2,651 research outputs found

    Dynamical System Description of the Solar Radiation Pressure and j2 Phase Space for End-Of-life Design and Frozen Orbit Design

    Get PDF
    n this work we review the effect of solar radiation pressure on the eccentricity of circumterrestrial orbits, perturbed also by the oblateness of the Earth. We compute the equilibrium points of a reduced system of equations describing the time evolution of the eccentricity, the longitude of the ascending node and the argument of pericenter, and their linear stability. This analysis is the basis for understanding how the phase space is organized in terms of central and hyperbolic orbits. The role of the initial phase with respect to the Sun and of the magnitude of the inclination evolution is also examined. The results follow previous investigations performed by the authors, providing a more complete picture of the whole dynamics, that can be applied to design convenient end-of-life strategies for small satellites equipped with a solar sail or to determine quasi stable Sun-following orbits for satellites swarms

    D028 L’expression des gĂšnes PAI-1, tPA et uPA est fortement rĂ©gulĂ©e pendant la diffĂ©renciation des cellules souches embryonnaires en myocytes et adipocytes

    Get PDF
    PAI-1 est l’inhibiteur physiologique des activateurs du plasminogĂšne uPA et tPA et inhibe le complexe formĂ© entre uPA et son rĂ©cepteur, et par voie de consĂ©quence, entre la vitronectine et l’intĂ©grine alphav beta3. PAI-1 est impliquĂ© dans l’adhĂ©sion et la migration des cellules endothĂ©liales, dans la diffĂ©renciation adipocytaire et dans la rĂ©ponse Ă  l’insuline; in vivo, il facilite la thrombose, la fibrose et le remodelage tissulaire. Des taux Ă©levĂ©s circulants de PAI-1 reprĂ©sentent un biomarqueur de l’obĂ©sitĂ© centrale et sont un facteur pronostic du diabĂšte de type 2. Les propriĂ©tĂ©s biologiques de PAI-1 ont conduit Ă  l’hypothĂšse que PAI-1 serait impliquĂ© directement dans le dĂ©veloppement du tissu adipeux. Notre objectif est d’évaluer les rĂŽles spĂ©cifiques des gĂšnes PAI-1, uPA et tPA dans les mĂ©canismes molĂ©culaires de la diffĂ©renciation des cellules souches embryonnaires (cellules ES) de souris dans diffĂ©rents lignages.IndĂ©tectables Ă  l’état indiffĂ©renciĂ©, les expressions de PAI-1, uPA et tPA et les activitĂ©s enzymatiques uPA et tPA sont fortement rĂ©gulĂ©es durant la diffĂ©renciation des cellules ES. Les activitĂ©s uPA et tPA sont rapidement augmentĂ©es durant la phase prĂ©coce de dĂ©termination du processus, sans expression dĂ©tectable de PAI-1. Puis, l’expression de PAI-1 augmente progressivement dans les surnageants de culture des cellules bien diffĂ©renciĂ©es, corrĂ©lant avec une inhibition concomittante des activitĂ©s uPA et tPA. Des expĂ©riences d’immunohistochimie montrent que PAI-1 est exprimĂ© Ă  la fois dans les myotubes et dans les adipocytes matures.Le rĂŽle potentiel de ces rĂ©gulations successives est analysĂ© par la construction de lignĂ©es de cellules ES surexprimant le cDNA de PAI- 1 dĂšs l’état indiffĂ©renciĂ©. Les effets d’une surexpression ectopique de PAI-1 Ă  diffĂ©rent temps pendant la diffĂ©renciation des cellules ES sont recherchĂ©s.De plus, le traitement prĂ©coce des cellules ES en diffĂ©renciation par l’amiloride, inhibiteur spĂ©cifique d’uPA, provoque une diminution de la myogĂ©nĂšse et une augmentation de la diffĂ©renciation adipocytaire. Par contre ces effets ne sont pas retrouvĂ©s en traitant les cellules par l’EACA, inhibiteur de la plasmine ou le DMA, un dĂ©rivĂ© inactif de l’amiloride

    Ventilator-associated pneumonia in patients with covid-19: A systematic review and meta-analysis

    Get PDF
    The aim of this systematic review and meta-analysis was to estimate the pooled occurrence of ventilator-associated pneumonia (VAP) among patients admitted to an intensive care unit with COVID-19 and mortality of those who developed VAP. We performed a systematic search on PubMed, EMBASE and Web of Science from inception to 2nd March 2021 for nonrandomized studies specifically addressing VAP in adult patients with COVID-19 and reporting data on at least one primary outcome of interest. Random effect single-arm meta-analysis was performed for the occurrence of VAP and mortality (at the longest follow up) and ICU length of stay. Twenty studies were included in the systematic review and meta-analysis, for a total of 2611 patients with at least one episode of VAP. The pooled estimated occurrence of VAP was of 45.4% (95% C.I. 37.8–53.2%; 2611/5593 patients; I2 = 96%). The pooled estimated occurrence of mortality was 42.7% (95% C.I. 34–51.7%; 371/946 patients; I2 = 82%). The estimated summary estimated metric mean ICU LOS was 28.58 days (95% C.I. 21.4–35.8; I2 = 98%). Sensitivity analysis showed that patients with COVID-19 may have a higher risk of developing VAP than patients without COVID-19 (OR 3.24; 95% C.I. 2.2–4.7; P = 0.015; I2 = 67.7%; five studies with a comparison group)

    Ocean acidification impairs vermetid reef recruitment.

    Get PDF
    Vermetids form reefs in sub-tropical and warm-temperate waters that protect coasts from erosion, regulate sediment transport and accumulation, serve as carbon sinks and provide habitat for other species. The gastropods that form these reefs brood encapsulated larvae; they are threatened by rapid environmental changes since their ability to disperse is very limited. We used transplant experiments along a natural CO2 gradient to assess ocean acidification effects on the reef-building gastropod Dendropoma petraeum. We found that although D. petraeum were able to reproduce and brood at elevated levels of CO2, recruitment success was adversely affected. Long-term exposure to acidified conditions predicted for the year 2100 and beyond caused shell dissolution and a significant increase in shell Mg content. Unless CO2 emissions are reduced and conservation measures taken, our results suggest these reefs are in danger of extinction within this century, with significant ecological and socioeconomic ramifications for coastal systems

    Saturated high-repetition-rate 18.9-nm tabletop laser in nickel-like molybdenum

    Get PDF
    Includes bibliographical references (page 167).We report saturated operation of an 18.9-nm laser at 5-Hz repetition rate. An amplification with a gain-length product GL of 15.5 is obtained in the 4d 1S0―4p 1P1 laser line of Ni-like Mo in plasmas heated at grazing incidence with ~1-J pulses of 8.1-ps duration from a tabletop laser system. Lasing is obtained over a broad range of time delays and pumping conditions. We also measure a GL of 13.5 in the 22.6-nm transition of the same ion. The results are of interest for numerous applications requiring high-repetition-rate lasers at wavelengths below 20 nm
    • 

    corecore