Paul Sabatier University

About: Paul Sabatier University is a education organization based out in Toulouse, France. It is known for research contribution in the topics: Population & Catalysis. The organization has 15431 authors who have published 23386 publications receiving 858364 citations.

Spectroscopy of Polycyclic Aromatic Hydrocarbons and Very Small Grains in Photodissociation Regions

Abstract: We have coupled a singular value decomposition method with a Monte Carlo search algorithm to analyse the mid- infrared ISOCAMspectral maps of photodissociation regions (PDRs) in NGC 7023 and ρ Oph-SR3.Three different spectra and their associated spatial distribution were extracted from this analysis. It is shown that they can be associated with polycyclic aromatic hydrocarbons (PAHs) in their cationic and neutral forms and a third population of carbonaceous very small grains (VSGs). The method allows for the first time (i) to separate the contribution of neutral PAHs to the interstellar emission spectrum from that of cationic PAHs; (ii) to show that the 7.8 µm component of the "7.7 µm" broad feature is carried by VSGs, whereas the 7.6 µm component is due to PAHs; and (iii) to give evidence that free-flying PAHs are produced in PDRs by photoevaporation of VSGs. It is proposed that these carbonaceous VSGs are indeed PAH clusters. We derived a minimal size of 400 carbon atoms per cluster and estimated a UV absorption power of the order of 10 −24 WC −1 for their dissociation.

Diversity and carbon storage across the tropical forest biome

Abstract: Tropical forests are global centres of biodiversity and carbon storage. Many tropical countries aspire to protect forest to fulfil biodiversity and climate mitigation policy targets, but the conservation strategies needed to achieve these two functions depend critically on the tropical forest tree diversity-carbon storage relationship. Assessing this relationship is challenging due to the scarcity of inventories where carbon stocks in aboveground biomass and species identifications have been simultaneously and robustly quantified. Here, we compile a unique pan-tropical dataset of 360 plots located in structurally intact old-growth closed-canopy forest, surveyed using standardised methods, allowing a multi-scale evaluation of diversity-carbon relationships in tropical forests. Diversity-carbon relationships among all plots at 1 ha scale across the tropics are absent, and within continents are either weak (Asia) or absent (Amazonia, Africa). A weak positive relationship is detectable within 1 ha plots, indicating that diversity effects in tropical forests may be scale dependent. The absence of clear diversity-carbon relationships at scales relevant to conservation planning means that carbon-centred conservation strategies will inevitably miss many high diversity ecosystems. As tropical forests can have any combination of tree diversity and carbon stocks both require explicit consideration when optimising policies to manage tropical carbon and biodiversity.

Experimental evidence for spatial self-organization and its emergent effects in mussel bed ecosystems.

Abstract: Spatial self-organization is the main theoretical explanation for the global occurrence of regular or otherwise coherent spatial patterns in ecosystems. Using mussel beds as a model ecosystem, we provide an experimental demonstration of spatial self-organization. Under homogeneous laboratory conditions, mussels developed regular patterns, similar to those in the field. An individual-based model derived from our experiments showed that interactions between individuals explained the observed patterns. Furthermore, a field study showed that pattern formation affected ecosystem-level processes in terms of improved growth and resistance to wave action. Our results imply that spatial self-organization is an important determinant of the structure and functioning of ecosystems, and it needs to be considered in their conservation.