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[en] Magnet cryosystem options utilizing the thermomechanical effect of He II and the mechano-caloric effect for refrigeration (referred to as vortex refrigeration) are examined. The performance of the existing He II magnet refrigeration system is briefly reviewed, with attention given to superleak properties, vortex shedding, heat input, and thermodynamic cycle. It is concluded that the possibilities of magnet heat leak use for energetics and stability improvements are promising when He II is selected as magnet coolant. 7 references

[en] At temperatures below about 1 K, a series of dc superconducting quantum interference devices (SQUID's) exhibited an apparent flux noise with a spectral density scaling as 1/f/sup //sup α/, where 0.58<α<0.80. Typically, the magnitude of the noise increased as the temperature was lowered below 1 K, tending to flatten out at low temperatures with a value of 7 +- 3 μPhi₀Hz^-1/sup //² at 1 Hz that was nearly independent of the parameters and materials of the SQUID's. Although a large number of hypothetical sources of the noise have been eliminated, the origin remains unidentified

[en] The effect of mechanical power control on the transient stability of a superconducting alternator for symmetrical and unsymmetrical fault conditions is studied. A detailed governor-turbine model, with electrohydraulic governors and fast valving is considered

[en] A method is described for the fabrication of a multifilament superconducting wire of the type A/sub 3/B where A is selected from the group consisting of Nb and V, and B is selected from the group consisting of Sn and Ga which comprises the steps of: (a) filling the center of one or more copper tubes with B or with a predominantly B-copper alloy and drawing the tubes to form copper -B wires, the ratio of B to Cu in the wire being between 10-50 weight % B; (b) cabling a plurality of the copper -B wires around a core predominantly A wire; (c) bundling a plurality of the cables of step (b) with an enveloping layer of copper; (d) drawing the assembly of step (c) to reduce its diameter to a desired size; and (e) heat treating the product of step (d) to cause B to diffuse and form A/sub 3/B at the surface of the A filaments

[en] We have studied the response of several Nb--a-Si--Nb junctions to far-infrared laser radiation at a frequency within 10% of their plasma frequencies ω/sub p/, and have depressed ω/sub p/ by similar amounts with a magnetic field. Because of the complexity of the response, the dc I-V characteristics of the irradiated junctions show striking qualitative differences even for these small differences in ω/sub p/. We can accurately reproduce these characteristics with analog simulations including appropriate noise levels, allowing us to determine the plasma frequency within a few-percent accuracy

[en] The authors have started a study to overcome difficulties and investigate the feasibility of laboratory detection of post-newtonian h/sup ↔//sub 0/ fields, as that given by the Lense-Thirring effect induced by the rotating earth. They discuss the state of advancement of two projects which involve the Josephson effect. At this time the analysis is completed and starts the realization of a superfluid He/sup 4/ analog of the rfSQUID. Preliminary experimental results have begun with a prototype of a SQUID gyromagnetic detector of absolute rotation proposed earlier

[en] In conclusion, this study shows that in a coherent array, the ac Josephson oscillations occur with the same phase for a given frequency in all the junctions. The construction of coherent arrays is based on the frequency pulling and phase-locking effects that arise when the ac Josephson oscillation in a single junction interacts nonlinearly with the signal from another source. It becomes another Josephson junction or an external oscillator. The model here discussed, while leaving for the moment frequency-pulling effects out of considerations, is able to describe both the maintenance of coherence in a suitably prepared array of Josephson junctions and the appearance of self-synchronization (phase-locking) in the array dynamics, starting from a completely uncorrelated initial condition. Furthermore, the appearance of chaotic behaviour when dissipation (leakage) of electromagnetic field is inhibited, is also described on the basis of the same general model

[en] In the present work are collected some recent results obtained concerning the thermal fluctuations and macroscopic quantum tunneling in Josphson systems mostly in connection with their effect on their current-voltage I-V characteristics of a tunnel junction. This study considers both underdamped and overdamped situations looking for proper expressions for the lifetime of both ''locked'' and ''running'' states corresponding to zero and finite voltage current-carrying states of the junction. In this way the authors investigate some aspects of the influence of noise on the I-V curves of Josephson junctions. Using the first-time passage technique developed by Stratonovich expressions which extend the classical Kramers results are obtained. In conclusion, considered is the non-stationary case to explain the presence of hysteresis and sharp transitions in the I-V curves in presence of thermal noise. It is easy to understand how the previous considerations on the activation processes also leads to the stationary case. If during the observations the average on times is larger than both tau-right arrow and tau-left arrow the process is stationary and single-value rounded I-V curves are observed

[en] A complex new magnetic refrigerant, suitable for the ideal Ericsson cycle, has been investigated. Above --15 K it is necessary to use ferromagnets as a magnetic refrigerant. However, temperature variation for the magnetic entropy change in a homogeneous ferromagnet is not suitable for the Ericsson cycle. The present paper verifies, from theoretical analysis, that a complex ferromagnetic material, for instance, (ErAl₂)/sub 0.312/(HoAl₂)/sub 0.198/ (Ho/sub 0.5/Dy/sub 0.5/Al₂)/sub 0.490/, has the most suitable characteristics for the ideal Ericsson cycle, including two kinds of isomagnetic field processes. On the basis of the above consideration, a sintered layer structural complex has been prepared, composed of three kinds of RAl/sub 2.15/ layers, where R's are rare-earth atoms. From specific heat measurements made on this complex, its entropy and entropy change have been determined. It has been concluded that the complex magnetic material is the most hopeful refrigerant for the Ericsson cycle