79 research outputs found
Natural selection as coarsening
Analogies between evolutionary dynamics and statistical mechanics, such as
Fisher's second-law-like "fundamental theorem of natural selection" and
Wright's "fitness landscapes", have had a deep and fruitful influence on the
development of evolutionary theory. Here I discuss a new conceptual link
between evolution and statistical physics. I argue that natural selection can
be viewed as a coarsening phenomenon, similar to the growth of domain size in
quenched magnets or to Ostwald ripening in alloys and emulsions. In particular,
I show that the most remarkable features of coarsening---scaling and
self-similarity---have strict equivalents in evolutionary dynamics. This
analogy has three main virtues: it brings a set of well-developed mathematical
tools to bear on evolutionary dynamics; it suggests new problems in theoretical
evolution; and it provides coarsening physics with a new exactly soluble model.Comment: Submitted to J. Stat. Phys. for special issue on evolutionary
dynamic
A blackbody is not a blackbox
We discuss carefully the blackbody approximation, stressing what it is (a
limit case of radiative transfer), and what it is not (the assumption that the
body is perfectly absorbing, i.e. black). Furthermore, we derive the Planck
spectrum without enclosing the field in a box, as is done in most textbooks.
Athough convenient, this trick conceals the nature of the idealization
expressed in the concept of a blackbody: first, the most obvious examples of
approximate blackbodies, stars, are definitely not enclosed in boxes; second,
the Planck spectrum is continuous, while the stationary modes of radiation in a
box are discrete. Our derivation, although technically less elementary, is
conceptually more consistent, and brings the opportunity to introduce to
students the important concept of local density of states, via the resolvent
formalism.Comment: 6 page
Comment on `Lost in Translation: Topological Singularities in Group Field Theory'
Gurau argued in [arXiv:1006.0714] that the gluing spaces arising as Feynman
diagrams of three-dimensional group field theory are not all pseudo-manifolds.
I dispute this conclusion: albeit not properly triangulated, these spaces are
genuine pseudo-manifolds, viz. their singular locus is of codimension at least
two
Stochastic thermodynamics of entropic transport
Seifert derived an exact fluctuation relation for diffusion processes using
the concept of "stochastic system entropy". In this note we extend his
formalism to entropic transport. We introduce the notion of relative stochastic
entropy, or "relative surprisal", and use it to generalize Seifert's
system/medium decomposition of the total entropy. This result allows to apply
the concepts of stochastic thermodynamics to diffusion processes in confined
geometries, such as ion channels, cellular pores or nanoporous materials. It
can be seen as the equivalent for diffusion processes of Esposito and
Schaller's generalized fluctuation theorem for "Maxwell demon feedbacks".Comment: 3 pages, wording change
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