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optical disk

(Encyclopedia)optical disk, any of a variety of information storage disks that are played or read using a laser. Optical disks include compact discs (CDs and CD-ROMs), laser discs (see videodisc), and digital versa...

magnetic resonance imaging

(Encyclopedia)magnetic resonance imaging (MRI), noninvasive diagnostic technique that uses nuclear magnetic resonance to produce cross-sectional images of organs and other internal body structures. The patient lies...

cesarean section

(Encyclopedia)cesarean section sĭzârˈēən [key], delivery of an infant by surgical removal from the uterus through an abdominal incision. The operation is of ancient origin: indeed, the name derives from the le...

Callahan, Harry Morey

(Encyclopedia)Callahan, Harry Morey, 1912–99, American photographer, b. Detroit. Self-taught, he began taking pictures (1938) as a hobby and, inspired by the work of Ansel Adams, began to produce professional-qua...

stun gun

(Encyclopedia)stun gun, hand-held electronic device that produces a high-voltage pulse that can immobilize a person for several minutes with no permanent damage in most cases. It is powered by ordinary batteries, w...

teleportation, in physics

(Encyclopedia)teleportation, in physics, the transfer of key properties from one particle (or group of particles) to another a significant distance apart without a physical connection between the two particles (or ...

Alcman

(Encyclopedia)Alcman ălkˈmən [key], fl. 620 b.c., Greek lyric poet of Sparta. He was the earliest writer of Dorian choral poetry whose work has survived. Short choral fragments and a longer one (part of a parthe...

Chalkley, Thomas

(Encyclopedia)Chalkley, Thomas chôˈklē [key], 1675–1741, Quaker mariner and missionary preacher, b. England. He made his home after 1701 in Philadelphia. He traded chiefly with the West Indies, navigating his ...

Némcová, Božena

(Encyclopedia)Némcová, Božena bôˈzhĕnä nĕmˈtsôvä [key], 1820–62, Czech novelist and storyteller. Némcová developed the regional tale, which she enhanced with an original prose style. Her work provide...

Archimedes' screw

(Encyclopedia)Archimedes' screw, a simple mechanical device believed to have been invented by Archimedes in the 3d cent. b.c. It consists of a cylinder inside of which a continuous screw, extending the length of th...