We report here the results of an extensive experimental investigation of soliton dynamics in Josephson junctions of different annular geometries. The annular geometry is unique in that it allows for the study of undisturbed soliton motion as well as soliton–antisoliton collisons, since there are no boundary effects. We have successfully trapped a single soliton in an annular junction and found good agreement with perturbation theory at low soliton velocity, and evidence of departure from perturbation theory at higher velocity. We also discuss the observation of fine structure on the I-V curve for a single trapped soliton, and evidence linking the stability of the soliton to surface damping.
Digital computer simultations have been used to map parameters of the transition to chaos in an rf current driven Josephson junction. Our results are qualitatively like those reported by others using analog techniques, but differ quantitatively. Our calculations show that the parameters for the onset of chaos are the same as those required for high parametric gain. This leads to the conclusion that the ’’noise rise’’ in Josephson junction parametric amplifiers is due to chaos.
The electrical properties of thin mica crystals have been measured between 4 and 520 OK, and have been related to optical absorption measurements and to electron microscope observations. The dc conductivity and breakdown strength depends on the concentration of iron and titanium in the mica. It is suggested that impurities act as localized centres for electrical conduction in mica and that the Poole-Frenkel model applies a t high temperatures while electrons tunnel between the centres at low temperatures. The conductivity of mica depends on the frequency of the applied field. Two types of breakdown have been found. The results are interpreted as avalanche breakdown in synthetic micas and thermal breakdown in natural micas.Une etude a BtB faite des proprihtes Blectriques des lames minces de mica entre 4 et 520 OK; ces proprietes ont 6th reliees 8, des mesures d'absorption optique ainsi qu' 8, des observations faites au microscope electronique. La conductivite en courant direct et la resistance 8, la rupture dependent de la concentration en fer et en titane du mica. I1 est suggere que les impuretes jouent le r61e de centres localises pour la conduction hlectrique dam le mica et que le modhle de Poole-Frenkel est valable aux tempbratures elevhes, tandis qu'aux temperatures basses les electrons passent d'un site B un autre par un effet tunnel. La conductivite du mica depend de la frBquence du champ appliquh. Deux types de rupture ont BtB trouvBs. On explique les resultats par une rupture en avalanche dans le mica synthetique, et par une rupture thermique dans le mica naturel.
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