5,151 research outputs found
Simulating anthropogenic impacts to bird communities in tropical rain forests
We used an aggregated modelling approach to simulate the impacts ofanthropogenic disturbances on the long-term dynamics of faunal diversityin tropical rain forests. We restricted our study to bird communities eventhough the approach is more general. We developed a model calledBIODIV which simulated the establishment of hypothetical bird speciesin a forest. Our model was based on the results of a simple matrix modelwhich calculated the spatio-temporal dynamics of a tropical rain forest inMalaysia. We analysed the establishment of bird species in a secondaryforest succession and the impacts of 60 different logging scenarios on thediversity of the bird community. Of the three logging parameters(cycle length, method, intensity), logging intensity had the most servereimpact on the bird community. In the worst case the number of bird specieswas reduced to 23% of the species richness found in a primary forest
Analyzing the Fierz Rearrangement Freedom for Local Chiral Two-Nucleon Potentials
Chiral effective field theory is a framework to derive systematic nuclear
interactions. It is based on the symmetries of quantum chromodynamics and
includes long-range pion physics explicitly, while shorter-range physics is
expanded in a general operator basis. The number of low-energy couplings at a
particular order in the expansion can be reduced by exploiting the fact that
nucleons are fermions and therefore obey the Pauli exclusion principle. The
antisymmetry permits the selection of a subset of the allowed contact operators
at a given order. When local regulators are used for these short-range
interactions, however, this "Fierz rearrangement freedom" is violated. In this
paper, we investigate the impact of this violation at leading order (LO) in the
chiral expansion. We construct LO and next-to-leading order (NLO) potentials
for all possible LO-operator pairs and study their reproduction of phase
shifts, the He ground-state energy, and the neutron-matter energy at
different densities. We demonstrate that the Fierz rearrangement freedom is
partially restored at NLO where subleading contact interactions enter. We also
discuss implications for local chiral three-nucleon interactions.Comment: 11 pages, 5 figure
Vandalism: A General View
Dr. Edward A. Huth is Professor of Sociology, Chairman of the Department of Sociology, and has taught at the U niversity of Dayton since 1939
On the complexity of semantic self-minimization
Partial Kripke structures model only parts of a state space and so enable aggressive abstraction of systems prior to verifying them with respect to a formula of temporal logic. This partiality of models means that verifications may reply with true (all refinements satisfy the formula under check), false (no refinement satisfies the formula under check) or dont know. Generalized model checking is the most precise verification for such models (all dont know answers imply that some refinements satisfy the formula, some dont), but computationally expensive. A compositional model-checking algorithm for partial Kripke structures is efficient, sound (all answers true and false are truthful), but may lose precision by answering dont know instead of a factual true or false. Recent work has shown that such a loss of precision does not occur for this compositional algorithm for most practically relevant patterns of temporal logic formulas. Formulas that never lose precision in this manner are called semantically self-minimizing. In this paper we provide a systematic study of the complexity of deciding whether a formula of propositional logic, propositional modal logic or the propositional modal mu-calculus is semantically self-minimizing. © 2009 Elsevier B.V. All rights reserved
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