Toward a better system for short range precision force measurements

Many precision experiments have been done in the Casimir regime and in short range gravity when the separation between the interacting bodies is in the sub-micron range. Experimental complexity is minimized when one of the bodies is a sphere and the other one is a plate, making the alignment between the two bodies ubiquitous. Our group has produced the most precise Casimir measurements, and the best limits on predicted Yukawa-like potentials by measuring a force between a R∼150μm sphere attached to a (500μm)2 micro-mechanical oscillator and a planar source mass. By replacing the spherical surface with a fraction of a 500μm long cylinder with R∼150μm, the force sensitivity can be greatly enhanced. Here, it is paramount to know the angular deviation between the long axis of the cylinder and both the axis of rotation of the oscillator and the plate. Tests between a cylinder and a structure etched into a silicon wafer show that deviations of 20μrad are readily accessible. Additionally, a scaled up experiment is used to investigate if capacitance measurements can determine the orientation of the cylinder with respect to a plane with the required precision

Estimating the role of a ditch network in groundwater recharge in a Mediterranean catchment using a water balance approach

Water balance variables were monitored in a farmed Mediterranean catchment characterized by a dense ditch network to allow for the separate estimation of the diffuse and concentrated recharge terms during flood events. The 27 ha central part of the catchment was equipped with (i) rain gauges, (ii) ditch gauge stations, (iii) piezometers, (iv) neutron probes, and (v) an eddy covariance mast including a 3D sonic anemometer and a fast hygrometer. The water balance was calculated for two autumnal rain and flood events. We also estimated the uncertainty of this approach with Monte Carlo simulations. Results show, that although ditch area represents only 6% of the total study area, concentrated recharge appeared to be the main source of groundwater recharge. Indeed, it was 40-50% of the total groundwater recharge for autumnal events, which are the major annual recharge events. This indicate that both, concentrated and diffuse recharge should be taken into account in any hydrological modeling approach for Mediterranean catchments. This also means that, since they collect overland flow that is often largely contaminated by chemicals, ditches may be a place where groundwater contamination is likely to occur. The uncertainty analysis indicates that recharge estimates based on water balance exhibit large uncertainty ranges. Nevertheless, Monte Carlo simulations showed that concentrated recharge was higher than expected based on their area

Effect of agricultural practices on volatile organic compound (VOC) emissions from winter wheat

International audienceDespite the important land cover of crops, biogenic volatile organic compounds (BVOCs) emissions from agricultural areas remain poorly characterized, especially from field experiments. There is even less knowledge about the effect of agricultural practices (fertilization, pesticide spreading, etc.) on these emissions. The global aim of the present study is to reinforce our knowledge on BVOC emissions from agricultural crops. A field campaign was carried out at a measurement station located at Grignon ICOS site(France), 40 km southwest from Paris. The goal of the study was i) to quantify BVOC fluxes over a wheat stand and ii) to evaluate the effect of agricultural practices (manure and pesticide spreading) on these emissions. The experimental set-up consisted in measuring eddy covariance fluxes of momentum, latent and sensible heat, CO2 and BVOCs (with a PTR-Qi-TOF-MS - national instrument within the ANAEE-France framework). Results show that methanol was the most emitted BVOC, in agreement with few reported studies about wheat. Immediately after manure spreading, an increase of emissions of several compounds was observed. Especially, m/z 109.06 (C7H8O), which was previously characterized as strongly emitted by liquid manure, was observed in the field. We also report the first online measurement of pesticide with a PTR-Qi-TOF-MS. The spread fungicide Chlorothalonil was surprisingly still detected in the gas phase 21 days after spreading. Our results provide new insights in BVOC emissions from crops and the effect of pesticide and manure spreading on these emissions