395 research outputs found
Computing solutions of the modified Bessel differential equation for imaginary orders and positive arguments
Reproducibility and validity of a diet quality index for children assessed using a FFQ
The diet quality index (DQI) for preschool children is a new index developed to reflect compliance with four main food-based dietary guidelines for preschool children in Flanders. The present study investigates: (1) the validity of this index by comparing DQI scores for preschool children with nutrient intakes, both of which were derived from 3d estimated diet records; (2) the reproducibility of the DQI for preschoolers based on a parentally reported forty-seven-item FFQ DQI, which was repeated after 5 weeks; (3) the relative validity of the FFQ DQI with 3d record DQI scores as reference. The study sample included 510 and 58 preschoolers (2-5-6.5 years) for validity and reproducibility analyses, respectively. Increasing 3d record DQI scores were associated with decreasing consumption of added sugars, and increasing intakes of fibre, water, Ca and many micronutrients. Mean FFQ DQI test-retest scores were not significantly different: 72 (so 11) v. 71 (Si) 10) (P-=0-218) out of a maximum of 100. Mean 3d record DQI score (66 (so 10)) was significantly lower than mean FFQ DQI (71 (so 10);
The - divergence and Mixing times of quantum Markov processes
We introduce quantum versions of the -divergence, provide a detailed
analysis of their properties, and apply them in the investigation of mixing
times of quantum Markov processes. An approach similar to the one presented in
[1-3] for classical Markov chains is taken to bound the trace-distance from the
steady state of a quantum processes. A strict spectral bound to the convergence
rate can be given for time-discrete as well as for time-continuous quantum
Markov processes. Furthermore the contractive behavior of the
-divergence under the action of a completely positive map is
investigated and contrasted to the contraction of the trace norm. In this
context we analyse different versions of quantum detailed balance and, finally,
give a geometric conductance bound to the convergence rate for unital quantum
Markov processes
Evanescence in Coined Quantum Walks
In this paper we complete the analysis begun by two of the authors in a
previous work on the discrete quantum walk on the line [J. Phys. A 36:8775-8795
(2003) quant-ph/0303105 ]. We obtain uniformly convergent asymptotics for the
"exponential decay'' regions at the leading edges of the main peaks in the
Schr{\"o}dinger (or wave-mechanics) picture. This calculation required us to
generalise the method of stationary phase and we describe this extension in
some detail, including self-contained proofs of all the technical lemmas
required. We also rigorously establish the exact Feynman equivalence between
the path-integral and wave-mechanics representations for this system using some
techniques from the theory of special functions. Taken together with the
previous work, we can now prove every theorem by both routes.Comment: 32 pages AMS LaTeX, 5 figures in .eps format. Rewritten in response
to referee comments, including some additional references. v3: typos fixed in
equations (131), (133) and (134). v5: published versio
Evaluation of Modern 3He(alpha,gamma)7Be Data
In both the Sun and the early universe, the 3He(alpha,gamma)7Be reaction
plays a key role. The rate of this reaction is the least certain nuclear input
needed to calculate both the primordial 7Li abundance in big bang
nucleosynthesis (BBN) and the solar neutrino flux. Taking advantage of several
recent highly precise experiments, we analyse modern 3He(alpha,gamma)7Be data
using a robust and minimally model dependent approach capable of handling
discrepant data sets dominated by systematic rather than statistical errors. We
find S34(0)=0.580 pm 0.043(0.054) keV b at the 68.3(95.4)% confidence level.Comment: 13 pages, 5 figure
Topological Phases in Graphitic Cones
The electronic structure of graphitic cones exhibits distinctive topological
features associated with the apical disclinations. Aharonov-Bohm
magnetoconductance oscillations (period Phi_0) are completely absent in rings
fabricated from cones with a single pentagonal disclination. Close to the apex,
the local density of states changes qualitatively, either developing a cusp
which drops to zero at the Fermi energy, or forming a region of nonzero density
across the Fermi energy, a local metalization of graphene.Comment: 4 pages, RevTeX 4, 3 PostScript figure
Digital Quantum Simulation of the Statistical Mechanics of a Frustrated Magnet
Many interesting problems in physics, chemistry, and computer science are
equivalent to problems of interacting spins. However, most of these problems
require computational resources that are out of reach by classical computers. A
promising solution to overcome this challenge is to exploit the laws of quantum
mechanics to perform simulation. Several "analog" quantum simulations of
interacting spin systems have been realized experimentally. However, relying on
adiabatic techniques, these simulations are limited to preparing ground states
only. Here we report the first experimental results on a "digital" quantum
simulation on thermal states; we simulated a three-spin frustrated magnet, a
building block of spin ice, with an NMR quantum information processor, and we
are able to explore the phase diagram of the system at any simulated
temperature and external field. These results serve as a guide for identifying
the challenges for performing quantum simulation on physical systems at finite
temperatures, and pave the way towards large scale experimental simulations of
open quantum systems in condensed matter physics and chemistry.Comment: 7 pages for the main text plus 6 pages for the supplementary
material
Perturbative Approach to the Quasinormal Modes of Dirty Black Holes
Using a recently developed perturbation theory for uasinormal modes (QNM's),
we evaluate the shifts in the real and imaginary parts of the QNM frequencies
due to a quasi-static perturbation of the black hole spacetime. We show the
perturbed QNM spectrum of a black hole can have interesting features using a
simple model based on the scalar wave equation.Comment: Published in PR
Quantum kinetic Ising models
We introduce a quantum generalization of classical kinetic Ising models,
described by a certain class of quantum many body master equations. Similarly
to kinetic Ising models with detailed balance that are equivalent to certain
Hamiltonian systems, our models reduce to a set of Hamiltonian systems
determining the dynamics of the elements of the many body density matrix. The
ground states of these Hamiltonians are well described by matrix product, or
pair entangled projected states. We discuss critical properties of such
Hamiltonians, as well as entanglement properties of their low energy states.Comment: 20 pages, 4 figures, minor improvements, accepted in New Journal of
Physic
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