10,693 research outputs found
The constant magnetic field of xi 1 CMa: geometry or slow rotation?
We report recent observations of the sharp-lined magnetic beta Cep pulsator
xi 1 CMa (= HD 46328). The longitudinal magnetic field of this star is detected
consistently, but it is not observed to vary strongly, during nearly 5 years of
observation. In this poster we evaluate whether the nearly constant
longitudinal field is due to intrinsically slow rotation, or rather if the
stellar or magnetic geometry is responsible
Emergent behaviour in a chlorophenol-mineralising three-tiered microbial `food web'
Anaerobic digestion enables the water industry to treat wastewater as a
resource for generating energy and recovering valuable by-products. The
complexity of the anaerobic digestion process has motivated the development of
complex models. However, this complexity makes it intractable to pin-point
stability and emergent behaviour. Here, the widely used Anaerobic Digestion
Model No. 1 (ADM1) has been reduced to its very backbone, a syntrophic
two-tiered microbial food chain and a slightly more complex three-tiered
microbial food web, with their stability analysed as function of the inflowing
substrate concentration and dilution rate. Parameterised for phenol and
chlorophenol degradation, steady-states were always stable and non-oscillatory.
Low input concentrations of chlorophenol were sufficient to maintain
chlorophenol- and phenol-degrading populations but resulted in poor conversion
and a hydrogen flux that was too low to sustain hydrogenotrophic methanogens.
The addition of hydrogen and phenol boosted the populations of all three
organisms, resulting in the counterintuitive phenomena that (i) the phenol
degraders were stimulated by adding hydrogen, even though hydrogen inhibits
phenol degradation, and (ii) the dechlorinators indirectly benefitted from
measures that stimulated their hydrogenotrophic competitors; both phenomena
hint at emergent behaviour.Comment: 19 pages, 8 figure
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Modelling fixed plant and algal dynamics in rivers: an application to the River Frome
The development of eutrophication in river systems is poorly understood given the complex relationship between fixed plants, algae, hydrodynamics, water chemistry and solar radiation. However there is a pressing need to understand the relationship between the ecological status of
rivers and the controlling environmental factors to help the reasoned implementation of the Water Framework Directive and Catchment Sensitive Farming in the UK. This research aims to create a dynamic, process-based, mathematical in-stream model to simulate the growth and competition of different vegetation types (macrophytes, phytoplankton and benthic algae) in rivers. The model,
applied to the River Frome (Dorset, UK), captured well the seasonality of simulated vegetation types (suspended algae, macrophytes, epiphytes, sediment biofilm). Macrophyte results showed that local knowledge is important for explaining unusual changes in biomass. Fixed algae simulations indicated the need for the more detailed representation of various herbivorous grazer groups,
however this would increase the model complexity, the number of model parameters and the required observation data to better define the model. The model results also highlighted that simulating only phytoplankton is insufficient in river systems, because the majority of the suspended algae have benthic origin in short retention time rivers. Therefore, there is a need for modelling tools that link the benthic and free-floating habitats
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