Numerical experiments using mesonh/forefire coupled Atmospheric-fire model

International audienceIn this study we attempt to couple the MesoNH atmospheric model in its large eddy simulation configuration with a fire contour model, ForeFire. Coupling is performed at each atmospheric time step, with the fire propagation model inputting the wind fields and outputting heat and vapour fluxes to the atmospheric model. ForeFire model is a Lagrangian front tracking model that runs at a typical front resolution of 1 meter. If the approach is similar to other successful attempts of fire-atmosphere coupled models, the use of MesoNH and ForeFire implied the development of an original coupling method. Fluxes outputted to the atmospheric models are integrated using polygon clipping method between the fire front position and the atmospheric mesh. Another originality of the approach is the fire rate of spread model that integrates wind effect by calculating the flame tilt. This reduced physical model is based on the radiating panel hypothesis. A set of idealized simulation are presented to illustrate the coupled effects between fire and the atmosphere. Preliminary results show that the coupled model is able to reproduce results that are comparable to other existing numerical experiments with a relatively small computational cost (one hour for a typical idealized case on a 200 GFlops capable computer). MesoNH serves as a research model for the meteorological systems in France and Europe, and is well integrated within the operational tool chain. Future validation scenarios will be performed on nested simulations of real large wildfires

Long term highly saturated fat diet does not induce NASH in Wistar rats

BACKGROUND: Understanding of nonalcoholic steatohepatitis (NASH) is hampered by the lack of a suitable model. Our aim was to investigate whether long term high saturated-fat feeding would induce NASH in rats. METHODS: 21 day-old rats fed high fat diets for 14 weeks, with either coconut oil or butter, and were compared with rats feeding a standard diet or a methionine choline-deficient (MCD) diet, a non physiological model of NASH. RESULTS: MCDD fed rats rapidly lost weight and showed NASH features. Rats fed coconut (86% of saturated fatty acid) or butter (51% of saturated fatty acid) had an increased caloric intake (+143% and +30%). At the end of the study period, total lipid ingestion in term of percentage of energy intake was higher in both coconut (45%) and butter (42%) groups than in the standard (7%) diet group. No change in body mass was observed as compared with standard rats at the end of the experiment. However, high fat fed rats were fattier with enlarged white and brown adipose tissue (BAT) depots, but they showed no liver steatosis and no difference in triglyceride content in hepatocytes, as compared with standard rats. Absence of hepatic lipid accumulation with high fat diets was not related to a higher lipid oxidation by isolated hepatocytes (unchanged ketogenesis and oxygen consumption) or hepatic mitochondrial respiration but was rather associated with a rise in BAT uncoupling protein UCP1 (+25–28% vs standard). CONCLUSION: Long term high saturated fat feeding led to increased "peripheral" fat storage and BAT thermogenesis but did not induce hepatic steatosis and NASH

The genetic architecture of the human cerebral cortex

The cerebral cortex underlies our complex cognitive capabilities, yet little is known about the specific genetic loci that influence human cortical structure. To identify genetic variants that affect cortical structure, we conducted a genome-wide association meta-analysis of brain magnetic resonance imaging data from 51,665 individuals. We analyzed the surface area and average thickness of the whole cortex and 34 regions with known functional specializations. We identified 199 significant loci and found significant enrichment for loci influencing total surface area within regulatory elements that are active during prenatal cortical development, supporting the radial unit hypothesis. Loci that affect regional surface area cluster near genes in Wnt signaling pathways, which influence progenitor expansion and areal identity. Variation in cortical structure is genetically correlated with cognitive function, Parkinson's disease, insomnia, depression, neuroticism, and attention deficit hyperactivity disorder

Multi-scale Simulation of a Very Large Fire Incident. Computation From the Combustion to the Atmospheric Meso-scale

International audienceValle male fire devastated more than 3000ha of Mediterranean maquis and pine forest in July 2009. Simulation of combustion processes as well as atmospherics dynamics represents a challenge for such scenarios because of the scale of the phenomenon. A coupled approach between Meso-NH (Non-Hydrostatic) LES (Large Eddy Simulation) meso/microscale scale atmospheric model and ForeFire area simulator is proposed for predicting fine-scale to large-scale phenomenon's involved in such wildfire, showing that using current supercomputers such simulation is possible in a reasonable time. To be representative of the phenomenon, typical resolution required for the simulation of a fire front combustion must be sub-meter (to represent an explicit flame thickness) while atmospheric simulation of a typical domain (several tens of square kilometres) may not be performed at a resolution of finer than 50 meters in a reasonable computational time. The two-way coupling in a Meso-NH/ForeFire simulation typically involve the surface wind to drive the fire, heat (combustion) and water vapour fluxes to be injected in the atmosphere at each atmospheric time step. The ForeFire code has been built so that several front velocity function could be easily defined and applied at different locations of the surface (e.g. a fire front velocity model could be different in forest with canopy than in grassland), likewise surface combustion models can be added and defined in the same way to force the atmospheric model. Meso-NH and ForeFire resolutions are independent and the computational time needed by the surface model is a typically a fraction of the atmospheric simulation. The most active part of the Valle male fire lasted 10 hours, while the computation of the 24 millions grid points took 9 hours on 900 computer cores

Forest fire impact on air quality: the Lançon-De-Provence 2005 case

International audienceForest fires release significant amounts of gases and aerosols into the atmosphere. Depending on meteorological conditions, fire emissions can efficiently spoil air quality and visibility far away from the source. The aim of this study is to evaluate the fire impact on air quality downwind of the burning region in the Mediterranean zone. Wildfire behaviour is simulated using a semi-physical model, ForeFire, based on an analytical resolution of the rate of spread. ForeFire provides the burnt area at high temporal and spatial resolutions; in the mesoscale non-hydrostatic meteorological model Meso-NH fire forcings, as heating and water vapor fluxes, are computed scaling them to the burnt area data given by ForeFire. A chemical scheme is coupled to Meso-NH to account for air quality evolution. Chemical emissions are scaled to the heating fluxes and based on emission factors for the Mediterranean vegetation. The model is used both in a 3D regional and 2D LES configurations. In 2005, an arson forest fire burned nearly 700 ha near Lançon-de-Provence, southeast France. ForeFire was successfully tested on this case study. Here, results from the coupled model, MesoNH-ForeFire, show the sensitivity of atmospheric dynamics and air quality situation to the coupling fire-atmosphere. Simulations put also on evidence how initial conditions and heat fluxes control fire emissions injection height. Finally, tracer distribution is simulated and its pattern shows that although the impact of the fire is visible several kilometres downwind of the burnt area, it remains confined within the planetary boundary layer. This behaviour is confirmed by comparing simulated aerosol particles concentrations with the air quality survey network available in southeastern France

Simulation of a Large Wildfire in a Coupled Fire-Atmosphere Model

The Aullene fire devastated more than 3000 ha of Mediterranean maquis and pine forest in July 2009. The simulation of combustion processes, as well as atmospheric dynamics represents a challenge for such scenarios because of the various involved scales, from the scale of the individual flames to the larger regional scale. A coupled approach between the Meso-NH (Meso-scale Non-Hydrostatic) atmospheric model running in LES (Large Eddy Simulation) mode and the ForeFire fire spread model is proposed for predicting fine- to large-scale effects of this extreme wildfire, showing that such simulation is possible in a reasonable time using current supercomputers. The coupling involves the surface wind to drive the fire, while heat from combustion and water vapor fluxes are injected into the atmosphere at each atmospheric time step. To be representative of the phenomenon, a sub-meter resolution was used for the simulation of the fire front, while atmospheric simulations were performed with nested grids from 2400-m to 50-m resolution. Simulations were run with or without feedback from the fire to the atmospheric model, or without coupling from the atmosphere to the fire. In the two-way mode, the burnt area was reproduced with a good degree of realism at the local scale, where an acceleration in the valley wind and over sloping terrain pushed the fire line to locations in accordance with fire passing point observations. At the regional scale, the simulated fire plume compares well with the satellite image. The study explores the strong fire-atmosphere interactions leading to intense convective updrafts extending above the boundary layer, significant downdrafts behind the fire line in the upper plume, and horizontal wind speeds feeding strong inflow into the base of the convective updrafts. The fire-induced dynamics is induced by strong near-surface sensible heat fluxes reaching maximum values of 240 kW m − 2 . The dynamical production of turbulent kinetic energy in the plume fire is larger in magnitude than the buoyancy contribution, partly due to the sheared initial environment, which promotes larger shear generation and to the shear induced by the updraft itself. The turbulence associated with the fire front is characterized by a quasi-isotropic behavior. The most active part of the Aullene fire lasted 10 h, while 9 h of computation time were required for the 24 million grid points on 900 computer cores

Wildfire and the atmosphere: modelling the chemical and dynamic interactions at the regional scale

International audienceForest fires release significant amounts of trace gases and aerosols into the atmosphere. Depending on meteorological conditions, fire emissions can efficiently reduce air quality and visibility, even far away from emission sources. In 2005, an arson forest fire burned nearly 700 ha near Lanc¸on-de-Provence, southeast France. This paper explores the impact of this Mediterranean fire on the atmospheric dynamics and chemistry downwind of the burning region. The fire smoke plume was observed by the MODIS-AQUA instrument several kilometres downwind of the burning area out of the Mediterranean coast. Signatures of the fire plume on air pollutants were measured at surface stations in southeastern France by the air quality network AtmoPACA. Ground-based measurements revealed unusually high concentrations of aerosols and a well marked depletion of ozone concentrations on the day of the fire. The Lanc¸on-de-Provence fire propagation was successfully simulated by the semi-physical fire spread model ForeFire. ForeFire provided the burnt area at high temporal and spatial resolutions. The burnt areas were scaled to compute the fire heat and water vapour fluxes in the three-dimensional meso-scale non-hydrostatic meteorological model MesoNH. The simulated fire plume kept confined in the boundary layer with high values of turbulent kinetic energy. The plume was advected several kilometres downwind of the ignition area by the Mistral winds in accordance with the MODIS and AtmoPACA observations. The vertical plume development was found to be more sensitive to the sensible heat flux than to the fire released moisture. The burnt area information is also used to compute emissions of a fire aerosol-like tracer and gaseous pollutants, using emission factors for Mediterranean vegetation. The coupled model simulated high concentrations of the fire aerosol-like tracer downwind of the burning zone at the right timing compared to ground-based measurements. A chemical reaction mechanism was coupled on-line to the MesoNH model to account for gaseous chemistry evolution in the fire plume. High levels of ozone precursors (NOx, CO) were simulated in the smoke plume which led to the depletion of ozone levels above and downwind of the burning zone. This depletion of ozone was indeed observed at ground-based stations but with a higher impact than simulated. The difference may be explained by the simplified design of the model with no anthropogenic sources and no interaction of the smoke aerosols with the photolysis rates. Ozone production was modelled tens of kilometres downwind of the ignition zone out of the coast

Hepatic endoderm differentiation from human embryonic stem cells

Primary human hepatocytes are a scarce resource with variable function which diminishes with time in culture. As a consequence their use in tissue modeling and therapy is restricted. Human embryonic stem cells (hESCs) could provide a stable source of human tissue due to their properties of self-renewal and their ability to give rise to all three germ layers. hESCs have the potential to provide an unlimited supply of hepatic endoderm (HE) which could offer efficient tools for drug discovery, disease modeling and therapeutic applications. There has been a major focus on developing protocols to derive functional HE from hESCs. This review focuses on human liver biology and the translation of observations of in vivo systems into developing differentiation protocols to yield hepatic endoderm. It also details the potential role of oxygen tension as a new regulatory mechanism in HE differentiation and points out the importance of mitochondrial function analysis in defining successful HE generation.</p