Liquid bridging of cylindrical colloids in near-critical solvents

Within mean field theory, we investigate the bridging transition between a pair of parallel cylindrical colloids immersed in a binary liquid mixture as a solvent which is close to its critical consolute point $T_c$. We determine the universal scaling functions of the effective potential and of the force between the colloids. For a solvent which is at the critical concentration and close to $T_c$, we find that the critical Casimir force is the dominant interaction at close separations. This agrees very well with the corresponding Derjaguin approximation for the effective interaction between the two cylinders, while capillary forces originating from the extension of the liquid bridge turn out to be more important at large separations. In addition, we are able to infer from the wetting characteristics of the individual colloids the first-order transition of the liquid bridge connecting two colloidal particles to the ruptured state. While specific to cylindrical colloids, the results presented here provide also an outline for identifying critical Casimir forces acting on bridged colloidal particles as such, and for analyzing the bridging transition between them.Comment: 23 pages, 12 figure

Alignment of cylindrical colloids near chemically patterned substrates induced by critical Casimir torques

Recent experiments have demonstrated a fluctuation-induced lateral trapping of spherical colloidal particles immersed in a binary liquid mixture near its critical demixing point and exposed to chemically patterned substrates. Inspired by these experiments, we study this kind of effective interaction, known as the critical Casimir effect, for elongated colloids of cylindrical shape. This adds orientational degrees of freedom. When the colloidal particles are close to a chemically structured substrate, a critical Casimir torque acting on the colloids emerges. We calculate this torque on the basis of the Derjaguin approximation. The range of validity of the latter is assessed via mean-field theory. This assessment shows that the Derjaguin approximation is reliable in experimentally relevant regimes, so that we extend it to Janus particles endowed with opposing adsorption preferences. Our analysis indicates that critical Casimir interactions are capable of achieving well-defined, reversible alignments both of chemically homogeneous and of Janus cylinders.Comment: 24 pages, 12 figures; v2: 22 pages, 12 figure

Getting simultaneous red and near-infrared band data from a single digital camera for plant monitoring applications: theoretical and practical study

Multispectral images, including red and near-infrared bands, have proved efficient for vegetation-soil discrimination and agricultural monitoring in remote-sensing applications. However, they remain little used in ground-based and unmanned aerial vehicle (UAV) imagery, due to a limited availability of adequate 2D imaging devices. A methodology is proposed to obtain simultaneously the near-infrared and red bands from a standard single RGB camera, after having removed the near-infrared blocking filter inside. Its ability to provide satisfactory NDVI (normalised difference vegetation index) computation for vegetation and soil has been assessed through spectral simulations. Application in field conditions with Canon 500 D and Canon 350D cameras has then been considered, taking into account signal-noise and demosaicing concerns. The results obtained have proved the practical usability of this approach, opening new technical possibilities for crop monitoring and agricultural robotics

Getting simultaneous red and near infrared bands from a single digital camera for plant monitoring applications

International audienceLes images multispectrales incluant une bande rouge et une bande infrarouge ont prouvé leur efficacité pour la discrimination entre sol et végétation et le suivi cultural en télédétection. Mais elles restent rarement utilisées pour l'imagerie au sol ou par drone, du fait de la non disponibilité de capteurs adaptés. Nous proposons ici une solution originale pour obtenir simultanément les bandes rouge et infrarouge à partir d'un appareil photographique couleur ordinaire, après avoir retiré le filtre interne bloquant l'infrarouge. Nous décrivons d'abord l'approche théorique, ainsi que des résultats simulés sur un jeu de données spectrales, pour deux types d'appareils. Des exemples d'acquisition sur le terrain en conditions réelles sont ensuite présentés, et comparés à une acquisition couleur standard pour la discrimination sol/plantes. Dans la plupart des cas notre approche apporte une amélioration significative, ouvrant de nouvelles opportunités pour les applications de suivi de culture. / Multispectral images including red and near-infrared bands have proved their efficiency for vegetation-soil discrimination and agricultural monitoring in remote sensing applications. But they remain rarely used in ground and UAV imagery, due to a limited availability of adequate 2D imaging devices. In this paper, we propose and evaluate an original solution to obtain simultaneously the near-infrared and red bands from a standard RGB camera, after having removed the near-infrared blocking filter inside. First, the theoretical approach is described, as well as simulated results on a set of soil and vegetation luminance spectra with two different still cameras (Canon 500D and Sigma SD14). Then examples of images obtained in real field conditions are given, and compared with standard colour image acquisition for pixel-based plant/soil discrimination, using an automatic thresholding method. It appears that in most cases our new acquisition procedure brings a significative improvement, opening new opportunities for crop monitoring applications

Bioactive flavanones from Luma chequen

A bioassay-guided chemical study of a methanolic extract of fresh leaves of Luma chequen led to the isolation of lumaflavanones A (1), B (2) and C (3) whose structures are proposed on the basis of NMR spectroscopic data. The structure of lumaflavanone A was confirmed by X-ray analysis. Antifeedant (Spodoptera littoralis), brine shrimp (Artemia salina) and fungistatic (Botrytis cinerea) bioassays showed that while 3 was the most active in the first two assays the mixture of 1 and 2 was more effective as a fungistatic

Apports de la technologie LIDAR dans l’objectivation écologique d’un territoire en amont d’un projet d’aménagement : aide à la caractérisation de l’habitat de l’Outarde canepetière dans la ZPS des Costières de Nîmes

International audienceDans le cadre du programme de recherche INTERMOPES1, des investigations ont été menées sur les technologies qui permettraient d’améliorer la caractérisation d’habitat d’espèces afin de développer des méthodes et outils d’objectivation écologiques du territoire. Le poster que nous proposons présentera les résultats d’une expérimentation réalisée avec un LIDAR terrestre dans le but d’analyser et de cartographier finement les hauteurs de végétation et de relier les informations acquises avec la présence de mâles ou de femelles d’Outardes canepetière. L’objectif de ces travaux est d’affiner les connaissances sur la répartition de l’oiseau dans le paysage de la Zone de Protection Spéciale des Costières de Nîmes (France) et de développer une méthode généralisable d’analyse instrumentée des potentialités écologiques d’un paysage

Atmospheric corrections of low altitude thermal infrared airborne images acquired over a tropical cropped area

Corrections atmosphériques d'images thermiques de cultures tropicales acquises à basse altitude. / Accurate corrections of atmospheric effects on thermal infrared remote sensing data are an essential pre-requisite for the development of thermal infrared airborne-derived crop water stress indices. These corrections can be performed using ground surface temperature measurements, which are time consuming and expensive. Atmospheric effects can also be corrected using radiative transfer models that require knowledge of atmospheric status. The latter can be accurately characterized from radiosoundings, but these are usually unavailable. It can also be derived from meteorological model simulations, but spatial and temporal resolution are often too coarse. This study proposes performing atmospheric corrections by using temperature and relative humidity profiles acquired in flight from onboard sensors during data collection. Such measurements are used to document the atmospheric radiative transfer model MATISSE. First results from an experimentation over a tropical cropped area show that corrections are made with a 1.46 °K accuracy

DAF-18/PTEN signals through AAK-1/AMPK to inhibit MPK-1/MAPK in feedback control of germline stem cell proliferation

Under replete growth conditions, abundant nutrient uptake leads to the systemic activation of insulin/IGF-1 signalling (IIS) and the promotion of stem cell growth/proliferation. Activated IIS can stimulate the ERK/MAPK pathway, the activation of which also supports optimal stem cell proliferation in various systems. Stem cell proliferation rates can further be locally refined to meet the resident tissue’s need for differentiated progeny. We have recently shown that the accumulation of mature oocytes in the C. elegans germ line, through DAF-18/PTEN, inhibits adult germline stem cell (GSC) proliferation, despite high systemic IIS activation. We show here that this feedback occurs through a novel cryptic signalling pathway that requires PAR-4/LKB1, AAK-1/AMPK and PAR-5/14-3-3 to inhibit the activity of MPK-1/MAPK, antagonize IIS, and inhibit both GSC proliferation and the production of additional oocytes. Interestingly, our results imply that DAF-18/PTEN, through PAR-4/LKB1, can activate AAK-1/AMPK in the absence of apparent energy stress. As all components are conserved, similar signalling cascades may regulate stem cell activities in other organisms and be widely implicated in cancer

The GREATS Hβ\beta+[OIII] Luminosity Function and Galaxy Properties at z∼8\mathbf{z\sim8}: Walking the Way of JWST

The James Webb Space Telescope will allow to spectroscopically study an unprecedented number of galaxies deep into the reionization era, notably by detecting [OIII] and H$\beta$ nebular emission lines. To efficiently prepare such observations, we photometrically select a large sample of galaxies at $z\sim8$ and study their rest-frame optical emission lines. Combining data from the GOODS Re-ionization Era wide-Area Treasury from Spitzer (GREATS) survey and from HST, we perform spectral energy distribution (SED) fitting, using synthetic SEDs from a large grid of photoionization models. The deep Spitzer/IRAC data combined with our models exploring a large parameter space enables to constrain the [OIII]+H$\beta$ fluxes and equivalent widths for our sample, as well as the average physical properties of $z\sim8$ galaxies, such as the ionizing photon production efficiency with $\log(\xi_\mathrm{ion}/\mathrm{erg}^{-1}\hspace{1mm}\mathrm{Hz})\geq25.77$. We find a relatively tight correlation between the [OIII]+H$\beta$ and UV luminosity, which we use to derive for the first time the [OIII]+H$\beta$ luminosity function (LF) at $z\sim8$. The $z\sim8$ [OIII]+H$\beta$ LF is higher at all luminosities compared to lower redshift, as opposed to the UV LF, due to an increase of the [OIII]+H$\beta$ luminosity at a given UV luminosity from $z\sim3$ to $z\sim8$. Finally, using the [OIII]+H$\beta$ LF, we make predictions for JWST/NIRSpec number counts of $z\sim8$ galaxies. We find that the current wide-area extragalactic legacy fields are too shallow to use JWST at maximal efficiency for $z\sim8$ spectroscopy even at 1hr depth and JWST pre-imaging to $\gtrsim30$ mag will be required.Comment: 13 pages, 9 figures, accepted for publication in MNRA

Adaptive structures for whole-life energy savings

The design methodology described in this paper takes a substantial shift from conventional methods. Traditionally sizing is based on the worst expected load scenario. By contrast to this conventional passive approach the method presented here replaces passive member strategically with active elements (actuators) which are only activated when the loads reach a certain threshold. The structure can withstand low level of loads passively. Above the threshold, actuation comes in to allow the structure to cope with high but rare loading scenarios. Active control introduces operational energy consumption in addition to the energy embodied in a passive design. In this paper we use this dual design to minimize the overall energy required by the structures. This methodology has been used on a simple truss structure and it was showed that it allows significant weight saving compared to conventional passive design. We extend the application of the methodology to a more complex 3D structure. It is confirmed that an optimum activation threshold exists that leads to design that minimises the total energy of the structure. Compared to an optimised passive design we show that the total energy saving is 10-fold