Identifying and prioritising services in European terrestrial and freshwater ecosystems

Ecosystems are multifunctional and provide humanity with a broad array of vital services. Effective management of services requires an improved evidence base, identifying the role of ecosystems in delivering multiple services, which can assist policy-makers in maintaining them. Here, information from the literature and scientific experts was used to systematically document the importance of services and identify trends in their use and status over time for the main terrestrial and freshwater ecosystems in Europe. The results from this review show that intensively managed ecosystems contribute mostly to vital provisioning services (e.g. agro-ecosystems provide food via crops and livestock, and forests provide wood), while semi-natural ecosystems (e.g. grasslands and mountains) are key contributors of genetic resources and cultural services (e.g. aesthetic values and sense of place). The most recent European trends in human use of services show increases in demand for crops from agro-ecosystems, timber from forests, water flow regulation from rivers, wetlands and mountains, and recreation and ecotourism in most ecosystems, but decreases in livestock production, freshwater capture fisheries, wild foods and virtually all services associated with ecosystems which have considerably decreased in area (e.g. semi-natural grasslands). The condition of the majority of services show either a degraded or mixed status across Europe with the exception of recent enhancements in timber production in forests and mountains, freshwater provision, water/erosion/natural hazard regulation and recreation/ecotourism in mountains, and climate regulation in forests. Key gaps in knowledge were evident for certain services across all ecosystems, including the provision of biochemicals and natural medicines, genetic resources and the regulating services of seed dispersal, pest/disease regulation and invasion resistance

Primary processes: from atoms to diatomic molecules and clusters

International audienceThis article presents a short review of the main progresses achieved at the GANIL facilities during the last thirty years in the field of ion-atom and ion-diatomic molecule collisions. Thanks to the wide range of projectile energies and species available on the different beam lines of the facility, elementary processes such as electron capture, ionization and excitation have been extensively studied. Beside primary collision mechanisms, the relaxation processes of the collision partners after the collision have been another specific source of interest. Progresses on other fundamental processes such as Young type interferences induced by ion-molecule collisions or shake off ionization resulting from nuclear beta decay are also presented. 1. Introduction For the electronic structures of atoms and molecules, precise theoretical knowledge and high-resolution experimental data are available. But the complete understanding of dynamic processes in atomic collisions remains a challenge, due to large theoretical problems in describing time-dependent many-particle reactions, and to experimental difficulties in performing complete experiments in which all relevant quantities are accessible. Elementary collisions involving ions, atoms and molecules play an important role in many gaseous and plasma environments, where they provide both the heating and cooling mechanisms. The study of such collisions is thus not only of fundamental importance, it is also essential for the understanding of large-scale systems such as astrophysical plasmas, planetary atmospheres, gas discharge lasers, semiconductor processing plasmas, and fusion plasmas. Collisions between ions and atoms (or simple molecules) give also access to the elementary processes responsible for energy transfer in ion-matter and ion-biological molecule collisions. Complete knowledge of these elementary processes is thus of primordial importance for ion induced modification of materials as well as for radiolysis, radiotherapy and biological damages due to radiation exposure

Sections efficaces de destruction de l'alignement des niveaux 2p de l'atome d'argon par collision contre des atomes d'hélium, de néon, d'argon et de krypton dans l'état fondamental

The author measures the effective cross sections for the destruction of the alignment of most of the 2 p levels of an argon atom by collision with helium, neon, argon and krypton ground state atoms, using the Hanle effect in a discharge tube method. The results are compared with Omont's theory (J. Physique 26 (1965) 26).L'auteur mesure les sections efficaces de destruction de l'alignement de la plupart des niveaux 2 p de l'atome d'argon par collision contre des atomes d'hélium, de néon, d'argon et de krypton dans l'état fondamental, en utilisant la méthode d'effet Hanle dans un tube à décharge. Les résultats sont comparés à la théorie d'Omont (J. Physique 26 (1965) 26)

Dépolarisation par collision des niveaux 2p de l'argon excités sélectivement dans une décharge au moyen d'un laser accordable

Most of the 2p levels of argon have been selectively excited in a discharge by a tunable dye laser. Measurements have been made by the Hanle effect of the effective cross sections for the destruction of orientation and alignment in these levels by collision with helium, neon argon and krypton ground state atoms. The results are compared with Omont's theory (J. Physique 26 (1965) 26).Les niveaux 2p de l'argon sont pour la plupart excités sélectivement dans une décharge au moyen d'un laser accordable. On mesure par effet Hanle les sections efficaces de destruction de l'orientation et de l'alignement de ces niveaux par collision contre des atomes d'hélium, de néon, d'argon et de krypton dans l'état fondamental. Les résultats sont comparés à la théorie d'Omont (J. Physique 26 (1965) 26)

Etude de la dépendance en température des sections efficaces de dépolarisation par collision des niveaux 2p de l'atome d'argon

The temperature dependence of the effective cross-sections for the destruction of orientation and alignment of 2p levels of argon atom, by collisions with helium, neon, argon and krypton ground state atoms is studied between 300 and 700 K. The observed variations are in agreement with the hypothesis of an R-6 attractive potential for heavy perturbers (argon and krypton), and demonstrate the influence of the repulsive part of the interaction potential for helium and neon perturbers. The anomalous behaviour of 2p2 level cross-sections is attributed to short-range modification of the coupling between this level and the other levels of the configuration.On étudie la variation avec la température, entre 300 et 700 K, des sections efficaces de destruction de l'orientation et de l'alignement des niveaux 2p de l'atome d'argon par collisions contre des atomes d'hélium, de néon, d'argon et de krypton à l'état fondamental. Les variations obtenues sont en accord avec l'hypothèse d'un potentiel attractif en R-6 dans le cas des perturbateurs les plus lourds (argon et krypton) et mettent en évidence l'influence de la partie répulsive du potentiel d'interaction dans le cas de l'hélium et du néon. Le comportement singulier des sections efficaces du niveau 2p2 est attribué à la modification, à courte portée, du couplage de ce niveau avec les autres niveaux de la configuration

Diamagnetic behaviour of xenon Rydberg states studied by the R.F. optogalvanic method

The diamagnetic behaviour of xenon nf Rydberg states is studied using single-mode dye laser excitation and an R.F. optogalvanic detection method The levels are followed from their zero-field positions, through the inter-l and inter-n diamagnetic mixing regimes, until they reach the zero-field 2P3/2 ionization threshold, where the so-called « quasi Landau » regime is observed and up to 20 cm -1 above this threshold The positions of the dominant lines are found to be in agreement with the results of hydrogenic calculations and with the predictions of a semi-classical approximation.On étudie le comportement diamagnétique d'états de Rydberg nf du xénon au moyen d'une excitation par laser à colorant monomode et de la méthode de détection R.F. optogalvanique. Les niveaux sont suivis depuis leur position en champ nul, au travers des régimes de mélange diamagnétique des l puis des n, jusqu'a ce qu'ils atteignent la limite d'ionisation en champ nul 2P3/2, où l'on observe le régime dit de « quasi Landau » puis jusqu'a environ 20 cm-1 au-delà de cette limite. On vérifie que les positions des raies dominantes sont en accord avec les résultats de calculs effectués sur un modèle hydrogénoïde et avec les prédictions d'une approximation semi-classique

R.F. OPTOGALVANIC DETECTION OF RYDBERG AND AUTOIONIZING LEVELS OF RARE GASES : DIAMAGNETIC BEHAVIOUR OF XENON RYDBERG STATES

Quand un oscillateur R.F. est utilisé pour produire une décharge dans une cellule contenant un gaz, le régime et donc la consommation de l'oscillateur peuvent être très sensibles aux variations d'impédance du plasma, telles que celles résultant de l'excitation laser de transitions entre niveaux d'excitation électronique de l'élément considéré. Ceci constitue le principe de la méthode de détection R.F. optogalvanique que nous appliquons à l'étude de niveaux de Rydberg et autoionisants du krypton et du xénon. On montre dans le cas de niveaux de Rydberg du xénon que la méthode s'applique particulièrement bien à la détection en présence d'un champ magnétique fort.When a R.F. oscillator is used to produce a discharge in a gas cell, the rate and hence the power consumption of the oscillator may be very sensitive to impedance variations of the plasma, such as those induced by laser transition between electronic excitation levels of the considered element. This is the basis of the R.F. optogalvanic detection method which we apply to the study of Rydberg and autoionizing levels of krypton and xenon. It is shown in the case of xenon Rydberg states that the method is especially suitable for detection in presence of a strong magnetic field

Structure hyperfine des niveaux 7p(3/2)2 et 7p(5/2)2 de 129Xe et 131Xe

Using laser excitation and level crossing method we have determined the hyperfine structure constants of 7p(3/2)2 and 7p(5/2)2 levels for the isotopes 129 and 131 of xenon. Landé factors have also been determined for the same levels of even isotopes by magnetic resonance. The measured values are A129 = - 31.457(17) mK, A131 = 9.329(8) mK, B131 = 0.283(24) mK, gJ = 1.351 9(6) for 7p(3/2)2 level and A129 = - 44.118(31) mK, A 131 = 13.082(14) mK, B131 = 8.204(30) mK, g J = 1.127 6(5) for 7p(5/2)2 level.Par excitation laser et méthode de croisements de niveaux nous avons déterminé les constantes de structure hyperfine des niveaux 7p(3/2)2 et 7p(5/2)2 des isotopes 129 et 131 du xénon. Les facteurs de Landé des mêmes niveaux des isotopes pairs ont également été déterminés par résonance magnétique. Les valeurs mesurées sont A 129 = — 31,457(17) mK, A131 = 9,329(8) mK, B131 = 0,283(24) mK, gJ = 1,3519(6) pour le niveau 7p(3/2)2 et A129 = - 44,118(31) mK, A 131 = 13,082(14) mK, B131 = 8,204(30) mK, g J = 1,127 6(5) pour le niveau 7p(5/2)2

Mesure de la structure hyperfine de niveaux 6p, 7p, 4f et 5f du 129Xe et 131Xe

The authors have measured the h.f.s. of 5 levels of the 5p5(6p + 7p) configurations, 1 level of the 5p5 4f and 1 level of the 5p5 5f configuration of 129Xe and 131Xe by a level crossing technique.Les auteurs ont mesuré les constantes de structure hyperfine de 5 niveaux des configurations 5p5(6p + 7p), de 1 niveau de la configuration 5p5 4f et de 1 niveau de la configuration 5p5 5f des xénon 129 et 131 par une méthode de croisement de niveaux