Ultracold neutrons are defined and their general physical properties are explained. Their relations with modern physics and how they can be produced in laboratories are discussed. Superthermal production in superfluid liquid helium, the most promising method, is presented, quoting the results of Mark 3000, a superthermal ultracold neutron generator.
After a brief history of the International System of Units (SI), the effects of a recent revision of the Japanese Measurement Law, in particular those of its policy of mandatory use of SI units, are described together with their backgrounds. Some of the conventional units for force and pressure such as kilogram-force and Torr shall be relinquished from the official use in trade and certification activities not later than September 30, 1999 so as to harmonize with the trend in international certification systems. Major problems are explained and some countermeasures are suggested.
In multiply-twisted superconducting cables exposed to an external AC transverse magnetic field, a component of the magnetic field parallel to the strand axis brings about an additional AC loss (longitudinal AC loss) in the strands. We have experimentally evaluated the longitudinal AC loss in two types of triply-twisted superconducting cables composed of insulated strands with different diameters, by eliminating the hysteresis loss and the transverse coupling-current loss from the total loss in the strands. The evaluated longitudinal AC losses were quantitatively explained by a theoretical expression obtained so far, under consideration of the effects of the longitudinal component of the applied field to the strand. The present results suggest that the longitudinal loss can be dominant in AC magnetic fields with a relatively large amplitude. To minimize the total loss of the strand in multiply-twisted cables, we discuss an optimum condition for the twist pitch of the strand.