The Interaction Of Multiple Convection Zones In A-type Stars

A-type stars have a complex internal structure with the possibility of multiple convection zones. If not sufficiently separated, such zones will interact through the convectively stable regions that lie between them. It is therefore of interest to ask whether the typical conditions that exist within such stars are such that these convections zones can ever be considered as disjoint. In this paper we present results from numerical simulations that help in understanding how increasing the distance between the convectively unstable regions are likely to interact through the stable region that separates them. This has profound implications for mixing and transport within these stars.Comment: 9 pages, 15 figures, Preprint accepted for publication in MNRA

Ispitivanja statičke kompresije i rezonantne vibracije celularnih materijala dobivenih gravitacijskim sinterovanjem šupljih brončanih kugli

The cylindrical and rod-shaped specimens were prepared by gravity sintering from Cu-Sn hollow spheres. On these samples, both static compression tests and measurements of resonance frequencies were performed. The compressive stress-strain curves revealed the features characteristic for a closed-cell ductile cellular solid. The removal of in general open porosity among loosely packed closed metallic hollow spheres was recognized as the principal mode of plastic deformation. The approximative effective moduli of elasticity were determined for cellular materials under consideration by means of the measurements of resonance frequencies on rod-shaped specimens.Cilindrični i šipkasti uzorci su pripremljeni gravitacionim sinterovanjem šupljih Cu-Sn kugli. Na tim uzorcima su provedena ispitivanja statičke kompresije i mjerenja rezonantnih frekvencija. Krivulja naprezanje-rastezanje nam pokazuje svojstva karakteristična za plastične celularne krute materijale sa zatvorenim ćelijama. Uklanjanje uglavnom otvorene povezanosti među labavo povezanim šupljim metalnim kuglama prepoznajemo kao glavni način plastične deformacije. Za celularne materijale koji se razmatraju određeni su približno učinkoviti moduli elastičnosti mjerenjem frekvencija rezonancije na šipkasto oblikovanim uzorcima

Developing an online positive psychology application for people with bipolar disorder:‘How expectations of consumers and professionals turned into an intervention.’

INTRODUCTION: In Bipolar Disorder (BD), people report a lower quality of life and lower levels of well-being than the general population. Additionally, patients with bipolar disorder have unmet needs which are closely linked to elements of positive psychology. OBJECTIVES: The current study aimed to gain insight from patients with BD and care professionals about their thoughts of online Positive Psychology Interventions (PPI) to develop an app containing PPI’s for people with BD. METHODS: The study is conducted in accordance with the CeHRes roadmap principles. Data were collected by focus groups, questionnaires, rapid prototyping and online feedback from the participants. Three focus groups meetings (FGM) were held with consumers (8) and professionals (5). RESULTS: The FGM reveals a need for positive psychology interventions to cover some of the unmet needs that can be applied in an app in addition to the guidelines-advised treatment. Patients and professionals expect that PPIs in the current treatment in BD can meet some of the needs that are currently still unmet, specifically offering hope, increasing self-esteem, expressing feelings, acceptation and preventing social isolation. The process of contextual inquiry and value specification is helpful to guide this process. CONCLUSIONS: The consensus on the different topics about the use of positive psychology intervention shows that both consumers and professionals underline the importance of applying PPI’s in BD. The use during subsyndrome and mild depressive episodes seem the most beneficial periods for patients with BD. A more extended study has to be conducted to confirm if these findings are more generalizable DISCLOSURE: No significant relationships

Theoretical isochrones for the Delta a photometric system

We have calculated theoretical isochrones for the photometric Delta a system to derive astrophysical parameters such as the age, reddening and distance modulus for open clusters. The Delta a system samples the flux depression at 520 nm which is highly efficient to detect chemically peculiar (CP) objects of the upper main sequence. The evolutionary status of CP stars is still a matter of debate and very important to test, for example, the dynamo and diffusion theories. In fact, the dynamo or fossil origin of the magnetic fields present in this kind of stars it still not clear. Using the stellar evolutionary models by Claret (1995), a grid of isochrones with different initial chemical compositions for the Delta a system was generated. The published data of 23 open clusters were used to fit these isochrones with astrophysical parameters (age, reddening and distance modulus) from the literature. As an additional test, isochrones with the same parameters for Johnson UBV data of these open clusters were also considered. The fits show a good agreement between the observations and the theoretical grid. We find that the accuracy of fitting isochrones to Delta a data without the knowledge of the cluster parameters is between 5 and 15%.Comment: 5 pages, 4 figures, accepted by A&

Critical evaluation of magnetic field detections reported for pulsating B-type stars in the light of ESPaDOnS, Narval and reanalyzed FORS1/2 observations

Recent spectropolarimetric studies of 7 SPB and $\beta$ Cep stars have suggested that photospheric magnetic fields are more common in B-type pulsators than in the general population of B stars, suggesting a significant connection between magnetic and pulsational phenomena. We present an analysis of new and previously published spectropolarimetric observations of these stars. New Stokes $V$ observations obtained with the high-resolution ESPaDOnS and Narval instruments confirm the presence of a magnetic field in one of the stars ($\epsilon$ Lup), but find no evidence of magnetism in 5 others. A re-analysis of the published longitudinal field measurements obtained with the low-resolution FORS1/2 spectropolarimeters finds that the measurements of all stars show more scatter from zero than can be attributed to Gaussian noise, suggesting the presence of a signal and/or systematic under-estimation of error bars. Re-reduction and re-measurement of the FORS1/2 spectra from the ESO archive demonstrates that small changes in reduction procedure lead to substantial changes in the inferred longitudinal field, and substantially reduces the number of field detections at the 3$\sigma$ level. Furthermore, we find that the published periods are not unique solutions to the time series of either the original or the revised FORS1/2 data. We conclude that the reported field detections, proposed periods and field geometry models for $\alpha$ Pyx, 15 CMa, 33 Eri and V1449 Aql are artefacts of the data analysis and reduction procedures, and that magnetic fields at the reported strength are no more common in SPB/$\beta$ Cep stars than in the general population of B stars.Comment: 10 pages, 5 figures, accepted for publication in ApJ, 2012, typo correcte

CCD photometric search for peculiar stars in open clusters. VII. Berkeley 11, Berkeley 94, Haffner 15, Lynga 1, NGC 6031, NGC 6405, NGC 6834 and Ruprecht 130

The detection of magnetic chemically peculiar (CP2) stars in open clusters of the Milky Way can be used to study the influence of different galactic environments on the (non-)presence of peculiarities, which has to be taken into account in stellar evolution models. Furthermore it is still unknown if the CP2 phenomenon evolves, i.e. does the strength of the peculiarity feature at 5200A, increase or decrease with age. We have observed eight young to intermediate age open clusters in the Delta a photometric system. This intermediate band photometric system samples the depth of the 5200A, flux depression by comparing the flux at the center with the adjacent regions having bandwidths of 110A, to 230A. The Delta a photometric system is most suitable to detect CP2 stars with high efficiency, but is also capable of detecting a small percentage of non-magnetic CP objects. Also, the groups of (metal-weak) lambda Bootis, as well as classical Be/shell stars, can be successfully investigated. This photometric system allows one to determine the age, reddening and distance modulus by fitting isochrones. Among the presented sample of eight galactic clusters, we have detected twenty three CP2, eight Be/Ae and eight metal-weak stars. Another six objects show a peculiar behaviour which is most probably due to a non-membership,variability or duplicity. Fitting isochrones to Delta a photometry yields estimates of the age, reddening and distance that are in excellent agreement with published values