70,318 research outputs found
Discontinuous Transition in a Boundary Driven Contact Process
The contact process is a stochastic process which exhibits a continuous,
absorbing-state phase transition in the Directed Percolation (DP) universality
class. In this work, we consider a contact process with a bias in conjunction
with an active wall. This model exhibits waves of activity emanating from the
active wall and, when the system is supercritical, propagating indefinitely as
travelling (Fisher) waves. In the subcritical phase the activity is localised
near the wall. We study the phase transition numerically and show that certain
properties of the system, notably the wave velocity, are discontinuous across
the transition. Using a modified Fisher equation to model the system we
elucidate the mechanism by which the the discontinuity arises. Furthermore we
establish relations between properties of the travelling wave and DP critical
exponents.Comment: 14 pages, 9 figure
Cohomological characterization of vector bundles on multiprojective spaces
We show that Horrock's criterion for the splitting of vector bundles on
\PP^n can be extended to vector bundles on multiprojective spaces and to
smooth projective varieties with the weak CM property (see Definition 3.11). As
a main tool we use the theory of -blocks and Beilinson's type spectral
sequences. Cohomological characterizations of vector bundles are also showed
The synthesis of the light Mo and Ru isotopes: how now, no need for an exotic solution ?
The most detailed calculations of the p-process call for its development in
the O/Ne layers of Type II supernovae. In spite of their overall success in
reproducing the solar system content of p-nuclides, they suggest a significant
underproduction of the light Mo and Ru isotopes. On grounds of a model for the
explosion of a 25 solar mass star with solar metallicity, we demonstrate that
this failure might just be related to the uncertainties left in the rate of the
22Ne(alpha,n)25Mg neutron producing reaction. The latter indeed have a direct
impact on the distribution of the s-process seeds for the p-process.Comment: 4 pages, 4 figures. LaTex2e with aa.cls. A&A Letters, in pres
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