New technique to measure the cavity defects of Fabry-Perot interferometers

(Abridged): We define and test a new technique to accurately measure the cavity defects of air-spaced FPIs, including distortions due to the spectral tuning process typical of astronomical observations. We further develop a correction technique to maintain the shape of the cavity as constant as possible during the spectral scan. These are necessary steps to optimize the spectral transmission profile of a two-dimensional spectrograph using one or more FPIs. We devise a generalization of the techniques developed for the so-called phase-shifting interferometry to the case of FPIs. The technique is applicable to any FPI that can be tuned via changing the cavity spacing ($z$-axis), and can be used for any etalon regardless of the coating' reflectivity. The major strength of our method is the ability to fully characterize the cavity during a spectral scan, allowing for the determination of scan-dependent modifications of the plates. As a test, we have applied this technique to three 50 mm diameter interferometers, with cavity gaps ranging between 600 micron and 3 mm, coated for use in the visible range. We obtain accurate and reliable measures of the cavity defects of air-spaced FPIs, and of their evolution during the entire spectral scan. Our main, and unexpected, result is that the relative tilt between the two FPI plates varies significantly during the spectral scan, and can dominate the cavity defects; in particular, we observe that the tilt component at the extremes of the scan is sensibly larger than at the center of the scan. Exploiting the capability of the electronic controllers to set the reference plane at any given spectral step, we develop a correction technique that allows the minimization of the tilt during a complete spectral scan. The correction remains highly stable over long periods, well beyond the typical duration of astronomical observations.Comment: 15 pages, 20+ figures, accepted for publication in A&A. Two additional movies are available in the online version of the pape

Optimal Pacing for Running 400 m and 800 m Track Races

Physicists seeking to understand complex biological systems often find it rewarding to create simple "toy models" that reproduce system behavior. Here a toy model is used to understand a puzzling phenomenon from the sport of track and field. Races are almost always won, and records set, in 400 m and 800 m running events by people who run the first half of the race faster than the second half, which is not true of shorter races, nor of longer. There is general agreement that performance in the 400 m and 800 m is limited somehow by the amount of anaerobic metabolism that can be tolerated in the working muscles in the legs. A toy model of anaerobic metabolism is presented, from which an optimal pacing strategy is analytically calculated via the Euler-Lagrange equation. This optimal strategy is then modified to account for the fact that the runner starts the race from rest; this modification is shown to result in the best possible outcome by use of an elementary variational technique that supplements what is found in undergraduate textbooks. The toy model reproduces the pacing strategies of elite 400 m and 800 m runners better than existing models do. The toy model also gives some insight into training strategies that improve performance.Comment: 14 pages, 4 figures, submitted to the American Journal of Physic

Psychosocial and behavioural correlates of attitudes towards antiretroviral therapy (ART) in a sample of South African mineworkers

Despite being one of the worst affected sectors in South Africa, the mining sector has proven to be one of the most active in intervention efforts in the fight against HIV and AIDS (Ellis, 2007). Owing to low uptake rates of antiretroviral therapy (ART) in mining companies in recent years (Connelly & Rosen, 2006) and the positive relationship between attitudes towards ART and ART uptake (Cooper et al., 2002; Horne, Cooper, Gellaitry, Leake, & Fisher, 2007), this study sought to describe and investigate the psychosocial and behavioural correlates of attitudes towards ART in a sample of South African mineworkers. A total of 806 mineworkers from a large South African mine participated in this quantitative study. Despite a high rate of HIV testing behaviour (83.0%) as well as favourable attitudes towards ART, analysis indicated that temporary employees and contractors were more vulnerable in terms of HIV risk, HIV testing behaviours and ART knowledge and attitudes. Employees who had more positive attitudes towards ART were more knowledgeable of ART and, importantly, had a more favourable attitude towards the mine’s HIV/AIDS treatment programme. These findings are discussed in relation to the low ART uptake rates in this context and recommendations for the improvement of ART uptake amongst employees at this mining site.Keywords: mining sector, workplace, ART uptake, attitudes.Le secteur minier reste l’un des secteurs les plus affectés par le VIH et SIDA en Afrique du Sud et aussi l’un des plus actifs dans la lutte contre la maladie (Ellis, 2007). En raison du faible taux d’utilisation de la thérapie antirétrovirale (ART) dans les années récentes par des compagnies minières (Connelly & Rosen, 2006) et les attitudes positives envers ART et ART absorption (Cooper et al., 2002; Horne, Cooper, Gellaitry, Leake, & Fisher, 2007) pour trouver des solutions pour les malades du VIH/SIDA, cette étude á pour objectif d’examiner les comportements psychosociaux et le traitement de la thérapie antirétrovirale d’un groupe de mineurs Sud-Africains. Huit cent six mineurs Sud-Africains ont participé à cette étude quantitative. Soit un taux de dépistage VIH élevé (83.0%) et des attitudes très favorables envers ART, les analyses indiquent qu’en termes de risque du VIH les employés temporaires et les entrepreneurs sont plus exposés á la maladie. Mais cependant, les employés qui sont bien informés de la méthode ART grâce à la connaissance et à l’information bénéficient d’un programme de traitement contre le VIH/SIDA. Ces résultats font l’objet de discussion sur le faible taux d’ART dans ce contexte et quelques recommandations et améliorations de l’absorption de l’ART pour les employés de ce site minier

Solar Atmospheric Oscillations and the Chromospheric Magnetic Topology

We investigate the oscillatory properties of the quiet solar chromosphere in relation to the underlying photosphere, with particular regard to the effects of the magnetic topology. We perform a Fourier analysis on a sequence of line-of-sight velocities measured simultaneously in a photospheric (Fe I 709.0 nm) and a chromospheric line (Ca II 854.2 nm). The velocities were obtained from full spectroscopic data acquired at high spatial resolution with the Interferometric BIdimensional Spectrometer (IBIS). The field of view encompasses a full supergranular cell, allowing us to discriminate between areas with different magnetic characteristics. We show that waves with frequencies above the acoustic cut-off propagate from the photosphere to upper layers only in restricted areas of the quiet Sun. A large fraction of the quiet chromosphere is in fact occupied by ``magnetic shadows'', surrounding network regions, that we identify as originating from fibril-like structures observed in the core intensity of the Ca II line. We show that a large fraction of the chromospheric acoustic power at frequencies below the acoustic cut-off, residing in the proximity of the magnetic network elements, directly propagates from the underlying photosphere. This supports recent results arguing that network magnetic elements can channel low-frequency photospheric oscillations into the chromosphere, thus providing a way to input mechanical energy in the upper layers.Comment: 4 pages, 3 figure, A&A Letters in pres

Inhibition of neurogenic inflammation attenuates the inflammatory response following traumatic brain injury in rats

© 2004 by MEDIMOND The document attached has been archived with permission from the Medimond International Proceedings Division. An external link to the publisher’s web site is included.A profound inflammatory response is initiated following traumatic brain injury (TBI). It has been proposed that serum IL-6 levels may serve as a marker for the severity of the injury. Using the rat impact-acceleration model of TBI, the study examined whether drugs which are able to inhibit neurogenic inflammation (capsaicin, NK1 antagonist), might influence the post-traumatic inflammatory response. In non-treated animals, TBI resulted in a significant increase in serum IL-6 levels. However, in animals pre-treated with capsaicin prior to injury, or treated with an NK1 antagonist following injury, this rise in IL-6 levels was not observed. We conclude that the inhibition of neurogenic inflammation may attenuate the inflammatory reaction associated with TBI, and help improve outcome.K. Reardon, D. Heath, A. Nimmo, R. Vink and K. Whitfieldhttp://www.medimond.com/proceedings/moreinfo/20040912.ht

“Just keep pushing”: parents’ experiences of accessing child and adolescent mental health services for child anxiety problems

Background:Anxiety disorders are among the most common psychopathologies in childhood, however a high proportion of children with anxiety disorders do not access effective treatments.The aim of the present qualitative study was to understand families’ experiences of seeking help and accessing specialist treatment for difficulties with childhood anxiety.Methods:Parents of 16 children (aged 7-12 years) referred to a child mental health service for difficulties with anxiety, were interviewed about their experiences of seeking and accessing treatment within CAMHS. All interviews were transcribed verbatim and thematically analysed for similarities and differences in families’ experiences. Results:Factors that helped and/or hindered families accessing treatment related to: i) parental recognition, ii) contact with professionals, iii) reaching CAMHS, iv) parental effort, and v) parental knowledge and concerns. High demands on services and parents’ uncertainty surrounding the help-seeking process presented key hurdles for families. The critical role of parental persistence and support from GPs and school staff was evident across interviews.Conclusions:Findings highlighted the need for information and guidance on identifying child anxiety difficulties and professional, peer and self-help support; and ensuring sufficient provision is available to allow families prompt access to support

A prototype of a large tunable Fabry–Pérot interferometer for solar spectroscopy

Large Fabry-Pérot Interferometers (FPIs) are used in a variety of astronomical instrumentation, including spectro-polarimeters for 4 m class solar telescopes. In this work we comprehensively characterize the cavity of a prototype 150 mm FPI, sporting a novel, fully symmetric design. Of particular interest, we define a new method to properly assess the gravity effects on the interferometer's cavity when the system is used in either the vertical or horizontal configuration, both typical of solar observations. We show that the symmetric design very effectively limits the combined effects of pre-load and gravity forces to only a few nm over a 120 mm diameter illuminated surface, with gravity contributing ~2 nm peak-to-valley (~0.3 nm rms) in either configuration. We confirm a variation of the tilt between the plates of the interferometer during the spectral scan, which can be mitigated with appropriate corrections to the spacing commands. Finally, we show that the dynamical response of the new system fully satisfies typical operational scenarios. We conclude that large, fully symmetric FPIs can be safely used within solar instrumentation in both, horizontal and vertical position, with the latter better suited to limiting the overall volume occupied by such an instrument