Velocimetry with refractive index matching for complex flow configurations, phase 1

The feasibility of obtaining detailed velocity field measurements in large Reynolds number flow of the Space Shuttle Main Engine (SSME) main injector bowl was demonstrated using laser velocimetry and the developed refractive-index-matching technique. An experimental system to provide appropriate flow rates and temperature control of refractive-index-matching fluid was designed and tested. Test results are presented to establish the feasibility of obtaining accurate velocity measurements that map the entire field including the flow through the LOX post bundles: sample mean velocity, turbulence intensity, and spectral results are presented. The results indicate that a suitable fluid and control system is feasible for the representation of complex rocket-engine configurations and that measurements of velocity characteristics can be obtained without the optical access restrictions normally associated with laser velocimetry. The refractive-index-matching technique considered needs to be further developed and extended to represent other rocket-engine flows where current methods either cannot measure with adequate accuracy or they fail

A review on the biodiversity of hard substrate invertebrate communities in the Aegean Sea

This review attempts to estimate the biodiversity of the macrobenthic communities that develop on hard bottoms in the Aegean Sea. Literature analysis revealed that 1,171 species inhabit the hard substrate communities, constituting 20.9% of the total Mediterranean species. The hierarchical cluster analysis of the available data identified five major types: (1) the supralittoral communities, (2) the midlittoral communities, (3) the port communities, (4) the various facies of the photophilic algae community, and (5) the facies of the sciaphilic algae community. Thus, hard bottom communities in the Aegean seem to be separated mainly according to vertical zonation. A total of 68 hard-bottom species are under multiple exploitation, providing considerable economic profit. Taking into account the structural complexity of hard substrate benthic communities and their sensitivity to disturbances, it is essential to preserve the biodiversity of these biotopes

Learning accurate path integration in a ring attractor model of the head direction system

Ring attractor models for angular path integration have recently received strong experimental support. To function as integrators, head-direction (HD) circuits require precisely tuned connectivity, but it is currently unknown how such tuning could be achieved. Here, we propose a network model in which a local, biologically plausible learning rule adjusts synaptic efficacies during development, guided by supervisory allothetic cues. Applied to the Drosophila HD system, the model learns to path-integrate accurately and develops a connectivity strikingly similar to the one reported in experiments. The mature network is a quasi-continuous attractor and reproduces key experiments in which optogenetic stimulation controls the internal representation of heading, and where the network remaps to integrate with different gains. Our model predicts that path integration requires supervised learning during a developmental phase. The model setting is general and also applies to architectures that lack the physical topography of a ring, like the mammalian HD system

The impacts of climate change on the ecology of a migrant wetland warbler

Climate-change has the potential to affect migratory birds by altering prey availability across their annual cycle. Observational and experimental approaches were used to understand the causes and consequences of these changes on the breeding productivity, mass regulation and survival of a wetland bird; the Eurasian reed warbler Acrocephalus scirpaceus. Climatic influences on wetland invertebrate populations were assessed by monitoring natural and experimentally-induced variations in temperature. Further increases in early spring temperatures are likely to result in earlier availability of prey resources. The responses of breeding birds to changes in their prey were tested with food supplementations, which advanced egg-laying dates, reduced the laying interval and incubation duration, and increased nestling growth rate. These effects enable earlier first fledglings and increase the opportunity for second breeding attempts within the peak invertebrate prey window. The consequences of prey availability on wintering body condition were tested by comparing resources and energy reserves in contrasting habitats in West Africa during the non-breeding period. Birds occupying prey-rich habitats maintained lower body reserves than conspecifics occupying prey-poor dry-scrub habitats, consistent with strategic buffering of reserves against starvation in food-poor habitat. These results suggest how reed warblers are able to survive in lower quality habitats and potentially avoid density-dependent mortality associated with drought as observed in other wetland migrants. Analysis of long term (>30 year) weather effects on survival revealed measurable but minor impacts, suggesting reed warblers are very adaptive to environmental change. Overall, this study provides strong support for climate-driven advance in spring invertebrate availability and identifies the reed warbler breeding and survival parameters most affected by increases to prey availability. This study provides an integrated and original understanding of the mechanisms which may underlie current levels of population growth in what appears to be one of the few long-distance migratory European songbird species currently benefiting from climate-change

The effectiveness of deterrent measures to minimize disturbance impacts to breeding European nightjar at an upland wind farm site in South Wales, UK

The Pen y Cymoedd windfarm in South Wales, UK, is set in an upland area currently dominated by coniferous forestry with a varied age structure resulting from standard forestry management practices.The site supports an important population of European nightjar Caprimulgus europaeus. The activities associated with wind farm construction have the potential to damage and disturb nightjar nests during the breeding season whilst long term operation has the potential for collision mortality. To mitigate for potential impacts during construction, we implemented measures to allow nest avoidance including the identification and demarcation of active nest sites. Due to the difficulty in locating nightjar nests and the potential for false negative results, additional measures were deployed at 17 turbine locations to deter nightjars from establishing nesting territories. Deterrent measures involved regular removal of vegetation on the construction areas. We tested the effectiveness of the deterrent measures by comparing levels ofmale nightjar territorial display activity in treated and untreated locations over one breeding season.Territorial behaviour was recorded using standard nightjar presence-absence survey methods. We found no significant difference between levels of territorial display activity in treated and untreated areas. This suggests that the deterrent measures utilised at Pen y Cymoedd in 2016 were ineffective in deterring male nightjar display activity during windfarm construction

Using UAV‐mounted thermal cameras to detect the presence of nesting nightjar in upland clear‐fell: A case study in South Wales, UK

1. Confirming the presence and location of European Nightjar Caprimulgus europaeus nests is a significant fieldwork challenge in ecological monitoring. Nest sites can be located through direct observation or capture and radio tracking of breeding individuals; however, such work is time consuming, disturbing and costly.2. Unmanned aerial vehicles (UAV) equipped with thermal sensors may enable rapid survey over large areas by detecting nest locations based on the contrast of relatively warm nests and the surrounding cooler ground. The application of this concept using UAV‐mounted thermal sensors was trialled in two upland clear‐fell forestry sites in South Wales, UK.3. Detection trials were undertaken at five known nightjar nest sites to assess optimal timing and flight height for surveys. Nest heat signatures were clear during dusk and dawn, but not during the daytime. Nests were identifiable at flight heights up to 25 m, but flight heights of 12–20 m were optimal for the numbers of pixels per nest.4. This approach was tested in a field trial of a 17‐ha forestry site where the presence and position of nesting nightjars were unknown. An automated transect at dusk and dawn at 15 m flight elevation identified two active nightjar nests and four male nightjar roost sites. Without image analysis automation, the process of manual inspection of 2607 images for ‘hotspots’ of the approximate size and shape of nightjar nests was laborious.5. The UAV approach took around 18 h including survey time, processing and ground verification, whilst a nightjar nest finding survey would take 35 h for the same area. The small size of nightjars and the low resolution of the thermal sensors requires low altitude flight in order to maximize detectability and pixel coverage. Low flight elevation requires more consideration of the risk of collision with trees or posts. Consequently, the approach would not be suitable for covering areas of highly variable terrain

Sustainable management of fish stock: An assessment of small-scale fishing in Greece

The aim of this study was to identify the main métiers practiced by gillnet, trammel net and combined net fishery in the Kalymnos Island. The catch was obtained every 15 days of the small-scale fleet for the period from February 2013 to May 2014 by interviews during unloading. A total 315 fishing operations were recorded. Multivariate analysis applied to either species landings composition or economic revenue. The most important métiers identified were those B. boops with gillnet, intense fishing activity during December-February and mesh size 26 mm, métier which targeting S. porcus and S. officinalis with fishing gear trammel net, intense fishing activity during April-May and mesh size 26 mm. Both of these métiers appeared high produce and income. The results of this study confirm the multi-species natural of small-scale fishing and fishing activity in the area of Kalymnos specific difference from the other area in Greece