Stabilization of crossflow instability with plasma actuators: linearized navier stokes simulations

This paper describes work carried out within the European Union (EU)-Russia Buterfli project to look at the control of transition-causing “target” stationary cross flow vortices, by the use of distributed plasma actuation to generate sub-dominant “killer” modes. The objective is to use the “killer” modes to control the “target” modes through a non-linear stabilizing mechanism. The numerical modelling and results are compared to experimental studies performed at the TsAGI T124 tunnel for a swept plate subject to a favorable pressure gradient flow. A mathematical model for the actuator developed at TsAGI was implemented in a linearized Navier Stokes (LNS) solver and used to model and hence predict “killer” mode amplitudes at a measurement plane in the experiment. The LNS analysis shows good agreement with experiment, and the results are used as input for non-linear PSE analysis to predict the effect of these modes on crossflow transition. Whilst the numerical model indicates a delay in transition, experimental results indicated an advance in transition rather than delay. This was determined to be due to actuator induced unsteadiness arising in the experiment, resulting in the generation of travelling crossflow disturbances which tended to obscure and thus dominate the plasma stabilized stationary disturbances

Development of Tollmien-Schlichting disturbances in the presence of laminar separation bubbles on an unswept infinite wavy wing

The effect of long-wavelength sinusoidal surface waviness on the development of Tollmien-Schlichting (TS) wave instabilities is investigated. The analysis is based on the compressible flow that forms over an unswept infinite wavy wing with surface variations of variable amplitude, wavelength, and phase. Boundary layer profiles are extracted directly from solutions of a Navier-Stokes solver, which allows a thorough parametric analysis to be undertaken. Many wavy surface configurations are examined that can be sufficient to establish localized pockets of separated flow. Linear stability analysis is undertaken using parabolized stability equations (PSE) and linearized Navier-Stokes (LNS) methods, and surface waviness is generally found to enhance unstable behavior. Results of the two schemes are compared and criteria for PSE to establish accurate solutions in separated flows are determined, which are based on the number of TS waves per wavelength of the surface deformation. Relationships are formulated, relating the instability variations to the surface parameters, which are consistent with previous observations regarding the growth of TS waves on a flat plate. Additionally, some long-wavelength surface deformations are found to stabilize TS disturbances

Acoustic receptivity and transition modeling of Tollmien-Schlichting disturbances induced by distributed surface roughness

Acoustic receptivity to Tollmien-Schlichting waves in the presence of surface roughness is investigated for a flat plate boundary layer using the time-harmonic incompressible linearized Navier-Stokes equations. It is shown to be an accurate and efficient means of predicting receptivity amplitudes, and therefore to be more suitable for parametric investigations than other approaches with DNS-like accuracy. Comparison with literature provides strong evidence of the correctness of the approach, including the ability to quantify non-parallel flow effects. These effects are found to be small for the efficiency function over a wide range of frequencies and local Reynolds numbers. In the presence of a two-dimensional wavy-wall, non-parallel flow effects are quite significant, producing both wavenumber detuning and an increase in maximum amplitude. However, a smaller influence is observed when considering an oblique Tollmien-Schlichting wave. This is explained by considering the non-parallel effects on receptivity and on linear growth which may, under certain conditions, cancel each other out. Ultimately, we undertake a Monte-Carlo type uncertainty quantification analysis with two-dimensional distributed random roughness. Its power spectral density (PSD) is assumed to follow a power law with an associated uncertainty following a probabilistic Gaussian distribution. The effects of the acoustic frequency over the mean amplitude of the generated two-dimensional Tollmien-Schlichting waves are studied. A strong dependence on the mean PSD shape is observed and discussed according to the basic resonance mechanisms leading to receptivity. The growth of Tollmien-Schlichting waves is predicted with non-linear parabolized stability equations computations to assess the effects of stochasticity in transition location

Peer influence as a driver of technological innovation in the UK National Health Service: a qualitative study of clinicians’ experiences and attitudes

Background Accelerating innovation to improve quality is a key policy target for healthcare systems around the world. Effectively influencing individuals’ behaviour is crucial to the success of innovation initiatives. This study explores UK clinicians’ lived experiences of, and attitudes towards, clinical peers endorsing healthcare innovations. Methods Qualitative interviews with UK-based clinicians in one of two groups: (1) clinicians working in ‘front-line’ service provision and (2) clinicians in strategic leadership roles within health institutions. Participants were identified through purposive sampling, and participated in semistructured telephone interviews. Thematic analysis was used to identify and analyse themes in the data. Results 17 participants were recruited: eight clinicians from front-line UK healthcare settings and nine clinicians in leadership roles. Two major themes were identified from the interviews: power and trust. Participants recognised and valued peers’ powerful influence, exerted in person via social networks and routine work-related activities. Peers were implicitly trusted, although often on condition of their credibility and deservingness of respect, supporting evidence and absence of conflict of interest. While the groups shared similar views, they diverged on the subject of institutions, felt to be powerful by strategic leaders yet scarcely mentioned by front-line clinicians. Conclusions UK clinicians view peers as a powerful and trustworthy source to promote innovative technologies. Policies that aim to support this process should seek to control the wider conditions that nurture peer-to-peer influence. Further research into interpersonal influence in health settings may improve implementation of change initiatives

Sleep disturbance as a predictor of anxiety in children with Fetal Alcohol Spectrum Disorders and typically developing children

Background: High levels of anxiety and sleep problems are common features of Fetal Alcohol Spectrum Disorders (FASD). The strong association between sleep and anxiety has been documented in typically developing (TD) populations and is thought to be bidirectional. The association between sleep and anxiety in children with FASD has not yet been examined. Methods: Caregivers of children with FASD (n = 91) and TD children (n = 103) aged 6–16 completed the Children’s Sleep Habits Questionnaire (CSHQ), Spence Children’s Anxiety Scale (SCAS), and a background questionnaire. Hierarchical multiple regression analyses, group comparisons and ANCOVA interaction models were used to test the associations between sleep and anxiety within and between the two groups. Results: Sleep disturbances and anxiety were at clinical levels for the majority of the FASD group, and significantly higher in the FASD group than the TD group. After controlling for age and sex, 27 % of the variance in anxiety scores in TD children was attributable to sleep problems, and 33 % in children with FASD. Conclusion: This study highlights associations between parent-reported sleep and anxiety in FASD. Sleep disturbances were significant predictors of anxiety in both children with FASD and in TD children. Given the importance of sleep to healthy neurodevelopment, there is a pressing need for sleep intervention studies in children with FASD. Early identification and intervention for sleep problems in this condition should be a therapeutic priority

Acoustic-roughness receptivity in subsonic boundary-layer flows over aerofoils

The generation of a viscous–inviscid instability through scattering of an acoustic wave by localised and distributed roughness on the upper surface of a NACA 0012 aerofoil is studied with a time-harmonic compressible adjoint linearised Navier–Stokes approach. This extends previous work by the authors dedicated to flat plate geometries. The key advancement lies in the modelling of the inviscid acoustic field external to the aerofoil boundary layer, requiring a numerical solution of the convected Helmholtz equation in a non-uniform inviscid field to determine the unsteady pressure field on the curved aerofoil surface. This externally imposed acoustic pressure field subsequently drives the acoustic boundary layer, which fundamentally determines the amplitudes of acoustic-roughness receptivity. A study of receptivity in the presence of Gaussian-shaped roughness and sinusoidally distributed roughness at Mach number M∞ = 0.4 and Strouhal numbers S ≈ {46, 69, 115} shows the effects of various parameters, most notably angle of attack, angle of incidence of the externally imposed plane acoustic wave and geometry of surface roughness; the latter is varied from viewpoint of its placement on the aerofoil surface and its wavelength. The parametric study suggests that non-parallel effects are quite substantial and that considerable differences arise when using parallel flow theory to estimate the optimal width of Gaussian-shaped roughness elements to provoke the greatest response. Furthermore, receptivity amplitudes for distributed roughness are observed to be generally higher for lower angles of attack, i.e. for less adverse pressure gradients. It is also shown that the boundary layer is more receptive to upstream-travelling acoustic waves

Rapid Evidence Review of Community Engagement and Resources in the UK during the COVID-19 Pandemic: How Can Community Assets Redress Health Inequities?

Community engagement, such as participating in arts, nature or leisurely activities, is positively associated with psychological and physiological wellbeing. Community-based engagement during the COVID-19 pandemic facilitated informal and local mutual aid between individuals. This rapid evidence review assesses the emergence of community-based arts, nature, music, theatre and other types of cultural engagement amongst UK communities in response to the COVID-19 pandemic. Here, we focus on all community engagement with a sub-focus on provisions accessed by and targeted towards vulnerable groups. Two hundred and fifty-six resources were included that had been created between February 2020 and January 2021. Resources were identified through Google Scholar, PubMed, Web of Science, MedRXic, PsycharXiv and searches for grey literature and items in the public domain. The majority reported services that had been adapted to become online, telephone-based or delivered at a distance from doorsteps. Several quality assessment frameworks were used to evaluate the quality of data. Whilst a number of peer-reviewed, grey literature and public domain articles were identified, less than half of the identified literature met quality thresholds. The pace of the response to the pandemic may have meant that robust evaluation procedures were not always in place

Sleep and Cognition in Children with Fetal Alcohol Spectrum Disorders (FASD) and Children with Autism Spectrum Disorders (ASD)

Children with Fetal Alcohol Spectrum Disorders (FASD) and Autism Spectrum Disorders (ASD) experience significantly higher rates of sleep disturbances than their typically developing peers. However, little is known about the association between sleep and the cognitive phenotype in these clinical populations. Structural damage affecting cortical and subcortical connectivity occurs as a result of prenatal alcohol exposure in children with FASD, whilst it is believed an abundance of short-range connectivity explains the phenotypic manifestations of childhood ASD. These underlying neural structural and connectivity differences manifest as cognitive patterns, with some shared and some unique characteristics between FASD and ASD. This is the first study to examine sleep and its association with cognition in individuals with FASD, and to compare sleep in individuals with FASD and ASD. We assessed children aged 6–12 years with a diagnosis of FASD (n = 29), ASD (n = 21), and Typically Developing (TD) children (n = 46) using actigraphy (CamNTech Actiwatch 8), digit span tests of working memory (Weschler Intelligence Scale), tests of nonverbal mental age (MA; Ravens Standard Progressive Matrices), receptive vocabulary (British Picture Vocabulary Scale), and a choice reaction time (CRT) task. Children with FASD and ASD presented with significantly shorter total sleep duration, lower sleep efficiency, and more nocturnal wakings than their TD peers. Sleep was significantly associated with scores on the cognitive tests in all three groups. Our findings support the growing body of work asserting that sleep is significant to cognitive functioning in these neurodevelopmental conditions; however, more research is needed to determine cause and effect

Nightmares in Children with Foetal Alcohol Spectrum Disorders, Autism Spectrum Disorders, and Their Typically Developing Peers

Children with Foetal Alcohol Spectrum Disorders (FASD) and Autism Spectrum Disorders (ASD) experience significantly higher rates of sleep disturbances than their typically developing (TD) peers. Pre-sleep anxiety and waking emotional content is known to affect the content and frequency of nightmares, which can be distressing to children and caregivers. This is the first study to analyse nightmare frequency and content in FASD, and to assess its association with psychometric outcomes. Using online caregiver questionnaires, we assessed reports from 277 caregivers of children with ASD (n = 61), FASD (n = 112), and TD children (n = 104) using the Children’s Sleep Habits Questionnaire (CSHQ), the Child Behaviour Checklist (CBCL), the Spence Children’s Anxiety Scale (SCAS), and the Behaviour Rating Inventory for Executive Functioning (BRIEF). Within the ASD group, 40.3% of caregivers reported their children had nightmares. Within the FASD group, 73.62% of caregivers reported their children had nightmares, and within the TD group, 21.36% of caregivers reported their children had nightmares. Correlation analysis revealed significant associations between anxiety and nightmares, maladaptive behaviour and nightmares, and executive functioning and nightmares in the TD and FASD groups, but not ASD group. This paper adds to the emerging body of work supporting the need for sleep interventions as part of clinical practice with regard to children with ASD and FASD. As a relatively niche but important area of study, this warrants much needed further research