Aeroacoustics of an axial ducted low Mach-number stage: numerical and experimental investigation

International audienceThis paper presents an experimental and numerical investigation of a ducted low-speed axial fan.The stator row is heterogeneous with 3 thickened vanes expected to have a non-negligible impact on the radiated noise.A good agreement for pressure ratio / mass flow rate characteristics is obtained between numerical and experimental results up to the onset of rotating stall.Hot-wire velocity profiles at the inlet assessed the effectiveness of a turbulence control screen added to prevent from inflow distortions.Induct acoustic measurements allowed a detailed description from wall-pressure spectra up to modal decompositions upstream and downstream of the fan.Acoustic modes were identified at the first two blade passing frequencies, which should be cut-off with a homogeneous stator row

Adaptive traits of cysts of the snow alga Sanguina nivaloides unveiled by 3D subcellular imaging

International audienceAbstract Sanguina nivaloides is the main alga forming red snowfields in high mountains and Polar Regions. It is non-cultivable. Analysis of environmental samples by X-ray tomography, focused-ion-beam scanning-electron-microscopy, physicochemical and physiological characterization reveal adaptive traits accounting for algal capacity to reside in snow. Cysts populate liquid water at the periphery of ice, are photosynthetically active, can survive for months, and are sensitive to freezing. They harbor a wrinkled plasma membrane expanding the interface with environment. Ionomic analysis supports a cell efflux of K + , and assimilation of phosphorus. Glycerolipidomic analysis confirms a phosphate limitation. The chloroplast contains thylakoids oriented in all directions, fixes carbon in a central pyrenoid and produces starch in peripheral protuberances. Analysis of cells kept in the dark shows that starch is a short-term carbon storage. The biogenesis of cytosolic droplets shows that they are loaded with triacylglycerol and carotenoids for long-term carbon storage and protection against oxidative stress

CHARACTERIZATION OF ALPINE SNOWPACKS USING A LOW COMPLEXITY PORTABLE MIMO RADAR SYSTEM

International audienceThis paper presents experimental results of the 3-D characterization of alpine snowpacks, obtained using a low complexity portable MIMO radar system that operates at C-band. Different types of snow at different altitudes and seasons are studied. The acquired datasets are processed using the Back Projection Algorithm and the resulting tomograms are compared to Meteo France ground measurements (Snow Micro Pen transects, density and stratigraphy profiles and liquid water content). The obtained tomograms show that the system mostly detects melt forms and faceted crystals. These measurements provide 3-D electromagnetic ground truth that can be used to confirm the results obtained by Sentinel-1

Adaptive traits of cysts of the snow alga Sanguina nivaloides unveiled by 3D subcellular imaging

Sanguina nivaloides is the main alga forming red snowfields in high mountains and Polar Regions. It is non-cultivable. Analysis of environmental samples by X-ray tomography, focused-ion-beam scanning-electron-microscopy, physicochemical and physiological characterization reveal adaptive traits accounting for algal capacity to reside in snow. Cysts populate liquid water at the periphery of ice, are photosynthetically active, can survive for months, and are sensitive to freezing. They harbor a wrinkled plasma membrane expanding the interface with environment. Ionomic analysis supports a cell efflux of K+, and assimilation of phosphorus. Glycerolipidomic analysis confirms a phosphate limitation. The chloroplast contains thylakoids oriented in all directions, fixes carbon in a central pyrenoid and produces starch in peripheral protuberances. Analysis of cells kept in the dark shows that starch is a short-term carbon storage. The biogenesis of cytosolic droplets shows that they are loaded with triacylglycerol and carotenoids for long-term carbon storage and protection against oxidative stress

Spatial variability of Saharan dust deposition revealed through a citizen science campaign

International audienceSaharan dust outbreaks have profound effects on ecosystems, climate, human health, and the cryosphere in Europe. However, the spatial deposition pattern of Saharan dust is poorly known due to a sparse network of ground measurements. Following the extreme dust deposition event of February 2021 across Europe, a citizen science campaign was launched to sample dust on snow over the Pyrenees and the European Alps. This somewhat improvised campaign triggered wide interest since 152 samples were collected from the snow in the Pyrenees, the French Alps, and the Swiss Alps in less than 4 weeks. Among the 152 samples, 113 in total could be analysed, corresponding to 70 different locations. The analysis of the samples showed a large variability in the dust properties and amount. We found a decrease in the deposited mass and particle sizes with distance from the source along the transport path. This spatial trend was also evident in the elemental composition of the dust as the iron mass fraction decreased from 11 % in the Pyrenees to 2 % in the Swiss Alps. At the local scale, we found a higher dust mass on south-facing slopes, in agreement with estimates from high-resolution remote sensing data. This unique dataset, which resulted from the collaboration of several research laboratories and citizens, is provided as an open dataset to benefit a large community and to enable further scientific investigations. Data presented in this study are available at https://doi.org/10.5281/zenodo.7969515 (Dumont et al., 2022a)