1,879 research outputs found
An XMM-Newton observation of the young open cluster NGC 2547: coronal activity at 30 Myr
We report XMM-Newton observations of the young open cluster NGC 2547 which
allow us to characterise coronal activity in solar-type stars at an age of 30
Myr. X-ray emission peaks among G-stars at luminosities (0.3-3keV) of
Lx~10^{30.5} erg/s and declines to Lx<=10^{29.0} erg/s among M-stars. Coronal
spectra show evidence for multi-temperature differential emission measures and
low coronal metal abundances (Z~0.3). The G- and K-type stars follow the same
relationship between X-ray activity and Rossby number established in older
clusters and field stars, although most solar-type stars in NGC 2547 exhibit
saturated/super-saturated X-ray activity levels. Median levels of Lx and
Lx/Lbol in the solar-type stars of NGC 2547 are similar to T-Tauri stars of the
Orion Nebula cluster (ONC), but an order of magnitude higher than in the older
Pleiades. The spread in X-ray activity levels among solar-type stars in NGC
2547 is much smaller than in older or younger clusters. Coronal temperatures
increase with Lx, Lx/Lbol and surface X-ray flux. Active solar-type stars in
NGC 2547 have coronal temperatures between those in the ONC and the most active
older ZAMS stars. A flaring rate (for total flare energies [0.3-3keV] >10^{34}
erg) of 1 every 350^{+350}_{-120} ks was found for solar-type stars, similar to
rates found in the ONC and Pleiades. Comparison with ROSAT HRI data taken 7
years previously reveals that only 10-15 percent of solar-type stars or stars
with Lx>3x10^{29} erg/s exhibit X-ray variability by more than a factor of two.
The similar levels of X-ray activity and rate of occurrence for large flares in
NGC 2547 and the ONC demonstrate that the X-ray radiation environment around
young solar-type stars remains relatively constant over their first 30 Myr
(abridged).Comment: Accepted for publication in MNRAS. Electronic tables available from
the autho
A CAT with caveats: is the Consensual Assessment Technique a reliable measure of graphic design creativity?
The Consensual Assessment Technique (CAT) is considered one of the gold standards for creativity assessment, and graphic design, arguably, is the most ubiquitous domain within the creative industries. For the first time, this study tests two tasks to measure graphic design creativity, and by extension, the reliability of the CAT as a measure of graphic design creativity. Initial research suggested the level of consensus amongst judges (often referred to as inter-rater reliability) was too low to be reliable, and may be unduly influenced by a judgeâs preference for technical execution. In this study, 16 professional graphic designers were randomly assigned instructions to discount technical execution from creativity ratings, or given instruction that gave no stipulation, for 60 artworks. Inter-rater reliability scores were acceptable for each task and experimental condition, but were higher for judges that received instructions to discount technical execution. These and other results are discussed, and the argument presented that, for future CAT studies in this domain, specific instructions to discount technical execution offers a more reliable measure of graphic design creativity
The suppression of magnetism and the development of superconductivity within the collapsed tetragonal phase of Ca0.67Sr0.33Fe2As2 at high pressure
Structural and electronic characterization of (Ca0.67Sr0.33)Fe2As2 has been
performed as a func- tion of pressure up to 12 GPa using conventional and
designer diamond anvil cells. The compound (Ca0.67Sr0.33)Fe2As2 behaves
intermediate between its end members-CaFe2As2 and SrFe2As2- displaying a
suppression of magnetism and the onset of superconductivity. Like other members
of the AEFe2As2 family, (Ca0.67Sr0.33)Fe2As2 undergoes a pressure-induced
isostructural volume collapse, which we associate with the development of As-As
bonding across the mirror plane of the structure. This collapsed tetragonal
phase abruptly cuts off the magnetic state, giving rise to superconductivity
with a maximum Tc=22.2 K. The maximum Tc of the superconducting phase is not
strongly correlated with any structural parameter, but its proximity to the
abrupt suppression of magnetism as well as the volume collapse transition
suggests that magnetic interactions and structural inhomogeneity may play a
role in its development. The pressure-dependent evolution of the ordered states
and crystal structures in (Ca,Sr)Fe2As2 provides an avenue to understand the
generic behavior of the other members of the AEFe2As2 family.Comment: 9 pages, 9 figure
Inelastic contribution of the resistivity in the hidden order in URu2Si2
In the hidden order of URu2Si2 the resistivity at very low temperature shows
no T^2 behavior above the transition to superconductivity. However, when
entering the antiferromagnetic phase, the Fermi liquid behavior is recovered.
We discuss the change of the inelastic term when entering the AF phase with
pressure considering the temperature dependence of the Grueneisen parameter at
ambient pressure and the influence of superconductivity by an extrapolation of
high field data.Comment: 5 pages, 2 figures, SCES conference proceedin
Elements in Scenario-Based Simulation Associated with Nursing Studentsâ Self-Confidence and Satisfaction: A Cross-Sectional Study
Aim: To identify elements in scenarioâbased simulation associated with nursing students' satisfaction with the simulation activity and selfâconfidence in managing the simulated patient situation. The study will provide insight to improve the use of simulation as a learning strategy.
Design: A crossâsectional study.
Method: The Student Satisfaction and SelfâConfidence in Learning scale was used as the outcome measure to identify associations with elements of the Simulation Design Scale and the Educational Practices Questionnaire scale after scenarioâbased simulation using patient simulators. Firstâyear nursing students at a university college in Norway (N = 202) were invited to participate and (N = 187) responded to the questionnaires.
Results: The mean scores for selfâconfidence and satisfaction were 4.16 and 4.57, respectively. In the final multiple linear regression analysis, active learning was associated with satisfaction with the simulation activity, while clear objectives and active learning were associated with selfâconfidence in managing the simulated patient situation.publishedVersio
An XMMâNewton observation of the young open cluster NGC 2547: coronal activity at 30 Myr
We report on XMMâNewton observations of the young open cluster NGC 2547 which allow us to characterize coronal activity in solar-type stars, and stars of lower mass, at an age of 30 Myr. X-ray emission is seen from stars at all spectral types, peaking among G stars at luminosities (0.3-3 keV) of Lxâ 1030.5 erg sâ1 and declining to Lx†1029.0 erg sâ1 among M stars with masses â„0.2 Mâ. Coronal spectra show evidence for multi-temperature differential emission measures and low coronal metal abundances of Zâ 0.3. The G- and K-type stars of NGC 2547 follow the same relationship between X-ray activity and Rossby number established in older clusters and field stars, although most of the solar-type stars in NGC 2547 exhibit saturated or even supersaturated X-ray activity levels. The median levels of Lx and Lx/Lbol in the solar-type stars of NGC 2547 are very similar to those in T-Tauri stars of the Orion Nebula cluster (ONC), but an order of magnitude higher than in the older Pleiades. The spread in X-ray activity levels among solar-type stars in NGC 2547 is much smaller than in older or younger clusters. Coronal temperatures increase with Lx, Lx/Lbol and surface X-ray flux. The most active solar-type stars in NGC 2547 have coronal temperatures intermediate between those in the ONC and the most active older zero-age main-sequence (ZAMS) stars. We show that simple scaling arguments predict higher coronal temperature in coronally saturated stars with lower gravities. A number of candidate flares were identified among the low-mass members and a flaring rate [for total flare energies (0.3-3 keV) > 1034 erg] of one every 350+350â120 ks was found for solar-type stars, which is similar to rates found in the ONC and Pleiades. Comparison with ROSAT High Resolution Imager (HRI) data taken 7 yr earlier reveals that only 10-15 per cent of solar-type stars or stars with Lx > 3 Ă 1029 erg sâ1 exhibit X-ray variability by more than a factor of 2. This is comparable with clusters of similar age but less than in both older and younger clusters. The similar median levels of X-ray activity and rate of occurrence for large flares in NGC 2547 and the ONC demonstrate that the X-ray radiation environment around young solar-type stars remains relatively constant over their first 30 My
X-rays from the Mira AB Binary System
We present the results of XMM-Newton X-ray observations of the Mira AB binary
system, which consists of a pulsating, asymptotic giant branch primary and
nearby (~0.6'' separation) secondary of uncertain nature. The EPIC CCD (MOS and
pn) X-ray spectra of Mira AB are relatively soft, peaking at ~1 keV, with only
very weak emission at energies > 3 keV; lines of Ne IX, Ne X, and O VIII are
apparent. Spectral modeling indicates a characteristic temperature T_X ~ 10^7 K
and intrinsic luminosity L_X ~ 5x10^29 erg s^{-1}, and suggests enhanced
abundances of O and, possibly, Ne and Si in the X-ray-emitting plasma. Overall,
the X-ray spectrum and luminosity of the Mira AB system more closely resemble
those of late-type, pre-main sequence stars or late-type, magnetically active
main sequence stars than those of accreting white dwarfs. We conclude that Mira
B is most likely a late-type, magnetically active, main-sequence dwarf, and
that X-rays from the Mira AB system arise either from magnetospheric accretion
of wind material from Mira A onto Mira B, or from coronal activity associated
with Mira B itself, as a consequence of accretion-driven spin-up. One (or both)
of these mechanisms also could be responsible for the recently discovered,
point-like X-ray sources within planetary nebulae.Comment: 14 pages, 3 figures; to appear in the Astrophysical Journa
- âŠ