41,137 research outputs found
Video switcher for coupling video cameras to single TV monitor
Device couples up to 60 TV cameras to single monitor. Video switching is provided by diode matrix arranged in a 60-by-1 configuration. Switcher can be operated manually or automatically
Enhanced low-temperature entropy and flat-band ferromagnetism in the t-J model on the sawtooth lattice
Using the example of the sawtooth chain, we argue that the t-J model shares
important features with the Hubbard model on highly frustrated lattices. The
lowest single-fermion band is completely flat (for a specific choice of the
hopping parameters in the case of the sawtooth chain), giving rise to
single-particle excitations which can be localized in real space. These
localized excitations do not interact for sufficient spatial separations such
that exact many-electron states can also be constructed. Furthermore, all these
excitations acquire zero energy for a suitable choice of the chemical potential
. This leads to: (i) a jump in the particle density at zero temperature,
(ii) a finite zero-temperature entropy, (iii) a ferromagnetic ground state with
a charge gap when the flat band is fully occupied and (iv) unusually large
temperature variations when is varied adiabatically at finite
temperature.Comment: 2 pages including 2 figures, uses elsart style files; (proceedings of
ICM 2006
Comment on "Density of States and Critical Behavior of the Coulomb Glass"
In a recent numerical investigation of the Coulomb glass, Surer et al. [Phys.
Rev. Lett. 102, 067205 (2009)] concluded that their simulation results are
consistent with the Efros Shklovskii prediction for the density of states in
the three-dimensional case. Here, we show that this statement has no relevance
concerning the problem of the asymptotic behavior in the Coulomb gap since it
is based on unjustified assumptions. Moreover, for the random-displacement
Coulomb glass model, we demonstrate that a part of the density of states data
by Surer et al. erroneously exhibit a broad gap. This is related to the
staggered occupation being instable contrary to their findings.Comment: Submitted to Physical Review Letters, 1 page, 1 figur
Optical counterparts of ROSAT X-ray sources in two selected fields at low vs. high Galactic latitudes
The optical identification of large number of X-ray sources such as those
from the ROSAT All-Sky Survey is challenging with conventional spectroscopic
follow-up observations. We investigate two ROSAT All-Sky Survey fields of size
10 * 10 degrees each, one at galactic latitude b = 83 deg (Com), the other at b
= -5 deg (Sge), in order to optically identify the majority of sources. We used
optical variability, among other more standard methods, as a means of
identifying a large number of ROSAT All-Sky Survey sources. All objects fainter
than about 12 mag and brighter than about 17 mag, in or near the error circle
of the ROSAT positions, were tested for optical variability on hundreds of
archival plates of the Sonneberg field patrol.
The present paper contains probable optical identifications of altogether 256
of the 370 ROSAT sources analysed. In particular, we found 126 AGN (some of
them may be misclassified CVs), 17 likely clusters of galaxies, 16 eruptive
double stars (mostly CVs), 43 chromospherically active stars, 65 stars brighter
than about 13 mag, 7 UV Cet stars, 3 semiregular resp. slow irregular variable
stars of late spectral type, 2 DA white dwarfs, 1 Am star, 1 supernova remnant
and 1 planetary nebula.
X-ray emission is, expectedly, tightly correlated with optical variability,
and thus our new method for optically identifying X-ray sources is demonstrated
to be feasible.Comment: 92 pages, 521 figures, A&A (accepted
Analytic approach to nuclear rotational states: The role of spin - A minimal model -
We use a simple field theory model to investigate the role of the nucleon
spin for the magnetic sum rules associated with the low-lying collective
scissors mode in deformed nuclei. Various constraints from rotational symmetry
are elucidated and discussed. We put special emphasis on the coupling of the
spin part of the M1 operator to the low lying collective modes, and investigate
how this coupling changes the sum rules.Comment: 15 pages, 4 figure
Comment on "138La-138Ce-136Ce nuclear cosmochronometer of the supernova neutrino process"
The nuclear chosmochronometer suggested by Hayakawa et al. [Phys. Rev.C 77,
065802 (2008)] based on the 138La-138Ce-136Ce abundance ratio in presolar
grains would be affected by the existence of a hitherto unknown low-energy 1+
state in 138La. Results of a recent high-resolution study of the 138Ba(3He,t)
reaction under kinematics selectively populating 1+ states in 138La through
Gamow-Teller transitions provides strong evidence against the existence of such
a hypothetical state.Comment: Comment on Phys. Rev. C 77, 065802 (2008), submittted to Phys. Rev.
Random Matrices and Chaos in Nuclear Physics: Nuclear Reactions
The application of random-matrix theory (RMT) to compound-nucleus (CN)
reactions is reviewed. An introduction into the basic concepts of nuclear
scattering theory is followed by a survey of phenomenological approaches to CN
scattering. The implementation of a random-matrix approach into scattering
theory leads to a statistical theory of CN reactions. Since RMT applies
generically to chaotic quantum systems, that theory is, at the same time, a
generic theory of quantum chaotic scattering. It uses a minimum of input
parameters (average S-matrix and mean level spacing of the CN). Predictions of
the theory are derived with the help of field-theoretical methods adapted from
condensed-matter physics and compared with those of phenomenological
approaches. Thorough tests of the theory are reviewed, as are applications in
nuclear physics, with special attention given to violation of symmetries
(isospin, parity) and time-reversal invariance.Comment: 50 pages, 26 figure
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