On the invariant symmetries of the D\mathcal{D}-metrics

We analyze the symmetries and other invariant qualities of the $\mathcal{D}$-metrics (type D aligned Einstein Maxwell solutions with cosmological constant whose Debever null principal directions determine shear-free geodesic null congruences). We recover some properties and deduce new ones about their isometry group and about their quadratic first integrals of the geodesic equation, and we analyze when these invariant symmetries characterize the family of metrics. We show that the subfamily of the Kerr-NUT solutions are those admitting a Papapetrou field aligned with the Weyl tensor.Comment: 18 pages; v2: minor change

Past and present potential distribution of the Iberian Abies species: A phytogeographic approach using pollen data and species distribution models

This is the accepted version of the following article: Alba-Sánchez, F., López-Sáez, J. A., Pando, B. B.-d., Linares, J. C., Nieto-Lugilde, D. and López-Merino, L. (2010), Past and present potential distribution of the Iberian Abies species: a phytogeographic approach using fossil pollen data and species distribution models. Diversity and Distributions, 16: 214–228, which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1111/j.1472-4642.2010.00636.x/abstract.Aim - Quaternary palaeopalynological records collected throughout the Iberian Peninsula and species distribution models (SDMs) were integrated to gain a better understanding of the historical biogeography of the Iberian Abies species (i.e. Abies pinsapo and Abies alba). We hypothesize that SDMs and Abies palaeorecords are closely correlated, assuming a certain stasis in climatic and topographic ecological niche dimensions. In addition, the modelling results were used to assign the fossil records to A. alba or A. pinsapo, to identify environmental variables affecting their distribution, and to evaluate the ecological segregation between the two taxa. Location - The Iberian Peninsula. Methods - For the estimation of past Abies distributions, a hindcasting process was used. Abies pinsapo and A. alba were modelled individually, first calibrating the model for their current distributions in relation to the present climate, and then projecting it into the past—the last glacial maximum (LGM) and the Middle Holocene periods—in relation to palaeoclimate simulations. The resulting models were compared with Iberian-wide fossil pollen records to detect areas of overlap. Results - The overlap observed between past Abies refugia—inferred from fossil pollen records—and the SDMs helped to construct the Quaternary distribution of the Iberian Abies species. SDMs yielded two well-differentiated potential distributions: A. pinsapo throughout the Baetic mountain Range and A. alba along the Pyrenees and Cantabrian Range. These results propose that the two taxa remained isolated throughout the Quaternary, indicating a significant geographical and ecological segregation. In addition, no significant differences were detected comparing the three projections (present-day, Mid-Holocene and LGM), suggesting a relative climate stasis in the refuge areas during the Quaternary. Main conclusions - Our results confirm that SDM projections can provide a useful complement to palaeoecological studies, offering a less subjective and spatially explicit hypothesis concerning past geographic patterns of Iberian Abies species. The integration of ecological-niche characteristics from known occurrences of Abies species in conjunction with palaeoecological studies could constitute a suitable tool to define appropriate areas in which to focus proactive conservation strategies.The Andalusian Innovation, Science, and Industry Regional Ministry and the National Plan of the Spanish Government

Vacuum type I spacetimes and aligned Papapetrou fields: symmetries

We analyze type I vacuum solutions admitting an isometry whose Killing 2--form is aligned with a principal bivector of the Weyl tensor, and we show that these solutions belong to a family of type I metrics which admit a group $G_3$ of isometries. We give a classification of this family and we study the Bianchi type for each class. The classes compatible with an aligned Killing 2--form are also determined. The Szekeres-Brans theorem is extended to non vacuum spacetimes with vanishing Cotton tensor.Comment: 19 pages; a reference adde

Sideritis royoi (Lamiaceae): A New Orophilous Species from Northeastern Spain

Sideritis royoi is found in the rocky limestone habitats of the Port Massif (southern Catalonia, Spain). The species was first collected by the local botanist Lluís de Torres in the late part of the 20th century, but the specimens have remained unidentified positively in herbaria for over 40 years. Sideritis royoi likely belongs to section Sideritis subsection Hyssopifoliae and shows some morphological affinities with the relatively widespread South European species S. hyssopifolia L., but it differs from this species because it has subspinescent upper leaves, the main surfaces of its leaves are glabrous or glabrescent, the main abaxial surface of its bracts is without eglandular hairs, and due to the fact that it has shorter inflorescences. Weaker similarities have also been observed with some species belonging to S. subsection Fruticulosae Obón & D.Rivera. In this paper, a description for the new orophilous species is provided, along with a detailed illustration, field photographs, and a comparison with closely related species. We include an assessment of its conservation status and a dichotomous key for the identification of all the species of Sideritis subsection Hyssopifoliae

An intrinsic characterization of 2+2 warped spacetimes

We give several equivalent conditions that characterize the 2+2 warped spacetimes: imposing the existence of a Killing-Yano tensor $A$ subject to complementary algebraic restrictions; in terms of the projector $v$ (or of the canonical 2-form $U$) associated with the 2-planes of the warped product. These planes are principal planes of the Weyl and/or Ricci tensors and can be explicitly obtained from them. Therefore, we obtain the necessary and sufficient (local) conditions for a metric tensor to be a 2+2 warped product. These conditions exclusively involve explicit concomitants of the Riemann tensor. We present a similar analysis for the conformally 2+2 product spacetimes and give an invariant classification of them. The warped products correspond to two of these invariant classes. The more degenerate class is the set of product metrics which are also studied from an invariant point of view.Comment: 18 pages; submitted to Class. Quantum Grav

Simulación en ordenadores de una cadena completa de transmisión de mensajes binarios en códigos BCH, con decodificación para corrección de errores múltiples

La finalidad última do codificación y decodificación es conseguir que el mensaje reconstituido sea idéntico al original. Sin la teoría de códigos los mensajes binarios se caracterizan por vectores o también por polinomios con coeficientes pertenecientes al cuerpo dé Galois GF [0,l]. Sobre los conceptos de código, código lineal, código cíclico,generación polinómica de códigos, distancia, síndrome, relaciones con los elementos de un cuerpo finito, detección y corrección, etc., el mejor autor de referencia sigue siendo Peterso

Relativistic positioning: four-dimensional numerical approach in Minkowski space-time

We simulate the satellite constellations of two Global Navigation Satellite Systems: Galileo (EU) and GPS (USA). Satellite motions are described in the Schwarzschild space-time produced by an idealized spherically symmetric non rotating Earth. The trajectories are then circumferences centered at the same point as Earth. Photon motions are described in Minkowski space-time, where there is a well known relation, Coll, Ferrando & Morales-Lladosa (2010), between the emission and inertial coordinates of any event. Here, this relation is implemented in a numerical code, which is tested and applied. The first application is a detailed numerical four-dimensional analysis of the so-called emission coordinate region and co-region. In a second application, a GPS (Galileo) satellite is considered as the receiver and its emission coordinates are given by four Galileo (GPS) satellites. The bifurcation problem (double localization) in the positioning of the receiver satellite is then pointed out and discussed in detail.Comment: 16 pages, 9 figures, published (online) in Astrophys. Space Sc

Sobre la circunscripción y posición taxonómica de Centaurea caballeroi (Compositae)

Se aportan datos sobre algunos táxones del grupo de Centaurea linifolia presentes en las sierras de la Comunidad Valenciana y áreas limítrofes. Como resultado se propone reconocer en C. antennata tres subespecies, con síndromes de caracteres propios, que ocupan áreas geográficas bien delimitadas y presentan un comportamiento ecológico diferenciado. Según esto, se propone la nueva combinación C. antennata subsp. caballeroi para las poblaciones del sur de Tarragona y norte de Castellón, seleccionándose además un lectótipo. Para cada taxon aceptado se indican sus caracteres morfológicos diferenciales, distribución y ecología. Además, se aporta una clave de identificación.Data are reported on several taxa of the aggregate of Centaurea linifolia that grow in the mountains of the Valencian Community and neighboring areas. As a result, in the complex of C. antennata three taxa are accepted at the subspecific rank, which have their own syndrome of morphological characters, occur in well-defined territories and show different ecological behavior. The new combination C. antennata subsp. caballeroi is stated to name populations from southern Tarragona and northern Castellón provinces. Moreover, a lectotype is selected for the latter name. For each accepted taxon, its diagnostic morphological traits, distribution and ecology are commented. An identification key is also presented

On the Weyl transverse frames in type I spacetimes

We apply a covariant and generic procedure to obtain explicit expressions of the transverse frames that a type I spacetime admits in terms of an arbitrary initial frame. We also present a simple and general algorithm to obtain the Weyl scalars $\Psi_2^T$, $\Psi_0^T$ and $\Psi_4^T$ associated with these transverse frames. In both cases it is only necessary to choose a particular root of a cubic expression.Comment: 12 pages, submitted to Gen. Rel. Grav. (6-3-2004