60,248 research outputs found
Summary and recent results from the NASA advanced High Speed Propeller Research Program
Advanced high-speed propellers offer large performance improvements for aircraft that cruise in the Mach 0.7 to 0.8 speed regime. The current status of the NASA research program on high-speed propeller aerodynamics, acoustics, and aeroelastics is described. Recent wind tunnel results for five 8- to 10-blade advanced models are compared with analytical predictions. Test results show that blade sweep was important in achieving net efficiencies near 80 percent at Mach 0.8 and reducing near-field cruise noise by dB. Lifting line and lifting surface aerodynamic analysis codes are under development and some initial lifting line results are compared with propeller force and probe data. Some initial laser velocimeter measurements of the flow field velocities of an 8-bladed 45 deg swept propeller are shown. Experimental aeroelastic results indicate that cascade effects and blade sweep strongly affect propeller aeroelastic characteristics. Comparisons of propeller near-field noise data with linear acoustic theory indicate that the theory adequate predicts near-field noise for subsonic tip speeds but overpredicts the noise for supersonic tip speeds. Potential large gains in propeller efficiency of 7 to 11 percent at Mach 0.8 may be possible with advanced counter-rotation propellers
High speed turboprops for executive aircraft, potential and recent test results
Four high speed propeller models were designed and tested in an 8x6 foot wind tunnel in order to evaluate the potential of advanced propeller technology. Results from these tests show that the combination of: increased blade number, aerodynamically integrated propeller/nacelles, reduced blade thickness, spinner area ruling, and blade sweep are important in achieving high propeller efficiency at the high cruise speeds
Theology at the coal-face of hospitalisation - the development and evaluation of a postgraduate certificate in Healthcare Chaplaincy
Healthcare chaplaincy is working towards recognition as a registered health profession. An accredited programme of professional education is part of that process. The University of Glasgow supported by NHS Education for Scotland have developed a programme of professional education for healthcare chaplains that is integrated into an MSc. (MedSci) in healthcare. This article outlines the commissioning, development and evaluation of a postgraduate certificate in healthcare chaplaincy by students, clinical mentors and experienced healthcare chaplains. It also highlights an innovative approach to practice development in spiritual and religious care in healthcare
A Generic Algorithm for IACT Optical Efficiency Calibration using Muons
Muons produced in Extensive Air Showers (EAS) generate ring-like images in
Imaging Atmospheric Cherenkov Telescopes when travelling near parallel to the
optical axis. From geometrical parameters of these images, the absolute amount
of light emitted may be calculated analytically. Comparing the amount of light
recorded in these images to expectation is a well established technique for
telescope optical efficiency calibration. However, this calculation is usually
performed under the assumption of an approximately circular telescope mirror.
The H.E.S.S. experiment entered its second phase in 2012, with the addition of
a fifth telescope with a non-circular 600m mirror. Due to the differing
mirror shape of this telescope to the original four H.E.S.S. telescopes,
adaptations to the standard muon calibration were required. We present a
generalised muon calibration procedure, adaptable to telescopes of differing
shapes and sizes, and demonstrate its performance on the H.E.S.S. II array.Comment: In Proceedings of the 34th International Cosmic Ray Conference
(ICRC2015), The Hague, The Netherland
Alternative Adaptive Filter Structures for Improved Radio Frequency Interference Cancellation in Radio Astronomy
In radio astronomy, reference signals from auxiliary antennas that receive
only the radio frequency interference (RFI) can be modified to model the RFI
environment at the astronomy receivers. The RFI can then be canceled from the
astronomy signal paths. However, astronomers typically only require signal
statistics. If the RFI statistics are changing slowly, the cancellation can be
applied to the signal correlations at a much lower rate than is required for
standard adaptive filters. In this paper we describe five canceler setups;
precorrelation and postcorrelation cancelers that use one or two reference
signals in different ways. The theoretical residual RFI and added noise levels
are examined and are demonstrated using microwave television RFI at the
Australia Telescope Compact Array. The RFI is attenuated to below the system
noise, a reduction of at least 20 dB. While dual-reference cancelers add more
reference noise than single-reference cancelers, this noise is zero-mean and
only adds to the system noise, decreasing the sensitivity. The residual RFI
that remains in the output of single-reference cancelers (but not
dual-reference cancelers) sets a nonzero noise floor that does not act like
random system noise and may limit the achievable sensitivity. Thus,
dual-reference cancelers often result in superior cancellation. Dual-reference
precorrelation cancelers require a double-canceler setup to be useful and to
give equivalent results to dual-reference postcorrelation cancelers.Comment: 11 pages created using emulateap
Hypothesis testing near singularities and boundaries
The likelihood ratio statistic, with its asymptotic distribution at
regular model points, is often used for hypothesis testing. At model
singularities and boundaries, however, the asymptotic distribution may not be
, as highlighted by recent work of Drton. Indeed, poor behavior of a
for testing near singularities and boundaries is apparent in
simulations, and can lead to conservative or anti-conservative tests. Here we
develop a new distribution designed for use in hypothesis testing near
singularities and boundaries, which asymptotically agrees with that of the
likelihood ratio statistic. For two example trinomial models, arising in the
context of inference of evolutionary trees, we show the new distributions
outperform a .Comment: 32 pages, 12 figure
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