1,547 research outputs found
Intrinsic Josephson Effect in the Layered Two-dimensional t-J Model
The intrinsic Josephson effect in the high-Tc superconductors is studied
using the layered two-dimensional t-J model. The d.c.Josephson current which
flows perpendicular to the t-J planes is obtained within the mean-field
approximation and the Gutzwiller approximation. We find that the Josephson
current has its maximum near the optimum doping region as a function of the
doping rate.Comment: 4 pages, 3 figure
Okaramine insecticidal alkaloids show similar activity on both exon 3c and exon 3b variants of glutamate-gated chloride channels of the larval silkworm, Bombyx mori
The okaramine indole alkaloids were recently shown to be more selective than ivermectin in activating the glutamate-gated chloride channels of the silkworm larvae of Bombyx mori (BmGluCls). Those studies were carried out using the exon 3b variant as a representative of BmGluCls. However, it remains unknown whether okaramines are similarly effective on other silkworm GluCl variants and whether they share the same binding site as ivermectin on GluCls. To begin to address these questions, we examined the potency of four okaramines on the exon 3c variant of BmGluCls by two-electrode voltage clamp voltage recordings of glutamate-induced chloride currents. The potency of okaramines in activating the exon 3c BmGluCl agreed well with findings on the exon 3b BmGluCl and insecticidal potency. Okaramine B (10μM) reduced the maximum binding (Bmax) but not the dissociation constant (KD) of [(3)H]ivermectin in studies on plasma membrane fractions of HEK293 cells expressing the exon 3c variant. These findings indicate that activation of GluCls is important in the insecticidal actions of okaramines
Collective Dynamics of Josephson Vortices in Intrinsic Josephson Junctions :Exploration of In-phase Locked Superradiant Vortex Flow States
In order to clarify the ``superradiant'' conditions for the moving Josephson
vortices to excite in-phase AC electromagnetic fields over all junctions, we
perform large scale simulations of realistic dimensions for intrinsic Josephson
junctions under the layer parallel magnetic field. Three clear step-like
structures in the I-V curve are observed above a certain high field (
in the present simulations), at which we find structural transitions in the
moving flux-line lattice. The Josephson vortex flow states are accordingly
classified into four regions (region I IV with increasing current), in
each of which the power spectrum for the electric field oscillations at the
sample edge are measured and typical snapshots for Josephson vortex
configurations are displayed. Among the four regions, especially in the region
III, an in-phase rectangular vortex lattice flow state emerges and the power
spectrum shows remarkably sharp peak structure, i.e., superradiant state.
Comparison of the simulation results with an eigenmode analysis for the
transverse propagating Josephson plasma oscillations reveals that the
resonances between Josephson vortex flow states and some of the eigenmodes are
responsible for the clear flux lattice structural transitions. Furthermore, the
theoretical analysis clarifies that the width of the superradiant state region
in the I-V characteristics enlarges with decreasing both the superconducting
and insulating layer thickness.Comment: 8 pages, Revtex, 7 figures; figure arrangements improved. no changes
in tex
Anisotropic spin freezing in the S=1/2 zigzag ladder compound SrCuO2
Using magnetic neutron scattering we characterize an unusual low temperature
phase in orthorhombic SrCuO2. The material contains zigzag spin ladders formed
by pairs of S=1/2 chains (J=180 meV) coupled through a weak frustrated
interaction |J'|<0.1J. At T<Tc1=5.0(4)K an elastic peak develops in a gapless
magnetic excitation spectrum indicating spin freezing on a time scale larger
than 200 picoseconds. While the frozen state has long range commensurate
antiferromagnetic order along the chains with the correlation length exceeding
200 lattice periods along the c-axis and a substantial correlation length of
60(25) spacings along the a-axis perpendicular to the zigzag plane, only 2
lattice units are correlated along the b-axis which is the direction of the
frustrated interactions. The frozen magnetic moment of each Cu ion is very
small, 0.033(7) Bohr magneton even at T=0.35K, and has unusual temperature
dependence with a cusp at Tc2=1.5K reminiscent of a phase transition. We argue
that slow dynamics of stripe-like cooperative magnetic defects in tetragonal
a-c planes yield this anisotropic frozen state.Comment: 4 pages, LaTeX, submitted to PR
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