shows that the fitted estimates should be even smaller, because current methods of refinement over-fit the Bragg diffraction, leading to a component of the disorder that is not based on any experimental data, and could be characterized as a guess. Real-space refinement is less susceptible than other methods, but its application depends on the availability of very accurate experimental phases. A future challenge will be the collection of such data without resort to cryo-techniques, so that a physiologically relevant understanding can be achieved. PMID:11222306

  18. Real-space visualization of conformation-independent oligothiophene electronic structure

    NASA Astrophysics Data System (ADS)

    Taber, Benjamen N.; Kislitsyn, Dmitry A.; Gervasi, Christian F.; Mills, Jon M.; Rosenfield, Ariel E.; Zhang, Lei; Mannsfeld, Stefan C. B.; Prell, James S.; Briseno, Alejandro L.; Nazin, George V.

    2016-05-01

    We present scanning tunneling microscopy and spectroscopy (STM/STS) investigations of the electronic structures of different alkyl-substituted oligothiophenes on the Au(111) surface. STM imaging showed that on Au(111), oligothiophenes adopted distinct straight and bent conformations. By combining STS maps with STM images, we visualize, in real space, particle-in-a-box-like oligothiophene molecular orbitals. We demonstrate that different planar conformers with significant geometrical distortions of oligothiophene backbones surprisingly exhibit very similar electronic structures, indicating a low degree of conformation-induced electronic disorder. The agreement of these results with gas-phase density functional theory calculations implies that the oligothiophene interaction with the Au(111) surface is generally insensitive to molecular conformation.

  19. Accurate Nanoscale Crystallography in Real-Space Using Scanning Transmission Electron Microscopy.

    PubMed

    Dycus, J Houston; Harris, Joshua S; Sang, Xiahan; Fancher, Chris M; Findlay, Scott D; Oni, Adedapo A; Chan, Tsung-Ta E; Koch, Carl C; Jones, Jacob L; Allen, Leslie J; Irving, Douglas L; LeBeau, James M

    2015-08-01

    Here, we report reproducible and accurate measurement of crystallographic parameters using scanning transmission electron microscopy. This is made possible by removing drift and residual scan distortion. We demonstrate real-space lattice parameter measurements with <0.1% error for complex-layered chalcogenides Bi2Te3, Bi2Se3, and a Bi2Te2.7Se0.3 nanostructured alloy. Pairing the technique with atomic resolution spectroscopy, we connect local structure with chemistry and bonding. Combining these results with density functional theory, we show that the incorporation of Se into Bi2Te3 causes charge redistribution that anomalously increases the van der Waals gap between building blocks of the layered structure. The results show that atomic resolution imaging with electrons can accurately and robustly quantify crystallography at the nanoscale.

  20. Real-space Wigner-Seitz Cells Imaging of Potassium on Graphite via Elastic Atomic Manipulation

    PubMed Central

    Yin, Feng; Koskinen, Pekka; Kulju, Sampo; Akola, Jaakko; Palmer, Richard E.

    2015-01-01

    Atomic manipulation in the scanning tunnelling microscopy, conventionally a tool to build nanostructures one atom at a time, is here employed to enable the atomic-scale imaging of a model low-dimensional system. Specifically, we use low-temperature STM to investigate an ultra thin film (4 atomic layers) of potassium created by epitaxial growth on a graphite substrate. The STM images display an unexpected honeycomb feature, which corresponds to a real-space visualization of the Wigner-Seitz cells of the close-packed surface K atoms. Density functional simulations indicate that this behaviour arises from the elastic, tip-induced vertical manipulation of potassium atoms during imaging, i.e. elastic atomic manipulation, and reflects the ultrasoft properties of the surface under strain. The method may be generally applicable to other soft e.g. molecular or biomolecular systems. PMID:25651973

  1. Examining the Agreement of Direct Behavior Ratings and Systematic Direct Observation Data for On-Task and Disruptive Behavior

    ERIC Educational Resources Information Center

    Riley-Tillman, T. Chris; Chafouleas, Sandra M.; Sassu, Kari A.; Chanese, Julie A. M.; Glazer, Amy D.

    2008-01-01

    The purpose of this study was to replicate previous findings indicating a moderate association between teacher perceptions of behavior as measured by direct behavior ratings (DBRs) and systematic direct observation (SDO) conducted by an external observer. In this study, data regarding student on-task and disruptive behavior were collected via SDO…

  2. DIRECT OBSERVATION OF A COROTATING INTERACTION REGION BY THREE SPACECRAFT

    SciTech Connect

    Tappin, S. J. Howard, T. A

    2009-09-10

    White-light observations of interplanetary disturbances have been dominated by interplanetary coronal mass ejections (ICMEs). This is because the other type of disturbance, the corotating interaction region (CIR), has proved difficult to detect using white-light imagers. Recently, a number of papers have appeared presenting CIR observations using the Solar Terrestrial Relations Observatory (STEREO) Heliospheric Imagers (HIs), but have mostly only focused on a single spacecraft and imager. In this paper, we present observations of a single CIR that was observed by all three current white-light heliospheric imagers (SMEI and both STEREO HIs), as well as the in situ instruments on both STEREO satellites and ACE. We begin with a discussion of the geometry of the CIR structure, and show how the apparent leading edge structure is expected to change as it corotates relative to the observer. We use these calculations to predict elongation-time profiles for CIRs of different speeds for each of the imagers, and also to predict the arrival times at the in situ instruments. We show that although all three measured different parts, they combine to produce a self-consistent picture of the CIR. Finally, we offer some thoughts on why CIRs have proved so difficult to detect in white-light heliospheric images.

  3. Real-space method for first-principles electron transport calculations: Self-energy terms of electrodes for large systems

    NASA Astrophysics Data System (ADS)

    Ono, Tomoya; Tsukamoto, Shigeru

    2016-01-01

    We present a fast and stable numerical technique to obtain the self-energy terms of electrodes for first-principles electron transport calculations. Although first-principles calculations based on the real-space finite-difference method are advantageous for execution on massively parallel computers, large-scale transport calculations are hampered by the computational cost and numerical instability of the computation of the self-energy terms. Using the orthogonal complement vectors of the space spanned by the generalized Bloch waves that actually contribute to transport phenomena, the computational accuracy of transport properties is significantly improved with a moderate computational cost. To demonstrate the efficiency of the present technique, the electron transport properties of a Stone-Wales (SW) defect in graphene and silicene are examined. The resonance scattering of the SW defect is observed in the conductance spectrum of silicene since the σ* state of silicene lies near the Fermi energy. In addition, we found that one conduction channel is sensitive to a defect near the Fermi energy, while the other channel is hardly affected. This characteristic behavior of the conduction channels is interpreted in terms of the bonding network between the bilattices of the honeycomb structure in the formation of the SW defect. The present technique enables us to distinguish the different behaviors of the two conduction channels in graphene and silicene owing to its excellent accuracy.

  4. The nature of the redshift and directly observed quasar statistics.

    PubMed

    Segal, I E; Nicoll, J F; Wu, P; Zhou, Z

    1991-07-01

    The nature of the cosmic redshift is one of the most fundamental questions in modern science. Hubble's discovery of the apparent Expansion of the Universe is derived from observations on a small number of galaxies at very low redshifts. Today, quasar redshifts have a range more than 1000 times greater than those in Hubble's sample, and represent more than 100 times as many objects. A recent comprehensive compilation of published measurements provides the basis for a study indicating that quasar observations are not in good agreement with the original predictions of the Expanding Universe theory, but are well fit by the predictions of an alternative theory having fewer adjustable parameters.

  5. Direct observation of condensate and vortex confinement in nanostructured superconductors

    NASA Astrophysics Data System (ADS)

    Timmermans, M.; Serrier-Garcia, L.; Perini, M.; Van de Vondel, J.; Moshchalkov, V. V.

    2016-02-01

    In this work we report a scanning tunneling microscopy investigation of lithographically defined superconducting nanosquares. The obtained spectroscopic maps reveal the spatial evolution of both the superconducting condensate and the screening currents as a function of the applied magnetic field. The symmetry of the nanostructure is imposed on the condensate and it controls the distribution of the vortices inside the nanosquare. Our local study allows exploring the impact of small structural defects, omnipresent in these kind of structures, on both the supercurrent and vortex distribution. As a result, direct experimental evidence of vortex pinning and current crowding at the nanoscale has been obtained.

  6. Clear Direction. The Montessori Observer. Volume 32, Number 2

    ERIC Educational Resources Information Center

    International Montessori Society (NJ3), 2011

    2011-01-01

    "The Montessori Observer" is mailed four times each year, in March, May, September and November, to Society members throughout the world. The purpose is to provide news and information about the Society's work in Montessori education, and to extend awareness of Montessori principles throughout the world. This issue contains a feature article,…

  7. Direct observation of warping in the plasma sheet of Saturn

    NASA Astrophysics Data System (ADS)

    Carbary, J. F.; Mitchell, D. G.; Paranicas, C.; Roelof, E. C.; Krimigis, S. M.

    2008-12-01

    The ENA images from the Ion Neutral CAmera (INCA) on the Cassini spacecraft are projected onto the noon-midnight plane of Sun-Saturn orbital coordinates, and a composite ``image'' of Saturn's plasma sheet is constructed from dawn-side observations of 20-50 keV hydrogens obtained from days 352 to 361 in 2004. The maxima in the intensity contours define the center of the plasma sheet in the noon-midnight plane. This plasma sheet surface displays a distinct bending or ``warping'' above Saturn's equatorial plane at radial distances of beyond ~15 RS on the nightside. On the dayside, the plasma sheet lies close to the equator all the way to the magnetopause. The observed warping agrees with the ``bowl'' model derived from measurements of Saturn's magnetic field, but fits more closely a simple third-order polynomial.

  8. Direct observation of bubble-assisted electroluminescence in liquid xenon

    NASA Astrophysics Data System (ADS)

    Erdal, E.; Arazi, L.; Chepel, V.; Rappaport, M. L.; Vartsky, D.; Breskin, A.

    2015-11-01

    Bubble formation in liquid xenon underneath a Thick Gaseous Electron Multiplier (THGEM) electrode immersed in liquid xenon was observed with a CCD camera. With voltage across the THGEM, the appearance of bubbles was correlated with that of electroluminescence signals induced by ionization electrons from alpha-particle tracks. This confirms recent indirect evidence that the observed photons are due to electroluminescence within a xenon vapor layer trapped under the electrode. The bubbles seem to emerge spontaneously due to heat flow from 300 K into the liquid, or in a controlled manner by locally boiling the liquid with resistive wires. Controlled bubble formation resulted in energy resolution of σ/E ≈ 7.5% for ~ 6000 ionization electrons. The phenomenon could pave ways towards the conception of large-volume `local dual-phase' noble-liquid TPCs.

  9. 49 CFR 40.67 - When and how is a directly observed collection conducted?

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 49 Transportation 1 2011-10-01 2011-10-01 false When and how is a directly observed collection... directly observed collection conducted? (a) As an employer, you must direct an immediate collection under... paragraphs (a) and (b) of this section); or (2) You observed materials brought to the collection site or...

  10. Direct observation of closure domain wall mediated spin waves

    SciTech Connect

    Mozooni, Babak McCord, Jeffrey

    2015-07-27

    The generation and guiding of spin waves from and by magnetic domain walls are demonstrated. The spin waves radiate from pinned and oscillating magnetic closure domain walls and propagate linearly along a narrow path formed by the surrounding 180° asymmetric Bloch domain walls. The propagating spin wave modes are directly visualized by time-resolved magneto-optical Kerr microscopy with picosecond temporal resolution. A linear relationship between excitation frequency, wavelength, and number of spin waves per domain exists. Independent of the field excitation frequency, a constant phase velocity of spin waves propagation is obtained. Spin waves characteristics can be tuned by varying the magnetic domain dynamics, allowing for variable spin wave characteristics with magnetic field characteristics and histories.

  11. Direct observation of closure domain wall mediated spin waves

    NASA Astrophysics Data System (ADS)

    Mozooni, Babak; McCord, Jeffrey

    2015-07-01

    The generation and guiding of spin waves from and by magnetic domain walls are demonstrated. The spin waves radiate from pinned and oscillating magnetic closure domain walls and propagate linearly along a narrow path formed by the surrounding 180° asymmetric Bloch domain walls. The propagating spin wave modes are directly visualized by time-resolved magneto-optical Kerr microscopy with picosecond temporal resolution. A linear relationship between excitation frequency, wavelength, and number of spin waves per domain exists. Independent of the field excitation frequency, a constant phase velocity of spin waves propagation is obtained. Spin waves characteristics can be tuned by varying the magnetic domain dynamics, allowing for variable spin wave characteristics with magnetic field characteristics and histories.

  12. Real-Space Density Functional Theory on Graphical Processing Units: Computational Approach and Comparison to Gaussian Basis Set Methods.

    PubMed

    Andrade, Xavier; Aspuru-Guzik, Alán

    2013-10-01

    We discuss the application of graphical processing units (GPUs) to accelerate real-space density functional theory (DFT) calculations. To make our implementation efficient, we have developed a scheme to expose the data parallelism available in the DFT approach; this is applied to the different procedures required for a real-space DFT calculation. We present results for current-generation GPUs from AMD and Nvidia, which show that our scheme, implemented in the free code Octopus, can reach a sustained performance of up to 90 GFlops for a single GPU, representing a significant speed-up when compared to the CPU version of the code. Moreover, for some systems, our implementation can outperform a GPU Gaussian basis set code, showing that the real-space approach is a competitive alternative for DFT simulations on GPUs. PMID:26589153

  13. Real-Space Density Functional Theory on Graphical Processing Units: Computational Approach and Comparison to Gaussian Basis Set Methods.

    PubMed

    Andrade, Xavier; Aspuru-Guzik, Alán

    2013-10-01

    We discuss the application of graphical processing units (GPUs) to accelerate real-space density functional theory (DFT) calculations. To make our implementation efficient, we have developed a scheme to expose the data parallelism available in the DFT approach; this is applied to the different procedures required for a real-space DFT calculation. We present results for current-generation GPUs from AMD and Nvidia, which show that our scheme, implemented in the free code Octopus, can reach a sustained performance of up to 90 GFlops for a single GPU, representing a significant speed-up when compared to the CPU version of the code. Moreover, for some systems, our implementation can outperform a GPU Gaussian basis set code, showing that the real-space approach is a competitive alternative for DFT simulations on GPUs.

  14. Task Learning of an Arm Robot in Real Space by Using a Learning System in Virtual Space

    NASA Astrophysics Data System (ADS)

    Tsubone, Tadashi; Kurimoto, Kenichi; Sugiyama, Koichi; Wada, Yasuhiro

    Reinforced learning by which a robot acquires control rules through trial and error has gotten a lot of attention. However, it is quite difficult for robots to acquire control rules by reinforcement learning in real space because many learning trials are needed to achieve the control rules; the robot itself may lose control, or there may be safety problems with the control objects. In this paper, we propose a method in which a robot in real space learns a virtual task; then the task is transferred from virtual to real space. The robot eventually acquires the task in a real environment. We show that a real robot can acquire a task in virtual space with an input device by an example of an inverted pendulum. Next, we verify availability that the acquired task in virtual space can be applied to a real world task. We emphasize the utilization of virtual space to effectively obtain the real world task.

  15. Direct observation of fungal aggregates in sand dune soil.

    PubMed

    Clough, K S; Sutton, J C

    1978-03-01

    The mycorrhizal fungus Glomerus in association with bean hosts, Phaseolus vulgaris L., growing in pot cultures and grass hosts, Calamovilfa longiflora (Hook). Scribn and Andropogon sp. growing on Lake Huron sand dunes produced extensive external mycelium. This mycelium was the dominant factor in the aggregation of soil particles. Light and scanning electron microscope studies indicated that the sand grains were attached to the hyphae. An amorphous deposit was often present at the interfaces of sand grains and hyphae. It appeared to act as an adhesive. Staining procedures indicated that this material contained polysaccharide. Other microogranisms were observed in association with the Glomus hyphae and the amorphous deposits.

  16. Direct Observation of Ultralow Vertical Emittance using a Vertical Undulator

    SciTech Connect

    Wootton, Kent

    2015-09-17

    In recent work, the first quantitative measurements of electron beam vertical emittance using a vertical undulator were presented, with particular emphasis given to ultralow vertical emittances [K. P. Wootton, et al., Phys. Rev. ST Accel. Beams, 17, 112802 (2014)]. Using this apparatus, a geometric vertical emittance of 0.9 #6;± 0.3 pm rad has been observed. A critical analysis is given of measurement approaches that were attempted, with particular emphasis on systematic and statistical uncertainties. The method used is explained, compared to other techniques and the applicability of these results to other scenarios discussed.

  17. Providers' response to child eating behaviors: A direct observation study.

    PubMed

    Tovar, Alison; Vaughn, Amber E; Fallon, Megan; Hennessy, Erin; Burney, Regan; Østbye, Truls; Ward, Dianne S

    2016-10-01

    Child care providers play an important role in feeding young children, yet little is known about children's influence on providers' feeding practices. This qualitative study examines provider and child (18 months -4 years) feeding interactions. Trained data collectors observed 200 eating occasions in 48 family child care homes and recorded providers' responses to children's meal and snack time behaviors. Child behaviors initiating provider feeding practices were identified and practices were coded according to higher order constructs identified in a recent feeding practices content map. Analysis examined the most common feeding practices providers used to respond to each child behavior. Providers were predominately female (100%), African-American (75%), and obese (77%) and a third of children were overweight/obese (33%). Commonly observed child behaviors were: verbal and non-verbal refusals, verbal and non-verbal acceptance, being "all done", attempts for praise/attention, and asking for seconds. Children's acceptance of food elicited more autonomy supportive practices vs. coercive controlling. Requests for seconds was the most common behavior, resulting in coercive controlling practices (e.g., insisting child eat certain food or clean plate). Future interventions should train providers on responding to children's behaviors and helping children become more aware of internal satiety and hunger cues. PMID:27328098

  18. Direct observation of intermediate states in model membrane fusion

    PubMed Central

    Keidel, Andrea; Bartsch, Tobias F.; Florin, Ernst-Ludwig

    2016-01-01

    We introduce a novel assay for membrane fusion of solid supported membranes on silica beads and on coverslips. Fusion of the lipid bilayers is induced by bringing an optically trapped bead in contact with the coverslip surface while observing the bead’s thermal motion with microsecond temporal and nanometer spatial resolution using a three-dimensional position detector. The probability of fusion is controlled by the membrane tension on the particle. We show that the progression of fusion can be monitored by changes in the three-dimensional position histograms of the bead and in its rate of diffusion. We were able to observe all fusion intermediates including transient fusion, formation of a stalk, hemifusion and the completion of a fusion pore. Fusion intermediates are characterized by axial but not lateral confinement of the motion of the bead and independently by the change of its rate of diffusion due to the additional drag from the stalk-like connection between the two membranes. The detailed information provided by this assay makes it ideally suited for studies of early events in pure lipid bilayer fusion or fusion assisted by fusogenic molecules. PMID:27029285

  19. Direct observation of intermediate states in model membrane fusion.

    PubMed

    Keidel, Andrea; Bartsch, Tobias F; Florin, Ernst-Ludwig

    2016-01-01

    We introduce a novel assay for membrane fusion of solid supported membranes on silica beads and on coverslips. Fusion of the lipid bilayers is induced by bringing an optically trapped bead in contact with the coverslip surface while observing the bead's thermal motion with microsecond temporal and nanometer spatial resolution using a three-dimensional position detector. The probability of fusion is controlled by the membrane tension on the particle. We show that the progression of fusion can be monitored by changes in the three-dimensional position histograms of the bead and in its rate of diffusion. We were able to observe all fusion intermediates including transient fusion, formation of a stalk, hemifusion and the completion of a fusion pore. Fusion intermediates are characterized by axial but not lateral confinement of the motion of the bead and independently by the change of its rate of diffusion due to the additional drag from the stalk-like connection between the two membranes. The detailed information provided by this assay makes it ideally suited for studies of early events in pure lipid bilayer fusion or fusion assisted by fusogenic molecules. PMID:27029285

  20. Direct Experimental Observation of a Practical AC Zeeman Force

    NASA Astrophysics Data System (ADS)

    Fancher, Charles; Pyle, Andrew; Rotunno, Andrew; Du, Shuangli; Aubin, Seth

    2016-05-01

    We present measurements of the spin-dependent AC Zeeman force produced by microwave magnetic near-field gradients on an atom chip. We measure the AC Zeeman force on ultracold 87 Rb atoms by observing its effect on the motion of atoms in free-fall and on those confined in a trap. We have studied the force as a function of microwave frequency detuning from a hyperfine transition at 6.8 GHz at several magnetic field strengths and have observed its characteristic bipolar and resonant features predicted by two-level dressed atom theory. We find that the force is several times the strength of gravity in our setup, and that it can be targeted to a specific hyperfine transition while leaving other hyperfine states and transitions relatively unaffected. We find that our measurements are reasonably consistent with theory and are working towards a parameter-free comparison. AC Zeeman potentials offer the possibility of targeting qualitatively different trapping potentials to different spin states, a capability currently absent from the toolbox of atomic quantum control techniques. In particular, an AC Zeeman potential could be used as the beamsplitter for a spin-dependent atom interferometer or for engineering a quantum gate. Work supported by AFOSR and W&M, and in part by AFRL.

  1. Direct observation of electron dynamics in the attosecond domain.

    PubMed

    Föhlisch, A; Feulner, P; Hennies, F; Fink, A; Menzel, D; Sanchez-Portal, D; Echenique, P M; Wurth, W

    2005-07-21

    Dynamical processes are commonly investigated using laser pump-probe experiments, with a pump pulse exciting the system of interest and a second probe pulse tracking its temporal evolution as a function of the delay between the pulses. Because the time resolution attainable in such experiments depends on the temporal definition of the laser pulses, pulse compression to 200 attoseconds (1 as = 10(-18) s) is a promising recent development. These ultrafast pulses have been fully characterized, and used to directly measure light waves and electronic relaxation in free atoms. But attosecond pulses can only be realized in the extreme ultraviolet and X-ray regime; in contrast, the optical laser pulses typically used for experiments on complex systems last several femtoseconds (1 fs = 10(-15) s). Here we monitor the dynamics of ultrafast electron transfer--a process important in photo- and electrochemistry and used in solid-state solar cells, molecular electronics and single-electron devices--on attosecond timescales using core-hole spectroscopy. We push the method, which uses the lifetime of a core electron hole as an internal reference clock for following dynamic processes, into the attosecond regime by focusing on short-lived holes with initial and final states in the same electronic shell. This allows us to show that electron transfer from an adsorbed sulphur atom to a ruthenium surface proceeds in about 320 as. PMID:16034414

  2. New Directions in the NOAO Observing Proposal System

    NASA Astrophysics Data System (ADS)

    Gasson, David; Bell, Dave

    For the past eight years NOAO has been refining its on-line observing proposal system. Virtually all related processes are now handled electronically. Members of the astronomical community can submit proposals through email, web form, or via the Gemini Phase I Tool. NOAO staff can use the system to do administrative tasks, scheduling, and compilation of various statistics. In addition, all information relevant to the TAC process is made available on-line, including the proposals themselves (in HTML, PDF and PostScript) and technical comments. Grades and TAC comments are entered and edited through web forms, and can be sorted and filtered according to specified criteria. Current developments include a move away from proprietary solutions, toward open standards such as SQL (in the form of the MySQL relational database system), Perl, PHP and XML.

  3. Direct observation of light focusing by single photoreceptor cell nuclei.

    PubMed

    Błaszczak, Zuzanna; Kreysing, Moritz; Guck, Jochen

    2014-05-01

    The vertebrate retina is inverted with respect to its optical function, which requires light to pass through the entire tissue prior to detection. The last significant barrier for photons to overcome is the outer nuclear layer formed by photoreceptor cell (PRC) nuclei. Here we experimentally characterise the optical properties of PRC nuclei using bright-field defocusing microscopy to capture near-field intensity distributions behind individual nuclei. We find that some nuclei efficiently focus incident light confirming earlier predictions based on comparative studies of chromatin organisation in nocturnal and diurnal mammals. The emergence of light focusing during the development of mouse nuclei highlights the acquired nature of the observed lens-like behaviour. Optical characterisation of these nuclei is an important first step towards an improved understanding of how light transmission through the retina is influenced by its constituents.

  4. Direct observation of dynamic shear jamming in dense suspensions

    NASA Astrophysics Data System (ADS)

    Peters, Ivo R.; Majumdar, Sayantan; Jaeger, Heinrich M.

    2016-04-01

    Liquid-like at rest, dense suspensions of hard particles can undergo striking transformations in behaviour when agitated or sheared. These phenomena include solidification during rapid impact, as well as strong shear thickening characterized by discontinuous, orders-of-magnitude increases in suspension viscosity. Much of this highly non-Newtonian behaviour has recently been interpreted within the framework of a jamming transition. However, although jamming indeed induces solid-like rigidity, even a strongly shear-thickened state still flows and thus cannot be fully jammed. Furthermore, although suspensions are incompressible, the onset of rigidity in the standard jamming scenario requires an increase in particle density. Finally, whereas shear thickening occurs in the steady state, impact-induced solidification is transient. As a result, it has remained unclear how these dense suspension phenomena are related and how they are connected to jamming. Here we resolve this by systematically exploring both the steady-state and transient regimes with the same experimental system. We demonstrate that a fully jammed, solid-like state can be reached without compression and instead purely with shear, as recently proposed for dry granular systems. This state is created by transient shear-jamming fronts, which we track directly. We also show that shear stress, rather than shear rate, is the key control parameter. From these findings we map out a state diagram with particle density and shear stress as variables. We identify discontinuous shear thickening with a marginally jammed regime just below the onset of full, solid-like jamming. This state diagram provides a unifying framework, compatible with prior experimental and simulation results on dense suspensions, that connects steady-state and transient behaviour in terms of a dynamic shear-jamming process.

  5. Direct observation of dynamic shear jamming in dense suspensions.

    PubMed

    Peters, Ivo R; Majumdar, Sayantan; Jaeger, Heinrich M

    2016-04-14

    Liquid-like at rest, dense suspensions of hard particles can undergo striking transformations in behaviour when agitated or sheared. These phenomena include solidification during rapid impact, as well as strong shear thickening characterized by discontinuous, orders-of-magnitude increases in suspension viscosity. Much of this highly non-Newtonian behaviour has recently been interpreted within the framework of a jamming transition. However, although jamming indeed induces solid-like rigidity, even a strongly shear-thickened state still flows and thus cannot be fully jammed. Furthermore, although suspensions are incompressible, the onset of rigidity in the standard jamming scenario requires an increase in particle density. Finally, whereas shear thickening occurs in the steady state, impact-induced solidification is transient. As a result, it has remained unclear how these dense suspension phenomena are related and how they are connected to jamming. Here we resolve this by systematically exploring both the steady-state and transient regimes with the same experimental system. We demonstrate that a fully jammed, solid-like state can be reached without compression and instead purely with shear, as recently proposed for dry granular systems. This state is created by transient shear-jamming fronts, which we track directly. We also show that shear stress, rather than shear rate, is the key control parameter. From these findings we map out a state diagram with particle density and shear stress as variables. We identify discontinuous shear thickening with a marginally jammed regime just below the onset of full, solid-like jamming. This state diagram provides a unifying framework, compatible with prior experimental and simulation results on dense suspensions, that connects steady-state and transient behaviour in terms of a dynamic shear-jamming process. PMID:27042934

  6. The cosmic microwave background: observing directly the early universe

    NASA Astrophysics Data System (ADS)

    de Bernardis, Paolo; Masi, Silvia

    2012-09-01

    The Cosmic Microwave Background (CMB) is a relict of the early universe. Its perfect 2.725K blackbody spectrum demonstrates that the universe underwent a hot, ionized early phase; its anisotropy (about 80 µK rms) provides strong evidence for the presence of photon-matter oscillations in the primeval plasma, shaping the initial phase of the formation of structures; its polarization state (about 3 µK rms), and in particular its rotational component (less than 0.1 µK rms) might allow to study the inflation process in the very early universe, and the physics of extremely high energies, impossible to reach with accelerators. The CMB is observed by means of microwave and mm-wave telescopes, and its measurements drove the development of ultra-sensitive bolometric detectors, sophisticated modulators, and advanced cryogenic and space technologies. Here we focus on the new frontiers of CMB research: the precision measurements of its linear polarization state, at large and intermediate angular scales, and the measurement of the inverse-Compton effect of CMB photons crossing clusters of Galaxies. In this framework, we will describe the formidable experimental challenges faced by ground-based, near-space and space experiments, using large arrays of detectors. We will show that sensitivity and mapping speed improvement obtained with these arrays must be accompanied by a corresponding reduction of systematic effects (especially for CMB polarimeters), and by improved knowledge of foreground emission, to fully exploit the huge scientific potential of these missions.

  7. Direct observation of completely processed calcium carbonate dust particles.

    PubMed

    Laskin, Alexander; Iedema, Martin J; Ichkovich, Aviad; Graber, Ellen R; Taraniuk, Ilya; Rudich, Yinon

    2005-01-01

    This study presents, for the first time, field evidence of complete, irreversible processing of solid calcium carbonate (calcite)-containing particles and quantitative formation of liquid calcium nitrate particles apparently as a result of heterogeneous reaction of calcium carbonate-containing mineral dust particles with gaseous nitric acid. Formation of nitrates from individual calcite and sea salt particles was followed as a function of time in aerosol samples collected at Shoresh, Israel. Morphology and compositional changes of individual particles were observed using conventional scanning electron microscopy with energy dispersive analysis of X-rays (SEM/EDX) and computer controlled SEM/EDX. Environmental scanning electron microscopy (ESEM) was utilized to determine and demonstrate the hygroscopic behavior of calcium nitrate particles found in some of the samples. Calcium nitrate particles are exceptionally hygroscopic and deliquesce even at very low relative humidity (RH) of 9-11% which is lower than typical atmospheric environments. Transformation of non-hygroscopic dry mineral dust particles into hygroscopic wet aerosol may have substantial impacts on light scattering properties, the ability to modify clouds and heterogeneous chemistry.

  8. Direct observation of catch bonds involving cell-adhesion molecules

    NASA Astrophysics Data System (ADS)

    Marshall, Bryan T.; Long, Mian; Piper, James W.; Yago, Tadayuki; McEver, Rodger P.; Zhu, Cheng

    2003-05-01

    Bonds between adhesion molecules are often mechanically stressed. A striking example is the tensile force applied to selectin-ligand bonds, which mediate the tethering and rolling of flowing leukocytes on vascular surfaces. It has been suggested that force could either shorten bond lifetimes, because work done by the force could lower the energy barrier between the bound and free states (`slip'), or prolong bond lifetimes by deforming the molecules such that they lock more tightly (`catch'). Whereas slip bonds have been widely observed, catch bonds have not been demonstrated experimentally. Here, using atomic force microscopy and flow-chamber experiments, we show that increasing force first prolonged and then shortened the lifetimes of P-selectin complexes with P-selectin glycoprotein ligand-1, revealing both catch and slip bond behaviour. Transitions between catch and slip bonds might explain why leukocyte rolling on selectins first increases and then decreases as wall shear stress increases. This dual response to force provides a mechanism for regulating cell adhesion under conditions of variable mechanical stress.

  9. Direct Observation of Completely Processed Calcium Carbonate Dust Particles

    SciTech Connect

    Laskin, Alexander; Iedema, Martin J.; Ichkovich, Aviad; Graber, Ellen R.; Taraniuk, Ilya; Rudich, Yinon

    2005-05-27

    This study presents, for the first time, field evidence of complete, irreversible processing of solid calcium carbonate (calcite)-containing particles and quantitative formation of liquid calcium nitrate particles apparently as a result of heterogeneous reaction of calcium carbonate-containing mineral dust particles with gaseous nitric acid. Formation of nitrates from individual calcite and sea salt particles was followed as a function of time in aerosol samples collected at Shoresh, Israel. Morphology and compositional changes of individual particles were observed using conventional scanning electron microscopy with energy dispersive analysis of X-rays (SEM/EDX) and computer controlled SEM/EDX. Environmental scanning electron microscopy (ESEM) was utilized to determine and demonstrate the hygroscopic behavior of calcium nitrate particles found in some of the samples. Calcium nitrate particles are exceptionally hygroscopic and deliquesce even at very low relative humidity (RH) of 9 -11% which is lower than typical atmospheric environments. Transformation of non-hygroscopic dry mineral dust particles into hygroscopic wet aerosol may have substantial impacts on light scattering properties, the ability to modify clouds and heterogeneous chemistry.

  10. Direct observation of OH formation from stabilised Criegee intermediates.

    PubMed

    Novelli, A; Vereecken, L; Lelieveld, J; Harder, H

    2014-10-01

    The syn-CH3CHOO Criegee intermediate formed from the ozonolysis of propene and (E)-2-butene was detected via unimolecular decomposition and subsequent detection of OH radicals by a LIF-FAGE instrument. An observed time dependent OH concentration profile was analysed using a detailed model focusing on the speciated chemistry of Criegee intermediates based on the recent literature. The absolute OH concentration was found to depend on the steady state concentration of syn-CH3CHOO at the injection point while the time dependence of the OH concentration profile was influenced by the sum of the rates of unimolecular decomposition of syn-CH3CHOO and wall loss. By varying the most relevant parameters influencing the SCI chemistry in the model and based on the temporal OH concentration profile, the unimolecular decomposition rate k (293 K) of syn-CH3CHOO was shown to lie within the range 3-30 s(-1), where a value of 20 ± 10 s(-1) yields the best agreement with the CI chemistry literature. PMID:25119645

  11. Direct observation of resonance effects in laser cluster interactions

    SciTech Connect

    Zweiback, J

    1999-06-01

    Time resolved dynamics of high intensity laser interactions with atomic clusters have been studied with both theoretical analysis and experiment. A short-pulse Ti:sapphire laser system, which could produce 50 mJ of energy in a 50 fs pulse, was built to perform these experiments. The laser used a novel single grating stretcher and was pumped, in part, by a custom Nd:YLF laser system, including 19 mm Nd:YLF amplifiers. It was found that there is an optimal pulse width to maximize absorption for a given cluster size. This optimal pulse width ranged from 400 fs for 85 A radius xenon clusters to 1.2 ps for 205 {angstrom} radius xenon clusters. Using a pump-probe configuration, the absorption of the probe radiation was observed to reach a maximum for a particular time delay between pump and probe, dependent on the cluster size. The delay for peak absorption was 800, 1400, and 2100 fs for 85 {angstrom}, 130 {angstrom}, and 170 {angstrom} radius xenon clusters respectively. Model calculations suggest that these effects are due to resonant heating of the spherical plasma in agreement with the hydrodynamic interpretation of cluster interactions. While this simple hydrodynamic code produces reasonable agreement with data, it does not include bulk plasma or non-linear propagation effects and is limited to the regime where resonant behavior dominates. We also measured the scattered laser light from the laser-cluster interaction. Similar to the absorption measurements, there is an optimal pulse width which maximizes the scattered signal. This pulse width is larger than the optimal pulse width for absorption. This disagrees with model calculations which show both pulse widths being similar. Further experiments measuring the scattered light in a pump-probe configuration should help to resolve this disagreement.

  12. Relation between Direct Observation of Relaxation and Self-Reported Mindfulness and Relaxation States

    ERIC Educational Resources Information Center

    Hites, Lacey S.; Lundervold, Duane A.

    2013-01-01

    Forty-four individuals, 18-47 (MN 21.8, SD 5.63) years of age, took part in a study examining the magnitude and direction of the relationship between self-report and direct observation measures of relaxation and mindfulness. The Behavioral Relaxation Scale (BRS), a valid direct observation measure of relaxation, was used to assess relaxed behavior…

  13. Real-Space Mapping of Surface Trap States in CIGSe Nanocrystals Using 4D Electron Microscopy.

    PubMed

    Bose, Riya; Bera, Ashok; Parida, Manas R; Adhikari, Aniruddha; Shaheen, Basamat S; Alarousu, Erkki; Sun, Jingya; Wu, Tom; Bakr, Osman M; Mohammed, Omar F

    2016-07-13

    Surface trap states in copper indium gallium selenide semiconductor nanocrystals (NCs), which serve as undesirable channels for nonradiative carrier recombination, remain a great challenge impeding the development of solar and optoelectronics devices based on these NCs. In order to design efficient passivation techniques to minimize these trap states, a precise knowledge about the charge carrier dynamics on the NCs surface is essential. However, selective mapping of surface traps requires capabilities beyond the reach of conventional laser spectroscopy and static electron microscopy; it can only be accessed by using a one-of-a-kind, second-generation four-dimensional scanning ultrafast electron microscope (4D S-UEM) with subpicosecond temporal and nanometer spatial resolutions. Here, we precisely map the collective surface charge carrier dynamics of copper indium gallium selenide NCs as a function of the surface trap states before and after surface passivation in real space and time using S-UEM. The time-resolved snapshots clearly demonstrate that the density of the trap states is significantly reduced after zinc sulfide (ZnS) shelling. Furthermore, the removal of trap states and elongation of carrier lifetime are confirmed by the increased photocurrent of the self-biased photodetector fabricated using the shelled NCs. PMID:27228321

  14. Real-Space x-ray tomographic reconstruction of randomly oriented objects with sparse data frames.

    PubMed

    Ayyer, Kartik; Philipp, Hugh T; Tate, Mark W; Elser, Veit; Gruner, Sol M

    2014-02-10

    Schemes for X-ray imaging single protein molecules using new x-ray sources, like x-ray free electron lasers (XFELs), require processing many frames of data that are obtained by taking temporally short snapshots of identical molecules, each with a random and unknown orientation. Due to the small size of the molecules and short exposure times, average signal levels of much less than 1 photon/pixel/frame are expected, much too low to be processed using standard methods. One approach to process the data is to use statistical methods developed in the EMC algorithm (Loh & Elser, Phys. Rev. E, 2009) which processes the data set as a whole. In this paper we apply this method to a real-space tomographic reconstruction using sparse frames of data (below 10(-2) photons/pixel/frame) obtained by performing x-ray transmission measurements of a low-contrast, randomly-oriented object. This extends the work by Philipp et al. (Optics Express, 2012) to three dimensions and is one step closer to the single molecule reconstruction problem.

  15. First Principles Real-Space GW+BSE Calculations for Confined Systems

    NASA Astrophysics Data System (ADS)

    Hung, Linda; Ogut, Serdar; Souto, Jaime; Lee, Alex; Lena, Charles; Chelikowsky, James R.; Jornada, Felipe H. Da; Louie, Steven G.

    2014-03-01

    We investigate the performance of various levels of GW theories for electronic excitations as well as the resulting solutions of the Bethe-Salpeter-Equation (BSE) for optical excitations in a wide range of confined systems including atoms, ions, diatomic molecules, and organic molecules relevant for photovoltaic applications. Starting with solutions of the Kohn-Sham equations for ground state properties computed via the real-space ab initio pseudopotential code PARSEC, we perform the GW calculations in the space of single-particle transitions at various levels of theory, and compare the results with photoemission data. The levels of theory include such approximations as G0W0 with RPA screening, G0Wf that includes vertex corrections through the use of a dielectric screening within the time-dependent-local-density approximation (TDLDA), the GW0 , and the self-consistent GW. The resulting quasiparticle energies and wave functions from the GW calculations are used to solve the BSE for optical excitations, which are then compared with experiments and results from calculations performed within the TDLDA. The effects of the vertex corrections, self-consistency in GW, and core-valence partitioning are discussed. Supported by DOE Grant No. DE-SC0001853.

  16. A divide and conquer real space finite-element Hartree-Fock method

    NASA Astrophysics Data System (ADS)

    Alizadegan, R.; Hsia, K. J.; Martinez, T. J.

    2010-01-01

    Since the seminal contribution of Roothaan, quantum chemistry methods are traditionally expressed using finite basis sets comprised of smooth and continuous functions (atom-centered Gaussians) to describe the electronic degrees of freedom. Although this approach proved quite powerful, it is not well suited for large basis sets because of linear dependence problems and ill conditioning of the required matrices. The finite element method (FEM), on the other hand, is a powerful numerical method whose convergence is also guaranteed by variational principles and can be achieved systematically by increasing the number of degrees of freedom and/or the polynomial order of the shape functions. Here we apply the real-space FEM to Hartree-Fock calculations in three dimensions. The method produces sparse, banded Hermitian matrices while allowing for variable spatial resolution. This local-basis approach to electronic structure theory allows for systematic convergence and promises to provide an accurate and efficient way toward the full ab initio analysis of materials at larger scales. We introduce a new acceleration technique for evaluating the exchange contribution within FEM and explore the accuracy and robustness of the method for some selected test atoms and molecules. Furthermore, we applied a divide-and-conquer (DC) method to the finite-element Hartree-Fock ab initio electronic-structure calculations in three dimensions. This DC approach leads to facile parallelization and should enable reduced scaling for large systems.

  17. Probing Critical Surfaces in Momentum Space Using Real-Space Entanglement Entropy: Bose versus Fermi

    NASA Astrophysics Data System (ADS)

    Yang, Kun; Lai, Hsin-Hua

    A co-dimension one critical surface in the momentum space can be either a familiar Fermi surface, which separates occupied states from empty ones in the non-interacting fermion case, or a novel Bose surface, where gapless bosonic excitations are anchored. Their presence gives rise to logarithmic violation of entanglement entropy area law. When they are convex, we show that the shape of these critical surfaces can be determined by inspecting the leading logarithmic term of real space entanglement entropy. The fundamental difference between a Fermi surface and a Bose surface is revealed by the fact that the logarithmic terms in entanglement entropies differ by a factor of two: SlogBose = 2SlogFermi , even when they have identical geometry. Our method has remarkable similarity with determining Fermi surface shape using quantum oscillation. We also discuss possible probes of concave critical surfaces in momentum space. HHL and KY acknowledge the National Science Foundation through Grants No. DMR-1004545, DMR-1157490, No. DMR-1442366, and State of Florida. HHL is also partially supported by NSF Grant No. DMR-1309531, and the Smalley Postdoctoral Fellowship in Quantum Ma.

  18. Real Space Multigrid (RMG) Open Source Software Suite for Multi-Petaflops Electronic Structure Calculations

    NASA Astrophysics Data System (ADS)

    Briggs, Emil; Hodak, Miroslav; Lu, Wenchang; Bernholc, Jerry; Li, Yan

    RMG is a cross platform open source package for ab initio electronic structure calculations that uses real-space grids, multigrid pre-conditioning, and subspace diagonalization to solve the Kohn-Sham equations. The code has been successfully used for a wide range of problems ranging from complex bulk materials to multifunctional electronic devices and biological systems. RMG makes efficient use of GPU accelerators, if present, but does not require them. Recent work has extended GPU support to systems with multiple GPU's per computational node, as well as optimized both CPU and GPU memory usage to enable large problem sizes, which are no longer limited by the memory of the GPU board. Additional enhancements include increased portability, scalability and performance. New versions of the code are regularly released at sourceforge.net/projects/rmgdft/. The releases include binaries for Linux, Windows and MacIntosh systems, automated builds for clusters using cmake, as well as versions adapted to the major supercomputing installations and platforms.

  19. Precise estimate of correlation length exponents from simple real-space renormalization group analysis

    NASA Astrophysics Data System (ADS)

    Kubica, Aleksander; Yoshida, Beni

    2014-03-01

    We invent a novel real-space renormalization group (RG) scheme which accurately estimates correlation length exponents ν near criticality of quantum Ising and clock models in higher dimensions. The method, based on a recent proposal by Miyazaki et al., Phys. Rev. E 83, 051103 (2011), is remarkably simple (often analytical), grouping only a few spins into a block spin so that renormalized Hamiltonian has a closed form. A previous difficulty of spatial anisotropy and unwanted terms arising in higher-dimensional RG schemes is avoided by incorporating rotational invariance and internal Zq symmetries of the Hamiltonian. By applying this scheme to (2+1)-dim Ising model on a triangular lattice, we obtained ν = 0 . 6300 which is within statistical error of the current best Monte-Carlo result and ϕ4 theory estimation with seven-loop corrections. We also apply the scheme to higher-dimensional clock (Potts) models for which ordinary Monte-Carlo methods are not efficient due to suppression of quantum fluctuation in first-order phase transition.

  20. Direct Observation of Teacher-Directed IEP Meetings: Establishing the Need for Student IEP Meeting Instruction

    ERIC Educational Resources Information Center

    Martin, James E.; Van Dycke, Jamie L.; Greene, Barbara A.; Gardner, J. Emmett; Christensen, W. Robert; Woods, Lee L.; Lovett, David L.

    2006-01-01

    The 1997 reauthorization of the Individuals with Disabilities Education Act (IDEA) called for an increase in student involvement in individualized education program (IEP) meetings. To determine the extent of student involvement in educational planning, this study observed 109 middle and high school IEP meetings; 90% of the participants completed a…

  1. Real space mapping of Li-ion transport in amorphous Si anodes with nanometer resolution

    SciTech Connect

    Balke, N.; Jesse, S.; Kim, Y.; Adamczyk, L.; Tselev, A.; Ivanov, I.; Dudney, N. J.; Kalinin, S. V.

    2010-09-08

    The electrical bias driven Li-ion motion in silicon anode materials in thin film battery heterostructures is investigated using electrochemical strain microscopy (ESM), which is a newly developed scanning probe microscopy based characterization method. ESM utilizes the intrinsic link between bias-controlled Li-ion concentration and molar volume of electrode materials, providing the capability for studies on the sub-20 nm scale, and allows the relationship between Li-ion flow and microstructure to be established. The evolution of Li-ion transport during the battery charging is directly observed.

  2. Real Space Imaging of Nanoparticle Assembly at Liquid-Liquid Interfaces with Nanoscale Resolution.

    PubMed

    Costa, Luca; Li-Destri, Giovanni; Thomson, Neil H; Konovalov, Oleg; Pontoni, Diego

    2016-09-14

    Bottom up self-assembly of functional materials at liquid-liquid interfaces has recently emerged as method to design and produce novel two-dimensional (2D) nanostructured membranes and devices with tailored properties. Liquid-liquid interfaces can be seen as a "factory floor" for nanoparticle (NP) self-assembly, because NPs are driven there by a reduction of interfacial energy. Such 2D assembly can be characterized by reciprocal space techniques, namely X-ray and neutron scattering or reflectivity. These techniques have drawbacks, however, as the structural information is averaged over the finite size of the radiation beam and nonperiodic isolated assemblies in 3D or defects may not be easily detected. Real-space in situ imaging methods are more appropriate in this context, but they often suffer from limited resolution and underperform or fail when applied to challenging liquid-liquid interfaces. Here, we study the surfactant-induced assembly of SiO2 nanoparticle monolayers at a water-oil interface using in situ atomic force microscopy (AFM) achieving nanoscale resolved imaging capabilities. Hitherto, AFM imaging has been restricted to solid-liquid interfaces because applications to liquid interfaces have been hindered by their softness and intrinsic dynamics, requiring accurate sample preparation methods and nonconventional AFM operational schemes. Comparing both AFM and grazing incidence X-ray small angle scattering data, we unambiguously demonstrate correlation between real and reciprocal space structure determination showing that the average interfacial NP density is found to vary with surfactant concentration. Additionally, the interaction between the tip and the interface can be exploited to locally determine the acting interfacial interactions. This work opens up the way to studying complex nanostructure formation and phase behavior in a range of liquid-liquid and complex liquid interfaces. PMID:27571473

  3. Dynamical electron diffraction simulation for non-orthogonal crystal system by a revised real space method.

    PubMed

    Lv, C L; Liu, Q B; Cai, C Y; Huang, J; Zhou, G W; Wang, Y G

    2015-01-01

    In the transmission electron microscopy, a revised real space (RRS) method has been confirmed to be a more accurate dynamical electron diffraction simulation method for low-energy electron diffraction than the conventional multislice method (CMS). However, the RRS method can be only used to calculate the dynamical electron diffraction of orthogonal crystal system. In this work, the expression of the RRS method for non-orthogonal crystal system is derived. By taking Na2 Ti3 O7 and Si as examples, the correctness of the derived RRS formula for non-orthogonal crystal system is confirmed by testing the coincidence of numerical results of both sides of Schrödinger equation; moreover, the difference between the RRS method and the CMS for non-orthogonal crystal system is compared at the accelerating voltage range from 40 to 10 kV. Our results show that the CMS method is almost the same as the RRS method for the accelerating voltage above 40 kV. However, when the accelerating voltage is further lowered to 20 kV or below, the CMS method introduces significant errors, not only for the higher-order Laue zone diffractions, but also for zero-order Laue zone. These indicate that the RRS method for non-orthogonal crystal system is necessary to be used for more accurate dynamical simulation when the accelerating voltage is low. Furthermore, the reason for the increase of differences between those diffraction patterns calculated by the RRS method and the CMS method with the decrease of the accelerating voltage is discussed. PMID:26461207

  4. Real Space Imaging of Nanoparticle Assembly at Liquid-Liquid Interfaces with Nanoscale Resolution.

    PubMed

    Costa, Luca; Li-Destri, Giovanni; Thomson, Neil H; Konovalov, Oleg; Pontoni, Diego

    2016-09-14

    Bottom up self-assembly of functional materials at liquid-liquid interfaces has recently emerged as method to design and produce novel two-dimensional (2D) nanostructured membranes and devices with tailored properties. Liquid-liquid interfaces can be seen as a "factory floor" for nanoparticle (NP) self-assembly, because NPs are driven there by a reduction of interfacial energy. Such 2D assembly can be characterized by reciprocal space techniques, namely X-ray and neutron scattering or reflectivity. These techniques have drawbacks, however, as the structural information is averaged over the finite size of the radiation beam and nonperiodic isolated assemblies in 3D or defects may not be easily detected. Real-space in situ imaging methods are more appropriate in this context, but they often suffer from limited resolution and underperform or fail when applied to challenging liquid-liquid interfaces. Here, we study the surfactant-induced assembly of SiO2 nanoparticle monolayers at a water-oil interface using in situ atomic force microscopy (AFM) achieving nanoscale resolved imaging capabilities. Hitherto, AFM imaging has been restricted to solid-liquid interfaces because applications to liquid interfaces have been hindered by their softness and intrinsic dynamics, requiring accurate sample preparation methods and nonconventional AFM operational schemes. Comparing both AFM and grazing incidence X-ray small angle scattering data, we unambiguously demonstrate correlation between real and reciprocal space structure determination showing that the average interfacial NP density is found to vary with surfactant concentration. Additionally, the interaction between the tip and the interface can be exploited to locally determine the acting interfacial interactions. This work opens up the way to studying complex nanostructure formation and phase behavior in a range of liquid-liquid and complex liquid interfaces.

  5. Development of a Computer-Based System for the Unobtrusive Collection of Direct Observational Data.

    ERIC Educational Resources Information Center

    Johnson, Happy; And Others

    1995-01-01

    This article describes a computer-based system, the "Direct Observation Data System" (DODS), which allows for unobtrusive collection of direct observational data in the classroom and natural settings. At present, DODS consists of event-recording and duration-recording programs which can be remotely accessed. The device has implications for…

  6. 10 CFR 26.115 - Collecting a urine specimen under direct observation.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 10 Energy 1 2010-01-01 2010-01-01 false Collecting a urine specimen under direct observation. 26.115 Section 26.115 Energy NUCLEAR REGULATORY COMMISSION FITNESS FOR DUTY PROGRAMS Collecting Specimens for Testing § 26.115 Collecting a urine specimen under direct observation. (a) Procedures...

  7. 10 CFR 26.115 - Collecting a urine specimen under direct observation.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 10 Energy 1 2013-01-01 2013-01-01 false Collecting a urine specimen under direct observation. 26.115 Section 26.115 Energy NUCLEAR REGULATORY COMMISSION FITNESS FOR DUTY PROGRAMS Collecting Specimens for Testing § 26.115 Collecting a urine specimen under direct observation. (a) Procedures...

  8. 10 CFR 26.115 - Collecting a urine specimen under direct observation.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 10 Energy 1 2014-01-01 2014-01-01 false Collecting a urine specimen under direct observation. 26.115 Section 26.115 Energy NUCLEAR REGULATORY COMMISSION FITNESS FOR DUTY PROGRAMS Collecting Specimens for Testing § 26.115 Collecting a urine specimen under direct observation. (a) Procedures...

  9. 10 CFR 26.115 - Collecting a urine specimen under direct observation.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 10 Energy 1 2011-01-01 2011-01-01 false Collecting a urine specimen under direct observation. 26.115 Section 26.115 Energy NUCLEAR REGULATORY COMMISSION FITNESS FOR DUTY PROGRAMS Collecting Specimens for Testing § 26.115 Collecting a urine specimen under direct observation. (a) Procedures...

  10. 10 CFR 26.115 - Collecting a urine specimen under direct observation.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 10 Energy 1 2012-01-01 2012-01-01 false Collecting a urine specimen under direct observation. 26.115 Section 26.115 Energy NUCLEAR REGULATORY COMMISSION FITNESS FOR DUTY PROGRAMS Collecting Specimens for Testing § 26.115 Collecting a urine specimen under direct observation. (a) Procedures...

  11. Direct Retrieval of Line-of-Sight Atmospheric Structure From Limb Sounding Observations

    NASA Technical Reports Server (NTRS)

    Livesey, N.; Read, W.

    1999-01-01

    Optimal estimation of atmospheric temperature and composition from limb sounding observations is extended to the direct retrieval of line-of-sight atmospheric structure that can be obtained in certain limb viewing geometries.

  12. Direct retrieval of ocean surface evaporation and latent heat flux from the spacebased observations

    NASA Technical Reports Server (NTRS)

    Liu, W. T.; Tang, W.

    2000-01-01

    The Tropical Rain Measuring Mission (TRMM) provides the opportunity to improve the spacebased estimation of evaporation. An algorithm for retrieving evaporation directly from the radiances observed by the TRMM Microwave Imager and its validation results are described.

  13. Nuclear structure from direct reactions with rare isotopes: observables, methods and highlights

    NASA Astrophysics Data System (ADS)

    Obertelli, Alexandre

    2016-09-01

    An overview of direct reactions employed for nuclear structure studies is presented. The basic and most used analysis methods of elastic and inelastic scattering, transfer reactions and intermediate-energy removal reactions are reviewed. The most relevant observables from direct reactions regarding the nuclear many-body problem, as well as related experimental techniques, are illustrated through recent achievements with unstable nuclei.

  14. Direct Observation of Sub-Poissonian Number Statistics in a Degenerate Bose Gas

    SciTech Connect

    Chuu, C.-S.; Schreck, F.; Meyrath, T.P.; Hanssen, J.L.; Price, G.N.; Raizen, M.G.

    2005-12-31

    We report the direct observation of sub-Poissonian number fluctuation for a degenerate Bose gas confined in an optical trap. Reduction of number fluctuations below the Poissonian limit is observed for average numbers that range from 300 to 60 atoms.

  15. Direct observation of the transition from indirect to direct bandgap in atomically thin epitaxial MoSe2.

    PubMed

    Zhang, Yi; Chang, Tay-Rong; Zhou, Bo; Cui, Yong-Tao; Yan, Hao; Liu, Zhongkai; Schmitt, Felix; Lee, James; Moore, Rob; Chen, Yulin; Lin, Hsin; Jeng, Horng-Tay; Mo, Sung-Kwan; Hussain, Zahid; Bansil, Arun; Shen, Zhi-Xun

    2014-02-01

    Quantum systems in confined geometries are host to novel physical phenomena. Examples include quantum Hall systems in semiconductors and Dirac electrons in graphene. Interest in such systems has also been intensified by the recent discovery of a large enhancement in photoluminescence quantum efficiency and a potential route to valleytronics in atomically thin layers of transition metal dichalcogenides, MX2 (M = Mo, W; X = S, Se, Te), which are closely related to the indirect-to-direct bandgap transition in monolayers. Here, we report the first direct observation of the transition from indirect to direct bandgap in monolayer samples by using angle-resolved photoemission spectroscopy on high-quality thin films of MoSe2 with variable thickness, grown by molecular beam epitaxy. The band structure measured experimentally indicates a stronger tendency of monolayer MoSe2 towards a direct bandgap, as well as a larger gap size, than theoretically predicted. Moreover, our finding of a significant spin-splitting of ∼ 180 meV at the valence band maximum of a monolayer MoSe2 film could expand its possible application to spintronic devices.

  16. Anodal transcranial direct current stimulation over premotor cortex facilitates observational learning of a motor sequence.

    PubMed

    Wade, Stephanie; Hammond, Geoff

    2015-06-01

    Motor skills, including complex movement sequences, can be acquired by observing a model without physical practice of the skill, a phenomenon known as observational learning. Observational learning of motor skills engages the same memory substrate as physical practice, and is thought to be mediated by the action observation network, a bilateral fronto-parietal circuit with mirror-like properties. We examined the effects of anodal transcranial direct current stimulation (tDCS) over premotor cortex, a key node of the action observation network, on observational learning of a serial response time task. Results showed that anodal tDCS during observation of the to-be-learned sequence facilitated reaction times in the subsequent behavioral test. The study provides evidence that increasing excitability of the action observation network during observation can facilitate later motor skill acquisition.

  17. Electronic structure calculations with GPAW: a real-space implementation of the projector augmented-wave method

    NASA Astrophysics Data System (ADS)

    Enkovaara, J.; Rostgaard, C.; Mortensen, J. J.; Chen, J.; Dułak, M.; Ferrighi, L.; Gavnholt, J.; Glinsvad, C.; Haikola, V.; Hansen, H. A.; Kristoffersen, H. H.; Kuisma, M.; Larsen, A. H.; Lehtovaara, L.; Ljungberg, M.; Lopez-Acevedo, O.; Moses, P. G.; Ojanen, J.; Olsen, T.; Petzold, V.; Romero, N. A.; Stausholm-Møller, J.; Strange, M.; Tritsaris, G. A.; Vanin, M.; Walter, M.; Hammer, B.; Häkkinen, H.; Madsen, G. K. H.; Nieminen, R. M.; Nørskov, J. K.; Puska, M.; Rantala, T. T.; Schiøtz, J.; Thygesen, K. S.; Jacobsen, K. W.

    2010-06-01

    Electronic structure calculations have become an indispensable tool in many areas of materials science and quantum chemistry. Even though the Kohn-Sham formulation of the density-functional theory (DFT) simplifies the many-body problem significantly, one is still confronted with several numerical challenges. In this article we present the projector augmented-wave (PAW) method as implemented in the GPAW program package (https://wiki.fysik.dtu.dk/gpaw) using a uniform real-space grid representation of the electronic wavefunctions. Compared to more traditional plane wave or localized basis set approaches, real-space grids offer several advantages, most notably good computational scalability and systematic convergence properties. However, as a unique feature GPAW also facilitates a localized atomic-orbital basis set in addition to the grid. The efficient atomic basis set is complementary to the more accurate grid, and the possibility to seamlessly switch between the two representations provides great flexibility. While DFT allows one to study ground state properties, time-dependent density-functional theory (TDDFT) provides access to the excited states. We have implemented the two common formulations of TDDFT, namely the linear-response and the time propagation schemes. Electron transport calculations under finite-bias conditions can be performed with GPAW using non-equilibrium Green functions and the localized basis set. In addition to the basic features of the real-space PAW method, we also describe the implementation of selected exchange-correlation functionals, parallelization schemes, ΔSCF-method, x-ray absorption spectra, and maximally localized Wannier orbitals.

  18. EDF: Computing electron number probability distribution functions in real space from molecular wave functions

    NASA Astrophysics Data System (ADS)

    Francisco, E.; Pendás, A. Martín; Blanco, M. A.

    2008-04-01

    Given an N-electron molecule and an exhaustive partition of the real space ( R) into m arbitrary regions Ω,Ω,…,Ω ( ⋃i=1mΩ=R), the edf program computes all the probabilities P(n,n,…,n) of having exactly n electrons in Ω, n electrons in Ω,…, and n electrons ( n+n+⋯+n=N) in Ω. Each Ω may correspond to a single basin (atomic domain) or several such basins (functional group). In the later case, each atomic domain must belong to a single Ω. The program can manage both single- and multi-determinant wave functions which are read in from an aimpac-like wave function description ( .wfn) file (T.A. Keith et al., The AIMPAC95 programs, http://www.chemistry.mcmaster.ca/aimpac, 1995). For multi-determinantal wave functions a generalization of the original .wfn file has been introduced. The new format is completely backwards compatible, adding to the previous structure a description of the configuration interaction (CI) coefficients and the determinants of correlated wave functions. Besides the .wfn file, edf only needs the overlap integrals over all the atomic domains between the molecular orbitals (MO). After the P(n,n,…,n) probabilities are computed, edf obtains from them several magnitudes relevant to chemical bonding theory, such as average electronic populations and localization/delocalization indices. Regarding spin, edf may be used in two ways: with or without a splitting of the P(n,n,…,n) probabilities into α and β spin components. Program summaryProgram title: edf Catalogue identifier: AEAJ_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEAJ_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 5387 No. of bytes in distributed program, including test data, etc.: 52 381 Distribution format: tar.gz Programming language: Fortran 77 Computer

  19. First-Principles Calculation of the Real-Space Order Parameter and Condensation Energy Density in Phonon-Mediated Superconductors.

    PubMed

    Linscheid, A; Sanna, A; Floris, A; Gross, E K U

    2015-08-28

    We show that the superconducting order parameter and condensation energy density of phonon-mediated superconductors can be calculated in real space from first principles density functional theory for superconductors. This method highlights the connection between the chemical bonding structure and the superconducting condensation and reveals new and interesting properties of superconducting materials. Understanding this connection is essential to describe nanostructured superconducting systems where the usual reciprocal space analysis hides the basic physical mechanism. In a first application we present results for MgB2, CaC6 and hole-doped graphane.

  20. First-Principles Calculation of the Real-Space Order Parameter and Condensation Energy Density in Phonon-Mediated Superconductors.

    PubMed

    Linscheid, A; Sanna, A; Floris, A; Gross, E K U

    2015-08-28

    We show that the superconducting order parameter and condensation energy density of phonon-mediated superconductors can be calculated in real space from first principles density functional theory for superconductors. This method highlights the connection between the chemical bonding structure and the superconducting condensation and reveals new and interesting properties of superconducting materials. Understanding this connection is essential to describe nanostructured superconducting systems where the usual reciprocal space analysis hides the basic physical mechanism. In a first application we present results for MgB2, CaC6 and hole-doped graphane. PMID:26371675

  1. Controlling Virtual Clouds and Making it Rain Particle Systems in Real Spaces Using Situated Augmented Simulation and Portable Virtual Environments

    NASA Astrophysics Data System (ADS)

    Hedley, N.; Lonergan, C. D.

    2012-07-01

    The research described in this paper reports on the design, rationale, development and implementation of a set of new geospatial interfaces that combine multi-touch interaction, portable virtual environments, 'geosimulation gaming', and mobile augmented reality. The result is a set of new ways for us to combine the capabilities of geospatial virtual environments, augmented realitiy and geosimulation. These new hybrid interfaces deliver new geospatial information experiences - new ways of connecting spatial data, simulations, and abstract concepts to real spaces. Their potential to enhance environmental perception and learning must be explored.

  2. Photographic observation of magnetic domain structure with three-dimensional local magnetization direction

    NASA Astrophysics Data System (ADS)

    Meguro, Sakae; Akahane, Koichi; Saito, Shin

    2016-07-01

    The direction of magnetization of a magnetic material is possibly oriented three-dimensionally because of the presence of magnetic anisotropy field, self-demagnetizing field, and stray field. Therefore, the three-dimensional detection of the direction of magnetization is required. The method of magnetic domain observation by photographic imaging utilizing the Kerr effect is widely used. If the perpendicular magnetization components exist, there is a problem that obliquely incident light has superimposed longitudinal Kerr and polar Kerr effects. To perform the three-dimensional detection of magnetization direction, it is necessary to eliminate the influence of the polar Kerr effect from the Kerr effect of obliquely incident light. We report the photographic observation of the magnetic domain structure and the detection of the three-dimensional local magnetization direction using the Kerr effect, applying only an in-plane saturation magnetic field.

  3. A connection between domain-averaged Fermi hole orbitals and electron number distribution functions in real space

    NASA Astrophysics Data System (ADS)

    Francisco, E.; Martín Pendás, A.; Blanco, M. A.

    2009-09-01

    We show in this article how for single-determinant wave functions the one-electron functions derived from the diagonalization of the Fermi hole, averaged over an arbitrary domain Ω of real space, and expressed in terms of the occupied canonical orbitals, describe coarse-grained statistically independent electrons. With these domain-averaged Fermi hole (DAFH) orbitals, the full electron number distribution function (EDF) is given by a simple product of one-electron events. This useful property follows from the simultaneous orthogonality of the DAFH orbitals in Ω, Ω'=R3-Ω, and R3. We also show how the interfragment (shared electron) delocalization index, δΩ,Ω', transforms into a sum of one-electron DAFH contributions. Description of chemical bonding in terms of DAFH orbitals provides a vivid picture relating bonding and delocalization in real space. DAFH and EDF analyses are performed on several test systems to illustrate the close relationship between both concepts. Finally, these analyses clearly prove how DAFH orbitals well localized in Ω or Ω' can be simply ignored in computing the EDFs and/or δΩ,Ω', and thus do not contribute to the chemical bonding between the two fragments.

  4. Real-space electronic structure calculations with full-potential all-electron precision for transition metals

    NASA Astrophysics Data System (ADS)

    Ono, Tomoya; Heide, Marcus; Atodiresei, Nicolae; Baumeister, Paul; Tsukamoto, Shigeru; Blügel, Stefan

    2010-11-01

    We have developed an efficient computational scheme utilizing the real-space finite-difference formalism and the projector augmented-wave (PAW) method to perform precise first-principles electronic-structure simulations based on the density-functional theory for systems containing transition metals with a modest computational effort. By combining the advantages of the time-saving double-grid technique and the Fourier-filtering procedure for the projectors of pseudopotentials, we can overcome the egg box effect in the computations even for first-row elements and transition metals, which is a problem of the real-space finite-difference formalism. In order to demonstrate the potential power in terms of precision and applicability of the present scheme, we have carried out simulations to examine several bulk properties and structural energy differences between different bulk phases of transition metals and have obtained excellent agreement with the results of other precise first-principles methods such as a plane-wave-based PAW method and an all-electron full-potential linearized augmented plane-wave (FLAPW) method.

  5. Direct observation of molecularly-aligned molecules in the second physisorbed layer-CO/Ag(110)

    SciTech Connect

    Lee, J.-G.; Hong, S.-H.; Ahner, J.; Zhao, X.; Chen, L.; Johnson, J.K.; Yates, J.T., Jr.

    2006-01-25

    We report the direct observation of oriented second-layer physisorbed molecules on a single crystal surface by electron stimulated desorption. Experiments and simulations show that the orientation of the second-layer physisorbed CO molecules on Ag(110) is the result of both electrostatic and dispersion forces from the underlying chemisorbed CO and Ag atoms. At 25 K, the physisorbed C-O bond is tilted and azimuthally oriented with the C-O bond axis inclined in an azimuthal plane at 45° to the principal Ag( 110) azimuthal crystallographic directions. The O atom in CO is directed outward, giving an O+ beam at 43° to the normal.

  6. Predicted and observed directional dependence of meteoroid/debris impacts on LDEF thermal blankets

    NASA Technical Reports Server (NTRS)

    Drolshagen, Gerhard

    1993-01-01

    The number of impacts from meteoroids and space debris particles to the various LDEF rows is calculated using ESABASE/DEBRIS, a 3-D numerical analysis tool. It is based on recent reference environment flux models and includes geometrical and directional effects. A comparison of model predictions and actual observations is made for penetrations of the thermal blankets which covered the UHCR experiment. The thermal blankets were located on all LDEF rows, except 3, 9, and 12. Because of their uniform composition and thickness, these blankets allow a direct analysis of the directional dependence of impacts and provide a test case for the latest meteoroid and debris flux models.

  7. Direct observation of grain growth from molten silicon formed by micro-thermal-plasma-jet irradiation

    PubMed Central

    Hayashi, Shohei; Fujita, Yuji; Kamikura, Takahiro; Sakaike, Kohei; Akazawa, Muneki; Ikeda, Mitsuhisa; Hanafusa, Hiroaki; Higashi, Seiichiro

    2012-01-01

    Phase transformation of amorphous-silicon during millisecond annealing using micro-thermal-plasma-jet irradiation was directly observed using a high-speed camera with microsecond time resolution. An oval-shaped molten-silicon region adjacent to the solid phase crystallization region was clearly observed, followed by lateral large grain growth perpendicular to a liquid-solid interface. Furthermore, leading wave crystallization (LWC), which showed intermittent explosive crystallization, was discovered in front of the moving molten region. The growth mechanism of LWC has been investigated on the basis of numerical simulation implementing explosive movement of a thin liquid layer driven by released latent heat diffusion in a lateral direction. PMID:23185095

  8. Direct observation of grain growth from molten silicon formed by micro-thermal-plasma-jet irradiation

    SciTech Connect

    Hayashi, Shohei; Fujita, Yuji; Kamikura, Takahiro; Sakaike, Kohei; Akazawa, Muneki; Ikeda, Mitsuhisa; Hanafusa, Hiroaki; Higashi, Seiichiro

    2012-10-22

    Phase transformation of amorphous-silicon during millisecond annealing using micro-thermal-plasma-jet irradiation was directly observed using a high-speed camera with microsecond time resolution. An oval-shaped molten-silicon region adjacent to the solid phase crystallization region was clearly observed, followed by lateral large grain growth perpendicular to a liquid-solid interface. Furthermore, leading wave crystallization (LWC), which showed intermittent explosive crystallization, was discovered in front of the moving molten region. The growth mechanism of LWC has been investigated on the basis of numerical simulation implementing explosive movement of a thin liquid layer driven by released latent heat diffusion in a lateral direction.

  9. Directional surface plasmon coupled chemiluminescence from nickel thin films: Fixed angle observation

    NASA Astrophysics Data System (ADS)

    Weisenberg, Micah; Aslan, Kadir; Hortle, Elinor; Geddes, Chris D.

    2009-04-01

    Directional surface plasmon coupled chemiluminescence (SPCC) from nickel thin films is demonstrated. Free-space and angular-dependent SPCC emission from blue, green and turquoise chemiluminescent solutions placed onto nickel thin films attached to a hemispherical prism were measured. SPCC emission was found to be highly directional and preferentially p-polarized, in contrast to the unpolarized and isotropic chemiluminescence emission. The largest SPCC emission for all chemiluminescence solutions was observed at a fixed observation angle of 60°, which was also predicted by theoretical Fresnel calculations. It was found that nickel thin films did not have a catalytic effect on chemiluminescence emission.

  10. Using direct clinical observation to assess the quality of cesarean delivery in Afghanistan: an exploratory study

    PubMed Central

    2014-01-01

    Background As part of a National Emergency Obstetric and Newborn Care (EmONC) Needs Assessment, a special study was undertaken in July 2010 to examine the quality of cesarean deliveries in Afghanistan and examine the utility of direct clinical observation as an assessment method in low-resource settings. Methods This cross-sectional assessment of the quality of cesareans at 14 facilities in Afghanistan included a survey of surgeons regarding their routine cesarean practices, direct observation of 29 cesarean deliveries and comparison of observations with facility records for 34 additional cesareans conducted during the 3 days prior to the observation period at each facility. For both observed cases and record reviews, we assessed time intervals between specified points of care-arrival to the ward, first evaluation, detection of a complication, decision for cesarean, incision, and birth. Results All time intervals with the exception of “decision to skin incision” were longer in the record reviews than in observed cases. Prior cesarean was the most common primary indication for all cases. All mothers in both groups observed survived through one hour postpartum. Among newborns there were two stillbirths (7%) in observed births and seven (21%) record reviews. Although our sample is too small to show statistical significance, the difference is noteworthy. In six of the reviewed cesareans resulting in stillbirth, a fetal heart rate was recorded in the operating theater, although four were recorded as macerated. For the two fresh stillbirths, the cesarean surgeries were recorded as scheduled and not urgent. Conclusions Direct observation of cesarean deliveries enabled us to assess a number of preoperative, postoperative, and intraoperative procedures that are often not described in medical records in low resource settings. Comparison of observations with findings from provider interviews and facility records allowed us to infer whether observed practices were typical

  11. Observation of trichomonads infection in a child with periodontitis by direct microscopy at the dental office.

    PubMed

    Marty, Mathieu; Bonner, Mark; Vaysse, Frédéric

    2015-09-01

    The pathogenicity of Trichomonas species is well documented. Although their exact involvement in gum disease is not fully understood, recent studies suggest a correlation between these protozoa and periodontitis. This case report details the first chair-side observation in Europe of an oral trichomonad infection in a child with periodontitis, by direct microscopy. The dramatic recovery of the patient, observed following administration of an anti-parasitic treatment, confirms the necessity of further investigation in this field.

  12. Observing Grasping Actions Directed to Emotion-Laden Objects: Effects upon Corticospinal Excitability

    PubMed Central

    Nogueira-Campos, Anaelli A.; Saunier, Ghislain; Della-Maggiore, Valeria; De Oliveira, Laura A. S.; Rodrigues, Erika C.; Vargas, Claudia D.

    2016-01-01

    The motor system is recruited whenever one executes an action as well as when one observes the same action being executed by others. Although it is well established that emotion modulates the motor system, the effect of observing other individuals acting in an emotional context is particularly elusive. The main aim of this study was to investigate the effect induced by the observation of grasping directed to emotion-laden objects upon corticospinal excitability (CSE). Participants classified video-clips depicting the right-hand of an actor grasping emotion-laden objects. Twenty video-clips differing in terms of valence but balanced in arousal level were selected. Motor evoked potentials (MEPs) were then recorded from the first dorsal interosseous using transcranial magnetic stimulation (TMS) while the participants observed the selected emotional video-clips. During the video-clip presentation, TMS pulses were randomly applied at one of two different time points of grasping: (1) maximum grip aperture, and (2) object contact time. CSE was higher during the observation of grasping directed to unpleasant objects compared to pleasant ones. These results indicate that when someone observes an action of grasping directed to emotion-laden objects, the effect of the object valence promotes a specific modulation over the motor system. PMID:27625602

  13. Observing Grasping Actions Directed to Emotion-Laden Objects: Effects upon Corticospinal Excitability.

    PubMed

    Nogueira-Campos, Anaelli A; Saunier, Ghislain; Della-Maggiore, Valeria; De Oliveira, Laura A S; Rodrigues, Erika C; Vargas, Claudia D

    2016-01-01

    The motor system is recruited whenever one executes an action as well as when one observes the same action being executed by others. Although it is well established that emotion modulates the motor system, the effect of observing other individuals acting in an emotional context is particularly elusive. The main aim of this study was to investigate the effect induced by the observation of grasping directed to emotion-laden objects upon corticospinal excitability (CSE). Participants classified video-clips depicting the right-hand of an actor grasping emotion-laden objects. Twenty video-clips differing in terms of valence but balanced in arousal level were selected. Motor evoked potentials (MEPs) were then recorded from the first dorsal interosseous using transcranial magnetic stimulation (TMS) while the participants observed the selected emotional video-clips. During the video-clip presentation, TMS pulses were randomly applied at one of two different time points of grasping: (1) maximum grip aperture, and (2) object contact time. CSE was higher during the observation of grasping directed to unpleasant objects compared to pleasant ones. These results indicate that when someone observes an action of grasping directed to emotion-laden objects, the effect of the object valence promotes a specific modulation over the motor system. PMID:27625602

  14. Observing Grasping Actions Directed to Emotion-Laden Objects: Effects upon Corticospinal Excitability

    PubMed Central

    Nogueira-Campos, Anaelli A.; Saunier, Ghislain; Della-Maggiore, Valeria; De Oliveira, Laura A. S.; Rodrigues, Erika C.; Vargas, Claudia D.

    2016-01-01

    The motor system is recruited whenever one executes an action as well as when one observes the same action being executed by others. Although it is well established that emotion modulates the motor system, the effect of observing other individuals acting in an emotional context is particularly elusive. The main aim of this study was to investigate the effect induced by the observation of grasping directed to emotion-laden objects upon corticospinal excitability (CSE). Participants classified video-clips depicting the right-hand of an actor grasping emotion-laden objects. Twenty video-clips differing in terms of valence but balanced in arousal level were selected. Motor evoked potentials (MEPs) were then recorded from the first dorsal interosseous using transcranial magnetic stimulation (TMS) while the participants observed the selected emotional video-clips. During the video-clip presentation, TMS pulses were randomly applied at one of two different time points of grasping: (1) maximum grip aperture, and (2) object contact time. CSE was higher during the observation of grasping directed to unpleasant objects compared to pleasant ones. These results indicate that when someone observes an action of grasping directed to emotion-laden objects, the effect of the object valence promotes a specific modulation over the motor system.

  15. Observations of the directional distribution of the wind energy input function over swell waves

    NASA Astrophysics Data System (ADS)

    Shabani, Behnam; Babanin, Alex V.; Baldock, Tom E.

    2016-02-01

    Field measurements of wind stress over shallow water swell traveling in different directions relative to the wind are presented. The directional distribution of the measured stresses is used to confirm the previously proposed but unverified directional distribution of the wind energy input function. The observed wind energy input function is found to follow a much narrower distribution (β∝cos⁡3.6θ) than the Plant (1982) cosine distribution. The observation of negative stress angles at large wind-wave angles, however, indicates that the onset of negative wind shearing occurs at about θ≈ 50°, and supports the use of the Snyder et al. (1981) directional distribution. Taking into account the reverse momentum transfer from swell to the wind, Snyder's proposed parameterization is found to perform exceptionally well in explaining the observed narrow directional distribution of the wind energy input function, and predicting the wind drag coefficients. The empirical coefficient (ɛ) in Snyder's parameterization is hypothesised to be a function of the wave shape parameter, with ɛ value increasing as the wave shape changes between sinusoidal, sawtooth, and sharp-crested shoaling waves.

  16. Ethical aspects of directly observed treatment for tuberculosis: a cross-cultural comparison

    PubMed Central

    2013-01-01

    Background Tuberculosis is a major global public health challenge, and a majority of countries have adopted a version of the global strategy to fight Tuberculosis, Directly Observed Treatment, Short Course (DOTS). Drawing on results from research in Ethiopia and Norway, the aim of this paper is to highlight and discuss ethical aspects of the practice of Directly Observed Treatment (DOT) in a cross-cultural perspective. Discussion Research from Ethiopia and Norway demonstrates that the rigid enforcement of directly observed treatment conflicts with patient autonomy, dignity and integrity. The treatment practices, especially when imposed in its strictest forms, expose those who have Tuberculosis to extra burdens and costs. Socially disadvantaged groups, such as the homeless, those employed as day labourers and those lacking rights as employees, face the highest burdens. Summary From an ethical standpoint, we argue that a rigid practice of directly observed treatment is difficult to justify, and that responsiveness to social determinants of Tuberculosis should become an integral part of the management of Tuberculosis. PMID:23819555

  17. Directly Observed Interaction within Adolescent Romantic Relationships: What Have We Learned?

    ERIC Educational Resources Information Center

    Welsh, Deborah P.; Shulman, Shmuel

    2008-01-01

    Review and conceptual analysis of the papers in this special issue calls attention to several important methodological and conceptual issues surrounding the direct observation of adolescent romantic couples. It also provides an important new foundation of knowledge about the nature of adolescents' romantic relationships. Connections with previous…

  18. Considering Systematic Direct Observation after a Century of Research--Commentary on the Special Issue

    ERIC Educational Resources Information Center

    Stichter, Janine P.; Riley-Tillman, T. Chris

    2014-01-01

    Systematic Direct Observation (SDO) has played a pivotal role in the field of Emotional and/or Behavioral Disorders (EBD) since its inception as a key part of understanding more about the behaviors, contexts that impact them, and the effective supports necessary for this population. This methodology is an ongoing charge for everyone. The authors…

  19. Observational Learning of Academic and Social Behaviors during Small-Group Direct Instruction

    ERIC Educational Resources Information Center

    Ledford, Jennifer R.; Wolery, Mark

    2015-01-01

    Many studies have shown that small-group direct instruction is effective and efficient for teaching students with and without disabilities, although relatively few studies have been conducted with heterogeneous groups of preschool participants. In addition, previous studies have primarily assessed whether observational learning occurred for…

  20. Affective Evaluations of Objects Are Influenced by Observed Gaze Direction and Emotional Expression

    ERIC Educational Resources Information Center

    Bayliss, Andrew P.; Frischen, Alexandra; Fenske, Mark J.; Tipper, Steven P.

    2007-01-01

    Gaze direction signals another person's focus of interest. Facial expressions convey information about their mental state. Appropriate responses to these signals should reflect their combined influence, yet current evidence suggests that gaze-cueing effects for objects near an observed face are not modulated by its emotional expression. Here, we…

  1. The Impact of Observation Duration on the Accuracy of Data Obtained from Direct Behavior Rating (DBR)

    ERIC Educational Resources Information Center

    Riley-Tillman, T. Chris; Christ, Theodore J.; Chafouleas, Sandra M.; Boice-Mallach, Christina H.; Briesch, Amy

    2011-01-01

    In this study, evaluation of direct behavior rating (DBR) occurred with regard to two primary areas: (a) accuracy of ratings with varied instrumentation (anchoring: proportional or absolute) and procedures (observation length: 5 min, 10 min, or 20 min) and (b) one-week test-retest reliability. Participants viewed video clips of a typical third…

  2. Standardizing the Pre-Licensure Supervision Process: A Commentary on Advocating for Direct Observation of Skills

    ERIC Educational Resources Information Center

    Gray, Neal D.; Erickson, Paul

    2013-01-01

    The present paper advocates for standardized regulations and laws for supervision of pre-licensed counselors in the United States, particularly for direct observation of clinical skills. A review of regulations by the American Counseling Association (ACA) Office of Professional Affairs (2012) reveals that only two states (Arizona and North…

  3. Assessing nurses' hand hygiene practices by direct observation or self-report.

    PubMed

    Larson, Elaine L; Aiello, Allison E; Cimiotti, Jeannie P

    2004-01-01

    Methods of obtaining data on hand hygiene practices have not been well validated. The purpose of this study was to compare two methods of assessment of hand hygiene practices--direct observation and self-report using diaries. For 22 months, nursing staff (n = 119) from two neonatal ICUs recorded their hand hygiene practices on a diary card one shift/month (n = 1,071 diary cards). The same data were collected in monthly 1-hour direct observation sessions (n = 206 hours). Amount of time in gloves and total hand hygiene episodes/hour did not differ significantly by diary or observation, but four other specific parameters were significantly different. If hand hygiene practices are to be assessed over time, the same method must be used. Given these measurement limitations, more valid, practical, and less costly methods are needed.

  4. A Review of Direct Observation Research within the Past Decade in the Field of Emotional and Behavioral Disorders

    ERIC Educational Resources Information Center

    Adamson, Reesha M.; Wachsmuth, Sean T.

    2014-01-01

    This study reviewed prominent journals within the field of emotional and behavioral disorders to identify direct observation approaches, reported reliability statistics, and key features of direct observation. Selected journals were systematically reviewed for the past 10 years identifying and quantifying specific direct observation systems and…

  5. Evaluating worker vibration exposures using self-reported and direct observation estimates of exposure duration.

    PubMed

    McCallig, Margaret; Paddan, Gurmail; Van Lente, Eric; Moore, Ken; Coggins, Marie

    2010-12-01

    The objective of this study was to compare objective and subjective methods of collecting exposure time data for hand arm vibration (HAV) and whole-body vibration (WBV), and to evaluate the impact of inaccurate exposure times' on the calculation of the average vibration exposure over an 8 h working day A(8). The study was carried out in the engineering services and maintenance departments of a construction and property management company. Worker exposure time data was collected using three methods, questionnaire surveys, daily worker interviews and 8 h direct workplace observations. Vibration magnitudes (m/s(2)) were measured for a range of hand tools and vehicles, and daily vibration exposure estimates A(8) were calculated using exposure times observed, reported in interview and self reported in the questionnaire. Results from the study showed that self-reported exposure time estimates from the questionnaire survey were a factor of 9.0 (median value) times greater for HAV and a factor of 6.0 (median value) times greater for WBV when compared with direct observation estimates. Exposure times reported in interview were higher, than those observed, but more reliable than those self reported in the questionnaire; a factor of 2.1 (median value) times greater for HAV and a factor of 1.4 (median value) times greater for WBV. A(8) values calculated using questionnaire exposure times were up to 66% and 75% greater for sources of HAV and WBV respectively when compared to A(8) values calculated using observed exposure times. For the purposes of carrying out a reliable risk assessment, results from this study indicate that direct measurements of worker exposure time are not recommended over questionnaires especially where work is highly variable for example in construction and property management. Worker interviews or direct workplace observation methods were found to be reliable alternative methods for collecting exposure time.

  6. THE STRUCTURE OF A SELF-GRAVITATING PROTOPLANETARY DISK AND ITS IMPLICATIONS FOR DIRECT IMAGING OBSERVATIONS

    SciTech Connect

    Muto, Takayuki

    2011-09-20

    We consider the effects of self-gravity on the hydrostatic balance in the vertical direction of a gaseous disk and discuss the possible signature of the self-gravity that may be captured by direct imaging observations of protoplanetary disks in the future. In this paper, we consider a vertically isothermal disk in order to isolate the effects of self-gravity. The specific disk model we consider in this paper is the one with a radial surface density gap, at which the Toomre's Q-parameter of the disk varies rapidly in the radial direction. We calculate the vertical structure of the disk including the effects of self-gravity. We then calculate the scattered light and the dust thermal emission. We find that if the disk is massive enough and the effects of self-gravity come into play, a weak bump-like structure at the gap edge appears in the near-infrared (NIR) scattered light, while no such bump-like structure is seen in the submillimeter (sub-mm) dust continuum image. The appearance of the bump is caused by the variation of the height of the surface in the NIR wavelength. If such a bump-like feature is detected in future direct imaging observations, combined with sub-mm observations, it will give us useful information about the physical states of the disk.

  7. Direct observation of photonic jets and corresponding backscattering enhancement at microwave frequencies

    NASA Astrophysics Data System (ADS)

    Zhao, L.; Ong, C. K.

    2009-06-01

    We report the direct observation of photonic nanojets that emerged from the shadow side of a dielectric cylinder illuminated by plane waves in the microwave frequencies (8-13 GHz). Using our recently developed two-dimensional spatial field mapping system, we carried out a point-by-point measurement of both the phase and intensity of spatial electric field distribution inside and around scattering dielectric cylinders. The direct electric field maps confirm the subwavelength waist of the photonic jet. In addition, we also confirmed the superbackscattering enhancement induced by the presence of a particle much smaller than the initial focusing cylinder within the photonic jet.

  8. Real-space investigation of a transverse wave in a liquid system generated by a molecular-dynamics simulation

    NASA Astrophysics Data System (ADS)

    Munejiri, Shuji; Shimojo, Fuyuki; Hoshino, Kozo

    2011-01-01

    We have invented a simple intuitive method for describing the existence of microscopic transverse wave in a liquid system produced by molecular-dynamics simulations. The method is based on an idea of using a velocity field which is determined by the velocity of atoms in liquids. One of the significant advantages of our method over a conventional method is that the waves are investigated in real space rather than in wavenumber space. This will help to visualize microscopic waves by computer graphics. We have applied the method to liquid tin at three thermodynamic states generated by ab initio molecular-dynamics simulations and found that it can distinguish whether the liquids have transverse waves or not in the same way as the conventional method. We have also shown that the velocity autocorrelation function consists of the transverse and longitudinal parts.

  9. Real-space multiple scattering theory calculations of LEED (low-energy electron diffraction) intensities for stepped surfaces

    SciTech Connect

    Zhang, X.-G.; Rous, P.J.; Van Hove, M.A. ); MacLaren, J.M. ); Gonis, A. ); Somorjai, G.A. California Univ., Berkeley, CA . Dept. of Chemistry)

    1990-07-25

    We use a newly developed real-space multiple scattering theory (RS-MST) to calculate low-energy electron diffraction (LEED) intensities from stepped surfaces. In this calculation the electron wavefunctions are expanded in terms of an angular momentum basis, utilizing the property of removal invariance of systems with semi-infinite periodicity. This strongly reduces the dependence of the calculation on the interlayer spacing and thus opens up the possibility of treating more open surfaces. This includes in particular stepped surfaces, to which conventional methods cannot be applied. Applications of the formalism to various stepped surfaces are presented. In particular, the results for Cu(311) and (331) surfaces obtained from both the layer doubling and RS-MST methods are compared. In addition, numerical techniques which can improve the convergence as well as the speed of the RS-MST approach are discussed. 6 refs., 3 figs.

  10. Massively-parallel electron dynamics calculations in real-time and real-space: Toward applications to nanostructures of more than ten-nanometers in size

    SciTech Connect

    Noda, Masashi; Ishimura, Kazuya; Nobusada, Katsuyuki; Yabana, Kazuhiro; Boku, Taisuke

    2014-05-15

    A highly efficient program of massively parallel calculations for electron dynamics has been developed in an effort to apply the method to optical response of nanostructures of more than ten-nanometers in size. The approach is based on time-dependent density functional theory calculations in real-time and real-space. The computational code is implemented by using simple algorithms with a finite-difference method in space derivative and Taylor expansion in time-propagation. Since the computational program is free from the algorithms of eigenvalue problems and fast-Fourier-transformation, which are usually implemented in conventional quantum chemistry or band structure calculations, it is highly suitable for massively parallel calculations. Benchmark calculations using the K computer at RIKEN demonstrate that the parallel efficiency of the program is very high on more than 60 000 CPU cores. The method is applied to optical response of arrays of C{sub 60} orderly nanostructures of more than 10 nm in size. The computed absorption spectrum is in good agreement with the experimental observation.

  11. A two-phase charge-density real-space-pairing model of high-Tc superconductivity.

    PubMed

    Humphreys

    1999-03-01

    It is usually assumed that high-T(c) superconductors have a periodic band structure and a periodic charge density, although amorphous low-T(c) superconductors are known. In this paper, it is suggested that the CuO(2) conduction planes of cuprate superconductors consist of regions of two different charge densities which do not normally repeat periodically. It is suggested that the pairing of holes occurs in real space in cuprate superconductors. It is proposed that the hole-pairing mechanism is magnetic exchange coupling and the pairing force is strong, the pairing energy being greater than kT at room temperature. The bound hole pair is essentially a bipolaron. A real-space model is very tentatively suggested in which the CuO(2) planes of YBa(2)Cu(3)O(7) contain nanodomains of a 3 x 3 hole lattice surrounded by interfaces one unit cell wide in which the holes are paired. In the superconducting state in this model, the existing hole pairs condense and move coherently and collectively around the insulating nanodomains, like trams running around blocks of houses, with one hole on each tramline. The hole pairs move in an elegant manner with hole pairs hopping from oxygen to oxygen via adjacent copper sites. The model explains the superconducting current being in the ab plane and it also explains the very short coherence lengths. Because the pairing force is strong, the model suggests that room-temperature superconductivity might be possible in carefully designed new oxide materials.

  12. Real-space measurement of potential distribution in PECVD ONO electrets by Kelvin probe force microscopy.

    PubMed

    Emmerich, F; Thielemann, C

    2016-05-20

    Multilayers of silicon oxide/silicon nitride/silicon oxide (ONO) are known for their good electret properties due to deep energy traps near the material interfaces, facilitating charge storage. However, measurement of the space charge distribution in such multilayers is a challenge for conventional methods if layer thickness dimensions shrink below 1 μm. In this paper, we propose an atomic force microscope based method to determine charge distributions in ONO layers with spatial resolution below 100 nm. By applying Kelvin probe force microscopy (KPFM) on freshly cleaved, corona-charged multilayers, the surface potential is measured directly along the z-axis and across the interfaces. This new method gives insights into charge distribution and charge movement in inorganic electrets with a high spatial resolution.

  13. Real-space measurement of potential distribution in PECVD ONO electrets by Kelvin probe force microscopy

    NASA Astrophysics Data System (ADS)

    Emmerich, F.; Thielemann, C.

    2016-05-01

    Multilayers of silicon oxide/silicon nitride/silicon oxide (ONO) are known for their good electret properties due to deep energy traps near the material interfaces, facilitating charge storage. However, measurement of the space charge distribution in such multilayers is a challenge for conventional methods if layer thickness dimensions shrink below 1 μm. In this paper, we propose an atomic force microscope based method to determine charge distributions in ONO layers with spatial resolution below 100 nm. By applying Kelvin probe force microscopy (KPFM) on freshly cleaved, corona-charged multilayers, the surface potential is measured directly along the z-axis and across the interfaces. This new method gives insights into charge distribution and charge movement in inorganic electrets with a high spatial resolution.

  14. Gravity Waves Generated by Convection: A New Idealized Model Tool and Direct Validation with Satellite Observations

    NASA Astrophysics Data System (ADS)

    Alexander, M. Joan; Stephan, Claudia

    2015-04-01

    In climate models, gravity waves remain too poorly resolved to be directly modelled. Instead, simplified parameterizations are used to include gravity wave effects on model winds. A few climate models link some of the parameterized waves to convective sources, providing a mechanism for feedback between changes in convection and gravity wave-driven changes in circulation in the tropics and above high-latitude storms. These convective wave parameterizations are based on limited case studies with cloud-resolving models, but they are poorly constrained by observational validation, and tuning parameters have large uncertainties. Our new work distills results from complex, full-physics cloud-resolving model studies to essential variables for gravity wave generation. We use the Weather Research Forecast (WRF) model to study relationships between precipitation, latent heating/cooling and other cloud properties to the spectrum of gravity wave momentum flux above midlatitude storm systems. Results show the gravity wave spectrum is surprisingly insensitive to the representation of microphysics in WRF. This is good news for use of these models for gravity wave parameterization development since microphysical properties are a key uncertainty. We further use the full-physics cloud-resolving model as a tool to directly link observed precipitation variability to gravity wave generation. We show that waves in an idealized model forced with radar-observed precipitation can quantitatively reproduce instantaneous satellite-observed features of the gravity wave field above storms, which is a powerful validation of our understanding of waves generated by convection. The idealized model directly links observations of surface precipitation to observed waves in the stratosphere, and the simplicity of the model permits deep/large-area domains for studies of wave-mean flow interactions. This unique validated model tool permits quantitative studies of gravity wave driving of regional

  15. Direct observation of electric field induced pattern formation and particle aggregation in ferrofluids

    SciTech Connect

    Rajnak, Michal; Kopcansky, Peter; Timko, Milan; Petrenko, Viktor I.; Avdeev, Mikhail V.; Ivankov, Olexandr I.; Feoktystov, Artem; Dolnik, Bystrik; Kurimsky, Juraj

    2015-08-17

    Ferrofluids typically respond to magnetic fields and can be manipulated by external magnetic fields. Here, we report on formation of visually observable patterns in a diluted low-polarity ferrofluid exposed to external electric fields. This presents a specific type of ferrofluid structure driven by a combined effect of electrohydrodynamics and electrical body forces. The free charge and permittivity variation are considered to play a key role in the observed phenomenon. The corresponding changes in the ferrofluid structure have been found at nanoscale as well. By small-angle neutron scattering (SANS), we show that the magnetic nanoparticles aggregate in direct current (dc) electric field with a strong dependence on the field intensity. The anisotropic aggregates preferably orient in the direction of the applied electric field. Conducting SANS experiments with alternating current (ac) electric fields of various frequencies, we found a critical frequency triggering the aggregation process. Our experimental study could open future applications of ferrofluids based on insulating liquids.

  16. Direct spectroscopic observation of a shallow hydrogenlike donor state in insulating SrTiO3.

    PubMed

    Salman, Z; Prokscha, T; Amato, A; Morenzoni, E; Scheuermann, R; Sedlak, K; Suter, A

    2014-10-10

    We present a direct spectroscopic observation of a shallow hydrogenlike muonium state in SrTiO(3) which confirms the theoretical prediction that interstitial hydrogen may act as a shallow donor in this material. The formation of this muonium state is temperature dependent and appears below ∼ 70K. From the temperature dependence we estimate an activation energy of ∼ 50 meV in the bulk and ∼ 23 meV near the free surface. The field and directional dependence of the muonium precession frequencies further supports the shallow impurity state with a rare example of a fully anisotropic hyperfine tensor. From these measurements we determine the strength of the hyperfine interaction and propose that the muon occupies an interstitial site near the face of the oxygen octahedron in SrTiO(3). The observed shallow donor state provides new insight for tailoring the electronic and optical properties of SrTiO(3)-based oxide interface systems.

  17. Direct observation of electric field induced pattern formation and particle aggregation in ferrofluids

    NASA Astrophysics Data System (ADS)

    Rajnak, Michal; Petrenko, Viktor I.; Avdeev, Mikhail V.; Ivankov, Olexandr I.; Feoktystov, Artem; Dolnik, Bystrik; Kurimsky, Juraj; Kopcansky, Peter; Timko, Milan

    2015-08-01

    Ferrofluids typically respond to magnetic fields and can be manipulated by external magnetic fields. Here, we report on formation of visually observable patterns in a diluted low-polarity ferrofluid exposed to external electric fields. This presents a specific type of ferrofluid structure driven by a combined effect of electrohydrodynamics and electrical body forces. The free charge and permittivity variation are considered to play a key role in the observed phenomenon. The corresponding changes in the ferrofluid structure have been found at nanoscale as well. By small-angle neutron scattering (SANS), we show that the magnetic nanoparticles aggregate in direct current (dc) electric field with a strong dependence on the field intensity. The anisotropic aggregates preferably orient in the direction of the applied electric field. Conducting SANS experiments with alternating current (ac) electric fields of various frequencies, we found a critical frequency triggering the aggregation process. Our experimental study could open future applications of ferrofluids based on insulating liquids.

  18. Direct observation of surface plasmons in YBCO by attenuated total reflection of light in the infrared

    NASA Astrophysics Data System (ADS)

    Walmsley, D. G.; Smyth, C. C.; Sellai, A.; McCafferty, P. G.; Dawson, P.; Morrow, T.; Graham, W. G.

    1994-02-01

    Surface plasmons have been observed directly in YBCO films in an Otto-geometry attenuated total reflection measurement at a wavelength of 3.392 μm. The laser deposited films are c-axis oriented on an MgO substrate. This observation confirms theoretical deductions from complex dielectric function data. Measured data have been fitted to a theoretical model and are compared with the optical constants determined by Bozovic [1]. The investigations have been extended to films with other orientations to investigate whether material anisotropy is reflected in the results and non-metallic behaviour is found.

  19. Direct observation of a photoinduced nonstabilized nitrile imine structure in the solid state.

    PubMed

    Zheng, Shao-Liang; Wang, Yizhong; Yu, Zhipeng; Lin, Qing; Coppens, Philip

    2009-12-23

    We report the direct observation of a bent geometry for a nonstabilized nitrile imine in a metal-coordination crystal. The photoinduced tetrazole ring rupture to release N(2) appears to depend on the size of voids around the N(3)-N(4) bond in the crystal lattice. We further observed the selective formation of the 1,3-addition product when a reactive nitrile imine was photogenerated in water. Overall, the bent nitrile imine geometry agrees with the 1,3-dipolar structure, a transient reactive species that mediates the photoinduced 1,3-dipolar cycloaddition in the aqueous medium.

  20. Directivity Patterns of Complex Solar Type III Radio Bursts: Stereoscopic Observations

    NASA Astrophysics Data System (ADS)

    Golla, T.; MacDowall, R. J.

    2014-12-01

    Complex solar type III-like radio bursts are a group of type III bursts that occur in association with slowly drifting type II radio bursts excited by coronal mass ejection (CME) driven shock waves. We presentsimultaneous observations of these radio bursts from the STEREO A, B and WIND spacecraft at low frequencies, located at different vantage points in the ecliptic plane. Using these stereoscopic observations, wedetermine the directivity of these complex radio bursts. We estimate the angles between the directions of the magnetic field at the sources and the lines connecting the source to the spacecraft (viewing angles) by assuming that the sources are located on the Parker spiral magnetic field lines emerging from the associated active regions into the spherically symmetric solar atmosphere. We estimate the normalized peak intensities of these bursts (directivity factors) at each spacecraft using their time profiles at each spacecraft. These observations indicate that the complex type III bursts can be divided into two groups: (1) bursts emitting into a very narrow cone centered around the tangent to the magnetic field, and (2) bursts emitting into a wider cone. We show that the bursts , which are emitted along the tangent to the spiral magnetic field lines at the source are very intense, and their intensities steadily fall as the viewing angles increase to higher values. We have developed a ray tracing code and computed the distributions of the trajectories of rays emitted at the fundamental and second harmonic of the electron plasma frequency. The comparison of the observed emission patterns with the computed distributions of the ray trajectories indicate that the intense bursts visible in a narrow range of angles around the magnetic field directions probably are emitted in the fundamental mode, whereas the relativelyweaker bursts visible to a wide range of angles are probably emitted in the harmonic mode.

  1. Direct time-domain observation of laser pulse filaments in transparent media

    SciTech Connect

    Dachraoui, H.; Oberer, C.; Michelswirth,; Heinzmann, U.

    2010-10-15

    The interplay among self-focusing, energy depletion, and plasma formation is fundamental to the understanding of laser-matter interaction. In this article, we present the first direct time-resolved observations of the propagation of intense femtosecond laser pulses experiencing conical emission, self-focusing, self-guiding, beam filamentation, plasma defocusing, and continuum generation in wide-band-gap dielectrics. We demonstrate that continuum generation involves different mechanisms as a function of deposited energy.

  2. Effect of illuminance on the directions of chromostereopsis and transverse chromatic aberration observed with natural pupils.

    PubMed

    Simonet, P; Campbell, M C

    1990-07-01

    The direction of chromostereopsis observed with a natural pupil and the direction of the monocularly perceived disparity between coloured targets (F and C lines - 486 and 656 nm) have been measured in a sample of 30 subjects at 10 and 1000 lx. At both illumination levels approximately equal numbers of subjects perceived positive and negative chromostereopsis. When the ambient illumination was increased, a reversal in the direction of the chromostereopsis occurred for 16 subjects. For six of them a change from a positive to a negative chromostereopsis was observed, a pattern not reported in previous studies. In most cases at both high and low illuminance, there was an absence of perception of a monocular disparity (transverse chromatic aberration), although chromostereopsis was reported, indicating that binocular information can be obtained from sub-threshold monocular disparities. At low illuminance, the lack of correlation between the direction of chromostereopsis and transverse chromatic aberration (TCA) may indicate that there may be a supplementary binocular factor in chromostereopsis.

  3. Controllability and observability analysis for vertex domination centrality in directed networks

    PubMed Central

    Wang, Bingbo; Gao, Lin; Gao, Yong; Deng, Yue; Wang, Yu

    2014-01-01

    Topological centrality is a significant measure for characterising the relative importance of a node in a complex network. For directed networks that model dynamic processes, however, it is of more practical importance to quantify a vertex's ability to dominate (control or observe) the state of other vertices. In this paper, based on the determination of controllable and observable subspaces under the global minimum-cost condition, we introduce a novel direction-specific index, domination centrality, to assess the intervention capabilities of vertices in a directed network. Statistical studies demonstrate that the domination centrality is, to a great extent, encoded by the underlying network's degree distribution and that most network positions through which one can intervene in a system are vertices with high domination centrality rather than network hubs. To analyse the interaction and functional dependence between vertices when they are used to dominate a network, we define the domination similarity and detect significant functional modules in glossary and metabolic networks through clustering analysis. The experimental results provide strong evidence that our indices are effective and practical in accurately depicting the structure of directed networks. PMID:24954137

  4. Three-dimensional atomic force microscopy: interaction force vector by direct observation of tip trajectory.

    PubMed

    Sigdel, Krishna P; Grayer, Justin S; King, Gavin M

    2013-11-13

    The prospect of a robust three-dimensional atomic force microscope (AFM) holds significant promise in nanoscience. Yet, in conventional AFM, the tip-sample interaction force vector is not directly accessible. We scatter a focused laser directly off an AFM tip apex to rapidly and precisely measure the tapping tip trajectory in three-dimensional space. This data also yields three-dimensional cantilever spring constants, effective masses, and hence, the tip-sample interaction force components via Newton's second law. Significant lateral forces representing 49 and 13% of the normal force (Fz = 152 ± 17 pN) were observed in common tapping mode conditions as a silicon tip intermittently contacted a glass substrate in aqueous solution; as a consequence, the direction of the force vector tilted considerably more than expected. When addressing the surface of a lipid bilayer, the behavior of the force components differed significantly from that observed on glass. This is attributed to the lateral mobility of the lipid membrane coupled with its elastic properties. Direct access to interaction components Fx, Fy, and Fz provides a more complete view of tip dynamics that underlie force microscope operation and can form the foundation of a three-dimensional AFM in a plurality of conditions.

  5. Controllability and observability analysis for vertex domination centrality in directed networks

    NASA Astrophysics Data System (ADS)

    Wang, Bingbo; Gao, Lin; Gao, Yong; Deng, Yue; Wang, Yu

    2014-06-01

    Topological centrality is a significant measure for characterising the relative importance of a node in a complex network. For directed networks that model dynamic processes, however, it is of more practical importance to quantify a vertex's ability to dominate (control or observe) the state of other vertices. In this paper, based on the determination of controllable and observable subspaces under the global minimum-cost condition, we introduce a novel direction-specific index, domination centrality, to assess the intervention capabilities of vertices in a directed network. Statistical studies demonstrate that the domination centrality is, to a great extent, encoded by the underlying network's degree distribution and that most network positions through which one can intervene in a system are vertices with high domination centrality rather than network hubs. To analyse the interaction and functional dependence between vertices when they are used to dominate a network, we define the domination similarity and detect significant functional modules in glossary and metabolic networks through clustering analysis. The experimental results provide strong evidence that our indices are effective and practical in accurately depicting the structure of directed networks.

  6. Warming experiments elucidate the drivers of observed directional changes in tundra vegetation

    PubMed Central

    Hollister, Robert D; May, Jeremy L; Kremers, Kelseyann S; Tweedie, Craig E; Oberbauer, Steven F; Liebig, Jennifer A; Botting, Timothy F; Barrett, Robert T; Gregory, Jessica L

    2015-01-01

    Few studies have clearly linked long-term monitoring with in situ experiments to clarify potential drivers of observed change at a given site. This is especially necessary when findings from a site are applied to a much broader geographic area. Here, we document vegetation change at Barrow and Atqasuk, Alaska, occurring naturally and due to experimental warming over nearly two decades. An examination of plant cover, canopy height, and community indices showed more significant differences between years than due to experimental warming. However, changes with warming were more consistent than changes between years and were cumulative in many cases. Most cases of directional change observed in the control plots over time corresponded with a directional change in response to experimental warming. These included increases in canopy height and decreases in lichen cover. Experimental warming resulted in additional increases in evergreen shrub cover and decreases in diversity and bryophyte cover. This study suggests that the directional changes occurring at the sites are primarily due to warming and indicates that further changes are likely in the next two decades if the regional warming trend continues. These findings provide an example of the utility of coupling in situ experiments with long-term monitoring to accurately document vegetation change in response to global change and to identify the underlying mechanisms driving observed changes. PMID:26140204

  7. Warming experiments elucidate the drivers of observed directional changes in tundra vegetation.

    PubMed

    Hollister, Robert D; May, Jeremy L; Kremers, Kelseyann S; Tweedie, Craig E; Oberbauer, Steven F; Liebig, Jennifer A; Botting, Timothy F; Barrett, Robert T; Gregory, Jessica L

    2015-05-01

    Few studies have clearly linked long-term monitoring with in situ experiments to clarify potential drivers of observed change at a given site. This is especially necessary when findings from a site are applied to a much broader geographic area. Here, we document vegetation change at Barrow and Atqasuk, Alaska, occurring naturally and due to experimental warming over nearly two decades. An examination of plant cover, canopy height, and community indices showed more significant differences between years than due to experimental warming. However, changes with warming were more consistent than changes between years and were cumulative in many cases. Most cases of directional change observed in the control plots over time corresponded with a directional change in response to experimental warming. These included increases in canopy height and decreases in lichen cover. Experimental warming resulted in additional increases in evergreen shrub cover and decreases in diversity and bryophyte cover. This study suggests that the directional changes occurring at the sites are primarily due to warming and indicates that further changes are likely in the next two decades if the regional warming trend continues. These findings provide an example of the utility of coupling in situ experiments with long-term monitoring to accurately document vegetation change in response to global change and to identify the underlying mechanisms driving observed changes.

  8. Full data acquisition in Kelvin Probe Force Microscopy: Mapping dynamic electric phenomena in real space.

    PubMed

    Collins, Liam; Belianinov, Alex; Somnath, Suhas; Balke, Nina; Kalinin, Sergei V; Jesse, Stephen

    2016-08-12

    Kelvin probe force microscopy (KPFM) has provided deep insights into the local electronic, ionic and electrochemical functionalities in a broad range of materials and devices. In classical KPFM, which utilizes heterodyne detection and closed loop bias feedback, the cantilever response is down-sampled to a single measurement of the contact potential difference (CPD) per pixel. This level of detail, however, is insufficient for materials and devices involving bias and time dependent electrochemical events; or at solid-liquid interfaces, where non-linear or lossy dielectrics are present. Here, we demonstrate direct recovery of the bias dependence of the electrostatic force at high temporal resolution using General acquisition Mode (G-Mode) KPFM. G-Mode KPFM utilizes high speed detection, compression, and storage of the raw cantilever deflection signal in its entirety at high sampling rates. We show how G-Mode KPFM can be used to capture nanoscale CPD and capacitance information with a temporal resolution much faster than the cantilever bandwidth, determined by the modulation frequency of the AC voltage. In this way, G-Mode KPFM offers a new paradigm to study dynamic electric phenomena in electroactive interfaces as well as a promising route to extend KPFM to the solid-liquid interface.

  9. Full data acquisition in Kelvin Probe Force Microscopy: Mapping dynamic electric phenomena in real space

    PubMed Central

    Collins, Liam; Belianinov, Alex; Somnath, Suhas; Balke, Nina; Kalinin, Sergei V.; Jesse, Stephen

    2016-01-01

    Kelvin probe force microscopy (KPFM) has provided deep insights into the local electronic, ionic and electrochemical functionalities in a broad range of materials and devices. In classical KPFM, which utilizes heterodyne detection and closed loop bias feedback, the cantilever response is down-sampled to a single measurement of the contact potential difference (CPD) per pixel. This level of detail, however, is insufficient for materials and devices involving bias and time dependent electrochemical events; or at solid-liquid interfaces, where non-linear or lossy dielectrics are present. Here, we demonstrate direct recovery of the bias dependence of the electrostatic force at high temporal resolution using General acquisition Mode (G-Mode) KPFM. G-Mode KPFM utilizes high speed detection, compression, and storage of the raw cantilever deflection signal in its entirety at high sampling rates. We show how G-Mode KPFM can be used to capture nanoscale CPD and capacitance information with a temporal resolution much faster than the cantilever bandwidth, determined by the modulation frequency of the AC voltage. In this way, G-Mode KPFM offers a new paradigm to study dynamic electric phenomena in electroactive interfaces as well as a promising route to extend KPFM to the solid-liquid interface. PMID:27514987

  10. Real-space imaging of the Verwey transition at the (100) surface of magnetite

    NASA Astrophysics Data System (ADS)

    de la Figuera, Juan; Novotny, Zbynek; Setvin, Martin; Liu, Tijiang; Mao, Zhiqiang; Chen, Gong; N'Diaye, Alpha T.; Schmid, Michael; Diebold, Ulrike; Schmid, Andreas K.; Parkinson, Gareth S.

    2013-10-01

    Effects of the Verwey transition on the (100) surface of magnetite were studied using scanning tunneling microscopy and spin polarized low-energy electron microscopy. On cooling through the transition temperature TV, the initially flat surface undergoes a rooflike distortion with a periodicity of ˜0.5 μm due to ferroelastic twinning within monoclinic domains of the low-temperature monoclinic structure. The monoclinic c axis orients in the surface plane, along the [001]c directions. At the atomic scale, the charge-ordered (2×2)R45∘ reconstruction of the (100) surface is unperturbed by the bulk transition, and is continuous over the twin boundaries. Time resolved low-energy electron microscopy movies reveal the structural transition to be first order at the surface, indicating that the bulk transition is not an extension of the Verwey-like (2×2)R45∘ reconstruction. Although conceptually similar, the charge-ordered phases of the (100) surface and sub-TV bulk of magnetite are unrelated phenomena.

  11. Full data acquisition in Kelvin Probe Force Microscopy: Mapping dynamic electric phenomena in real space.

    PubMed

    Collins, Liam; Belianinov, Alex; Somnath, Suhas; Balke, Nina; Kalinin, Sergei V; Jesse, Stephen

    2016-01-01

    Kelvin probe force microscopy (KPFM) has provided deep insights into the local electronic, ionic and electrochemical functionalities in a broad range of materials and devices. In classical KPFM, which utilizes heterodyne detection and closed loop bias feedback, the cantilever response is down-sampled to a single measurement of the contact potential difference (CPD) per pixel. This level of detail, however, is insufficient for materials and devices involving bias and time dependent electrochemical events; or at solid-liquid interfaces, where non-linear or lossy dielectrics are present. Here, we demonstrate direct recovery of the bias dependence of the electrostatic force at high temporal resolution using General acquisition Mode (G-Mode) KPFM. G-Mode KPFM utilizes high speed detection, compression, and storage of the raw cantilever deflection signal in its entirety at high sampling rates. We show how G-Mode KPFM can be used to capture nanoscale CPD and capacitance information with a temporal resolution much faster than the cantilever bandwidth, determined by the modulation frequency of the AC voltage. In this way, G-Mode KPFM offers a new paradigm to study dynamic electric phenomena in electroactive interfaces as well as a promising route to extend KPFM to the solid-liquid interface. PMID:27514987

  12. Full data acquisition in Kelvin Probe Force Microscopy: Mapping dynamic electric phenomena in real space

    NASA Astrophysics Data System (ADS)

    Collins, Liam; Belianinov, Alex; Somnath, Suhas; Balke, Nina; Kalinin, Sergei V.; Jesse, Stephen

    2016-08-01

    Kelvin probe force microscopy (KPFM) has provided deep insights into the local electronic, ionic and electrochemical functionalities in a broad range of materials and devices. In classical KPFM, which utilizes heterodyne detection and closed loop bias feedback, the cantilever response is down-sampled to a single measurement of the contact potential difference (CPD) per pixel. This level of detail, however, is insufficient for materials and devices involving bias and time dependent electrochemical events; or at solid-liquid interfaces, where non-linear or lossy dielectrics are present. Here, we demonstrate direct recovery of the bias dependence of the electrostatic force at high temporal resolution using General acquisition Mode (G-Mode) KPFM. G-Mode KPFM utilizes high speed detection, compression, and storage of the raw cantilever deflection signal in its entirety at high sampling rates. We show how G-Mode KPFM can be used to capture nanoscale CPD and capacitance information with a temporal resolution much faster than the cantilever bandwidth, determined by the modulation frequency of the AC voltage. In this way, G-Mode KPFM offers a new paradigm to study dynamic electric phenomena in electroactive interfaces as well as a promising route to extend KPFM to the solid-liquid interface.

  13. Real-space quadrature: A convenient, efficient representation for multipole expansions

    SciTech Connect

    Rogers, David M.

    2015-02-21

    Multipoles are central to the theory and modeling of polarizable and nonpolarizable molecular electrostatics. This has made a representation in terms of point charges a highly sought after goal, since rotation of multipoles is a bottleneck in molecular dynamics implementations. All known point charge representations are orders of magnitude less efficient than spherical harmonics due to either using too many fixed charge locations or due to nonlinear fitting of fewer charge locations. We present the first complete solution to this problem—completely replacing spherical harmonic basis functions by a dramatically simpler set of weights associated to fixed, discrete points on a sphere. This representation is shown to be space optimal. It reduces the spherical harmonic decomposition of Poisson’s operator to pairwise summations over the point set. As a corollary, we also shows exact quadrature-based formulas for contraction over trace-free supersymmetric 3D tensors. Moreover, multiplication of spherical harmonic basis functions translates to a direct product in this representation.

  14. Real-space finite difference scheme for the von Neumann equation with the Dirac Hamiltonian

    NASA Astrophysics Data System (ADS)

    Schreilechner, Magdalena; Pötz, Walter

    2016-07-01

    A finite difference scheme for the numerical treatment of the von Neumann equation for the (2+1)D Dirac Hamiltonian is presented. It is based on a sequential left-right (ket-bra) application of a staggered space-time scheme for the pure-state Dirac equation and offers a numerical treatment of the general mixed-state dynamics of an isolated quantum system within the von Neumann equation. Thereby this direct scheme inherits all the favorable features of the finite-difference scheme for the pure-state Dirac equation, such as the single-cone energy-momentum dispersion, convergence conditions, and scaling behavior. A conserved functional is identified. Moreover this scheme is shown to conserve both Hermiticity and positivity. Numerical tests comprise a numerical analysis of stability, as well as the simulation of a mixed-state time-evolution of Gaussian wave functions, illustrating Zitterbewegung and transverse current oscillations. Imaginary-potential absorbing boundary conditions and parameters which pertain to topological insulator surface states were used in the numerical simulations.

  15. Real-space imaging of plasmon propagation dynamics in the near-field

    NASA Astrophysics Data System (ADS)

    Lewis, William; Muller, Eric; Raschke, Markus

    2014-03-01

    We directly image plasmon propagation and dynamics in the near-field using femtosecond scattering-scanning near-field optical microscopy (s-SNOM). The spatio-temporal dynamics of surface plasmon polariton (SPP) propagation on a gold surface is measured via interferometric time-resolved imaging of the optical near-field. The output of a regenerative amplifier (800nm, 50fs pulses, ~ 150kHz) is focused onto a metallic coated atomic force microscope (AFM) tip, launching a SPP on a flat gold sample. The SPP is scattered by surface defects and propagates back to the tip, where the SPP near-field is scattered to detectible far-field. To maximize coupling of light to the SPP and for far-field background subtraction, we synchronize the repetition rate of the regenerative amplifier to the dither frequency of an AFM cantilever (~ 75kHz). The measurement demonstrates the capability of femtosecond s-SNOM for spatio-temporal imaging on the 10nm-10fs scale. The technique also lends itself to the extension of a variety of multidimensional spectroscopies to the nano-scale.

  16. Direct observation of imprinted antiferromagnetic vortex state in CoO/Fe/Ag(001) disks

    SciTech Connect

    Wu, J.; Carlton, D.; Park, J. S.; Meng, Y.; Arenholz, E.; Doran, A.; Young, A.T.; Scholl, A.; Hwang, C.; Zhao, H. W.; Bokor, J.; Qiu, Z. Q.

    2010-12-21

    In magnetic thin films, a magnetic vortex is a state in which the magnetization vector curls around the center of a confined structure. A vortex state in a thin film disk, for example, is a topological object characterized by the vortex polarity and the winding number. In ferromagnetic (FM) disks, these parameters govern many fundamental properties of the vortex such as its gyroscopic rotation, polarity reversal, core motion, and vortex pair excitation. However, in antiferromagnetic (AFM) disks, though there has been indirect evidence of the vortex state through observations of the induced FM-ordered spins in the AFM disk, they have never been observed directly in experiment. By fabricating single crystalline NiO/Fe/Ag(001) and CoO/Fe/Ag(001) disks and using X-ray Magnetic Linear Dichroism (XMLD), we show direct observation of the vortex state in an AFM disk of AFM/FM bilayer system. We observe that there are two types of AFM vortices, one of which has no analog in FM structures. Finally, we show that a frozen AFM vortex can bias a FM vortex at low temperature.

  17. CRITIC2: A program for real-space analysis of quantum chemical interactions in solids

    NASA Astrophysics Data System (ADS)

    Otero-de-la-Roza, A.; Johnson, Erin R.; Luaña, Víctor

    2014-03-01

    -chemical interactions in periodic solids by means of atoms-in-molecules and related formalisms. Solution method: Critical point search using Newton’s algorithm, atomic basin integration using bisection, qtree and grid-based algorithms, diverse graphical representations and computation of the non-covalent interactions index on a three-dimensional grid. Additional comments: !!!!! The distribution file for this program is over 330 Mbytes and therefore is not delivered directly when download or Email is requested. Instead a html file giving details of how the program can be obtained is sent. !!!!! Running time: Variable, depending on the crystal and the source of the underlying scalar field.

  18. Phases and Interfaces from Real Space Atomically Resolved Data: Physics-Based Deep Data Image Analysis.

    PubMed

    Vasudevan, Rama K; Ziatdinov, Maxim; Jesse, Stephen; Kalinin, Sergei V

    2016-09-14

    Advances in electron and scanning probe microscopies have led to a wealth of atomically resolved structural and electronic data, often with ∼1-10 pm precision. However, knowledge generation from such data requires the development of a physics-based robust framework to link the observed structures to macroscopic chemical and physical descriptors, including single phase regions, order parameter fields, interfaces, and structural and topological defects. Here, we develop an approach based on a synergy of sliding window Fourier transform to capture the local analog of traditional structure factors combined with blind linear unmixing of the resultant 4D data set. This deep data analysis is ideally matched to the underlying physics of the problem and allows reconstruction of the a priori unknown structure factors of individual components and their spatial localization. We demonstrate the principles of this approach using a synthetic data set and further apply it for extracting chemical and physically relevant information from electron and scanning tunneling microscopy data. This method promises to dramatically speed up crystallographic analysis in atomically resolved data, paving the road toward automatic local structure-property determinations in crystalline and quasi-ordered systems, as well as systems with competing structural and electronic order parameters. PMID:27517608

  19. Phases and Interfaces from Real Space Atomically Resolved Data: Physics-Based Deep Data Image Analysis.

    PubMed

    Vasudevan, Rama K; Ziatdinov, Maxim; Jesse, Stephen; Kalinin, Sergei V

    2016-09-14

    Advances in electron and scanning probe microscopies have led to a wealth of atomically resolved structural and electronic data, often with ∼1-10 pm precision. However, knowledge generation from such data requires the development of a physics-based robust framework to link the observed structures to macroscopic chemical and physical descriptors, including single phase regions, order parameter fields, interfaces, and structural and topological defects. Here, we develop an approach based on a synergy of sliding window Fourier transform to capture the local analog of traditional structure factors combined with blind linear unmixing of the resultant 4D data set. This deep data analysis is ideally matched to the underlying physics of the problem and allows reconstruction of the a priori unknown structure factors of individual components and their spatial localization. We demonstrate the principles of this approach using a synthetic data set and further apply it for extracting chemical and physically relevant information from electron and scanning tunneling microscopy data. This method promises to dramatically speed up crystallographic analysis in atomically resolved data, paving the road toward automatic local structure-property determinations in crystalline and quasi-ordered systems, as well as systems with competing structural and electronic order parameters.

  20. Phases and interfaces from real space atomically resolved data: Physics-based deep data image analysis

    DOE PAGESBeta

    Vasudevan, Rama K.; Ziatdinov, Maxim; Jesse, Stephen; Kalinin, Sergei V.

    2016-08-12

    Advances in electron and scanning probe microscopies have led to a wealth of atomically resolved structural and electronic data, often with ~1–10 pm precision. However, knowledge generation from such data requires the development of a physics-based robust framework to link the observed structures to macroscopic chemical and physical descriptors, including single phase regions, order parameter fields, interfaces, and structural and topological defects. Here, we develop an approach based on a synergy of sliding window Fourier transform to capture the local analog of traditional structure factors combined with blind linear unmixing of the resultant 4D data set. This deep data analysismore » is ideally matched to the underlying physics of the problem and allows reconstruction of the a priori unknown structure factors of individual components and their spatial localization. We demonstrate the principles of this approach using a synthetic data set and further apply it for extracting chemical and physically relevant information from electron and scanning tunneling microscopy data. Furthermore, this method promises to dramatically speed up crystallographic analysis in atomically resolved data, paving the road toward automatic local structure–property determinations in crystalline and quasi-ordered systems, as well as systems with competing structural and electronic order parameters.« less

  1. Home Videophones Improve Direct Observation in Tuberculosis Treatment: A Mixed Methods Evaluation

    PubMed Central

    Wade, Victoria A.; Karnon, Jonathan; Eliott, Jaklin A.; Hiller, Janet E.

    2012-01-01

    Background The use of direct observation to monitor tuberculosis treatment is controversial: cost, practical difficulties, and lack of patient acceptability limit effectiveness. Telehealth is a promising alternative delivery method for improving implementation. This study aimed to evaluate the clinical and cost-effectiveness of a telehealth service delivering direct observation, compared to an in-person drive-around service. Methodology/Principal Findings The study was conducted within a community nursing service in South Australia. Telehealth patients received daily video calls at home on a desktop videophone provided by the nursing call center. A retrospective cohort study assessed the effectiveness of the telehealth and traditional forms of observation, defined by the proportion of missed observations recorded in case notes. This data was inputted to a model, estimating the incremental cost-effectiveness ratio (ICER) of telehealth. Semi-structured interviews were conducted with current patients, community nursing and Chest Clinic staff, concerning service acceptability, usability and sustainability. The percentage of missed observations for the telehealth service was 12.1 (n = 58), compared to 31.1 for the in-person service (n = 70). Most of the difference of 18.9% (95% CI: 12.2 – 25.4) was due to fewer pre-arranged absences. The economic analysis calculated the ICER to be AUD$1.32 (95% CI: $0.51 – $2.26) per extra day of successful observation. The video service used less staff time, and became dominant if implemented on a larger scale and/or with decreased technology costs. Qualitative analysis found enabling factors of flexible timing, high patient acceptance, staff efficiency, and Chest Clinic support. Substantial technical problems were manageable, and improved liaison between the nursing service and Chest Clinic was an unexpected side-benefit. Conclusions/Significance Home video observation is a patient-centered, resource efficient way of

  2. Direct observation of Li diffusion in Li-doped ZnO nanowires

    NASA Astrophysics Data System (ADS)

    Li, Guohua; Yu, Lei; Hudak, Bethany M.; Chang, Yao-Jen; Baek, Hyeonjun; Sundararajan, Abhishek; Strachan, Douglas R.; Yi, Gyu-Chul; Guiton, Beth S.

    2016-05-01

    The direct observation of Li diffusion in Li-doped zinc oxide nanowires (NWs) was realized by using in situ heating in the scanning transmission electron microscope (STEM). A continuous increase of low atomic mass regions within a single NW was observed between 200 °C and 600 °C when heated in vacuum, which was explained by the conversion of interstitial to substitutional Li in the ZnO NW host lattice. A kick-out mechanism is introduced to explain the migration and conversion of the interstitial Li (Lii) to Zn-site substitutional Li (LiZn), and this mechanism is verified with low-temperature (11 K) photoluminescence measurements on as-grown and annealed Li-doped zinc oxide NWs, as well as the observation of an increase of NW surface roughing with applied bias.

  3. Understanding conductivity in molecular switches: a real space approach in octaphyrins.

    PubMed

    Woller, T; Ramos-Berdullas, N; Mandado, M; Alonso, M; de Proft, F; Contreras-García, J

    2016-04-28

    In recent years, expanded porphyrins have emerged as a promising class of π-conjugated molecules that display unique electronic, optical and conformational properties. Several expanded porphyrins can switch between planar and twisted conformations, which have different photophysical properties. Such a change of topology involves a Hückel-Möbius aromaticity switch in a single molecule and it can be induced by solvent, pH and metallation. These features make expanded porphyrins suitable for the development of a novel type of molecular switches for molecular electronic devices. Octaphyrins consisting of eight pyrrole rings, exhibit twisted-Hückel, Möbius and Hückel π-conjugation topologies depending on the oxidation and protonation state, with distinct electronic structures and aromaticity. Our working hypothesis is that a significant change in the conductance of expanded porphyrins will be observed after the topology switching. Despite the potential of Hückel-Möbius systems as conductance switches, the relationship between the conductance and the molecular topology is not yet understood. We have explored the performance of local descriptors of conductivity in simple molecules, as well as the relationship with conductance. Since these indexes provide a qualitative measure of delocalization and conductance in the probe molecules, we have carried out a local analysis of electrical conductance changes as a function of the π-conjugation in two examples. In one of them, the locality of the electronic changes ensures the ability of these indexes to describe the conductance as local. Moreover, it enables to identify which conformational switch would be more efficient from an electronic device perspective. However, we also show that it is not always possible to reduce conductance changes to one bond, and in those molecules where a deep rearrangement occurs far from the structural perturbation, local measures show a limited efficiency. This is a first step for the

  4. Observations of black carbon induced semi direct effect over Northeast India

    NASA Astrophysics Data System (ADS)

    Panicker, A. S.; Pandithurai, G.; Safai, P. D.; Dipu, S.; Prabha, T. V.; Konwar, M.

    2014-12-01

    This article reports observational evidence of Black Carbon (BC) induced cloud burning effect (Semi direct effect) for the first time over a mountainous location in North east India. Simultaneous aircraft observations of Black Carbon (BC) mass concentrations and cloud microphysical parameters were carried out over Guwahati, in Northeast India during Cloud Aerosol Interactions and Precipitation Enhancement Experiment (CAIPEEX) Phase-I in 2009. Elevated pollution layers of BC (concentration exceeding 1 μg m-3) were observed over the site up to 7 km on different experimental days (August 30, September 4 and 6 in 2009) in the cloud regime. The vertical heating rate and radiative forcing induced by elevated BC layers in the cloud regime were estimated using an optical model along with a radiative transfer model. The instantaneous vertical heating rate induced by BC in cloud layers is found to be as high as 2.65 K/day. The instantaneous vertical heating by BC is found to be inducing a significant reduction in the measured cloud liquid water content (LWC) over the site. Subsequently, the BC stimulated heating has been found to be reducing the cloud fraction (CFR) and thus inducing a “cloud burning effect (Semi direct effect)”, over the region. The estimated instantaneous BC induced radiative forcing in the cloud regime is found to be +12.7-+45.1 W m-2 during the experimental periods. This large warming and reduction in cloudiness can decrease the precipitation over the region. However, more simultaneous BC-cloud observations and further research are necessary to establish a stable “semi-direct effect” over the region.

  5. An accuracy measurement method for star trackers based on direct astronomic observation.

    PubMed

    Sun, Ting; Xing, Fei; Wang, Xiaochu; You, Zheng; Chu, Daping

    2016-03-07

    Star tracker is one of the most promising optical attitude measurement devices and it is widely used in spacecraft for its high accuracy. However, how to realize and verify such an accuracy remains a crucial but unsolved issue until now. The authenticity of the accuracy measurement method of a star tracker will eventually determine the satellite performance. A new and robust accuracy measurement method for a star tracker based on the direct astronomical observation is proposed here. In comparison with the conventional method with simulated stars, this method utilizes real navigation stars as observation targets which makes the measurement results more authoritative and authentic. Transformations between different coordinate systems are conducted on the account of the precision movements of the Earth, and the error curves of directional vectors are obtained along the three axes. Based on error analysis and accuracy definitions, a three-axis accuracy evaluation criterion has been proposed in this paper, which could determine pointing and rolling accuracy of a star tracker directly. Experimental measurements confirm that this method is effective and convenient to implement. Such a measurement environment is close to the in-orbit conditions and it can satisfy the stringent requirement for high-accuracy star trackers.

  6. Investigating common clinical presentations in first opinion small animal consultations using direct observation

    PubMed Central

    Robinson, N. J.; Dean, R. S.; Cobb, M.; Brennan, M. L.

    2015-01-01

    Understanding more about the clinical presentations encountered in veterinary practice is vital in directing research towards areas relevant to practitioners. The aim of this study was to describe all problems discussed during a convenience sample of consultations using a direct observation method. A data collection tool was used to gather data by direct observation during small animal consultations at eight sentinel practices. Data were recorded for all presenting and non-presenting specific health problems discussed. A total of 1901 patients were presented with 3206 specific health problems discussed. Clinical presentation varied widely between species and between presenting and non-presenting problems. Skin lump, vomiting and inappetence were the most common clinical signs reported by the owner while overweight/obese, dental tartar and skin lump were the most common clinical examination findings. Skin was the most frequently affected body system overall followed by non-specific problems then the gastrointestinal system. Consultations are complex, with a diverse range of different clinical presentations seen. Considering the presenting problem only may give an inaccurate view of the veterinary caseload, as some common problems are rarely the reason for presentation. Understanding the common diagnoses made is the next step and will help to further focus questions for future research. PMID:25564472

  7. Direct observation and quantification of extracellular long-range electron flow in anaerobic bacteria

    NASA Astrophysics Data System (ADS)

    Malvankar, Nikhil; Yalcin, Sibel; Vargas, Madeline; Tuominen, Mark; Lovley, Derek

    2013-03-01

    Some anaerobic microorganisms are capable of transporting electrons outside their cell to distant electron acceptors such as metals, minerals or partner species. Previous studies have focused primarily on transport over short distances (< 1 μm) via diffusion of molecular intermediates, or alternatively via tunneling or thermally-activated hopping across biomolecules. However, we have found that Geobacter sulfurreducens can transport electrons over long distances (> 10 μm) using pili filaments that show organic metal-like conductivity. Pili also enable direct exchange of electrons among syntrophic Geobacter co-cultures. In order to establish the physical principles underlying this remarkable electron transport, we have employed a novel scanning probe microscopy-based method to perform quantitative measurements of electron flow at a single cell level under physiological conditions. Using this nanoscopic approach, we have directly observed the propagation and distribution of injected electrons in individual native bacterial extracellular proteins. Our direct measurements demonstrate unambiguously for the first time that the pili of G. sulfurreducens are a novel class of electronically functional proteins that can sustain electron flow in a surprising manner that has not been observed previously in any other natural protein. Funded by Office of Naval Research, DOE Genomic Sciences and NSF-NSEC Center for Hierarchical Manufacturing grant no. CMMI-1025020.

  8. An accuracy measurement method for star trackers based on direct astronomic observation

    PubMed Central

    Sun, Ting; Xing, Fei; Wang, Xiaochu; You, Zheng; Chu, Daping

    2016-01-01

    Star tracker is one of the most promising optical attitude measurement devices and it is widely used in spacecraft for its high accuracy. However, how to realize and verify such an accuracy remains a crucial but unsolved issue until now. The authenticity of the accuracy measurement method of a star tracker will eventually determine the satellite performance. A new and robust accuracy measurement method for a star tracker based on the direct astronomical observation is proposed here. In comparison with the conventional method with simulated stars, this method utilizes real navigation stars as observation targets which makes the measurement results more authoritative and authentic. Transformations between different coordinate systems are conducted on the account of the precision movements of the Earth, and the error curves of directional vectors are obtained along the three axes. Based on error analysis and accuracy definitions, a three-axis accuracy evaluation criterion has been proposed in this paper, which could determine pointing and rolling accuracy of a star tracker directly. Experimental measurements confirm that this method is effective and convenient to implement. Such a measurement environment is close to the in-orbit conditions and it can satisfy the stringent requirement for high-accuracy star trackers. PMID:26948412

  9. An accuracy measurement method for star trackers based on direct astronomic observation.

    PubMed

    Sun, Ting; Xing, Fei; Wang, Xiaochu; You, Zheng; Chu, Daping

    2016-01-01

    Star tracker is one of the most promising optical attitude measurement devices and it is widely used in spacecraft for its high accuracy. However, how to realize and verify such an accuracy remains a crucial but unsolved issue until now. The authenticity of the accuracy measurement method of a star tracker will eventually determine the satellite performance. A new and robust accuracy measurement method for a star tracker based on the direct astronomical observation is proposed here. In comparison with the conventional method with simulated stars, this method utilizes real navigation stars as observation targets which makes the measurement results more authoritative and authentic. Transformations between different coordinate systems are conducted on the account of the precision movements of the Earth, and the error curves of directional vectors are obtained along the three axes. Based on error analysis and accuracy definitions, a three-axis accuracy evaluation criterion has been proposed in this paper, which could determine pointing and rolling accuracy of a star tracker directly. Experimental measurements confirm that this method is effective and convenient to implement. Such a measurement environment is close to the in-orbit conditions and it can satisfy the stringent requirement for high-accuracy star trackers. PMID:26948412

  10. Investigating common clinical presentations in first opinion small animal consultations using direct observation.

    PubMed

    Robinson, N J; Dean, R S; Cobb, M; Brennan, M L

    2015-05-01

    Understanding more about the clinical presentations encountered in veterinary practice is vital in directing research towards areas relevant to practitioners. The aim of this study was to describe all problems discussed during a convenience sample of consultations using a direct observation method. A data collection tool was used to gather data by direct observation during small animal consultations at eight sentinel practices. Data were recorded for all presenting and non-presenting specific health problems discussed. A total of 1901 patients were presented with 3206 specific health problems discussed. Clinical presentation varied widely between species and between presenting and non-presenting problems. Skin lump, vomiting and inappetence were the most common clinical signs reported by the owner while overweight/obese, dental tartar and skin lump were the most common clinical examination findings. Skin was the most frequently affected body system overall followed by non-specific problems then the gastrointestinal system. Consultations are complex, with a diverse range of different clinical presentations seen. Considering the presenting problem only may give an inaccurate view of the veterinary caseload, as some common problems are rarely the reason for presentation. Understanding the common diagnoses made is the next step and will help to further focus questions for future research. PMID:25564472

  11. Apparatus for Direct Optical Fiber Through-Lens Illumination of Microscopy or Observational Objects

    NASA Technical Reports Server (NTRS)

    Kadogawa, Hiroshi (Inventor)

    2001-01-01

    In one embodiment of the invention, a microscope or other observational apparatus, comprises a hollow tube, a lens mounted to the tube, a light source and at least one flexible optical fiber having an input end and an output end. The input end is positioned to receive light from the light source, and the output end is positioned within the tube so as to directly project light along a straight path to the lens to illuminate an object to be viewed. The path of projected light is uninterrupted and free of light deflecting elements. By passing the light through the lens, the light can be diffused or otherwise defocused to provide more uniform illumination across the surface of the object, increasing the quality of the image of the object seen by the viewer. The direct undeflected and uninterrupted projection of light, without change of direction, eliminates the need for light-deflecting elements, such as beam-splitters, mirrors, prisms, or the like, to direct the projected light towards the object.

  12. Increasing Reliability of Direct Observation Measurement Approaches in Emotional and/or Behavioral Disorders Research Using Generalizability Theory

    ERIC Educational Resources Information Center

    Gage, Nicholas A.; Prykanowski, Debra; Hirn, Regina

    2014-01-01

    Reliability of direct observation outcomes ensures the results are consistent, dependable, and trustworthy. Typically, reliability of direct observation measurement approaches is assessed using interobserver agreement (IOA) and the calculation of observer agreement (e.g., percentage of agreement). However, IOA does not address intraobserver…

  13. An Unroofing Method to Observe the Cytoskeleton Directly at Molecular Resolution Using Atomic Force Microscopy

    PubMed Central

    Usukura, Eiji; Narita, Akihiro; Yagi, Akira; Ito, Shuichi; Usukura, Jiro

    2016-01-01

    An improved unroofing method enabled the cantilever of an atomic force microscope (AFM) to reach directly into a cell to visualize the intracellular cytoskeletal actin filaments, microtubules, clathrin coats, and caveolae in phosphate-buffered saline (PBS) at a higher resolution than conventional electron microscopy. All of the actin filaments clearly exhibited a short periodicity of approximately 5–6 nm, which was derived from globular actins linked to each other to form filaments, as well as a long helical periodicity. The polarity of the actin filaments appeared to be determined by the shape of the periodic striations. Microtubules were identified based on their thickness. Clathrin coats and caveolae were observed on the cytoplasmic surface of cell membranes. The area containing clathrin molecules and their terminal domains was directly visualized. Characteristic ridge structures located at the surface of the caveolae were observed at high resolution, similar to those observed with electron microscopy (EM). Overall, unroofing allowed intracellular AFM imaging in a liquid environment with a level of quality equivalent or superior to that of EM. Thus, AFMs are anticipated to provide cutting-edge findings in cell biology and histology. PMID:27273367

  14. An Unroofing Method to Observe the Cytoskeleton Directly at Molecular Resolution Using Atomic Force Microscopy.

    PubMed

    Usukura, Eiji; Narita, Akihiro; Yagi, Akira; Ito, Shuichi; Usukura, Jiro

    2016-01-01

    An improved unroofing method enabled the cantilever of an atomic force microscope (AFM) to reach directly into a cell to visualize the intracellular cytoskeletal actin filaments, microtubules, clathrin coats, and caveolae in phosphate-buffered saline (PBS) at a higher resolution than conventional electron microscopy. All of the actin filaments clearly exhibited a short periodicity of approximately 5-6 nm, which was derived from globular actins linked to each other to form filaments, as well as a long helical periodicity. The polarity of the actin filaments appeared to be determined by the shape of the periodic striations. Microtubules were identified based on their thickness. Clathrin coats and caveolae were observed on the cytoplasmic surface of cell membranes. The area containing clathrin molecules and their terminal domains was directly visualized. Characteristic ridge structures located at the surface of the caveolae were observed at high resolution, similar to those observed with electron microscopy (EM). Overall, unroofing allowed intracellular AFM imaging in a liquid environment with a level of quality equivalent or superior to that of EM. Thus, AFMs are anticipated to provide cutting-edge findings in cell biology and histology. PMID:27273367

  15. Direct Observation of Aggregative Nanoparticle Growth: Kinetic Modeling of the Size Distribution and Growth Rate

    SciTech Connect

    Woehl, Taylor J.; Park, Chiwoo; Evans, James E.; Arslan, Ilke; Ristenpart, William D.; Browning, Nigel D.

    2014-01-08

    Direct observations of solution-phase nanoparticle growth using in situ liquid transmission electron microscopy (TEM) have demonstrated the importance of “non-classical” growth mechanisms, such as aggregation and coalescence, on the growth and final morphology of nanocrystals at the atomic and single nanoparticle scales. To date, groups have quantitatively interpreted the mean growth rate of nanoparticles in terms of the Lifshitz-Slyozov-Wagner (LSW) model for Ostwald ripening, but less attention has been paid to modeling the corresponding particle size distribution. Here we use in situ fluid stage scanning TEM to demonstrate that silver nanoparticles grow by a length-scale dependent mechanism, where individual nanoparticles grow by monomer attachment but ensemble-scale growth is dominated by aggregation. Although our observed mean nanoparticle growth rate is consistent with the LSW model, we show that the corresponding particle size distribution is broader and more symmetric than predicted by LSW. Following direct observations of aggregation, we interpret the ensemble-scale growth using Smoluchowski kinetics and demonstrate that the Smoluchowski model quantitatively captures the mean growth rate and particle size distribution.

  16. Tracking individual membrane proteins and their biochemistry: The power of direct observation.

    PubMed

    Barden, Adam O; Goler, Adam S; Humphreys, Sara C; Tabatabaei, Samaneh; Lochner, Martin; Ruepp, Marc-David; Jack, Thomas; Simonin, Jonathan; Thompson, Andrew J; Jones, Jeffrey P; Brozik, James A

    2015-11-01

    The advent of single molecule fluorescence microscopy has allowed experimental molecular biophysics and biochemistry to transcend traditional ensemble measurements, where the behavior of individual proteins could not be precisely sampled. The recent explosion in popularity of new super-resolution and super-localization techniques coupled with technical advances in optical designs and fast highly sensitive cameras with single photon sensitivity and millisecond time resolution have made it possible to track key motions, reactions, and interactions of individual proteins with high temporal resolution and spatial resolution well beyond the diffraction limit. Within the purview of membrane proteins and ligand gated ion channels (LGICs), these outstanding advances in single molecule microscopy allow for the direct observation of discrete biochemical states and their fluctuation dynamics. Such observations are fundamentally important for understanding molecular-level mechanisms governing these systems. Examples reviewed here include the effects of allostery on the stoichiometry of ligand binding in the presence of fluorescent ligands; the observation of subdomain partitioning of membrane proteins due to microenvironment effects; and the use of single particle tracking experiments to elucidate characteristics of membrane protein diffusion and the direct measurement of thermodynamic properties, which govern the free energy landscape of protein dimerization. The review of such characteristic topics represents a snapshot of efforts to push the boundaries of fluorescence microscopy of membrane proteins to the absolute limit. This article is part of the Special Issue entitled 'Fluorescent Tools in Neuropharmacology'.

  17. Direct observation of the ferroelectric polarization in the layered perovskite Bi4Ti3O12

    NASA Astrophysics Data System (ADS)

    Urushihara, Daisuke; Komabuchi, Mai; Ishizawa, Nobuo; Iwata, Makoto; Fukuda, Koichiro; Asaka, Toru

    2016-10-01

    We investigated the crystal structure and ferroelectric domains of Bi4Ti3O12 (BTO) by means of transmission electron microscopy (TEM) and single-crystal X-ray diffractometry. From the extinction rule, we determined that the space group in the ferroelectric phase of BTO is P1a1 rather than B2cb and B1a1 which have been proposed previously. We successfully refined the crystal structure based on the space group P1a1. The 180° and 90° ferroelectric domain structures were observed by the [001]-zone dark-field TEM imaging. In the 180° domain structure, we determined that one component of the polarization vector is parallel to the a-axis. An annular bright-field scanning transmission electron microscopy (ABF-STEM) was performed for the direct observation of the crystal structures. The ABF-STEM images displayed the contrasts with respect to every atomic position in spite of the highly distorted structure of BTO. We could evaluate the tilting and distortion of the [TiO6] octahedra relatively. Therefore, we directly observed the ferroelectric displacements of Bi and Ti ions.

  18. Counseling and directly observed medication for primary care buprenorphine/naloxone maintenance: A pilot study

    PubMed Central

    Moore, Brent A.; Barry, Declan T.; Sullivan, Lynn E.; O’Connor, Patrick G.; Cutter, Christopher J.; Schottenfeld, Richard S.; Fiellin, David A.

    2012-01-01

    Objectives Counseling and medication adherence can affect opioid agonist treatment outcomes. We investigated the impact of two counseling intensities and two medication dispensing methods in patients receiving buprenorphine (BUP) in primary care. Methods In a 12-week trial, patients were assigned to Physician Management (PM) with weekly BUP dispensing (n = 28) vs. PM and directly observed, thrice-weekly BUP and cognitive behavioral therapy (PM+DOT/CBT; n = 27) based on therapist availability. Fifteen minute PM visits were provided at entry, after induction and then monthly. CBT was weekly 45-minute sessions provided by trained therapists. Results Treatment groups differed on baseline characteristics of years of opioid use, history of detoxification from opioids, and opioid negative urines during induction. Analyses adjusting for baseline characteristics showed no significant differences between groups on retention or drug use based on self-report or urines. Patient satisfaction was high across conditions, indicating acceptability of CBT counseling with observed medication. The number of CBT sessions attended was significantly associated with improved outcome, and session attendance was associated with a greater abstinence the following week. Conclusions Although the current findings were non-significant, DOT plus individual CBT sessions was feasible and acceptable to patients. Additional research evaluating the independent effect of directly observed medication and CBT counseling is needed. PMID:22614936

  19. Photoacoustics of single laser-trapped nanodroplets for the direct observation of nanofocusing in aerosol photokinetics

    NASA Astrophysics Data System (ADS)

    Cremer, Johannes W.; Thaler, Klemens M.; Haisch, Christoph; Signorell, Ruth

    2016-03-01

    Photochemistry taking place in atmospheric aerosol droplets has a significant impact on the Earth's climate. Nanofocusing of electromagnetic radiation inside aerosols plays a crucial role in their absorption behaviour, since the radiation flux inside the droplet strongly affects the activation rate of photochemically active species. However, size-dependent nanofocusing effects in the photokinetics of small aerosols have escaped direct observation due to the inability to measure absorption signatures from single droplets. Here we show that photoacoustic measurements on optically trapped single nanodroplets provide a direct, broadly applicable method to measure absorption with attolitre sensitivity. We demonstrate for a model aerosol that the photolysis is accelerated by an order of magnitude in the sub-micron to micron size range, compared with larger droplets. The versatility of our technique promises broad applicability to absorption studies of aerosol particles, such as atmospheric aerosols where quantitative photokinetic data are critical for climate predictions.

  20. Photoacoustics of single laser-trapped nanodroplets for the direct observation of nanofocusing in aerosol photokinetics.

    PubMed

    Cremer, Johannes W; Thaler, Klemens M; Haisch, Christoph; Signorell, Ruth

    2016-01-01

    Photochemistry taking place in atmospheric aerosol droplets has a significant impact on the Earth's climate. Nanofocusing of electromagnetic radiation inside aerosols plays a crucial role in their absorption behaviour, since the radiation flux inside the droplet strongly affects the activation rate of photochemically active species. However, size-dependent nanofocusing effects in the photokinetics of small aerosols have escaped direct observation due to the inability to measure absorption signatures from single droplets. Here we show that photoacoustic measurements on optically trapped single nanodroplets provide a direct, broadly applicable method to measure absorption with attolitre sensitivity. We demonstrate for a model aerosol that the photolysis is accelerated by an order of magnitude in the sub-micron to micron size range, compared with larger droplets. The versatility of our technique promises broad applicability to absorption studies of aerosol particles, such as atmospheric aerosols where quantitative photokinetic data are critical for climate predictions. PMID:26979973

  1. Direct observation shows superposition and large scale flexibility within cytoplasmic dynein motors moving along microtubules

    PubMed Central

    Imai, Hiroshi; Shima, Tomohiro; Sutoh, Kazuo; Walker, Matthew L.; Knight, Peter J.; Kon, Takahide; Burgess, Stan A.

    2015-01-01

    Cytoplasmic dynein is a dimeric AAA+ motor protein that performs critical roles in eukaryotic cells by moving along microtubules using ATP. Here using cryo-electron microscopy we directly observe the structure of Dictyostelium discoideum dynein dimers on microtubules at near-physiological ATP concentrations. They display remarkable flexibility at a hinge close to the microtubule binding domain (the stalkhead) producing a wide range of head positions. About half the molecules have the two heads separated from one another, with both leading and trailing motors attached to the microtubule. The other half have the two heads and stalks closely superposed in a front-to-back arrangement of the AAA+ rings, suggesting specific contact between the heads. All stalks point towards the microtubule minus end. Mean stalk angles depend on the separation between their stalkheads, which allows estimation of inter-head tension. These findings provide a structural framework for understanding dynein's directionality and unusual stepping behaviour. PMID:26365535

  2. Direct assessment of groundwater vulnerability from single observations of multiple contaminants

    USGS Publications Warehouse

    Worrall, F.; Kolpin, D.W.

    2003-01-01

    Groundwater vulnerability is a central concept in pollution risk assessment, yet its estimation has been largely a matter of expert judgment. This work applies a method for the direct calculation of vulnerability from monitoring well observations of pesticide concentrations. The method has two major advantages: it is independent of the compounds being examined, and it has a direct probabilistic interpretation making it ideal for risk assessment. The methodology was applied to data from a groundwater monitoring program in the midwestern United States. The distribution of the vulnerabilities was skewed toward zero. Spatial distribution of the vulnerabilities shows them to be controlled by both regional and local factors. Methods are presented for estimating the necessary sample sizes for vulnerability studies. The further application of the approach developed in this study to understanding groundwater pollution is discussed.

  3. Photoacoustics of single laser-trapped nanodroplets for the direct observation of nanofocusing in aerosol photokinetics

    PubMed Central

    Cremer, Johannes W.; Thaler, Klemens M.; Haisch, Christoph; Signorell, Ruth

    2016-01-01

    Photochemistry taking place in atmospheric aerosol droplets has a significant impact on the Earth's climate. Nanofocusing of electromagnetic radiation inside aerosols plays a crucial role in their absorption behaviour, since the radiation flux inside the droplet strongly affects the activation rate of photochemically active species. However, size-dependent nanofocusing effects in the photokinetics of small aerosols have escaped direct observation due to the inability to measure absorption signatures from single droplets. Here we show that photoacoustic measurements on optically trapped single nanodroplets provide a direct, broadly applicable method to measure absorption with attolitre sensitivity. We demonstrate for a model aerosol that the photolysis is accelerated by an order of magnitude in the sub-micron to micron size range, compared with larger droplets. The versatility of our technique promises broad applicability to absorption studies of aerosol particles, such as atmospheric aerosols where quantitative photokinetic data are critical for climate predictions. PMID:26979973

  4. Direct observation of multistep energy transfer in LHCII with fifth-order 3D electronic spectroscopy

    NASA Astrophysics Data System (ADS)

    Zhang, Zhengyang; Lambrev, Petar H.; Wells, Kym L.; Garab, Győző; Tan, Howe-Siang

    2015-07-01

    During photosynthesis, sunlight is efficiently captured by light-harvesting complexes, and the excitation energy is then funneled towards the reaction centre. These photosynthetic excitation energy transfer (EET) pathways are complex and proceed in a multistep fashion. Ultrafast two-dimensional electronic spectroscopy (2DES) is an important tool to study EET processes in photosynthetic complexes. However, the multistep EET processes can only be indirectly inferred by correlating different cross peaks from a series of 2DES spectra. Here we directly observe multistep EET processes in LHCII using ultrafast fifth-order three-dimensional electronic spectroscopy (3DES). We measure cross peaks in 3DES spectra of LHCII that directly indicate energy transfer from excitons in the chlorophyll b (Chl b) manifold to the low-energy level chlorophyll a (Chl a) via mid-level Chl a energy states. This new spectroscopic technique allows scientists to move a step towards mapping the complete complex EET processes in photosynthetic systems.

  5. Direct observation of a highly spin-polarized organic spinterface at room temperature

    PubMed Central

    Djeghloul, F.; Ibrahim, F.; Cantoni, M.; Bowen, M.; Joly, L.; Boukari, S.; Ohresser, P.; Bertran, F.; Le Fèvre, P.; Thakur, P.; Scheurer, F.; Miyamachi, T.; Mattana, R.; Seneor, P.; Jaafar, A.; Rinaldi, C.; Javaid, S.; Arabski, J.; Kappler, J. -P; Wulfhekel, W.; Brookes, N. B.; Bertacco, R.; Taleb-Ibrahimi, A.; Alouani, M.; Beaurepaire, E.; Weber, W.

    2013-01-01

    Organic semiconductors constitute promising candidates toward large-scale electronic circuits that are entirely spintronics-driven. Toward this goal, tunneling magnetoresistance values above 300% at low temperature suggested the presence of highly spin-polarized device interfaces. However, such spinterfaces have not been observed directly, let alone at room temperature. Thanks to experiments and theory on the model spinterface between phthalocyanine molecules and a Co single crystal surface, we clearly evidence a highly efficient spinterface. Spin-polarised direct and inverse photoemission experiments reveal a high degree of spin polarisation at room temperature at this interface. We measured a magnetic moment on the molecule's nitrogen π orbitals, which substantiates an ab-initio theoretical description of highly spin-polarised charge conduction across the interface due to differing spinterface formation mechanisms in each spin channel. We propose, through this example, a recipe to engineer simple organic-inorganic interfaces with remarkable spintronic properties that can endure well above room temperature. PMID:23412079

  6. Direct observation shows superposition and large scale flexibility within cytoplasmic dynein motors moving along microtubules

    NASA Astrophysics Data System (ADS)

    Imai, Hiroshi; Shima, Tomohiro; Sutoh, Kazuo; Walker, Matthew L.; Knight, Peter J.; Kon, Takahide; Burgess, Stan A.

    2015-09-01

    Cytoplasmic dynein is a dimeric AAA+ motor protein that performs critical roles in eukaryotic cells by moving along microtubules using ATP. Here using cryo-electron microscopy we directly observe the structure of Dictyostelium discoideum dynein dimers on microtubules at near-physiological ATP concentrations. They display remarkable flexibility at a hinge close to the microtubule binding domain (the stalkhead) producing a wide range of head positions. About half the molecules have the two heads separated from one another, with both leading and trailing motors attached to the microtubule. The other half have the two heads and stalks closely superposed in a front-to-back arrangement of the AAA+ rings, suggesting specific contact between the heads. All stalks point towards the microtubule minus end. Mean stalk angles depend on the separation between their stalkheads, which allows estimation of inter-head tension. These findings provide a structural framework for understanding dynein's directionality and unusual stepping behaviour.

  7. Real-space indicators for chemical bonding. Experimental and theoretical electron density studies of four deltahedral boranes.

    PubMed

    Mebs, Stefan; Kalinowski, Roman; Grabowsky, Simon; Förster, Diana; Kickbusch, Rainer; Justus, Eugen; Morgenroth, Wolfgang; Paulmann, Carsten; Luger, Peter; Gabel, Detlef; Lentz, Dieter

    2011-01-01

    In an approach combining high-resolution X-ray diffraction at low temperatures with density functional theory calculations, two closo-borates, B(12)H(12)(2-) (1) and B(10)H(10)(2-) (2), and two arachno-boranes, B(10)H(12)L(2) [L = amine (3) or acetonitrile (4)], were analyzed by means of the atoms-in-molecules (AIM) theory and electron localizability indicator (ELI-D). The two-electron three-center (2e3c) bonds of the borane cages are investigated with the focus on real-space indicators for chemical bonding and electron delocalization. In compound 2, only two of the three expected bond critical points (bcp's) are found. However, a weakly populated ELI-D basin is found for this pair of adjacent B atoms and the delocalization index and the Source contributions are on the same order of magnitude as those for the other pairs. The opposite situation is found in the arachno-boranes, where no ELI-D basins are found for two types of B-B pairs, which, in turn, exhibit a bcp. However, again the delocalization index is on the same order of magnitude for this bonding interaction. The results show that an unambiguous real-space criterion for chemical bonding is not given yet for this class of compounds. The arachno-boranes carry a special B-B bond, which is the edge of the crown-shaped molecule. This bond is very long and extremely curved inward the B-B-B ring. Nevertheless, the corresponding bond ellipticity is quite small and the ELI-D value at the attractor position of the disynaptic valence basin is remarkably larger than those for all other B-B valence basins. Furthermore, the value of the ED is large in relation to the B-B bond length, so that only this bond type does not follow a linear relationship of the ED value at the bcp versus B-B bond distances, which is found for all other B-B bcp's. The results indicate that both 2e2c and 2e3c bonding play a distinct role in borane chemistry. PMID:21114266

  8. Direct Observation of a Localized Magnetic Soliton in a Spin-Transfer Nanocontact.

    PubMed

    Backes, D; Macià, F; Bonetti, S; Kukreja, R; Ohldag, H; Kent, A D

    2015-09-18

    We report the direct observation of a localized magnetic soliton in a spin-transfer nanocontact using scanning transmission x-ray microscopy. Experiments are conducted on a lithographically defined 150 nm diameter nanocontact to an ultrathin ferromagnetic multilayer with perpendicular magnetic anisotropy. Element-resolved x-ray magnetic circular dichroism images show an abrupt onset of a magnetic soliton excitation localized beneath the nanocontact at a threshold current. However, the amplitude of the excitation ≃25° at the contact center is far less than that predicted (⪅180°), showing that the spin dynamics is not described by existing models. PMID:26431016

  9. Direct observation of resonant scattering phase shifts and their energy dependence.

    PubMed

    Gensemer, Stephen D; Martin-Wells, Ross B; Bennett, Aaron W; Gibble, Kurt

    2012-12-28

    We scan the collision energy of two clouds of cesium atoms between 12 and 50  μK in an atomic fountain clock. By directly detecting the difference of s-wave scattering phase shifts, we observe a rapid variation of a scattering phase shift through a series of Feshbach resonances. At the energies we use, resonances that overlap at threshold become resolved. Our statistical phase uncertainty of 8 mrad can be improved in future precision measurements of Feshbach resonances to accurately determine the Cs-Cs interactions, which may provide stringent limits on the time variation of fundamental constants.

  10. Direct CW - NMR observation of forbidden transitions at double larmor frequency in hydrogen

    NASA Astrophysics Data System (ADS)

    Skrbek, L.; Sebek, J.; Safrata, R. S.

    1990-08-01

    By means of the classical transverse continuous wave nuclear magnetic resonance (NMR) the forbidden transitions at double Larmor frequency for hydrogen have been observed. The NMR spectra have been measured directly by scanning the external magnetic field up to 10 mT at temperatures about 30 mK. The intensity of the forbidden transition at double Larmor frequency I 2 is of the same order of magnitude as the intensity I 1 of the main Larmor line under these conditions. The intensity ratio I 1/I 2 depends on the external magnetic field in accordance with Cheng theory and NMR-SQUID measurements of Kohl and coworkers.

  11. Direct observation of voids in the vacancy excess region of ion bombarded silicon

    NASA Astrophysics Data System (ADS)

    Williams, J. S.; Conway, M. J.; Williams, B. C.; Wong-Leung, J.

    2001-05-01

    The results reported in this letter indicate that the spatial separation of the vacancy and interstitial excesses which result from ion bombardment gives rise to stable voids upon annealing at 850 °C even for implants where the projected ion range is only of the order of a few thousand Ångstrom. Such voids have been observed directly by transmission electron microscopy. Furthermore, in cases where both voids and interstitial-based defects are present at different depths, it is found that Au has a strong preference for decorating void surfaces and hence Au can, indeed, be used as a selective detector of open volume defects in Si.

  12. Direct Observation of the Injection Dynamics of a Laser Wakefield Accelerator Using Few-Femtosecond Shadowgraphy.

    PubMed

    Sävert, A; Mangles, S P D; Schnell, M; Siminos, E; Cole, J M; Leier, M; Reuter, M; Schwab, M B; Möller, M; Poder, K; Jäckel, O; Paulus, G G; Spielmann, C; Skupin, S; Najmudin, Z; Kaluza, M C

    2015-07-31

    We present few-femtosecond shadowgraphic snapshots taken during the nonlinear evolution of the plasma wave in a laser wakefield accelerator with transverse synchronized few-cycle probe pulses. These snapshots can be directly associated with the electron density distribution within the plasma wave and give quantitative information about its size and shape. Our results show that self-injection of electrons into the first plasma-wave period is induced by a lengthening of the first plasma period. Three-dimensional particle-in-cell simulations support our observations. PMID:26274425

  13. Direct Observation of the Injection Dynamics of a Laser Wakefield Accelerator Using Few-Femtosecond Shadowgraphy.

    PubMed

    Sävert, A; Mangles, S P D; Schnell, M; Siminos, E; Cole, J M; Leier, M; Reuter, M; Schwab, M B; Möller, M; Poder, K; Jäckel, O; Paulus, G G; Spielmann, C; Skupin, S; Najmudin, Z; Kaluza, M C

    2015-07-31

    We present few-femtosecond shadowgraphic snapshots taken during the nonlinear evolution of the plasma wave in a laser wakefield accelerator with transverse synchronized few-cycle probe pulses. These snapshots can be directly associated with the electron density distribution within the plasma wave and give quantitative information about its size and shape. Our results show that self-injection of electrons into the first plasma-wave period is induced by a lengthening of the first plasma period. Three-dimensional particle-in-cell simulations support our observations.

  14. Diversity of sub-bandgap states in lead-sulfide nanocrystals: real-space spectroscopy and mapping at the atomic-scale.

    PubMed

    Gervasi, Christian F; Kislitsyn, Dmitry A; Allen, Thomas L; Hackley, Jason D; Maruyama, Ryuichiro; Nazin, George V

    2015-12-14

    Colloidal semiconductor nanocrystals have emerged as a promising class of technological materials with optoelectronic properties controllable through quantum-confinement effects. Despite recent successes in this field, an important factor that remains difficult to control is the impact of the nanocrystal surface structure on the photophysics and electron transport in nanocrystal-based materials. In particular, the presence of surface defects and irregularities can result in the formation of localized sub-bandgap states that can dramatically affect the dynamics of charge carriers and electronic excitations. Here we use Scanning Tunneling Spectroscopy (STS) to investigate, in real space, sub-bandgap states in individual ligand-free PbS nanocrystals. In the majority of studied PbS nanocrystals, spatial mapping of electronic density of states with STS shows atomic-scale variations attributable to the presence of surface reconstructions. STS spectra show that the presence of surface reconstructions results in formation of surface-bound sub-bandgap electronic states. The nature of the surface reconstruction varies depending on the surface stoichiometry, with lead-rich surfaces producing unoccupied sub-bandgap states, and sulfur-rich areas producing occupied sub-bandgap states. Highly off-stoichiometric areas produce both occupied and unoccupied states showing dramatically reduced bandgaps. Different reconstruction patterns associated with specific crystallographic directions are also found for different nanocrystals. This study provides insight into the mechanisms of sub-bandgap state formation that, in a modified form, are likely to be applicable to ligand-passivated nanocrystal surfaces, where steric hindrance between ligands can result in under-coordination of surface atoms.

  15. Direct observation of TALE protein dynamics reveals a two-state search mechanism.

    PubMed

    Cuculis, Luke; Abil, Zhanar; Zhao, Huimin; Schroeder, Charles M

    2015-06-01

    Transcription activator-like effector (TALE) proteins are a class of programmable DNA-binding proteins for which the fundamental mechanisms governing the search process are not fully understood. Here we use single-molecule techniques to directly observe TALE search dynamics along DNA templates. We find that TALE proteins are capable of rapid diffusion along DNA using a combination of sliding and hopping behaviour, which suggests that the TALE search process is governed in part by facilitated diffusion. We also observe that TALE proteins exhibit two distinct modes of action during the search process-a search state and a recognition state-facilitated by different subdomains in monomeric TALE proteins. Using TALE truncation mutants, we further demonstrate that the N-terminal region of TALEs is required for the initial non-specific binding and subsequent rapid search along DNA, whereas the central repeat domain is required for transitioning into the site-specific recognition state.

  16. Direct Observation of a Gas Molecule (H2, Ar) Swallowed by C60

    SciTech Connect

    Sawa, H.; Kakiuchi, T.; Wakabayashi, Y.; Murata, Y.; Murata, M.; Komatsu, K.; Yakigaya, K.; Takagi, H.; Dragoe, N.

    2007-01-19

    Various types of endohedral fullerene complexes are known to date. The well known metallofullerenes are generally produced by arc-discharge method, but the use of such extremely drastic conditions is apparently not suitable for encapsulation of unstable molecules or gases. We recently succeeded in incorporation of a H2 molecule or an Ar atom in 100% into a C60. In order to observe the endohedral gas molecule directly, the X-ray diffraction analysis using synchrotron radiation were carried out. We observed a gas molecule encapsulated in each fullerene cage using structure analysis and the maximum entropy method. These gas molecules are floating inside of the hollow cavities and are completely isolated from the outside.

  17. Direct self-repairing control for a helicopter via quantum multi-model and disturbance observer

    NASA Astrophysics Data System (ADS)

    Chen, Fuyang; Cai, Ling; Jiang, Bin; Tao, Gang

    2016-02-01

    In this paper, a new direct self-repairing control scheme is developed for a helicopter flight control system with unknown actuator faults and external disturbance. The design of multi-model-based adaptive control is used to accommodate the faulty system under different fault conditions. By appropriate switching based on quantum information technique, the system can be converted to the best model and the corresponding controller. Asymptotic model following performance and system stability is guaranteed. A disturbance observer is introduced to observe the disturbance of the system, which can produce corresponding control signals according to the disturbance. The results including a numerical simulation and a semi-physical verification demonstrate the effectiveness of the proposed self-repairing control approach for the helicopter flight control system.

  18. Direct coupling of photonic modes and surface plasmon polaritons observed in 2-photon PEEM.

    PubMed

    Word, Robert C; Fitzgerald, Joseph P S; Könenkamp, Rolf

    2013-12-16

    We report the direct microscopic observation of optical energy transfer from guided photonic modes in an indium tin oxide (ITO) thin film to surface plasmon polaritons (SPP) at the surfaces of a single crystalline gold platelet. The photonic and SPP modes appear as an interference pattern in the photoelectron emission yield across the surface of the specimen. We explore the momentum match between the photonic and SPP modes in terms of simple waveguide theory and the three-layer slab model for bound SPP modes of thin metal films. We show that because the gold is thin (30-40 nm), two SPP modes exist and that momentum of the spatially confined asymmetric field mode coincides with the dominant mode of the ITO waveguide. The results demonstrate that photoemission electron microscopy (PEEM) can be an important tool for the observation of photonic to SPP interactions in the study of integrated photonic circuits. PMID:24514628

  19. Direct observation of frictional contacts: New insights for state-dependent properties

    USGS Publications Warehouse

    Dieterich, J.H.; Kilgore, B.D.

    1994-01-01

    Rocks and many other materials display a rather complicated, but characteristic, dependence of friction on sliding history. These effects are well-described by empirical rate- and state-dependent constitutive formulations which have been utilized for analysis of fault slip and earthquake processes. We present a procedure for direct quantitative microscopic observation of frictional contacts during slip. The observations reveal that frictional state dependence represents an increase of contact area with contact age. Transient changes of sliding resistance correlate with changes in contact area and arise from shifts of contact population age. Displacement-dependent replacement of contact populations is shown to cause the diagnostic evolution of friction over a characteristic sliding distance that occurs whenever slip begins or sliding conditions change. ?? 1994 Birkha??user Verlag.

  20. Interactions between C and Cu atoms in single-layer graphene: direct observation and modelling.

    PubMed

    Kano, Emi; Hashimoto, Ayako; Kaneko, Tomoaki; Tajima, Nobuo; Ohno, Takahisa; Takeguchi, Masaki

    2016-01-01

    Metal doping into the graphene lattice has been studied recently to develop novel nanoelectronic devices and to gain an understanding of the catalytic activities of metals in nanocarbon structures. Here we report the direct observation of interactions between Cu atoms and single-layer graphene by transmission electron microscopy. We document stable configurations of Cu atoms in the graphene sheet and unique transformations of graphene promoted by Cu atoms. First-principles calculations based on density functional theory reveal a reduction of energy barrier that caused rotation of C-C bonds near Cu atoms. We discuss two driving forces, electron irradiation and in situ heating, and conclude that the observed transformations were mainly promoted by electron irradiation. Our results suggest that individual Cu atoms can promote reconstruction of single-layer graphene.

  1. Direct observation of an abrupt insulator-to-metal transition in dense liquid deuterium

    NASA Astrophysics Data System (ADS)

    Knudson, M. D.; Desjarlais, M. P.; Becker, A.; Lemke, R. W.; Cochrane, K. R.; Savage, M. E.; Bliss, D. E.; Mattsson, T. R.; Redmer, R.

    2015-06-01

    Eighty years ago, it was proposed that solid hydrogen would become metallic at sufficiently high density. Despite numerous investigations, this transition has not yet been experimentally observed. More recently, there has been much interest in the analog of this predicted metallic transition in the dense liquid, due to its relevance to planetary science. Here, we show direct observation of an abrupt insulator-to-metal transition in dense liquid deuterium. Experimental determination of the location of this transition provides a much-needed benchmark for theory and may constrain the region of hydrogen-helium immiscibility and the boundary-layer pressure in standard models of the internal structure of gas-giant planets.

  2. Direct observation of TALE protein dynamics reveals a two-state search mechanism

    PubMed Central

    Cuculis, Luke; Abil, Zhanar; Zhao, Huimin; Schroeder, Charles M.

    2015-01-01

    Transcription activator-like effector (TALE) proteins are a class of programmable DNA-binding proteins for which the fundamental mechanisms governing the search process are not fully understood. Here we use single-molecule techniques to directly observe TALE search dynamics along DNA templates. We find that TALE proteins are capable of rapid diffusion along DNA using a combination of sliding and hopping behaviour, which suggests that the TALE search process is governed in part by facilitated diffusion. We also observe that TALE proteins exhibit two distinct modes of action during the search process—a search state and a recognition state—facilitated by different subdomains in monomeric TALE proteins. Using TALE truncation mutants, we further demonstrate that the N-terminal region of TALEs is required for the initial non-specific binding and subsequent rapid search along DNA, whereas the central repeat domain is required for transitioning into the site-specific recognition state. PMID:26027871

  3. Direct observation of transition paths during the folding of proteins and nucleic acids.

    PubMed

    Neupane, Krishna; Foster, Daniel A N; Dee, Derek R; Yu, Hao; Wang, Feng; Woodside, Michael T

    2016-04-01

    Transition paths, the fleeting trajectories through the transition states that dominate the dynamics of biomolecular folding reactions, encapsulate the critical information about how structure forms. Owing to their brief duration, however, they have not previously been observed directly. We measured transition paths for both nucleic acid and protein folding, using optical tweezers to observe the microscopic diffusive motion of single molecules traversing energy barriers. The average transit times and the shapes of the transit-time distributions agreed well with theoretical expectations for motion over the one-dimensional energy landscapes reconstructed for the same molecules, validating the physical theory of folding reactions. These measurements provide a first look at the critical microscopic events that occur during folding, opening exciting new avenues for investigating folding phenomena. PMID:27124461

  4. Direct observation of stochastic domain-wall depinning in magnetic nanowires

    SciTech Connect

    Im, Mi-Young; Bocklage, Lars; Fischer, Peter; Meier, Guido

    2008-11-01

    The stochastic field-driven depinning of a domain wall pinned at a notch in a magnetic nanowire is directly observed using magnetic X-ray microscopy with high lateral resolution down to 15 nm. The depinning-field distribution in Ni{sub 80}Fe{sub 20} nanowires considerably depends on the wire width and the notch depth. The difference in the multiplicity of domain-wall types generated in the vicinity of a notch is responsible for the observed dependence of the stochastic nature of the domain wall depinning field on the wire width and the notch depth. Thus the random nature of the domain wall depinning process is controllable by an appropriate design of the nanowire.

  5. Direct observation of TALE protein dynamics reveals a two-state search mechanism

    NASA Astrophysics Data System (ADS)

    Cuculis, Luke; Abil, Zhanar; Zhao, Huimin; Schroeder, Charles M.

    2015-06-01

    Transcription activator-like effector (TALE) proteins are a class of programmable DNA-binding proteins for which the fundamental mechanisms governing the search process are not fully understood. Here we use single-molecule techniques to directly observe TALE search dynamics along DNA templates. We find that TALE proteins are capable of rapid diffusion along DNA using a combination of sliding and hopping behaviour, which suggests that the TALE search process is governed in part by facilitated diffusion. We also observe that TALE proteins exhibit two distinct modes of action during the search process--a search state and a recognition state--facilitated by different subdomains in monomeric TALE proteins. Using TALE truncation mutants, we further demonstrate that the N-terminal region of TALEs is required for the initial non-specific binding and subsequent rapid search along DNA, whereas the central repeat domain is required for transitioning into the site-specific recognition state.

  6. Direct observation of a long-lived single-atom catalyst chiseling atomic structures in graphene.

    PubMed

    Wang, Wei Li; Santos, Elton J G; Jiang, Bin; Cubuk, Ekin Dogus; Ophus, Colin; Centeno, Alba; Pesquera, Amaia; Zurutuza, Amaia; Ciston, Jim; Westervelt, Robert; Kaxiras, Efthimios

    2014-02-12

    Fabricating stable functional devices at the atomic scale is an ultimate goal of nanotechnology. In biological processes, such high-precision operations are accomplished by enzymes. A counterpart molecular catalyst that binds to a solid-state substrate would be highly desirable. Here, we report the direct observation of single Si adatoms catalyzing the dissociation of carbon atoms from graphene in an aberration-corrected high-resolution transmission electron microscope (HRTEM). The single Si atom provides a catalytic wedge for energetic electrons to chisel off the graphene lattice, atom by atom, while the Si atom itself is not consumed. The products of the chiseling process are atomic-scale features including graphene pores and clean edges. Our experimental observations and first-principles calculations demonstrated the dynamics, stability, and selectivity of such a single-atom chisel, which opens up the possibility of fabricating certain stable molecular devices by precise modification of materials at the atomic scale.

  7. Direct Observation of the Three-State Folding of a Single Protein Molecule

    NASA Astrophysics Data System (ADS)

    Cecconi, Ciro; Shank, Elizabeth A.; Bustamante, Carlos; Marqusee, Susan

    2005-09-01

    We used force-measuring optical tweezers to induce complete mechanical unfolding and refolding of individual Escherichia coli ribonuclease H (RNase H) molecules. The protein unfolds in a two-state manner and refolds through an intermediate that correlates with the transient molten globule-like intermediate observed in bulk studies. This intermediate displays unusual mechanical compliance and unfolds at substantially lower forces than the native state. In a narrow range of forces, the molecule hops between the unfolded and intermediate states in real time. Occasionally, hopping was observed to stop as the molecule crossed the folding barrier directly from the intermediate, demonstrating that the intermediate is on-pathway. These studies allow us to map the energy landscape of RNase H.

  8. Interactions between C and Cu atoms in single-layer graphene: direct observation and modelling

    NASA Astrophysics Data System (ADS)

    Kano, Emi; Hashimoto, Ayako; Kaneko, Tomoaki; Tajima, Nobuo; Ohno, Takahisa; Takeguchi, Masaki

    2015-12-01

    Metal doping into the graphene lattice has been studied recently to develop novel nanoelectronic devices and to gain an understanding of the catalytic activities of metals in nanocarbon structures. Here we report the direct observation of interactions between Cu atoms and single-layer graphene by transmission electron microscopy. We document stable configurations of Cu atoms in the graphene sheet and unique transformations of graphene promoted by Cu atoms. First-principles calculations based on density functional theory reveal a reduction of energy barrier that caused rotation of C-C bonds near Cu atoms. We discuss two driving forces, electron irradiation and in situ heating, and conclude that the observed transformations were mainly promoted by electron irradiation. Our results suggest that individual Cu atoms can promote reconstruction of single-layer graphene.Metal doping into the graphene lattice has been studied recently to develop novel nanoelectronic devices and to gain an understanding of the catalytic activities of metals in nanocarbon structures. Here we report the direct observation of interactions between Cu atoms and single-layer graphene by transmission electron microscopy. We document stable configurations of Cu atoms in the graphene sheet and unique transformations of graphene promoted by Cu atoms. First-principles calculations based on density functional theory reveal a reduction of energy barrier that caused rotation of C-C bonds near Cu atoms. We discuss two driving forces, electron irradiation and in situ heating, and conclude that the observed transformations were mainly promoted by electron irradiation. Our results suggest that individual Cu atoms can promote reconstruction of single-layer graphene. Electronic supplementary information (ESI) available: Three TEM movies, additional TEM data corresponding to movies, calculated models, and lifetime results. See DOI: 10.1039/c5nr05913e

  9. Performing Gram stain directly on catheter tips: assessment of the quality of the observation process.

    PubMed

    Guembe, M; Pérez-Granda, M J; Rivera, M L; Martín-Rabadán, P; Bouza, E

    2015-06-01

    A previous study performed in our institution showed that catheter tip (CT) staining by combining acridine orange and Gram stain (GS) before culture anticipated catheter colonization with exhaustive and careful observation by a highly trained technician. Our objective was to assess the validity values of GS without acridine orange on an external smear of CT for predicting catheter colonization and catheter-related bloodstream infection (C-RBSI). We compared different periods of observation and the results of two technicians with different levels of professional experience. Over a 5-month period, the roll-plate technique was preceded by direct GS of all CTs sent to the microbiology laboratory. The reading was taken at ×100 by two observers with different skill levels. Each observer performed a routine examination (3 min along three longitudinal lines) and an exhaustive examination (5 min along five longitudinal lines). The presence of at least one cell was considered positive. All slides were read before culture results were known. We included a total of 271 CTs from 209 patients. The prevalence of catheter colonization and C-RBSI was 16.2 % and 5.1 %, respectively. Routine and exhaustive examinations revealed only 29.5 % and 40.9 % of colonized catheters, respectively (p < 0.001). In contrast, they revealed high negative predictive values for C-RBSI (96.5 % and 96.3 %, respectively). Our study shows that the yield of GS performed directly on CTs is greater when staining is performed exhaustively. However, the decision to implement this approach in daily routine will depend on the prevalence rate of catheter colonization at each institution.

  10. A multimethod investigation including direct observation of 3751 patient visits to 120 dental offices

    PubMed Central

    Wotman, Stephen; Demko, Catherine A; Victoroff, Kristin; Sudano, Joseph J; Lalumandier, James A

    2010-01-01

    This report defines verbal interactions between practitioners and patients as core activities of dental practice. Trained teams spent four days in 120 Ohio dental practices observing 3751 patient encounters with dentists and hygienists. Direct observation of practice characteristics, procedures performed, and how procedure and nonprocedure time was utilized during patient visits was recorded using a modified Davis Observation Code that classified patient contact time into 24 behavioral categories. Dentist, hygienist, and patient characteristics were gathered by questionnaire. The most common nonprocedure behaviors observed for dentists were chatting, evaluation feedback, history taking, and answering patient questions. Hygienists added preventive counseling. We distinguish between preventive procedures and counseling in actual dental offices that are members of a practice-based research network. Almost a third of the dentist’s and half of the hygienist’s patient contact time is utilized for nonprocedure behaviors during patient encounters. These interactions may be linked to patient and practitioner satisfaction and effectiveness of self-care instruction. PMID:23662080

  11. Ballistic graphene nanoribbon metal-oxide-semiconductor field-effect transistors: A full real-space quantum transport simulation

    NASA Astrophysics Data System (ADS)

    Liang, Gengchiau; Neophytou, Neophytos; Lundstrom, Mark S.; Nikonov, Dmitri E.

    2007-09-01

    A real-space quantum transport simulator for graphene nanoribbon (GNR) metal-oxide-semiconductor field-effect transistors (MOSFETs) has been developed and used to examine the ballistic performance of GNR MOSFETs. This study focuses on the impact of quantum effects on these devices and on the effect of different type of contacts. We found that two-dimensional (2D) semi-infinite graphene contacts produce metal-induced-gap states (MIGS) in the GNR channel. These states enhance quantum tunneling, particularly in short channel devices, they cause Fermi level pinning and degrade the device performance in both the ON-state and OFF-state. Devices with infinitely long contacts having the same width as the channel do not indicate MIGS. Even without MIGS quantum tunneling effects such as band-to-band tunneling still play an important role in the device characteristics and dominate the OFF-state current. This is accurately captured in our nonequilibrium Greens' function quantum simulations. We show that both narrow (1.4 nm width) and wider (1.8 nm width) GNRs with 12.5 nm channel length have the potential to outperform ultrascaled Si devices in terms of drive current capabilities and electrostatic control. Although their subthreshold swings under forward bias are better than in Si transistors, tunneling currents are important and prevent the achievement of the theoretical limit of 60 mV/dec.

  12. Fourth order real space solver for the time-dependent Schrödinger equation with singular Coulomb potential

    NASA Astrophysics Data System (ADS)

    Majorosi, Szilárd; Czirják, Attila

    2016-11-01

    We present a novel numerical method and algorithm for the solution of the 3D axially symmetric time-dependent Schrödinger equation in cylindrical coordinates, involving singular Coulomb potential terms besides a smooth time-dependent potential. We use fourth order finite difference real space discretization, with special formulae for the arising Neumann and Robin boundary conditions along the symmetry axis. Our propagation algorithm is based on merging the method of the split-operator approximation of the exponential operator with the implicit equations of second order cylindrical 2D Crank-Nicolson scheme. We call this method hybrid splitting scheme because it inherits both the speed of the split step finite difference schemes and the robustness of the full Crank-Nicolson scheme. Based on a thorough error analysis, we verified both the fourth order accuracy of the spatial discretization in the optimal spatial step size range, and the fourth order scaling with the time step in the case of proper high order expressions of the split-operator. We demonstrate the performance and high accuracy of our hybrid splitting scheme by simulating optical tunneling from a hydrogen atom due to a few-cycle laser pulse with linear polarization.

  13. Real-space pseudopotential study of vibrational properties and Raman spectra in Si-Ge core-shell nanocrystals.

    PubMed

    Bobbitt, N Scott; Chelikowsky, James R

    2016-03-28

    We examine the vibrational properties and Raman spectra of Si-Ge core-shell nanostructures using real-space pseudopotentials constructed within density functional theory. Our method uses no empirical parameters, unlike many popular methods for predicting Raman spectra for nanocrystals. We find the dominant features of the Raman spectrum for the Si-Ge core-shell structure to be a superposition of the Raman spectra of the Ge and Si nanocrystals with optical peaks around 300 and 500 cm(-1), respectively. We also find a Si-Ge "interface" peak at 400 cm(-1). The Ge shell causes the Si core to expand from the equilibrium structure. This strain induces significant redshift in the Si contribution to the vibrational and Raman spectra, while the Ge shell is largely unstrained and does not exhibit this shift. We find that the ratio of peak heights is strongly related to the relative size of the core and shell regions. This finding suggests that Raman spectroscopy may be used to characterize the size of the core and shell in these structures. PMID:27036430

  14. Ab initio phasing by molecular averaging in real space with new criteria: application to structure determination of a betanodavirus.

    PubMed

    Yoshimura, Masato; Chen, Nai Chi; Guan, Hong Hsiang; Chuankhayan, Phimonphan; Lin, Chien Chih; Nakagawa, Atsushi; Chen, Chun Jung

    2016-07-01

    Molecular averaging, including noncrystallographic symmetry (NCS) averaging, is a powerful method for ab initio phase determination and phase improvement. Applications of the cross-crystal averaging (CCA) method have been shown to be effective for phase improvement after initial phasing by molecular replacement, isomorphous replacement, anomalous dispersion or combinations of these methods. Here, a two-step process for phase determination in the X-ray structural analysis of a new coat protein from a betanodavirus, Grouper nervous necrosis virus, is described in detail. The first step is ab initio structure determination of the T = 3 icosahedral virus-like particle using NCS averaging (NCSA). The second step involves structure determination of the protrusion domain of the viral molecule using cross-crystal averaging. In this method, molecular averaging and solvent flattening constrain the electron density in real space. To quantify these constraints, a new, simple and general indicator, free fraction (ff), is introduced, where ff is defined as the ratio of the volume of the electron density that is freely changed to the total volume of the crystal unit cell. This indicator is useful and effective to evaluate the strengths of both NCSA and CCA. Under the condition that a mask (envelope) covers the target molecule well, an ff value of less than 0.1, as a new rule of thumb, gives sufficient phasing power for the successful construction of new structures. PMID:27377380

  15. Many-body localization: construction of the emergent local conserved operators via block real-space renormalization

    NASA Astrophysics Data System (ADS)

    Monthus, Cécile

    2016-03-01

    A fully many-body localized (FMBL) quantum disordered system is characterized by the emergence of an extensive number of local conserved operators that prevents the relaxation towards thermal equilibrium. These local conserved operators can be seen as the building blocks of the whole set of eigenstates. In this paper, we propose to construct them explicitly via block real-space renormalization. The principle is that each renormalization group step diagonalizes the smallest remaining blocks and produces a conserved operator for each block. The final output for a chain of N spins is a hierarchical organization of the N conserved operators with ≤ft(\\frac{\\ln N}{\\ln 2}\\right) layers. The system size nature of the conserved operators of the top layers is necessary to describe the possible long-range order of the excited eigenstates and the possible critical points between different FMBL phases. We discuss the similarities and the differences with the strong disorder RSRG-X method that generates the whole set of the 2 N eigenstates via a binary tree of N layers. The approach is applied to the long-range quantum spin-glass Ising model, where the constructed excited eigenstates are found to be exactly like ground states in another disorder realization, so that they can be either in the paramagnetic phase, in the spin-glass phase or critical.

  16. Using NASA Data in the Classroom: Promoting STEM Learning in Formal Education using Real Space Science Data

    NASA Astrophysics Data System (ADS)

    Lawton, B.; Hemenway, M. K.; Mendez, B.; Odenwald, S.

    2013-04-01

    Among NASA's major education goals is the training of students in the Science, Technology, Engineering, and Math (STEM) disciplines. The use of real data, from some of the most sophisticated observatories in the world, provides formal educators the opportunity to teach their students real-world applications of the STEM subjects. Combining real space science data with lessons aimed at meeting state and national education standards provides a memorable educational experience that students can build upon throughout their academic careers. Many of our colleagues have adopted the use of real data in their education and public outreach (EPO) programs. There are challenges in creating resources using real data for classroom use that include, but are not limited to, accessibility to computers/Internet and proper instruction. Understanding and sharing these difficulties and best practices with the larger EPO community is critical to the development of future resources. In this session, we highlight three examples of how NASA data is being utilized in the classroom: the Galaxies and Cosmos Explorer Tool (GCET) that utilizes real Hubble Space Telescope data; the computer image-analysis resources utilized by the NASA WISE infrared mission; and the space science derived math applications from SpaceMath@NASA featuring the Chandra and Kepler space telescopes. Challenges and successes are highlighted for these projects. We also facilitate small-group discussions that focus on additional benefits and challenges of using real data in the formal education environment. The report-outs from those discussions are given here.

  17. Tubular crystals and helical arrays: structural determination of HIV-1 capsid assemblies using iterative helical real-space reconstruction.

    PubMed

    Zhang, Peijun; Meng, Xin; Zhao, Gongpu

    2013-01-01

    Helical structures are important in many different life forms and are well-suited for structural studies by cryo-EM. A unique feature of helical objects is that a single projection image contains all the views needed to perform a three-dimensional (3D) crystallographic reconstruction. Here, we use HIV-1 capsid assemblies to illustrate the detailed approaches to obtain 3D density maps from helical objects. Mature HIV-1 particles contain a conical- or tubular-shaped capsid that encloses the viral RNA genome and performs essential functions in the virus life cycle. The capsid is composed of capsid protein (CA) oligomers which are helically arranged on the surface. The N-terminal domain (NTD) of CA is connected to its C-terminal domain (CTD) through a flexible hinge. Structural analysis of two- and three-dimensional crystals provided molecular models of the capsid protein (CA) and its oligomer forms. We determined the 3D density map of helically assembled HIV-1 CA hexamers at 16 Å resolution using an iterative helical real-space reconstruction method. Docking of atomic models of CA-NTD and CA-CTD dimer into the electron density map indicated that the CTD dimer interface is retained in the assembled CA. Furthermore, molecular docking revealed an additional, novel CTD trimer interface.

  18. Ab initio phasing by molecular averaging in real space with new criteria: application to structure determination of a betanodavirus

    PubMed Central

    Yoshimura, Masato; Chen, Nai-Chi; Guan, Hong-Hsiang; Chuankhayan, Phimonphan; Lin, Chien-Chih; Nakagawa, Atsushi; Chen, Chun-Jung

    2016-01-01

    Molecular averaging, including noncrystallographic symmetry (NCS) averaging, is a powerful method for ab initio phase determination and phase improvement. Applications of the cross-crystal averaging (CCA) method have been shown to be effective for phase improvement after initial phasing by molecular replacement, isomorphous replacement, anomalous dispersion or combinations of these methods. Here, a two-step process for phase determination in the X-ray structural analysis of a new coat protein from a betanodavirus, Grouper nervous necrosis virus, is described in detail. The first step is ab initio structure determination of the T = 3 icosahedral virus-like particle using NCS averaging (NCSA). The second step involves structure determination of the protrusion domain of the viral molecule using cross-crystal averaging. In this method, molecular averaging and solvent flattening constrain the electron density in real space. To quantify these constraints, a new, simple and general indicator, free fraction (ff), is introduced, where ff is defined as the ratio of the volume of the electron density that is freely changed to the total volume of the crystal unit cell. This indicator is useful and effective to evaluate the strengths of both NCSA and CCA. Under the condition that a mask (envelope) covers the target molecule well, an ff value of less than 0.1, as a new rule of thumb, gives sufficient phasing power for the successful construction of new structures. PMID:27377380

  19. Tubular Crystals and Helical Arrays: Structural Determination of HIV-1 Capsid Assemblies Using Iterative Helical Real-Space Reconstruction

    PubMed Central

    Zhang, Peijun; Meng, Xin; Zhao, Gongpu

    2013-01-01

    Helical structures are important in many different life forms and are well-suited for structural studies by cryo-EM. A unique feature of helical objects is that a single projection image contains all the views needed to perform a three-dimensional (3D) crystallographic reconstruction. Here, we use HIV-1 capsid assemblies to illustrate the detailed approaches to obtain 3D density maps from helical objects. Mature HIV-1 particles contain a conical- or tubular-shaped capsid that encloses the viral RNA genome and performs essential functions in the virus life cycle. The capsid is composed of capsid protein (CA) oligomers which are helically arranged on the surface. The N-terminal domain (NTD) of CA is connected to its C-terminal domain (CTD) through a flexible hinge. Structural analysis of two- and three-dimensional crystals provided molecular models of the capsid protein (CA) and its oligomer forms. We determined the 3D density map of helically assembled HIV-1 CA hexamers at 16 Å resolution using an iterative helical real-space reconstruction method. Docking of atomic models of CA-NTD and CA-CTD dimer into the electron density map indicated that the CTD dimer interface is retained in the assembled CA. Furthermore, molecular docking revealed an additional, novel CTD trimer interface. PMID:23132072

  20. Influence of atmospheric relative humidity on ultraviolet flux and aerosol direct radiative forcing: Observation and simulation

    NASA Astrophysics Data System (ADS)

    Xia, Dong; Chen, Ling; Chen, Huizhong; Luo, Xuyu; Deng, Tao

    2016-08-01

    The atmospheric aerosols can absorb moisture from the environment due to their hydrophilicity and thus affect atmospheric radiation fluxes. In this article, the ultraviolet radiation and relative humidity (RH) data from ground observations and a radiative transfer model were used to examine the influence of RH on ultraviolet radiation flux and aerosol direct radiative forcing under the clear-sky conditions. The results show that RH has a significant influence on ultraviolet radiation because of aerosol hygroscopicity. The relationship between attenuation rate and RH can be fitted logarithmically and all of the R2 of the 4 sets of samples are high, i.e. 0.87, 0.96, 0.9, and 0.9, respectively. When the RH is 60%, 70%, 80% and 90%, the mean aerosol direct radiative forcing in ultraviolet is -4.22W m-2, -4.5W m-2, -4.82W m-2 and -5.4W m-2, respectively. For the selected polluted air samples the growth factor for computing aerosol direct radiative forcing in the ultraviolet for the RH of 80% varies from 1.19 to 1.53, with an average of 1.31.

  1. Direct radiative feedback due to biogenic secondary organic aerosol estimated from boreal forest site observations

    NASA Astrophysics Data System (ADS)

    Lihavainen, H.; Asmi, E.; Aaltonen, V.; Makkonen, U.; Kerminen, V. M.

    2015-12-01

    Biogenic secondary organic aerosol (BSOA) originating from the emissions of volatile organic compounds from terrestrial vegetation constitutes an important part of the natural aerosol system. According to large-scale model simulations, the direct and indirect radiative effects of the BSOA are potentially large, yet poorly quantified. We used more than 5 years of continuous aerosol measurements to estimate the direct radiative feedback associated with the formation of biogenic secondary organic aerosol at a remote continental site at the edge of the boreal forest zone in Northern Finland. Our upper-limit estimate for this feedback during the summer period (ambient temperatures above 10 °C) was -97±66 mW m-2 K-1 (mean ± STD) when using measurements of the aerosol optical depth (fAOD) and -63±40 mW m-2 K-1 when using measurements of the "dry" aerosol scattering coefficient at the ground level (fσ). Here STD represents the variability in f caused by the observed variability in the quantities used to derive the value of f. Compared with our measurement site, the magnitude of this direct radiative feedback is expected to be larger in warmer continental regions with more abundant biogenic emissions, and even larger in regions where biogenic emissions are mixed with anthropogenic pollution.

  2. Cortical kinematic processing of executed and observed goal-directed hand actions.

    PubMed

    Marty, Brice; Bourguignon, Mathieu; Jousmäki, Veikko; Wens, Vincent; Op de Beeck, Marc; Van Bogaert, Patrick; Goldman, Serge; Hari, Riitta; De Tiège, Xavier

    2015-10-01

    Motor information conveyed by viewing the kinematics of an agent's action helps to predict how the action will unfold. Still, how observed movement kinematics is processed in the brain remains to be clarified. Here, we used magnetoencephalography (MEG) to determine at which frequency and where in the brain, the neural activity is coupled with the kinematics of executed and observed motor actions. Whole-scalp MEG signals were recorded from 11 right-handed healthy adults while they were executing (Self) or observing (Other) similar goal-directed hand actions performed by an actor placed in front of them. Actions consisted of pinching with the right hand green foam-made pieces mixed in a heap with pieces of other colors placed on a table, and put them in a plastic pot on the right side of the heap. Subjects' and actor's forefinger movements were monitored with an accelerometer. The coherence between movement acceleration and MEG signals was computed at the sensor level. Then, cortical sources coherent with movement acceleration were identified with Dynamic Imaging of Coherent Sources. Statistically significant sensor-level coherence peaked at the movement frequency (F0) and its first harmonic (F1) in both movement conditions. Apart from visual cortices, statistically significant local maxima of coherence were observed in the right posterior superior temporal gyrus (F0), bilateral superior parietal lobule (F0 or F1) and primary sensorimotor cortex (F0 or F1) in both movement conditions. These results suggest that observing others' actions engages the viewer's brain in a similar kinematic-related manner as during own action execution. These findings bring new insights into how human brain activity covaries with essential features of observed movements of others. PMID:26123380

  3. Cortical kinematic processing of executed and observed goal-directed hand actions.

    PubMed

    Marty, Brice; Bourguignon, Mathieu; Jousmäki, Veikko; Wens, Vincent; Op de Beeck, Marc; Van Bogaert, Patrick; Goldman, Serge; Hari, Riitta; De Tiège, Xavier

    2015-10-01

    Motor information conveyed by viewing the kinematics of an agent's action helps to predict how the action will unfold. Still, how observed movement kinematics is processed in the brain remains to be clarified. Here, we used magnetoencephalography (MEG) to determine at which frequency and where in the brain, the neural activity is coupled with the kinematics of executed and observed motor actions. Whole-scalp MEG signals were recorded from 11 right-handed healthy adults while they were executing (Self) or observing (Other) similar goal-directed hand actions performed by an actor placed in front of them. Actions consisted of pinching with the right hand green foam-made pieces mixed in a heap with pieces of other colors placed on a table, and put them in a plastic pot on the right side of the heap. Subjects' and actor's forefinger movements were monitored with an accelerometer. The coherence between movement acceleration and MEG signals was computed at the sensor level. Then, cortical sources coherent with movement acceleration were identified with Dynamic Imaging of Coherent Sources. Statistically significant sensor-level coherence peaked at the movement frequency (F0) and its first harmonic (F1) in both movement conditions. Apart from visual cortices, statistically significant local maxima of coherence were observed in the right posterior superior temporal gyrus (F0), bilateral superior parietal lobule (F0 or F1) and primary sensorimotor cortex (F0 or F1) in both movement conditions. These results suggest that observing others' actions engages the viewer's brain in a similar kinematic-related manner as during own action execution. These findings bring new insights into how human brain activity covaries with essential features of observed movements of others.

  4. Direct estimation of QBO-related gravity wave drag from satellite observations

    NASA Astrophysics Data System (ADS)

    Ern, Manfred; Ploeger, Felix; Preusse, Peter; Kalisch, Silvio; Riese, Martin

    2014-05-01

    The quasi-biennial oscillation (QBO) of the zonal wind in the tropical stratosphere is an important process in atmospheric dynamics. Effects of the QBO are found also in the mesosphere and in the extra-tropics. The QBO even has influence on the surface weather and climate, for example during winter in the northern hemisphere at midlatitudes. Still, climate models have large difficulties in reproducing a realistic QBO. The QBO is driven by atmospheric waves. Both global scale waves and mesoscale gravity waves (GWs) contribute. It has been proposed that the driving of the QBO by GWs is more important than that of the global scale waves. The relative importance of GWs is however still highly uncertain, and a direct estimation of the QBO driving by GWs from global observations is still missing. We derive GW temperature variances, GW momentum fluxes and GW drag from three years of High Resolution Dynamics Limb Sounder (HIRDLS) and from 11 years of Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) satellite data. These observations are compared with the drag that is still missing in the tropical momentum budget of the ECMWF ERA Interim (ERAI) reanalysis after considering zonal wind tendency, Coriolis force, advection terms and drag of resolved global-scale waves. The meteorological fields of ERAI are quite realistic because ERAI is strongly constrained by data assimilation. Therefore this missing drag can be attributed to GWs not resolved by the model. We find good qualitative agreement between observed GW drag and the missing drag in ERAI. During eastward QBO wind shear even the magnitude of observed and ERAI missing drag are in good agreement. During westward shear, however, observed drag is much lower than the ERAI missing drag. This asymmetry might hint at uncertainties in the advection terms of ERAI. Further, observed GW spectra indicate that QBO-related GW dissipation is mainly due to critical level filtering.

  5. Direct Observation of Photoinduced Charge Separation in Ruthenium Complex/Ni(OH)2 Nanoparticle Hybrid

    DOE PAGESBeta

    Tang, Yu; Pattengale, Brian A.; Ludwig, John M.; Atifi, Abderrahman; Zinovev, Alexander V.; Dong, Bin; Kong, Qingyu; Zuo, Xiaobing; Zhang, Xiaoyi; Huang, Jier

    2015-12-17

    We report that Ni(OH)2 have emerged as important functional materials for solar fuel conversion because of their potential as cost-effective bifunctional catalysts for both hydrogen and oxygen evolution reactions. However, their roles as photocatalysts in the photoinduced charge separation (CS) reactions remain unexplored. In this paper, we investigate the CS dynamics of a newly designed hybrid catalyst by integrating a Ru complex with Ni(OH)2 nanoparticles (NPs). Using time resolved X-ray absorption spectroscopy (XTA), we directly observed the formation of the reduced Ni metal site (~60 ps), unambiguously demonstrating CS process in the hybrid through ultrafast electron transfer from Ru complexmore » to Ni(OH)2 NPs. Compared to the ultrafast CS process, the charge recombination in the hybrid is ultraslow (>>50 ns). These results not only suggest the possibility of developing Ni(OH)2 as solar fuel catalysts, but also represent the first time direct observation of efficient CS in a hybrid catalyst using XTA.« less

  6. The Exozodiacal Dust Problem for Direct Observations of ExoEarths

    NASA Technical Reports Server (NTRS)

    Roberge, Aki; Chen, Christine H.; Millan-Gabet, Rafael; Weinberger, Alycia J.; Hinz, Philip M.; Stapelfeldt, Karl R.; Absil, Olivier; Kuchner, Marc J.; Bryden, Geoffrey

    2012-01-01

    Debris dust in the habitable zones of stars otherwise known as exozodiacal dust comes from extrasolar asteroids and comets and is thus an expected part of a planetary system. Background flux from the Solar Systems zodiacal dust and the exozodiacal dust in the target system is likely to be the largest source of astrophysical noise in direct observations of terrestrial planets in the habitable zones of nearby stars. Furthermore, dust structures like clumps, thought to be produced by dynamical interactions with exoplanets, are a possible source of confusion. In this paper, we qualitatively assess the primary impact of exozodical dust on high-contrast direct imaging at optical wavelengths, such as would be performed with a coronagraph. Then we present the sensitivity of previous, current, and near-term facilities to thermal emission from debris dust at all distances from nearby solar-type stars, as well as our current knowledge of dust levels from recent surveys. Finally, we address the other method of detecting debris dust, through high-contrast imaging in scattered light. This method is currently far less sensitive than thermal emission observations, but provides high spatial resolution for studying dust structures. This paper represents the first report of NASA's Exoplanet Exploration Program Analysis Group (ExoPAG).

  7. Direct in situ observation of nanoparticle synthesis in a liquid crystal surfactant template.

    PubMed

    Parent, Lucas R; Robinson, David B; Woehl, Taylor J; Ristenpart, William D; Evans, James E; Browning, Nigel D; Arslan, Ilke

    2012-04-24

    Controlled and reproducible synthesis of tailored materials is essential in many fields of nanoscience. In order to control synthesis, there must be a fundamental understanding of nanostructure evolution on the length scale of its features. Growth mechanisms are usually inferred from methods such as (scanning) transmission electron microscopy ((S)TEM), where nanostructures are characterized after growth is complete. Such post mortem analysis techniques cannot provide the information essential to optimize the synthesis process, because they cannot measure nanostructure development as it proceeds in real time. This is especially true in the complex rheological fluids used in preparation of nanoporous materials. Here we show direct in situ observations of synthesis in a highly viscous lyotropic liquid crystal template on the nanoscale using a fluid stage in the STEM. The nanoparticles nucleate and grow to ∼5 nm particles, at which point growth continues through the formation of connections with other nanoparticles around the micelles to form clusters. Upon reaching a critical size (>10-15 nm), the clusters become highly mobile in the template, displacing and trapping micelles within the growing structure to form spherical, porous nanoparticles. The final products match those synthesized in the lab ex situ. This ability to directly observe synthesis on the nanoscale in rheological fluids, such as concentrated aqueous surfactants, provides an unprecedented understanding of the fundamental steps of nanomaterial synthesis. This in turn allows for the synthesis of next-generation materials that can strongly impact important technologies such as organic photovoltaics, energy storage devices, catalysis, and biomedical devices.

  8. Direct observation of the superfluid phase transition in ultracold Fermi gases.

    PubMed

    Zwierlein, Martin W; Schunck, Christian H; Schirotzek, André; Ketterle, Wolfgang

    2006-07-01

    Phase transitions are dramatic phenomena: water freezes into ice, atomic spins spontaneously align in a magnet, and liquid helium becomes superfluid. Sometimes, such a drastic change in behaviour is accompanied by a visible change in appearance. The hallmark of Bose-Einstein condensation and superfluidity in trapped, weakly interacting Bose gases is the sudden formation of a dense central core inside a thermal cloud. However, in strongly interacting gases--such as the recently observed fermionic superfluids--there is no longer a clear separation between the superfluid and the normal parts of the cloud. The detection of fermion pair condensates has required magnetic field sweeps into the weakly interacting regime, and the quantitative description of these sweeps presents a major theoretical challenge. Here we report the direct observation of the superfluid phase transition in a strongly interacting gas of 6Li fermions, through sudden changes in the shape of the clouds--in complete analogy to the case of weakly interacting Bose gases. By preparing unequal mixtures of the two spin components involved in the pairing, we greatly enhance the contrast between the superfluid core and the normal component. Furthermore, the distribution of non-interacting excess atoms serves as a direct and reliable thermometer. Even in the normal state, strong interactions significantly deform the density profile of the majority spin component. We show that it is these interactions that drive the normal-to-superfluid transition at the critical population imbalance of 70 +/- 5 per cent (ref. 12).

  9. A simple hardware model for the direct observation of voltage-clamp performance under realistic conditions.

    PubMed

    Draguhn, A; Pfeiffer, M; Heinemann, U; Polder, R

    1997-12-30

    A new hardware cell model for electrophysiological recording has been constructed which allows for the assessment of voltage clamp accuracy in different recording situations. Each compartment consists of a capacitor in parallel with a variable resistor and can be connected to other compartments by a variable axial resistance. The simulated membrane resistance can be changed extrinsically by a command voltage input which is optically coupled to the cell without any direct galvanic contact. Each compartment possesses a buffer amplifier which reads out the potential at the simulated membrane element, (e.g. 'somatic' or 'dendritic' potential). The model allows for the direct observation of typical situations and problems arising in electrophysiological experiments. We used the model to monitor deviations between the 'intracellular' and the command voltage, e.g. due to series resistance errors. We also used the model to simulate synaptic currents which were generated by triangular membrane conductance changes. The results demonstrate the strong influence of synaptic location and series resistance on voltage clamp fidelity. The cell model is a new and easy-to-handle tool for the observation of voltage control under realistic experimental conditions. PMID:9497006

  10. Direct TEM observations of growth mechanisms of two-dimensional MoS2 flakes

    NASA Astrophysics Data System (ADS)

    Fei, Linfeng; Lei, Shuijin; Zhang, Wei-Bing; Lu, Wei; Lin, Ziyuan; Lam, Chi Hang; Chai, Yang; Wang, Yu

    2016-07-01

    A microscopic understanding of the growth mechanism of two-dimensional materials is of particular importance for controllable synthesis of functional nanostructures. Because of the lack of direct and insightful observations, how to control the orientation and the size of two-dimensional material grains is still under debate. Here we discern distinct formation stages for MoS2 flakes from the thermolysis of ammonium thiomolybdates using in situ transmission electron microscopy. In the initial stage (400 °C), vertically aligned MoS2 structures grow in a layer-by-layer mode. With the increasing temperature of up to 780 °C, the orientation of MoS2 structures becomes horizontal. When the growth temperature reaches 850 °C, the crystalline size of MoS2 increases by merging adjacent flakes. Our study shows direct observations of MoS2 growth as the temperature evolves, and sheds light on the controllable orientation and grain size of two-dimensional materials.

  11. Direct estimation of tidally induced Earth rotation variations observed by VLBI

    NASA Astrophysics Data System (ADS)

    Englich, S.; Heinkelmann, R.; BOHM, J.; Schuh, H.

    2009-09-01

    The subject of our study is the investigation of periodical variations induced by solid Earth tides and ocean tides in Earth rotation parameters (ERP: polar motion, UT1)observed by VLBI. There are two strategies to determine the amplitudes and phases of Earth rotation variations from observations of space geodetic techniques. The common way is to derive time series of Earth rotation parameters first and to estimate amplitudes and phases in a second step. Results obtained by this means were shown in previous studies for zonal tidal variations (Englich et al.; 2008a) and variations caused by ocean tides (Englich et al.; 2008b). The alternative method is to estimate the tidal parameters directly within the VLBI data analysis procedure together with other parameters such as station coordinates, tropospheric delays, clocks etc. The purpose of this work was the application of this direct method to a combined VLBI data analysis using the software packages OCCAM (Version 6.1, Gauss-Markov-Model) and DOGSCS (Gerstl et al.; 2001). The theoretical basis and the preparatory steps for the implementation of this approach are presented here.

  12. The Exozodiacal Dust Problem for Direct Observations of Exo-Earths

    NASA Astrophysics Data System (ADS)

    Roberge, Aki; Chen, Christine H.; Millan-Gabet, Rafael; Weinberger, Alycia J.; Hinz, Philip M.; Stapelfeldt, Karl R.; Absil, Olivier; Kuchner, Marc J.; Bryden, Geoffrey

    2012-08-01

    Debris dust in the habitable zones of stars—otherwise known as exozodiacal dust—comes from extrasolar asteroids and comets and is thus an expected part of a planetary system. Background flux from the solar system's zodiacal dust and the exozodiacal dust in the target system is likely to be the largest source of astrophysical noise in direct observations of terrestrial planets in the habitable zones of nearby stars. Furthermore, dust structures like clumps, thought to be produced by dynamical interactions with exoplanets, are a possible source of confusion. In this article, we qualitatively assess the primary impact of exozodiacal dust on high-contrast direct imaging at optical wavelengths, such as would be performed with a coronagraph. Then we present the sensitivity of previous, current, and near-term facilities to thermal emission from debris dust at all distances from nearby solar-type stars, as well as our current knowledge of dust levels from recent surveys. Finally, we address the other method of detecting debris dust, through high-contrast imaging in scattered light. This method is currently far less sensitive than thermal emission observations, but provides high spatial resolution for studying dust structures. This article represents the first report of NASA's Exoplanet Exploration Program Analysis Group (ExoPAG).

  13. Direct spectroscopic observation of a shallow hydrogenlike donor state in insulating SrTiO3.

    PubMed

    Salman, Z; Prokscha, T; Amato, A; Morenzoni, E; Scheuermann, R; Sedlak, K; Suter, A

    2014-10-10

    We present a direct spectroscopic observation of a shallow hydrogenlike muonium state in SrTiO(3) which confirms the theoretical prediction that interstitial hydrogen may act as a shallow donor in this material. The formation of this muonium state is temperature dependent and appears below ∼ 70K. From the temperature dependence we estimate an activation energy of ∼ 50 meV in the bulk and ∼ 23 meV near the free surface. The field and directional dependence of the muonium precession frequencies further supports the shallow impurity state with a rare example of a fully anisotropic hyperfine tensor. From these measurements we determine the strength of the hyperfine interaction and propose that the muon occupies an interstitial site near the face of the oxygen octahedron in SrTiO(3). The observed shallow donor state provides new insight for tailoring the electronic and optical properties of SrTiO(3)-based oxide interface systems. PMID:25375730

  14. Direct TEM observations of growth mechanisms of two-dimensional MoS2 flakes

    PubMed Central

    Fei, Linfeng; Lei, Shuijin; Zhang, Wei-Bing; Lu, Wei; Lin, Ziyuan; Lam, Chi Hang; Chai, Yang; Wang, Yu

    2016-01-01

    A microscopic understanding of the growth mechanism of two-dimensional materials is of particular importance for controllable synthesis of functional nanostructures. Because of the lack of direct and insightful observations, how to control the orientation and the size of two-dimensional material grains is still under debate. Here we discern distinct formation stages for MoS2 flakes from the thermolysis of ammonium thiomolybdates using in situ transmission electron microscopy. In the initial stage (400 °C), vertically aligned MoS2 structures grow in a layer-by-layer mode. With the increasing temperature of up to 780 °C, the orientation of MoS2 structures becomes horizontal. When the growth temperature reaches 850 °C, the crystalline size of MoS2 increases by merging adjacent flakes. Our study shows direct observations of MoS2 growth as the temperature evolves, and sheds light on the controllable orientation and grain size of two-dimensional materials. PMID:27412892

  15. Not seeing or feeling is still believing: conscious and non-conscious pain modulation after direct and observational learning

    PubMed Central

    Egorova, Natalia; Park, Joel; Orr, Scott P.; Kirsch, Irving; Gollub, Randy L.; Kong, Jian

    2015-01-01

    Our experience with the world is shaped not only directly through personal exposure but also indirectly through observing others and learning from their experiences. Using a conditioning paradigm, we investigated how directly and observationally learned information can affect pain perception, both consciously and non-consciously. Differences between direct and observed cues were manifest in higher pain ratings and larger skin conductance responses to directly experienced cues. However, the pain modulation effects produced by conditioning were of comparable magnitude for direct and observational learning. These results suggest that social observation can induce positive and negative pain modulation. Importantly, the fact that cues learned by observation and activated non-consciously still produced a robust conditioning effect that withstood extinction highlights the role of indirect exposure in placebo and nocebo effects. PMID:26578164

  16. Not seeing or feeling is still believing: conscious and non-conscious pain modulation after direct and observational learning.

    PubMed

    Egorova, Natalia; Park, Joel; Orr, Scott P; Kirsch, Irving; Gollub, Randy L; Kong, Jian

    2015-11-18

    Our experience with the world is shaped not only directly through personal exposure but also indirectly through observing others and learning from their experiences. Using a conditioning paradigm, we investigated how directly and observationally learned information can affect pain perception, both consciously and non-consciously. Differences between direct and observed cues were manifest in higher pain ratings and larger skin conductance responses to directly experienced cues. However, the pain modulation effects produced by conditioning were of comparable magnitude for direct and observational learning. These results suggest that social observation can induce positive and negative pain modulation. Importantly, the fact that cues learned by observation and activated non-consciously still produced a robust conditioning effect that withstood extinction highlights the role of indirect exposure in placebo and nocebo effects.

  17. Direct Observations of the Composition of Sub-20 Nanometer Ambient Aerosol

    NASA Astrophysics Data System (ADS)

    Moore, K. F.; Smith, J. N.; Eisele, F. L.; McMurry, P. H.

    2002-12-01

    Understanding new particle formation in the atmosphere depends upon many factors including detailed knowledge of their chemical composition. The chemical composition of sub-20 nanometer ambient aerosol particles, however, is typically inferred from observations of the aerosol behavior when subjected to varying conditions during sampling. Direct observations of aerosol chemical composition are usually limited to or dominated by larger particles of higher mass. Recently a new instrument has been developed - the Thermal Desorption Chemical Ionization Mass Spectrometer (TDCIMS) - which can directly measure the chemical composition of sub-20 nanometer aerosol particles. Briefly, the front end of the TDCIMS functions as an electrostatic precipitator using a strong electric field to collect charged aerosol particles onto a sample wire. After volatilization by heating, the component species of the collected particles are subjected to chemical ionization prior to introduction into the mass spectrometer for analysis. Detection limits on the order of picograms permit sample collection periods as small as five minutes for ambient aerosol concentrations providing near "real-time" resolution. For selected periods from April through June 2002, we used the TDCIMS to measure the chemical composition of ambient aerosol for the first time. We investigated both the positive and negative ion spectrums produced by sub-20 nanometer ambient aerosol particles at the National Center for Atmospheric Research in Boulder, Colorado. Principal species identified include ammonium, sulfate and nitrate although additional peaks consistent with particle-phase origin were readily observed. Diurnal concentration profiles appear to be present and the relative proportion of sulfate and nitrate to each other can vary appreciably over several hours and between days. Validation of the TDCIMS' performance and the interpretation of its results will also be discussed.

  18. Direct in situ observation of synergism between cellulolytic enzymes during the biodegradation of crystalline cellulose fibers.

    PubMed

    Wang, Jingpeng; Quirk, Amanda; Lipkowski, Jacek; Dutcher, John R; Clarke, Anthony J

    2013-12-01

    High-resolution atomic force microscopy (AFM) was used to image the real-time in situ degradation of crystalline by three types of T. reesei cellulolytic enzymes-TrCel6A, TrCel7A, and TrCel7B-and their mixtures. TrCel6A and TrCel7A are exo-acting cellobiohydrolases processing cellulose fibers from the nonreducing and reducing ends, respectively. TrCel7B is an endoglucanase that hydrolyzes amorphous cellulose within fibers. When acting alone on native cellulose fibers, each of the three enzymes is incapable of significant degradation. However, mixtures of two enzymes exhibited synergistic effects. The degradation effects of this synergism depended on the order in which the enzymes were added. Faster hydrolysis rates were observed when TrCel7A (exo) was added to fibers pretreated first with TrCel7B (endo) than when adding the enzymes in the opposite order. Endo-acting TrCel7B removed amorphous cellulose, softened and swelled the fibers, and exposed single microfibrils, facilitating the attack by the exo-acting enzymes. AFM images revealed that exo-acting enzymes processed the TrCel7B-pretreated fibers preferentially from one specific end (reducing or nonreducing). The most efficient (almost 100%) hydrolysis was observed with the mixture of the three enzymes. In this mixture, TrCel7B softened the fiber and TrCel6A and TrCel7A were directly observed to process it from the two opposing ends. This study provides high-resolution direct visualization of the nature of the synergistic relation between T. reesei exo- and endo-acting enzymes digesting native crystalline cellulose.

  19. Toward the Direct Measurement of Coronal Magnetic Fields: An Airborne Infrared Spectrometer for Eclipse Observations

    NASA Astrophysics Data System (ADS)

    Samra, J.; DeLuca, E. E.; Golub, L.; Cheimets, P.

    2014-12-01

    The solar magnetic field enables the heating of the corona and provides its underlying structure. Energy stored in coronal magnetic fields is released in flares and coronal mass ejections (CME) and provides the ultimate source of energy for space weather. Therefore, direct measurements of the coronal magnetic field have significant potential to enhance understanding of coronal dynamics and improve solar forecasting models. Of particular interest are observations of coronal field lines in the transitional region between closed and open flux systems, providing important information on the origin of the slow solar wind. While current instruments routinely observe only the photospheric and chromospheric magnetic fields, a proposed airborne spectrometer will take a step toward the direct observation of coronal fields by measuring plasma emission in the infrared at high spatial and spectral resolution. The targeted lines are four forbidden magnetic dipole transitions between 2 and 4 μm. The airborne system will consist of a telescope, grating spectrometer, and pointing/stabilization system to be flown on the NSF/NCAR High-performance Instrumented Airborne Platform for Environmental Research (HIAPER) during the August 2017 total solar eclipse. The project incorporates several optical engineering challenges, centered around maintaining adequate spectral and spatial resolution in a compact and inexpensive package and on a moving platform. Design studies are currently underway to examine the tradeoffs between various optical geometries and control strategies for the pointing/stabilization system. The results will be presented and interpreted in terms of the consequences for the scientific questions. In addition, results from a laboratory prototype and simulations of the final system will be presented.

  20. Validation of a New Counter for Direct Observation of Physical Activity in Parks

    PubMed Central

    Han, Bing; Cohen, Deborah A.; Derose, Kathryn Pitkin; Marsh, Terry; Williamson, Stephanie; Raaen, Laura

    2015-01-01

    Purpose Prior tools to observe large groups of people in parks have not allowed disaggregation of physical activity levels by age group and gender simultaneously, making it impossible to determine which subgroups engaged in moderate to vigorous physical activity (MVPA). This study aims to examine the reliability of a 12-button counter to simultaneously assess MVPA by age and gender subgroups in park settings. Methods A total of 1,160 pairs of observations were conducted in 481 target areas of 19 neighborhood parks in the great Los Angeles area between June 2013 and March 2014. Inter-rater reliability was assessed by Pearson’s correlation, intra-class correlation (ICC), and agreement probability in the total metabolic equivalents (METs) and METs spent in MVPA. Cosine similarity was used to check the resemblance of distributions among age and gender categories. Pictures taken in a total of 112 target areas at the beginning of the observations were used as a second check on the reliability of direct observation. Results Inter-rater reliability was high for the total METs and METs in all age and gender categories (between 0.82 and 0.97), except for male seniors (correlations and ICC between 0.64 and 0.77, agreement probability 0.85 to 0.86). Reliability was higher for total METs than for METs spent in MVPA. Correlation and ICC between observers’ measurement and picture-based counts are also high (between 0.79 and 0.94). Conclusion Trained observers can reliably use the 12-button counter to accurately assess PA distribution and disparities by age and gender. PMID:26103584

  1. Direct observations of the influence of solution composition on magnesite dissolution

    NASA Astrophysics Data System (ADS)

    King, Helen E.; Putnis, Christine V.

    2013-05-01

    In situ observations during atomic force microscopy experiments and ex situ observations after static and flow-through experiments were used to explore the effect of three different electrolytes on magnesite (MgCO3) dissolution at pH 2. The experiments showed that the magnesite dissolution rate varied in the order NO3->Cl>SO42- when these anions were present in solution. Under the experimental conditions magnesite dissolution occurred via the removal of successive single surface layers, where changes in magnesite reactivity in the presence of different electrolytes could be observed as variations in the cycle length for the removal of one unit cell layer. The cycles began with the formation of sporadically distributed etch pits followed by the nucleation of homogeneously distributed etch pits. Coalescence of the etch pits formed isolated sections of the remnant surface, which then dissolved away. The timing of sporadic and homogeneous etch pit nucleation was constant despite the presence of different anions. However, the cycles in surface roughness and etch pit spreading rates indicate that the different anions affect step retreat rates and hence dissolution rates. Differences in magnesite reactivity can be attributed to the direct interaction of sulphate with the magnesite surface and the indirect effects of chloride and nitrate on the magnesite surface hydration and hydration of the Mg2+ ion in solution. In all experiments during the dissolution process evidence for the precipitation of a new phase was observed, either directly as precipitates forming on the magnesite surface in the AFM and after the experiments, seen in SEM analysis, or as changes in the Mg outlet concentration during flow-through experiments. EDX and Raman spectroscopy were used to analyse the composition of the precipitate and although it could not be definitively identified, considering previous observations the precipitate is most likely a hydrated Mg-carbonate phase with a MgCO3·xH2O

  2. Direct observation of aqueous secondary organic aerosol from biomass-burning emissions

    PubMed Central

    Massoli, Paola; Paglione, Marco; Giulianelli, Lara; Carbone, Claudio; Rinaldi, Matteo; Decesari, Stefano; Sandrini, Silvia; Costabile, Francesca; Gobbi, Gian Paolo; Pietrogrande, Maria Chiara; Visentin, Marco; Scotto, Fabiana; Fuzzi, Sandro; Facchini, Maria Cristina

    2016-01-01

    The mechanisms leading to the formation of secondary organic aerosol (SOA) are an important subject of ongoing research for both air quality and climate. Recent laboratory experiments suggest that reactions taking place in the atmospheric liquid phase represent a potentially significant source of SOA mass. Here, we report direct ambient observations of SOA mass formation from processing of biomass-burning emissions in the aqueous phase. Aqueous SOA (aqSOA) formation is observed both in fog water and in wet aerosol. The aqSOA from biomass burning contributes to the “brown” carbon (BrC) budget and exhibits light absorption wavelength dependence close to the upper bound of the values observed in laboratory experiments for fresh and processed biomass-burning emissions. We estimate that the aqSOA from residential wood combustion can account for up to 0.1–0.5 Tg of organic aerosol (OA) per y in Europe, equivalent to 4–20% of the total OA emissions. Our findings highlight the importance of aqSOA from anthropogenic emissions on air quality and climate. PMID:27551086

  3. DIRECT OBSERVATION OF THE COOLING OF THE CASSIOPEIA A NEUTRON STAR

    SciTech Connect

    Heinke, Craig O.; Ho, Wynn C. G. E-mail: wynnho@slac.stanford.ed

    2010-08-20

    The cooling rate of young neutron stars (NSs) gives direct insight into their internal makeup. Although the temperatures of several young NSs have been measured, until now a young NS has never been observed to decrease in temperature over time. We fit nine years of archival Chandra ACIS spectra of the likely NS in the {approx}330 yr old Cassiopeia A supernova remnant with our non-magnetic carbon atmosphere model. Our fits show a relative decline in the surface temperature by 4% (5.4{sigma}, from (2.12 {+-} 0.01) x 10{sup 6} K in 2000 to (2.04 {+-} 0.01) x 10{sup 6} K in 2009) and the observed flux by 21%. Using a simple model for NS cooling, we show that this temperature decline could indicate that the NS became isothermal sometime between 1965 and 1980, and constrains some combinations of neutrino emission mechanisms and envelope compositions. However, the NS is likely to have become isothermal soon after formation, in which case the temperature history suggests episodes of additional heating or more rapid cooling. Observations over the next few years will allow us to test possible explanations for the temperature evolution.

  4. Direct observation of aqueous secondary organic aerosol from biomass-burning emissions.

    PubMed

    Gilardoni, Stefania; Massoli, Paola; Paglione, Marco; Giulianelli, Lara; Carbone, Claudio; Rinaldi, Matteo; Decesari, Stefano; Sandrini, Silvia; Costabile, Francesca; Gobbi, Gian Paolo; Pietrogrande, Maria Chiara; Visentin, Marco; Scotto, Fabiana; Fuzzi, Sandro; Facchini, Maria Cristina

    2016-09-01

    The mechanisms leading to the formation of secondary organic aerosol (SOA) are an important subject of ongoing research for both air quality and climate. Recent laboratory experiments suggest that reactions taking place in the atmospheric liquid phase represent a potentially significant source of SOA mass. Here, we report direct ambient observations of SOA mass formation from processing of biomass-burning emissions in the aqueous phase. Aqueous SOA (aqSOA) formation is observed both in fog water and in wet aerosol. The aqSOA from biomass burning contributes to the "brown" carbon (BrC) budget and exhibits light absorption wavelength dependence close to the upper bound of the values observed in laboratory experiments for fresh and processed biomass-burning emissions. We estimate that the aqSOA from residential wood combustion can account for up to 0.1-0.5 Tg of organic aerosol (OA) per y in Europe, equivalent to 4-20% of the total OA emissions. Our findings highlight the importance of aqSOA from anthropogenic emissions on air quality and climate. PMID:27551086

  5. Direct observation of the two-plasmon-decay common plasma wave using ultraviolet Thomson scattering.

    PubMed

    Follett, R K; Edgell, D H; Henchen, R J; Hu, S X; Katz, J; Michel, D T; Myatt, J F; Shaw, J; Froula, D H

    2015-03-01

    A 263-nm Thomson-scattering beam was used to directly probe two-plasmon-decay (TPD) excited electron plasma waves (EPWs) driven by between two and five 351-nm beams on the OMEGA Laser System. The amplitude of these waves was nearly independent of the number of drive beams at constant overlapped intensity, showing that the observed EPWs are common to the multiple beams. In an experimental configuration where the Thomson-scattering diagnostic was not wave matched to the common TPD EPWs, a broad spectrum of TPD-driven EPWs was observed, indicative of nonlinear effects associated with TPD saturation. Electron plasma waves corresponding to Langmuir decay of TPD EPWs were observed in both Thomson-scattering spectra, suggesting the Langmuir decay instability as a TPD saturation mechanism. Simulated Thomson-scattering spectra from three-dimensional numerical solutions of the extended Zakharov equations of TPD are in excellent agreement with the experimental spectra and verify the presence of the Langmuir decay instability.

  6. Direct observation of the two-plasmon-decay common plasma wave using ultraviolet Thomson scattering

    SciTech Connect

    Follett, R. K.; Edgell, D. H.; Henchen, R. J.; Hu, S. X.; Katz, J.; Michel, D. T.; Myatt, J. F.; Shaw, J.; Froula, D. H.

    2015-03-26

    A 263-nm Thomson-scattering beam was used to directly probe two-plasmon-decay (TPD) excited electron plasma waves (EPWs) driven by between two and five 351-nm beams on the OMEGA Laser System. The amplitude of these waves was nearly independent of the number of drive beams at constant overlapped intensity, showing that the observed EPWs are common to the multiple beams. In an experimental configuration where the Thomson-scattering diagnostic was not wave matched to the common TPD EPWs, a broad spectrum of TPD-driven EPWs was observed, indicative of nonlinear effects associated with TPD saturation. Electron plasma waves corresponding to Langmuir decay of TPD EPWs were observed in both Thomson-scattering spectra, suggesting the Langmuir decay instability as a TPD saturation mechanism. Simulated Thomson-scattering spectra from three-dimensional numerical solutions of the extended Zakharov equations of TPD are in excellent agreement with the experimental spectra and verify the presence of the Langmuir decay instability.

  7. Direct Observation of a Majorana Quasiparticle Heat Capacity in 3He

    NASA Astrophysics Data System (ADS)

    Bunkov, Y. M.

    2014-04-01

    The Majorana fermion, which acts as its own antiparticle, was suggested by Majorana in 1937 (Nuovo Cimento 14:171). While no stable particle with Majorana properties has yet been observed, Majorana quasiparticles (QP) may exist at the boundaries of topological insulators. Here we report the preliminary results of direct observation of Majorana QPs by a precise measurements of superfluid 3He heat capacity. The bulk superfluid 3He heat capacity falls exponentially with cooling at the temperatures significantly below the energy gap. Owing to the zero energy gap mode the Majorana heat capacity falls in a power law. The Majorana heat capacity can be larger than bulk one at some temperature, which depends on surface to volume ratio of the experimental cell. Some times ago we developed the Dark matter particles detector (DMD) on a basis of superfluid 3He which is working at the frontier of extremely low temperatures (Winkelmann et al., Nucl. Instrum. Meth. A 559:384-386, 2006). Here we report the observation of zero gap mode of Majorana, follows from the new analyses of DMD heat capacity, published early. We have found a 10 % deviation from the bulk superfluid 3He heat capacity at the temperature of 135 μK. This deviation corresponds well to the theoretical value for Majorana heat capacity at such low temperature. (Note, there were no fitting parameters).

  8. Direct observation of aqueous secondary organic aerosol from biomass-burning emissions

    NASA Astrophysics Data System (ADS)

    Gilardoni, Stefania; Massoli, Paola; Paglione, Marco; Giulianelli, Lara; Carbone, Claudio; Rinaldi, Matteo; Decesari, Stefano; Sandrini, Silvia; Costabile, Francesca; Gobbi, Gian Paolo; Chiara Pietrogrande, Maria; Visentin, Marco; Scotto, Fabiana; Fuzzi, Sandro; Facchini, Maria Cristina

    2016-09-01

    The mechanisms leading to the formation of secondary organic aerosol (SOA) are an important subject of ongoing research for both air quality and climate. Recent laboratory experiments suggest that reactions taking place in the atmospheric liquid phase represent a potentially significant source of SOA mass. Here, we report direct ambient observations of SOA mass formation from processing of biomass-burning emissions in the aqueous phase. Aqueous SOA (aqSOA) formation is observed both in fog water and in wet aerosol. The aqSOA from biomass burning contributes to the “brown” carbon (BrC) budget and exhibits light absorption wavelength dependence close to the upper bound of the values observed in laboratory experiments for fresh and processed biomass-burning emissions. We estimate that the aqSOA from residential wood combustion can account for up to 0.1-0.5 Tg of organic aerosol (OA) per y in Europe, equivalent to 4-20% of the total OA emissions. Our findings highlight the importance of aqSOA from anthropogenic emissions on air quality and climate.

  9. Direct observation by using Brewster angle microscopy of the diacetylene polimerization in mixed Langmuir film.

    PubMed

    Ariza-Carmona, Luisa; Martín-Romero, María T; Giner-Casares, Juan J; Camacho, Luis

    2015-12-01

    Mixed Langmuir monolayers of 10,12-Pentacosadiynoic acid (DA) and amphiphilic hemicyanine (HSP) have been fabricated at the air-water interface. The mixed monolayer has been proved to be completely homogeneous. The DA molecules are arranged in a single monolayer within the mixed Langmuir monolayer, as opposed to the typical trilayer architecture for the pure DA film. Brewster angle microscopy has been used to reveal the mesoscopic structure of the mixed Langmuir monolayer. Flower shape domains with internal anisotropy due the ordered alignment of hemicyanine groups have been observed. Given the absorption features of the hemicyanine groups at the wavelength used in the BAM experiments, the enhancement of reflection provoked by the absorption process leads to the observed anisotropy. The ordering of such groups is promoted by their strong self-aggregation tendency. Under UV irradiation at the air-water interface, polydiacetylene (PDA) has been fabricated. In spite a significant increase in the domains reflectivity has been observed owing to the modification in the mentioned enhanced reflection, the texture of the domains remains equal. The PDA polymer chain therefore grows in the same direction in which the HSP molecules are aligned. This study is expected to enrich the understanding and design of fabrication of PDA at interfaces. PMID:26263495

  10. Deformation Twinning in Zirconium: Direct Experimental Observations and Polycrystal Plasticity Predictions

    NASA Astrophysics Data System (ADS)

    Singh, Jaiveer; Mahesh, Sivasambu; Kumar, Gulshan; Pant, Prita; Srivastava, D.; Dey, G. K.; Saibaba, N.; Samajdar, I.

    2015-11-01

    Deformation twinning was directly observed in three commercial zirconium alloy samples during split channel die plane-strain compression. One pair of samples had similar starting texture but different grain size distributions, while another pair had similar grain size distribution but different starting textures. Extension twinning was found to be more sensitive to the starting texture than to the grain size distribution. Also, regions of intense deformation near grain boundaries were observed. A hierarchical binary tree-based polycrystal plasticity model, implementing the Chin-Hosford-Mendorf twinning criterion, captured the experimentally observed twinning grains' lattice orientation distribution, and the twin volume fraction evolution, provided the critical resolved shear stress for extension twinning, τ0 , was assumed much larger than any of the values reported in the literature, based on the viscoplastic self-consistent model. A comparison of the models suggests that τ0 obtained using the present model and the viscoplastic self-consistent models physically correspond to the critical stress required for twin nucleation, and twin growth, respectively.

  11. Direct observation of the two-plasmon-decay common plasma wave using ultraviolet Thomson scattering.

    PubMed

    Follett, R K; Edgell, D H; Henchen, R J; Hu, S X; Katz, J; Michel, D T; Myatt, J F; Shaw, J; Froula, D H

    2015-03-01

    A 263-nm Thomson-scattering beam was used to directly probe two-plasmon-decay (TPD) excited electron plasma waves (EPWs) driven by between two and five 351-nm beams on the OMEGA Laser System. The amplitude of these waves was nearly independent of the number of drive beams at constant overlapped intensity, showing that the observed EPWs are common to the multiple beams. In an experimental configuration where the Thomson-scattering diagnostic was not wave matched to the common TPD EPWs, a broad spectrum of TPD-driven EPWs was observed, indicative of nonlinear effects associated with TPD saturation. Electron plasma waves corresponding to Langmuir decay of TPD EPWs were observed in both Thomson-scattering spectra, suggesting the Langmuir decay instability as a TPD saturation mechanism. Simulated Thomson-scattering spectra from three-dimensional numerical solutions of the extended Zakharov equations of TPD are in excellent agreement with the experimental spectra and verify the presence of the Langmuir decay instability. PMID:25871046

  12. Direct observation of mobility state transitions in RNA trajectories by sensitive single molecule feedback tracking

    PubMed Central

    Spille, Jan-Hendrik; Kaminski, Tim P.; Scherer, Katharina; Rinne, Jennifer S.; Heckel, Alexander; Kubitscheck, Ulrich

    2015-01-01

    Observation and tracking of fluorescently labeled molecules and particles in living cells reveals detailed information about intracellular processes on the molecular level. Whereas light microscopic particle observation is usually limited to two-dimensional projections of short trajectory segments, we report here image-based real-time three-dimensional single particle tracking in an active feedback loop with single molecule sensitivity. We tracked particles carrying only 1–3 fluorophores deep inside living tissue with high spatio-temporal resolution. Using this approach, we succeeded to acquire trajectories containing several hundred localizations. We present statistical methods to find significant deviations from random Brownian motion in such trajectories. The analysis allowed us to directly observe transitions in the mobility of ribosomal (r)RNA and Balbiani ring (BR) messenger (m)RNA particles in living Chironomus tentans salivary gland cell nuclei. We found that BR mRNA particles displayed phases of reduced mobility, while rRNA particles showed distinct binding events in and near nucleoli. PMID:25414330

  13. Direct observation by using Brewster angle microscopy of the diacetylene polimerization in mixed Langmuir film.

    PubMed

    Ariza-Carmona, Luisa; Martín-Romero, María T; Giner-Casares, Juan J; Camacho, Luis

    2015-12-01

    Mixed Langmuir monolayers of 10,12-Pentacosadiynoic acid (DA) and amphiphilic hemicyanine (HSP) have been fabricated at the air-water interface. The mixed monolayer has been proved to be completely homogeneous. The DA molecules are arranged in a single monolayer within the mixed Langmuir monolayer, as opposed to the typical trilayer architecture for the pure DA film. Brewster angle microscopy has been used to reveal the mesoscopic structure of the mixed Langmuir monolayer. Flower shape domains with internal anisotropy due the ordered alignment of hemicyanine groups have been observed. Given the absorption features of the hemicyanine groups at the wavelength used in the BAM experiments, the enhancement of reflection provoked by the absorption process leads to the observed anisotropy. The ordering of such groups is promoted by their strong self-aggregation tendency. Under UV irradiation at the air-water interface, polydiacetylene (PDA) has been fabricated. In spite a significant increase in the domains reflectivity has been observed owing to the modification in the mentioned enhanced reflection, the texture of the domains remains equal. The PDA polymer chain therefore grows in the same direction in which the HSP molecules are aligned. This study is expected to enrich the understanding and design of fabrication of PDA at interfaces.

  14. Chemotaxis study using optical tweezers to observe the strength and directionality of forces of Leishmania amazonensis

    NASA Astrophysics Data System (ADS)

    Pozzo, Liliana d. Y.; Fontes, Adriana; de Thomaz, André A.; Barbosa, Luiz C.; Ayres, Diana C.; Giorgio, Selma; Cesar, Carlos L.

    2006-08-01

    The displacements of a dielectric microspheres trapped by an optical tweezers (OT) can be used as a force transducer for mechanical measurements in life sciences. This system can measure forces on the 50 femto Newtons to 200 pico Newtons range, of the same order of magnitude of a typical forces induced by flagellar motion. The process in which living microorganisms search for food and run away from poison chemicals is known is chemotaxy. Optical tweezers can be used to obtain a better understanding of chemotaxy by observing the force response of the microorganism when placed in a gradient of attractors and or repelling chemicals. This report shows such observations for the protozoa Leishmania amazomenzis, responsible for the leishmaniasis, a serious tropical disease. We used a quadrant detector to monitor the movement of the protozoa for different chemicals gradient. This way we have been able to observe both the force strength and its directionality. The characterization of the chemotaxis of these parasites can help to understand the infection mechanics and improve the diagnosis and the treatments employed for this disease.

  15. Social communication with virtual agents: The effects of body and gaze direction on attention and emotional responding in human observers.

    PubMed

    Marschner, Linda; Pannasch, Sebastian; Schulz, Johannes; Graupner, Sven-Thomas

    2015-08-01

    In social communication, the gaze direction of other persons provides important information to perceive and interpret their emotional response. Previous research investigated the influence of gaze by manipulating mutual eye contact. Therefore, gaze and body direction have been changed as a whole, resulting in only congruent gaze and body directions (averted or directed) of another person. Here, we aimed to disentangle these effects by using short animated sequences of virtual agents posing with either direct or averted body or gaze. Attention allocation by means of eye movements, facial muscle response, and emotional experience to agents of different gender and facial expressions were investigated. Eye movement data revealed longer fixation durations, i.e., a stronger allocation of attention, when gaze and body direction were not congruent with each other or when both were directed towards the observer. This suggests that direct interaction as well as incongruous signals increase the demands of attentional resources in the observer. For the facial muscle response, only the reaction of muscle zygomaticus major revealed an effect of body direction, expressed by stronger activity in response to happy expressions for direct compared to averted gaze when the virtual character's body was directed towards the observer. Finally, body direction also influenced the emotional experience ratings towards happy expressions. While earlier findings suggested that mutual eye contact is the main source for increased emotional responding and attentional allocation, the present results indicate that direction of the virtual agent's body and head also plays a minor but significant role. PMID:26004021

  16. Direct Observation of Morphological Tranformation from Twisted Ribbons into Helical Ribbons

    SciTech Connect

    Pashuck, E.Thomas; Stupp, Samuel I.

    2010-07-01

    We report on the direct observation of a nanostructural transformation from a twisted ribbon to a helical ribbon in supramolecular assemblies of peptide amphiphiles. Using cryogenic electron microscopy, a peptide amphiphile molecule containing aromatic residues was found to first assemble into short twisted ribbons in the time range of seconds, which then elongate in the time scale of minutes, and finally transform into helical ribbons over the course of weeks. By synthesizing an analogous molecule without the aromatic side groups, it was found that a cylindrical nanostructure is formed that does not undergo any transitions during the same time period. The study of metastable states in peptide aggregation can contribute to our understanding of amyloid-related diseases, such as Alzheimer's disease.

  17. Direct Observation of Single DNA Structural Alterations at Low Forces with Surface-Enhanced Raman Scattering

    PubMed Central

    Rao, Satish; Raj, Saurabh; Cossins, Benjamin; Marro, Monica; Guallar, Victor; Petrov, Dmitri

    2013-01-01

    DNA experiences numerous mechanical events, necessitating single-molecule force spectroscopy techniques to provide insight into DNA mechanics as a whole system. Inherent Brownian motion limits current force spectroscopy methods from observing possible bond level structural changes. We combine optical trapping and surface-enhanced Raman scattering to establish a direct relationship between DNA’s extension and structure in the low force, entropic regime. A DNA molecule is trapped close to a surface-enhanced Raman scattering substrate to facilitate a detectable Raman signal. DNA Raman modes shift in response to applied force, indicating phosphodiester mechanical alterations. Molecular dynamic simulations confirm the local structural alterations and the Raman sensitive band identified experimentally. The combined Raman and force spectroscopy technique, to our knowledge, is a novel methodology that can be generalized to all single-molecule studies. PMID:23332068

  18. Direct observations of American eels migrating across the continental shelf to the Sargasso Sea.

    PubMed

    Béguer-Pon, Mélanie; Castonguay, Martin; Shan, Shiliang; Benchetrit, José; Dodson, Julian J

    2015-10-27

    Since inferring spawning areas from larval distributions in the Sargasso Sea a century ago, the oceanic migration of adult American eels has remained a mystery. No adult eel has ever been observed migrating in the open ocean or in the spawning area. Here, we track movements of maturing eels equipped with pop-up satellite archival tags from the Scotian Shelf (Canada) into the open ocean, with one individual migrating 2,400 km to the northern limit of the spawning site in the Sargasso Sea. The reconstructed routes suggest a migration in two phases: one over the continental shelf and along its edge in shallow waters; the second in deeper waters straight south towards the spawning area. This study is the first direct evidence of adult Anguilla migrating to the Sargasso Sea and represents an important step forward in the understanding of routes and migratory cues.

  19. Preliminary findings of an intervention integrating modified directly observed therapy and risk reduction counseling.

    PubMed

    Mitchell, C G; Freels, S; Creticos, C M; Oltean, A; Douglas, R

    2007-04-01

    Various interventions have been proposed to address these ongoing needs of HIV-positive patients as they encounter challenges with medication adherence and risk reduction. This report presents the findings of a study that pilots 'DAART+', an intervention that integrates modified directly observed therapy (MDOT), and risk reduction counseling for a population of marginally housed, substance-using persons. The pilot study intended to assess the feasibility of the intervention and to obtain data to assess the intervention's potential effectiveness. The preliminary data reveal that 83% of participants who completed the intervention (n=18) had undetectable viral load (VL) (VL< or =400 copies/mL) which represents a 2.15 log(10) decrease from baseline. Risk behaviors also changed modestly with self-reported increases in condom usage.

  20. Direct observations of American eels migrating across the continental shelf to the Sargasso Sea

    PubMed Central

    Béguer-Pon, Mélanie; Castonguay, Martin; Shan, Shiliang; Benchetrit, José; Dodson, Julian J.

    2015-01-01

    Since inferring spawning areas from larval distributions in the Sargasso Sea a century ago, the oceanic migration of adult American eels has remained a mystery. No adult eel has ever been observed migrating in the open ocean or in the spawning area. Here, we track movements of maturing eels equipped with pop-up satellite archival tags from the Scotian Shelf (Canada) into the open ocean, with one individual migrating 2,400 km to the northern limit of the spawning site in the Sargasso Sea. The reconstructed routes suggest a migration in two phases: one over the continental shelf and along its edge in shallow waters; the second in deeper waters straight south towards the spawning area. This study is the first direct evidence of adult Anguilla migrating to the Sargasso Sea and represents an important step forward in the understanding of routes and migratory cues. PMID:26505325

  1. Direct observation of half-metallicity in the Heusler compound Co2MnSi.

    PubMed

    Jourdan, M; Minár, J; Braun, J; Kronenberg, A; Chadov, S; Balke, B; Gloskovskii, A; Kolbe, M; Elmers, H J; Schönhense, G; Ebert, H; Felser, C; Kläui, M

    2014-01-01

    Ferromagnetic thin films of Heusler compounds are highly relevant for spintronic applications owing to their predicted half-metallicity, that is, 100% spin polarization at the Fermi energy. However, experimental evidence for this property is scarce. Here we investigate epitaxial thin films of the compound Co2MnSi in situ by ultraviolet-photoemission spectroscopy, taking advantage of a novel multi-channel spin filter. By this surface sensitive method, an exceptionally large spin polarization of (93(-11)(+7)) % at room temperature is observed directly. As a more bulk sensitive method, additional ex situ spin-integrated high energy X-ray photoemission spectroscopy experiments are performed. All experimental results are compared with advanced band structure and photoemission calculations which include surface effects. Excellent agreement is obtained with calculations, which show a highly spin polarized bulk-like surface resonance ingrained in a half metallic bulk band structure.

  2. Build a better mouse: directly-observed issues in computer use for adults with SMI.

    PubMed

    Black, Anne C; Serowik, Kristin L; Schensul, Jean J; Bowen, Anne M; Rosen, Marc I

    2013-03-01

    Integrating information technology into healthcare has the potential to bring treatment to hard-to-reach people. Individuals with serious mental illness (SMI), however, may derive limited benefit from these advances in care because of lack of computer ownership and experience. To date, conclusions about the computer skills and attitudes of adults with SMI have been based primarily on self-report. In the current study, 28 psychiatric outpatients with co-occurring cocaine use were interviewed about their computer use and opinions, and 25 were then directly observed using task analysis and think aloud methods as they navigated a multi-component health informational website. Participants reported low rates of computer ownership and use, and negative attitudes towards computers. Self-reported computer skills were higher than demonstrated in the task analysis. However, some participants spontaneously expressed more positive attitudes and greater computer self-efficacy after navigating the website. Implications for increasing access to computer-based health information are discussed.

  3. Direct observation of Kramers-Kronig self-phasing in coherently combined fiber lasers.

    PubMed

    Chiang, Hung-Sheng; Leger, James R; Nilsson, Johan; Sahu, Jayanta

    2013-10-15

    A highly stable coherent beam-combining system has been designed to measure self-phasing in fiber lasers due to nonlinear effects. Whereas self-phasing in previous coherent combination experiments has been principally attributed to wavelength shifting, these wavelength effects have been efficiently suppressed in our experiment by using a dual-core fiber with closely balanced optical path lengths. The self-phasing from nonlinear effects could then be measured independently and directly by common-path interferometry with a probe laser. The Kramers-Kronig effect in the fiber gain media was observed to induce a phase shift that effectively canceled the applied path length errors, resulting in efficient lasing under all phase conditions. This process was demonstrated to result in robust lasing over a large range of pump conditions.

  4. Direct Observation of Sulfur Radicals as Reaction Media in Lithium Sulfur Batteries

    DOE PAGESBeta

    Wang, Qiang; Zheng, Jianming; Walter, Eric; Pan, Huilin; Lv, Dongping; Zuo, Pengjian; Chen, Honghao; Deng, Z. D.; Liaw, Bor Y.; Yu, Xiqian; et al

    2015-01-09

    Lithium sulfur (Li-S) battery has been regaining tremendous interest in recent years because of its attractive attributes such as high gravimetric energy, low cost and environmental benignity. However, it is still not conclusively known how polysulfide ring/chain participates in the whole cycling and whether the discharge and charge processes follow the same pathway. Herein, we demonstrate the direct observation of sulfur radicals by using in situ electron paramagnetic resonance (EPR) technique. Based on the concentration changes of sulfur radicals at different potentials and the electrochemical characteristics of the cell, it is revealed that the chemical and electrochemical reactions in Li-Smore » cell are driving each other to proceed through sulfur radicals, leading to two completely different reaction pathways during discharge and charge. The proposed radical mechanism may provide new perspectives to investigate the interactions between sulfur species and the electrolyte, inspiring novel strategies to develop Li-S battery technology.« less

  5. Direct Observation of Sulfur Radicals as Reaction Media in Lithium Sulfur Batteries

    SciTech Connect

    Wang, Qiang; Zheng, Jianming; Walter, Eric; Pan, Huilin; Lv, Dongping; Zuo, Pengjian; Chen, Honghao; Deng, Z. D.; Liaw, Bor Y.; Yu, Xiqian; Yang, Xiao-Qing; Zhang, Ji-Guang; Liu, Jun; Xiao, Jie

    2015-01-09

    Lithium sulfur (Li-S) battery has been regaining tremendous interest in recent years because of its attractive attributes such as high gravimetric energy, low cost and environmental benignity. However, it is still not conclusively known how polysulfide ring/chain participates in the whole cycling and whether the discharge and charge processes follow the same pathway. Herein, we demonstrate the direct observation of sulfur radicals by using in situ electron paramagnetic resonance (EPR) technique. Based on the concentration changes of sulfur radicals at different potentials and the electrochemical characteristics of the cell, it is revealed that the chemical and electrochemical reactions in Li-S cell are driving each other to proceed through sulfur radicals, leading to two completely different reaction pathways during discharge and charge. The proposed radical mechanism may provide new perspectives to investigate the interactions between sulfur species and the electrolyte, inspiring novel strategies to develop Li-S battery technology.

  6. Direct observation of magnetization dynamics generated by nanocontact spin-torque vortex oscillators

    NASA Astrophysics Data System (ADS)

    Keatley, P. S.; Sani, S. R.; Hrkac, G.; Mohseni, S. M.; Dürrenfeld, P.; Loughran, T. H. J.; Åkerman, J.; Hicken, R. J.

    2016-08-01

    Time-resolved scanning Kerr microscopy has been used to directly image the magnetization dynamics of nanocontact (NC) spin-torque vortex oscillators (STVOs) when phase locked to an injected microwave (rf) current. The Kerr images reveal free-layer magnetization dynamics that extend outside the NC footprint, where they cannot be detected electrically, but which are crucial to phase-lock STVOs that share common magnetic layers. For a single NC, dynamics were observed not only when the STVO frequency was fully locked to that of the rf current, but also for a partially locked state characterized by periodic changes in the core trajectory at the rf frequency. For a pair of NCs, we explore the correlation between the spatial character of injection-locked dynamics and the free-running spectra. Insight gained from these images may improve understanding of the conditions required for mutual phase locking of multiple STVOs, and hence enhanced microwave power emission.

  7. Cardiac-induced physiologic noise in tissue is a direct observation of cardiac-induced fluctuations.

    PubMed

    Bhattacharyya, Pallab K; Lowe, Mark J

    2004-01-01

    Recent studies have shown that in certain cases, cardiac and respiratory rate fluctuations in BOLD-weighted MRI time courses may be an artifact unique to rapid sampled acquisitions and may not be present in longer repetition-time acquisitions. The implication of this is that, in these cases, cardiac and respiratory rate fluctuations are not aliased into data that undersample these effects and do not affect the resulting time course measurements. In this study, we show that these cases are specific to regions of large cerebrospinal fluid content and are not generally true for gray matter regions of the brain. We demonstrate that in many brain regions of interest, these fluctuations are directly observed as BOLD fluctuations and thus will affect measurements that undersample these effects.

  8. A novel approach to directly observed therapy for tuberculosis in an HIV-endemic area.

    PubMed Central

    Desvarieux, M; Hyppolite, P R; Johnson, W D; Pape, J W

    2001-01-01

    OBJECTIVES: This study evaluated a novel approach to the delivery of directly observed therapy (DOT) for tuberculosis in Haiti. METHODS: A total of 194 patients (152 HIV seropositive, 42 HIV seronegative) received daily unsupervised triple-drug therapy for 4 to 8 weeks, followed by twice-weekly 2-drug therapy for the remainder of the 6-month period. DOT was deferred until initiation of the twice-weekly phase. RESULTS: A total of 169 of 194 patients (87.1%) completed the 6-month course. The program of deferred DOT had an effectiveness of 85%. Overall cost was reduced by approximately 40%. CONCLUSIONS: Flexible approaches to DOT, integrating behavioral knowledge, cost considerations, and practicality may improve completion rates and program effectiveness. PMID:11189809

  9. Direct Observation of Sulfur Radicals as Reaction Media in lithium Sulfur Batteries

    SciTech Connect

    Wang, Qiang; Zheng, Jianming; Walter, Eric D.; Pan, Huilin; Lu, Dongping; Zuo, Pengjian; Chen, Honghao; Deng, Zhiqun; Liaw, Bor Yann; Yu, Xiqian; Yang, Xiaoning; Zhang, Jiguang; Liu, Jun; Xiao, Jie

    2014-12-09

    Lithium sulfur (Li-S) battery has been regaining tremendous interest in recent years because of its attractive attributes such as high gravimetric energy, low cost and environmental benignity. However, it is still not conclusively known how polysulfide ring/chain participates in the whole cycling and whether the discharge and charge process follow the same pathway. Herein, we demonstrate the direct observation of sulfur radicals by using in situ electron paramagnetic resonance (EPR) technique. Based on the concentration changes of sulfur radicals at different potentials, it is revealed that the chemical and electrochemical reactions in Li-S cell are driven each other to proceed through sulfur radicals, leading to two completely different reaction pathways during discharge and charge. The proposed radical mechanism may provide new insights to investigate the interactions between sulfur species and the electrolyte, inspiring novel strategies to develop Li-S battery technology.

  10. Copernicus observations of interstellar matter in the direction of HR 1099

    NASA Technical Reports Server (NTRS)

    Anderson, R. C.; Weiler, E. J.

    1978-01-01

    Results are reported for high-resolution Copernicus U1 and V2 scans of the bright RS CVn spectroscopic binary HR 1099. The observations reveal strong UV emission lines at L-alpha and Mg II h and k from the stars as well as interstellar H I and D I L-alpha absorption lines and interstellar Mg II h and k absorption in the direction of the binary system. Column densities, bulk velocities, and temperatures are derived for the interstellar features. A comparison of the derived number density of interstellar H I with data for the nearby star Epsilon Eri indicates an inhomogeneous distribution of interstellar hydrogen along the line of sight. The range of values obtained for the D/H ratio is shown to be consistent with results of other studies. A depletion factor of at least 5 with respect to the solar abundance is estimated for the interstellar magnesium.

  11. Copernicus observations of neutral hydrogen and deuterium in the direction of HR 1099

    NASA Technical Reports Server (NTRS)

    Anderson, R. C.; Weiler, E. J.

    1979-01-01

    High-resolution Copernicus U1 scans were obtained of the bright RS CVn binary HR 1099 (d = 33 pc, galactic longitude = 185 deg, galactic latitude = -41 deg) in October 1977. Strong emission at L-alpha was detected. The interstellar L-alpha absorption features of H I and D I were also observed. Analyses of these interstellar lines are reported in this paper. The average density of neutral H in the direction of this system is found to be 0.006-0.012 per cu cm, which, because the local density is higher, requires a marked inhomogeneity along this line of sight. This result, when combined with other recent studies of the local interstellar medium, suggests the sun is located within a moderate-density H I region.

  12. Direct observations of American eels migrating across the continental shelf to the Sargasso Sea.

    PubMed

    Béguer-Pon, Mélanie; Castonguay, Martin; Shan, Shiliang; Benchetrit, José; Dodson, Julian J

    2015-01-01

    Since inferring spawning areas from larval distributions in the Sargasso Sea a century ago, the oceanic migration of adult American eels has remained a mystery. No adult eel has ever been observed migrating in the open ocean or in the spawning area. Here, we track movements of maturing eels equipped with pop-up satellite archival tags from the Scotian Shelf (Canada) into the open ocean, with one individual migrating 2,400 km to the northern limit of the spawning site in the Sargasso Sea. The reconstructed routes suggest a migration in two phases: one over the continental shelf and along its edge in shallow waters; the second in deeper waters straight south towards the spawning area. This study is the first direct evidence of adult Anguilla migrating to the Sargasso Sea and represents an important step forward in the understanding of routes and migratory cues. PMID:26505325

  13. Direct observation of hierarchical nucleation of martensite and size-dependent superelasticity in shape memory alloys.

    PubMed

    Liu, Lifeng; Ding, Xiangdong; Li, Ju; Lookman, Turab; Sun, Jun

    2014-02-21

    Martensitic transformation usually creates hierarchical internal structures beyond mere change of the atomic crystal structure. Multi-stage nucleation is thus required, where nucleation (level-1) of the underlying atomic crystal lattice does not have to be immediately followed by the nucleation of higher-order superstructures (level-2 and above), such as polysynthetic laths. Using in situ transmission electron microscopy (TEM), we directly observe the nucleation of the level-2 superstructure in a Cu-Al-Ni single crystal under compression, with critical super-nuclei size L2c around 500 nm. When the sample size D decreases below L2c, the superelasticity behavior changes from a flat stress plateau to a continuously rising stress-strain curve. Such size dependence definitely would impact the application of shape memory alloys in miniaturized MEMS/NEMS devices.

  14. Direct observation of resistive heating at graphene wrinkles and grain boundaries

    SciTech Connect

    Grosse, Kyle L.; Dorgan, Vincent E.; Estrada, David; Wood, Joshua D.; Vlassiouk, Ivan V; Eres, Gyula; Lyding, Joseph W; King, William P.; Pop, Eric

    2014-01-01

    We directly measure the nanometer-scale temperature rise at wrinkles and grain boundaries (GBs) in functioning graphene devices by scanning Joule expansion microscopy with 50 nm spatial and 0.2K temperature resolution. We observe a small temperature increase at select wrinkles and a large (100 K) temperature increase at GBs between coalesced hexagonal grains. Comparisons of measurements with device simulations estimate the GB resistivity (8 150 X lm) among the lowest reported for graphene grown by chemical vapor deposition. An analytical model is developed, showing that GBs can experience highly localized resistive heating and temperature rise, most likely affecting the reliability of graphene devices. Our studies provide an unprecedented view of thermal effects surrounding nanoscale defects in nanomaterials such as graphene.

  15. Direct observation of hierarchical nucleation of martensite and size-dependent superelasticity in shape memory alloys.

    PubMed

    Liu, Lifeng; Ding, Xiangdong; Li, Ju; Lookman, Turab; Sun, Jun

    2014-02-21

    Martensitic transformation usually creates hierarchical internal structures beyond mere change of the atomic crystal structure. Multi-stage nucleation is thus required, where nucleation (level-1) of the underlying atomic crystal lattice does not have to be immediately followed by the nucleation of higher-order superstructures (level-2 and above), such as polysynthetic laths. Using in situ transmission electron microscopy (TEM), we directly observe the nucleation of the level-2 superstructure in a Cu-Al-Ni single crystal under compression, with critical super-nuclei size L2c around 500 nm. When the sample size D decreases below L2c, the superelasticity behavior changes from a flat stress plateau to a continuously rising stress-strain curve. Such size dependence definitely would impact the application of shape memory alloys in miniaturized MEMS/NEMS devices. PMID:24384687

  16. Direct observations of gas-hydrate formation in natural porous media on the micro-scale

    NASA Astrophysics Data System (ADS)

    Chaouachi, M.; Sell, K.; Falenty, A.; Enzmann, F.; Kersten, M.; Pinzer, B.; Saenger, E. H.; Kuhs, W. F.

    2013-12-01

    Gas hydrates (GH) are crystalline, inclusion compounds consisting of hydrogen-bonded water network encaging small gas molecules such as methane, ethane, CO2, etc (Sloan and Koh 2008). Natural gas hydrates are found worldwide in marine sediments and permafrost regions as a result of a reaction of biogenic or thermogenic gas with water under elevated pressure. Although a large amount of research on GH has been carried out over the years, the micro-structural aspects of GH growth, and in particular the contacts with the sedimentary matrix as well as the details of the distribution remain largely speculative. The present study was undertaken to shed light onto the well-established but not fully understood seismic anomalies, in particular the unusual attenuation of seismic waves in GH-bearing sediments, which may well be linked to micro-structural features. Observations of in-situ GH growth have been performed in a custom-build pressure cell (operating pressures up to several bar) mounted at the TOMCAT beam line of SLS/ PSI. In order to provide sufficient absorption contrast between phases and reduce pressure requirements for the cell we have used Xe instead of CH4. To the best of our knowledge this represents the first direct observation of GH growth in natural porous media with sub-micron spatial resolution and gives insight into the nucleation location and growth process of GH. The progress of the formation of sI Xe-hydrate in natural quartz sand was observed with a time-resolution of several minutes; the runs were conducted with an excess of a free-gas phase and show that the nucleation starts at the gas-water interface. Initially, a GH film is formed at this interface with a typical thickness of several μm; this film may well be permeable to gas as suggested in the past - which would explain the rapid transport of gas molecules for further conversion of water to hydrate, completed in less than 20 min. Clearly, initially the growth is directed mainly into the

  17. The Analysis of Optical, Direct Detection Communication Systems with Point Process Observations

    NASA Astrophysics Data System (ADS)

    Brady, David Paul

    1990-01-01

    The central theme of this work is the analysis of direct-detection optical communication channels based on point process observations. For example, we consider an optical DPSK receiver which is based on a binary hypothesis test with conditionally Poisson count observations. The error probability is influenced by the transmitting laser phase noise as well as the statistical nature of light, and decreases to the quantum limit as the transmitting laser linewidth vanishes. We bound the bit error rate by bounding the conditional photon arrival rates, and were shown to converge as the laser linewidth decreases. We also derive the exact error rate of a noncoherent, optical, asynchronous, CDMA system. The receiver utilizes fiber optic tap delay lines to create and correlate the signature sequence with the received point process, and compares an electron count to a threshold to decide for the data of the user of interest. The optical intensity on a surface illuminated by several phase-coherent signals is determined, and it is shown that the approximation of noncoherent addition in the fiber optic tap delay line is justified. The bit error rate is found for arbitrary photomultipliers and signature sequence sets, adheres fully to the semi-classical model of light, and does not depend on approximations for large user groups, strong received optical fields, or chip synchronism. The capacity of a direct-detection photon counting channel is addressed in this work. The limiting form of the capacity is found as the signal and noise energies increase proportionally, and it is shown that the capacity grows logarithmically with the signal energy constraint. When the noise energy increases polynomially with the signal energy, the limiting capacity coincides with that of a Gaussian channel with a positivity and variance constraint. Bounds on the capacity are considered for small and moderate energies by restricting attention to binary inputs. These bounds are arbitrarily tight, and are

  18. Direct single-molecule observation of calcium-dependent misfolding in human neuronal calcium sensor-1.

    PubMed

    Heidarsson, Pétur O; Naqvi, Mohsin M; Otazo, Mariela R; Mossa, Alessandro; Kragelund, Birthe B; Cecconi, Ciro

    2014-09-01

    Neurodegenerative disorders are strongly linked to protein misfolding, and crucial to their explication is a detailed understanding of the underlying structural rearrangements and pathways that govern the formation of misfolded states. Here we use single-molecule optical tweezers to monitor misfolding reactions of the human neuronal calcium sensor-1, a multispecific EF-hand protein involved in neurotransmitter release and linked to severe neurological diseases. We directly observed two misfolding trajectories leading to distinct kinetically trapped misfolded conformations. Both trajectories originate from an on-pathway intermediate state and compete with native folding in a calcium-dependent manner. The relative probability of the different trajectories could be affected by modulating the relaxation rate of applied force, demonstrating an unprecedented real-time control over the free-energy landscape of a protein. Constant-force experiments in combination with hidden Markov analysis revealed the free-energy landscape of the misfolding transitions under both physiological and pathological calcium concentrations. Remarkably for a calcium sensor, we found that higher calcium concentrations increased the lifetimes of the misfolded conformations, slowing productive folding to the native state. We propose a rugged, multidimensional energy landscape for neuronal calcium sensor-1 and speculate on a direct link between protein misfolding and calcium dysregulation that could play a role in neurodegeneration. PMID:25157171

  19. Direct radiative feedback due to biogenic secondary organic aerosol estimated from boreal forest site observations

    NASA Astrophysics Data System (ADS)

    Lihavainen, Heikki; Asmi, Eija; Aaltonen, Veijo; Makkonen, Ulla; Kerminen, Veli-Matti

    2015-10-01

    We used more than five years of continuous aerosol measurements to estimate the direct radiative feedback parameter associated with the formation of biogenic secondary organic aerosol (BSOA) at a remote continental site at the edge of the boreal forest zone in Northern Finland. Our upper-limit estimate for this feedback parameter during the summer period (ambient temperatures above 10 °C) was -97 ± 66 mW m-2 K-1 (mean ± STD) when using measurements of the aerosol optical depth (fAOD) and -63 ± 40 mW m-2 K-1 when using measurements of the ‘dry’ aerosol scattering coefficient at the ground level (fσ). Here STD represents the variability in f caused by the observed variability in the quantities used to derive the value of f. Compared with our measurement site, the magnitude of the direct radiative feedback associated with BSOA is expected to be larger in warmer continental regions with more abundant biogenic emissions, and even larger in regions where biogenic emissions are mixed with anthropogenic pollution.

  20. Direct single-molecule observation of calcium-dependent misfolding in human neuronal calcium sensor-1

    PubMed Central

    Heidarsson, Pétur O.; Naqvi, Mohsin M.; Otazo, Mariela R.; Mossa, Alessandro; Kragelund, Birthe B.; Cecconi, Ciro

    2014-01-01

    Neurodegenerative disorders are strongly linked to protein misfolding, and crucial to their explication is a detailed understanding of the underlying structural rearrangements and pathways that govern the formation of misfolded states. Here we use single-molecule optical tweezers to monitor misfolding reactions of the human neuronal calcium sensor-1, a multispecific EF-hand protein involved in neurotransmitter release and linked to severe neurological diseases. We directly observed two misfolding trajectories leading to distinct kinetically trapped misfolded conformations. Both trajectories originate from an on-pathway intermediate state and compete with native folding in a calcium-dependent manner. The relative probability of the different trajectories could be affected by modulating the relaxation rate of applied force, demonstrating an unprecedented real-time control over the free-energy landscape of a protein. Constant-force experiments in combination with hidden Markov analysis revealed the free-energy landscape of the misfolding transitions under both physiological and pathological calcium concentrations. Remarkably for a calcium sensor, we found that higher calcium concentrations increased the lifetimes of the misfolded conformations, slowing productive folding to the native state. We propose a rugged, multidimensional energy landscape for neuronal calcium sensor-1 and speculate on a direct link between protein misfolding and calcium dysregulation that could play a role in neurodegeneration. PMID:25157171

  1. Direct observation of Landau levels of massless and massive Dirac fermions.

    NASA Astrophysics Data System (ADS)

    Li, Guohong; Andrei, Eva Y.

    2007-03-01

    The low energy quasiparticles in graphene resemble massless relativistic particles (Dirac fermions): they have a linear energy-momentum spectrum and possess internal degrees of freedom arising from the crystal symmetry of the honeycomb lattice, leading to particle anti-particle pairs. When two layers of graphene are coupled together, the quasiparticles acquire a band-mass and are transformed into chiral massive fermions. Both types of quasiparticles develop unusual Landau levels in a magnetic field which profoundly alter the magneto-transport properties. We will report the direct observation of the Landau levels associated with these quasiparticles using a low temperature STM in fields up to 12 Tesla. The experiments reveal two independent sequences of Landau levels that provide evidence for the coexistence of massless and massive Dirac fermions. The energy levels of the former exhibit a square-root dependence on both field and Landau-level index n, while the latter are linear in field with a Landau-level index dependence of [n(n+1)]^1/2. Both sequences exhibit a zero energy Landau level which is a unique and direct consequence of the quantum-relativistic nature of these quasiparticles.

  2. Direct Observation of α-Synuclein Amyloid Aggregates in Endocytic Vesicles of Neuroblastoma Cells

    PubMed Central

    Subramaniam, Vinod; Canters, Gerard W.; Schmidt, Thomas; Aartsma, Thijs J.

    2016-01-01

    Aggregation of α-synuclein has been linked to both familial and sporadic Parkinson’s disease. Recent studies suggest that α-synuclein aggregates may spread from cell to cell and raise questions about the propagation of neurodegeneration. While continuous progress has been made characterizing α-synuclein aggregates in vitro, there is a lack of information regarding the structure of these species inside the cells. Here, we use confocal fluorescence microscopy in combination with direct stochastic optical reconstruction microscopy, dSTORM, to investigate α-synuclein uptake when added exogenously to SH-SY5Y neuroblastoma cells, and to probe in situ morphological features of α-synuclein aggregates with near nanometer resolution. We demonstrate that using dSTORM, it is possible to follow noninvasively the uptake of extracellularly added α-synuclein aggregates by the cells. Once the aggregates are internalized, they move through the endosomal pathway and accumulate in lysosomes to be degraded. Our dSTORM data show that α-synuclein aggregates remain assembled after internalization and they are shortened as they move through the endosomal pathway. No further aggregation was observed inside the lysosomes as speculated in the literature, nor in the cytoplasm of the cells. Our study thus highlights the super-resolution capability of dSTORM to follow directly the endocytotic uptake of extracellularly added amyloid aggregates and to probe the morphology of in situ protein aggregates even when they accumulate in small vesicular compartments. PMID:27105068

  3. Low Frequency Radio Observations of Bi-directional Electron Beams in the Solar Corona

    NASA Astrophysics Data System (ADS)

    Carley, E.; Reid, H.; Vilmer, N.; Gallagher, P.

    2015-12-01

    The radio signature of a shock travelling through the solar corona is known as a type II solar radio burst. In rare cases, these bursts can exhibit a fine structure known as 'herringbones' which are a direct indicator of particle acceleration occurring at the shock front. However, few studies have been performed on herringbones and the details of the underlying particle acceleration processes are unknown. Here, we use an image processing technique known as the Hough transform to statistically analyse the herringbone fine structure in a radio burst at 20-90MHz observed from the Rosse Solar-Terrestrial Observatory on 2011 September 22. We identify 188 individual bursts which are signatures of bi-directional electron beams continuously accelerated to speeds of 0.16 c. This occurs at a shock acceleration site initially at a constant altitude of 0.6 Rsun in the corona, followed by a shift to 0.5 Rsun. The anti-sunward beams travel a distance of 170 Mm (and possibly further) away from the acceleration site, while those travelling toward the sun come to a stop sooner, reaching a smaller distance of 112 Mm. We show that the stopping distance for the sunward beams may depend on the total number density and the velocity of the beam. Our study concludes that a detailed statistical analysis of herringbone fine structure can provide information on the physical properties of the corona which lead to these relatively rare radio bursts.

  4. Ultrasound Open Channel Flow-Speed Measurement Based on the Lateral Directional Echo Observations

    NASA Astrophysics Data System (ADS)

    Nishimura, Ichiro; Ishigamori, Mitsuhide; Yamada, Akira

    2012-07-01

    Conventional ultrasonic flowmeters have a problem in measuring the small open channel fluid flow. To solve this problem, a lateral observation technique using a single transmitter/receiver transducer attached at the bottom of the pipe was proposed. Pulse echo signals scattered from the particles in the medium were repetitively recorded with a constant time interval. From the slope of the correlation peak amplitude with the variation in pulse echo excitation time, the flow speed of the medium was estimated. The method has an advantage in that the variation in flow speed in the vertical depth direction is directly measured with a minimum measurement space. Moreover, the fluctuations caused by the turbulent water can be avoided compared with the case of a conventional method based on the time estimation method. Bubbles were generated by an aspirator and flour powder was mixed with water as scatterers in the imitated drainage water. The flow speed of water was measured with respect to the inflowing fluid volume. Moreover, vertical flow speed profiles were measured and compared with fluid flow simulation results. The results showed that the precision of the measured flow speed was satisfactory and tolerant against the turbulence of the water flow medium.

  5. Direct observation of slow intersystem crossing in an aromatic ketone, fluorenone.

    PubMed

    Soep, Benoît; Mestdagh, Jean-Michel; Briant, Marc; Gaveau, Marc-André; Poisson, Lionel

    2016-08-17

    Direct measurements of Single vibronic Level InterSystem Crossing (SLISC) have been performed on the fluorenone molecule in the gas phase, by time resolved photoelectron and photoion spectroscopy. Vibronic transitions above the S1 nπ* origin were excited in the 432-420 nm region and the decay of S1 and growth of T1(3)ππ* could be observed within a 10 ns time domain. The ionization potential is measured as 8.33 ± 0.04 eV. The energy of the first excited triplet state of fluorenone, T1 has been characterized directly at 18 640 ± 250 cm(-1). The internal conversion of S1 to S0 is found to amount to ∼15% of the population decay, thus ISC is the dominant electronic relaxation process. ISC, although favored by the S1(1)nπ*-T1(3)ππ* coupling scheme, is 3 orders of magnitude less efficient than in the similar molecule benzophenone. Thus, the planarity of the fluorenone molecule disfavors the exploration of the configuration space where surface crossings would create high ISC probability, which occurs in benzophenone through surface crossings. The time evolution of S1 fluorenone is well accounted for by the statistical decay of individual levels into a quasi-continuum of T1 vibronic levels. PMID:27485671

  6. BCL::EM-Fit: rigid body fitting of atomic structures into density maps using geometric hashing and real space refinement.

    PubMed

    Woetzel, Nils; Lindert, Steffen; Stewart, Phoebe L; Meiler, Jens

    2011-09-01

    Cryo-electron microscopy (cryoEM) can visualize large macromolecular assemblies at resolutions often below 10Å and recently as good as 3.8-4.5 Å. These density maps provide important insights into the biological functioning of molecular machineries such as viruses or the ribosome, in particular if atomic-resolution crystal structures or models of individual components of the assembly can be placed into the density map. The present work introduces a novel algorithm termed BCL::EM-Fit that accurately fits atomic-detail structural models into medium resolution density maps. In an initial step, a "geometric hashing" algorithm provides a short list of likely placements. In a follow up Monte Carlo/Metropolis refinement step, the initial placements are optimized by their cross correlation coefficient. The resolution of density maps for a reliable fit was determined to be 10 Å or better using tests with simulated density maps. The algorithm was applied to fitting of capsid proteins into an experimental cryoEM density map of human adenovirus at a resolution of 6.8 and 9.0 Å, and fitting of the GroEL protein at 5.4 Å. In the process, the handedness of the cryoEM density map was unambiguously identified. The BCL::EM-Fit algorithm offers an alternative to the established Fourier/Real space fitting programs. BCL::EM-Fit is free for academic use and available from a web server or as downloadable binary file at http://www.meilerlab.org.

  7. BCL::EM-Fit: Rigid body fitting of atomic structures into density maps using geometric hashing and real space refinement

    PubMed Central

    Woetzel, Nils; Lindert, Steffen; Stewart, Phoebe L.; Meiler, Jens

    2011-01-01

    Cryo-Electron Microscopy can visualize large macromolecular assemblies at resolutions often below 10 Å and recently as good as 3.8–4.5 Å. These density maps provide important insights into the biological functioning of molecular machineries such as viruses or the ribosome, in particular if atomic-resolution crystal structures or models of individual components of the assembly can be placed into the density map. The present work introduces a novel algorithm termed BCL::EM-Fit that accurately fits atomic-detail structural models into medium resolution density maps. In an initial step, a “geometric hashing” algorithm provides a short list of likely placements. In a follow up Monte Carlo/Metropolis refinement step, the initial placements are optimized by their cross correlation coefficient. The resolution of density maps for a reliable fit was determined to be 10 Å or better using tests with simulated density maps. The algorithm was applied to fitting of capsid proteins into an experimental cryoEM density map of human adenovirus at a resolution of 6.8 and 9.0 Å, and fitting of the GroEL protein at 5.4 Å. In the process, the handedness of the cryoEM density map was unambiguously identified. The BCL::EM-Fit algorithm offers an alternative to the established Fourier/Real space fitting programs. BCL::EM-Fit is free for academic use and available from a webserver or as downloadable binary file at http://www.meilerlab.org. PMID:21565271

  8. Direct Observation of Controlled Melting and Resolidification of Succinonitrile Mixtures in a Microgravity Environment

    NASA Technical Reports Server (NTRS)

    Grugel, R. N.; Anilkumar, A. V.; Lee, C. P.

    2004-01-01

    In support of the Pore Formation and Mobility Investigation (PFMI) direct observation of experiments on the controlled melting and subsequent resolidification of succinonitrile were conducted in the glovebox facility (GBX) of the International Space Station (ISS). Samples were prepared on ground by filling glass tubes, 1 cm ID and approximately 30 cm in length, with pure succinonitrile (SCN) and SCN-Water mixtures under 450 millibar of nitrogen. Experimental processing parameters of temperature gradient and translation speed, as well as camera settings, were remotely monitored and manipulated from the ground Telescience Center (TSC) at the Marshall Space Flight Center. Sample temperatures are monitored by six in situ thermocouples. Real time visualization during melt back revealed bubbles of different sizes initiating at the solid/liquid interface, their release, interactions, and movement into the temperature field ahead of them. Subsequent re-solidification examined planar interface breakdown and the transition to steady-state dendritic growth. A preliminary analysis of the observed phenomena and its implication to future microgravity experiments is presented and discussed.

  9. Direct observations of evolving subglacial drainage beneath the Greenland Ice Sheet.

    PubMed

    Andrews, Lauren C; Catania, Ginny A; Hoffman, Matthew J; Gulley, Jason D; Lüthi, Martin P; Ryser, Claudia; Hawley, Robert L; Neumann, Thomas A

    2014-10-01

    Seasonal acceleration of the Greenland Ice Sheet is influenced by the dynamic response of the subglacial hydrologic system to variability in meltwater delivery to the bed via crevasses and moulins (vertical conduits connecting supraglacial water to the bed of the ice sheet). As the melt season progresses, the subglacial hydrologic system drains supraglacial meltwater more efficiently, decreasing basal water pressure and moderating the ice velocity response to surface melting. However, limited direct observations of subglacial water pressure mean that the spatiotemporal evolution of the subglacial hydrologic system remains poorly understood. Here we show that ice velocity is well correlated with moulin hydraulic head but is out of phase with that of nearby (0.3-2 kilometres away) boreholes, indicating that moulins connect to an efficient, channelized component of the subglacial hydrologic system, which exerts the primary control on diurnal and multi-day changes in ice velocity. Our simultaneous measurements of moulin and borehole hydraulic head and ice velocity in the Paakitsoq region of western Greenland show that decreasing trends in ice velocity during the latter part of the melt season cannot be explained by changes in the ability of moulin-connected channels to convey supraglacial melt. Instead, these observations suggest that decreasing late-season ice velocity may be caused by changes in connectivity in unchannelized regions of the subglacial hydrologic system. Understanding this spatiotemporal variability in subglacial pressures is increasingly important because melt-season dynamics affect ice velocity beyond the conclusion of the melt season. PMID:25279921

  10. Direct reconstruction of dynamical dark energy from observational Hubble parameter data

    NASA Astrophysics Data System (ADS)

    Liu, Zhi-E.; Yu, Hao-Ran; Zhang, Tong-Jie; Tang, Yan-Ke

    2016-12-01

    Reconstructing the evolution history of the dark energy equation of state parameter w(z) directly from observational data is highly valuable in cosmology, since it contains substantial clues in understanding the nature of the accelerated expansion of the Universe. Many works have focused on reconstructing w(z) using Type Ia supernova data, however, only a few studies pay attention to Hubble parameter data. In the present work, we explore the merit of Hubble parameter data and make an attempt to reconstruct w(z) from them through the principle component analysis approach. We find that current Hubble parameter data perform well in reconstructing w(z) ; though, when compared to supernova data, the data are scant and their quality is worse. Both ΛCDM and evolving w(z) models can be constrained within 10 % at redshifts z ≲ 1.5 and even 5 % at redshifts 0.1 ≲ z ≲ 1 by using simulated H(z) data of observational quality.

  11. Incorporating a disturbance observer with direct velocity feedback for control of human-induced vibrations

    NASA Astrophysics Data System (ADS)

    Nyawako, Donald; Reynolds, Paul; Hudson, Emma

    2016-04-01

    Feedback control strategies are desirable for disturbance rejection of human-induced vibrations in civil engineering structures as human walking forces cannot easily be measured. In relation to human-induced vibration control studies, most past researches have focused on floors and footbridges and the widely used linear controller implemented in the trials has been the direct velocity feedback (DVF) scheme. With appropriate compensation to enhance its robustness, it has been shown to be effective at damping out the problematic modes of vibration of the structures in which the active vibration control systems have been implemented. The work presented here introduces a disturbance observer (DOB) that is used with an outer-loop DVF controller. Results of analytical studies presented in this work based on the dynamic properties of a walkway bridge structure demonstrate the potential of this approach for enhancing the vibration mitigation performance offered by a purely DVF controller. For example, estimates of controlled frequency response functions indicate improved attenuation of vibration around the dominant frequency of the walkway bridge structure as well as at higher resonant frequencies. Controlled responses from three synthesized walking excitation forces on a walkway bridge structure model show that the inclusion of the disturbance observer with an outer loop DVF has potential to improve on the vibration mitigation performance by about 3.5% at resonance and 6-10% off-resonance. These are realised with hard constraints being imposed on the low frequency actuator displacements.

  12. Direct observations of evolving subglacial drainage beneath the Greenland Ice Sheet.

    PubMed

    Andrews, Lauren C; Catania, Ginny A; Hoffman, Matthew J; Gulley, Jason D; Lüthi, Martin P; Ryser, Claudia; Hawley, Robert L; Neumann, Thomas A

    2014-10-01

    Seasonal acceleration of the Greenland Ice Sheet is influenced by the dynamic response of the subglacial hydrologic system to variability in meltwater delivery to the bed via crevasses and moulins (vertical conduits connecting supraglacial water to the bed of the ice sheet). As the melt season progresses, the subglacial hydrologic system drains supraglacial meltwater more efficiently, decreasing basal water pressure and moderating the ice velocity response to surface melting. However, limited direct observations of subglacial water pressure mean that the spatiotemporal evolution of the subglacial hydrologic system remains poorly understood. Here we show that ice velocity is well correlated with moulin hydraulic head but is out of phase with that of nearby (0.3-2 kilometres away) boreholes, indicating that moulins connect to an efficient, channelized component of the subglacial hydrologic system, which exerts the primary control on diurnal and multi-day changes in ice velocity. Our simultaneous measurements of moulin and borehole hydraulic head and ice velocity in the Paakitsoq region of western Greenland show that decreasing trends in ice velocity during the latter part of the melt season cannot be explained by changes in the ability of moulin-connected channels to convey supraglacial melt. Instead, these observations suggest that decreasing late-season ice velocity may be caused by changes in connectivity in unchannelized regions of the subglacial hydrologic system. Understanding this spatiotemporal variability in subglacial pressures is increasingly important because melt-season dynamics affect ice velocity beyond the conclusion of the melt season.

  13. Direct observation and control of supported lipid bilayer formation with interferometric scattering microscopy.

    PubMed

    Andrecka, Joanna; Spillane, Katelyn M; Ortega-Arroyo, Jaime; Kukura, Philipp

    2013-12-23

    Supported lipid bilayers (SLB) are frequently used to study processes associated with or mediated by lipid membranes. The mechanism by which SLBs form is a matter of debate, largely due to the experimental difficulty associated with observing the adsorption and rupture of individual vesicles. Here, we used interferometric scattering microscopy (iSCAT) to directly visualize membrane formation from nanoscopic vesicles in real time. We observed a number of previously proposed phenomena such as vesicle adsorption, rupture, movement, and a wave-like bilayer spreading. By varying the vesicle size and the lipid-surface interaction strength, we rationalized and tuned the relative contributions of these phenomena to bilayer formation. Our results support a model where the interplay between bilayer edge tension and the overall interaction energy with the surface determine the mechanism of SLB formation. The unique combination of sensitivity, speed, and label-free imaging capability of iSCAT provides exciting prospects not only for investigations of SLB formation, but also for studies of assembly and disassembly processes on the nanoscale with previously unattainable accuracy and sensitivity.

  14. Direct observation of interfacial Au atoms on TiO₂ in three dimensions.

    PubMed

    Gao, Wenpei; Sivaramakrishnan, Shankar; Wen, Jianguo; Zuo, Jian-Min

    2015-04-01

    Interfacial atoms, which result from interactions between the metal nanoparticles and support, have a large impact on the physical and chemical properties of nanoparticles. However, they are difficult to observe; the lack of knowledge has been a major obstacle toward unraveling their role in chemical transformations. Here we report conclusive evidence of interfacial Au atoms formed on the rutile (TiO2) (110) surfaces by activation using high-temperature (∼500 °C) annealing in air. Three-dimensional imaging was performed using depth-sectioning enabled by aberration-corrected scanning transmission electron microscopy. Results show that the interface between Au nanocrystals and TiO2 (110) surfaces consists of a single atomic layer with Au atoms embedded inside Ti-O. The number of interfacial Au atoms is estimated from ∼1-8 in an interfacial atomic column. Direct impact of interfacial Au atoms is observed on an enhanced Au-TiO2 interaction and the reduction of surface TiO2; both are critical to Au catalysis.

  15. Direct observation of small cluster mobility and ripening. [during annealing of metal films on amorphous substrates

    NASA Technical Reports Server (NTRS)

    Heinemann, K.; Poppa, H.

    1975-01-01

    Direct evidence is reported for the simultaneous occurrence of Ostwald ripening and short-distance cluster mobility during annealing of discontinuous metal films on clean amorphous substrates. The annealing characteristics of very thin particulate deposits of silver on amorphized clean surfaces of single crystalline thin graphite substrates were studied by in-situ transmission electron microscopy (TEM) under controlled environmental conditions (residual gas pressure of 10 to the minus 9th power torr) in the temperature range from 25 to 450 C. Sputter cleaning of the substrate surface, metal deposition, and annealing were monitored by TEM observation. Pseudostereographic presentation of micrographs in different annealing stages, the observation of the annealing behavior at cast shadow edges, and measurements with an electronic image analyzing system were employed to aid the visual perception and the analysis of changes in deposit structure recorded during annealing. Slow Ostwald ripening was found to occur in the entire temperature range, but the overriding surface transport mechanism was short-distance cluster mobility.

  16. Direct observation of lipid hydroperoxides in phospholipid vesicles by electrospray mass spectrometry.

    PubMed

    Spickett, C M; Pitt, A R; Brown, A J

    1998-09-01

    Positive ion electrospray ionization mass spectrometry was used to obtain a lipid profile of vesicles prepared from egg yolk lethicin and enriched with arachidonylstearoyl phosphatidylcholine and dipalmitoyl phosphatidylcholine. The vesicles were oxidized by treatment with tert-butylhydroperoxide and iron (II) sulfate, and the formation of hydroperoxides of the polyunsaturated lipid arachidonylstearoyl phosphatidylcholine was observed. The native lipid signal at 832 a.m.u. decreased and new signals appeared at 864, 896, and 928 a.m.u., corresponding to the addition of one (+32), two (+64), and three (+96) molecules of dioxygen. The dihydroperoxide was found to be the most favourable peroxide product, but it appeared that a degradation of the hydroperoxides was occurring concomitant with their formation, and only their net formation was observed. The rate of depletion of the polyunsaturated lipid and the rate of accumulation of the hydroperoxides was found to increase with the Fe2+ concentration between 10 microM and 2 mM, and was also dependent on the tert-butylhydroperoxide concentration. This is the first report of analysis of lipid hydroperoxides by electrospray mass spectrometry, showing that technique offers a sensitive, direct, and informative approach to the study of oxidative damage to biological membranes. PMID:9741599

  17. Direct observations of the photoinduced change in dimerization in K-TCNQ

    NASA Astrophysics Data System (ADS)

    Ishikawa, Tadahiko; Hosoda, Ryosuke; Okimoto, Yoichi; Tanaka, Sei'ichi; Onda, Ken; Koshihara, Shinya; Kumai, Reiji

    2016-05-01

    The photoinduced dynamics of a potassium-tetracyanoquinodimethane (K-TCNQ) single crystal in the generalized Peierls phase are evaluated via time-resolved vibrational spectroscopy. The transient reflectivity spectrum of the photoinduced state in the mid-IR range shows a decrease in the height and width of the reflectivity band because of the electron-molecular-vibration-coupled CN stretching mode at approximately 2180 cm-1. This spectral change suggests that the photoexcitation of the charge transfer in TCNQ molecules induces melting of the dimerization of the molecules. From detailed analysis of the spectral evolution, the relaxation time constant from the photoinduced state to the dimerized state is estimated to be approximately 0.6 ps. Even after the recovery of the dimerization, a fluctuation is still observed, probably because of a domain-wall soliton. The fluctuation gradually dissipates with a time constant of approximately 2.3 ps. Direct observation of the dimerization process reveals the true dynamics of the photoinduced cooperative phenomenon within this system.

  18. Determination of miscibility pressure by direct-observation method. Quarterly report, July 1-September 30, 1982

    SciTech Connect

    Wang, G.C.

    1982-01-01

    The objective of the project is to conduct laboratory tests to: (1) develop a method for determining miscibility pressure (MMP) through direct observation using a high pressure cell; and (2) determine feasibility of in-situ foam generation by visual observation and microphotographic technique. The project is organized and carried out in three major tasks, i.e., (1) MMP test; (2) high pressure sampling and chemical analysis; and (3) foam study and displacement test. The MMP test was 100% completed. The summary and results were presented in the last quarterly report. Chemical analysis using the HP5880-A was continued for SACROC crude oil at 76/sup 0/F and 150/sup 0/F and was also conducted for Rock Creek crude oil at 78/sup 0/F and 120/sup 0/F. Generally speaking, the changes of crude oil composition caused by CO/sub 2/ extraction are similar for both crude oils. During this reporting period, 29 displacements were performed for SACROC and Rock Creek crude soils. Results are discussed. 5 figures, 1 table.

  19. Influence of Observed Diurnal Cycles of Aerosol Optical Depth on Aerosol Direct Radiative Effect

    NASA Technical Reports Server (NTRS)

    Arola, A.; Eck, T. F.; Huttunen, J.; Lehtinen, K. E. J.; Lindfors, A. V.; Myhre, G.; Smirinov, A.; Tripathi, S. N.; Yu, H.

    2013-01-01

    The diurnal variability of aerosol optical depth (AOD) can be significant, depending on location and dominant aerosol type. However, these diurnal cycles have rarely been taken into account in measurement-based estimates of aerosol direct radiative forcing (ADRF) or aerosol direct radiative effect (ADRE). The objective of our study was to estimate the influence of diurnal aerosol variability at the top of the atmosphere ADRE estimates. By including all the possible AERONET sites, we wanted to assess the influence on global ADRE estimates. While focusing also in more detail on some selected sites of strongest impact, our goal was to also see the possible impact regionally.We calculated ADRE with different assumptions about the daily AOD variability: taking the observed daily AOD cycle into account and assuming diurnally constant AOD. Moreover, we estimated the corresponding differences in ADREs, if the single AOD value for the daily mean was taken from the the Moderate Resolution Imaging Spectroradiometer (MODIS) Terra or Aqua overpass times, instead of accounting for the true observed daily variability. The mean impact of diurnal AOD variability on 24 h ADRE estimates, averaged over all AERONET sites, was rather small and it was relatively small even for the cases when AOD was chosen to correspond to the Terra or Aqua overpass time. This was true on average over all AERONET sites, while clearly there can be much stronger impact in individual sites. Examples of some selected sites demonstrated that the strongest observed AOD variability (the strongest morning afternoon contrast) does not typically result in a significant impact on 24 h ADRE. In those cases, the morning and afternoon AOD patterns are opposite and thus the impact on 24 h ADRE, when integrated over all solar zenith angles, is reduced. The most significant effect on daily ADRE was induced by AOD cycles with either maximum or minimum AOD close to local noon. In these cases, the impact on 24 h ADRE was

  20. Mid-depth recirculation observed in the interior Labrador and Irminger seas by direct velocity measurements

    PubMed

    Lavender; Davis; Owens

    2000-09-01

    The Labrador Sea is one of the sites where convection exports surface water to the deep ocean in winter as part of the thermohaline circulation. Labrador Sea water is characteristically cold and fresh, and it can be traced at intermediate depths (500-2,000 m) across the North Atlantic Ocean, to the south and to the east of the Labrador Sea. Widespread observations of the ocean currents that lead to this distribution of Labrador Sea water have, however, been difficult and therefore scarce. We have used more than 200 subsurface floats to measure directly basin-wide horizontal velocities at various depths in the Labrador and Irminger seas. We observe unanticipated recirculations of the mid-depth (approximately 700 m) cyclonic boundary currents in both basins, leading to an anticyclonic flow in the interior of the Labrador basin. About 40% of the floats from the region of deep convection left the basin within one year and were rapidly transported in the anticyclonic flow to the Irminger basin, and also eastwards into the subpolar gyre. Surprisingly, the float tracks did not clearly depict the deep western boundary current, which is the expected main pathway of Labrador Sea water in the thermohaline circulation. Rather, the flow along the boundary near Flemish Cap is dominated by eddies that transport water offshore. Our detailed observations of the velocity structure with a high data coverage suggest that we may have to revise our picture of the formation and spreading of Labrador Sea water, and future studies with similar instrumentation will allow new insights on the intermediate depth ocean circulation.

  1. An instrument for direct observations of seismic and normal-mode rotational oscillations of the Earth.

    PubMed

    Cowsik, R

    2007-04-24

    The rotations around the vertical axis associated with the normal mode oscillations of the Earth and those induced by the seismic and other disturbances have been very difficult to observe directly. Such observations will provide additional information for 3D modeling of the Earth and for understanding earthquakes and other underground explosions. In this paper, we describe the design of an instrument capable of measuring the rotational motions associated with the seismic oscillations of the Earth, including the lowest frequency normal mode at nu approximately 3.7 x 10(-4) Hz. The instrument consists of a torsion balance with a natural frequency of nu(0) approximately 1.6 x 10(-4) Hz, which is observed by an autocollimating optical lever of high angular resolution and dynamic range. Thermal noise limits the sensitivity of the apparatus to amplitudes of approximately 1.5 x 10(-9) rad at the lowest frequency normal mode and the sensitivity improves as nu(-3/2) with increasing frequency. Further improvements in sensitivity by about two orders of magnitude may be achieved by operating the balance at cryogenic temperatures. Alternatively, the instrument can be made more robust with a reduced sensitivity by increasing nu(0) to approximately 10(-2) Hz. This instrument thus complements the ongoing effort by Igel and others to study rotational motions using ring laser gyroscopes and constitutes a positive response to the clarion call for developments in rotation seismology by Igel, Lee, and Todorovska [H. Igel, W.H.K. Lee and M.I. Todorovska, AGU Fall Meeting 2006, Rotational Seismology Sessions: S22A,S23B, Inauguration of the International Working Group on Rotational Seismology (IWGoRS)].

  2. Wide-field direct CCD observations supporting the Astro-1 Space Shuttle mission's Ultraviolet Imaging Telescope

    NASA Technical Reports Server (NTRS)

    Hintzen, Paul; Angione, Ron; Talbert, Freddie; Cheng, K.-P.; Smith, Eric; Stecher, Theodore P.

    1993-01-01

    Wide field direct CCD observations are being obtained to support and complement the vacuum-ultraviolet (VUV) images provided by Astro's Ultraviolet Imaging Telescope (UIT) during a Space Shuttle flight in December 1990. Because of the wide variety of projects addressed by UIT, the fields observed include (1) galactic supernova remnants such as the Cygnus Loop and globular clusters such as Omega Cen and M79; (2) the Magellanic Clouds, M33, M81, and other galaxies in the Local Group; and (3) rich clusters of galaxies, principally the Perseus cluster and Abell 1367. Ground-based observations have been obtained for virtually all of the Astro-1 UIT fields. The optical images allow identification of individual UV sources in each field and provide the long baseline in wavelength necessary for accurate analysis of UV-bright sources. To facilitate use of our optical images for analysis of UIT data and other projects, we plan to archive them, with the UIT images, at the National Space Science Data Center (NSSDC), where they will be universally accessible via anonymous FTP. The UIT, one of three telescopes comprising the Astro spacecraft, is a 38-cm f/9 Ritchey-Chretien telescope on which high quantum efficiency, solar-blind image tubes are used to record VUV images on photographic film. Five filters with passbands centered between 1250A and 2500A provide both VUV colors and a measurement of extinction via the 2200A dust feature. The resulting calibrated VUV pictures are 40 arcminutes in diameter at 2.5 arcseconds resolution. The capabilities of UIT, therefore, complement HST's WFPC: the latter has 40 times greater collecting area, while UIT's usable field has 170 times WFPC's field area.

  3. Direct Observation of Formation Behavior of Metal Emulsion in Sn/Salt System

    NASA Astrophysics Data System (ADS)

    Yoshida, Hironori; Liu, Jiang; Kim, Sun-Joong; Gao, Xu; Ueda, Shigeru; Maruoka, Nobuhiro; Ono, Shinpei; Kitamura, Shin-ya

    2016-08-01

    Using two systems with different interfacial tensions, the behavior of metal emulsions during bottom blowing was observed directly with a high-speed camera. The interfacial tension between molten salt (KCl-LiCl-NaCl) and molten Sn was measured by a pendant drop method, and it decreased to about 100 mN/m when the Te content in Sn increased from 0 to 0.5 pct. In both systems, two types of metal emulsion behaviors were observed. In Mode A, fine metal droplets were formed after the metal film ruptured at the interface. In Mode B, the formation of coarse droplets was observed after the disintegration of the column generated by the rising bubble, and the number of droplets increased with the gas flow rate compared to that in Mode A. The generating frequency of each mode revealed that Mode B became dominant with increasing gas flow rate. In the pure Sn/salt system, the numbers of droplets of Mode B showed a local maximum at high gas flow rates, but the numbers of droplets in Sn-0.5 pctTe/salt increased continuously even in the same flow range. Regarding the size distribution, the percentage of coarse metal droplets in the Sn-0.5 pctTe alloy/salt was larger than that in the pure Sn/salt. Furthermore, the effect of interfacial tension on the variation in surface area and volume of the droplets showed a similar tendency for the column height. Therefore, a decrement of the interfacial tension led to an increment of the column height when Mode B occurred and finally resulted in a higher interfacial area.

  4. Mid-depth recirculation observed in the interior Labrador and Irminger seas by direct velocity measurements

    PubMed

    Lavender; Davis; Owens

    2000-09-01

    The Labrador Sea is one of the sites where convection exports surface water to the deep ocean in winter as part of the thermohaline circulation. Labrador Sea water is characteristically cold and fresh, and it can be traced at intermediate depths (500-2,000 m) across the North Atlantic Ocean, to the south and to the east of the Labrador Sea. Widespread observations of the ocean currents that lead to this distribution of Labrador Sea water have, however, been difficult and therefore scarce. We have used more than 200 subsurface floats to measure directly basin-wide horizontal velocities at various depths in the Labrador and Irminger seas. We observe unanticipated recirculations of the mid-depth (approximately 700 m) cyclonic boundary currents in both basins, leading to an anticyclonic flow in the interior of the Labrador basin. About 40% of the floats from the region of deep convection left the basin within one year and were rapidly transported in the anticyclonic flow to the Irminger basin, and also eastwards into the subpolar gyre. Surprisingly, the float tracks did not clearly depict the deep western boundary current, which is the expected main pathway of Labrador Sea water in the thermohaline circulation. Rather, the flow along the boundary near Flemish Cap is dominated by eddies that transport water offshore. Our detailed observations of the velocity structure with a high data coverage suggest that we may have to revise our picture of the formation and spreading of Labrador Sea water, and future studies with similar instrumentation will allow new insights on the intermediate depth ocean circulation. PMID:10993072

  5. An instrument for direct observations of seismic and normal-mode rotational oscillations of the Earth

    PubMed Central

    Cowsik, R.

    2007-01-01

    The rotations around the vertical axis associated with the normal mode oscillations of the Earth and those induced by the seismic and other disturbances have been very difficult to observe directly. Such observations will provide additional information for 3D modeling of the Earth and for understanding earthquakes and other underground explosions. In this paper, we describe the design of an instrument capable of measuring the rotational motions associated with the seismic oscillations of the Earth, including the lowest frequency normal mode at ν ≈ 3.7 × 10−4 Hz. The instrument consists of a torsion balance with a natural frequency of ν0 ≈ 1.6 × 10−4 Hz, which is observed by an autocollimating optical lever of high angular resolution and dynamic range. Thermal noise limits the sensitivity of the apparatus to amplitudes of ≈ 1.5 × 10−9 rad at the lowest frequency normal mode and the sensitivity improves as ν−3/2 with increasing frequency. Further improvements in sensitivity by about two orders of magnitude may be achieved by operating the balance at cryogenic temperatures. Alternatively, the instrument can be made more robust with a reduced sensitivity by increasing ν0 to ≈10−2 Hz. This instrument thus complements the ongoing effort by Igel and others to study rotational motions using ring laser gyroscopes and constitutes a positive response to the clarion call for developments in rotation seismology by Igel, Lee, and Todorovska [H. Igel, W.H.K. Lee and M.I. Todorovska, AGU Fall Meeting 2006, Rotational Seismology Sessions: S22A,S23B, Inauguration of the International Working Group on Rotational Seismology (IWGoRS)]. PMID:17438268

  6. Direct Observation of Photoinduced Tautomerization in Single Molecules at a Metal Surface.

    PubMed

    Böckmann, H; Liu, S; Mielke, J; Gawinkowski, S; Waluk, J; Grill, L; Wolf, M; Kumagai, T

    2016-02-10

    Molecular switches are of fundamental importance in nature, and light is an important stimulus to selectively drive the switching process. However, the local dynamics of a conformational change in these molecules remain far from being completely understood at the single-molecule level. Here, we report the direct observation of photoinduced tautomerization in single porphycene molecules on a Cu(111) surface by using a combination of low-temperature scanning tunneling microscopy and laser excitation in the near-infrared to ultraviolet regime. It is found that the thermodynamically stable trans configuration of porphycene can be converted to the metastable cis configuration in a unidirectional fashion by photoirradiation. The wavelength dependence of the tautomerization cross section exhibits a steep increase around 2 eV and demonstrates that excitation of the Cu d-band electrons and the resulting hot carriers play a dominant role in the photochemical process. Additionally, a pronounced isotope effect in the cross section (∼100) is observed when the transferred hydrogen atoms are substituted with deuterium, indicating a significant contribution of zero-point energy in the reaction. Combined with the study of inelastic tunneling electron-induced tautomerization with the STM, we propose that tautomerization occurs via excitation of molecular vibrations after photoexcitation. Interestingly, the observed cross section of ∼10(-19) cm(2) in the visible-ultraviolet region is much higher than that of previously studied molecular switches on a metal surface, for example, azobenzene derivatives (10(-23)-10(-22) cm(2)). Furthermore, we examined a local environmental impact on the photoinduced tautomerization by varying molecular density on the surface and find substantial changes in the cross section and quenching of the process due to the intermolecular interaction at high density. PMID:26796945

  7. Measuring Learning Styles with Questionnaires versus Direct Observation of Preferential Choice Behavior in Authentic Learning Situations: The Visualizer/Verbalizer Behavior Observation Scale (VV-BOS).

    ERIC Educational Resources Information Center

    Leutner, Detlev; Plass, Jan L.

    1998-01-01

    Describes the development of the VV-BOS (Visualizer/Verbalizer Behavior Observation Scale), a computer-based instrument for direct observation of students' preferences for visual or verbal learning material. Results of a study with second-language learners indicated a high degree of reliability as an alternative to conventional questionnaires.…

  8. Low frequency radio observations of bi-directional electron beams in the solar corona

    NASA Astrophysics Data System (ADS)

    Carley, Eoin P.; Reid, Hamish; Vilmer, Nicole; Gallagher, Peter T.

    2015-09-01

    The radio signature of a shock travelling through the solar corona is known as a type II solar radio burst. In rare cases these bursts can exhibit a fine structure known as "herringbones", which are a direct indicator of particle acceleration occurring at the shock front. However, few studies have been performed on herringbones and the details of the underlying particle acceleration processes are unknown. Here, we use an image processing technique known as the Hough transform to statistically analyse the herringbone fine structure in a radio burst at ~20-90 MHz observed from the Rosse Solar-Terrestrial Observatory on 2011 September 22. We identify 188 individual bursts which are signatures of bi-directional electron beams continuously accelerated to speeds of 0.16-0.10+0.11 c. This occurs at a shock acceleration site initially at a constant altitude of ~0.6 R⊙ in the corona, followed by a shift to ~0.5 R⊙. The anti-sunward beams travel a distance of 170-97+174 Mm (and possibly further) away from the acceleration site, while those travelling toward the Sun come to a stop sooner, reaching a smaller distance of 112-76+84 Mm. We show that the stopping distance for the sunward beams may depend on the total number density and the velocity of the beam. Our study concludes that a detailed statistical analysis of herringbone fine structure can provide information on the physical properties of the corona which lead to these relatively rare radio bursts.

  9. Direct observation of roaming radicals in the thermal decomposition of acetaldehyde.

    SciTech Connect

    Sivaramakrishnan, R.; Michael, J. V.; Klippenstein, S. J.; Chemical Sciences and Engineering Division

    2010-01-21

    The thermal dissociation of acetaldehyde has been studied with the reflected shock tube technique using H(D)-atom atomic resonance absorption spectrometry detection. The use of an unreversed light source yields extraordinarily sensitive H atom detection. As a result, we are able to measure both the total decomposition rate and the branching to radical versus molecular channels. This branching provides a direct measure of the contribution from the roaming radical mechanism since the contributions from the usual tight transition states are predicted by theory to be negligible. The experimental observations also provide a measure of the rate coefficient for H + CH{sub 3}CHO. Another set of experiments employing C{sub 2}H{sub 5}I as an H-atom source provides additional data for this rate coefficient that extends to lower temperature. An evaluation of the available experimental results for H + CH{sub 3}CHO can be expressed by a three-parameter Arrhenius expression as k = 7.66 x 10{sup -20}T{sup 2.75} exp((-486 K)/T) cm{sup 3} molecule{sup -1} s{sup -1} (298-1415 K). Analogous experiments employing C{sub 2}D{sub 5}I as a D-atom source allow for the study of the isotopically substituted reaction. The present experiments are the only direct measure for this reaction rate constant, and the results can be expressed by an Arrhenius expression as k = 5.20 x 10{sup -10} exp((-4430 K)/T) cm{sup 3} molecule{sup -1} s{sup -1} (1151-1354 K). The H/D + CH{sub 3}CHO reactions are also studied with ab initio transition-state theory, and the results are in remarkably good agreement with the current experimental data.

  10. Effects of the observation method (direct v. from video) and of the presence of an observer on behavioural results in veal calves.

    PubMed

    Leruste, H; Bokkers, E A M; Sergent, O; Wolthuis-Fillerup, M; van Reenen, C G; Lensink, B J

    2013-11-01

    This study aimed at assessing the effect of the observation method (direct or from video) and the effect of the presence of an observer on the behavioural results in veal calves kept on a commercial farm. To evaluate the effect of the observation method, 20 pens (four to five calves per pen) were observed by an observer for 60 min (two observation sessions of 30 min) and video-recorded at the same time. To evaluate the effect of the presence of the observer in front of the pen, 24 pens were video-recorded on 4 consecutive days and an observer was present in front of each pen for 60 min (two observation sessions of 30 min) on the third day. Behaviour was recorded using instantaneous scan sampling. For the study of the observer's effect, the analysis was limited to the posture, abnormal oral behaviour and manipulation of substrates. The two observation methods gave similar results for the time spent standing, but different results for all other behaviours. The presence of an observer did not affect the behaviour of calves at day level; however, their behaviour was affected when the observer was actually present in front of the pens. A higher percentage of calves were standing and were manipulating substrate in the presence of the observer, but there was no effect on abnormal oral behaviour. In conclusion, direct observations are a more suitable observation method than observations from video recordings for detailed behaviours in veal calves. The presence of an observer has a short-term effect on certain behaviours of calves that will have to be taken into consideration when monitoring these behaviours.

  11. Objectively Optimized Observation Direction System Providing Situational Awareness for a Sensor Web

    NASA Astrophysics Data System (ADS)

    Aulov, O.; Lary, D. J.

    2010-12-01

    There is great utility in having a flexible and automated objective observation direction system for the decadal survey missions and beyond. Such a system allows us to optimize the observations made by suite of sensors to address specific goals from long term monitoring to rapid response. We have developed such a prototype using a network of communicating software elements to control a heterogeneous network of sensor systems, which can have multiple modes and flexible viewing geometries. Our system makes sensor systems intelligent and situationally aware. Together they form a sensor web of multiple sensors working together and capable of automated target selection, i.e. the sensors “know” where they are, what they are able to observe, what targets and with what priorities they should observe. This system is implemented in three components. The first component is a Sensor Web simulator. The Sensor Web simulator describes the capabilities and locations of each sensor as a function of time, whether they are orbital, sub-orbital, or ground based. The simulator has been implemented using AGIs Satellite Tool Kit (STK). STK makes it easy to analyze and visualize optimal solutions for complex space scenarios, and perform complex analysis of land, sea, air, space assets, and shares results in one integrated solution. The second component is target scheduler that was implemented with STK Scheduler. STK Scheduler is powered by a scheduling engine that finds better solutions in a shorter amount of time than traditional heuristic algorithms. The global search algorithm within this engine is based on neural network technology that is capable of finding solutions to larger and more complex problems and maximizing the value of limited resources. The third component is a modeling and data assimilation system. It provides situational awareness by supplying the time evolution of uncertainty and information content metrics that are used to tell us what we need to observe and the

  12. CAN-DOO: The Climate Action Network through Direct Observations and Outreach

    NASA Astrophysics Data System (ADS)

    Taubman, B.; Sherman, J. P.; Perry, L. B.; Markham, J.; Kelly, G.

    2011-12-01

    The urgency of climate change demands a greater understanding of our climate system, not only by the leaders of today, but by the scientists, policy makers, and citizens of tomorrow. Unfortunately, a large segment of the population currently possesses inadequate knowledge of climate science. In direct response to a need for greater scientific literacy with respect to climate science, researchers from Appalachian State University's Appalachian Atmospheric Interdisciplinary Research (AppalAIR) group, with support from NASA, have developed CAN-DOO: the Climate Action Network through Direct Observations and Outreach. CAN-DOO addresses climate science literacy by 1) Developing the infrastructure for sustaining and expanding public outreach through long-term climate measurements capable of complementing existing NASA measurements, 2) Enhancing public awareness of climate science and NASA's role in advancing our understanding of the Earth System, and 3) Introducing Science, Technology, Engineering, and Mathematics principles to homeschooled, public school, and Appalachian State University students through applied climate science activities. Project partners include the Grandfather Mountain Stewardship Foundation, Pisgah Astronomical Research Institute, and local elementary schools. In partnership with Grandfather Mountain, climate science awareness is promoted through citizen science activities, interactive public displays, and staff training. CAN-DOO engages students by involving them in the entire scientific investigative process as applied to climate science. We introduce local elementary and middle school students, homeschooled students throughout North Carolina, and undergraduate students in a new Global Climate Change course and select other courses at Appalachian State University to instrument assembly, measurement techniques, data collection, hypothesis testing, and drawing conclusions. Results are placed in the proper context via comparisons with other student

  13. Direct Observation (DO) for Drug-Resistant Tuberculosis: Do We Really DO?

    PubMed Central

    Benbaba, Stella; Isaakidis, Petros; Das, Mrinalini; Jadhav, Sonakshi; Reid, Tony; Furin, Jennifer

    2015-01-01

    Introduction Directly-observed therapy (DOT) is recommended for drug-resistant tuberculosis (DR-TB) patients during their entire treatment duration. However, there is limited published evidence on implementation of direct observation (DO) in the field. This study aims to detail whether DO was followed with DR-TB patients in a Médecins Sans Frontières (MSF) tuberculosis program in Mumbai, India. Methods This was a cross-sectional, mixed-methods study. Existing qualitative data from a purposively-selected subset of 12 patients, 5 DOT-providers and 5 family members, were assessed in order to determine how DO was implemented. A questionnaire-based survey of DR-TB patients, their DOT-providers and MSF staff was completed between June and August 2014. Patients were defined as”following Strict DO” and “following DO” if a DOT-provider had seen the patient swallow his/her medications “every day” or “most of the days” respectively. If DO was not followed, reasons were also recorded. The qualitative data were analysed for theme and content and used to supplement the questionnaire-based data. Results A total of 70 DR-TB patients, 65 DOT-providers and 21 MSF health staff were included. Fifty-five per cent of the patients were HIV-co-infected and 41% had multidrug-resistant-TB plus additional resistance to a fluoroquinolone. Among all patients, only 14% (10/70) and 20% (14/70) self-reported “following Strict DO” and “following DO” respectively. Among DOT-providers, 46% (30/65) reported that their patients “followed DO”. MSF health staff reported none of the patients “followed DO”. Reasons for not implementing DO included the unavailability of DOT-provider, time spent, stigma and treatment adverse events. The qualitative data also revealed that “Strict DO” was rarely followed and noted the same reasons for lack of implementation. Conclusion This mixed-methods study has found that a majority of patients with DR-TB in Mumbai did not follow DO

  14. Determination of miscibility pressure by direct observation method. Quarterly report, January 1-March 31, 1982

    SciTech Connect

    Wang, G. C.

    1982-01-01

    The objective of the project is to conduct laboratory tests to: (1) develop a method for determining MMP through direct observation using a high pressure cell; (2) determine feasibility of in-situ foam generation by visual observation and microphotographic technique. The project is presently organized and carried out in three major fronts: (1) MMP test; (2) high pressure sampling and chemical analysis; and (3) foam study and displacement test. The technical progress in each of these areas is discussed. The effects of temperature on MMP and appearance of CO/sub 2/-rich phase for four crude oils tested are plotted. The MMP is the pressure at which the CO/sub 2/-rich phase becomes miscible with CO/sub 2/ vapor. The results of gas chromatographic analysis for the four crude oils tested are presented. As previously stated the richness of C/sub 5/ to C/sub 20/ components is the key factor for determining the quality and stability of the miscible transition zone. The surfactant/CO/sub 2/ ratio relative to foam quality and foam quantity are presented in a table and also plotted. The plotted figures show: (1) the foam qualities increased as the surfactant rates are decreased; (2) at 75/sup 0/F, the foam quality increases as the pressure is decreased whereas the reverse is true for temperature at 120/sup 0/F; (3) foam generating rate increased with increasing surfactant/CO/sub 2/ ratio; (4) high temperatures tend to lower the rate and high pressures tend to increase the rate at 120/sup 0/F but to decrease at 75/sup 0/F; (5) foam quality was found to be affected more by surfactant/CO/sub 2/ ratio, and to a lesser degree by pressure and temperature. (ATT)

  15. Quantifying Aerosol Direct Effects from Broadband Irradiance and Spectral Aerosol Optical Depth Observations

    SciTech Connect

    Creekmore, Torreon N.; Joseph, Everette; Long, Charles N.; Li, Siwei

    2014-05-16

    We outline a methodology using broadband and spectral irradiances to quantify aerosol direct effects on the surface diffuse shortwave (SW) irradiance. Best Estimate Flux data span a 13 year timeframe at the Department of Energy Atmospheric Radiation Measurement Program’s Southern Great Plains (SGP) site. Screened clear-sky irradiances and aerosol optical depth (AOD), for solar zenith angles ≤ 65°, are used to estimate clear-sky diffuse irradiances. We validate against detected clear-sky observations from SGP’s Basic Radiation System (BRS). BRS diffuse irradiances were in accordance with estimates, producing a root-mean-square error and mean bias errors of 4.0 W/m2 and -1.4 W/m2, respectively. Absolute differences show 99% of estimates within ±10 W/m2 (10%) of the mean BRS observations. Clear-sky diffuse estimates are used to derive quantitative estimates of aerosol radiative effects, represented as the aerosol diffuse irradiance (ADI). ADI is the contribution of diffuse SW to global SW, attributable to scattering of atmospheric transmission by natural plus anthropogenic aerosols. Estimated slope for the ADI as a function of AOD indicates an increase of ~22 W/m2 in diffuse SW for every 0.1 increase in AOD. Such significant increases in the diffuse fraction could possibly increase photosynthesis. Annual mean ADI is 28.2 W/m2, and heavy aerosol loading at SGP provides up to a maximum increase of 120 W/m2 in diffuse SW over background conditions. With regard to seasonal variation, the mean diffuse forcings are 17.2, 33.3, 39.0, and 23.6 W/m2 for winter, spring, summer, and fall, respectively.

  16. Implications of directly observed therapy in tuberculosis control measures among IDUs.

    PubMed Central

    Curtis, R; Friedman, S R; Neaigus, A; Jose, B; Goldstein, M; Des Jarlais, D C

    1994-01-01

    Tuberculosis (TB) is a rapidly growing problem among injecting drug users (IDU), especially those infected with human immunodeficiency virus. The authors review IDUs' responses to current TB control strategies and discuss the implications of their findings for the proposed implementation of directly observed therapy (DOT), a method for ensuring that patients take prescribed medication. Field workers carried out 210 ethnographic interviews with 68 IDUs in a Brooklyn, NY, community during 1990-93. Case studies suggested that many IDUs are uninformed about TB and often misinformed about their personal TB status. Ethnographic interviews and observations indicated that the threat of TB-related involuntary detainment may lead IDUs to avoid TB diagnostic procedures, treatment for TB, or drug abuse treatment, and to avoid AIDS outreach workers and other health-related services. IDUs who tested positive for the purified protein derivative (PPD) of TB sometimes have left hospitals before definitive diagnoses were made, because of a perceived lack of respectful treatment, fear of detention, or lack of adequate methadone therapy to relieve the symptoms of withdrawal from drugs. Current TB diagnosis and treatment systems are, at best, inadequate. The threat of TB-related detention discourages some IDUs from seeking any type of health care. There is an urgent need to educate IDUs about TB and to educate and sensitize health care providers about the lifestyles of IDUs. DOT may help in servicing this difficult-to-serve population, particularly if techniques are incorporated that have been developed for other successful public health interventions for IDUs. PMID:8190855

  17. Structure of HIV-1 capsid assemblies by cryo-electron microscopy and iterative helical real-space reconstruction.

    PubMed

    Meng, Xin; Zhao, Gongpu; Zhang, Peijun

    2011-01-01

    Cryo-electron microscopy (cryo-EM), combined with image processing, is an increasingly powerful tool for structure determination of macromolecular protein complexes and assemblies. In fact, single particle electron microscopy and two-dimensional (2D) electron crystallography have become relatively routine methodologies and a large number of structures have been solved using these methods. At the same time, image processing and three-dimensional (3D) reconstruction of helical objects has rapidly developed, especially, the iterative helical real-space reconstruction (IHRSR) method, which uses single particle analysis tools in conjunction with helical symmetry. Many biological entities function in filamentous or helical forms, including actin filaments, microtubules, amyloid fibers, tobacco mosaic viruses, and bacteria flagella, and, because a 3D density map of a helical entity can be attained from a single projection image, compared to the many images required for 3D reconstruction of a non-helical object, with the IHRSR method, structural analysis of such flexible and disordered helical assemblies is now attainable. In this video article, we provide detailed protocols for obtaining a 3D density map of a helical protein assembly (HIV-1 capsid is our example), including protocols for cryo-EM specimen preparation, low dose data collection by cryo-EM, indexing of helical diffraction patterns, and image processing and 3D reconstruction using IHRSR. Compared to other techniques, cryo-EM offers optimal specimen preservation under near native conditions. Samples are embedded in a thin layer of vitreous ice, by rapid freezing, and imaged in electron microscopes at liquid nitrogen temperature, under low dose conditions to minimize the radiation damage. Sample images are obtained under near native conditions at the expense of low signal and low contrast in the recorded micrographs. Fortunately, the process of helical reconstruction has largely been automated, with the

  18. Directly observing the motion of DNA molecules near solid-state nanopores.

    PubMed

    Ando, Genki; Hyun, Changbae; Li, Jiali; Mitsui, Toshiyuki

    2012-11-27

    We investigate the diffusion and the drift motion of λ DNA molecules near solid-state nanopores prior to their translocation through the nanopores using fluorescence microscopy. The radial dependence of the electric field near a nanopore generated by an applied voltage in ionic solution can be estimated quantitatively in 3D by analyzing the motion of negatively charged DNA molecules. We find that the electric field is approximately spherically symmetric around the nanopore under the conditions investigated. In addition, DNA clogging at the nanopore was directly observed. Surprisingly, the probability of the clogging event increases with increasing external bias voltage. We also find that DNA molecules clogging the nanopore reduce the electric field amplitude at the nanopore membrane surface. To better understand these experimental results, analytical method with Ohm's law and computer simulation with Poisson and Nernst-Planck (PNP) equations are used to calculate the electric field near the nanopore. These results are of great interest in both experimental and theoretical considerations of the motion of DNA molecules near voltage-biased nanopores. These findings will also contribute to the development of solid-state nanopore-based DNA sensing devices.

  19. Reliability of the direct observation of procedural skills assessment tool for ultrasound-guided regional anaesthesia.

    PubMed

    Chuan, A; Thillainathan, S; Graham, P L; Jolly, B; Wong, D M; Smith, N; Barrington, M J

    2016-03-01

    The Direct Observation of Procedural Skills (DOPS) form is used as a workplace-based assessment tool in the current Australian and New Zealand College of Anaesthetists curriculum. The objective of this study was to evaluate the reliability of DOPS when used to score trainees performing ultrasound-guided regional anaesthesia. Reliability of an assessment tool is defined as the reproducibility of scores given by different assessors viewing the same trainee. Forty-nine anaesthetists were recruited to score two scripted videos of trainees performing a popliteal sciatic nerve block and an axillary brachial plexus block. Reliability, as measured by intraclass correlation coefficients, was -0.01 to 0.43 for the individual items in DOPS, and 0.15 for the 'Overall Performance for this Procedure' item. Assessors demonstrated consistency of scoring within DOPS, with significant correlation of sum of individual item scores with the 'Overall Performance for this Procedure' item (r=0.78 to 0.80, P<0.001), and with yes versus no responses to the 'Was the procedure completed satisfactorily?' item (W=24, P=0.0004, Video 1, and W=65, P=0.003, Video 2). While DOPS demonstrated a good degree of internal consistency in this setting, inter-rater reliability did not reach levels generally recommended for formative assessment tools. Feasibility of the form could be improved by removing the 'Was the procedure completed satisfactorily?' item without loss of information.

  20. Direct observations of ice seasonality reveal changes in climate over the past 320–570 years

    NASA Astrophysics Data System (ADS)

    Sharma, Sapna; Magnuson, John J.; Batt, Ryan D.; Winslow, Luke A.; Korhonen, Johanna; Aono, Yasuyuki

    2016-04-01

    Lake and river ice seasonality (dates of ice freeze and breakup) responds sensitively to climatic change and variability. We analyzed climate-related changes using direct human observations of ice freeze dates (1443–2014) for Lake Suwa, Japan, and of ice breakup dates (1693–2013) for Torne River, Finland. We found a rich array of changes in ice seasonality of two inland waters from geographically distant regions: namely a shift towards later ice formation for Suwa and earlier spring melt for Torne, increasing frequencies of years with warm extremes, changing inter-annual variability, waning of dominant inter-decadal quasi-periodic dynamics, and stronger correlations of ice seasonality with atmospheric CO2 concentration and air temperature after the start of the Industrial Revolution. Although local factors, including human population growth, land use change, and water management influence Suwa and Torne, the general patterns of ice seasonality are similar for both systems, suggesting that global processes including climate change and variability are driving the long-term changes in ice seasonality.

  1. Directly observed treatment, short-course strategy and multidrug-resistant tuberculosis: are any modifications required?

    PubMed Central

    Bastian, I.; Rigouts, L.; Van Deun, A.; Portaels, F.

    2000-01-01

    Multidrug-resistant tuberculosis (MDRTB) should be defined as tuberculosis with resistance to at least isoniazid and rifampicin because these drugs are the cornerstone of short-course chemotherapy, and combined isoniazid and rifampicin resistance requires prolonged treatment with second-line agents. Short-course chemotherapy is a key ingredient in the tuberculosis control strategy known as directly observed treatment, short-course (DOTS). For populations in which multidrug-resistant tuberculosis is endemic, the outcome of the standard short-course chemotherapy regimen remains uncertain. Unacceptable failure rates have been reported and resistance to additional agents may be induced. As a consequence there have been calls for well-functioning DOTS programmes to provide additional services in areas with high rates of multidrug-resistant tuberculosis. These "DOTS-plus for MDRTB programmes" may need to modify all five elements of the DOTS strategy: the treatment may need to be individualized rather than standardized; laboratory services may need to provide facilities for on-site culture and antibiotic susceptibility testing; reliable supplies of a wide range of expensive second-line agents would have to be supplied; operational studies would be required to determine the indications for and format of the expanded programmes; financial and technical support from international organizations and Western governments would be needed in addition to that obtained from local governments. PMID:10743297

  2. Treatment Outcomes of Patients Placed on Treatment Under Directly Observed Therapy Short-Course (Dots)

    PubMed Central

    Kaur, Gurpreet; Goel, N.K.; Kumar, Dinesh; Janmeja, A.K.; Swami, H.M.; Kalia, Meenu

    2008-01-01

    Background: Tuberculosis continues to be a pressing health problem in India. The Revised National Tuberculosis Programme (RNTCP), an application of Directly Observed Treatment Short-course (DOTS) in India, launched in 1997 needs continuous evaluation. Objective: To study the outcomes of treatment among the patients put on DOTS under RNTCP in Chandigarh, UT. Material & Methods: A Longitudinal study was conducted during 2004-2005 in 13 Microscopic centres (MC's) spread over 2 Tuberculosis Units (TU's) under District Tuberculosis Centre (DTC) in Union Territory (UT), Chandigarh. A sample of 265 respondents, selected by two-stage stratified random sampling technique, was recruited in the study cohort. Data analysis was done using SPSS-10 statistical software package. Results: For Category I and Category II patients, the Success rate was 98.6% and 90.4% respectively. The overall default rate was 1.1% and failure rate was 2.6%. For re-treatment cases, failure rate was higher i.e. 5.8%. The sputum conversion rate among the new smear positive cases was 93.8% at 3 months of treatment. For the re-treatment cases, spu-tum conversion rate at 3 months was 94.1%. Conclusion: The study concludes that RNTCP is running successfully in UT Chandigarh, having high success rate and low default rate. The reasons for high failure rate should be explored in depth. PMID:20165654

  3. Direct nuclear magnetic resonance observation of odorant binding to mouse odorant receptor MOR244-3.

    PubMed

    Burger, Jessica L; Jeerage, Kavita M; Bruno, Thomas J

    2016-06-01

    Mammals are able to perceive and differentiate a great number of structurally diverse odorants through the odorant's interaction with odorant receptors (ORs), proteins found within the cell membrane of olfactory sensory neurons. The natural gas industry has used human olfactory sensitivity to sulfur compounds (thiols, sulfides, etc.) to increase the safety of fuel gas transport, storage, and use through the odorization of this product. In the United States, mixtures of sulfur compounds are used, but the major constituent of odorant packages is 2-methylpropane-2-thiol, also known as tert-butyl mercaptan. It has been fundamentally challenging to understand olfaction and odorization due to the low affinity of odorous ligands to the ORs and the difficulty in expressing a sufficient number of OR proteins. Here, we directly observed the binding of tert-butyl mercaptan and another odiferous compound, cis-cyclooctene, to mouse OR MOR244-3 on living cells by saturation transfer difference (STD) nuclear magnetic resonance (NMR) spectroscopy. This effort lays the groundwork for resolving molecular mechanisms responsible for ligand binding and resulting signaling, which in turn will lead to a clearer understanding of odorant recognition and competition.

  4. Direct observations of ice seasonality reveal changes in climate over the past 320–570 years

    USGS Publications Warehouse

    Sharma, Sapna; Magnuson, John J.; Batt, Ryan D; Winslow, Luke; Korhonen, Johanna; Yasuyuki Aono,

    2016-01-01

    Lake and river ice seasonality (dates of ice freeze and breakup) responds sensitively to climatic change and variability. We analyzed climate-related changes using direct human observations of ice freeze dates (1443–2014) for Lake Suwa, Japan, and of ice breakup dates (1693–2013) for Torne River, Finland. We found a rich array of changes in ice seasonality of two inland waters from geographically distant regions: namely a shift towards later ice formation for Suwa and earlier spring melt for Torne, increasing frequencies of years with warm extremes, changing inter-annual variability, waning of dominant inter-decadal quasi-periodic dynamics, and stronger correlations of ice seasonality with atmospheric CO2 concentration and air temperature after the start of the Industrial Revolution. Although local factors, including human population growth, land use change, and water management influence Suwa and Torne, the general patterns of ice seasonality are similar for both systems, suggesting that global processes including climate change and variability are driving the long-term changes in ice seasonality.

  5. Direct Observation of a Carbon Filament in Water-Resistant Organic Memory.

    PubMed

    Lee, Byung-Hyun; Bae, Hagyoul; Seong, Hyejeong; Lee, Dong-Il; Park, Hongkeun; Choi, Young Joo; Im, Sung-Gap; Kim, Sang Ouk; Choi, Yang-Kyu

    2015-07-28

    The memory for the Internet of Things (IoT) requires versatile characteristics such as flexibility, wearability, and stability in outdoor environments. Resistive random access memory (RRAM) to harness a simple structure and organic material with good flexibility can be an attractive candidate for IoT memory. However, its solution-oriented process and unclear switching mechanism are critical problems. Here we demonstrate iCVD polymer-intercalated RRAM (i-RRAM). i-RRAM exhibits robust flexibility and versatile wearability on any substrate. Stable operation of i-RRAM, even in water, is demonstrated, which is the first experimental presentation of water-resistant organic memory without any waterproof protection package. Moreover, the direct observation of a carbon filament is also reported for the first time using transmission electron microscopy, which puts an end to the controversy surrounding the switching mechanism. Therefore, reproducibility is feasible through comprehensive modeling. Furthermore, a carbon filament is superior to a metal filament in terms of the design window and selection of the electrode material. These results suggest an alternative to solve the critical issues of organic RRAM and an optimized memory type suitable for the IoT era.

  6. Direct observation of solid-state reversed transformation from crystals to quasicrystals in a Mg alloy

    PubMed Central

    Liu, Jian-Fang; Yang, Zhi-Qing; Ye, Heng-Qiang

    2015-01-01

    Phase transformation of quasicrystals is of interest in various fields of science and technology. Interestingly, we directly observed unexpected solid-state epitaxial nucleation and growth of Zn 6 Mg 3 Y icosahedral quasicrystals in a Mg alloy at about 573 K which is about 300 K below the melting point of Zn 6 Mg 3 Y, in contrast to formation of quasicrystals through solidification that was usually found in many alloys. Maximizing local packing density of atoms associated with segregation of Y and Zn in Mg adjacent to Mg/Zn 3 MgY interfaces triggered atomic rearrangement in Mg to form icosahedra coupled epitaxially with surface distorted icosahedra of Zn 3 MgY, which plays a critical role in the nucleation of icosahedral clusters. A local Zn:Mg:Y ratio close to 6:3:1, corresponding to a valence electron concentration of about 2.15, should have been reached to trigger the formation of quasicrystals at Mg/Zn 3 MgY interfaces. The solid-state icosahedral ordering in crystals opens a new window for growing quasicrystals and understanding their atomic origin mechanisms. Epitaxial growth of quasicrystals onto crystals can modify the surface/interface structures and properties of crystalline materials. PMID:26066096

  7. Direct observation of Thermal contact resistance of a Carbon Nanotube heat spreader

    NASA Astrophysics Data System (ADS)

    Hussain Baloch, Kamal; Voskanian, Norvik; Cumings, John

    2010-03-01

    For less than two decades the extraordinary thermal properties of carbon nanotubes (CNTs) have generated much interest in the scientific community. Even though they are a new material with one of the highest of thermal conductivities, the amount of heat CNTs can transport is limited by their thermal contact resistance. Several experiments have been performed to date to experimentally extract the thermal contact resistance of the CNTs. Thus far, all values reported in literature are extracted indirectly through models with assumptions about an uncharacterized heat source, typically Joule heating from within the nanotube itself. Values in the literature vary by more than an order of magnitude, suggesting fundamental uncertainties in the system. We report for the first time a direct in-situ observation of the thermal contact resistance of CNTs using Electron Thermal Microscopy, and we show that the strength of this thermal contact resistance can be manipulated through orders of magnitude. This study opens doors for using CNTs as effective nanoscale thermal transport devices in which the contact resistance of the CNTs could be controlled by design. Experimental results, simulations along with review of the experimental technique will be presented in this talk.

  8. Direct Observation of Intermediates Involved in the Interruption of the Bischler–Napieralski Reaction

    PubMed Central

    White, Kolby L.; Mewald, Marius; Movassaghi, Mohammad

    2015-01-01

    The first mechanistic investigation of electrophilic amide activation of α,α-disubstituted tertiary lactams and the direct observation of key intermediates by in situ FTIR, 1H, 13C, and 19F NMR in our interrupted Bischler–Napieralski based synthetic strategy to the aspidosperma alkaloids, including a complex tetracyclic diiminium ion, is discussed. The reactivity of a wide range of pyridines with trifluoromethanesulfonic anhydride was systematically examined, and characteristic IR absorption bands for the corresponding N-trifluoromethanesulfonylated pyridinium trifluoromethanesulfonates were assigned. The reversible formation of diiminium ether intermediates was studied, providing insight into divergent mechanistic pathways as a function of the steric environment of the amide substrate and stoichiometry of reagents. Importantly, when considering base additives during electrophilic amide activation, more hindered α-quaternary tertiary lactams require the use of non-nucleophilic pyridine additives in order to avoid deactivation via a competing desulfonylation reaction. The isolation and full characterization of a tetracyclic iminium trifluoromethanesulfonate provided additional correlation between in situ characterization of sensitive intermediates and isolable compounds involved in this synthetic transformation. PMID:26166404

  9. A FAR-INFRARED OBSERVATIONAL TEST OF THE DIRECTIONAL DEPENDENCE IN RADIATIVE GRAIN ALIGNMENT

    SciTech Connect

    Vaillancourt, John E.; Andersson, B.-G. E-mail: bg@sofia.usra.edu

    2015-10-10

    The alignment of interstellar dust grains with magnetic fields provides a key method for measuring the strength and morphology of the fields. In turn, this provides a means to study the role of magnetic fields from diffuse gas to dense star-forming regions. The physical mechanism for aligning the grains has been a long-term subject of study and debate. The theory of radiative torques, in which an anisotropic radiation field imparts sufficient torques to align the grains while simultaneously spinning them to high rotational velocities, has passed a number of observational tests. Here we use archival polarization data in dense regions of the Orion molecular cloud (OMC-1) at 100, 350, and 850 μm to test the prediction that the alignment efficiency is dependent upon the relative orientations of the magnetic field and radiation anisotropy. We find that the expected polarization signal, with a 180-degree period, exists at all wavelengths out to radii of 1.5 arcmin centered on the Becklin–Neugebauer Kleinmann-Low (BNKL) object in OMC-1. The probabilities that these signals would occur due to random noise are low (≲1%), and are lowest toward BNKL compared to the rest of the cloud. Additionally, the relative magnetic field to radiation anisotropy directions accord with theoretical predictions in that they agree to better than 15° at 100 μm and 4° at 350 μm.

  10. Direct observations of ice seasonality reveal changes in climate over the past 320–570 years

    PubMed Central

    Sharma, Sapna; Magnuson, John J.; Batt, Ryan D.; Winslow, Luke A.; Korhonen, Johanna; Aono, Yasuyuki

    2016-01-01

    Lake and river ice seasonality (dates of ice freeze and breakup) responds sensitively to climatic change and variability. We analyzed climate-related changes using direct human observations of ice freeze dates (1443–2014) for Lake Suwa, Japan, and of ice breakup dates (1693–2013) for Torne River, Finland. We found a rich array of changes in ice seasonality of two inland waters from geographically distant regions: namely a shift towards later ice formation for Suwa and earlier spring melt for Torne, increasing frequencies of years with warm extremes, changing inter-annual variability, waning of dominant inter-decadal quasi-periodic dynamics, and stronger correlations of ice seasonality with atmospheric CO2 concentration and air temperature after the start of the Industrial Revolution. Although local factors, including human population growth, land use change, and water management influence Suwa and Torne, the general patterns of ice seasonality are similar for both systems, suggesting that global processes including climate change and variability are driving the long-term changes in ice seasonality. PMID:27113125

  11. Direct observation of crystal growth from solution using optical investigation of a growing crystal face

    NASA Technical Reports Server (NTRS)

    Lal, Ravindra

    1994-01-01

    The first technical report for the period 1 Jan. 1993 till 31 Dec. 1993 for the research entitled, 'Direct observation of crystal growth from solution using Optical Investigation of a growing crystal Face' is presented. The work on the project did not start till 1 June 1993 due to the non-availability of the required personnel. The progress of the work during the period 1 June 1993 till the end of 1993 is described. Significant progress was made for testing various optical diagnostic techniques for monitoring crystal solution. Some of the techniques that are being tested are: heterodyne detection technique, in which changes in phase are measured as a interferometric function of time/crystal growth; a conventional technique, in which a fringe brightness is measured as a function of crystal growth/time; and a Mach-Zehnder interferometric technique in which a fringe brightness is measured as a function of time to obtain information on concentration changes. During the second year it will be decided to incorporate the best interferometric technique along with the ellipsometric technique, to obtain real time in-situ growth rate measurements. A laboratory mock-up of the first two techniques were made and tested.

  12. Direct observation of solid-state reversed transformation from crystals to quasicrystals in a Mg alloy.

    PubMed

    Liu, Jian-Fang; Yang, Zhi-Qing; Ye, Heng-Qiang

    2015-06-12

    Phase transformation of quasicrystals is of interest in various fields of science and technology. Interestingly, we directly observed unexpected solid-state epitaxial nucleation and growth of Zn6Mg3Y icosahedral quasicrystals in a Mg alloy at about 573 K which is about 300 K below the melting point of Zn6Mg3Y, in contrast to formation of quasicrystals through solidification that was usually found in many alloys. Maximizing local packing density of atoms associated with segregation of Y and Zn in Mg adjacent to Mg/Zn3MgY interfaces triggered atomic rearrangement in Mg to form icosahedra coupled epitaxially with surface distorted icosahedra of Zn3MgY, which plays a critical role in the nucleation of icosahedral clusters. A local Zn:Mg:Y ratio close to 6:3:1, corresponding to a valence electron concentration of about 2.15, should have been reached to trigger the formation of quasicrystals at Mg/Zn3MgY interfaces. The solid-state icosahedral ordering in crystals opens a new window for growing quasicrystals and understanding their atomic origin mechanisms. Epitaxial growth of quasicrystals onto crystals can modify the surface/interface structures and properties of crystalline materials.

  13. Direct observations of ice seasonality reveal changes in climate over the past 320-570 years.

    PubMed

    Sharma, Sapna; Magnuson, John J; Batt, Ryan D; Winslow, Luke A; Korhonen, Johanna; Aono, Yasuyuki

    2016-01-01

    Lake and river ice seasonality (dates of ice freeze and breakup) responds sensitively to climatic change and variability. We analyzed climate-related changes using direct human observations of ice freeze dates (1443-2014) for Lake Suwa, Japan, and of ice breakup dates (1693-2013) for Torne River, Finland. We found a rich array of changes in ice seasonality of two inland waters from geographically distant regions: namely a shift towards later ice formation for Suwa and earlier spring melt for Torne, increasing frequencies of years with warm extremes, changing inter-annual variability, waning of dominant inter-decadal quasi-periodic dynamics, and stronger correlations of ice seasonality with atmospheric CO2 concentration and air temperature after the start of the Industrial Revolution. Although local factors, including human population growth, land use change, and water management influence Suwa and Torne, the general patterns of ice seasonality are similar for both systems, suggesting that global processes including climate change and variability are driving the long-term changes in ice seasonality.

  14. Direct observation of unstable reaction intermediates by acid-base complex formation.

    PubMed

    Ohashi, Yuji

    2013-06-01

    The structures of several unstable or metastable reaction intermediates that were photoproduced in crystals were analyzed by using X-ray techniques. The presence of enough void space around the reactive group(s) is an essential factor for the reaction to occur with retention of the single-crystal form. To expand the void space, an acid group (COOH) was substituted onto the reactant molecule and acid-base complex crystals were prepared with several amines, such as dibenzylamine and dicyclohexylamine. Following the formation of such acid-base complexes in crystals, the metastable structures of nitrenes and red species of photochromic salicylideneanilines have been successfully analyzed by using X-ray techniques. Moreover, the structure of a Pt complex anion in the excited state has been analyzed, which formed acid-base complex crystals with various alkylammonium cations. The formation of acid-base complexes will be a powerful tool for directly observing the structure of unstable or metastable reaction intermediates by using X-ray techniques.

  15. The Age of the Directly Imaged Planet Host Star κ Andromedae Determined from Interferometric Observations

    NASA Astrophysics Data System (ADS)

    Jones, Jeremy; White, R. J.; Quinn, S.; Ireland, M.; Boyajian, T.; Schaefer, G.; Baines, E. K.

    2016-05-01

    κ Andromedae, an early-type star that hosts a directly imaged low-mass companion, is expected to be oblate due to its rapid rotational velocity (v sin i = ˜162 km s‑1). We observed the star with the CHARA Array’s optical beam combiner, PAVO, measuring its size at multiple orientations and determining its oblateness. The interferometric measurements, combined with photometry and this v sin i value are used to constrain an oblate star model that yields the fundamental properties of the star and finds a rotation speed that is ˜85% of the critical rate and a low inclination of ˜30°. Three modeled properties (the average radius, bolometric luminosity, and equatorial velocity) are compared to MESA evolution models to determine an age and mass for the star. In doing so, we determine an age for the system of {47}-40+27 Myr. Based on this age and previous measurements of the companion’s temperature, the BHAC15 evolution models imply a mass for the companion of {22}-9+8 M J.

  16. Direct observations of ice seasonality reveal changes in climate over the past 320-570 years.

    PubMed

    Sharma, Sapna; Magnuson, John J; Batt, Ryan D; Winslow, Luke A; Korhonen, Johanna; Aono, Yasuyuki

    2016-01-01

    Lake and river ice seasonality (dates of ice freeze and breakup) responds sensitively to climatic change and variability. We analyzed climate-related changes using direct human observations of ice freeze dates (1443-2014) for Lake Suwa, Japan, and of ice breakup dates (1693-2013) for Torne River, Finland. We found a rich array of changes in ice seasonality of two inland waters from geographically distant regions: namely a shift towards later ice formation for Suwa and earlier spring melt for Torne, increasing frequencies of years with warm extremes, changing inter-annual variability, waning of dominant inter-decadal quasi-periodic dynamics, and stronger correlations of ice seasonality with atmospheric CO2 concentration and air temperature after the start of the Industrial Revolution. Although local factors, including human population growth, land use change, and water management influence Suwa and Torne, the general patterns of ice seasonality are similar for both systems, suggesting that global processes including climate change and variability are driving the long-term changes in ice seasonality. PMID:27113125

  17. Direct Observation of a Carbon Filament in Water-Resistant Organic Memory.

    PubMed

    Lee, Byung-Hyun; Bae, Hagyoul; Seong, Hyejeong; Lee, Dong-Il; Park, Hongkeun; Choi, Young Joo; Im, Sung-Gap; Kim, Sang Ouk; Choi, Yang-Kyu

    2015-07-28

    The memory for the Internet of Things (IoT) requires versatile characteristics such as flexibility, wearability, and stability in outdoor environments. Resistive random access memory (RRAM) to harness a simple structure and organic material with good flexibility can be an attractive candidate for IoT memory. However, its solution-oriented process and unclear switching mechanism are critical problems. Here we demonstrate iCVD polymer-intercalated RRAM (i-RRAM). i-RRAM exhibits robust flexibility and versatile wearability on any substrate. Stable operation of i-RRAM, even in water, is demonstrated, which is the first experimental presentation of water-resistant organic memory without any waterproof protection package. Moreover, the direct observation of a carbon filament is also reported for the first time using transmission electron microscopy, which puts an end to the controversy surrounding the switching mechanism. Therefore, reproducibility is feasible through comprehensive modeling. Furthermore, a carbon filament is superior to a metal filament in terms of the design window and selection of the electrode material. These results suggest an alternative to solve the critical issues of organic RRAM and an optimized memory type suitable for the IoT era. PMID:26056735

  18. Direct observation of stick-slip movements of water nanodroplets induced by an electron beam

    PubMed Central

    Mirsaidov, Utkur M.; Zheng, Haimei; Bhattacharya, Dipanjan; Casana, Yosune; Matsudaira, Paul

    2012-01-01

    Dynamics of the first few nanometers of water at the interface are encountered in a wide range of physical, chemical, and biological phenomena. A simple but critical question is whether interfacial forces at these nanoscale dimensions affect an externally induced movement of a water droplet on a surface. At the bulk-scale water droplets spread on a hydrophilic surface and slip on a nonwetting, hydrophobic surface. Here we report the experimental description of the electron beam-induced dynamics of nanoscale water droplets by direct imaging the translocation of 10- to 80-nm-diameter water nanodroplets by transmission electron microscopy. These nanodroplets move on a hydrophilic surface not by a smooth flow but by a series of stick-slip steps. We observe that each step is preceded by a unique characteristic deformation of the nanodroplet into a toroidal shape induced by the electron beam. We propose that this beam-induced change in shape increases the surface free energy of the nanodroplet that drives its transition from stick to slip state. PMID:22517747

  19. Direct observation of stick-slip movements of water nanodroplets induced by an electron beam.

    PubMed

    Mirsaidov, Utkur M; Zheng, Haimei; Bhattacharya, Dipanjan; Casana, Yosune; Matsudaira, Paul

    2012-05-01

    Dynamics of the first few nanometers of water at the interface are encountered in a wide range of physical, chemical, and biological phenomena. A simple but critical question is whether interfacial forces at these nanoscale dimensions affect an externally induced movement of a water droplet on a surface. At the bulk-scale water droplets spread on a hydrophilic surface and slip on a nonwetting, hydrophobic surface. Here we report the experimental description of the electron beam-induced dynamics of nanoscale water droplets by direct imaging the translocation of 10- to 80-nm-diameter water nanodroplets by transmission electron microscopy. These nanodroplets move on a hydrophilic surface not by a smooth flow but by a series of stick-slip steps. We observe that each step is preceded by a unique characteristic deformation of the nanodroplet into a toroidal shape induced by the electron beam. We propose that this beam-induced change in shape increases the surface free energy of the nanodroplet that drives its transition from stick to slip state.

  20. Direct observation of epitaxial organic film growth: temperature-dependent growth mechanisms and metastability.

    PubMed

    Marchetto, Helder; Schmidt, Thomas; Groh, Ullrich; Maier, Florian C; Lévesque, Pierre L; Fink, Rainer H; Freund, Hans-Joachim; Umbach, Eberhard

    2015-11-21

    The growth of the first ten layers of organic thin films on a smooth metallic substrate has been investigated in real-time using the model system PTCDA on Ag(111). The complex behaviour is comprehensively studied by electron microscopy, spectroscopy and diffraction in a combined PEEM/LEEM instrument revealing several new phenomena and yielding a consistent picture of this layer growth. PTCDA grows above room temperature in a Stranski-Krastanov mode, forming three-dimensional islands on a stable bi-layer, in competition with metastable 3rd and 4th layers. Around room temperature this growth mode changes into a quasi layer-by-layer growth, while at temperatures below about 250 K a Vollmer-Weber-like behaviour is observed. By means of laterally resolved soft X-ray absorption spectroscopy the orientation of all adsorbed molecules is found to be homogeneously flat lying on the surface, even during the growth process. The films grow epitaxially, showing long-range order with rotational domains. For the monolayer these domains could be directly analysed, showing an average size of several micrometers extending over substrate steps.

  1. Direct observation of epitaxial organic film growth: temperature-dependent growth mechanisms and metastability.

    PubMed

    Marchetto, Helder; Schmidt, Thomas; Groh, Ullrich; Maier, Florian C; Lévesque, Pierre L; Fink, Rainer H; Freund, Hans-Joachim; Umbach, Eberhard

    2015-11-21

    The growth of the first ten layers of organic thin films on a smooth metallic substrate has been investigated in real-time using the model system PTCDA on Ag(111). The complex behaviour is comprehensively studied by electron microscopy, spectroscopy and diffraction in a combined PEEM/LEEM instrument revealing several new phenomena and yielding a consistent picture of this layer growth. PTCDA grows above room temperature in a Stranski-Krastanov mode, forming three-dimensional islands on a stable bi-layer, in competition with metastable 3rd and 4th layers. Around room temperature this growth mode changes into a quasi layer-by-layer growth, while at temperatures below about 250 K a Vollmer-Weber-like behaviour is observed. By means of laterally resolved soft X-ray absorption spectroscopy the orientation of all adsorbed molecules is found to be homogeneously flat lying on the surface, even during the growth process. The films grow epitaxially, showing long-range order with rotational domains. For the monolayer these domains could be directly analysed, showing an average size of several micrometers extending over substrate steps. PMID:26462749

  2. Direct spectroscopic observation of ion deceleration accompanying laser plasma-wall interaction

    NASA Astrophysics Data System (ADS)

    Renner, O.; Krouský, E.; Liska, R.; Šmíd, M.; Larroche, O.; Dalimier, E.; Rosmej, F. B.

    2010-08-01

    Interactions of plasma jets with solid surfaces are extensively studied in context with development of future fusion devices. In experiments carried out on the iodine laser system PALS, the energetic ions were produced at double-foil Al/Mg targets irradiated by one or two counter-propagating laser beams. The plasma jets from the rear surface of the laser-exploded Al foil streamed towards the Mg target representing the wall preheated by the action of the high-energy photons, particle and/or laser beams. Instead of being trapped by the cold secondary-target material, the forward-accelerated Al ions collided with the counter-propagating matter ejected from the wall. The environmental conditions in near-wall plasmas were analyzed with the high-resolution x-ray spectroscopy and temporally-resolved x-ray imaging. The deceleration of the incident Al ions in the near-wall region was directly observed and quantitatively characterized via Doppler shifts of the J-satellite from the Al Lya spectral group. The interaction scenario was modelled using the 2D arbitrary Lagrangian Eulerian hydrocode PALE and the multifluid code MULTIF.

  3. Direct Pore-Level Observation of Permeability Increase by Seismic Waves

    NASA Astrophysics Data System (ADS)

    Beresnev, I. A.; Gaul, W.; Vigil, D.

    2011-12-01

    Increases in permeability of natural reservoirs and aquifers by passing seismic waves have been well documented. If the physical causes of this phenomenon can be understood, technological applications would be possible for controlling the flow in hydrologic systems or enhancing production from oil reservoirs. The explanation of the dynamically increased mobility of underground fluids lies at the pore level. The natural fluids can be viewed as two-phase systems, composed of water as the wetting phase and of dispersed non-wetting globules of gas or organic fluids flowing through tortuous constricted channels. Capillary forces prevent the free motion of the suspended non-wetting droplets, which tend to become immobilized in capillary constrictions. The capillary entrapment significantly reduces macroscopic permeability. In a controlled experiment with a constricted capillary channel, we immobilize the suspended ganglia and test the model of capillary entrapment: it agrees precisely with the experiment. We then demonstrate by direct optical pore-level observation that the vibrations applied to the wall of the channel liberate the trapped ganglia if a certain critical acceleration is reached. When the droplet begins to progressively advance, the permeability is restored. The mobilizing acceleration in the elastic wave, needed to "unplug" an immobile flow, is theoretically predicted within a factor of 1-5 of the experimental value. Overcoming the capillary entrapment in porous channels is hypothesized to be one of the principal mechanisms by which natural permeabilities are enhanced by the passage of seismic waves.

  4. Direct pore-level observation of permeability increase in two-phase flow by shaking

    NASA Astrophysics Data System (ADS)

    Beresnev, Igor; Gaul, William; Vigil, R. Dennis

    2011-10-01

    Increases in permeability of natural reservoirs and aquifers by passing seismic waves have been well documented. If the physical causes of this phenomenon can be understood, technological applications would be possible for controlling the flow in hydrologic systems or enhancing production from oil reservoirs. The explanation of the dynamically increased mobility of underground fluids must lie at the pore level. The natural fluids can be viewed as two-phase systems, composed of water as the wetting phase and of dispersed non-wetting globules of gas or organic fluids, flowing through tortuous constricted channels. Capillary forces prevent free motion of the suspended non-wetting droplets, which tend to become immobilized in capillary constrictions. The capillary entrapment significantly reduces macroscopic permeability. In a controlled experiment with a constricted capillary channel, we immobilize the suspended ganglia and test the model of capillary entrapment: it agrees precisely with the experiment. We then demonstrate by direct optical pore-level observation that the vibrations applied to the wall of the channel liberate the trapped ganglia if a predictable critical acceleration is reached. When the droplet begins to progressively advance, the permeability is restored. The mobilizing acceleration in the elastic wave, needed to “unplug” an immobile flow, is theoretically calculated within a factor of 1-5 of the experimental value. Overcoming the capillary entrapment in porous channels is hypothesized to be one of the principal pore-scale mechanisms by which natural permeabilities are enhanced by the passage of elastic waves.

  5. The Stochastic Engine Initiative: Improving Prediction of Behavior in Geologic Environments We Cannot Directly Observe

    SciTech Connect

    Aines, R; Nitao, J; Newmark, R; Carle, S; Ramirez, A; Harris, D; Johnson, J; Johnson, V; Ermak, D; Sugiyama, G; Hanley, W; Sengupta, S; Daily, W; Glaser, R; Dyer, K; Fogg, G; Zhang, Y; Yu, Z; Levine, R

    2002-05-09

    The stochastic engine uses modern computational capabilities to combine simulations with observations. We integrate the general knowledge represented by models with specific knowledge represented by data, using Bayesian inferencing and a highly efficient staged Metropolis-type search algorithm. From this, we obtain a probability distribution characterizing the likely configurations of the system consistent with existing data. The primary use will be optimizing knowledge about the configuration of a system for which sufficient direct observations cannot be made. Programmatic applications include underground systems ranging from environmental contamination to military bunkers, optimization of complex nonlinear systems, and timely decision-making for complex, hostile environments such as battlefields or the detection of secret facilities. We create a stochastic ''base representation'' of system configurations (states) from which the values of measurable parameters can be calculated using forward simulators. Comparison of these predictions to actual measurements drives embedded Bayesian inferencing, updating the distributions of states in the base representation using the Metropolis method. Unlike inversion methods that generate a single bestcase deterministic solution, this method produces all the likely solutions, weighted by their likelihoods. This flexible method is best applied to highly non-linear, multi-dimensional problems. Staging of the Metropolis searches permits us to run the simplest model systems, such as lithology estimators, at the lower stages. The majority of possible configurations are thus eliminated from further consideration by more complex simulators, such as flow and transport models. Because the method is fully automated, large data sets of a variety of types can be used to refine the system configurations. The most important prerequisites for optimal use of this method are well-characterized forward simulators, realistic base representations

  6. 49 CFR 40.67 - When and how is a directly observed collection conducted?

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... other specimen. (g) As the collector, you must ensure that the observer is the same gender as the employee. You must never permit an opposite gender person to act as the observer. The observer can be a... else is to observe the collection (e.g., in order to ensure a same gender observer), you must...

  7. Direct observation of extrasolar planets and the development of the gemini planet imager integral field spectrograph

    NASA Astrophysics Data System (ADS)

    Chilcote, Jeffrey Kaplan

    This thesis is focused on the development and testing of a new instrument capable of finding and characterizing recently-formed Jupiter-sized planets orbiting other stars. To observe these planets, I present the design, construction and testing of the Gemini Planet Imager (GPI) Integral Field Spectrograph (IFS). GPI is a facility class instrument for the Gemini Observatory with the primary goal of directly detecting young Jovian planets. The GPI IFS utilizes an infrared transmissive lenslet array to sample a rectangular 2.7 x 2.7 arcsecond field of view and provide low-resolution spectra across five bands between 1 and 2.5 mum. The dispersing element can be replaced with a Wollaston prism to provide broadband polarimetry across the same five filter bands. The IFS construction was based at the University of California, Los Angeles in collaboration with the Universite de Montreal, Immervision and Lawrence Livermore National Laboratory. I will present performance results, from in-lab testing, of the Integral Field Spectrograph (IFS) for the Gemini Planet Imager (GPI). The IFS is a large, complex, cryogenic, optical system requiring several years of development and testing. I will present the design and integration of the mechanical and optical performance of the spectrograph optics. The IFS passed its pre-ship review in 2011 and was shipped to University of California, Santa Cruz for integration with the remaining sub-systems of GPI. The UCLA built GPI IFS was integrated with the rest of GPI and is delivering high quality spectral datacubes of GPI's coronagraphic field. Using the NIRC2 instrument located at the Keck Observatory, my collaborators and I observed the planetary companion to beta Pictoris in L' (3.5--4.1mum). Observations taken in the fall of 2009 and 2012 are used to find the location and inclination of the planet relative to the massive debris disk orbiting beta Pictoris. We find that the planet's orbit has a position angle on the sky of 211

  8. The Photochemical Reflectance Index from Directional Cornfield Reflectances: Observations and Simulations

    NASA Technical Reports Server (NTRS)

    Cheng, Yen-Ben; Middleton, Elizabeth M.; Zhang, Qingyuan; Corp, Lawrence A.; Dandois, Jonathan; Kustas, William P.

    2012-01-01

    The two-layer Markov chain Analytical Canopy Reflectance Model (ACRM) was linked with in situ hyperspectral leaf optical properties to simulate the Photochemical Reflectance Index (PRI) for a corn crop canopy at three different growth stages. This is an extended study after a successful demonstration of PRI simulations for a cornfield previously conducted at an early vegetative growth stage. Consistent with previous in situ studies, sunlit leaves exhibited lower PRI values than shaded leaves. Since sunlit (shaded) foliage dominates the canopy in the reflectance hotspot (coldspot), the canopy PRI derived from field hyperspectral observations displayed sensitivity to both view zenith angle and relative azimuth angle at all growth stages. Consequently, sunlit and shaded canopy sectors were most differentiated when viewed along the azimuth matching the solar principal plane. These directional PRI responses associated with sunlit/shaded foliage were successfully reproduced by the ACRM. As before, the simulated PRI values from the current study were closer to in situ values when both sunlit and shaded leaves were utilized as model input data in a two-layer mode, instead of a one-layer mode with sunlit leaves only. Model performance as judged by correlation between in situ and simulated values was strongest for the mature corn crop (r = 0.87, RMSE = 0.0048), followed by the early vegetative stage (r = 0.78; RMSE = 0.0051) and the early senescent stage (r = 0.65; RMSE = 0.0104). Since the benefit of including shaded leaves in the scheme varied across different growth stages, a further analysis was conducted to investigate how variable fractions of sunlit/shaded leaves affect the canopy PRI values expected for a cornfield, with implications for 20 remote sensing monitoring options. Simulations of the sunlit to shaded canopy ratio near 50/50 +/- 10 (e.g., 60/40) matching field observations at all growth stages were examined. Our results suggest in the importance of the

  9. Direct Observation, Molecular Structure, and Location of Oxidation Debris on Graphene Oxide Nanosheets.

    PubMed

    Chen, Xiaoxiao; Chen, Baoliang

    2016-08-16

    The presence of oxidation debris (OD) complicates the structures and properties of graphene oxide (GO) nanosheets, thereby impacting their potential applications. However, the origin of OD is still in dispute. Moreover, characterizing the structure and location of supposed OD on nanosheets of GO produced during the oxidation process is difficult. Herein, the attached state and size of OD on graphene oxide nanosheets were directly observed using HRTEM, the molecular structure of OD was initially proposed based on the spectroscopic characterization and Q-TOF mass spectrometry, and the locations of OD on the GO nanosheets were detected through the adsorption of probe molecules onto as-prepared GO (a-GO) and base-washed GO (bw-GO). The results indicated that OD possesses a highly crystalline structure and can be defined as several nanometre-sized polyaromatic molecules with a considerable number of oxygen-containing functional groups attached on the edges. The dark nanodot seated on a-GO was clearly observed in the HRTEM images, whereas it appeared as a clean nanosheet in the image of bw-GO, indicating that OD is removed by base-washing treatment. Following the base-washing treatment, the contents of carboxyl groups on bw-GO unexpectedly increased and subsequently contributed to the desorption of OD from a-GO due to the electrostatic repulsion being stronger than primary π-π interactions. Compared with a-GO, the adsorption of phenanthrene, as an aromatic probe, onto bw-GO increased by 6-fold via π-π stacking interactions, whereas the increase in the adsorption of m-dinitrobenzene, as a defect probe, was not as remarkable as that of phenanthrene. Reasonably, the OD nanoparticles were primarily located at the sp(2) structures on the GO nanosheets through π-π interactions rather than attached on defects/edges. The insights regarding the existence, molecular structures and attached sites of OD nanoparticles on GO nanosheets provide a theoretical basis for preparing

  10. Direct observation of phase transitions: in situ diffraction measurements at the crystal scale

    NASA Astrophysics Data System (ADS)

    Bernier, J. V.; Barton, N. R.; Farber, D.; Wenk, H.; Kunz, M.; Lienert, U.

    2012-12-01

    Phase transitions often display determinate crystallographic orientation relationships between parent and symmetrically degenerate daughter domains. Preferred variant selection and orientation memory under the influence of deviatoric stress are the 'fingerprints' of the transformation mechanism, driving force, and microstructure. For the α-ɛ transition in iron - significant to the structure and anisotropy of the Earth's inner core - these have been studied primarily by texture analysis of polycrystalline powders; the convoluted nature of these data, however, render it essentially impossible to examine variant selection, and even precise orientation relationships themselves. Recently developed X-ray diffraction techniques have made it possible to answer these questions. Results from two measurements are presented. First, heterogeneous variant selection was observed and the specific α/ɛ orientation relationship was determined under quasi-static loading using High Energy Diffraction Microscopy at beamline 1-ID of APS-ANL. Second, the spatial heterogeneity and mutual exclusivity among ɛ variants was observed at the incipient transition using the Laue μ-diffraction technique at beamline 12.3.2. of ALS-LBNL. In both cases, a 60x25μm single crystal of iron was pressurized in a DAC and measured before and after the α-ɛ transition at 13GPa. In the HEDM experiment, spatial resolution is sacrificed for domain-averaged orientation and strain resoltuion, making it possible to quantify the magnitude of the applied deviatoric stress in situ. In the Laue μ-Diffraction technique, the local lattice orientations are mapped with 1μm resolution, displaying marked spatial variation. These pilot experiments open new possibilities for investigating high pressure/high temperature transformations in situ. By mapping both orientations and lattice strains, the nature of the mechanisms and driving forces can be illuminated. This work was performed under the auspices of the U

  11. Direct observation of markovian behavior of the mechanical unfolding of individual proteins.

    PubMed

    Cao, Yi; Kuske, Rachel; Li, Hongbin

    2008-07-01

    Single-molecule force-clamp spectroscopy is a valuable tool to analyze unfolding kinetics of proteins. Previous force-clamp spectroscopy experiments have demonstrated that the mechanical unfolding of ubiquitin deviates from the generally assumed Markovian behavior and involves the features of glassy dynamics. Here we use single molecule force-clamp spectroscopy to study the unfolding kinetics of a computationally designed fast-folding mutant of the small protein GB1, which shares a similar beta-grasp fold as ubiquitin. By treating the mechanical unfolding of polyproteins as the superposition of multiple identical Poisson processes, we developed a simple stochastic analysis approach to analyze the dwell time distribution of individual unfolding events in polyprotein unfolding trajectories. Our results unambiguously demonstrate that the mechanical unfolding of NuG2 fulfills all criteria of a memoryless Markovian process. This result, in contrast with the complex mechanical unfolding behaviors observed for ubiquitin, serves as a direct experimental demonstration of the Markovian behavior for the mechanical unfolding of a protein and reveals the complexity of the unfolding dynamics among structurally similar proteins. Furthermore, we extended our method into a robust and efficient pseudo-dwell-time analysis method, which allows one to make full use of all the unfolding events obtained in force-clamp experiments without categorizing the unfolding events. This method enabled us to measure the key parameters characterizing the mechanical unfolding energy landscape of NuG2 with improved precision. We anticipate that the methods demonstrated here will find broad applications in single-molecule force-clamp spectroscopy studies for a wide range of proteins.

  12. Unimolecular thermal decomposition of phenol and d5-phenol: Direct observation of cyclopentadiene formation via cyclohexadienone

    NASA Astrophysics Data System (ADS)

    Scheer, Adam M.; Mukarakate, Calvin; Robichaud, David J.; Nimlos, Mark R.; Carstensen, Hans-Heinrich; Barney Ellison, G.

    2012-01-01

    The pyrolyses of phenol and d5-phenol (C6H5OH and C6D5OH) have been studied using a high temperature, microtubular (μtubular) SiC reactor. Product detection is via both photon ionization (10.487 eV) time-of-flight mass spectrometry and matrix isolation infrared spectroscopy. Gas exiting the heated reactor (375 K-1575 K) is subject to a free expansion after a residence time in the μtubular reactor of approximately 50-100 μs. The expansion from the reactor into vacuum rapidly cools the gas mixture and allows the detection of radicals and other highly reactive intermediates. We find that the initial decomposition steps at the onset of phenol pyrolysis are enol/keto tautomerization to form cyclohexadienone followed by decarbonylation to produce cyclopentadiene; C6H5OH → c-C6H6 = O → c-C5H6 + CO. The cyclopentadiene loses a H atom to generate the cyclopentadienyl radical which further decomposes to acetylene and propargyl radical; c-C5H6 → c-C5H5 + H → HC≡CH + HCCCH2. At higher temperatures, hydrogen loss from the PhO-H group to form phenoxy radical followed by CO ejection to generate the cyclopentadienyl radical likely contributes to the product distribution; C6H5O-H → C6H5O + H → c-C5H5 + CO. The direct decarbonylation reaction remains an important channel in the thermal decomposition mechanisms of the dihydroxybenzenes. Both catechol (o-HO-C6H4-OH) and hydroquinone (p-HO-C6H4-OH) are shown to undergo decarbonylation at the onset of pyrolysis to form hydroxycyclopentadiene. In the case of catechol, we observe that water loss is also an important decomposition channel at the onset of pyrolysis.

  13. Rates of ingestion and their variability between individual calanoid copepods: Direct observations

    SciTech Connect

    Paffenhoefer, G.A.; Lewis, K.D.; Bundy, M.H. |; Metz, C.

    1995-12-01

    The goals of this study were to determine rates of ingestion and fecal pellet release, and their variability, for individual planktonic copepods over extended periods of time (>20 min). Ingestions and rejections of individual cells of the diatom Thalassiosira eccentrica by a adult females of the calanoid Paracalanus aculeatus were directly quantified by observing individual copepods continuously at cell concentrations ranging from 0.1 to 1.2 mm{sup 3} l{sup {minus}1}. Average ingestion rates increased with increasing food concentration, but were not significantly different between 0.3 and 1.0 mm{sup 3} l{sup {minus}1} (9.8 and 32.7 {mu}g Cl{sup {minus}1}) of T.eccentrica. Rates of cell rejections were low and similar at 0.1 and 0.3. but were significantly higher at 1.0 mm{sup 3} l{sup {minus}1}. The coefficients of variation for average ingestion rates of individual copepods hardly differed between food concentrations, ranging from 17 to 22%, and were close to those for average fecal pellet release intervals which ranged from 15 to 21%. A comparison between individuals at each food concentration found no significant differences at 1.0; at 0.1 and 0.3 mm{sup 3} l{sup {minus}1}, respectively, ingestion rates of four out of five females did not differ significantly from each other. Average intervals between fecal pellet releases were similar at 0.3 and 1.0 mm{sup 3} l{sup {minus}1}. Fecal pellet release intervals between individuals were significantly different at each food concentration; these significant differences were attributed to rather narrow ranges of pellet release intervals of each individual female. Potential sources/causes of variability in the sizes and rates of copepods in the ocean are evaluated.

  14. Major outcomes of patients with tuberculous meningitis on directly observed thrice a week regime

    PubMed Central

    Iype, Thomas; Pillai, Ayyappan Kunjukrishna; Cherian, Ajith; Nujum, Zinia T.; Pushpa, Chithra; Dae, Dalus; Krishnapillai, Vijayakumar

    2014-01-01

    Background: Revised National Tuberculosis Control Programme (RNTCP) of Government of India provides intermittent thrice-a-week directly observed treatment short course (RNTCP regimen). Objective: Assessments of all-cause mortality and nine-month morbidity outcomes of patients with tuberculous meningitis (TBM) on RNTCP regimen. Materials and Methods: We prospectively followed up patients registered with RNTCP center, with a diagnosis of TBM from January 1st, 2010 to December 31st, 2011. Morbidity was assessed using modified Rankin Scale (mRS). Results: We had 43 patients with median duration for follow-up of 396 days and that of survivors of 425 days. Two patients defaulted. Fourteen patients (32.5%) had mRS score of 4 to 6 and 29 had mRS of 0 to 3 after 9-month treatment. Severe disability was not related to any factor on logistic regression. Severe disability was seen in one patient (6.66%) among the 15 patients with stage 1, nine (37.5%) out of 24 patients with stage 2 and three (75%) out of 4 patients with stage 3 disease. Eight patients died (18.6%) of whom 4 died during the intensive phase and 4 during the continuation phase of RNTCP regimen. Mortality was independently related to treatment failure with adjusted Hazard ratio of 8.29 (CI: 1.38-49.78) (P = 0.02). One patient (6.66%) died out of the 15 patients with stage 1 disease, 5 (20.8%) out of 24 patients with stage 2 disease and 2 (50%) out of the 4 with stage 3 disease. Discussion and Conclusion: RNTCP regimen was associated with good compliance, comparable mortality and morbidity. PMID:25221396

  15. Gulf Stream Power Characteristics near Cape Hatteras; Regional Model vs. Direct Current Observations

    NASA Astrophysics Data System (ADS)

    Lowcher, C.; Bane, J.; Gong, Y.; He, R.; Muglia, M.

    2014-12-01

    The Gulf Stream has current velocities reaching approximately 2 meters per second, which distinguish it as a potential source of marine hydrokinetic (MHK) energy. The upper continental slope off Cape Hatteras is a desirable area for development of offshore renewable energy because of the closeness of the Gulf Stream to the shelf edge and its minimal meanderings there. Using data from a moored 150-kHz ADCP and from the Mid-Atlantic Bight and South Atlantic Bight (MABSAB) ocean circulation model, MHK power characteristics have been computed for this area. These calculations quantify the Gulf Stream power resource and its temporal and spatial variations. During August 2013 - April 2014 at the moored ADCP site 30 meters below the surface and within the Stream's cyclonic shear zone, a comparison of the ADCP and MABSAB model reveals that the average current speeds from the two sources are nearly identical and have a magnitude of 1.15 m/s. A comparison for the same time period was made for Betz power, which yielded an observed average of 0.8 kW/m2 and a model average of 0.7 kW/m2, a difference of about 13%. The model has shown to be more conservative than the ADCP in its computation of current speed and Betz power, and it shows somewhat less variability than the ADCP in directionality of the Stream. Additionally, model data have been used to calculate annual average vector velocities and yearly Betz power averages for a number of years, and at various locations over the NC continental slope. These results depict the variation of the Stream's position along the NC coastline over the most recent years, and show that yearly averaged Betz power at a given location has significant inter-annual variations, with average power during one year being nearly four times greater than in another year.

  16. Direct and in vitro observation of growth hormone receptor molecules in A549 human lung epithelial cells by nanodiamond labeling

    NASA Astrophysics Data System (ADS)

    Cheng, C.-Y.; Perevedentseva, E.; Tu, J.-S.; Chung, P.-H.; Cheng, C.-L.; Liu, K.-K.; Chao, J.-I.; Chen, P.-H.; Chang, C.-C.

    2007-04-01

    This letter presents direct observation of growth hormone receptor in one single cancer cell using nanodiamond-growth hormone complex as a specific probe. The interaction of surface growth hormone receptor of A549 human lung epithelial cells with growth hormone was observed using nanodiamond's unique spectroscopic signal via confocal Raman mapping. The growth hormone molecules were covalent conjugated to 100nm diameter carboxylated nanodiamonds, which can be recognized specifically by the growth hormone receptors of A549 cell. The Raman spectroscopic signal of diamond provides direct and in vitro observation of growth hormone receptors in physiology condition in a single cell level.

  17. Direct observation of subtropical mode water circulation in the western North Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Fratantoni, David M.; Kwon, Young-Oh; Hodges, Benjamin A.

    2013-07-01

    Eighteen Degree Water (EDW) is the dominant subtropical mode water of the North Atlantic subtropical gyre and is hypothesized as an interannual reservoir of anomalous heat, nutrients and CO2. Although isolated beneath the stratified upper-ocean at the end of each winter, EDW may re-emerge in subsequent years to influence mixed layer properties and consequently air-sea interaction and primary productivity. Here we report on recent quasi-Lagrangian measurements of EDW circulation and stratification in the western subtropical gyre using an array of acoustically-tracked, isotherm-following, bobbing profiling floats programmed to track and intensively sample the vertically homogenized EDW layer and directly measure velocity on the 18.5 °C isothermal surface. The majority of the CLIVAR Mode Water Dynamics Experiment (CLIMODE) bobbers drifted within the subtropical gyre for 2.5-3.5 years, many exhibiting complex looping patterns indicative of an energetic eddy field. Bobber-derived Lagrangian integral time and length scales (3 days, 68 km) associated with motion on 18.5 °C were consistent with previous measurements in the Gulf Stream extension region and fall between previous estimates at the ocean surface and thermocline depth. Several bobbers provided evidence of long-lived submesoscale coherent vortices associated with substantial EDW thickness. While the relative importance of such vortices remains to be determined, our observations indicate that these features can have a profound effect on EDW distribution. EDW thickness (defined using a vertical temperature gradient criterion) exhibits seasonal changes in opposition to a layer bounded by the 17 °C and 19 °C isotherms. In particular, EDW thickness is generally greatest in winter (as a result of buoyancy-forced convection), while the 17°-19 °C layer is thickest in summer consistent with seasonal Ekman pumping. Contrary to previous hypotheses, the bobber data suggest that a substantial fraction of subducted EDW

  18. Unimolecular Thermal Decomposition of Phenol and d5-Phenol: Direct Observation of Cyclopentadiene Formation via Cyclohexadienone

    SciTech Connect

    Scheer, A. M.; Mukarakate, C.; Robichaud, D. J.; Nimlos, M. R.; Carstensen, H. H.; Barney, E. G.

    2012-01-28

    The pyrolyses of phenol and d{sub 5}-phenol (C{sub 6}H{sub 5}OH and C{sub 6}D{sub 5}OH) have been studied using a high temperature, microtubular ({mu}tubular) SiC reactor. Product detection is via both photon ionization (10.487 eV) time-of-flight mass spectrometry and matrix isolation infrared spectroscopy. Gas exiting the heated reactor (375 K-1575 K) is subject to a free expansion after a residence time in the {mu}tubular reactor of approximately 50-100 {micro}s. The expansion from the reactor into vacuum rapidly cools the gas mixture and allows the detection of radicals and other highly reactive intermediates. We find that the initial decomposition steps at the onset of phenol pyrolysis are enol/keto tautomerization to form cyclohexadienone followed by decarbonylation to produce cyclopentadiene; C{sub 6}H{sub 5}OH {yields} c-C{sub 6}H{sub 6} = O {yields} c-C{sub 5}H{sub 6} + CO. The cyclopentadiene loses a H atom to generate the cyclopentadienyl radical which further decomposes to acetylene and propargyl radical; c-C{sub 5}H{sub 6} {yields} c-C{sub 5}H{sub 5} + H {yields} HC {triple_bond} CH + HCCCH{sub 2}. At higher temperatures, hydrogen loss from the PhO-H group to form phenoxy radical followed by CO ejection to generate the cyclopentadienyl radical likely contributes to the product distribution; C{sub 6}H{sub 5}O-H {yields} C{sub 6}H{sub 5}O + H {yields} c-C{sub 5}H{sub 5} + CO. The direct decarbonylation reaction remains an important channel in the thermal decomposition mechanisms of the dihydroxybenzenes. Both catechol (o-HO-C{sub 6}H{sub 4}-OH) and hydroquinone (p-HO-C{sub 6}H{sub 4}-OH) are shown to undergo decarbonylation at the onset of pyrolysis to form hydroxycyclopentadiene. In the case of catechol, we observe that water loss is also an important decomposition channel at the onset of pyrolysis.

  19. 49 CFR 40.67 - When and how is a directly observed collection conducted?

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... TRANSPORTATION WORKPLACE DRUG AND ALCOHOL TESTING PROGRAMS Urine Specimen Collections § 40.67 When and how is a... other specimen. (g) As the collector, you must ensure that the observer is the same gender as the employee. You must never permit an opposite gender person to act as the observer. The observer can be...

  20. 49 CFR 40.67 - When and how is a directly observed collection conducted?

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... TRANSPORTATION WORKPLACE DRUG AND ALCOHOL TESTING PROGRAMS Urine Specimen Collections § 40.67 When and how is a... other specimen. (g) As the collector, you must ensure that the observer is the same gender as the employee. You must never permit an opposite gender person to act as the observer. The observer can be...

  1. The Biasing Effects of Labels on Direct Observation by Preservice Teachers

    ERIC Educational Resources Information Center

    Allday, R. Allan; Duhon, Gary J.; Blackburn-Ellis, Sarah; Van Dycke, Jamie L.

    2011-01-01

    Observational bias can significantly affect results attained through observation. This study focused on 122 preservice teacher educators who conducted a structured observation, using momentary time sampling procedures with 10-second intervals, to measure student on-task and off-task behaviors. The experimental variable altered was the…

  2. A Direct Observation the Asteroid's Structure from Deep Interior to Regolith: Why and How do it?

    NASA Astrophysics Data System (ADS)

    Herique, A.

    2015-01-01

    The NEA internal structure has never been measured directly. Radar operating from a spacecraft is the only technique to characterize structure and heterogeneity from submetric to global scale for science, planetary defence and exploration benefit.

  3. Direct laboratory observation of fluid distribution and its influence on acoustic properties of patchy saturated rocks

    NASA Astrophysics Data System (ADS)

    Lebedev, M.; Clennell, B.; Pervukhina, M.; Shulakova, V.; Mueller, T.; Gurevich, B.

    2009-04-01

    samples (38 mm in diameter, approximately 60 mm long) were dried in oven under reduced pressure. In dynamic saturation experiments, samples were jacketed in the experimental cell, made from transparent for X-radiation material (PMMA). Distillate water was injected into the sample from the one side. Fluid distribution in such "dynamic" experiment: both spatial and time dependant was measured using X-ray Computer Tomograph (CT) with resolution 0.2 x 0.2 x 1 mm3. Velocities (Vp, and Vs) at ultrasonic frequency of 1 MHz, were measured in the direction perpendicular to initial direction of the fluid flow injection. Sample saturation was estimated from the CT results. In "quasi static" experiments samples were saturated during long period of time (over 2 weeks) to achieve uniform distribution of liquid inside the sample. Saturation was determined by measurement of the weight of water fraction. All experiments were performed at laboratory environments at temperature 25 C. Ultrasonic velocities and fluid saturations were measured simultaneously during water injection into sandstone core samples. The experimental results obtained on low-permeability samples show that at low saturation values the velocity-saturation dependence can be described by the Gassmann-Wood relationship. However, with increasing saturation a sharp increase of P-wave velocity is observed, eventually approaching the Gassmann-Hill relationship. We connect the characteristics of the transition behavior of the velocity-saturation relationships to the increasing size of the patches inside the rock sample. In particular, we show that for relatively large fluid injection rate this transition occurs at smaller degrees of saturation as compared with high injection rate. We model the experimental data using the so-called White model (Toms 2007) that assumes fluid patch distribution as a periodic assemblage of concentric spheres. We can observe reasonable agreement between experimental results and theoretical

  4. Numerical observation of preferred directionality in ion ejection from stretched rectilinear ion traps

    NASA Astrophysics Data System (ADS)

    Krishnaveni, A.; Kumar Verma, Neeraj; Menon, A. G.; Mohanty, Atanu K.

    2008-08-01

    We report on numerical investigations of directionality of ion ejection in stretched rectilinear ion traps (RIT). Three 4-electrode trap geometries have been investigated. In all cases, one pair of electrodes has slits at their center and the other pair has no slits. The studied traps include the RIT-S, in which the mass analyzer electrodes are symmetrically positioned around the central axis; the RIT-X, in which the mass analyzer has a stretch in the direction of the electrodes which have slits (labeled as x-direction); and the RIT-Y, in which the mass analyzer has a stretch in the direction of the electrodes which have no slits (labeled as y-direction). Our analysis has been carried out on two-dimensional (2D) fields at the centre of an infinitely long mass analyzer. The boundary element method (BEM) has been used for field computations. The trajectory of ion motion has been generated using Runge Kutta fourth order integration. Three sets of simulations have been carried out on each of the RIT-S, the RIT-X and the RIT-Y to check for directionality of ion ejection. In the first, we numerically obtain the stability region on the potential (Udc- Vrf) axes. In the second we generate an escape velocity plot with UdcD0 for different values of Vrf. In the third, we simulate the mass selective boundary ejection experiment on a single ion. In the symmetric RIT-S, as expected, all three simulations show that there is an equal probability of ion reaching the trap boundary in either of the x- or y-directions. For the stretched traps, however, the results are dramatically different. For the RIT-X, all three simulations suggest that ion destabilization at the stability boundary occurs in the x-directionE Similarly, for the RIT-Y, ions preferentially get destabilized in the y-direction. That is, ions reaching the trap boundary overwhelmingly prefer the stretch direction.

  5. Isolating observer-based reference directions in human spatial memory: Head, body, and the self-to-array axis

    PubMed Central

    Waller, David; Lippa, Yvonne; Richardson, Adam

    2007-01-01

    Several lines of research have suggested the importance of egocentric reference systems for determining how the spatial properties of one’s environment are mentally organized. Yet relatively little is known about the bases for egocentric reference systems in human spatial memory. In three experiments, we examine the relative importance of observer-based reference directions in human memory by controlling the orientation of head and body during acquisition. Experiment 1 suggests that spatial memory is organized by a head-aligned reference direction; however, Experiment 2 shows that a body-aligned reference direction can be more influential than a head-aligned direction when the axis defined by the relative positions of the observer and the learned environment (the “self-to-array” axis) is properly controlled. A third experiment shows that the self-to-array axis is distinct from – and can dominate – retina, head, and body-based egocentric reference systems. PMID:17316594

  6. Direct observation of large quantum interference effect in anthraquinone solid-state junctions.

    PubMed

    Rabache, Vincent; Chaste, Julien; Petit, Philippe; Della Rocca, Maria Luisa; Martin, Pascal; Lacroix, Jean-Christophe; McCreery, Richard L; Lafarge, Philippe

    2013-07-17

    Quantum interference in cross-conjugated molecules embedded in solid-state devices was investigated by direct current-voltage and differential conductance transport measurements of anthraquinone (AQ)-based large area planar junctions. A thin film of AQ was grafted covalently on the junction base electrode by diazonium electroreduction, while the counter electrode was directly evaporated on top of the molecular layer. Our technique provides direct evidence of a large quantum interference effect in multiple CMOS compatible planar junctions. The quantum interference is manifested by a pronounced dip in the differential conductance close to zero voltage bias. The experimental signature is well developed at low temperature (4 K), showing a large amplitude dip with a minimum >2 orders of magnitude lower than the conductance at higher bias and is still clearly evident at room temperature. A temperature analysis of the conductance curves revealed that electron-phonon coupling is the principal decoherence mechanism causing large conductance oscillations at low temperature.

  7. Direct observation of glycogen synthesis in human muscle with sup 13 C NMR

    SciTech Connect

    Jue, T.; Rothman, D.L.; Shulman, G.I.; Tavitian, B.A.; DeFronzo, R.A.; Shulman, R.G. )

    1989-06-01

    On the basis of previous indirect measurements, skeletal muscle has been implicated as the major site of glucose uptake and it has been suggested that muscle glycogen formation is the dominant pathway. However, direct measurements of the rates of glycogen synthesis have not been possible by previous techniques. The authors have developed {sup 13}C NMR methods to measure directly the rate of human muscle glycogen formation from infused, isotopically labeled (1-{sup 13}C)glucose. They show that under conditions of imposed hyperglycemia and hyperinsulinemia, a majority of the infused glucose was converted to muscle glycogen in a normal man. This directly shows that muscle is the major site of glucose disposal under these conditions, and provides quantitation of the glucose flux to muscle glycogen.

  8. Direct Observation Of Nanoparticle-Surfactant Interactions Using Small Angle Neutron Scattering

    NASA Astrophysics Data System (ADS)

    Kumar, Sugam; Aswal, V. K.

    2010-12-01

    Interactions of anionic silica nanoparticles with anionic, cationic and nonionic surfactants have directly been studied by contrast variation small angle neutron scattering (SANS). The measurements are performed on 1 wt% of both silica nanoparticles and surfactants of anionic sodium dodecyle sulphate (SDS), cationic dodecyltrimethyl ammonium bromide (DTAB) and non-ionic polyoxyethylene 10 lauryl ether (C12E10) in aqueous solution. We show that there is no direct interaction in the case of SDS with silica particles, whereas strong interaction for DTAB leads to the aggregation of silica particles. The interaction of C12E10 is found through the micelles adsorbed on the silica particles.

  9. Assessing the Accuracy of Classwide Direct Observation Methods: Two Analyses Using Simulated and Naturalistic Data

    ERIC Educational Resources Information Center

    Dart, Evan H.; Radley, Keith C.; Briesch, Amy M.; Furlow, Christopher M.; Cavell, Hannah J.; Briesch, Amy M.

    2016-01-01

    Two studies investigated the accuracy of eight different interval-based group observation methods that are commonly used to assess the effects of classwide interventions. In Study 1, a Microsoft Visual Basic program was created to simulate a large set of observational data. Binary data were randomly generated at the student level to represent…

  10. Hot-electron real-space transfer and longitudinal transport in dual AlGaN/AlN/{AlGaN/GaN} channels

    NASA Astrophysics Data System (ADS)

    Šermukšnis, E.; Liberis, J.; Matulionis, A.; Avrutin, V.; Ferreyra, R.; Özgür, Ü.; Morkoç, H.

    2015-03-01

    Real-space transfer of hot electrons is studied in dual-channel GaN-based heterostructure operated at or near plasmon-optical phonon resonance in order to attain a high electron drift velocity at high current densities. For this study, pulsed electric field is applied in the channel plane of a nominally undoped Al0.3Ga0.7N/AlN/{Al0.15Ga0.85N/GaN} structure with a composite channel of Al0.15Ga0.85N/GaN, where the electrons with a sheet density of 1.4 × 1013 cm-2, estimated from the Hall effect measurements, are confined. The equilibrium electrons are situated predominantly in the Al0.15Ga0.85N layer as confirmed by capacitance-voltage experiment and Schrödinger-Poisson modelling. The main peak of the electron density per unit volume decreases as more electrons occupy the GaN layer at high electric fields. The associated decrease in the plasma frequency induces the plasmon-assisted decay of non-equilibrium optical phonons (hot phonons) confirmed by the decrease in the measured hot-phonon lifetime from 0.95 ps at low electric fields down below 200 fs at fields of E \\gt 4 kV cm-1 as the plasmon-optical phonon resonance is approached. The onset of real-space transfer is resolved from microwave noise measurements: this source of noise dominates for E \\gt 8 kV cm-1. In this range of fields, the longitudinal current exceeds the values measured for a mono channel reference Al0.3Ga0.7N/AlN/GaN structure. The results are explained in terms of the ultrafast decay of hot phonons and reduced alloy scattering caused by the real-space transfer in the composite channel.

  11. Nano-aquarium for dynamic observation of aquatic microorganisms fabricated by femtosecond laser direct writing of photostructurable glass

    NASA Astrophysics Data System (ADS)

    Hanada, Y.; Sugioka, K.; Kawano, H.; Ishikawa, I.; Miyawaki, A.; Midorikawa, K.

    2008-02-01

    We demonstrate the fabrication of three-dimensional (3-D) hollow microstructures embedded in photostructurable glass by a femtosecond (fs) laser direct writing. Fs laser direct writing followed by annealing and successive wet etching in dilute hydrofluoric (HF) acid solution resulted in the rapid manufacturing of microchips with 3-D hollow microstructures for the dynamic observation of living microorganisms in fresh water. The embedded microchannel structure enables us to analyze the continuous motion of Euglena gracilis. A microchamber with a movable microneedle demonstrates its ability for the elucidation of the information transmission process in Pleurosira laevis. Such microchips, referred to as nano-aquariums realize the efficient and highly functional observation of microorganisms.

  12. Direct Observation of Ultralow Vertical Emittance using a Vertical Undulator - presentation slides

    SciTech Connect

    Wootton, Kent

    2015-09-17

    Direct emittance measurement based on vertical undulator is discussed. Emittance was evaluated from peak ratios, the smallest measured being 𝜀𝑦 =0.9 ±0.3 pm rad. The angular distribution of undulator radiation departs from Gaussian approximations, a fact of which diffraction-limited light sources should be aware.

  13. An observation of direct-gap electroluminescence in GaAs structures with Ge quantum wells

    SciTech Connect

    Aleshkin, V. Ya.; Dikareva, N. V.; Dubinov, A. A.; Zvonkov, B. N.; Kudryavtsev, K. E.; Nekorkin, S. M.

    2015-02-15

    A light-emitting diode structure based on GaAs with eight narrow Ge quantum wells is grown by laser sputtering. An electroluminescence line polarized predominately in the plane parallel to the constituent layers of the structure is revealed. The line corresponds to the direct optical transitions in momentum space in the Ge quantum wells.

  14. The underlying magnetic field direction in Ulysses observations of the southern polar heliosphere

    SciTech Connect

    Forsyth, R.J.; Balogh, A.; Smith, E.J.; Murphy, N.; McComas, D.J.

    1996-07-01

    Magnetic field data provided by the Ulysses spacecraft between May 1993 and January 1995 are presented for the south latitudes 30-80 dg. The deflections of the magnetic field direction are attributed to the intense Alfven waves. {copyright} {bold 1997 American Institute of Physics.}

  15. Direct Behavior Rating (DBR): Generalizability and Dependability across Raters and Observations

    ERIC Educational Resources Information Center

    Christ, Theodore J.; Riley-Tillman, T. Chris; Chafouleas, Sandra M.; Boice, Christina H.

    2010-01-01

    Generalizability theory was used to examine the generalizability and dependability of outcomes from two single-item Direct Behavior Rating (DBR) scales: DBR of actively manipulating and DBR of visually distracted. DBR is a behavioral assessment tool with specific instrumentation and procedures that can be used by a variety of service delivery…

  16. Anna Freud: the Hampstead War Nurseries and the role of the direct observation of children for psychoanalysis.

    PubMed

    Midgley, Nick

    2007-08-01

    The psychoanalytic tradition of direct observation of children has a long history, going back to the early 20th century, when psychoanalysis and the emerging field of 'child studies' came into fruitful contact in Freud's Vienna. As a leading figure in the attempted integration of direct observation with the new psychoanalytic knowledge emerging from the consulting room, Anna Freud played a crucial role in the emergence of this field. But her major contribution to the theory and practice of observing children came during the Second World War, when she founded the Hampstead War Nurseries. The author describes in detail this important period of Anna Freud's career, and discusses the impact it had on later work. He explores the theoretical contribution that Anna Freud made in the post-war years to the debate about the place of direct observation in psychoanalysis, and concludes that Anna Freud's 'double approach' (direct observation plus analytic reconstruction) still has a great deal to offer as a method of both psychoanalytic research and education.

  17. Observation of direct hadronic pairs in nucleus-nucleus collisions in JACEE emulsion chambers

    NASA Technical Reports Server (NTRS)

    Burnett, T. H.; Dake, S.; Fuki, M.; Gregory, J. C.; Hayashi, T.; Hayashi, T.; Holynski, R.; Iwai, J.; Jones, W. V.; Jurak, A.

    1985-01-01

    In a number of high energy ( or = 1 TeV/amu) nucleus-nucleus collisions observed in Japanese-American Cooperative Emulsion Experiment (JACEE) emulsion chambers, nonrandom spatial association of produced charged particles, mostly hadronic pairs, are observed. Similar narrow pairs are observed in about 100 events at much low energy (20 to 60 GeV/amu). Analysis shows that 30 to 50% of Pair abundances are understood by the Hambury-Brown-Twiss effect, and the remainder seems to require other explanations.

  18. OBSERVATIONAL EVIDENCE OF A CORONAL MASS EJECTION DISTORTION DIRECTLY ATTRIBUTABLE TO A STRUCTURED SOLAR WIND

    SciTech Connect

    Savani, N. P.; Owens, M. J.; Forsyth, R. J.; Rouillard, A. P.; Davies, J. A.

    2010-05-01

    We present the first observational evidence of the near-Sun distortion of the leading edge of a coronal mass ejection (CME) by the ambient solar wind into a concave structure. On 2007 November 14, a CME was observed by coronagraphs onboard the STEREO-B spacecraft, possessing a circular cross section. Subsequently the CME passed through the field of view of the STEREO-B Heliospheric Imagers where the leading edge was observed to distort into an increasingly concave structure. The CME observations are compared to an analytical flux rope model constrained by a magnetohydrodynamic solar wind solution. The resultant bimodal speed profile is used to kinematically distort a circular structure that replicates the initial shape of the CME. The CME morphology is found to change rapidly over a relatively short distance. This indicates an approximate radial distance in the heliosphere where the solar wind forces begin to dominate over the magnetic forces of the CME influencing the shape of the CME.

  19. Direct /TEM/ observation of the catalytic oxidation of amorphous carbon by Pd particles

    NASA Technical Reports Server (NTRS)

    Moorhead, R. D.; Poppa, H.; Heinemann, K.

    1980-01-01

    The catalytic oxidation of amorphous carbon substrates by Pd particles is observed by in situ transmission electron microscopy. Various modes of selective attack of the carbon substrate in the immediate neighborhood of Pd particles are observed, which can be correlated with different degrees of particle mobility. Using amorphous substrates we have been able to demonstrate that the particle-substrate interaction is influenced by the structure of the particle. This has not previously been noted.

  20. Direct experimental observation of weakly-bound character of the attached electron in europium anion.

    PubMed

    Cheng, Shi-Bo; Castleman, A W

    2015-01-01

    Direct experimental determination of precise electron affinities (EAs) of lanthanides is a longstanding challenge to experimentalists. Considerable debate exists in previous experiment and theory, hindering the complete understanding about the properties of the atomic anions. Herein, we report the first precise photoelectron imaging spectroscopy of europium (Eu), with the aim of eliminating prior contradictions. The measured EA (0.116 ± 0.013 eV) of Eu is in excellent agreement with recently reported theoretical predictions, providing direct spectroscopic evidence that the additional electron is weakly attached. Additionally, a new experimental strategy is proposed that can significantly increase the yield of the lanthanide anions, opening up the best opportunity to complete the periodic table of the atomic anions. The present findings not only serve to resolve previous discrepancy but also will help in improving the depth and accuracy of our understanding about the fundamental properties of the atomic anions. PMID:26198741