Specializations emerge and evolve in response to changing needs and opportunities, and focus on many different interlocking and cross-cutting aspects and dimensions of a field. The established branches of engineering illustrate this process in a very high degree. There are specializations by engineering artifact — automobile, aeronautical, naval and chemical engineering; by problem world — civil and mining engineering; and by requirement — production engineering, industrial and transportation engineering. There are specializations in theoretical foundations — control and structural engineering; in techniques for solving mathematical problems that arise in the analysis of engineering products — finite-element analysis and control-volume analysis; in engineering components for use in larger systems — electric motors, and internal combustion engines; in technology and material — reinforced concrete, conductive plastics; and in other dimensions too.