2,387 research outputs found
Stratified spatiotemporal chaos in anisotropic reaction-diffusion systems
Numerical simulations of two dimensional pattern formation in an anisotropic
bistable reaction-diffusion medium reveal a new dynamical state, stratified
spatiotemporal chaos, characterized by strong correlations along one of the
principal axes. Equations that describe the dependence of front motion on the
angle illustrate the mechanism leading to stratified chaos
Breathing Spots in a Reaction-Diffusion System
A quasi-2-dimensional stationary spot in a disk-shaped chemical reactor is
observed to bifurcate to an oscillating spot when a control parameter is
increased beyond a critical value. Further increase of the control parameter
leads to the collapse and disappearance of the spot. Analysis of a bistable
activator-inhibitor model indicates that the observed behavior is a consequence
of interaction of the front with the boundary near a parity breaking front
bifurcation.Comment: 4 pages RevTeX, see also http://chaos.ph.utexas.edu/ and
http://t7.lanl.gov/People/Aric
Controlling domain patterns far from equilibrium
A high degree of control over the structure and dynamics of domain patterns
in nonequilibrium systems can be achieved by applying nonuniform external
fields near parity breaking front bifurcations. An external field with a linear
spatial profile stabilizes a propagating front at a fixed position or induces
oscillations with frequency that scales like the square root of the field
gradient. Nonmonotonic profiles produce a variety of patterns with controllable
wavelengths, domain sizes, and frequencies and phases of oscillations.Comment: Published version, 4 pages, RevTeX. More at
http://t7.lanl.gov/People/Aric
Order Parameter Equations for Front Transitions: Planar and Circular Fronts
Near a parity breaking front bifurcation, small perturbations may reverse the
propagation direction of fronts. Often this results in nonsteady asymptotic
motion such as breathing and domain breakup. Exploiting the time scale
differences of an activator-inhibitor model and the proximity to the front
bifurcation, we derive equations of motion for planar and circular fronts. The
equations involve a translational degree of freedom and an order parameter
describing transitions between left and right propagating fronts.
Perturbations, such as a space dependent advective field or uniform curvature
(axisymmetric spots), couple these two degrees of freedom. In both cases this
leads to a transition from stationary to oscillating fronts as the parity
breaking bifurcation is approached. For axisymmetric spots, two additional
dynamic behaviors are found: rebound and collapse.Comment: 9 pages. Aric Hagberg: http://t7.lanl.gov/People/Aric/; Ehud Meron:
http://www.bgu.ac.il/BIDR/research/staff/meron.htm
Formal support, mental disorders and personal characteristics: a 25-year follow-up study of a total cohort of older people.
The present study was designed to describe the pattern of long-term formal support received by people with mental disorders, and to investigate the relationship between the medical, psychological and social characteristics of the participants and types of formal support. This study is based on a cohort (n = 192) of people born in 1902 and 1903 in a community in Southern Sweden. The research participants were assessed using interviews, psychological tests and medical examinations. Information was collected about the use of primary healthcare and social services. The first assessment took place when the cohort was aged 67 years, and then on eight further occasions until they were 92. The participation rate ranged from 72% to 100%. During the observation period of 25 years, 53% of people with dementia eventually received both home help and institutional care compared to 34% of people with other psychiatric diagnoses and 12% of people with good mental health. The last group had all physical health problems and/or problems with activities of daily living. However, 35% of the dementia group, 46% with other psychiatric diagnoses and 52% of people with good mental health did not receive any formal support. Males and self-employed people were significantly less likely to use formal support. The institutionalised group reported loneliness significantly more often than the other two groups. In a logistic regression analysis, loneliness, low social class, high blood pressure and low problem-solving ability were predictors of formal support use. People with a mental disorder, including dementia, were significantly more likely to use formal support compared to people with good mental health. Social factors were the main factors predicting formal support
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