A system, method, program product and service for navigating and displaying hierarchically structured data. The balloon catheter has a plurality of longitudinally-extending, circumferentially spaced apart slots formed in it to define a plurality of elongate members between the slots. The storage controller is scalable independently of the storage system it controls. The secondary oxide comprises praseodymium or ytterbium, and another cation selected from the group consisting of the rare earth elements, yttrium, and scandium. A mono signal encoding unit encodes the mono signal. The cleaning etching rates are extremely high.