149 research outputs found
Evaluating local average and quantile treatment effects under endogeneity based on instruments: a review
This paper provides a review of methodological advancements in the evaluation of heterogeneous treatment effect models based on instrumental variable (IV) methods. We focus on models that achieve identification through a monotonicity assumption on the selection equation and analyze local average and quantile treatment effects for the subpopulation of compliers. We start with a comprehensive discussion of the binary treatment and binary instrument case which is relevant for instance in randomized experiments with imperfect compliance. We then review extensions to identification and estimation with covariates, multi-valued and multiple treatments and instruments, outcome attrition and measurement error, and the identification of direct and indirect treatment effects, among others. We also discuss testable implications and possible relaxations of the IV assumptions, approaches to extrapolate from local to global treatment effects, and the relationship to other IV approaches
The Physical Parameters of the Retired A Star HD185351
We report here an analysis of the physical stellar parameters of the giant
star HD185351 using Kepler short-cadence photometry, optical and near infrared
interferometry from CHARA, and high-resolution spectroscopy. Asteroseismic
oscillations detected in the Kepler short-cadence photometry combined with an
effective temperature calculated from the interferometric angular diameter and
bolometric flux yield a mean density, rho_star = 0.0130 +- 0.0003 rho_sun and
surface gravity, logg = 3.280 +- 0.011. Combining the gravity and density we
find Rstar = 5.35 +- 0.20 Rsun and Mstar = 1.99 +- 0.23 Msun. The trigonometric
parallax and CHARA angular diameter give a radius Rstar = 4.97 +- 0.07 Rsun.
This smaller radius,when combined with the mean stellar density, corresponds to
a stellar mass Mstar = 1.60 +- 0.08 Msun, which is smaller than the
asteroseismic mass by 1.6-sigma. We find that a larger mass is supported by the
observation of mixed modes in our high-precision photometry, the spacing of
which is consistent only for Mstar =~ 1.8 Msun. Our various and independent
mass measurements can be compared to the mass measured from interpolating the
spectroscopic parameters onto stellar evolution models, which yields a
model-based mass M_star = 1.87 +- 0.07 Msun. This mass agrees well with the
asteroseismic value,but is 2.6-sigma higher than the mass from the combination
of asteroseismology and interferometry. The discrepancy motivates future
studies with a larger sample of giant stars. However, all of our mass
measurements are consistent with HD185351 having a mass in excess of 1.5 Msun.Comment: ApJ accepte
Improving health care from the bottom up: Factors for the successful implementation of kaizen in acute care hospitals
Background
Kaizenâa management technique increasingly employed in health careâenables employees, regardless of their hierarchy level, to contribute to the improvement of their organization. The approach puts special emphasis on frontline employees because it represents one of their main opportunities to participate directly in decision making. In this study, we aimed to (1) understand the experiences of nurses in two hospitals that had recently implemented kaizen, and (2) identify factors affecting the implementation of the technique.
Methods
By means of purposeful sampling, we selected 30 nurses from different units in two private acute care hospitals in Switzerland in May 2018. We used the Organizational Transformation Model to conduct semi-structured interviews and perform qualitative content analysis. Lastly, originating from Herzbergâs motivation theory, we suggest two types of factor influencing the implementation of kaizenâhygiene factors that may prevent nurses from getting demotivated, and motivational factors that may boost their motivation.
Results
Nurses generally experienced kaizen as a positive practice that enabled them to discuss work-related activities in a more comprehensive manner. In some cases, however, a lack of visible improvement in the workplace lowered nursesâ motivation to make suggestions. Nursesâ attitudes towards kaizen differed across both hospitals depending on the available managerial support, resources such as infrastructure and staffing levels.
Conclusions
From our findings, we derived several coping strategies to help health practitioners implement kaizen for the benefit of their organization and employees: Strong managerial support, appropriate use of kaizen tools, and a greater sense of team cohesion, among other factors, can influence how effectively hospital teams implement kaizen. To reap the benefits of kaizen, hospital managers should promote the exchange of opinions across hierarchy levels, allocate the necessary resources in terms of personnel and infrastructure, and show nurses how the technique can help them improve their workplace
The CHARA Array Angular Diameter of HR 8799 Favors Planetary Masses for Its Imaged Companions
HR 8799 is an hF0 mA5 gamma Doradus, lambda Bootis, Vega-type star best known
for hosting four directly imaged candidate planetary companions. Using the
CHARA Array interferometer, we measure HR 8799's limb-darkened angular diameter
to be 0.342 +/- 0.008 mas; this is the smallest interferometrically measured
stellar diameter to date, with an error of only 2%. By combining our
measurement with the star's parallax and photometry from the literature, we
greatly improve upon previous estimates of its fundamental parameters,
including stellar radius (1.44 +/- 0.06 R_Sun), effective temperature (7193 +/-
87 K, consistent with F0), luminosity (5.05 +/- 0.29 L_Sun), and the extent of
the habitable zone (1.62 AU to 3.32 AU). These improved stellar properties
permit much more precise comparisons with stellar evolutionary models, from
which a mass and age can be determined, once the metallicity of the star is
known. Considering the observational properties of other lambda Bootis stars
and the indirect evidence for youth of HR 8799, we argue that the internal
abundance, and what we refer to as the effective abundance, is most likely
near-solar. Finally, using the Yonsei-Yale evolutionary models with uniformly
scaled solar-like abundances, we estimate HR 8799's mass and age considering
two possibilities: 1.516 +0.038/-0.024 M_Sun and 33 +7/-13 Myr if the star is
contracting toward the zero age main-sequence or 1.513 +0.023/-0.024 M_Sun and
90 +381/-50 Myr if it is expanding from it. This improved estimate of HR 8799's
age with realistic uncertainties provides the best constraints to date on the
masses of its orbiting companions, and strongly suggests they are indeed
planets. They nevertheless all appear to orbit well outside the habitable zone
of this young star.Comment: Accepted for publication in ApJ; 37 pages, 6 tables, 13 figure
Three temperate Neptunes orbiting nearby stars
We present the discovery of three modestly irradiated, roughly Neptune-mass planets orbiting three nearby Solartype stars. HD 42618 b has a minimum mass of 15.4±2.4 Mâ, a semimajor axis of 0.55 au, an equilibrium temperature of 337 K, and is the first planet discovered to orbit the solar analogue host star, HD 42618. We also discover new planets orbiting the known exoplanet host stars HD 164922 and HD 143761 (p CrB). The new planet orbiting HD 164922 has a minimum mass of 12.9±1.6 Mâ and orbits interior to the previously known Jovian mass planet orbiting at 2.1 au. HD 164922 c has a semimajor axis of 0.34 au and an equilibrium temperature of 418 K. HD 143761 c orbits with a semimajor axis of 0.44 au, has a minimum mass of 25±2 Mâ, and is the warmest of the three new planets with an equilibrium temperature of 445 K. It orbits exterior to the previously known warm Jupiter in the system. A transit search using space-based CoRoT data and ground-based photometry from the Automated Photometric Telescopes (APTs) at Fairborn Observatory failed to detect any transits, but the precise, high-cadence APT photometry helped to disentangle planetary-reflex motion from stellar activity. These planets were discovered as part of an ongoing radial velocity survey of bright, nearby, chromospherically inactive stars using the Automated Planet Finder (APF) telescope at Lick Observatory. The high-cadence APF data combined with nearly two decades of radial velocity data from Keck Observatory and gives unprecedented sensitivity to both short-period low-mass, and long-period intermediate-mass planets
Stellar Diameters and Temperatures VI. High angular resolution measurements of the transiting exoplanet host stars HD 189733 and HD 209458 and implications for models of cool dwarfs
We present direct radii measurements of the well-known transiting exoplanet
host stars HD 189733 and HD 209458 using the CHARA Array interferometer. We
find the limb-darkened angular diameters to be theta_LD = 0.3848 +/- 0.0055 and
0.2254 +/- 0.0072 milliarcsec for HD 189733 and HD 209458, respectively. HD
189733 and HD 209458 are currently the only two transiting exoplanet systems
where detection of the respective planetary companion's orbital motion from
high resolution spectroscopy has revealed absolute masses for both star and
planet. We use our new measurements together with the orbital information from
radial velocity and photometric time series data, Hipparcos distances, and
newly measured bolometric fluxes to determine the stellar effective
temperatures (T_eff = 4875 +/- 43, 6093 +/- 103 K), stellar linear radii (R_* =
0.805 +/- 0.016, 1.203 +/- 0.061 R_sun), mean stellar densities (rho_* = 1.62
+/- 0.11, 0.58 +/- 0.14 rho_sun), planetary radii (R_p = 1.216 +/- 0.024, 1.451
+/- 0.074 R_Jup), and mean planetary densities (rho_p = 0.605 +/- 0.029, 0.196
+/- 0.033 rho_Jup) for HD 189733 b and HD 209458 b, respectively. The stellar
parameters for HD 209458, a F9 dwarf, are consistent with indirect estimates
derived from spectroscopic and evolutionary modeling. However, we find that
models are unable to reproduce the observational results for the K2 dwarf, HD
189733. We show that, for stellar evolutionary models to match the observed
stellar properties of HD 189733, adjustments lowering the solar-calibrated
mixing length parameter from 1.83 to 1.34 need to be employed
Three Temperate Neptunes Orbiting Nearby Stars
We present the discovery of three modestly irradiated, roughly Neptune-mass planets orbiting three nearby Solar-type stars. HD 42618 b has a minimum mass of 15.4 ± 2.4 M_â, a semimajor axis of 0.55 au, an equilibrium temperature of 337 K, and is the first planet discovered to orbit the solar analogue host star, HD 42618. We also discover new planets orbiting the known exoplanet host stars HD 164922 and HD 143761 (Ï CrB). The new planet orbiting HD 164922 has a minimum mass of 12.9 ± 1.6 M_â and orbits interior to the previously known Jovian mass planet orbiting at 2.1 au. HD 164922 c has a semimajor axis of 0.34 au and an equilibrium temperature of 418 K. HD 143761 c orbits with a semimajor axis of 0.44 au, has a minimum mass of 25 ± 2 M_â, and is the warmest of the three new planets with an equilibrium temperature of 445 K. It orbits exterior to the previously known warm Jupiter in the system. A transit search using space-based CoRoT data and ground-based photometry from the Automated Photometric Telescopes (APTs) at Fairborn Observatory failed to detect any transits, but the precise, high-cadence APT photometry helped to disentangle planetary-reflex motion from stellar activity. These planets were discovered as part of an ongoing radial velocity survey of bright, nearby, chromospherically inactive stars using the Automated Planet Finder (APF) telescope at Lick Observatory. The high-cadence APF data combined with nearly two decades of radial velocity data from Keck Observatory and gives unprecedented sensitivity to both short-period low-mass, and long-period intermediate-mass planets
A planet within the debris disk around the pre-main-sequence star AU Microscopii
AU Microscopii (AU Mic) is the second closest pre main sequence star, at a
distance of 9.79 parsecs and with an age of 22 million years. AU Mic possesses
a relatively rare and spatially resolved3 edge-on debris disk extending from
about 35 to 210 astronomical units from the star, and with clumps exhibiting
non-Keplerian motion. Detection of newly formed planets around such a star is
challenged by the presence of spots, plage, flares and other manifestations of
magnetic activity on the star. Here we report observations of a planet
transiting AU Mic. The transiting planet, AU Mic b, has an orbital period of
8.46 days, an orbital distance of 0.07 astronomical units, a radius of 0.4
Jupiter radii, and a mass of less than 0.18 Jupiter masses at 3 sigma
confidence. Our observations of a planet co-existing with a debris disk offer
the opportunity to test the predictions of current models of planet formation
and evolution.Comment: Nature, published June 24th [author spelling name fix
Collins and Sivers transverse-spin asymmetries in inclusive muoproduction of mesons
The production of vector mesons in deep inelastic scattering is an
interesting yet scarsely explored channel to study the transverse spin
structure of the nucleon and the related phenomena. The COMPASS collaboration
has performed the first measurement of the Collins and Sivers asymmetries for
inclusively produced mesons. The analysis is based on the data set
collected in deep inelastic scattering in using a
beam impinging on a transversely polarized target. The
mesons are selected from oppositely charged hadron pairs, and the
asymmetries are extracted as a function of the Bjorken- variable, the
transverse momentum of the pair and the fraction of the energy carried by
the pair. Indications for positive Collins and Sivers asymmetries are observed
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