11,838 research outputs found
Some remarks on UV-radiation at "Reserva Florestal Ducke" forest pilot scheme near Manaus, Amazon
The N=1 effective actions of D-branes in Type IIA and IIB orientifolds
We discuss the four-dimensional N=1 effective actions of single space-time
filling Dp-branes in general Type IIA and Type IIB Calabi-Yau orientifold
compactifications. The effective actions depend on an infinite number of normal
deformations and gauge connection modes. For D6-branes the N=1 Kaehler
potential, the gauge-coupling function, the superpotential and the D-terms are
determined as functions of these fields. They can be expressed as integrals
over chains which end on the D-brane cycle and a reference cycle. The infinite
deformation space will reduce to a finite-dimensional moduli space of special
Lagrangian submanifolds upon imposing F- and D-term supersymmetry conditions.
We show that the Type IIA moduli space geometry is captured by three real
functionals encoding the deformations of special Lagrangian submanifolds,
holomorphic three-forms and Kaehler two-forms of Calabi-Yau manifolds. These
elegantly combine in the N=1 Kaehler potential, which reduces after applying
mirror symmetry to the results previously determined for space-time filling
D3-, D5- and D7-branes. We also propose general chain integral expressions for
the Kaehler potentials of Type IIB D-branes.Comment: 61 pages, v2: typos corrected and refs adde
Chaos in Periodically Perturbed Monopole + Quadrupole Like Potentials
The motion of a particle that suffers the influence of simple inner (outer)
periodic perturbations when it evolves around a center of attraction modeled by
an inverse square law plus a quadrupole-like term is studied. The equations of
motion are used to reduce the Melnikov method to the study of simple graphics.Comment: 12 pages, 6 Postscript figure
Visual observation to identify sexes in subspecies of adult Black Skimmers (Rynchops niger)
Identifying sexes in birds from visual observations could be a useful and inexpensive method. While sexual dichromatism and ornaments are readily used by observers, sexual size dimorphism can also be used to identify sexes in some bird species. This study assessed the applicability of visual observation of size differences to identify sexes in adult Black Skimmers (Rynchops niger). Black Skimmers do not have sexual dichromatism; however, Black Skimmer males are skeletally larger (6.7–31.7% depending on trait) and 33.3–37.5% heavier than females. The study focused on two subspecies: Amazonian (R. n. cinerascens) and South American (R. n. intercedens) Black Skimmers. Sex identified by visually observing size differences was consistent with the sex identified at specimen preparation from examining gonads (RGLMM = 0.996 ± 0.004). The identification of sexes from photographs using visual observation of size had a very high within- (RGLMM = 0.995 ± 0.001) and between- (RGLMM = 0.984 ± 0.002) observer repeatability. Non-invasive methods for identifying sex by visual observation may allow enhanced use of data from photographic datasets, citizen science projects, and surveys using direct observation or images
Using field photography to study avian moult
Methods to obtain moult data from wild birds have not changed much over the last century and most studies still depend on checking museum specimens or capturing birds. Here we assess the applicability of systematic field photography for detecting and scoring moult in adult Black Skimmers Rynchops niger from southern Brazil. Moult data extracted from photographs have a high within- (RGLMM = 0.98) and between-observer repeatability (RGLMM = 0.97) and show very good fit to current Underhill–Zucchini moult models (R2 = 0.75). Photography offers the advantages of being less invasive, requiring less equipment and human effort, being feasible in areas where captures may not be possible, and causing less disturbance, so enhancing the number of sampled individuals
Ion motion in the wake driven by long particle bunches in plasmas
We explore the role of the background plasma ion motion in self-modulated
plasma wakefield accelerators. We employ J. Dawson's plasma sheet model to
derive expressions for the transverse plasma electric field and ponderomotive
force in the narrow bunch limit. We use these results to determine the on-set
of the ion dynamics, and demonstrate that the ion motion could occur in
self-modulated plasma wakefield accelerators. Simulations show the motion of
the plasma ions can lead to the early suppression of the self-modulation
instability and of the accelerating fields. The background plasma ion motion
can nevertheless be fully mitigated by using plasmas with heavier plasmas.Comment: 23 pages, 6 figure
Stabilized jellium model and structural relaxation effects on the fragmentation energies of ionized silver clusters
Using the stabilized jellium model in two schemes of `relaxed' and `rigid',
we have calculated the dissociation energies and the fission barrier heights
for the binary fragmentations of singly-ionized and doubly-ionized Ag clusters.
In the calculations, we have assumed spherical geometries for the clusters.
Comparison of the fragmentation energies in the two schemes show differences
which are significant in some cases. This result reveals the advantages of the
relaxed SJM over the rigid SJM in dynamical processes such as fragmentation.
Comparing the relaxed SJM results and axperimental data on fragmentation
energies, it is possible to predict the sizes of the clusters just before their
fragmentations.Comment: 9 pages, 12 JPG figure
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