Tertiary sector of the economyThe tertiary sector of the economy, generally known as the service sector, is the third of the three economic sectors in the three-sector model (also known as the economic cycle). The others are the primary sector (raw materials) and the secondary sector (manufacturing). The tertiary sector consists of the provision of services instead of end products. Services (also known as "intangible goods") include attention, advice, access, experience and affective labour.
Three-sector modelThe three-sector model in economics divides economies into three sectors of activity: extraction of raw materials (primary), manufacturing (secondary), and service industries which exist to facilitate the transport, distribution and sale of goods produced in the secondary sector (tertiary). The model was developed by Allan Fisher, Colin Clark, and Jean Fourastié in the first half of the 20th century, and is a representation of an industrial economy. It has been criticised as inappropriate as a representation of the economy in the 21st century.
Public serviceA public service or service of general (economic) interest is any service intended to address specific needs pertaining to the aggregate members of a community. Public services are available to people within a government jurisdiction as provided directly through public sector agencies or via public financing to private businesses or voluntary organizations (or even as provided by family households, though terminology may differ depending on context). Other public services are undertaken on behalf of a government's residents or in the interest of its citizens.
Business administrationBusiness administration, also known as business management, is the administration of a commercial enterprise. It includes all aspects of overseeing and supervising the business operations of an organization. From the point of view of management and leadership, it also covers fields that include office building administration, accounting, finance, designing, development, quality assurance, data analysis, sales, project management, information-technology management, research and development, marketing and communication studies.
Euler equations (fluid dynamics)In fluid dynamics, the Euler equations are a set of quasilinear partial differential equations governing adiabatic and inviscid flow. They are named after Leonhard Euler. In particular, they correspond to the Navier–Stokes equations with zero viscosity and zero thermal conductivity. The Euler equations can be applied to incompressible or compressible flow. The incompressible Euler equations consist of Cauchy equations for conservation of mass and balance of momentum, together with the incompressibility condition that the flow velocity is a solenoidal field.
Compressible flowCompressible flow (or gas dynamics) is the branch of fluid mechanics that deals with flows having significant changes in fluid density. While all flows are compressible, flows are usually treated as being incompressible when the Mach number (the ratio of the speed of the flow to the speed of sound) is smaller than 0.3 (since the density change due to velocity is about 5% in that case). The study of compressible flow is relevant to high-speed aircraft, jet engines, rocket motors, high-speed entry into a planetary atmosphere, gas pipelines, commercial applications such as abrasive blasting, and many other fields.
