Experimental constraints on the distinct effects of ash, lapilli, and larger pyroclasts on entrainment and mixing in volcanic plumes

International audienceThe rate at which atmosphere is entrained and mixed into relatively dense explosive volcanic jets of gas and pyroclasts (ash, lapilli) determines whether they rise into the atmosphere as buoyant plumes or collapse to form pyroclastic flows. Here, we use analog experiments on grid-stirred turbulence to isolate particle inertial effects related to the motions of ash and lapilli on the quantitative dynamical conditions for the onset of turbulent entrainment and mixing. From energetic considerations, we estimate the distinct effects of ash and lapilli on the entrainment rate. We find that, whereas large ash- and lapilli-sized pyroclasts contribute angular momentum to entraining eddies and may enhance entrainment into volcanic jets by 37% compared to expectations without inertial particles, ash is dissipative and may reduce entrainment by 14%. We also show that the internal turbulent mixing properties are largely insensitive to particle inertial effects. Our results predict that highly explosive events involving water or ice should, for example, feed plumes that rise higher than eruption columns that are enriched in larger pyroclasts, although these events are also more likely to produce pyroclastic flows

Farming system modelling for agri-environmental policy design: The case of a spatially non-aggregated allocation of conservation measures

This paper addresses the issue of designing policies for habitat conservation on agricultural land. The case under study requires a non-aggregated spatial distribution of the fields to be enrolled in an agri-environmental programme. A spatially explicit mathematical programming farm-based model, which accounts for three spatial levels (field, farm and landscape), is coupled with a relevant spatial pattern index (the Ripley L-function) to analyse the design and implementation of an agri-environmental programme aimed to preserve the 'Tetrax tetrax' in the Plaine de Niort, France. The model is run using a stylised map with heterogeneous soil types and both crop growing and mixed dairy farms. Results show that valuable insights into agri-environmental programme design are gained through a detailed representation of farming system management. The suitable, non-aggregated spatial pattern for T. tetrax conservation is more costly than less-suitable, more aggregated patterns, because it tends to require equal participation of all farms. The policy simulations reveal that the various spatial patterns can be obtained through relatively simple uniform contract structures. An effective contract structure entails a set of two degressive payments which encourages all farms to enroll at least a small share of their land in the program

Determination of MICING

Our work was focused on a new assay for characterising clinically important yeast. This assay was developed due to the need for new diagnostic methods for recognising potentially virulent strains of increasingly important non-albicans yeast pathogens, such as Saccharomyces cerevisiae and Candida glabrata. With the great diversity among strains for virulence and virulence factors, identification to the species level is not sufficienttherefore, testing for specific virulent traits remains the best option. We show here that the proposed assay uncovers the relationships between the three most important yeast virulence traits in a single test: the ability of a strain to invade solid medium, while resisting the presence of an antimycotic and high temperature (37 °C). We combined the quantitative agar invasion assay with classical antimycotic susceptibility testing into a single assay. Similarly to the minimal inhibitory concentration (MIC) value, we defined the MICING (minimal inhibitory concentration of antimycotic for invasive growth) as the concentration of an antimycotic above which the yeast invasive growth is significantly repressed. In this study, we tested three of the most common antimycotics: fluconazole, itraconazole and amphotericin B. The response of yeast strains invasion was characteristic of each antimycotic, indicating their mechanisms of action. In addition to MICING, the assay provides quantitative information about the superficial and invasive growth, and also about the relative invasion, which helps in identifying clinically important yeast, such as azole-resistant and/or invasive strains of S. cerevisiae and C. glabrata