27,519 research outputs found
Using presence-absence data to establish reserve selection procedures that are robust to temporal species turnover
Previous studies suggest that a network of nature reserves with maximum efficiency (obtained by selecting the minimum area such that each species is represented once) is likely to be insufficient to maintain species in the network over time. Here, we test the performance of three selection strategies which require presence-absence data, two of them previously proposed (multiple representations and selecting an increasing percentage of each species' range) and a novel one based on selecting the site where each species has exhibited a higher permanence rate in the past. Multiple representations appear to be a safer strategy than selecting a percentage of range because the former gives priority to rarer species while the latter favours the most widespread.
The most effective strategy was the one based on the permanence rate, indicating that the robustness of reserve networks can be improved by adopting reserve selection procedures that integrate information about the relative value of sites. This strategy was also very efficient, suggesting that the investment made in the monitoring schemes may be compensated for by a lower cost in reserve acquisition
Terrain Database Correlation Assessment Using an Open Source Tool
Configuring networked simulators for training military teams in a distributed
environment requires the usage of a set of terrain databases to represent the
same training area. The results of simulation exercises can be degraded if the
terrain databases are poorly correlated. A number of methodologies for
determining the correlation between terrain databaHowever, there are few
computational tools for this task and most of them were developed to address
government needs, have limited availability, and handle specific digital
formats. The goal of this paper is thus to present a novel open source tool
developed as part of an academic research project.Comment: 12 pages, I/ITSEC 201
Galaxy rotation curves from General Relativity with Renormalization Group corrections
We consider the application of quantum corrections computed using
renormalization group arguments in the astrophysical domain and show that, for
the most natural interpretation of the renormalization group scale parameter, a
gravitational coupling parameter varying of its value across a
galaxy (which is roughly a variation of per light-year) is
sufficient to generate galaxy rotation curves in agreement with the
observations. The quality of the resulting fit is similar to the Isothermal
profile quality once both the shape of the rotation curve and the mass-to-light
ratios are considered for evaluation. In order to perform the analysis, we use
recent high quality data from nine regular disk galaxies. For the sake of
comparison, the same set of data is modeled also for the Modified Newtonian
Dynamics (MOND) and for the recently proposed Scalar Tensor Vector Gravity
(STVG). At face value, the model based on quantum corrections clearly leads to
better fits than these two alternative theories.Comment: 35 pages, 12 PDF figures. v4: Version accepted in JCAP. Improved
comments on the galactic gas effects to our model, stressed the relevance of
our MOND and STVG fits, slightly extended discussion on our perspectives and
minor additional comments. Ref's added
The Quantum Algebraic Structure of the Twisted XXZ Chain
We consider the Quantum Inverse Scattering Method with a new R-matrix
depending on two parameters and . We find that the underlying algebraic
structure is the two-parameter deformed algebra enlarged by
introducing an element belonging to the centre. The corresponding Hamiltonian
describes the spin-1/2 XXZ model with twisted periodic boundary conditions.Comment: LateX file, 9 pages, Minor changes (including authors` names in the
hep-th heading
On duality of the noncommutative extension of the Maxwell-Chern-Simons model
We study issues of duality in 3D field theory models over a canonical
noncommutative spacetime and obtain the noncommutative extension of the
Self-Dual model induced by the Seiberg-Witten map. We apply the dual projection
technique to uncover some properties of the noncommutative Maxwell-Chern-Simons
theory up to first-order in the noncommutative parameter. A duality between
this theory and a model similar to the ordinary self-dual model is
estabilished. The correspondence of the basic fields is obtained and the
equivalence of algebras and equations of motion are directly verified. We also
comment on previous results in this subject.Comment: Revtex, 9 pages, accepted for publication PL
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