13,906 research outputs found
Time outdoors and the prevention of myopia
Recent epidemiological evidence suggests that children who spend more time outdoors are less likely to be, or to become myopic, irrespective of how much near work they do, or whether their parents are myopic. It is currently uncertain if time outdoors also blocks progression of myopia. It has been suggested that the mechanism of the protective effect of time outdoors involves light-stimulated release of dopamine from the retina, since increased dopamine release appears to inhibit increased axial elongation, which is the structural basis of myopia. This hypothesis has been supported by animal experiments which have replicated the protective effects of bright light against the development of myopia under laboratory conditions, and have shown that the effect is, at least in part, mediated by dopamine, since the D2-dopamine antagonist spiperone reduces the protective effect. There are some inconsistencies in the evidence, most notably the limited inhibition by bright light under laboratory conditions of lens-induced myopia in monkeys, but other proposed mechanisms possibly associated with time outdoors such as relaxed accommodation, more uniform dioptric space, increased pupil constriction, exposure to UV light,
changes in the spectral composition of visible light, or increased physical activity have little epidemiological
or experimental support. Irrespective of the mechanisms involved, clinical trials are now underway
to reduce the development of myopia in children by increasing the amount of time they spend outdoors. These trials would benefit from more precise definition of thresholds for protection in terms of intensity and duration of light exposures. These can be investigated in animal experiments in appropriate models, and can also be determined in epidemiological studies, although more precise measurement of exposures than those currently provided by questionnaires is desirable
A procedure to analyze nonlinear density waves in Saturn's rings using several occultation profiles
Cassini radio science experiments have provided multiple occultation optical
depth profiles of Saturn's rings that can be used in combination to analyze
density waves. This paper establishes an accurate procedure of inversion of the
wave profiles to reconstruct the wave kinematic parameters as a function of
semi-major axis, in the nonlinear regime. This procedure is achieved from
simulated data in the presence of realistic noise perturbations, to control the
reconstruction error. By way of illustration we have applied our procedure to
the Mimas 5:3 density wave. We were able to recover precisely the kinematic
parameters from the radio experiment occultation data in most of the
propagation region; a preliminary analysis of the pressure-corrected dispersion
allowed us to determine new but still uncertain values for the opacity
( cm/g) and velocity dispersion of ( cm/s) in
the wave region. Our procedure constitutes the first step in our planned
analysis of the density waves of Saturn's rings. It is very accurate and
efficient in the far-wave region. However, improvements are required within the
first wavelength. The ways in which this method can be used to establish
diagnostics of ring physics are outlined.Comment: 50 pages,13 figures, 2 tables. Published in Icarus
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DEveloping a Complex Intervention for DEteriorating Patients using Theoretical Modelling (DECIDE study): study protocol
AIM: To develop a theory-based complex intervention (targeting nursing staff), to enhance enablers and overcome barriers to enacting expected behaviour when monitoring patients and responding to abnormal vital signs that signal deterioration.
DESIGN: A mixed method design including structured observations on hospital wards, field notes, brief, un-recorded interviews and semi-structured interviews to inform the development of an intervention to enhance practice.
METHODS: Semi-structured interviews will be conducted with nursing staff using a topic guide informed by the Theoretical Domains Framework. Semi-structured interviews will be transcribed verbatim and coded deductively into the 14 Theoretical Domains Framework domains and then inductively into 'belief statements'. Priority domains will be identified and mapped to appropriate behaviour change techniques. Intervention content and mode of delivery (how behaviour change techniques are operationalised) will be developed using nominal groups, during which participants (clinicians) will rank behaviour change techniques /mode of delivery combinations according to acceptability and feasibility. Findings will be synthesised to develop an intervention manual.
DISCUSSION: Despite being a priority for clinicians, researchers and policymakers for two decades, 'sub-optimal care' of the deteriorating ward patient persists. Existing interventions have been largely educational (i.e., targeting assumed knowledge deficits) with limited evidence that they change staff behaviour. Staff behaviour when monitoring and responding to abnormal vital signs is likely influenced by a range of mediators that includes barriers and enablers.
IMPACT: Systematically applying theory and evidence-based methods, will result in the specification of an intervention which is more likely to result in behaviour change and can be tested empirically in future research. This article is protected by copyright. All rights reserved
Violation of the isotropic- approximation in overdoped La_{2-x}Sr_xCuO_4
Magnetotransport measurements on the overdoped cuprate La_{1.7}Sr_{0.3}CuO_4
are fitted using the Ong construction and band parameters inferred from
angle-resolved photoemission. Within a band picture, the low temperature Hall
data can only be fitted satisfactorily by invoking strong basal-plane
anisotropy in the mean-free-path . This violation of the isotropic-
approximation supports a picture of dominant small-angle elastic scattering in
cuprates due to out-of-plane substitutional disorder. We show that both band
anisotropy and anisotropy in the elastic scattering channel strongly
renormalize the Hall coefficient in overdoped La_{2-x}Sr_xCuO_4 over a wide
doping and temperature range.Comment: 4 pages, 4 figure
Single shot measurement of a silicon single electron transistor
We have fabricated a custom cryogenic Complementary Metal-Oxide-Semiconductor
(CMOS) integrated circuit that has a higher measurement bandwidth compared with
conventional room temperature electronics. This allowed implementing single
shot operations and observe the real-time evolution of the current of a
phosphorous-doped silicon single electron transistor that was irradiated with a
microwave pulse. Relaxation times up to 90 us are observed, suggesting the
presence of well isolated electron excitations within the device. It is
expected that these are associated with long decoherence time and the device
may be suitable for quantum information processing
Molecule Microscopy
Contains research objectives and reports on three research projects.Francis L. Friedman ChairNational Institutes of Health (Grant AM-31546
Statistical Theory of Parity Nonconservation in Compound Nuclei
We present the first application of statistical spectroscopy to study the
root-mean-square value of the parity nonconserving (PNC) interaction matrix
element M determined experimentally by scattering longitudinally polarized
neutrons from compound nuclei. Our effective PNC interaction consists of a
standard two-body meson-exchange piece and a doorway term to account for
spin-flip excitations. Strength functions are calculated using realistic
single-particle energies and a residual strong interaction adjusted to fit the
experimental density of states for the targets, ^{238} U for A\sim 230 and
^{104,105,106,108} Pd for A\sim 100. Using the standard Desplanques, Donoghue,
and Holstein estimates of the weak PNC meson-nucleon coupling constants, we
find that M is about a factor of 3 smaller than the experimental value for
^{238} U and about a factor of 1.7 smaller for Pd. The significance of this
result for refining the empirical determination of the weak coupling constants
is discussed.Comment: Latex file, no Fig
A Spectroscopic Survey of the Fields of 28 Strong Gravitational Lenses: Implications for
Strong gravitational lensing provides an independent measurement of the
Hubble parameter (). One remaining systematic is a bias from the
additional mass due to a galaxy group at the lens redshift or along the
sightline. We quantify this bias for more than 20 strong lenses that have
well-sampled sightline mass distributions, focusing on the convergence
and shear . In 23% of these fields, a lens group contributes a 1%
convergence bias; in 57%, there is a similarly significant line-of-sight group.
For the nine time delay lens systems, is overestimated by 11%
on average when groups are ignored. In 67% of fields with total
0.01, line-of-sight groups contribute more convergence than
do lens groups, indicating that the lens group is not the only important mass.
Lens environment affects the ratio of four (quad) to two (double) image
systems; all seven quads have lens groups while only three of 10 doubles do,
and the highest convergences due to lens groups are in quads. We calibrate the
- relation: with a rms scatter of 0.34 dex.
Shear, which, unlike convergence, can be measured directly from lensed images,
can be a poor predictor of ; for 19% of our fields, is
. Thus, accurate cosmology using strong gravitational lenses
requires precise measurement and correction for all significant structures in
each lens field.Comment: 34 pages, 11 figures, accepted for publication in Ap
Life history differences across a latitudinal gradient in side-blotched lizards (Uta stansburiana)
Latitudinal variation has long been known to affect life history. Bergmann and Allen made latitudinal ârulesâ for mammalian anatomy and Lack, Skutch, and Moreau described differences in life history in birds. Trade-offs occur between important life history processes, like self maintenance (immunity) and other expensive but necessary processes. It is likely that trade-offs occur mostly when resources are limited. Side-blotched lizards have a wide geographic range, and more northerly lizards have been observed to have longer lifespans than their southern conspecifics. We hypothesized that northern sideblotched lizards would invest more energy into self-maintenance compared to shorter-lived southern animals
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