THIS paper concerns maximal subgroups of symmetric groups on infinite, usually countable, sets. Our main aim is to give examples of maximal subgroups which could claim to be almost stabilisers of familiar combinatorial structures. We emphasise that maximal subgroup always means maximal proper subgroup. Throughout this paper, Cl will denote an infinite set, usually countable. The power set of Q ...

The full data set from an ultrasonic array comprises the time-domain signals from every possible transmitter-receiver pair in the array. The possibility of experimentally obtaining the full data set that is afforded by some new array controller systems massively increases the potential of ultrasonic arrays. Firstly, any conventional array imaging procedure (e.g. B-scans, angular scans, dynamic ...