2,084 research outputs found
Noise-Driven Mechanism for Pattern Formation
We extend the mechanism for noise-induced phase transitions proposed by
Ibanes et al. [Phys. Rev. Lett. 87, 020601-1 (2001)] to pattern formation
phenomena. In contrast with known mechanisms for pure noise-induced pattern
formation, this mechanism is not driven by a short-time instability amplified
by collective effects. The phenomenon is analyzed by means of a modulated mean
field approximation and numerical simulations
Comprehensive study of phase transitions in relaxational systems with field-dependent coefficients
We present a comprehensive study of phase transitions in single-field systems
that relax to a non-equilibrium global steady state. The mechanism we focus on
is not the so-called Stratonovich drift combined with collective effects, but
is instead similar to the one associated with noise-induced transitions a la
Horsthemke-Lefever in zero-dimensional systems. As a consequence, the noise
interpretation (e.g., Ito vs Stratonvich) merely shifts the phase boundaries.
With the help of a mean-field approximation, we present a broad qualitative
picture of the various phase diagrams that can be found in these systems. To
complement the theoretical analysis we present numerical simulations that
confirm the findings of the mean-field theory
Critical Behaviour of Non-Equilibrium Phase Transitions to Magnetically Ordered States
We describe non-equilibrium phase transitions in arrays of dynamical systems
with cubic nonlinearity driven by multiplicative Gaussian white noise.
Depending on the sign of the spatial coupling we observe transitions to
ferromagnetic or antiferromagnetic ordered states. We discuss the phase
diagram, the order of the transitions, and the critical behaviour. For global
coupling we show analytically that the critical exponent of the magnetization
exhibits a transition from the value 1/2 to a non-universal behaviour depending
on the ratio of noise strength to the magnitude of the spatial coupling.Comment: 4 pages, 5 figure
Spatial Patterns Induced Purely by Dichotomous Disorder
We study conditions under which spatially extended systems with coupling a la
Swift-Hohenberg exhibit spatial patterns induced purely by the presence of
quenched dichotomous disorder. Complementing the theoretical results based on a
generalized mean-field approximation, we also present numerical simulations of
particular dynamical systems that exhibit the proposed phenomenology
Stochastic Stokes' drift of a flexible dumbbell
We consider the stochastic Stokes drift of a flexible dumbbell. The dumbbell
consists of two isotropic Brownian particles connected by a linear spring with
zero natural length, and is advected by a sinusoidal wave. We find an
asymptotic approximation for the Stokes drift in the limit of a weak wave, and
find good agreement with the results of a Monte Carlo simulation. We show that
it is possible to use this effect to sort particles by their flexibility even
when all the particles have the same diffusivity.Comment: 12 pages, 1 figur
Respiratie bij vogels: een functioneel-anatomische benadering
The mechanism of avian respiration is still controversial. It is fundamentally different from respiration in mammals. Although during in-and expiration a continuous caudocranial airflow is present within the tertiary bronchi and the air capillaries of the avian lung, the air flow within the entire respiratory system is still equivocal. Several patterns explaining the air flow during in-and expiration have been proposed during the past century. Moreover, various anatomical structures and aerodynamic mechanisms have recently been described in an attempt to explain the proposed mechanisms of respiration. This manuscript gives an overview of the anatomy of the avian respiratory system and the hypotheses concerning the physiology of avian respiration
Dissipative collapse of the adiabatic piston
An adiabatic piston, separating two granular gases prepared in the same
macroscopic state, is found to eventually collapse to one of the sides. This
new instability is explained by a simple macroscopic theory which is
furthermore in qualitative agreement with hard disk molecular dynamics.Comment: 7 pages, 5 figure
Fatness and muscularity as risk indicators of child mortality in rural Congo
OBJECTIVES: To examine the relationship of anthropometrical indicators of
fatness and muscularity with mortality in children in a rural African
community. BACKGROUND: A prospective cohort study was carried out in the
rural health zone of Bwamanda, Northern Congo using a random cluster
sample of 5167 children, aged 0-5 years. MAIN OUTCOME MEASURES: Short- and
long-term mortality rates, being deaths within 3 months and deaths in
3-month periods observed 3-30 months after enrolment. Rates of all cause
mortality and of mortality from kwashiorkor or marasmus, by level of
baseline fatness and muscularity. Indicators of fatness and muscularity
were obtained by correcting anthropometric arm fat and arm muscle areas
for age, sex, weight and height. RESULTS: The relationship of both the
fatness and muscularity scores with short-term mortality was marked by a
clear threshold (-0.5 SDS) below which there was a significant rise in
mortality from all causes as well as from kwashiorkor and marasmus. These
excess mortalities were also found in normal weight children. Fatness and
muscularity scores remained significant determining factors of short-term
mortality in a multiple logistic regression analysis with sex, age, season
and weight-for-age. A ROC curve analysis showed that fat and muscularity
scores had better predictive abilities than weight-for-age. Low fat status
had a bad prognosis on the long-term in underweight children. CONCLUSIONS:
Measures of current nutritional status should not be based on weight
indices alone. Objective and/or clinical evaluation of fat and muscle
status (also in normal weight children) should be added in order to detect
a higher proportion of malnourished children and to more accurately
evaluate mortality risk
- …