640 research outputs found

    Parametrically Excited Surface Waves: Two-Frequency Forcing, Normal Form Symmetries, and Pattern Selection

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    Motivated by experimental observations of exotic standing wave patterns in the two-frequency Faraday experiment, we investigate the role of normal form symmetries in the pattern selection problem. With forcing frequency components in ratio m/n, where m and n are co-prime integers, there is the possibility that both harmonic and subharmonic waves may lose stability simultaneously, each with a different wavenumber. We focus on this situation and compare the case where the harmonic waves have a longer wavelength than the subharmonic waves with the case where the harmonic waves have a shorter wavelength. We show that in the former case a normal form transformation can be used to remove all quadratic terms from the amplitude equations governing the relevant resonant triad interactions. Thus the role of resonant triads in the pattern selection problem is greatly diminished in this situation. We verify our general results within the example of one-dimensional surface wave solutions of the Zhang-Vinals model of the two-frequency Faraday problem. In one-dimension, a 1:2 spatial resonance takes the place of a resonant triad in our investigation. We find that when the bifurcating modes are in this spatial resonance, it dramatically effects the bifurcation to subharmonic waves in the case of forcing frequencies are in ratio 1/2; this is consistent with the results of Zhang and Vinals. In sharp contrast, we find that when the forcing frequencies are in ratio 2/3, the bifurcation to (sub)harmonic waves is insensitive to the presence of another spatially-resonant bifurcating mode.Comment: 22 pages, 6 figures, late

    Hexagons, Kinks and Disorder in Oscillated Granular Layers

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    Experiments on vertically oscillated granular layers in an evacuated container reveal a sequence of well-defined pattern bifurcations as the container acceleration is increased. Period doublings of the layer center of mass motion and a parametric wave instability interact to produce hexagons and more complicated patterns composed of distinct spatial domains of different relative phase separated by kinks (phase discontinuities). Above a critical acceleration, the layer becomes disordered in both space and time.Comment: 4 pages. The RevTeX file has a macro allowing various styles. The appropriate style is "myprint" which is the defaul

    End-tidal carbon dioxide monitoring during bag valve ventilation: the use of a new portable device

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    <p>Abstract</p> <p>Background</p> <p>For healthcare providers in the prehospital setting, bag-valve mask (BVM) ventilation could be as efficacious and safe as endotracheal intubation. To facilitate the evaluation of efficacious ventilation, capnographs have been further developed into small and convenient devices able to provide end- tidal carbon dioxide (ETCO<sub>2</sub>). The aim of this study was to investigate whether a new portable device (EMMAâ„¢) attached to a ventilation mask would provide ETCO<sub>2 </sub>values accurate enough to confirm proper BVM ventilation.</p> <p>Methods</p> <p>A prospective observational trial was conducted in a single level-2 centre. Twenty-two patients under general anaesthesia were manually ventilated. ETCO<sub>2 </sub>was measured every five minutes with the study device and venous PCO<sub>2 </sub>(PvCO<sub>2</sub>) was simultaneously measured for comparison. Bland- Altman plots were used to compare ETCO<sub>2, </sub>and PvCO<sub>2</sub>.</p> <p>Results</p> <p>The patients were all hemodynamically and respiratory stable during anaesthesia. End-tidal carbon dioxide values were corresponding to venous gases during BVM ventilation under optimal conditions. The bias, the mean of the differences between the two methods (device versus venous blood gases), for time points 1-4 ranges from -1.37 to -1.62.</p> <p>Conclusion</p> <p>The portable device, EMMAâ„¢ is suitable for determining carbon dioxide in expired air (kPa) as compared to simultaneous samples of PvCO<sub>2</sub>. It could therefore, be a supportive tool to asses the BVM ventilation in the demanding prehospital and emergency setting.</p

    Faraday instability on viscous ferrofluids in a horizontal magnetic field: Oblique rolls of arbitrary orientation

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    A linear stability analysis of the free surface of a horizontally unbounded ferrofluid layer of arbitrary depth subjected to vertical vibrations and a horizontal magnetic field is performed. A nonmonotonic dependence of the stability threshold on the magnetic field is found at high frequencies of the vibrations. The reasons of the decrease of the critical acceleration amplitude caused by a horizontal magnetic field are discussed. It is revealed that the magnetic field can be used to select the first unstable pattern of Faraday waves. In particular, a rhombic pattern as a superposition of two different oblique rolls can occur. A scaling law is presented which maps all data into one graph for the tested range of viscosities, frequencies, magnetic fields and layer thicknesses.Comment: 8 pages, 6 figures, RevTex

    "Ordinary, the same as anywhere else": notes on the management of spoiled identity in 'marginal' middle class neighbourhoods

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    Urban sociologists are becoming increasingly interested in neighbourhood as a source of middle-class identity. Particular emphasis is currently being given to two types of middle-class neighbourhood; gentrified urban neighbourhoods of ‘distinction’ and inconspicuous ‘suburban landscapes of privilege’. However, there has been a dearth of work on ‘marginal’ middle-class neighbourhoods that are similarly ‘inconspicuous’ rather than distinctive, but less exclusive, thus containing sources of ‘spoiled identity’. This article draws on data gathered from two ‘marginal’ middleclass neighbourhoods that contained a particular source of ‘spoiled identity’: social renters. Urban sociological analyses of neighbour responses to these situations highlight a process of dis-identification with the maligned object, which exacerbates neighbour differences. Our analysis of data from the ‘marginal’ middle-class neighbourhoods suggests something entirely different and Goffmanesque. This entailed the management of spoiled identity, which emphasized similarities rather than differences between neighbours.</p

    Amplitude measurements of Faraday waves

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    A light reflection technique is used to measure quantitatively the surface elevation of Faraday waves. The performed measurements cover a wide parameter range of driving frequencies and sample viscosities. In the capillary wave regime the bifurcation diagrams exhibit a frequency independent scaling proportional to the wavelength. We also provide numerical simulations of the full Navier-Stokes equations, which are in quantitative agreement up to supercritical drive amplitudes of 20%. The validity of an existing perturbation analysis is found to be limited to 2.5% overcriticaly.Comment: 7 figure

    Pain Catastrophizing and Fear of Pain predict the Experience of Pain in Body Parts not targeted by a Delayed-Onset Muscle Soreness procedure

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    The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.The present study examined whether pain catastrophizing and pain-related fear predict the experience of pain in body regions that are not targeted by an experimental muscle injury protocol. A delayed-onset muscle soreness (DOMS) protocol was used to induce pain unilaterally in the pectoralis, serratus, trapezius, latissimus dorsi, and deltoid muscles. The day after the DOMS protocol, participants were asked to rate their pain as they lifted weighted canisters with their targeted (ie, injured) arm and their nontargeted arm. The lifting task is a nonnoxious stimulus unless participants are already experiencing musculoskeletal pain. Therefore, reports of pain on the nontargeted arm were operationalized as pain in response to a nonnoxious stimulus. Eighty-two healthy university students (54 men, 28 women) completed questionnaires on pain catastrophizing and fear of pain and went through the DOMS protocol. The analyses revealed that catastrophizing and pain-related fear prospectively predicted pain experience in response to a nonnoxious stimulus. The possible mechanisms underlying this effect and clinical implications are discussed

    Inclusive eta' Production from the Upsilon(1S)

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    Using the CLEO II detector at CESR, we measure the eta' - gluon - gluon form-factor in Y(1S) decays. This form-factor especially at large eta' energies may provide an explanation of the large rate for B -> Xs eta'. Our data do not support a large anomalous coupling at higher q^2 and thus the large eta' rate remains a mystery, possibly requiring a non-Standard Model explanation.Comment: 14 pages postscript, also available through http://w4.lns.cornell.edu/public/CLNS, submitted to PR
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