Weighted random--geometric and random--rectangular graphs: Spectral and eigenfunction properties of the adjacency matrix

Within a random-matrix-theory approach, we use the nearest-neighbor energy level spacing distribution $P(s)$ and the entropic eigenfunction localization length $\ell$ to study spectral and eigenfunction properties (of adjacency matrices) of weighted random--geometric and random--rectangular graphs. A random--geometric graph (RGG) considers a set of vertices uniformly and independently distributed on the unit square, while for a random--rectangular graph (RRG) the embedding geometry is a rectangle. The RRG model depends on three parameters: The rectangle side lengths $a$ and $1/a$, the connection radius $r$, and the number of vertices $N$. We then study in detail the case $a=1$ which corresponds to weighted RGGs and explore weighted RRGs characterized by $a\sim 1$, i.e.~two-dimensional geometries, but also approach the limit of quasi-one-dimensional wires when $a\gg1$. In general we look for the scaling properties of $P(s)$ and $\ell$ as a function of $a$, $r$ and $N$. We find that the ratio $r/N^\gamma$, with $\gamma(a)\approx -1/2$, fixes the properties of both RGGs and RRGs. Moreover, when $a\ge 10$ we show that spectral and eigenfunction properties of weighted RRGs are universal for the fixed ratio $r/{\cal C}N^\gamma$, with ${\cal C}\approx a$.Comment: 8 pages, 6 figure

Disrupted asteroid P/2016 G1. II. Follow-up observations from the Hubble Space Telescope

After the early observations of the disrupted asteroid P/2016 G1 with the 10.4m Gran Telescopio Canarias (GTC), and the modeling of the dust ejecta, we have performed a follow-up observational campaign of this object using the Hubble Space Telescope (HST) during two epochs (June 28 and July 11, 2016). The analysis of these HST images with the same model inputs obtained from the GTC images revealed a good consistency with the predicted evolution from the GTC images, so that the model is applicable to the whole observational period from late April to early July 2016. This result confirms that the resulting dust ejecta was caused by a relatively short-duration event with onset about 350 days before perihelion, and spanning about 30 days (HWHM). For a size distribution of particles with a geometric albedo of 0.15, having radii limits of 1 $\mu$m and 1 cm, and following a power-law with index --3.0, the total dust mass ejected is $\sim$2$\times$10$^7$ kg. As was the case with the GTC observations, no condensations in the images that could be attributed to a nucleus or fragments released after the disruption event were found. However, the higher limiting magnitude reachable with the HST images in comparison with those from GTC allowed us to impose a more stringent upper limit to the observed fragments of $\sim$30 m.Comment: 10 pages, 2 figures Accepted by Astronomical Journal, Nov. 2, 201

Ancient Martian Floods in a Plausible Variable Climatic Environment as Revealed from the Sequential Growth of Allan Hills 84001 Carbonate Globules

No abstract available

Análisis y validación de modelos digitales de elevaciones mediante datos LIDAR

entre otras, siendo en muchas ocasiones uno de los factores determinantes de la calidad de sus estudios. En este trabajo se realiza un análisis comparativo entre Modelos Digitales de Elevaciones (MDE) generados mediante diferentes métodos de interpolación y uno obtenido mediante tecnología LIDAR. De esta forma, asumiendo este último como verdad-terreno, se establece cual de los modelos interpolados representa con mayor fidelidad la superficie terrestre. Las técnicas de interpolación utilizadas han sido la lineal, splines, TIN y ANUDEM obteniendo un total de 4 MDEs interpolados. El análisis de los errores en los diferentes modelos se ha llevado a cabo mediante tres procedimientos 1. Análisis de la distribución del error de las elevaciones en los MDEs interpolados. 2. Evaluación de los errores en varias capas de variables derivadas del MDE 3. Evaluación de los errores de localización de las redes de drenaje extraídas de los diferentes modelos respecto a la red generada a partir del modelo LIDAR. Con respecto a la ubicación de la red de drenaje, se han estimado dos tipos de error: error de omisión y error de comisión.Terrain modelling is an important task in many scientific areas such as climatology, hydrology among others, with a deep influence on the quality of the results. In this work we make a comparative analysis of Digital Elevation Model (DEM) generated by different interpolation algorithms with one obtained by LIDAR technology, assuming the later as ground truth. Four different interpolation algorithms have been used: linear splines, TIN and ANUDEM, that means a total of four interpolated DEMs. The analysis of errors in the different models was carried out with three different procedures: 1. Error distribution analysis in the interpolated DEMs. 2. Error evaluation in terrain parameters derived from DEM. 3. Analysis of the positional errors in the extract

Clasificación geomorfométrica a partir de datos lidiar en un área minera degradada

Las características del cualquier entorno varían considerablemente en función de la topografía, siendo un factor indispensable a tener en cuenta en cualquier estudio, y más concretamente en la Sierra Minera de Cartagena – La Unión; zona de clima semiárido en la que históricamente ha tenido lugar una gran actividad de minería extractiva que ha modificado todos sus componentes morfológicos (relieve, pendiente, etc.), resultando por tanto de especial interés la clasificación de los elementos geomorfológicos allí presentes. En este estudio se ha utilizado un Modelo Digital de Elevaciones (MDE) de 4 metros de resolución espacial obtenido a partir de un vuelo LiDAR (Light Detection and Ranging) con el objetivo de hacer una clasificación geomorfométrica. Para ello, se realiza una primera aproximación a la realidad de la zona de estudio mediante una clasificación no supervisada, utilizando como técnica cluster el algoritmo ISODATA (Iterative Self- Organizing Data Analysis Technique), e introduciendo los atributos topográficos derivados directamente del MDE para caracterizar las clases. Asimismo, se realiza una clasificación supervisada basada en áreas de entrenamiento de los principales elementos geomorfológicos.The characteristics of any environment vary widely in relation with the topography, being an indispensable factor to take into account in any study, and more specifically in the mining range of Cartagena - La Unión. It is a semiarid area in which, historically, large mining activity has changed all its morphological components (relief, slope, etc..), being of special interest the classification of its geomorphological elements. The data used in the classifications were derived from a four-meter grid LIDAR- DEM. Firstly, we perform an approximation to the reality of the study area by unsupervised classification, using the ISODATA (Iterative Self- Organizing Data Analysis Technique) algorithm cluster technique, introducing the topographic attributes derived directly from the DEM to characterize classes. Also a supervised classification based on training areas of the main geomorphological elements is performed

Étude de la corrosion du cuivre par microélectrochimie: Comparaison entre microélectrode et microcellule

Ce travail présente la comparaison de mesures électrochimiques réalisées à l'aide d'une microcellule et de microélectrodes conventionnelles. Des mesures de voltamétrie cyclique et d’impédances électrochimiques ont été réalisées sur des électrodes de cuivre pur, électrode classique couplée à des capillaires et microélectrodes, au potentiel de corrosion dans une solution NaCl 0,1 M, La comparaison entre ces deux types de mesure apporte des informations relatives à leurs sensibilités et limitations. En particulier, le domaine des basses fréquences du diagramme d’impédance est sensible à la géométrie de la microcellule ainsi qu'au positionnement relatif des électrodes