383 research outputs found
<Poster Presentation 3>Covariant Lyapunov Analysis of Chaotic Kolmogorov Flows and Time-correlation Function
[Date] November 28 (Mon) - December 2 (Fri), 2011: [Place] Kyoto University Clock Tower Centennial Hall, Kyoto, JAPA
Search for Photon-Photon Elastic Scattering in the X-ray Region
We report the first results of a search for real photon-photon scattering
using X rays. A novel system is developed to split and collide X-ray pulses by
applying interferometric techniques. A total of pulses (each
containing about photons) from an X-ray Free-Electron Laser are
injected into the system. No scattered events are observed, and an upper limit
of (95% C.L.) is obtained on the
photon-photon elastic scattering cross section at 6.5 keV
Coherent Acoustic Perturbation of Second-Harmonic-Generation in NiO
We investigate the structural and magnetic origins of the unusual ultrafast
second-harmonicgeneration (SHG) response of femtosecond-laser-excited nickel
oxide (NiO) previously attributed to oscillatory reorientation dynamics of the
magnetic structure induced by d-d excitations. Using time-resolved x-ray
diffraction from the (3/2 3/2 3/2) magnetic planes, we show that changes in the
magnitude of the magnetic structure factor following ultrafast optical
excitation are limited to = 1.5% in the first 30 ps. An
extended investigation of the ultrafast SHG response reveals a strong
dependence on wavelength as well as characteristic echoes, both of which give
evidence for an acoustic origin of the dynamics. We therefore propose an
alternative mechanism for the SHG response based on perturbations of the
nonlinear susceptibility via optically induced strain in a spatially confined
medium. In this model, the two observed oscillation periods can be understood
as the times required for an acoustic strain wave to traverse one coherence
length of the SHG process in either the collinear or anti-collinear geometries.Comment: 26 pages, 7 figure
Dynamics of the photoinduced insulator-to-metal transition in a nickelate film
The control of materials properties with light is a promising approach
towards the realization of faster and smaller electronic devices. With phases
that can be controlled via strain, pressure, chemical composition or
dimensionality, nickelates are good candidates for the development of a new
generation of high performance and low consumption devices. Here we analyze the
photoinduced dynamics in a single crystalline NdNiO film upon excitation
across the electronic gap. Using time-resolved reflectivity and resonant x-ray
diffraction, we show that the pump pulse induces an insulator-to-metal
transition, accompanied by the melting of the charge order. Finally we compare
our results to similar studies in manganites and show that the same model can
be used to describe the dynamics in nickelates, hinting towards a unified
description of these photoinduced phase transitions.Comment: 17 pages, 6 figure
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Single-shot 3D coherent diffractive imaging of core-shell nanoparticles with elemental specificity.
We report 3D coherent diffractive imaging (CDI) of Au/Pd core-shell nanoparticles with 6.1 nm spatial resolution with elemental specificity. We measured single-shot diffraction patterns of the nanoparticles using intense x-ray free electron laser pulses. By exploiting the curvature of the Ewald sphere and the symmetry of the nanoparticle, we reconstructed the 3D electron density of 34 core-shell structures from these diffraction patterns. To extract 3D structural information beyond the diffraction signal, we implemented a super-resolution technique by taking advantage of CDI's quantitative reconstruction capabilities. We used high-resolution model fitting to determine the Au core size and the Pd shell thickness to be 65.0 ± 1.0 nm and 4.0 ± 0.5 nm, respectively. We also identified the 3D elemental distribution inside the nanoparticles with an accuracy of 3%. To further examine the model fitting procedure, we simulated noisy diffraction patterns from a Au/Pd core-shell model and a solid Au model and confirmed the validity of the method. We anticipate this super-resolution CDI method can be generally used for quantitative 3D imaging of symmetrical nanostructures with elemental specificity
Damage threshold investigation using grazing incidence irradiation by hard X-ray free electron laser
T. Koyama, H. Yumoto, K. Tono, T. Sato, T. Togashi, Y. Inubushi, T. Katayama, J. Kim, S. Matsuyama, H. Mimura, M. Yabashi, K. Yamauchi, and H. Ohashi "Damage threshold investigation using grazing incidence irradiation by hard x-ray free electron laser", Proc. SPIE 8848, Advances in X-Ray/EUV Optics and Components VIII, 88480T (27 September 2013); https://doi.org/10.1117/12.2025377
Single-shot 3D coherent diffractive imaging of core-shell nanoparticles with elemental specificity
We report 3D coherent diffractive imaging (CDI) of Au/Pd core-shell nanoparticles with 6.1 nm spatial resolution with elemental specificity. We measured single-shot diffraction patterns of the nanoparticles using intense x-ray free electron laser pulses. By exploiting the curvature of the Ewald sphere and the symmetry of the nanoparticle, we reconstructed the 3D electron density of 34 core-shell structures from these diffraction patterns. To extract 3D structural information beyond the diffraction signal, we implemented a super-resolution technique by taking advantage of CDI's quantitative reconstruction capabilities. We used high-resolution model fitting to determine the Au core size and the Pd shell thickness to be 65.0 +/- 1.0 nm and 4.0 +/- 0.5 nm, respectively. We also identified the 3D elemental distribution inside the nanoparticles with an accuracy of 3%. To further examine the model fitting procedure, we simulated noisy diffraction patterns from a Au/Pd core-shell model and a solid Au model and confirmed the validity of the method. We anticipate this super-resolution CDI method can be generally used for quantitative 3D imaging of symmetrical nanostructures with elemental specificity.111Ysciescopu
Generation of Intense Phase-Stable Femtosecond Hard X-ray Pulse Pairs
Coherent nonlinear spectroscopies and imaging in the X-ray domain provide
direct insight into the coupled motions of electrons and nuclei with resolution
on the electronic length and time scale. The experimental realization of such
techniques will strongly benefit from access to intense, coherent pairs of
femtosecond X-ray pulses. We have observed phase-stable X-ray pulse pairs
containing more thank 3 x 10e7 photons at 5.9 keV (2.1 Angstrom) with about 1
fs duration and 2-5 fs separation. The highly directional pulse pairs are
manifested by interference fringes in the superfluorescent and seeded
stimulated manganese K-alpha emission induced by an X-ray free-electron laser.
The fringes constitute the time-frequency X-ray analogue of the Young
double-slit interference allowing for frequency-domain X-ray measurements with
attosecond time resolution.Comment: 39 pages, 13 figures, to be publishe
Nutritional regulation of proteases involved in fetal rat insulin secretion and islet cell proliferation
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