61,024 research outputs found
Phylogenetics of Olea (Oleaceae) based on plastid and nuclear ribosomal DNA sequences: Tertiary climatic shifts and lineage differentiation times
Background and Aims The genus Olea (Oleaceae) includes approx. 40 taxa of evergreen shrubs and trees classified in three subgenera, Olea, Paniculatae and Tetrapilus, the first of which has two sections (Olea and Ligustroides). Olive trees (the O. europaea complex) have been the subject of intensive research, whereas little is known about the phylogenetic relationships among the other species. To clarify the biogeographical history of this group, a molecular analysis of Olea and related genera of Oleaceae is thus necessary. Methods A phylogeny was built of Olea and related genera based on sequences of the nuclear ribosomal internal transcribed spacer-1 and four plastid regions. Lineage divergence and the evolution of abaxial peltate scales, the latter character linked to drought adaptation, were dated using a Bayesian method. Key Results Olea is polyphyletic, with O. ambrensis and subgenus Tetrapilus not sharing a most recent common ancestor with the main Olea clade. Partial incongruence between nuclear and plastid phylogenetic reconstructions suggests a reticulation process in the evolution of subgenus Olea. Estimates of divergence times for major groups of Olea during the Tertiary were obtained. Conclusions This study indicates the necessity of revising current taxonomic boundaries in Olea. The results also suggest that main lines of evolution were promoted by major Tertiary climatic shifts: (1) the split between subgenera Olea and Paniculatae appears to have taken place at the Miocene-Oligocene boundary; (2) the separation of sections Ligustroides and Olea may have occurred during the Early Miocene following the Mi-1 glaciation; and (3) the diversification within these sections (and the origin of dense abaxial indumentum in section Olea) was concomitant with the aridification of Africa in the Late Miocen
Conserved charges for black holes in Einstein-Gauss-Bonnet gravity coupled to nonlinear electrodynamics in AdS space
Motivated by possible applications within the framework of anti-de Sitter
gravity/Conformal Field Theory (AdS/CFT) correspondence, charged black holes
with AdS asymptotics, which are solutions to Einstein-Gauss-Bonnet gravity in D
dimensions, and whose electric field is described by a nonlinear
electrodynamics (NED) are studied. For a topological static black hole ansatz,
the field equations are exactly solved in terms of the electromagnetic stress
tensor for an arbitrary NED Lagrangian, in any dimension D and for arbitrary
positive values of Gauss-Bonnet coupling. In particular, this procedure
reproduces the black hole metric in Born-Infeld and conformally invariant
electrodynamics previously found in the literature. Altogether, it extends to
D>4 the four-dimensional solution obtained by Soleng in logarithmic
electrodynamics, which comes from vacuum polarization effects. Fall-off
conditions for the electromagnetic field that ensure the finiteness of the
electric charge are also discussed. The black hole mass and vacuum energy as
conserved quantities associated to an asymptotic timelike Killing vector are
computed using a background-independent regularization of the gravitational
action based on the addition of counterterms which are a given polynomial in
the intrinsic and extrinsic curvatures.Comment: 30 pages, no figures; a few references added; final version for PR
An efficient estimator for locally stationary Gaussian long-memory processes
This paper addresses the estimation of locally stationary long-range
dependent processes, a methodology that allows the statistical analysis of time
series data exhibiting both nonstationarity and strong dependency. A
time-varying parametric formulation of these models is introduced and a Whittle
likelihood technique is proposed for estimating the parameters involved. Large
sample properties of these Whittle estimates such as consistency, normality and
efficiency are established in this work. Furthermore, the finite sample
behavior of the estimators is investigated through Monte Carlo experiments. As
a result from these simulations, we show that the estimates behave well even
for relatively small sample sizes.Comment: Published in at http://dx.doi.org/10.1214/10-AOS812 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Holographic correlation functions in Critical Gravity
We compute the holographic stress tensor and the logarithmic energy-momentum
tensor of Einstein-Weyl gravity at the critical point. This computation is
carried out performing a holographic expansion in a bulk action supplemented by
the Gauss-Bonnet term with a fixed coupling. The renormalization scheme defined
by the addition of this topological term has the remarkable feature that all
Einstein modes are identically cancelled both from the action and its
variation. Thus, what remains comes from a nonvanishing Bach tensor, which
accounts for non-Einstein modes associated to logarithmic terms which appear in
the expansion of the metric. In particular, we compute the holographic
-point functions for a generic boundary geometric source.Comment: 21 pages, no figures,extended discussion on two-point functions,
final version to appear in JHE
Spiky ice and penitente tilting
Indexación: Scopus.Under certain conditions, at high altitude, the surface of snow develops spike-like structures known as penitentes. This is a rather counterintuitive phenomenon, which is a consequence of surface sublimation at a given point as a result of the incidence of light scattered by the surrounding region. Following the existing literature, we model the time evolution of the phenomenon described above as a 1D diffusion equation with a non-local source term, as it represents the light coming from all the line of sight defined for a point of the curve. For small initial perturbations in the surface, the system undergoes a thermodynamic instability which triggers the formation of spikes. For sunlight coming in at a given angle, numerical simulations account for a feature observed in the real system: penitentes get tilted in the direction of the sunlight. © Published under licence by IOP Publishing Ltd.We thank R. Rojas and R. Soto for interesting discussions. P.G. was financially supported by Facultad de Ciencias Exactas, UNAB, to attend SOCHIFI 2016 Meeting.https://iopscience.iop.org/article/10.1088/1742-6596/1043/1/01200
- …