15,589 research outputs found
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
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