Engineers are professionals who invent, design, analyze, build and test machines, complex systems, structures, gadgets, and materials to fulfill functional objectives. Most engineers specialize in one or more engineering disciplines. Civil engineering, for example, includes structural and transportation engineering and materials engineering includes ceramic, metallurgical, and polymer engineering. Mechanical engineering cuts across just about every discipline since its core essence is applied physics. Engineers also may specialize in one industry, such as motor vehicles, or in one type of technology, such as turbines or semiconductor materials.