Coating-free mirrors for high precision interferometric experiments

Thermal noise in mirror optical coatings may not only limit the sensitivity of future gravitational-wave detectors in their most sensitive frequency band but is also a major impediment for experiments that aim to reach the standard quantum limit or cool mechanical systems to their quantum ground state. We present the design and experimental characterization of a highly reflecting mirror without any optical coating. This coating-free mirror is based on total internal reflection and Brewster-angle coupling. In order to characterize its performance, the coating-free mirror was incorporated into a triangular ring cavity together with a high quality conventional mirror. The finesse of this cavity was measured using an amplitude transfer function to be about F 4000. This finesse corresponds to a reflectivity of the coating-free mirror of about R 99.89%. In addition, the dependence of the reflectivity on rotation was mapped out

Exergoeconomic optimisation of steam networks connecting solar-thermal dish arrays

We optimise steam network trees that connect Big Dish paraboloidal collectors to a central power block. Exergy costs, pipe material costs, and installation costs are estimated using an exergoeconomic model and used to optimise pipe links in network trees. The optimal network tree is then found for a 10MWe collector field using a genetic algorithm. An optimised tree is found for a 20MWe network. The optimised 20MWe network has additional east-west branches not seen in the optimal 10MWe network, that reduce steam transport costs from network extremities. Exergy costs from heat loss and pressure drop account for approximately 60% of total network cost in both cases. Total network costs are, respectively, 8.9% and 9.5% of potential plant revenue for the 10MWe and the 20MWe networks

A gradient-descent method for optimisation of solar collector arrays

We present a numerical function for approximating shading losses around two-axis tracking solar collectors. It is used in a gradient descent algorithm to optimise relative collector position. System yield is increased by 1%-2%

Shading and land use in regularly-spaced sun-tracking collectors

We present a new methodology for defining regularly-spaced collector layouts for the purpose of simulating annual system cost in two-axis sun-tracking collector arrays, such as those comprising solar-thermal dish collectors or two-axis tracking PV. We thoroughly consider all layout combinations of aspect ratio, offset, ground-cover-ratio, and rotation. Collector position is optimised to reduce annual shading for a range of collector densities for the site of Barstow, California. Optimal layouts are rectangular in shape for ground cover ratios less than 0.23. Diamond layouts collect up to 1.4% more absolute annual solar energy for higher ground cover ratios. From these results, a correlation for determining optimal array layouts subject to the chosen position-dependent cost function is presented. This approach can be used for design of large arrays of two-axis sun-tracking collectors where collector position and costs proportional to land use affect levelised plant cost

Derivation of Error Sources from Experimentally Determined Heliostat Surface Shapes

Data gathered using photogrammetry that represents the surface and structure of a heliostat mirror panel is investigated in detail. A curve-fitting approach that allows the retrieval of four distinct mirror error components, while prioritizing the best fit possible to paraboloidal terms in the curve fitting equation, is presented. The angular errors associated with each of the four surfaces are calculated, and the relative magnitude for each of them is given. It is found that in this case, the mirror had a significant structural twist, and an estimate of the improvement to the mirror surface quality in the case of no twist was mad

Heat flux and temperature measurement technologies for concentrating solar power

Heat flux and temperature are two fundamental quantities to be determined in the design of solar receivers for concentrating solar power (CSP) plants. Heat flux measurement allows the determination of the efficiency of solar receivers; a range of radiome

Does intensive care always have to be expensive care?

Demands on health care are increasing while resources are being decreased. Difficult decisions that often involve trade-offs have to be addressed. Intensive care resources can be better managed by application of sound medical principles, such as evidence-based medicine and distributive justice. Intensive care admission criteria, appropriateness of therapeutic interventions, treatment in general, and unnecessary prolongation of life are areas that need to be better defined. If unnecessary use of expensive care is continued, the patients and populations that physicians need to treat will be less than ideally managed. There are no didactic answers to these contentious issues, and this article is aimed to stimulate much needed discussion

A new topology for the control of complex interferometers

We discuss a new control topology which will generate control signals for the output optics of complex interferometers operating on a pure dark fringe. Our system, which involves the injection of a modulated control field through the output port of the interferometer, is also compatible with the use of squeezed light. We discuss this topology in the context of the control of an interferometer featuring a variable reflectivity signal recycling mirror and present results from a coupled cavity geometry to demonstrate some of the features