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AC losses in a monofilamentary MgB 2 round wire with niobium and copper metal sheaths and carrying alternating transport currents are evaluated at several temperatures and frequencies. First, the transport current losses are observed electrically using a lock-in amplifier. Experimental results show that the AC losses decrease with an increase in the temperature if the amplitude of the transport current normalized by the corresponding critical current is maintained constant. On the other hand, the AC losses increase slightly with the frequency. Next, the AC losses are calculated numerically by a finite difference method. The numerical results for the superconductor filament show a good agreement with the results of the conventional theoretical expression formulated using the Bean model over a wide range of current amplitudes. It is also found that the AC losses in the niobium sheath are negligible whereas those in the copper sheath are comparable with those in the superconductor. On the basis of the numerical calculations, an expression is analytically derived for estimating the eddy current loss occurring in a metal sheath. The derived expression well reproduces the AC loss properties of both the copper and niobium sheaths.

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AC losses in stator windings of fully superconducting motors with an MgB 2 wire are numerically evaluated by means of a finite element method using edge elements for self magnetic field. The physical properties of the MgB 2 wire for numerical calculations are obtained from the corresponding experiments with an existing wire. It is assumed that the voltage-current characteristics of the MgB 2 wire are given by Bean's critical state model, in which the critical current density is independent of the local magnetic field. The influences of core slot size and turn number of windings on the AC losses are discussed quantitatively toward the optimum design of the stator winding with the MgB 2 wire.

An NMR method was developed that allows for real-time monitoring of reactions (on the order of seconds) induced by a temperature jump. In a recycle flow system, heating and cooling baths were integrated, with the latter inside the NMR probe. A refolding reaction of ribonuclease A was triggered by rapid cooling and monitored by a series of NMR measurements over 12 s. Data were processed by principal component analysis, in which a factor related to the structural change with an exponential rate constant of 0.2-0.7 s(-1) was successfully separated from factors related to baseline instability and/or noise. Temperature dependency of the rate constant revealed the entropy-driven formation of the transition state of the refolding reaction.