8,275 research outputs found
Ring Width Variation and Heartwood Development in Quercus Faginea
High-value exploitation of endogenous forest species may help in fighting the threat to their sustainability, as is the case for Quercus faginea Lam. (Portuguese oak) for which research is underway to determine the wood potential for high-quality products. Ring widths were measured in 20 trees in two sites in Portugal and within-tree heartwood and sapwood development was determined. The wood shows distinct ring porosity. The mean annual radial growth at dbh was 2.3 and 1.0 mm for the two sites, respectively. Ring width decreased with cambial age, ie 3.1 ± 1.2 mm in the first 10 rings to 1.3 ± 0.8 mm at around 40 yr (site 1). Ring width decreased axially from the tree base upward but the variation was small. The trees showed a relatively high proportion of heartwood, ie 60-70% heartwood for 20-25 cm wood diameters that decreased with height, and followed the stem profile. Heartwood diameter was modeled as a function of stem diameter, to be used for heartwood estimation in standing trees. Sapwood width was relatively constant. Overall the stem quality was found to be good for production of solid wood products regarding ring and heartwood features
BPS black holes, the Hesse potential, and the topological string
The Hesse potential is constructed for a class of four-dimensional N=2
supersymmetric effective actions with S- and T-duality by performing the
relevant Legendre transform by iteration. It is a function of fields that
transform under duality according to an arithmetic subgroup of the classical
dualities reflecting the monodromies of the underlying string compactification.
These transformations are not subject to corrections, unlike the
transformations of the fields that appear in the effective action which are
affected by the presence of higher-derivative couplings. The class of actions
that are considered includes those of the FHSV and the STU model. We also
consider heterotic N=4 supersymmetric compactifications. The Hesse potential,
which is equal to the free energy function for BPS black holes, is manifestly
duality invariant. Generically it can be expanded in terms of powers of the
modulus that represents the inverse topological string coupling constant,
, and its complex conjugate. The terms depending holomorphically on
are expected to correspond to the topological string partition function and
this expectation is explicitly verified in two cases. Terms proportional to
mixed powers of and are in principle present.Comment: 28 pages, LaTeX, added comment
Aplicação conjunta de rizobactérias e bactérias endofíticas para o biocontrole do Fusarium oxysporum f. sp. Cubense.
Bactérias endofíticas e rizobactérias têm sido relacionadas com o incremento da produção agrícola devido à sua atuação como promotoras do crescimento de plantas, ou biocontrole de doenças e pragas. Assim, o objetivo do trabalho foi selecionar rizobactérias e bactérias endofíticas e avaliar sua ação conjunta como agentes de biocontrole de Fusarium oxysporum f. sp. cubense (FOC)
Field propagation in de Sitter black holes
We present an exhaustive analysis of scalar, electromagnetic and
gravitational perturbations in the background of Schwarzchild-de Sitter and
Reissner-Nordstrom-de Sitter spacetimes. The field propagation is considered by
means of a semi-analytical (WKB) approach and two numerical schemes: the
characteristic and general initial value integrations. The results are compared
near the extreme cosmological constant regime, where analytical results are
presented. A unifying picture is established for the dynamics of different spin
fields.Comment: 15 pages, 16 figures, published versio
Quasi-normal modes of toroidal, cylindrical and planar black holes in anti-de Sitter spacetimes: scalar, electromagnetic and gravitational perturbations
We study the quasi-normal modes (QNM) of scalar, electromagnetic and
gravitational perturbations of black holes in general relativity whose horizons
have toroidal, cylindrical or planar topology in an asymptotically anti-de
Sitter (AdS) spacetime. The associated quasinormal frequencies describe the
decay in time of the corresponding test field in the vicinities of the black
hole. In terms of the AdS/CFT conjecture, the inverse of the frequency is a
measure of the dynamical timescale of approach to thermal equilibrium of the
corresponding conformal field theory.Comment: Latex, 16 pages. Minor change
Quasinormal modes of a Schwarzschild black hole surrounded by free static spherically symmetric quintessence: Electromagnetic perturbations
In this paper, we evaluated the quasinormal modes of electromagnetic
perturbation in a Schwarzschild black hole surrounded by the static spherically
symmetric quintessence by using the third-order WKB approximation when the
quintessential state parameter in the range of . Due to
the presence of quintessence, Maxwell field damps more slowly. And when at
, it is similar to the black hole solution in the ds/Ads
spacetime. The appropriate boundary conditions need to be modified.Comment: 6 pages, 3 figure
Quasinormal modes of d-dimensional spherical black holes with a near extreme cosmological constant
We derive an expression for the quasinormal modes of scalar perturbations in
near extreme d-dimensional Schwarzschild-de Sitter and Reissner-Nordstrom-de
Sitter black holes. We show that, in the near extreme limit, the dynamics of
the scalar field is characterized by a Poschl-Teller effective potential. The
results are qualitatively independent of the spacetime dimension and field
mass.Comment: 5 pages, REVTeX4, version to be published in Physical Review
A Note on Exact Solutions and Attractor Mechanism for Non-BPS Black Holes
We obtain two extremal, spherically symmetric, non-BPS black hole solutions
to 4D supergravity, one of which carries D2-D6 charges and the other carries
D0-D2-D4 charges. For the D2-D6 case, rather than solving the equations of
motion directly, we assume the form of the solution and then find that the
assumption satisfies the equations of motion and the constraint. Our D2-D6
solution is manifestly dual to the solution presented in 0710.4967. The
D0-D2-D4 solution is obtained by performing certain
duality transformations on the D0-D4 solution in 0710.4967.Comment: 20 pages, LaTe
One entropy function to rule them all
We study the entropy of extremal four dimensional black holes and five
dimensional black holes and black rings is a unified framework using Sen's
entropy function and dimensional reduction. The five dimensional black holes
and black rings we consider project down to either static or stationary black
holes in four dimensions. The analysis is done in the context of two derivative
gravity coupled to abelian gauge fields and neutral scalar fields. We apply
this formalism to various examples including minimal supergravity.Comment: 29 pages, 2 figures, revised version for publication, details adde
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