1,210 research outputs found
Disassembly kinetics of thick filaments in rabbit skeletal muscle fibers. Effects of ionic strength, Ca2+ concentration, pH, temperature, and cross-bridges on the stability of thick filament structure
The kinetics of dissociation from both ends of thick filaments in a muscle fiber was investigated by an optical diffraction method. The dissociation velocity of thick filaments at a sarcomere length of 2.75 microns increased with increasing the KCl concentration (from 60 mM to 0.5 M), increasing the pH value (from 6.2 to 8.0) or decreasing the temperature (from 25 to 5 degrees C) in the presence of 10 mM pyrophosphate and 5 mM MgCl2. Micromolar concentrations of Ca2+ suppressed the dissociation velocity markedly at shorter sarcomere lengths. The dissociation velocity, v, decreased as thick filaments became shorter, and v = -db/dt = vo exp (alpha b), where b is the length of the thick filament at time t and vo and alpha are constants. The vo value was largely dependent on the KCl concentration but the alpha value was not. The stiffness of a muscle fiber decreased nearly in proportion to the decrease of overlap between thick and thin filaments induced by the dissociation of thick filaments. This indicates that cross-bridges are uniformly distributed and contribute independently to the stiffness of a muscle fiber during the dissociation of thick filaments
Magnetic-field induced competition of two multiferroic orders in a triangular-lattice helimagnet MnI2
Magnetic and dielectric properties with varying magnitude and direction of
magnetic field H have been investigated for a triangular lattice helimagnet
MnI2. The in-plane electric polarization P emerges in the proper screw magnetic
ground state below 3.5 K, showing the rearrangement of six possible
multiferroic domains as controlled by the in-plane H. With every 60-degree
rotation of H around the [001]-axis, discontinuous 120-degree flop of P-vector
is observed as a result of the flop of magnetic modulation vector q. With
increasing the in-plane H above 3 T, however, the stable q-direction changes
from q|| to q||, leading to a change of P-flop patterns under
rotating H. At the critical field region (~3 T), due to the phase competition
and resultant enhanced q-flexibility, P-vector smoothly rotates clockwise twice
while H-vector rotates counter-clockwise once.Comment: 4 pages, 3 figures. Accepted in Physical Review Letter
Perovskite Manganites Hosting Versatile Multiferroic Phases with Symmetric and Antisymmetric Exchange Strictions
Complete magnetoelectric (ME) phase diagrams of orthorhombic MnO
with and without magnetic moments on the ions have been established. Three
kinds of multiferroic ground states, the -cycloidal, the -cycloidal,
and the collinear -type phases, have been identified by the distinct ME
responses. The electric polarization of the -type phase dominated by the
symmetric spin exchange () is more than 10 times as
large as that of the -cycloidal phase dominated by the antisymmetric one
(), and the ME response is enhanced near the
bicritical phase boundary between these multiferroic phases of different
origins. These findings will provide an important clue for the development of
the magnetically induced multiferroics.Comment: 5 pages, 3 figure
Synchrotron Radiation from the Galactic Center in Decaying Dark Matter Scenario
We discuss the synchrotron radiation flux from the Galactic center in
unstable dark matter scenario. Motivated by the anomalous excess of the
positron fraction recently reported by the PAMELA collaboration, we consider
the case that the dark matter particle is unstable (and long-lived), and that
energetic electron and positron are produced by the decay of dark matter. Then,
the emitted electron and positron becomes the source of the synchrotron
radiation. We calculate the synchrotron radiation flux for models of decaying
dark matter, which can explain the PAMELA positron excess. Taking the lifetime
of the dark matter of O(10^26 sec), which is the suggested value to explain the
PAMELA anomaly, the synchrotron radiation flux is found to be O(1 kJy/str) or
smaller, depending on the particle-physics and cosmological parameters.Comment: 20 pages, 6 figure
Electromagnons in the multiferroic state of perovskite manganites with symmetric-exchange striction
We have investigated electrically-active magnetic excitations
(electromagnons) in perovskite manganites with the -type (up-up-down-down)
spin structure by terahertz spectroscopy. EuYMnO (0.11) and YLuMnO (01) without magnetic -moments,
which host collinear sinusoidal, -type, cycloidal, and -type spin orders,
are used to examine the systematics of possible electromagnons. Three-peak
structures (23, 35, 45 cm) of magnetic origin show up in the -type
phase with little composition () dependence of frequencies, making a
contrast with the electromagnons observed in the cycloidal-spin ()
phases. One of these electromagnon is ascribed to the zone-edge magnon mode
based on the calculated magnon dispersions.Comment: 5 pages, 4 figure
Electromagnons in the multiferroic state of perovskite manganites with symmetric-exchange striction
We have investigated electrically-active magnetic excitations
(electromagnons) in perovskite manganites with the -type (up-up-down-down)
spin structure by terahertz spectroscopy. EuYMnO (0.11) and YLuMnO (01) without magnetic -moments,
which host collinear sinusoidal, -type, cycloidal, and -type spin orders,
are used to examine the systematics of possible electromagnons. Three-peak
structures (23, 35, 45 cm) of magnetic origin show up in the -type
phase with little composition () dependence of frequencies, making a
contrast with the electromagnons observed in the cycloidal-spin ()
phases. One of these electromagnon is ascribed to the zone-edge magnon mode
based on the calculated magnon dispersions.Comment: 5 pages, 4 figure
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