Persistent current measurements

Figure 2 Experimental arrangement for establishing and measuring a persistent current. Switch S2 is closed to send current through the loop, Si is closed to confine the current flow to the loop, and the magnetometer is employed to measure the magnetic field through the loop and thereby determine the current (from Ref 8, p. 34)...

However, in the spring of 2004, the entire column was nearly uniform in salinity at about 86 ppt (see Table 3), indicating that winter convection was likely to had been able to destroy the meromictic conditions, and the enhanced stratification was an intermittent rather than permanent feature. By the late summer of 2004, a new type of stratification had arisen, which persisted in aummns until the fall of 2006. This stratification was mainly three-layered, involving two salinity maxima, one at the surface, and the other one at the bottom, separated by a relatively fresh intermediate layer (Fig. 6). Despite the salinity inversion just below the upper mixed layer, the column was maintained in a stable state by a steep thermocline. The deeper salinity maximum was best developed in 2005, but a hint of it was also observed in the fall of 2006, when there was a marked bottom mixed layer, indicating the presence of strong currents in the bottom layer (which was also confirmed by direct current measurements). 

First, we note that the standard photodetection is a local measurement of the field variables (intensities). At the same time, the Aharonov-Bohm effect represents a topological measurement referred to the properties of vector potential along some loop. In the usual form, the Aharonov-Bohm effect deals with static or slowly time-varying magnetic fields [101]. The effect consists in the appearance of a persistent current in a metallic loop over which the magnetic flux passes. This current is a periodic function of magnetic flux with the period of flux quantum hc/e. Besides that, certain resistance oscillations in the loop incorporated into an external circuit with the same period can occur. 

Critical Current Measurements. When the generator is stopped, the current remains persistent if the critical current of the circuit has not been exceeded otherwise it decays until the critical value is reached. In this way it is possible to determine quite large critical currents with reasonable accuracy. A strip of soldering tin alloy of 1.4 mm thickness and 6 mm width carried 305 amp. 

Fig. 24. Twin boundary pinning in Y- and Nd-123 single crystals as deduced from magnetic measurements (a) Angular dependence of Am at various angles near to the c-direction note that twin boundary pirming (PE ) disappears for misaligninent angles above 8° (Kupfer et al. 19%). (b) Persistent currents as a function of field for various oxygen deficiencies ri note that PE, disappears for 5 > 0.08 (Wolf et al. 1997).

Even with the superposition of the ac with a cathodic protection current, a large part of the anodic half wave persists for anodic corrosion. This process cannot be detected by the normal method (Section 3.3.2.1) of measuring the pipe/soil potential. The IR-free measurable voltage between an external probe and the reference electrode can be used as evidence of more positive potentials than the protection potential during the anodic phase. Investigations have shown, however, that the corrosion danger is considerably reduced, since only about 0.1 to 0.2% contributes to corrosion. 

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