Turbulence-induced melting of a nonequilibrium vortex crystal in a forced thin fluid film

To develop an understanding of recent experiments on the turbulence-induced melting of a periodic array of vortices in a thin fluid film, we perform a direct numerical simulation of the two-dimensional Navier-Stokes equations forced such that, at low Reynolds numbers, the steady state of the film is a square lattice of vortices. We find that, as we increase the Reynolds number, this lattice undergoes a series of nonequilibrium phase transitions, first to a crystal with a different reciprocal lattice and then to a sequence of crystals that oscillate in time. Initially the temporal oscillations are periodic; this periodic behaviour becomes more and more complicated, with increasing Reynolds number, until the film enters a spatially disordered nonequilibrium statistical steady that is turbulent. We study this sequence of transitions by using fluid-dynamics measures, such as the Okubo-Weiss parameter that distinguishes between vortical and extensional regions in the flow, ideas from nonlinear dynamics, e.g., \Poincare maps, and theoretical methods that have been developed to study the melting of an equilibrium crystal or the freezing of a liquid and which lead to a natural set of order parameters for the crystalline phases and spatial autocorrelation functions that characterise short- and long-range order in the turbulent and crystalline phases, respectively.Comment: 31 pages, 56 figures, movie files not include

Type 2 diabetes and risk of diverticular disease:a Danish cohort study

OBJECTIVES: To investigate the association between type 2 diabetes and risk of diverticular disease. Unlike previous studies, which have found conflicting results, we aimed to distinguish between diabetes types and adjust for modifiable risk factors. DESIGN: Observational cohort study. SETTING: Population-based Danish medical databases, covering the period 2005–2018. PARTICIPANTS: Respondents of the 2010 or the 2013 Danish National Health Survey, of which there were 15 047 patients with type 2 diabetes and 210 606 patients without diabetes. PRIMARY AND SECONDARY OUTCOME MEASURES: Hazard ratios (HRs) for incident hospital diagnosis of diverticular disease adjusted for survey year, sex, age, body mass index (BMI), physical activity intensity, smoking behaviour, diet and education based on Cox regression analysis. As latency may affect the association between type 2 diabetes and diverticular disease, patients with type 2 diabetes were stratified into those with <2.5, 2.5–4.9 and ≥5 years duration of diabetes prior to cohort entry. RESULTS: For patients with and without diabetes the incidence rates of diverticular disease were 0.76 and 0.54 events per 1000 person years, corresponding to a crude HR of 1.08 (95% CI 1.00 to 1.16) and an adjusted HR of 0.88 (95% CI 0.80 to 0.96). The HR was lower among patients with ≥5 years duration of diabetes (adjusted HR: 0.76, 95% CI 0.67 to 0.87) than among those with 2.5–4.9 years or <2.5 years duration. CONCLUSION: We found that patients with type 2 diabetes had a higher incidence rate of diverticular disease compared with patients without diabetes. However, after adjustment for modifiable risk factors, driven by BMI, type 2 diabetes appeared to be associated with a slightly lower risk of diverticular disease. Lack of adjustment for BMI may partially explain the conflicting findings of previous studies

Edible crabs “Go West”: migrations and incubation cycle of Cancer pagurus revealed by electronic tags

Crustaceans are key components of marine ecosystems which, like other exploited marine taxa, show seasonable patterns of distribution and activity, with consequences for their availability to capture by targeted fisheries. Despite concerns over the sustainability of crab fisheries worldwide, difficulties in observing crabs’ behaviour over their annual cycles, and the timings and durations of reproduction, remain poorly understood. From the release of 128 mature female edible crabs tagged with electronic data storage tags (DSTs), we demonstrate predominantly westward migration in the English Channel. Eastern Channel crabs migrated further than western Channel crabs, while crabs released outside the Channel showed little or no migration. Individual migrations were punctuated by a 7-month hiatus, when crabs remained stationary, coincident with the main period of crab spawning and egg incubation. Incubation commenced earlier in the west, from late October onwards, and brooding locations, determined using tidal geolocation, occurred throughout the species range. With an overall return rate of 34%, our results demonstrate that previous reluctance to tag crabs with relatively high-cost DSTs for fear of loss following moulting is unfounded, and that DSTs can generate precise information with regards life-history metrics that would be unachievable using other conventional means

Improved very short-term spatio-temporal wind forecasting using atmospheric regimes

We present a regime‐switching vector autoregressive method for very short‐term wind speed forecasting at multiple locations with regimes based on large‐scale meteorological phenomena. Statistical methods for wind speed forecasting based on recent observations outperform numerical weather prediction for forecast horizons up to a few hours, and the spatio‐temporal interdependency between geographically dispersed locations may be exploited to improve forecast skill. Here, we show that conditioning spatio‐temporal interdependency on “atmospheric modes” derived from gridded numerical weather data can further improve forecast performance. Atmospheric modes are based on the clustering of surface wind and sea‐level pressure fields, and the geopotential height field at the 5000‐hPa level. The data fields are extracted from the MERRA‐2 reanalysis dataset with an hourly temporal resolution over the UK; atmospheric patterns are clustered using self‐organising maps and then grouped further to optimise forecast performance. In a case study based on 6 years of measurements from 23 weather stations in the UK, a set of 3 atmospheric modes are found to be optimal for forecast performance. The skill of 1‐ to 6‐hour‐ahead forecasts is improved at all sites compared with persistence and competitive benchmarks. Across the 23 test sites, 1‐hour‐ahead root mean squared error is reduced by between 0.3% and 4.1% compared with the best performing benchmark and by an average of 1.6% over all sites; the 6‐hour‐ahead accuracy is improved by an average of 3.1%