Coaxial Ion Source : pressure dependence of gas flow and field ion emission

We investigated the pressure dependence of gas flow and field ion intensity of a coaxial ion source operating at room temperature over a wide pressure range, testing various gases and ionisation voltages. Flow conductance measurements taking into account the different gases' viscosity and molecular mass consistently exhibit a generic pattern. Three different flow regimes appear with increasing upstream pressure. Since the coaxial ion source supplies the gas locally, very near the apex of the tip where ionisation occurs, large ionisation currents can be obtained without degrading the propagation conditions of the beam. Compared with field ionisation in a partial pressure chamber, using the coaxial ion source increases the ion current a hundredfold for the same residual low pressure. We also show that the gas flow regime does not impact ionisation yield. Although a fuller characterisation remains to be performed, brightness reaches 3 x 10 11 A/m 2 /sr at 12kV extracting voltage. a) https://www.cinam.univ-mrs.fr

Holography in education and popular science: a new versatile and vibrationless color device

International audienceFollowing the success of the pedagogic tool for monochromatic holography realized for pedagogic and popular science purposes a few years ago [Th. Voslion and A. Escarguel, Eur. J. Phys 33, 1803 (2012)], an upgrade has been developed. The resulting device includes all the necessary equipment to produce far more spectacular 4" × 5" color holograms for science outreach purposes. Graduate schools are also offered several experiments such as holographic diffraction gratings. Optimized to be extremely robust to vibrations, particularly by using the weight of the object to avoid unwanted vibrations during hologram exposure, the robustness of this device is demonstrated through optical microscopy measurements

La traçabilité : définitions, règlementation, objectifs, technologies

National audienceA la suite de crises sanitaires et alimentaires, les pouvoirs publics européens ont imposé des règles de traçabilité en particulier pour réassurer les consommateurs et leur redonner confiance. Les objectifs de cette politique fixent de nouvelles exigences à tous les stades de la chaîne de production et de commercialisation des produits alimentaires. La mise en oeuvre de ces objectifs laisse entrevoir des changements dans les rapports établis entre les acteurs. Au-delà des outils en effet, elle suscite de nouveaux enjeux autour de l'information. Le document donne un aperçu documenté et synthétique sur les définitions et les enjeux de la traçabilité ainsi que sur la réglementation qui en découle. Il présente les outils utilisés dans la mise en oeuvre du concept et propose une méthode axée sur une approche globale adaptée au nouveau contexte en construction

A new approach to gas field ion sources

International audienc

Preparing a celadonite electron source and estimating its brightness

International audienceSHORT ABSTRACT: The article presents a protocol to prepare the celadonite source and estimate its brightness for use in a long-range imaging low-energy electron point-source projection microscope.LONG ABSTRACT: The electron celadonite source described in this article performs well in a low-energy electron point-source projection microscope in long-range imaging. It presents major advantages compared to sharp metal tips. Its robustness affords a lifetime of months and it can be used under relatively high pressure. The celadonite crystal is deposited at the apex of a carbon fiber, maintained itself in a coaxial structure ensuring a spherical beam shape and easy mechanical positioning to align the source, the object and the electron-optical system axis. There is a single crystal deposition via generation of celadonite-containing water droplets with a micropipette. Scanning electron microscopy observation can be performed to verify the deposition. However, this adds steps and therefore increases the risk of damaging the source. Thus, after preparation, the source is usually inserted directly under vacuum in the projection microscope. A first high voltage supply provides the kick-off needed to start the electron emission. The field emission process involved is then measured: it has already been observed for dozens of electron sources prepared in this way. The brightness is underestimated through an over-estimation of source size, intensity at one energy and cone angle measured in a projection system

SPIDER : SPatial extrapolation of the vIne water status at the whole DEnomination scale from a Reference site

International audienceThe objective of this work is to test an approach to extrapolate the vine water status over a whole denomination. The method has already been tested at the field level, but it has never been validated on a spatial scale that large. Methods and Results: The extrapolation model is based on an empirical approach that relies on the collaboration of a reference measurement and a spatial model of the plant water status. Experiments were carried out over the 2946 ha of the denomination of Tavel (Gard, France). This site presents a significant spatial variability in soil (3 different soil units) and in elevation. The vineyard is not irrigated and is submited to mediterranean climate. This context leads to a strong spatial variability of the plant water status. The study focused on the most common variety, Grenache. A data base of predawn leaf water potential (PLWP) was built over three consecutive years (2008, 2009 and 2010). Respectively 10, 24 and 24 sites located throughout the denomination have been monitored in predawn leaf water potential. The monitoring consisted respectively in 7, 10 and 8 measurement dates. The spatial model was calibrated from 2009 and 2010 data and the prediction was tested on 2008 data. The results show that the approach is completely transferable over a large territory like Tavel. The model improves significantly the quality of the prediction (R² = 0.9) compared to a conventionnal method based on the mean (R² = 0.61). Conclusion: On the basis of a single measurement taken at time “t” on a reference site, the model makes it possible to estimate the plant water status on any site of the study area. Therefore, this study demonstrated the ability to extrapolate a PLWP measurement made on a reference site over the whole denomination constituted of three different soil units. Significance and impact of the study: This study represents a significant step since it demonstrates the existence of a spatial model of the vine water status at a scale larger than the single field. This study provides critical knowledge to consider the use of an empirical spatial model across a relatively large territory. This step opens up the possibility to provide spatial extrapolation model of the plant water status based on data assimilation or on existing data base.L’objectif de ce travail est de tester une approche permettant d’extrapoler l’état hydrique de la vigne à l’échelle de toute une appellation. Le modèle d’extrapolation se base sur une approche empirique qui fait collaborer une mesure de référence et un modèle spatial de l’état hydrique de la vigne. La méthode a déjà été testée au niveau parcellaire, mais n’a jamais été validée à une échelle aussi importante

Bright sources under the projection microscope: using an insulating crystal on a conductor as electron source

International audienceThe development of bright sources is allowing technological breakthroughs, especially in the field of microscopy. This requires a very advanced control and understanding of the emission mechanisms. For bright electron sources, a projection microscope with a field emission tip provides an interference image that corresponds to a holographic recording. Image reconstruction can be performed digitally to form a "real" image of the object. However, interference images can only be obtained with a bright source that is small: often, an ultra-thin tip of tungsten whose radius of curvature is of the order of 10nm. The contrast and ultimate resolution of this image-projecting microscope depend only on the size of the apparent source. Thus, a projection microscope can be used to characterize source brightness: for example, analyzing the interference contrast enables the size of the source to be estimated. Ultra-thin W tips are not the only way to obtain bright sources: field emission can also be achieved by applying voltages leading to a weak macroscopic electric field ( 10µm). Moreover, analyzing the holograms reveals the source size, and the brightness of these new emitters equals that of traditional field emission sources

Low-macroscopic field emission structure: Using the shape of the conductor to identify a local difference in electric potential

International audienceThe emission of electrons from an insulating crystal deposited on a conductor occurs at a macroscopic electric field of a few volts per micrometer, three orders of magnitude below the field emission from a clean metal. This is due to the local field enhancement induced by the presence of the insulating crystal. The emission profiles depend on the shape of the conductive substrate; analyzing these profiles enables the local difference in electric potential and the opening angleto be traced. Given the thickness of the crystal, the local difference in potential indicates the local field enhancement of a few volts per nanometer applied to the conductor

Single mineral particles makes an electron point source

International audienceA mineral (celadonite, kaolinite) nanometer-thick particle deposited on a flat carbon film or at the apex of a carbon fiber provides electron emission at low applied fields. Voltage and time dependences of the emission intensity are studied, and a model of the underlying mechanism is proposed. An electron point source providing emission from a single particle is built and characterized