5,233 research outputs found
Measurement and prediction of the resistance of a laser sailing dinghy
This study explores the insight that can be gained into the performance of a conventional sailing dinghy from a program of tanks testing in a range of displacement and trim conditions, and further investigates the extent to which performance can be predicted using a regression approach developed for sailing yachts, with the ultimate aim of developing performance prediction tools customised for sailing dinghies. The upright resistance of a Laser Dinghy is examined through tank-testing at three different displacements and with a range of trims. Results show that residuary resistance is substantially affected by displacement, and that trim can have a beneficial effect at the lower and upper extremes of the speed range. Comparison with tank test results show that the Delft regression approach does not predict the resistance of a Laser particularly accurately, substantially underestimates the weight sensitivity of a Laser, and cannot reliably predict the impact of trim
Development of flying qualities criteria for single pilot instrument flight operations
Flying qualities criteria for Single Pilot Instrument Flight Rule (SPIFR) operations were investigated. The ARA aircraft was modified and adapted for SPIFR operations. Aircraft configurations to be flight-tested were chosen and matched on the ARA in-flight simulator, implementing modern control theory algorithms. Mission planning and experimental matrix design were completed. Microprocessor software for the onboard data acquisition system was debugged and flight-tested. Flight-path reconstruction procedure and the associated FORTRAN program were developed. Algorithms associated with the statistical analysis of flight test results and the SPIFR flying qualities criteria deduction are discussed
Retrograde Accretion and Merging Supermassive Black Holes
We investigate whether a circumbinary gas disc can coalesce a supermassive
black hole binary system in the centre of a galaxy. This is known to be
problematic for a prograde disc. We show that in contrast, interaction with a
retrograde circumbinary disc is considerably more effective in shrinking the
binary because there are no orbital resonances. The binary directly absorbs
negative angular momentum from the circumbinary disc by capturing gas into a
disc around the secondary black hole, or discs around both holes if the binary
mass ratio is close to unity. In many cases the binary orbit becomes eccentric,
shortening the pericentre distance as the eccentricity grows. In all cases the
binary coalesces once it has absorbed the angular momentum of a gas mass
comparable to that of the secondary black hole. Importantly, this conclusion is
unaffected even if the gas inflow rate through the disc is formally
super--Eddington for either hole. The coalescence timescale is therefore always
, where is the secondary black hole mass and
the inflow rate through the circumbinary disc.Comment: 8 pages, 4 figures. Accepted for publication in MNRAS. Movies of the
simulations can be found at:
http://www.astro.le.ac.uk/users/cjn12/RetroBinaryMovies.htm
50 Years of Spaceflight with Fourier Transform Spectrometers (FTS) Built at NASA GSFC
Over the past 50 years, NASA Goddard Space Flight Center (GSFC) has been developing, building, testing and flying a series of Fourier Transform Spectrometers (FTS). This began with the IRIS instruments on the Earth-orbiting Nimbus satellites and progressed to more sophisticated designs optimized for interplanetary spacecraft sent to Mars and later to the outer solar system. Adaptions have been made over time, including progressively higher spectral resolution, sensitivity, numbers of detectors and complexity. Instrument operating temperatures have decreased to enable remote sensing of the cold giant planet systems. In this paper we describe the historical evolution of this instrument line, comparing and contrasting different aspects such as optical design and materials, detector types and data handling. We conclude by looking towards the future. At present the CIRS-Lite prototype is being tested at NASA GSFC for potential use on a future mission to the ice giants, Uranus and Neptune. Surpassing the previous performance of the Voyager IRIS instruments remains challenging, and new technologies that could enable these measurements are discussed
Measurement of CHD on Titan at Submillimeter Wavelengths
We present the first radio/submillimeter detection of monodeuterated methane
(CHD) in Titan's atmosphere, using archival data from of the Atacama Large
Millimeter/submillimeter Array (ALMA). The and
transitions at 465.235 and 465.250 GHz ( mm) were measured at
significance levels of and , respectively. These two
lines were modeled using the Non-linear optimal Estimator for MultivariatE
spectral analySIS (NEMESIS) radiative transfer code to determine the
disk-averaged CHD volume mixing ratio = in Titan's
stratosphere (at altitudes km). By comparison with the CH vertical
abundance profile measured by Cassini-Huygens mass spectrometry, the resulting
value for D/H in CH is . This is consistent
with previous ground-based and in-situ measurements from the Cassini-Huygens
mission, though slightly lower than the average of the previous values.
Additional CHD observations at higher spatial resolution will be required
to determine a value truly comparable with the Cassini-Huygens CH
measurements, by measuring CHD with ALMA close to Titan's equator. In the
post-Cassini era, spatially resolved observations of CHD with ALMA will
enable the latitudinal distribution of methane to be determined, making this an
important molecule for further studies.Comment: 9 pages, 4 figure
Abundance Measurements of Titan's Stratospheric HCN, HCN, CH, and CHCN from ALMA Observations
Previous investigations have employed more than 100 close observations of
Titan by the Cassini orbiter to elucidate connections between the production
and distribution of Titan's vast, organic-rich chemical inventory and its
atmospheric dynamics. However, as Titan transitions into northern summer, the
lack of incoming data from the Cassini orbiter presents a potential barrier to
the continued study of seasonal changes in Titan's atmosphere. In our previous
work (Thelen et al., 2018), we demonstrated that the Atacama Large
Millimeter/submillimeter Array (ALMA) is well suited for measurements of
Titan's atmosphere in the stratosphere and lower mesosphere (~100-500 km)
through the use of spatially resolved (beam sizes <1'') flux calibration
observations of Titan. Here, we derive vertical abundance profiles of four of
Titan's trace atmospheric species from the same 3 independent spatial regions
across Titan's disk during the same epoch (2012 to 2015): HCN, HCN,
CH, and CHCN. We find that Titan's minor constituents exhibit large
latitudinal variations, with enhanced abundances at high latitudes compared to
equatorial measurements; this includes CHCN, which eluded previous
detection by Cassini in the stratosphere, and thus spatially resolved abundance
measurements were unattainable. Even over the short 3-year period, vertical
profiles and integrated emission maps of these molecules allow us to observe
temporal changes in Titan's atmospheric circulation during northern spring. Our
derived abundance profiles are comparable to contemporary measurements from
Cassini infrared observations, and we find additional evidence for subsidence
of enriched air onto Titan's south pole during this time period. Continued
observations of Titan with ALMA beyond the summer solstice will enable further
study of how Titan's atmospheric composition and dynamics respond to seasonal
changes.Comment: 15 pages, 16 figures, 2 tables. Accepted for publication in Icarus,
September 201
Titan's Surface Temperatures from Cassini CIRS
The surface brightness temperature of Titan can be measured from Cassini through a spectral window at 19 microns where the atmosphere is low in opacity. The Composite Infrared Spectrometer (CIRS) on Cassini observes this wavelength in its far-infrared channel. Because the Cassini tour has provided global coverage and a range of viewing geometries, CIRS has been able to go beyond the earlier flyby results of Voyager IRIS Near the equator, CIRS measures the zonally-averaged surface brightness temperature to be 917 K, very close to the temperature found at the surface by Huygens. Latitude maps show that Titan's surface temperatures drop off by about 2 K toward the south and by about 3 K toward the north. This temperature distribution is consistent with Titan's late northern winter when the data were taken. As the seasons progress, CIRS is continuing to search for corresponding changes in the temperatures of the surface and lower atmosphere. CIRS is also extending global mapping to both latitude and longitude to look for correlations between surface temperatures and geological features
Randomised, controlled trial of alternating pressure mattresses compared with alternating pressure overlays for the prevention of pressure ulcers : PRESSURE (pressure relieving support surfaces) trial
Objective To compare whether differences exist between alternating pressure overlays and alternating pressure mattresses in the development of new pressure ulcers, healing of existing pressure ulcers, and patient acceptability. Design Pragmatic, open, multicentre, randomised controlled trial. Setting 11 hospitals in six NHS trusts. Participants 1972 people admitted to hospital as acute or elective patients. Interventions Participants were randomised to an alternating pressure mattress (n = 982) of- an alternating pressure overlay (n = 990). Main outcome measures The proportion of participants developing a new pressure ulcer of grade 2 or worse; time to development of new pressure ulcers; proportions of participants developing a new ulcer within 30 days; healing of existing pressure ulcers; and patient acceptability Results Intention to treat analysis found no difference in the proportions of participants developing a new pressure ulcer of grade 2 or worse (10.7% overlay patients, 10.3% mattress patients; difference 0.4%, 95% confidence interval - 23% to 3.1%, P = 0.75). More overlay patients requested change owing to dissatisfaction (23.3%) than mattress patients (18.9%, P = 0.02). Conclusion No difference was found between alternating pressure mattresses and alternating pressure overlays in the proportion of people who develop a pressure ulcer
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