Forward and adjoint quasi-geostrophic models of the geomagnetic secular variation

International audienceWe introduce a quasi-geostrophic model of core dynamics, which aims at describ- ing core processes on geomagnetic secular variation timescales. It extends the for- malism of Alfv ́en torsional oscillations by incorporating non-zonal motions. Within this framework, the magnetohydrodynamics takes place in the equatorial plane; it involves quadratic magnetic quantities, which are averaged along the direction of ro- tation of the Earth. In addition, the equatorial flow is projected on the core-mantle boundary. It interacts with the magnetic field at the core surface, through the radial component of the magnetic induction equation. That part of the model connects the dynamics and the observed secular variation, with the radial component of the magnetic field acting as a passive tracer. We resort to variational data assimilation to construct formally the relationship between model predictions and observations. Variational data assimilation seeks to minimize an objective function, by computing its sensitivity to its control variables. The sensitivity is efficiently calculated after in- tegration of the adjoint model. We illustrate that framework with twin experiments, performed first in the case of the kinematic core flow inverse problem, and then in the case of Alfv ́en torsional oscillations. In both cases, using the adjoint model allows us to retrieve core state variables which, while taking part in the dynamics, are not directly sampled at the core surface. We study the effect of several factors on the solution (width of the assimilation time window, amount and quality of data), and we discuss the potential of the model to deal with real geomagnetic observations

Evaluation of candidate geomagnetic field models for IGRF-12

Background: The 12th revision of the International Geomagnetic Reference Field (IGRF) was issued in December 2014 by the International Association of Geomagnetism and Aeronomy (IAGA) Division V Working Group V-MOD (http://www.ngdc.noaa.gov/IAGA/vmod/igrf.html). This revision comprises new spherical harmonic main field models for epochs 2010.0 (DGRF-2010) and 2015.0 (IGRF-2015) and predictive linear secular variation for the interval 2015.0-2020.0 (SV-2010-2015). Findings: The models were derived from weighted averages of candidate models submitted by ten international teams. Teams were led by the British Geological Survey (UK), DTU Space (Denmark), ISTerre (France), IZMIRAN (Russia), NOAA/NGDC (USA), GFZ Potsdam (Germany), NASA/GSFC (USA), IPGP (France), LPG Nantes (France), and ETH Zurich (Switzerland). Each candidate model was carefully evaluated and compared to all other models and a mean model using well-defined statistical criteria in the spectral domain and maps in the physical space. These analyses were made to pinpoint both troublesome coefficients and the geographical regions where the candidate models most significantly differ. Some models showed clear deviation from other candidate models. However, a majority of the task force members appointed by IAGA thought that the differences were not sufficient to exclude models that were well documented and based on different techniques. Conclusions: The task force thus voted for and applied an iterative robust estimation scheme in space. In this paper, we report on the evaluations of the candidate models and provide details of the algorithm that was used to derive the IGRF-12 produc

Acute respiratory failure in kidney transplant recipients: a multicenter study

International audienceINTRODUCTION: Data on pulmonary complications in renal transplant recipients are scarce. The aim of this study was to evaluate acute respiratory failure (ARF) in renal transplant recipients. METHODS: We conducted a retrospective observational study in nine transplant centers of consecutive kidney transplant recipients admitted to the intensive care unit (ICU) for ARF from 2000 to 2008. RESULTS: Of 6,819 kidney transplant recipients, 452 (6.6%) required ICU admission, including 200 admitted for ARF. Fifteen (7.5%) of these patients had combined kidney-pancreas transplantations. The most common causes of ARF were bacterial pneumonia (35.5%), cardiogenic pulmonary edema (24.5%) and extrapulmonary acute respiratory distress syndrome (ARDS) (15.5%). Pneumocystis pneumonia occurred in 11.5% of patients. Mechanical ventilation was used in 93 patients (46.5%), vasopressors were used in 82 patients (41%) and dialysis was administered in 104 patients (52%). Both the in-hospital and 90-day mortality rates were 22.5%. Among the 155 day 90 survivors, 115 patients (74.2%) were dialysis-free, including 75 patients (65.2%) who recovered prior renal function. Factors independently associated with in-hospital mortality were shock at admission (odds ratio (OR) 8.70, 95% confidence interval (95% CI) 3.25 to 23.29), opportunistic fungal infection (OR 7.08, 95% CI 2.32 to 21.60) and bacterial infection (OR 2.53, 95% CI 1.07 to 5.96). Five factors were independently associated with day 90 dialysis-free survival: renal Sequential Organ Failure Assessment (SOFA) score on day 1 (OR 0.68/SOFA point, 95% CI 0.52 to 0.88), bacterial infection (OR 0.43, 95% CI 0.21 to 0.90), three or four quadrants involved on chest X-ray (OR 0.44, 95% CI 0.21 to 0.91), time from hospital to ICU admission (OR 0.98/day, 95% CI 0.95 to 0.99) and oxygen flow at admission (OR 0.93/liter, 95% CI 0.86 to 0.99). CONCLUSIONS: In kidney transplant recipients, ARF is associated with high mortality and graft loss rates. Increased Pneumocystis and bacterial prophylaxis might improve these outcomes. Early ICU admission might prevent graft loss

International Geomagnetic Reference Field: the 12th generation

The 12th generation of the International Geomagnetic Reference Field (IGRF) was adopted in December 2014 by the Working Group V-MOD appointed by the International Association of Geomagnetism and Aeronomy (IAGA). It updates the previous IGRF generation with a definitive main field model for epoch 2010.0, a main field model for epoch 2015.0, and a linear annual predictive secular variation model for 2015.0-2020.0. Here, we present the equations defining the IGRF model, provide the spherical harmonic coefficients, and provide maps of the magnetic declination, inclination, and total intensity for epoch 2015.0 and their predicted rates of change for 2015.0-2020.0. We also update the magnetic pole positions and discuss briefly the latest changes and possible future trends of the Earth’s magnetic fiel

Sex difference and intra-operative tidal volume: Insights from the LAS VEGAS study

BACKGROUND: One key element of lung-protective ventilation is the use of a low tidal volume (VT). A sex difference in use of low tidal volume ventilation (LTVV) has been described in critically ill ICU patients.OBJECTIVES: The aim of this study was to determine whether a sex difference in use of LTVV also exists in operating room patients, and if present what factors drive this difference.DESIGN, PATIENTS AND SETTING: This is a posthoc analysis of LAS VEGAS, a 1-week worldwide observational study in adults requiring intra-operative ventilation during general anaesthesia for surgery in 146 hospitals in 29 countries.MAIN OUTCOME MEASURES: Women and men were compared with respect to use of LTVV, defined as VT of 8 ml kg-1 or less predicted bodyweight (PBW). A VT was deemed 'default' if the set VT was a round number. A mediation analysis assessed which factors may explain the sex difference in use of LTVV during intra-operative ventilation.RESULTS: This analysis includes 9864 patients, of whom 5425 (55%) were women. A default VT was often set, both in women and men; mode VT was 500 ml. Median [IQR] VT was higher in women than in men (8.6 [7.7 to 9.6] vs. 7.6 [6.8 to 8.4] ml kg-1 PBW, P < 0.001). Compared with men, women were twice as likely not to receive LTVV [68.8 vs. 36.0%; relative risk ratio 2.1 (95% CI 1.9 to 2.1), P < 0.001]. In the mediation analysis, patients' height and actual body weight (ABW) explained 81 and 18% of the sex difference in use of LTVV, respectively; it was not explained by the use of a default VT.CONCLUSION: In this worldwide cohort of patients receiving intra-operative ventilation during general anaesthesia for surgery, women received a higher VT than men during intra-operative ventilation. The risk for a female not to receive LTVV during surgery was double that of males. Height and ABW were the two mediators of the sex difference in use of LTVV.TRIAL REGISTRATION: The study was registered at Clinicaltrials.gov, NCT01601223

Extracorporeal Membrane Oxygenation for Severe Acute Respiratory Distress Syndrome associated with COVID-19: An Emulated Target Trial Analysis.

RATIONALE: Whether COVID patients may benefit from extracorporeal membrane oxygenation (ECMO) compared with conventional invasive mechanical ventilation (IMV) remains unknown. OBJECTIVES: To estimate the effect of ECMO on 90-Day mortality vs IMV only Methods: Among 4,244 critically ill adult patients with COVID-19 included in a multicenter cohort study, we emulated a target trial comparing the treatment strategies of initiating ECMO vs. no ECMO within 7 days of IMV in patients with severe acute respiratory distress syndrome (PaO2/FiO2 <80 or PaCO2 ≥60 mmHg). We controlled for confounding using a multivariable Cox model based on predefined variables. MAIN RESULTS: 1,235 patients met the full eligibility criteria for the emulated trial, among whom 164 patients initiated ECMO. The ECMO strategy had a higher survival probability at Day-7 from the onset of eligibility criteria (87% vs 83%, risk difference: 4%, 95% CI 0;9%) which decreased during follow-up (survival at Day-90: 63% vs 65%, risk difference: -2%, 95% CI -10;5%). However, ECMO was associated with higher survival when performed in high-volume ECMO centers or in regions where a specific ECMO network organization was set up to handle high demand, and when initiated within the first 4 days of MV and in profoundly hypoxemic patients. CONCLUSIONS: In an emulated trial based on a nationwide COVID-19 cohort, we found differential survival over time of an ECMO compared with a no-ECMO strategy. However, ECMO was consistently associated with better outcomes when performed in high-volume centers and in regions with ECMO capacities specifically organized to handle high demand. This article is open access and distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives License 4.0 (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Modèle dynamique et assimilation de données de la variation séculaire du champ magnétique terrestre

The changes in the Earth's magnetic field on a wide range of time and space scales reflect the various time and space scales of core processes. I propose a simplified model of the rapid dynamics of the Earth's core, tailored to the study of the rapid variations of the geomagnetic field ranging from years to centuries, referred to as the geomagnetic secular variation. The quasi-geostrophic approximation used in the model relies on the prevalence of rotation forces over magnetic forces on short timescales. The axisymmetric component of the model corresponds to the formalism of Alfvén torsional waves. Within this framework, the magnetohydrodynamics takes place in the equatorial plane. At the core-mantle boundary, the equatorial flow interacts with the radial magnetic field through the radial component of the magnetic induction equation. This component of the model connects the dynamics with the observations. Variational data assimilation allows for the interpretation of the secular variation in terms of the underlying dynamics. It seeks to minimize an objective function by computing its sensitivity to its control variables through the integration of the adjoint model. I illustrate this inversion scheme with twin experiments, performed for a steady flow and in a torsional wave scenario. It enables the retrieval of core state variables which are not directly measured. By assimilating core flow models at the core surface, the inferred magnetic tension (the restoring force of torsional waves) yields a large magnetic field inside the core, at least on the order of 3-4 mT. Such fast torsional waves are consistent with a 6-year signal in the length-of-day variation timeseries.Les changements du champ magnétique terrestre sur une grande gamme d'échelles spatiales et temporelles reflètent les processus variés de la éeodynamo. Je propose un modèle simplifié de la dynamique rapide du noyau, adapté à l'étude des variations du champ magnétique de l'année au siècle ; la variation séculaire. L'hypothèse quasi-géostrophique du modèle est basée sur la prépondérance des forces de rotation par rapport aux forces magnétiques à ces échelles de temps. La partie axisymétrique correspond au formalisme d'ondes de torsion d'Alfvén. La dynamique se place dans le plan équatorial. A la frontière noyau-manteau, l'écoulement interagit avec le champ magnétique radial via la composante radiale de l'équation d'induction. Cette partie du modèle connecte la dynamique et les observations. L'assimilation variationnelle de données permet d'interpréter la variation séculaire en terme de dynamique. Une fonction objectif est minimisée en calculant sa sensibilité par rapport aux variables de contrôle via l'intégration du modèle adjoint. J'illustre cette inversion par des expériences jumelles pour un écoulement stationnaire dans le noyau et pour des ondes de torsion. On accède ainsi à des variables d'état qui ne sont pas directement observées. En utilisant comme observations des écoulements reconstruits à la surface du noyau, cette méthode permet de déduire que la tension magnétique dans le noyau, force de rappel des ondes de torsion, correspond à un champ magnétique fort, au minimum 3-4 mT. De telles ondes de torsion rapides sont cohérentes avec un signal à 6 ans dans les données de variations de la longueur du jour

Troubles attentionnels chez les sujets schizophrènes évalués par le continuous performance test (une revue de la littérature)

Les troubles de l'attention dans la schizophrénie sont largement décrits dans la littérature. Le Continuous Performance Test (CPT) est un test attentionnel qui a été initialement utilisé chez des patients présentant des lésions cérébrales, il a permis de mettre en évidence des déficits attentionnels chez les schizophrènes. Les versions plus récentes du test permettent d'explorer non seulement les sujets schizophrènes mais aussi des sujets à risque comme leurs apparentés sains, démarche qui s'inscrit dans le cadre de la recherche et de l'étude des marqueurs de vulnérabilité pour la schizophrénie. Un faisceau d'arguments laisse penser que les troubles de l'attention et plus particulièrement ceux mesurés par le CPT représentent de possibles marqueurs de vulnérabilité, ce qui ouvre la voie à des recherches génétiques.ROUEN-BU Médecine-Pharmacie (765402102) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

Excitation of travelling torsional normal modes in an Earth's core model

The proximity between the 6 yr recurrence time of the torsional Alfvén waves that have been inferred in the Earth’s outer core over 1940–2010 and their 4 yr traveltime across the fluid core is nicely explained if these travelling waves are to be considered as normal modes. We discuss to what extent the emergence of free torsional modes from a stochastic forcing in the fluid core is compatible with some dissipation, specifically with an electromagnetic torque strong enough to account for the observed length of day variations of 6 yr period. In a spherical cavity enclosed by an insulating mantle, torsional normal modes consist of standing waves. In the presence of a conducting mantle, they transform into outward travelling waves very similar to the torsional waves that have been detected in the Earth’s outer core. With such a resonant response a periodic forcing is not required to explain the regular recurrence of torsional waves; neither is the search for a source of motions in the vicinity of the cylindrical surface tangent to the inner core, where travelling waves seem to emerge. We discuss these results in the light of the reflection properties of torsional waves at the equator. We are able to reproduce the properties found for geophysical time-series of geostrophic flows (detection of a normal mode, almost total absorption at the equator) if the conductance of the lowermost mantle is 3 × 107 to 108 S.ISSN:0956-540XISSN:1365-246