1,284 research outputs found
Intelligent Design and the Constitution: The Truth Will Set Us Free (Reflections on Kitzmiller v. Dover Area School District)
Crossed molecular beam study of the reactive scattering of K + I2 - Product KI recoil /velocity-angle/ distributions and energy dependence of reaction cross section
Molecular beam study of reaction of velocity selected potassium beam crossed with thermal iodine bea
S-ACF: A selective estimator for the autocorrelation function of irregularly sampled time series
We present a generalised estimator for the autocorrelation function, S-ACF,
which is an extended version of the standard estimator of the autocorrelation
function (ACF). S-ACF is a versatile definition that can robustly and
efficiently extract periodicity and signal shape information from a time
series, independent of the time sampling and with minimal assumptions about the
underlying process. Calculating the autocorrelation of irregularly sampled time
series becomes possible by generalising the lag of the standard estimator of
the ACF to a real parameter and introducing the notion of selection and weight
functions. We show that the S-ACF reduces to the standard ACF estimator for
regularly sampled time series. Using a large number of synthetic time series we
demonstrate that the performance of the S-ACF is as good or better than
commonly used Gaussian and rectangular kernel estimators, and is comparable to
a combination of interpolation and the standard estimator. We apply the S-ACF
to astrophysical data by extracting rotation periods for the spotted star KIC
5110407, and compare our results to Gaussian process (GP) regression and
Lomb-Scargle (LS) periodograms. We find that the S-ACF periods typically agree
better with those from GP regression than from LS periodograms, especially in
cases where there is evolution in the signal shape. The S-ACF has a wide range
of potential applications and should be useful in quantitative science
disciplines where irregularly sampled time series occur. A Python
implementation of the S-ACF is available under the MIT license
Fluorosilicone and silicone o-ring aging study.
Fluorosilicone o-ring aging studies were performed. These studies examined the compressive force loss of fluorosilicone o-rings at accelerated (elevated) temperatures and were then used to make predictions about force loss at room temperature. The results were non-Arrhenius with evidence for a lowering in Arrhenius activation energies as the aging temperature was reduced. The compression set of these fluorosilicone o-rings was found to have a reasonably linear correlation with the force loss. The aging predictions based on using the observed curvature of the Arrhenius aging plots were validated by field aged o-rings that yielded degradation values reasonably close to the predictions. Compression set studies of silicone o-rings from a previous study resulted in good correlation to the force loss predictions for the fluorosilicone o-rings from this study. This resulted in a preliminary conclusion that an approximately linear correlation exists between compression set and force decay values for typical fluorosilicone and silicone materials, and that the two materials age at similar rates at low temperatures. Interestingly, because of the observed curvature of the Arrhenius plots available from longer-term, lower temperature accelerated exposures, both materials had faster force decay curves (and correspondingly faster buildup of compression set) at room temperature than anticipated from typical high-temperature exposures. A brief study on heavily filled conducting silicone o-rings resulted in data that deviated from the linear relationship, implying that a degree of caution must be exercised about any general statement relating force decay and compression set
NGTS-4b: A sub-Neptune transiting in the desert
We report the discovery of NGTS-4b, a sub-Neptune-sized planet transiting a 13th magnitude K-dwarf in a 1.34 d orbit. NGTS-4b has a mass M = 20.6 ± 3.0 M⊕ and radius R = 3.18 ± 0.26 R⊕, which places it well within the so-called ‘Neptunian Desert’. The mean density of the planet (3.45 ± 0.95 g cm−3) is consistent with a composition of 100  per cent H2O or a rocky core with a volatile envelope. NGTS-4b is likely to suffer significant mass loss due to relatively strong EUV/X-ray irradiation. Its survival in the Neptunian desert may be due to an unusually high-core mass, or it may have avoided the most intense X-ray irradiation by migrating after the initial activity of its host star had subsided. With a transit depth of 0.13 ± 0.02 per cent, NGTS-4b represents the shallowest transiting system ever discovered from the ground, and is the smallest planet discovered in a wide-field ground-based photometric survey
Single-particle-sensitive imaging of freely propagating ultracold atoms
We present a novel imaging system for ultracold quantum gases in expansion.
After release from a confining potential, atoms fall through a sheet of
resonant excitation laser light and the emitted fluorescence photons are imaged
onto an amplified CCD camera using a high numerical aperture optical system.
The imaging system reaches an extraordinary dynamic range, not attainable with
conventional absorption imaging. We demonstrate single-atom detection for
dilute atomic clouds with high efficiency where at the same time dense
Bose-Einstein condensates can be imaged without saturation or distortion. The
spatial resolution can reach the sampling limit as given by the 8 \mu m pixel
size in object space. Pulsed operation of the detector allows for slice images,
a first step toward a 3D tomography of the measured object. The scheme can
easily be implemented for any atomic species and all optical components are
situated outside the vacuum system. As a first application we perform
thermometry on rubidium Bose-Einstein condensates created on an atom chip.Comment: 24 pages, 10 figures. v2: as publishe
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Nuclear power plant accident simulations of gasket materials under simultaneous radiation plus thermal plus mechanical stress conditions
In order to probe the response of silicone door gasket materials to a postulated severe accident in an Italian nuclear power plant, compression stress relaxation (CSR) and compression set (CS) measurements were conducted under combined radiation (approximately 6 kGy/h) and temperature (up to 230{degrees}C) conditions. By making some reasonable initial assumptions, simplified constant temperature and dose rates were derived that should do a reasonable job of simulating the complex environments for worst-case severe events that combine overall aging plus accidents. Further simplification coupled with thermal-only experiments allowed us to derive thermal-only conditions that can be used to achieve CSR and CS responses similar to those expected from the combined environments that are more difficult to simulate. Although the thermal-only simulations should lead to sealing forces similar to those expected during a severe accident, modulus and density results indicate that significant differences in underlying chemistry are expected for the thermal-only and the combined environment simulations. 15 refs., 31 figs., 15 tabs
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