14,662 research outputs found
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
Recommended from our members
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
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
Contaminants in Unionid Mussels from the Confluence of the Mississippi and Illinois Rivers
Unionid mussels were collected from three mussel beds near the confluence of the Mississippi and Illinois rivers in 2003 to evaluate concentrations of selected elements and organic compounds in three abundant species and to preliminarily investigate the relative contribution of these waterways to observed contaminant burdens. Copper (Cu), selenium (Se), and zinc (Zn) concentrations were higher and lead (Pb) concentrations were lower in Amblema plicata collected downstream of the confluence than in those collected upstream. Mean concentrations of nickel (Ni), total mercury (Hg), methylmercury (MeHg), Pb, and Zn varied by species. Concentrations of cadmium (Cd) decreased with age in A. plicata from two of three sites. Tissue concentrations of some elements, e.g., arsenic (As), Cd, Cu, Pb, Se, and Zn, were similar to or higher than those previously reported for unionid mussels from areas of contaminated sediment. Concentrations of Cd, Cu, and Zn in A. plicata were comparable to those collected from the Mississippi River approximately 450 and 900 km upstream from our study sites (Naimo et al. 1992). Although total Hg concentrations we observed were an order of magnitude lower than in that study, MeHg concentrations were above those associated with reductions in soft tissue mass in a study of Elliptio complanata (Salazar et al. 1995). A number of polychlorinated biphenyl (PCB) congeners were detected in A. plicata tissues, with 85% of detections occurring in mussels from downstream of the confluence. Concentrations of individual PCB congeners were ???33 ng/g ww and the maximum summed PCB congener concentration was 100.2 ng/g ww. Although few persistent pesticides were detected, -hexachlorocyclohexane (HCH) was detected in each of the species collected from below the confluence of the two rivers, and in A. plicata collected above it on both the Mississippi and Illinois rivers, at a maximum concentration of 103.5 ng/g ww. Aldrin, ??-HCH and dichlorodiphenyltrichloroethane (DDT) were detected in few of the specimens collected. The findings of this preliminary investigation suggest that unionid mussels from near the confluence of the Mississippi and Illinois rivers may be at risk of negative health effects of elevated exposure to certain environmental contaminants. Studies examining the health and productivity of unionid mussels from this area appear warranted.published or submitted for publicationis peer reviewe
Anisotropic Magneto-Thermopower: the Contribution of Interband Relaxation
Spin injection in metallic normal/ferromagnetic junctions is investigated
taking into account the anisotropic magnetoresistance (AMR) occurring in the
ferromagnetic layer. It is shown, on the basis of a generalized two channel
model, that there is an interface resistance contribution due to anisotropic
scattering, beyond spin accumulation and giant magnetoresistance (GMR). The
corresponding expression of the thermopower is derived and compared with the
expression for the thermopower produced by the GMR. First measurements of
anisotropic magnetothermopower are presented in electrodeposited Ni nanowires
contacted with Ni, Au and Cu. The results of this study show that while the
giant magnetoresistance and corresponding thermopower demonstrates the role of
spin-flip scattering, the observed anisotropic magnetothermopower indicates
interband s-d relaxation mechanisms.Comment: 20 pages, 4 figure
Condition Reporting and Resolution
This procedure facilitates a safety conscious work environment by providing a mechanism for employees to make management aware of existing and potential conditions. This procedure establishes the responsibilities and process to be used to ensure that conditions related to, but not limited to, the environment, safety, health, waste isolation, operations, security, or quality of items and services associated with Office of Civilian Radioactive Waste Management (OCRWM) work activities are promptly identified, controlled, evaluated, and corrected as soon as practical. This procedure describes the process flow, controls, interfaces, and requirements for condition identification and resolution. This includes adverse conditions as well as opportunities for improvement and suggestions
- …