4,120 research outputs found
LSS reference platform control
The long range objective of this task is to develop basic technology in the design, mechanization, and analysis of control systems for large flexible space structures. The focus of the FY'81 platform control effort was on the pointing control problems associated with multiple independently controlled experiment packages operating simultaneously on a single platform. Particular emphasis was placed on obtaining a quantitative comparison of controller performance with and without base motion compensation
Physical activity barriers in the workplace : an exploration of factors contributing to non-participation in a UK workplace physical activity intervention
Purpose– The purpose of this paper is to explore factors contributing to non-participation in a workplace physical activity (PA) intervention in a large UK call centre.
Design/methodology/approach – In total, 16 inactive individuals (nine male/seven female), aged 27±9 years, who had not taken part in the intervention were interviewed to explore their perceptions of PA, the intervention and factors which contributed to their non-participation. Transcripts were analysed using thematic analysis.
Findings – Six superordinate themes were identified: self-efficacy for exercise; attitudes towards PA; lack of time and energy; facilities and the physical environment; response to the PA programme and PA culture. Barriers occurred at multiple levels of influence, and support the use of ecological or multilevel models to help guide future programme design/delivery.
Research limitations/implications – The 16 participants were not selected to be representative of the workplace gender or structure. Future intentions relating to PA participation were not considered and participants may have withheld negative opinions about the workplace or intervention despite use of an external researcher.
Practical implications – In this group of employees education about the importance of PA for young adults and providing opportunities to gain social benefits from PA would increase perceived benefits and reduce perceived costs of PA. Workplace cultural norms with respect to PA must also be addressed to create a shift in PA participation.
Originality/value – Employees’ reasons for non-participation in workplace interventions remain poorly understood and infrequently studied. The study considers a relatively under-studied population of employed young adults, providing practical recommendations for future interventions
Mariner Mars 1971 attitude control subsystem
The Mariner Mars 1971 attitude control subsystem (ACS) is discussed. It is comprised of a sun sensor set, a Canopus tracker, an inertial reference unit, two cold gas reaction control assemblies, two rocket engine gimbal actuators, and an attitude control electronics unit. The subsystem has the following eight operating modes: (1) launch, (2) sun acquisition, (3) roll search, (4) celestial cruise, (5) all-axes inertial, (6) roll inertial, (7) commanded turn, and (8) thrust vector control. In the celestial cruise mode, the position control is held to plus or minus 0.25 deg. Commanded turn rates are plus or minus 0.18 deg/s. The attitude control logic in conjunction with command inputs from other spacecraft subsystems establishes the ACS operating mode. The logic utilizes Sun and Canopus acquisition signals generated within the ACS to perform automatic mode switching so that dependence of ground control is minimized when operating in the sun acquisition, roll search, and celestial cruise modes. The total ACS weight is 65.7 lb, and includes 5.4 lb of nitrogen gas. Total power requirements vary from 9 W for the celestial cruise mode to 54 W for the commanded turn mode
Control system design for the large space systems technology reference platform
Structural models and classical frequency domain control system designs were developed for the large space systems technology (LSST) reference platform which consists of a central bus structure, solar panels, and platform arms on which a variety of experiments may be mounted. It is shown that operation of multiple independently articulated payloads on a single platform presents major problems when subarc second pointing stability is required. Experiment compatibility will be an important operational consideration for systems of this type
Levels and patterns of physical activity in children and adolescents with Type 1 diabetes and associated metabolic and physiologic health outcomes
Background: The present study objectively assessed physical activity (PA) levels and patterns in children and adolescents with type 1 diabetes and compared the metabolic and physiologic health profiles of those achieving and those not achieving the current recommendation of 60 minutes a day (minutes.D-1) of at least moderate intensity PA. Method: 37 children and adolescents (20 boys, 17 girls) aged 12.7 ± 2.1 years (mean ± SD), disease duration 5.9 ± 3.0 years participated. PA was assessed using heart rate monitoring. Peak VO2 , BMI, sum of 5 skinfolds, HbA1c and daily insulin dosage were also determined. Results: Mean accumulated time in moderate-to-vigorous intensity PA was 53.6 ± 31.4 minutes.D-1. Levels of vigorous-intensity PA were low, mean 8.3 ± 10.2 minutes.D-1. When controlling for age, no differences in metabolic or physiologic health outcomes were evident between those individuals achieving, and those not achieving, 60minutes.D-1 of moderate-to-vigorous intensity PA. PA predominantly occurred in short bouts lasting 5 minutes or less. Conclusion: The efficacy of accumulating 60 minutes.D-1 of moderate-to-vigorous intensity PA, in the form of short duration, intermittent bouts of largely unplanned PA, to promote health gains in children and adolescents with type 1 diabetes is questionable
The SCUBA Local Universe Galaxy Survey I: First Measurements of the Submillimetre Luminosity and Dust Mass Functions
We have used SCUBA to observe a complete sample of 104 galaxies selected at
60 microns from the IRAS BGS and we present here the 850 micron measurements.
Fitting the 60,100 and 850 micron fluxes with a single temperature dust model
gives the sample mean temperature T=36 K and beta = 1.3. We do not rule out the
possibility of dust which is colder than this, if a 20 K component was present
then our dust masses would increase by factor 1.5-3. We present the first
measurements of the luminosity and dust mass functions, which were well fitted
by Schechter functions (unlike those 60 microns). We have correlated many
global galaxy properties with the submillimetre and find that there is a
tendancy for less optically luminous galaxies to contain warmer dust and have
greater star formation efficiencies (cf. Young 1999). The average gas-to-dust
ratio for the sample is 581 +/- 43 (using both atomic and molecular hydrogen),
significantly higher than the Galactic value of 160. We believe this
discrepancy is due to a cold dust component at T < 20 K. There is a suprisingly
tight correlation between dust mass and the mass of molecular hydrogen as
estimated from CO measurements, with an intrinsic scatter of ~50%.Comment: 24 pages, 15 figures, 8 tables, accepted for publication in MNRA
Experimental quantum verification in the presence of temporally correlated noise
Growth in the complexity and capabilities of quantum information hardware
mandates access to practical techniques for performance verification that
function under realistic laboratory conditions. Here we experimentally
characterise the impact of common temporally correlated noise processes on both
randomised benchmarking (RB) and gate-set tomography (GST). We study these
using an analytic toolkit based on a formalism mapping noise to errors for
arbitrary sequences of unitary operations. This analysis highlights the role of
sequence structure in enhancing or suppressing the sensitivity of quantum
verification protocols to either slowly or rapidly varying noise, which we
treat in the limiting cases of quasi-DC miscalibration and white noise power
spectra. We perform experiments with a single trapped Yb ion as a
qubit and inject engineered noise () to probe protocol
performance. Experiments on RB validate predictions that the distribution of
measured fidelities over sequences is described by a gamma distribution varying
between approximately Gaussian for rapidly varying noise, and a broad, highly
skewed distribution for the slowly varying case. Similarly we find a strong
gate set dependence of GST in the presence of correlated errors, leading to
significant deviations between estimated and calculated diamond distances in
the presence of correlated errors. Numerical simulations demonstrate
that expansion of the gate set to include negative rotations can suppress these
discrepancies and increase reported diamond distances by orders of magnitude
for the same error processes. Similar effects do not occur for correlated
or errors or rapidly varying noise processes,
highlighting the critical interplay of selected gate set and the gauge
optimisation process on the meaning of the reported diamond norm in correlated
noise environments.Comment: Expanded and updated analysis of GST, including detailed examination
of the role of gauge optimization in GST. Full GST data sets and
supplementary information available on request from the authors. Related
results available from
http://www.physics.usyd.edu.au/~mbiercuk/Publications.htm
Oral human papillomavirus (HPV) infection in men who have sex with men: prevalence and lack of anogenital concordance.
To estimate the prevalence of oral detectable human papillomavirus (HPV) DNA in HIV-negative men who have sex with men (MSM) attending a sexual health clinic in London and concordance with anogenital HPV infection. Such data are important to improve our understanding of the epidemiology of oral HPV and the potential use of vaccines to prevent oropharyngeal cancers
Gemini Spectroscopic Survey of Young Star Clusters in Merging/Interacting Galaxies. II. NGC 3256 Clusters
We present Gemini optical spectroscopy of 23 young star clusters in NGC3256.
We find that the cluster ages range are from few Myr to ~150 Myr. All these
clusters are relatively massive (2--40)x 10^{5} \msun$ and appear to be of
roughly 1.5 \zo metallicity. The majority of the clusters in our sample follow
the same rotation curve as the gas and hence were presumably formed in the
molecular-gas disk. However, a western subsample of five clusters has
velocities that deviate significantly from the gas rotation curve. These
clusters may either belong to the second spiral galaxy of the merger or may
have formed in tidal-tail gas falling back into the system. We discuss our
observations in light of other known cluster populations in merging galaxies,
and suggest that NGC 3256 is similar to Arp 220, and hence may become an
Ultra-luminous Infrared Galaxy as the merger progresses and the star-formation
rate increases.
Some of the clusters which appeared as isolated in our ground-based images
are clearly resolved into multiple sub-components in the HST-ACS images. The
same effect has been observed in the Antennae galaxies, showing that clusters
are often not formed in isolation, but instead tend to form in larger groups or
cluster complexes.Comment: 20 pages, 10 figures, 3 tables; Accepted Ap
Diffuse X-ray emission in spiral galaxies
We compare the soft diffuse X-ray emission from Chandra images of 12 nearby
intermediate inclination spiral galaxies to the morphology seen in Halpha,
molecular gas, and mid-infrared emission. We find that diffuse X-ray emission
is often located along spiral arms in the outer parts of spiral galaxies but
tends to be distributed in a rounder morphology in the center. The X-ray
morphology in the spiral arms matches that seen in the mid-infrared or Halpha
and so implies that the X-ray emission is associated with recent active star
formation. We see no strong evidence for X-ray emission trailing the location
of high mass star formation in spiral arms. However, population synthesis
models predict a high mechanical energy output rate from supernovae for a time
period that is about 10 times longer than the lifetime of massive ionizing
stars, conflicting with the narrow appearance of the arms in X-rays. The
fraction of supernova energy that goes into heating the ISM must depend on
environment and is probably higher near sites of active star formation. The
X-ray estimated emission measures suggest that the volume filling factors and
scale heights are high in the galaxy centers but low in the outer parts of
these galaxies. The differences between the X-ray properties and morphology in
the centers and outer parts of these galaxies suggest that galactic fountains
operate in outer galaxy disks but that winds are primarily driven from galaxy
centers.Comment: 28 pages, 4 figures, to be submitted to Ap
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