1,051 research outputs found
Using debris disk observations to infer substellar companions orbiting within or outside a parent planetesimal belt
Aims. We analyze whether the effects of secular perturbations, originating
from a substellar companion, on the dust dynamics in a debris disk can be
investigated with spatially resolved observations.
Methods. We numerically simulated the collisional evolution of narrow and
eccentric cold planetesimal belts around a star of spectral type A3V that are
secularly perturbed by a companion that orbits either closer to or farther from
the star than the belt. Based on the resulting spatial dust distributions, we
simulated spatially resolved maps of their surface brightness in the , ,
and bands and at wavelengths of 70m and 1300m.
Results. Assuming a nearby debris disk seen face-on, we find that the
brightness distribution varies significantly with observing wavelength, for
example between the and band. This can be explained by the varying
relative contribution of the emission of the smallest grains near the blowout
limit. The orbits of both the small grains that form the halo and the large
grains close to the parent belt precess due to the secular perturbations
induced by a companion orbiting inward of the belt. The halo, being composed of
older grains, trails the belt. The magnitude of the trailing decreases with
increasing perturber mass and hence with increasing strength of the
perturbation, a trend we recovered in synthetic maps of surface brightness by
fitting ellipses to lines of constant brightness. Systems with an outer
perturber do not show a uniform halo precession since the orbits of small
grains are strongly altered. We identified features of the brightness
distributions suitable for distinguishing between systems with a potentially
detectable inner or outer perturber, especially with a combined observation
with JWST/MIRI in the band tracing small grain emission and with ALMA at mm
wavelengths tracing the position of the parent planetesimal belt.Comment: Accepted for publication in Astronomy & Astrophysics. 25 pages, 21
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Exploring within-person variability in qualitative negative and positive Emotional Granularity by means of Latent Markov Factor Analysis
Emotional granularity (EG) is an individual’s ability to describe their emotional experiences in a nuanced and specific way. In this paper, we propose that researchers adopt latent Markov factor analysis (LMFA) to investigate within-person variability in qualitative EG (i.e., variability in distinct granularity patterns between specific emotions across time). LMFA clusters measurement occasions into latent states according to state-specific measurement models. We argue that state-specific measurement models of repeatedly assessed emotion items can provide information about qualitative EG at a given point in time. Applying LMFA to the area of EG for negative and positive emotions separately by using data from an experience sampling study with 11,662 measurement occasions across 139 participants, we found three latent EG states for the negative emotions and three for the positive emotions. Momentary stress significantly predicted transitions between the EG states for both the negative and positive emotions. We further identified two and three latent classes of individuals who differed in state trajectories for negative and positive emotions, respectively. Neuroticism and dispositional mood regulation predicted latent class membership for negative (but not for positive) emotions. We conclude that LMFA may enrich EG research by enabling more fine-grained insights into variability in qualitative EG patterns
How much large dust could be present in hot exozodiacal dust systems?
An infrared excess over the stellar photospheric emission of main-sequence
stars has been found in interferometric surveys, commonly attributed to the
presence of hot exozodiacal dust (HEZD). While submicrometer-sized grains in
close vicinity to their host star have been inferred to be responsible for the
found near-infrared excesses, the presence and amount of larger grains as part
of the dust distributions are weakly constrained. We quantify how many larger
grains (above-micrometer-sized) could be present in addition to
submicrometer-sized grains, while being consistent with observational
constraints. This is important in order to distinguish between various
scenarios for the origin of HEZD and to better estimate its observational
appearance when observed with future instruments. We extended a model suitable
to reproduce current observations of HEZD to investigate a bimodal size
distribution. By deriving the characteristics of dust distributions whose
observables are consistent with observational limits from interferometric
measurements in the and bands we constrained the radii of sub- and
above-micrometer-sized grains as well as their mass, number, and flux density
ratios. In the most extreme cases of some of the investigated systems, large
grains m might dominate the mass budget of HEZD while
contributing up to 25% of the total flux density originating from the dust
at a wavelength of 2.13m and up to 50% at a wavelength of
4.1m; at a wavelength of 11.1m their emission might clearly
dominate over the emission of small grains. While it is not possible to detect
such hot-dust distributions using ALMA, the ngVLA might allow us to detect HEZD
at millimeter wavelengths. Large dust grains might have a more important impact
on the observational appearance of HEZD than previously assumed, especially at
longer wavelengths.Comment: Accepted for publication in Astronomy & Astrophysics. 18 pages, 7
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Single centre experience of the application of self navigated 3D whole heart cardiovascular magnetic resonance for the assessment of cardiac anatomy in congenital heart disease.
BACKGROUND: For free-breathing cardiovascular magnetic resonance (CMR), the self-navigation technique recently emerged, which is expected to deliver high-quality data with a high success rate. The purpose of this study was to test the hypothesis that self-navigated 3D-CMR enables the reliable assessment of cardiovascular anatomy in patients with congenital heart disease (CHD) and to define factors that affect image quality.
METHODS: CHD patients ≥2 years-old and referred for CMR for initial assessment or for a follow-up study were included to undergo a free-breathing self-navigated 3D CMR at 1.5T. Performance criteria were: correct description of cardiac segmental anatomy, overall image quality, coronary artery visibility, and reproducibility of great vessels diameter measurements. Factors associated with insufficient image quality were identified using multivariate logistic regression.
RESULTS: Self-navigated CMR was performed in 105 patients (55% male, 23 ± 12y). Correct segmental description was achieved in 93% and 96% for observer 1 and 2, respectively. Diagnostic quality was obtained in 90% of examinations, and it increased to 94% if contrast-enhanced. Left anterior descending, circumflex, and right coronary arteries were visualized in 93%, 87% and 98%, respectively. Younger age, higher heart rate, lower ejection fraction, and lack of contrast medium were independently associated with reduced image quality. However, a similar rate of diagnostic image quality was obtained in children and adults.
CONCLUSION: In patients with CHD, self-navigated free-breathing CMR provides high-resolution 3D visualization of the heart and great vessels with excellent robustness
Disease management at the wildlife-livestock interface: using whole-genome sequencing to study the role of elk in Mycobacterium bovis transmission in Michigan, USA
The role of wildlife in the persistence and spread of livestock diseases is difficult to quantify and control. These difficulties are exacerbated when several wildlife species are potentially involved. Bovine tuberculosis (bTB), caused by Mycobacterium bovis, has experienced an ecological shift in Michigan, with spillover from cattle leading to an endemically infected white‐tailed deer (deer) population. It has potentially substantial implications for the health and well‐being of both wildlife and livestock and incurs a significant economic cost to industry and government. Deer are known to act as a reservoir of infection, with evidence of M. bovis transmission to sympatric elk and cattle populations. However, the role of elk in the circulation of M. bovis is uncertain; they are few in number, but range further than deer, so may enable long distance spread. Combining Whole Genome Sequences (WGS) for M. bovis isolates from exceptionally well‐observed populations of elk, deer and cattle with spatiotemporal locations, we use spatial and Bayesian phylogenetic analyses to show strong spatiotemporal admixture of M. bovis isolates. Clustering of bTB in elk and cattle suggests either intraspecies transmission within the two populations, or exposure to a common source. However, there is no support for significant pathogen transfer amongst elk and cattle, and our data are in accordance with existing evidence that interspecies transmission in Michigan is likely only maintained by deer. This study demonstrates the value of whole genome population studies of M. bovis transmission at the wildlife‐livestock interface, providing insights into bTB management in an endemic system
Hydroxyurea reduces the transfusion burden in children with sickle cell anemia: the reach experience
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A large ozone-circulation feedback and its implications for global warming assessments.
State-of-the-art climate models now include more climate processes which are simulated at higher spatial resolution than ever1. Nevertheless, some processes, such as atmospheric chemical feedbacks, are still computationally expensive and are often ignored in climate simulations1,2. Here we present evidence that how stratospheric ozone is represented in climate models can have a first order impact on estimates of effective climate sensitivity. Using a comprehensive atmosphere-ocean chemistry-climate model, we find an increase in global mean surface warming of around 1°C (~20%) after 75 years when ozone is prescribed at pre-industrial levels compared with when it is allowed to evolve self-consistently in response to an abrupt 4×CO2 forcing. The difference is primarily attributed to changes in longwave radiative feedbacks associated with circulation-driven decreases in tropical lower stratospheric ozone and related stratospheric water vapour and cirrus cloud changes. This has important implications for global model intercomparison studies1,2 in which participating models often use simplified treatments of atmospheric composition changes that are neither consistent with the specified greenhouse gas forcing scenario nor with the associated atmospheric circulation feedbacks3-5.We thank the European Research Council for funding through the ACCI project,
project number 267760. The model development was part of the QESM-ESM project
supported by the UK Natural Environment Research Council (NERC) under contract
numbers RH/H10/19 and R8/H12/124. We acknowledge use of the MONSooN
system, a collaborative facility supplied under the Joint Weather and Climate
Research Programme, which is a strategic partnership between the UK Met Office
and NERC. A.C.M. acknowledges support from an AXA Postdoctoral Research
Fellowship.This is the accepted manuscript. The final version is available from Nature Publishing at http://www.nature.com/nclimate/journal/v5/n1/full/nclimate2451.html
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