Theory of the generalized Ginzburg-Landau parameter κ2 for strong-coupling superconductors at arbitrary impurity concentration

We study strong-coupling effects on the slope of the magnetization curve at the upper critical field of a type II superconductor, parametrized by the generalized Ginzburg-Landau parameter ₂. The use of the quasiclassical approach to the BCS-Gorkov theory, valid for all temperatures, allows us to present the calculations in a transparent manner. We obtain closed expressions for ₂ in terms of the solution of the eigenvalue problem determining the upper critical field, which we evaluate numerically. In the weak-coupling limit, previous results are reproduced, apart from a small correction.     

Pair breaking and charge relaxation in superconductors

We present a general formalism based on the quasiclassical Green's function for calculating charge imbalance in nonequilibrium superconductors. Our discussion is sufficiently general that it applies at arbitrary temperatures, and under conditions when the width of quasiparticle states are appreciable due to pair breaking processes, and when strong coupling effects are significant. As a first application we demonstrate in detail how in the limit of small pair breaking and for a weak coupling superconductor the collision term in the formalism reduces to the one in the quasiparticle Boltzmann equation. We next treat the case of charge imbalance generated by tunnel injection, with pair breaking by phonons and magnetic impurities. Over the range of temperatures investigated experimentally to date, the calculated charge imbalance is rather close to that evaluated using the Boltzmann equation, even if pair breaking is so strong as almost to destroy superconductivity. Finally we consider charge imbalance generated by the combined influence of a supercurrent and a temperature gradient. We give calculations for a dirty superconductor with scattering by phonons as the pair breaking mechanism, and the results give a reasonable account of the experimental data of Clarke, Fjordbøge, and Lindelof. We carry out calculations for the case of impurity scattering alone which are valid not only in the clean and dirty limits, but also for intermediate situations. These enable us to see how the large contribution to the charge imbalance found for energies close to the gap edge in the clean case is reduced with increasing impurity scattering.The research was supported in part by the National Science Foundation grant NSF DMR-78-21068.     

Direct current testing to measure corrosiveness of wood preservatives

A qualitative test that mimics the corrosion behaviour of metals in contact with treated wood without using wood specimens would be of great value in rapidly evaluating the corrosiveness of new wood preservatives. The objective of this study was to determine whether the linear polarisation resistance of metals immersed in a solution of preservative chemicals is related to corrosion of metals in wood. This technique was used to measure the corrosion rate of four types of metals in three different aqueous solutions of wood preservatives. The four metals were UNS G10180 (SAE 1018 steel), UNS S30400 (AISI 304 stainless steel), UNS S43000 (AISI 430 stainless steel), and UNS Z15001 (zinc). The metals were subjected to various concentrations of alkaline copper quat (ACQ-D), ammoniacal copper citrate (CC), and chromated copper arsenate type C (CCA-C). It was found that the corrosion of metals in the solutions of the wood preservatives did not correlate well to what is known about the corrosion of metals in contact with wood.     

Energy efficient demand controlled ventilation in single family houses

This paper presents a strategy for a simple demand controlled ventilation system for single family houses where all sensors and controls are located in the air handling unit. The strategy is based on sensing CO₂-concentration and moisture content in the outdoor air and exhaust air. The CO₂-concentration is used to ensure adequate ventilation during occupancy and the moisture content is used to ensure adequate removal of moisture produced in the house. The ventilation rate can be switched between two flow rates: a high rate and a low rate. The high flow rate is based on existing requirements in the Danish building regulations and the low flow rate is based on minimum requirements in indoor air quality standards. Measurements were performed on an existing single family house where the controls were installed on the existing mechanical ventilation system. The results showed that the ventilation can be reduced to the low rate 37% of the time without significant changes in the CO₂-concentration and moisture level in the house. In theory this gives a 35% saving on electric energy for fans.