Finite-size scaling as a way to probe near-criticality in natural swarms

Collective behaviour in biological systems is often accompanied by strong correlations. The question has therefore arisen of whether correlation is amplified by the vicinity to some critical point in the parameters space. Biological systems, though, are typically quite far from the thermodynamic limit, so that the value of the control parameter at which correlation and susceptibility peak depend on size. Hence, a system would need to readjust its control parameter according to its size in order to be maximally correlated. This readjustment, though, has never been observed experimentally. By gathering three-dimensional data on swarms of midges in the field we find that swarms tune their control parameter and size so as to maintain a scaling behaviour of the correlation function. As a consequence, correlation length and susceptibility scale with the system's size and swarms exhibit a near-maximal degree of correlation at all sizes.Comment: Selected for Viewpoint in Physics; PRL Editor's Suggestio

Doctors Ask These Questions

It has been suggested that the Question Box be resumed in the pages of THE LINACRE QUARTERLY. To include this feature regularly, we will need contributions from our readers. Rare is the physician who has not on occasion been confronted with a specific problem of medical ethics in which the application of general principles may seem uncertain. Although a correct answer may be secured promptly by appropriate consultation, physicians who have encountered such problems are invited to submit them to the Editor here. Answers will be provided from authoritative sources. It is hoped in this fashion to afford wider circulation for specific medico-moral problems and solutions, and to stimulate interest in this aspect of medical practice. Apart from queries regarding ethical problems, questions and comments of general interest to Catholic physicians are also welcome. Although identification of the writer is preferred, anonymity will be respected if requested. We are grateful to Father John J. Lynch, S.J., Professor of Moral Theology at Weston College. Weston, Mass. and medico-moral consultant to the Federation, who prepared material for this issue. He answers questions that have been submitted to him at meetings with doctors

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