311,371 research outputs found
Bifurcations in Globally Coupled Map Lattices
The dynamics of globally coupled map lattices can be described in terms of a
nonlinear Frobenius--Perron equation in the limit of large system size. This
approach allows for an analytical computation of stationary states and their
stability. The complete bifurcation behaviour of coupled tent maps near the
chaotic band merging point is presented. Furthermore the time independent
states of coupled logistic equations are analyzed. The bifurcation diagram of
the uncoupled map carries over to the map lattice. The analytical results are
supplemented with numerical simulations.Comment: 19 pages, .dvi and postscrip
Segmented Strings in
We study segmented strings in flat space and in . In flat space, these
well known classical motions describe strings which at any instant of time are
piecewise linear. In , the worldsheet is composed of faces each of which
is a region bounded by null geodesics in an subspace of . The
time evolution can be described by specifying the null geodesic motion of kinks
in the string at which two segments are joined. The outcome of collisions of
kinks on the worldsheet can be worked out essentially using considerations of
causality. We study several examples of closed segmented strings in and
find an unexpected quasi-periodic behavior. We also work out a WKB analysis of
quantum states of yo-yo strings in and find a logarithmic term
reminiscent of the logarithmic twist of string states on the leading Regge
trajectory.Comment: 38 pages, 5 figure
New modelling technique for aperiodic-sampling linear systems
A general input-output modelling technique for aperiodic-sampling linear
systems has been developed. The procedure describes the dynamics of the system
and includes the sequence of sampling periods among the variables to be
handled. Some restrictive conditions on the sampling sequence are imposed in
order to guarantee the validity of the model. The particularization to the
periodic case represents an alternative to the classic methods of
discretization of continuous systems without using the Z-transform. This kind
of representation can be used largely for identification and control purposes.Comment: 19 pages, 0 figure
Non-Linear Heart Rate Variability and Risk Stratification in Cardiovascular Disease
Traditional time and frequency domain heart rate variability (HRV) have cardiac patients at risk of mortality post-myocardial infarction. More recently, non linear HRV has been applied to risk stratification of cardiac patients. In this review we describe studies of non linear HRV and outcome in cardiac patients. We have included studies that used the three most common non-linear indices: power law slope, the short term fractal scaling exponent and measures based on Poincaré plots. We suggest that a combination of traditional and non-linear HRV may be optimal for risk stratification. Considerations in using non linear HRV in a clinical setting are described
Quantum Big Bang without fine-tuning in a toy-model
The question of possible physics before Big Bang (or after Big Crunch) is
addressed via a schematic non-covariant simulation of the loss of observability
of the Universe. Our model is drastically simplified by the reduction of its
degrees of freedom to the mere finite number. The Hilbert space of states is
then allowed time-dependent and singular at the critical time . This
option circumvents several traditional theoretical difficulties in a way
illustrated via solvable examples. In particular, the unitary evolution of our
toy-model quantum Universe is shown interruptible, without any fine-tuning, at
the instant of its bang or collapse .Comment: 20 pp., 1 fig., invited talk for the conference "10th Workshop on
Quantization, Dualities and Integrable Systems" (April 22 - 24, 2011),
http://qdis.emu.edu.tr/index.htm
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