Press Release: Freedom Summer 1992

Press release for Freedom Summer 1992, a 20-city emergency voter registration effort. Date: June 22, 1992 Box 23 Folder 1

Study of two coupled three-wave interactions with a quadratic non-linearly in the presence of dissipation and frequency mismatch

The non-linear dynamic behaviour of two three-wave systems in plasma with two waves in common has been studied, including the possibility of negative energy waves and also the effect of linear damping or growth and frequency mismatch. Depending on the various initial conditions solutions of different types have been discussed. It has also been shown that one of the triplets can be stabilized by the other one against explosive instability depending on the relative strength of the coupling factor

Sea Clam Wave Energy Converter

After five years of research, the U.K. wave energy programme is nearing a point of decision on whether to progress towards full-scale testing or to continue on a research basis with reduced funding . The decision will be almost certainly based on the potential economics of wave energy and as a result, several device research teams are firming up on their designs prior to a cost assessment by consultants towards the end of this year. The chosen device or devices will probably have to produce electricity for the national grid at an estimated cost of less than 5 pence per unit at today's prices based on the costings of a 2 GW station located off the Outer Hebrides. Sea Energy Associates Limited and the Coventry (Lanchester) Polytechnic have been involved in the national wave energy programme since 1975, first, on the 1/lOth scale duck programme, (1, 2) and then more recently, on the second generation device known as the Clam (3). The Clam arose out of the need to redl'ce the high costs attributed to the first generation of wave energy devices and represented a new approach to the problem by an experienced team. By defining a sjmple concept which utilised components already identified as attractive, whilst at the same time avoiding known problem areas, the Clam quickly evolved into its 1979 design (3). This design has been tesled at 1/SOth scale in both natural and indoor waves with very satisfying results. Optimisation of the 1979 design has led to further design improvements which reduce the capital cost and increase the overall productivity. The final 1981 design should meet the cost criteria laid down and still retain some potential for further development. This paper discusses the merits of the Clam device and reviews the progress to date. of a floating spine breathe in response to wave forces. This causes air to be forced through self-rectifying turbines into and out of the hollow spine, allowing interchange of air between Clam bags. The randomness of sea wave patterns allows phased operation of the Clam elements, enabling the spine to act as a stable reference body. Typically a 1 OMW generating unit would feature ten Clam elements on a 27 5 m long spine, moored at an angle to tne waves, as illustrated on the cover

Costing Annexe To Consultants Preliminary Report

The procedure for costing the Reference Designs of the Wave Power Devices is described in Chapter 3 of the Consultant's Preliminary Report. The detailed breakdown of the prices determined for each Device, together with tabulated comparisons of the data received from contractors, is given as an Appendix to this Cost Annexe. The following tabulated summaries cover the overall capital cost of the construction of a 200 MW installed capacity power station for each Device. They should not be taken outside the context of the Consultants Preliminary Report, in which the reservations to be placed both on the preliminary Reference Designs and on the preliminary costing exercise are clearly stated. During this study, time did not permit the exploration of the many avenues which are available for potential cost reduction both by redesign and the study of alternative construction procedures. In particular there has been no opportunity for discussion of the costing exercise with the Device Teams. However, a study of the cost breakdowns indicates areas in each Device where cost savings should be achieved by appropriate design changes or more detailed analysis

Influence of wall thickness and diameter on arterial shear wave elastography: a phantom and finite element study

Quantitative, non-invasive and local measurements of arterial mechanical properties could be highly beneficial for early diagnosis of cardiovascular disease and follow up of treatment. Arterial shear wave elastography (SWE) and wave velocity dispersion analysis have previously been applied to measure arterial stiffness. Arterial wall thickness (h) and inner diameter (D) vary with age and pathology and may influence the shear wave propagation. Nevertheless, the effect of arterial geometry in SWE has not yet been systematically investigated. In this study the influence of geometry on the estimated mechanical properties of plates (h = 0.5–3 mm) and hollow cylinders (h = 1, 2 and 3 mm, D = 6 mm) was assessed by experiments in phantoms and by finite element method simulations. In addition, simulations in hollow cylinders with wall thickness difficult to achieve in phantoms were performed (h = 0.5–1.3 mm, D = 5–8 mm). The phase velocity curves obtained from experiments and simulations were compared in the frequency range 200–1000 Hz and showed good agreement (R2 = 0.80 ± 0.07 for plates and R2 = 0.82 ± 0.04 for hollow cylinders). Wall thickness had a larger effect than diameter on the dispersion curves, which did not have major effects above 400 Hz. An underestimation of 0.1–0.2 mm in wall thickness introduces an error 4–9 kPa in hollow cylinders with shear modulus of 21–26 kPa. Therefore, wall thickness should correctly be measured in arterial SWE applications for accurate mechanical properties estimation

Tails of plane wave spacetimes: Wave-wave scattering in general relativity

One of the most important characteristics of light in flat spacetime is that it satisfies Huygens' principle: Initial data for the vacuum Maxwell equations evolves sharply along null (and not timelike) geodesics. In flat spacetime, there are no tails which linger behind expanding wavefronts. Tails generically do exist, however, if the background spacetime is curved. The only non-flat vacuum geometries where electromagnetic fields satisfy Huygens' principle are known to be those associated with gravitational plane waves. This paper investigates whether perturbations to the plane wave geometry itself also propagate without tails. First-order perturbations to all locally-constructed curvature scalars are indeed found to satisfy Huygens' principles. Despite this, gravitational tails do exist. Locally, they can only perturb one plane wave spacetime into another plane wave spacetime. A weak localized beam of gravitational radiation passing through an arbitrarily-strong plane wave therefore leaves behind only a slight perturbation to the waveform of the background plane wave. The planar symmetry of that wave cannot be disturbed by any linear tail. These results are obtained by first deriving the retarded Green function for Lorenz-gauge metric perturbations and then analyzing its consequences for generic initial-value problems.Comment: 13 pages, 1 figure, minor typos correcte

The Availability Model: Consultant's Working Paper Number 32

This note describes some results obtained from the Consultant's Availability Model. They are based on preliminary data provided by Y-ard on the reliability of devices, and by Kennedy & Donkin on the transmission scheme. It is estimated that about 20% of the total energy output of a system might be lost due to repairs of its component. (This does not include lossed due to routine maintenance activities) . Assuming a value of 5p/kwh, this is equivalent to a cost of about £40m per annum for a 2gw station. station. There are several possible ways of reducing such losses, however , the most important being: - The reduction of failure rates by improvements in design, added redundancy in critical areas, or additional preventive maintenance. The use of larger numbers of repair crews, boats, etc .. - The reduction of live repair times in order to take advantage of the short weather windows which occur during the winter months, and/or the improvement of access to devices so that repair work can be carried out in more severe sea conditions. The trade-offs which exist between investing money in these areas and the resultant savings in energy losses are discussed, with the conclusion that the optimal solution for any scheme is likely to be one that reduces such losses to a minimum, by capital investment or high O+M expenditure. The appendices give an outline of the Availability Model and a revision of the sea-state information given in Working Paper 24, based on a more extensive analysis of the data