1,895 research outputs found
Network Physiology: Mapping interactions between complex physiological systems
The human organism is an integrated network where multi-component organ systems, each with its own regulatory mechanisms, continuously interact to optimize and coordinate their function. Organ-to-organ interactions occur at multiple levels and spatiotemporal time scales to produce distinct physiologic states: wake and sleep; light and deep sleep; consciousness and unconsciousness. Disrupting organ communications can lead to dysfunction of individual systems or to collapse of the entire organism. Yet, we know almost nothing about the nature of the interactions between diverse organ systems and their collective role in maintaining health.
We propose a framework to probe dynamical interactions among physiological systems, and we identify a physiological network. We find that each physiological state is characterized by a specific network structure, demonstrating a robust interplay between network topology and physiologic function. Across physiological states, the network undergoes topological transitions associated with fast reorganization of physiological interactions on time scales of a few minutes, indicating high network flexibility in response to perturbations. The proposed system-wide integrative approach facilitates the development of a new field, Network PhysiologyUniversidad de Málaga. Campus de Excelencia Internacional AndalucĂa Tech
Systems with Correlations in the Variance: Generating Power-Law Tails in Probability Distributions
We study how the presence of correlations in physical variables contributes
to the form of probability distributions. We investigate a process with
correlations in the variance generated by (i) a Gaussian or (ii) a truncated
L\'{e}vy distribution. For both (i) and (ii), we find that due to the
correlations in the variance, the process ``dynamically'' generates power-law
tails in the distributions, whose exponents can be controlled through the way
the correlations in the variance are introduced. For (ii), we find that the
process can extend a truncated distribution {\it beyond the truncation cutoff},
which leads to a crossover between a L\'{e}vy stable power law and the present
``dynamically-generated'' power law. We show that the process can explain the
crossover behavior recently observed in the S&P500 stock index.Comment: 7 pages, five figures. To appear in Europhysics Letters (2000
Spurious detection of phase synchronization in coupled nonlinear oscillators
Coupled nonlinear systems under certain conditions exhibit phase
synchronization, which may change for different frequency bands or with
presence of additive system noise. In both cases, Fourier filtering is
traditionally used to preprocess data. We investigate to what extent the phase
synchronization of two coupled R\"{o}ssler oscillators depends on (1) the
broadness of their power spectrum, (2) the width of the band-pass filter, and
(3) the level of added noise. We find that for identical coupling strengths,
oscillators with broader power spectra exhibit weaker synchronization. Further,
we find that within a broad band width range, band-pass filtering reduces the
effect of noise but can lead to a spurious increase in the degree of
synchronization with narrowing band width, even when the coupling between the
two oscillators remains the same.Comment: 4 pages,6 figure
Simulation of Jahn-Teller-Dicke Magnetic Structural Phase Transition with Trapped Ions
We study theoretically the collective Ee Jahn-Teller-Dicke
distortion in a system of trapped ions. We focus in the limit of infinite range
interactions in which an ensemble of effective spins interacts with two
collective vibrational modes with U(1) symmetric couplings. Our model is
exactly solvable in the thermodynamical limit and it is amenable to be solved
by exact numerical diagonalization for a moderate number of ions. We show that
trapped ions are ideally suited to study the emergence of spontaneous symmetry
breaking of a continuous symmetry and magnetic structural phase transition in a
mesoscopic system.Comment: 19 pages, 7 figure
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