194 research outputs found

    Enseignement transmissif, apprentissage actif : usages du podcasting par les étudiants universitaires

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    Publier des enregistrements audiovisuels de cours ou des séquences complémentaires sous forme de podcasts à l’attention des étudiants ne va pas sans poser de questions : comment utilisent-ils ces médias ? Est-ce une échappatoire au cours en présentiel ? Quels sont les impacts sur l’apprentissage ? L’investissement en temps de l’enseignant est-il rentabilisé ? Les résultats issus de recherches antérieures peuvent être qualifiés de dichotomiques : les uns arguant que le podcasting n’a pas d’effet notable, les autres concluant que l’outil opère certains effets positifs sur les résultats, la motivation ou l’anxiété. Complémentairement à ces études considérant les technologies comme des entités indépendantes des individus et des contextes, notre recherche adopte une approche centrée sur les utilisateurs afin d’analyser la manière dont les étudiants, au sein d’un dispositif donné, intègrent le podcasting dans leurs stratégies d’apprentissage. La recherche a été réalisée auprès d’étudiants provenant de douze cours de l’Université libre de Bruxelles en utilisant un questionnaire (n = 2247), des entretiens compréhensifs (n = 23) et une grille d’analyse des dispositifs pédagogiques. Le croisement de ces analyses de données permet de saisir le sens que les étudiants accordent au podcast, la manière dont ils se l’approprient et infléchissent certaines de ses modalités afin qu’il réponde au mieux à leurs besoins en termes d’apprentissage.Publishing audiovisual recordings of courses or complementary videos for students is not without asking some questions: how do students use these media? Is it a way of escaping classroom activities? What are the impacts on learning? Is it worth the teacher’s investment in time? The results of previous researches are inconsistent: some argue that podcasting has no significant effect, while others have concluded that it shows positive effects on results, motivation or anxiety. Complementing studies that consider that technologies are independent of individuals and contexts, our research takes a user-based approach in analysing how students integrate podcasting in their learning strategies. The research was conducted with students from twelve courses of the Université Libre de Bruxelles using a questionnaire (n= 2247), comprehensive interviews (n= 23) and an analysis grid of teaching devices. Crossing these data gives an understanding of the meaning of the podcasts for the students and the way that they use them to learn

    3D super-resolved in vitro multiphoton microscopy by saturation of excitation

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    We demonstrate a significant resolution enhancement beyond the conventional limit in multiphoton microscopy (MPM) using saturated excitation of fluorescence. Our technique achieves super-resolved imaging by temporally modulating the excitation laser-intensity and demodulating the higher harmonics from the saturated fluorescence signal. The improvement of the lateral and axial resolutions is measured on a sample of fluorescent microspheres. While the third harmonic already provides an enhanced resolution, we show that a further improvement can be obtained with an appropriate linear combination of the demodulated harmonics. Finally, we present in vitro imaging of fluorescent microspheres incorporated in HeLa cells to show that this technique performs well in biological samples

    From fabrication to mode mapping in silicon nitride microdisks with embedded colloidal quantum dots

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    We report on the fabrication of free-standing and optically active microdisks with cadmium-based colloidal quantum dots embedded directly into silicon nitride. We show that the process optimization results in low-loss silicon nitride microdisks. The Si 3 N 4 matrix provides the stability necessary to preserve the optical properties of the quantum dots and observe efficient coupling of the photoluminescence to the resonating microdisk modes. Using a spectrally and spatially resolved microphotoluminescence measurement, we map the emission pattern from the microdisk. This technique allows us to identify the resonant modes. The results show good agreement with numerical mode simulations. © 2012 American Institute of Physics.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

    Implementing two-photon interference in the frequency domain with electro-optic phase modulators

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    Frequency-entangled photons can be readily produced using parametric down-conversion. We have recently shown how such entanglement could be manipulated and measured using electro-optic phase modulators and narrow-band frequency filters, thereby leading to two-photon interference patterns in the frequency domain. Here we introduce new theoretical and experimental developments showing that this method is potentially a competitive platform for the realization of quantum communication protocols in standard telecommunication fibres. We derive a simple theoretical expression for the coincidence probabilities and use it to optimize a Bell inequality. Furthermore, we establish an equivalence between the entangled- photon scheme and a classical interference scheme. Our measurements of two-photon interference in the frequency domain yield raw visibilities in excess of 99%. We use our high quality setup to experimentally validate the theoretical predictions, and in particular we report a violation of the CH74 inequality by more than 18 standard deviations.Comment: 19 pages, 3 figure

    On-chip parametric amplification with 26.5~dB gain at telecommunication wavelengths using CMOS-compatible hydrogenated amorphous silicon waveguides

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    We present the first study of parametric amplification in hydrogenated amorphous silicon waveguides. Broadband on/off amplification up to 26.5~dB at telecom wavelength is reported. Measured nonlinear parameter is 770~W−1m−1\textrm{W}^{-1} \textrm{m}^{-1}, nonlinear absorption 28~W−1m−1\textrm{W}^{-1} \textrm{m}^{-1}, bandgap 1.611.61~eV.Comment: 3 pages, 2 figures, accepted to Optics Letter

    Low power inelastic light scattering at small detunings in silicon wire waveguides at telecom wavelengths

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    When a pump beam is propagating through a silicon nanophotonic waveguide, a very small fraction of the light is scattered to other frequencies. At very low intensity, the amount of scattered light is proportional to the power of the pump beam. We show that the scattering intensity increases linearly within the temperature range 300-575 K and that the photon flux decreases as the inverse of the frequency detuning {\nu} over the investigated bandwidth 0.4 THz < |{\nu}| < 2.5 THz. The simplest interpretation of these observations is that the pump beam is scattered on a 1 dimensional thermal bath of excitations. Finally, the implications of this scattering process for quantum optics applications of silicon nanophotonic structures are discussed.Comment: 11 pages, 5 figures, to submit to Journal of the Optical Society

    Optical solitons :physics and applications for communications

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