Surface-effect corrections for oscillation frequencies of evolved stars

Accurate modelling of solar-like oscillators requires that modelled mode frequencies are corrected for the systematic shift caused by improper modelling of the near-surface layers, known as the surface effect. ... We investigate how much additional uncertainty is introduced to stellar model parameters by our uncertainty about the functional form of the surface effect. At the same time, we test whether any of the parametrizations is significantly better or worse at modelling observed subgiants and low-luminosity red giants. We model six stars observed by Kepler that show clear mixed modes. We fix the input physics of the stellar models and vary the choice of surface correction ... Models using a solar-calibrated power law correction consistently fit the observations more poorly than the other four corrections. Models with the remaining four corrections generally fit ... about equally well, with the combined surface correction by Ball & Gizon perhaps being marginally superior. The fits broadly agree on the model parameters within about the $2\sigma$ uncertainties, with discrepancies between the modified Lorentzian and free power law corrections occasionally exceeding the $3\sigma$ level. Relative to the best-fitting values, the total uncertainties on the masses, radii and ages of the stars are all less than 2, 1 and 6 per cent, respectively. A solar-calibrated power law ... appears unsuitable for use with more evolved solar-like oscillators. Among the remaining surface corrections, the uncertainty in the model parameters introduced by the surface effects is about twice as large as the uncertainty in the individual fits for these six stars. Though the fits are thus somewhat less certain because of our uncertainty of how to manage the surface effect, these results also demonstrate that it is feasible to model the individual mode frequencies of subgiants and low-luminosity red giants. ...Comment: Accepted for publication in Astronomy & Astrophysics. 13 pages, 6 figures, 5 tables. Abstract slightly abridged to meet arXiv's 1920 character limi

Tungsten thermal neutron dosimeter

Tungsten-185 activity, which is produced by neutron activation of tungsten-184, determines thermal neutron flux. Radiochemical separation methods and counting techniques for irradiated tungsten provide accurate determination of the radiation exposure

Health, the outdoors and safety

While the public health benefits accruing from exposure to the outdoors, and especially the natural environment, have gained greater recognition, this has exposed rifts in thinking between those focusing on the pathology of injury and those pursuing a wider health agenda which recognizes the restorative potential of encounters with nature. In retrospect, the classification of injury as a public health issue in the mid-20th century triggered complex societal responses which generated unintended consequences affecting healthful activities. Responses generally aim to reduce or minimize the risk of injury and come in different forms, including formal and informal codes of practice, standards, management systems and regulation. Well-intentioned as these interventions may have been, the new emphasis on harm shifted attention away from what causes health and resulted in increasing control over activities, including those taking place outdoors. This article, which draws on long-term qualitative policy research, describes examples of these on-going tensions in the context of the public enjoyment of the outdoors. In conclusion, the situation presented is considered from a number of theoretical perspectives, and proposals are made for resolving the issues. These include improved communication between sectors and, on the technical side, the introduction of a compensatory decision process which enables policy makers to take account of both the health benefits and risks of exposure to the natural environment

End-wall boundary layer measurements in a two-stage fan

Detailed flow measurements made in the casing boundary layer of a two-stage transonic fan are summarized. These measurements were taken at a station upstream of the fan, between all blade rows, and downstream of the last row. Conventional boundary layer parameters were calculated from the measured data. A classical two dimensional casing boundary layer was measured at the fan inlet and extended inward to approximately 15 percent of span. A highly three dimensional boundary layer was measured at the exit of each blade row and extended inward to approximately 10 percent of span. The steep radial gradient of axial velocity noted at the exit of the rotors was reduced substantially as the flow passed through the stators. This reduced gradient is attributed to flow mixing. The amount of flow mixing was reflected in the radial redistribution of total temperature as the flow passed through the stators. The blockage factors calculated from the measured data show an increase in blockage across the rotors and a decrease across the stators. For this fan the calculated blockages for the second stage were essentially the same as those for the first stage

Effect of Reynolds number on overall performance of a 6-inch radial bladed centrifugal compressor

Overall performance of centrifugal compressor over range of inlet pressures and corresponding Reynolds numbe