Scaling and Intermittency in Animal Behavior

Scale-invariant spatial or temporal patterns and L\'evy flight motion have been observed in a large variety of biological systems. It has been argued that animals in general might perform L\'evy flight motion with power law distribution of times between two changes of the direction of motion. Here we study the temporal behaviour of nesting gilts. The time spent by a gilt in a given form of activity has power law probability distribution without finite average. Further analysis reveals intermittent eruption of certain periodic behavioural sequences which are responsible for the scaling behaviour and indicates the existence of a critical state. We show that this behaviour is in close analogy with temporal sequences of velocity found in turbulent flows, where random and regular sequences alternate and form an intermittent sequence.Comment: 10 page

Stochastic to deterministic crossover of fractal dimension for a Langevin equation

Using algorithms of Higuchi and of Grassberger and Procaccia, we study numerically how fractal dimensions cross over from finite-dimensional Brownian noise at short time scales to finite values of deterministic chaos at longer time scales for data generated from a Langevin equation that has a strange attractor in the limit of zero noise. Our results suggest that the crossover occurs at such short time scales that there is little chance of finite-dimensional Brownian noise being incorrectly identified as deterministic chaos.Comment: 12 pages including 3 figures, RevTex and epsf. To appear Phys. Rev. E, April, 199

Generating long streams of 1/falpha1/f^alpha noise

We review existing methods for generating long streams of 1/f^alpha noise ($0<\alpha\le 2$) focusing on the digital filtering of white noise. We detail the formalism to conceive an efficient random number generator (white outside some bounds) in order to generate very long streams of noise without an exhaustive computer memory load. For $\alpha=2$ it is shown why the process is equivalent to a random-walk and can be obtained simply by a first order filtering of white noise. As soon as $\alpha<2$ the problem becomes non linear and we show why the exact digital filtering method becomes inefficient. Instead, we work out the formalism of using several 1/f^2 filters spaced logarithmically, to approximate the spectrum at the percent level. Finally, from work on logistic maps, we give hints on how to design generators with $\alpha>2$. The software is available from http://planck.lal.in2p3.fr/article.php3?id\_article=8Comment: Last version (corrected web site

Noninvasive positive pressure ventilation in acute asthmatic attack

Asthma is characterised by reversible airway obstruction. In most patients, control of disease activity is easily achieved. However, in a small minority, asthma may be fatal. Between the two extremes lie patients with severe asthmatic attacks, refractory to standard treatment. These patients are at an increased risk of recurrent severe attacks, with respiratory failure, and mechanical ventilation. Invasive mechanical ventilation of the asthmatic patient is associated with a higher risk of complications and, therefore, is a measure of last resort. Noninvasive positive pressure ventilation (NPPV) is another treatment modality that may be beneficial in patients with severe asthmatic attack who are at an increased risk of developing respiratory failure. These patients have the potential to benefit from early respiratory support in the form of NPPV. However, reports of NPPV in asthmatic patients are scarce, and its usage in asthmatic attacks is, therefore, still controversial. Only a few reports of NPPV in asthma have been published over the last decade. These studies mostly involve small numbers of patients and those who have problematic methodology. In this article we review the available evidence for NPPV in asthma and try to formulate our recommendations for NPPV application in asthma based on the available evidence and reports