Note 1 to entry: The alternating component of the quantity x(t) is denoted by x ∼ (t) MathType@MTEF@5@5@+=feaagCart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbbjxAHXgaruavP1wzZbItLDhis9wBH5garmWu51MyVXgarqqtubsr4rNCHbGeaGqipG0dh9qqWrVepG0dbbL8F4rqqrVepeea0xe9LqFf0xc9q8qqaqFn0lXdHiVcFbIOFHK8Feea0dXdar=Jb9hs0dXdHuk9fr=xfr=xfrpeWZqaaiqaciWaamGadaGadeaabaGaaqaaaOqaceaau3GaamiEamaaBaaajaa4baacdaqcLbwacqWF8iIFaKqaGhqaaOGaaiikaiaadshacaGGPaaaaa@3DB9@ .