X-ray polarization: General formalism and polarization analysis

The polarization of x-rays plays an outstanding role in experimental techniques such as non-resonant magnetic x-ray scattering and resonant x-ray scattering of magnetic and multipolar order. Different instrumental methods applied to synchrotron light can transform its natural polarization into an arbitrary polarization state. Several synchrotron applications, in particular in the field of magnetic and resonant scattering rely on the improvement in the signal/noise ratio or the deeper insight into the ordered state and the scattering process made possible through these polarization techniques. Here, we present the mathematical framework for the description of fully and partially polarized x-rays, with some applications such as linear x-ray polarization analysis for the determination of the scattered beam's polarization, and the Ge K-edge resonant scattering.Comment: 12 pages, 6 figures and 1 table. To be published in proceedings of the workshop "Resonant Elastic X-ray Scattering", Aussois, France (2011

Competitive adsorption of phenolic compounds from aqueous solution using sludge‐based activated carbon.

Preparation of activated carbon from sewage sludge is a promising approach to produce cheap and efficient adsorbent for pollutants removal as well as to dispose of sewage sludge. The first objective of this study was to investigate the physical and chemical properties (BET surface area, ash and elemental content, surface functional groups by Boehm titration and weight loss by thermogravimetric analysis) of the sludge‐based activated carbon (SBAC) so as to give a basic understanding of its structure and to compare to those of two commercial activated carbons, PICA S23 and F22. The second and main objective was to evaluate the performance of SBAC for single and competitive adsorption of four substituted phenols (p‐nitrophenol, p‐chlorophenol, p‐hydroxy benzoic acid and phenol) from their aqueous solutions. The results indicated that, despite moderate micropore and mesopore surface areas, SBAC had remarkable adsorption capacity for phenols, though less than PICA carbons. Uptake of the phenolic compound was found to be dependent on both the porosity and surface chemistry of the carbons. Furthermore, the electronegativity and the hydrophobicity of the adsorbate have significant influence on the adsorption capacity. The Langmuir and Freundlich models were used for the mathematical description of the adsorption equilibrium for single‐solute isotherms. Moreover, the Langmuir–Freundlich model gave satisfactory results for describing multicomponent system isotherms. The capacity of the studied activated carbons to adsorb phenols from a multi‐solute system was in the following order: p‐nitrophenol > p‐chlorophenol > PHBA > phenol

A re-examination of the anatomy and systematics of the tomistomine crocodylians from the Miocene of Italy and Malta

Once a much more globally widespread crocodylian clade, Tomistominae is today represented by just one species, Tomistoma schlegelii (the false gharial), restricted to south-east Asia. Although tomistomine fossil occurrences are recognized from the early Eocene (∼55 Ma) onwards, their remains are often incomplete, making appropriate taxonomic classification within the group problematic. This is especially pertinent to several taxa from the Miocene of Europe, which were historically erected from fragmentary remains. Here we re-examine and describe four approximately contemporaneous taxa from Malta and Italy to determine their taxonomy and phylogenetic affinities: Melitosaurus champsoides, Tomistoma calaritanum, Tomistoma gaudense and Tomistoma lyceense. We place them into a phylogenetic analysis for the first time, comprising 70 taxa scored for 244 characters, several of which are revised or novel, and apply a number of character weighting strategies. Whereas ‘Tomistoma lyceense’ is deemed to be an indeterminate tomistomine, a unique combination of features confirms Melitosaurus champsoides, Tomistoma calaritanum and Tomistoma gaudense as three distinct species. These three taxa are recovered as derived tomistomines, with characters such as a posterior maxillary process between the lacrimal and nasal, large supratemporal fenestrae that are wider than long, and the posteromedial alignment of the last three premaxillary teeth, suggesting a close relationship with the approximately contemporaneous European taxa, Tomistoma lusitanica and Gavialosuchus eggenburgensis. It is unlikely that any of these species belong to Tomistoma, with the possibility that they can all be classified under Melitosaurus and Gavialosuchus. However, we retain them in open nomenclature pending reassessment of the remaining European Miocene tomistomines. Our taxonomic and phylogenetic revision helps to elucidate past tomistomine diversity in the Miocene of the Mediterranean region, prior to the group’s extirpation, and is an important first step in resolving the complicated history of European tomistomine systematics

An HST Imaging Survey of Low-Mass Stars in the Chamaeleon I Star Forming region

We present new HST/WFPC2 observations of 20 fields centered around T Tauri stars in the Chamaeleon I star forming region. Images have been obtained in the F631N ([OI]6300A), F656N (Ha) and F673N ([SII]6716A+6731A) narrow-band filters, plus the Johnson V-band equivalent F547M filter. We detect 31 T Tauri stars falling within our fields. We discuss the optical morphology of 10 sources showing evidence of either binarity, circumstellar material, or mass loss. We supplement our photometry with a compilation of optical, infrared and sub-millimeter data from the literature, together with new sub-mm data for three objects, to build the Spectral Energy Distributions (SED) of 19 single sources. Using an SED model fitting tool, we self-consistently estimate a number of stellar and disk parameters, while mass accretion rates are directly derived from our Ha photometry. We find that bolometric luminosities derived from dereddened optical data tend to be underestimated in systems with high alpha(2-24} IR spectral index, suggesting that disks seen nearly edge-on may occasionally be interpreted as low luminosity (and therefore more evolved) sources. On the other hand, the same alpha(2-24) spectral index, a tracer of the amount of dust in the warmer layers of the circumstellar disks, and the mass accretion rate appear to decay with the isocronal stellar age, suggesting that the observed age spread (~0.5-5 Myr) within the cluster is real. Our sample contains a few outliers that may have dissipated their circumstellar disks on shorter time-scale.Comment: to appear on Astronomical Journal, accepted April 16, 2012 (AJ-10740

Evaluation of changing surface water abstraction reliability for supplemental irrigation under climate change

In many temperate parts of the world, supplemental irrigation is crucial to assure both crop yield and quality. Climate change could increase the risks of irrigation being restricted by increasing crop water requirements and/or decreasing water availability. In England, water abstraction for irrigation is limited by maximum annual volumetric limits, as specified in the abstraction licences, and surface water abstraction restrictions imposed by the regulator during drought. This paper assesses how climate change might impact future irrigation abstraction reliability from surface water in England. Firstly, the probability of annual abstraction being close to the maximum licence limit was estimated for the baseline (1961–1990) and future (2071–2098) periods in each catchment based on observed relationships between annual weather and irrigation abstraction in three licence usage groups. Secondly, the current river discharge triggers for mandatory drought restrictions were used to assess the annual probability of surface water abstraction restrictions being imposed by the regulator in each period. Results indicate significant future increases in irrigated abstraction licence use due to an increase in aridity, particularly in the most productive agricultural areas located in eastern and southern England, assuming no adaptation. The annual probability of having less than 20% licence headroom in the highest usage group is projected to exceed 0.7 in 45% of the management units, mostly in the south and east. In contrast, irrigators in central and western England face an increased risk of drought restrictions due to the lower buffering capacity of groundwater on river flows, with the annual probability of mandatory drought restrictions reaching up to 0.3 in the future. Our results highlight the increasing abstraction reliability risks for irrigators due to climate change, and the need for the farming community and the regulator to adapt and collaborate to mitigate the associated impacts

HST measures of Mass Accretion Rates in the Orion Nebula Cluster

The present observational understanding of the evolution of the mass accretion rates (Macc) in pre-main sequence stars is limited by the lack of accurate measurements of Macc over homogeneous and large statistical samples of young stars. Such observational effort is needed to properly constrain the theory of star formation and disk evolution. Based on HST/WFPC2 observations, we present a study of Macc for a sample of \sim 700 sources in the Orion Nebula Cluster, ranging from the Hydrogen-burning limit to M\ast \sim 2M\odot. We derive Macc from both the U-band excess and the H{\alpha} luminosity (LH{\alpha}), after determining empirically both the shape of the typical accretion spectrum across the Balmer jump and the relation between the accretion luminosity (Lacc) and LH{\alpha}, that is Lacc/L\odot = (1.31\pm0.03)\cdotLH{\alpha}/L\odot + (2.63\pm 0.13). Given our large statistical sample, we are able to accurately investigate relations between Macc and the parameters of the central star such as mass and age. We clearly find Macc to increase with stellar mass, and decrease over evolutionary time, but we also find strong evidence that the decay of Macc with stellar age occurs over longer timescales for more massive PMS stars. Our best fit relation between these parameters is given by: log(Macc/M\odot\cdotyr)=(-5.12 \pm 0.86) -(0.46 \pm 0.13) \cdot log(t/yr) -(5.75 \pm 1.47)\cdot log(M\ast/M\odot) + (1.17 \pm 0.23)\cdot log(t/yr) \cdot log(M\ast/M\odot). These results also suggest that the similarity solution model could be revised for sources with M\ast > 0.5M\odot. Finally, we do not find a clear trend indicating environmental effects on the accretion properties of the sources.Comment: 17 pages, 15 figures, accepted for publication in Ap

Expression of a truncated form of hHb1 hair keratin in human breast carcinomas.

Human hHb1 belongs to the type II hard keratin family and is physiologically expressed in hair shafts. In the present study, using specific 3' and 5' probes for hHb1, we established that breast carcinomas ectopically express a hHb1 5'-truncated mRNA, and that this transcript is restricted to malignant epithelial cells. Furthermore, an in vitro study indicated that it could be translated. We concluded that, in breast carcinomas, expression of truncated hHb1 is related to epithelial cell transformation. Because the hHb1 gene maps to 12q11-q13, a chromosome region known to present several breakpoints in solid tumours, we propose that the hHb1 gene might represent a target for such alterations

RE2O3 dissolution kinetics and mechanisms in CAS silicate melt: Influence of the rare earth

Fine particles of sand, dust or volcanic ashes ingested by aircraft engines are well-known to damage 8YPSZ Thermal Barrier Coating (TBC). In service, these particles deposit on hot TBC surface (≥ 1200°C) as molten silicate and infiltrate coating porous microstructure. They are mainly constituted of CaO-MgO-Al2O3-SiO2 (CMAS) in variable proportions and also contain metallic oxides. Gd2Zr2O7 TBC has shown efficiency to mitigate synthetic CMAS infiltration due to its reactivity with CMAS [1]. Indeed, the dissolution reaction leads to rapid formation of a sealing-layer in the topcoat mainly constituted of crystalline Ca2Gd8(SiO4)6O2 apatite. However, this phase is not always stable in contact with CMAS and many rare-earth silicates may compete with apatite crystallization [2]. Several rare-earth oxides RE2O3 can be considered to replace yttria in ZrO2-based TBC but little is known on reaction kinetics and thermodynamics involving RE2O3 and multi-component CMAS system. Please click Additional Files below to see the full abstract