Braids and their monotone clones

In this paper we investigate properties of the monotone clones of certain ordered sets known asbraids. This class of ordered sets arose naturally in the study of how the clone of monotone functions on an ordered set could satisfy, or fail to satisfy, Mal'cev conditions. One version of the main result can be stated as follows. IfB is a finite braid with reachr(B)>2 (defined in the text), then the only idempotent order-preserving functionsfBⁿB are then projections. It then follows, for example, that no algebra of monotone functions on a finite braidB withr(B)>2 generates a congruence-modular variety.Dedicated to Bjarni Jónsson on the occasion of his 70th birthday.Presented by G. McNulty.This research was supported by ARC grant A68831070 (Davey) and in part by NSF grant 87-03540 (Nation) and 89-04014 (McKenzie).     

Low group velocity traveling wave tube amplifiers

We report experimental and theoretical results from research into high power X-band traveling wave tube amplifiers designed to eliminate sidebands caused by reflections from the output of such structures. These amplifiers have a low energy velocity, such that the time it takes a wave to be reflected from the output to the input is of the order of, or greater than, the electron beam pulse duration. The elimination of sidebands and the effects of reflections is achieved by this transit time isolation, The bandwidth of the output spectrum is limited by the low pass-band of the periodic structures. Such amplifiers have been operated at power levels of up to 160 MW at 9 GHz for 50 ns pulse durations