Educación científica : el regreso del ciudadano y de la ciudadana

Este trabajo aborda la problemática de la educación científica desde el punto de vista de la formación ciudadana. Se presenta el concepto de competencia profana. La escuela debería dar a todos los estudiantes la oportunidad de iniciarse en la política de las tecnociencias, a fin de que ellos puedan participar en su elaboración y en su puesta en práctica tanto local como global, involucrándose en la solución de las controversias científico-tecnológicas que atraviesan la sociedad actual.This paper focuses on science education from the point of view of citizen education. The concept of profane expertise is presented. Schools should give all students the opportunity to be initiated in technoscientific policies, so that they can participate in their elaboration and performance both locally and globally. Students need to get involved in the solution of the scientific and technological controversies that are present in contemporary society

Enseigner et apprendre les sciences : représentations sociales de futurs enseignants et enseignantes

Au cours de cette recherche, nous nous sommes intéressés à repérer le «savoir théorique» de dix apprentis-enseignants sur le monde et la pratique de l'enseignement et l'apprentissage des sciences. À cette fin, nous avons fait usage du concept de représentation sociale comme instrument conceptuel pourapprocher les conceptions de l'enseignement et de l'apprentissage en cause, et tenter d'y cerner l'intrication entre le cognitif et le social de même que la réciprocité entre les savoirs théorique et pratique qu'elles sont susceptibles de receler. Basée sur une méthodologie qualitative et, plus particulièrement, sur l'analyse des discours recueillis lors d'entretiens individuels, cette recherche permet de mettre en évidence l'ancrage socioculturel des propos exprimés par ces futurs enseignants et enseignantes de sciences

Du concept à la chose: la notion de particule dans les propos d’étudiants à l’égard de phénomènes physiques

Cet article est une synthèse des résultats obtenus lors d’une étude que nous avons réalisée auprès de 12 étudiants de la fin du collégial, et qui visait à élucider leurs usages et représentations du concept de particule. Nous verrons comment le point de vue développé dans le domaine de la psychosociologie des représentations (Moscovici, 1961, 1984) quant aux modes d’appropriation par lesquels le savoir scientifique peut être rendu digeste fournit un éclairage intéressant sur la tendance marquée que nous avons pu observer, une fois de plus, dans les discours des étudiants, et que l’on peut résumer comme suit: l’imputation aux phénomènes et concepts scientifiques d’un statut similaire à celui des objets du réel usuel. Our study considers twelve graduating high school students’ practical and theoretical understandings of the concept of particles. The psychology of representations (Moscovici, 1961, 1984) suggests how scientific knowledge can be rendered digestible, and helps to explain the marked tendency in student discourse to give to scientific phenomena and concepts the same status accorded to ordinary material objects.

La formation à l'enseignement des sciences : le virage épistémologique

Depuis plusieurs années, les travaux que nous avons effectués dans le domaine de l'éducation à la science, suivant une perspective constructiviste, nous ont permis de distinguer, parmi les nombreux problèmes qui jalonnent l'enseignement et l'apprentissage des sciences, des problèmes d'ordre épistémologique. Dans la recherche que nous relatons succinctement dans cet article, nous nous intéressons cette fois à la formation à l'enseignement des sciences. Nous avons en particulier conçu et mis à l'épreuve, en contexte universitaire, une stratégie de formation qui, tout en puisant aux travaux contemporains en épistémologie, en sociologie et en histoire des sciences, se préoccupe de faciliter chez les apprentis-enseignants le développement d'un point de vue réflexif et averti à l'égard de leur propre épistémologie «spontanée» et de ses inévitables effets sur leur pratique professionnelle

Prospectives

Tiré de: Prospectives, vol. 23, no 4, déc. 1987Titre de l'écran-titre (visionné le 24 janv. 2013

Optimization criteria and design of few-mode erbium-doped fibers for cladding-pumped amplifiers

We propose a novel optimization method that combines two design criteria to reduce the differential modal gain (DMG) in few-mode cladding-pumped erbium-doped fiber amplifiers (FM-EDFAs). In addition to the standard criterion that considers the mode intensity and dopant profile overlap, we introduce a second criterion that ensures that all doped regions have the same saturation behavior. With these two criteria, we define a figure-of-merit (FOM) that allows the design of MM-EDFAs with low DMG without high computational cost. We illustrate this method with the design of six-mode erbium-doped fibers (EDFs) for amplification over the C-Band targeting designs that are compatible with standard fabrication processes. The fibers have either a step-index or a staircase refractive index profile (RIP), with two ring-shaped erbium-doped regions in the core. With a staircase RIP, a fiber length of 29 m and 20 W of pump power injected in the cladding, our best design leads to a minimum gain of 22.6 dB while maintaining a DMGmax under 0.18 dB. We further show that the FOM optimization achieves a robust design with low DMG over a wide range of variations in signal power, pump power and fiber length

Does hyperthermia constrain flight duration in a short-distance migrant?

While some migratory birds perform non-stop flights of over 11 000 km, many species only spend around 15% of the day in flight during migration, posing a question as to why flight times for many species are so short. Here, we test the idea that hyperthermia might constrain flight duration (FD) in a short-distance migrant using remote biologging technology to measure heart rate, hydrostatic pressure and body temperature in 19 migrating eider ducks (Somateria mollissima), a short-distance migrant. Our results reveal a stop-and-go migration strategy where migratory flights were frequent (14 flights day(−1)) and short (15.7 min), together with the fact that body temperature increases by 1°C, on average, during such flights, which equates to a rate of heat storage index (HSI) of 4°C h(−1). Furthermore, we could not find any evidence that short flights were limited by heart rate, together with the fact that the numerous stops could not be explained by the need to feed, as the frequency of dives and the time spent feeding were comparatively small during the migratory period. We thus conclude that hyperthermia appears to be the predominant determinant of the observed migration strategy, and suggest that such a physiological limitation to FD may also occur in other species. This article is part of the themed issue ‘Moving in a moving medium: new perspectives on flight’

Absence of system xc⁻ on immune cells invading the central nervous system alleviates experimental autoimmune encephalitis

Background: Multiple sclerosis (MS) is an autoimmune demyelinating disease that affects the central nervous system (CNS), leading to neurodegeneration and chronic disability. Accumulating evidence points to a key role for neuroinflammation, oxidative stress, and excitotoxicity in this degenerative process. System x(c)- or the cystine/glutamate antiporter could tie these pathological mechanisms together: its activity is enhanced by reactive oxygen species and inflammatory stimuli, and its enhancement might lead to the release of toxic amounts of glutamate, thereby triggering excitotoxicity and neurodegeneration. Methods: Semi-quantitative Western blotting served to study protein expression of xCT, the specific subunit of system x(c)-, as well as of regulators of xCT transcription, in the normal appearing white matter (NAWM) of MS patients and in the CNS and spleen of mice exposed to experimental autoimmune encephalomyelitis (EAE), an accepted mouse model of MS. We next compared the clinical course of the EAE disease, the extent of demyelination, the infiltration of immune cells and microglial activation in xCT-knockout (xCT(-/-)) mice and irradiated mice reconstituted in xCT(-/-) bone marrow (BM), to their proper wild type (xCT(+/+)) controls. Results: xCT protein expression levels were upregulated in the NAWM of MS patients and in the brain, spinal cord, and spleen of EAE mice. The pathways involved in this upregulation in NAWM of MS patients remain unresolved. Compared to xCT(+/+) mice, xCT(-/-) mice were equally susceptible to EAE, whereas mice transplanted with xCT(-/-) BM, and as such only exhibiting loss of xCT in their immune cells, were less susceptible to EAE. In none of the above-described conditions, demyelination, microglial activation, or infiltration of immune cells were affected. Conclusions: Our findings demonstrate enhancement of xCT protein expression in MS pathology and suggest that system x(c)- on immune cells invading the CNS participates to EAE. Since a total loss of system x(c)- had no net beneficial effects, these results have important implications for targeting system x(c)- for treatment of MS

The Euchromatic and Heterochromatic Landscapes Are Shaped by Antagonizing Effects of Transcription on H2A.Z Deposition

A role for variant histone H2A.Z in gene expression is now well established but little is known about the mechanisms by which it operates. Using a combination of ChIP–chip, knockdown and expression profiling experiments, we show that upon gene induction, human H2A.Z associates with gene promoters and helps in recruiting the transcriptional machinery. Surprisingly, we also found that H2A.Z is randomly incorporated in the genome at low levels and that active transcription antagonizes this incorporation in transcribed regions. After cessation of transcription, random H2A.Z quickly reappears on genes, demonstrating that this incorporation utilizes an active mechanism. Within facultative heterochromatin, we observe a hyper accumulation of the variant histone, which might be due to the lack of transcription in these regions. These results show how chromatin structure and transcription can antagonize each other, therefore shaping chromatin and controlling gene expression