Thinking critically about rapport and collusion in feminist research: relationships, contexts and ethical practice

This is an introductory paper to the WSIF Special Issue on 'Rapport and collusion in feminist research' by the co-editors, Dr Georgia Philip and Dr Linda Bell

Long Term Evolution of Magnetic Turbulence in Relativistic Collisionless Shocks: Electron-Positron Plasmas

We study the long term evolution of magnetic fields generated by a collisionless relativistic $e^+e^-$ shock which is initially unmagnetized. Our 2D particle-in-cell numerical simulations show that downstream of such a Weibel-mediated shock, particle distributions are close to isotropic, relativistic Maxwellians, and the magnetic turbulence is highly intermittent spatially, with the non-propagating magnetic fields forming relatively isolated regions with transverse dimension $\sim 10-20$ skin depths. These structures decay in amplitude, with little sign of downstream merging. The fields start with magnetic energy density $\sim (0.1-0.2)$ of the upstream kinetic energy within the shock transition, but rapid downstream decay drives the fields to much smaller values, below $10^{-3}$ of equipartition after $10^3$ skin depths. In an attempt to construct a theory that follows field decay to these smaller values, we explore the hypothesis that the observed damping is a variant of Landau damping in an unmagnetized plasma. The model is based on the small value of the downstream magnetic energy density, which suggests that particle orbits are only weakly perturbed from straight line motion, if the turbulence is homogeneous. Using linear kinetic theory applied to electromagnetic fields in an isotropic, relativistic Maxwellian plasma, we find a simple analytic form for the damping rates, $\gamma_k$, in two and three dimensions for small amplitude, subluminous electromagnetic fields. We find that magnetic energy does damp due to phase mixing of current carrying particles as $(\omega_p t)^{-q}$ with $q \sim 1$. (abridged)Comment: 10 pages, 6 figures, accepted to ApJ; Downsampled version for arXiv. Full resolution figures available at http://astro.berkeley.edu/~pchang/full_res_weibel.pd

Reviews

Seels, Barbara B. and Richey, Rita C, Instructional Technology: The Definition and Domains of the Field, Washington DC, Association for Educational Communications and Technology, 1994. ISBN 0–89240–072–2

“What comes to mind when you think of science? The perfumery!”: Documenting science‐related cultural learning pathways across contexts and timescales

In this paper, we explore the details of one youth's science‐related learning in‐ and out‐of‐school at the time of her participation in an ethnography of youth science and technology learning across contexts and over time. We use the Cultural Learning Pathways Framework to analyze the youth's interests, and the related sociocultural, historical, material, and affect‐laden practices in which she and her family participated. The following question guided our analysis: How do everyday moments—experienced across settings, pursuits, social groups, and time—result in scientific learning, expertise development, and identification? We found that this youth's interest in various aspects of the sciences was years in the making, embedded in situated events that were part of a space–time continuum bound by passion for the practices involved, influenced by specific cultural practices, and explored with the help of close family collaborators. We also found that school science activity in which the youth in question participated both supported and could have potentially constrained her science‐related cultural learning pathways. © 2013 Wiley Periodicals, Inc. J Res Sci Teach 51: 260–285, 2014Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106138/1/tea21134.pd

The stellar mass-accretion rate relation in T Tauri stars and brown dwarfs

Recent observations show a strong correlation between stellar mass and accretion rate in young stellar and sub-stellar objects, with the scaling $\dot{M}_{acc} \propto M_*^2$ holding over more than four orders of magnitude in accretion rate. We explore the consequences of this correlation in the context of disk evolution models. We note that such a correlation is not expected to arise from variations in disk angular momentum transport efficiency with stellar mass, and suggest that it may reflect a systematic trend in disk initial conditions. In this case we find that brown dwarf disks initially have rather larger radii than those around more massive objects. By considering disk evolution, and invoking a simple parametrization for a shut-off in accretion at the end of the disk lifetime, we show that such models predict that the scatter in the stellar mass-accretion rate relationship should increase with increasing stellar mass, in rough agreement with current observations.Comment: 4 pages, 2 figures. Accepted for publication in ApJ Letter