983 research outputs found
Portable remote laser sensor for methane leak detection
A portable laser system for remote detection of methane gas leaks and concentrations is disclosed. The system transmitter includes first and second lasers, tuned respectively to a wavelength coincident with a strong absorption line of methane and a reference wavelength which is weakly absorbed by methane gas. The system receiver includes a spherical mirror for collecting the reflected laser radiation and focusing the collected radiation through a narrowband optical filter onto an optial detector. The filter is tuned to the wavelength of the two lasers, and rejects background noise. The output of the optical detector is processed by a lock-in detector synchronized to the chopper, and which measures the difference between the first wavelength signal and the reference wavelength signal
Metastatic Squamous Cell Carcinoma in a Hereford Cow
On Jan. 4th, 1951 a 12-year-old Hereford cow was admitted to Stange Memorial Clinic with a history of having had what was thought to be infectious keratitis of the right eye. The condition was not treated and became infested with screw-worms. The animal was gradually becoming emaciated
High accuracy measure of atomic polarizability in an optical lattice clock
Despite being a canonical example of quantum mechanical perturbation theory,
as well as one of the earliest observed spectroscopic shifts, the Stark effect
contributes the largest source of uncertainty in a modern optical atomic clock
through blackbody radiation. By employing an ultracold, trapped atomic ensemble
and high stability optical clock, we characterize the quadratic Stark effect
with unprecedented precision. We report the ytterbium optical clock's
sensitivity to electric fields (such as blackbody radiation) as the
differential static polarizability of the ground and excited clock levels:
36.2612(7) kHz (kV/cm)^{-2}. The clock's fractional uncertainty due to room
temperature blackbody radiation is reduced an order of magnitude to 3 \times
10^{-17}.Comment: 5 pages, 3 figures, 2 table
Children\u27s physical activity and screen time : qualitative comparison of views of parents of infants and preschool children
BackgroundWhile parents are central to the development of behaviours in their young children, little is known about how parents view their role in shaping physical activity and screen time behaviours.MethodsUsing an unstructured focus group design, parental views and practices around children′s physical activity and screen time (television and computer use) were explored with eight groups of new parents (n=61; child age <12 months) and eight groups of parents with preschool-aged (3–5 year old) children (n=36) in Melbourne, Australia.ResultsParents generally believed children are naturally active, which may preclude their engagement in strategies designed to increase physical activity. While parents across both age groups shared many overarching views concerning parenting for children′s physical activity and screen time behaviours, some strategies and barriers differed depending on the age of the child. While most new parents were optimistic about their ability to positively influence their child′s behaviours, many parents of preschool-aged children seemed more resigned to strategies that worked for them, even when aware such strategies may not be ideal.ConclusionsInterventions aiming to increase children′s physical activity and decrease screen time may need to tailor strategies to the age group of the child and address parents′ misconceptions and barriers to optimum parenting in these domains.<br /
Posterior probability intervals in Bayesian wavelet estimation
We use saddlepoint approximation to derive credible intervals for Bayesian wavelet regression estimates. Simulations show that the resulting intervals perform better than the best existing metho
The Palomar Kernel Phase Experiment: Testing Kernel Phase Interferometry for Ground-based Astronomical Observations
At present, the principal limitation on the resolution and contrast of
astronomical imaging instruments comes from aberrations in the optical path,
which may be imposed by the Earth's turbulent atmosphere or by variations in
the alignment and shape of the telescope optics. These errors can be corrected
physically, with active and adaptive optics, and in post-processing of the
resulting image. A recently-developed adaptive optics post-processing
technique, called kernel phase interferometry, uses linear combinations of
phases that are self-calibrating with respect to small errors, with the goal of
constructing observables that are robust against the residual optical
aberrations in otherwise well-corrected imaging systems. Here we present a
direct comparison between kernel phase and the more established competing
techniques, aperture masking interferometry, point spread function (PSF)
fitting and bispectral analysis. We resolve the alpha Ophiuchi binary system
near periastron, using the Palomar 200-Inch Telescope. This is the first case
in which kernel phase has been used with a full aperture to resolve a system
close to the diffraction limit with ground-based extreme adaptive optics
observations. Excellent agreement in astrometric quantities is found between
kernel phase and masking, and kernel phase significantly outperforms PSF
fitting and bispectral analysis, demonstrating its viability as an alternative
to conventional non-redundant masking under appropriate conditions.Comment: Accepted to MNRA
An atomic clock with instability
Atomic clocks have been transformational in science and technology, leading
to innovations such as global positioning, advanced communications, and tests
of fundamental constant variation. Next-generation optical atomic clocks can
extend the capability of these timekeepers, where researchers have long aspired
toward measurement precision at 1 part in . This milestone will
enable a second revolution of new timing applications such as relativistic
geodesy, enhanced Earth- and space-based navigation and telescopy, and new
tests on physics beyond the Standard Model. Here, we describe the development
and operation of two optical lattice clocks, both utilizing spin-polarized,
ultracold atomic ytterbium. A measurement comparing these systems demonstrates
an unprecedented atomic clock instability of after
only hours of averaging
Preschool and childcare center characteristics associated with children’s physical activity during care hours: an observational study
STROBE Statement—Checklist of items included in this study. (DOCX 28 kb
Poisson transition rates from time-domain measurements with finite bandwidth
In time-domain measurements of a Poisson two-level system, the observed
transition rates are always smaller than those of the actual system, a general
consequence of finite measurement bandwidth in an experiment. This
underestimation of the rates is significant even when the measurement and
detection apparatus is ten times faster than the process under study. We derive
here a quantitative form for this correction using a straightforward
state-transition model that includes the detection apparatus, and provide a
method for determining a system's actual transition rates from
bandwidth-limited measurements. We support our results with computer
simulations and experimental data from time-domain measurements of
quasiparticle tunneling in a single-Cooper-pair transistor.Comment: 4 pages, 5 figure
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