Determining crystal structures through crowdsourcing and coursework

We show here that computer game players can build high-quality crystal structures. Introduction of a new feature into the computer game Foldit allows players to build and real-space refine structures into electron density maps. To assess the usefulness of this feature, we held a crystallographic model-building competition between trained crystallographers, undergraduate students, Foldit players and automatic model-building algorithms. After removal of disordered residues, a team of Foldit players achieved the most accurate structure. Analysing the target protein of the competition, YPL067C, uncovered a new family of histidine triad proteins apparently involved in the prevention of amyloid toxicity. From this study, we conclude that crystallographers can utilize crowdsourcing to interpret electron density information and to produce structure solutions of the highest quality

Polymodal faulting: Time for a new angle on shear failure

Conjugate, or bimodal, fault patterns dominate the geological literature on shear failure. Based on Anderson's (1905) application of the Mohr-Coulomb failure criterion, these patterns have been interpreted from all tectonic regimes, including normal, strike-slip and thrust (reverse) faulting. However, a fundamental limitation of the Mohr-Coulomb failure criterion – and others that assume faults form parallel to the intermediate principal stress, σ2 – is that only plane strain can result from slip on the conjugate faults. However, deformation in the Earth is widely accepted as being three-dimensional, with truly triaxial stresses (σ1 > σ2 > σ3) and strains. Polymodal faulting, with three or more sets of faults forming and slipping simultaneously, can generate three-dimensional strains from truly triaxial stresses. Laboratory experiments and outcrop studies have verified the occurrence of polymodal fault patterns in nature. These fault patterns present a fundamental challenge to our understanding of shear failure in rocks (and other materials) and an opportunity to improve our understanding of seismic hazards and fluid flow in the subsurface. In this review, we assess the published evidence, theories and models for polymodal faulting before suggesting ways to produce a truly general and valid failure criterion for triaxial failure

The Dynamic Mosaic Disturbance and Development of Antarctic Benthic Communities

The continental shelf is the platform for many of the planet’s most productive ecosystems but it is exposed to high disturbance. At high latitudes, massive grounded ice sheets have extended and retreated during glaciations whilst at lower latitudes sea level changes alternately emerse it as land or deepen it below the euphotic zone. The magnitude, frequency and mode of disturbances differ around the planet and in this chapter we describe these for the the Antarctic region, where icebergs and the highest wind speeds and wave heights in the world result in communities in a continuous cycle of disturbance and recolonization. Concepts of disturbance, colonization and early development or succession have been a source of considerable interest to ecologists for more than a century but now, with increasing realisation that the world’s coastal areas are facing unprecedented and accelerating anthropogenic threats (Jackson et al.,2001) these concepts have assumed new importance