Density regulation in strictly metric-free swarms

There is now experimental evidence that nearest-neighbour interactions in flocks of birds are metric free, i.e. they have no characteristic interaction length scale. However, models that involve interactions between neighbours that are assigned topologically are naturally invariant under spatial expansion, supporting a continuous reduction in density towards zero, unless additional cohesive interactions are introduced or the density is artificially controlled, e.g. via a finite system size. We propose a solution that involves a metric-free motional bias on those individuals that are topologically identified to be on an edge of the swarm. This model has only two primary control parameters, one controlling the relative strength of stochastic noise to the degree of co-alignment and another controlling the degree of the motional bias for those on the edge, relative to the tendency to co-align. We find a novel power-law scaling of the real-space density with the number of individuals N as well as a familiar order-to-disorder transition

The Role of Projection in the Control of Bird Flocks

Swarming is a conspicuous behavioural trait observed in bird flocks, fish shoals, insect swarms and mammal herds. It is thought to improve collective awareness and offer protection from predators. Many current models involve the hypothesis that information coordinating motion is exchanged between neighbors. We argue that such local interactions alone are insufficient to explain the organization of large flocks of birds and that the mechanism for the exchange of long-ranged information necessary to control their density remains unknown. We show that large flocks self-organize to the maximum density at which a typical individual is still just able to see out of the flock in many directions. Such flocks are marginally opaque - an external observer can also just still see a substantial fraction of sky through the flock. Although seemingly intuitive we show that this need not be the case; flocks could easily be highly diffuse or entirely opaque. The emergence of marginal opacity strongly constrains how individuals interact with each other within large swarms. It also provides a mechanism for global interactions: An individual can respond to the projection of the flock that it sees. This provides for faster information transfer and hence rapid flock dynamics, another advantage over local models. From a behavioural perspective it optimizes the information available to each bird while maintaining the protection of a dense, coherent flock.Comment: PNAS early edition published online at http://www.pnas.org/cgi/doi/10.1073/pnas.140220211

Emergent behavioural phenotypes of swarming models revealed by mimicking a frustrated anti-ferromagnet

Self-propelled particle (SPP) models are often compared with animal swarms. However, the collective animal behaviour observed in experiments often leaves considerable unconstrained freedom in the structure of a proposed model. Essentially, multiple models can describe the observed behaviour of animal swarms in simple environments. To tackle this degeneracy, we study swarms of SPPs in non-trivial environments as a new approach to distinguish between candidate models. We restrict swarms of SPPs to circular (periodic) channels where they polarize in one of two directions (like spins) and permit information to pass through windows between neighbouring channels. Co-alignment between particles then couples the channels (anti-ferromagnetically) so that they tend to counter-rotate. We study channels arranged to mimic a geometrically frustrated anti-ferromagnet and show how the effects of this frustration allow us to better distinguish between SPP models. Similar experiments could therefore improve our understanding of collective motion in animals. Finally, we discuss how the spin analogy can be exploited to construct universal logic gates, and therefore swarming systems that can function as Turing machines

Multiple aneurysms in childhood

AbstractArterial aneurysms in children are rare. When present, they are often associated with connective tissue disorders or arteritidies. Idiopathic aneurysms occurring at multiple sites throughout the arterial tree are rare, with only ten cases reported. This report describes a case of multiple arterial aneurysms of uncertain origin involving upper-extremity, extracranial cerebrovascular, aortoiliac, and renal arteries in a 14-year-old boy. The clinical presentation, vascular reconstruction, pathologic findings, and a brief review of the literature are described

Is occupational physical activity associated with mortality in UK Biobank?

BackgroundCurrent physical activity guidelines do not distinguish between activity accumulated in different behavioural domains but some studies suggest that occupational physical activity (OPA) may not confer health benefits and could even be detrimental. The purpose of this study was to investigate associations between OPA and mortality outcomes.MethodsFrom baseline (2006-2010), 460,901 UK Biobank participants (aged 40-69 years) were followed for a median 12.0 (IQR: 11.3-12.7) years. OPA was categorised by cross-tabulating degree of manual work and walking/standing work amongst those in paid employment (n = 267,765), and combined with categories of occupational status for those not in paid employment (n = 193,136). Cox proportional hazards models were used to estimate sex-stratified hazard ratios (HR) and 95% confidence intervals (CI) for mortality from all causes, CVD, and cancer by occupational group, and for working hours/week and non-occupational physical activity stratified by occupational group. Models included adjustment for age and a range of lifestyle, socio-economic and health-related covariates.ResultsDuring 5,449,989 person-years of follow-up, 28,740 deaths occurred. Compared to those reporting no heavy manual or walking/standing work (e.g. sedentary office workers) and adjusting for covariates, retirement was associated with lower mortality in women (HR = 0.62, CI: 0.53-0.72) and men (HR = 0.80, CI: 0.71-0.90), whereas unemployment was associated with higher mortality in men only (HR = 1.24, CI: 1.07-1.45). Within the working population, there was no evidence of differences in all-cause, CVD or cancer mortality by OPA group when comparing those reporting higher levels of OPA to the lowest OPA reference group for both women and men. Working ConclusionsJobs classified as higher levels of OPA may not be as active as reported, or the types of physical activity performed in those jobs are not health-enhancing. Irrespective of OPA category or employment status, non-occupational physical activity appears to provide health benefits

Fused particle fabrication 3-D printing: Recycled materials’ optimization and mechanical properties

Fused particle fabrication (FPF) (or fused granular fabrication (FGF)) has potential for increasing recycled polymers in 3-D printing. Here, the open source Gigabot X is used to develop a new method to optimize FPF/FGF for recycled materials. Virgin polylactic acid (PLA) pellets and prints were analyzed and were then compared to four recycled polymers including the two most popular printing materials (PLA and acrylonitrile butadiene styrene (ABS)) as well as the two most common waste plastics (polyethylene terephthalate (PET) and polypropylene (PP)). The size characteristics of the various materials were quantified using digital image processing. Then, power and nozzle velocity matrices were used to optimize the print speed, and a print test was used to maximize the output for a two-temperature stage extruder for a given polymer feedstock. ASTM type 4 tensile tests were used to determine the mechanical properties of each plastic when they were printed with a particle drive extruder system and were compared with filament printing. The results showed that the Gigabot X can print materials 6.5× to 13× faster than conventional printers depending on the material, with no significant reduction in the mechanical properties. It was concluded that the Gigabot X and similar FPF/FGF printers can utilize a wide range of recycled polymer materials with minimal post processing

Superconductivity and the upper critical field in the chiral noncentrosymmetric superconductor NbRh2B2

NbRh2B2 crystallises in a chiral noncentrosymmetric structure and exhibits bulk type-II superconductivity below 7.46(5) K. Here we show that the temperature dependence of the upper critical field deviates from the behaviour expected for both Werthamer-Helfand-Hohenberg and the Ginzburg-Landau models and that μ0Hc2 (0) ~ 18 T exceeds the Pauli paramagnetic limit, μ0HP = 13.9 T. We explore the reasons for this enhancement. Transverse-field muon spectroscopy measurements suggest that the superconducting gap is either s-wave or (s + s)-wave, a the pressure dependence of Tc reveals the superconducting gap is primarily s- wave in character. The magnetic penetration depth lambda(0) = 595(5) nm. Heat capacity measurements reveal the presence of a multigap (s + s)-wave superconducting order parameter and moderate electron-phonon coupling

Specific physical activities, sedentary behaviours and sleep as long-term predictors of accelerometer-measured physical activity in 91,648 adults: a prospective cohort study.

BACKGROUND: The evidence for the prospective relationships between specific physical activities (PA), sedentary behaviours (SB) and sleep on subsequent total PA levels is scarce. The purpose of this study was to examine prospective associations of self-reported PA, SB and sleep, and changes in these with subsequent accelerometer-measured PA. METHODS: A sub-sample of 91,648 UK Biobank participants reported moderate-to-vigorous PA (MVPA), lifestyle activities, TV viewing, computer use and sleep through screen-based questionnaires at baseline (2006-2010), and provided valid accelerometry data (dominant wrist-worn for 7 days between 2013 and 2015). A further sub-sample of 7709 participants repeated the screen-based questionnaires between 2012 and 2013. RESULTS: In both women (n = 51,545) and men (n = 40,103), positive associations were observed between all self-reported measures of PA at baseline (MVPA, lifestyle/job-related activities, active transporting modes) and accelerometer-measured PA levels at follow-up (median 5.7 years); an exception was 'walking/standing at work' in women. Sedentary time at work, TV viewing and computer use were inversely associated with PA at follow-up. Sleeping either more or less than 7 h/day at baseline was associated with lower PA at follow-up (except for ≤6 h/day in men). In the repeat self-report sub-sample (median 4.3 years), relatively higher physical activity at follow-up was observed in those who maintained or achieved favourable levels of MVPA, walking for pleasure, strenuous sports, other exercises, heavy DIY (in women), heavy physical work, and walking/standing at work (in women), sedentary time at work, getting about methods (in women), commuting methods (in women), TV viewing, computer use or sleep. CONCLUSIONS: Initial levels of PA, SB and sleep, and changes in these variables were generally associated with subsequent accelerometer-measured PA in the expected directions, suggesting these specific behaviours all contribute to the total volume of physical activity over time and could thus be targets for intervention.This work was supported by the UK Medical Research Council [MC_UU_12015/1 and MC_UU_12015/3], the NIHR Biomedical Research Centre Cambridge [IS-BRC-1215-20014], an Intermediate Basic Science Research Fellowship of British Heart Foundation (FS/12/58/29709 to KW), and a PhD studentship from MedImmune (to TW)

Age, Growth, and Mortality of Atlantic Tripletail in the North-Central Gulf of Mexico

In the southeastern USA and the Gulf of Mexico (GOM), Atlantic Tripletail Lobotes surinamensis are increasingly targeted by recreational anglers, indicating that stock status should be assessed. A critical need for such assessments is age-specific data; however, previous studies have drawn conflicting conclusions regarding the most appropriate structure for aging. Moreover, growth parameters and mortality rates for GOM Atlantic Tripletail are unknown. Therefore, the goals of this study were to (1) evaluate sagittal otoliths and first dorsal spines as aging structures; (2) model combined and sex-specific growth; and (3) estimate mortality rates for GOM Atlantic Tripletail. From 2012 to 2019, Atlantic Tripletail (N = 230, including a near-record-size specimen) were collected from the north-central GOM via hook and line and were aged using otoliths and first dorsal spines. Total length ranged from 212 to 940 mm, and age ranged from 0.07 to 5.27 years. Otoliths produced higher percent agreement (95.0%) and lower average percent error (3.0%) between readers compared to spines (82.9% and 6.5%, respectively). The von Bertalanffy growth parameters differed slightly between the otolith-based data (mean asymptotic length [L∞] = 762.42 mm, Brody growth rate coefficient [k] = 0.69 year−1, and hypothetical age at which length equals zero [t0] = −0.58 year) and spine-based data (L∞ = 718.83 mm, k = 0.79 year−1, and t0 = −0.56 year). For both otolith- and spine-based sex-specific data, the best-fitting version of the von Bertalanffy growth function permitted L∞ to vary by sex. Chapman– Robson estimates of instantaneous total mortality rate and total annual mortality rate were 1.15 and 68.66%, respectively. Based on empirical, life history-based methods, the instantaneous natural mortality rate was estimated at 0.75–0.97 and the instantaneous fishing mortality rate was estimated at 0.18–0.45, suggesting low levels of exploitation. These growth parameters and mortality estimates will provide information for future stock assessments, thereby ensuring sustainability of the GOM stock of Atlantic Tripletail

The incidence, prevalence and mortality of granulomatosis with polyangiitis in the UK Clinical Practice Research Datalink

Objectives: To estimate the incidence, prevalence and mortality of Granulomatosis with polyangiitis (GPA) in the United Kingdom. Methods: We conducted a historical cohort study using data from the Clinical Practice Research Datalink and Hospital Episode Statistics (CPRD-HES). We calculated incidence rate ratios, adjusted for age, gender and ethnicity, using Poisson regression. Results: We identified 462 cases diagnosed between 1997 and 2013. Our overall estimate of incidence was 11.8 (95% CI 10.7-12.9)/million person-years. Incidence in children (aged <16 years) was 0.88 (95% CI 0.40-1.96), and adults 14.0 (95% CI 12.8-15.4). The incidence was lower in females (adjusted IRR 0.68; 95% CI 0.56-0.81) and highest in the 55-69 year age-group (adjusted IRR 9.5, 95% CI 6.9-13.0; reference group 0-39 years). Incidence was not significantly different in the Black / Minority Ethnic population compared to the white population (adjusted odds ratio 0.78, 95% CI 0.53-1.13, p=0.13). The prevalence in 2013 was 134.9 (121.3-149.6) /million. Mortality was 13.6% at 1-year, and higher in HES than CPRD-identified cases (Hazard ratio 3.16, 95% CI 2.19-4.56, p<0.001). Conclusions: By combining primary and secondary care datasets we have found the incidence and mortality of granulomatosis with polyangiitis to be higher than previously reported. We predict that at present each year in the UK there will be approximately 700 new cases of whom 95 will die within 12 months