681 research outputs found
Exomoon habitability constrained by energy flux and orbital stability
Detecting massive satellites of extrasolar planets has now become feasible,
which led naturally to questions about their habitability. In a previous study
we presented constraints on the habitability of moons from stellar and
planetary illumination as well as from tidal heating. Here I refine our model
by including the effect of eclipses on the orbit-averaged illumination. Moons
in low-mass stellar systems must orbit their planet very closely to remain
bound, which puts them at risk of strong tidal heating. I first describe the
effect of eclipses on stellar illumination of satellites. Then I calculate the
orbit-averaged energy flux including illumination from the planet and tidal
heating. Habitability is defined by a scaling relation at which a moon loses
its water by the runaway greenhouse process. As a working hypothesis, orbital
stability is assumed if the moon's orbital period is less than 1/9 of the
planet's orbital period. Due to eclipses, a satellite in a close orbit can
experience a reduction in orbit-averaged stellar flux by up to about 6%. The
smaller the semi-major axis and the lower the inclination of the moon's orbit,
the stronger the reduction. I find a lower mass limit of ~0.2M_sun for exomoon
host stars to avoid the runaway greenhouse effect. Precise estimates depend on
the satellite's orbital eccentricity. Deleterious effects on exomoon
habitability may occur up to ~0.5M_sun. Although the habitable zone lies close
to low-mass stars, which allows for many transits of planet-moon binaries
within a given observation cycle, resources should not be spent to trace
habitable satellites around them. Gravitational perturbations by the star,
another planet, or another satellite induce eccentricities that likely make any
moon uninhabitable. Estimates for individual systems require dynamical
simulations that include perturbations among all bodies and tidal heating in
the satellite.Comment: 4 pages, 2 figures, accepted by A&
New business histories! Plurality in business history research methods
We agree with de Jong et al.'s argument that business historians should make their methods more explicit and welcome a more general debate about the most appropriate methods for business historical research. But rather than advocating one ‘new business history’, we argue that contemporary debates about methodology in business history need greater appreciation for the diversity of approaches that have developed in the last decade. And while the hypothesis-testing framework prevalent in the mainstream social sciences favoured by de Jong et al. should have its place among these methodologies, we identify a number of additional streams of research that can legitimately claim to have contributed novel methodological insights by broadening the range of interpretative and qualitative approaches to business history. Thus, we reject privileging a single method, whatever it may be, and argue instead in favour of recognising the plurality of methods being developed and used by business historians – both within their own field and as a basis for interactions with others
The Hunt for Exomoons with Kepler (HEK): IV. A Search for Moons around Eight M-Dwarfs
With their smaller radii and high cosmic abundance, transiting planets around
cool stars hold a unique appeal. As part of our on-going project to measure the
occurrence rate of extrasolar moons, we here present results from a survey
focussing on eight Kepler planetary candidates associated with M-dwarfs. Using
photodynamical modeling and Bayesian multimodal nested sampling, we find no
compelling evidence for an exomoon in these eight systems. Upper limits on the
presence of such bodies probe down to in the best case. For
KOI-314, we are able to confirm the planetary nature of two out of the three
known transiting candidates using transit timing variations. Of particular
interest is KOI-314c, which is found to have a mass of
, making it the lowest mass transiting planet
discovered to date. With a radius of , this
Earth-mass world is likely enveloped by a significant gaseous envelope
comprising % of the planet by radius. We find evidence to
support the planetary nature of KOI-784 too via transit timing, but we advocate
further observations to verify the signals. In both systems, we infer that the
inner planet has a higher density than the outer world, which may be indicative
of photo-evaporation. These results highlight both the ability of Kepler to
search for sub-Earth mass moons and the exciting ancillary science which often
results from such efforts.Comment: 15 pages, 13 figures, 6 tables. Accepted in Ap
The Hunt for Exomoons with Kepler (HEK): II. Analysis of Seven Viable Satellite-Hosting Planet Candidates
From the list of 2321 transiting planet candidates announced by the Kepler
Mission, we select seven targets with favorable properties for the capacity to
dynamically maintain an exomoon and present a detectable signal. These seven
candidates were identified through our automatic target selection (TSA)
algorithm and target selection prioritization (TSP) filtering, whereby we
excluded systems exhibiting significant time-correlated noise and focussed on
those with a single transiting planet candidate of radius less than 6 Earth
radii. We find no compelling evidence for an exomoon around any of the seven
KOIs but constrain the satellite-to-planet mass ratios for each. For four of
the seven KOIs, we estimate a 95% upper quantile of M_S/M_P<0.04, which given
the radii of the candidates, likely probes down to sub-Earth masses. We also
derive precise transit times and durations for each candidate and find no
evidence for dynamical variations in any of the KOIs. With just a few systems
analyzed thus far in the in-going HEK project, projections on eta-moon would be
premature, but a high frequency of large moons around
Super-Earths/Mini-Neptunes would appear to be incommensurable with our results
so far.Comment: 32 pages, 11 figures, 23 tables, Accepted to Ap
Prevalence and associated harm of engagement in self-Asphyxial behaviours ('choking game') in young people:A systematic review
OBJECTIVE: To assess the prevalence of engagement in self-asphyxial (risk-taking) behaviour (SAB) (‘choking game’) and associated morbidity and mortality in children and young people up to age 20. DESIGN: Systematic literature review. SEARCH STRATEGY: Electronic database search of MEDLINE, Embase, PsycINFO, CINAHL, PubMed, Web of Science Core Collection, BIOSIS citation index and the Cochrane register with no language or date limits applied. References of key papers were reviewed, and experts were contacted to identify additional relevant papers. ELIGIBILITY CRITERIA: Systematic reviews, cross-sectional, cohort and case–control studies, and case reports examining SAB with regard to individuals aged 0–20 years, without explicitly stated autoerotic, suicidal or self-harm intentions were included. RESULTS: Thirty-six relevant studies were identified, and SAB was reported in 10 countries. In North America, France and Colombia, awareness of SAB ranged from 36% to 91% across studies/settings, and the median lifetime prevalence of engagement in SAB was 7.4%. Six studies identified the potential for SAB to be associated with engagement in other risk behaviours. Ninety-nine fatal cases were reported. Of the 24 cases described in detail, most occurred when individuals engaged in SAB alone and used a ligature. CONCLUSIONS: The current evidence on SAB among young people is limited, and stems predominantly from North America and France. Awareness of SAB among young people is high, and engagement varies by setting. Further research is needed to understand the level of risk and harm associated with SAB, and to determine the appropriate public health response
The Hunt for Exomoons with Kepler (HEK): III. The First Search for an Exomoon around a Habitable-Zone Planet
Kepler-22b is the first transiting planet to have been detected in the
habitable-zone of its host star. At 2.4 Earth radii, Kepler-22b is too large to
be considered an Earth-analog, but should the planet host a moon large enough
to maintain an atmosphere, then the Kepler-22 system may yet possess a telluric
world. Aside from being within the habitable-zone, the target is attractive due
to the availability of previously measured precise radial velocities and low
intrinsic photometric noise, which has also enabled asteroseismology studies of
the star. For these reasons, Kepler-22b was selected as a target-of-opportunity
by the 'Hunt for Exomoons with Kepler' (HEK) project. In this work, we conduct
a photodynamical search for an exomoon around Kepler-22b leveraging the
transits, radial velocities and asteroseismology plus several new tools
developed by the HEK project to improve exomoon searches. We find no evidence
for an exomoon around the planet and exclude moons of mass >0.5 Earth masses to
95% confidence. By signal injection and blind retrieval, we demonstrate that an
Earth-like moon is easily detected for this planet even when the
time-correlated noise of the data set is taken into account. We provide updated
parameters for the planet Kepler-22b including a revised mass of <53 Earth
masses to 95% confidence and an eccentricity of 0.13(-0.13)(+0.36) by
exploiting Single-body Asterodensity Profiling (SAP). Finally, we show that
Kepler-22b has a >95% probability of being within the empirical habitable-zone
but a <5% probability of being within the conservative habitable-zone.Comment: 19 pages, 11 figures, 7 tables. Accepted in ApJ. Planet-moon transit
animations available at https://www.cfa.harvard.edu/~dkipping/kepler22.htm
Total Chiral Symmetry Breaking during Crystallization: Who needs a "Mother Crystal"?
Processes that can produce states of broken chiral symmetry are of particular
interest to physics, chemistry and biology. Chiral symmetry breaking during
crystallization of sodium chlorate occurs via the production of secondary
crystals of the same handedness from a single "mother crystal" that seeds the
solution. Here we report that a large and "symmetric" population of D- and
L-crystals moves into complete chiral purity disappearing one of the
enantiomers. This result shows: (i) a new symmetry breaking process
incompatible with the hypothesis of a single "mother crystal"; (ii) that
complete symmetry breaking and chiral purity can be achieved from an initial
system with both enantiomers. These findings demand a new explanation to the
process of total symmetry breaking in crystallization without the intervention
of a "mother crystal" and open the debate on this fascinating phenomenon. We
present arguments to show that our experimental data can been explained with a
new model of "complete chiral purity induced by nonlinear autocatalysis and
recycling".Comment: 5 pages, 4 figures, Added reference
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