Period-adding bifurcations and chaos in a periodically stimulated excitable neural relaxation oscillator

The response of an excitable neuron to trains of electrical spikes is relevant to the understanding of the neural code. In this paper we study a neurobiologically motivated relaxation oscillator, with appropriately identified fast and slow coordinates, that admits an explicit mathematical analysis. An application of geometric singular perturbation theory shows the existence of an attracting invariant manifold which is used to construct the Fenichel normal form for the system. This facilitates the calculation of the response of the system to pulsatile stimulation and allows the construction of a so-called extended isochronal map. The isochronal map is shown to have a single discontinuity and be of a type that can admit three types of response: mode-locked, quasi-periodic and chaotic. The bifurcation structure of the system is seen to be extremely rich and supports period-adding bifurcations separated by windows of both chaos and periodicity. A bifurcation analysis of the isochronal map is presented in conjunction with a description of the various routes to chaos in this system

Pushing the limits of excited-state g-factor measurements

Current developments in excited-state g-factor measurements are discussed with an emphasis on cases where the experimental methodology is being extended into new regimes. The transient-field technique, the recoil in vacuum method, and moment measurements with LaBr3 detectors are discussed.This research was supported in part by the Australian Research Council grant numbers DP140102986, DP140103317 and DP70101673. B.P.M. T.J.G. and B.J.C. acknowledge the support of the Australian Government Research Training Program. Support for the Heavy Ion Accelerator Facility operations through the Australian National Collaborative Research Infrastructure Strategy (NCRIS) program is acknowledged

Conserving tropical biodiversity via market forces and spatial targeting

The recent report from the Secretariat of the Convention on Biological Diversity [(2010) Global Biodiversity Outlook 3] acknowledges that ongoing biodiversity loss necessitates swift, radical action. Protecting undisturbed lands, although vital, is clearly insufficient, and the key role of unprotected, private land owned is being increasingly recognized. Seeking to avoid common assumptions of a social planner backed by government interventions, the present work focuses on the incentives of the individual landowner. We use detailed data to show that successful conservation on private land depends on three factors: conservation effectiveness (impact on target species), private costs (especially reductions in production), and private benefits (the extent to which conservation activities provide compensation, for example, by enhancing the value of remaining production). By examining the high-profile issue of palm-oil production in a major tropical biodiversity hotspot, we show that the levels of both conservation effectiveness and private costs are inherently spatial; varying the location of conservation activities can radically change both their effectiveness and private cost implications. We also use an economic choice experiment to show that consumers’ willingness to pay for conservation-grade palm-oil products has the potential to incentivize private producers sufficiently to engage in conservation activities, supporting vulnerable International Union for Conservation of Nature Red Listed species. However, these incentives vary according to the scale and efficiency of production and the extent to which conservation is targeted to optimize its cost-effectiveness. Our integrated, interdisciplinary approach shows how strategies to harness the power of the market can usefully complement existing—and to-date insufficient—approaches to conservation

The non-motile phenotype of Salmonella hha ydgT mutants is mediated through PefI-SrgD

<p>Abstract</p> <p>Background</p> <p>Two ancestral nucleoid-associated proteins called Hha and YdgT contribute to the negative regulation of several virulence-associated genes in <it>Salmonella enterica </it>serovar Typhimurium. Our previous work showed that Hha and YdgT proteins are required for negative regulation of <it>Salmonella </it>Pathogenicity Island-2 and that <it>hha ydgT </it>double mutants are attenuated for murine infection. Interestingly, <it>hha ydgT </it>mutant bacteria exhibited a non-motile phenotype suggesting that Hha and YdgT have a role in flagellar regulation.</p> <p>Results</p> <p>In this study we show that the non-motile phenotype of <it>hha ydgT </it>mutants is due to decreased levels of the master transcriptional regulator FlhD₄C₂resulting in down-regulation of class II/III and class III flagellar promoters and lack of surface flagella on these cells. The horizontally acquired <it>pefI-srgD </it>region was found to be partially responsible for this phenotype since deletion of <it>pefI-srgD </it>in a <it>hha ydgT </it>deletion background resulted in transient restoration of class II/III and III transcription, expression of surface flagella, and motility in the quadruple mutant.</p> <p>Conclusion</p> <p>These data extend our current understanding of the mechanisms through which Hha and YdgT regulate flagellar biosynthesis and further describe how <it>S</it>. Typhimurium has integrated horizontal gene acquisitions into ancestral regulatory networks.</p

Retro-orbital oedema and transient blindness following endoscopic oesophagogastroduodenoscopy: a case report

This case report looks at the association of an endoscopic oesophagogastroduodenoscopy and the onset of retro-orbital oedema in a young female. A literature search was performed in order to find any common factors between an endoscopic investigation and retroorbital oedema. An association between increased vascular permeability secondary to alcohol abuse and retroorbital oedema has been made. The case also describes the clinical signs of retro-orbital oedema and other possible causes. A link has been made between acute reversible retroorbital oedema following endoscopic oesophagogastroduodenoscopy

Pushing the limits of excited-state gg-factor measurements

Current developments in excited-state $g$-factor measurements are discussed with an emphasis on cases where the experimental methodology is being extended into new regimes. The transient-field technique, the recoil in vacuum method, and moment measurements with LaBr$_3$ detectors are discussed.Comment: 5 pages, 6 figure

Environmental supportiveness for physical activity in English schoolchildren: a study using Global Positioning Systems.

BACKGROUND: There is increasing evidence that the environment plays a role in influencing physical activity in children and adults. As children have less autonomy in their behavioural choices, neighbourhood environment supportiveness may be an important determinant of their ability to be active. Yet we know rather little about the types of environment that children use for bouts of physical activity. This study uses accelerometery and global positioning system technologies to identify the charactieristics of environments being used for bouts of continuous moderate to vigorous physical activity (MVPA) in a sample of English schoolchildren. METHODS: The study used a convenience sample of 100 children from SPEEDY (Sport, Physical activity and Eating behaviour: Environmental Determinants in Young people), a cohort of 2064 9-10 year-olds from Norfolk, England, recruited in 2007. Children wore an ActiGraph GT1M accelerometer and a Garmin Forerunner 205 GPS unit over four consecutive days. Accelerometery data points were matched to GPS locations and bouts (5 minutes or more) of MVPA were identified. Bout locations were overlaid with a detailed landcover dataset developed in a GIS to identify the types of environment supporting MVPA. Findings are presented using descriptive statistics. RESULTS: Boys were also more active than girls, spending an average of 20 (SD 23) versus 11 (SD 15) minutes per day in MVPA bouts. Children who spent more time outside the home were more active (p = 0.002), especially girls and children living in rural locations (both p < 0.05). Children tended to be active close to home, with 63% of all bout time occurring inside neighbourhoods, although boys (p = 0.05) and rural children (p = 0.01) were more likely to roam outside their neighbourhood. Amongst urban children, gardens (28% of bout time) and the street environment (20%) were the most commonly used environments for MVPA bouts. Amongst rural children farmland (22%) and grassland (18%) were most frequently used. CONCLUSION: The study has developed a new methodology for the identification of environments in which bouts of continuous physical activity are undertaken. The results highlight the importance of the provision of urban gardens and greenspaces, and the maintenance of safe street environments as places for children to be active.RIGHTS : This article is licensed under the BioMed Central licence at http://www.biomedcentral.com/about/license which is similar to the 'Creative Commons Attribution Licence'. In brief you may : copy, distribute, and display the work; make derivative works; or make commercial use of the work - under the following conditions: the original author must be given credit; for any reuse or distribution, it must be made clear to others what the license terms of this work are

Clearing the undergrowth: detection and quantification of low level impurities using 19F NMR

A new 19F NMR method, ODYSSEUS, allows low level impurities to be detected without interference from 13C satellites.</p

Longitudinal association between change in the neighbourhood built environment and the wellbeing of local residents in deprived areas: an observational study.

BACKGROUND: Features of the urban neighbourhood influence the physical, social and mental wellbeing of residents and communities. We explored the longitudinal association between change to the neighbourhood built environment and the wellbeing of local residents in deprived areas of Glasgow, Scotland. METHODS: A cohort of residents (n = 365; mean age 50 years; 44% male; 4.1% of the 9000 mailed surveys at baseline) responded to a postal survey in 2005 and 2013. Wellbeing was assessed with the mental (MCS-8) and physical (PCS-8) components of the SF-8 scale. We developed software to aid identification of visible changes in satellite imagery occurring over time. We then used a Geographical Information System to calculate the percentage change in the built environment occurring within an 800 m buffer of each participant's home. RESULTS: The median change in the neighbourhood built environment was 3% (interquartile range 6%). In the whole sample, physical wellbeing declined by 1.5 units on average, and mental wellbeing increased by 0.9 units, over time. In multivariable linear regression analyses, participants living in neighbourhoods with a greater amount of change in the built environment (unit change = 1%) experienced significantly reduced physical (PCS-8: -0.13, 95% CI -0.26 to 0.00) and mental (MCS-8: -0.16, 95% CI -0.31 to - 0.02) wellbeing over time compared to those living in neighbourhoods with less change. For mental wellbeing, a significant interaction by baseline perception of financial strain indicated a larger reduction in those experiencing greater financial strain (MCS-8: -0.22, 95% CI -0.39 to - 0.06). However, this relationship was reversed in those experiencing lower financial strain, whereby living in neighbourhoods with a greater amount of change was associated with significantly improved mental wellbeing over time (MCS-8: 0.38, 95% CI 0.04 to 0.72). CONCLUSIONS: Overall, we found some evidence that living in neighbourhoods experiencing higher levels of physical change worsened wellbeing in local residents. However, we found a stronger negative relationship in those with lower financial security and a positive relationship in those with higher financial security. This is one of few studies exploring the longitudinal relationship between the environment and health