1,030 research outputs found
Extrasolar planets and brown dwarfs around A-F type stars - VII. Theta Cygni radial velocity variations: planets or stellar phenomenon?
(abridged) In the frame of the search for extrasolar planets and brown dwarfs
around early-type main-sequence stars, we present the results obtained on the
early F-type star Theta Cygni. Elodie and Sophie at OHP were used to obtain the
spectra. Our dedicated radial-velocity measurement method was used to monitor
the star's radial velocities over five years. We also use complementary, high
angular resolution and high-contrast images taken with PUEO at CFHT. We show
that Theta Cygni radial velocities are quasi-periodically variable, with a
~150-day period. These variations are not due to the ~0.35-Msun stellar
companion that we detected in imaging at more than 46 AU from the star. The
absence of correlation between the bisector velocity span variations and the
radial velocity variations for this 7 km/s vsini star, as well as other
criteria indicate that the observed radial velocity variations are not due to
stellar spots. The observed amplitude of the bisector velocity span variations
also seems to rule out stellar pulsations. However, we observe a peak in the
bisector velocity span periodogram at the same period as the one found in the
radial velocity periodogram, which indicates a probable link between these
radial velocity variations and the low amplitude lineshape variations which are
of stellar origin. Long-period variations are not expected from this type of
star to our knowledge. If a stellar origin (hence of new type) was to be
confirmed for these long-period radial velocity variations, this would have
several consequences on the search for planets around main-sequence stars, both
in terms of observational strategy and data analysis. An alternative
explanation for these variable radial velocities is the presence of at least
one planet of a few Jupiter masses orbiting at less than 1 AU. (abridged)Comment: 9 pages, accepted in A
A purely geometric distance to the binary star Atlas, a member of the Pleiades
We present radial velocity and new interferometric measurements of the double
star Atlas, which permit, with the addition of published interferometric data,
to precisely derive the orbital parameters of the binary system and the masses
of the components. The derived semi-major axis, compared with its measured
angular size, allows to determine a distance to Atlas of 132+-4 pc in a purely
geometrical way. Under the assumption that the location of Atlas is
representative of the average distance of the cluster, we confirm the distance
value generally obtained through main sequence fitting, in contradiction with
the early Hipparcos result (118.3+-3.5 pc).Comment: 5 pages, 3 figures, accepted for publication in A&A Letter
Prevalence and factors associated with fatigue in the Lausanne middle-aged population: a population-based, cross-sectional survey.
To assess the prevalence and factors associated with fatigue in the general population.
Population-based, cross-sectional survey performed between May 2014 and April 2017.
General population of the city of Lausanne, Switzerland.
2848 participants (53.2% women, age range 45-86 years).
Prevalence of fatigue the previous week, defined as a score of ≥4 using the Fatigue Severity Scale.
The prevalence of fatigue was 21.9% (95% CI 20.4% to 23.4%) in the total sample. On bivariate analysis, participants with fatigue were younger, had a higher body mass index, a lower handgrip strength and lower ferritin levels. Participants with fatigue were more frequently women, had a lower educational level, presented more frequently with clinical insomnia, diabetes, anaemia, depression and low thyroid stimulating hormone (TSH) values, had a higher consumption of antihistamines, antidepressants and hypnotics, and rated more frequently their health as bad or very bad. Multivariable analysis showed that obesity (OR 1.40 (95% CI 1.03 to 1.91)), insomnia categories (p value for trend <0.001), depression (OR 3.26 (95% CI 2.38 to 4.46)), anaemia (OR 1.70 (95% CI 1.00 to 2.89)) and low self-rated health status (p value for trend <0.001) were positively associated with fatigue, while older age (p value for trend 0.002) was negatively associated with fatigue. Conversely, no association was found for diabetes, TSH levels, antihistamines or hypnotics.
In a population-based sample aged 45-86, fatigue was present in one out of five subjects. Regarding clinical factors, sleep disturbances such as insomnia and sleep apnoea should be assessed first, followed by depression. Regarding biological factors, anaemia should be ruled out, while screening for hypothyroidism is not recommended as a first step. Sleep complaints and fatigue in older subjects are not due to ageing and should prompt identification of the underlying cause
Nonlinear characterisation of a silicon integrated Bragg waveguide filter
Bragg waveguides are promising optical filters for pump suppression in
spontaneous Four-Wave Mixing (FWM) photon sources. In this work, we investigate
the generation of unwanted photon pairs in the filter itself. We do this by
taking advantage of the relation between spontaneous and classical FWM, which
allows for the precise characterisation of the nonlinear response of the
device. The pair generation rate estimated from the classical measurement is
compared with the theoretical value calculated by means of a full quantum model
of the filter, which also allows to investigate the spectral properties of the
generated pairs. We find a good agreement between theory and experiment,
confirming that stimulated FWM is a valuable approach to characterise the
nonlinear response of an integrated filter, and that the pairs generated in a
Bragg waveguide are not a serious issue for the operation of a fully integrated
nonclassical source
An integrated source of spectrally filtered correlated photons for large scale quantum photonic systems
We demonstrate the generation of quantum-correlated photon-pairs combined
with the spectral filtering of the pump field by more than 95dB using Bragg
reflectors and electrically tunable ring resonators. Moreover, we perform
demultiplexing and routing of signal and idler photons after transferring them
via a fiber to a second identical chip. Non-classical two-photon temporal
correlations with a coincidence-to-accidental ratio of 50 are measured without
further off-chip filtering. Our system, fabricated with high yield and
reproducibility in a CMOS process, paves the way toward truly large-scale
quantum photonic circuits by allowing sources and detectors of single photons
to be integrated on the same chip.Comment: 4 figure
Sleep hygiene intervention for youth aged 10 to 18 years with problematic sleep: a before-after pilot study
BACKGROUND: The current study aimed to examine the changes following a sleep hygiene intervention on sleep hygiene practices, sleep quality, and daytime symptoms in youth. METHODS: Participants aged 10–18 years with self-identified sleep problems completed our age-appropriate F.E.R.R.E.T (an acronym for the categories of Food, Emotions, Routine, Restrict, Environment and Timing) sleep hygiene programme; each category has three simple rules to encourage good sleep. Participants (and parents as appropriate) completed the Adolescent Sleep Hygiene Scale (ASHS), Pittsburgh Sleep Quality Index (PSQI), Sleep Disturbance Scale for Children (SDSC), Pediatric Daytime Sleepiness Scale (PDSS), and wore Actical® monitors twice before (1 and 2 weeks) and three times after (6, 12 and 20 weeks) the intervention. Anthropometric data were collected two weeks before and 20 weeks post-intervention. RESULTS: Thirty-three youths (mean age 12.9 years; M/F = 0.8) enrolled, and retention was 100%. ASHS scores significantly improved (p = 0.005) from a baseline mean (SD) of 4.70 (0.41) to 4.95 (0.31) post-intervention, as did PSQI scores [7.47 (2.43) to 4.47 (2.37); p < 0.001] and SDSC scores [53.4 (9.0) to 39.2 (9.2); p < 0.001]. PDSS scores improved from a baseline of 16.5 (6.0) to 11.3 (6.0) post- intervention (p < 0.001). BMI z-scores with a baseline of 0.79 (1.18) decreased significantly (p = 0.001) post-intervention to 0.66 (1.19). Despite these improvements, sleep duration as estimated by Actical accelerometry did not change. There was however a significant decrease in daytime sedentary/light energy expenditure. CONCLUSIONS: Our findings suggest the F.E.R.R.E.T sleep hygiene education programme might be effective in improving sleep in children and adolescents. However because this was a before and after study and a pilot study with several limitations, the findings need to be addressed with caution, and would need to be replicated within a randomised controlled trial to prove efficacy. TRIAL REGISTRATION: Australian New Zealand Clinical Trials Registry: ACTRN1261200064981
Energy correlations of photon pairs generated by a silicon microring resonator probed by Stimulated Four Wave Mixing
Compact silicon integrated devices, such as micro-ring resonators, have
recently been demonstrated as efficient sources of quantum correlated photon
pairs. The mass production of integrated devices demands the implementation of
fast and reliable techniques to monitor the device performances. In the case of
time-energy correlations, this is particularly challenging, as it requires high
spectral resolution that is not currently achievable in coincidence
measurements. Here we reconstruct the joint spectral density of photons pairs
generated by spontaneous four-wave mixing in a silicon ring resonator by
studying the corresponding stimulated process, namely stimulated four wave
mixing. We show that this approach, featuring high spectral resolution and
short measurement times, allows one to discriminate between nearly-uncorrelated
and highly-correlated photon pairs.Comment: 7 pages, 4 figure
Genetic variability and founder effect in the pitcher plant Sarracenia purpurea (Sarraceniaceae) in populations introduced into Switzerland: from inbreeding to invasion
BACKGROUND AND AIMS: The long-lived and mainly outcrossing species Sarracenia purpurea has been introduced into Switzerland and become invasive. This creates the opportunity to study reactions to founder effect and how a species can circumvent deleterious effects of bottlenecks such as reduced genetic diversity, inbreeding and extinction through mutational meltdown, to emerge as a highly invasive plant. METHODS: A population genetic survey by random amplified polymorphism DNA markers (RAPD) together with historical insights and a field pollination experiment were carried out. KEY RESULTS: At the regional scale, S. purpurea shows low structure (thetast=0.072) due to a recent founder event and important subsequent growth. Nevertheless, multivariate statistical analyses reveal that, because of a bottleneck that shifted allele frequencies, most of the variability is independent among populations. In one population (Tenasses) the species has become invasive and genetic analysis reveals restricted gene flow and family structure (thetast=0.287). Although inbreeding appears to be high (Fis >0.410 from a Bayesian estimation), a field pollination experiment failed to detect significant inbreeding depression upon F1 seed number and seed weight fitness-traits. Furthermore, crosses between unrelated individuals produced F1 seeds with significantly reduced fitness, thus showing local outbreeding depression. CONCLUSIONS: The results suggest that, under restricted gene flow among families, the species may not only have rapidly purged deleterious alleles, but also have undergone some form of selection for inbreeding due to co-adaptation between loci
Component Separation for Spectral X-Ray Imaging Using the XPAD3 Hybrid Pixel Camera
The advent of hybrid pixel cameras in X-ray imaging opens the way to the acquisition of spectral measurements. These new devices for which photon counting replaces charge integration incorporate a dedicated readout electronic for each pixel including a capability of selecting energies via the setup of an energy threshold. This ability is of uppermost importance for the development of new polychromatic X-ray imaging approaches that will exploit spectral information on the detected X-rays. Spectral measurements in X-ray imaging pave the way to the separation of images in several components of physical and biological interest: the photoelectric and the Compton contributions can be separated while several contrast agents can be simultaneously localized. We investigate the capability to perform component separation by using the newly developed XPAD3 hybrid pixel camera incorporated in the micro-CT demonstrator PIXSCAN. Firstly, we propose an approach to configure the acquisition setup in order to optimize the component separation problem with respect to the robustness to the photon noise. The method is based on the Cramer-Rao Bound (CRB) that indicates the lowest reachable variance for the estimation of each component whatever the algorithm. Secondly, we investigate the separation problem with two components namely the photoelectric and the Compton ones. We show on noisy simulated data that such a separation with optimized setup i) enhances the contrast and the Contrast to Noise Ratio (CNR) between biological materials (adipose, soft tissues) and water; ii) cancels the artifacts of the beam-hardening effect that may strongly degrade the image quality. On going work involves two steps: first, dealing with Monte Carlo simulations and real data acquired with the PIXSCAN demonstrator; second, dealing with component separation with more than two components by adding several contrast agents, for which PIXSCAN has already proved its ability to separate them
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