SEPTEMBER 26, 1960 SOLAR COSMIC RAY EVENT

Solar cosmic ray event - september 26, 196

Raised cortisol excretion rate in urine and contamination by topical steroids

No abstract available

Dissipative effects on the sustainment of a magnetorotational dynamo in Keplerian shear flow

The magnetorotational (MRI) dynamo has long been considered one of the possible drivers of turbulent angular momentum transport in astrophysical accretion disks. However, various numerical results suggest that this dynamo may be difficult to excite in the astrophysically relevant regime of magnetic Prandtl number (Pm) significantly smaller than unity, for reasons currently not well understood. The aim of this article is to present the first results of an ongoing numerical investigation of the role of both linear and nonlinear dissipative effects in this problem. Combining a parametric exploration and an energy analysis of incompressible nonlinear MRI dynamo cycles representative of the transitional dynamics in large aspect ratio shearing boxes, we find that turbulent magnetic diffusion makes the excitation and sustainment of this dynamo at moderate magnetic Reynolds number (Rm) increasingly difficult for decreasing Pm. This results in an increase in the critical Rm of the dynamo for increasing kinematic Reynolds number (Re), in agreement with earlier numerical results. Given its very generic nature, we argue that turbulent magnetic diffusion could be an important determinant of MRI dynamo excitation in disks, and may also limit the efficiency of angular momentum transport by MRI turbulence in low Pm regimes.Comment: 7 pages, 6 figure

Magnetorotational dynamo chimeras. The missing link to turbulent accretion disk dynamo models?

In Keplerian accretion disks, turbulence and magnetic fields may be jointly excited through a subcritical dynamo process involving the magnetorotational instability (MRI). High-resolution simulations exhibit a tendency towards statistical self-organization of MRI dynamo turbulence into large-scale cyclic dynamics. Understanding the physical origin of these structures, and whether they can be sustained and transport angular momentum efficiently in astrophysical conditions, represents a significant theoretical challenge. The discovery of simple periodic nonlinear MRI dynamo solutions has recently proven useful in this respect, and has notably served to highlight the role of turbulent magnetic diffusion in the seeming decay of the dynamics at low magnetic Prandtl number Pm (magnetic diffusivity larger than viscosity), a common regime in accretion disks. The connection between these simple structures and the statistical organization reported in turbulent simulations remained elusive, though. Here, we report the numerical discovery in moderate aspect ratio Keplerian shearing boxes of new periodic, incompressible, three-dimensional nonlinear MRI dynamo solutions with a larger dynamical complexity reminiscent of such simulations. These "chimera" cycles are characterized by multiple MRI-unstable dynamical stages, but their basic physical principles of self-sustainment are nevertheless identical to those of simpler cycles found in azimuthally elongated boxes. In particular, we find that they are not sustained at low Pm either due to subcritical turbulent magnetic diffusion. These solutions offer a new perspective into the transition from laminar to turbulent instability-driven dynamos, and may prove useful to devise improved statistical models of turbulent accretion disk dynamos.Comment: 12 pages, 8 figures, submitted to A&

Lattice Gauge Fixing and the Violation of Spectral Positivity

Spectral positivity is known to be violated by some forms of lattice gauge fixing. The most notable example is lattice Landau gauge, where the effective gluon mass is observed to rise rather than fall with increasing distance. We trace this violation to the use of quenched auxiliary fields in the lattice gauge fixing process, and show that violation of spectral positivity is a general feature of quenching. We illustrate this with a simple quenched mass-mixing model in continuum field theory, and with a quenched form of the Ising model. For lattice gauge fixing associated with Abelian projection and lattice Landau gauge, we show that spectral positivity is violated by processes similar to those found in quenched QCD. For covariant gauges parametrized by a gauge-fixing parameter $\alpha$, the SU(2) gluon propagator is well described by a simple quenched mass-mixing formula. The gluon mass parameter appears to be independent of $\alpha$ for sufficiently large $\alpha$.Comment: 8 pages, 6 eps figures, RevTeX4; shortene

An updated review of the toxicology and ecotoxicology of sodium fluoroacetate (1080) in relation to its use as a pest control tool in New Zealand

Sodium fluoroacetate (1080) is a vertebrate pesticide, originally developed in the 1940s and principally used for the control of unwanted introduced animals in New Zealand and Australia. Fluoroacetate is also a toxic component of poisonous plants found in Australia, Africa, South America, and India. In relation to its use as a pesticide, recent research has focused on further elucidation of its potential sub-lethal effects, on animal welfare issues, on understanding and reducing its risk to non-target species, on its ecotoxicology, and fate in the environment following use in baits. 1080 acts by interfering with cellular energy production through inhibition of the tricarboxylic acid cycle and lethal doses can kill animal pests within 6–48 h of eating baits. Exposure to sub-lethal doses has been shown to have harmful effects on the heart and testes in animal studies, and strict safety precautions are enforced to protect contractors and workers in the pest control industry. Considerable care must be taken when using 1080 for the control of animal pests. Primary poisoning of non-target birds and secondary poisoning of dogs must be minimised to ensure that benefits in terms of conservation outcomes and pest and disease control significantly outweigh the risks associated with its use. Despite over 60 years of research and practical experience, the use of 1080 is still embroiled in controversy, while research efforts continue to improve its target specificity when it is used as a conservation tool or for Tb vector control

Molecular line opacity of LiCl in the mid-infrared spectra of brown dwarfs

We present a complete line list for the X 1Sigma+ electronic ground state of LiCl computed using fully quantum-mechanical techniques. This list includes transition energies and oscillator strengths in the spectral region 0.3-39,640.7 cm-1 for all allowed rovibrational transitions in absorption within the electronic ground state. The calculations were performed using an accurate hybrid potential constructed from a spectral inversion fit of experimental data and from recent multi-reference single- and double-excitation configuration interaction calculations. The line list was incorporated into the stellar atmosphere code PHOENIX to compute spectra for a range of young to old T dwarf models. The possibility of observing a signature of LiCl in absorption near 15.8 microns is addressed and the proposal to use this feature to estimate the total lithium elemental abundance for these cool objects is discussed.Comment: 8 pages, 2 figures, 1 table. Accepted for publication in ApJ 613, Sept. 20 200