164 research outputs found
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Does early schooling narrow outcome gaps for advantaged and disadvantaged children?
This paper explores how starting school at a younger age affects the developmental score gaps between relatively advantaged and disadvantaged children. While previous findings suggest that delaying school entry may improve school readiness, less is known about whether it has differential effects for advantaged and disadvantaged children. For disadvantaged children, starting school early may be a better alternative to staying at home for longer as school provides a more stable and educational environment than the family home, overcompensating for the penalties of starting school early. This may be less applicable to relatively advantaged children who generally have greater access to resources in the home and who are more likely to utilise formal pre-school services. We use the Longitudinal Study of Australian Children to investigate if there is support for this hypothesis. The endogeneity of school starting age is addressed using the regression discontinuity design. We find that an early school start generally improves childrenâs cognitive skills, which is even more pronounced for disadvantaged children. In contrast, an early school start tends to negatively affect childrenâs non-cognitive skills with both advantaged and disadvantaged children affected in similar ways. Thus, our findings suggest that an earlier school entry may narrow the gaps in cognitive skills, whereas the gaps in non-cognitive skills are not affected by the school starting age
Pulsation in the atmosphere of the roAp star HD 24712. I. Spectroscopic observations and radial velocity measurements
We have investigated the structure of the pulsating atmosphere of one of the
best studied rapidly oscillating Ap stars, HD 24712. For this purpose we
analyzed spectra collected during 2001-2004. An extensive data set was obtained
in 2004 simultaneously with the photometry of the Canadian MOST mini-satellite.
This allows us to connect directly atmospheric dynamics observed as radial
velocity variations with light variations seen in photometry. We directly
derived for the first time and for different chemical elements, respectively
ions, phase shifts between photometric and radial velocity pulsation maxima
indicating, as we suggest, different line formation depths in the atmosphere.
This allowed us to estimate for the first time the propagation velocity of a
pulsation wave in the outer stellar atmosphere of a roAp star to be slightly
lower than the sound speed. We confirm large pulsation amplitudes (150-400 m/s)
for REE lines and the Halpha core, while spectral lines of the other elements
(Mg, Si, Ca, and Fe-peak elements) have nearly constant velocities. We did not
find different pulsation amplitudes and phases for the lines of rare-earth
elements before and after the Balmer jump, which supports the hypothesis of REE
concentration in the upper atmosphere above the hydrogen line-forming layers.
We also discuss radial velocity amplitudes and phases measured for individual
spectral lines as tools for a 3D tomography of the atmosphere of HD 24712.Comment: accepted by A&
Highly directional and coherent emission from dark excitons enabled by bound states in the continuum
A double-edged sword in two-dimensional material science and technology is an
optically forbidden dark exciton. On the one hand, it is fascinating for
condensed matter physics, quantum information processing, and optoelectronics
due to its long lifetime. On the other hand, it is notorious for being
optically inaccessible from both excitation and detection standpoints. Here, we
provide an efficient and low-loss solution to the dilemma by reintroducing
photonics bound states in the continuum (BICs) to manipulate dark excitons in
the momentum space. In a monolayer tungsten diselenide under normal incidence,
we observed a giant enhancement with an enhancement factor of ~3,100 for dark
excitons enabled by transverse magnetic BICs with intrinsic out-of-plane
electric fields. By further employing widely tunable Friedrich-Wintgen BICs, we
demonstrated highly directional emission from the dark excitons with a
divergence angle of merely 7 degrees. We found that the directional emission is
coherent at room temperature, unambiguously shown in polarization analyses and
interference measurements. Therefore, the BICs reintroduced as a momentum-space
photonic environment could be an intriguing platform to reshape and redefine
light-matter interactions in nearby quantum materials, such as low-dimensional
materials, otherwise challenging or even impossible to achieve
A 3D study of the photosphere of HD 99563 - I. Pulsation analysis
We have used high-speed spectroscopy of the rapidly oscillating Ap (roAp) star HD 99563 to study the pulsation amplitude and phase behaviour of elements in its stratified atmosphere over one 2.91-d rotation cycle. We identify spectral features related to patches in the surface distribution of chemical elements and study the pulsation amplitudes and phases as the patches move across the stellar disc. The variations are consistent with a distorted non-radial dipole pulsation mode. We measure a 1.6 km sâ1 rotational variation in the mean radial velocities of Hα and argue that this is the first observation of Hα abundance spots caused by He settling through suppression of convection by the magnetic field on an oblique rotator, in support of a prime theory for the excitation mechanism of roAp star pulsation. We demonstrate that HD 99563 is the second roAp star to show aspect dependence of blue-to-red running wave line profile variations in Nd iii spots
Carbon Abundances of Three Carbon-Enhanced Metal-Poor Stars from High-Resolution Gemini-S/bHROS Spectra of the 8727A [C I] Line
We present the results from an analysis of the 8727ang forbidden [C I] line
in high-resolution Gemini-S/bHROS spectra of three CEMP stars. We find the
[C/Fe] ratios based on the [C I] abundances of the two most Fe-rich stars in
our sample (HIP 0507-1653: [Fe/H] = -1.42 and HIP 0054-2542: [Fe/H] = -2.66) to
be in good agreement with previously determined CH and C_2 line-based values.
For the most Fe-deficient star in our sample (HIP 1005-1439: [Fe/H] = -3.08),
however, the [C/Fe] ratio is found to be 0.34 dex lower than the published
molecular-based value. We have carried out 3D local thermodynamic equilibrium
(LTE) calculations for [C I], and the resulting corrections are found to be
modest for all three stars, suggesting that the discrepancy between the [C I]
and molecular-based C abundances of HIP 1005-1439 is due to more severe 3D
effects on the molecular lines. Carbon abundances are also derived from C I
high-excitation lines and are found to be 0.45-0.64 dex higher than the [C
I]-based abundances. Previously published non-LTE C I abundance corrections
bring the [C I] and C I abundances into better agreement; however, targeted
NLTE calculations for CEMP stars are clearly needed. We have also derived the
abundances of N, K, and Fe for each star. The Fe abundances agree well with
previously derived values, and the K abundances are similar to those of
C-normal metal-poor stars. Nitrogen abundances have been derived from resolved
lines of the CN red system. The abundances are found to be approximately 0.44
dex larger than literature values, which have been derived from CN blue bands
near 3880 and 4215 ang. We discuss evidence that suggests that analyses of the
CN blue system bands underestimate the N abundances of metal-poor giants.Comment: Accepted for publication in AJ; 42 pages, 6 figures, 7 table
MOST photometry of the roAp star 10 Aql
Context: We present 31.2 days of nearly continuous MOST photometry of the
roAp star 10Aql. Aims:The goal was to provide an unambiguous frequency
identification for this little studied star, as well as to discuss the detected
frequencies in the context of magnetic models and analyze the influence of the
magnetic field on the pulsation. Methods: Using traditional Fourier analysis
techniques on three independent data reductions, intrinsic frequencies for the
star are identified. Theoretical non-adiabatic axisymmetric modes influenced by
a magnetic field having polar field strengths Bp = 0-5kG were computed to
compare the observations to theory. Results: The high-precision data allow us
to identify three definite intrinsic pulsation frequencies and two other
candidate frequencies with low S/N. Considering the observed spacings, only one
(50.95microHz) is consistent with the main sequence nature of roAp stars. The
comparison with theoretical models yields a best fit for a 1.95Msun model
having solar metallicity, suppressed envelope convection, and homogenous helium
abundance. Furthermore, our analysis confirms the suspected slow rotation of
the star and sets new lower limits to the rotation period (Prot>1 month) and
inclination (i>30\pm10deg.). Conclusions:The observed frequency spectrum is not
rich enough to unambiguously identify a model. On the other hand, the models
hardly represent roAp stars in detail due to the approximations needed to
describe the interactions of the magnetic field with stellar structure and
pulsation. Consequently, errors in the model frequencies needed for the fitting
procedure can only be estimated. Nevertheless, it is encouraging that models
which suppress convection and include solar metallicity, in agreement with
current concepts of roAp stars, fit the observations best.Comment: accepted by A&
Enlargement and the Historical Origins of the European Community's Democratic Identity, 1961â1978
This article examines how and when democracy entered the discursive politics of the European Community to become one of the fundamental tenets of European political identity â and in the process influenced how decision-makers approached the question of enlargement. Building on multiple archival sources, the article traces how all three Community institutions (Commission, Council and European Parliament) legitimised the expansion and continuation of the process of European integration through the discursive construction of democracy. It focuses on the debates elicited by the attempts of southern European countries to accede to the EEC in the 1960s and 1970s
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Intergenerational persistence in health in developing countries : the penalty of gender inequality?
This paper is motivated to investigate the often neglected payoff to investments in the health of girls and women in terms of next generation outcomes. This paper investigates the intergenerational persistence of health across time and region as well as across the distribution of maternal health. It uses comparable microdata on as many as 2.24 million children born of about 0.6 million mothers in 38 developing countries in the 31 year period, 1970â2000. Mother's health is indicated by her height, BMI and anemia status. Child health is indicated by mortality risk and anthropometric failure. We find a positive relationship between maternal and child health across indicators and highlight non-linearities in these relationships. The results suggest that both contemporary and childhood health of the mother matter and that the benefits to the next generation are likely to be persistent. Averaging across the sample, persistence shows a considerable decline over time. Disaggregation shows that the decline is only significant in Latin America. Persistence has remained largely constant in Asia and has risen in Africa. The paper provides the first cross-country estimates of the intergenerational persistence in health and the first estimates of trends
Working with Indigenous, local and scientific knowledge in assessments of nature and nature's linkages with people
Working with indigenous and local knowledge (ILK) is vital for inclusive assessments of nature and nature's linkages with people. Indigenous peoples' concepts about what constitutes sustainability, for example, differ markedly from dominant sustainability discourses. The Intergovernmental Platform on Biodiversity and Ecosystems Services (IPBES) is promoting dialogue across different knowledge systems globally. In 2017, member states of IPBES adopted an ILK Approach including: procedures for assessments of nature and nature's linkages with people; a participatory mechanism; and institutional arrangements for including indigenous peoples and local communities. We present this Approach and analyse how it supports ILK in IPBES assessments through: respecting rights; supporting care and mutuality; strengthening communities and their knowledge systems; and supporting knowledge exchange. Customary institutions that ensure the integrity of ILK, effective empowering dialogues, and shared governance are among critical capacities that enable inclusion of diverse conceptualizations of sustainability in assessments
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