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

The Lifshitz-Slyozov-Wagner equation for reaction-controlled kinetics

We rigorously derive a weak form of the Lifshitz-Slyozov-Wagner equation as the homogenization limit of a Stefan-type problem describing reaction-controlled coarsening of a large number of small spherical particles. Moreover, we deduce that the effective mean-field description holds true in the particular limit of vanishing surface-area density of particles.Comment: 15 pages, LaTeX; minor revision, change of titl

Long-time asymptotics for polymerization models

This study is devoted to the long-term behavior of nucleation, growth and fragmentation equations, modeling the spontaneous formation and kinetics of large polymers in a spatially homogeneous and closed environment. Such models are, for instance, commonly used in the biophysical community in order to model in vitro experiments of fibrillation. We investigate the interplay between four processes: nucleation, polymeriza-tion, depolymerization and fragmentation. We first revisit the well-known Lifshitz-Slyozov model, which takes into account only polymerization and depolymerization, and we show that, when nucleation is included, the system goes to a trivial equilibrium: all polymers fragmentize, going back to very small polymers. Taking into account only polymerization and fragmentation, modeled by the classical growth-fragmentation equation, also leads the system to the same trivial equilibrium, whether or not nucleation is considered. However, also taking into account a depolymer-ization reaction term may surprisingly stabilize the system, since a steady size-distribution of polymers may then emerge, as soon as polymeriza-tion dominates depolymerization for large sizes whereas depolymerization dominates polymerization for smaller ones-a case which fits the classical assumptions for the Lifshitz-Slyozov equations, but complemented with fragmentation so that " Ostwald ripening " does not happen.Comment: https://link.springer.com/article/10.1007/s00220-018-3218-

Non-self-similar behavior in the LSW theory of Ostwald ripening

The classical Lifshitz-Slyozov-Wagner theory of domain coarsening predicts asymptotically self-similar behavior for the size distribution of a dilute system of particles that evolve by diffusional mass transfer with a common mean field. Here we consider the long-time behavior of measure-valued solutions for systems in which particle size is uniformly bounded, i.e., for initial measures of compact support. We prove that the long-time behavior of the size distribution depends sensitively on the initial distribution of the largest particles in the system. Convergence to the classically predicted smooth similarity solution is impossible if the initial distribution function is comparable to any finite power of distance to the end of the support. We give a necessary criterion for convergence to other self-similar solutions, and conditional stability theorems for some such solutions. For a dense set of initial data, convergence to any self-similar solution is impossible.Comment: 31 pages, LaTeX2e; Revised version, to appear in J. Stat. Phy

Macroscopic limit of the Becker-D\"oring equation via gradient flows

This work considers gradient structures for the Becker-D\"oring equation and its macroscopic limits. The result of Niethammer [17] is extended to prove the convergence not only for solutions of the Becker-D\"oring equation towards the Lifshitz-Slyozov-Wagner equation of coarsening, but also the convergence of the associated gradient structures. We establish the gradient structure of the nonlocal coarsening equation rigorously and show continuous dependence on the initial data within this framework. Further, on the considered time scale the small cluster distribution of the Becker--D\"oring equation follows a quasistationary distribution dictated by the monomer concentration

On thermodynamically consistent Stefan problems with variable surface energy

A thermodynamically consistent two-phase Stefan problem with temperature-dependent surface tension and with or without kinetic undercooling is studied. It is shown that these problems generate local semiflows in well-defined state manifolds. If a solution does not exhibit singularities, it is proved that it exists globally in time and converges towards an equilibrium of the problem. In addition, stability and instability of equilibria is studied. In particular, it is shown that multiple spheres of the same radius are unstable if surface heat capacity is small; however, if kinetic undercooling is absent, they are stable if surface heat capacity is sufficiently large.Comment: To appear in Arch. Ration. Mech. Anal. The final publication is available at Springer via http://dx.doi.org/10.1007/s00205-015-0938-y. arXiv admin note: substantial text overlap with arXiv:1101.376

Μερικές διαφορικές εξισώσεις και προβλήματα αλλαγής φάσεων

Η παρούσα διατριβή αποτελείται από δύο εργασίες στην περιοχή των μερικών διαφορικών εξισώσεων, οι οποίες ασχολούνται με δύο φυσικά φαινόμενα αλλαγής φάσεων. Η πρώτη ασχολείται με το φαινόμενο της ωρίμασης Ostwald και αναπαράγει μία εκδοχή της θεωρίας των Lifshitz, Slyozov και Wagner μέσω ομογενοποίησης ενός προβλήματος Stefan, ενώ η δεύτερη ασχολείται με την εξαγωγή των συνθηκών Plateau για τις γωνίες στις τριπλές συμβολές διεπιφανειών στον τριδιάστατο χώρο από τη διανυσματική εξίσωση Allen–Cahn μέσω ενός τανυστή τάσης που συνδέεται με την εξίσωση.The present dissertation comprises two papers in the area of partial differential equations, which study two physical phenomena of phase transitions. The first is about the phenomenon of Ostwald ripening and derives a version of the Lifshitz–Slyozov–Wagner theory through the homogenization of a Stefan problem, while the second is about the derivation of the Plateau angle conditions at triple junctions of interfaces in three-dimensional space from the vector-valued Allen–Cahn equation via an associated stress tensor

Μερικές διαφορικές εξισώσεις και προβλήματα αλλαγής φάσεων

Η διατριβή αυτή αποτελείται από δύο εργασίες στην περιοχή των μερικών διαφορικών εξισώσεων, οι οποίες ασχολούνται με δύο φυσικά φαινόμενα αλλαγής φάσεων. Η πρώτη ασχολείται με το φαινόμενο της ωρίμασης Ostwald και αναπαράγει μία εκδοχή της θεωρίας των Lifshitz, Slyozov και Wagner μέσω ομογενοποίησης ενός προβλήματος Stefan. Η δεύτερη εργασία ασχολείται με την εξαγωγή των συνθηκών Plateau για τις γωνίες στις τριπλές συμβολές διεπιφανειών στον τριδιάστατο χώρο από τη διανυσματική εξίσωση Allen–Cahn μέσω ενός τανυστή τάσης που συνδέεται με την εξίσωση