shape memory, property possessed by certain alloys that allows them to return, when heated, to their original shape after having been deformed. This effect results because, as the alloy is deformed, it undergoes a martensitic (or athermal) transformation—a solid-state transition that rapidly changes the crystalline structure of the alloy without thermal activation—that is readily reversed once an appropriate amount of heat is applied. Among the alloys are copper-aluminum-nickel, copper-zinc-aluminum, nickel-titanium, and iron-manganese-silicon. Applications of shape memory include heat-activated fasteners, switches, eyeglass frames, orthopedic devices, teeth braces, and blood clot filters.

U.S. a cappella singing style incorporating many folk hymns and utilizing a special musical notation. The seven-note scale used by some singers is sung not to the syllables do-re-mi-fa-sol-la-ti but to a four-syllable system brought to America by early English colonists: fa-sol-la-fa-sol-la-mi. The system reflects the fact that a series of three intervals repeats itself in the major scale. A differently shaped note head is used for each of the four syllables. The singer reads the music by following the shapes; singers unfamiliar with the system can read the notes according to their placement on the staff. The tradition started in New England and moved South and West as more sophisticated forms of music reached the U.S. Shape-note singing had largely died out except in rural areas by the 1880s, but it has experienced a revival in recent years. The traditional shape-note hymnal, The Sacred Harp, first published in 1844, remains in use today.

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