1,889 research outputs found
Analysis of ischaemic crisis using the informational causal entropy-complexity plane
In the present work, an ischaemic process, mainly focused on the reperfusion stage, is studied using the informational causal entropy-complexity plane. Ischaemic wall behavior under this condition was analyzed through wall thickness and ventricular pressure variations, acquired during an obstructive flow maneuver performed on left coronary arteries of surgically instrumented animals. Basically, the induction of ischaemia depends on the temporary occlusion of left circumflex coronary artery (which supplies blood to the posterior left ventricular wall) that lasts for a few seconds. Normal perfusion of the wall was then reestablished while the anterior ventricular wall remained adequately perfused during the entire maneuver. The obtained results showed that system dynamics could be effectively described by entropy-complexity loops, in both abnormally and well perfused walls. These results could contribute to making an objective indicator of the recovery heart tissues after an ischaemic process, in a way to quantify the restoration of myocardial behavior after the supply of oxygen to the ventricular wall was suppressed for a brief period.Fil: Legnani, Walter. Universidad Tecnológica Nacional. Facultad Regional Buenos Aires; Argentina. Universidad Nacional de Lanús; ArgentinaFil: Traversaro Varela, Francisco. Instituto Tecnológico de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Redelico, Francisco Oscar. Hospital Italiano; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes; ArgentinaFil: Cymberknop, Leandro Javier. Instituto Tecnologico de Buenos Aires. Departamento de Bioingenieria; Argentina. Universidad Tecnológica Nacional. Facultad Regional Buenos Aires; ArgentinaFil: Armentano, Ricardo Luis. Universidad Tecnológica Nacional. Facultad Regional Buenos Aires; Argentina. Instituto Tecnologico de Buenos Aires. Departamento de Bioingenieria; ArgentinaFil: Rosso, Osvaldo Aníbal. Universidad de los Andes; Chile. Universidade Federal de Alagoas; Brasil. Hospital Italiano; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin
Universal interface width distributions at the depinning threshold
We compute the probability distribution of the interface width at the
depinning threshold, using recent powerful algorithms. It confirms the
universality classes found previously. In all cases, the distribution is
surprisingly well approximated by a generalized Gaussian theory of independant
modes which decay with a characteristic propagator G(q)=1/q^(d+2 zeta); zeta,
the roughness exponent, is computed independently. A functional renormalization
analysis explains this result and allows to compute the small deviations, i.e.
a universal kurtosis ratio, in agreement with numerics. We stress the
importance of the Gaussian theory to interpret numerical data and experiments.Comment: 4 pages revtex4. See also the following article cond-mat/030146
Higher correlations, universal distributions and finite size scaling in the field theory of depinning
Recently we constructed a renormalizable field theory up to two loops for the
quasi-static depinning of elastic manifolds in a disordered environment. Here
we explore further properties of the theory. We show how higher correlation
functions of the displacement field can be computed. Drastic simplifications
occur, unveiling much simpler diagrammatic rules than anticipated. This is
applied to the universal scaled width-distribution. The expansion in
d=4-epsilon predicts that the scaled distribution coincides to the lowest
orders with the one for a Gaussian theory with propagator G(q)=1/q^(d+2 \zeta),
zeta being the roughness exponent. The deviations from this Gaussian result are
small and involve higher correlation functions, which are computed here for
different boundary conditions. Other universal quantities are defined and
evaluated: We perform a general analysis of the stability of the fixed point.
We find that the correction-to-scaling exponent is omega=-epsilon and not
-epsilon/3 as used in the analysis of some simulations. A more detailed study
of the upper critical dimension is given, where the roughness of interfaces
grows as a power of a logarithm instead of a pure power.Comment: 15 pages revtex4. See also preceding article cond-mat/030146
On quantization of r-matrices for Belavin-Drinfeld Triples
We suggest a formula for quantum universal -matrices corresponding to
quasitriangular classical -matrices classified by Belavin and Drinfeld for
all simple Lie algebras. The -matrices are obtained by twisting the standard
universal -matrix.Comment: 12 pages, LaTe
Depinning of elastic manifolds
We compute roughness exponents of elastic d-dimensional manifolds in
(d+1)-dimensional embedding spaces at the depinning transition for d=1,...,4.
Our numerical method is rigorously based on a Hamiltonian formulation; it
allows to determine the critical manifold in finite samples for an arbitrary
convex elastic energy. For a harmonic elastic energy, we find values of the
roughness exponent between the one-loop and the two-loop functional
renormalization group result, in good agreement with earlier cellular automata
simulations. We find that the harmonic model is unstable with respect both to
slight stiffening and to weakening of the elastic potential. Anharmonic
corrections to the elastic energy allow us to obtain the critical exponents of
the quenched KPZ class.Comment: 4 pages, 4 figure
Width distribution of contact lines on a disordered substrate
We have studied the roughness of a contact line of a liquid meniscus on a
disordered substrate by measuring its width distribution. The comparison
between the measured width distribution and the width distribution calculated
in previous works, extended here to the case of open boundary conditions,
confirms that the Joanny-de Gennes model is not sufficient to describe the
dynamics of contact lines at the depinning threshold. This conclusion is in
agreement with recent measurements which determine the roughness exponent by
extrapolation to large system sizes.Comment: 4 pages, 3 figure
Roughness at the depinning threshold for a long-range elastic string
In this paper, we compute the roughness exponent zeta of a long-range elastic
string, at the depinning threshold, in a random medium with high precision,
using a numerical method which exploits the analytic structure of the problem
(`no-passing' theorem), but avoids direct simulation of the evolution
equations. This roughness exponent has recently been studied by simulations,
functional renormalization group calculations, and by experiments (fracture of
solids, liquid meniscus in 4He). Our result zeta = 0.390 +/- 0.002 is
significantly larger than what was stated in previous simulations, which were
consistent with a one-loop renormalization group calculation. The data are
furthermore incompatible with the experimental results for crack propagation in
solids and for a 4He contact line on a rough substrate. This implies that the
experiments cannot be described by pure harmonic long-range elasticity in the
quasi-static limit.Comment: 4 pages, 3 figure
Three-frequency resonances in dynamical systems
We investigate numerically and experimentally dynamical systems having three
interacting frequencies: a discrete mapping (a circle map), an exactly solvable
model (a system of coupled ordinary differential equations), and an
experimental device (an electronic oscillator). We compare the hierarchies of
three-frequency resonances we find in each of these systems. All three show
similar qualitative behaviour, suggesting the existence of generic features in
the parameter-space organization of three-frequency resonances.Comment: See home page http://lec.ugr.es/~julya
Bandt-Pompe symbolization dynamics for time series with tied values: A data-driven approach
In 2002, Bandt and Pompe [Phys. Rev. Lett. 88, 174102 (2002)] introduced a successfully symbolic encoding scheme based on the ordinal relation between the amplitude of neighboring values of a given data sequence, from which the permutation entropy can be evaluated. Equalities in the analyzed sequence, for example, repeated equal values, deserve special attention and treatment as was shown recently by Zunino and co-workers [Phys. Lett. A 381, 1883 (2017)]. A significant number of equal values can give rise to false conclusions regarding the underlying temporal structures in practical contexts. In the present contribution, we review the different existing methodologies for treating time series with tied values by classifying them according to their different strategies. In addition, a novel data-driven imputation is presented that proves to outperform the existing methodologies and avoid the false conclusions pointed by Zunino and co-workers.Fil: Traversaro Varela, Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Lanús; ArgentinaFil: Redelico, Francisco Oscar. Hospital Italiano; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes; ArgentinaFil: Risk, Marcelo. Hospital Italiano; Argentina. Instituto Tecnológico de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Frery, Alejandro César. Universidade Federal de Alagoas; BrasilFil: Rosso, Osvaldo Aníbal. Hospital Italiano; Argentina. Universidade Federal de Alagoas; Brasil. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Los Andes; Chil
Functional renormalization group for anisotropic depinning and relation to branching processes
Using the functional renormalization group, we study the depinning of elastic
objects in presence of anisotropy. We explicitly demonstrate how the KPZ-term
is always generated, even in the limit of vanishing velocity, except where
excluded by symmetry. We compute the beta-function to one loop taking properly
into account the non-analyticity. This gives rise to additional terms, missed
in earlier studies. A crucial question is whether the non-renormalization of
the KPZ-coupling found at 1-loop order extends beyond the leading one. Using a
Cole-Hopf-transformed theory we argue that it is indeed uncorrected to all
orders. The resulting flow-equations describe a variety of physical situations.
A careful analysis of the flow yields several non-trivial fixed points. All
these fixed points are transient since they possess one unstable direction
towards a runaway flow, which leaves open the question of the upper critical
dimension. The runaway flow is dominated by a Landau-ghost-mode. For SR
elasticity, using the Cole-Hopf transformed theory we identify a non-trivial
3-dimensional subspace which is invariant to all orders and contains all above
fixed points as well as the Landau-mode. It belongs to a class of theories
which describe branching and reaction-diffusion processes, of which some have
been mapped onto directed percolation.Comment: 20 pages, 30 figures, revtex
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