maintenance channels
71Telephone exchange — A telephone operator manually connecting calls with cord pairs at a telephone switchboard. In the field of telecommunications, a telephone exchange or telephone switch is a system of electronic components that connects telephone calls. A central… …
72Cardiac action potential — The cardiac action potential is a specialized action potential in the heart, with unique properties necessary for function of the electrical conduction system of the heart.The cardiac action potential differs significantly in different portions… …
73endocrine system, human — ▪ anatomy Introduction group of ductless glands (gland) that regulate body processes by secreting chemical substances called hormones (hormone). Hormones act on nearby tissues or are carried in the bloodstream to act on specific target organs… …
74Columbia River — Coordinates: 46°14′39″N 124°3′29″W / 46.24417°N 124.05806°W / 46.24417; 124.05806 …
75Synchronous optical networking — (SONET) and Synchronous Digital Hierarchy (SDH), are two closely related multiplexing protocols for transferring multiple digital bit streams using lasers or light emitting diodes (LEDs) over the same optical fiber. The method was developed to… …
76Public broadcasting — includes radio, television and other electronic media outlets whose primary mission is public service. Public broadcasters receive funding from diverse sources including license fees, individual contributions, public financing and commercial… …
77Chesapeake Bay Bridge-Tunnel — Not to be confused with Chesapeake Bay Bridge. Chesapeake Bay Bridge Tunnel Coming down from the high level portion near the north end. Official name Lucius J. Kellam Jr. Bridge Tunnel Carries …
78State machine replication — Introduction from Schneider s 1990 survey: : Distributed software is often structured in terms of clients and services. Each service comprises one or more servers and exports operations that clients invoke by making requests. Although using a… …
79Mobile radio — This article is about professional equipment. For mobile radios used in amateur radio, see amateur radio mobile operation. Mobile radio or mobiles refer to wireless communications systems and devices which are based on radio frequencies, and… …
80Iran — /i ran , i rahn , uy ran /, n. a republic in SW Asia. 67,540,002; ab. 635,000 sq. mi. (1,644,650 sq. km). Cap.: Teheran. Formerly (until 1935), Persia. * * * Iran Introduction Iran Background: Known as Persia until 1935, Iran became an Islamic… …
