Atomic, molecular, and optical physics the origin of the index of refraction treated an electron in an atomic system classically according to the model of Paul Drude and Hendrik Lorentz. The theory was developed to attempt to provide an origin for the wavelength-dependent refractive index "n" of a material. In this model, incident electromagnetic waves forced an electron bound to an atom to oscillate. The amplitude of the oscillation would then have a relationship to the frequency of the incident electromagnetic wave and the resonant frequencies of the oscillator. The superposition of these emitted waves from many oscillators would then lead to a wave which
Desktop metaphor been extended and stretched with various implementations of desktop environments, since access to features and usability of the computer are usually more important than maintaining the 'purity' of the metaphor. Hence we find trash cans on the desktop, as well as disks and network volumes (which can be thought of as filing cabinets—not something normally found "on" a desktop). Other features such as menu bars or taskbars have no counterpart on a real-world desktop. The desktop metaphor was first introduced by Alan Kay at Xerox PARC in 1970 and elaborated in a series of innovative software applications developed by PARC