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Films of AlN were grown on MgO(100), Al2O3, and Si under vacuum pressure (10-3 to 10-4 Torr) at different substrate temperatures. They were examined ex situ with infrared reflectance spectroscopy, scanning electron microscopy, x-ray diffraction and rutherford backscattering spectroscopy. Highly oriented smooth films were grown at film thicknesses below 1 μm. Thicker films showed significantly more roughness but remained oriented with respect to the substrate. AIN growth was faster on Si than MgO(100) or Al2O3 and Si was the only substrate that growth was observed at 500°C.
Mires are terrestrial ecosystems which conserve organic production in the form of peat because their soils are waterlogged. Scotland's damp climate makes it rich in mires, with fens, raised mires and blanket mires occurring widely. Intact examples are mostly treeless due to wind exposure. They have two functional layers of soil: a shallow acrotelm overlying the catotelm or peat deposit proper. The acrotelm is the main region of diagenesis and contains the water table, which lies close to the surface for most of the time. Evapotranspiration depends on water table depth and surface vegetation. In the catotelm, water transmission is described by Darcy's law with sufficient exactness to allow prediction of the water table profile. An analysis of seepage using Dupuit–Forchheimer theory predicts a hemi-elliptical profile whose curvature is governed by the water balance in dry years and which, in its turn, closely controls the overall shape of the mire. Water flow is more rapid in the acrotelm, where it creates a regular series of different soil physical regimes which are linked with distinct combinations of surface topography and vegetation arranged sequentially from the centre of a mire to its edge. Such regular arrangements are most clearly seen in the Flowe Country of E Sutherland and Caithness. Acrotelm structure also permits variation in flow rate with depth, so that the amplitude of water table oscillations is narrowly confined and the mire thus protected against both desiccation and sheet flow.
An extensive reed bed on the north shore of the inner Tay Estuary is briefly described. Studies in the summers of 1975, 1976 and 1978 showed it to comprise monodominant stands of Phragmites communis Trin. The standing crop of shoots was sampled at the end of the season of vegetative growth and analysed by simple biometrical methods. Certain important spatial and architectural characteristics of the community varied in a regular manner with position in the bed. Estimates of the above ground productivity of intact stands ranged from 100 to 150 tonnes/ha in a poor growing season. Commercial harvesting operations, conducted since 1975, produced an immediate and consistent decrease in shoot stature, apparently followed by a slow increase in density and productivity. The behaviour of the downshore edge of the bed and the details of its annual development above and below ground require further study.