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Title 
Universal Extremal Statistics in a Freely Expanding Jepsen Gas 

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Published in  Physical Review. E. 2007, vol. 75, no. 051103, p. 13 p.  
Abstract  We study the extremal dynamics emerging in an outofequilibrium onedimensional Jepsen gas of $(N+1)$ hardpoint particles. The particles undergo binary elastic collisions, but move ballistically inbetween collisions. The gas is initally uniformly distributed in a box $[L,0]$ with the "leader" (or the rightmost particle) at X=0, and a random positive velocity, independently drawn from a distribution $phi(V)$, is assigned to each particle. The gas expands freely at subsequent times. We compute analytically the distribution of the leader's velocity at time $t$, and also the mean and the variance of the number of collisions that are undergone by the leader up to time $t$. We show that in the thermodynamic limit and at fixed time $tgg 1$ (the socalled "growing regime"), when interactions are strongly manifest, the velocity distribution exhibits universal scaling behavior of only three possible varieties, depending on the tail of $phi(V)$. The associated scaling functions are novel and different from the usual extremevalue distributions of uncorrelated random variables. In this growing regime the mean and the variance of the number of collisions of the leader up to time $t$ increase logarithmically with $t$, with universal prefactors that are computed exactly. The implications of our results in the context of biological evolution modeling are pointed out.  
Stable URL  http://archiveouverte.unige.ch/unige:13099  
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arXiv: condmat/0701130 

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