INTERACTIONS OF SWIFT H, H+2 AND H+3 WITH THIN FOILS

Some specific effects seen in the interactions of swift hydrogenic beams penetrating thin foils are presented. We describe first dynamic effects due to periodic electron density fluctuations trailing fast charged particles moving in solids which can sustain plasmon oscillations. Studies of non equilibrated charge distribution dowstream very thim foils permit us to separate the role played by projectile and target electrons in neutral atom production. The observation of bound molecules emerging from thin target raises questions about their formation and the processes involved. Finally we show how original measurements on the dissociation of fast molecular ions by thin foils has opened up new possibilities for the investigation of molecular ion structure

Du pollen aux paysages : nouvelles méthodologies pour reconstituer les paysages

International audienceLes données polliniques fossiles offrent la possibilité de reconstituer l'histoire de la végétation à différentes échelles spatio-temporelles. Récemment, des modèles de la relation pollen-végétation qui prennent en compte les processus de dispersion et de déposition des pollens ont été développés pour interpréter et convertir les assemblages polliniques en pourcentage de couverture de plantes, groupes de plantes ou composantes paysagères pour une échelle régionale (≥ 50 km) et locale (≤ 2 km) autour des points d'enregistrements. Des reconstitutions quantitatives du couvert végétal dans le passé sont nécessaires pour résoudre les questions de recherche actuelles dans les domaines de l'histoire des climats, de l'archéologie et de la conservation (entretien) des paysages. Dans un premier volet, cet article exposera les nouveaux concepts, outils développés par le réseau POLLANDCAL (POLlen LANDscape CALibration) pour reconstituer le couvert végétal régional et local à partir des données polliniques fossiles en utilisant deux modèles : REVEALS (Regional Estimates of Vegetation Abundance from Large Lakes) et LOVE (Local Vegetation Estimates). Puis, dans un deuxième volet, nous illustrerons la mise en place de cette démarche quantitative sur le massif jurassien et les premiers résultats obtenu

Estimating the Relevant Source Area of Pollen in the past cultural landscapes of southern Sweden -- A forward modelling approach

International audienceMiddle and Late Holocene in southern Sweden, in order to explore the possible effects of past changes in vegetation composition, openness and structure in terms of patch size and spatial distribution. The RSAP of small basins (bogs or lakes) in the past has to be estimated if quantitative reconstruction of past vegetation at the local spatial scale is to be achieved using Sugita's Landscape Reconstruction Algorithm (LRA). In this study we apply a forward modelling approach to estimate past RSAP using the computer simulation model HUMPOL. The landscape designs are based on past landscape maps produced using a combination of palaeobotanical, archaeological and historical data, and the area's geology and soil characteristics. Four time windows characterised by different landscape/land-use were selected, i.e. Early Neolithic, Late Bronze Age, Viking Age, and Middle Ages. We found that RSAP estimates for hypothetical past landscapes in Skåne differ by ca. 600 m to 1200 m between the selected time periods, whatever the size of the basin (lake or bog, 25- 250 m radius). The most probable explanation for the differences in RSAP between time slices is variable patch size and spatial distribution of patches in the landscape. The RSAPs vary between ca. 1200 and 2300 m for small basins (25 m and 70 m radius), and between ca. 2000 and 3000 m for larger basins (250 m radius). These values are within the range of earlier estimates of modern and past RSAPs for southern Scandinavia obtained using simulated or empirical data. These results suggest that, given the type of setting of that region in terms of taxa composition and traditional land-use, the RSAP for small-size lakes (25-250 m radius) will generally be in the range ca. 1200-3000 m. The forward modelling approach is found to be useful to assess the possible effects on RSAP of changes in vegetation/landscape characteristics between different periods of the past. Moreover, comparison of RSAP estimates obtained using both the forward and backward modelling approaches will be important to identify the most credible RSAP estimates for the past

Effects of land use and climate change on erosion intensity and sediment geochemistry at Lake Lehmilampi, Finland

International audienceThis paper aims to evaluate the possible relationships between erosion intensity and changes in climate and land use during the past 5.5 cal. k years at Lake Lehmilampi, eastern Finland. In this study we compare a detailed geochemical sediment record with (1) forest and land use history inferred from the first pollen and charcoal records from Lake Lehmilampi, and (2) existing archaeological surveys and independent proxy-records of climate change in the study region. The physical and geochemical sediment parameters examined include grain size analysis data and 23 chemical elements, determined with four selective extractions and ICP-MS. There are indications of possible human impact in the lake catchment as early as the Neolithic period, c. 3000-2550 bc, but the first undisputable signs are dated to 1800-100 bc. Cereal pollen reappears at c. ad 1700 and increases rapidly until c. ad 1950. The Holocene Thermal Maximum, its end c. 2000 bc, and the 'Medieval Climate Anomaly' were major climate events that had a prominent effect on erosion intensity, while human impact was a more significant factor during the period 3000 bc-ad 800 and from ad 1500 onwards. Although signs of changes in erosion intensity found in the sediment were small in this small catchment, they were significant enough to have a clear impact on the fraction of potentially mobile element species. This fraction increases with decreasing erosion intensity, which is probably related to a higher degree of chemical weathering and leaching during periods of decreased erosio

Testing the effect of site selection and parameter setting on REVEALS-model estimates of plant abundance using th Czech Quaternary Palynological database

International audiencetypes, PFTs) is used in the LANDCLIM project to assess the effect of human-induced land-cover change on past climate in NW Europe. Using the Czech Quaternary Pollen Database, this case study evaluates the extent to which selection of data and input parameters for the REVEALS model applications would affect reconstruction outcomes. The REVEALS estimates of PFTs (grid-cell based REVEALS PFT estimates, GB REVEALS PFT-s) are calculated for five time windows of the Holocene using fossil pollen records available in each 1°×1°grid cell of the Czech Republic. The input data and parameters selected for testing are: basin type and size, number of 14C dates used to establish the chronology of the pollen records, number of taxa, and pollen productivity estimates (PPE). We used the Spearman correlation coefficient to test the hypothesis that there is no association between GB REVEALS PFT-s using different data and parameter inputs. The results show that differences in the basin size and type, number of dates, number and type of taxa (entomophilous included or not), and PPE dataset do not affect the rank orders of the GB REVEALS PFT-s significantly, except for the cases when entomophilous taxa are included. It implies that, given careful selection of data and parameter and interpretation of results, REVEALS applications can use pollen records from lakes and bogs of different sizes together for reconstruction of past land cover at the regional to sub-continental spatial scales for purposes such as the study of past land cover-climate interactions. Our study also provides useful criteria to set up protocols for data compilation REVEALS applications of this kind

Probing the liquid-t-gas like phase transition in a cluster via a caloric curve

IP

Eye and Orbital Anatomy in Metopic Synostosis

Background: Metopic synostosis patients have a high prevalence of orthoptic anomalies, including hyperopia, astigmatism, and amblyopia. We hypothesized altered orbital anatomy contributes to suboptimal visual outcomes by adversely affecting eye anatomy and growth from early life onward. Therefore, we aimed to investigate eye and orbital anatomy in metopic synostosis. Methods: We conducted a retrospective study in nonsyndromic metopic synostosis patients (n = 134, median age 0.43 years [IQR 0.45]) with nonsyndromic sagittal synostosis patients (n = 134, median age 0.27 years [IQR 0.23]) as controls. Primary analyses focused on eye dimensions (axial length, width, and globe height) and orbital dimensions, correcting for sex and age. Measurements were obtained from preoperative computed tomography scans. Results: Axial length and width in metopic synostosis patients did not differ from sagittal synostosis patients, but globe height was significantly smaller (P = 0.0002). Lateral wall interorbital length, lateral orbital wall length, anterior medial interorbital length, and maximal medial interorbital length were significantly smaller, and anterior vertical orbital height and maximal vertical orbital height were significantly larger (P &lt; 0.001). The central orbital axis and interorbital angle were significantly narrower, and medial-to-lateral orbital wall angle was wider (P &lt; 0.001). Conclusions: Metopic synostosis patients have more shallow, wider, and higher orbits. Eye dimensions are similar in sagittal synostosis patients, although globe height was smaller. Altered orbital and eye dimensions in metopic synostosis probably have a causal relation with an unknown order of development. How these dimensions relate to future orthoptic anomalies (eg, refractive error) needs further investigation.</p

Total partial and electron-capture cross sections for ionization of water vapor by 20-150 keV protons

IP

Reply to the comment on direct experimental evidence for a negative heat capacity in the liquid to gas phase transition in hydrogen cluster ions backbending of the caloric curve

IP

Collision induced cluster fragmentation: From fragment size distributions to the caloric curve

IPMInternational audienceWe report on a cluster fragmentation study involving collisions of high-energy (60 keV/amu) H3+(H2)m hydrogen cluster ions (m=9, 11) with atomic helium or fullerenes. The experimental characterisation of the cluster fragmentation not only by the average fragment size distribution but also by a statistical analysis of the fragmentation events has become possible owing to a recently developed multi-coincidence technique in which all the fragments of all collisions occurring in the experiment are mass analysed on an event-by-event basis. By selecting specific decay reactions we can start after the energizing collision with a microcanonical cluster ion ensemble of fixed excitation energy. From the respective fragment distributions for these selected decay reactions we derive corresponding temperatures of the decaying cluster ions. The relation between this temperature and the excitation energy (caloric curve) exhibits the typical prerequisites of a first order phase transition in a finite system, in the present case signalling the transition from a bound cluster type situation to the free gas phase