19,837 research outputs found
Structural aspects of Hamilton-Jacobi theory
In our previous papers [11,13] we showed that the Hamilton-Jacobi problem can
be regarded as a way to describe a given dynamics on a phase space manifold in
terms of a family of dynamics on a lower-dimensional manifold. We also showed
how constants of the motion help to solve the Hamilton-Jacobi equation. Here we
want to delve into this interpretation by considering the most general case: a
dynamical system on a manifold that is described in terms of a family of
dynamics (`slicing vector fields') on lower-dimensional manifolds. We identify
the relevant geometric structures that lead from this decomposition of the
dynamics to the classical Hamilton-Jacobi theory, by considering special cases
like fibred manifolds and Hamiltonian dynamics, in the symplectic framework and
the Poisson one. We also show how a set of functions on a tangent bundle can
determine a second-order dynamics for which they are constants of the motion.Comment: 26 pages. Minor changes (some minor mistakes are corrected
Spin-orbit induced mixed-spin ground state in NiO perovskites probed by XAS: new insight into the metal to insulator transition
We report on a Ni L edges x-ray absorption spectroscopy (XAS) study
in NiO perovskites. These compounds exhibit a metal to insulator ()
transition as temperature decreases. The L edge presents a clear
splitting in the insulating state, associated to a less hybridized ground
state. Using charge transfer multiplet calculations, we establish the
importance of the crystal field and 3d spin-orbit coupling to create a
mixed-spin ground state. We explain the transition in NiO
perovskites in terms of modifications in the Ni crystal field splitting
that induces a spin transition from an essentially low-spin (LS) to a
mixed-spin state.Comment: 4 pages, 4 figures, accepted as PRB - Rapid Comm. Dez. 200
Long-term effects of zero pruning on Grenache vines under drought conditions
Under drought conditions the influence of zero pruning (ZP) and hand pruning (HP) on yield, total soluble solids (degrees Brix), sugar production, dry matter production and total leaf area development of Grenache vines (Vitis vinifera L.) was assessed from 1988 to 1996. ZP was superior to HP for yield, sugar production and dry matter production. Total soluble solids were occasionally reduced by ZP. These effects of ZP can be explained by the larger total leaf area. These results are specifically important with regard to low-yield viticulture with a severely limited total leaf area
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