1,020 research outputs found

    Toward Simultaneous Velocity and Density Measurements Using FLEET and Laser Rayleigh Scattering

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    Femtosecond laser electronic excitation tagging (FLEET) velocimetry and laser Rayleigh scattering are conducted concurrently and are evaluated for their suitability to measure velocity and density simultaneously in NASA Langleys 0.3-m Transonic Cryogenic Tunnel. FLEET velocimetry measurements are shown to be accurate to within 1.5 percent of the measured velocity throughout the facility testing envelope and exhibit a zero-velocity precision of 0.4 m/s. Rayleigh scattering density measurements indicate a characteristically linear dependence on flow density while having an accuracy within 5.4 percent of the measured density and a precision less than or equal to 6 percent. The preliminary assessment indicates that the joint technique would be advantageous for deployment in high-pressure, cryogenic test facilities

    SiO Maser Survey towards off-plane O-rich AGBs around the orbital plane of the Sagittarius Stellar Stream

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    We conducted an SiO maser survey towards 221 O-rich AGB stars with the aim of identifying maser emission associated with the Sagittarius stellar stream. In this survey, maser emission was detected in 44 targets, of which 35 were new detections. All of these masers are within 5 kpc of the Sun. We also compiled a Galactic SiO maser catalogue including ~2300 SiO masers from the literature. The distribution of these SiO masers give a scale height of 0.40 kpc, while 42 sources deviate from the Galactic plane by more than 1.2 kpc, half of which were found in this survey. Regarding SiO masers in the disc, we found both the rotational speeds and the velocity dispersions vary with the Galactic plane distance. Assuming Galactic rotational speed Θ\Theta0 = 240 km/s , we derived the velocity lags are 15 km/s and 55 km/s for disc and off-plane SiO masers respectively. Moreover, we identified three groups with significant peculiar motions (with 70% confidence). The most significant group is in the thick disc that might trace stream/peculiar motion of the Perseus arm. The other two groups are mainly made up of off-plane sources. The northern and southern off-plane sources were found to be moving at ~33 km/s and 54 km/s away from the Galactic plane, respectively. Causes of these peculiar motions are still unclear. For the two off-plane groups, we suspect they are thick disc stars whose kinematics affected by the Sgr stellar stream or very old Sgr stream debris.Comment: 27 pages, 17 figures, MNRAS accepted 2017 September 1

    Deriving prevalence estimates of depressive symptoms throughout middle and old age in those living in the community

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    BACKGROUND: There is considerable debate about the prevalence of depression in old age. Epidemiological surveys and clinical studies indicate mixed evidence for the association between depression and increasing age. We examined the prevalence of probable depression in the middle aged to the oldest old in a project designed specifically to investigate the aging process. METHODS: Community-living participants were drawn from several Australian longitudinal studies of aging that contributed to the Dynamic Analyses to Optimise Ageing (DYNOPTA) project. Different depression scales from the contributing studies were harmonized to create a binary variable that reflected "probable depression" based on existing cut-points for each harmonized scale. Weighted prevalence was benchmarked to the Australian population which could be compared with findings from the 1997 and 2007 National Surveys of Mental Health and Well-Being (NSMHWB). RESULTS: In the DYNOPTA project, females were more likely to report probable depression. This was consistent across age levels. Both NSMHWB surveys and DYNOPTA did not report a decline in the likelihood of reporting probable depression for the oldest old in comparison with mid-life. CONCLUSIONS: Inconsistency in the reports of late-life depression prevalence in previous epidemiological studies may be explained by either the exclusion and/or limited sampling of the oldest old. DYNOPTA addresses these limitations and the results indicated no change in the likelihood of reporting depression with increasing age. Further research should extend these findings to examine within-person change in a longitudinal context and control for health covariates.NHMRC (National Health and Medical Research Council of Australia

    Rayleigh Scattering Density Measurements from Ultrafast Lasers in High-Pressure, Cryogenic Wind Tunnels

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    The Rayleigh scattering signal from femtosecond laser pulses is examined for its utility at making instantaneous density measurements in the NASA Langley 0.3-m Transonic Cryogenic Tunnel. An electron-multiplying CCD camera is used to visualize Rayleigh scattering signal taken concurrently with velocity measurements utilizing the femtosecond laser tagging velocimetry technique (FLEET). The results indicate a strong potential for making instantaneous measurements. Viable single-shot images are obtained over the full operational envelope of the facility, and shot-to-shot variations are found to be on average 6 percent (at 95 percent confidence level) and tend to decrease as the facility density is increased. The Rayleigh scattering signals observed before the optical focus exhibit a characteristically linear dependence on the mass-density of the gas, while signals after the focus exhibit a nonlinear (sublinear) density dependence, indicative of stronger absorption at higher densities. The measured Rayleigh scattering signals compare favorably to theoretical assessments made at the tunnel operating conditions

    Unseeded Velocity Measurements Around a Transonic Airfoil Using Femtosecond Laser Tagging

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    Femtosecond laser electronic excitation tagging (FLEET) velocimetry was used to study the flowfield around a symmetric, transonic airfoil in the NASA Langley 0.3-m TCT facility. A nominal Mach number of 0.85 was investigated with a total pressure of 125 kPa and total temperature of 280 K. Two-components of velocity were measured along vertical profiles at different locations above, below, and aft of the airfoil at angles of attack of 0, 3.5, and 7. Velocity profiles within the wake showed sufficient accuracy, precision, and sensitivity to resolve both the mean and fluctuating velocities and general flow physics such as shear layer growth. Evidence of flow separation is found at high angles of attack. Velocity measurements were assessed for their accuracy, precision, dynamic range, spatial resolution, and overall measurement uncertainty as they relate to the present experiments. Measurement precisions as low as 1 m/s were observed, while the velocity dynamic range was found to be nearly a factor of 500. The spatial resolution of between 1 mm and 5 mm was found to be primarily limited by the FLEET spot size and advection of the flow. Overall measurement uncertainties ranged from 3 to 4 percent

    Implementation of a Pulsed-Laser Measurement System in the National Transonic Facility

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    A remotely-adjustable laser transmission and imaging system has been developed for use in a high-pressure, cryogenic wind tunnel. Implementation in the National Transonic Facility has proven the system suitable for velocity and signal lifetime measurements over a range of operating conditions. The measurement system allows for the delivery of high-powered laser pulses through the outer pressure shell and into the test section interior from a mezzanine where the laser is free from environmental disturbances (such as vibrations and excessive condensation) associated with operation of the wind tunnel. Femtosecond laser electronic excitation tagging (FLEET) was utilized to provide freestream velocity measurements, and first results show typical data that may be obtained using the system herein described

    Bow shocks in water fountain jets

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    We briefly introduce the VLBI maser astrometric analysis of IRAS 18043-2116 and IRAS 18113-2503, two remarkable and unusual water fountains with spectacular bipolar bow shocks in their high-speed collimated jet-driven outflows. The 22 GHz H2O maser structures and velocities clearly show that the jets are formed in very short-lived, episodic outbursts, which may indicate episodic accretion in an underlying binary system.Comment: To appear in the proceedings of the IAU Symposium 336: Astrophysical Masers: Unlocking the Mysteries of the Universe (4-8 September 2017, Cagliari, Italy) - IAU Proceedings Series, eds. A. Tarchi, M. J. Reid, and P. Castangi
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