Autonomous search for a diffusive source in an unknown environment

The paper presents an approach to olfactory search for a diffusive emitting source of tracer (e.g. aerosol, gas) in an environment with unknown map of randomly placed and shaped obstacles. The measurements of tracer concentration are sporadic, noisy and without directional information. The search domain is discretised and modelled by a finite two-dimensional lattice. The links is the lattice represent the traversable paths for emitted particles and for the searcher. A missing link in the lattice indicates a blocked paths, due to the walls or obstacles. The searcher must simultaneously estimate the source parameters, the map of the search domain and its own location within the map. The solution is formulated in the sequential Bayesian framework and implemented as a Rao-Blackwellised particle filter with information-driven motion control. The numerical results demonstrate the concept and its performance.Comment: 11 pages, 7 figure

Integration of organic poultry in whole farm systems: manure nutrient budgets

This report was presented at the UK Organic Research 2002 Conference. The aim of this project was to examine how rotations incorporating organic poultry use the cycling of nutrients between soil, crops and birds. Poultry studies have measured nutrient values of manure in slow growing meat birds at about day 81 when fed typical broiler rations versus “Label Rouge” rations. Nutrient (N, P, K) balances were constructed to assess the viability of integrating poultry production within a theoretical organic rotation. The readilyplant- available nitrogen in manure from Ross 308 birds fed either presumed non-limiting rations or Label Rouge rations was within the range reported for intensive broilers. For ISA 657 birds, the manure readily-plant-available nitrogen was similar to the mean value reported for broilers, when fed presumed non limiting rations, but towards the lower range when fed Label Rouge rations. As breed growth and feed intakes differ it is suggested that to optimise the utilisation of nutrients, the nutrient content of table bird manures should be checked prior to land application. The nutrient budgets were similar for N and P regardless of the length of rotation or form of poultry production. On average, there was a surplus of 85 kg/ha N over all the scenarios. There tended to be a deficit of K in all scenarios (average: 10 kg/ha)

The Budget will give clues as to how far English devolution marks a radical change for local government

For all the focus on Europe, it could be devolution that is the critical constitutional change of our era. Ahead of tomorrow’s Budget announcement, Andrew Walker looks in depth at the prospects for radical change in local government

Agricultural transformation and the politics of hydrology in Northern Thailand: a case study of water supply and demand

Water resource tensions in upland areas of northern Thailand are often attributed to reductions in water supply caused by forest clearing. This paper argues that the hydrological evidence for such reductions in supply is very weak and that, rather, the key hydrological issue in upland catchments is a significant increase in water demand, especially during the dry season. The arguments are illustrated with a detailed examination of the Mae Uam catchment, located in Chiang Mai province, where the development of dry-season soybean cultivation appears to have approached the hydrological limit of the catchment, and even exceeded this limit in drier years. The paper argues that a shift in focus from water supply to water demand has fundamentally important political implications. As long as the focus of public debate is on water supply, the regulatory focus will be on those resident in the forested upland areas that are seen as being crucial in securing downstream flows. But if the water management focus is shifted to water demand, then regulatory attention must shift to the diverse sources of that demand that exist throughout the hydrological system