Elastic interactions of active cells with soft materials

Anchorage-dependent cells collect information on the mechanical properties of the environment through their contractile machineries and use this information to position and orient themselves. Since the probing process is anisotropic, cellular force patterns during active mechanosensing can be modelled as anisotropic force contraction dipoles. Their build-up depends on the mechanical properties of the environment, including elastic rigidity and prestrain. In a finite sized sample, it also depends on sample geometry and boundary conditions through image strain fields. We discuss the interactions of active cells with an elastic environment and compare it to the case of physical force dipoles. Despite marked differences, both cases can be described in the same theoretical framework. We exactly solve the elastic equations for anisotropic force contraction dipoles in different geometries (full space, halfspace and sphere) and with different boundary conditions. These results are then used to predict optimal position and orientation of mechanosensing cells in soft material.Comment: Revtex, 38 pages, 8 Postscript files included; revised version, accepted for publication in Phys. Rev.

Tomato: a crop species amenable to improvement by cellular and molecular methods

Tomato is a crop plant with a relatively small DNA content per haploid genome and a well developed genetics. Plant regeneration from explants and protoplasts is feasable which led to the development of efficient transformation procedures. In view of the current data, the isolation of useful mutants at the cellular level probably will be of limited value in the genetic improvement of tomato. Protoplast fusion may lead to novel combinations of organelle and nuclear DNA (cybrids), whereas this technique also provides a means of introducing genetic information from alien species into tomato. Important developments have come from molecular approaches. Following the construction of an RFLP map, these RFLP markers can be used in tomato to tag quantitative traits bred in from related species. Both RFLP's and transposons are in the process of being used to clone desired genes for which no gene products are known. Cloned genes can be introduced and potentially improve specific properties of tomato especially those controlled by single genes. Recent results suggest that, in principle, phenotypic mutants can be created for cloned and characterized genes and will prove their value in further improving the cultivated tomato.

Understanding construction reform discourses

This is an Accepted Manuscript of an article published by Taylor & Francis in Construction Management and Economics on 8th May 2014, available online: http://wwww.tandfonline.com/10.1080/01446193.2014.909049Attempts to drive change and reform of the UK construction industry have been an ongoing concern for numerous stakeholders, both in government and across industry, for years. The issue is a seemingly perennially topical one which shows little sign of abating. Scholarly analyses of the reform agenda have tended to adopt a Critical Theory perspective. Such an approach, however, lacks a certain nuance and perhaps only reveals one layer of social reality. What is arguably lacking is a more fundamental exposition concerning the historical, social and cultural explanatory forces at play. While it is illuminating to expose vested interests, ideology and power, what has led to the development of various views? How have they come to achieve such high accord in discussions? Drawing on the works of Max Weber, Georg Simmel and Barbara Adam, this paper seeks to develop a broader theoretical lens. It considers the wider socio-cultural structures and forces that influence behaviour, shape and constrain these views. This approach will contribute to a much needed broader philosophical and theoretical debate within the construction management community (and beyond) on the need to better engage with, and understand, the sources influencing the issue of policy formulation and diffusion. © 2014 Taylor & Francis

Consistent patterns of common species across tropical tree communities

Trees structure the Earth’s most biodiverse ecosystem, tropical forests. The vast number of tree species presents a formidable challenge to understanding these forests, including their response to environmental change, as very little is known about most tropical tree species. A focus on the common species may circumvent this challenge. Here we investigate abundance patterns of common tree species using inventory data on 1,003,805 trees with trunk diameters of at least 10 cm across 1,568 locations1,2,3,4,5,6 in closed-canopy, structurally intact old-growth tropical forests in Africa, Amazonia and Southeast Asia. We estimate that 2.2%, 2.2% and 2.3% of species comprise 50% of the tropical trees in these regions, respectively. Extrapolating across all closed-canopy tropical forests, we estimate that just 1,053 species comprise half of Earth’s 800 billion tropical trees with trunk diameters of at least 10 cm. Despite differing biogeographic, climatic and anthropogenic histories7, we find notably consistent patterns of common species and species abundance distributions across the continents. This suggests that fundamental mechanisms of tree community assembly may apply to all tropical forests. Resampling analyses show that the most common species are likely to belong to a manageable list of known species, enabling targeted efforts to understand their ecology. Although they do not detract from the importance of rare species, our results open new opportunities to understand the world’s most diverse forests, including modelling their response to environmental change, by focusing on the common species that constitute the majority of their trees

Response of the ocean natural carbon storage to projected twenty-first-century climate change

The separate impacts of wind stress, buoyancy fluxes, and CO2 solubility on the oceanic storage of natural carbon are assessed in an ensemble of twentieth- to twenty-first-century simulations, using a coupled atmosphere–ocean–carbon cycle model. Time-varying perturbations for surface wind stress, temperature, and salinity are calculated from the difference between climate change and preindustrial control simulations, and are imposed on the ocean in separate simulations. The response of the natural carbon storage to each perturbation is assessed with novel prognostic biogeochemical tracers, which can explicitly decompose dissolved inorganic carbon into biological, preformed, equilibrium, and disequilibrium components. Strong responses of these components to changes in buoyancy and winds are seen at high latitudes, reflecting the critical role of intermediate and deep waters. Overall, circulation-driven changes in carbon storage are mainly due to changes in buoyancy fluxes, with wind-driven changes playing an opposite but smaller role. Results suggest that climate-driven perturbations to the ocean natural carbon cycle will contribute 20 Pg C to the reduction of the ocean accumulated total carbon uptake over the period 1860–2100. This reflects a strong compensation between a buildup of remineralized organic matter associated with reduced deep-water formation (+96 Pg C) and a decrease of preformed carbon (?116 Pg C). The latter is due to a warming-induced decrease in CO2 solubility (?52 Pg C) and a circulation-induced decrease in disequilibrium carbon storage (?64 Pg C). Climate change gives rise to a large spatial redistribution of ocean carbon, with increasing concentrations at high latitudes and stronger vertical gradients at low latitudes

Towards numeracy for the third millennium: A study of the future of mathematics and mathematics education

The research reported here has sought to identify target skills and abilities that will compose a future numeracy, so that new expertise can be incorporated and the exposed "deficiencies" remedied within a dynamic rather than static concept of competency. A nation-wide selection of panellists contributed to a three-round Delphi process, with the final data comprising both structured responses and qualitative comment. The scope of the items covered calculating activities, writing activities, reading activities, physical skills, supporting (mental) skills, applications, and problem solving. Responses to the structured items have provided priorities for numeracy for the turn of the century, in terms of both expected and desired characteristics. In general, expectations for numeracy fall short of the levels deemed desirable by panel consensus. The qualitative comments have been incorporated into three scenarios reflecting altermative visions for the future. A comparison of the scenarios uncovers wide differences between informed thinkers with respect to future visions of the ends, means, and mechanics of learning. These differences among individuals who are otherwise consistent in their views of future needs must be addressed if the identified priorities are not to be lost in a quagmire of conflicting interests, opinions, priorities, and values