26,654 research outputs found
Infrared absorption and Raman scattering on coupled plasmon--phonon modes in superlattices
We consider theoretically a superlattice formed by thin conducting layers
separated spatially between insulating layers. The dispersion of two coupled
phonon-plasmon modes of the system is analyzed by using Maxwell's equations,
with the influence of retardation included. Both transmission for the finite
plate as well as absorption for the semi-infinite superlattice in the infrared
are calculated. Reflectance minima are determined by the longitudinal and
transverse phonon frequencies in the insulating layers and by the density-state
singularities of the coupled modes. We evaluate also the Raman cross section
from the semi-infinite superlattice.Comment: 20 pages,14 figure
Complete homochirality induced by the nonlinear autocatalysis and recycling
A nonlinear autocatalysis of a chiral substance is shown to achieve
homochirality in a closed system, if the back-reaction is included. Asymmetry
in the concentration of two enantiomers or the enantiometric excess increases
due to the nonlinear autocatalysis. Furthermore, when the back-reaction is
taken into account, the reactant supplied by the decomposition of the
enantiomers is recycled to produce more and more the dominant one, and
eventually the homochirality is established.Comment: 4 pages, 2 figure
Attosecond screening dynamics mediated by electron-localization
Transition metals with their densely confined and strongly coupled valence
electrons are key constituents of many materials with unconventional
properties, such as high-Tc superconductors, Mott insulators and
transition-metal dichalcogenides. Strong electron interaction offers a fast and
efficient lever to manipulate their properties with light, creating promising
potential for next-generation electronics. However, the underlying dynamics is
a fast and intricate interplay of polarization and screening effects, which is
poorly understood. It is hidden below the femtosecond timescale of electronic
thermalization, which follows the light-induced excitation. Here, we
investigate the many-body electron dynamics in transition metals before
thermalization sets in. We combine the sensitivity of intra-shell transitions
to screening effects with attosecond time resolution to uncover the interplay
of photo-absorption and screening. First-principles time-dependent calculations
allow us to assign our experimental observations to ultrafast electronic
localization on d-orbitals. The latter modifies the whole electronic structure
as well as the collective dynamic response of the system on a timescale much
faster than the light-field cycle. Our results demonstrate a possibility for
steering the electronic properties of solids prior to electron thermalization,
suggesting that the ultimate speed of electronic phase transitions is limited
only by the duration of the controlling laser pulse. Furthermore, external
control of the local electronic density serves as a fine tool for testing
state-of-the art models of electron-electron interactions. We anticipate our
study to facilitate further investigations of electronic phase transitions,
laser-metal interactions and photo-absorption in correlated electron systems on
its natural timescale
Phase statistics of seismic coda waves
We report the analysis of the statistics of the phase fluctuations in the
coda of earthquakes recorded during a temporary experiment deployed at Pinyon
Flats Observatory, California. The practical measurement of the phase is
discussed and the main pitfalls are underlined. For large values, the
experimental distributions of the phase first, second and third derivatives
obey universal power-law decays whose exponents are remarkably well predicted
by circular Gaussian statistics. For small values, these distributions are
flat. The details of the transition between the plateau and the power-law
behavior are governed by the wavelength. The correlation function of the first
phase derivative along the array shows a simple algebro-exponential decay with
the mean free path as the only length scale. Although only loose bounds are
provided in this study, our work suggests a new method to estimate the degree
of heterogeneity of the crComment: 4 figures, submitted to Physical Review Letter
Four-spin-exchange- and magnetic-field-induced chiral order in two-leg spin ladders
We propose a mechanism of a vector chiral long-range order in two-leg
spin-1/2 and spin-1 antiferromagnetic ladders with four-spin exchanges and a
Zeeman term. It is known that for one-dimensional quantum systems, spontaneous
breakdown of continuous symmetries is generally forbidden. Any vector chiral
order hence does not appear in spin-rotationally [SU(2)]-symmetric spin
ladders. However, if a magnetic field is added along the S^z axis of ladders
and the SU(2) symmetry is reduced to the U(1) one, the z component of a vector
chiral order can emerge with the remaining U(1) symmetry unbroken. Making use
of Abelian bosonization techniques, we actually show that a certain type of
four-spin exchange can yield a vector chiral long-range order in spin-1/2 and
spin-1 ladders under a magnetic field. In the chiral-ordered phase, the Z_2
interchain-parity (i.e., chain-exchange) symmetry is spontaneously broken. We
also consider effects of perturbations breaking the parity symmetry.Comment: 8 pages, 1 figure, RevTex, published versio
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Distance constraints on activation of TRPV4 channels by AKAP150-bound PKCα in arterial myocytes.
TRPV4 (transient receptor potential vanilloid 4) channels are Ca2+-permeable channels that play a key role in regulating vascular tone. In arterial myocytes, opening of TRPV4 channels creates local increases in Ca2+ influx, detectable optically as "TRPV4 sparklets." TRPV4 sparklet activity can be enhanced by the action of the vasoconstrictor angiotensin II (AngII). This modulation depends on the activation of subcellular signaling domains that comprise protein kinase C α (PKCα) bound to the anchoring protein AKAP150. Here, we used super-resolution nanoscopy, patch-clamp electrophysiology, Ca2+ imaging, and mathematical modeling approaches to test the hypothesis that AKAP150-dependent modulation of TRPV4 channels is critically dependent on the distance between these two proteins in the sarcolemma of arterial myocytes. Our data show that the distance between AKAP150 and TRPV4 channel clusters varies with sex and arterial bed. Consistent with our hypothesis, we further find that basal and AngII-induced TRPV4 channel activity decays exponentially as the distance between TRPV4 and AKAP150 increases. Our data suggest a maximum radius of action of âŒ200 nm for local modulation of TRPV4 channels by AKAP150-associated PKCα
Implication of Omega_m through the Morphological Analysis of Weak Lensing Fields
We apply the morphological descriptions of two-dimensional contour map, the
so-called Minkowski functionals (the area fraction, circumference, and Euler
characteristics), to the convergence field of the
large-scale structure reconstructed from the shear map produced by the
ray-tracing simulations. The perturbation theory of structure formation has
suggested that the non-Gaussian features on the Minkowski functionals with
respect to the threshold in the weakly nonlinear regime are induced by the
three skewness parameters of that are sensitive to the density
parameter of matter, . We show that, in the absence of noise
due to the intrinsic ellipticities of source galaxies with which the
perturbation theory results can be recovered, the accuracy of
determination is improved by using the Minkowski functionals
compared to the conventional method of using the direct measure of skewness.Comment: 4 pages, 3 figures, to appear in ApJ Lette
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