X-ray fluorescenceX-ray fluorescence (XRF) is the emission of characteristic "secondary" (or fluorescent) X-rays from a material that has been excited by being bombarded with high-energy X-rays or gamma rays. The phenomenon is widely used for elemental analysis and chemical analysis, particularly in the investigation of metals, glass, ceramics and building materials, and for research in geochemistry, forensic science, archaeology and art objects such as paintings.
Performative utteranceIn the philosophy of language and speech acts theory, performative utterances are sentences which not only describe a given reality, but also change the social reality they are describing. In a 1955 lecture series, later published as How to Do Things with Words, J. L. Austin argued against a positivist philosophical claim that the utterances always "describe" or "constate" something and are thus always true or false.
