992 research outputs found
Quaternary pulse position modulation electronics for free-space laser communications
The development of a high data-rate communications electronic subsystem for future application in free-space, direct-detection laser communications is described. The dual channel subsystem uses quaternary pulse position modulation (QPPM) and operates at a throughput of 650 megabits per second. Transmitting functions described include source data multiplexing, channel data multiplexing, and QPPM symbol encoding. Implementation of a prototype version in discrete gallium arsenide logic, radiofrequency components, and microstrip circuitry is presented
A Candidate Young Massive Planet in Orbit around the Classical T Tauri Star CI Tau
The ~2 Myr old classical T Tauri star CI Tau shows periodic variability in
its radial velocity (RV) variations measured at infrared (IR) and optical
wavelengths. We find that these observations are consistent with a massive
planet in a ~9-day period orbit. These results are based on 71 IR RV
measurements of this system obtained over 5 years, and on 26 optical RV
measurements obtained over 9 years. CI Tau was also observed photometrically in
the optical on 34 nights over ~one month in 2012. The optical RV data alone are
inadequate to identify an orbital period, likely the result of star spot and
activity induced noise for this relatively small dataset. The infrared RV
measurements reveal significant periodicity at ~9 days. In addition, the full
set of optical and IR RV measurements taken together phase coherently and with
equal amplitudes to the ~9 day period. Periodic radial velocity signals can in
principle be produced by cool spots, hot spots, and reflection of the stellar
spectrum off the inner disk, in addition to resulting from a planetary
companion. We have considered each of these and find the planet hypothesis most
consistent with the data. The radial velocity amplitude yields an Msin(i) of
~8.1 M_Jup; in conjunction with a 1.3 mm continuum emission measurement of the
circumstellar disk inclination from the literature, we find a planet mass of
~11.3 M_Jup, assuming alignment of the planetary orbit with the disk.Comment: 61 pages, 13 figures, accepted for publication in The Astrophysical
Journa
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Individual and joint trajectories of change in bone, lean mass and physical performance in older men.
BackgroundDeclines in bone, muscle and physical performance are associated with adverse health outcomes in older adults. However, few studies have described concurrent age-related patterns of change in these factors. The purpose of this study was to characterize change in four properties of muscle, physical performance, and bone in a prospective cohort study of older men.MethodsUsing repeated longitudinal data from up to four visits across 6.9 years from up to 4681 men (mean age at baseline 72.7 yrs. ±5.3) participating in the Osteoporotic Fractures in Men (MrOS) Study, we used group-based trajectory models (PROC TRAJ in SAS) to identify age-related patterns of change in four properties of muscle, physical performance, and bone: total hip bone mineral (BMD) density (g/m2) and appendicular lean mass/ht2 (kg/m2), by DXA; grip strength (kg), by hand dynamometry; and walking speed (m/s), by usual walking pace over 6 m. We also described joint trajectories in all pair-wise combinations of these measures. Mean posterior probabilities of placement in each trajectory (or joint membership in latent groups) were used to assess internal reliability of the model. The number of trajectories for each individual factor was limited to three, to ensure that the pair-wise determination of joint trajectories would yield a tractable number of groups as well as model fit considerations.ResultsThe patterns of change identified were generally similar for all measures, with three district groups declining over time at roughly similar rates; joint trajectories revealed similar patterns with no cross-over or convergence between groups. Mean posterior probabilities for all trajectories were similar and consistently above 0.8 indicating reasonable model fit to the data.ConclusionsOur description of trajectories of change with age in bone mineral density, grip strength, walking speed and appendicular lean mass found that groups identified by these methods appeared to have little crossover or convergence of change with age, even when considering joint trajectories of change in these factors
Treatment‐related changes in bone turnover and fracture risk reduction in clinical trials of antiresorptive drugs: proportion of treatment effect explained
Few analyses of antiresorptive (AR) treatment trials relate short‐term changes in bone turnover markers (BTMs) to subsequent fracture reduction seeking to estimate the proportion of treatment effect explained (PTE) by BTMs. Pooling such information would be useful to assess new ARs or novel dosing regimens. In the Foundation for the National Institutes of Health (FNIH) Bone Quality project, we analyzed individual‐level data from up to 62,000 participants enrolled in 12 bisphosphonate (BP) and four selective estrogen receptor modulator (SERM) placebo‐controlled fracture endpoint trials. Using BTM results for two bone formation markers (bone‐specific alkaline phosphatase [bone ALP] and pro‐collagen I N‐propeptide [PINP]) and one bone resorption marker (C‐terminal telopeptide of type I collagen [CTX]) and incident fracture outcome data, we estimated the PTE using two different models. Separate analyses were performed for incident morphometric vertebral, nonvertebral, and hip fractures over 1 to 5 years of follow‐up. For vertebral fracture, the results showed that changes in all three BTMs at 6 months explained a large proportion of the treatment effect of ARs (57 to >100%), but not for and non‐vertebral or hip fracture. We conclude that short‐term AR treatment‐related changes in bone ALP, PINP, and CTX account for a large proportion of the treatment effect for vertebral fracture. Change in BTMs is a useful surrogate marker to study the anti‐fracture efficacy of new AR compounds or novel dosing regiments with approved AR drugs. © 2020 The Authors. Journal of Bone and Mineral Research published by American Society for Bone and Mineral Research
Frailty and Risk of Falls, Fracture, and Mortality in Older Women: The Study of Osteoporotic Fractures
Background. A standard phenotype of frailty was associated with an increased risk of adverse outcomes including mortality in a recent study of older adults. However, the predictive validity of this phenotype for fracture outcomes and across risk subgroups is uncertain. Methods. To determine whether a standard frailty phenotype was independently associated with risk of adverse health outcomes in older women and to evaluate the consistency of associations across risk subgroups defined by age and body mass index (BMI), we ascertained frailty status in a cohort of 6724 women ≥ 69 years and followed them prospectively for incident falls, fractures, and mortality. Frailty was defined by the presence of three or more of the following criteria: unintentional weight loss, weakness, self-reported poor energy, slow walking speed, and low physical activity. Incident recurrent falls were defined as at least two falls during the subsequent year. Incident fractures (confirmed with x-ray reports), including hip fractures, and deaths were ascertained during an average of 9 years of follow-up. Results. After controlling for multiple confounders such as age, health status, medical conditions, functional status, depressive symptoms, cognitive function, and bone mineral density, frail women were subsequently at increased risk of recurrent falls (multivariate odds ratio = 1.38, 95% confidence interval [CI], 1.02-1.88), hip fracture (multivariate hazards ratio [MHR] = 1.40, 95% CI, 1.03-1.90), any nonspine fracture (MHR = 1.25, 95% CI, 1.05-1.49), and death (MHR = 1.82, 95% CI, 1.56-2.13). The associations between frailty and these outcomes persisted among women ≥ 80 years. In addition, associations between frailty and an increased risk of falls, fracture, and mortality were consistently observed across categories of BMI, including BMI ≥ 30 kg/m2. Conclusion. Frailty is an independent predictor of adverse health outcomes in older women, including very elderly women and older obese wome
A data-driven approach to constraining the atmospheric temperature structure of KELT-9b
Context. Observationally constraining the atmospheric temperature-pressure
(TP) profile of exoplanets is an important step forward for improving planetary
atmosphere models, further enabling one to place the detection of spectral
features and the measurement of atomic and molecular abundances through
transmission and emission spectroscopy on solid ground. Aims. The aim is to
constrain the TP profile of the ultra-hot Jupiter KELT-9b by fitting synthetic
spectra to the observed H and H lines and identify why
self-consistent planetary TP models are unable to fit the observations.
Methods. We construct 126 one-dimensional TP profiles varying the lower and
upper atmospheric temperatures, as well as the location and gradient of the
temperature rise. For each TP profile, we compute transmission spectra of the
H and H lines employing the Cloudy radiative transfer code,
which self-consistently accounts for non-local thermodynamic equilibrium (NLTE)
effects. Results. The TP profiles leading to best fit the observations are
characterised by an upper atmospheric temperature of 10000-11000 K and by an
inverted temperature profile at pressures higher than 10 bar. We find
that the assumption of local thermodynamic equilibrium (LTE) leads to
overestimate the level population of excited hydrogen by several orders of
magnitude, and hence to significantly overestimate the strength of the Balmer
lines. The chemical composition of the best fitting models indicate that the
high upper atmospheric temperature is most likely driven by metal
photoionisation and that FeII and FeIII have comparable abundances at pressures
lower than 10 bar, possibly making the latter detectable. Conclusions.
Modelling the atmospheres of ultra-hot Jupiters requires one to account for
metal photoionisation. [abridged]Comment: Accepted for publication by A&
UK Housing Market: Time Series Processes with Independent and Identically Distributed Residuals
The paper examines whether a univariate data generating process can be identified which explains the data by having residuals that are independent and identically distributed, as verified by the BDS test. The stationary first differenced natural log quarterly house price index is regressed, initially with a constant variance and then with a conditional variance. The only regression function that produces independent and identically distributed standardised residuals is a mean process based on a pure random walk format with Exponential GARCH in mean for the conditional variance. There is an indication of an asymmetric volatility feedback effect but higher frequency data is required to confirm this. There could be scope for forecasting the index but this is tempered by the reduction in the power of the BDS test if there is a non-linear conditional variance process
Flares, Rotation, Activity Cycles and a Magnetic Star-Planet Interaction Hypothesis for the Far Ultraviolet Emission of GJ 436
Variability in the far ultraviolet (FUV) emission produced by stellar
activity affects photochemistry and heating in orbiting planetary atmospheres.
We present a comprehensive analysis of the FUV variability of GJ 436, a
field-age, M2.5V star ( d) orbited by a warm,
Neptune-size planet (, ,
d). Observations at three epochs from 2012 to 2018
span nearly a full activity cycle, sample two rotations of the star and two
orbital periods of the planet, and reveal a multitude of brief flares. Over
2012-2018, the star's yr activity cycle produced the largest
observed variations, % in the summed flux of major FUV emission lines.
In 2018, variability due to rotation was %. An additional %
scatter at 10 min cadence, treated as white noise in fits, likely has both
instrumental and astrophysical origins. Flares increased time-averaged emission
by 15% over the 0.88 d of cumulative exposure, peaking as high as 25
quiescence. We interpret these flare values as lower limits given that flares
too weak or too infrequent to have been observed likely exist. GJ 436's flare
frequency distribution (FFD) at FUV wavelengths is unusual compared to other
field-age M dwarfs, exhibiting a statistically-significant dearth of high
energy ( erg) events that we hypothesize to be the result of
a magnetic star-planet interaction (SPI) triggering premature flares. If an SPI
is present, GJ 436 b's magnetic field strength must be 100 G to
explain the statistically insignificant increase in orbit-phased FUV emission.Comment: 18 pages, 9 figures, accepted to the Astronomical Journa
Vitamin D levels and menopause-related symptoms.
Objective: To determine whether vitamin D levels are associated with menopause-related symptoms in older women. Methods: A randomly selected subset of 1,407 women, among 26,104 potentially eligible participants of the Women’s Health Initiative Calcium and Vitamin D (CaD) trial of postmenopausal women aged 51-80 years, had 25-hydroxyvitamin D [25(OH)D] levels measured at the CaD trial baseline visit. Information about menopause-related symptoms at baseline was obtained by questionnaire and included overall number of symptoms and composite measures of sleep disturbance, emotional well-being, and energy/fatigue, as well as individual symptoms. After exclusions for missing data, 530 women [mean age 66.2 years (SD 6.8)] were included in these analyses. Results: There were borderline significant associations between 25(OH)D levels and total number of menopausal symptoms (p values ranging from 0.05 to 0.06 for fully adjusted models); however, the effect was clinically insignificant and disappeared with correction for multiple testing. There were no associations between 25(OH)D levels and composite measures of sleep disturbance, emotional well-being, or energy/fatigue (p’s > 0.10 for fully adjusted models). Conclusions: There was no evidence of a clinically important association between serum 25(OH)D levels and menopause-related symptoms in postmenopausal women
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