731 research outputs found

    The effects of flow on Atlantic salmon (Salmo salar) redd distribution in a UK chalk stream between 1980 and 2015

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    Atlantic salmon are an ecologically and economically important migratory fish in the UK, whose stocks have been declining over the past 30 years. Future climate and water use changes have the potential to alter the reproductive behaviour and distribution of salmon within a river, by restricting times and ability to access suitable spawning areas. As the survival of emergent salmon juveniles is density dependent, understanding how climate-driven changes in flow affect the location of salmon redds is important for future conservation efforts. This study examined how flow conditions affect the distribution of redds within a UK chalk stream, the river Frome in Dorset. Sixteen years of redd distribution and flow data between 1980 and 2015 were analysed using linear mixed-effects modelling. Generally, highest redd densities occurred within middle reaches of the main river. Mean flow during the river Frome critical migration period (October–December) did not affect the density of redds directly but affected the relationship between redd density and distance from tidal limit: redd densities were spread more uniformly throughout the river under high flow conditions, whereas redds were more aggregated in the middle river reaches under low flow conditions. Together, these findings suggest that access to upstream spawning grounds was limited under low flow conditions, which could have negative repercussions on juvenile survival. This study has revealed the distribution of redds along the river Frome for the first time and provided a basis for further study into the effects of redd distribution on subsequent juvenile life stages

    Velocity Profiles in Slowly Sheared Bubble Rafts

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    Measurements of average velocity profiles in a bubble raft subjected to slow, steady-shear demonstrate the coexistence between a flowing state and a jammed state similar to that observed for three-dimensional foams and emulsions [Coussot {\it et al,}, Phys. Rev. Lett. {\bf 88}, 218301 (2002)]. For sufficiently slow shear, the flow is generated by nonlinear topological rearrangements. We report on the connection between this short-time motion of the bubbles and the long-time averages. We find that velocity profiles for individual rearrangement events fluctuate, but a smooth, average velocity is reached after averaging over only a relatively few events.Comment: typos corrected, figures revised for clarit

    Shear-Induced Stress Relaxation in a Two-Dimensional Wet Foam

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    We report on experimental measurements of the flow behavior of a wet, two-dimensional foam under conditions of slow, steady shear. The initial response of the foam is elastic. Above the yield strain, the foam begins to flow. The flow consists of irregular intervals of elastic stretch followed by sudden reductions of the stress, i.e. stress drops. We report on the distribution of the stress drops as a function of the applied shear rate. We also comment on our results in the context of various two-dimensional models of foams

    Vindscreening ved Multimediehuset

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    Analyse af vindklima ved Navitas Park

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    Estimating the number needed to treat from continuous outcomes in randomised controlled trials: methodological challenges and worked example using data from the UK Back Pain Exercise and Manipulation (BEAM) trial

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    Background Reporting numbers needed to treat (NNT) improves interpretability of trial results. It is unusual that continuous outcomes are converted to numbers of individual responders to treatment (i.e., those who reach a particular threshold of change); and deteriorations prevented are only rarely considered. We consider how numbers needed to treat can be derived from continuous outcomes; illustrated with a worked example showing the methods and challenges. Methods We used data from the UK BEAM trial (n = 1, 334) of physical treatments for back pain; originally reported as showing, at best, small to moderate benefits. Participants were randomised to receive 'best care' in general practice, the comparator treatment, or one of three manual and/or exercise treatments: 'best care' plus manipulation, exercise, or manipulation followed by exercise. We used established consensus thresholds for improvement in Roland-Morris disability questionnaire scores at three and twelve months to derive NNTs for improvements and for benefits (improvements gained+deteriorations prevented). Results At three months, NNT estimates ranged from 5.1 (95% CI 3.4 to 10.7) to 9.0 (5.0 to 45.5) for exercise, 5.0 (3.4 to 9.8) to 5.4 (3.8 to 9.9) for manipulation, and 3.3 (2.5 to 4.9) to 4.8 (3.5 to 7.8) for manipulation followed by exercise. Corresponding between-group mean differences in the Roland-Morris disability questionnaire were 1.6 (0.8 to 2.3), 1.4 (0.6 to 2.1), and 1.9 (1.2 to 2.6) points. Conclusion In contrast to small mean differences originally reported, NNTs were small and could be attractive to clinicians, patients, and purchasers. NNTs can aid the interpretation of results of trials using continuous outcomes. Where possible, these should be reported alongside mean differences. Challenges remain in calculating NNTs for some continuous outcomes

    New strategies for sustainable fisheries management: A case study of Atlantic salmon

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    This briefing paper considers the alarming declines in fish stocks in recent years, and how holistic, integrated approaches can help manage fish stocks within biologically sustainable limits. Using Atlantic salmon as a case study, the authors highlight the challenges facing fisheries management and conservation, and the implications for policy and management
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