217 research outputs found
On observability of Renyi's entropy
Despite recent claims we argue that Renyi's entropy is an observable
quantity. It is shown that, contrary to popular belief, the reported domain of
instability for Renyi entropies has zero measure (Bhattacharyya measure). In
addition, we show the instabilities can be easily emended by introducing a
coarse graining into an actual measurement. We also clear up doubts regarding
the observability of Renyi's entropy in (multi--)fractal systems and in systems
with absolutely continuous PDF's.Comment: 18 pages, 1 EPS figure, REVTeX, minor changes, accepted to Phys. Rev.
Suboptimal quantum-error-correcting procedure based on semidefinite programming
In this paper, we consider a simplified error-correcting problem: for a fixed
encoding process, to find a cascade connected quantum channel such that the
worst fidelity between the input and the output becomes maximum. With the use
of the one-to-one parametrization of quantum channels, a procedure finding a
suboptimal error-correcting channel based on a semidefinite programming is
proposed. The effectiveness of our method is verified by an example of the
bit-flip channel decoding.Comment: 6 pages, no figure, Some notations differ from those in the PRA
versio
Scaling, self-similar solutions and shock waves for V-shaped field potentials
We investigate a (1+1)-dimensional nonlinear field theoretic model with the
field potential It can be obtained as the universal small
amplitude limit in a class of models with potentials which are symmetrically
V-shaped at their minima, or as a continuum limit of certain mechanical system
with infinite number of degrees of freedom. The model has an interesting
scaling symmetry of the 'on shell' type. We find self-similar as well as shock
wave solutions of the field equation in that model.Comment: Two comments and one reference adde
Finite-temperature form factors in the free Majorana theory
We study the large distance expansion of correlation functions in the free
massive Majorana theory at finite temperature, alias the Ising field theory at
zero magnetic field on a cylinder. We develop a method that mimics the spectral
decomposition, or form factor expansion, of zero-temperature correlation
functions, introducing the concept of "finite-temperature form factors". Our
techniques are different from those of previous attempts in this subject. We
show that an appropriate analytical continuation of finite-temperature form
factors gives form factors in the quantization scheme on the circle. We show
that finite-temperature form factor expansions are able to reproduce expansions
in form factors on the circle. We calculate finite-temperature form factors of
non-interacting fields (fields that are local with respect to the fundamental
fermion field). We observe that they are given by a mixing of their
zero-temperature form factors and of those of other fields of lower scaling
dimension. We then calculate finite-temperature form factors of order and
disorder fields. For this purpose, we derive the Riemann-Hilbert problem that
completely specifies the set of finite-temperature form factors of general
twist fields (order and disorder fields and their descendants). This
Riemann-Hilbert problem is different from the zero-temperature one, and so are
its solutions. Our results agree with the known form factors on the circle of
order and disorder fields.Comment: 40 pp.; v2: 42 pp., refs and acknowledgment added, typos corrected,
description of general matrix elements corrected and extended; v3: 47 pp.,
appendix adde
Measuring non-extensitivity parameters in a turbulent Couette-Taylor flow
We investigate probability density functions of velocity differences at
different distances r measured in a Couette-Taylor flow for a range of Reynolds
numbers Re. There is good agreement with the predictions of a theoretical model
based on non-extensive statistical mechanics (where the entropies are
non-additive for independent subsystems). We extract the scale-dependent
non-extensitivity parameter q(r, Re) from the laboratory data.Comment: 8 pages, 5 figure
Metastability, negative specific heat and weak mixing in classical long-range many-rotator system
We perform a molecular dynamical study of the isolated classical
Hamiltonian , known to
exhibit a second order phase transition, being disordered for and ordered otherwise ( total energy
and ). We focus
on the nonextensive case and observe that, for , a
basin of attraction exists for the initial conditions for which the system
quickly relaxes onto a longstanding metastable state (whose duration presumably
diverges with like ) which eventually crosses over to the
microcanonical Boltzmann-Gibbs stable state. The temperature associated with
the (scaled) average kinetic energy per particle is lower in the metastable
state than in the stable one. It is exhibited for the first time that the
appropriately scaled maximal Lyapunov exponent
, where, for all values of ,
numerically coincides with {\it one third} of its value for , hence
decreases from 1/9 to zero when increases from zero to unity,
remaining zero thereafter. This new and simple {\it connection between
anomalies above and below the critical point} reinforces the nonextensive
universality scenario.Comment: 9 pages and 4 PS figure
Acceleration and vortex filaments in turbulence
We report recent results from a high resolution numerical study of fluid
particles transported by a fully developed turbulent flow. Single particle
trajectories were followed for a time range spanning more than three decades,
from less than a tenth of the Kolmogorov time-scale up to one large-eddy
turnover time. We present some results concerning acceleration statistics and
the statistics of trapping by vortex filaments.Comment: 10 pages, 5 figure
Joint spatiotemporal models to predict seabird densities at sea
Introduction: Seabirds are abundant, conspicuous members of marine ecosystems worldwide. Synthesis of distribution data compiled over time is required to address regional management issues and understand ecosystem change. Major challenges when estimating seabird densities at sea arise from variability in dispersion of the birds, sampling effort over time and space, and differences in bird detection rates associated with survey vessel type.
Methods: Using a novel approach for modeling seabirds at sea, we applied joint dynamic species distribution models (JDSDM) with a vector-autoregressive spatiotemporal framework to survey data collected over nearly five decades and archived in the North Pacific Pelagic Seabird Database. We produced monthly gridded density predictions and abundance estimates for 8 species groups (77% of all birds observed) within Cook Inlet, Alaska. JDSDMs included habitat covariates to inform density predictions in unsampled areas and accounted for changes in observed densities due to differing survey methods and decadal-scale variation in ocean conditions.
Results: The best fit model provided a high level of explanatory power (86% of deviance explained). Abundance estimates were reasonably precise, and consistent with limited historical studies. Modeled densities identified seasonal variability in abundance with peak numbers of all species groups in July or August. Seabirds were largely absent from the study region in either fall (e.g., murrelets) or spring (e.g., puffins) months, or both periods (shearwaters).
Discussion: Our results indicated that pelagic shearwaters (Ardenna spp.) and tufted puffin (Fratercula cirrhata) have declined over the past four decades and these taxa warrant further investigation into underlying mechanisms explaining these trends. JDSDMs provide a useful tool to estimate seabird distribution and seasonal trends that will facilitate risk assessments and planning in areas affected by human activities such as oil and gas development, shipping, and offshore wind and renewable energy
Magnetic behavior of a non-extensive S-spin system: possible connections to manganites
We analyzed the magnetic behavior of a S-spin system within framework of the
Tsallis nonextensive statistics, employing the normalized approach. Unusual
properties on magnetization, entropy and susceptibility emerge, as a
consequence of nonextensivity. We further show that the nonextensive approach
can be relevant to the field of manganites, materials which exhibit long-range
interactions and fractality, two basic ingredients for nonextensivity. Our
results are in qualitative agreement to experimental data in
LaCaMnO and
PrCaMnGaO manganites.Comment: 5 pages and 6 figures. Submitted to Phys. Rev.
From Davydov solitons to decoherence-free subspaces: self-consistent propagation of coherent-product states
The self-consistent propagation of generalized [coherent-product]
states and of a class of gaussian density matrix generalizations is examined,
at both zero and finite-temperature, for arbitrary interactions between the
localized lattice (electronic or vibronic) excitations and the phonon modes. It
is shown that in all legitimate cases, the evolution of states reduces
to the disentangled evolution of the component states. The
self-consistency conditions for the latter amount to conditions for
decoherence-free propagation, which complement the Davydov soliton
equations in such a way as to lift the nonlinearity of the evolution for the
on-site degrees of freedom. Although it cannot support Davydov solitons, the
coherent-product ansatz does provide a wide class of exact density-matrix
solutions for the joint evolution of the lattice and phonon bath in compatible
systems. Included are solutions for initial states given as a product of a
[largely arbitrary] lattice state and a thermal equilibrium state of the
phonons. It is also shown that external pumping can produce self-consistent
Frohlich-like effects. A few sample cases of coherent, albeit not solitonic,
propagation are briefly discussed.Comment: revtex3, latex2e; 22 pages, no figs.; to appear in Phys.Rev.E
(Nov.2001
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