A model of hyphal tip growth involving microtubule-based transport

We propose a simple model for mass transport within a fungal hypha and its subsequent growth. Inspired by the role of microtubule-transported vesicles, we embody the internal dynamics of mass inside a hypha with mutually excluding particles progressing stochastically along a growing one-dimensional lattice. The connection between long range transport of materials for growth, and the resulting extension of the hyphal tip has not previously been addressed in the modelling literature. We derive and analyse mean-field equations for the model and present a phase diagram of its steady state behaviour, which we compare to simulations. We discuss our results in the context of the filamentous fungus, Neurospora crassa.Comment: 5 pages, 5 figure

Techniques for assessing the performance of a landscape-based sediment source and transport model: sensitivity trials and physical methods

Widespread degradation of aquatic habitat and water quality has occurred since European settlement of Australia. Repairing this degradation is expensive and hence on-ground management needs to be carefully focussed. The Sediment River Network model, SedNet, used for the estimation of the sources and transport of sediment spatially and at catchment scales, potentially provides a useful tool to assist land managers in focusing this work. The complete model, whilst broadly applied has not been systematically tested to assess its accuracy or sensitivity to its various model components. The aim of this paper is to propose a framework for such testing. Results from the work will be used to prioritise data acquisition, and improve the structure and parameterisation of the model where necessary. The research is also particularly relevant for shifting application of the model from continental to catchment scales. The testing will comprise two components - sensitivity assessment and accuracy assessment. This paper provides a brief introduction to the SedNet model and a framework for assessing the model. Examples of sensitivity assessment and accuracy assessment are provided and discussed

Investment prioritization based on broadscale spatial budgeting to meet downstream targets for suspended sediment loads

On the basis of a spatially distributed sediment budget across a large basin, costs of achieving certain sediment reduction targets in rivers were estimated. A range of investment prioritization scenarios were tested to identify the most cost-effective strategy to control suspended sediment loads. The scenarios were based on successively introducing more information from the sediment budget. The relationship between spatial heterogeneity of contributing sediment sources on cost effectiveness of prioritization was investigated. Cost effectiveness was shown to increase with sequential introduction of sediment budget terms. The solution which most decreased cost was achieved by including spatial information linking sediment sources to the downstream target location. This solution produced cost curves similar to those derived using a genetic algorithm formulation. Appropriate investment prioritization can offer large cost savings because the magnitude of the costs can vary by several times depending on what type of erosion source or sediment delivery mechanism is targeted. Target settings which only consider the erosion source rates can potentially result in spending more money than random management intervention for achieving downstream targets. Coherent spatial patterns of contributing sediment emerge from the budget model and its many inputs. The heterogeneity in these patterns can be summarized in a succinct form. This summary was shown to be consistent with the cost difference between local and regional prioritization for three of four test catchments. To explain the effect for the fourth catchment, the detail of the individual sediment sources needed to be taken into account

E-learning as a tool for knowledge transfer through traditional and independent study at two UK higher educational institutes: a case study

Much has been made of the advances in computer aided learning activities. Websites, virtual campus, the increased use of Web CT and chat rooms and further advances in the use of WebCT are becoming more commonplace in UK universities. This paper looks for ways of changing higher education students’ perception of the usefulness of recommended internet web sites for learning purposes, with the intention of increasing the usage rate of recommended module web-sites. The change could represent an adaptation of the existing, well-known technology to change students’ perception regarding its potentially formative role. Subsequently, the outcomes from this preliminary research could be used in order to enhance the quality of the Internet use for teaching and learning purposes

Environmentally-acquired bacteria influence microbial diversity and natural innate immune responses at gut surfaces

Background: Early microbial colonization of the gut reduces the incidence of infectious, inflammatory and autoimmune diseases. Recent population studies reveal that childhood hygiene is a significant risk factor for development of inflammatory bowel disease, thereby reinforcing the hygiene hypothesis and the potential importance of microbial colonization during early life. The extent to which early-life environment impacts on microbial diversity of the adult gut and subsequent immune processes has not been comprehensively investigated thus far. We addressed this important question using the pig as a model to evaluate the impact of early-life environment on microbe/host gut interactions during development. Results: Genetically-related piglets were housed in either indoor or outdoor environments or in experimental isolators. Analysis of over 3,000 16S rRNA sequences revealed major differences in mucosa-adherent microbial diversity in the ileum of adult pigs attributable to differences in early-life environment. Pigs housed in a natural outdoor environment showed a dominance of Firmicutes, in particular Lactobacillus, whereas animals housed in a hygienic indoor environment had reduced Lactobacillus and higher numbers of potentially pathogenic phylotypes. Our analysis revealed a strong negative correlation between the abundance of Firmicutes and pathogenic bacterial populations in the gut. These differences were exaggerated in animals housed in experimental isolators. Affymetrix microarray technology and Real-time Polymerase Chain Reaction revealed significant gut-specific gene responses also related to early-life environment. Significantly, indoor-housed pigs displayed increased expression of Type 1 interferon genes, Major Histocompatibility Complex class I and several chemokines. Gene Ontology and pathway analysis further confirmed these results. Conclusion: Early-life environment significantly affects both microbial composition of the adult gut and mucosal innate immune function. We observed that a microbiota dominated by lactobacilli may function to maintain mucosal immune homeostasis and limit pathogen colonization

Conceptual learning : the priority for higher education

The common sense notion of learning as the all-pervasive acquisition of new behaviour and knowledge, made vivid by experience, is an incomplete characterisation, because it assumes that the learning of behaviour and the learning of knowledge are indistinguishable, and that acquisition constitutes learning without reference to transfer. A psychological level of analysis is used to argue that conceptual learning should have priority in higher education

Hierarchically coupled ultradian oscillators generating robust circadian rhythms

Ensembles of mutually coupled ultradian cellular oscillators have been proposed by a number of authors to explain the generation of circadian rhythms in mammals. Most mathematical models using many coupled oscillators predict that the output period should vary as the square root of the number of participating units, thus being inconsistent with the well-established experimental result that ablation of substantial parts of the suprachiasmatic nuclei (SCN), the main circadian pacemaker in mammals, does not eliminate the overt circadian functions, which show no changes in the phases or periods of the rhythms. From these observations, we have developed a theoretical model that exhibits the robustness of the circadian clock to changes in the number of cells in the SCN, and that is readily adaptable to include the successful features of other known models of circadian regulation, such as the phase response curves and light resetting of the phase

UBVRIz Light Curves of 51 Type II Supernovae

We present a compilation of UBV RIz light curves of 51 type II supernovae discovered during the course of four different surveys during 1986 to 2003: the Cerro Tololo Supernova Survey, the Calan/Tololo Supernova Program (C&T), the Supernova Optical and Infrared Survey (SOIRS), and the Carnegie Type II Supernova Survey (CATS). The photometry is based on template-subtracted images to eliminate any potential host galaxy light contamination, and calibrated from foreground stars. This work presents these photometric data, studies the color evolution using different bands, and explores the relation between the magnitude at maximum brightness and the brightness decline parameter (s) from maximum light through the end of the recombination phase. This parameter is found to be shallower for redder bands and appears to have the best correlation in the B band. In addition, it also correlates with the plateau duration, being thus shorter (longer) for larger (smaller) s values.Comment: 110 pages, 9 Figures, 6 Tables, accepted in A