2,307 research outputs found
Acute Type B Dissection
Aortic dissections are catastrophic vascular emergencies, and early recognition and appropriate interventions can be crucial to survival. Research has changed the way aortic dissections are managed over the past two decades and will continue to contribute to the evolution of treatment modalities. Early treatment for uncomplicated type B dissections still remains controversial but certain characteristics may benefit from early intervention
Survival and dynamics of rings of co-orbital planets under perturbations
In co-orbital planetary systems, two or more planets share the same orbit
around their star. Here we test the dynamical stability of co-orbital rings of
planets perturbed by outside forces. We test two setups: i) 'stationary' rings
of planets that, when unperturbed, remain equally-spaced along their orbit; and
ii) horseshoe constellation systems, in which planets are continually
undergoing horseshoe librations with their immediate neighbors. We show that a
single rogue planet crossing the planets' orbit more massive than a few lunar
masses (0.01-0.04 Earth masses) systematically disrupts a co-orbital ring of 6,
9, 18, or 42 Earth-mass planets located at 1 au. Stationary rings are more
resistant to perturbations than horseshoe constellations, yet when perturbed
they can transform into stable horseshoe constellation systems. Given
sufficient time, any co-orbital ring system will be perturbed into either
becoming a horseshoe constellation or complete destabilization.Comment: 5 pages, 4 figures. Re-submitted to MNRAS. Blog post about co-orbital
constellations here:
https://planetplanet.net/2023/04/20/constellations-of-co-orbital-planets
Constellations of co-orbital planets: horseshoe dynamics, long-term stability, transit timing variations, and potential as SETI beacons
Co-orbital systems contain two or more bodies sharing the same orbit around a
planet or star. The best-known flavors of co-orbital systems are tadpoles (in
which two bodies' angular separations oscillate about the L4/L5 Lagrange points
apart) and horseshoes (with two bodies periodically exchanging
orbital energy to trace out a horseshoe shape in a co-rotating frame). Here, we
use N-body simulations to explore the parameter space of many-planet horseshoe
systems. We show that up to 24 equal-mass, Earth-mass planets can share the
same orbit at 1 au, following a complex pattern in which neighboring planets
undergo horseshoe oscillations. We explore the dynamics of horseshoe
constellations, and show that they can remain stable for billions of years and
even persist through their stars' post-main sequence evolution. With sufficient
observations, they can be identified through their large-amplitude, correlated
transit timing variations. Given their longevity and exotic orbital
architectures, horseshoe constellations may represent potential SETI beacons.Comment: 10 pages, 10 figures. Published in MNRAS. YouTube playlist with
animations of horseshoe constellation systems here:
https://www.youtube.com/playlist?list=PLelMZVM3ka3F335LGLxkxrD1ieiLJYQ5N .
Blog post here:
https://planetplanet.net/2023/04/20/constellations-of-co-orbital-planets
Born extra-eccentric: A broad spectrum of primordial configurations of the gas giants that match their present-day orbits
In a recent paper we proposed that the giant planets' primordial orbits may
have been eccentric (~0.05), and used a suite of dynamical simulations to show
outcomes of the giant planet instability that are consistent with their
present-day orbits. In this follow-up investigation, we present more
comprehensive simulations incorporating superior particle resolution, longer
integration times, and eliminating our prior means of artificially forcing
instabilities to occur at specified times by shifting a planets' position in
its orbit. While we find that the residual phase of planetary migration only
minimally alters the the planets' ultimate eccentricities, our work uncovers
several intriguing outcomes in realizations where Jupiter and Saturn are born
with extremely large eccentricities (~0.10 and ~0.25, respectively). In
successful simulations, the planets' orbits damp through interactions with the
planetesimal disk prior to the instability, thus loosely replicating the
initial conditions considered in our previous work. Our results therefore
suggest an even wider range of plausible evolutionary pathways are capable of
replicating Jupiter and Saturn's modern orbital architecture.Comment: 12 pages, 3 figures, 2 tables, accepted for publication in Icaru
PIV data clustering of a buoyant jet in a stratified environment
Three spatial clustering approaches of a high-Reynolds number transient buoyant jet in
a linearly stratified environment are applied along with proper orthogonal decomposition to
identify similar/consistent regions in the domain of interest. The velocity fields analyzed are
obtained from an experimental test with large scale, time-resolved, particle image velocimetry
(PIV) measurements. Clustering is performed by the k-means method considering: (a) crosssection velocity profiles, (b) point-wise energy spectra, and (c) point-wise Reynolds stress tensor
components. Three metrics are used for the assessment of clustering approaches, namely: (a)
within-cluster sum of squares, (b) average silhouette, and (c) within-cluster number of POD
modes required to resolve prescribed levels of total variance/energy. Results are promising
and lay the foundation for an in depth analysis of local features of complex flows as well as the
formulation of efficient reduced order models
Sub-bandgap voltage electroluminescence and magneto-oscillations in a WSe2 light-emitting van der Waals heterostructure
We report on experimental investigations of an electrically driven WSe2 based
light-emitting van der Waals heterostructure. We observe a threshold voltage
for electroluminescence significantly lower than the corresponding single
particle band gap of monolayer WSe2. This observation can be interpreted by
considering the Coulomb interaction and a tunneling process involving excitons,
well beyond the picture of independent charge carriers. An applied magnetic
field reveals pronounced magneto-oscillations in the electroluminescence of the
free exciton emission intensity with a 1/B-periodicity. This effect is ascribed
to a modulation of the tunneling probability resulting from the Landau
quantization in the graphene electrodes. A sharp feature in the differential
conductance indicates that the Fermi level is pinned and allows for an
estimation of the acceptor binding energy.Comment: Accepted for publication in Nano Letter
BEATVIC, a body-oriented resilience therapy using kickboxing exercises for people with a psychotic disorder:a feasibility study
BACKGROUND: People with a psychotic disorder have an increased risk of becoming the victim of a crime. To prevent victimization a body-oriented resilience therapy using kickboxing exercises was developed. This study aims to explore the feasibility of the therapy, to improve the therapy protocol and to explore suitable outcomes for a RCT. METHODS: Twenty-four adults with a psychotic disorder received 20 weekly group sessions in which potential risk factors for victimization and strategies for dealing with them were addressed. Sessions were evaluated weekly. During pre and post assessment participants completed questionnaires on, among other, victimization, aggression regulation and social functioning. RESULTS: The short recruitment period indicates the interest in such an intervention and the willingness of clients to participate. Mean attendance was 85.3 and 88% of the participants completed fifteen or more sessions. The therapy protocol was assessed as adequate and exercises as relevant with some small improvements to be made. The victimization and aggression regulation questionnaires were found to be suitable outcome measurements for a subsequent RCT. CONCLUSION: The results support the feasibility of the BEATVIC therapy. Participants subjectively evaluated the intervention as helpful in their attempt to gain more self-esteem and assertiveness. With some minor changes in the protocol the effects of BEATVIC can be tested in a RCT. TRIAL REGISTRATION: The trial registration number (TRN) is 35949 (date submitted 09/11/2018). Retrospectively registered
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Improved sub-seasonal forecasts to support preparedness action for meningitis outbreak in Africa
West African countries are hit annually by meningitis outbreaks which occur during the dry season and are linked to atmospheric variability. This paper describes an innovative co-production process between the African Centre of Meteorological Applications for Development (ACMAD; forecast producer) and the World Health Organisation Regional Office for Africa (WHO AFRO; forecast user) to support awareness, preparedness and response actions for meningitis outbreaks. Using sub-seasonal to seasonal (S2S) forecasts, this co-production enables ACMAD and WHO AFRO to build initiative that increases the production of useful climate services in the health sector. Temperature and relative humidity forecasts are combined with dust forecasts to operationalize a meningitis early warning system (MEWS) across the African meningitis belt with a two-week lead time. To prevent and control meningitis, the MEWS is produced from week 1 to 26 of the year. This study demonstrates that S2S forecasts have good skill at predicting dry and warm atmospheric conditions precede meningitis outbreaks. Vigilance levels objectively defined within the MEWS are consistent with reported cases of meningitis. Alongside developing a MEWS, the co-production process provided a framework for analysis of climate and environmental risks based on reanalysis data, meningitis burden, and health service assessment, to support the development of a qualitative roadmap of country prioritization for defeating meningitis by 2030 across the WHO African region. The roadmap has enabled the identification of countries most vulnerable to meningitis epidemics, and in the context of climate change, supports plans for preventing, preparing, and responding to meningitis outbreaks
Semiexclusive pionic double charge exchange on 4 He
The semiexclusive reaction {}^{4}\mathrm{He}({\ensuremath{\pi}}^{+},{\ensuremath{\pi}}^{\ensuremath{-}}pp)pp has been studied at pion kinetic energies of 105 MeV and 115 MeV. Signatures from the production of the hypothetical \ensuremath{\pi}\mathrm{NN} resonance {d}^{\ensuremath{'}} have been searched for in the invariant mass {M}_{\ensuremath{\pi}\mathrm{pp}} spectra. No hint for a dominant {d}^{\ensuremath{'}} production, as anticipated from double charge exchange excitation functions on nuclei, has been found. The data are satisfactorily described by sequential single charge exchange
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