5,894 research outputs found
Magnetic phase diagram of the Hubbard model
The competition between commensurate and incommensurate spin-density-wave
phases in the infinite-dimensional single-band Hubbard model is examined with
quantum Monte Carlo simulation and strong and weak coupling approximations.
Quantum fluctuations modify the weak-coupling phase diagram by factors of order
unity and produce remarkable agreement with the quantum Monte Carlo data, but
strong-coupling theories (that map onto effective Falicov-Kimball models)
display pathological behavior. The single-band model can be used to describe
much of the experimental data in Cr and its dilute alloys with V and Mn.Comment: 12 pages plus 3 uuencoded postscript figures, ReVTe
Decay of accelerated particles
We study how the decay properties of particles are changed by acceleration.
It is shown that under the influence of acceleration (1) the lifetime of
particles is modified and (2) new processes (like the decay of the proton)
become possible. This is illustrated by considering scalar models for the decay
of muons, pions, and protons. We discuss the close conceptual relation between
these processes and the Unruh effect.Comment: Latex2e, 12 pages, 6 Postscript figures included with epsfig, to
appear in Phys. Rev.
Correcting the polarization effect in low frequency Dielectric Spectroscopy
We demonstrate a simple and robust methodology for measuring and analyzing
the polarization impedance appearing at interface between electrodes and ionic
solutions, in the frequency range from 1 to Hz. The method assumes no
particular behavior of the electrode polarization impedance and it only makes
use of the fact that the polarization effect dies out with frequency. The
method allows a direct and un-biased measurement of the polarization impedance,
whose behavior with the applied voltages and ionic concentration is
methodically investigated. Furthermore, based on the previous findings, we
propose a protocol for correcting the polarization effect in low frequency
Dielectric Spectroscopy measurements of colloids. This could potentially lead
to the quantitative resolution of the -dispersion regime of live cells
in suspension
Vacuum polarization for lukewarm black holes
We compute the renormalized expectation value of the square of a quantum scalar field on a Reissner-Nordström–de Sitter black hole in which the temperatures of the event and cosmological horizons are equal (“lukewarm” black hole). Our numerical calculations for a thermal state at the same temperature as the two horizons indicate that this renormalized expectation value is regular on both the event and cosmological horizons. We are able to show analytically, using an approximation for the field modes near the horizons, that this is indeed the case
Retinal glia promote dorsal root ganglion axon regeneration.
Axon regeneration in the adult central nervous system (CNS) is limited by several factors including a lack of neurotrophic support. Recent studies have shown that glia from the adult rat CNS, specifically retinal astrocytes and Müller glia, can promote regeneration of retinal ganglion cell axons. In the present study we investigated whether retinal glia also exert a growth promoting effect outside the visual system. We found that retinal glial conditioned medium significantly enhanced neurite growth and branching of adult rat dorsal root ganglion neurons (DRG) in culture. Furthermore, transplantation of retinal glia significantly enhanced regeneration of DRG axons past the dorsal root entry zone after root crush in adult rats. To identify the factors that mediate the growth promoting effects of retinal glia, mass spectrometric analysis of retinal glial conditioned medium was performed. Apolipoprotein E and secreted protein acidic and rich in cysteine (SPARC) were found to be present in high abundance, a finding further confirmed by western blotting. Inhibition of Apolipoprotein E and SPARC significantly reduced the neuritogenic effects of retinal glial conditioned medium on DRG in culture, suggesting that Apolipoprotein E and SPARC are the major mediators of this regenerative response.This work was supported by a van Geest Fight for Sight Early Career Investigator Award, grant number 1868 [BL].This is the final version of the article. It first appeared at http://journals.plos.org/plosone/article?id=10.1371/journal.pone.011599
Spin and charge excitations in incommensurate spin density waves
Collective excitations both for spin- and charge-channels are investigated in
incommensurate spin density wave (or stripe) states on two-dimensional Hubbard
model. By random phase approximation, the dynamical susceptibility
\chi(q,\omega) is calculated for full range of (q,\omega) with including all
higher harmonics components. An intricate landscape of the spectra in
\chi(q,\omega) is obtained. We discuss the anisotropy of the dispersion cones
for spin wave excitations, and for the phason excitation related to the motion
of the stripe line. Inelastic neutron experiments on Cr and its alloys and
stripe states of underdoped cuprates are proposed
Expression of an Activated Integrin Promotes Long-Distance Sensory Axon Regeneration in the Spinal Cord.
UNLABELLED: After CNS injury, axon regeneration is blocked by an inhibitory environment consisting of the highly upregulated tenascin-C and chondroitin sulfate proteoglycans (CSPGs). Tenascin-C promotes growth of axons if they express a tenascin-binding integrin, particularly α9β1. Additionally, integrins can be inactivated by CSPGs, and this inhibition can be overcome by the presence of a β1-binding integrin activator, kindlin-1. We examined the synergistic effect of α9 integrin and kindlin-1 on sensory axon regeneration in adult rat spinal cord after dorsal root crush and adeno-associated virus transgene expression in dorsal root ganglia. After 12 weeks, axons from C6-C7 dorsal root ganglia regenerated through the tenascin-C-rich dorsal root entry zone into the dorsal column up to C1 level and above (>25 mm axon length) through a normal pathway. Animals also showed anatomical and electrophysiological evidence of reconnection to the dorsal horn and behavioral recovery in mechanical pressure, thermal pain, and ladder-walking tasks. Expression of α9 integrin or kindlin-1 alone promoted much less regeneration and recovery. SIGNIFICANCE STATEMENT: The study demonstrates that long-distance sensory axon regeneration over a normal pathway and with sensory and sensory-motor recovery can be achieved. This was achieved by expressing an integrin that recognizes tenascin-C, one of the components of glial scar tissue, and an integrin activator. This enabled extensive long-distance (>25 mm) regeneration of both myelinated and unmyelinated sensory axons with topographically correct connections in the spinal cord. The extent of growth and recovery we have seen would probably be clinically significant. Restoration of sensation to hands, perineum, and genitalia would be a significant improvement for a spinal cord-injured patient
Searching for the Slater Transition in the Pyrochlore CdOsO with Infrared Spectroscopy
Infrared reflectance measurements were made on the single crystal pyrochlore
CdOsO in order to examine the transformations of the
electronic structure and crystal lattice across the boundary of the metal
insulator transition at . All predicted IR active phonons are
observed in the conductivity over all temperatures and the oscillator strength
is found to be temperature independent. These results indicate that charge
ordering plays only a minor role in the MIT and that the transition is strictly
electronic in nature. The conductivity shows the clear opening of a gap with
. The gap opens continuously, with a temperature
dependence similar to that of BCS superconductors, and the gap edge having a
distinct dependence. All of these
observables support the suggestion of a Slater transition in CdOsO.Comment: 4 pages, 4 figure
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