On the origin of microturbulence in hot stars

We present results from the first extensive study of convection zones in the envelopes of hot massive stars, which are caused by opacity peaks associated with iron and helium ionization. These convective regions can be located very close to the stellar surface. Recent observations of microturbulence in massive stars from the VLT-Flames survey are in good agreement with our predictions concerning the occurrence and the strength of sub-surface convection in hot stars. We argue further that convection close to the surface may trigger clumping at the base of the stellar wind of massive stars.Comment: to appear in Comm. in Astroseismology - Proceedings of the 38th LIAC/HELAS-ESTA/BAG, 200

Thin Ice Target for 16^{16}O(p,p') experiment

A windowless and self-supporting ice target is described. An ice sheet with a thickness of 29.7 mg/cm$^2$ cooled by liquid nitrogen was placed at the target position of a magnetic spectrometer and worked stably in the $^{16}$O$(p,p')$ experiment at $E_{p}=392$ MeV. Background-free spectra were obtained.Comment: 14 pages, 4 figures, Nucl. Instr. & Meth. A (in press

Teacher (mis)perceptions of preschoolers’ academic skills: Predictors and associations with longitudinal outcomes.

Preschool teachers have important impacts on children’s academic outcomes, and teachers’ misperceptions of children’s academic skills could have negative consequences, particularly for low-income preschoolers. This study utilized data gathered from 123 preschool teachers and their 760 preschoolers from 70 low-income, racially diverse centers. Hierarchical linear modeling was utilized to account for the nested data structure. Even after controlling for children’s actual academic skill, older children, children with stronger social skills, and children with fewer inattentive symptoms were perceived to have stronger academic abilities. Contrary to hypotheses, preschoolers with more behavior problems were perceived by teachers to have significantly better pre-academic abilities than they actually had. Teachers’ perceptions were not associated with child gender or child race/ethnicity. Although considerable variability was due to teacher-level characteristics, child characteristics explained 42% of the variability in teachers’ perceptions about children’s language and pre-literacy ability and 41% of the variability in teachers’ perceptions about mathability. Notably, these perceptions appear to have important impacts over time. Controlling for child baseline academic skill and child characteristics, teacher perceptions early in the preschool year were significantly associated with child academic outcomes during the spring for both language and pre-literacy and math. Study implications with regard to the achievement gap are discussed

Predicting teacher participation in a classroom-based, integrated preventive intervention for preschoolers

Preschools provide a promising setting in which to conduct preventive interventions for childhood problems, but classroom programs can only be effective if teachers are willing and able to implement them. This study is one of the first to investigate predictors of the frequency of teacher participation in a classroom-based, randomized controlled trial of an integrated prevention program for preschoolers. The intervention was designed to promote school readiness with an integrated social and academic program, to be implemented by teachers with the support of classroom consultants. The current study is part of a larger project conducted with Head Start and community child care centers that serve primarily economically disadvantaged families; 49 teachers from 30 centers participated in this study. Overall, teachers conducted approximately 70% of the program activities. Participation decreased significantly over time from the first to the final week of the intervention, and also decreased within each week of the intervention, from the first to the final weekly activity. Teachers working at community child care centers implemented more intervention activities than did Head Start teachers. Teacher concerns about the intervention, assessed prior to training, predicted less participation. In addition, teachers' participation was positively related to their perception that their centers and directors were supportive, collegial, efficient, and fair, as well as their job satisfaction and commitment. Teacher experience, education, ethnicity, and self-efficacy were not significantly related to participation. In multi-level models that considered center as a level of analysis, substantial variance was accounted for by centers, pointing to the importance of considering center-level predictors in future research

Knockout of proton-neutron pairs from 16^{16}O with electromagnetic probes

After recent improvements to the Pavia model of two-nucleon knockout from $^{16}$O with electromagnetic probes the calculated cross sections are compared to experimental data from such reactions. Comparison with data from a measurement of the $^{16}$O(e,e$'$pn) reaction show much better agreement between experiment and theory than was previously observed. In a comparison with recent data from a measurement of the $^{16}$O($\gamma$,pn) reaction the model over-predicts the measured cross section at low missing momentum.Comment: 6 pages, 5 figure

Implementing efficient concerted rotations using Mathematica and C code

In this article we demonstrate a general and efficient metaprogramming implementation of concerted rotations using Mathematica. Concerted rotations allow the movement of a fixed portion of a polymer backbone with fixed bending angles, like a protein, while maintaining the correct geometry of the backbone and the initial and final points of the portion fixed. Our implementation uses Mathematica to generate a C code which is then wrapped in a library by a Python script. The user can modify the Mathematica notebook to generate a set of concerted rotations suited for a particular backbone geometry, without having to write the C code himself. The resulting code is highly optimized, performing on the order of thousands of operations per second

Sub-surface convection zones in hot massive stars and their observable consequences

We study the convection zones in the outer envelope of hot massive stars which are caused by opacity peaks associated with iron and helium ionization. We determine the occurrence and properties of these convection zones as function of the stellar parameters. We then confront our results with observations of OB stars. A stellar evolution code is used to compute a grid of massive star models at different metallicities. In these models, the mixing length theory is used to characterize the envelope convection zones. We find the iron convection zone (FeCZ) to be more prominent for lower surface gravity, higher luminosity and higher initial metallicity. It is absent for luminosities below about 10^{3.2}\Lsun, 10^{3.9}\Lsun, and $10^{4.2}$\Lsun$ for the Galaxy, LMC and SMC, respectively. We map the strength of the FeCZ on the Hertzsprung-Russell diagram for three metallicities, and compare this with the occurrence of observational phenomena in O stars: microturbulence, non-radial pulsations, wind clumping, and line profile variability. The confirmation of all three trends for the FeCZ as function of stellar parameters by empirical microturbulent velocities argues for a physical connection between sub-photospheric convective motions and small scale stochastic velocities in the photosphere of O- and B-type stars. We further suggest that clumping in the inner parts of the winds of OB stars could be caused by the same mechanism, and that magnetic fields produced in the FeCZ could appear at the surface of OB stars as diagnosed by discrete absorption components in ultraviolet absorption lines.Comment: Accepted for publication in Astronomy and Astrophysic

Teacher (mis)perceptions of preschoolers’ academic skills: Predictors and associations with longitudinal outcomes.

Preschool teachers have important impacts on children’s academic outcomes, and teachers’ misperceptions of children’s academic skills could have negative consequences, particularly for low-income preschoolers. This study utilized data gathered from 123 preschool teachers and their 760 preschoolers from 70 low-income, racially diverse centers. Hierarchical linear modeling was utilized to account for the nested data structure. Even after controlling for children’s actual academic skill, older children, children with stronger social skills, and children with fewer inattentive symptoms were perceived to have stronger academic abilities. Contrary to hypotheses, preschoolers with more behavior problems were perceived by teachers to have significantly better pre-academic abilities than they actually had. Teachers’ perceptions were not associated with child gender or child race/ethnicity. Although considerable variability was due to teacher-level characteristics, child characteristics explained 42% of the variability in teachers’ perceptions about children’s language and pre-literacy ability and 41% of the variability in teachers’ perceptions about mathability. Notably, these perceptions appear to have important impacts over time. Controlling for child baseline academic skill and child characteristics, teacher perceptions early in the preschool year were significantly associated with child academic outcomes during the spring for both language and pre-literacy and math. Study implications with regard to the achievement gap are discussed