The impact of non-ideal magnetohydrodynamics on binary star formation

This is the final version of the article. Available from the publisher via the DOI in this record.We investigate the effect of non-ideal magnetohydrodynamics (MHD) on the formation of binary stars using a suite of three-dimensional smoothed particle magnetohydrodynamics simulations of the gravitational collapse of 1 M⊙, rotating, perturbed molecular-cloud cores. Alongside the role of Ohmic resistivity, ambipolar diffusion and the Hall effect, we also examine the effects of magnetic field strength, orientation and amplitude of the density per- turbation. When modelling sub-critical cores, ideal MHD models do not collapse whereas non-ideal MHD models collapse to form single protostars. In supercritical ideal MHD models, increasing the magnetic field strength or decreasing the initial-density perturbation amplitude decreases the initial binary separation. Strong magnetic fields initially perpendicular to the rotation axis suppress the formation of binaries and yield discs with magnetic fields ∼10 times stronger than if the magnetic field was initially aligned with the rotation axis. When non-ideal MHD is included, the resulting discs are larger and more massive, and the binary forms on a wider orbit. Small differences in the supercritical cores caused by non-ideal MHD effects are amplified by the binary interaction near periastron. Overall, the non-ideal effects have only a small impact on binary formation and early evolution, with the initial conditions playing the dominant role.JW and MRB acknowledge support from the European Research Council under the European Community’s Seventh Framework Programme (FP7/2007–2013 grant agreement no. 339248). JW also acknowledges support from the Australian Research Council (ARC) Discovery Projects Grant DP130102078. DJP is funded by ARC Future Fellowship FT130100034. This work was supported by resources on the gSTAR national facility at Swinburne University of Technology and by Zen. gSTAR is funded by Swinburne and the Australian Government’s Education Investment Fund. Several calculations for this paper were performed on the University of Exeter Supercomputer, a DiRAC Facility jointly funded by STFC, the Large Facilities Capital Fund of BIS, and the University of Exeter

The collapse of a molecular cloud core to stellar densities using radiation non-ideal magnetohydrodynamics (article)

This is the final version of the article. Available from Oxford University Press via the DOI in this record.The dataset associated with this article is located in ORE at: http://hdl.handle.net/10871/32503We present results from radiation non-ideal magnetohydrodynamics (MHD) calculations that follow the collapse of rotating, magnetized, molecular cloud cores to stellar densities. These are the first such calculations to include all three non-ideal effects: ambipolar diffusion, Ohmic resistivity, and the Hall effect. We employ an ionization model in which cosmic ray ionization dominates at low temperatures and thermal ionization takes over at high temperatures. We explore the effects of varying the cosmic ray ionization rate from ζcr = 10−10 to 10−16 s−1. Models with ionization rates ≳10−12 s−1 produce results that are indistinguishable from ideal MHD. Decreasing the cosmic ray ionization rate extends the lifetime of the first hydrostatic core up to a factor of 2, but the lifetimes are still substantially shorter than those obtained without magnetic fields. Outflows from the first hydrostatic core phase are launched in all models, but the outflows become broader and slower as the ionization rate is reduced. The outflow morphology following stellar core formation is complex and strongly dependent on the cosmic ray ionization rate. Calculations with high ionization rates quickly produce a fast (≈14 km s−1) bipolar outflow that is distinct from the first core outflow, but with the lowest ionization rate, a slower (≈3−4 km s−1) conical outflow develops gradually and seamlessly merges into the first core outflow.JW and MRB acknowledge support from the European Research Council under the European Commission's Seventh Framework Programme (FP7/2007- 2013 grant agreement no. 339248). DJP and JW were funded by Australian Research Council grants FT130100034 andDP130102078. The calculations for this paper were performed on the University of Exeter Supercomputer, a DiRAC Facility jointly funded by STFC, the Large Facilities Capital Fund of BIS, and the University of Exeter. We used splash (Price 2007) for the column density figures

Does turbulence determine the initial mass function?

Published onlineThis is the author accepted manuscript. The final version is available from Oxford University Press via the DOI in this record.We test the hypothesis that the initial mass function (IMF) is determined by the density probability distribution function (PDF) produced by supersonic turbulence. We compare 14 simulations of star cluster formation in 50 M molecular cloud cores where the initial turbulence contains either purely solenoidal or purely compressive modes, in each case resolving fragmentation to the opacity limit to determine the resultant IMF. We find statistically indistinguishable IMFs between the two sets of calculations, despite a factor of 2 difference in the star formation rate and in the standard deviation of log (ρ). This suggests that the density PDF, while determining the star formation rate, is not the primary driver of the IMF.We thank the anonymous referee for comments which have improved the paper. We acknowledge CPU time on gSTAR, funded by Swinburne University and the Australian Government. This project was funded via Australian Research Council Discovery Project DP130102078 and Future Fellowship FT130100034. We used SPLASH (Price 2007)

Jučer, danas, sutra

Usvojena Strategija obrazovanja; Promaknućem u zvanje nagrađeni najbolji i najuspješniji odgajatelji, učitelji i nastavnici; U Zagrebu održan drugi dio Wanda edukacije; U Budimpešti proslavljena 20. godišnjica Koraka; Gostovanje profesora Ferrea Laeversa u Hrvatsko

The effect of sole hardness on the metatarsophalangeal joint in children

Conference abstract

DIE QUELLEN DER AKZENTSCHWANKUNGEN IN DEN NEUEREN WÖRTERBÜCHERN DES KROATISCHES

U članku su opisana dva temeljna izvorišta naglasnih nepodudarnosti u novijoj rječničkoj literaturi. Jedno se očituje u raskoraku između zapisane norme i naglasne prakse, a drugo se opaža na onim područjima na kojima naglasna norma danas još nije posve ustaljena pa se javljaju dvostrukosti (katkad i trostrukosti), kako je primjerice u dijelu pridjevnih složenica.In diesem Artikel wurden zwei Grundquellbereiche der Nichtübereinstimmung beim Akzentuieren in der neueren Wörterbücherliteratur dargestellt. Die erste äußert sich in der Unstimmigkeit zwischen der vorgeschriebenen Sprachnorm und der Anwendung des Akzentes. Die zweite ist in jenen Bereichen zu bemerken, wo die Akzentuierungsnorm heute noch nicht ganz stabil ist und deshalb kommen sie als doppelte Formen (manchmal sogar als dreifach) vor, wie das beispielsweise im Teil der Adjektivazusammensetzungen der Fall ist. Die Schwankungen können nur durch die klare Darstellung von Stilschichten des Akzentes beseitigt werden, indem dabei klargelegt wird, was annehmbar ist, was sich dublierenlaßt, was in der stilistischen Reserve bleibt und was unannehmbar ist. Eine ausführliche Darstellung des Zustandes mit allen Einzelheiten auf allen vier Akzentsebenen ist in den Akzentswörterbüchern oder in dem speziellen prosodischen Handbuch zu erwarten. In anderen Typen von Wörterbüchern aber wird die Wahl einigermaßen verengt

Practical approach on frail older patients attended for acute heart failure

Acute heart failure (AHF) is a multi-organ dysfunction syndrome. In addition to known cardiac dysfunction, non-cardiac comorbidity, frailty and disability are independent risk factors of mortality, morbidity, cognitive and functional decline, and risk of institutionalization. Frailty, a treatable and potential reversible syndrome very common in older patients with AHF, increases the risk of disability and other adverse health outcomes. This position paper highlights the need to identify frailty in order to improve prognosis, the risk-benefits of invasive diagnostic and therapeutic procedures, and the definition of older-person-centered and integrated care plans

On the origin of magnetic fields in stars II: The effect of numerical resolution

This is the author accepted manuscript. The final version is available from Oxford University Press via the DOI in this recordAre the kG-strength magnetic fields observed in young stars a fossil field left over from their formation or are they generated by a dynamo? Our previous numerical study concluded that magnetic fields must originate by a dynamo process. Here, we continue that investigation by performing even higher numerical resolution calculations of the gravitational collapse of a 1 Msun rotating, magnetised molecular cloud core through the first and second collapse phases until stellar densities are reached. Each model includes Ohmic resistivity, ambipolar diffusion, and the Hall effect. We test six numerical resolutions, using between 10^5 and 3.0 x 10^7 particles to model the cloud. At all but the lowest resolutions, magnetic walls form in the outer parts of the first hydrostatic core, with the maximum magnetic field strength located within the wall rather than at the centre of the core. At high resolution, this magnetic wall is disrupted by the Hall effect, producing a magnetic field with a spiral-shaped distribution of intensity. As the second collapse occurs, this field is dragged inward and grows in strength, with the maximum field strength increasing with resolution. As the second core forms, the maximum field strength exceeds 1 kG in our highest resolution simulations, and the stellar core field strength exceeds this threshold at the highest resolution. Our resolution study suggests that kG-strength magnetic fields may be implanted in low-mass stars during their formation, and may persist over long timescales given that the diffusion timescale for the magnetic field exceeds the age of the Universe.European Union FP7University of St AndrewsAustralian Research Council (ARC

Searching for online information on the fit of children’s footwear during the COVID-19 pandemic: an analysis of Google Trends data

Background Selecting footwear with appropriate fit in children is challenging due the changes with foot size and dimensions which occur throughout childhood. Access to appropriate footwear is important but recent challenges with the COVID-19 pandemic resulted in closure of retail stores for prolonged periods where parents/carers could not physically purchase footwear for their children and the footwear industry suffered disruption to their supply chain, and falls in retail sales. Simultaneously increased use of social media platforms for health information seeking throughout the pandemic have been documented. This likely would have included parents/carers seeking information online to support footwear purchases for their children. The primary aim of this work was to explore how searches for online fitting information for children changed throughout the COVID-19 pandemic lockdown periods. A secondary aim was to identify how searches were influenced by footwear style. Methods We employed Google Trends to obtain search engine traffic related to footwear fitting information for children. We collected data spanning the three years pre, during and post the main national lockdown for three eight-week windows: (1) first eight weeks of the U.K. national lockdown; (2) the first eight weeks of the calendaryear; (3) the eight weeks leading up to children going back-to-school for the new academic year in the U.K. The search terms reflected parents/carers searching for footwear fit information relating to children and were grouped by style of footwear: children, infants, babies and toddlers as well as school shoes. Results We identified increased searching for footwear fit information for children during the pandemic, which reduced following post pandemic in all except the searches which related to school shoes. We saw reductions in searching related to fit of school shoes as schools closed indefinitely and an increase in online searches with the pandemic. This was also maintained post-pandemic despite shops reopening, suggesting that some of these changes in information reflect new consumer behaviours which may continue. Conclusions Increased searches for online resources regarding footwear fit highlights the importance of ensuring high quality accessible online information on footwear fit is available to support those buying footwear for their children