Index-matching materialIn optics, an index-matching material is a substance, usually a liquid, cement (adhesive), or gel, which has an index of refraction that closely approximates that of another object (such as a lens, material, fiber-optic, etc.). When two substances with the same index are in contact, light passes from one to the other with neither reflection nor refraction. As such, they are used for various purposes in science, engineering, and art.
Model-driven engineeringModel-driven engineering (MDE) is a software development methodology that focuses on creating and exploiting domain models, which are conceptual models of all the topics related to a specific problem. Hence, it highlights and aims at abstract representations of the knowledge and activities that govern a particular application domain, rather than the computing (i.e. algorithmic) concepts. MDE is a subfield of a software design approach referred as round-trip engineering.
European single marketThe European single market, also known as the European internal market or the European common market, is the single market comprising mainly the member states of the European Union (EU). With certain exceptions, it also comprises the Iceland, Liechtenstein, and Norway (through the Agreement on the European Economic Area) and Switzerland (through sectoral treaties). The single market seeks to guarantee the free movement of goods, capital, services, and people, known collectively as the "four freedoms".
Aether drag hypothesisIn the 19th century, the theory of the luminiferous aether as the hypothetical medium for the propagation of light waves was widely discussed. The aether hypothesis arose because physicists of that era could not conceive of light waves propagating without a physical medium in which to do so. When experiments failed to detect the hypothesized luminiferous aether, physicists conceived explanations, which preserved the hypothetical aether's existence, for the experiments' failure to detect it.
Freedom of movementFreedom of movement, mobility rights, or the right to travel is a human rights concept encompassing the right of individuals to travel from place to place within the territory of a country, and to leave the country and return to it. The right includes not only visiting places, but changing the place where the individual resides or works. Such a right is provided in the constitutions of numerous states, and in documents reflecting norms of international law.
