3,750 research outputs found
Robustness of reserve selection procedures under temporal species turnover
Complementarity-based algorithms for the selection of reserve networks emphasize the need to represent biodiversity features efficiently, but this may not be sufficient to maintain those features in the long term. Here, we use data from the Common Birds Census in Britain as an exemplar data set to determine guidelines for the selection of reserve networks which are more robust to temporal turnover in features. The extinction patterns found over the 1981-1991 interval suggest that two such guidelines are to represent species in the best sites where they occur (higher local abundance) and to give priority to the rarer species. We tested five reserve selection strategies, one which finds the minimum representation set and others which incorporate the first or both guidelines proposed. Strategies were tested in terms of their efficiency (inversely related to the total area selected) and effectiveness (inversely related to the percentage of species lost) using data on eight pairs of ten-year intervals.
The minimum set strategy was always the most efficient, but suffered higher species loss than the others, suggesting that there is a trade-off between efficiency and effectiveness. A desirable compromise can be achieved by embedding the concerns about the long-term maintenance of the biodiversity features of interest in the complementarity-based algorithms
GC Verification of the Spacecraft Atmosphere Monitor
International Space Station crew members face the unique challenge of maintaining air quality due to the volatile organic compounds (VOCs) that have the potential to accumulate at unsafe levels. The Spacecraft Atmosphere Monitor (SAM) is a miniature gas chromatograph/mass spectrometer (GCMS) designed to measure major constituents (such as N2, O2 and CO2) and trace VOCs within the cabin of the spacecraft. The gas chromatograph is responsible for separating the sample into its components in order to be characterized. The oven of the gas chromatograph must reach a temperature of 150°C in order to heat constituents of the analyte into the gas phase. The heater was tested to determine the proper operating parameters. An appropriate operating point was found to adequately heat the oven of the GC. Further work to determine the proper operating parameters of the preconcentrator (PC), a component of the instrument for adequate peak separation, should be done, leading to the improvement of the GCMS instrument for SAM
Spectral characteristics for a spherically confined -1/r + br^2 potential
We consider the analytical properties of the eigenspectrum generated by a
class of central potentials given by V(r) = -a/r + br^2, b>0. In particular,
scaling, monotonicity, and energy bounds are discussed. The potential is
considered both in all space, and under the condition of spherical confinement
inside an impenetrable spherical boundary of radius R. With the aid of the
asymptotic iteration method, several exact analytic results are obtained which
exhibit the parametric dependence of energy on a, b, and R, under certain
constraints. More general spectral characteristics are identified by use of a
combination of analytical properties and accurate numerical calculations of the
energies, obtained by both the generalized pseudo-spectral method, and the
asymptotic iteration method. The experimental significance of the results for
both the free and confined potential V(r) cases are discussed.Comment: 16 pages, 4 figure
Spatial/Spectral Resolution of a Galactic Bulge K3 Giant Stellar Atmosphere via Gravitational Microlensing
We present two Keck HIRES spectra (R=40,000) of a bulge K3 giant taken on
successive nights during the second caustic crossing of the binary microlensing
event EROS BLG-2000-5. This caustic crossing served to effectively resolve the
surface of the source star: the spectrum from the second night is dominated by
the limb, while the spectrum from the first night is comprised of light from a
broader range of radii. To demonstrate that the spectra are adequate to resolve
the differences between them, we analyze the H-alpha line. The equivalent width
is ~8% smaller on the second night, and the signal-to-noise ratio per
resolution element (165 and 75 on the two nights respectively) is sufficient to
show that the difference is approximately constant over the ~2A (~15 resolution
element) extent of the line. The sign of the difference is in the expected
direction since the limb is the coolest part of the star and therefore should
have the weakest H-alpha. We invite atmosphere modelers to predict the
difference spectrum from the entire spectral range 5500<lambda<7900A so that
these predictions can be compared to our observations.Comment: 12 pages, 3 figures, Accepted by ApJ Letters 2001 Jan
A Broadband Study of the Emission from the Composite Supernova Remnant MSH 11-62
MSH 11-62 (G291.1-0.9) is a composite supernova remnant for which radio and
X-ray observations have identified the remnant shell as well as its central
pulsar wind nebula. The observations suggest a relatively young system
expanding into a low density region. Here we present a study of MSH 11-62 using
observations with the Chandra, XMM-Newton, and Fermi observatories, along with
radio observations from the Australia Telescope Compact Array (ATCA). We
identify a compact X-ray source that appears to be the putative pulsar that
powers the nebula, and show that the X-ray spectrum of the nebula bears the
signature of synchrotron losses as particles diffuse into the outer nebula.
Using data from the Fermi LAT, we identify gamma-ray emission originating from
MSH 11-62. With density constraints from the new X-ray measurements of the
remnant, we model the evolution of the composite system in order to constrain
the properties of the underlying pulsar and the origin of the gamma-ray
emission.Comment: 12 Pages, 12 figures. Accepted for publication in the Astrophysical
Journa
Complete Analysis of Baryon Magnetic Moments in 1/N_c
We generate a complete basis of magnetic moment operators for the N_c = 3
ground-state baryons in the 1/N_c expansion, and compute and tabulate all
associated matrix elements. We then compare to previous results derived in the
literature and predict additional relations among baryon magnetic moments
holding to subleading order in 1/N_c and flavor SU(3) breaking. Finally, we
predict all unknown diagonal and transition magnetic moments to <= 0.15 mu_N
accuracy, and suggest possible experimental measurements to improve the
analysis even further.Comment: 28 pages (including 11 tables), ReVTeX. One reference and grant
acknowledgment adde
TCT-121 First Human Transcatheter Aortic Valve Implantation of the Colibri Heart Valve, A Pre-mounted, Pre-packaged, Low Profile Ready for Use, Dry Valve in a 14 French Delivery System. Six Months Follow up.
Localization for Yang-Mills Theory on the Fuzzy Sphere
We present a new model for Yang-Mills theory on the fuzzy sphere in which the
configuration space of gauge fields is given by a coadjoint orbit. In the
classical limit it reduces to ordinary Yang-Mills theory on the sphere. We find
all classical solutions of the gauge theory and use nonabelian localization
techniques to write the partition function entirely as a sum over local
contributions from critical points of the action, which are evaluated
explicitly. The partition function of ordinary Yang-Mills theory on the sphere
is recovered in the classical limit as a sum over instantons. We also apply
abelian localization techniques and the geometry of symmetric spaces to derive
an explicit combinatorial expression for the partition function, and compare
the two approaches. These extend the standard techniques for solving gauge
theory on the sphere to the fuzzy case in a rigorous framework.Comment: 55 pages. V2: references added; V3: minor corrections, reference
added; Final version to be published in Communications in Mathematical
Physic
Bosonizing one-dimensional cold atomic gases
We present results for the long-distance asymptotics of correlation functions
of mesoscopic one-dimensional systems with periodic and open (Dirichlet)
boundary conditions, as well as at finite temperature in the thermodynamic
limit. The results are obtained using Haldane's harmonic-fluid approach (also
known as ``bosonization''), and are valid for both bosons and fermions, in
weakly and strongly interacting regimes. The harmonic-fluid approach and the
method to compute the correlation functions using conformal transformations are
explained in great detail. As an application relevant to one-dimensional
systems of cold atomic gases, we consider the model of bosons interacting with
a zero-range potential. The Luttinger-liquid parameters are obtained from the
exact solution by solving the Bethe-ansatz equations in finite-size systems.
The range of applicability of the approach is discussed, and the prefactor of
the one-body density matrix of bosons is fixed by finding an appropriate
parametrization of the weak-coupling result. The formula thus obtained is shown
to be accurate, when compared with recent diffusion Montecarlo calculations,
within less than 10%. The experimental implications of these results for Bragg
scattering experiments at low and high momenta are also discussed.Comment: 39 pages + 14 EPS figures; typos corrected, references update
Elevation drives taxonomic, functional and phylogenetic β-diversity of phyllostomid bats in the Amazon biome
Aim: We evaluated the relative importance of geographical and environment variables for taxonomic, phylogenetic and functional β-diversity of phyllostomid bats along
the entire Amazon biome and specifically in the lowlands.
Location: Amazon biome.
Taxon: Chiroptera.
Methods: We carried out a bibliographic review and compiled a wide and unprecedented database of 106 phyllostomid bat species at 102 sites throughout the Amazon
biome. For all possible pairs of sites in both datasets, we estimated the Jaccard pairwise dissimilarity, that is, β-diversity, considering its three dimensions—taxonomic,
phylogenetic and functional—for its two components—turnover (substitution of species) and differences in species richness. The association between dissimilarity measurements and geographical and environment variables was assessed using multiple
regressions on distance matrices (MRM).
Results: We found that turnover and differences in species richness had similar contributions to the taxonomic β-diversity. However, for phylogenetic and functional
β-diversity, lineages and functions richness differences contribute slightly more than turnover for total β-diversity. In the lowlands, species, lineages and functions richness differences were slightly higher than turnover for all diversity dimensions. When
accounting for all the sites, elevation was the main predictor of phyllostomid bats'
taxonomic, phylogenetic and functional turnover. For lowland sites, ecoregions was
the main (but relatively weak) predictor associated with all β-diversity dimensions.
Main conclusions: Analysis of filtering sites according to elevation revealed that species in the Amazonian lowlands are taxonomically and phylogenetically different from
species in the Andes, and present taxonomic, phylogenetic and functional redundancy between assemblages. When accounting for the whole range of distribution of
bats, results showed the predominant effect of elevation over other geographical and
environmental predictors. This indicates that the diversity of good dispersers such as
bats is more affected by specialisation along environment and climatic gradients than
by geographical barriers throughout the Amazon biomeBat Conservation International;
Coordenação de Aperfeiçoamento de
Pessoal de Nível Superior; National
Geographic Society; Neotropical
Grassland Conservancy; Rufford
Foundatio
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