University of Rennes 1

Low temperature thermochronometry (LTT) dating is a powerful tool in geoscience, used worldwide, to provide unique information on the thermal history of rocks. Using these insights geologists can achieve a better understanding of geological processes that have occurred over million year timescales even in settings where erosion has removed much of the geological record. Despite the success of these techniques in tackling geological problems, there still exists a major gap in our knowledge over the fundamental principles that underlie these dating systems. Much of this uncertainty stems from an incomplete understanding of inter and intra-crystal compositional variation and the influence this has on the kinetics of the dating system. Reaching a complete understanding of crustal thermal histories also remains a major challenge as the lowest temperature thermochronometers, apatite fission track (AFT) and apatite (U-Th)/He (AHe), are only sensitive over a temperature range of c. 120 – 40°C. The lower temperature limit of this range is also dependant on apatites having low degrees of radiation damage that can enhance retention of He within apatite. This project will advance AFT and AHe methodology by focusing on apatites enriched in U and Th from geological settings considered stable. The first goal is to obtain detailed REE compositional analysis using LA-ICP-MS to refine fission track annealing models and obtain high precision measurements of parent elements to improve AFT age data. The second goal is to ensure that the maximum amount of thermal history information is extract from the 4He concentration profile in the apatite crystal. This will be achieved by a combination of 4He/3He analysis and multi-single-grain AHe analysis of broken apatite crystals. By achieving these two goals the project will advance methodology, establish analytical capabilities at the host organisation and provide new insights into the thermal history of the crust at stable geological settings.

Subsurface bacteria represent a fundamental, yet poorly known, component of the Earth’s biosphere. These communities are key in biogeochemical cycles and in a range of problems in Environmental and Geosciences, ranging from water resources management and bioremediation, to CO2 sequestration and geothermal energy. Until recently, the opacity of 3D porous media-the natural habitat of subsurface bacteria-had prevented in situ and in vivo imaging of bacterial dynamics in such environments. Recent experimental and theoretical breakthroughs at the host institution have led to the discovery that flows in natural porous media are chaotic in nature. Since chaotic mixing is known to yield and sustain strong chemical gradients at micro-scale, this discovery challenges the assumption of homogeneous nutrient distributions, broadly-used in current models of subsurface microbial processes. The goal of MicroMix is thus to explore the effect of chaotic mixing on bacterial growth and colonization in 3D porous media under positive stimuli (WP1: mixing-limited nutrient resources) and negative stimuli (WP2: antibiotic source, nutrient rerouting by bioclogging). To do so, we will develop a novel bioreactor system, primarily based upon coupling high-resolution Laser Induced Fluorescence and optical index matching, which will allow us to obtain the first joint imaging of chemical landscapes and bacterial colonies in 3D porous media. The project builds upon the combined expertise of the ER in the field of biomicrofluidics, of the supervisor in mixing dynamics, and of the secondment supervisor on biofilm dynamics in porous media. Through a detailed career development plan, a tailored training program and access to key experimental facilities and scientific networks, MicroMix will ensure an efficient re-integration of the ER and place him at the forefront of research on environmental fluid dynamics.

Nobody knows why a soap bubble collapses. When the liquid film forming the bubble, stabilised by surfactants, becomes too thin, it collapses. This seemingly simple problem, ruled by the classical laws of fluid mechanics and of statistical physics, is still a challenge for the physicist. The rupture criteria based on a stability analysis in the vicinity of the film equilibrium state fail to reproduce the observations. However the film ruptures in a foam obey some simple phenomenological laws, which suggest that underlying fundamental laws exist and wait to be determined. The state-of-the-art conjecture is that ruptures are related to hydrodynamical processes in the films, a field in which I have now an international leadership. Recent experimental data I obtained open the possibility to address this question using a fully non-linear approach in the far from equilibrium regime. In this aim, DISFILM will develop an innovative technique to measure the interface velocity and surfactant concentration, based on the use of fluorescent surfactants. The risk relies in the adaptation to dynamical conditions of advanced optical techniques. These quantities have never been measured on flowing interfaces yet, and my technique will be an important breakthrough in the field of free interface flows in presence of surfactants. A set-up will be designed to reproduce on few thin films the deformations occurring in a foam sample. The dynamical path leading to the rupture of the film will be identified and modelled. The results obtained on an isolated film will be implemented to predict the 3D foam stability and the approach will be extended to emulsions. Foams and emulsions are widely used in industry and most of the stability issues have been solved. Nevertheless, most of the industrial formulations must currently be modified in order to use green surfactants. This adaptation will be extremely more efficient and possible with the results of DISFILM as a guideline.

The recent discovery of benzonitrile in a nearby cold molecular cloud (Taurus) marks the first detection of an aromatic species in the interstellar medium by radio astronomy. Benzonitrile provides a key link to benzene, which may be a low-temperature precursor to more complex polycyclic aromatic hydrocarbons (PAHs). Understanding the origin of PAHs will help answer fundamental questions about their role in forming interstellar dust as well as potentially prebiotic molecules—material that may be incorporated into new planetary systems. Computational models are used to pinpoint individual chemical pathways by inputting kinetic rates of various formation and destruction reactions and aiming to reproduce the molecular abundances determined by radio astronomy. Many of these rates have not been measured in the laboratory, especially at low temperature. The MIRAGE project aims to measure reaction kinetics of functionalized benzenes at temperatures relevant to the cold interstellar medium and use these measurements to understand radio observations of aromatics in Taurus molecular cloud. To do this, we will use a new technique in development at the Université de Rennes 1 that combines chirped-pulse (sub)mm-wave (CPMW) rotational spectroscopy with uniform supersonic flows generated by the CRESU technique. This apparatus (one of only a few in development worldwide) will be used to measure kinetics for reactions of benzene. These data are critical to accurately explain the observed abundance of benzonitrile, as well as predicting the abundances of other aromatic species currently targeted for detection.