667 research outputs found
Mécanismes de précipitation de carbonate de calcium dans les biofilms photosynthétiques
La prĂ©cipitation de carbonate de calcium dans les systĂšmes benthiques est souvent associĂ©e aux biofilms photosynthĂ©tiques, et notamment observĂ©e au sein de structures d'une grande complexitĂ© morphologique comme les tapis microbiens, les stromatolithes et les microbialithes. Cette biocalcification modifie les flux de CO2, de calcium et d'alcalinitĂ© dans les hydrosystĂšmes (sĂ©questration du carbone inorganique et d'alcalinitĂ©). Ce processus paraĂźt donc trĂšs sensible aux impacts anthropiques, e.g. la perturbation globale du cycle du carbone et les contaminations atmosphĂ©riques. Son Ă©tude revĂȘt une importance capitale pour la comprĂ©hension des palĂ©oenvironnements. DiffĂ©rentes hypothĂšses ont Ă©tĂ© avancĂ©es pour expliquer la biocalcification dans ces biofilms. L'activitĂ© photosynthĂ©tique des cyanobactĂ©ries est souvent mise en cause, mais ce mĂ©canisme est parfois contestĂ©, privilĂ©giant l'activitĂ© mĂ©tabolique des bactĂ©ries organohĂ©tĂ©rotrophes, e.g. les bactĂ©ries sulfato-rĂ©ductrices, qui sont associĂ©es aux micro-organismes phototrophes dans les biofilms La calcification peut aussi ĂȘtre contrĂŽlĂ©e directement par l'interaction du calcium avec la matiĂšre organique, notamment les polymĂšres extracellulaires sĂ©crĂ©tĂ©s par les microorganismes (EPS) ou les fractions macromolĂ©culaires riches en acides aspartique et glutamique de la matiĂšre organique dissoute (MOD)
Functional diversity and redundancy across fish gut, sediment and water bacterial communities.
This article explores the functional diversity and redundancy in a bacterial metacommunity constituted of three habitats (sediment, water column and fish gut) in a coastal lagoon under anthropogenic pressure. Comprehensive functional gene arrays covering a wide range of ecological processes and stress resistance genes to estimate the functional potential of bacterial communities were used. Then, diversity partitioning was used to characterize functional diversity and redundancy within (α), between (ÎČ) and across (Îł) habitats. It was showed that all local communities exhibit a highly diversified potential for the realization of key ecological processes and resistance to various environmental conditions, supporting the growing evidence that macro-organisms microbiomes harbour a high functional potential and are integral components of functional gene dynamics in aquatic bacterial metacommunities. Several levels of functional redundancy at different scales of the bacterial metacommunity were observed (within local communities, within habitats and at the metacommunity level). The results suggested a high potential for the realization of spatial ecological insurance within this ecosystem, that is, the functional compensation among microorganisms for the realization and maintenance of key ecological processes, within and across habitats. Finally, the role of macro-organisms as dispersal vectors of microbes and their potential influence on marine metacommunity dynamics were discussed
Impact of thermomechanical fiber pre-treatment using twin-screw extrusion on the production and properties of renewable binderless coriander fiberboards
The aim of this study consisted of manufacturing renewable binderless fiberboards from coriander straw and a deoiled coriander press cake, thus at the same time ensuring the valorization of crop residues and process by-products. The press cake acted as a natural binder inside the boards owing to the thermoplastic behavior of its protein fraction during thermopressing. The influence of different fiber-refining methods was evaluated and it was shown that a twin-screw extrusion treatment effectively improved fiber morphology and resulted in fiberboards with enhanced performance as compared to a conventional grinding process. The best fiberboard was produced with extrusion-refined straw using a 0.4 liquid/solid (L/S) ratio and with 40% press cake addition. The water sensitivity of the boards was effectively reduced by 63% through the addition of an extrusion raw material premixing operation and thermal treatment of the panels at 200 °C, resulting in materials with good performance showing a flexural strength of 29 MPa and a thickness swelling of 24%. Produced without the use of any chemical adhesives, these fiberboards could thus present viable, sustainable alternatives for current commercial wood-based materials such as oriented strand board, particleboard and medium-density fiberboard, with high cost-effectiveness
Experimental study of radiative shocks at PALS facility
We report on the investigation of strong radiative shocks generated with the
high energy, sub-nanosecond iodine laser at PALS. These shock waves are
characterized by a developed radiative precursor and their dynamics is analyzed
over long time scales (~50 ns), approaching a quasi-stationary limit. We
present the first preliminary results on the rear side XUV spectroscopy. These
studies are relevant to the understanding of the spectroscopic signatures of
accretion shocks in Classical T Tauri Stars.Comment: 21 pages, 1 table, 7 figure
Quasi-periodic X-ray Flares from the Protostar YLW15
With ASCA, we have detected three X-ray flares from the Class I protostar
YLW15. The flares occurred every ~20 hours and showed an exponential decay with
time constant 30-60 ks. The X-ray spectra are explained by a thin thermal
plasma emission. The plasma temperature shows a fast-rise and slow-decay for
each flare with kT_{peak}~4-6 keV. The emission measure of the plasma shows
this time profile only for the first flare, and remains almost constant during
the second and third flares at the level of the tail of the first flare. The
peak flare luminosities L_{X,peak} were ~5-20 * 10^{31} erg s^{-1}, which are
among the brightest X-ray luminosities observed to date for Class I protostars.
The total energy released in each flare was 3-6*10^{36} ergs. The first flare
is well reproduced by the quasi-static cooling model, which is based on solar
flares, and it suggests that the plasma cools mainly radiatively, confined by a
semi-circular magnetic loop of length ~14 Ro with diameter-to-length ratio
\~0.07. The two subsequent flares were consistent with the reheating of the
same magnetic structure as of the first flare. The large-scale magnetic
structure and the periodicity of the flares imply that the reheating events of
the same magnetic loop originate in an interaction between the star and the
disk due to the differential rotation.Comment: Accepted by ApJ, 9 pages incl. 4 ps figure
Histoire de lâinnovation et des technologies de lâinformation
Larissa Zakharova, maĂźtresse de confĂ©rencesYves Bouvier, maĂźtre de confĂ©rences Ă lâUniversitĂ© de SavoieLĂ©onard Laborie, ValĂ©rie Schafer, chargĂ©s de recherche au CNRSStĂ©phanie Le Gallic, allocataire-moniteur Ă lâUniversitĂ© Paris-SorbonneBenjamin Thierry, PRAG Ă lâIUFM Paris-Sorbonne Le sĂ©minaire a permis de mener une rĂ©flexion collective autour des technologies de lâinformation et de la communication, en sâintĂ©ressant aux acteurs de lâinnovation (individuels et collectifs), Ă leurs interaction..
Rotation and X-ray emission from protostars
The ASCA satellite has recently detected variable hard X-ray emission from
two Class I protostars in the rho Oph cloud, YLW15 (IRS43) and WL6, with a
characteristic time scale ~20h. In YLW15, the X-ray emission is in the form of
quasi-periodic energetic flares, which we explain in terms of strong magnetic
shearing and reconnection between the central star and the accretion disk. In
WL6, X-ray flaring is rotationally modulated, and appears to be more like the
solar-type magnetic activity ubiquitous on T Tauri stars. We find that YLW15 is
a fast rotator (near break-up), while WL6 rotates with a significantly longer
period. We derive a mass M_\star ~ 2 M_\odot and \simlt 0.4 M_\odot for the
central stars of YLW15 and WL6 respectively. On the long term, the interactions
between the star and the disk results in magnetic braking and angular momentum
loss of the star. On time scales t_{br} ~ a few 10^5 yrs, i.e., of the same
order as the estimated duration of the Class~I protostar stage. Close to the
birthline there must be a mass-rotation relation, t_{br} \simpropto M_\star,
such that stars with M_\star \simgt 1-2 M_\odot are fast rotators, while their
lower-mass counterparts have had the time to spin down. The rapid rotation and
strong star-disk magnetic interactions of YLW15 also naturally explain the
observation of X-ray ``superflares''. In the case of YLW15, and perhaps also of
other protostars, a hot coronal wind (T~10^6 K) may be responsible for the VLA
thermal radio emission. This paper thus proposes the first clues to the
rotation status and evolution of protostars.Comment: 13 pages with 6 figures. To be published in ApJ (April 10, 2000 Part
1 issue
Therapeutic Potential of a New Jumbo Phage That Infects Vibrio coralliilyticus, a Widespread Coral Pathogen
Biological control using bacteriophages is a promising approach for mitigating the devastating effects of coral diseases. Several phages that infect Vibrio coralliilyticus, a widespread coral pathogen, have been isolated, suggesting that this bacterium is permissive to viral infection and is, therefore, a suitable candidate for treatment by phage therapy. In this study, we combined functional and genomic approaches to evaluate the therapeutic potential of BONAISHI, a novel V. coralliilyticus phage, which was isolated from the coral reef in Van Phong Bay (Vietnam). BONAISHI appears to be strictly lytic for several pathogenic strains of V. coralliilyticus and remains infectious over a broad range of environmental conditions. This candidate has an unusually large dsDNA genome (303 kb), with no genes that encode known toxins or implicated in lysogeny control. We identified several proteins involved in host lysis, which may offer an interesting alternative to the use of whole bacteriophages for controlling V. coralliilyticus. A preliminary therapy test showed that adding BONAISHI to an infected culture of Symbiodinium sp. cells reduced the impact of V. coralliilyticus on Symbiodinium sp. photosynthetic activity. This study showed that BONAISHI is able to mitigate V. coralliilyticus infections, making it a good candidate for phage therapy for coral disease
Accretion and outflow-related X-rays in T Tauri stars
We report on accretion- and outflow-related X-rays from T Tauri stars, based on results from the "XMM-Newton Extended Survey of the Taurus Molecular Cloud.â X-rays potentially form in shocks of accretion streams near the stellar surface, although we hypothesize that direct interactions between the streams and magnetic coronae may occur as well. We report on the discovery of a "soft excessâ in accreting T Tauri stars supporting these scenarios. We further discuss a new type of X-ray source in jet-driving T Tauri stars. It shows a strongly absorbed coronal component and a very soft, weakly absorbed component probably related to shocks in microjets. The excessive coronal absorption points to dust-depletion in the accretion stream
IMPACT OF CT-GUIDED VALVE SIZING ON POST-PROCEDURAL AORTIC REGURGITATION IN TRANSCATHETER AORTIC VALVE IMPLANTATION
- âŠ