La construction de l'insertion socioprofessionnelle des jeunes à l'épreuve du temps : une enquête longitudinale: Rapport final

La recherche dont nous rendons compte ici est une recherche au long cours, qui s'inscrit dans la durée et procède par enquêtes répétées. Il convient donc dans un premier temps de rappeler quelques éléments de sa construction initiale, qui ont été présentés plus longuement dans le premier rapport de recherche rédigé en 20001. Certains de ces éléments ne bougent pas, restent stables et permettent la comparaison ; d'autres évoluent dans le temps, au fur et à mesure que se construisent les trajectoires d'insertion. Nous commencerons donc ici par rappeler les principes de base, les hypothèses et les choix méthodologiques effectués dès le début de cette entreprise. Nous ferons ensuite le point sur la méthodologie de l'enquête et sur l'évolution de la population du panel, lors des trois vagues d'enquête qui ont déjà été réalisées. Nous préciserons ensuite les questions traitées ici, autour du thème central des évolutions des façons dont les jeunes abordent le monde du travail. Entrant ensuite dans la comparaison temporelle proprement dite, nous présenterons et discuterons des mouvements qui se sont produits dans la répartition des jeunes dans des catégories de trajectoires. Celles-ci avaient été identifiées il y a trois ans. Nous les reprenons pour voir comment les jeunes s'y situent aujourd'hui. Nous préciserons ensuite plus rapidement quelques points-clés de ces évolutions : les bifurcations biographiques et la notion de projet, l'évolution des réseaux de relations personnelles au moment de l'entrée dans la vie professionnelle, l'utilisation éventuelle de ces relations pour trouver du travail, les autres dimensions de l'entrée dans la vie adulte et les trajectoires de décohabitation parentale, pour discuter enfin du rôle relatif du travail dans l'accès au statut d'adulte

Les liens invisibles entre agriculture de proximité et commerce alimentaire dit "ethnique"

International audienceLa littérature scientifique concernant les agricultures de proximité, i.e. celles qui se pratiquent à proximité des marchés qu’elles desservent, s’est beaucoup renouvelée ces dernières années sous l’effet d’un intérêt réaffirmé pour l’agriculture urbaine et périurbaine . Si ces études ont surtout été attentives aux logiques de reterritorialisation que traduisent ces agricultures, certains auteurs soulignent la nécessité, d’une part, de mieux appréhender la diversité de ces agricultures de proximité, de leurs protagonistes, de leurs facteurs d’évolution et, d’autre part, de reconsidérer leurs transformations du point de vue agricole (géographie et sociologie agricoles, agronomie) . Elles appellent de surcroît une mise en tension avec les situations d’injustice socio-spatiale qui naissent tant de l’évolution des relations villes / campagnes que de la dynamique des systèmes agro-alimentaires . De nouvelles formes de vulnérabilité se repèrent en effet : difficultés d’accès à une alimentation de qualité pour les consommateurs ; mise à l’écart d’une partie des consommateurs et des producteurs des nouveaux réseaux malgré la proximité géographique ; précarisation des conditions de travail de certains agriculteurs .La recherche exploratoire dont nous proposons de présenter les résultats dans cette communication se penche sur des pratiques agricoles qui se déploient en marge des agricultures de proximité classiquement étudiées et des représentations positives associées actuellement aux agricultures urbaines et périurbaines du point de vue des « populations aisées et éduquées » des centres-villes. Elle vient souligner la diversité de cette nouvelle catégorie tant en termes d’acteurs que de modes d’exploitation (statut foncier, main d’œuvre, assolements, commercialisation….)Un premier travail sur deux paysages d’« agriculture de filières longues » (la Plaine de France dans le Val-d’Oise et le Comtat Venaissin dans les Bouches-du-Rhône) a ainsi permis de mettre à jour l’existence de certaines formes d’exploitations agricoles directement liées à des marchés urbains de niche du commerce dit « ethnique » (alimentation méditerranéenne ou asiatique). Le caractère « invisible » ou caché de ces formes d’agricultures de proximité (lieux d’installation, parcellaire singulier, statut précaire, informalité…) a impliqué de mobiliser plusieurs méthodes d’investigation : exploration empirique, observation participante sur l’exploitation, entretiens semi-directifs et photo-interprétation, enquêtes sur les marchés de revente. Les premiers résultats obtenus permettent de montrer l’existence de liens originaux entre le commerce dit « ethnique » implanté dans les centres urbains et la réorganisation spatiale des espaces agricoles de proximité. Ils apportent aussi des éléments sur les différentes trajectoires des travailleurs agricoles au sein de ces réseaux d’agriculture de proximité

High throughput methodology for synthesis, screening, and optimization of solid state Lithium ion electrolytes

A study of the lithium ion conductor Li3xLa2/3–xTiO3 solid solution and the surrounding composition space was carried out using a high throughput physical vapor deposition system. An optimum total ionic conductivity value of 5.45 × 10–4 S cm–1 was obtained for the composition Li0.17La0.29Ti0.54 (Li3xLa2/3–xTiO3x = 0.11). This optimum value was calculated using an artificial neural network model based on the empirical data. Due to the large scale of the data set produced and the complexity of synthesis, informatics tools were required to analyze the data. Partition analysis was carried out to determine the synthetic parameters of importance and their threshold values. Multivariate curve resolution and principal component analysis were applied to the diffraction data set. This analysis enabled the construction of phase distribution diagrams, illustrating both the phases obtained and the compositional zones in which they occur. The synthetic technique presented has significant advantages over other thin film and bulk methodologies, in terms of both the compositional range covered and the nature of the materials produce

Early adaptation to oxygen is key to the industrially important traits of Lactococcus lactis ssp. cremoris during milk fermentation

Background: Lactococcus lactis is the most used species in the dairy industry. Its ability to adapt to technological stresses, such as oxidative stress encountered during stirring in the first stages of the cheese-making process, is a key factor to measure its technological performance. This study aimed to understand the response to oxidative stress of Lactococcus lactis subsp. cremoris MG1363 at the transcriptional and metabolic levels in relation to acidification kinetics and growth conditions, especially at an early stage of growth. For those purposes, conditions of hyper-oxygenation were initially fixed for the fermentation. Results: Kinetics of growth and acidification were not affected by the presence of oxygen, indicating a high resistance to oxygen of the L. lactis MG1363 strain. Its resistance was explained by an efficient consumption of oxygen within the first 4 hours of culture, leading to a drop of the redox potential. The efficient consumption of oxygen by the L. lactis MG1363 strain was supported by a coherent and early adaptation to oxygen after 1 hour of culture at both gene expression and metabolic levels. In oxygen metabolism, the over-expression of all the genes of the nrd (ribonucleotide reductases) operon or fhu (ferrichrome ABC transports) genes was particularly significant. In carbon metabolism, the presence of oxygen led to an early shift at the gene level in the pyruvate pathway towards the acetate/2,3-butanediol pathway confirmed by the kinetics of metabolite production. Finally, the MG1363 strain was no longer able to consume oxygen in the stationary growth phase, leading to a drastic loss of culturability as a consequence of cumulative stresses and the absence of gene adaptation at this stage. Conclusions: Combining metabolic and transcriptomic profiling, together with oxygen consumption kinetics, yielded new insights into the whole genome adaptation of L. lactis to initial oxidative stress. An early and transitional adaptation to oxidative stress was revealed for L. lactis subsp. cremoris MG1363 in the presence of initially high levels of oxygen. This enables the cells to maintain key traits that are of great importance for industry, such as rapid acidification and reduction of the redox potential of the growth media

Optical control of the spin of a magnetic atom in a semiconductor quantum dot

International audienceThe control of single spins in solids is a key but challenging step for any spin-based solid-state quantum-computing device. Thanks to their expected long coherence time, localized spins on magnetic atoms in a semiconductor host could be an interesting media to store quantum information in the solid state. Optical probing and control of the spin of individual or pairs of Mn atoms (S=5/2) have been obtained in II-VI and III-V semiconductor quantum dots during the last years. In this paper , we review recently developed optical control experiments of the spin of an individual Mn atoms in II-VI semiconductor self-assembled or strain free quantum dots. We first show that the fine structure of the Mn atom and especially a strained induced magnetic anisotropy is the main parameter controlling the spin memory of the magnetic atom at zero magnetic field. We then demonstrate that the energy of any spin state of a Mn atom or pairs of Mn atom can be independently tuned by using the optical Stark effect induced by a resonant laser field. The strong coupling with the resonant laser field modifies the Mn fine structure and consequently its dynamics. We then describe the spin dynamics of a Mn atom under this strong resonant optical excitation. In addition to standard optical pumping expected for a resonant excitation, we show that the Mn spin population can be trapped in the state which is resonantly excited. This effect is modeled considering the coherent spin dynamics of the coupled electronic and nuclear spin of the Mn atom optically dressed by a resonant laser field. Finally, we discuss the spin dynamics of a Mn atom in strain free quantum dots and show that these structures should permit a fast optical coherent control of an individual Mn spin

A many-body singlet prepared by a central spin qubit

Controllable quantum many-body systems are platforms for fundamental investigations into the nature of entanglement and promise to deliver computational speed-up for a broad class of algorithms and simulations. In particular, engineering entanglement within a dense spin ensemble can turn it into a robust quantum memory or a computational platform. Recent experimental progress in dense central spin systems motivates the design of algorithms that use a central-spin qubit as a convenient proxy for the ensemble. Here we propose a protocol that uses a central spin to initialize two dense spin ensembles into a pure anti-polarized state and from there creates a many-body entangled state -- a singlet -- from the combined ensemble. We quantify the protocol performance for multiple material platforms and show that it can be implemented even in the presence of realistic levels of decoherence. Our protocol introduces an algorithmic approach to preparation of a known many-body state and to entanglement engineering in a dense spin ensemble, which can be extended towards a broad class of collective quantum states.Comment: 11 pages, 6 figures, and supplementary material

Collective Quantum Memory Activated by a Driven Central Spin

Coupling a qubit coherently to an ensemble is the basis for collective quantum memories. A single driven electron in a quantum dot can deterministically excite low-energy collective modes of a nuclear spin ensemble in the presence of lattice strain. We propose to gate a quantum state transfer between this central electron and these low-energy excitations—spin waves—in the presence of a strong magnetic field, where the nuclear coherence time is long. We develop a microscopic theory capable of calculating the exact time evolution of the strained electron-nuclear system. With this, we evaluate the operation of quantum state storage and show that fidelities up to 90% can be reached with a modest nuclear polarization of only 50%. These findings demonstrate that strain-enabled nuclear spin waves are a highly suitable candidate for quantum memory.We thank E. Chekhovich for helpful discussions. This work was supported by the ERC PHOENICS grant (617985), the EPSRC Quantum Technology Hub NQIT (EP/M013243/1), and the Royal Society (RGF/EA/181068). D. A. G. acknowledges support from St. John’s College Title A Fellowship. E. V. D. and J. M. acknowledge funding from the Danish Council for Independent Research (Grant No. DFF-4181-00416). C. L. G. acknowledges support from a Royal Society Dorothy Hodgkin Fellowship

APOE genotype influences the gut microbiome structure and function in humans and mice: relevance for Alzheimer’s disease pathophysiology

Apolipoprotein E (APOE) genotype is the strongest prevalent genetic risk factor for Alzheimer’s disease (AD). Numerous studies have provided insights into the pathologic mechanisms. However, a comprehensive understanding of the impact ofAPOEgenotype onmicroflora speciation and metabolismis completely lacking. In this study,we investigated the association between APOE genotype and the gut microbiome composition in human and APOE–targeted replacement (TR) transgenic mice. Fecal microbiota amplicon sequencing from matched individuals with different APOE genotypes revealed no significant differences in overall microbiota diversity in group aggregated human APOE genotypes. However, several bacterial taxa showed significantly different relative abundance between APOE genotypes. Notably, we detected an association of Prevotellaceae and Ruminococcaceae and several butyrate-producing genera abundances with APOE genotypes. These findings were confirmed by comparing the gutmicrobiota ofAPOE-TRmice. Furthermore, metabolomic analysis of murine fecalwater detected significant differences in microbe-associated amino acids and short-chain fatty acids between APOE genotypes. Together, these findings indicate that APOE genotype is associated with specific gut microbiome profiles in both humans and APOE-TR mice. This suggests that the gut microbiome is worth further investigation as a potential target to mitigate the deleterious impact of the APOE4 allele on cognitive decline and the prevention of A