929 research outputs found
Changes in rod and frame test scores recorded in schoolchildren during development--a longitudinal study.
The Rod and Frame Test has been used to assess the degree to which subjects rely on the visual frame of reference to perceive vertical (visual field dependence-independence perceptual style). Early investigations found children exhibited a wide range of alignment errors, which reduced as they matured. These studies used a mechanical Rod and Frame system, and presented only mean values of grouped data. The current study also considered changes in individual performance. Changes in rod alignment accuracy in 419 school children were measured using a computer-based Rod and Frame test. Each child was tested at school Grade 2 and retested in Grades 4 and 6. The results confirmed that children displayed a wide range of alignment errors, which decreased with age but did not reach the expected adult values. Although most children showed a decrease in frame dependency over the 4 years of the study, almost 20% had increased alignment errors suggesting that they were becoming more frame-dependent. Plots of individual variation (SD) against mean error allowed the sample to be divided into 4 groups; the majority with small errors and SDs; a group with small SDs, but alignments clustering around the frame angle of 18°; a group showing large errors in the opposite direction to the frame tilt; and a small number with large SDs whose alignment appeared to be random. The errors in the last 3 groups could largely be explained by alignment of the rod to different aspects of the frame. At corresponding ages females exhibited larger alignment errors than males although this did not reach statistical significance. This study confirms that children rely more heavily on the visual frame of reference for processing spatial orientation cues. Most become less frame-dependent as they mature, but there are considerable individual differences
Estimating magnetic filling factors from simultaneous spectroscopy and photometry : disentangling spots, plage, and network
A.C.C. acknowledges support from the Science and Technology Facilities Council (STFC) consolidated grant number ST/R000824/1.State-of-the-art radial velocity (RV) exoplanet searches are limited by the effects of stellar magnetic activity. Magnetically active spots, plage, and network regions each have different impacts on the observed spectral lines and therefore on the apparent stellar RV. Differentiating the relative coverage, or filling factors, of these active regions is thus necessary to differentiate between activity-driven RV signatures and Doppler shifts due to planetary orbits. In this work, we develop a technique to estimate feature-specific magnetic filling factors on stellar targets using only spectroscopic and photometric observations. We demonstrate linear and neural network implementations of our technique using observations from the solar telescope at HARPS-N, the HK Project at the Mt. Wilson Observatory, and the Total Irradiance Monitor onboard SORCE. We then compare the results of each technique to direct observations by the Solar Dynamics Observatory. Both implementations yield filling factor estimates that are highly correlated with the observed values. Modeling the solar RVs using these filling factors reproduces the expected contributions of the suppression of convective blueshift and rotational imbalance due to brightness inhomogeneities. Both implementations of this technique reduce the overall activity-driven rms RVs from 1.64 to 1.02 m s(-1), corresponding to a 1.28 m s(-1) reduction in the rms variation. The technique provides an additional 0.41 m s(-1) reduction in the rms variation compared to traditional activity indicators.PostprintPeer reviewe
Evaluation of the effects of a VEGFR-2 inhibitor compound on alanine aminotransferase gene expression and enzymatic activity in the rat liver
Article deposited according to agreement with BMC, December 6, 2010.YesFunding provided by the Open Access Authors Fund
A rocky planet transiting a nearby low-mass star
M-dwarf stars -- hydrogen-burning stars that are smaller than 60 per cent of
the size of the Sun -- are the most common class of star in our Galaxy and
outnumber Sun-like stars by a ratio of 12:1. Recent results have shown that M
dwarfs host Earth-sized planets in great numbers: the average number of M-dwarf
planets that are between 0.5 to 1.5 times the size of Earth is at least 1.4 per
star. The nearest such planets known to transit their star are 39 parsecs away,
too distant for detailed follow-up observations to measure the planetary masses
or to study their atmospheres. Here we report observations of GJ 1132b, a
planet with a size of 1.2 Earth radii that is transiting a small star 12
parsecs away. Our Doppler mass measurement of GJ 1132b yields a density
consistent with an Earth-like bulk composition, similar to the compositions of
the six known exoplanets with masses less than six times that of the Earth and
precisely measured densities. Receiving 19 times more stellar radiation than
the Earth, the planet is too hot to be habitable but is cool enough to support
a substantial atmosphere, one that has probably been considerably depleted of
hydrogen. Because the host star is nearby and only 21 per cent the radius of
the Sun, existing and upcoming telescopes will be able to observe the
composition and dynamics of the planetary atmosphere.Comment: Published in Nature on 12 November 2015, available at
http://dx.doi.org/10.1038/nature15762. This is the authors' version of the
manuscrip
An ultra-short period rocky super-Earth orbiting the G2-star HD 80653
Ultra-short period (USP) planets are a class of exoplanets with periods
shorter than one day. The origin of this sub-population of planets is still
unclear, with different formation scenarios highly dependent on the composition
of the USP planets. A better understanding of this class of exoplanets will,
therefore, require an increase in the sample of such planets that have accurate
and precise masses and radii, which also includes estimates of the level of
irradiation and information about possible companions. Here we report a
detailed characterization of a USP planet around the solar-type star HD 80653
EP 251279430 using the K2 light curve and 108 precise radial
velocities obtained with the HARPS-N spectrograph, installed on the Telescopio
Nazionale Galileo. From the K2 C16 data, we found one super-Earth planet
() transiting the star on a short-period orbit
( d). From our radial velocity measurements, we
constrained the mass of HD 80653 b to . We also
detected a clear long-term trend in the radial velocity data. We derived the
fundamental stellar parameters and determined a radius of
and mass of , suggesting that HD 80653, has an age of Gyr. The bulk
density ( g cm) of the planet is consistent with
an Earth-like composition of rock and iron with no thick atmosphere. Our
analysis of the K2 photometry also suggests hints of a shallow secondary
eclipse with a depth of 8.13.7 ppm. Flux variations along the orbital
phase are consistent with zero. The most important contribution might come from
the day-side thermal emission from the surface of the planet at K.Includes STFC
An 11 Earth-mass, Long-period Sub-Neptune Orbiting a Sun-like Star
Although several thousands of exoplanets have now been detected and
characterized, observational biases have led to a paucity of long-period,
low-mass exoplanets with measured masses and a corresponding lag in our
understanding of such planets. In this paper we report the mass estimation and
characterization of the long-period exoplanet Kepler-538b. This planet orbits a
Sun-like star (V = 11.27) with M_* = 0.892 +/- (0.051, 0.035) M_sun and R_* =
0.8717 +/- (0.0064, 0.0061) R_sun. Kepler-538b is a 2.215 +/- (0.040, 0.034)
R_earth sub-Neptune with a period of P = 81.73778 +/- 0.00013 d. It is the only
known planet in the system. We collected radial velocity (RV) observations with
HIRES on Keck I and HARPS-N on the TNG. We characterized stellar activity by a
Gaussian process with a quasi-periodic kernel applied to our RV and cross
correlation function full width at half maximum (FWHM) observations. By
simultaneously modeling Kepler photometry, RV, and FWHM observations, we found
a semi-amplitude of K = 1.68 +/- (0.39, 0.38) m s^-1 and a planet mass of M_p =
10.6 +/- (2.5, 2.4) M_earth. Kepler-538b is the smallest planet beyond P = 50 d
with an RV mass measurement. The planet likely consists of a significant
fraction of ices (dominated by water ice), in addition to rocks/metals, and a
small amount of gas. Sophisticated modeling techniques such as those used in
this paper, combined with future spectrographs with ultra high-precision and
stability will be vital for yielding more mass measurements in this poorly
understood exoplanet regime. This in turn will improve our understanding of the
relationship between planet composition and insolation flux and how the rocky
to gaseous transition depends on planetary equilibrium temperature
Detection Limits of Low-mass, Long-period Exoplanets Using Gaussian Processes Applied to HARPS-N Solar Radial Velocities
Radial velocity (RV) searches for Earth-mass exoplanets in the habitable zone
around Sun-like stars are limited by the effects of stellar variability on the
host star. In particular, suppression of convective blueshift and brightness
inhomogeneities due to photospheric faculae/plage and starspots are the
dominant contribution to the variability of such stellar RVs. Gaussian process
(GP) regression is a powerful tool for statistically modeling these
quasi-periodic variations. We investigate the limits of this technique using
800 days of RVs from the solar telescope on the High Accuracy Radial velocity
Planet Searcher for the Northern hemisphere (HARPS-N) spectrograph. These data
provide a well-sampled time series of stellar RV variations. Into this data
set, we inject Keplerian signals with periods between 100 and 500 days and
amplitudes between 0.6 and 2.4 m s. We use GP regression to fit the
resulting RVs and determine the statistical significance of recovered periods
and amplitudes. We then generate synthetic RVs with the same covariance
properties as the solar data to determine a lower bound on the observational
baseline necessary to detect low-mass planets in Venus-like orbits around a
Sun-like star. Our simulations show that discovering planets with a larger mass
( 0.5 m s) using current-generation spectrographs and GP
regression will require more than 12 yr of densely sampled RV observations.
Furthermore, even with a perfect model of stellar variability, discovering a
true exo-Venus ( 0.1 m s) with current instruments would take over
15 yr. Therefore, next-generation spectrographs and better models of stellar
variability are required for detection of such planets
Separating planetary reflex Doppler shifts from stellar variability in the wavelength domain
Stellar magnetic activity produces time-varying distortions in the
photospheric line profiles of solar-type stars. These lead to systematic errors
in high-precision radial-velocity measurements, which limit efforts to discover
and measure the masses of low-mass exoplanets with orbital periods of more than
a few tens of days. We present a new data-driven method for separating Doppler
shifts of dynamical origin from apparent velocity variations arising from
variability-induced changes in the stellar spectrum. We show that the
autocorrelation function (ACF) of the cross-correlation function used to
measure radial velocities is effectively invariant to translation. By
projecting the radial velocities on to a subspace labelled by the observation
identifiers and spanned by the amplitude coefficients of the ACF's principal
components, we can isolate and subtract velocity perturbations caused by
stellar magnetic activity. We test the method on a 5-year time sequence of 853
daily 15-minute observations of the solar spectrum from the HARPS-N instrument
and solar-telescope feed on the 3.58-m Telescopio Nazionale Galileo. After
removal of the activity signals, the heliocentric solar velocity residuals are
found to be Gaussian and nearly uncorrelated. We inject synthetic low-mass
planet signals with amplitude cm s into the solar observations at
a wide range of orbital periods. Projection into the orthogonal complement of
the ACF subspace isolates these signals effectively from solar activity
signals. Their semi-amplitudes are recovered with a precision of cm
s, opening the door to Doppler detection and characterization of
terrestrial-mass planets around well-observed, bright main-sequence stars
across a wide range of orbital periods
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Detection Limits of Low-mass, Long-period Exoplanets Using Gaussian Processes Applied to HARPS-N Solar Radial Velocities
Radial velocity (RV) searches for Earth-mass exoplanets in the habitable zone around Sun-like stars are limited by the effects of stellar variability on the host star. In particular, suppression of convective blueshift and brightness inhomogeneities due to photospheric faculae/plage and starspots are the dominant contribution to the variability of such stellar RVs. Gaussian process (GP) regression is a powerful tool for statistically modeling these quasi-periodic variations. We investigate the limits of this technique using 800 days of RVs from the solar telescope on the High Accuracy Radial velocity Planet Searcher for the Northern hemisphere (HARPS-N) spectrograph. These data provide a well-sampled time series of stellar RV variations. Into this data set, we inject Keplerian signals with periods between 100 and 500 days and amplitudes between 0.6 and 2.4 msâ1. We use GP regression to fit the resulting RVs and determine the statistical significance of recovered periods and amplitudes. We then generate synthetic RVs with the same covariance properties as the solar data to determine a lower bound on the observational baseline necessary to detect low-mass planets in Venus-like orbits around a Sun-like star. Our simulations show that discovering planets with a larger mass (âŒ0.5 msâ1) using current-generation spectrographs and GP regression will require more than 12 yr of densely sampled RV observations. Furthermore, even with a perfect model of stellar variability, discovering a true exo-Venus (âŒ0.1 m s â1 ) with current instruments would take over 15 yr. Therefore, next-generation spectrographs and better models of stellar variability are required for detection of such planets
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