Oxygen uptake and denitrification in soil aggregates

A mathematical model of oxygen uptake by bacteria in agricultural soils is presented with the goal of predicting anaerobic regions in which denitrification occurs. In an environment with a plentiful supply of oxygen, microorganisms consume oxygen through normal respiration. When the local oxygen concentration falls below a threshold level, denitrification may take place leading to the release of nitrous oxide, a potent agent for global warming. A two-dimensional model is presented in which one or more circular soil aggregates are located at a distance below the ground-level at which the prevailing oxygen concentration is prescribed. The level of denitrification is estimated by computing the area of any anaerobic cores which may develop in the interior of the aggregates. The oxygen distribution throughout the model soil is calculated first for an aggregated soil for which the ratio of the oxygen diffusivities between an aggregate and its surround is small via an asymptotic analysis. Second, the case of a non-aggregated soil featuring one or more microbial hotspots, for which the diffusion ratio is arbitrary, is examined numerically using the boundary-element method. Calculations with multiple aggregates demonstrate a sheltering effect whereby some aggregates receive less oxygen than their neighbours. In the case of an infinite regular triangular network representing an aggregated soil, it is shown that there is an optimal inter-aggregate spacing which minimises the total anaerobic core area

What Do We Really Know about Cognitive Inhibition? Task Demands and Inhibitory Effects across a Rang

Our study explores inhibitory control across a range of widely recognised memory and behavioural tasks. Eighty-seven never-depressed participants completed a series of tasks designed to measure inhibitory control in memory and behaviour. Specifically, a variant of the selective retrieval-practice and the Think/No-Think tasks were employed as measures of memory inhibition. The Stroop-Colour Naming and the Go/No-Go tasks were used as measures of behavioural inhibition. Participants completed all 4 tasks. Task presentation order was counterbalanced across 3 separate testing sessions for each participant. Standard inhibitory forgetting effects emerged on both memory tasks but the extent of forgetting across these tasks was not correlated. Furthermore, there was no relationship between memory inhibition tasks and either of the main behavioural inhibition measures. At a time when cognitive inhibition continues to gain acceptance as an explanatory mechanism, our study raises fundamental questions about what we actually know about inhibition and how it is affected by the processing demands of particular inhibitory tasks

Disseminated cryptococcosis initially presenting as cellulitis in a patient suffering from nephrotic syndrome

<p>Abstract</p> <p>Background</p> <p>Cryptococcosis is considered as an opportunistic infection because it mainly occurs in immunosuppressed hosts. C. neoformans is usually acquired by the respiratory route and then may disseminate hematogenously to other places, such as meninges, bone and skin. Cutaneous involvement is a rare but important feature of disseminated cryptococcosis with a poor outcome if misdiagnosis. We reported the first case of patients with nephrotic syndrome suffering from disseminated cryptococcosis initially presented as cellulitis.</p> <p>Case presentation</p> <p>A 34-year-old man developed severe cellulitis on his both lower extremities without any preceding injury and allergies. The patient had been treated with systemic corticosteroids nearly one year for nephrotic syndrome. According to the outcome of blood culture, the wound area was interpreted as bacterial cellulitis at first. However, the antimicrobial treatment made no response and the skin biopsy revealed the presence of Cryptococcus neoformans, which was subsequently confirmed by microbiological culture. Though the initiation of therapy with fluconazole 400 mg per day was immediately adopted, the patient’s conditions suddenly plummeted and he died in the end.</p> <p>Conclusion</p> <p>Since the poor outcome of disseminated cryptococcosis if unrecognized and untreated in time, it should be investigated rigorously as a differential diagnosis in patients with nephrotic syndrome suffering from cutaneous diseases.</p