Viscous coupling of shear-free turbulence across nearly flat fluid interfaces

The interactions between shear-free turbulence in two regions (denoted as + and − on either side of a nearly flat horizontal interface are shown here to be controlled by several mechanisms, which depend on the magnitudes of the ratios of the densities, ρ+/ρ−, and kinematic viscosities of the fluids, μ+/μ−, and the root mean square (r.m.s.) velocities of the turbulence, u0+/u0−, above and below the interface. This study focuses on gas–liquid interfaces so that ρ+/ρ− ≪ 1 and also on where turbulence is generated either above or below the interface so that u0+/u0− is either very large or very small. It is assumed that vertical buoyancy forces across the interface are much larger than internal forces so that the interface is nearly flat, and coupling between turbulence on either side of the interface is determined by viscous stresses. A formal linearized rapid-distortion analysis with viscous effects is developed by extending the previous study by Hunt & Graham (J. Fluid Mech., vol. 84, 1978, pp. 209–235) of shear-free turbulence near rigid plane boundaries. The physical processes accounted for in our model include both the blocking effect of the interface on normal components of the turbulence and the viscous coupling of the horizontal field across thin interfacial viscous boundary layers. The horizontal divergence in the perturbation velocity field in the viscous layer drives weak inviscid irrotational velocity fluctuations outside the viscous boundary layers in a mechanism analogous to Ekman pumping. The analysis shows the following. (i) The blocking effects are similar to those near rigid boundaries on each side of the interface, but through the action of the thin viscous layers above and below the interface, the horizontal and vertical velocity components differ from those near a rigid surface and are correlated or anti-correlated respectively. (ii) Because of the growth of the viscous layers on either side of the interface, the ratio uI/u0, where uI is the r.m.s. of the interfacial velocity fluctuations and u0 the r.m.s. of the homogeneous turbulence far from the interface, does not vary with time. If the turbulence is driven in the lower layer with ρ+/ρ− ≪ 1 and u0+/u0− ≪ 1, then uI/u0− ~ 1 when Re (=u0−L−/ν−) ≫ 1 and R = (ρ−/ρ+)(v−/v+)1/2 ≫ 1. If the turbulence is driven in the upper layer with ρ+/ρ− ≪ 1 and u0+/u0− ≫ 1, then uI/u0+ ~ 1/(1 + R). (iii) Nonlinear effects become significant over periods greater than Lagrangian time scales. When turbulence is generated in the lower layer, and the Reynolds number is high enough, motions in the upper viscous layer are turbulent. The horizontal vorticity tends to decrease, and the vertical vorticity of the eddies dominates their asymptotic structure. When turbulence is generated in the upper layer, and the Reynolds number is less than about 106–107, the fluctuations in the viscous layer do not become turbulent. Nonlinear processes at the interface increase the ratio uI/u0+ for sheared or shear-free turbulence in the gas above its linear value of uI/u0+ ~ 1/(1 + R) to (ρ+/ρ−)1/2 ~ 1/30 for air–water interfaces. This estimate agrees with the direct numerical simulation results from Lombardi, De Angelis & Bannerjee (Phys. Fluids, vol. 8, no. 6, 1996, pp. 1643–1665). Because the linear viscous–inertial coupling mechanism is still significant, the eddy motions on either side of the interface have a similar horizontal structure, although their vertical structure differs

Decadal trends in beach morphology on the east coast of South Africa and likely causative factors

Sandy shorelines are dynamic with constant changes that can cause hazards in developed areas. The causes of change may be either natural or anthropogenic. This paper evaluates evidence for shoreline changes and their causative factors using a case study on the east coast of South Africa. Beach morphology trends were found to be location-specific, but overall the beaches show a receding trend. It was hypothesized that wave, tide, sea level and wind trends as well as anthropogenic influences are causative factors, and their contributions to shoreline changes were evaluated. Maximum significant wave heights, average wave direction, peak period and storm event frequencies all show weak increasing trends, but only the increases in peak period and wave direction are statistically significant. The chronic beach erosion cannot be attributed to wave climate changes since they are still too small to explain the observations. Instead, the impacts of sea level rise and reductions in the supply of beach sediments are suggested as the main causative factors. The analysis also identifies a trend in the frequency of severe erosion events due to storms that coincide with a 4.5-yr extreme tide cycle, which demonstrates the potential impact of future sea level rise

Capturing pharmacists' impact in general practice: an e-Delphi study to attempt to reach consensus amongst experts about what activities to record

Background: In the UK, there is ongoing integration of pharmacists into general practice as a new healthcare service in primary care. Evaluation of the service involves national measures that require pharmacists to record their work, on the general practice clinical computer systems, using electronic activity codes. No national agreement, however, has been established on what activities to record. The purpose of this study was to attempt to reach consensus on what activities general practice-based pharmacists should record. Methods: The e-Delphi method was chosen as it is an excellent technique for achieving consensus. The study began with an initial stage in which screening of a general practice clinical computer system and discussion groups with pharmacists from two ‘pharmacists in general practice’ sites identified 81 codes potentially relevant to general practice-based pharmacists’ work. Twenty-nine experts (pharmacists and pharmacy technicians from the two sites along with experts recruited through national committees) were then invited by e-mail to participate as a panel in three e-Delphi questionnaire rounds. In each round, panellists were asked to grade or rank codes and justify their choices. In every round, panellists were provided with anonymised feedback from the previous round which included their individual choices along with their co-panellists’ views. Final consensus (in Round 3) was defined as at least 80% agreement. Commentaries on the codes from all e-Delphi rounds were pooled together and analysed thematically. Results: Twenty-one individual panellists took part in the study (there were 12 responses in Round 1, 18 in Round 2 and 16 in Round 3). Commentaries on the codes included three themes: challenges and facilitators; level of detail; and activities related to funding. Consensus was achieved for ten codes, eight of which related to activities (general and disease specific medication reviews, monitoring of high-risk drugs and medicines reconciliation) and two to patient outcomes (presence of side effects and satisfactory understanding of medication). Conclusions: A formal consensus method revealed general practice-based pharmacists’ preferences for activity coding. Findings will inform policy so that any future shaping of activity coding for general practice-based pharmacists takes account of pharmacists’ actual needs and preferences

Datathons and Software to Promote Reproducible Research

Background: Datathons facilitate collaboration between clinicians, statisticians, and data scientists in order to answer important clinical questions. Previous datathons have resulted in numerous publications of interest to the critical care community and serve as a viable model for interdisciplinary collaboration. Objective: We report on an open-source software called Chatto that was created by members of our group, in the context of the second international Critical Care Datathon, held in September 2015. Methods: Datathon participants formed teams to discuss potential research questions and the methods required to address them. They were provided with the Chatto suite of tools to facilitate their teamwork. Each multidisciplinary team spent the next 2 days with clinicians working alongside data scientists to write code, extract and analyze data, and reformulate their queries in real time as needed. All projects were then presented on the last day of the datathon to a panel of judges that consisted of clinicians and scientists. Results: Use of Chatto was particularly effective in the datathon setting, enabling teams to reduce the time spent configuring their research environments to just a few minutes—a process that would normally take hours to days. Chatto continued to serve as a useful research tool after the conclusion of the datathon. Conclusions: This suite of tools fulfills two purposes: (1) facilitation of interdisciplinary teamwork through archiving and version control of datasets, analytical code, and team discussions, and (2) advancement of research reproducibility by functioning postpublication as an online environment in which independent investigators can rerun or modify analyses with relative ease. With the introduction of Chatto, we hope to solve a variety of challenges presented by collaborative data mining projects while improving research reproducibility

The validity of the Spelling and Grammar Waiver as a reasonable accommodation in Leaving Certificate examinations in Ireland

In Ireland, dyslexic students can apply for reasonable accommodations in Leaving Certificate examinations. One such accommodation is the Spelling and Grammar Waiver (SGW). Questions have been raised regarding its validity, and it has been suggested that it gives an unfair advantage. Mock Leaving Certificate English paper scripts were collected from 31 dyslexic students who had been granted an SGW and 31 nondyslexic students who had not been granted any accommodations. All scripts were marked twice, eight weeks apart, by the same marker, once in the standard fashion and once with an SGW. Dyslexic students’ scripts marked with an SGW had a significantly higher mean score than when marked in the standard way, and it was similar to the mean unaccommodated score of nondyslexic students. However, nondyslexic students also received a similar boost in scores when accommodated. Two-way repeated measures ANOVA showed no “differential boost” for the dyslexic group, but a significant boost for both groups when accommodated. Results suggest that the SGW is not a valid accommodation but confers an advantage to those that have it. This study needs replication using larger numbers, with real Leaving Certificate scripts and examiners, and the reasons for the increase in scores also need investigation

A review of cricket injuries and the effectiveness of strategies to prevent cricket injuries at all levels

Objective. This review evaluates the scientific research on cricket injuries, including long-term injury surveillance studies, the consensus statement paper for injury surveillance, specific counter-measures to reduce the risk of cricket injuries and finally identifies areas of future concern. Results. The literature shows that three major cricketplaying countries, Australia, England and South Africa, have collected long-term injury data. While these sets of data show definite trends, it was not always possible to make direct comparisons between data collected in various countries. As a result a consensus statement paper with regards to definitions and methods to calculate injury rates, incidence and prevalence was developed. The first study using this newly accepted injury surveillance method showed injury patterns in West Indies domestic and national cricket teams. There have been three primary studies carried out with regards to interventions aimed at reducing the risk of injury to fast bowlers. These included a coaching interventions programme, the use of a bowling aid in an attempt to modify bowling technique and a study that evaluated the recommended bowling workloads in young cricketers. The implications of the changes to the laws relating to the bowling action and the increased usage of the sliding stop in fielding are reviewed. Conclusion. From the review it is evident that there is a need to continue with injury surveillance, as well as a need to continue with and increase the number of studies that evaluate the efficacy of intervention strategies in order to reduce the risk of injury to cricketers. South African Journal of Sports Medicine Vol. 19 (5) 2007: pp. 129-13

Incidence and nature of epidemiological injuries to elite South African cricket players

Objectives. The study investigated the incidence and nature of injuries sustained by elite cricketers during a season and the possible risk factors associated with these injuries.Methods. Fourteen physiotherapists and three doctors recorded 163 injuries sustained by 88 cricketers.Results. Bowling accounted for 40.5% of the injuries, while fielding and batting accounted for 25.6% and 21.5% of the injuries, respectively. The injuries occurred while practising for or playing in club (3.7%), provincial 'B' (8.0%), provincial (51.5%) and international (36.8%) matches and occurred primarily during 4- and 5-day (33.1 %) and 1-day (27.0%) matches. First-time injuries made up 63.6% of the injuries, recurrent injuries from previous seasons made up 28.4% and 8.0% of the injuries recurred again at a later stage during the season. Of the injuries 62.6% were acute, 14.7% chronic and 22.7% were acute injuries on existing chronic injuries. The majority of the injuries were muscle (37.4%), joint (20.9%) and tendon (15.3%) injuries. The primary mechanisms of injury were as a result of overuse (30.7%); running to catch or field (15.3%); during the bowling delivery or follow-through (12.3%); and being struck by the ball while batting (11.0%).Conclusions. Coaches, players and the medical support team need to be aware of the incidence, nature and cause of injuries, so that the risk of injury can be further reduced

Generating more profit from your farm business

This report outlines the main drivers of profit – price, production, costs and management. Knowing a farm’s profit drivers assists managers to analyse the risk and resilience of their business and to make more informed expenditure decisions. With significant volatility in both prices and production, farm managers need to have strategies that smooth price volatility and allow adjustments to costs of production. When analysing business profitability it is important to look beyond gross margins and capture all cost items particularly large fixed costs like finance and machinery allowance costs. By critically examining the full cost structure of their business managers can: assess the flexibility of their business in different production scenarios know the profit implications of pricing decisions evaluate expenditure on inputs plan more effectively for the future