... Bruce MacA Thomas 11 February 1999 Introduction In this discussion document, the antenna principles underpinning some of the concepts discussed in Ref 1 for the LF-SKA are extended to illustrate the potential difficulty of achieving constant collecting area, and hence the practical realisation of the "magic-carpet" concept. Applications to the "randomised" antenna-element approach to array-station design, and the trade-offs that need to be considered, are briefly discussed. ...

metrologia The leap second: its history and possible future R. A. Nelson, D. D. McCarthy , S. Malys, J. Levine, B. Guinot, H. F. Fliegel , R. L. Beard and T. R. Bartholome w Abstract. This paper reviews the theoretica l motivatio n for the leap second in the context of the historica l evolutio n of time measurement . Th e periodic insertio n of a leap second step into th e scale of Coordinate d Universal Time (UTC) necessitates frequent changes in comple x timekeepin g systems an d is currentl y th e