Drifting plasma collection by a positive biased tether wire in LEO-like plasma conditions: current measurement and plasma diagnostic

BETs is a three-year project financed by the Space Program of the European Commission, aimed at developing an efficient deorbit system that could be carried on board any future satellite launched into Low Earth Orbit (LEO). The operational system involves a conductive tape-tether left bare to establish anodic contact with the ambient plasma as a giant Langmuir probe. As a part of this project, we are carrying out both numerical and experimental approaches to estimate the collected current by the positive part of the tether. This paper deals with experimental measurements performed in the IONospheric Atmosphere Simulator (JONAS) plasma chamber of the Onera-Space Environment Department. The JONAS facility is a 9- m3 vacuum chamber equipped with a plasma source providing drifting plasma simulating LEO conditions in terms of density and temperature. A thin metallic cylinder, simulating the tether, is set inside the chamber and polarized up to 1000 V. The Earth's magnetic field is neutralized inside the chamber. In a first time, tether collected current versus tether polarization is measured for different plasma source energies and densities. In complement, several types of Langmuir probes are used at the same location to allow the extraction of both ion densities and electron parameters by computer modeling (classical Langmuir probe characteristics are not accurate enough in the present situation). These two measurements permit estimation of the discrepancies between the theoretical collection laws, orbital motion limited law in particular, and the experimental data in LEO-like conditions without magnetic fields. In a second time, the spatial variations and the time evolutions of the plasma properties around the tether are investigated. Spherical and emissive Langmuir probes are also used for a more extensive characterization of the plasma in space and time dependent analysis. Results show the ion depletion because of the wake effect and the accumulation of- ions upstream of the tether. In some regimes (at large positive potential), oscillations are observed on the tether collected current and on Langmuir probe collected current in specific sites.

Fibroblast growth factor 23 and markers of mineral metabolism in individuals with preserved renal function

Fibroblast growth factor 23 (FGF23) is a bone-derived hormone that regulates phosphate homeostasis. Circulating FGF23 is elevated in chronic kidney disease (CKD) and independently associated with poor renal and cardiovascular outcomes and mortality. Because the study of FGF23 in individuals with normal renal function has received little attention, we examined in a large, population based study of 1128 participants the associations of FGF23 with markers of mineral metabolism and renal function. The median estimated glomerular filtration rate (eGFR) of the cohort was 105 ml/min per 1.73 m2, and the median plasma FGF23 was 78.5 RU/ml. FGF23 increased and plasma 1,25-dihydroxyvitamin D3 decreased significantly below an eGFR threshold of 102 and 99 ml/min per 1.73 m2, respectively. In contrast, plasma parathyroid hormone increased continuously with decreasing eGFR and was first significantly elevated at an eGFR of 126 ml/min per 1.73 m2. On multivariable analysis adjusting for sex, age, body mass index, and GFR, FGF23 was negatively associated with 1,25-dihydroxyvitamin D3, and urinary absolute and fractional calcium excretion but not with serum calcium or parathyroid hormone. We found a positive association of FGF23 with plasma phosphate, but no association with urinary absolute or fractional phosphate excretion and, unexpectedly, a positive association with tubular maximum phosphate reabsorption/GFR. Thus, in the absence of CKD, parathyroid hormone increases earlier than FGF23 when the eGFR decreases. The increase in FGF23 occurs at a higher eGFR threshold than previously reported and is closely associated with a decrease in 1,25-dihydroxyvitamin D3. We speculate that the main demonstrable effect of FGF23 in the setting of preserved renal function is suppression of 1,25-dihydroxyvitamin D3 rather than stimulation of renal phosphate excretion.

Paris de Monmartel (Jean) banquier de la cour, receveur des rentes de la ville de Paris, 1690-1766. : Origine et vie des frères Paris, munitionnaires des vivres et financiers. Les logis de Monmertel.

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ICCU

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ICCU

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Mode of access: Internet.