α μ = μ θ − μ ref μ ref ( θ− θ ref ) MathType@MTEF@5@5@+=feaagCart1ev2aqatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbbjxAHXgaruavP1wzZbItLDhis9wBH5garmWu51MyVXgarqqtubsr4rNCHbGeaGqipG0dh9qqWrVepG0dbbL8F4rqqrVepeea0xe9LqFf0xc9q8qqaqFn0lXdHiVcFbIOFHK8Feea0dXdar=Jb9hs0dXdHuk9fr=xfr=xfrpeWZqaaeaaciWacmGadaGadeaabaGaaqaaaOqaaiabeg7aHnaaBaaaleaacqaH8oqBaeqaaOGaeyypa0ZaaSaaaeaacqaH8oqBdaWgaaWcbaGaeqiUdehabeaakiabgkHiTiabeY7aTnaaBaaaleaacaqGYbGaaeyzaiaabAgaaeqaaaGcbaGaeqiVd02aaSbaaSqaaiaabkhacaqGLbGaaeOzaaqabaGcdaqadaqaaiabeI7aXjabgkHiTiabeI7aXnaaBaaaleaacaqGYbGaaeyzaiaabAgaaeqaaaGccaGLOaGaayzkaaaaaaaa@50C0@
where µθ and µref are the permeabilities at temperatures θ and θref respectively