Nuclear Medium Effects in the Relativistic Treatment of Quasifree Electron Scattering

Non-relativistic reduction of the S-matrix for the quasifree electron scattering process $A\left(~e, e'p~\right)A-1$ is studied in order to understand the source of differences between non-relativistic and relativistic models. We perform an effective Pauli reduction on the relativistic expression for the S-matrix in the one-photon exchange approximation. The reduction is applied to the nucleon current only; the electrons are treated fully relativistically. An expansion of the amplitude results in a power series in the nuclear potentials. The series is found to converge rapidly only if the nuclear potentials are included in the nuclear current operator. The results can be cast in a form which reproduces the non-relativistic amplitudes in the limit that the potentials are removed from the nuclear current operator. Large differences can be found between calculations which do and do not include the nuclear potentials in the different orders of the nuclear current operator. In the high missing momentum region we find that the non-relativistic calculations with potentials included in the nuclear current up to second order give results which are close to those of the fully relativistic calculation. This behavior is an indication of the importance of the medium modifications of the nuclear currents in this model, which are naturally built into the relativistic treatment of the reaction.Comment: Latex, 26 pages including 5 uuencoded postscript figures. accepted for publication in Phys. Rev. C

Dating of the Butte de Clermont basaltic maar by means of the quartz inclusion method

Is an image without frame possible ? The nowadays virtual realities could induce us to believe it, since the worlds they offer seem to have broken the usual limits of image. This article, on the contrary, tries to point that the notion of frame, although it can be reconsidered, remains one of the necessary conditions of representation

Tephrostratigraphie et prehistoire des 160 derniers millenaires en Limagne d'Auvergne (Massif Central, France)

pdf dépôsé avec l'autorisation de l'éditeurNational audienceThe Geocler 1 core extracted from the Clermont crater lake sediments and surface studies made in several localities north of Clermont provided numerous stratigraphic, environmental and chronological data (TL and radiocarbon) which allow us to present a chronostratigraphy of the Limagne for the past 160 ky. The Clermont maar eruption has been previously TL dated around 160 ky. In the crater-lake sediments, between 86 and 28 m deep, 111 well identified ash-falls have been encountered. No acid tephra has been discovered, but several layers rich in acicular minerals indicate acid eruptions, the origin of which remains unclear. Between 15 and 7 ky, 14 main ash-falls have been recognized and for some of them, the volcano has been iden-tified: Puy de La Nugère, Puy de Dôme, Puy Chopine, Kilian Crater and Puy de Pariou contribute greatly to the local tephra succession. Perspectives for an increase in prehistoric studies of volcanic areas are outlined.Une tephrostratigraphie des retombées cendreuses en Limagne est établie à partir d'affleurements et du sondage profond Géocler 1 dans le maar de Clermont. Elle est étayée par des calages naturalistes et physiques (radiocarbone, thermoluminescence). Entre 160 et 40 ka BP, cent-onze retombées (chiffre minimum) caractérisent le volcanisme de la bordure de Limagne et la Chaîne des Puys ancienne qui sont bien différenciés minéralogiquement. Pendant cette période, huit apports ponctuels de minéraux aciculaires témoignent d'une activité acide lointaine qui reste à lo-caliser. Entre 15 et 7 ka BP, la Chaîne des Puys récente est très active : dans le secteur étudié, les tephra du Puy de la Nugère, du Puy de Dôme, du Puy Chopine, du Cratère Kilian et du Puy de Pariou contribuent largement à la téphrostratigraphie locale. Pour chacune de ces périodes, les implications éventuelles de l'activité éruptive sur la distribution du peuplement préhistorique sont discutées. En conclusion, les perspectives de développement de la recherche préhistorique en zone volcanique sont esquissées

The toxicity of trace metal elements in Downy Oak in Gardanne Mining Basin

International audienceThe Gardanne mining basin is undoubtedly one of the peri‐urban territories of the Bouches‐du‐Rhône where air pollution is a major issue both in terms of public health and the preservation of natural environments. The various industrial activities, including the aluminum smelter, have contributed to exacerbating pollution with metallic trace elements [1;2]. Indeed, Bauxite manufacturing by the Bayer process in alumina production is associated with a by‐product, bauxite residue (BR), also termed “red mud”, a complex mixture of elemental constituents. Throughout the world, BR storage sites have been sources of adverse effects on the environment and the Mange Gary site is not an exception. The purpose of this work falls within the context of the environmental transition policy undertaken by the aluminum plant.We investigated the impact of the BR from Mange Garri on some populations of Quercus pubescens

The toxicity of trace metal elements in Downy Oak in Gardanne Mining Basin

International audienceThe Gardanne mining basin is undoubtedly one of the peri‐urban territories of the Bouches‐du‐Rhône where air pollution is a major issue both in terms of public health and the preservation of natural environments. The various industrial activities, including the aluminum smelter, have contributed to exacerbating pollution with metallic trace elements [1;2]. Indeed, Bauxite manufacturing by the Bayer process in alumina production is associated with a by‐product, bauxite residue (BR), also termed “red mud”, a complex mixture of elemental constituents. Throughout the world, BR storage sites have been sources of adverse effects on the environment and the Mange Gary site is not an exception. The purpose of this work falls within the context of the environmental transition policy undertaken by the aluminum plant.We investigated the impact of the BR from Mange Garri on some populations of Quercus pubescens

A chronological framework for a long persistant archeological record: Melka Kunture, Ethiopia

International audienceNew 40Ar/39Ar geochronological data for several volcanic ash horizons from Melka Kunture, Ethiopia, allow for significantly more precise age constraints to be placed upon the lithostratigraphy, archaeology and paleontology from this long record. Ashes from the Melka Kunture Formation at Gombore yielded the most reliable age constraints, from 1.393 ± 0.162 Ma2 (millions of years ago) near the base of the section to 0.709 ± 0.013 Ma near the top. Dating the Garba section proved more problematic, but the base of the section, which contains numerous Oldowan obsidian artifacts, may be >1.719 ± 0.199 Ma, while the top is securely dated to 0.869 ± 0.020 Ma. The large ignimbrite from the Kella Formation at Kella and Melka Garba is dated to 1.262 ± 0.034 Ma and pre-dates Acheulean artifacts in the area. The Gombore II site, which has yielded two Homo skull fragments, 'twisted bifaces,' and a preserved butchery site, is now constrained between 0.875 ±0.010 Ma and 0.709 ± 0.013 Ma. Additional ashes from these and other sites further constrain the timing of deposition throughout the section. Integration with previously published magnetostratigraphy has allowed for the first time a relatively complete, reliable timeline for the deposition of sediments, environmental changes, archaeology, and paleontology at Melka Kunture

20th century sediment budget trends on the Western Gulf of Lions shoreface (France): An application of an integrated method for the study of sediment coastal reservoirs

International audienceThis paper presents a shoreface sediment budget established for the 20th century (1895–1984–2009) along the microtidal wave-dominated coast of the western Gulf of Lions (Languedoc-Roussillon, Mediterranean Sea, SE France). The implementation of a diachronic bathymetric approach, coupled with the definition of sand reservoirs (upper sand unit — USU) by very high-resolution seismic surveys and the results of LiDAR investigations, offers a new means of defining precisely the magnitude and change trends of the sediment budget. The aim of this study is to link the Large Scale Coastal Behaviour (LSCB) of the littoral prism (expressed in terms of shoreface sediment budget, shoreface sediment volume and spatial distribution pattern of cells) to climatic change, river sediment input to the coast, longshore sediment transport distribution, impact of hard coastal defence structures and artificial beach nourishment. The results show a significant reduction of the volume of the western Gulf of Lions littoral prism over 114 years (− 26.1 ± 4.6 × 106 m3). From 1895 to 1984, the overall budget is slightly positive, with a volume estimated at 4.1 ± 3.5 × 106 m3. For 1984–2009, however, the estimated sediment budgets clearly indicate that erosion is dominant over the last 25 years, with a volume loss of − 30.2 ± 4.2 × 106 m3. In relation to the long-term sediment budget and longshore drift pattern, the long-term trend of the USU volume distribution displays strong spatio-temporal contrasts linked to longshore sediment drift, spatial distribution of fluvial sediment inputs and hard engineering structures. Locally, the sedimentary reservoir is significantly eroded within a century (− 80% of USU), since the initial amount present was low and not sustainable. The emphasis is on the importance of considering the volume changes of available sediment reservoirs rather than their losses and gains. Erosion of the Languedoc-Roussillon shoreface is likely to continue in the future due to the “natural” decrease of river sediment input and the sand removal for human purposes. Consequently the littoral sand prism results in sedimentary reservoirs that are gradually being used up