| 1. |
- Ademuyiwa, Adesoji O., et al.
(författare)
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Determinants of morbidity and mortality following emergency abdominal surgery in children in low-income and middle-income countries
- 2016
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Ingår i: BMJ Global Health. - : BMJ Publishing Group Ltd. - 2059-7908. ; 1:4
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Tidskriftsartikel (refereegranskat)abstract
- Background: Child health is a key priority on the global health agenda, yet the provision of essential and emergency surgery in children is patchy in resource-poor regions. This study was aimed to determine the mortality risk for emergency abdominal paediatric surgery in low-income countries globally.Methods: Multicentre, international, prospective, cohort study. Self-selected surgical units performing emergency abdominal surgery submitted prespecified data for consecutive children aged <16 years during a 2-week period between July and December 2014. The United Nation's Human Development Index (HDI) was used to stratify countries. The main outcome measure was 30-day postoperative mortality, analysed by multilevel logistic regression.Results: This study included 1409 patients from 253 centres in 43 countries; 282 children were under 2 years of age. Among them, 265 (18.8%) were from low-HDI, 450 (31.9%) from middle-HDI and 694 (49.3%) from high-HDI countries. The most common operations performed were appendectomy, small bowel resection, pyloromyotomy and correction of intussusception. After adjustment for patient and hospital risk factors, child mortality at 30 days was significantly higher in low-HDI (adjusted OR 7.14 (95% CI 2.52 to 20.23), p<0.001) and middle-HDI (4.42 (1.44 to 13.56), p=0.009) countries compared with high-HDI countries, translating to 40 excess deaths per 1000 procedures performed.Conclusions: Adjusted mortality in children following emergency abdominal surgery may be as high as 7 times greater in low-HDI and middle-HDI countries compared with high-HDI countries. Effective provision of emergency essential surgery should be a key priority for global child health agendas.
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| 2. |
- Gan, L., et al.
(författare)
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An experimental investigation of forced steady rotating turbulence
- 2016
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Ingår i: European journal of mechanics. B, Fluids. - : Elsevier. - 0997-7546 .- 1873-7390. ; 58, s. 59-69
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents some of the principal findings of an experimental investigation of forced statistically steady turbulence in a rapidly rotating background. The experiment is conducted in a large cylindrical mixing tank and bulk rotation is produced by two large co-rotating impellers installed near the top and the bottom of the tank. The mean flow motion generated in such a configuration is axisymmetric and close to but not exactly solid-body rotation. The focus of this work is on the region in the vicinity of the rotation axis where the flow is Rayleigh stable. The unique features of this facility allow forcing and thus permit turbulence to be maintained at a certain level without a mean decay. The facility also allows an easy experimental access of statistical quantities. The bulk rotation rates and the amount of turbulence are adjusted to a Rossby number (Ro) of (1). Under this condition, some physical phenomena commonly seen in solid-body rotating turbulent flows at low Ro are also observed, despite the differences in other parameters. A flow visualisation at one of the testing conditions using pearlescence clearly shows the presence of cyclonic columnar structures. Two-dimensional particle image velocimetry (2DPIV) measurements are carried out in a plane normal to the axis of the rotation and near the middle height of the tank. Symmetry breaking between cyclonic and anti-cyclonic vorticity in the flow is revealed by the skewness of the fluctuating vorticity. It is found that skewness is not a monotonic function of Ro; in this particular experimental arrangement, symmetry is broken to a maximum extent at Ro ∼1.5 based on velocity length scale. Turbulence quantities are also computed along with the turbulent energy dissipation, which is estimated using velocity structure functions and lends support to previous findings that purport that dissipation is suppressed in such flows.
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| 3. |
- Maffioli, Andrea, et al.
(författare)
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Mixing efficiency in stratified turbulence
- 2016
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Ingår i: Journal of Fluid Mechanics. - : Cambridge University Press. - 0022-1120 .- 1469-7645. ; 794
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Tidskriftsartikel (refereegranskat)abstract
- We consider mixing of the density field in stratified turbulence and argue that, at sufficiently high Reynolds numbers, stationary turbulence will have a mixing efficiency and closely related mixing coefficient described solely by the turbulent Froude number (Formula presented.), where (Formula presented.) is the kinetic energy dissipation, (Formula presented.) is a turbulent horizontal velocity scale and (Formula presented.) is the Brunt–Väisälä frequency. For (Formula presented.), in the limit of weakly stratified turbulence, we show through a simple scaling analysis that the mixing coefficient scales as (Formula presented.), where (Formula presented.) and (Formula presented.) is the potential energy dissipation. In the opposite limit of strongly stratified turbulence with (Formula presented.), we argue that (Formula presented.) should reach a constant value of order unity. We carry out direct numerical simulations of forced stratified turbulence across a range of (Formula presented.) and confirm that at high (Formula presented.), (Formula presented.), while at low (Formula presented.) it approaches a constant value close to (Formula presented.). The parametrization of (Formula presented.) based on (Formula presented.) due to Shih et al. (J. Fluid Mech., vol. 525, 2005, pp. 193–214) can be reinterpreted in this light because the observed variation of (Formula presented.) in their study as well as in datasets from recent oceanic and atmospheric measurements occurs at a Froude number of order unity, close to the transition value (Formula presented.) found in our simulations.
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| 4. |
- Maffioli, Andrea
(författare)
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Vertical spectra of stratified turbulence at large horizontal scales
- 2017
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Ingår i: Physical Review Fluids. - : American Physical Society. - 2469-990X. ; 2:10
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Tidskriftsartikel (refereegranskat)abstract
- Stably stratified turbulence is investigated with the aim of increasing our limited understanding of the vertical structure of this type of turbulent flow. For strongly stratified turbulence there is a theoretical prediction that the energy spectra in the vertical direction of gravity are very steep, possessing the well-known form E-h(k(v)) alpha N(2)kv(-3) , where N is the Brunt-Vaisala frequency and kv is the vertical wave number, but supporting evidence from experiments and numerical simulations is lacking. We conduct direct numerical simulation (DNS) with uniform background stratification and forcing at large scales. In order to consider the large anisotropic scales only, the vertical energy spectra are decomposed into large-scale vertical spectra E-large(k(v)) and small-scale vertical spectra E-small(k(v)) using a horizontal demarcation scale. We find that this approach gives results that are in close agreement with E-large(k(v)) alpha N(2)k(v)(-3) for the DNS runs performed. This result holds approximately over the wave-number range k(b) <= k(v) <= k(oz), where kb is the buoyancy wave number and koz is the Ozmidov wave number, in agreement with theory. Similarly, large-scale vertical spectra of potential energy are found to be E-p,E-large(k(v)) alpha N(2)k(v)(-3) , over a narrower range of wave numbers. The evidence supports the existence of a scale-by-scale balance between inertia and buoyancy occurring in strongly stratified turbulence at large horizontal scales. Finally, the current results are put in the context of ocean turbulence by making a comparison with measurements of vertical shear spectra made in the ocean interior.
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