Status on the Michigan‐MIT ultra‐cold polarized hydrogen jet target

Progress on the Mark‐II ultra‐cold polarized atomic hydrogen gas Jet target for the experiments NEPTUN‐A and NEPTUN at UNK is presented. We describe the performance and the present status of different components of the jet.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87525/2/698_1.pd

A market road to sustainable agriculture? Ecological agriculture, green food and organic agriculture in China

To the extent that free markets show little concern for the existence of externalities, they are unlikely to produce optimum outcomes with regard to the protection and enhancement of the natural environment. Accordingly, the increasing emphasis on markets to deliver development in China under Deng Xiaoping and his successors has the capacity to threaten the long-term environmental sustainability of that development. While there are good reasons to remain sceptical about the ability of market mechanisms to promote sustainable rural development in many respects, market reforms in China and the opening of the country to the outside world have nevertheless provided opportunities for farmers to engage in ecologically sensitive agriculture in the form of `green' food and organic farming. Given that these forms of agriculture reduce farmers' use of chemicals compared to conventional farming — chemicals which are costly to produce and environmentally degrading to use — they contribute to ensuring a more environmentally sustainable future for Chinese farming, post-WTO entry, whilst providing opportunities for farmers to enrich themselves at the same time: a `win–win' state of affairs. This will remain the case, however, only so long as the state is prepared to create and reinforce appropriate institutional arrangement

Compensatory dynamics are rare in natural ecological communities

In population ecology, there has been a fundamental controversy about the relative importance of competition-driven (density-dependent) population regulation vs. abiotic influences such as temperature and precipitation. The same issue arises at the community level; are population sizes driven primarily by changes in the abundances of cooccurring competitors (i.e., compensatory dynamics), or do most species have a common response to environmental factors? Competitive interactions have had a central place in ecological theory, dating back to Gleason, Volterra, Hutchison and MacArthur, and, more recently, Hubbell's influential unified neutral theory of biodiversity and biogeography. If competitive interactions are important in driving year-to-year fluctuations in abundance, then changes in the abundance of one species should generally be accompanied by compensatory changes in the abundances of others. Thus, one necessary consequence of strong compensatory forces is that, on average, species within communities will covary negatively. Here we use measures of community covariance to assess the prevalence of negative covariance in 41 natural communities comprising different taxa at a range of spatial scales. We found that species in natural communities tended to covary positively rather than negatively, the opposite of what would be expected if compensatory dynamics were important. These findings suggest that abiotic factors such as temperature and precipitation are more important than competitive interactions in driving year-to-year fluctuations in species abundance within communities