14,007 research outputs found
Electrical switching in cadmium boracite single crystals
Cadmium boracite single crystals at high temperatures ( 300 C) were found to exhibit a reversible electric field-induced transition between a highly insulative and a conductive state. The switching threshold is smaller than a few volts for an electrode spacing of a few tenth of a millimeter corresponding to an electric field of 100 to 1000 V/cm. This is much smaller than the dielectric break-down field for an insulator such as boracite. The insulative state reappears after voltage removal. A pulse technique revealed two different types of switching. Unstable switching occurs when the pulse voltage slightly exceeds the switching threshold and is characterized by a pre-switching delay and also a residual current after voltage pulse removal. A stable type of switching occurs when the voltage becomes sufficiently high. Possible device applications of this switching phenomenon are discussed
Distinguished self-adjoint extensions of Dirac operators via Hardy-Dirac inequalities
We prove some Hardy-Dirac inequalities with two different weights including
measure valued and Coulombic ones. Those inequalities are used to construct
distinguished self-adjoint extensions of Dirac operators for a class of
diagonal potentials related to the weights in the above mentioned inequalities.Comment: 16 page
Spin-Peierls instability in a quantum spin chain with Dzyaloshinskii-Moriya interaction
We analysed the ground state energy of some dimerized spin-1/2 transverse XX
and Heisenberg chains with Dzyaloshinskii-Moriya (DM) interaction to study the
influence of the latter interaction on the spin-Peierls instability. We found
that DM interaction may act either in favour of the dimerization or against it.
The actual result depends on the dependence of DM interaction on the distortion
amplitude in comparison with such dependence for the isotropic exchange
interaction.Comment: 12 pages, latex, 3 figure
Giant mass and anomalous mobility of particles in fermionic systems
We calculate the mobility of a heavy particle coupled to a Fermi sea within a
non-perturbative approach valid at all temperatures. The interplay of particle
recoil and of strong coupling effects, leading to the orthogonality catastrophe
for an infinitely heavy particle, is carefully taken into account. We find two
novel types of strong coupling effects: a new low energy scale and
a giant mass renormalization in the case of either near-resonant scattering or
a large transport cross section . The mobility is shown to obey two
different power laws below and above . For ,
where is the Fermi wave length, an exponentially large effective
mass suppresses the mobility.Comment: 4 pages, 4 figure
Spectroscopic confirmation of a cluster of galaxies at z=1 in the field of the gravitational lens MG2016+112
We present new optical data on the cluster AX J2019+1127 identified by the
X-ray satellite ASCA at z\sim 1 (Hattori et al. 1997). The data suggest the
presence of a high-redshift cluster of galaxies responsible for the large
separation triple quasar MG2016+112. Our deep photometry reveals an excess of
z\sim 1 galaxy candidates, as already suspected by Benitez et al. (1999). Our
spectroscopic survey of 44 objects in the field shows an excess of 6 red
galaxies securely identified at z \sim 1, with a mean redshift of z =1.005 +/-
0.002. We estimate a velocity dispersion of \sigma = 771 (+430/-160) km s(-1)
based on these 6 galaxies and a V-band mass-to-light ratio of 215 (+308/-77)
h_50 M/L_sol. Our observations thus confirm the existence of a massive
structure acting as the lens, which explains the unusual configuration of the
triple quasar. Hence, there is no more need to invoke the existence of a ``dark
cluster'' to understand this lens system.Comment: 8 pages, 4 figures, uses aa.cls, accepted to Astronomy and
Astrophysics with minor change
Quantum fluctuation induced ordered phase in the Blume-Capel model
We consider the Blume-Capel model with the quantum tunneling between the
excited states. We find a magnetically ordered phase transition induced by
quantum fluctuation in a model. The model has no phase transition in the
corresponding classical case. Usually, quantum fluctuation breaks ordered phase
as in the case of the transverse field Ising model. However, in present case,
an ordered phase is induced by quantum fluctuation. Moreover, we find a phase
transition between a quantum paramagnetic phase and a classical diamagnetic
phase at zero temperature. We study the properties of the phase transition by
using a mean field approximation (MFA), and then, by a quantum Monte Carlo
method to confirm the result of the MFA.Comment: 7 pages, 6 figures, corrected some typo
Iterative Perturbation Theory for Strongly Correlated Electron Systems with Orbital Degeneracy
A new scheme of the iterative perturbation theory is proposed for the
strongly correlated electron systems with orbital degeneracy. The method is
based on the modified self-energy of Yeyati, et al. which interpolates between
the weak and the strong correlation limits, but a much simpler scheme is
proposed which is useful in the case of the strong correlation with orbital
degeneracy. It will be also useful in the study of the electronic structures
combined with the band calculations.Comment: 6 pages, 3 Postscript figures, to appear in J. Phys. Cond. Matte
Spin matrix elements in 2D Ising model on the finite lattice
We present explicit formulas for all spin matrix elements in the 2D Ising
model with the nearest neighbor interaction on the finite periodic square
lattice. These expressions generalize the known results [Phys. Rev. D19,
(1979), 2477--2479; hep-th/0107117; hep-th/0112167] (coincide with them in the
appropriate limits) and fulfill the test of straightforward transfer matrix
calculations for finite .Comment: old paper (2003) posted for archival purpose
The SBF Survey of Galaxy Distances. II. Local and Large-Scale Flows
We present analysis of local large scale flows using the Surface Brightness
Fluctuation (SBF) Survey for the distances to 300 early-type galaxies. Our
models of the distribution function of mean velocity and velocity dispersion at
each point in space include a uniform thermal velocity dispersion and spherical
attractors whose position, amplitude, and radial shape are free to vary. Our
fitting procedure performs a maximum likelihood fit of the model to the
observations. We obtain a Hubble constant of Ho = 77 +/- 4 +/- 7 km/s/Mpc, but
a uniform Hubble flow is not acceptable fit to the data. Inclusion of two
attractors, one of whose fit location coincides with the Virgo cluster and the
other whose fit location is slightly beyond the Centaurus clusters nearly
explain the peculiar velocities, but the quality of the fit can be further
improved by the addition of a quadrupole correction to the Hubble flow.
Although the dipole and quadrupole may be genuine manifestations of more
distant density fluctuations, we find evidence that they are more likely due to
non-spherical attractors. We find no evidence for bulk flows which include our
entire survey volume (R < 3000 km/s); our volume is at rest with respect to the
CMB. The fits to the attractors both have isothermal radial profiles (v ~ 1/r)
over a range of overdensity between about 10 and 1, but fall off more steeply
at larger radius. The best fit value for the small scale, cosmic thermal
velocity is 180 +/- 14 km/s.Comment: 37 pages, AASTeX Latex, including 30 Postscript figures, submitted to
Astrophysical Journal, July 2, 199
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