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Strained Silicon On Insulator wafers are today envisioned as a natural and powerfulenhancement to standard SOI and/or bulk-like strained Si layers. For MOSFETs applications, thisnew technology potentially combines enhanced devices scalability allowed by thin films andenhanced electron and hole mobility in strained silicon. This paper is intended to demonstrate byexperimental results how a layer transfer technique such as the Smart Cut™ technology can be usedto obtain good quality tensile Strained Silicon On insulator wafers. Detailed experiments andcharacterizations will be used to characterize these engineered substrates and show that they arecompatible with the applications.
In Africa, the term dry forest covers vegetation types dominated by a more or less continuous tree cover (70%), experiencing pronounced drought during more than three months per year, and occurring within the savanna biome. They may be called (open) woodlands or (dense) dry forests according to tree density and understory structure (Menaut 1983). The Yangambi classification establishes the following (Boughey, 1957a, b; Monod, 1963; Aubréville, 1965).
A woodland has an upper stratum of deciduous trees of small or medium size, with their crowns more or less touching above a sparse woody understory. Tree density is high enough to affect the herbaceous stratum which differs floristically from the adjacent savanna. The ground layer consists of grasses, herbs and suffrutescent plants in sufficient density to allow for annual burnings. The canopy of a woodland tends to be dominated by one or very few species.
A dry forest, strictly speaking, is defined as a closed stand with several woody strata. The grass layer, when present, is weak and discontinuous, only allowing for episodic and sparse fires. In most cases, the trees of the upper stratum are deciduous whereas the understory is composed of evergreen and/or deciduous shrubs which differ from the canopy floristically. The canopy is multispecific and often devoid of woodland dominants. In both dry forest and woodland, the tree species which make up most of the canopy are present but never dominant in the surrounding savanna.
Some authors have considered dry forests to be a tropophilous extension of the rain forest, with adaptations to xeric conditions in characteristics of stems but not of leaves (Schnell, 1976–7).
The food habits of four hypogeous Macrotermitinae species were studied using stable carbon isotope analysis in several biotopes of a humid savanna of West Africa (Lamto, Côte d'Ivoire). The proportion of woody and herbaceous material in the diet of the different species was determined by measuring the 13C natural abundance in the fungus comb. The diet varied with season and biotope, especially tree density. The results confirm the flexibility of the food habits of the fungus-growing termites as a consequence of their exosymbiosis with the fungus Termitomyces sp.
Two weeks after irrigation there was a temporary water-table between 30 and 127 cm. below the soil surface in four different parts of a grapefruit orchard. As the temporary water-table rose closer to the soil surface the percentage of soil water in the root zone increased and tree size, number of leaves per branch, and leaf size all decreased. Shallow water-tables also induced more die-back and reduced yields significantly. Analyses of soils at various sites indicated that there was no problem of salinity or alkalinity, but physical soil analyses showed that the percentage of clay increased with increased shallowness of the water-table, in line with the soil moisture characteristic curves.
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