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Effect of clocking on compressor noise generation

The effect of stator clocking on the acoustic noise generation characteristics in an axial high-pressure compressor is analysed. A realistic geometry with one-and-a-half stages is assessed using high fidelity and low-order numerical methods for different clocking positions at approach operating conditions. The compressor efficiency and the acoustic noise emission is found to vary insignificantly between the simulated clocking configurations. Nonetheless, the pressure distribution is altered significantly right upstream of the inlet guide vanes. Although the cut-on modes exhibit at least 10 dB higher amplitudes, the cut-off modes contribute decisively to the wave pattern in the near field. Optimal acoustic liner design can expand on the differently evolving interference pattern of acoustic waves at discrete frequencies. The low-order model is found to predict the directionality of the acoustic waves and the cut-on criteria for the individual modes in excellent agreement with the high fidelity simulations. However, the phase cannot be estimated due to the simplicity of the low-order formulation.The authors wish to express their sincere gratitude to Rolls-Royce plc for the permission to publish this paper, which partly developed through the Rolls-Royce plc and Innovate UK Aerospace Technology Institute funded research programme, ACAPELLA

Entropy and vorticity wave generation in realistic gas turbine combustors

Understanding the nature of the unsteady flow at the combustor exit is required to accurately simulate time dependent phenomena in the turbine entry, such as indirect noise generation. Using Large Eddy Simulations of the combustion process in a realistic geometry, we analyse the flow at its exit. Two realistic, near-ground certification operating conditions are considered. Different mechanisms for large-scale flow and thermal structure generation are described, which are ejected into the turbine. Modal decomposition methods are used to extract the spatial and temporal scales at the turbine entry. We find that, depending on the operating condition, the entropy waves convect as elongated streaks in the core of the combustor annulus or the proximity of the walls. The dominant unsteady character of the fluctuations exhibits different spectral properties, i.e. low-frequency in the core and high-frequency towards walls. At the combustor exit, the vortical field is dominated by the swirl in the air inlet, which is found to have little influence on the entropy perturbations. Further, the importance of considering the interaction of multiple fuel injectors and combustion zones in an annular combustor is investigated. It is shown that pulsating circumferential vorticity modes can occur in multi-sector annular combustors but these, however, do not affect the entropy wave distribution.The authors wish to express their sincere gratitude to Rolls-Royce plc for permission to publish this paper. This work was conducted within the EU Horizon 2020 Framework Research Programme - Clean Sky (CORNET-CORE Noise Technologies), project number: H2020-CS2-CFP01-2014-01/ 686332

Nutrient availability and invasive fish jointly drive community dynamics in an experimental aquatic system

Species invasions increasingly occur alongside other forms of ecosystem change, highlighting the need to understand how invasion outcomes are influenced by environmental factors. Within freshwaters, two of the most widespread drivers of change are introduced fishes and nutrient loading, yet it remains difficult to predict how interactions between these drivers affect invasion success and consequences for native communities. To test competing theories about interactions between nutrients and invasions, we conducted a 2 × 3 factorial mesocosm experiment, varying western mosquitofish (Gambusia affinis) presence and nutrient availability within aquatic communities. Based on theory, increased nutrients could either (1) facilitate coexistence between predatory mosquitofish and native species by increasing prey availability (the invader attenuation hypothesis) or (2) strengthen predation effects by enhancing fish productivity more than native community members (the invader amplification hypothesis). In outdoor mesocosms designed to mimic observed nutrient conditions and local community structure, mosquitofish directly reduced the abundances of zooplankton and three native amphibian species, leading to indirect increases in phytoplankton, periphyton, and freshwater snail biomass through trophic cascades. Nutrient additions increased native amphibian growth but had especially pronounced effects on the productivity of invasive mosquitofish. The elevated nutrient condition supported ~5 times more juvenile mosquitofish and 30% higher biomass than the low nutrient condition. Increased nutrients levels did not weaken the top‐down effects of mosquitofish on invertebrates or amphibians. Collectively, our results support the invader amplification hypothesis, suggesting that increased nutrient loading may benefit invasive species without attenuating their undesirable effects on native community members.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/143635/1/ecs22153_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/143635/2/ecs22153.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/143635/3/ecs22153-sup-0001-AppendixS1.pd

Stimulus-preceding negativity in ADHD

Children with ADHD often show disrupted response preparation as indicated by attenuated stimulus-preceding negativity (SPN). This study examined response preparation in a relatively short cue-stimulus interval. No differences in SPN occurred between children with ADHD and their normal peers. A strong positive relationship was found between SPN and mean reaction time in both groups. Children with ADHD are able to mentally prepare themselves for upcoming events in short cue-stimulus intervals. © 2013 Springer-Verlag Wien

The role of configurality in the Thatcher illusion: an ERP study.

The Thatcher illusion (Thompson in Perception, 9, 483-484, 1980) is often explained as resulting from recognising a distortion of configural information when 'Thatcherised' faces are upright but not when inverted. However, recent behavioural studies suggest that there is an absence of perceptual configurality in upright Thatcherised faces (Donnelly et al. in Attention, Perception & Psychophysics, 74, 1475-1487, 2012) and both perceptual and decisional sources of configurality in behavioural tasks with Thatcherised stimuli (Mestry, Menneer et al. in Frontiers in Psychology, 3, 456, 2012). To examine sources linked to the behavioural experience of the illusion, we studied inversion and Thatcherisation of faces (comparing across conditions in which no features, the eyes, the mouth, or both features were Thatcherised) on a set of event-related potential (ERP) components. Effects of inversion were found at the N170, P2 and P3b. Effects of eye condition were restricted to the N170 generated in the right hemisphere. Critically, an interaction of orientation and eye Thatcherisation was found for the P3b amplitude. Results from an individual with acquired prosopagnosia who can discriminate Thatcherised from typical faces but cannot categorise them or perceive the illusion (Mestry, Donnelly et al. in Neuropsychologia, 50, 3410-3418, 2012) only differed from typical participants at the P3b component. Findings suggest the P3b links most directly to the experience of the illusion. Overall, the study showed evidence consistent with both perceptual and decisional sources and the need to consider both in relation to configurality

Effects of etizolam and ethyl loflazepate on the P300 event-related potential in healthy subjects

<p>Abstract</p> <p>Background</p> <p>Benzodiazepines carry the risk of inducing cognitive impairments, which may go unnoticed while profoundly disturbing social activity. Furthermore, these impairments are partly associated with the elimination half-life (EH) of the substance from the body. The object of the present study was to examine the effects of etizolam and ethyl loflazepate, with EHs of 6 h and 122 h, respectively, on information processing in healthy subjects.</p> <p>Methods</p> <p>Healthy people were administered etizolam and ethyl loflazepate acutely and subchronically (14 days). The auditory P300 event-related potential and the neuropsychological batteries described below were employed to assess the effects of drugs on cognition. The P300 event-related potential was recorded before and after drug treatments. The digit symbol test, trail making test, digit span test and verbal paired associates test were administered to examine mental slowing and memory functioning.</p> <p>Results</p> <p>Acute administration of drugs caused prolongation in P300 latency and reduction in P300 amplitude. Etizolam caused a statistically significant prolongation in P300 latency compared to ethyl loflazepate. Furthermore, subchronic administration of etizolam, but not ethyl loflazepate, still caused a weak prolongation in P300 latency. In contrast, neuropsychological tests showed no difference.</p> <p>Conclusions</p> <p>The results indicate that acute administration of ethyl loflazepate induces less effect on P300 latency than etizolam.</p