25,873 research outputs found
Resonance expansions in quantum mechanics
The goal of this contribution is to discuss various resonance expansions that
have been proposed in the literature.Comment: 10 pages and 1 figure; presented at the Istanbul workshop on
pseudo-Hermitian Hamiltonian
Comparison of |Q|=1 and |Q|=2 gauge-field configurations on the lattice four-torus
It is known that exactly self-dual gauge-field configurations with
topological charge |Q|=1 cannot exist on the untwisted continuum 4-torus. We
explore the manifestation of this remarkable fact on the lattice 4-torus for
SU(3) using advanced techniques for controlling lattice discretization errors,
extending earlier work of De Forcrand et. al. for SU(2). We identify three
distinct signals for the instability of |Q|=1 configurations, and show that
these manifest themselves early in the cooling process, long before the
would-be instanton has shrunk to a size comparable to the lattice
discretization threshold. These signals do not appear for our |Q|=2
configurations. This indicates that these signals reflect the truly global
nature of the instability, rather than local discretization effects.
Monte-Carlo generated SU(3) gauge field configurations are cooled to the
self-dual limit using an O(a^4)-improved gauge action chosen to have small but
positive O(a^6) errors. This choice prevents lattice discretization errors from
destroying instantons provided their size exceeds the dislocation threshold of
the cooling algorithm. Lattice discretization errors are evaluated by comparing
the O(a^4)-improved gauge-field action with an O(a^4)-improved action
constructed from the square of an O(a^4)-improved lattice field-strength
tensor, thus having different O(a^6) discretization errors. The number of
action-density peaks, the instanton size and the topological charge of
configurations is monitored. We observe a fluctuation in the total topological
charge of |Q|=1 configurations, and demonstrate that the onset of this unusual
behavior corresponds with the disappearance of multiple-peaks in the action
density. At the same time discretization errors are minimal.Comment: 12 pages, 9 figures, submitted to Phys. Rev.
On field theory quantization around instantons
With the perspective of looking for experimentally detectable physical
applications of the so-called topological embedding, a procedure recently
proposed by the author for quantizing a field theory around a non-discrete
space of classical minima (instantons, for example), the physical implications
are discussed in a ``theoretical'' framework, the ideas are collected in a
simple logical scheme and the topological version of the Ginzburg-Landau theory
of superconductivity is solved in the intermediate situation between type I and
type II superconductors.Comment: 27 pages, 5 figures, LaTe
Modelling Tropical Deforestation: A Comparison of Approaches
International audienceTropical deforestation, as an important factor in global change, is a topic that recently has received considerable attention. GIS-based spatially explicit models that intend to predict the location of land use/cover change (LUCC) can help scientists and policy makers to understand, anticipate and possibly prevent the adverse effects of land-use change. There are many approaches and softwares to model LUCC such as CLUE-S, DINAMICA GEOMOD and IDRISI. This study intends to compare these four modelling approaches. First, a review of methods and tools employed by each software to carry out the simulation was done. Then, the four packages were applied to a "virtual" case which involves a map of deforestation, which comprises two types of deforestation (forest to shifting agriculture and forest to pasture lands), along with several explanatory variables (drivers). Deforestation was modelled using the four approaches and the output maps were compared
Instantons and Condensate
We argue that the is similar to .Comment: 6 pages, 1 fig., 1 tab., RevTeX to be use
Chiral fermions and torsion in the early Universe
Torsion arising from fermionic matter in the Einstein-Cartan formulation of
general relativity is considered in the context of Robertson-Walker geometries
and the early Universe. An ambiguity in the way torsion arising from hot
fermionic matter in chiral models should be implemented is highlighted and
discussed. In one interpretation, chemical potentials in chiral models can
contribute to the Friedmann equation and give a negative contribution to the
energy density.Comment: 5 pages revtex4; error in v1 corrected
Morphological traits and type of dairy goats registered in Brazil from 1976 to 2009.
Abstract: Data from 2439 goats of the Saanen, Alpine, Anglo Nubian and Toggenburg breeds recorded from 1976 to 2009 by the Association of Goats and Sheep Breeders of Minas Gerais were used in principal component analysis. After consistency of data, six morphological variables (thorax perimeter, body length, withers height, height, width and length of the rump) and 12 variables related to breed standard score and fitness (breed characteristic, head, palette and topline, feet and legs, dairy type, body capacity, udder, rear and front ligament, udder texture, teat and final score) were analyzed. Based on the magnitude of the eigenvalue (lower than 0.7), eleven variables considered redundant were discarded, resulting in reduced costs of technician labor to evaluate the animals. Maintenance of records on height, length, rump width, breed characteristic, dairy type, front ligament and udder texture is recommended
Molecular genetic evaluation of the Stylosanthes capitata Vog. and Stylosanthes macrocephala Ferr. et Costa germoplasms.
Ticks on Didelphis albiventris from a Cerrado area in the Midwestern Brazil.
This experiment studied tick fauna associated to Didelphis albiventris Lund 1840 from a Cerrado area (Mato Grosso do Sul State, non-adjoining to Pantanal) inserted in a pasture and agricultural activities matrix, with few natural preserved forest patches. Authors also summarized data on ticks parasitizing Didelphis spp. in Brazil, and discussed infestation patterns in different biomes and locations. Study took place in Cervinho Farm, Bandeirantes Municipality. For captures, Tomahawk-like traps were distributed along two forest patches (30 each) during five nights. Captures occurred monthly (July/2013 to September/2014), sampling both fragments on alternate months. Animals were sedated and ticks were collected and stored in vials containing ethanol (70%) for identification. 51 D. albiventris were captured in 15 campaigns. Tick prevalence was 100%, and 49.5% of the animals were co-infested by two or more tick species. Four parasitizing species were found: Amblyomma sculptum Berlese, 1888 (78 nymphs), Ixodes loricatus Neumann, 1899 (56 adults), Amblyomma dubitatum Neumann, 1899 (45 nymphs), Amblyomma coelebs Neumann, 1899 (32 nymphs) and Amblyomma sp. (123 larvae). A. sculptum was the most abundant tick, but most frequent species were A. coelebs and A. dubitatum, followed by I. loricatus. Co-occurrences of more than two species were observed among all tick pairs. D. albiventris usually presents high prevalence of tick infestation. However, this study presented 100% prevalence. Knowledge of host-parasite relation and interactions between different ticks that coexist on a same host are essential, since such interaction may favor pathogen dissemination. This is of special relevance regarding D. albiventris, known for participating in maintenance of ecological cycles of Spotted Fever Group rickettsiae
An Imaging Survey of Early-Type Barred Galaxies
This paper presents the results of a high-resolution imaging survey, using
both ground-based and Hubble Space Telescope images, of a complete sample of
nearby barred S0--Sa galaxies in the field, with a particular emphasis on
identifying and measuring central structures within the bars: secondary bars,
inner disks, nuclear rings and spirals, and off-plane dust. A discussion of the
frequency and statistical properties of the various types of inner structures
has already been published. Here, we present the data for the individual
galaxies and measurements of their bars and inner structures. We set out the
methods we use to find and measure these structures, and how we discriminate
between them. In particular, we discuss some of the deficiencies of ellipse
fitting of the isophotes, which by itself cannot always distinguish between
bars, rings, spirals, and dust, and which can produce erroneous measurements of
bar sizes and orientations.Comment: LaTeX, 66 pages (including 42 figures, 36 in color). To appear in The
Astrophysical Journal Supplement. Full-resolution and text-only versions
available at http://www.iac.es/galeria/erwin/research
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