Constraining the metallicities, ages, star formation histories, and ionizing continua of extragalactic massive star populations

We infer the properties of massive star populations using the far-ultraviolet stellar continua of 61 star-forming galaxies: 42 at low-z observed with HST and 19 at z~2 from the Megasaura sample. We fit each stellar continuum with a linear combination of up to 50 single age and single metallicity Starburst99 models. From these fits, we derive light-weighted ages and metallicities, which agree with stellar wind and photospheric spectral features, and infer the spectral shapes and strengths of the ionizing continua. Inferred light-weighted stellar metallicities span 0.05-1.5 Z$_\odot$ and are similar to the measured nebular metallicities. We quantify the ionizing continua using the ratio of the ionizing flux at 900\AA\ to the non-ionizing flux at 1500\AA\ and demonstrate the evolution of this ratio with stellar age and metallicity using theoretical single burst models. These single burst models only match the inferred ionizing continua of half of the sample, while the other half are described by a mixture of stellar ages. Mixed age populations produce stronger and harder ionizing spectra than continuous star formation histories, but, contrary to previous studies that assume constant star formation, have similar stellar and nebular metallicities. Stellar population age and metallicity affect the far-UV continua in different and distinguishable ways; assuming a constant star formation history diminishes the diagnostic power. Finally, we provide simple prescriptions to determine the ionizing photon production efficiency ($\xi_{ion}$) from the stellar population properties. $\xi_{ion}$ has a range of log($\xi_{ion})=24.4-25.7$ Hz erg$^{-1}$ that depends on stellar age, metallicity, star formation history, and contributions from binary star evolution. These stellar population properties must be observationally determined to determine the number of ionizing photons generated by massive stars.Comment: 31 pages, 23 figures, resubmitted to ApJ after incorporating the referee's comments. Comments encourage

Problematising separated children:a policy analysis of the UK ‘Safeguarding Strategy: Unaccompanied asylum seeking and refugee children’

While international and national policies, strategies and legislation have been designed to address the problems of forced displacement, they also form a vital role in the discursive construction, governance and regulation of those who have been displaced. This paper critically interrogates the ‘UK Safeguarding Strategy: Unaccompanied Asylum Seeking and Refugee Children’ to highlight the ways in which unaccompanied asylum seeking children (UASC) are implicitly constructed as a policy problem. Drawing on Foucault, and using a novel analytic method (WPR) for studying problematisation within policy, this paper moves beyond the policy definition of an unaccompanied asylum seeking child to unearth characterisations that the policy ascribes to this group of children, and in particular the conceptual boundaries established for the way society thinks about UASC. These conceptual boundaries are divisive in nature, including suspicion around routes of arrival to the UK; constructions of risk; and questions about the responsibility of providing care and of being in need of care. The significance of the paper lies in its aim to use the examination of the discursive practices of the UK’s Safeguarding Strategy as a starting point to open a broader discussion around how UASC are constructed and governed, nationally and internationally.</p

Accurately predicting the escape fraction of ionizing photons using restframe ultraviolet absorption lines

The fraction of ionizing photons that escape high-redshift galaxies sensitively determines whether galaxies reionized the early universe. However, this escape fraction cannot be measured from high-redshift galaxies because the opacity of the intergalactic medium is large at high redshifts. Without methods to indirectly measure the escape fraction of high-redshift galaxies, it is unlikely that we will know what reionized the universe. Here, we analyze the far-ultraviolet (UV) H I (Lyman series) and low-ionization metal absorption lines of nine low-redshift, confirmed Lyman continuum emitting galaxies. We use the H I covering fractions, column densities, and dust attenuations measured in a companion paper to predict the escape fraction of ionizing photons. We find good agreement between the predicted and observed Lyman continuum escape fractions (within $1.4\sigma$) using both the H I and ISM absorption lines. The ionizing photons escape through holes in the H I, but we show that dust attenuation reduces the fraction of photons that escape galaxies. This means that the average high-redshift galaxy likely emits more ionizing photons than low-redshift galaxies. Two other indirect methods accurately predict the escape fractions: the Ly$\alpha$ escape fraction and the optical [O III]/[O II] flux ratio. We use these indirect methods to predict the escape fraction of a sample of 21 galaxies with rest-frame UV spectra but without Lyman continuum observations. Many of these galaxies have low escape fractions ($f_{\rm esc} \le 1$\%), but 11 have escape fractions $>1$\%. The methods presented here will measure the escape fractions of high-redshift galaxies, enabling future telescopes to determine whether star-forming galaxies reionized the early universe.Comment: Accepted for publication in A&A. 12 pages, 5 figure

Modelling split-Hopkinson pressure bar tests on quartz sand

FE modelling of a confined split Hopkinson pressure bar (SHPB) test on dry quartz sand was carried out using LS-DYNA in order to assess whether Material Model 5 could replicate experimental results, which would enable a more detailed investigation of the stress state in SHPB specimen. Quasi-static test data was used to select the material model input, and the model SHPB was set up to replicate the experimental conditions. The results show that Material Model 5 replicates the volumetric response provided as input data, but fails to predict the shear response observed in the quasi-static experiments. This was found to be due to the model treating the shear modulus as a constant rather than it increasing with strain, a feature which makes the Material Model 5 unsuitable for modelling SHPB tests on sand

Reaching older people with PA delivered in football clubs: the reach, adoption and implementation characteristics of the Extra Time Programme.

Background Older adults (OA) represent a core priority group for physical activity and Public Health policy. As a result, significant interest is placed on how to optimise adherence to interventions promoting these approaches. Extra Time (ET) is an example of a national programme of physical activity interventions delivered in professional football clubs for OA aged 55+ years. This paper aims to examine the outcomes from ET, and unpick the processes by which these outcomes were achieved. Methods This paper represents a secondary analysis of data collected during the evaluation of ET. From the 985 OA reached by ET, n=486 adopted the programme and completed post-intervention surveys (typically 12 weeks). We also draw on interview data with 18 ET participants, and 7 staff who delivered the programme. Data were subject to thematic analysis to generate overarching and sub themes. Results Of the 486 participants, the majority 95%, (n= 462) were White British and 59.7% (n=290) were female. Most adopters (65.4%/n=318) had not participated in previous interventions in the host clubs. Social interaction was the most frequently reported benefit of participation (77.2%, n=375). While the reach of the club badge was important in letting people know about the programme, further work enhanced adoption and satisfaction. These factors included (i) listening to participants, (ii) delivering a flexible age-appropriate programme of diverse physical and social activities, (iii) offering activities which satisfy energy drives and needs for learning and (iv) extensive opportunities for social engagement. Conclusions Findings emerging from this study indicate that physical activity and health interventions delivered through professional football clubs can be effective for engaging OA

Transcatheter management of adult aortic coarctation with “Railway” technique

We report the case of a 21-year-old man with complete atresia of the aorta who underwent percutaneous aortic intervention and successfully recanalize the atresia of the aorta with the artery “Railway” technique. A fully atretic aorta poses a challenge for a percutaneous solution and is often subject to open repair, considering the risk of perforation and technical failure. However, our case demonstrates that a strategic and structured approach is safe and successful to even tackle complete aortic atresia without complications such as rupture or bleeding

Bullying and the need to belong: Early adolescents’ bullying-related behavior and the acceptance they desire and receive from particular classmates

Based on the notion that one of the motives underlying children's antisocial behavior is their need to belong to particular peers, it was examined how each of four types of bullying-related behavior would be related to the acceptance that 10 to 13-year-old children desired and received from same- and other-sex children with different bullying-related behavioral styles. Bullying-related behavior was assessed using a peer nomination procedure. Children rated the importance of being accepted by each particular classmate and their own acceptance of these same classmates. Among boys, antisocial involvement in bullying was related to a desire to be accepted by other antisocial boys and to actually being rejected by boys in general. Among girls, antisocial involvement in bullying was related to a desire to be accepted by boys in general. © Blackwell Publishing Ltd. 2007

Proof of the Formulae for the Molecular Orbitals and Energy Levels of Mobius Annulenes, Based on the Theory of Skew-Circulant Matrices

The formulae for the molecular orbitals and corresponding energy-levels that arise in a Huckel molecular-orbital (HMO) treatment of Miobius systems are derived by appeal to the theory of skew-circulant matrices. The approach adopted is analogous to that previously used to obtain the orbital energies and HMO\u27s of \u27Huckel\u27 annulenes from the theory of circulant matrices