Learning by Doing, by Wondering, by Figuring Things Out: A New Look at Contemporary Homeschooling and Pedagogical Progressivism

Pedagogical progressive education, as defined through the work of John Dewey, Helen Parkhurst, and Carleton Washburne was the precursor to the contemporary homeschooling movement in ideology, practice, and rhetoric as defined by the writing and pedagogy of John Holt. Their shared beliefs in community, student freedom, and good experience as pertinent to education marked the relationship between these two pedagogical methods. Despite Holt\u27s departure from the classroom through his unschooling method, the ideological consistencies between the movement are undeniable, suggesting we rethink the relationship between progressive education and homeschooling and our basic assumptions about the legacy of both movements

Effect of incoming radiation on the non-LTE spectrum of Xe at Te = 100 eV

The effect of a diluted Planckian radiation field on a Xe gas at the electron temperature of 100 eV is investigated within the framework of a Collisional Radiative Model, using the HULLAC code. The atomic model spans 19 charge states, includes 20 375 configurations and contains more than 2 10^6 levels. We have simulated detailed spectra comprising more than 10^9 transitions with the Mixed UTA model. The radiation temperature Tr is varied from 0 to 1.5 Te. The dilution factor, D, applied to decrease the radiation field, is varied independently from 0 to 3 at fixed Tr = Te. In both cases, the average charge state Z* increases from 15 to 27, but in different ways. It is shown that even a dilution D = 0.01 changes Z* by more than 1.5. Different combinations of Tr and D yielding exactly the same Z*, may give line ratios sufficiently different to be observed. This fact is explained by the interplay of the shape of the radiation field and the atomic structure

On the influence of opacity variation on spatial structure of radiative shocks

International audienceWe provide a theoretical analysis of Radiative Shocks, defined as supercritical shocks accompanied by an ionization wave in front of the density jump. In particular, we look at the influence of opacity variation with temperature and photon energy on spatial structure of radiative shocks, with a view to understanding a split precursor feature observed in recent experiments. We show that multigroup processing, a more refined angular description and improved low temperature opacities are needed to explore the radiative precursor structure, at least in some temperature regimes where rapid change of ionization can be found

The Chandra Iron-L X-Ray Line Spectrum of Capella

An analysis of the iron L-shell emission in the publicly available spectrum of the Capella binary system, as obtained by the High Energy Transmission Grating Spectrometer on board the Chandra X-ray Observatory, is presented. The atomic-state model, based on the HULLAC code, is shown to be especially adequate for analyzing high-resolution x-ray spectra of this sort. Almost all of the spectral lines in the 10 - 18 Angstrom wavelength range are identified. It is shown that, for the most part, these lines can be attributed to emission from L-shell iron ions in the Capella coronae. Possibilities for electron temperature diagnostics using line ratios of Fe16+ are demonstrated. It is shown that the observed iron-L spectrum can be reproduced almost entirely by assuming a single electron temperature of kTe= 600 eV. This temperature is consistent with both the measured fractional ion abundances of iron and with the temperature derived from ratios of Fe16+ lines. A volume emission measure of 1053 cm-3 is calculated for the iron L-shell emitting regions of the Capella coronae indicating a rather small volume of 1029 cm3 for the emitting plasma if an electron density of 1012 cm-3 is assumed.Comment: Accepted to Ap

Infrared coronal emission lines and the possibility of their maser emission in Seyfert nuclei

Energetic emitting regions have traditionally been studied via x-ray, UV and optical emission lines of highly ionized intermediate mass elements. Such lines are often referred to as 'coronal lines' since the ions, when produced by collisional ionization, reach maximum abundance at electron temperatures of approx. 10(exp 5) - 10(exp 6) K typical of the sun's upper atmosphere. However, optical and UV coronal lines are also observed in a wide variety of Galactic and extragalactic sources including the Galactic interstellar medium, nova shells, supernova remnants, galaxies and QSOs. Infrared coronal lines are providing a new window for observation of energetic emitting regions in heavily dust obscured sources such as infrared bright merging galaxies and Seyfert nuclei and new opportunities for model constraints on physical conditions in these sources. Unlike their UV and optical counterparts, infrared coronal lines can be primary coolants of collisionally ionized plasmas with 10(exp 4) less than T(sub e)(K) less than 10(exp 6) which produce little or no optical or shorter wavelength coronal line emission. In addition, they provide a means to probe heavily dust obscured emitting regions which are often inaccessible to optical or UV line studies. In this poster, we provide results from new model calculations to support upcoming Infrared Space Observatory (ISO) and current ground-based observing programs involving infrared coronal emission lines in AGN. We present a complete list of infrared (lambda greater than 1 micron) lines due to transitions within the ground configurations 2s(2)2p(k) and 3s(2)3p(k) (k = 1 to 5) or the first excited configurations 2s2p and 3s3p of highly ionized (x greater than or equal to 100 eV) astrophysically abundant (n(X)/n(H) greater than or equal to 10(exp -6)) elements. Included are approximately 74 lines in ions of O, Ne, Na, Mg, Al, Si, S, Ar, Ca, Fe, and Ni spanning a wavelength range of approximately 1 - 280 microns. We present new results from detailed balance calculations, new critical densities for collisional de-excitation, intrinsic photon rates, branching ratios, and excitation temperatures for the majority of the compiled transitions. The temperature and density parameter space for dominant cooling via infrared coronal lines is presented, and the relationship of infrared to optical coronal lines is discussed

The Fe XXII I(11.92 A)/I(11.77 A) Density Diagnostic Applied to the Chandra High Energy Transmission Grating Spectrum of EX Hydrae

Using the Livermore X-ray Spectral Synthesizer, which calculates spectral models of highly charged ions based primarily on HULLAC atomic data, we investigate the temperature, density, and photoexcitation dependence of the I(11.92 A)/I(11.77 A) line ratio of Fe XXII. We find that this line ratio has a critical density n_c \approx 5x10^13 cm^-3, is approximately 0.3 at low densities and 1.5 at high densities, and is very insensitive to temperature and photoexcitation, so is a useful density diagnostic for sources like magnetic cataclysmic variables in which the plasma densities are high and the efficacy of the He-like ion density diagnostic is compromised by the presence of a bright ultraviolet continuum. Applying this diagnostic to the Chandra High Energy Transmission Grating spectrum of the intermediate polar EX Hya, we find that the electron density of its T_e \approx 12 MK plasma is n_e = 1.0^{+2.0}_{-0.5} x 10^14 cm^-3, orders of magnitude greater than that typically observed in the Sun or other late-type stars.Comment: 11 pages including 3 encapsulated postscript figures; LaTeX format, uses aastex.cls; accepted on 2003 April 3 for publication in The Astrophysical Journa

Inner-shell 1s - 2p Soft X-ray Absorption Lines

The HULLAC atomic code is used to compute wavelengths and oscillator strengths for the 1s - np inner-shell absorption lines in Li-like to F-like ions of neon, magnesium, aluminum, silicon, sulfur, argon, calcium, and iron. Many of these lines are expected to be observed in Chandra and XMM-Newton high-resolution X-ray spectra of active galaxies. The new atomic data are incorporated in the ION code for spectral modeling of photoionized plasmas. The calculated spectra are subsequently compared with the spectrum of NGC 3783 and show very good agreement. The usefulness of these lines as diagnostics for the ionization state, column densities, and velocities in line-of-sight photoionized gas is called attention to.Comment: Scheduled for the v570 n1 ApJ May 1, 2002 issu