On the Bardeen-Petterson Effect in black hole accretion discs

We investigate the effect of black hole spin on warped or misaligned accretion discs - in particular i) whether or not the inner disc edge aligns with the black hole spin and ii) whether the disc can maintain a smooth transition between an aligned inner disc and a misaligned outer disc, known as the Bardeen-Petterson effect. We employ high resolution 3D smoothed particle hydrodynamics simulations of $\alpha$-discs subject to Lense-Thirring precession, focussing on the bending wave regime where the disc viscosity is smaller than the aspect ratio $\alpha \lesssim H/R$. We first address the controversy in the literature regarding possible steady-state oscillations of the tilt close to the black hole. We successfully recover such oscillations in 3D at both small and moderate inclinations ($\lesssim 15^{\circ}$), provided both Lense-Thirring and Einstein precession are present, sufficient resolution is employed, and provided the disc is not so thick so as to simply accrete misaligned. Second, we find that discs inclined by more than a few degrees in general steepen and break rather than maintain a smooth transition, again in contrast to previous findings, but only once the disc scale height is adequately resolved. Finally, we find that when the disc plane is misaligned to the black hole spin by a large angle, the disc 'tears' into discrete rings which precess effectively independently and cause rapid accretion, consistent with previous findings in the diffusive regime ($\alpha \gtrsim H/R$). Thus misalignment between the disc and the spin axis of the black hole provides a robust mechanism for growing black holes quickly, regardless of whether the disc is thick or thin.Comment: 15 pages, 18 figures, movies available at http://users.monash.edu.au/~rnealon/ or YouTub

On the Papaloizou-Pringle instability in tidal disruption events

We demonstrate that the compact, thick disc formed in a tidal disruption event may be unstable to non-axisymmetric perturbations in the form of the Papaloizou-Pringle instability. We show this can lead to rapid redistribution of angular momentum that can be parameterised in terms of an effective Shakura-Sunyaev $\alpha$ parameter. For remnants that have initially weak magnetic fields, this may be responsible for driving mass accretion prior to the onset of the magneto-rotational instability. For tidal disruptions around a $10^6$ M$_{\odot}$ black hole, the measured accretion rate is super-Eddington but is not sustainable over many orbits. We thus identify a method by which the torus formed in tidal disruption event may be significantly accreted before the magneto-rotational instability is established.Comment: 9 pages, 10 figures, accepted for publication in MNRAS. Movies of simulations available at https://youtu.be/kBLAjY8n9vI and https://youtu.be/F8F0tmLbX3

Generalized Warped Disk Equations

The manner in which warps in accretion disks evolve depends on the magnitude of the viscosity. ... See full text for complete abstract

Resources and student achievement – evidence from a Swedish policy reform

This paper utilizes a policy change to estimate the effect of teacher density on student performance. We find that an increase in teacher density has a positive effect on student achievement. The baseline estimate – obtained by using the grade point average as the outcome variable – implies that resource increases corresponding to the class-size reduction in the STAR-experiment (i.e., a reduction of 7 students) improves performance by 2.6 percentile ranks (or 0.08 standard deviations). When we use test score data for men, potentially a more objective measure of student performance, the effect of resources appears to be twice the size of the baseline estimate.Student performance; teacher/student ratio; policy reform; differences-in-differences

Predictive and experimental approaches for elucidating protein–protein interactions and quaternary structures

The elucidation of protein–protein interactions is vital for determining the function and action of quaternary protein structures. Here, we discuss the difficulty and importance of establishing protein quaternary structure and review in vitro and in silico methods for doing so. Determining the interacting partner proteins of predicted protein structures is very time-consuming when using in vitro methods, this can be somewhat alleviated by use of predictive methods. However, developing reliably accurate predictive tools has proved to be difficult. We review the current state of the art in predictive protein interaction software and discuss the problem of scoring and therefore ranking predictions. Current community-based predictive exercises are discussed in relation to the growth of protein interaction prediction as an area within these exercises. We suggest a fusion of experimental and predictive methods that make use of sparse experimental data to determine higher resolution predicted protein interactions as being necessary to drive forward development

A Device for Quantitative Analysis of the Thumb Ulnar Collateral Ligament

A device to quantitatively assess the ulnar collateral ligament of the thumb was developed to facilitate rapid and accurate diagnosis of the ligamentous injury known as Skier’s thumb. Topics: Wound

Challenging the nice girl

Louise Nealon is a writer from county Kildare. She plays corner back for her local camogie club, Cappagh GAA. This piece based on a presentation given at a conference entitled, Sidelines, Touchlines and Hemlines: Irish Women in Sport, in Dundalk County Museum on February 2020

ElGamal-type signature schemes in modular arithmetic and Galois fields

A digital signature is like a handwritten signature for a file, such that it ensures the identity of the person responsible for the file and prevents any unauthorized changes to the original file. Digital signatures use the same technology as most public key cryptosystems in which there is a public and private key. Most mathematical operations are done over a field Zp where p is some large prime. It is possible to do the same operations over other finite fields. My project explains and studies the different finite fields that can be used as well as ways to implement and experiment with them. It turns out that operations over Zp run the fastest, but with polynomial basis in a close second. Normal basis did not prove to be efficient at all. These results turned out to be against most claims of others, especially in hardware implementations. Large integer libraries are so efficient and fast that is was hard to beat the times with custom bit manipulation structures. Various secure signature schemes have proven to be practical and it is likely that they will be used much more in the near future in many applications