Magnetic fields and radiative feedback in the star formation process

Star formation is a complex process involving the interplay of many physical effects, including gravity, turbulent gas dynamics, magnetic fields and radiation. Our understanding of the process has improved substantially in recent years, primarily as a result of our increased ability to incorporate the relevant physics in numerical calculations of the star formation process. In this contribution we present an overview of our recent studies of star cluster formation in turbulent, magnetised clouds using self-gravitating radiation-magnetohydrodynamics calculations (Price and Bate 2008, 2009). Our incorporation of magnetic fields and radiative transfer into the Smoothed Particle Hydrodynamics method are discussed. We highlight how magnetic fields and radiative heating of the gas around newborn stars can solve several of the key puzzles in star formation, including an explanation for why star formation is such a slow and inefficient process. However, the presence of magnetic fields at observed strengths in collapsing protostellar cores also leads to problems on smaller scales, including a difficulty in forming protostellar discs and binary stars (Price and Bate 2007, Hennebelle and Teyssier 2008), which suggests that our understanding of the role of magnetic fields in star formation is not yet complete.Comment: 14 pages aip conf. format, 5 figures, submitted to AIP conf proc. of "Plasmas in the Laboratory and in the Universe: Interactions, Patterns and Turbulence", Como, Italy 1st-4th Dec 2009, eds. Bertin et al. Relevant movies at http://users.monash.edu.au/~dprice/mclusterRT/index.html#movie

Smoothed particle magnetohydrodynamic simulations of protostellar outflows with misaligned magnetic field and rotation axes

We have developed a modified form of the equations of smoothed particle magnetohydrodynamics which are stable in the presence of very steep density gradients. Using this formalism, we have performed simulations of the collapse of magnetised molecular cloud cores to form protostars and drive outflows. Our stable formalism allows for smaller sink particles (< 5 AU) than used previously and the investigation of the effect of varying the angle, {\theta}, between the initial field axis and the rotation axis. The nature of the outflows depends strongly on this angle: jet-like outflows are not produced at all when {\theta} > 30{\deg}, and a collimated outflow is not sustained when {\theta} > 10{\deg}. No substantial outflows of any kind are produced when {\theta} > 60{\deg}. This may place constraints on the geometry of the magnetic field in molecular clouds where bipolar outflows are seen.Comment: Accepted for publication in MNRAS, 13 pages, 14 figures. Animations can be found at http://www.astro.ex.ac.uk/people/blewis/research/outflows_misaligned_fields.htm

Constrained hyperbolic divergence cleaning in smoothed particle magnetohydrodynamics with variable cleaning speeds

We present an updated constrained hyperbolic/parabolic divergence cleaning algorithm for smoothed particle magnetohydrodynamics (SPMHD) that remains conservative with wave cleaning speeds which vary in space and time. This is accomplished by evolving the quantity $\psi / c_h$ instead of $\psi$. Doing so allows each particle to carry an individual wave cleaning speed, $c_h$, that can evolve in time without needing an explicit prescription for how it should evolve, preventing circumstances which we demonstrate could lead to runaway energy growth related to variable wave cleaning speeds. This modification requires only a minor adjustment to the cleaning equations and is trivial to adopt in existing codes. Finally, we demonstrate that our constrained hyperbolic/parabolic divergence cleaning algorithm, run for a large number of iterations, can reduce the divergence of the field to an arbitrarily small value, achieving $\nabla \cdot B=0$ to machine precision.Comment: 23 pages, 16 figures, accepted for publication in Journal of Computational Physic

Exploring relationships between moral reasoning, distorted cognitions and problem solving in male offenders with intellectual disabilities

Background: The study explored the relationship between moral reasoning, distorted cognitions and problem solving in male offenders and non-offenders with intellectual disabilities (IDs). The psychometric properties for an adapted measure of distorted cognitions for people with IDs were explored. The difference in cognitive distortions, moral reasoning and problem solving between offenders and non-offenders were explored. Very few published studies explored these constructs in this way. Methods: A between-groups design and additional correlations were used to explore the hypotheses. Two groups were recruited: ID offenders (n=34) and ID non-offenders (n=38). Both groups completed the Socio-Moral Reflection Measure-Short Form (SRM-SF), How I Think Questionnaire (HIT) and the Social Problem Solving Inventory Short-Form (SPSI-R-SF). Results: The results indicated that offenders with IDs demonstrated Stage 2(3) reasoning when compared to non-offenders with IDs who demonstrated Stage 2 reasoning. The difference in some of the moral reasoning constructs was significant. A modified version of the HIT demonstrated good internal consistency and test-retest reliability. Significant positive relationships were identified between moral reasoning and problem solving, and moral reasoning and cognitive distortions for men with IDs. Conclusions: There was a relationship between moral development, cognitive distortions and problem solving and that these constructs were interdependent. The results supported Gibbs Sociomoral Stages and tentative support for Garrigan and Langdon’s Developmental Social Information Processing Model of Moral Judgement and Behaviour. An adequately powered sample size was used. Social desirability, recruitment and treatment implications were limitations. Further studies should replicate the findings, using a longitudinal design along with the adapted measures. Keywords: Intellectual disabilities; moral reasoning; moral development; cognitive distortions; problem solvin

Genomic biomarkers in prostate cancer.

Prostate cancer is the most common non-cutaneous cancer among men in the United States. In the last decade there has been a rapid expansion in the field of biomarker assays for diagnosis, prognosis, and treatment prediction in prostate cancer. The evidence base for these assays is rapidly evolving. With several commercial assays available at each stage of the disease, deciding which genomic assays are appropriate for which patients can be nuanced for physicians. In an effort to help guide these decisions in clinical practice, we aim to give an update on the current status of the biomarker field of prostate cancer

Investigating prescriptions for artificial resistivity in smoothed particle magnetohydrodynamics

In numerical simulations, artificial terms are applied to the evolution equations for stability. To prove their validity, these terms are thoroughly tested in test problems where the results are well known. However, they are seldom tested in production-quality simulations at high resolution where they interact with a plethora of physical and numerical algorithms. We test three artificial resistivities in both the Orszag-Tang vortex and in a star formation simulation. From the Orszag-Tang vortex, the Price et. al. (2017) artificial resistivity is the least dissipative thus captures the density and magnetic features; in the star formation algorithm, each artificial resistivity algorithm interacts differently with the sink particle to produce various results, including gas bubbles, dense discs, and migrating sink particles. The star formation simulations suggest that it is important to rely upon physical resistivity rather than artificial resistivity for convergence.Comment: 8 pages, 7 figures. Proceedings of the "12th international SPHERIC workshop", Ourense, Spain, 13-15 June 201

Photon counting compressive depth mapping

We demonstrate a compressed sensing, photon counting lidar system based on the single-pixel camera. Our technique recovers both depth and intensity maps from a single under-sampled set of incoherent, linear projections of a scene of interest at ultra-low light levels around 0.5 picowatts. Only two-dimensional reconstructions are required to image a three-dimensional scene. We demonstrate intensity imaging and depth mapping at 256 x 256 pixel transverse resolution with acquisition times as short as 3 seconds. We also show novelty filtering, reconstructing only the difference between two instances of a scene. Finally, we acquire 32 x 32 pixel real-time video for three-dimensional object tracking at 14 frames-per-second.Comment: 16 pages, 8 figure