Flight-test nacelles

Design modifications for acoustically absorbing flight test nacelles of DC-8 turbofan engin

Exploring mechanisms of change in a pilot randomised trial of a distant delivery mindfulness intervention for people with Parkinson’s disease

People with Parkinson’s disease report high levels of non-motor symptoms, including anxiety and depression, that are difficult to treat pharmacologically. Mindfulness-based interventions have been shown to be effective in other long-term conditions. This pilot study explored how a mindfulness-based intervention may have had an effect and for whom, with a view to informing future studies. Volunteers were randomised to a remote delivery, eight-week mindfulness cognitive behavioural group therapy intervention (n=40) or wait-list (n=38), and measures for psychological outcomes and putative mediators were taken at baseline, 4 weeks, 8 weeks and 20-week follow-up. The study showed that all the outcome measures changed in a positive health direction in the intervention group. The intervention had a small effect on decentering (d=.36) and acceptance (d=.27) by mid-point, before depression at 8 weeks (d=-.28) and anxiety at follow-up (d=-.29), indicating an indirect effect between trial arm and levels of distress. Mediation and moderation analysis were conducted using PROCESS, time-lagging the mediators to the outcome variables, but no combined or individual indirect effects had confidence intervals entirely above or below zero, thus mediation cannot be confirmed. When the end of intervention mediators were analysed with the follow-up levels of anxiety and depression, there is evidence of inconsistent mediation, or possible suppression effects. Moderation analysis revealed that the effect on anxiety levels was moderated by gender, with women benefitting more from the mindfulness intervention. Moderated mediation analysis also indicated that the effect of the trial arm on levels of acceptance was conditional by age and time since diagnosis, and the effect of trial arm on levels of mindfulness skills by age, meaning that younger, newly-diagnosed patients were more able to increase mindfulness skills and acceptance

Visualising the structure of document search results: A comparison of graph theoretic approaches

This is the post-print of the article - Copyright @ 2010 Sage PublicationsPrevious work has shown that distance-similarity visualisation or ‘spatialisation’ can provide a potentially useful context in which to browse the results of a query search, enabling the user to adopt a simple local foraging or ‘cluster growing’ strategy to navigate through the retrieved document set. However, faithfully mapping feature-space models to visual space can be problematic owing to their inherent high dimensionality and non-linearity. Conventional linear approaches to dimension reduction tend to fail at this kind of task, sacrificing local structural in order to preserve a globally optimal mapping. In this paper the clustering performance of a recently proposed algorithm called isometric feature mapping (Isomap), which deals with non-linearity by transforming dissimilarities into geodesic distances, is compared to that of non-metric multidimensional scaling (MDS). Various graph pruning methods, for geodesic distance estimation, are also compared. Results show that Isomap is significantly better at preserving local structural detail than MDS, suggesting it is better suited to cluster growing and other semantic navigation tasks. Moreover, it is shown that applying a minimum-cost graph pruning criterion can provide a parameter-free alternative to the traditional K-neighbour method, resulting in spatial clustering that is equivalent to or better than that achieved using an optimal-K criterion

Constraining the variation of fundamental constants using 18cm OH lines

We describe a new technique to estimate variations in the fundamental constants using 18cm OH absorption lines. This has the advantage that all lines arise in the same species, allowing a clean comparison between the measured redshifts. In conjunction with one additional transition (for example, an HCO$^+$ line), it is possible to simultaneously measure changes in $\alpha$, $g_p$ and $y \equiv m_e/m_p$. At present, only the 1665 MHz and 1667 MHz lines have been detected at cosmological distances; we use these line redshifts in conjunction with those of HI 21cm and mm-wave molecular absorption in a gravitational lens at $z\sim 0.68$ to constrain changes in the above three parameters over the redshift range $0 < z \lesssim 0.68$. While the constraints are relatively weak ($\lesssim$ 1 part in $10^3$), this is the first simultaneous constraint on the variation of all three parameters. We also demonstrate that either one (or more) of $\alpha$, $g_p$ and $y$ must vary with cosmological time or there must be systematic velocity offsets between the OH, HCO$^+$ and HI absorbing clouds.Comment: 5 pages, no figures. Accepted for publication in Phys. Rev. Let

Acoustic, psychophysical, and neuroimaging measurements of the effectiveness of active cancellation during auditory functional magnetic resonance imaging

Functional magnetic resonance imaging (fMRI) is one of the principal neuroimaging techniques for studying human audition, but it generates an intense background sound which hinders listening performance and confounds measures of the auditory response. This paper reports the perceptual effects of an active noise control (ANC) system that operates in the electromagnetically hostile and physically compact neuroimaging environment to provide significant noise reduction, without interfering with image quality. Cancellation was first evaluated at 600 Hz, corresponding to the dominant peak in the power spectrum of the background sound and at which cancellation is maximally effective. Microphone measurements at the ear demonstrated 35 dB of acoustic attenuation [from 93 to 58 dB sound pressure level (SPL)], while masked detection thresholds improved by 20 dB (from 74 to 54 dB SPL). Considerable perceptual benefits were also obtained across other frequencies, including those corresponding to dips in the spectrum of the background sound. Cancellation also improved the statistical detection of sound-related cortical activation, especially for sounds presented at low intensities. These results confirm that ANC offers substantial benefits for fMRI research