6,852 research outputs found
The dynamics of a low-order coupled ocean-atmosphere model
A system of five ordinary differential equations is studied which combines
the Lorenz-84 model for the atmosphere and a box model for the ocean. The
behaviour of this system is studied as a function of the coupling parameters.
For most parameter values, the dynamics of the atmosphere model is dominant.
For a range of parameter values, competing attractors exist. The Kaplan-Yorke
dimension and the correlation dimension of the chaotic attractor are
numerically calculated and compared to the values found in the uncoupled Lorenz
model. In the transition from periodic behaviour to chaos intermittency is
observed. The intermittent behaviour occurs near a Neimark-Sacker bifurcation
at which a periodic solution loses its stability. The length of the periodic
intervals is governed by the time scale of the ocean component. Thus, in this
regime the ocean model has a considerable influence on the dynamics of the
coupled system.Comment: 20 pages, 15 figures, uses AmsTex, Amssymb and epsfig package.
Submitted to the Journal of Nonlinear Scienc
Soil-borne microorganisms and soil-type affect pyrrolizidine alkaloids in Jacobaea vulgaris
Secondary metabolites like pyrrolizidine alkaloids (PAs) play a crucial part in plant defense. We studied the effects of soil-borne microorganisms and soil-type on pyrrolizidine alkaloids in roots and shoots of Jacobaea vulgaris. We used clones of two genotypes from a dune area (Meijendel), propagated by tissue culture and grown on two sterilized soils and sterilized soils inoculated with 5% of non-sterilized soil of either of the two soil-types. Soil-borne microorganisms and soil-type affected the composition of PAs. By changing the composition rather than the total concentration below and aboveground, plants have a more complex defense strategy than formerly thought. Interestingly, a stronger negative effect on plant growth was found in sterilized soils inoculated with their ‘own’ microbial community suggesting that pathogenic and/or other plant inhibiting microorganisms were adapted to their ‘own’ soil conditions
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