7,836 research outputs found
Reducing the Bias of Causality Measures
Measures of the direction and strength of the interdependence between two
time series are evaluated and modified in order to reduce the bias in the
estimation of the measures, so that they give zero values when there is no
causal effect. For this, point shuffling is employed as used in the frame of
surrogate data. This correction is not specific to a particular measure and it
is implemented here on measures based on state space reconstruction and
information measures. The performance of the causality measures and their
modifications is evaluated on simulated uncoupled and coupled dynamical systems
and for different settings of embedding dimension, time series length and noise
level. The corrected measures, and particularly the suggested corrected
transfer entropy, turn out to stabilize at the zero level in the absence of
causal effect and detect correctly the direction of information flow when it is
present. The measures are also evaluated on electroencephalograms (EEG) for the
detection of the information flow in the brain of an epileptic patient. The
performance of the measures on EEG is interpreted, in view of the results from
the simulation study.Comment: 30 pages, 12 figures, accepted to Physical Review
Testing for Multipartite Quantum Nonlocality Using Functional Bell Inequalities
We show that arbitrary functions of continuous variables, e.g. position and
momentum, can be used to generate tests that distinguish quantum theory from
local hidden variable theories. By optimising these functions, we obtain more
robust violations of local causality than obtained previously. We analytically
calculate the optimal function and include the effect of nonideal detectors and
noise, revealing that optimized functional inequalities are resistant to
standard forms of decoherence. These inequalities could allow a loophole-free
Bell test with efficient homodyne detection
Necessary and sufficient detection efficiency for the Mermin inequalities
We prove that the threshold detection efficiency for a loophole-free Bell
experiment using an -qubit Greenberger-Horne-Zeilinger state and the
correlations appearing in the -partite Mermin inequality is . If
the detection efficiency is equal to or lower than this value, there are local
hidden variable models that can simulate all the quantum predictions. If the
detection efficiency is above this value, there is no local hidden variable
model that can simulate all the quantum predictions.Comment: REVTeX4, 5 pages, 1 figur
Natural Lifetimes of Excited-states of Neutral Nitrogen Determined By Time-resolved Laser Spectroscopy
Radiative lifetimes were determined for three quartet states of neutral nitrogen, and sequences of Rydberg states were studied using depletion spectroscopy. Free nitrogen atoms were generated by photodissociation of N2O using frequency-tripled dye-laser radiation that was two-photon resonant with the 2p(2)3p 4S or 4D states. Further quartet states were reached by a subsequent single-photon absorption. We obtain tau(2p(2)3p 4D7/2) = 44(2) ns, tau(2p(2)3p 4S3/2) = 26.0(1.5) ns, and tau(2p(2)6s4P5/2) = 41(7) ns
Disoriented Chiral Condensates in Hadron-Hadron Collisions
We review recent progress in the description and understanding of disoriented
chiral condensates. Certain important unsolved issues are underlined, and the
preliminary results of our program of investigation of these issues in the
framework of the classical linear sigma model are reported. We also briefly
review a formalism which could be useful at the full non-equilibrium quantum
field theory level of analysis.Comment: 9 pages, LaTex. Presented by G. Amelino-Camelia at the 10th
International Conference on Problems of Quantum Field Theory, Alushta,
Crimea, Ukraine, May 13-18, 1996. To appear in the proceeding
Relativity and the lead-acid battery
The energies of the solid reactants in the lead-acid battery are calculated
ab initio using two different basis sets at non-relativistic, scalar
relativistic, and fully relativistic levels, and using several
exchange-correlation potentials. The average calculated standard voltage is
2.13 V, compared with the experimental value of 2.11 V. All calculations agree
in that 1.7-1.8 V of this standard voltage arise from relativistic effects,
mainly from PbO2 but also from PbSO4
Violation of local realism vs detection efficiency
We put bounds on the minimum detection efficiency necessary to violate local
realism in Bell experiments. These bounds depends of simple parameters like the
number of measurement settings or the dimensionality of the entangled quantum
state. We derive them by constructing explicit local-hidden variable models
which reproduce the quantum correlations for sufficiently small detectors
efficiency.Comment: 6 pages, revtex. Modifications in the discussion for many parties in
section 3, small erros and typos corrected, conclusions unchange
Hom-quantum groups I: quasi-triangular Hom-bialgebras
We introduce a Hom-type generalization of quantum groups, called
quasi-triangular Hom-bialgebras. They are non-associative and non-coassociative
analogues of Drinfel'd's quasi-triangular bialgebras, in which the
non-(co)associativity is controlled by a twisting map. A family of
quasi-triangular Hom-bialgebras can be constructed from any quasi-triangular
bialgebra, such as Drinfel'd's quantum enveloping algebras. Each
quasi-triangular Hom-bialgebra comes with a solution of the quantum
Hom-Yang-Baxter equation, which is a non-associative version of the quantum
Yang-Baxter equation. Solutions of the Hom-Yang-Baxter equation can be obtained
from modules of suitable quasi-triangular Hom-bialgebras.Comment: 21 page
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