Learning Science Through Enacted Astronomy Rollinde, E.
International journal of science and mathematical education/International journal of science and mathematics education,
02/2019, Volume:
17, Issue:
2
Journal Article
Peer reviewed
Open access
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.
We present the transverse flux correlation function of the Lyα forest in quasar absorption spectra at z∼ 2.1 from VLT-FORS and VLT-UVES observations of a total of 32 pairs of quasars; 26 pairs with ...separations in the range 0.6 < θ < 4 arcmin and six pairs with 4 < θ < 10 arcmin. Correlation is detected at the 3σ level up to separations of the order of ∼4 arcmin (or ∼4.4 h
−1 Mpc comoving at z= 2.1 for Ωm= 0.3 and ΩΛ= 0.7). We have, furthermore, measured the longitudinal correlation function at a somewhat higher mean redshift (z= 2.39) from 20 lines of sight observed with high spectral resolution and high signal-to-noise ratio with VLT-UVES. We compare the observed transverse and longitudinal correlation functions to that obtained from numerical simulations and illustrate the effect of spectral resolution, thermal broadening and peculiar motions. The shape and correlation length of the correlation functions are in good agreement with those expected from absorption by the filamentary and sheet-like structures in the photoionized warm intergalactic medium predicted in cold dark matter (CDM)-like models for structures formation. Using a sample of 139 C iv systems detected along the lines of sight towards the pairs of quasars we also investigate the transverse correlation of metals on the same scales. The observed transverse correlation function of intervening C iv absorption systems is consistent with that of a randomly distributed population of absorbers. This is likely due to the small number of pairs with separation less than 2 arcmin. We detect, however, a significant overdensity of systems in the sightlines towards the quartet Q 0103−294A&B, Q 0102−2931 and Q 0102−293 which extends over the redshift range 1.5 ≤z≤ 2.2 and an angular scale larger than 10 arcmin.
We discuss the implementation of Bayesian inversion methods in order to recover the properties of the intergalactic medium from observations of the neutral hydrogen Lyman α absorptions observed in ...the spectra of high-redshift quasars (the so-called Lyman α forest). We use two complementary schemes: (i) a constrained Gaussian random field linear approach, and (ii) a more general non-linear explicit Bayesian deconvolution method, which offers in particular the possibility to constrain the parameters of the equation of state for the gas. The interpolation ability of the first approach is shown to be equivalent to the second one in the limit of negligible measurement errors, low-resolution spectra and null mean prior. While relying on prior assumption for the two-point correlation functions, we show how to recover, at least qualitatively, the three-dimensional topology of the large-scale structures in redshift space by inverting a suitable network of adjacent, low-resolution lines of sight. The methods are tested on regular bundles of lines of sight using N-body simulations specially designed to tackle this problem. We also discuss the inversion of single lines of sight observed at high spectral resolution. Our preliminary investigations suggest that the explicit Bayesian method can be used to derive quantitative information on the physical state of the gas when the effects of redshift distortion are negligible. The information in the spectra remains degenerate with respect to two parameters (the temperature scale factor and the polytropic index) describing the equation of state of the gas. Redshift distortion is considered by simultaneous constrained reconstruction of the velocity and the density field in real space, while assuming statistical correlation between the two fields. The method seems to work well in the strong prior régime where peculiar velocities are assumed to be the most likely realization in the density field. Finally, we investigate the effect of line-of-sight separation and number of lines of sight. Our analyses suggest that multiple low-resolution lines of sight could be used to improve the most likely velocity reconstruction on a high-resolution line of sight.
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