Drosophila germ-band extension (GBE) is an example of the convergence and extension movements that elongate and narrow embryonic tissues. To understand the collective cell behaviours underlying tissue morphogenesis, we have continuously quantified cell intercalation and cell shape change during GBE. We show that the fast, early phase of GBE depends on cell shape change in addition to cell intercalation. In antero-posterior patterning mutants such as those for the gap gene Krüppel, defective polarized cell intercalation is compensated for by an increase in antero-posterior cell elongation, such that the initial rate of extension remains the same. Spatio-temporal patterns of cell behaviours indicate that an antero-posterior tensile force deforms the germ band, causing the cells to change shape passively. The rate of antero-posterior cell elongation is reduced in twist mutant embryos, which lack mesoderm. We propose that cell shape change contributing to germ-band extension is a passive response to mechanical forces caused by the invaginating mesoderm.

The dynamic reshaping of tissues during morphogenesis results from a combination of individual cell behaviours and collective cell rearrangements. However, a comprehensive framework to unambiguously measure and link cell behaviour to tissue morphogenesis is lacking. Here we introduce such a kinematic framework, bridging cell and tissue behaviours at an intermediate, mesoscopic, level of cell clusters or domains. By measuring domain deformation in terms of the relative motion of cell positions and the evolution of their shapes, we characterize the basic invariant quantities that measure fundamental classes of cell behaviour, namely tensorial rates of cell shape change and cell intercalation. In doing so we introduce an explicit definition of cell intercalation as a continuous process. We demonstrate how spatiotemporal mapping of strain rates in three models of tissue morphogenesis leads to new insight into morphogenetic mechanisms. Our quantitative approach has broad relevance for the precise characterisation and comparison of morphogenetic phenotypes.

A comparison of support schemes for market-based deployment of renewable energy in the UK and Germany shows that the feed-in tariff reduces costs to consumers and results in larger deployment. A survey among project developers suggests two explanations: (1) Site selection presents the biggest obstacle under the feed-in tariff. Uncertain financing of other schemes reduces efforts at initial project stages and planning permits become a major obstacle. (2) Project developers do not compete in price but for good sites under the feed-in tariff. Most importantly, turbine producers and construction services contribute to most of the costs, and face at least equal levels of competition under the feed-in tariff. r

We explore the relationship between low-carbon objectives and the strategic security of electricity in the context of the UK electricity system. We consider diversity of fuel source mix to represent one dimension of security-robustness against interruptions of any one source-and apply two different diversity indices to the range of electricity system scenarios produced by the UK government and independent researchers. Our results show that low-carbon objectives are uniformly associated with greater long-term diversity in UK electricity generation. With reference to data on wind generation we also consider the impact of source variability on a second dimension of security-the reliability of generation availability. We conclude that this does not undermine our fundamental conclusion that lowcarbon scenarios are associated with greater strategic security of supply in UK electricity. We discuss reasons for this result, explore sensitivities, and briefly discuss possible policy instruments associated with diversity and their limitations.

Investment planning models inform investment decisions and government policies. Current models do not capture the intermittent nature of renewable energy sources, restricting the applicability of the models for high penetrations of renewables. We provide a methodology to capture spatial variation in wind output in combination with transmission constraints. The representation of wind distributions with stochastic approaches or an extensive historic data set would exceed computational constraints for real world application. Hence we restrict the amount of input data, and use boot-strapping to illustrate the robustness of the results. For the UK power system we model wind deployment and the value of transmission capacity.