3,275 research outputs found
Effective transport barriers in nontwist systems
In fluids and plasmas with zonal flow reversed shear, a peculiar kind of transport barrier appears in the shearless region, one that is associated with a proper route of transition to chaos. These barriers have been identified in symplectic nontwist maps that model such zonal flows. We use the so-called standard nontwist map, a paradigmatic example of nontwist systems, to analyze the parameter dependence of the transport through a broken shearless barrier. On varying a proper control parameter, we identify the onset of structures with high stickiness that give rise to an effective barrier near the broken shearless curve. Moreover, we show how these stickiness structures, and the concomitant transport reduction in the shearless region, are determined by a homoclinic tangle of the remaining dominant twin island chains. We use the finite-time rotation number, a recently proposed diagnostic, to identify transport barriers that separate different regions of stickiness. The identified barriers are comparable to those obtained by using finite-time Lyapunov exponents.FAPESPCNPqCAPESMCT/CNEN (Rede Nacional de Fusao)Fundacao AraucariaUS Department of Energy DE-FG05-80ET-53088Physic
Experimental observation of a complex periodic window
The existence of a special periodic window in the two-dimensional parameter
space of an experimental Chua's circuit is reported. One of the main reasons
that makes such a window special is that the observation of one implies that
other similar periodic windows must exist for other parameter values. However,
such a window has never been experimentally observed, since its size in
parameter space decreases exponentially with the period of the periodic
attractor. This property imposes clear limitations for its experimental
detection.Comment: 4.2 pages, 4 figure
Length Dependence of Ionization Potentials of Trans-Acetylenes: Internally-Consistent DFT/GW Approach
We follow the evolution of the Ionization Potential (IP) for the paradigmatic
quasi-one-dimensional trans-acetylene family of conjugated molecules, from
short to long oligomers and to the infinite polymer trans-poly-acetylene (TPA).
Our results for short oligomers are very close to experimental available data.
We find that the IP varies with oligomer length and converges to the given
value for TPA with a smooth, coupled inverse-length-exponential behavior. Our
prediction is based on an "internally-consistent" scheme to adjust the exchange
mixing parameter of the PBEh hybrid density functional, so as to
obtain a description of the electronic structure consistent with the
quasiparticle approximation for the IP. This is achieved by demanding that the
corresponding quasiparticle correction, in the GW@PBEh approximation, vanishes
for the IP when evaluated at PBEh(). We find that is
also system-dependent and converges with increasing oligomer length, allowing
to capture the dependence of IP and other electronic properties.Comment: 22 pages with 9 figures, submitted to Physical Review
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