Ground-state of graphene in the presence of random charged impurities

We calculate the carrier density dependent ground state properties of graphene in the presence of random charged impurities in the substrate taking into account disorder and interaction effects non-perturbatively on an equal footing in a self-consistent theoretical formalism. We provide detailed quantitative results on the dependence of the disorder-induced spatially inhomogeneous two-dimensional carrier density distribution on the external gate bias, the impurity density, and the impurity location. We find that the interplay between disorder and interaction is strong, particularly at lower impurity densities. We show that for the currently available typical graphene samples, inhomogeneity dominates graphene physics at low ($\lesssim 10^{12}$ cm$^{-2}$) carrier density with the density fluctuations becoming larger than the average density.Comment: Final version, accepted for publication in Phys. Rev. Let

Health and safety management in the offshore oil industry

This work-based project is an investigation of the interaction between multicultural crews and safety management systems and the influences of this interaction on health and safety in the offshore oil Industry. This study has been carried out in partial fulfilment of the requirements for the Doctorate of Professional Studies at the Institute of Work Based Learning, Middlesex University, London. The aim of this project is to minimise occupational casualties in the industry by exploring the social science paradigms of human action and cultural diversity, and it relies heavily on ethnographic methodologies. The qualitative data collection techniques chosen are structured observations, semistructured interviews, focus groups and a research diary. The key themes that emerged from the project highlighted the perception of high consequences/low probability risk among the working community. In this context, the cultural relativity of the hazard perception is an instrument used to maintain group solidarity. The group that emerged from this work-based research is culturally-biased according to a ‘way of life’ that characterises it, and predisposes it to adopt a particular view of society at work. The data collected and analysed in this ethnographic investigation establish the fact that cultural bias and shared values have influenced how safety is lived and, most importantly, seen and perceived by the workforce community. The concept of “cross-cultural safety consciousness” is proposed in this research, along with a conceptual model for a practical approach to safety based on its findings, with the aim being to reduce the number of incidents in the offshore oil industry. The project may have an international impact and relevance; professional organisations and maritime trade unions have displayed interest in the outcomes of this investigation

Quasi-Dirac neutrinos and solar neutrino data

We present an analysis of the solar neutrino data in the context of a quasi-Dirac neutrino model in which the lepton mixing matrix is given at tree level by the tribimaximal matrix. When radiative corrections are taken into account, new effects in neutrino oscillations, as $\nu_e \to \nu_s$, appear. This oscillation is constrained by the solar neutrino data. In our analysis, we have found an allowed region for our two free parameters $\epsilon$ and $m_1$. The radiative correction, $\epsilon$, can vary approximately from $5\times 10^{-9}$ to $10^{-6}$ and the calculated fourth mass eigenstate, $m_4$, 0.01 eV to 0.2 eV at 2$\sigma$ level. These results are very similar to the ones presented in the literature.Comment: 24 pages, 7 figures and 2 tables. Results and conclusion unchanged. Version published in EPJC. Figures improve

Surface mixing and biological activity in the four Eastern Boundary Upwelling Systems

Eastern Boundary Upwelling Systems (EBUS) are characterized by a high productivity of plankton associated with large commercial fisheries, thus playing key biological and socio-economical roles. The aim of this work is to make a comparative study of these four upwelling systems focussing on their surface stirring, using the Finite Size Lyapunov Exponents (FSLEs), and their biological activity, based on satellite data. First, the spatial distribution of horizontal mixing is analysed from time averages and from probability density functions of FSLEs. Then we studied the temporal variability of surface stirring focussing on the annual and seasonal cycle. There is a global negative correlation between surface horizontal mixing and chlorophyll standing stocks over the four areas. To try to better understand this inverse relationship, we consider the vertical dimension by looking at the Ekman-transport and vertical velocities. We suggest the possibility of a changing response of the phytoplankton to sub/mesoscale turbulence, from a negative effect in the very productive coastal areas to a positive one in the open ocean.Comment: 12 pages. NPG Special Issue on "Nonlinear processes in oceanic and atmospheric flows". Open Access paper, available also at the publisher site: http://www.nonlin-processes-geophys.net/16/557/2009