The Human Orrery is a representation of the Solar System at a human scale, on which positions of planets over time are symbolized by different discs. Learners can then walk along the orbits of the ...planets with the right pace. This pedagogical tool uses the principles of enacted cognition to promote a better understanding of the scientific laws of dynamics. Enaction assumes that cognition is based on action. Applied to pedagogy, it implies that learning of concepts must be based on gestures and perceptions first. I applied during 2 years an enacted pedagogical sequence using our Human Orrery to different populations of learners. The main purpose was the understanding of velocity and inertia by KS4 classes (14–16 years old). Interviews and closed questions reveal a qualitative enhancement of the motivation and well-being of the learners during the enacted sequence. To evaluate further the impact of the enacted sequence, I formulated 2 open questions. The first one concerns the relation between distance, duration, and velocity through the period of planets. The second one focuses on inertia and gravity through the comparison of the free fall of an apple on Earth and the orbit of the Moon around Earth. The questions were asked to KS4 pupils after the enacted sequence (experimental classes) and to KS4, undergraduate and pre-teachers after a classical lecture on dynamics (demonstration classes). Quantitative analysis of the answers reveals specific cognitive insight, especially for students reasoning about velocity and trajectories. The general purpose of this paper is thus to illustrate the use of the Human Orrery in the context of science education in the classroom and to make a first, preliminary demonstration of its efficiency.
Enacting planets to learn physics Rollinde, E; Decamp, N
Journal of physics. Conference series,
08/2019, Volume:
1287, Issue:
1
Journal Article
Peer reviewed
Open access
The Solar System motivates students to interest themselves in sciences, as a large number of concepts may be easily introduced through the observation and understanding of planet's motion. Using a ...large representation of the Solar System at a human scale ("a human Orrery"), we intend to show how cognitive activities about kinematics and dynamics are activated and linked to the sensori-motors activities. In the last three years, we have conducted different activities with 10 to 16 years old children. In this contribution, we discuss the different scientific concepts covered by the Human Orrery, and the enaction theory that provides a theoretical background to those activities. We detail the enaction of velocity with a description of the gestures in relation with the abstract concepts involved in kinematics.
We compare the observed probability distribution function (PDF) of the transmission in the H i Lyman α forest, measured from the Ultraviolet and Visual Echelle Spectrograph (UVES) 'Large Programme' ...sample at redshifts z = 2, 2.5, 3, to results from the gimic cosmological simulations. Our measured values for the mean transmission and its PDF are in good agreement with published results. Errors on statistics measured from high-resolution data are typically estimated using bootstrap or jackknife resampling techniques after splitting the spectra into chunks. We demonstrate that these methods tend to underestimate the sample variance unless the chunk size is much larger than is commonly the case. We therefore estimate the sample variance from the simulations. We conclude that observed and simulated transmission statistics are in good agreement; in particular, we do not require the temperature-density relation to be 'inverted'.
Context. Baryonic acoustic oscillations (BAO) and their effects on the matter power spectrum can be studied using the Lyman-α absorption signature of the matter density field along quasar (QSO) lines ...of sight. A measurement sufficiently accurate to provide useful cosmological constraints requires the observation of ~ 105 quasars in the redshift range 2.2 < z < 3.5 over ~ 8000deg2. Such a survey is planned by the Baryon Oscillation Spectroscopic Survey (BOSS) project of the Sloan Digital Sky Survey (SDSS-III). Aims. We assess one of the challenges for this project, that of building from five-band imaging data a list of targets that contains the largest number of quasars in the required redshift range. In practice, we perform a stellar rejection of more than two orders of magnitude with a selection efficiency for quasars better than 50% to magnitudes as bright as g ~ 22. Methods. To obtain an appropriate target list and estimate quasar redshifts, we develop artificial neural networks (ANNs) with a multilayer perceptron architecture. The input variables are photometric measurements, i.e., the object magnitudes and their errors in the five bands (ugriz) of the SDSS photometry. The ANN developed for target selection provides a continuous output variable between 0 for non-quasar point-like objects to 1 for quasars. A second ANN estimates the QSO redshift z using the photometric information. Results. For target selection, we achieve a non-quasar point-like object rejection of 99.6% and 98.5% for a quasar efficiency of, respectively, 50% and 85%, comparable to the performances of traditional methods. The photometric redshift precision is on the order of 0.1 over the region relevant to BAO studies. These statistical methods, developed in the context of the BOSS project, can easily be extended to any quasar selection and/or determination of their photometric redshift.
From a principal component analysis (PCA) of 78 z ~ 3 high-quality quasar spectra in the SDSS-DR7 we derive the principal components that characterize the QSO continuum over the full available ...wavelength range. The shape of the mean continuum is similar to that measured at low-z (z ~ 1), but the equivalent width of the emission lines is larger at low redshift. We calculate the correlation between fluxes at different wavelengths and find that the emission line fluxes in the red part of the spectrum are correlated with those in the blue part. We construct a projection matrix to predict the continuum in the Lyman-α forest from the red part of the spectrum. We apply this matrix to quasars in the SDSS-DR7 to derive the evolution with redshift of the mean flux in the Lyman-α forest caused by the absorption by the intergalactic neutral hydrogen. A change in the evolution of the mean flux is apparent around z ~ 3 as a steeper decrease of the mean flux at higher redshifts. The same evolution is found when the continuum is estimated from the extrapolation of a power-law continuum fitted in the red part of the quasar spectrum if a correction derived from simple simulations is applied. Our findings are consistent with previous determinations using high spectral resolution data. We provide the PCA eigenvectors over the wavelength range 1020−2000 Å and the distribution of their weights that can be used to simulate QSO mock spectra.
We investigate how well the three-dimensional density field of neutral hydrogen in the intergalactic medium (IGM) can be reconstructed using the Lyman α absorptions observed along lines-of-sight to ...quasars separated by arcmin distances in projection on the sky. We use cosmological hydrodynamical simulations to compare the topologies of different fields: dark matter, gas and neutral hydrogen optical depth and to investigate how well the topology of the IGM can be recovered from the Wiener interpolation method implemented by Pichon et al. The global statistical and topological properties of the recovered field are analysed quantitatively through the power spectrum, the probability distribution function (PDF), the Euler characteristics, its associated critical point counts and the filling factor of underdense regions. The local geometrical properties of the field are analysed using the local skeleton by defining the concept of interskeleton distance. As a consequence of the nearly lognormal nature of the density distribution at the scales under consideration, the tomography is best carried out on the logarithm of the density rather than the density itself. At scales larger than ∼1.4 〈dLOS〉, where 〈dLOS〉 is the mean separation between lines-of-sight, the reconstruction accurately recovers the topological features of the large-scale density distribution of the gas, in particular the filamentary structures: the interskeleton distance between the reconstruction and the exact solution is smaller than 〈dLOS〉. At scales larger than the intrinsic smoothing length of the inversion procedure, the power spectrum of the recovered H i density field matches well that of the original one and the low-order moments of the PDF are well recovered as well as the shape of the Euler characteristic. The integral errors on the PDF and the critical point counts are indeed small, less than 20 per cent for a mean line-of-sight separation smaller than ∼2.5 arcmin. The small deviations between the reconstruction and the exact solution mainly reflect departures from the lognormal behaviour that are ascribed to highly non-linear objects in overdense regions.
We investigate how well the three-dimensional density field of neutral hydrogen in the intergalactic medium (IGM) can be reconstructed using the Lyman alpha absorptions observed along lines-of-sight ...to quasars separated by arcmin distances in projection on the sky. We use cosmological hydrodynamical simulations to compare the topologies of different fields: dark matter, gas and neutral hydrogen optical depth and to investigate how well the topology of the IGM can be recovered from the Wiener interpolation method implemented by Pichon et al. The global statistical and topological properties of the recovered field are analysed quantitatively through the power spectrum, the probability distribution function (PDF), the Euler characteristics, its associated critical point counts and the filling factor of underdense regions. The local geometrical properties of the field are analysed using the local skeleton by defining the concept of interskeleton distance.As a consequence of the nearly lognormal nature of the density distribution at the scales under consideration, the tomography is best carried out on the logarithm of the density rather than the density itself. At scales larger than similar to 1.4 , where is the mean separation between lines-of-sight, the reconstruction accurately recovers the topological features of the large-scale density distribution of the gas, in particular the filamentary structures: the interskeleton distance between the reconstruction and the exact solution is smaller than . At scales larger than the intrinsic smoothing length of the inversion procedure, the power spectrum of the recovered Hi density field matches well that of the original one and the low-order moments of the PDF are well recovered as well as the shape of the Euler characteristic. The integral errors on the PDF and the critical point counts are indeed small, less than 20 per cent for a mean line-of-sight separation smaller than similar to 2.5 arcmin. The small deviations between the reconstruction and the exact solution mainly reflect departures from the lognormal behaviour that are ascribed to highly non-linear objects in overdense regions.
Context. The imprint of baryonic acoustic oscillations (BAO) on the matter power spectrum can be constrained using the neutral hydrogen density in the intergalactic medium (IGM) as a tracer of the ...matter density. One of the goals of the baryon oscillation spectroscopic survey (BOSS) of the Sloan Digital Sky Survey (SDSS-III) is to derive the Hubble expansion rate and the angular scale from the BAO signal in the IGM. To this aim, the Lyman-α forest about 150 000 quasars will be observed in the redshift range 2.2 < z < 3.5 and over ~10 000 deg2. Aims. We simulated the BOSS QSO survey to estimate the statistical accuracy on the BAO scale determination provided by such a large-scale survey. In particular, we discuss the effect of the poorly constrained estimate of the quasar’s unabsorbed intrinsic spectrum. Methods. The volume of current N-body simulations being too small for such studies, we resorted to Gaussian random field (GRF) simulations. We validated the use of GRFs by comparing the output of GRF simulations with that of the Horizon-4Π N-body dark-matter-only simulation with the same initial conditions. Realistic mock samples of QSO Lyman-α forest were generated and their power spectrum computed and fitted to obtain the BAO scale. The rms of the results for 100 different simulations provides an estimate of the statistical error expected from the BOSS survey. Results. We confirm the results from the Fisher matrix estimate. In the absence of error on the quasar’s unabsorbed spectrum, our simulations give an expected uncertainty of 2.3% for the BOSS quasar survey measurement of the BAO scale. The expected uncertainties for the transverse and radial BAO scales are 6.8% and 3.9%, respectively. The significance of the BAO detection is assessed by an average Δχ2 = 17 but Δχ2 ranges from 2 to 35 for individual realizations. The error on the quasar’s unabsorbed spectrum increases the error on the BAO scale by 10 to 20% and results in a subpercent bias.
New observations from the Hubble Ultra Deep Field suggest that the star formation rate at z > 7 drops off faster than previously thought. Using a newly determined star formation rate for the normal ...mode of Population II/I (PopII/I) stars, including this new constraint, we compute the Thomson scattering optical depth and find a result that is marginally consistent with Wilkinson Microwave Anisotropy Probe 5 results. We also reconsider the role of Population III (PopIII) stars in light of cosmological and stellar evolution constraints. While this input may be needed for reionization, we show that it is essential in order to account for cosmic chemical evolution in the early universe. We investigate the consequences of PopIII stars on the local metallicity distribution function of the Galactic halo (from the recent Hamburg/European Southern Observatory (ESO) survey of metal-poor stars) and on the evolution of abundances with metallicity (based on the ESO large programme on very metal-poor stars), with special emphasis on carbon-enhanced metal-poor stars. The metallicity distribution function shape is well reproduced at low iron abundance (Fe/H≳−4), in agreement with other studies. However, the Hamburg/ESO survey hints at a sharp decrease of the number of low-mass stars at very low iron abundance, which is not reproduced in models with only PopII/I stars. The presence of PopIII stars, of typical masses 30–40 M⊙, helps us to reproduce this feature, leading to a prompt initial enrichment before the onset of PopII/I stars. The metallicity at which this cut-off occurs is sensitive to the lowest mass of the massive PopIII stars, which makes the metallicity distribution function a promising tool to constrain this population. Our most important results show that the nucleosynthetic yields of PopIII stars lead to abundance patterns in agreement with those observed in extremely metal-poor stars. This can be demonstrated by the transition discriminant (a criterion for low-mass star formation taking into account the cooling due to C ii and O i). In this chemical approach to cosmic evolution, PopIII stars prove to be a compulsory ingredient, and extremely metal-poor stars are inevitably born at high redshift.
Context: The runaway star HD 34078, initially selected to investigate small scale structure in a foreground diffuse cloud, has been shown to be surrounded by highly excited H2, the origin of which is ...unclear. Aims: We first search for an association between the foreground cloud and HD 34078. Second, we extend previous investigations of temporal absorption line variations (CH, CH^+, H2) in order to better characterize them and understand their relation to small-scale structure in the molecular gas. Methods: We have mapped the 12CO(2-1) emission at 12´´ resolution around HD 34078's position, using the 30 m IRAM antenna. The follow-up of CH and CH+ absorption lines has been extended over 5 more years: 26 visible spectra have been acquired since 2003 at high or intermediate resolution. In parallel, CH absorption towards the reddened star ζ Per has been monitored to check the instrumental stability and homogeneity of our measurements. Three more FUSE spectra have been obtained to search for N(H2) variations. Results: CO observations show a pronounced maximum near HD 34078's position, clearly indicating that the star and diffuse cloud are associated. The optical spectra confirm the reality of strong, rapid and correlated CH and CH+ fluctuations (up to 26% for N(CH^+) between 2007 and 2008). On the other hand, N(H2, J=0) has varied by less than 5% over 4 years, indicating the absence of marked density structure at scales below 100 AU. We also discard N(CH) variations towards ζ Per at scales less than 20 AU. Conclusions: Observational constraints from this work and from 24 μm dust emission appear to be consistent with H2 excitation but inconsistent with steady-state bow shock models and rather suggest that the shell of compressed gas surrounding HD 34078 or lying at the boundary of a small foreground clump is seen at an early stage of the interaction. The CH and CH+ time variations as well as their high abundances are likely due to chemical structure in the shocked gas layer located at the stellar wind/ambient cloud interface. Finally, the lack of variation in both N(H2, J=0) towards HD 34078 and N(CH) towards ζ Per suggests that quiescent molecular gas is not subject to pronounced small-scale structure. Based on observations made mainly at IRAM, Observatoire de Haute Provence (France), McDonald Observatory (USA) and with FUSE.
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