6,419 research outputs found
Crisis bifurcations in plane Poiseuille flow
Many shear flows follow a route to turbulence that has striking similarities
to bifurcation scenarios in low-dimensional dynamical systems. Among the
bifurcations that appear, crisis bifurcations are important because they cause
global transitions between open and closed attractors, or indicate drastic
increases in the range of the state space that is covered by the dynamics. We
here study exterior and interior crisis bifurcations in direct numerical
simulations of transitional plane Poiseuille flow in a mirror-symmetric
subspace. We trace the state space dynamics from the appearance of the first
three-dimensional exact coherent structures to the transition from an attractor
to a chaotic saddle in an exterior crisis. For intermediate Reynolds numbers,
the attractor undergoes several interior crises, in which new states appear and
intermittent behavior can be observed. The bifurcations contribute to
increasing the complexity of the dynamics and to a more dense coverage of state
space
Topological susceptibility and the sampling of field space in lattice QCD simulations
We present a measurement of the topological susceptibility in two flavor QCD.
In this observable, large autocorrelations are present and also sizable cutoff
effects have to be faced in the continuum extrapolation. Within the statistical
accuracy of the computation, the result agrees with the expectation from
leading order chiral perturbation theory.Comment: 22 pages, 7 figures; References added, minor clarifications in the
text, results unchange
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