1,279 research outputs found
Observation and absolute frequency measurements of the 1S0 - 3P0 optical clock transition in ytterbium
We report the direct excitation of the highly forbidden (6s^2) 1S0 - (6s6p)
3P0 optical transition in two odd isotopes of ytterbium. As the excitation
laser frequency is scanned, absorption is detected by monitoring the depletion
from an atomic cloud at ~70 uK in a magneto-optical trap. The measured
frequency in 171Yb (F=1/2) is 518,295,836,593.2 +/- 4.4 kHz. The measured
frequency in 173Yb (F=5/2) is 518,294,576,850.0 +/- 4.4 kHz. Measurements are
made with a femtosecond-laser frequency comb calibrated by the NIST cesium
fountain clock and represent nearly a million-fold reduction in uncertainty.
The natural linewidth of these J=0 to J=0 transitions is calculated to be ~10
mHz, making them well-suited to support a new generation of optical atomic
clocks based on confinement in an optical lattice.Comment: 4 pages, 3 figure
Effects of OEF/OIF-Related Physical and Emotional Co-Morbidities on Associative Learning: Concurrent Delay and Trace Eyeblink Classical Conditioning
This study examined the performance of veterans and active duty personnel who served in Operation Enduring Freedom and/or Operation Iraqi Freedom (OEF/OIF) on a basic associative learning task. Eighty-eight individuals participated in this study. All received a comprehensive clinical evaluation to determine the presence and severity of posttraumatic stress disorder (PTSD) and traumatic brain injury (TBI). The eyeblink conditioning task was composed of randomly intermixed delay and trace conditioned stimulus (CS) and unconditioned stimulus (US) pairs (acquisition) followed by a series of CS only trials (extinction). Results revealed that those with a clinical diagnosis of PTSD or a diagnosis of PTSD with comorbid mTBI acquired delay and trace conditioned responses (CRs) to levels and at rates similar to a deployed control group, thus suggesting intact basic associative learning. Differential extinction impairment was observed in the two clinical groups. Acquisition of CRs for both delay and trace conditioning, as well as extinction of trace CRs, was associated with alcoholic behavior across all participants. These findings help characterize the learning and memory function of individuals with PTSD and mTBI from OEF/OIF and raise the alarming possibility that the use of alcohol in this group may lead to more significant cognitive dysfunction
Filtration of submicrometer particles by pelagic tunicates
Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of National Academy of Sciences for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences of the United States of America 107 (2010): 15129-15134, doi:10.1073/pnas.1003599107.Salps are common in oceanic waters and have higher per individual filtration rates than any other
zooplankton filter feeder. Though salps are centimeters in length, feeding via particle capture
occurs on a fine, mucous mesh (fiber diameter d ~ 0.1 Όm) at low velocity (U = 1.6 ± 0.6 cm s-1,
mean ± SD) and is thus a low-Reynolds number (Re ~ 10-3) process. In contrast to the current
view that particle encounter is dictated by simple sieving of particles larger than the mesh
spacing, a low-Re mathematical model of encounter rates by the salp feeding apparatus for
realistic oceanic particle size distributions shows that submicron particles, due to their higher
abundances, are encountered at higher rates (particles per time) than larger particles. Data from
feeding experiments with 0.5, 1 and 3 ÎŒm diameter polystyrene spheres corroborate these results.
Though particles larger than 1 ÎŒm (e.g. flagellates, small diatoms) represent a larger carbon pool,
smaller particles in the 0.1â1 ÎŒm range (e.g. bacteria, Prochlorococcus) may be more quickly
digestible because they present more surface area, and we find that particles smaller than the
mesh size (1.4 ÎŒm) can fully satisfy salp energetic needs. Furthermore, by packaging
submicrometer particles into rapidly sinking fecal pellets, pelagic tunicates can substantially
change particle size spectra and increase downward fluxes in the ocean.This work was supported by the National Science
Foundation (OCE-0647723 to LPM and OCE-074464- CAREER to RS) and the WHOI Ocean
Life Institute
Characterisation of the clinical importance of porcine group C rotavirus in a swine nursery production network in Quebec
Enteric infectious diseases in swine have considerable economic impact on the industry due either to mortality, cost of treatment or reduced growth rates which can lead to extended production periods. The consequences can be catastrophic especially in nursery sites since young piglets are in a susceptible period associated with immature immune system and are often affected by rapid dehydration related to neonatal diseases
Energy production in varying {\alpha} theories
Aims. On the basis the theoretical model proposed by Bekenstein for
{\alpha}'s variation, we analyze the equations that describe the energy
exchange between matter and both the electromagnetic and the scalar fields.
Methods. We determine how the energy flow of the material is modified by the
presence of a scalar field. We estimate the total magnetic energy of matter
from the "sum rules techniques". We compare the results with data obtained from
the thermal evolution of the Earth and other planets. Results. We obtain
stringent upper limits to the variations in {\alpha} that are comparable with
those obtained from atomic clock frequency variations. Conclusions. Our
constraints imply that the fundamental length scale of Bekenstein's theory "lB"
cannot be larger than Planck's length "lP"
The CHEOPS mission
The CHaracterising ExOPlanet Satellite (CHEOPS) was selected on October 19, 2012, as the first small mission (S-mission) in the ESA Science Programme and successfully launched on December 18, 2019, as a secondary passenger on a Soyuz-Fregat rocket from Kourou, French Guiana. CHEOPS is a partnership between ESA and Switzerland with important contributions by ten additional ESA Member States. CHEOPS is the first mission dedicated to search for transits of exoplanets using ultrahigh precision photometry on bright stars already known to host planets. As a follow-up mission, CHEOPS is mainly dedicated to improving, whenever possible, existing radii measurements or provide first accurate measurements for a subset of those planets for which the mass has already been estimated from ground-based spectroscopic surveys. The expected photometric precision will also allow CHEOPS to go beyond measuring only transits and to follow phase curves or to search for exo-moons, for example. Finally, by unveiling transiting exoplanets with high potential for in-depth characterisation, CHEOPS will also provide prime targets for future instruments suited to the spectroscopic characterisation of exoplanetary atmospheres. To reach its science objectives, requirements on the photometric precision and stability have been derived for stars with magnitudes ranging from 6 to 12 in the V band. In particular, CHEOPS shall be able to detect Earth-size planets transiting G5 dwarf stars (stellar radius of 0.9R(circle dot)) in the magnitude range 6 <= V <= 9 by achieving a photometric precision of 20 ppm in 6 hours of integration time. In the case of K-type stars (stellar radius of 0.7R(circle dot)) of magnitude in the range 9 <= V <= 12, CHEOPS shall be able to detect transiting Neptune-size planets achieving a photometric precision of 85 ppm in 3 hours of integration time. This precision has to be maintained over continuous periods of observation for up to 48 hours. This precision and stability will be achieved by using a single, frame-transfer, back-illuminated CCD detector at the focal plane assembly of a 33.5 cm diameter, on-axis Ritchey-Chretien telescope. The nearly 275 kg spacecraft is nadir-locked, with a pointing accuracy of about 1 arcsec rms, and will allow for at least 1 Gbit/day downlink. The sun-synchronous dusk-dawn orbit at 700 km altitude enables having the Sun permanently on the backside of the spacecraft thus minimising Earth stray light. A mission duration of 3.5 years in orbit is foreseen to enable the execution of the science programme. During this period, 20% of the observing time is available to the wider community through yearly ESA call for proposals, as well as through discretionary time approved by ESA's Director of Science. At the time of this writing, CHEOPS commissioning has been completed and CHEOPS has been shown to fulfill all its requirements. The mission has now started the execution of its science programme
Nuclear halo and its scaling laws
We have proposed a procedure to extract the probability for valence particle
being out of the binding potential from the measured nuclear asymptotic
normalization coefficients. With this procedure, available data regarding the
nuclear halo candidates are systematically analyzed and a number of halo nuclei
are confirmed. Based on these results we have got a much relaxed condition for
nuclear halo occurrence. Furthermore, we have presented the scaling laws for
the dimensionless quantity of nuclear halo in terms of the
analytical expressions of the expectation value for the operator in a
finite square-well potential.Comment: 14 pages, 3 figure
Comparison of low--energy resonances in 15N(alpha,gamma)19F and 15O(alpha,gamma)19Ne and related uncertainties
A disagreement between two determinations of Gamma_alpha of the astro-
physically relevant level at E_x=4.378 MeV in 19F has been stated in two recent
papers by Wilmes et al. and de Oliveira et al. In this work the uncertainties
of both papers are discussed in detail, and we adopt the value
Gamma_alpha=(1.5^{+1.5}_{-0.8})10^-9eV for the 4.378 MeV state. In addition,
the validity and the uncertainties of the usual approximations for mirror
nuclei Gamma_gamma(19F) approx Gamma_gamma(19Ne), theta^2_alpha(19F) approx
theta^2_alpha(19Ne) are discussed, together with the resulting uncertainties on
the resonance strengths in 19Ne and on the 15O(alpha,gamma)19Ne rate.Comment: 9 pages, Latex, To appear in Phys. Rev.
A stellar occultation by the transneptunian object (50000) Quaoar observed by CHEOPS
Context. Stellar occultation is a powerful technique that allows the determination of some physical parameters of the occulting object. The result depends on the photometric accuracy, the temporal resolution, and the number of chords obtained. Space telescopes can achieve high photometric accuracy as they are not affected by atmospheric scintillation.
Aims. Using ESAâs CHEOPS space telescope, we observed a stellar occultation by the transneptunian object (50000) Quaoar. We compare the obtained chord with previous occultations by this object and determine its astrometry with sub-milliarcsecond precision. Also, we determine upper limits to the presence of a global methane atmosphere on the occulting body.
Methods. We predicted and observed a stellar occultation by Quaoar using the CHEOPS space telescope. We measured the occultation light curve from this dataset and determined the dis- and reappearance of the star behind the occulting body. Furthermore, a ground-based telescope in Australia was used to constrain Quaoarâs limb. Combined with results from previous works, these measurements allowed us to obtain a precise position of Quaoar at the occultation time.
Results. We present the results obtained from the first stellar occultation by a transneptunian object using a space telescope orbiting Earth; it was the occultation by Quaoar observed on 2020 June 11. We used the CHEOPS light curve to obtain a surface pressure upper limit of 85 nbar for the detection of a global methane atmosphere. Also, combining this observation with a ground-based observation, we fitted Quaoarâs limb to determine its astrometric position with an uncertainty below 1.0 mas.
Conclusions. This observation is the first of its kind, and it shall be considered as a proof of concept of stellar occultation observations of transneptunian objects with space telescopes orbiting Earth. Moreover, it shows significant prospects for the James Webb Space Telescope
New insight into the low-energy He spectrum
The spectrum of He was studied by means of the He(,)He
reaction at a lab energy of 25 MeV/n and small center of mass (c.m.) angles.
Energy and angular correlations were obtained for the He decay products by
complete kinematical reconstruction. The data do not show narrow states at
1.3 and 2.4 MeV reported before for He. The lowest resonant
state of He is found at about 2 MeV with a width of 2 MeV and is
identified as . The observed angular correlation pattern is uniquely
explained by the interference of the resonance with a virtual state
(limit on the scattering length is obtained as fm), and with
the resonance at energy MeV.Comment: 5 pages, 4 figures, 2 table
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