Free-energy profiles along reduction pathways of MoS2 M-edge and S-edge by dihydrogen: a first-principles study

We present the results of DFT calculations of free energy profiles along the reaction pathways starting from 50% coverage of MoS2 M-edge and 100% coverage of S-edge by sulfur, and leading to 37% coverage, i.e. creation of anionic vacancies, upon reduction by dihydrogen and production of H2S. Significant entropic and enthalpic corrections to electronic energies are deduced from the sets of normal modes vibration frequencies computed for all stationary and transition states. On that basis, we revisit and discuss the surface phase diagrams for M- and S- edges as a function of temperature, H2 partial pressure and H2S/H2 molar ratio, with respect to ranges of conditions relevant to industrial hydrotreating operations. We show that in such conditions, anionic vacancies on the M-edge, and surface SH groups on the M- and S- edges, may coexist at equilibrium. Moderate activation barriers connect stationary states along all paths explored

Similar patterns of patterns of community organization characterize distinct groups of different trophic levels in the plankton of the NW Mediterranean Sea

International audiencePlanktonic populations were sampled over a 4 week period in the NW Mediterranean, at a site subject to little vertical advection during the Dynaproc 2 cruise in 2004. The characteristics of the phytoplankton, the tintinnid community and the zooplankton have recently been described in detail. Based on these studies, we compared the characteristics of 3 well-circumscribed assemblages of different trophic levels: Ceratium of the phytoplankton, herbivorous tintinnids of the microzooplankton, and large (>500μm) omnivorous and carnivorous copepods of the metazoan zooplankton. In all three groups, diversity as H' or species richness, wasless variable than concentration of organisms. Plotting time against species accumulation, the curves approached plateau values for Ceratium spp, tintinnids and large copepods but only a small number of species were consistently present (core species) and these accounted for most of the populations. or Ceratium core species numbered 10, for tintinnids 11 species, and for large copepods, core species numbered 4 during the day and 16 at night. Ceratium, tintinnids and large copepods showed some similar patterns of community structure in terms of species abundance distributions. Ceratium species were distributed in a log-normal pattern. Tintinnid species showed a log-series distribution. Large copepod assemblages were highly dominated with night samples showing much higher abundances and greater species richness than day samples. However, species abundance distributions were similar between day and night and were mostly log- normal. The paradox of the plankton, describing phytoplankton communities as super-saturated with species, extends to the microzooplankton and zooplankton

Electronic structure of NiS_{1-x}Se_x

We investigate the electronic structure of the metallic NiS$_{1-x}$Se$_x$ system using various electron spectroscopic techniques. The band structure results do not describe the details of the spectral features in the experimental spectrum, even for this paramagnetic metallic phase. However, a parameterized many-body multi-band model is found to be successful in describing the Ni~2$p$ core level and valence band, within the same model. The asymmetric line shape as well as the weak intensity feature in the Ni~2$p$ core level spectrum has been ascribed to extrinsic loss processes in the system. The presence of satellite features in the valence band spectrum shows the existence of the lower Hubbard band, deep inside the $pd$ metallic regime, consistent with the predictions of the dynamical mean field theory.Comment: To be published in Physical Review B, 18 pages and 5 figure

Commentaires sur le Premier Code des Lois de Huahine: E Ture No Huahine (1822-1823)

Le 5 mars 1797 débarquèrent du «Duff», les premiers missionnaires de la London Missionary Society. Ils commencèrent l’évangélisation des populations au début du XIXème siècle, tout d’abord à Tahiti et Moorea, puis dans les îles-sous-le-vent. Avec la progression du christianisme, des pans entiers de l’ancienne religion s’effondraient et les repères de la société se dissolvaient lentement. Le roi Pomare II sut tirer le meilleur parti de l’influence des missionnaires pour accroître son pouvoir sur des populations jusque là soumises à de nombreuses autorités. Les missionnaires se servirent de l’appui des Pomare pour réaliser leur évangélisation. Rapidement la nécessité apparue de rédiger des codes de lois, sorte de codes de bonne conduite qui feraient pendant dans le domaine profane à la Bible que les missionnaires faisaient découvrir en langue vernaculaire aux populations. Ces codes relatent les derniers aspects de la coutume, dans une société de tradition orale en plein bouleversement Ainsi furent promulgués par le roi Pomare II en 1819 les 19 articles du premier code de lois en Polynésie: le code E Ture1 No Tahiti. L’année suivante, en 1820 le roi Tamatoa aux îles-sous-le-vent proclama les 25 articles du code E Ture No Raiatea e no Tahaa e no Porapora e no Maupiti…. En 1823, la reine de Huahine, Teri’itaria fille de Tamatoa roi des îles-sous-le-vent et belle-soeur et concubine de Pomare II promulgua le premier code de lois de l’île de Huahine réalisé par des missionnaires et quelques chefs de l’île. Il comportait 30 articles et représentait la législation la plus aboutie en ce début de XIXème siècle en Polynésie

Structure and thermal behavior of nanocrystalline boehmite

First, the structural features of nanocrystalline boehmite synthesized by hydrolysis of aluminum sec-butoxide according to the Yoldas method are reported. The nanosized boehmite consists of rectangular platelets averaging 8 by 9 nm and 2–3 nm in thickness which contain a large excess of water. Dehydration by heating under vacuum induced an increase in the specific surface area, down to a minimum water content ( 0.2 H2O per Al2O3); values up to 470 m2/g can be reached. However this enlargement of specific surface area only results from water loss, the surface area remaining constant. The particle morphology, the excess of water, as well as the specific surface area, depend on the amount of acid used for the peptization during the synthesis. Second, a comprehensive investigation of the dehydration kinetics is presented. The simulations of the non-isothermal experiments at constant heating rates show that thermally stimulated transformation of nanocrystalline boehmite into alumina can be accurately modeled by a 4-reaction mechanism involving: (I) the loss of physisorbed water, (II) the loss of chemisorbed water, (III) the conversion of boehmite into transition alumina, (IV) the dehydration of transition alumina (loss of residual hydroxyl groups). The activation energy of each step is found to be very similar for experiments done in various conditions (heating rate, atmosphere, kind of sample,…)

Phaeoviruses discovered in kelp (Laminariales)

Phaeoviruses are latent double-stranded DNA viruses that insert their genomes into those of their brown algal (Phaeophyceae) hosts. So far these viruses are known only from members of the Ectocarpales, which are small and short-lived macroalgae. Here we report molecular and morphological evidence for a new Phaeovirus cluster, referred to as sub-group C, infecting kelps (Laminariales) of the genera Laminaria and Saccharina, which are ecologically and commercially important seaweeds. Epifluorescence and TEM observations indicate that the Laminaria digitata Virus (LdigV), the type species of sub-group C, targets the host nucleus for its genome replication, followed by gradual degradation of the chloroplast and assembly of virions in the cytoplasm of both vegetative and reproductive cells. This study is the first to describe phaeoviruses in kelp. In the field, these viruses infected two thirds of their host populations; however, their biological impact remains unknown

MR imaging for diagnostic evaluation of encephalopathy in the newborn.

Magnetic resonance (MR) imaging is used with increasing frequency to evaluate the neonatal brain because it can provide important diagnostic and prognostic information that is needed for optimal treatment and appropriate counseling. Special care must be taken in preparing encephalopathic neonates for an MR study, transporting them from the intensive care unit, monitoring their vital signs, and optimizing MR sequences and protocols. Moreover, to accurately interpret the findings, specific knowledge is needed about the normal MR imaging appearances of the physiologic processes of myelination, cell migration, and sulcation, as well as patterns of injury, in the neonatal brain at various stages of gestational development. Hypoxic-ischemic injury, the most common cause of neonatal encephalopathy, has characteristic appearances that depend on the severity and duration of the insult as well as the stage of brain development. Diffusion-weighted MR imaging and MR spectroscopy depict abnormalities earlier than do conventional MR imaging sequences. However, diffusion-weighted imaging, if performed in the first 24 hours after the insult, might lead to underestimation of the extent of injury. When the MR findings are atypical, the differential diagnosis of neonatal encephalopathy also should include congenital and metabolic disorders and infectious diseases. Despite recent advances in the MR imaging-based characterization of these conditions, the clinical history must be borne in mind to achieve an accurate diagnosis