On the efficient calculation of ordinary and generalized spherical harmonics

Algorithms for the stable computation of generalized and ordinary spherical harmonics are presented. The algorithms are fast and have the useful property that they can compute harmonics for isolated harmonic degrees. fortran and C programs implementing these algorithms are available from the authors.     

Surface-wave polarization data and global anisotropic structure

In the past few years, seismic tomography has begun to provide detailed images of seismic velocity in the Earth's interior which, for the first time, give direct observational constraints on the mechanisms of heat and mass transfer. The study of surface waves has led to quite detailed maps of upper-mantle structure, and the current global models agree reasonably well down to wavelengths of approximately 2000 km. Usually, the models contain only elastic isotropic structure, which provides an excellent fit to the data in most cases. For example, the variance reduction for minor and major arc phase data in the frequency range 7–15 mHz is typically 65–92 per cent and the data are fit to within 1–2 standard deviations. The fit to great-circle phase data, which are not subject to bias from unknown source or instrument effects, is even better. However, there is clear evidence for seismic anisotropy in various places on the globe. This study demonstrates how much (or little) the fit to the data is improved by including anisotropy in the modelling process. It also illuminates some of the trade-offs between isotropic and anisotropic structure and gives an estimate of how much bias is introduced by neglecting anisotropy. Finally, we show that the addition of polarization data has the potential for improving recovery of anisotropic structure by diminishing the trade-offs between isotropic and anisotropic effects.     

Towards domestic fair trade? Farm labor, food localism, and the ‘family scale’ farm

Over the past several decades, consumers in the global North have increasingly looked to fair or alternative trading systems as a means to promote ecologically and socially sustainable agricultural production. While fair trade has historically been limited to international commodity networks, US-based agro-food activists have recently turned their attentions towards building a domestic movement, to bring fair trade principles and standards ‘home.’ Through an exploration of this growing movement, we consider the potential for third party certification and labeling to incorporate social justice into US-based agricultural production, with a particular focus on the implications for farm workers. We view current efforts to bring the principles of fair trade to the domestic arena as a reflection of several interrelated developments: a growing need on the part of small and mid-sized farmers to garner price premiums due to the erosion of the organic price premium; a recognition of the failure of organic certification to advance a holistic vision of sustainability; and the strategic embrace of voluntary regulatory mechanisms as an alternative to public regulation and collective bargaining. Initial research suggests that this has led to particular framings of the domestic fair trade concept, which may undermine the movement’s ability to address the social relations of agro-food production. Specifically, prioritization of the ‘family-scale’ farm and an undercurrent of food localism may obscure farm workers’ role in valorizing the US agricultural landscape.

Assessing the additive risks of PSII herbicide exposure to the Great Barrier Reef

Herbicide residues have been measured in the Great Barrier Reef lagoon at concentrations which have the potential to harm marine plant communities. Monitoring on the Great Barrier Reef lagoon following wet season discharge show that 80% of the time when herbicides are detected, more than one are present. These herbicides have been shown to act in an additive manner with regards to photosystem-II inhibition. In this study, the area of the Great Barrier Reef considered to be at risk from herbicides is compared when exposures are considered for each herbicide individually and also for herbicide mixtures. Two normalisation indices for herbicide mixtures were calculated based on current guidelines and PSII inhibition thresholds. The results show that the area of risk for most regions is greatly increased under the proposed additive PSII inhibition threshold and that the resilience of this important ecosystem could be reduced by exposure to these herbicides.