7,074 research outputs found
Locally embedded presages of global network bursts
Spontaneous, synchronous bursting of neural population is a widely observed
phenomenon in nervous networks, which is considered important for functions and
dysfunctions of the brain. However, how the global synchrony across a large
number of neurons emerges from an initially non-bursting network state is not
fully understood. In this study, we develop a new state-space reconstruction
method combined with high-resolution recordings of cultured neurons. This
method extracts deterministic signatures of upcoming global bursts in "local"
dynamics of individual neurons during non-bursting periods. We find that local
information within a single-cell time series can compare with or even
outperform the global mean field activity for predicting future global bursts.
Moreover, the inter-cell variability in the burst predictability is found to
reflect the network structure realized in the non-bursting periods. These
findings demonstrate the deterministic mechanisms underlying the locally
concentrated early-warnings of the global state transition in self-organized
networks
Propagation of a short laser pulse in a plasma
The propagation of an electromagnetic pulse in a plasma is studied for pulse
durations that are comparable to the plasma period. When the carrier frequency
of the incident pulse is much higher than the plasma frequency, the pulse
propagates without distortion at its group speed. When the carrier frequency is
comparable to the plasma frequency, the pulse is distorted and leaves behind it
an electromagnetic wake.Comment: 6 pages, 5 figures, REVTeX. To be published in Physical Review E,
vol. 56, December 1, 199
c-axis Raman Scattering in MgB2: Observation of a Dirty-Limit Gap in the pi-bands
Raman scattering spectra from the ac-face of thick MgB2 single crystals were
measured in zz, xz and xx polarisations. In zz and xz polarisations a threshold
at around 29 cm^{-1} forms in the below Tc continuum but no pair-breaking peak
is seen, in contrast to the sharp pair-breaking peak at around 100 cm^{-1} seen
in xx polarisation. The zz and xz spectra are consistent with Raman scattering
from a dirty superconductor while the sharp peak in the xx spectra argues for a
clean system. Analysis of the spectra resolves this contradiction, placing the
larger and smaller gap magnitudes in the sigma and pi bands, and indicating
that relatively strong impurity scattering is restricted to the pi bands.Comment: Revised manuscript accepted for publication in Physical Review
Letter
Carbon-substitution effect on the electronic properties of MgB single crystals
The electronic properties of the carbon substituted MgB single crystals
are reported. The carbon substitution drops T below 2 K. In-plane
resistivity shows a remarkable increase in residual resistivity by
C-substitution, while the change of in-plane/out-of-plane Hall coefficients is
rather small. Raman scattering spectra indicate that the E-phonon
frequency radically hardens with increasing the carbon-content, suggesting the
weakening of electron-phonon coupling. Another striking C-effect is the
increases of the second critical fields in both in-plane and out-of-plane
directions, accompanied by a reduction in the anisotropy ratio. The possible
changes in the electronic state and the origin of T-suppression by
C-substitution are discussed.Comment: 6 pages, 8 figure
Signatures of current loop coalescence in solar flares
The nonlinear coalescence instability of current carrying solar loops can explain many of the characteristics of the solar flares such as their impulsive nature, heating and high energy particle acceleration, amplitude oscillations of electromagnetic emission as well as the characteristics of 2-D microwave images obtained during a solar flare. The physical characteristics of the explosive coalescence of currents are presented in detail through computer simulation and theory. Canonical characteristics of the explosive coalescence are: (1) a large amount of impulsive increase of kinetic energies of electrons and ions; (2) simultaneous heating and acceleration of electrons and ions in high and low energy spectra; (3) ensuing quasi-periodic amplitude oscillations in fields and particle quantities; and (4) the double peak (or triple peak) structure in these profiles, participate in the coalescence process, yielding varieties of phenomena
Tilted-Cone Induced Cusps and Nonmonotonic Structures in Dynamical Polarization Function of Massless Dirac Fermions
The polarization function of electrons with the tilted Dirac cone found in
organic conductors is studied using the tilted Weyl equation. The dynamical
property is explored based on the analytical treatment of the particle-hole
excitation. It is shown that the polarization function as the function of both
the frequency and the momentum exhibits cusps and nonmonotonic structures. The
polarization function depends not only on the magnitude but also the direction
of the external momentum. These properties are characteristic of the tilted
Dirac cone, and are contrast to the isotropic case of grapheme. Further, the
results are applied to calculate the optical conductivity, the plasma frequency
and the screening of Coulomb interaction, which are also strongly influenced by
the tilted cone.Comment: 28 pages, 12 figures, to be published in Journal of the Physical
Society of Japan Vol. 79 (2010) No. 1
Nuclear prolate-shape dominance with the Woods-Saxon potential
We study the prolate-shape predominance of the nuclear ground-state
deformation by calculating the masses of more than two thousand even-even
nuclei using the Strutinsky method, modified by Kruppa, and improved by us. The
influences of the surface thickness of the single-particle potentials, the
strength of the spin-orbit potential, and the pairing correlations are
investigated by varying the parameters of the Woods-Saxon potential and the
pairing interaction. The strong interference between the effects of the surface
thickness and the spin-orbit potential is confirmed to persist for six sets of
the Woods-Saxon potential parameters. The observed behavior of the ratios of
prolate, oblate, and spherical nuclei versus potential parameters are rather
different in different mass regions. It is also found that the ratio of
spherical nuclei increases for weakly bound unstable nuclei. Differences of the
results from the calculations with the Nilsson potential are described in
detail.Comment: 16 pages, 17 figure
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