We study a class of planar billiards having the remarkable property that their phase space consists up to a set of zero measure of two invariant sets formed by orbits moving in opposite directions. The tables of these billiards are tubular neighborhoods of differentiable Jordan curves that are unions of finitely many segments and arcs of circles. We prove that under proper conditions on the seg...

This paper tracks the rise in the percentage of employees who have never become union members (‘nevermembers’) since the early 1980s and shows that it is the reduced likelihood of ever becoming a member rather than the haemorrhaging of existing members which is behind the decline in overall union membership in Britain. We estimate the determinants of ‘never-membership’ and consider how much of ...

The need for automating behavioral observations and the evolution of systems developed for that purpose is outlined. Video tracking systems enable researchers to study behavior in a reliable and consistent way and over longer time periods than if they were using manual recording. To overcome limitations of currently available systems, we have designed EthoVision, an integrated system for automa...

Today there are thousands of kilometers of freight trackage in the United States over which two—and often more—railways operate regularly and safely. Tracks in Argentina, Canada, Chile, and Japan also have multiple users. Thus there is no question that rail infrastructure can be separated from operations. The question is when it should be, and what are the costs, benefits, and challenges of doi...