4,996 research outputs found
Spin-Wave Spectrum in `Single-Domain' Magnetic Ground State of Triangular Lattice Antiferromagnet CuFeO2
By means of neutron scattering measurements, we have investigated spin-wave
excitation in a collinear four-sublattice (4SL) magnetic ground state of a
triangular lattice antiferromagnet CuFeO2, which has been of recent interest as
a strongly frustrated magnet, a spin-lattice coupled system and a multiferroic.
To avoid mixing of spin-wave spectrum from magnetic domains having three
different orientations reflecting trigonal symmetry of the crystal structure,
we have applied uniaxial pressure on [1-10] direction of a single crystal
CuFeO2. By elastic neutron scattering measurements, we have found that only 10
MPa of the uniaxial pressure results in almost 'single domain' state in the 4SL
phase. We have thus performed inelastic neutron scattering measurements using
the single domain sample, and have identified two distinct spin- wave branches.
The dispersion relation of the upper spin-wave branch cannot be explained by
the previous theoretical model [R. S. Fishman: J. Appl. Phys. 103 (2008)
07B109]. This implies the importance of the lattice degree of freedom in the
spin-wave excitation in this system, because the previous calculation neglected
the effect of the spin-driven lattice distortion in the 4SL phase. We have also
discussed relationship between the present results and the recently discovered
"electromagnon" excitation.Comment: 5 pages, 3 figures, accepted for publication in J. Phys. Soc. Jp
An automata characterisation for multiple context-free languages
We introduce tree stack automata as a new class of automata with storage and
identify a restricted form of tree stack automata that recognises exactly the
multiple context-free languages.Comment: This is an extended version of a paper with the same title accepted
at the 20th International Conference on Developments in Language Theory (DLT
2016
Development of a low-mass and high-efficiency charged particle detector
We developed a low-mass and high-efficiency charged particle detector for an
experimental study of the rare decay . The
detector is important to suppress the background with charged particles to the
level below the signal branching ratio predicted by the Standard Model
(O(10)). The detector consists of two layers of 3-mm-thick plastic
scintillators with wavelength shifting fibers embedded and Multi Pixel Photon
Counters for readout. We manufactured the counter and evaluated the performance
such as light yield, timing resolution, and efficiency. With this design, we
achieved the inefficiency per layer against penetrating charged particles to be
less than , which satisfies the requirement of the KOTO
experiment determined from simulation studies.Comment: 20 pages, 18 figure
An aerogel Cherenkov detector for multi-GeV photon detection with low sensitivity to neutrons
We describe a novel photon detector which operates under an intense flux of
neutrons. It is composed of lead-aerogel sandwich counter modules. Its salient
features are high photon detection efficiency and blindness to neutrons. As a
result of Monte Carlo (MC) simulations, the efficiency for photons with the
energy larger than 1 GeV is expected to be higher than 99.5% and that for 2
GeV/ neutrons less than 1%. The performance on the photon detection under
such a large flux of neutrons was measured for a part of the detector. It was
confirmed that the efficiency to photons with the energy 1 GeV was
consistent with the MC expectation within 8.2% uncertainty.Comment: 16 pages, 16 figures, submitted to Prog. Theor. Exp. Phy
Centrifugally Stimulated Exospheric Ion Escape at Mercury
We investigate the transport of ions in the low-altitude magnetosphere magnetosphere of Mercury. We show that, because of small spatial scales, the centrifugal effect due to curvature of the E B drift paths can lead to significant particle energization in the parallel direction. We demonstrate that because of this effect, ions with initial speed smaller than the escape speed such as those produced via thermal desorption can overcome gravity and escape into the magnetosphere. The escape route of this low-energy exosphere originating material is largely controlled by the magnetospheric convection rate. This escape route spreads over a narrower range of altitudes when the convection rate increases. Bulk transport of low-energy planetary material thus occurs within a limited region of space once moderate magnetospheric convection is established. These results suggest that, via release of material otherwise gravitationally trapped, the E B related centrifugal acceleration is an important mechanism for the net supply of plasma to the magnetosphere of Mercury
Lepton-nucleus scattering in the impulse approximation regime
We discuss theoretical calculations of electron- and neutrino-nucleus
scattering, carried out using realistic nuclear spectral functions and
including the effect of final state interactions. Comparison between electron
scattering data and the calculated inclusive cross sections off oxygen shows
that the Fermi gas model fails to provide a satisfactory description of the
measured cross sections, and inclusion of nuclear dynamics is needed. The role
of Pauli blocking in charged-current neutrino induced reactions at low is
also analyzed.Comment: To be published in the Proceedings of NUFACT05 (Nucl. Phys. B,
Proceedings Supplements
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