The following sections of this BookRags Literature Study Guide is offprint from Gale's For Students Series: Presenting Analysis, Context, and Criticism on Commonly Studied Works: Introduction, Author Biography, Plot Summary, Characters, Themes, Style, Historical Context, Critical Overview, Criticism and Critical Essays, Media Adaptations, Topics for Further Study, Compare & Contrast, What Do I Read Next?, For Further Study, and Sources.
(c)1998-2002; (c)2002 by Gale. Gale is an imprint of The Gale Group, Inc., a division of Thomson Learning, Inc. Gale and Design and Thomson Learning are trademarks used herein under license.
The following sections, if they exist, are offprint from Beacham's Encyclopedia of Popular Fiction: "Social Concerns", "Thematic Overview", "Techniques", "Literary Precedents", "Key Questions", "Related Titles", "Adaptations", "Related Web Sites". (c)1994-2005, by Walton Beacham.
The following sections, if they exist, are offprint from Beacham's Guide to Literature for Young Adults: "About the Author", "Overview", "Setting", "Literary Qualities", "Social Sensitivity", "Topics for Discussion", "Ideas for Reports and Papers". (c)1994-2005, by Walton Beacham.
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The process of electron tunneling was discovered in 1957 by the Japanese physicist Leo Esaki and the Norwegian physicist Ivar Giaever. Tunneling is the process by which a charged particle is able to pass through an apparently insurmountable energy barrier. The process is possible because of the wave nature of particles. In 1962, Brian Josephson, then a graduate student at Cambridge University, predicted tunneling could occur with Cooper pairs of electrons. Cooper pairs are electron pairs that form when a substance is cooled to the point where it becomes superconductive (usually, close to absolute zero). Josephson predicted that Cooper pairs could pass from one point to another even if there was no voltage drop between the two points. He said that the current would flow in one direction (DC current) if there was no external voltage applied to the system or in both directions (AC current) if there was. He also hypothesized that these currents would be very sensitive to magnetic fields in their vicinity. Josephson's predictions were confirmed by laboratory experiments completed by Anderson and Rowell for DC currents and by Shapiro for AC currents. A Josephson junction consists of a pair of superconducting metals separated by a thin sheet (about 10 Å thick) of insulating material. In the absence of an external electrical source, a small DC current flows across the insulating barrier. When an external voltage is applied, a high frequency AC current develops, but with no net flow in either direction. As predicted, the presence of an external magnetic field near a Josephson junction causes very rapid changes in the current across the junction. The sensitivity of the Josephson junction is valuable in a number of applications. Since relatively small magnetic fields induce significant current changes, the junction can be used in the design of computers and scientific instruments. For example, one type of device, the SQUID (superconducting quantum interference device) is used as a voltmeter for low current measurements, as a medical device, as a magnetometer for sensitive geological measurements, and in high-speed computers.