On the Phenomenology of Hydrodynamic Shear Turbulence

The question of a purely hydrodynamic origin of turbulence in accretion disks is reexamined, on the basis of a large body of experimental and numerical evidence on various subcritical (i.e., linearly stable) hydrodynamic flows. One of the main points of this paper is that the length scale and velocity fluctuation amplitude which are characteristic of turbulent transport in these flows scale like $Re_m^{-1/2}$, where $Re_m$ is the minimal Reynolds number for the onset of fully developed turbulence. From this scaling, a simple explanation of the dependence of $Re_m$ with relative gap width in subcritical Couette-Taylor flows is developed. It is also argued that flows in the shearing sheet limit should be turbulent, and that the lack of turbulence in all such simulations performed to date is most likely due to a lack of resolution, as a consequence of the effect of the Coriolis force on the large scale fluctuations of turbulent flows. These results imply that accretion flows should be turbulent through hydrodynamic processes. If this is the case, the Shakura-Sunyaev $\alpha$ parameter is constrained to lie in the range $10^{-3}-10^{-1}$ in accretion disks, depending on unknown features of the mechanism which sustains turbulence. Whether the hydrodynamic source of turbulence is more efficient than the MHD one where present is an open question.Comment: 31 pages, 3 figures. Accepted for publication in Ap

Rotated stripe order and its competition with superconductivity in La1.88_{1.88}Sr0.12_{0.12}CuO4_4

We report the observation of a bulk charge modulation in La$_{1.88}$Sr$_{0.12}$CuO$_4$ (LSCO) with a characteristic in-plane wave-vector of (0.236, $\pm \delta$), with $\delta$=0.011 r.l.u. The transverse shift of the ordering wave-vector indicates the presence of rotated charge-stripe ordering, demonstrating that the charge ordering is not pinned to the Cu-O bond direction. On cooling through the superconducting transition, we find an abrupt change in the growth of the charge correlations and a suppression of the charge order parameter indicating competition between the two orderings. Orthorhombic LSCO thus helps bridge the apparent disparities between the behavior previously observed in the tetragonal "214" cuprates and the orthorhombic yttrium and bismuth-based cuprates and thus lends strong support to the idea that there is a common motif to charge order in all cuprate families.Comment: 6 pages, 4 figue

Bird mortality related to collisions with ski–lift cables: do we estimate just the tip of the iceberg?

Collisions with ski–lift cables are an important cause of death for grouse species living close to alpine ski resorts. As several biases may reduce the detection probability of bird carcasses, the mortality rates related to these collisions are generally underestimated. The possibility that injured birds may continue flying for some distance after striking cables represents a major source of error, known as crippling bias. Estimating the crippling losses resulting from birds dying far from the ski–lift corridors is difficult and it is usually assessed by systematic searches of carcasses on both sides of the ski–lifts. Using molecular tracking, we were able to demonstrate that a rock ptarmigan hen flew up to 600 m after striking a ski–lift cable, a distance preventing its detection by traditional carcasses surveys. Given the difficulty in conducting systematic searches over large areas surrounding the ski–lifts, only an experiment using radio–tagged birds would allow us to estimate the real mortality rate associated with cable collision

Assessment of PM10 and heavy metal concentration in a ceramic cluster (NE Spain) and the influence on nearby soils

Environmental pollution control is one of the most important goals in pollution risk assessment today. The aim of this study is to conduct a retrospective view of the evolution of matter particulate (PM10) and the heavy metals (Cd, Ni and Pb) at different localities (Alcora, Castellón and Onda) in the Spanish cluster ceramic in a period between January 2007 and December 2011. The study area is in the province of Castellón. This province is a strategic area in the framework of European Union Pollution control. Approximately 80% of European ceramic tiles and ceramic frits manufacturers are concentrated in two areas, forming the so-called "ceramic clusters"; one is in Modena (Italy) and the other in Castellón (Spain). In these kind of areas, there are a lot of pollutants from this industry that represent an important contribution to soil contamination so it is necessary to control their air quality. In these areas atmospheric particles are deposited in the ground through both dry and wet deposition. Soil is a major sink for heavy metals released into the environment. For this purpose the levels of PM10 in ambient air and the corresponding annual and seasonal trend were calculated. The results of the study show that the PM10 and heavy metal concentrations are below the limit values recommended by European Union Legislation for the protection of human health and ecosystems in the study period. There is an important reduction of them from 2009 in all control stations due to economic crisis and subsequent decrease of industrial activity. The atmospheric seasonal tendency of pollutant concentrations is marked by the rate of industrial activity and additionally by the temperature. Complementarily, a comparative study of heavy metal levels in soils was performed in this area. Soils with low pollution by Ni and Pb were detected, while different pollution by Cd was found depending on the sampling site. Although there is an evident reduction of PM10 and heavy metal levels, the results show that these pollut

Quantitative X-ray phase-contrast microtomography from a compact laser-driven betatron source

X-ray phase-contrast imaging has recently led to a revolution in resolving power and tissue contrast in biomedical imaging, microscopy and materials science. The necessary high spatial coherence is currently provided by either large-scale synchrotron facilities with limited beamtime access or by microfocus X-ray tubes with rather limited flux. X-rays radiated by relativistic electrons driven by well-controlled high-power lasers offer a promising route to a proliferation of this powerful imaging technology. A laser-driven plasma wave accelerates and wiggles electrons, giving rise to a brilliant keV X-ray emission. This so-called betatron radiation is emitted in a collimated beam with excellent spatial coherence and remarkable spectral stability. Here we present a phase-contrast microtomogram of a biological sample using betatron X-rays. Comprehensive source characterization enables the reconstruction of absolute electron densities. Our results suggest that laser-based X-ray technology offers the potential for filling the large performance gap between synchrotron- and current X-ray tube-based sources

Motivating doctors into leadership and management: a cross-sectional survey

Purpose: Calls for doctors to enter management are louder as the benefits of medical leadership become clearer. But supply is not meeting demand. This study asks doctors: what might encourage you to go into leadership, and what do you see as the disincentives? The same was asked about leadership training. First, the paper attempts to understand doctors’ motivation to lead, specifically, to explore the job characteristics that might act as incentives and disincentives. Second, the study points to organisational obstacles that further shrink the medical leadership pipeline. Method: Doctors were surveyed through the Organization of Danish Medical Societies. Our key variables included: 1) willingness to take on a management or leadership position; 2) the incentives to go into leadership or management; 3) disincentives to do so; and 4) incentives for participating in leadership training. Our sample includes 3534 doctors (17% response rate). Findings: Nearly 70% of doctors said that they would consider leadership or management positions. Overwhelmingly, the main incentive reported was to have a positive impact. Doctors are put off by fears of extra administration, longer hours, burnout, lack of resources, and by organisational cultures resistant to change. But they are fully aware of their need for leadership training. Practical implications: Health systems should adapt to reflect the motivations of their potential medical leaders, especially the best talent, who may not be the first to apply for management positions. It is also essential they offer leadership training. These findings, that aid succession planning, are especially important as more is known about the influence of medical leaders on organisational outcomes, and at a time of high reported stress, burnout, and staff recruitment and retention challenges

Cross-sectional survey of users of internet depression communities

Background: Internet-based depression communities provide a forum for individuals to communicate and share information and ideas. There has been little research into the health status and other characteristics of users of these communities. Methods: Online cross-sectional survey of Internet depression communities to identify depressive morbidity among users of Internet depression communities in six European countries; to investigate whether users were in contact with health services and receiving treatment; and to identify user perceived effects of the communities. Results: Major depression was highly prevalent among respondents (varying by country from 40% to 64%). Forty-nine percent of users meeting criteria for major depression were not receiving treatment, and 35% had no consultation with health services in the previous year. Thirty-six percent of repeat community users who had consulted a health professional in the previous year felt that the Internet community had been an important factor in deciding to seek professional help. Conclusions: There are high levels of untreated and undiagnosed depression in users of Internet depression communities. This group represents a target for intervention. Internet communities can provide information and support for stigmatizing conditions that inhibit more traditional modes of information seeking