1,183 research outputs found
Linear growth of streaming instability in pressure bumps
Streaming instability is a powerful mechanism which concentrates dust grains
in pro- toplanetary discs, eventually up to the stage where they collapse
gravitationally and form planetesimals. Previous studies inferred that it
should be ineffective in viscous discs, too efficient in inviscid discs, and
may not operate in local pressure maxima where solids accumulate. From a linear
analysis of stability, we show that streaming instability behaves differently
inside local pressure maxima. Under the action of the strong differential
advection imposed by the bump, a novel unstable mode develops and grows even
when gas viscosity is large. Hence, pressure bumps are found to be the only
places where streaming instability occurs in viscous discs. This offers a
promising way to conciliate models of planet formation with recent observations
of young discs.Comment: 11 pages, 17 figures, accepted for publication in MNRA
Free energy and complexity of spherical bipartite models
We investigate both free energy and complexity of the spherical bipartite
spin glass model. We first prove a variational formula in high temperature for
the limiting free energy based on the well-known Crisanti-Sommers
representation of the mixed p-spin spherical model. Next, we show that the mean
number of local minima at low levels of energy is exponentially large in the
size of the system and we derive a bound on the location of the ground state
energy.Comment: 22 page
Limiting geodesics for first-passage percolation on subsets of
It is an open problem to show that in two-dimensional first-passage
percolation, the sequence of finite geodesics from any point to has a
limit in . In this paper, we consider this question for first-passage
percolation on a wide class of subgraphs of : those whose vertex
set is infinite and connected with an infinite connected complement. This
includes, for instance, slit planes, half-planes and sectors. Writing for
the sequence of boundary vertices, we show that the sequence of geodesics from
any point to has an almost sure limit assuming only existence of finite
geodesics. For all passage-time configurations, we show existence of a limiting
Busemann function. Specializing to the case of the half-plane, we prove that
the limiting geodesic graph has one topological end; that is, all its infinite
geodesics coalesce, and there are no backward infinite paths. To do this, we
prove in the Appendix existence of geodesics for all product measures in our
domains and remove the moment assumption of the Wehr-Woo theorem on absence of
bigeodesics in the half-plane.Comment: Published in at http://dx.doi.org/10.1214/13-AAP999 the Annals of
Applied Probability (http://www.imstat.org/aap/) by the Institute of
Mathematical Statistics (http://www.imstat.org
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