Gas-Liquid Mass Transfer Characterization in a Thin Shrinking Film at an Atomization Nozzle

International audienceIn this paper, a light absorption method is applied to estimate the thickness of an atomizing liquid film at microscale that exits a spraying nozzle. By using a dioxygen sensitive dye, called resazurin, it is also possible to determine the local profile of dioxygen concentration resulting from the gas-liquid transfer from air into the liquid film. The method relies on the use of the well-known Beer-Lambert law, the linearity of which has been experimentally proved for the optical system and the dye concentration used in this study. From thickness and dye concentration measurements in the liquid film formed at the outlet of the nozzle, a mass transfer analysis is performed, providing a local description of the dioxygen mass transfer (concentration fluxes, etc.) occurring in this film. This optical method, leading to a dual measurement of thickness and mass transfer, is the first to be successfully implemented in this type of thin liquid film in sprays (≈ 30 µm) at microscale and with such high velocities (≈ 8 m/s). The method is non-invasive and does not disturb the flow, in comparison with classical liquid phase measurements where the liquid is collected to be titrated. The values of the mass transfer coefficients, ! , deduced from our analysis for the liquid film (2.2 x 10-3-1.2 x 10-2 m/s) are consistent with global measurements already obtained, validating our measurement and giving more insight into the mass transfer occurring in this film

Direct observation of the microfiltration of yeast cells at the micro-scale: Characterization of cake properties

International audienceThis study examines the accumulation of yeast cells at the membrane surface and the morphology of the formed cake through microscale monitoring and analysis of the microfiltration process. An original dead-end microfiltration device with a model membrane was designed and coupled with an optical imaging system to provide direct observation from the side, allowing in-situ real time study of the filtration operation (Valencia et al. 2020 [1]). Here, the deposition of yeast cells, monodispersed and polydispersed particles, in the same size range that yeast cells, was analyzed. Image processing was used to perform a quantitative characterization of cake morphological properties in terms of height, porosity, permeability, Kozeny coefficient and specific resistance. The cakes formed by monodispersed spherical and non-spherical rigid particles exhibit a similar incompressible behavior with higher porosity than yeast cakes, with mean porosity values of 0.38 for the rigid particles and 0.15 for the yeast at the end of the filtration run, respectively. The cake obtained by the microfiltration of a model suspension of polydispersed particles close to yeast size and shape is more compact (porosity of 0.29) and less permeable. However, polydispersity does not fully explain yeast cake properties, in particular its compressibility. Indeed, the yeast cake has a high compressibility index n = 1.1, which is reflected in a significant volume expansion of the yeast cake after transmembrane pressure was removed

Probing the interactions between bubbles (gas / liquid) and (bio)interfaces at the molecular scale using FluidFM technology

International audienceUnderstanding the molecular mechanisms underlying bubble-(bio)surfaces interactions is currently a challenge that if overcame, would allow to understand and control the various processes in which they are involved. Atomic force microscopy is a valuable tool to measure such interactions, but it is limited by the large size and instability of bubbles. To overcome these challenges, we here develop a new method to probe more accurately the interactions between bubbles and (bio)-interfaces by using the fluidic force microscopy technology (FluidFM) that combines AFM with microfluidics. In this study, we use FluidFM in an original manner, to produce microsized bubbles. We characterized the bubbles produced using this method, and their interactions with hydrophobic surfaces were probed, showing that bubbles behave like hydrophobic surfaces. Thus they can be used to measure the hydrophobic properties of microorganisms' surfaces. Finally we developed a strategy to functionalize their surface, thereby modulating their interactions with microorganisms' surfaces. This new method provides a valuable tool to understand bubble-(bio)surfaces interactions but also to engineer them. 1 nN 1.5 µm P. aeruginosa Interactions of cells with bubbles are controlled by bubble functionalization CONCLUSIONS Here we provide the possibility to (i) modify easily the surface of the bubbles produced using FluidFM, and (ii) to show in what way the modification of the bubble surface influences the nature and strength of the interaction with cells. In future projects, this strategy could also be used to specifically separate cell populations from each other; for example to separate bacterial cells from human blood cells in the case of sepsis, but many other applications can now be envisioned

Probing the interactions between air bubbles and (bio)interfaces at the nanoscale using FluidFM technology

International audienceUnderstanding the molecular mechanisms underlying bubble-(bio)surfaces interactions is currently a challenge that if overcame, would allow to understand and control the various processes in which they are involved. Atomic force microscopy is a useful technique to measure such interactions, but it is limited by the large size and instability of the bubbles that it can use, attached either on cantilevers or on surfaces. We here present new developments where microsized and stable bubbles are produced using FluidFM technology, which combines AFM and microfluidics. The air bubbles produced were used to probe the interactions with hydrophobic samples, showing that bubbles in water behave like hydrophobic surfaces. They thus could be used to measure the hydrophobic properties of microorganisms’ surfaces, but in this case the interactions are also influenced by electrostatic forces. Finally a strategy was developed to functionalize their surface, thereby modulating their interactions with microorganism interfaces. This new method provides a valuable tool to understand bubble-(bio)surfaces interactions but also to engineer them

Fluidic force microscopy to access the interactions between gaz/liquid and biological interfaces

International audienceThe interactions between gaz/liquid interfaces (bubbles) and cells are involved in manybioprocesses. For example in bioreactors, breathing microorganisms interact with theirgrowth medium but also with the gases present in the medium under the form of bub-bles. While many studies are dedicated to the modelling of such processes, none of themhave yet looked into the interactions between the cells and the bubbles. Thus questioningthese interactions is highly original, and provides relevant data that can be used in manybiotechnological applications. But accessing such interactions presents several technologicalchallenges, the main one being to produce microsized bubbles, stable over time. In this pre-sentation, we show recent developments in which we produce stable bubbles using FluidFMtechnology that combines AFM with microfluidic AFM probes1. In this system, a micro-sized microfluidic channel is integrated in an AFM cantilever and connected to a pressurecontroller system, thus creating a continuous and closed fluidic conduit that can be filledwith air, while the tool can be immersed in a liquid environment. An aperture at the endof the cantilever allows the air to be pushed out of the probe into the liquid, resulting inthe creation of a bubble. Force feedback is then ensured by a standard AFM laser detectionsystem that measures the deflection of the cantilever and thus, interactions can be probeddirectly with cells. Finally, the bubbles produced using this technique can be functionalizedwith surfactants, which allows to modulate the interactions between the bubble and cells

Probing the interactions between air bubbles and (bio)-interfaces at the molecular scale using FluidFM technology

International audienceUnderstanding the molecular mechanisms underlying bubble-(bio)surfaces interactions is currently a challenge that if overcame, would allow to understand and control the various processes in which they are involved. Atomic force microscopy is a valuable tool to measure such interactions, but it is limited by the large size and instability of bubbles that can be attached on surfaces or on AFM cantilevers. To overcome these challenges, we here develop a new method to probe more accurately the interactions between bubbles and (bio)-interfaces by taking advantage of the fluidic force microscopy technology (FluidFM) that combines AFM with microfluidics. In this system, a micro-sized channel is integrated into an AFM cantilever and connected to a pressure controller system, thus creating a continuous and closed fluidic conduit that can be filled with a solution, while the tool can be immersed in a liquid environment [1]. An aperture at the end of the cantilever allows liquids to be dispensed locally. In this study, we use FluidFM in an original manner, to produce microsized bubbles of 8 µm in diameter, directly at the aperture of the microchanneled FluidFM cantilevers. For that, as shown in Figure 1 instead of liquid, the cantilever is filled with air and immersed in a liquid environment. By applying a positive pressure inside the cantilever, we succeeded in forming bubbles of controlled size directly at its aperture. Because the same pressure is maintained in the cantilever during the experiment, the dissolution of the gases from the bubble is compensated, which allows keeping the size of the bubble constant over time. After the characterization of the bubbles produced using this method, their interactions with hydrophobic surfaces were probed, showing that bubbles behave like hydrophobic surfaces. Thus they can be used to measure the hydrophobic properties of microorganisms’ surfaces, but in this case the interactions are also influenced by electrostatic forces. Finally we developed a strategy to functionalize their surface, thereby modulating their interactions with microorganisms’ surfaces. This new method provides a valuable tool to understand bubble-(bio)surfaces interactions but also to engineer them

EIT and LASCO Observations of the Initiation of a Coronal Mass Ejection

We present the first observations of the initiation of a coronal mass ejection (CME) seen on the disk of the Sun. Observations with the EIT experiment on SOHO show that the CME began in a small volume and was initially associated with slow motions of prominence material and a small brightening at one end of the prominence. Shortly afterward, the prominence was accelerated to about 100 km s[SUP]-1[/SUP] and was preceded by a bright loop-like structure, which surrounded an emission void, that traveled out into the corona at a velocity of 200 400 km s[SUP]-1[/SUP]. These three components, the prominence, the dark void, and the bright loops are typical of CMEs when seen at distance in the corona and here are shown to be present at the earliest stages of the CME. The event was later observed to traverse the LASCO coronagraphs fields of view from 1.1 to 30 Ro. Of particular interest is the fact that this large-scale event, spanning as much as 70 deg in latitude, originated in a volume with dimensions of roughly 35" (2.5 x 10[SUP]4[/SUP] km). Further, a disturbance that propagated across the disk and a chain of activity near the limb may also be associated with this event as well as a considerable degree of activity near the west limb

Observations of Coronal Structures Above an Active Region by EIT and Implications for Coronal Energy Deposition

Solar EUV images recorded by the EUV Imaging Telescope (EIT) on SOHO have been used to evaluate temperature and density as a function of position in two largescale features in the corona observed in the temperature range of 1.0-2.0MK. Such observations permit estimates of longitudinal temperature gradients (if present) in the corona and, consequently, estimates of thermal conduction and radiative losses as a function of position in the features. We examine two relatively cool features as recorded in EIT's Feix/x (171Å) and Fexii (195Å) bands in a decaying active region. The first is a long-lived loop-like feature with one leg, ending in the active region, much more prominent than one or more distant footpoints assumed to be rooted in regions of weakly enhanced field. The other is a near-radial feature, observed at the West limb, which may be either the base of a very high loop or the base of a helmet streamer. We evaluate energy requirements to support a steady-state energy balance in these features and find in both instances that downward thermal conductive losses (at heights above the transition region) are inadequate to support local radiative losses, which are the predominant loss mechanism. The requirement that a coronal energy deposition rate proportional to the square of the ambient electron density (or pressure) is present in these cool coronal features provides an additional constraint on coronal heating mechanisms

ANDES, the high resolution spectrograph for the ELT:Calibration Unit(s)

The instrumentation plan for the ELT foresees the ArmazoNes high Dispersion Echelle Spectrograph (ANDES). The ANDES-project and consortium entered phase B in January 2022 and underwent several (internal and external) revisions by now to ensure that the requirements and eventually the challenging goals can be met by the physical design of the spectrograph. Among its main scientific goals are the detection of atmospheres of exoplanets and the determination of fundamental physical constants. For this, high radial velocity precision and accuracy are required. Even though the ANDES-spectrograph is designed for maximum intrinsic stability, a calibration and thus a calibration unit is mandatory. To allow for maximum flexibility and modularity the calibration unit is physically split into three calibration units. We show the design of the calibration units and their individual components, where possible. This includes the electronics, the mechanics, the software supporting and controlling the light guiding and calibration sources.</p

First Results from EIT

peer reviewedThe Extreme-UV Imaging telescope has already produced more than 15000 wide-field images of the corona and transition region, on the disk and up to 1.5R_o above the limb, with a pixel size of 2.6\arcsec. By using four different emission lines, it provides the global temperature distribution in the quiet corona, in the range 0.5 to 3*E(6) K. Its excellent sensitivity and wide dynamic range allow unprecedented views of low emission features, even inside coronal holes. Those so-called ``quiet'' regions actually display a wide range of dynamical phenomena, in particular at small spatial scales and at time scales going down to only a few seconds, as revealed by all EIT time sequences of full- or partial-field images. The initial results presented here demonstrate the importance of this wide-field imaging experiment for a good coordination between SOHO and ground-based solar telescopes, as well as for science planning