A global model for the combustion of gas mixtures released from forest fuels

International audienc

Skeletal and global mechanisms for the combustion of gases released by crushed forest fuels

International audienc

Performance of a Protected Wireless Sensor Network in a Fire. Analysis of Fire Spread and Data Transmission

The paper deals with a Wireless Sensor Network (WSN) as a reliable solution for capturing the kinematics of a fire front spreading over a fuel bed. To provide reliable information in fire studies and support fire fighting strategies, a Wireless Sensor Network must be able to perform three sequential actions: 1) sensing thermal data in the open as the gas temperature; 2) detecting a fire i.e., the spatial position of a flame; 3) tracking the fire spread during its spatial and temporal evolution. One of the great challenges in performing fire front tracking with a WSN is to avoid the destruction of motes by the fire. This paper therefore shows the performance of Wireless Sensor Network when the motes are protected with a thermal insulation dedicated to track a fire spreading across vegetative fuels on a field scale. The resulting experimental WSN is then used in series of wildfire experiments performed in the open in vegetation areas ranging in size from 50 to 1,000 m2

A global model for the NO released in vegetation fires

Vegetation fires are a major emission source of CO, CO2, NOx, volatile organic compounds and particulates to the atmosphere, which in turn can form secondary pollutants with implications at local, regional or global scale. To describe the impact of these fires on the environment, especially on the atmosphere, and to model their pollutant emissions, it is necessary to understand the processes involved in the combustion of vegetation. Likewise, the analysis of combustion kinetics in the gas-phase is decisive for modeling vegetation fires behavior given that the rate and amount of energy released from the fuel are derived from the fundamental chemistry of the fuel and its combustion. However, the use of detailed reaction mechanisms, which involves a large number of species and reactions, is impractical owing to large computational time requirements. In this work, a numerical approach has been used to study the mechanisms of NO formation in vegetation fires at the source level, given that NO plays an important role on the formation of ground-level ozone. The major reaction mechanisms involved in NO chemistry have been identified using reactions path analysis and sensitivity analysis with a detailed kinetic mechanism (GDF-kin® 3.0). Moreover, a two-step global kinetic mechanism has been proposed herein to account for the conversion of volatile fuel-bound nitrogen to NO in the gas phase, considering that the volatile fraction of fuel-bound nitrogen is released as NH3. Data from simulations using the PSR code from CHEMKIN-II package with a detailed kinetic mechanism (GDF-kin® 3.0) have been used to formulate reaction rate expressions of the global model under typical wildfire conditions in terms of the inlet mixture composition, equivalence ratio and range of temperatures

A Wireless Sensor Network Deployment for Rural and Forest Fire Detection and Verification

Forest and rural fires are one of the main causes of environmental degradation in Mediterranean countries. Existing fire detection systems only focus on detection, but not on the verification of the fire. However, almost all of them are just simulations, and very few implementations can be found. Besides, the systems in the literature lack scalability. In this paper we show all the steps followed to perform the design, research and development of a wireless multisensor network which mixes sensors with IP cameras in a wireless network in order to detect and verify fire in rural and forest areas of Spain. We have studied how many cameras, sensors and access points are needed to cover a rural or forest area, and the scalability of the system. We have developed a multisensor and when it detects a fire, it sends a sensor alarm through the wireless network to a central server. The central server selects the closest wireless cameras to the multisensor, based on a software application, which are rotated to the sensor that raised the alarm, and sends them a message in order to receive real-time images from the zone. The camera lets the fire fighters corroborate the existence of a fire and avoid false alarms. In this paper, we show the test performance given by a test bench formed by four wireless IP cameras in several situations and the energy consumed when they are transmitting. Moreover, we study the energy consumed by each device when the system is set up. The wireless sensor network could be connected to Internet through a gateway and the images of the cameras could be seen from any part of the world

Heat transfers and energy released in the combustion of fine vegetation fuel beds

The study of the heat transfers and the energy released during the fire spread through beds of pine needles (Pinus pinaster) was conducted under slope and no slope conditions by using a Large Scale Heat Release (LSHR) calorimeter. The results revealed two regimes of propagation. For experiments along a flat surface, the heat release rate (HRR) reached a quasi-steady state whereas for experiments taking place under a slope, the HRR increased during the fire spread. This difference was due to a distortion of the fire front. Under no slope condition, the fire front was indeed linear and propagated with a nearly constant rate of spread. On the contrary, under slope conditions, the fire front had a V-shape leading to an increase of the derivative of the burnt surface per unit of time and therefore to a rise of the heat release rate during the fire spread. The study was then devoted to the characterization of the heat transfers. Firstly, the radiant fractions of the flame and the embers were calculated from the measurements of radiant heat fluxes, the HRR and the geometrical properties of the fire front. Then, the convective fraction was determined by using the temperatures recorded in the exhaust duct of the LSHR. The contribution of each mechanism of heat transfer to the fire spread was therefore quantified. The results showed an increase of the radiation heat transfer, when the fire spread under slope condition, which was mainly due to an increase of the radiant fraction of the flames. All these data give global information on the fire spread and are thus they are very useful to improve and validate physical models of wildland fires

Limited evidence for blood eQTLs in human sexual dimorphism

The genetic underpinning of sexual dimorphism is very poorly understood. The prevalence of many diseases differs between men and women, which could be in part caused by sex-specific genetic effects. Nevertheless, only a few published genome-wide association studies (GWAS) were performed separately in each sex. The reported enrichment of expression quantitative trait loci (eQTLs) among GWAS-associated SNPs suggests a potential role of sex-specific eQTLs in the sex-specific genetic mechanism underlying complex traits. To explore this scenario, we combined sex-specific whole blood RNA-seq eQTL data from 3447 European individuals included in BIOS Consortium and GWAS data from UK Biobank. Next, to test the presence of sex-biased causal effect of gene expression on complex traits, we performed sex-specific transcriptome-wide Mendelian randomization (TWMR) analyses on the two most sexually dimorphic traits, waist-to-hip ratio (WHR) and testosterone levels. Finally, we performed power analysis to calculate the GWAS sample size needed to observe sex-specific trait associations driven by sex-biased eQTLs. Among 9 million SNP-gene pairs showing sex-combined associations, we found 18 genes with significant sex-biased cis-eQTLs (FDR 5%). Our phenome-wide association study of the 18 top sex-biased eQTLs on >700 traits unraveled that these eQTLs do not systematically translate into detectable sex-biased trait-associations. In addition, we observed that sex-specific causal effects of gene expression on complex traits are not driven by sex-specific eQTLs. Power analyses using real eQTL- and causal-effect sizes showed that millions of samples would be necessary to observe sex-biased trait associations that are fully driven by sex-biased cis-eQTLs. Compensatory effects may further hamper their detection. Our results suggest that sex-specific eQTLs in whole blood do not translate to detectable sex-specific trait associations of complex diseases, and vice versa that the observed sex-specific trait associations cannot be explained by sex-specific eQTLs

Experimental study of laminar flames obtained by the homogenization of three forest fuels

International audienc

NRT2.1 phosphorylation prevents root high affinity nitrate uptake activity in Arabidopsis thaliana

In Arabidopsis thaliana, NRT2.1 codes for a main component of the root nitrate high-affinity transport system. Previous studies revealed that post-translational regulation of NRT2.1 plays an important role in the control of root nitrate uptake and that one mechanism could correspond to NRT2.1 C-terminus processing. To further investigate this hypothesis, we produced transgenic plants with truncated forms of NRT2.1. It revealed an essential sequence for NRT2.1 activity, located between the residues 494-513. Using a phospho-proteomic approach, we found that this sequence contains one phosphorylation site, at serine 501, which can inactivate NRT2.1 function when mimicking the constitutive phosphorylation of this residue in transgenic plants. This phenotype could neither be explained by changes in abundance of NRT2.1 and NAR2.1, a partner protein of NRT2.1, nor by a lack of interaction between these two proteins. Finally, the relative level of serine 501 phosphorylation was found to be modulated by nitrate in wildtype plants. Altogether, these observations allowed us to propose a model for a new and essential mechanism for the regulation of NRT2.1 activity