Manifestations électrocardiographiques de l'hyperkaliémie modérée à sévère

L'hyperpotassémie est un désordre électrolytique, qui dans des situations extrêmes, peut conduire au décès. Les premières études effectuées montraient un lien entre la progression du taux de potassium et l'apparition de modifications électrocardiographiques. Certaines études, plus récentes, ont mis en doute cette hypothèse. Notre étude a pour but de chercher quels sont les facteurs associés à l'apparition d'un pattern électrocardiographique typique, en cas d'hyperpotassémie modérée à sévère (≥7mmol/l), dans une population adulte hospitalière, non sélectionnée. Le 2ème objectif est d'estimer la mortalité liée à ce degré d'hyperkaliémie. Etude au design rétrospectif, sélectionnant les patients adultes avec K : ≥ 7mmol/L, entre 2009 et 2010 au CHUV, ayant un électrocardiogramme à disposition entre -1h et +2h de la prise de sang. Recueil des valeurs de laboratoires et des comorbidités de ces patients et analyse des électrocardiogrammes : fréquence cardiaque, durée QRS, durée QTc, amplitudes ondes T et RS, présence d'un trouble de la conduction, d'une fibrillation ou d'un flutter, d'un rythme jonctionnel. Résultats : Sur les 82 patients sélectionnés, l'analyse statistique a mis en évidence que le taux de potassium n'est corrélé ni à l'apparition de modifications électrocardiographiques typiques, ni à la mortalité. Le seul élément pouvant prédire, sur l'électrocardiogramme, l'apparition d'un pattern typique est le degré d'acidémie. Le risque de décès ou de présenter un arrêt cardiorespiratoire en cas d'hyperkaliémie modérée à sévère est principalement déterminé par la présence d'une acidose métabolique

Same but different — pseudo-pectin in the charophytic alga Chlorokybus atmophyticus

All land‐plant cell walls possess hemicelluloses, cellulose and anionic pectin. The walls of their cousins, the charophytic algae, exhibit some similarities to land plants’ but also major differences. Charophyte ‘pectins’ are extractable by conventional land‐plant methods, although they differ significantly in composition. Here, we explore ‘pectins’ of an early‐diverging charophyte, Chlorokybus atmophyticus, characterising the anionic polysaccharides that may be comparable to ‘pectins’ in other streptophytes. Chlorokybus ‘pectin’ was anionic and upon acid hydrolysis gave GlcA, GalA and sulphate, plus neutral sugars (Ara≈Glc>Gal>Xyl); Rha was undetectable. Most Gal was the l‐enantiomer. A relatively acid‐resistant disaccharide was characterised as β‐d‐GlcA‐(1→4)‐l‐Gal. Two Chlorokybus ‘pectin’ fractions, separable by anion‐exchange chromatography, had similar sugar compositions but different sulphate‐ester contents. No sugars were released from Chlorokybus ‘pectin’ by several endo‐hydrolases [(1,5)‐α‐l‐arabinanase, (1,4)‐β‐d‐galactanase, (1,4)‐β‐d‐xylanase, endo‐polygalacturonase] and exo‐hydrolases [α‐ and β‐d‐galactosidases, α‐(1,6)‐d‐xylosidase]. ‘Driselase’, which hydrolyses most land‐plant cell wall polysaccharides to mono‐ and disaccharides, released no sugars except traces of starch‐derived Glc. Thus, the Ara, Gal, Xyl and GalA of Chlorokybus ‘pectin’ were not non‐reducing termini with configurations familiar from land‐plant polysaccharides (α‐l‐Araf, α‐ and β‐d‐Galp, α‐ and β‐d‐Xylp and α‐d‐GalpA), nor mid‐chain residues of α‐(1→5)‐l‐arabinan, β‐(1→4)‐d‐galactan, β‐(1→4)‐d‐xylan or α‐(1→4)‐d‐galacturonan. In conclusion, Chlorokybus possesses anionic ‘pectic’ polysaccharides, possibly fulfilling pectic roles but differing fundamentally from land‐plant pectin. Thus, the evolution of land‐plant pectin since the last common ancestor of Chlorokybus and land plants is a long and meandering path involving loss of sulphate, most l‐Gal and most d‐GlcA; re‐configuration of Ara, Xyl and GalA; and gain of Rha

A method to localize gamma-ray bursts using POLAR

The hard X-ray polarimeter POLAR aims to measure the linear polarization of the 50-500 keV photons arriving from the prompt emission of gamma-ray bursts (GRBs). The position in the sky of the detected GRBs is needed to determine their level of polarization. We present here a method by which, despite of the polarimeter incapability of taking images, GRBs can be roughly localized using POLAR alone. For this purpose scalers are attached to the output of the 25 multi-anode photomultipliers (MAPMs) that collect the light from the POLAR scintillator target. Each scaler measures how many GRB photons produce at least one energy deposition above 50 keV in the corresponding MAPM. Simulations show that the relative outputs of the 25 scalers depend on the GRB position. A database of very strong GRBs simulated at 10201 positions has been produced. When a GRB is detected, its location is calculated searching the minimum of the chi2 obtained in the comparison between the measured scaler pattern and the database. This GRB localization technique brings enough accuracy so that the error transmitted to the 100% modulation factor is kept below 10% for GRBs with fluence Ftot \geq 10^(-5) erg cm^(-2) . The POLAR localization capability will be useful for those cases where no other instruments are simultaneously observing the same field of view.Comment: 13 pages, 10 figure

Fully Parallel Hyperparameter Search: Reshaped Space-Filling

Space-filling designs such as scrambled-Hammersley, Latin Hypercube Sampling and Jittered Sampling have been proposed for fully parallel hyperparameter search, and were shown to be more effective than random or grid search. In this paper, we show that these designs only improve over random search by a constant factor. In contrast, we introduce a new approach based on reshaping the search distribution, which leads to substantial gains over random search, both theoretically and empirically. We propose two flavors of reshaping. First, when the distribution of the optimum is some known $P_0$, we propose Recentering, which uses as search distribution a modified version of $P_0$ tightened closer to the center of the domain, in a dimension-dependent and budget-dependent manner. Second, we show that in a wide range of experiments with $P_0$ unknown, using a proposed Cauchy transformation, which simultaneously has a heavier tail (for unbounded hyperparameters) and is closer to the boundaries (for bounded hyperparameters), leads to improved performances. Besides artificial experiments and simple real world tests on clustering or Salmon mappings, we check our proposed methods on expensive artificial intelligence tasks such as attend/infer/repeat, video next frame segmentation forecasting and progressive generative adversarial networks

Hydrogen Variability in the Murray Formation, Gale Crater, Mars

The Mars Science Laboratory (MSL) Curiosity rover is exploring the Murray formation, a sequence of heterolithic mudstones and sandstones recording fluvial deltaic and lake deposits that comprise over 350 m of sedimentary strata within Gale crater. We examine >4,500 Murray formation bedrock points, employing recent laboratory calibrations for ChemCam laser‐induced breakdown spectroscopy H measurements at millimeter scale. Bedrock in the Murray formation has an interquartile range of 2.3–3.1 wt.% H₂O, similar to measurements using the Dynamic Albedo of Neutrons and Sample Analysis at Mars instruments. However, specific stratigraphic intervals include high H targets (6–18 wt.% H₂O) correlated with Si, Mg, Ca, Mn, or Fe, indicating units with opal, hydrated Mg sulfates, hydrated Ca sulfates, Mn‐enriched units, and akageneite or other iron oxyhydroxides, respectively. One stratigraphic interval with higher hydrogen is the Sutton Island unit and Blunts Point unit contact, where higher hydrogen is associated with Fe‐rich, Ca‐rich, and Mg‐rich points. A second interval with higher hydrogen occurs in the Vera Rubin ridge portion of the Murray formation, where higher hydrogen is associated with Fe‐rich, Ca‐rich, and Si‐rich points. We also observe trends in the H signal with grain size, separate from chemical variation, whereby coarser‐grained rocks have higher hydrogen. Variability in the hydrogen content of rocks points to a history of water‐rock interaction at Gale crater that included changes in lake water chemistry during Murray formation deposition and multiple subsequent groundwater episodes

Hydrogen Variability in the Murray Formation, Gale Crater, Mars

The Mars Science Laboratory (MSL) Curiosity rover is exploring the Murray formation, a sequence of heterolithic mudstones and sandstones recording fluvial deltaic and lake deposits that comprise over 350 m of sedimentary strata within Gale crater. We examine >4,500 Murray formation bedrock points, employing recent laboratory calibrations for ChemCam laser‐induced breakdown spectroscopy H measurements at millimeter scale. Bedrock in the Murray formation has an interquartile range of 2.3–3.1 wt.% H₂O, similar to measurements using the Dynamic Albedo of Neutrons and Sample Analysis at Mars instruments. However, specific stratigraphic intervals include high H targets (6–18 wt.% H₂O) correlated with Si, Mg, Ca, Mn, or Fe, indicating units with opal, hydrated Mg sulfates, hydrated Ca sulfates, Mn‐enriched units, and akageneite or other iron oxyhydroxides, respectively. One stratigraphic interval with higher hydrogen is the Sutton Island unit and Blunts Point unit contact, where higher hydrogen is associated with Fe‐rich, Ca‐rich, and Mg‐rich points. A second interval with higher hydrogen occurs in the Vera Rubin ridge portion of the Murray formation, where higher hydrogen is associated with Fe‐rich, Ca‐rich, and Si‐rich points. We also observe trends in the H signal with grain size, separate from chemical variation, whereby coarser‐grained rocks have higher hydrogen. Variability in the hydrogen content of rocks points to a history of water‐rock interaction at Gale crater that included changes in lake water chemistry during Murray formation deposition and multiple subsequent groundwater episodes

The potassic sedimentary rocks in Gale Crater, Mars, as seen by ChemCam on board Curiosity

The Mars Science Laboratory rover Curiosity encountered potassium-rich clastic sedimentary rocks at two sites in Gale Crater, the waypoints Cooperstown and Kimberley. These rocks include several distinct meters thick sedimentary outcrops ranging from fine sandstone to conglomerate, interpreted to record an ancient fluvial or fluvio-deltaic depositional system. From ChemCam Laser-Induced Breakdown Spectroscopy (LIBS) chemical analyses, this suite of sedimentary rocks has an overall mean K2O abundance that is more than 5 times higher than that of the average Martian crust. The combined analysis of ChemCam data with stratigraphic and geographic locations reveals that the mean K2O abundance increases upward through the stratigraphic section. Chemical analyses across each unit can be represented as mixtures of several distinct chemical components, i.e., mineral phases, including K-bearing minerals, mafic silicates, Fe-oxides, and Fe-hydroxide/oxyhydroxides. Possible K-bearing minerals include alkali feldspar (including anorthoclase and sanidine) and K-bearing phyllosilicate such as illite. Mixtures of different source rocks, including a potassium-rich rock located on the rim and walls of Gale Crater, are the likely origin of observed chemical variations within each unit. Physical sorting may have also played a role in the enrichment in K in the Kimberley formation. The occurrence of these potassic sedimentary rocks provides additional evidence for the chemical diversity of the crust exposed at Gale Crater

POLAR, an instrument to measure GRB polarization. Design and laboratory tests.

International audienceReliable polarization measurements of photons from Gamma Ray Bursts (GRB) would make the understanding of the GRB phenomenon progress enormously. POLAR is a concept for an instrument that would enable such a measurement. We report about performances predicted by of Monte-Carlo and on laboratory tests to validate some critical aspects of the desig

POLAR: a space borne GRB polarimeter

International audienceThe direction and the level of polarization of high energy photons emitted by astrophysics sources are valuable observables for the understanding of the corresponding emission mechanisms, source geometry and strength of magnetic fields at work. POLAR is a novel compact space-borne detector conceived for a precise measurement of hard X-ray polarization and optimized for the detection of Gamma-Ray Burst (GRB) photons in the energy range 50-500 keV. In POLAR, the GRB photons undergo Compton scattering in a target made out of 1600 plastic scintillator bars. The azimuthal distribution of the scattered photons inside the target provides the information on the GRB polarization. The target is divided into 5x5 units, each one consisting of 8x8 scintillator bars optically coupled with a multi-anode photomultiplier. POLAR, thanks to its large modulation factor (mu_100=40%), its large effective area (Aeff = 250 cm2), and its large field of view ( 1/3 of the sky) will be able to determine the degree and angle of polarization of a strong GRB with a minimum detectable polarization of less than 10% (3sigma). In this communication the present design and status of the POLAR project is presented. Expected results through deep Monte Carlo simulation studies as well as the recent results of laboratory measurements are detailed