The GRAVITY fringe tracker: correlation between optical path residuals and atmospheric parameters

After the first year of observations with the GRAVITY fringe tracker, we compute correlations between the optical path residuals and atmospheric and astronomical parameters. The median residuals of the optical path residuals are 180 nm on the ATs and 270 nm on the UTs. The residuals are uncorrelated with the target magnitudes for Kmag below 5.5 on ATs (9 on UTs). The correlation with the coherence time is however extremely clear, with a drop-off in fringe tracking performance below 3 ms.Comment: submitted to SPIE Astronomical Telescopes & Instrumentation 201

GRAVITY: getting to the event horizon of Sgr A*

We present the second-generation VLTI instrument GRAVITY, which currently is in the preliminary design phase. GRAVITY is specifically designed to observe highly relativistic motions of matter close to the event horizon of Sgr A*, the massive black hole at center of the Milky Way. We have identified the key design features needed to achieve this goal and present the resulting instrument concept. It includes an integrated optics, 4-telescope, dual feed beam combiner operated in a cryogenic vessel; near infrared wavefront sensing adaptive optics; fringe tracking on secondary sources within the field of view of the VLTI and a novel metrology concept. Simulations show that the planned design matches the scientific needs; in particular that 10 microarcsecond astrometry is feasible for a source with a magnitude of K=15 like Sgr A*, given the availability of suitable phase reference sources.Comment: 13 pages, 11 figures, to appear in the conference proceedings of SPIE Astronomical Instrumentation, 23-28 June 2008, Marseille, Franc

Circulating adrenomedullin estimates survival and reversibility of organ failure in sepsis: the prospective observational multinational Adrenomedullin and Outcome in Sepsis and Septic Shock-1 (AdrenOSS-1) study

Background: Adrenomedullin (ADM) regulates vascular tone and endothelial permeability during sepsis. Levels of circulating biologically active ADM (bio-ADM) show an inverse relationship with blood pressure and a direct relationship with vasopressor requirement. In the present prospective observational multinational Adrenomedullin and Outcome in Sepsis and Septic Shock 1 (, AdrenOSS-1) study, we assessed relationships between circulating bio-ADM during the initial intensive care unit (ICU) stay and short-term outcome in order to eventually design a biomarker-guided randomized controlled trial. Methods: AdrenOSS-1 was a prospective observational multinational study. The primary outcome was 28-day mortality. Secondary outcomes included organ failure as defined by Sequential Organ Failure Assessment (SOFA) score, organ support with focus on vasopressor/inotropic use, and need for renal replacement therapy. AdrenOSS-1 included 583 patients admitted to the ICU with sepsis or septic shock. Results: Circulating bio-ADM levels were measured upon admission and at day 2. Median bio-ADM concentration upon admission was 80.5 pg/ml [IQR 41.5-148.1 pg/ml]. Initial SOFA score was 7 [IQR 5-10], and 28-day mortality was 22%. We found marked associations between bio-ADM upon admission and 28-day mortality (unadjusted standardized HR 2.3 [CI 1.9-2.9]; adjusted HR 1.6 [CI 1.1-2.5]) and between bio-ADM levels and SOFA score (p < 0.0001). Need of vasopressor/inotrope, renal replacement therapy, and positive fluid balance were more prevalent in patients with a bio-ADM > 70 pg/ml upon admission than in those with bio-ADM ≤ 70 pg/ml. In patients with bio-ADM > 70 pg/ml upon admission, decrease in bio-ADM below 70 pg/ml at day 2 was associated with recovery of organ function at day 7 and better 28-day outcome (9.5% mortality). By contrast, persistently elevated bio-ADM at day 2 was associated with prolonged organ dysfunction and high 28-day mortality (38.1% mortality, HR 4.9, 95% CI 2.5-9.8). Conclusions: AdrenOSS-1 shows that early levels and rapid changes in bio-ADM estimate short-term outcome in sepsis and septic shock. These data are the backbone of the design of the biomarker-guided AdrenOSS-2 trial. Trial registration: ClinicalTrials.gov, NCT02393781. Registered on March 19, 2015

Effect of angiotensin-converting enzyme inhibitor and angiotensin receptor blocker initiation on organ support-free days in patients hospitalized with COVID-19

IMPORTANCE Overactivation of the renin-angiotensin system (RAS) may contribute to poor clinical outcomes in patients with COVID-19. Objective To determine whether angiotensin-converting enzyme (ACE) inhibitor or angiotensin receptor blocker (ARB) initiation improves outcomes in patients hospitalized for COVID-19. DESIGN, SETTING, AND PARTICIPANTS In an ongoing, adaptive platform randomized clinical trial, 721 critically ill and 58 non–critically ill hospitalized adults were randomized to receive an RAS inhibitor or control between March 16, 2021, and February 25, 2022, at 69 sites in 7 countries (final follow-up on June 1, 2022). INTERVENTIONS Patients were randomized to receive open-label initiation of an ACE inhibitor (n = 257), ARB (n = 248), ARB in combination with DMX-200 (a chemokine receptor-2 inhibitor; n = 10), or no RAS inhibitor (control; n = 264) for up to 10 days. MAIN OUTCOMES AND MEASURES The primary outcome was organ support–free days, a composite of hospital survival and days alive without cardiovascular or respiratory organ support through 21 days. The primary analysis was a bayesian cumulative logistic model. Odds ratios (ORs) greater than 1 represent improved outcomes. RESULTS On February 25, 2022, enrollment was discontinued due to safety concerns. Among 679 critically ill patients with available primary outcome data, the median age was 56 years and 239 participants (35.2%) were women. Median (IQR) organ support–free days among critically ill patients was 10 (–1 to 16) in the ACE inhibitor group (n = 231), 8 (–1 to 17) in the ARB group (n = 217), and 12 (0 to 17) in the control group (n = 231) (median adjusted odds ratios of 0.77 [95% bayesian credible interval, 0.58-1.06] for improvement for ACE inhibitor and 0.76 [95% credible interval, 0.56-1.05] for ARB compared with control). The posterior probabilities that ACE inhibitors and ARBs worsened organ support–free days compared with control were 94.9% and 95.4%, respectively. Hospital survival occurred in 166 of 231 critically ill participants (71.9%) in the ACE inhibitor group, 152 of 217 (70.0%) in the ARB group, and 182 of 231 (78.8%) in the control group (posterior probabilities that ACE inhibitor and ARB worsened hospital survival compared with control were 95.3% and 98.1%, respectively). CONCLUSIONS AND RELEVANCE In this trial, among critically ill adults with COVID-19, initiation of an ACE inhibitor or ARB did not improve, and likely worsened, clinical outcomes. TRIAL REGISTRATION ClinicalTrials.gov Identifier: NCT0273570

THE CVI-PROCESSING OF CERAMIC MATRIX COMPOSITES

Les céramiques peuvent, dans des conditions particulières, être déposées à partir de précurseurs gazeux au sein de substrats poreux. Ce procédé, désigné par infiltration chimique en phase vapeur (CVI) est particulièrement indiqué pour l'élaboration des matériaux composites à matrice céramique (CMC). Le remplissage d'un pore par CVI résulte de deux phénomènes : (i) une réaction de surface et (ii) un transfert de masse des réactifs et des produits dans la phase gazeuse. En CVI isotherme/isobare, les transferts de masse se font uniquement par diffusion. Il en résulte que la CVI doit être conduite à basse température et pression réduite pour donner un dépôt homogène en épaisseur le long des pores. En CVI forcée, les transferts de masse se font par convection forcée due à un gradient de pression. De plus un gradient inverse de température est appliqué. Il en résulte une vitesse de dépôt beaucoup plus élevée. La faisabilité du procédé CVI est établie pour diverses matrices incluant le carbone et Sic.Under specific conditions, ceramics can be deposited from gaseous precursors within porous substrates. This technique, referred to as chemical vapor infiltration (CVI) is particularly suited to the preparation of ceramic matrix composites (CMC). Pore filling by CVI results from two simultaneous phenomena : (i) a surface reaction and (ii) mass transfers of the reactants and products in the gas phase. In isothermal/isobaric CVI, mass transfers occur only by diffusion. As a result. ICVI has to be performed at low temperatures and under reduced pressures in order to lead to a deposit homogeneous in thickness along the pores. In forced-CVI, mass transfers are by forced convection due to a pressure gradient. Moreover, an inverse thermal gradient is applied resulting both in a much higher deposition rate. The feasibility of the CVI process is established for a number of ceramic matrices including carbon and Sic

The K2ZrF6 wetting process: Effect of surface chemistry on the ability of a SiC-Fiber preform to be impregnated by aluminum

International audienceSiC-ceramic materials, either as flat substrates or porous fiber preforms, are spontaneously wetted by aluminum at 700 °C to 800 °C when they have been pretreated with an aqueous solution of K2ZrF6. The wetting enhancement effect results from exothermic chemical reactions occurring at the SiC/Al interface. The first phenomenon thought to occur is a disruption of the alumina film covering liquid aluminum due to a reaction of A12O3 with K2ZrF6. Then alumina is totally dissolved at low temperatures by potassium/aluminum mixed fluorides, giving rise to a very fluid cryolitic liquid spreading out on the surface of liquid aluminum and to the true SiC/Al interface. Simultaneously, a large evolution of heat occurs, mainly due to the reduction of K2ZrF6 by aluminum and the formation of Al3Zr. The impregnation of 2D-SiC/SiC preforms by aluminum is modeled, and the effect of both the contact angle decrease and local temperature rise on the impregnation of the preforms, e.g., by gravity casting, is established

Control bandwidth improvements in GRAVITY fringe tracker by switching to a synchronous real time computer architecture

International audienceThe new VLTI (Very Large Telescope Interferometer) 1 instrument GRAVITY<SUP>5, 22, 23</SUP> is equipped with a fringe tracker<SUP>16</SUP> able to stabilize the K-band fringes on six baselines at the same time. It has been designed to achieve a performance for average seeing conditions of a residual OPD (Optical Path Difference) lower than 300 nm with objects brighter than K = 10. The control loop implementing the tracking is composed of a four stage real time computer system compromising: a sensor where the detector pixels are read in and the OPD and GD (Group Delay) are calculated; a controller receiving the computed sensor quantities and producing commands for the piezo actuators; a concentrator which combines both the OPD commands with the real time tip/tilt corrections offloading them to the piezo actuator; and finally a Kalman<SUP>15</SUP> parameter estimator. This last stage is used to monitor current measurements over a window of few seconds and estimate new values for the main Kalman<SUP>15</SUP> control loop parameters. The hardware and software implementation of this design runs asynchronously and communicates the four computers for data transfer via the Reflective Memory Network<SUP>3</SUP>. With the purpose of improving the performance of the GRAVITY<SUP>5, 23</SUP> fringe tracking<SUP>16, 22</SUP> control loop, a deviation from the standard asynchronous communication mechanism has been proposed and implemented. This new scheme operates the four independent real time computers involved in the tracking loop synchronously using the Reflective Memory Interrupts<SUP>2</SUP> as the coordination signal. This synchronous mechanism had the effect of reducing the total pure delay of the loop from 3.5 [ms] to 2.0 [ms] which then translates on a better stabilization of the fringes as the bandwidth of the system is substantially improved. This paper will explain in detail the real time architecture of the fringe tracker in both is synchronous and synchronous implementation. The achieved improvements on reducing the delay via this mechanism will be quantified