Shielding current density

In conclusion, as pointed out in the introduction, the results to be presented in sects. 5—8 are not aimed at a detailed discussion of these fundamental aspects of flux pinning and flux dynamics, but rather at possibilities to improve 7c in the 123 superconductors. We must be aware of the fact, however, that the Jc s quoted in the literature often do not refer to the true critical current densities, since the data are affected by creep and relaxation, and should rather be quoted as shielding current densities 7s- Furthermore, we will refiain from judgements of the nature of the boundary line, where 7s goes to zero, and will refer to it as the irreversibility line. This characteristic parameter is subject to the same restrictions as mentioned above i.e., sensitive to the resolution of the experiment and its time scale. It is useful to note that the shape of this curve (// c) follows a power law (with an exponent of 1.5) for more three-dimensional HTS, as predicted by Malozemoff et al. (1988) on the basis of a depiiming argument, but an exponential law for two-dimensional systems, as shown schematically in fig. 6. 

RoUs and other relatively simple shapes make use of inert shields and thieves to avoid edge buildup and produce a more even plate thickness. For more compUcated shapes having deeper recesses thicker deposits from cyanide copper baths have been used as an undercoat to the copper sulfate deposit. Acid copper baths operate near 100% efficient over a wide current density range. The cathode efficiency is usuaUy slightly less than the anode efficiency, bringing about a slow increase in copper unless drag-out losses are high. 

Conductive Polymers Anodes currently available consist of a conductive-polymer graphite material coated on to a multistrand copper conductor. The polymer provides an active surface but shields the conductor from chemical attack. A non-conductive outer braid may be used to give abrasion resistance and avoid direct contact with the cathode. The finished anode has the appearance of an electric cable and is claimed to have applications for buried/immersed structures and for internal protection of tanks, etc. Anode current densities are typically given as 14-30mAm ... 

Anode Shield protective covering of insulating material placed on a painted structure in the immediate vicinity of the anode to reduce the cathodic current density in that area, thus preventing the development of excessive alkalinity and stripping of the paint see Saponification). 

Theoretical calculation of NMR chemical shifts is usually done by first considering the electronic current density which is induced by the external magnetic field. Once this current has been calculated the chemical shift can be obtained by application of the Biot-Savard law, which describes the magnetic field created by it. The strength of this field at the position of an atom represents the NMR chemical shielding of this atom. 

Advantage of the CTOCD Method Continuous Transformation of the Origin of the Current Density. The CTOCD method for theoretical determination of hypermagnetizabilities and shielding polarizabilities is reported in detail in ref. (28). In this section we make only a very brief description of the theory involved in the formulation of CrOCZ)-Z>Z r and a1/ -... 

Previously, Stonehart11 had described the mechanism for diffusion of oxygen to an individual platinum crystallite on the carbon support surface. In this instance, at low current-densities, it was anticipated that hemispherical diffusion conditions operate, since the base of the platinum crystallite is shielded by the carbon support and thereby is inactive. 

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