Patches in a side-by-side configuration: a description of the flow and deposition fields

In the last few decades, a lot of research attention has been paid to flow-vegetation interactions. Starting with the description of the flow field around uniform macrophyte stands, research has evolved more recently to the description of flow fields around individual, distinct patches. However, in the field, vegetation patches almost never occur in isolation. As such, patches will influence each other during their development and interacting, complex flow fields can be expected. In this study, two emergent patches of the same diameter (D = 22 cm) and a solid volume fraction of 10% were placed in a side-by-side configuration in a lab flume. The patches were built as an array of wooden cylinders, and the distance between the patches (gap width Delta) was varied between Delta = 0 and 14 cm. Flow measurements were performed by a 3D Vectrino Velocimeter (Nortek AS) at mid-depth of the flow. Deposition experiments of suspended solids were performed for selected gap widths. Directly behind each patch, the wake evolved in a manner identical to that of a single, isolated patch. On the centerline between the patches, the maximum velocity U-max was found to be independent of the gap width Delta. However, the length over which this maximum velocity persists, the potential core L-j, increased linearly as the gap width increased. After the merging of the wakes, the centerline velocity reaches a minimum value U-min. The minimum centerline velocity decreased in magnitude as the gap width decreased. The velocity pattern within the wake is reflected in the deposition patterns. An erosion zone occurs on the centerline between the patches, where the velocity is elevated. Deposition occurs in the low velocity zones directly behind each patch and also downstream of the patches, along the centerline between the patches at the point of local velocity minimum. This downstream deposition zone, a result of the interaction of neighbouring patch wakes, may facilitate the establishment of new vegetation, which may eventually inhibit flow between the upstream patches and facilitate patch merger

Nuclear imaging in the diagnosis of primary aldosteronism.

PURPOSE OF REVIEW: Primary aldosteronism is increasingly recognized as a common secondary cause of hypertension. Successful demonstration of a unilateral cause (e.g. a classical 'Conn's adenoma') offers the potential for curative adrenalectomy. Adrenal vein sampling (AVS), in conjunction with cross-sectional imaging, remains the 'gold standard' for distinguishing unilateral and bilateral disease, but is technically demanding and frequently unsuccessful or inconclusive. As such, alternative strategies for lateralization, including nuclear medicine techniques, are being developed and brought into clinical practice. RECENT FINDINGS: Metomidate, a potent ligand of CYP11B1 and CYP11B2, can be C11H3-labelled as a PET tracer and has been shown to offer a rapid noninvasive alternative to AVS for localizing unilateral aldosterone-producing adenomas. SUMMARY: Increasing experience with 11C-metomidate PET-CT supports its use as an adjunct to AVS when this has failed, is ambiguous, or cannot be undertaken.A.S.P. and M.G. are supported by the National Institute for Health Research Cambridge Biomedical Research Centre. M.J.B. is a National Institute of Health Research Senior Investigator.This is the final published version. It first appeared at http://journals.lww.com/co-endocrinology/Fulltext/2015/06000/Nuclear_imaging_in_the_diagnosis_of_primary.3.aspx

Investigating populations via penguins and their poo!

We describe an activity that introduces students to population modelling, enables them to use estimates obtained from a sample to infer back to the population, and understands how the findings are translatable via penguins and their poo

Limaria hians (Mollusca : Limacea): a neglected reef-forming keystone species

1. A key component of physical habitat along braided river systems is the exposed riverine sediment within the active zone. The relatively unmanaged, gravel-bed Fiume Tagliamento, Italy, provides the focus for exploring two ecologically important properties of exposed riverine sediments: their within-patch and between-patch variability in calibre. 2. To characterize between-patch variation in exposed riverine sediments, replicate (within-patch) samples were obtained from three geomorphologically distinct locations along 130 km of the river: bar heads along the margin of the low-flow channel, the heads of major bars across the exposed surface of the active zone, and floodplain surfaces. A photographic technique enabled rapid and consistent field sampling of the coarse sediments at bar heads along the low-flow channel margin and on major bars across the dry bed. 3. A downstream decrease in particle size and an increase in within-patch heterogeneity in sediment size were observed within bar head sediments along the margin of the low-flow channel. Comparisons between major bar and low-flow channel samples revealed greatest within-patch variability in individual sediment size indices (D50, A- and B-axes of the larger particles) at headwater sites, greatest between-patch variability in the three measured indices in the central reaches, and lowest between-patch variability at downstream sites. However, there was a distinct increase in the overall heterogeneity in particle size, which was sustained across all patches, in a downstream direction. 4. There was a clear downstream decrease in the size of floodplain sediments in the headwaters, but thereafter there was no distinct downstream trend in any of the calculated particle size indices. 5. The geomorphological controls on the observed patterns and the potential ecological significance of the patterns, particularly for plant establishment, are discussed in relation to the relative relief of the active zone, and the highly variable hydrological and climatic regime along the river

Understanding processes of island development on an island braided river over timescales from days to decades

This is the peer reviewed version of the following article: Gurnell, A. M., Bertoldi, W., Francis, R. A., Gurnell, J., and Mardhiah, U. ( 2019) Understanding processes of island development on an island braided river over timescales from days to decades. Earth Surf. Process. Landforms, 44: 624– 640. https://doi.org/10.1002/esp.4494., which has been published in final form at https://doi.org/10.1002/esp.4494. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived VersionsBar colonization by vegetation and subsequent island formation is a key bio‐geomorphological process in fluvial landscape evolution. Here we investigate morphological and ecological evolution of river islands over timescales from single floods to decades, focusing on islands initiated by deposited trees that sprout to form vegetated patches. On a braided reach of the high‐energy Tagliamento River, Italy, we monitored 30 pioneer islands of 1 to 17 years age in comparison with unvegetated bar surfaces, open areas between islands, and established island surfaces. We integrated morphological, surface sediment and vegetation properties of islands initiated by different flood events, combining evidence from remotely‐sensed and ground observations, flow and climate time series. At a decadal timescale, pioneer islands aggrade rapidly to the elevation of the mean annual flood, showing a steady increase in vegetation canopy height, fining of surface sediments from predominantly gravel to silty‐sand with a notable clay and organic fraction. The standing vegetation included over 130 species, with the largest number on island surfaces of intermediate elevation and flood disturbance. As islands age, standing vegetation becomes comprised mainly of competitor species with transient seed banks and typical of woodland, scrub, pasture and wetland habitats, whereas the winter seedbank is dominated on all surfaces by ruderal species with persistent seedbanks, mainly associated with aquatic, wetland, pasture, arable and wasteland habitats. At shorter timescales, the biogeomorphological trajectory of pioneer islands is initiated by large flood events that control the elevation of deposited trees, and subsequent flows that control tree survival and establishment. Island morphological evolution depends on the frequency‐magnitude of sediment and seed delivery and redistribution by flood and possibly wind events, whereas island ability to retain sediments reflects the degree of vegetation establishment, which in the short‐term may vary with seasonal to annual moisture supply, substrate characteristics and climatic growth conditions.Ulfah Mardhiah's research was funded by the SMART Joint Doctoral Programme (Science for MAnagement of Rivers and their Tidal systems), which is financed by the Erasmus Mundus Programme of the European Union

Order effects in high stakes undergraduate examinations: An analysis of 5 years of administrative data in one UK medical school

This is the final version. Available from the publisher via the DOI in this record.Statistical code and data set are available from the authors on request: contact JBu ( [email protected]).Objective: To investigate the association between student performance in undergraduate objective structured clinical examinations (OSCEs) and the examination schedule to which they were assigned to undertake these examinations. Design: Analysis of routinely collected data. Setting: One UK medical school. Participants: 2331 OSCEs of 3 different types (obstetrics OSCE, paediatrics OSCE and simulated clinical encounter examination OSCE) between 2009 and 2013. Students were not quarantined between examinations. Outcomes: (1) Pass rates by day examination started, (2) pass rates by day station undertaken and (3) mean scores by day examination started. Results: We found no evidence that pass rates differed according to the day on which the examination was started by a candidate in any of the examinations considered (p>0.1 for all). There was evidence (p=0.013) that students were more likely to pass individual stations on the second day of the paediatrics OSCE (OR 1.27, 95% CI 1.05 to 1.54). In the cases of the simulated clinical encounter examination and the obstetrics and gynaecology OSCEs, there was no (p=0.42) or very weak evidence (p=0.099), respectively, of any such variation in the probability of passing individual stations according to the day they were attempted. There was no evidence that mean scores varied by day apart from the paediatric OSCE, where slightly higher scores were achieved on the second day of the examination. Conclusions: There is little evidence that different examination schedules have a consistent effect on pass rates or mean scores: students starting the examinations later were not consistently more or less likely to pass or score more highly than those starting earlier. The practice of quarantining students to prevent communication with (and subsequent unfair advantage for) subsequent examination cohorts is unlikely to be required.University of Cambridge School of Clinical Medicin