Browsing by Author "Tsien, Thomas Nai-Chen"
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Item Electromagnetic induction of rotating magnets(1970) Tsien, Thomas Nai-Chen; Hildebrandt, Alvin F.; Walker, Robert H.; Eisner, Melvin; Kern, John W.; Whitaker, Thomas N.A modified unipolar machine has been studied where the rotor conslts of two parallel magnets embedded in a superconducting lead casting. The voltage detection circuit Is well shielded with super-conducting materials and Is assured to be In zero magnetic field and insulated from the magnets. The same steady voltages as observed for the ordinary unipolar generator are measured on rotating the magnets inside a soft iron cylindrical shell at 4.2 °K. The results disagree with the conventional calculations using the polarization P = (v x M)/c[cubed], but can be explained in terms of [partial derivative]B/[partial derivative]t due to the rotation of the magnets. B of the rotating magnets at any time has been calculated by treating each magnet as if it were at rest with respect to the circuit. As time passes on, the rotating magnets undergo different orientations to give different values of B at the circuit and the resulting [partial derivative]B/[partial derivative]t induces the observed e.m.f. The analysis has been extended to show that the unipolar voltage is basically the result of an induction effect, provided the motion of the magnetic sources are followed.Item Review of the current theory of superconductivity(1967) Tsien, Thomas Nai-Chen; Walker, R. H.; Sinkhorn, Richard D.; Hildebrandt, Alvin F.A brief survey is given of early superconductivity experiments with emphasis on the classical theory of London, including Pippard's generalisation and the Ginsburg-Landau macroscopic theory. Later discoveries such as the isotope effect and gyromagnetic ratio measurement of the super-current carriers indicating how a successful microscopic theory should be formulated are described. The BOS theory is discussed in detail and the paper is concluded with applications of the BCS theory to explain the fundamental experiments.