Quantum information science relies on superpositions of quantum states with a definite phase relation, but such superpositions are inherently fragile against interactions with their environment. Fortunately, if some kind of common property bounds these interactions, it is possible, though by no means easy in a practical setting, to come up with states that are essentially immune to their enviro...

1. MOTIVATION Grammar inference is a challenging problem for statistical approaches to natural-language processing. The most successful grammar inference techniques involve stochastic finite-state language models such as hidden Markov models (HMMs) [1]. However, finite-state language models fail to represent the hierarchical structure of natural language. Therefore, stochastic versions of gramm...

our patient differed in one intriguing aspect: she had an associated SS. This association raises several issues. First, marked chronic immune activation (Table 1) and antibodies to histones with no anti-CD4 antibodies suggest CD4þ apoptosis as a possible pathogenetic mechanism. This is reminiscent of AIDS [5, 6], but no retrovirus could be found. Second, at least three viruses (HIV, HTLV-1 and ...

This paper considers the ad hoc development of ecotourism at Ostional, Costa Rica, and the potential bene®ts for the local community in the absence of government planning or intervention. In 1995, only four percent of Ostional households identi®ed tourism as a source of income; however, this was substantial in comparison to that derived from other economic activities. While most Ostional reside...