Propagation Failure in Excitable Media

We study a mechanism of pulse propagation failure in excitable media where stable traveling pulse solutions appear via a subcritical pitchfork bifurcation. The bifurcation plays a key role in that mechanism. Small perturbations, externally applied or from internal instabilities, may cause pulse propagation failure (wave breakup) provided the system is close enough to the bifurcation point. We derive relations showing how the pitchfork bifurcation is unfolded by weak curvature or advective field perturbations and use them to demonstrate wave breakup. We suggest that the recent observations of wave breakup in the Belousov-Zhabotinsky reaction induced either by an electric field or a transverse instability are manifestations of this mechanism.Comment: 8 pages. Aric Hagberg: http://cnls.lanl.gov/~aric; Ehud Meron:http://www.bgu.ac.il/BIDR/research/staff/meron.htm

Current developments in MRI for assessing rodent models of multiple sclerosis

MRI is a key radiological imaging technique that plays an important role in the diagnosis and characterization of heterogeneous multiple sclerosis (MS) lesions. Various MRI methodologies such as conventional T 1/T 2 contrast, contrast agent enhancement, diffusion-weighted imaging, magnetization transfer imaging and susceptibility weighted imaging have been developed to determine the severity of MS pathology, including demyelination/remyelination and brain connectivity impairment from axonal loss. The broad spectrum of MS pathology manifests in diverse patient MRI presentations and affects the accuracy of patient diagnosis. To study specific pathological aspects of the disease, rodent models such as experimental autoimmune encephalomyelitis, virus-induced and toxin-induced demyelination have been developed. This review aims to present key developments in MRI methodology for better characterization of rodent models of MS

Temporal proteomic profiling of postnatal human cortical development.

Healthy cortical development depends on precise regulation of transcription and translation. However, the dynamics of how proteins are expressed, function and interact across postnatal human cortical development remain poorly understood. We surveyed the proteomic landscape of 69 dorsolateral prefrontal cortex samples across seven stages of postnatal life and integrated these data with paired transcriptome data. We detected 911 proteins by liquid chromatography-mass spectrometry, and 83 were significantly associated with postnatal age (FDR < 5%). Network analysis identified three modules of co-regulated proteins correlated with age, including two modules with increasing expression involved in gliogenesis and NADH metabolism and one neurogenesis-related module with decreasing expression throughout development. Integration with paired transcriptome data revealed that these age-related protein modules overlapped with RNA modules and displayed collinear developmental trajectories. Importantly, RNA expression profiles that are dynamically regulated throughout cortical development display tighter correlations with their respective translated protein expression compared to those RNA profiles that are not. Moreover, the correspondence between RNA and protein expression significantly decreases as a function of cortical aging, especially for genes involved in myelination and cytoskeleton organization. Finally, we used this data resource to elucidate the functional impact of genetic risk loci for intellectual disability, converging on gliogenesis, myelination and ATP-metabolism modules in the proteome and transcriptome. We share all data in an interactive, searchable companion website. Collectively, our findings reveal dynamic aspects of protein regulation and provide new insights into brain development, maturation, and disease

Priority water research questions for South Africa developed through participatory processes

This paper describes a collaborative process of identifying and prioritising current and future water research questions from a wide range of water  specialists within South Africa. Over 1 600 questions were collected,  reduced in number and prioritised by specialists working in water research and practice. A total of 59 questions were finally proposed as an outcome of the study and are categorised under the themes of change, data, ecosystems, governance, innovation and resources. The questions range in scale, challenge and urgency, and are also aligned with prevailing  paradigms in water research. The majority of the questions dealt with relatively short- to medium-term research requirements and most focused on immediate issues such as water supply, service delivery and technical solutions. Formulations of long-term research questions were sparse,  partly because some of the principles and methods used in this study were difficult to apply in the South African context, and also because researchers are influenced by addressing what are believed to be the more immediate, short-term water-related challenges in South Africa. This is the first  initiative of its kind to produce a comprehensive and inclusive list of research priorities for water in South Africa.Keywords: research, questions, collaboration, prioritisation, South Afric

Misfit-dislocation generation by dissociated dislocations in quantum-well heterostructures

The mechanisms whereby 60° misfit dislocations are generated from dissociated threading dislocations in quantum-well heterostructures are considered. The two partial dislocations experience different misfit stresses, resulting in each partial having a different critical thickness. As a consequence, a number of different dislocation configurations are predicted, including the possibility of producing stacking faults of infinite width. © 1994 The American Physical Societ

The utility of hand-held mobile spirometer technology in a resource-constrained setting

CITATION: Du Plessis, E., et al. 2019. The utility of hand-held mobile spirometer technology in a resource-constrained setting. South African Medical Journal, 109(4):219-222, doi:10.7196/SAMJ.2019.v109i4.13845.The original publication is available at http://www.samj.org.zaBackground. Mobile phone-linked spirometry technology has been designed specifically for evaluating lung function at primary care level. The Air-Smart Spirometer is the first mobile spirometer accepted in Europe for the screening of patients with chronic respiratory diseases. Objectives. To prospectively assess the accuracy of the device in measuring forced expiratory volume in the first second (FEV1) and forced vital capacity (FVC) in a South African population, and to investigate the ability of the device to detect obstructive ventilatory impairment. Methods. A total of 200 participants were randomly assigned to perform spirometry with either the mobile spirometer connected to a smartphone or the desktop spirometer first, followed by the other. The FEV1/FVC ratio as well as the absolute FEV1 and FVC measurements were compared, using each participant as their own control. A Pearson correlation and Bland-Altman analysis were performed to measure the agreement between the two devices. We defined obstructive ventilatory impairment as FEV1/FVC <0.7 measured by desktop spirometry in order to calculate the sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of the Air-Smart Spirometer. Results. There was a strong correlation between the absolute FEV1 and FVC values and FEV1/FVC ratio measured with the mobile Air-Smart Spirometer and more conventional pulmonary function testing, with r=0.951, r=0.955 and r=0.898, respectively. The Air-Smart Spirometer had a sensitivity of 97.6%, specificity of 74.4%, PPV of 73.0% and NPV of 97.8% for obstructive ventilatory impairment. Conclusions. The mobile Air-Smart Spirometer compared well with conventional spirometry, making it an attractive and potentially affordable tool for screening purposes in a primary care setting. Moreover, it had a high sensitivity and NPV for obstructive ventilatory impairment.http://www.samj.org.za/index.php/samj/article/view/12582Publisher's versio

Sequence-based prediction for vaccine strain selection and identification of antigenic variability in foot-and-mouth disease virus

Identifying when past exposure to an infectious disease will protect against newly emerging strains is central to understanding the spread and the severity of epidemics, but the prediction of viral cross-protection remains an important unsolved problem. For foot-and-mouth disease virus (FMDV) research in particular, improved methods for predicting this cross-protection are critical for predicting the severity of outbreaks within endemic settings where multiple serotypes and subtypes commonly co-circulate, as well as for deciding whether appropriate vaccine(s) exist and how much they could mitigate the effects of any outbreak. To identify antigenic relationships and their predictors, we used linear mixed effects models to account for variation in pairwise cross-neutralization titres using only viral sequences and structural data. We identified those substitutions in surface-exposed structural proteins that are correlates of loss of cross-reactivity. These allowed prediction of both the best vaccine match for any single virus and the breadth of coverage of new vaccine candidates from their capsid sequences as effectively as or better than serology. Sub-sequences chosen by the model-building process all contained sites that are known epitopes on other serotypes. Furthermore, for the SAT1 serotype, for which epitopes have never previously been identified, we provide strong evidence - by controlling for phylogenetic structure - for the presence of three epitopes across a panel of viruses and quantify the relative significance of some individual residues in determining cross-neutralization. Identifying and quantifying the importance of sites that predict viral strain cross-reactivity not just for single viruses but across entire serotypes can help in the design of vaccines with better targeting and broader coverage. These techniques can be generalized to any infectious agents where cross-reactivity assays have been carried out. As the parameterization uses pre-existing datasets, this approach quickly and cheaply increases both our understanding of antigenic relationships and our power to control disease

Genetic diversity of Amylostereum areolatum, the fungal symbiont of the invasive woodwasp Sirex noctilio in South Africa

Amylostereum areolatum is a wood‐decaying homobasidiomycete fungal symbiont of Sirex noctilio. Together, they cause serious damage to pine plantations in the Southern Hemisphere. The fungus reproduces asexually and is vertically transmitted by S. noctilio females, which results in extensive spread of clones. Specific A. areolatum clones are often dominant in areas invaded by the wasp. This is in contrast with the high diversity and complex invasion pattern of S. noctilio in most of these regions. In South Africa, for example, nuclear and mitochondrial ribosomal loci and vegetative compatibility group (VCG) markers on a small number of isolates have shown that only one genotype is present in the country. The aim of this study was to develop microsatellite markers for A. areolatum and determine the genetic diversity and structure of a relatively large collection of isolates of the fungus in South Africa. From five sequenced A. areolatum genomes, a total of 233 microsatellite primer pairs were designed, of which 57 were polymorphic among the genomes. Eleven of these polymorphic markers were then used in a population genetics study including 55 South African isolates. In a surprising manner, nine multilocus genotypes were found among these isolates, and with no population structure among different regions across South Africa. The single VCG previously identified for isolates from the country clearly do not correspond to a clone. The detected A. areolatum variation has relevance for the biology of the Sirex‐Amylostereum symbiosis, its introduction history into South Africa and its management through biocontrol. The microsatellite primers and data emerging from them also provide powerful tools for the study of A. areolatum populations in other parts of the world.Members of the Tree Protection Co-o perative Programme (TPCP) and the National Research Foundation of South Africa.http://wileyonlinelibrary.com/journal/efp2019-12-01hj2019BiochemistryForestry and Agricultural Biotechnology Institute (FABI)Genetic

Risky Bodies in the Plasma Bioeconomy: A Feminist Analysis

© The Author(s) 2015 In 2003 the UK National Blood Service introduced a policy of ‘male donor preference’ which involved women’s plasma being discarded following blood collection. The policy was based on the view that data relating to the incidence of Transfusion-Related Acute Lung Injury (TRALI) was linked to transfusion with women’s plasma. While appearing to treat female donors as equal to male donors, exclusion criteria operate after donation at the stage of processing blood, thus perpetuating myths of universality even though only certain ‘extractions’ from women are retained for use in transfusion. Many women in the UK receive a plasma-derived product called Anti-D immunoglobulin which is manufactured from pooled male plasma. This article examines ways in which gender has significance for understanding blood relations, and how the blood economy is gendered. In our study of relations between blood donors and recipients, we explore how gendered bodies are produced through the discursive and material practices within blood services. We examine both how donation policies and the manufacturing and use of blood products produces gendered blood relations