Tune shift with amplitude of the system. When the tune reaches resonant values, it can be unstable, and thus a tune-shift with amplitude can limit the stability region, or dynamic aperture. In classical mechanics, a simple example of a system with tune shift with amplitude is a pendulum. In accelerator physics, both the transverse and the longitudinal dynamics show tune shift with amplitude. A simple model of the transverse dynamics is of an oscillator with a single sextupole, it is referred to as the Hénon map. Another model for this case is the Standard Map. An important example is the typical case of distributed
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