571 research outputs found
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Adaptation to Health States: A Micro-Econometric Approach
Health care funding decisions in the UK are based on valuations of the general public. However, it has been shown that there is a disparity between a hypothetical valuation of the impact of a specific condition on health and the effect of that health state by someone who experiences it. This paper examines the issue of adaptation to health states, which partially may explain the discrepancy between hypothetical and experienced health state valuations. We use the British Cohort Study (BCS70) which is a longitudinal dataset that tracks a sample of British individuals since their birth in 1970. We use four BCS70 waves containing information on self-assessed health (SAH), morbidity as well as a number of socio-economic characteristics. To estimate the issue of adaptation, we implement a dynamic ordered probit model that controls for (health) state dependence. The empirical specification controls for morbidity and also includes a variable for the duration of the illness. We find that, for most chronic conditions, duration has a positive impact on self-assessed health, while for some conditions-such as diabetes- this does not occur. We interpret our results as evidence in support of the hypothesis that adaptation to chronic diseases exists and may explain at least in part the differences between general public and patients’ health state valuations
Climbing the cosmic ladder with stellar twins
Distances to stars are key to revealing a three-dimensional view of the Milky
Way, yet their determination is a major challenge in astronomy. Whilst the
brightest nearby stars benefit from direct parallax measurements, fainter stars
are subject of indirect determinations with uncertainties exceeding 30%. We
present an alternative approach to measuring distances using
spectroscopically-identified twin stars. Given a star with known parallax, the
distance to its twin is assumed to be directly related to the difference in
their apparent magnitudes. We found 175 twin pairs from the ESO public HARPS
archives and report excellent agreement with Hipparcos parallaxes within 7.5%.
Most importantly, the accuracy of our results does not degrade with increasing
stellar distance. With the ongoing collection of high-resolution stellar
spectra, our method is well-suited to complement Gaia.Comment: published online on MNRA
High-precision analysis of binary stars with planets. I. Searching for condensation temperature trends in the HD 106515 system
We explore the probable chemical signature of planet formation in the
remarkable binary system HD 106515. The A star hosts a massive long-period
planet with 9 MJup detected by radial velocity. We also refine stellar and
planetary parameters by using non-solar-scaled opacities when modeling the
stars. Methods. We carried out a simultaneous determination of stellar
parameters and abundances, by applying for the first time non-solar-scaled
opacities in this binary system, in order to reach the highest possible
precision. Results. The stars A and B in the binary system HD 106515 do not
seem to be depleted in refractory elements, which is different when comparing
the Sun with solar-twins. Then, the terrestrial planet formation would have
been less efficient in the stars of this binary system. Together with HD
80606/7, this is the second binary system which does not seem to present a
(terrestrial) signature of planet formation, and hosting both systems an
eccentric giant planet. This is in agreement with numerical simulations, where
the early dynamical evolution of eccentric giant planets clear out most of the
possible terrestrial planets in the inner zone. We refined the stellar mass,
radius and age for both stars and found a notable difference of 78% in R
compared to previous works. We also refined the planet mass to mp sini = 9.08
+/- 0.20 MJup, which differs by 6% compared with literature. In addition, we
showed that the non-solar-scaled solution is not compatible with the classical
solar-scaled method, and some abundance differences are comparable to NLTE or
GCE effects specially when using the Sun as reference. Then, we encourage the
use of non-solar-scaled opacities in high-precision studies such as the
detection of Tc trends.[abridged]Comment: 9 pages, 10 figures, A&A accepted. arXiv admin note: text overlap
with arXiv:1507.0812
On the age of the magnetically active WW Psa and TX Psa members of the beta Pictoris association
There are a variety of different techniques available to estimate the ages of
pre-main-sequence stars. Components of physical pairs, thanks to their strict
coevality and the mass difference, such as the binary system analysed in this
paper, are best suited to test the effectiveness of these different techniques.
We consider the system WW Psa + TX Psa whose membership of the 25-Myr beta
Pictoris association has been well established by earlier works. We investigate
which age dating technique provides the best agreement between the age of the
system and that of the association. We have photometrically monitored WW Psa
and TX Psa and measured their rotation periods as P = 2.37d and P = 1.086d,
respectively. We have retrieved from the literature their Li equivalent widths
and measured their effective temperatures and luminosities. We investigate
whether the ages of these stars derived using three independent techniques are
consistent with the age of the beta Pictoris association. We find that the
rotation periods and the Li contents of both stars are consistent with the
distribution of other bona fide members of the cluster. On the contrary, the
isochronal fitting provides similar ages for both stars, but a factor of about
four younger than the quoted age of the association, or about 30% younger when
the effects of magnetic fields are included. We explore the origin of the
discrepant age inferred from isochronal fitting, including the possibilities
that either the two components may be unresolved binaries or that the basic
stellar parameters of both components are altered by enhanced magnetic
activity. The latter is found to be the more reasonable cause, suggesting that
age estimates based on the Li content is more reliable than isochronal fitting
for pre-main-sequence stars with pronounced magnetic activity.Comment: Accepted by Astronomy and Astrophysics on December 13, 2016. 13 pages
and 11 figure
100 MHz Amplitude and Polarization Modulated Optical Source for Free-Space Quantum Key Distribution at 850 nm
We report on an integrated photonic transmitter of up to 100 MHz repetition
rate, which emits pulses centered at 850 nm with arbitrary amplitude and
polarization. The source is suitable for free space quantum key distribution
applications. The whole transmitter, with the optical and electronic components
integrated, has reduced size and power consumption. In addition, the
optoelectronic components forming the transmitter can be space-qualified,
making it suitable for satellite and future space missions.Comment: 6 figures, 2 table
Phase-stable source of polarization-entangled photons in a linear double-pass configuration
We demonstrate a compact, robust, and highly efficient source of
polarization-entangled photons, based on linear bi-directional down-conversion
in a novel 'folded sandwich' configuration. Bi-directionally pumping a single
periodically poled KTiOPO (ppKTP) crystal with a 405-nm laser diode, we
generate entangled photon pairs at the non-degenerate wavelengths 784 nm
(signal) and 839 nm (idler), and achieve an unprecedented detection rate of
11.8 kcps for 10.4 W of pump power (1.1 million pairs / mW), in a 2.9-nm
bandwidth, while maintaining a very high two-photon entanglement quality, with
a Bell-state fidelity of %
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Adaptation to Health States: Sick yet better off?
Healthcare funding decisions in the UK rely on health state valuations of the general public. However, it has been shown that there is disparity between the valuation of the impact of hypothetical conditions on health and the reported health by those experiencing them. Patients' adaptation to health states is among the most common explanations for this discrepancy. Being diagnosed with a disease appears to affect individual perception of health over time so that better subjective health may be reported over a disease trajectory. This paper examines adaptation to health states using a longitudinal dataset. We use four waves of the British Cohort Study (BCS70), which tracks a sample of British individuals since birth in 1970 and contains information on self-assessed health (SAH), morbidity, and socioeconomic characteristics. We implement a dynamic ordered probit model controlling for health state dependence. Results are supportive of the existence of adaptation: Time since diagnosis has a positive impact on SAH. Moreover, adaptation happens over relatively long durations. We do not find significant results proving different adaptation paths for patients reporting prior better SAH. The analysis by specific conditions generally supports the existence of adaptation, but results are statistically significant only for a subset of conditions
Something borrowed, something blue:the nature of blue metal-poor stars inferred from their colours and chemical abundances
Blue metal-poor (BMP) stars are main sequence stars that appear bluer and more luminous than normal turnoff stars. They were originally singled out by using B−V and U−B colour cuts.Early studies found that a larger fraction of field BMP stars were binaries compared to normal halo stars. Thus, BMP stars are ideal field blue straggler candidates for investigating internal stellar evolution processes and binary interaction. In particular, the presence or depletion in lithium in their spectra is a powerful indicator of their origin. They are either old, halo blue stragglers experiencing internal mixing processes or mass transfer (Li-depletion), or intermediate-age, single stars of possibly extragalactic origin (2.2 dex halo plateau Li). However, we note that internal mixing processes can lead to an increased level of Li. Hence, this study combines photometry and spectroscopy to unveil the origin of various BMP stars. We first show how to separate binaries from young blue stars using photometry, metallicity and lithium. Using a sample of 80 BMP stars (T > 6300 K), we find that 97% of the BMP binaries have V−Ks0 < 1.08 ± 0.03, while BMP stars that are not binaries lie above this cut in two thirds of the cases. This cut can help classify stars that lack radial velocities from follow-up observations. We then trace the origin of two BMP stars from the photometric sample by conducting a full chemical analysis using new high-resolution and high signal-to-noise spectra. Based on their radial velocities, Li, α and s- and r-process abundances we show that BPS CS22874-042 is a single star (A(Li) = 2.38 ± 0.10 dex) while with A(Li)= 2.23 ± 0.07 dex CD-48 2445 is a binary, contrary to earlier findings. Our analysis emphasises that field blue stragglers can be segregated from single metal-poor stars, using (V−Ks) colours with a fraction of single stars polluting the binary sample, but not vice versa. These two groups can only be properly separated by using information from stellar spectra, illustrating the need for accurate and precise stellar parameters and high-resolution, high-S/N spectra in order to fully understand and classify this intriguing class of stars. Our high-resolution spectrum analysis confirms the findings from the colour cuts and shows that CS 22874−042 is single, while CD −48 2445 is most likely a binary. Moreover, the stellar abundances show that both stars formed in situ; CS 22874−042 carries traces of massive star enrichment and CD −48 2445 shows indications of AGB mass transfer mixed with gases ejected possibly from neutron star mergers
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Binary stars in the Galactic thick disc
The combination of asteroseismologically-measured masses with abundances from
detailed analyses of stellar atmospheres challenges our fundamental knowledge
of stars and our ability to model them. Ancient red-giant stars in the Galactic
thick disc are proving to be most troublesome in this regard. They are older
than 5 Gyr, a lifetime corresponding to an initial stellar mass of about
. So why do the masses of a sizeable fraction of
thick-disc stars exceed , with some as massive as
? We answer this question by considering duplicity in
the thick-disc stellar population using a binary population-nucleosynthesis
model. We examine how mass transfer and merging affect the stellar mass
distribution and surface abundances of carbon and nitrogen. We show that a few
per cent of thick-disc stars can interact in binary star systems and become
more massive than . Of these stars, most are single
because they are merged binaries. Some stars more massive than
form in binaries by wind mass transfer. We compare
our results to a sample of the APOKASC data set and find reasonable agreement
except in the number of these thick-disc stars more massive than
. This problem is resolved by the use of a
logarithmically-flat orbital-period distribution and a large binary fraction
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