Regimes of cosmic-ray diffusion in Galactic turbulence.

Cosmic-ray transport in astrophysical environments is often dominated by the diffusion of particles in a magnetic field composed of both a turbulent and a mean component. This process, which is two-fold turbulent mixing in that the particle motion is stochastic with respect to the field lines, needs to be understood in order to properly model cosmic-ray signatures. One of the most important aspects in the modeling of cosmic-ray diffusion is that fully resonant scattering, the most effective such process, is only possible if the wave spectrum covers the entire range of propagation angles. By taking the wave spectrum boundaries into account, we quantify cosmic-ray diffusion parallel and perpendicular to the guide field direction at turbulence levels above 5% of the total magnetic field. We apply our results of the parallel and perpendicular diffusion coefficient to the Milky Way. We show that simple purely diffusive transport is in conflict with observations of the inner Galaxy, but that just by taking a Galactic wind into account, data can be matched in the central 5 kpc zone. Further comparison shows that the outer Galaxy at > 5  kpc, on the other hand, should be dominated by perpendicular diffusion, likely changing to parallel diffusion at the outermost radii of the Milky Way.

The Magellanic Corona as the key to the formation of the Magellanic Stream.

The dominant gaseous structure in the Galactic halo is the Magellanic Stream. This extended network of neutral and ionized filaments surrounds the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC), the two most massive satellite galaxies of the Milky Way1-4. Recent observations indicate that the LMC and SMC are on their first passage around the Galaxy5, that the Magellanic Stream is made up of gas stripped from both clouds2,6,7 and that the majority of this gas is ionized8,9. Although it has long been suspected that tidal forces10,11 and ram-pressure stripping12,13 contributed to the formation of the Magellanic Stream, models have not been able to provide a full understanding of its origins3. Several recent developments-including the discovery of dwarf galaxies associated with the Magellanic group14-16, determination of the high mass of the LMC17, detection of highly ionized gas near stars in the LMC18,19 and predictions of cosmological simulations20,21-support the existence of a halo of warm (roughly 500,000 kelvin) ionized gas around the LMC (the 'Magellanic Corona'). Here we report that, by including this Magellanic Corona in hydrodynamic simulations of the Magellanic Clouds falling onto the Milky Way, we can reproduce the Magellanic Stream and its leading arm. Our simulations explain the filamentary structure, spatial extent, radial-velocity gradient and total ionized-gas mass of the Magellanic Stream. We predict that the Magellanic Corona will be unambiguously observable via high-ionization absorption lines in the ultraviolet spectra of background quasars lying near the LMC.

The impact of recent advances in laboratory astrophysics on our understanding of the cosmos.

An emerging theme in modern astrophysics is the connection between astronomical observations and the underlying physical phenomena that drive our cosmos. Both the mechanisms responsible for the observed astrophysical phenomena and the tools used to probe such phenomena-the radiation and particle spectra we observe-have their roots in atomic, molecular, condensed matter, plasma, nuclear and particle physics. Chemistry is implicitly included in both molecular and condensed matter physics. This connection is the theme of the present report, which provides a broad, though non-exhaustive, overview of progress in our understanding of the cosmos resulting from recent theoretical and experimental advances in what is commonly called laboratory astrophysics. This work, carried out by a diverse community of laboratory astrophysicists, is increasingly important as astrophysics transitions into an era of precise measurement and high fidelity modeling.

Stirring unmagnetized plasma.

A new concept for spinning unmagnetized plasma is demonstrated experimentally. Plasma is confined by an axisymmetric multicusp magnetic field and biased cathodes are used to drive currents and impart a torque in the magnetized edge. Measurements show that flow viscously couples momentum from the magnetized edge (where the plasma viscosity is small) into the unmagnetized core (where the viscosity is large) and that the core rotates as a solid body. To be effective, collisional viscosity must overcome the ion-neutral drag due to charge-exchange collisions.

Absence of complete finite-Larmor-radius stabilization in extended MHD.

The dominant finite-Larmour-radius (FLR) stabilization effects on interchange instability can be retained by taking into account the ion gyroviscosity or the generalized Ohm's law in an extended MHD model. However, recent simulations and theoretical calculations indicate that complete FLR stabilization of the interchange mode may not be attainable by ion gyroviscosity or the two-fluid effect alone in the framework of extended MHD. For a class of plasma equilibria in certain finite-beta or nonisentropic regimes, the critical wave number for complete FLR stabilization tends toward infinity.

Magnetic support of the optical emission line filaments in NGC 1275.

The giant elliptical galaxy NGC 1275, at the centre of the Perseus cluster, is surrounded by a well-known giant nebulosity of emission-line filaments, which are plausibly in excess of 10(8) years old. The filaments are dragged out from the centre of the galaxy by radio-emitting 'bubbles' rising buoyantly in the hot intracluster gas, before later falling back. They act as markers of the feedback process by which energy is transferred from the central massive black hole to the surrounding gas. The mechanism by which the filaments are stabilized against tidal shear and dissipation into the surrounding extremely hot (4 x 10(7) K) gas has been unclear. Here we report observations that resolve thread-like structures in the filaments. Some threads extend over 6 kpc, yet are only 70 pc wide. We conclude that magnetic fields in the threads, in pressure balance with the surrounding gas, stabilize the filaments, so allowing a large mass of cold gas to accumulate and delay star formation.

Conflict resolution at the University of Ottawa Faculty of Medicine: The Pelican and the sign of the triangle.

In 1997 the University of Ottawa Medical School adopted a conflict-resolution policy for informally dealing with complaints of abuse, harassment and intimidation, sexual harassment, and scientific misconduct or misappropriation of intellectual property. In collaboration with the university's Faculty of Law, general conflict-resolution workshops were given for faculty and administration and mediation training was provided to medical faculty designated "complaint officers" under the policy. In this article, the authors describe the policy and training and then analyze the first major incident arising after the policy's implementation: the publication of disrespectful misogynist material in The Pelican, a medical student society newsletter. The Pelican incident is used as a "lessons learned" case study both in terms of its multiple outcomes and as an opportunity to pinpoint some important policy and practical considerations that emerged in implementing a conflict-resolution policy. The article also describes the results of a learning environment survey conducted after the Pelican incident.