Ultra High Resolution Transmission Electron Microscopy of Matrix Mineral Grains in CM Chondrites: Preaccretionary or Parent Body Aqueous Processing?

CM chondrites are highly hydrated meteorites associated with a parent asteroid that has experienced significant aqueous processing. The meteoritic evidence indicates that these non-differentiated asteroids are formed by fine-grained minerals embedded in a nanometric matrix that preserves chemical clues of the forming environment. So far there are two hypothesis to explain the presence of hydrated minerals in the content of CM chondrites: one is based on textural features in chondrule-rim boundaries [1-3], and the other ‘preaccretionary’ hypothesis proposes the incorporation of hydrated phases from the protoplanetary disk [4-6]. The highly porous structure of these chondrites is inherited from the diverse materials present in the protoplanetary disk environment. These bodies were presumably formed by low relative velocity encounters that led to the accretion of silicate-rich chondrules, refractory Ca- and Al-rich inclusions (CAIs), metal grains, and the fine-grained materials forming the matrix. Owing to the presence of significant terrestrial water in meteorite finds [7], here we have focused on two CM chondrite falls with minimal terrestrial processing: Murchison and Cold Bokkeveld. Anhydrous carbonaceous chondrite matrices are usually represented by highly chemically unequilibrated samples that contain distinguishable stellar grains. Other chondrites have experienced hydration and chemical homogeneization that reveal parent body processes. We have studied CM chondrites because these meteorites have experienced variable hydration levels [8-10]. It is important to study the textural effects of aqueous alteration in the main minerals to decipher which steps and environments promote bulk chemistry changes, and create the distinctive alteration products. It is thought that aqueous alteration has particularly played a key role in modifying primordial bulk chemistry, and homogenizing the isotopic content of fine-grained matrix materials [7, 11, 12]. Fortunately, the mineralogy produced by parent-body and terrestrial aqueous alteration processes is distinctive [5, 11]

The collisional evolution of undifferentiated asteroids and the formation of chondritic meteoroids

Most meteorites are fragments from recent collisions experienced in the asteroid belt. In such a hyper-velocity collision, the smaller collision partner is destroyed, whereas a crater on the asteroid is formed or it is entirely disrupted, too. The present size distribution of the asteroid belt suggests that an asteroid with 100 km radius is encountered $10^{14}$ times during the lifetime of the Solar System by objects larger than 10 cm in radius; the formed craters cover the surface of the asteroid about 100 times. We present a Monte Carlo code that takes into account the statistical bombardment of individual infinitesimally small surface elements, the subsequent compaction of the underlying material, the formation of a crater and a regolith layer. For the entire asteroid, 10,000 individual surface elements are calculated. We compare the ejected material from the calculated craters with the shock stage of meteorites with low petrologic type and find that these most likely stem from smaller parent bodies that do not possess a significant regolith layer. For larger objects, which accrete a regolith layer, a prediction of the thickness depending on the largest visible crater can be made. Additionally, we compare the crater distribution of an object initially 100 km in radius with the shape model of the asteroid (21) Lutetia, assuming it to be initially formed spherical with a radius that is equal to its longest present ellipsoid length. Here, we find the shapes of both objects to show resemblance to each other.Comment: Accepted by Ap

Guías de práctica clínica en francés y español: análisis de la superestructura

The purpose of this paper is to provide elements that will help to further understand the clinical practice guideline genre in French and in Spanish, thereby facilitating the work of authors and translators. The study thus focuses on the analysis of the superstructure, with a view to offering guidelines for the construction of a sample prototype. First, we describe and define the genre in question. In the second section, we refer to the materials and methodological framework employed, describing the sub-domain chosen for analysis (rare diseases), the compilation and processing of the corpus and, finally, the research methodology implemented. The final section presents and discusses the results of the corpus analysis, which indicate the importance of advocating a single unique superstructure for the genre in question.El objetivo de este trabajo es proporcionar elementos que permitan un mejor conocimiento del género textual “guía de práctica clínica” en francés y en español que facilite su redacción y su traducción. Para ello, nos centramos en el estudio de la superestructura con la finalidad de ofrecer pautas para el establecimiento de un modelo prototípico. En primer lugar, se lleva a cabo una descripción y delimitación del género objeto de estudio. En segundo lugar, se recogen los datos relativos a los materiales y el marco metodológico, describiéndose el subdominio seleccionado (enfermedades raras), la compilación y el tratamiento del corpus, así como la metodología de investigación adoptada. En el apartado final, se presentan los datos obtenidos tras el análisis del corpus y se discuten los resultados, los cuales ponen de manifiesto la importancia de abogar por una estandarización superestructural del género

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

No abstract available

Preliminary study of the atmospheric pollen in "Sierra de las Nieves" Natural Park (Southern Spain)

‘Sierra de las Nieves’ is a Natural Park and a Biosphere Reserve located in the south of Spain. This protected area has a high diversity of ecosystems with abundant endangered species which have led it to be in ways to become a National Park. Some of those species have anemophilous pollination strategies. Since 1991, the Aerobiology research team of the University of Malaga has been sampling and studying airborne pollen in different cities of Malaga province. Nevertheless, a pollen trap has never been installed inside a Natural Park for a continuous sampling process. The objectives of this study were to determinate the atmospheric pollen behaviour of the main taxa registered during winter and spring months in this protected area, as well as compare the results with the data obtained in urban stations during the same period searching for significant differences. The pollen samplings were made by means of a Hirst-type volumetric pollen trap inside the protected area of the Natural Park. The samples obtained were mounted and counted according to the methodology proposed by the Spanish Aerobiology Network (REA). The high vegetal diversity of ‘Sierra de las Nieves’ are reflected in the pollen counts. Significant differences between the sampligs obtained at ‘Sierra de las Nieves’, Malaga and the neraby city of Ronda stations were found regarding to the daily pollen concentration. The qualitative and quantitative differences can be explained by the different land use, altitude, climatic characteristics and by the distance between aerobiological stations and pollen emission sources. There is an important influence of wind dymanic and others meteorological factors.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec