Normal state properties of high angle grain boundaries in (Y,Ca)Ba2Cu3O7-delta

By lithographically fabricating an optimised Wheatstone bridge geometry, we have been able to make accurate measurements of the resistance of grain boundaries in Y1-xCaxBa2Cu3O7-d between the superconducting transition temperature, Tc, and room temperature. Below Tc the normal state properties were assessed by applying sufficiently high currents. The behaviour of the grain boundary resistance versus temperature and of the conductance versus voltage are discussed in the framework charge transport through a tunnel barrier. The influence of misorientation angle, oxygen content, and calcium doping on the normal state properties is related to changes of the height and shape of the grain boundary potential barrier.Comment: 17 pages, 1 table, 5 figures, submitted to PR

Study protocol: can a school gardening intervention improve children's diets?

BACKGROUND: The current academic literature suggests there is a potential for using gardening as a tool to improve children's fruit and vegetable intake. This study is two parallel randomised controlled trials (RCT) devised to evaluate the school gardening programme of the Royal Horticultural Society (RHS) Campaign for School Gardening, to determine if it has an effect on children's fruit and vegetable intake. METHOD/DESIGN: Trial One will consist of 26 schools; these schools will be randomised into two groups, one to receive the intensive intervention as "Partner Schools" and the other to receive the less intensive intervention as "Associate Schools". Trial Two will consist of 32 schools; these schools will be randomised into either the less intensive intervention "Associate Schools" or a comparison group with delayed intervention. Baseline data collection will be collected using a 24-hour food diary (CADET) to collect data on dietary intake and a questionnaire exploring children's knowledge and attitudes towards fruit and vegetables. A process measures questionnaire will be used to assess each school's gardening activities. DISCUSSION: The results from these trials will provide information on the impact of the RHS Campaign for School Gardening on children's fruit and vegetable intake. The evaluation will provide valuable information for designing future research in primary school children's diets and school based interventions. TRIAL REGISTRATION: ISRCTN11396528

Validation of a cfd-based numerical wave tank of the wavestar wec

CFD-based numerical wave tank (CNWT) models, are a useful tool for the analysis of wave energy converters (WECs). During the development of a CNWT, model validation is important, to prove the accuracy of the numerical solution. This paper presents a validation study of a CNWT model for the 1:10 scale Wavestar point-absorber device. The previous studies reported by Ransley et al. (2017) and Windt et al. (2018b) are extended in this paper, by including cases in which the power-take off (PTO) system is engaged. In this study, the PTO is represented as a simple linear damping term in the CNWT WEC model, providing a first approximation to the full PTO dynamics, to be included in the CNWT in future work. The numerical results, for surface elevation and device position, are shown to compare well with the experimental measurements

Performance of a Direct-Driven Wave Energy Point Absorber with High Inertia Rotatory Power Take-off

An alternating rotatory generator using an eddy current break is developed as a physicalscale model of a direct-driven floating point absorber power take-off (PTO) for wave tank tests. It isshown that this design is a simple and cost-effective way to get an accurate linear damping PTO. Thedevice shows some beneficial characteristics, making it an interesting option for full scale devices:For similar weights the inertia can be significantly higher than for linear generators, allowing it tooperate with natural frequencies close to typical wave frequencies. The influence of the higher inertiaon the power absorption is tested using both a numerical simulation and physical wave tank tests.With the increased inertia the PTO is able to absorb more than double the energy of a comparabledirect-driven linear generator in some sea states. Moreover, the alternating rotatory generator allowsthe absorption characteristic to be tuned by changing the inertia and the generator damping

A Model Free Control Based on Machine Learning for Energy Converters in an Array

This paper introduces a machine learning based control strategy for energy converter arrays designed to work under realistic conditions where the optimal control parameter can not be obtained analytically. The control strategy neither relies on a mathematical model, nor does it need a priori information about the energy medium. Therefore several identical energy converters are arranged so that they are affected simultaneously by the energy medium. Each device uses a different control strategy, of which at least one has to be the machine learning approach presented in this paper. During operation all energy converters record the absorbed power and control output; the machine learning device gets the data from the converter with the highest power absorption and so learns the best performing control strategy for each situation. Consequently, the overall network has a better overall performance than each individual strategy. This concept is evaluated for wave energy converters (WECs) with numerical simulations and experiments with physical scale models in a wave tank. In the first of two numerical simulations, the learnable WEC works in an array with four WECs applying a constant damping factor. In the second simulation, two learnable WECs were learning with each other. It showed that in the first test the WEC was able to absorb as much as the best constant damping WEC, while in the second run it could absorb even slightly more. During the physical model test, the ANN showed its ability to select the better of two possible damping coefficients based on real world input data