defines

SUBJECT AREA: Ports and shipping

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Froude was educated at a preparatory school at Buckfastleigh, and then at Westminster School, London, before entering Oriel College, Oxford, to read mathematics and classics. Between 1836 and 1838 he served as a pupil civil engineer, and then he joined the staff of Isambard Kingdom Brunel on various railway engineering projects in southern England, including the South Devon Atmospheric Railway. He retired from professional work in 1846 and lived with his invalid father at Dartington Parsonage. The next twenty years, while apparently unproductive, were important to Froude as he concentrated his mind on difficult mathematical and scientific problems. Froude married in 1839 and had five children, one of whom, Robert Edmund Froude (1846–1924), was to succeed him in later years in his research work for the Admiralty. Following the death of his father, Froude moved to Paignton, and there commenced his studies on the resistance of solid bodies moving through fluids. Initially these were with hulls towed through a house roof storage tank by wires taken over a pulley and attached to falling weights, but the work became more sophisticated and was conducted on ponds and the open water of a creek near Dartmouth. Froude published work on the rolling of ships in the second volume of the Transactions of the then new Institution of Naval Architects and through this became acquainted with Sir Edward Reed. This led in 1870 to the Admiralty's offer of £2,000 towards the cost of an experimental tank for ship models at Torquay. The tank was completed in 1872 and tests were carried out on the model of HMS Greyhound following full-scale towing trials which had commenced on the actual ship the previous year. From this Froude enunciated his Law of Comparisons, which defines the rules concerning the relationship of the power required to move geometrically similar floating bodies across fluids. It enabled naval architects to predict, from a study of a much less expensive and smaller model, the resistance to motion and the power required to move a full-size ship. The work in the tank led Froude to design a model-cutting machine, dynamometers and machinery for the accurate ruling of graph paper. Froude's work, and later that of his son, was prodigious and covered many fields of ship design, including powering, propulsion, rolling, steering and stability. In only six years he had stamped his academic authority on the new science of hydrodynamics, served on many national committees and corresponded with fellow researchers throughout the world. His health suffered and he sailed for South Africa to recuperate, but he contracted dysentery and died at Simonstown. He will be remembered for all time as one of the greatest "fathers" of naval architecture.

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SUBJECT AREA: Electronics and information technology, Recording

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Nyquist (original family name Nykvist) emigrated from Sweden to the USA when he was 18 years old and settled in Minnesota. After teaching for a time, he studied electrical engineering at the University of North Dakota, gaining his first and Master's degrees in 1915 and 1916, and his PhD from Yale in 1917. He then joined the American Telegraph \& Telephone Company, moving to its Bell Laboratories in 1934 and remaining there until his retirement in 1954. A prolific inventor, he made many contributions to communication engineering, including the invention of vestigial-side band transmission. In the late 1920s he analysed the behaviour of analogue and digital signals in communication circuits, and in 1928 he showed that the thermal noise per unit bandwidth is given by 4 kT, where k is Boltzmann's constant and T the absolute temperature. However, he is best known for the Nyquist Criterion, which defines the conditions necessary for the stable, oscillation-free operation of amplifiers with a closed feedback loop. The problem of how to realize these conditions was investigated by his colleague Hendrik Bode.

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See also: Shannon, Claude Elwood