Interacción en el grupo y el encuentro con la exhibición : un estudio de aprendizaje en el museo de historia natural mediante el análisis de las epistemologías prácticas

En este estudio se presenta una forma de analizar el aprendizaje a un nivel discursivo en un museo de ciencias naturales. El material utilizado procede de la grabación en video de una actividad educativa en el Museo de Historia Natural en Estocolmo, Suecia. En dicha actividad los estudiantes, en pequeños grupos y con los textos de la exposición ocultos, realizan una interpretación de dioramas que representan escenas naturales. Mediante el uso de un análisis de las epistemológias practicas se describe como los estudiantes construyen el significado y desarrollan el conocimiento a partir de la interaccion en el grupo y el encuentro con el diorama en la exhibición. Los resultados del presente estudio demuestran que el uso de este tipo de análisis puede ser muy útil para describir el proceso de aprendizaje de las ciencias en museos y otros ambientes pedagógicos extramurales

Spatially resolved kinematics of the central regions of M83: hidden mass signatures and the role of supernovae

The barred grand-design spiral M83 (NGC 5236) is one of the most studied galaxies given its proximity, orientation, and particular complexity. Nonetheless, many aspects of the central regions remain controversial conveying our limited understanding of the inner gas and stellar kinematics, and ultimately of the nucleus evolution. In this work, we present AO VLT-SINFONI data of its central ~235x140 pc with an unprecedented spatial resolution of ~0.2 arcsec, corresponding to ~4 pc. We have focused our study on the distribution and kinematics of the stars and the ionised and molecular gas by studying in detail the Pa_alpha and Br_gamma emission, the H_2 1-0S(1) line at 2.122 micron and the [FeII] line at 1.644 micron, together with the CO absorption bands at 2.293 micron and 2.323 micron. Our results reveal a complex situation where the gas and stellar kinematics are totally unrelated. Supernova explosions play an important role in shaping the gas kinematics, dominated by shocks and inflows at scales of tens of parsecs that make them unsuitable to derive general dynamical properties. We propose that the location of the nucleus of M83 is unlikely to be related to the off-centre 'optical nucleus'. The study of the stellar kinematics reveals that the optical nucleus is a gravitationally bound massive star cluster with M_dyn = (1.1 \pm 0.4)x10^7 M_sun, formed by a past starburst. The kinematic and photometric analysis of the cluster yield that the stellar content of the cluster is well described by an intermediate age population of log T(yr) = 8.0\pm0.4, with a mass of M \simeq (7.8\pm2.4)x10^6 M_sun.Comment: 14 pages, 10 figures, accepted for publication in Ap

Spatially resolved kinematics, galactic wind, and quenching of star formation in the luminous infrared galaxy IRAS F11506-3851

We present a multi-wavelength integral field spectroscopic study of the low-z LIRG IRAS F11506-3851, on the basis of VIMOS and SINFONI (ESO-VLT) observations. The morphology and the 2D kinematics of the gaseous (neutral and ionized) and stellar components have been mapped using the NaD doublet, the H$\alpha$ line, and the near-IR CO(2-0) and CO(3-1) bands. The kinematics of the ionized gas and the stars are dominated by rotation, with large observed velocity amplitudes and centrally peaked velocity dispersion maps. The stars lag behind the warm gas and represent a dynamically hotter system, as indicated by the observed dynamical ratios. Thanks to these IFS data we have disentangled the contribution of the stars and the ISM to the NaD feature, finding that it is dominated by the absorption of neutral gas clouds in the ISM. The neutral gas 2D kinematics shows a complex structure dominated by two components. On the one hand, the thick slowly rotating disk lags significantly compared to the ionized gas and the stars, with an irregular and off-center velocity dispersion map. On the other hand, a kpc-scale neutral gas outflow is observed along the semi-minor axis of the galaxy, as revealed by large blueshifted velocities (30-154 km/s). We derive an outflowing mass rate in neutral gas of about 48 $\dot{M_{\rm w}}$/yr. Although this implies a global mass loading factor of 1.4, the 2D distribution of the ongoing SF suggests a much larger value of mass loading factor associated with the inner regions (R$<$200 pc), where the current SF represents only 3 percent of the total. All together these results strongly suggest that we are witnessing (nuclear) quenching due to SF feedback in IRAS F11506-3851. However, the relatively large mass of molecular gas detected in the nuclear region via the H2 1-0 S(1) line suggests that further episodes of SF may take place again

Cathodoluminescence microscopy of superconducting and non-superconducting Tl2Ba2CuO6+x polycrystals

International audienceLuminescence properties of Tl2Ba2CuO6+x samples with different superconducting transition temperatures have been studied by cathodoluminescence (CL) in the scanning electron microscope. Independent of the crystal structure, tetragonal or orthorhombic, the CL spectra show two resolved bands at about 430 nm (2.9 eV) and 540 nm (2.3 eV), respectively. The results show that the 2.3 eV emission is related to oxygen content and is more intense in low-oxygen content superconducting samples. It is proposed that this band is related to a complex center involving oxygen vacancies. A comparison of spectra from Tl2Ba2CuO6+x and from precursors used in the synthesis (CuOx, Tl2Ba205) has been carried out

Influence of Bi and Mn on the green luminescence of ZnO ceramics

The effect of the addition of Bi and Mn on the photoluminescence from ZnO ceramics has been investigated. The effect of the presence of impurities on the green luminescence band can be compared to the effect of oxidizing treatments. A narrow green band has been observed in Mn‐doped samples

Outflows of hot molecular gas in ultra-luminous infra-red galaxies mapped with VLT-SINFONI

We present the detection and morphological characterization of hot molecular gas outflows in nearby ultra-luminous infrared galaxies, using the near-IR integral-field spectrograph SINFONI on the VLT. We detect outflows observed in the 2.12 micron H$_{2}$ 1-0 S(1) line for three out of four ULIRGs analyzed; IRAS 12112+0305, 14348-1447, and 22491-1808. The outflows are mapped on scales of 0.7-1.6 kpc, show typical outflow velocities of 300-500 km/s, and appear to originate from the nuclear region. The outflows comprise hot molecular gas masses of ~6-8x10$^3$ M(sun). Assuming a hot-to-cold molecular gas mass ratio of 6x10$^{-5}$, as found in nearby luminous IR galaxies, the total (hot+cold) molecular gas mass in these outflows is expected to be ~1x10$^{8}$ M(sun). This translates into molecular mass outflow rates of ~30-85 M(sun)/yr, which is a factor of a few lower than the star formation rate in these ULIRGs. In addition, most of the outflowing molecular gas does not reach the escape velocity of these merger systems, which implies that the bulk of the outflowing molecular gas is re-distributed within the system and thus remains available for future star formation. The fastest H$_{2}$ outflow is seen in the Compton-thick AGN of IRAS 14348-1447, reaching a maximum outflow velocity of ~900 km/s. Another ULIRG, IRAS 17208-0014, shows asymmetric H$_{2}$ line profiles different from the outflows seen in the other three ULIRGs. We discuss several alternative explanations for its line asymmetries, including a very gentle galactic wind, internal gas dynamics, low-velocity gas outside the disk, or two superposed gas disks. We do not detect the hot molecular counterpart to the outflow previously detected in CO(2-1) in IRAS 17208-0014, but we note that our SINFONI data are not sensitive enough to detect this outflow if it has a small hot-to-cold molecular gas mass ratio of < 9x10$^{-6}$.Comment: Accepted for publication in A&A (11 pages, 10 figures

Kinetics and compositional dependence on the microwave power and DiH4/N flow ratio of silicon nitride deposited by electron cyclotron resonance plasmas

The archival version of this work was published in Journal of The Electrochemical Society. Hernández, M. J., Garrido, J., Martínez, J. and J. Piqueras. Kinetics and compositional dependence on the microwave power and DiH4/N flow ratio of silicon nitride deposited by electron cyclotron resonance plasmas. Journal of The Electrochemical Society 141.11 (1994): 3234-3237Silicon nitride layers have been deposited at a low temperature, 150ºC in an electron cyclotron plasma from nitrogen and silane as gas precursors. Deposition conditions have been varied in a wide range. Nitrogen flows from 25 to 400 sccm and silane flows from 2.5 to 35 sccm have been used in our experiments. The microwave power was varied from 100 to 1500 W. The result of the nitride growth kinetics show strong dependence on the silane to nitrogen flow ratio and on the microwave power. For large flow ratios and small powers the kinetics exhibits a nearly linear behavior whereas for low flow ratios and high powers a saturated regime was observed. Ellipsometry, infrared spectroscopy, and etch rate studies showed that the best material quality, 95% Si3N4, is obtained in the saturated regime for the lowest flow ratios and the highest powers used