Le problème de l'enseignement des mesures des grandeurs géométriques à partir de l'exemple des aires

Nous tentons dans cet article à la fois d'élucider un certain nombre de points théoriques concernant la mesure de ces grandeurs et de proposer quelques réflexions didactiques aussi bien sur les difficultés que doivent surmonter les élèves que sur les problèmes qu'on veut les amener à pouvoir résoudre. Nous avons plus particulièrement étudié le problème de la mesure des aires, c'est pourquoi notre réflexion sera plus approfondie dans ce cas que dans celui des volumes

MerriMaryvonne. Activité humaine et conceptualisation. Questions à Gérard Vergnaud

Cet ouvrage est issu du colloque qui s’est tenu à Paris du 28 au 31 janvier 2004 en l’honneur de Gérard Vergnaud. Le livre de 375 pages (dont 17 pages regroupant les références bibliographiques de tous les textes) est complété par un CD-ROM, ce qui donne un ouvrage de 826 pages composé de multiples contributions présentant, utilisant, questionnant, complétant l’œuvre de Vergnaud. Il n’est pas facile d’en rendre compte vu la quantité et la diversité des textes qu’il contient, à la frontière de..

Aires de surfaces planes et nombres décimaux : questions didactiques liées aux élèves en difficulté aux niveaux CM-6ème.

no summaryLa première partie de la thèse porte sur l'enseignement de la notion d'aire au cours moyen et en sixième. L'auteure commence par une analyse de la notion mathématique. Une étude de l'évolution des programmes, des manuels de sixième et des articles parus dans le bulletin de l'APMEP permet de repérer une rupture nette dans l'enseignement et d'en étudier la nature et les circonstances. Elle analyse ensuite une expérience et l'évaluation qui en a été faite par tests et entretiens. Ceci amène à faire de nouvelles propositions d'ingénierie didactique.La deuxième partie soulève quelques questions didactiques à partir de l'enseignement dans des classes composées en grande partie d'élèves de milieu défavorisé et ayant, pour la majorité d'entre eux, des difficultés scolaires. Il s'agit d'un travail exploratoire avec des visées surtout diagnostiques. Les principaux thèmes abordés sont les décimaux et rationnels, la proportionnalité et les aires. Le premier fait l'objet d'études complémentaires par tests dans diverses classes de collège. Elle a observé des classes de cours moyen et de sixième et reprenant des ingénieries didactiques déjà expérimentées. Elle a aussi réalisé une étude de cas, interrogé des élèves plus jeunes, questionné par écrit des élèves de deux cours moyen de recrutement social contrasté et interrogé des enseignants pour cerner les représentations des uns et des autres sur les mathématiques, leur apprentissage et leur enseignement. Les résultats portent sur les contenus abordés et sur l'analyse des facteurs qui nous paraissent contribuer au " non-apprentissage " de certains élèves

Transmission of oocyte DNA damage to preimplantation embryos after in vivo mouse exposure to daunorubicin and cytarabine.

International audienceStudy question: Does oocyte DNA damage induced by a previous in vivo mouse exposure to chemotherapy agents is transmissible to preimplantation embryos?Summary answer: DNA damage was observed in preimplantation embryos issued from mice previously exposed to daunorubicin and cytarabine.What is known already: In acute leukemia, the emergency to start a chemotherapydon’t allow a fertility preservation at the time of diagnosis. Some authors have proposed to cryopreserve mature oocytes or embryos after a controlled ovarian stimulation applied shortly after the induction chemotherapy,which is mainly composed by daunorubicin and cytarabine, and reputated to be less gonadotoxic than alkylant agents. We previously observed DNA damage on mouse oocytes issued from antral follicles exposed in vivo to daunorubicin and cytarabine.Little is known about the risk of transmission of oocyte DNA damage to preimplantation embryos after fecundation of oocytes recently exposed to chemotherapy.Study design, size, duration: By three time, two groups of mice (n = 11) were exposed for four days to cytarabine (10 mg/kg IP) or every two days to daunorubicin (1 mg/kg IV). Each group was compared with a negative control group (n = 11) and with a positive control group (n = 11) injected with cyclophosphamide(75 mg/kg IP). Females were mated one week after exposure and preimplantation embryos were collected by flushing the oviducts.Participants/materials, setting, methods: 4 weeks female CD1 mice were mated one week after exposure for studying embryos conceived from oocytes exposed to chemotherapy at late pre-antral stage of follicular development.Cytotoxicity has been assessed by ovulation and fertilization rates and by embryo morphology. DNA embryonic damage was assessed by: (i) alkaline comet assay to quantify the tail DNA (ii) fluorescent immunohistochemical staining in blastomeres to quantify accumulating γH2AX foci.Main results and the role of chance: In mouse, a recent exposure to daunorubicin and cytarabine did not alter the ovarian response to controlled ovarian stimulation with no adverse impact on the fertilization rate and the number of embryo conceived. Ovulation and fertilization rates in mice previouslyexposed to daunorubicin and cytarabine were similar to those in our negative control group. One week after exposure, we observed with the comet assay a significant increase of embryonic DNA damage after exposure to daunorubicin (16.57 ± 1.3, p = 0.0003) and cytarabine (16.46 ± 1.4, p =0.0003) Vs 26.16 ± 2.5 after cyclophosphamide exposure (p < 0.0001) and 7,01 ± 1,1 in negative control group exposed to an injection of sterile saline solution. The analysis γ-H2AX on embryos showed a significant increase of foci corresponding to DNA double-strand breaks, after exposure to daunorubicin (7.97 ± 1.1; p = 0.001), cytarabine (6.47 ± 0.7, p = 0.0039), cyclophosphamide (5.92 ± 0.9; p = 0.0148) compared with negative control group (2,8 ±0,7).Limitations, reasons for caution: Mouse oocyte DNA is not exactly similar to human oocyte DNA, and would be more sensitive to genotoxic effects of chemotherapy agents. After chemotherapy, the kinetic of DNA repair before and after fertilization has to be studied by further assays in exposed oocyte andin embryos.Wider implications of the findings: DNA damage in preimplantation embryos conceived from oocytes exposed to chemotherapy at late pre-antral stage of follicular development lead us to hypothese a transmission of oocyte DNA damage to preimplantation embryo. In acute leukemia, we strongly adviseto not cryopreserve mature oocytes or embryo early after induction chemotherapy.Trial registration number: Experimental protocols and animal handling procedures were reviewed by the French National Ethics Committee on Animal Experimentation (N° 2017033010523688)

Zero-velocity atom interferometry using a retroreflected frequency chirped laser

International audienceAtom interferometry using stimulated Raman transitions in a retroreflected configuration is the first choice in high-precision measurements because it provides low phase noise, a high-quality Raman wave front, and a simple experimental setup. However, it cannot be used for atoms at zero velocity because two pairs of Raman lasers are simultaneously resonant. Here we report a method which allows this degeneracy to be lifted by using a frequency chirp on the Raman lasers. Using this technique, we realize a Mach-Zehnder atom interferometer hybridized with a force balanced accelerometer which provides horizontal acceleration measurements with a short-term sensitivity of 3.2×10−5ms−2/Hz. This technique could be used for multiaxis inertial sensors, tiltmeters, or atom interferometry in a microgravity environment

L’ingenierie didactique entre recherche et ressource pour l’enseignement et la formation des maitres

Dans le présent cours, nous essayerons de dégager les points qui nous paraissent essentiels en appui sur ces références antérieures, en restant principalement dans le cadre de la théorie des situations, parfois associée à d’autres cadres

Prebiotic effects: metabolic and health benefits

The different compartments of the gastrointestinal tract are inhabited by populations of micro-organisms. By far the most important predominant populations are in the colon where a true symbiosis with the host exists that is a key for well-being and health. For such a microbiota, 'normobiosis' characterises a composition of the gut 'ecosystem' in which micro-organisms with potential health benefits predominate in number over potentially harmful ones, in contrast to 'dysbiosis', in which one or a few potentially harmful micro-organisms are dominant, thus creating a disease-prone situation. The present document has been written by a group of both academic and industry experts (in the ILSI Europe Prebiotic Expert Group and Prebiotic Task Force, respectively). It does not aim to propose a new definition of a prebiotic nor to identify which food products are classified as prebiotic but rather to validate and expand the original idea of the prebiotic concept (that can be translated in 'prebiotic effects'), defined as: 'The selective stimulation of growth and/or activity(ies) of one or a limited number of microbial genus(era)/species in the gut microbiota that confer(s) health benefits to the host.' Thanks to the methodological and fundamental research of microbiologists, immense progress has very recently been made in our understanding of the gut microbiota. A large number of human intervention studies have been performed that have demonstrated that dietary consumption of certain food products can result in statistically significant changes in the composition of the gut microbiota in line with the prebiotic concept. Thus the prebiotic effect is now a well-established scientific fact. The more data are accumulating, the more it will be recognised that such changes in the microbiota's composition, especially increase in bifidobacteria, can be regarded as a marker of intestinal health. The review is divided in chapters that cover the major areas of nutrition research where a prebiotic effect has tentatively been investigated for potential health benefits. The prebiotic effect has been shown to associate with modulation of biomarkers and activity(ies) of the immune system. Confirming the studies in adults, it has been demonstrated that, in infant nutrition, the prebiotic effect includes a significant change of gut microbiota composition, especially an increase of faecal concentrations of bifidobacteria. This concomitantly improves stool quality (pH, SCFA, frequency and consistency), reduces the risk of gastroenteritis and infections, improves general well-being and reduces the incidence of allergic symptoms such as atopic eczema. Changes in the gut microbiota composition are classically considered as one of the many factors involved in the pathogenesis of either inflammatory bowel disease or irritable bowel syndrome. The use of particular food products with a prebiotic effect has thus been tested in clinical trials with the objective to improve the clinical activity and well-being of patients with such disorders. Promising beneficial effects have been demonstrated in some preliminary studies, including changes in gut microbiota composition (especially increase in bifidobacteria concentration). Often associated with toxic load and/or miscellaneous risk factors, colon cancer is another pathology for which a possible role of gut microbiota composition has been hypothesised. Numerous experimental studies have reported reduction in incidence of tumours and cancers after feeding specific food products with a prebiotic effect. Some of these studies (including one human trial) have also reported that, in such conditions, gut microbiota composition was modified (especially due to increased concentration of bifidobacteria). Dietary intake of particular food products with a prebiotic effect has been shown, especially in adolescents, but also tentatively in postmenopausal women, to increase Ca absorption as well as bone Ca accretion and bone mineral density. Recent data, both from experimental models and from human studies, support the beneficial effects of particular food products with prebiotic properties on energy homaeostasis, satiety regulation and body weight gain. Together, with data in obese animals and patients, these studies support the hypothesis that gut microbiota composition (especially the number of bifidobacteria) may contribute to modulate metabolic processes associated with syndrome X, especially obesity and diabetes type 2. It is plausible, even though not exclusive, that these effects are linked to the microbiota-induced changes and it is feasible to conclude that their mechanisms fit into the prebiotic effect. However, the role of such changes in these health benefits remains to be definitively proven. As a result of the research activity that followed the publication of the prebiotic concept 15 years ago, it has become clear that products that cause a selective modification in the gut microbiota's composition and/or activity(ies) and thus strengthens normobiosis could either induce beneficial physiological effects in the colon and also in extra-intestinal compartments or contribute towards reducing the risk of dysbiosis and associated intestinal and systemic pathologies

Concevoir la ville à partir des gares, Rapport final du Projet Bahn.Ville 2 sur un urbanisme orienté vers le rail

Expérimenter de nouvelles façons de faire de l'aménagement et du développement urbain autour des gares ? C'est l'objectif du projet franco-allemand Bahn.Ville 2, recherche-action qui vise à promouvoir « un urbanisme orienté vers le rail ». Valoriser les investissements faits sur les lignes ferroviaires régionales périurbaines par des mesures d'accompagnement dans le domaine de l'urbanisme, optimiser les conditions d'accessibilité aux gares de ces lignes, améliorer la qualité du service rendu aux usagers dans les lieux d'échanges autour de ces gare telles sont les ambitions de ce projet réalisé sur la période 2007-2009. Il s'agit de tester les conditions de la mise en œuvre d'un urbanisme orienté vers le rail

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead