835 research outputs found

    Future orientation and planning in forestry: a comparison of forest managers' planning horizons in Germany and the Netherlands

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    Long range (or strategic) planning is an important tool for forest management to deal with the complex and unpredictable future. However, it is the ability to make meaningful predictions about the rapidly changing future that is questioned. What appears to be particularly neglected is the question of the length of time horizons and the limits (if any) to these horizons, despite being considered one of the most critical factors in strategic planning. As the future creation of values lies within individual responsibility, this research empirically explored the limits (if any) of individual foresters¿ time horizons. To draw comparisons between countries with different traditions in forest management planning, data were collected through telephone surveys of forest managers in the state/national forest services of the Netherlands and Germany. In order to minimize other cultural differences, the research in Germany concentrated on the federal state of Nordrhein-Westfalen, which has considerable similarities with the Netherlands, e.g. in topography, forest types and forest functions. The results show that, in practice, 15 years appears to be the most distant horizon that foresters can identify with. This is in sharp contrast to the time horizons spanning decades and even generations that are always said to exist in forestry. The ¿doctrine of the long run¿¿the faith in the capacity of foresters to overcome the barriers of the uncertain future and look ahead and plan for long-range goals¿which in many countries still underlies traditional forest management, can therefore be rejected

    Trace identities and their semiclassical implications

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    The compatibility of the semiclassical quantization of area-preserving maps with some exact identities which follow from the unitarity of the quantum evolution operator is discussed. The quantum identities involve relations between traces of powers of the evolution operator. For classically {\it integrable} maps, the semiclassical approximation is shown to be compatible with the trace identities. This is done by the identification of stationary phase manifolds which give the main contributions to the result. The same technique is not applicable for {\it chaotic} maps, and the compatibility of the semiclassical theory in this case remains unsettled. The compatibility of the semiclassical quantization with the trace identities demonstrates the crucial importance of non-diagonal contributions.Comment: LaTeX - IOP styl

    High-Order Variational Calculation for the Frequency of Time-Periodic Solutions

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    We develop a convergent variational perturbation theory for the frequency of time-periodic solutions of nonlinear dynamical systems. The power of the theory is illustrated by applying it to the Duffing oscillator.Comment: Author Information under http://www.physik.fu-berlin.de/~pelster/, http://www.physik.fu-berlin.de/~kleinert/ and http://www.informatik.uni-stuttgart.de/ipvr/bv/personen/schanz.htm

    Combinatorial identities for binary necklaces from exact ray-splitting trace formulae

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    Based on an exact trace formula for a one-dimensional ray-splitting system, we derive novel combinatorial identities for cyclic binary sequences (P\'olya necklaces).Comment: 15 page

    Universal spectral properties of spatially periodic quantum systems with chaotic classical dynamics

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    We consider a quasi one-dimensional chain of N chaotic scattering elements with periodic boundary conditions. The classical dynamics of this system is dominated by diffusion. The quantum theory, on the other hand, depends crucially on whether the chain is disordered or invariant under lattice translations. In the disordered case, the spectrum is dominated by Anderson localization whereas in the periodic case, the spectrum is arranged in bands. We investigate the special features in the spectral statistics for a periodic chain. For finite N, we define spectral form factors involving correlations both for identical and non-identical Bloch numbers. The short-time regime is treated within the semiclassical approximation, where the spectral form factor can be expressed in terms of a coarse-grained classical propagator which obeys a diffusion equation with periodic boundary conditions. In the long-time regime, the form factor decays algebraically towards an asymptotic constant. In the limit NN\to\infty, we derive a universal scaling function for the form factor. The theory is supported by numerical results for quasi one-dimensional periodic chains of coupled Sinai billiards.Comment: 33 pages, REVTeX, 13 figures (eps

    Can One Hear the Shape of a Graph?

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    We show that the spectrum of the Schrodinger operator on a finite, metric graph determines uniquely the connectivity matrix and the bond lengths, provided that the lengths are non-commensurate and the connectivity is simple (no parallel bonds between vertices and no loops connecting a vertex to itself). That is, one can hear the shape of the graph! We also consider a related inversion problem: A compact graph can be converted into a scattering system by attaching to its vertices leads to infinity. We show that the scattering phase determines uniquely the compact part of the graph, under similar conditions as above.Comment: 9 pages, 1 figur

    Spin-Boson Hamiltonian and Optical Absorption of Molecular Dimers

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    An analysis of the eigenstates of a symmetry-broken spin-boson Hamiltonian is performed by computing Bloch and Husimi projections. The eigenstate analysis is combined with the calculation of absorption bands of asymmetric dimer configurations constituted by monomers with nonidentical excitation energies and optical transition matrix elements. Absorption bands with regular and irregular fine structures are obtained and related to the transition from the coexistence to a mixing of adiabatic branches in the spectrum. It is shown that correlations between spin states allow for an interpolation between absorption bands for different optical asymmetries.Comment: 15 pages, revTeX, 8 figures, accepted for publication in Phys. Rev.

    If timber production did not require cutting down trees ... communicating timber management in society

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    De 'slachthuis-paradox' in de bosbouw; mensen houden van bos en van hout, maar niet van de noodzakelijke tussenstap: houtproductie en houtkap. Mogelijkheden om meer sociale acceptatie te krijgen voor de houtproductie-functie van het bo

    De Koninklijke Nederlandse Bosbouw Vereniging en het imago bij haar leden

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    Het bestuur van de Koninklijke Nederlandse Bosbouw Vereniging besloot in 2000 om door middel van een intern onderzoek onder de leden bouwstenen te vinden voor een nieuw verenigingsbeleid. Dit is gebeurd door middel van een enquête onder alle leden. De analyse van de antwoorden had betrekking op 44% van de leden, zijnde de respons. De functie van de KNBV wordt thans nog vooral gezien als een kennis- en informatieplatform, maar in de toekomst zou de KNBV meer als belangenorganisatie mogen fungeren. Leeftijd speelt een rol bij de mate van betrokkenheid bij en tevredenheid over de KNBV. Deze zijn groter naarmate men ouder is. Desondanks is meer aandacht voor de wensen en ideeën van de jongere leden noodzakelijk voor de ‘verjonging’ en het voortbestaan van de vereniging, zeker als 80% van de respondenten aangeeft het jammer te vinden als de KNBV zou worden opgeheven
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