Journal of Next-Generation Research 5.0
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La régression linéaire vue sous l'angle Bayesien
No full textThese notes aim at clarifying different strategies to perform linear regression from given dataset. Methods like the weighted and ordinary least squares, ridge regression or LASSO are proposed in the literature. The present article is my understanding of these methods which are, according to me, better unified in the Bayesian framework. The formulas to address linear regression with these methods are derived. The KIC for model selection is also derived in the end of the document
Upscaling Forest Biomass from Field to Satellite Measurements: Sources of Errors and Ways to Reduce Them
No full text[Departement_IRSTEA]Territoires [TR1_IRSTEA]SYNERGIE [Axe_IRSTEA]TETIS-ATTOS [ADD1_IRSTEA]Dynamique et fonctionnement des écosystèmesInternational audienceForest biomass monitoring is at the core of the research agenda due to the critical importance of forest dynamics in the carbon cycle. However, forest biomass is never directly measured; thus, upscaling it from trees to stand or larger scales (e.g., countries, regions) relies on a series of statistical models that may propagate large errors. Here, we review the main steps usually adopted in forest aboveground biomass mapping, highlighting the major challenges and perspectives. We show that there is room for improvement along the scaling-up chain from field data collection to satellite-based large-scale mapping, which should lead to the adoption of effective practices to better control the propagation of errors. We specifically illustrate how the increasing use of emerging technologies to collect massive amounts of high-quality data may significantly improve the accuracy of forest carbon maps. Furthermore, we discuss how sources of spatially structured biases that directly propagate into remote sensing models need to be better identified and accounted for when extrapolating forest carbon estimates, e.g., through a stratification design. We finally discuss the increasing realism of 3D simulated stands, which, through radiative transfer modelling, may contribute to a better understanding of remote sensing signals and open avenues for the direct calibration of large-scale products, thereby circumventing several current difficulties
Distribution trend of trace elements in digestate exposed to air: laboratory-scale investigations using DGT-based fractionation
No full textInternational audienceThe use of digestate as amendment for agricultural soils has already been proposed as an alternative to mineral fertilizers or undigested organic matter. However, little information is available concerning the effect of digestate atmospheric exposure on trace elements speciation and, consequently, on their mobility and bio-accessibility when digestate is stored in open tanks or handled before land spreading. In this study, we investigated at laboratory-scale the effect of digestate aeration on the distribution of Al, As, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Sb, Se and W using the diffusive gradients in thin films technique (DGT)-based fractionation. For this purpose, experiments were performed to assess the variation in distribution between the labile, soluble and particulate fractions over time in digested sewage sludge during passive and forced aeration. Results showed that aeration promoted a dissolution of Al, As, Co, Cr, Cu, Fe, Mn, Mo and Pb, suggesting a possible increase in their mobility that may likely occur during storage in open tanks or handling before land spreading. Labile elements' fraction increased only during forced aeration (except for Fe and Mn), suggesting that their short-term bio-accessibility can increase only after significant aeration as the one assumed to occur when land spreading takes plac
Exposure, vulnerability, and resiliency of French Polynesian coral reefs to environmental disturbances
No full textInternational audiencepreserving coral reef resilience is a major challenge in the Anthropocene, yet recent studiesdemonstrate failures of reef recovery from disturbance, globally. the wide and vigorous outer-reefsystem of French polynesia presents a rare opportunity to assess ecosystem resilience to disturbancesat a large-scale equivalent to the size of europe. In this purpose, we analysed long-term data on coralcommunity dynamics and combine the mixed-effects regression framework with a set of functionalresponse models to evaluate coral recovery trajectories. Analyses of 14 years data across 17 reefsallowed estimating impacts of a cyclone, bleaching event and crown-of-thorns starfish outbreak, whichgenerated divergence and asynchrony in coral community trajectory. We evaluated reef resilienceby quantifying levels of exposure, degrees of vulnerability, and descriptors of recovery of coralcommunities in the face of disturbances. our results show an outstanding rate of coral recovery, witha systematic return to the pre-disturbance state within only 5 to 10 years. Differences in the impactsof disturbances among reefs and in the levels of vulnerability of coral taxa to these events resulted indiverse recovery patterns. the consistent recovery of coral communities, and convergence toward pre-disturbance community structures, reveals that the processes that regulate ecosystem recovery stillprevail in French polynesia
Détermination de la déformée statique d'une structure en treillis par la méthode des éléments finis
No full textInternational audienc
Future Directions in Conservation Research on Petrels and Shearwaters
No full textInternational audienceShearwaters and petrels (hereafter petrels) are highly adapted seabirds that occuracross all the world’s oceans. Petrels are a threatened seabird group comprising 124species. They have bet-hedging life histories typified by extended chick rearing periods,low fecundity, high adult survival, strong philopatry, monogamy and long-term matefidelity and are thus vulnerable to change. Anthropogenic alterations on land and atsea have led to a poor conservation status of many petrels with 52 (42%) threatened species based on IUCN criteria and 65 (52%) suffering population declines. Somespecies are well-studied, even being used as bioindicators of ocean health, yet for othersthere are major knowledge gaps regarding their breeding grounds, migratory areas orother key aspects of their biology and ecology. We assembled 38 petrel conservationresearchers to summarize information regarding the most important threats accordingto the IUCN Red List of threatened species to identify knowledge gaps that mustbe filled to improve conservation and management of petrels. We highlight researchadvances on the main threats for petrels (invasive species at breeding grounds, bycatch,overfishing, light pollution, climate change, and pollution). We propose an ambitiousgoal to reverse at least some of these six main threats, through active efforts suchas restoring island habitats (e.g., invasive species removal, control and prevention),improving policies and regulations at global and regional levels, and engaging localcommunities in conservation efforts
Viral dynamics of delayed CTL-inclusive HIV-1 infection model with both virus-to-cell and cell-to-cell transmissions
No full textWe consider a mathematical model that describes a viral infection of HIV-1 with both virus-to-cell and cell-to-cell transmission, CTL response immune and four distributed delays, describing intracellular delays and immune response delay. One of the main features of the model is that it includes a constant production rate of CTLs export from thymus, and an immune response delay. We derive the basic reproduction number R 0 and establish that the global dynamics is completely determined by the values of R 0. We show that if R 0 ≤ 1, then the infection free equilibrium is globally asymptotically stable ; whereas, if R 0 > 1, then there exist a chronic infection equilibrium, which is globally asymptotically stable in absence of immune response delay. Furthermore, for the special case with only immune response delay, we determine some conditions for stability switches of the chronic infection equilibrium. Numerical simulations indicate that the intracellular delays and immune response delay can stabilize and/or destabilize the chronic infection equilibrium.Nous considerons un modèle qui décrit la dynamique de l'infection du VIH prenant en compte les transmissons virus-cellule et cellule-cellule et la réponse immunitaire. Ce modèle inclut quatre retards continus décrivant respectivement les retards intracellulaires et le retard de la réponse immunitaire. Ce modèle prend également en compte un taux de production des cellules CTL issue du thymus. Nous déterminons le taux de reproduction de base R 0 et montrons que la dynamique global est completement déterminé par sa valeur. Nous montrons que si R 0 ≤ 1 alors l'infection peut être éliminé ; alors que si R 0 > 1, il existe un équilibre endémique qui est globallement stable en absence du retard de la réponse immunitaire. Dans le cas spécial avec seulement la reponse immunitaire, nous déterminons des conditions de changement de stabilité de l'équilibre endémique. Des simulations numériques indiquent que les retards intracellulaires et le retard de la réponse immunitaire peuvent stabilisé et/ou destabilisé l'équilibre endémique
Very- and ultra-long-period seismic signals prior to and during caldera formation on La Réunion Island
No full textInternational audienceearly detection of the onset of a caldera collapse can provide crucial information to understand their formation and thus to minimize risks for the nearby population and visitors. Here, we analyse the 2007 caldera collapse of piton de la Fournaise on La Réunion Island recorded by a broadband seismic station. We show that this instrument recorded ultra-long period (ULP) signals with frequencies in the range (0.003-0.01 Hz) accompanied by very-long period (VLP) signals (between 0.02 and 0.50 Hz) prior to and during the caldera formation suggesting it is possible to detect the beginning of the collapse at depth and anticipate its surface formation. Interestingly, VLP wave packets with a similar duration of 20 s are identified prior to and during the caldera formation. We propose that these events could result from repeating piston-like successive collapses occurring through a ring-fault structure surrounding a magma reservoir from the following arguments: the source mechanism from the main collapse, the observations of slow source processes as well as observations from the field and the characteristic ring-fault seismicity. Caldera collapses are rare (only seven events over the last 100 years) and particularly destructive volcanic events that can induce catastrophic changes in the shape of a volcanic edifice and its environment 1. Identifying the occurrence of the first collapse at depth is of major importance in evaluating the triggering factors and anticipating the caldera surface formation. This detection can help to predict or at least indicate early future caldera collapses and subsequent consequences such as explosive eruptions, (e.g. those that followed the major Kīlauea Caldera collapse in 1470-1510 2), or atmospheric impacts 3. In the past two decades only four caldera collapses have been monitored by dense geophysical networks: chronologically, the 2000 Miyake-jima, Japan; the 2007 Piton de la Fournaise, La Réunion/France; the 2014-2015 Bárðarbunga, Iceland; and the 2018 Kīlauea, Hawai'i 4-7. Laboratory experiments and numerical analyses predicted the occurrence of precursory collapses at depth before the onset of the surface subsidence 8-12 but observations obtained from adequate broadband seismometers were lacking. Until the present study, the Miyake-jima caldera formation was the only known case with evidence of such deep collapses before the faults reached the surface. The deep collapses were suggested from observations of VLP seismic pulses of 20 s width 13. However, the timing of the first collapse at depth was not reported. VLP signals observed at volcanoes are generally considered having frequencies between 0.01-0.5 Hz (ref. 14) and until the 2000 Miyake-jima event, they were generally considered to result from inertial forces associated with changes in the flow of magma and gases through conduits 14. The VLP signals detected during the Miyake-jima caldera formation were explained by different physical mechanisms: (i) a buried geyser model 15 , (ii) a piston-like model 4,13,16 , and (iii) ring-faulting mechanisms related to shear failure on curved or cone-shaped fault structures 17,18. 46 step-like tilt changes (TC) were observed during the Miyake-jima caldera formation and among them 39 were accompanied by the VLP seismic signals 4,19,20. The origin of these TC associated with the VLP pulses have been attributed to either a piston model with a vertical rock column intermittently sinking into a magma reservoir 4,21 or to a magma sheet model with a large sill-lik
A graph theory approach for regional controllability of Boolean cellular automata
No full textInternational audienceControllability is one of the central concepts of modern control theory that allows a good understanding of a system's behaviour. It consists in constraining a system to reach the desired state from an initial state within a given time interval. When the desired objective affects only a sub-region of the domain, the control is said to be regional. The purpose of this paper is to study a particular case of regional control using cellular automata models since they are spatially extended systems where spatial properties can be easily defined thanks to their intrinsic locality. We investigate the case of boundary controls on the target region using an original approach based on graph theory. Necessary and sufficient conditions are given based on the Hamiltonian circuit and strongly connected component. The controls are obtained using a preimage approac
