Continuous Monitoring of STAR\u27s Main Time Projection Chamber

STAR refers to the Solenoidal Tracking instrument At RHIC (the Relativistic Heavy Ion Collider). For momenta above 500 MeV/c charged kaons are not separated from pions within STAR\u27s Main TPC (Time Projection Chamber) by track density alone and they are poorly separated below 500 MeV/c, even when using information from other sources like the vertex tracker. Within the TPC large numbers of kaons and pions decay into muons (and undetected neutrinos). Earlier work has shown parent pions and kaons whose decays are detected within a TPC may be distinguished uniquely from each other in a two-dimensional plot of muon-emission angle versus momentum difference (between each parent meson and its decay muon). Since pions and kaons have zero spin, each muon decay-product emerges isotropically in its parent meson\u27s rest frame. Identification of particle type provides the parent meson\u27s rest mass and, thus, its total energy. This means the measurement of each decay event is kinematically complete. Thus, Lorentz Transformations may be used to transform each component of the decaying muon\u27s laboratory four-momentum into the rest frame of its parent meson, where the muon decay is isotropic. An aggregated plot of muon directions from many parent rest frames will be isotropic in each (selected) sub-volume of the TPC unless there is a problem within the TPC or in its tracking algorithms. Continuous monitoring of a TPC is possible using this subset of detected charged particles

Weak magnetic fields in early-type stars: failed fossils

Weak magnetic fields have recently been detected in Vega and Sirius. Here, we explore the possibility that these fields are the remnants of some field inherited or created during or shortly after star formation and, unlike true fossil fields, are still evolving as we observe them. The timescale of this evolution is given in terms of the Alfven timescale and the rotation frequency by tau_evol ~ tau_A^2 Omega, which would be comparable to the age of the star. It is shown that it is likely that all intermediate- and high-mass stars contain fields of at least the order of the strength found so far in Vega and Sirius. Faster rotators are expected to have stronger magnetic fields. Stars may experience an increase in field strength during their early main-sequence, but for most of their lives field strength will decrease slowly. The length scale of the magnetic structure on the surface may be small in very young stars but should quickly increase to at least very approximately a fifth of the stellar radius.Comment: are welcome. Submitted to MNRAS. Five page

Revisiting the Flowers-Ruderman instability of magnetic stars

In 1977, Flowers and Ruderman described a perturbation that destabilises a purely dipolar magnetic field in a fluid star. They considered the effect of cutting the star in half along a plane containing the symmetry axis and rotating each half by 90\degr in opposite directions, which would cause the energy of the magnetic field in the exterior of the star to be greatly reduced, just as it happens with a pair of aligned magnets. We formally solve for the energy of the external magnetic field and check that it decreases monotonously along the entire rotation. We also describe the instability using perturbation theory, and see that it happens due to the work done by the interaction of the magnetic field with surface currents. Finally, we consider the stabilising effect of adding a toroidal field by studying the potential energy perturbation when the rotation is not done along a sharp cut, but with a continuous displacement field that switches the direction of rotation across a region of small but finite width. Using these results, we estimate the relative strengths of the toroidal and poloidal field needed to make the star stable to this displacement and see that the energy of the toroidal field required for stabilisation is much smaller than the energy of the poloidal field. We also show that, contrary to a common argument, the Flowers-Ruderman instability cannot be applied many times in a row to reduce the external magnetic energy indefinitely.Comment: Uploaded complete version with corrections from the MNRAS refere

Private law and the public sector's central counterparty prescription for the derivatives markets

In the wake of the financial crisis considerable momentum has built-up behind proposals to extend central counterparty (CCP) clearing in the over-the-counter derivatives markets. However, the implementation of new rules is proving complex. This paper argues that one cause of this complexity is that the public sector is seeking to incorporate into legislation (and require the wider use of) a privately owned and operated risk management mechanism. As a matter of law, the paper argues that CCP clearing can be understood as a market-generated ‘legal device’; in other words, one designed to support the markets by means of the interaction of various private law techniques. Following this analysis through, the paper highlights the benefits and drawbacks which derive from the legal techniques underlying CCP clearing (standardisation of contracts, asset-backing, netting, and so on) and argues that these qualities are inherent to the device. It concludes that the inherent capacity of CCP clearing gives rise to a qualitatively different set of challenges for policymakers than those arising from technical implementation, and it explains that both types of problem need to be addressed if the CCP prescription is to be effective

The stability of poloidal magnetic fields in rotating stars

The stability of large-scale magnetic fields in rotating stars is explored, using 3D numerical hydrodynamics to follow the evolution of an initial poloidal field. It is found that the field is subject to an instability, located initially on the magnetic equator, whereby the gas is displaced in a direction parallel to the magnetic axis. If the magnetic axis is parallel to the rotation axis, the rotation does not affect the initial linear growth of the instability, but does restrict the growth of the instability outside of the equatorial zone. The magnetic energy decays on a timescale which is a function of the Alfv\'en crossing time and the rotation speed, but short compared to any evolutionary timescale. No evidence is found for a possible stable end state to evolve from an initial axisymmetric poloidal field. The field of an oblique rotator is similarly unstable, in both cases regardless of the rotation speed.Comment: A&A accepted. Animations available at http://www.cita.utoronto.ca/~jon/research/rp_anims.htm

Social Capital, Rehabilitation, Tradition: Support for Restorative Justice in Japan and Australia

This paper investigates the attitudes and beliefs that the public hold about criminal behaviour in Japanese and Australian society, with a view to uncovering sources of resistance to, and support for, restorative justice. The study draws on a survey of 1,544 respondents from Japan and 1,967 respondents from Australia. In both societies, restorative justice met with greater acceptance among those who were (1) strong in social capital, (2) believed in offender reintegration and rehabilitation, (3) saw benefits for victims in forgiveness, and (4) were advocates for victims' voices being heard and amends made. The alternative 'just deserts' and deterrence models for dealing with crime were grounded in attitudes of punitiveness and fear of moral decay, and reservations about the value of reintegrating and rehabilitating offenders. Like restorative justice supporters, 'just deserts' and deterrence supporters expressed concern that victims' voices be heard and amends made. Winning public support for competing institutional arrangements may depend on who does best in meeting expectations for meeting the needs of victims