Having now fully specified the differential equation (26), it is recognized as being identical to Bessel's equation
of order zero, with scalar parameter [alpha] (the units of which are (see (20)) the reciprocal of the units of r).
I32, 28, 24]), and we shall only mention them briefly; the others, like a modification of the Prufer angle associated with Bessel's equation, will be considered in more detail.
1 Modified Prufer angle associated with bounded solutions of Bessel's equation
All solutions of Bessel's equation which are finite at r = 0 possess the same Prufer angle, [PSI](r), that in the neighborhood of r = 0 satisfies the condition