In a cross section of the stem of a woody plant, the amount of wood added during a single growth period. In temperate regions this period is usually one year, in which case the growth ring may be called an annual ring. In tropical regions growth rings may not be discernible or are not annual. Even in temperate regions growth rings are occasionally missing; and sometimes a second, or “false,” ring may be deposited during a single year (e.g., following defoliation by insects). Nevertheless, annual rings have been used in dating ancient wooden structures, especially those of American Indians in the dry U.S. Southwest. Changes in ring width are a source of information about ancient climates.
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Peptide hormone secreted by the anterior lobe of the pituitary gland. It promotes growth of bone and other body tissues by stimulating protein synthesis and fat breakdown (for energy). Excessive production causes gigantism, acromegaly, or other malformations; deficient production results in dwarfism, dramatically relieved if GH is given before puberty. Genetic engineering techniques now permit large-scale production of adequate amounts of GH for that purpose.
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Process of growing a crystal of a particular orientation on top of another crystal. If both crystals are of the same material, the process is known as homoepitaxy; if the materials are different, it is known as heteroepitaxy. Common types of epitaxy include vapour phase, liquid phase, and solid phase, according to the source of the atoms being arranged on the substrate. Epitaxy is most frequently employed in the production of semiconductor wafers for use in the creation of integrated circuits.
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Process by which a nation's wealth increases over time. The most widely used measure of economic growth is the real rate of growth in a country's total output of goods and services (gauged by the gross domestic product adjusted for inflation, or “real GDP”). Other measures (e.g., national income per capita, consumption per capita) are also used. The rate of economic growth is influenced by natural resources, human resources, capital resources, and technological development in the economy along with institutional structure and stability. Other factors include the level of world economic activity and the terms of trade. Seealso economic development.
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