6,920 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
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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
Ground Anchors Stabilize Highway Bridge Abutments
Calgary\u27s Glenmore Causeway, constructed in 1962 across the Elbow River, consists of an earthfill embankment with a waterway spanned by a 43 m long bridge, the abutments of which are supported on spread footings founded in the embankment fill. Between the 25 m deep sand and gravel embankment fill and the sub-horizontal bedrock surface is a compressible clay layer up to 5 m thick. To improve abutment stability during peak river flows, 126 post-tensioned Dywidag ground anchors up to 60 m long were installed through the concrete slabs armouring the abutment slopes. Twenty-two anchors were terminated in the embankment fill and the rest were grouted into bedrock. After a series of lift-off tests and anchor retensioning to compensate for ground consolidation, a procedure for predicting the rate of anchor load relaxation was developed. It was concluded the anchors are performing satisfactorily although periodic re-tensioning will be required
Are We Ovary-Acting? All Visuospatial Abilities May Not Be Equally Affected Throughout the Menstrual Cycle.
Are we ovary-acting? All visuospatial abilities may not be equally affected throughout the menstrual cycle.
Department of Psychological Sciences & Neuroscience, Belmont University, Nashville, TN
Visuospatial skills pertain to the ability to conceptualize and comprehend visual representations of objects and the spatial relationships among objects. They are integral for the proper functioning of other cognitive systems such as memory, attention, and reasoning (Kaufman, 2007). Sex hormones are one of many factors reported to affect visuospatial processing, with estrogen specially being associated with poor performance on visuospatial tasks in females (Hausmann, 2000). The current study investigated performance differences on three visuospatial domains (working memory, mental imagery, and spatial reasoning) in relation to estrogen modulations associated with femalesā menstrual cycles. It was hypothesized that performance would domain specific, rather than the widespread effects suggested in the literature. Spatial reasoning performance is expected to be lowest in the early luteal phase (high estrogen) and highest in the early follicular phase (low estrogen), with no performance differences expected for mental rotation and corsi block tasks. In the current study, participants completed a weekly visuospatial battery, once a week for 5 weeks, including three tasks (corsi block, mental rotation, and spatial reasoning), self-reports of menstrual cycle, and salivary samples. Pilot data from 33 females demonstrated highest performance during estrogen-low phases (early follicular) compared to lower performance during estrogen-high phases on the spatial reasoning task only. No cycle modulations were revealed on the other visuospatial domains of working memory and mental rotation. The current study aimed to increase studied sample size and compliment self-reports of cycle with tangible salivary estrogen biomarkers. Data collection is ongoing, and the findings will be reported at the conference. These findings address a void in the literature in terms of female-centric research and over-generalization of previous findings. This may help better elucidate true effects of modulating estrogen levels over the course of a menstrual cycle on visuospatial skills, demonstrating domain-specific effects rather than erroneous widespread sequalae.
Keywords: estrogen, spatial reasoning, working memory, mental rotation, sex hormones, biomarker
Investigating the origin of cyclical wind variability in hot, massive stars - II. Hydrodynamical simulations of co-rotating interaction regions using realistic spot parameters for the O giant Persei
OB stars exhibit various types of spectral variability historically
associated with wind structures, including the apparently ubiquitous discrete
absorption components (DACs). These features have been proposed to be caused
either by magnetic fields or non-radial pulsations. In this second paper of
this series, we revisit the canonical phenomenological hydrodynamical modelling
used to explain the formation of DACs by taking into account modern
observations and more realistic theoretical predictions. Using constraints on
putative bright spots located on the surface of the O giant Persei
derived from high precision space-based broadband optical photometry obtained
with the Microvariability and Oscillations of STars (MOST) space telescope, we
generate two-dimensional hydrodynamical simulations of co-rotating interaction
regions in its wind. We then compute synthetic ultraviolet (UV) resonance line
profiles using Sobolev Exact Integration and compare them with historical
timeseries obtained by the International Ultraviolet Explorer (IUE) to evaluate
if the observed behaviour of Persei's DACs is reproduced. Testing three
different models of spot size and strength, we find that the classical pattern
of variability can be successfully reproduced for two of them: the model with
the smallest spots yields absorption features that are incompatible with
observations. Furthermore, we test the effect of the radial dependence of
ionization levels on line driving, but cannot conclusively assess the
importance of this factor. In conclusion, this study self-consistently links
optical photometry and UV spectroscopy, paving the way to a better
understanding of cyclical wind variability in massive stars in the context of
the bright spot paradigm.Comment: 16 pages, 10 figures, accepted for publication by MNRA
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