Modelling of pyrocarbon chemical vapor infiltration

International audienceThe chemical vapor infiltration (CVI) of pyrocarbon is used to produce carbon matrix of C/C composites. This process involves complex physico-chemical phenomena such as the transport of gas mixtures (hydrocarbons and hydrogen) in the reactor and inside the fibrous preform, chemical reactions (pyrolysis and deposition), and the structural evolution of the preform. A global modelling approach has been developed for isobaric CVI. The most difficult point is to find a realistic chemical model for pyrocarbon deposition chemistry, simple enough to be implemented in a 2D or 3D fluid dynamics code. Such a model is proposed in this study, featuring a group of light species leading to smooth laminar pyrocarbon, a group of heavier species (polycyclic hydrocarbons) leading to rough laminar pyrocarbon, and associated homogeneous and heterogeneous reaction kinetics. This model has been developed and validated according to results of pyrocarbon CVD experiments from propane, and isothermal, isobaric CVI in a 1D model porous medium made of compact stacks of 100 μm diameter filaments

Diversity of Zoanthids (Anthozoa: Hexacorallia) on Hawaiian Seamounts: Description of the Hawaiian Gold Coral and Additional Zoanthids

The Hawaiian gold coral has a history of exploitation from the deep slopes and seamounts of the Hawaiian Islands as one of the precious corals commercialised in the jewellery industry. Due to its peculiar characteristic of building a scleroproteic skeleton, this zoanthid has been referred as Gerardia sp. (a junior synonym of Savalia Nardo, 1844) but never formally described or examined by taxonomists despite its commercial interest. While collection of Hawaiian gold coral is now regulated, globally seamounts habitats are increasingly threatened by a variety of anthropogenic impacts. However, impact assessment studies and conservation measures cannot be taken without consistent knowledge of the biodiversity of such environments. Recently, multiple samples of octocoral-associated zoanthids were collected from the deep slopes of the islands and seamounts of the Hawaiian Archipelago. The molecular and morphological examination of these zoanthids revealed the presence of at least five different species including the gold coral. Among these only the gold coral appeared to create its own skeleton, two other species are simply using the octocoral as substrate, and the situation is not clear for the final two species. Phylogenetically, all these species appear related to zoanthids of the genus Savalia as well as to the octocoral-associated zoanthid Corallizoanthus tsukaharai, suggesting a common ancestor to all octocoral-associated zoanthids. The diversity of zoanthids described or observed during this study is comparable to levels of diversity found in shallow water tropical coral reefs. Such unexpected species diversity is symptomatic of the lack of biological exploration and taxonomic studies of the diversity of seamount hexacorals

Heterogeneity of Glia in the Retina and Optic Nerve of Birds and Mammals

We have recently described a novel type of glial cell that is scattered across the inner layers of the avian retina [1]. These cells are stimulated by insulin-like growth factor 1 (IGF1) to proliferate, migrate distally into the retina, and up-regulate the nestin-related intermediate filament transitin. These changes in glial activity correspond with increased susceptibility of neurons to excitotoxic damage. This novel cell-type has been termed the Non-astrocytic Inner Retinal Glia-like (NIRG) cells. The purpose of the study was to investigate whether the retinas of non-avian species contain cells that resemble NIRG cells. We assayed for NIRG cells by probing for the expression of Sox2, Sox9, Nkx2.2, vimentin and nestin. NIRG cells were distinguished from astrocytes by a lack of expression for Glial Fibrilliary Acidic Protein (GFAP). We examined the retinas of adult mice, guinea pigs, dogs and monkeys (Macaca fasicularis). In the mouse retina and optic nerve head, we identified numerous astrocytes that expressed GFAP, S100β, Sox2 and Sox9; however, we found no evidence for NIRG-like cells that were positive for Nkx2.2, nestin, and negative for GFAP. In the guinea pig retina, we did not find astrocytes or NIRG cells in the retina, whereas we identified astrocytes in the optic nerve. In the eyes of dogs and monkeys, we found astrocytes and NIRG-like cells scattered across inner layers of the retina and within the optic nerve. We conclude that NIRG-like cells are present in the retinas of canines and non-human primates, whereas the retinas of mice and guinea pigs do not contain NIRG cells

Shedding Light on Vampires: The Phylogeny of Vampyrellid Amoebae Revisited

With the advent of molecular phylogenetic techniques the polyphyly of naked filose amoebae has been proven. They are interspersed in several supergroups of eukaryotes and most of them already found their place within the tree of life. Although the ‘vampire amoebae’ have attracted interest since the middle of the 19th century, the phylogenetic position and even the monophyly of this traditional group are still uncertain. In this study clonal co-cultures of eight algivorous vampyrellid amoebae and the respective food algae were established. Culture material was characterized morphologically and a molecular phylogeny was inferred using SSU rDNA sequence comparisons. We found that the limnetic, algivorous vampyrellid amoebae investigated in this study belong to a major clade within the Endomyxa Cavalier-Smith, 2002 (Cercozoa), grouping together with a few soil-dwelling taxa. They split into two robust clades, one containing species of the genus Vampyrella Cienkowski, 1865, the other containing the genus Leptophrys Hertwig & Lesser, 1874, together with terrestrial members. Supported by morphological data these clades are designated as the two families Vampyrellidae Zopf, 1885, and Leptophryidae fam. nov. Furthermore the order Vampyrellida West, 1901 was revised and now corresponds to the major vampyrellid clade within the Endomyxa, comprising the Vampyrellidae and Leptophryidae as well as several environmental sequences. In the light of the presented phylogenetic analyses morphological and ecological aspects, the feeding strategy and nutritional specialization within the vampyrellid amoebae are discussed

Early evolution of the LIM homeobox gene family

Background: LIM homeobox (Lhx) transcription factors are unique to the animal lineage and have patterning roles during embryonic development in flies, nematodes and vertebrates, with a conserved role in specifying neuronal identity. Though genes of this family have been reported in a sponge and a cnidarian, the expression patterns and functions of the Lhx family during development in non-bilaterian phyla are not known

Functional Dicer Is Necessary for Appropriate Specification of Radial Glia during Early Development of Mouse Telencephalon

Early telencephalic development involves transformation of neuroepithelial stem cells into radial glia, which are themselves neuronal progenitors, around the time when the tissue begins to generate postmitotic neurons. To achieve this transformation, radial precursors express a specific combination of proteins. We investigate the hypothesis that micro RNAs regulate the ability of the early telencephalic progenitors to establish radial glia. We ablate functional Dicer, which is required for the generation of mature micro RNAs, by conditionally mutating the Dicer1 gene in the early embryonic telencephalon and analyse the molecular specification of radial glia as well as their progeny, namely postmitotic neurons and basal progenitors. Conditional mutation of Dicer1 from the telencephalon at around embryonic day 8 does not prevent morphological development of radial glia, but their expression of Nestin, Sox9, and ErbB2 is abnormally low. The population of basal progenitors, which are generated by the radial glia, is disorganised and expanded in Dicer1-/- dorsal telencephalon. While the proportion of cells expressing markers of postmitotic neurons is unchanged, their laminar organisation in the telencephalic wall is disrupted suggesting a defect in radial glial guided migration. We found that the laminar disruption could not be accounted for by a reduction of the population of Cajal Retzius neurons. Together, our data suggest novel roles for micro RNAs during early development of progenitor cells in the embryonic telencephalon

The development of correct toothbrushing technique in preschool children.

This study examined the effects of an intensive training program on the toothbrushing skills of three preschool children, using both performance measures and outcome (plaque level) indicators. Toothbrushing was broken into 16 steps that involved actual manipulation of the brush in the mouth. Correct brushing included four criteria: (a) appropriate angle of bristles, (b) appropriate motion of brush, (c) appropriate tooth surface, and (d) minimum duration of brushing. Training included instructions, a three-phase modeling procedure, physical guidance, and reinforcement. Results of a multiple baseline design across subjects showed that the children completed an average of 8.6% of the steps prior to training, as compared with an average of 95.8% of the steps following training. Plaque levels decreased from an average of 58% during baseline to 24.6% after training. Follow-up measures revealed that 86.6% of the steps were maintained. The study demonstrated that the effectiveness of the procedures in teaching very young children a complex motor skill that is essential to their future health

Design and Fabrication of Electromechanical Tweezers based on CNT Ropes

International audienceThis paper deals with the design, modeling, fabrication and electrical characterization of electromechanical tweezers fabricated with carbon nanotubes (CNT) ropes. We used vertically grown multi-walled carbon nanotubes (MWCNTs) deposited by CVD technique. In this work we show a novel approach to develop CNTs tweezersconsisting of two arms of vertically aligned CNT ropes that will operate electromechanically. The device was fabricated by optical lithography combined with lift-off process. The same fabrication technique has been used to obtain prepatterned catalyst dots on patterned electrodes which results on CNT ropes on predefined locations. These ropes have 3 =m in diameter and 35 =m in length. The pull-in voltage measured on a first prototype was about 20 V for a tweezers gap of 5 =m. We calculated the moment of inertia of CNT rope and its average Young's modulus in order to calculate the pull-in voltage of CNT rope tweezers