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The ternary II-VT alloy Hg1-xCdxTe has become the material of choice for many infrared detector applications. Current state of the art Hg1-xCdxTe infrared focal plane arrays (IRFPAs) are constructed as hybrid structures consisting of an epitaxial sensing layer of Hg1-xCdxTe on either a CdTe or Cd1-xZnxTe substrate, hybridized to a silicon readout circuit chip. For backside illuminated structures, like the typical infrared Hg1-xCdxTe detector array, multilayer antireflective coatings (AR) are required on the backside of the detector chip. The next generation of higher performance IRFPAs will be based on high densities of smaller detector pixels fabricated on large area monolithic heteroepitaxial substrate materials. Since the ultimate performance of photovoltaic diodes of this type is determined by the signal to noise ratio of the device, reducing the size of the pixels while lowering the undesirable noise currents in the devices also reduces the amount of signal generated by the diode.
The methods of nature conservation applied within the Inner Hebrides are those which are now standard throughout Britain and are governed by legislation. The procedures for habitat or site protection and species protection are illustrated in the descriptions of the reserves, the Sites of Special Scientific Interest and the protected species within the archipelago. The reserves and sites cover interests in the geology, geomorphology, zoology, botany and ecology of the islands and the surrounding seabed. National Scenic Areas are also mentioned. Relationships between nature conservation and the uses of land and sea are discussed. With the exceptions of the commercial exploitation of the island pastures in sheep husbandry, with much uncontrolled burning, and the exploitation of fin fish and shell fish and consequent widespread depletion of stocks, the Inner Hebrides are comparatively undisturbed by modern industrial development.
This, the concluding paper of the Symposium, reviews the main issues in the Outer Hebrides concerning the interaction between the constituent parts of the environment and man's use of them, seeking to identify the existing impacts on the natural environment and speculating upon the character of possible future impacts. It aims to demonstrate how the findings of the environmental sciences, as exemplified by the information in the symposium papers, are relevant to the understanding and resolution of these issues and to identify important gaps in knowledge.
The relationship between land use planning and development control is discussed, particularly as it is reflected in the present system of Regional Reports, Structure Plans, Local Plans and the recently published National Planning Guidelines, and as it affects options for influencing future use of environmental resources in the Outer Hebrides.
Developments need management and, in some cases, monitoring. Both these activities require a contribution from the environmental sciences through an effective institutional framework.
The closing discussion examines some of the more general social issues, relating to the potential conflict between utilization of the environmental resource and conservation of the natural environment, which characterize isolated rural areas.
For eight years the Nature Conservancy has been studying the grey seals on the island reserve of North Rona to get the necessary facts for a grey seal conservation policy. The programme involves an annual visit to this most remote British island each October to count and mark the pups. The author, who is in charge of the programme, describes the methods used and the results so far, but it is still not known, for instance, whether seals born on North Rona return there to breed, and if not, where they do go.
The mineral base of the soils in Islay, Tiree, Coll and the Outer Hebrides is composed mainly of erosion products of Lewisian and Torridonian rocks, together with materials taken from solution in the sea biotically, and subsequently deposited in the form of shell-sand on the windward coasts. The soils composed for the most part of erosion products are acid, and those of marine products basic. Along transect lines at right angles to the coast there is in many places a wide range of soil conditions from calcareous sand to peat, in distances of about 1 kilometre.
The distribution of the Lumbricidæ, a group known to be affected by pH, available calcium content, and moisture content of the soil, is studied within this range in soil types. Seventeen species are involved, three of which are grouped (in numerical considerations) owing to taxonomic difficulties, and these are described in groups living in the main ecological zones of the soil habitat. Relationships are found between the abundance of those species and soil types.
The occurrence of earthworms in three different soil niches—open soil, in and under cow-pats, and under stones—is described, and niche preferences of the dominant species discussed.
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