The global carbon cycle and its changes over glacial–interglacial cycles

Carbon is an essential element for life, food and energy. It is also a key component of greenhouse gases and, thus, plays an important role in past and present climatic changes

Comparison of simulated and reconstructed variations in East African hydroclimate over the last millennium

The multi-decadal to centennial hydroclimate changes in East Africa over the last millennium are studied by comparing the results of forced transient simulations by six general circulation models (GCMs) with published hydroclimate reconstructions from four lakes: Challa and Naivasha in equatorial East Africa, and Masoko and Malawi in southeastern inter-tropical Africa. All GCMs simulate fairly well the unimodal seasonal cycle of precipitation in the Masoko-Malawi region, while the bimodal seasonal cycle characterizing the Challa-Naivasha region is generally less well captured by most models. Model results and lake-based hydroclimate reconstructions display very different temporal patterns over the last millennium. Additionally, there is no common signal among the model time series, at least until 1850. This suggests that simulated hydroclimate fluctuations are mostly driven by internal variability rather than by common external forcing. After 1850, half of the models simulate a relatively clear response to forcing, but this response is different between the models. Overall, the link between precipitation and tropical sea surface temperatures (SSTs) over the pre-industrial portion of the last millennium is stronger and more robust for the Challa-Naivasha region than for theMasoko-Malawi region. At the inter-annual timescale, last-millennium Challa-Naivasha precipitation is positively (negatively) correlated with western (eastern) Indian Ocean SST, while the influence of the Pacific Ocean appears weak and unclear. Although most often not significant, the same pattern of correlations between East African rainfall and the Indian Ocean SST is still visible when using the last-millennium time series smoothed to highlight centennial variability, but only in fixed-forcing simulations. This means that, at the centennial timescale, the effect of (natural) climate forcing can mask the imprint of internal climate variability in large-scale teleconnections

Gliomes de bas grade et plasticité cérébrale : Implications fondamentales et cliniques

La plasticité cérébrale post-lésionnelle (PCPL) décrit l’ensemble des processus permettant au système nerveux central de se réorganiser après une atteinte physique. Depuis l’influent travail de Broca et la prise de pouvoir des modèles « localisationnistes », il est largement admis que la PCPL est limitée, voire impossible, au sein des aires fonctionnelles majeures, dites éloquentes. Pourtant, depuis quelques années, de nouvelles données issues de la chirurgie des gliomes infiltrants de bas-grade (GIBG) sont venues bousculer ce dogme. Il apparaît en effet de plus en plus clairement que des excisions cérébrales massives peuvent être intégralement compensées, pour ne laisser place à aucun déficit fonctionnel détectable. Des techniques d’imagerie pré- et post-chirurgicales, ainsi que des procédures de stimulation peropératoire, permettent de suivre la nature et la cinétique de ces compensations. Celles-ci débutent avant la chirurgie, en réaction à l’invasion tumorale, et se consolident pendant et après la procédure opératoire. Les mécanismes de la compensation pré- et post-lésionnelle impliquent les aires périlésionnelles, les structures cérébrales ipsilatérales distantes et les homologues controlatéraux des zones réséquées. De tels résultats ont d’évidentes implications fondamentales et cliniques, et ouvrent d’importantes perspectives pour la compréhension de la dynamique cérébrale et des phénomènes de plasticité.Post-lesional plasticity (PLP) describes the processes that reorganize cerebral connections after an injury. Since Broca’s influential contribution and the common endorsement of “localisationist” models of brain physiology, it has been widely admitted that PLP was limited, not to say impossible in the so-called “eloquent areas”. However, recent observations associated with the surgical treatments of low grade gliomas have called this dogma into question. Indeed, more and more evidence suggest that large cerebral resections can be compensated so efficiently that no functional deficits can be detected after the surgery. Pre and post surgical investigations based on imaging techniques, as well as intra-surgical investigations involving electrical stimulations, allow to track the nature and the temporal characteristics of these compensations. Compensatory reactions begin before the operation, in response to the tumoral growth. They remain active during and after the surgery. These compensations can involve the perilesional adjacent areas, the distant ipsilateral cerebral structures and the homologous contra-lateral regions. When considered together these results have obvious fundamental and clinical implications. They open new perspectives for understanding cerebral dynamics and the process of brain plasticity

Identification of machining defects by Small Displacement Torsor and form parameterization method

In the context of product quality, the methods that can be used to estimate machining defects and predict causes of these defects are one of the important factors of a manufacturing process. The two approaches that are presented in this article are used to determine the machining defects. The first approach uses the Small Displacement Torsor (SDT) concept [BM] to determine displacement dispersions (translations and rotations) of machined surfaces. The second one, which takes into account form errors of machined surface (i.e. twist, comber, undulation), uses a geometrical model based on the modal shape's properties, namely the form parameterization method [FS1]. A case study is then carried out to analyze the machining defects of a batch of machined parts

Does a Peer Recommender Foster Students' Engagement in MOOCs?

International audienceOverall the social capital of MOOCs is under-exploited. For most students in MOOCs, autonomous learning often means learning alone. Students interested in adding a social dimension to their learning can browse discussion threads, join social medias and may decide to message other students… but usually in a random way. This common isolation might be a contributing factor on student attrition rate and on their general learning experience. To foster learners' persistence in MOOCs, we propose to enhance the MOOC experience with a recommender which provides each student with an individual list of rich-potential contacts, created in real-time on the basis of their own profile and activities. This paper describes a controlled study conducted from Sept. to Nov. 2015 during a MOOC on Project Management. A recommender panel was integrated to the users' interface and allowed to manage contacts, send them an instant message or consult their profile. The population (N = 8,673) was randomly split into 2 parts: a control group, without any recommendations, and an experimental group in which students could choose to activate and use the recommender. After having demonstrated that these populations were similar up to the activation of the recommender, we evaluate the effect of the recommender on the basis of four pillars of learners' persistence: attendance, completion, success and participation. Results suggest that the recommender improved all these four factors: students were much more likely to persist and engage in the MOOC if they received recommendations than if they did not

Increasing MOOC completion rates through social interactions: a recommendation system

International audienceE-learning research shows students who interact with their peers are less likely to drop out from a course, but is this applicable to MOOCs? This paper examines MOOC attrition issues and how encouraging social interactions can address them: using data from 4 sessions of the GdP MOOC, a popular Project Management MOOC, we confirm that students displaying a high level of social interaction succeed more than those who don't. We successively explore two approaches fostering social interactions: 1) in MOOC GdP5, we give access to private group forums, testing various group types and sizes, 2) in MOOC GdP6, we implement a recommendation system, suggesting relevant chat contacts using demographic and progression criteria. This papers presents our preliminary findings

Suivi scientifique de vingt-sept régénérations naturelles de chêne sessile et de hêtre en Ardenne: retour d'expérience

National audienceRégénérer naturellement le chêne apparaît très délicat en Ardenne et cela se traduit déjà par un déficit marqué de jeunes chênes au niveau régional. Afin de rechercher des solutions sylvicoles à ce problème, vingt-sept régénérations naturelles de hêtre et de chêne ont été suivies entre 2007 et 2011. L’analyse montre clairement les besoins en lumière des chênes par rapport aux hêtres et, surtout, l’importance d’effectuer des nettoiements afin de réduire les effets de la compétition des hêtres sur les chênes

Graphene in silicon photovoltaic cells

Graphene is an allotrope of carbon. Its structure is one-atom-thick planar sheets of carbon atoms that are densely packed in a honeycomb crystal lattice [1]. The richness of optical and electronic properties of graphene attracts enormous interest. Its true potential seems to be in photonics and optoelectronics, where the combination of its unique optical and electronic properties can be fully exploited. The optical absorption of graphene layers is proportional to the number of layers, each absorbing A=1-T=πα=2.3% over the visible spectrum [2].The rise of graphene in photonics and optoelectronics is shown by several recent results, ranging from solar cells and light emitting devices, to touch screens, photodetectors and ultrafast lasers. Current photovoltaic (PV) technology is dominated by Si cells, with an energy conversion coefficient up to 25% [3]. Such an inorganic PV consists in a current transparent conductor (TC) replacing one of the electrodes of a PIN photodiode. The standard material used so far for these electrodes is indium-tinoxide, or ITO. But indium is expensive and relatively rare, so the search has been on for a suitable replacement. A possible substitute made from inexpensive and ubiquitous carbon is graphene. Being only constituted of carbon, it will become cheap and easily recyclable. But at the moment, the major difficulty consists in its fabrication and/or transfer. Our project consists in synthetizing graphene by CVD (Chemical Vapor Deposition) on Cu and in transferring the obtained layer on silicon PV cells, and then in testing their energy conversion efficiency

De la station au territoire : quels contours pour les destinations touristiques ?

Dans le contexte du post-tourisme, les stations de sports d’hiver situées à proximité d’aires urbaines constituent un laboratoire d’observation de tendances plus générales. Dans le contexte de la périurbanisation, l’interpénétration des sphères du tourisme et du quotidien y est exacerbée. Fragmentation des séjours (réduits de un à trois jours, voire à de l’excursionisme à la journée) et nouvelles formes de résidentialité y sont souvent plus marquées. Ces dynamiques pèsent fortement sur l’évolution du modèle économique des stations fondé sur le séjour touristique. Dans cet article, nous proposons d’analyser ce phénomène au regard de l’ancrage territorial, traditionnellement considéré comme un facteur d’adaptation. À travers deux cas d’étude contrastés dans le pourtour de l’agglomération grenobloise, les Sept-Laux et Saint-Pierre-de-Chartreuse, nous montrerons comment cet ancrage peut également être une variable adaptative.In the context of post-tourism, ski resorts located near urban areas are a laboratory observation of broader trends. In the context of suburbanization, the interpenetration of the spheres of tourism and daily life is exacerbated. Fragmentation of stay (reduced to one to three days, or even to day trippers) and new forms of daily migration are often more marked there. These dynamics strongly influence the evolution of the economic model of the resorts based on the long stay holidays. In this paper, we propose to analyze this phenomenon in terms of local anchorage, traditionally regarded as an adaptation factor. Through two contrasted case studies in the periphery of Grenoble, Sept-Laux and Saint-Pierre-de-Chartreuse, we will show how this anchoring can also be an adaptive variable