36,843 research outputs found
Acoustic black holes from supercurrent tunneling
We present a version of acoustic black holes by using the principle of the
Josephson effect. We find that in the case two superconductors and are
separated by an insulating barrier, an acoustic black hole may be created in
the middle region between the two superconductors. We discuss in detail how to
describe an acoustic black hole in the Josephson junction and write the metric
in the langauge of the superconducting electronics. Our final results infer
that for big enough tunneling current and thickness of the junction,
experimental verification of the Hawking temperature could be possible.Comment: 15pages,1 figure, to appear in IJMP
Hierarchic Superposition Revisited
Many applications of automated deduction require reasoning in first-order
logic modulo background theories, in particular some form of integer
arithmetic. A major unsolved research challenge is to design theorem provers
that are "reasonably complete" even in the presence of free function symbols
ranging into a background theory sort. The hierarchic superposition calculus of
Bachmair, Ganzinger, and Waldmann already supports such symbols, but, as we
demonstrate, not optimally. This paper aims to rectify the situation by
introducing a novel form of clause abstraction, a core component in the
hierarchic superposition calculus for transforming clauses into a form needed
for internal operation. We argue for the benefits of the resulting calculus and
provide two new completeness results: one for the fragment where all
background-sorted terms are ground and another one for a special case of linear
(integer or rational) arithmetic as a background theory
Chemistry and kinematics of the pre-stellar core L1544: Constraints from H2D+
This paper explores the sensitivity of line profiles of H2D+, HCO+ and N2H+,
observed towards the center of L1544, to various kinematic and chemical
parameters. The total width of the H2D+ line can be matched by a static model
and by models invoking ambipolar diffusion and gravitational collapse. The
derived turbulent line width is b=0.15 km/s for the static case and <~ 0.05
km/s for the collapse case. However, line profiles of HC18O+ and N2H+ rule out
the static solution. The double-peaked H2D+ line shape requires either infall
speeds in the center that are much higher than predicted by ambipolar diffusion
models, or a shell-type distribution of H2D+, as is the case for HCO+ and N2H+.
At an offset of ~20 arcsec from the dust peak, the H2D+ abundance drops by a
factor of ~5.Comment: four pages, two colour figures; to appear in The Dense Interstellar
Medium in Galaxies, proceedings of the fourth Cologne-Bonn-Zermatt Symposium,
Sept 22-26, 200
Derived Demand for Fresh Cheese Products Imported into Japan
The objective of this article is to estimate the derived demand for imported fresh cheese products into Japan when fresh cheese import data are disaggregated by source country of production. We provide empirical measures of the sensitivity of demand to changes in total imports, own-price, and cross-prices among exporting countries for fresh cheese. Japan's derived demand for U.S. fresh cheese products is perfectly inelastic. Thus, the import demand competition among importing countries should be based upon differences in product characteristics.Demand and Price Analysis, International Relations/Trade,
Spin photocurrent, its spectra dependence, and current-induced spin polarization in an InGaAs/InAlAs two-dimensional electron gas
Converse effect of spin photocurrent and current induced spin polarization
are experimentally demonstrated in the same two-dimensional electron gas system
with Rashba spin splitting. Their consistency with the strength of the Rashba
coupling as measured from beating of the Shubnikov-de Haas oscillations reveals
a unified picture for the spin photocurrent, current-induced spin polarization
and spin orbit coupling. In addition, the observed spectral inversion of the
spin photocurrent indicates the system with dominating structure inversion
asymmetry.Comment: 13 pages, 4 figure
Cosmic Parallax in Ellipsoidal Universe
The detection of a time variation of the angle between two distant sources
would reveal an anisotropic expansion of the Universe. We study this effect of
"cosmic parallax" within the "ellipsoidal universe" model, namely a particular
homogeneous anisotropic cosmological model of Bianchi type I, whose attractive
feature is the potentiality to account for the observed lack of power of the
large-scale cosmic microwave background anisotropy. The preferred direction in
the sky, singled out by the axis of symmetry inherent to planar symmetry of
ellipsoidal universe, could in principle be constrained by future cosmic
parallax data. However, that will be a real possibility if and when the
experimental accuracy will be enhanced at least by two orders of magnitude.Comment: 9 pages, 2 figures, 1 table. Revised version to match published
version. References adde
Relating Quantum Information to Charged Black Holes
Quantum non-cloning theorem and a thought experiment are discussed for
charged black holes whose global structure exhibits an event and a Cauchy
horizon. We take Reissner-Norstr\"{o}m black holes and two-dimensional dilaton
black holes as concrete examples. The results show that the quantum non-cloning
theorem and the black hole complementarity are far from consistent inside the
inner horizon. The relevance of this work to non-local measurements is briefly
discussed.Comment: 14 pages, 2 figure
Coloured extension of GL_q(2) and its dual algebra
We address the problem of duality between the coloured extension of the
quantised algebra of functions on a group and that of its quantised universal
enveloping algebra i.e. its dual. In particular, we derive explicitly the
algebra dual to the coloured extension of GL_q(2) using the coloured RLL
relations and exhibit its Hopf structure. This leads to a coloured
generalisation of the R-matrix procedure to construct a bicovariant
differential calculus on the coloured version of GL_q(2). In addition, we also
propose a coloured generalisation of the geometric approach to quantum group
duality given by Sudbery and Dobrev.Comment: 10 pages LaTeX. Talk given at the "XXIII International Colloquium on
Group Theoretical Methods in Physics", July 31 - August 05, 2000, Dubna
(Russia); to appear in the proceeding
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