Université d'Orléans

More than 3.5 billion years ago, the surface of Mars experienced habitable conditions compatible with the emergence and development of primitive microbial life.Consequently, in the absence of plate tectonics, ancient biosignatures dating back several billion years could still be present at the surface of the red planet.Nevertheless, Mars has been continuously exposed to UV radiation and solar and galactic cosmic rays, which may have degraded these putative biosignatures at the surface over time.The European Space Agency′s ExoMars Rosalind Franklin mission, expected to land on Mars in 2030, is thus equipped with a drill to collect samples up to 2 m deep to increase the chances of detecting well preserved mols.Here, based on previous models, we first estimate the dose delivered in the first meters of Mars regolith over geol. time.We then describe experiments in which beta-carotene (a pigment commonly used by microorganisms) was irradiated using a 2.8 MeV proton beam and its degradation with increasing dose studied by Raman spectroscopy, using a unique device allowing in situ measurements to be carried out within the irradiation chamber.Specific sample preparation, consisting of placing a thin mineral layer on top of the pigment, was also developed to take into account the dose distribution profile within the sample.Finally, based on the dose estimated for Mars, we correlate the change in the Raman signal-to-noise ratio of beta-carotene to an equivalent depth and time on Mars.

The application of biomass-derived chars in soil amendment has revealed as a promising strategy as a bio-stimulant aimed to futuristic agriculture. Despite the good performance, the rationalization of the mechanisms and the influence of biochars properties upon driving such performance is far from been achieved. In this review we analyze the impact of the application of biochars and related biomass-derived carbons in agriculture soil management, with a focus on the characteristics of the biochars including the pH, ash content, macronutrients contents (mainly N,P,K), surface area, electron conductivity, cation exchange capacity, and the dose of biochars. Interesting results were found for some of these variables. As an attend to normalize the influence of the biochars properties upon different types of crop yields, an increase factor was introduced and up to 72 values were correlated with the dose of biochars. In addition, the effects of the crop type, irrigation, type of soil on crop yields in presence of biochars are also discussed, as well as the effect of biochars on density and microbial contents of soil. Thus, we do believe the quantity of data and the variety variables included in this review are statistically acceptable to stablish a proper assessment about the influence of using biochars as a sustainable amendment for agriculture management. A critical discussion is presented raising the importance of providing a detailed characterization and analysis of the biochars to understand the impact of their application on different crops at various stages of the seasonal crop cycle.

The objective of this work is to use an economical diagnostic tool - chemiluminescence of NH2* - to give direct information on the H2 preferential diffusion effects in premixed ammonia-air flames.Abundant quantities of NH2* are produced in ammonia-air flames which makes it an interesting tracer of heat release, as stated in a previous study.Evidence of preferential diffusion was observed using a Bunsen-type burner and attributed to ammonia decomposition into hydrogen leading to preferential diffusion.In this study, new analyses based on addnl. experiments and simulations are proposed to support and quantify this hypothesis.Mixtures of equivalence ratios 0.9-1.4 have been investigated.With a Bunsen burner, we were unable to stabilize flames leaner than 0.9.The flow velocities required to stabilize these flames are very low (<0.2 m/s) due to the low flame speed of ammonia/air mixturesSpectroscopic and local chemiluminescence measurements of the flames were calibrated against a quartz-tungsten halogen lamp.The unique spectrum of each equivalence ratio depicting the reactivity of the flame was studied, and the ratio of two excited species: NH2*/OH* was used to provide a rough estimate of the equivalence ratio.This NH2*/OH* ratio was later applied to estimate the local equivalence ratio along the flame contour.Anal. of the NH2* profiles along the flame contour for various cases revealed changes in intensity and profile thickness, indicating the effects of H2 preferential diffusion.Relative lower intensities and thicker profiles of NH2* indicated a low reactivity and vice-versa.Since NH2* can be used as a good indicator, a sub-mechanism to predict these profiles has been proposed.The rate constants of pure collision reactions were determined using the collision theory, and the rate constant of the chemiluminescence reaction was determined exptl.Other involved reactions and species were identified using a sensitivity anal. on NH2 and NH2*.The proposed sub-mechanism was compared with the exptl. profiles, and the impact of the base mechanism has been stated.