337 research outputs found
Practicing mentorship: Graduate-student supervision of undergraduate research assistants
Many research universities rely on graduate students to supervise undergraduate research assistants (RAs) who collect data and handle research logistics. This experience can be mutually beneficial, as RAs receive hands-on learning, and graduate students practice mentorship in preparation for assuming a faculty role. However, assistantships must be intentionally designed to meet educational (not just practical) goals. What training and support do graduate students receive to take on this mentorship role? In two surveys, RAs reported on their satisfaction, educational benefit, and desired changes; while graduate students reported on their goals, challenges, and the support they receive
Opposite magnetic polarity of two photospheric lines in single spectrum of the quiet Sun
We study the structure of the photospheric magnetic field of the quiet Sun by
investigating weak spectro-polarimetric signals. We took a sequence of Stokes
spectra of the Fe I 630.15 nm and 630.25 nm lines in a region of quiet Sun near
the disk center, using the POLIS spectro-polarimeter at the German VTT on
Tenerife. The line cores of these two lines form at different heights in the
atmosphere. The 3 noise level of the data is about 1.8 . We present co-temporal and co-spatial Stokes- profiles of the Fe I
630 nm line pair, where the two lines show opposite polarities in a single
spectrum. We compute synthetic line profiles and reproduce these spectra with a
two-component model atmosphere: a non-magnetic component and a magnetic
component. The magnetic component consists of two magnetic layers with opposite
polarity: the upper one moves upwards while the lower one moves downward.
In-between, there is a region of enhanced temperature. The Stokes- line pair
of opposite polarity in a single spectrum can be understood as a magnetic
reconnection event in the solar photosphere. We demonstrate that such a
scenario is realistic, but the solution may not be unique.Comment: 4 pages, 5 figures, accepted in Astronomy & Astrophysics Letter
Spectral Inversion of Multi-Line Full-Disk Observations of Quiet Sun Magnetic Fields
Spectral inversion codes are powerful tools to analyze spectropolarimetric
observations, and they provide important diagnostics of solar magnetic fields.
Inversion codes differ by numerical procedures, approximations of the
atmospheric model, and description of radiative transfer. Stokes Inversion
based on Response functions (SIR) is an implementation widely used by the solar
physics community. It allows to work with different atmospheric components,
where gradients of different physical parameters are possible, e.g., magnetic
field strength and velocities. The spectropolarimetric full-disk observations
were carried out with the Stokesmeter of the Solar Telescope for Operative
Predictions (STOP) at the Sayan Observatory on 3 February 2009, when neither an
active region nor any other extended flux concentration was present on the Sun.
In this study of quiet Sun magnetic fields, we apply the SIR code
simultaneously to 15 spectral lines. A tendency is found that weaker magnetic
field strengths occur closer to the limb. We explain this finding by the fact
that close to the limb, we are more sensitive to higher altitudes in an
expanding flux tube, where the field strength should be smaller since the
magnetic flux is conserved with height. Typically, the inversions deliver two
populations of magnetic elements: (1) high magnetic field strengths (1500-2000
G) and high temperatures (5500-6500 K) and (2) weak magnetic fields (50-150 G)
and low temperatures (5000-5300 K).Comment: 10 pages, 6 figures, accepted for Solar Physic
Acoustic Events in the Solar Atmosphere from Hinode/SOT NFI observations
We investigate the properties of acoustic events (AEs), defined as spatially
concentrated and short duration energy flux, in the quiet sun using
observations of a 2D field of view (FOV) with high spatial and temporal
resolution provided by the Solar Optical Telescope (SOT) onboard
\textit{Hinode}. Line profiles of Fe \textsc{i} 557.6 nm were recorded by the
Narrow band Filter Imager (NFI) on a FOV during 75 min with a
time step of 28.75 s and 0.08 pixel size. Vertical velocities were computed
at three atmospheric levels (80, 130 and 180 km) using the bisector technique
allowing the determination of energy flux in the range 3-10 mHz using two
complementary methods (Hilbert transform and Fourier power spectra). Horizontal
velocities were computed using local correlation tracking (LCT) of continuum
intensities providing divergences.
The net energy flux is upward. In the range 3-10 mHz, a full FOV space and
time averaged flux of 2700 W m (lower layer 80-130 km) and 2000 W
m (upper layer 130-180 km) is concentrated in less than 1% of the solar
surface in the form of narrow (0.3) AE. Their total duration (including rise
and decay) is of the order of s. Inside each AE, the mean flux is W m (lower layer) and W m (upper). Each
event carries an average energy (flux integrated over space and time) of J (lower layer) to J (upper). More than events
could exist permanently on the Sun, with a birth and decay rate of 3500
s. Most events occur in intergranular lanes, downward velocity regions,
and areas of converging motions.Comment: 18 pages, 10 figure
Reaction norm analysis reveals rapid shifts toward delayed maturation in harvested Lake Erie yellow perch (Perca flavescens )
Harvested marine fish stocks often show a rapid and substantial decline in the age and size at maturation. Such changes can arise from multiple processes including fisheriesâinduced evolution, phenotypic plasticity, and responses to environmental factors other than harvest. The relative importance of these processes could differ systematically between marine and freshwater systems. We tested for temporal shifts in the mean and withinâcohort variability of ageâ and sizeâbased maturation probabilities of female yellow perch (Perca flavescens Mitchill) from four management units (MUs) in Lake Erie. Lake Erie yellow perch have been commercially harvested for more than a century, and age and size at maturation have varied since sampling began in the 1980s. Our analysis compared probabilistic maturation reaction norms (PMRNs) for cohorts when abundance was lower and harvest higher (1993â1998) to cohorts when abundance was higher and harvest lower (2005â2010). PMRNs have been used in previous studies to detect signs of evolutionary change in response to harvest. Maturation size threshold increased between the early and late cohorts, and the increases were statistically significant for the youngest age in the western MU1 and for older ages in the eastern MU3. Maturation envelope widths, a measure of the variability in maturation among individuals in a cohort, also increased between early and late cohorts in the western MUs where harvest was highest. The highest rates of change in size at maturation for a given age were as large or larger than rates reported for harvested marine fishes where declines in age and size at maturation have been observed. Contrary to the general observation of earlier maturation evolving in harvested stocks, female yellow perch in Lake Erie may be rapidly evolving delayed maturation since harvest was relaxed in the late 1990s, providing a rare example of possible evolutionary recovery
Lines of Descent: Kuhn and Beyond
yesThomas S. Kuhn is famous both for his work on the Copernican Revolution and his âparadigmâ view of scientific revolutions. But Kuhn later abandoned the notion of paradigm (and related notions) in favour of a more âevolutionaryâ view of the history of science. Kuhnâs position therefore moved closer to âcontinuityâ models of scientific progress, for instance âchain-of-reasoningâ models, originally championed by D. Shapere. The purpose of this paper is to contribute to the debate around Kuhnâs new âdevelopmentalâ view and to evaluate these competing models with reference to some major innovations in the history of cosmology, from Copernicanism to modern cosmology. This evaluation is made possible through some unexpected overlap between Kuhnâs earlier discontinuity model and various versions of the later continuity models. It is the thesis of this paper that the âchain-of-reasoningâ model accounts better for the cosmological evidence than both Kuhnâs early paradigm model and his later developmental view of the history of science
Diversification and Specialization of Plant RBR Ubiquitin Ligases
Background: RBR ubiquitin ligases are components of the ubiquitin-proteasome system present in all eukaryotes. They are characterized by having the RBR (RING â IBR â RING) supradomain. In this study, the patterns of emergence of RBR genes in plants are described. Methodology/Principal Findings: Phylogenetic and structural data confirm that just four RBR subfamilies (Ariadne, ARA54, Plant I/Helicase and Plant II) exist in viridiplantae. All of them originated before the split that separated green algae from the rest of plants. Multiple genes of two of these subfamilies (Ariadne and Plant II) appeared in early plant evolution. It is deduced that the common ancestor of all plants contained at least five RBR genes and the available data suggest that this number has been increasing slowly along streptophyta evolution, although losses, especially of Helicase RBR genes, have also occurred in several lineages. Some higher plants (e. g. Arabidopsis thaliana, Oryza sativa) contain a very large number of RBR genes and many of them were recently generated by tandem duplications. Microarray data indicate that most of these new genes have low-level and sometimes specific expression patterns. On the contrary, and as occurs in animals, a small set of older genes are broadly expressed at higher levels. Conclusions/Significance: The available data suggests that the dynamics of appearance and conservation of RBR genes is quite different in plants from what has been described in animals. In animals, an abrupt emergence of many structurall
Epistemic insights: Contemplating tensions between policy influences and creativity in school science
Creativity and the way it could be supported in schools is understood differently by policy makers, practitioners and scientists. This article reviews, with a chronological lens, the development of policies that include teaching creativity and teaching for creativity. The epistemic tensions between the intentions of government and the nature of creativity as it emerges in learning or scientific work is introduced and reflected upon. There have been more than nine key educational policies that have been introduced over the last 50 years. Each of these are considered in this article and related to the ways that creativity is understood and expected to be taught, supported or enacted in schools by policy makers. In light of the need to support creativity as a key twentyâfirstâcentury skill, to ultimately enable current students (who will become the next generation of scientists) to develop the capabilities to address global concerns, this article highlights issues related to this issue. Epistemic insights are offered that relate to the development of aspects of creativity, including questioning, developing alternate ideas, âseeingâ things differently, innovation, curiosity, problem solving and evaluating. The ways that policy related to creativity in science appears not to recognise how creativity can be reified in these ways in schools suggests the need for rapid review, especially in light of the upcoming international creativity tests in 2021
Manganese and carbon lines as temperature indicators
Selected hyperfine structure broadened lines of various excitations and the carbon line at 5380 Ă
are tested as temperature diagnostics for photospheric heterogeneities. This is done by comparing the observed center-to-limb variation of the equivalent widths of these lines with predictions by several proposed models of homogeneous type. Model 10 (Elste, 1968), which also explains the limb-darkening of the continuum in the same spectral range, provides a better basis for the analysis of heterogeneities at different photospheric levels than other recent reference models.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43705/1/11207_2004_Article_BF00155340.pd
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