4,366 research outputs found
Using Critical Integrative Argumentation to Assess Socioscientific Argumentation Across Decision-Making Contexts
Socioscientific issues (SSI) are often used to facilitate studentsâ engagement in multiple scientific practices such as decision-making and argumentation, both of which are goals of STEM literacy, science literacy, and integrated STEM education. Literature often emphasizes scientific argumentation over socioscientific argumentation, which involves considering social factors in addition to scientific frameworks. Analyzing studentsâ socioscientific arguments may reveal how students construct such arguments and evaluate pedagogical tools supporting these skills. In this study, we examined studentsâ socioscientific arguments regarding three SSI on pre- and post-assessments in the context of a course emphasizing SSI-based structured decision-making. We employed critical integrative argumentation (CIA) as a theoretical and analytical framework, which integrates arguments and counterarguments with stronger arguments characterized by identifying and refuting counterarguments. We hypothesized that engaging in structured decision-making, in which students integrate multidisciplinary perspectives and consider tradeoffs of various solutions based upon valued criteria, may facilitate studentsâ development of integrated socioscientific arguments. Findings suggest that studentsâ arguments vary among SSI contexts and may relate to studentsâ identities and perspectives regarding the SSI. We conclude that engaging in structured decision-making regarding personally relevant SSI may foster more integrated argumentation skills, which are critical to engaging in information-laden democratic societies
The long-period Galactic Cepheid RS Puppis - III. A geometric distance from HST polarimetric imaging of its light echoes
As one of the most luminous Cepheids in the Milky Way, the 41.5-day RS Puppis
is an analog of the long-period Cepheids used to measure extragalactic
distances. An accurate distance to this star would therefore help anchor the
zero-point of the bright end of the period-luminosity relation. But, at a
distance of about 2 kpc, RS Pup is too far away for measuring a direct
trigonometric parallax with a precision of a few percent with existing
instrumentation. RS Pup is unique in being surrounded by a reflection nebula,
whose brightness varies as pulses of light from the Cepheid propagate outwards.
We present new polarimetric imaging of the nebula obtained with HST/ACS. The
derived map of the degree of linear polarization pL allows us to reconstruct
the three-dimensional structure of the dust distribution. To retrieve the
scattering angle from the pL value, we consider two different polarization
models, one based on a Milky Way dust mixture and one assuming Rayleigh
scattering. Considering the derived dust distribution in the nebula, we adjust
a model of the phase lag of the photometric variations over selected nebular
features to retrieve the distance of RS Pup. We obtain a distance of 1910 +/-
80 pc (4.2%), corresponding to a parallax of 0.524 +/- 0.022 mas. The agreement
between the two polarization models we considered is good, but the final
uncertainty is dominated by systematics in the adopted model parameters. The
distance we obtain is consistent with existing measurements from the
literature, but light echoes provide a distance estimate that is not subject to
the same systematic uncertainties as other estimators (e.g. the Baade-Wesselink
technique). RS Pup therefore provides an important fiducial for the calibration
of systematic uncertainties of the long-period Cepheid distance scale.Comment: 14 pages, 14 figures, accepted for publication in Astronomy &
Astrophysic
The long-period Galactic Cepheid RS Puppis - II. 3D structure and mass of the nebula from VLT/FORS polarimetry
The long-period Cepheid RS Pup is surrounded by a large dusty nebula
reflecting the light from the central star. Due to the changing luminosity of
the central source, light echoes propagate into the nebula. This remarkable
phenomenon was the subject of Paper I.The origin and physical properties of the
nebula are however uncertain: it may have been created through mass loss from
the star itself, or it could be the remnant of a pre-existing interstellar
cloud. Our goal is to determine the 3D structure of the nebula, and estimate
its mass. Knowing the geometrical shape of the nebula will also allow us to
retrieve the distance of RS Pup in an unambiguous manner using a model of its
light echoes (in a forthcoming work). The scattering angle of the Cepheid light
in the circumstellar nebula can be recovered from its degree of linear
polarization. We thus observed the nebula surrounding RS Pup using the
polarimetric imaging mode of the VLT/FORS instrument, and obtained a map of the
degree and position angle of linear polarization. From our FORS observations,
we derive a 3D map of the distribution of the dust, whose overall geometry is
an irregular and thin layer. The nebula does not present a well-defined
symmetry. Using a simple model, we derive a total dust mass of M(dust) = 2.9
+/- 0.9 Msun for the dust within 1.8 arcmin of the Cepheid. This translates
into a total mass of M(gas+dust) = 290 +/- 120 Msun, assuming a dust-to-gas
ratio of 1.0 +/- 0.3 %. The high mass of the dusty nebula excludes that it was
created by mass-loss from the star. However, the thinness nebula is an
indication that the Cepheid participated to its shaping, e.g. through its
radiation pressure or stellar wind. RS Pup therefore appears as a regular
long-period Cepheid located in an exceptionally dense interstellar environment.Comment: 14 pages, 21 figures. Accepted for publication in A&
Two Clusters with Radio-quiet Cooling Cores
Radio lobes inflated by active galactic nuclei at the centers of clusters are
a promising candidate for halting condensation in clusters with short central
cooling times because they are common in such clusters. In order to test the
AGN-heating hypothesis, we obtained Chandra observations of two clusters with
short central cooling times yet no evidence for AGN activity: Abell 1650 and
Abell 2244. The cores of these clusters indeed appear systematically different
from cores with more prominent radio emission. They do not have significant
central temperature gradients, and their central entropy levels are markedly
higher than in clusters with stronger radio emission, corresponding to central
cooling times ~ 1 Gigayear. Also, there is no evidence for fossil X-ray
cavities produced by an earlier episode of AGN heating. We suggest that either
(1) the central gas has not yet cooled to the point at which feedback is
necessary to prevent it from condensing, possibly because it is conductively
stabilized, or (2) the gas experienced a major heating event Gyr in
the past and has not required feedback since then. The fact that these clusters
with no evident feedback have higher central entropy and therefore longer
central cooling times than clusters with obvious AGN feedback strongly suggests
that AGNs supply the feedback necessary to suppress condensation in clusters
with short central cooling times.Comment: ApJ Letter, in pres
Hydrogen Two-Photon Continuum Emission from the Horseshoe Filament in NGC 1275
Far ultraviolet emission has been detected from a knot of Halpha emission in
the Horseshoe filament, far out in the NGC 1275 nebula. The flux detected
relative to the brightness of the Halpha line in the same spatial region is
very close to that expected from Hydrogen two-photon continuum emission in the
particle heating model of Ferland et al. (2009) if reddening internal to the
filaments is taken into account. We find no need to invoke other sources of far
ultraviolet emission such as hot stars or emission lines from CIV in
intermediate temperature gas to explain these data.Comment: 9 pages, 8 figures. Accepted for publication in MNRA
Dynamics of magnetization coupled to a thermal bath of elastic modes
We study the dynamics of magnetization coupled to a thermal bath of elastic
modes using a system plus reservoir approach with realistic magnetoelastic
coupling. After integrating out the elastic modes we obtain a self-contained
equation for the dynamics of the magnetization.
We find explicit expressions for the memory friction kernel and hence, {\em
via} the Fluctuation-Dissipation
Theorem, for the spectral density of the magnetization thermal fluctuations.
For magnetic samples in which the single domain approximation is valid, we
derive an equation for the dynamics of the uniform mode.
Finally we apply this equation to study the dynamics of the uniform
magnetization mode in insulating ferromagnetic thin films.
As experimental consequences we find that the fluctuation correlation time is
of the order of the ratio between the film thickness, , and the speed of
sound in the magnet and that the line-width of the ferromagnetic resonance peak
should scale as where is the magnetoelastic coupling constant.Comment: Revised version as appeared in print. 12 pages 9 figure
The MURALES survey II. Presentation of MUSE observations of 20 3C low-z radio galaxies and first results
We present observations of a complete sub-sample of 20 radio galaxies from
the Third Cambridge Catalog (3C) with redshift <0.3 obtained from VLT/MUSE
optical integral field spectrograph. These data have been obtained as part of
the survey MURALES (a MUse RAdio Loud Emission line Snapshot survey) with the
main goal of exploring the Active Galactic Nuclei (AGN) feedback process in a
sizeable sample of the most powerful radio sources at low redshift. We present
the data analysis and, for each source, the resulting emission line images and
the 2D gas velocity field. Thanks to their unprecedented depth (the median 3
sigma surface brightness limit in the emission line maps is 6X10^-18 erg s-1
cm-2 arcsec-2, these observations reveal emission line structures extending to
several tens of kiloparsec in most objects. In nine sources the gas velocity
shows ordered rotation, but in the other cases it is highly complex. 3C sources
show a connection between radio morphology and emission line properties.
Whereas, in three of the four Fanaroff and Riley Class I radio galaxies (FRIs),
the line emission regions are compact, ~1 kpc in size; in all but one of the
Class II radiogalaxies FRIIs, we detected large scale structures of ionized gas
with a median extent of 17 kpc. Among the FRIIs, those of high and low
excitation show extended gas structures with similar morphological properties,
suggesting that they both inhabit regions characterized by a rich gaseous
environment on kpc scale.Comment: Accepted for publication in A&
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