Retour sur un objet communicationnel situé

À partir d’observations en/hors ligne réalisées sur le collectif féministe #NousToutes et menées dans le cadre de recherches doctorales, la présente étude invite à une réflexion méthodologique au prisme des théories sur les savoirs situés. Plus particulièrement, il s’agit ici de questionner l’importance de l’« exposition située » du chercheur-e dans les processus de production de la recherche, en articulant ses expériences en/hors ligne et son rapport au terrain physique et/ou numérique.Based on off/online observations of the feminist collective #NousToutes carried out in doctoral research, this study proposes a methodological reflection through the prism of standpoint theories. More particularly, by focusing on the researcher’s physical/digital experiences, this study highlights the impact of “off/online standpoint” in the research production processe

Relative geomagnetic field intensity and reversals from Upper Miocene sections in Crete

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Tracing the sources of fine sediment in a nickel mining catchment using fallout and geogenic radionuclides (Thio River, New Caledonia)

International audienceSoil erosion and subsequent sediment transfer in rivers are exacerbated in tropical regions exposed to heavy rainfall. In New Caledonia, an island located in the southwestern part of the Southern Pacific Ocean, a significant fraction of this sediment is likely originating from tributaries draining nickel mining sites that are known to increase the terrigenous inputs to the rivers and, potentially to UNESCO World Heritage listed coastal lagoons. However, downstream contributions from these tributaries remain to be quantified. A pilot sediment tracing study has therefore been conducted in the 400-km 2 Thio River catchment. Fallout and geogenic radionuclides have been measured in sediment deposits collected in potential sources, i.e. (i) tributaries draining mines, (ii) tributaries draining 'natural' areas affected by landslides, and (iii) the main stem of the Thio River. Thorium-228 and Caesium-137 provide the best discrimination between sediment originating from the two tributaries. A distribution modelling approach was used to quantify the relative sediment contributions from these tributaries to the Thio River main stem. Results demonstrate that tributaries draining mining sites supply the majority of sediment (67-84%) to the main river. In the future, the validity of these results obtained on sediment deposits collected in April and May 2015 should be verified over a longer time period by applying a similar approach to sediment cores collected in the Thio river deltaic plain. Once validated, this method will be applicable to other catchments draining mines in New Caledonia to design appropriate measures to limit sediment supply to the lagoon

Modelling the dilution of radioactive contamination in sediment transiting Fukushima coastal rivers (2011-2015)

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Constraining sediment dynamics during flood events using fallout radionuclides (Be-7 and Pb-210(xs)): a pilot study in a tropical catchment of SE Asia

International audienceSoil erosion is particularly intense in mountainous subtropical regions where heavy storms result in the production of large quantities of suspended sediment, leading to both on-site and off-site siltation problems and conveying contaminants and biological compounds along streams. To implement efficient controls on sediment transfer, it is necessary to monitor suspended matter loads and determine whether sediments are directly exported from the catchment during a given flood or re-suspended from deposits left by previous floods. Determination of sediment residence time in catchments can be performed combining fallout radionuclides (Be-7, Pb-210 and Cs-137) measurements in both rainfall and suspended sediments, but prerequisites for their use as tracers during flood events are still required. We conducted experiments along a network of nested catchments with area increasing from 0.12 to 6.15 km$^2$ , and sampled rainfall and suspended sediment loads during a flood that occurred at the beginning of the rainy season in May 2012. The experiment was carried out in the Houay Xon catchment, part of the MSEC (Multi-Scale Environmental Changes, http://msec3.net/portal/) project in the Northern Luang Prabang province of Laos. This catchment, under shifting cultivation since the end of the 1960s for a large part of its surface, is characterized by a steep topography (slopes ranging from 3% to 350% with a mean slope of 56%) and a land use evolution prone to gully erosion. The seasonal distribution of rainfall controls the Be-7 and Pb-210(xs) activities of soils in the catchment. With a half-life of 53 days, the fallout Be-7 activity of the previous wet season should have sufficiently decayed during the 6-months dry period to be neglected compared to new supply by early rains of the following wet season. Atmospheric deposition of Be-7 and Pb-210(xs) was measured after flocculation of rainfall samples by aluminum chloride hexahydrate and after dehydration of 75 suspended sediment samples (0.5-128 g/L) collected by automatic samplers during the flood. Soils, gullies and riverbanks were also sampled across the catchment to document the potential sources of sediment supply to the river. Cumulative precipitation reached 27 mm in less than 50 minutes, leading to an overall export of ca. 274 tons of sediments from the catchment during the flood. The Be-7/Pb-210(xs) ratios of suspended particles were used to monitor "newly eroded" and "older re-suspended" sediment contributions to suspended matter transport along the network. Dynamic fingerprinting of rainwater vs. groundwater and soil-detached vs. re-suspended particles supplies at the river monitoring stations was confronted to results obtained using particles-Cs-137 activity, water-delta-O-18 and particulate organic matter-delta-C-13 measurements

Depth distribution of radiocesium in Fukushima paddy fields three years after the accident

International audienceRice paddy fields located in the vicinity of the Fukushima Dai-Ichi Nuclear Power Plant (FDNPP) were contaminated by radioactive fallout from the March 2011 accident. Although many studies have investigated the fate of radiocesium in soil in the months following the accident, the potential migration of radiocesium in rice paddy fields requires further examination after major typhoons occurred in this region in 2011 and 2013. Further investigations are also required because paddy fields are typically comprised of Andosols, a soil type in which radiocesium has been known to potentially migrate deeper in the depth profile. To investigate the depth migration of radiocesium we collected soil cores in 10 paddy fields located less than 20 km from the FDNPP in November 2013. The maximum depth penetration of 137Cs was attributed to field maintenance (e.g. grass cutting) (97% of 137Cs in the upper 5-cm) and farming operations (tillage/cultivation-83% of 137Cs in the upper 5-cm). The low migration observed in undisturbed paddy fields could be attributed to the presence of phyllosilicates that were detected by X-ray diffraction in Andosols. As radiocesium is mainly located in the uppermost soil layers, we recommend the rapid removal of these upper layers (e.g. the top 5 cm) to reduce radiocesium export during erosive events such as the major typhoons known to impact the region. Further research is required to thoroughly understand the impacts of erosion on the transfer and migration of radiocesium throughout the Fukushima Prefecture

Journal Pre-proof Group-level cortical surface parcellation with sulcal pits labeling

International audienc

Sparse description of the cortical surface pediatric development: a sulcal pits study

International audienceDespite the large variability of sulcal folds, their deepest points, namely the sulcal pits, provide a sparse and reproducible description of the cortical surface. Their role during the antenatal and pediatric development of the brain remains unclear. This work is the first study of the evolution of all sulcal pits during healthy pediatric development. We propose a new method to identify sulcal pits across subjects that benefits from the input of sulcal basins using a varifold metric. We then present a procedure to extract the amplitude and principal direction of sulcal pits trajectories