282 research outputs found
Structural perspective on constraint-based learning of Markov networks
Markov networks are probabilistic graphical models that employ undirected
graphs to depict conditional independence relationships among variables. Our
focus lies in constraint-based structure learning, which entails learning the
undirected graph from data through the execution of conditional independence
tests. We establish theoretical limits concerning two critical aspects of
constraint-based learning of Markov networks: the number of tests and the sizes
of the conditioning sets. These bounds uncover an exciting interplay between
the structural properties of the graph and the amount of tests required to
learn a Markov network. The starting point of our work is that the graph
parameter maximum pairwise connectivity, , that is, the maximum number
of vertex-disjoint paths connecting a pair of vertices in the graph, is
responsible for the sizes of independence tests required to learn the graph. On
one hand, we show that at least one test with the size of the conditioning set
at least is always necessary. On the other hand, we prove that any
graph can be learned by performing tests of size at most . This
completely resolves the question of the minimum size of conditioning sets
required to learn the graph. When it comes to the number of tests, our upper
bound on the sizes of conditioning sets implies that every -vertex graph can
be learned by at most tests with conditioning sets of sizes at
most . We show that for any upper bound on the sizes of the
conditioning sets, there exist graphs with vertices that require at
least tests to learn. This lower bound holds even when the
treewidth and the maximum degree of the graph are at most . On the
positive side, we prove that every graph of bounded treewidth can be learned by
a polynomial number of tests with conditioning sets of sizes at most .Comment: AISTATS 202
Diagnosis, natural course and treatment outcomes of groove pancreatitis
Background: Groove pancreatitis (GP) is a rare form of chronic pancreatitis with limited data on its diagnostics and treatment outcomes. The aim of this study was to assess its diagnostics, natural course, and treatment options. Methods: The study is a retrospective population-based study from Southern Finland, including all patients with suspected GP between January 2005 and December 2015. Two certified gastrointestinal radiologists re-reviewed the imaging studies. The radiological re-review, clinical judgment, and final histopathology confirmed the GP diagnoses. Results: Out of 67 patients with possible GP, 39 patients were considered to have high radiological certainty of GP. Out of these 39, five patients had cancer instead. Thirty-three patients with confirmed GP formed the final study cohort. Patients with GP were mostly middle-aged (median 55 years) men. All had at least moderate alcohol consumption. No intervention was needed in 14 patients. In five-year follow-up all conservatively treated patients became asymptomatic, while 10 out of 16 patients undergoing at least one intervention were asymptomatic at five years. Conclusion: The radiological diagnosis of GP is difficult, and a low threshold for cancer suspicion should be kept. Symptoms of GP decrease with time and suggest conservative treatment as the first-line option.Peer reviewe
Successful Curriculum Change in Health Management and Leadership Studies for the Specialist Training Programs in Medicine in Finland
In Finland, the specialization programs in Medicine and Dentistry can be undertaken at all five university medical faculties in 50 specialization programs and in five programs for Dentistry. The specialist training requires 5 or 6 years (300â360 ECTS credits) of medical practice including 9 months of service in primary health care centers, theoretical substance specific education, management studies, and passing a national written exam. The renovation of the national curriculum for the specialization programs was implemented, first in 2008 and officially in August 2009, when theoretical multi-professional social, health management and leadership studies (10â30 ECTS credits) were added to the curriculum. According to European Credit Transfer and Accumulation System (ECTS), 1 ECTS credit (henceforth, simply âECTSâ) means 27â30 h of academic work1 National guidelines for the multi-professional leadership training include the basics of organizational management and leadership, the social and healthcare system, human resources (HR) management, leadership interaction and organizational communication, healthcare economy, legislation (HR) and data management. Each medical faculty has implemented management studies autonomously but according to national guidelines. This paper will describe how the compulsory management studies (10 ECTS) have been executed at the Universities of Tampere and Turku. In Tampere, the 10 ECTS management studies follow a flexible design of six academic modules. Versatile modern teaching methods such as technology-assisted and student orientated learning are used. Advanced supplementary management studies (20 ECTS) are also available. In Turku, the 10 ECTS studies consist of academic lectures, portfolio and project work. Attendees select contact studies (4â6 ECTS) from yearly available 20 ECTS and proceed at their own pace. Portfolio and project comprise 2â5 ECTS each. The renovation of medical specializing physicians' management and leadership education has been a successful reform. It has been observed that positive attitudes and interest toward management overall are increasing among younger doctors. In addition, management and leadership education will presumably facilitate medical doctors' work as managers also. Continuous development of medical doctors' management and leadership education for physicians and dentists is needed while the changing and complex healthcare environment requires both professional and leadership expertise
Discovery of a substellar companion in the TESS light curve of the Scuti/ Doradus hybrid pulsator HD 31221
Close-in, sub-stellar companions to Scuti type stars present a
highly suitable testbed for examining how planetary-mass objects can influence
stellar pulsations. We aim to constrain the mass of HD 31221 b, probe its
atmosphere, and demonstrate how it affects the pulsational pattern of its host,
HD 31221. We made use of the available data from the short-cadence Transiting
Exoplanet Survey Satellite (TESS). We modeled the nine observed transits and
the out-of-phase variations, including Doppler beaming, ellipsoidal variations,
and the reflection effect. We also incorporated ground-based photometry from
the MuSCAT2 imager installed at the 1.52 m Telescopio Carlos Sanchez in the
Teide Observatory, Spain. We found HD 31221 b to have an orbital period of
days, with a radius of R and a mass
of M (from the ellipsoidal effect), making it consistent
with either a brown dwarf or a giant planet. As HD 31221 is a rapid rotator ( km s), we deduced the spin-orbit
misalignment to be and . The phase curve is dominated by the reflection effect, with a
geometric albedo of . We also found evidence that HD 31221 is a
Scuti/ Doradus hybrid pulsator. There are three cases for
which the rd, th, and st orbital harmonics almost exactly coincide
with peaks in the Fourier spectrum of the star, hinting at tidally perturbed
stellar oscillations. HD 31221 b is the third substellar object that is found
to be disrupting the pulsations of its host, following HAT-P-2 and WASP-33.
Additional photometric observations by CHEOPS and/or PLATO can be used to
further constrain its mass and provide a more in-depth analysis of its
atmosphere.Comment: Accepted for publication as a Letter in A&A, 12 pages, 10 figure
ESPRESSO Mass determination of TOI-263b: An extreme inhabitant of the brown dwarf desert
The TESS mission has reported a wealth of new planetary systems around bright
and nearby stars amenable for detailed characterization of the planet
properties and their atmospheres. However, not all interesting TESS planets
orbit around bright host stars. TOI-263b is a validated ultra-short period
substellar object in a 0.56-day orbit around a faint (V=18.97) M3.5 dwarf star.
The substellar nature of TOI-263b was explored using multi-color photometry,
which determined a true radius of 0.87+-0.21 Rj, establishing TOI-263b's nature
ranging from an inflated Neptune to a brown dwarf. The orbital period-radius
parameter space occupied by TOI-263b is quite unique, which prompted a further
characterization of its true nature. Here, we report radial velocity
measurements of TOI-263 obtained with 3 VLT units and the ESPRESSO spectrograph
to retrieve the mass of TOI-263b. We find that TOI-263b is a brown dwarf with a
mass of 61.6+-4.0 Mj. Additionally, the orbital period of the brown dwarf is
found to be synchronized with the rotation period of the host star, and the
system is found to be relatively active, possibly revealing a star--brown dwarf
interaction. All these findings suggest that the system's formation history
might be explained via disc fragmentation and later migration to close-in
orbits. If the system is found to be unstable, TOI-263 is an excellent target
to test the migration mechanisms before the brown dwarf becomes engulfed by its
parent star.Comment: Accepted for Publication in Astronomy and Astrophysic
Lower-than-expected flare temperatures for TRAPPIST-1
Although high energetic radiation from flares is a potential threat to
exoplanet atmospheres and may lead to surface sterilization, it might also
provide the extra energy for low-mass stars needed to trigger and sustain
prebiotic chemistry. We investigate two flares on TRAPPIST-1, an ultra-cool
dwarf star that hosts seven exoplanets of which three lie within its habitable
zone. The flares are detected in all four passbands of the MuSCAT2 allowing a
determination of their temperatures and bolometric energies. We analyzed the
light curves of the MuSCAT1 and MuSCAT2 instruments obtained between 2016 and
2021 in -filters. We conducted an automated flare search
and visually confirmed possible flare events. We studied the temperature
evolution, the global temperature, and the peak temperature of both flares. For
the first time we infer effective black body temperatures of flares that
occurred on TRAPPIST-1. The black body temperatures for the two TRAPPIST-1
flares derived from the SED are consistent with K and K. The flare
black body temperatures at the peak are also calculated from the peak SED
yielding K and K. We show that for the ultra-cool M-dwarf TRAPPIST-1 the
flare black body temperatures associated with the total continuum emission are
lower and not consistent with the usually adopted assumption of 9000-10000 K.
This could imply different and faster cooling mechanisms. Further multi-color
observations are needed to investigate whether or not our observations are a
general characteristic of ultra-cool M-dwarfs. This would have significant
implications for the habitability of exoplanets around these stars because the
UV surface flux is likely to be overestimated by the models with higher flare
temperatures.Comment: 17 pages, 11 figures, 2 tables, accepted for publication in A&
Bayesian Methods for Exoplanet Science
Exoplanet research is carried out at the limits of the capabilities of
current telescopes and instruments. The studied signals are weak, and often
embedded in complex systematics from instrumental, telluric, and astrophysical
sources. Combining repeated observations of periodic events, simultaneous
observations with multiple telescopes, different observation techniques, and
existing information from theory and prior research can help to disentangle the
systematics from the planetary signals, and offers synergistic advantages over
analysing observations separately. Bayesian inference provides a
self-consistent statistical framework that addresses both the necessity for
complex systematics models, and the need to combine prior information and
heterogeneous observations. This chapter offers a brief introduction to
Bayesian inference in the context of exoplanet research, with focus on time
series analysis, and finishes with an overview of a set of freely available
programming libraries.Comment: Invited revie
The transiting multi-planet system HD3167: a 5.7 MEarth Super-Earth and a 8.3 MEarth mini-Neptune
HD3167 is a bright (V=8.9 mag) K0V star observed by the NASA's K2 space
mission during its Campaign 8. It has been recently found to host two small
transiting planets, namely, HD3167b, an ultra short period (0.96 d)
super-Earth, and HD3167c, a mini-Neptune on a relatively long-period orbit
(29.85 d). Here we present an intensive radial velocity follow-up of HD3167
performed with the FIES@NOT, [email protected], and HARPS-N@TNG spectrographs. We
revise the system parameters and determine radii, masses, and densities of the
two transiting planets by combining the K2 photometry with our spectroscopic
data. With a mass of 5.69+/-0.44 MEarth, radius of 1.574+/-0.054 REarth, and
mean density of 8.00(+1.0)(-0.98) g/cm^3, HD3167b joins the small group of
ultra-short period planets known to have a rocky terrestrial composition.
HD3167c has a mass of 8.33 (+1.79)(-1.85) MEarth and a radius of
2.740(+0.106)(-0.100) REarth, yielding a mean density of 2.21(+0.56)(-0.53)
g/cm^3, indicative of a planet with a composition comprising a solid core
surrounded by a thick atmospheric envelope. The rather large pressure scale
height (about 350 km) and the brightness of the host star make HD3167c an ideal
target for atmospheric characterization via transmission spectroscopy across a
broad range of wavelengths. We found evidence of additional signals in the
radial velocity measurements but the currently available data set does not
allow us to draw any firm conclusion on the origin of the observed variation.Comment: 18 pages, 11 figures, 5 table
Multicolour photometry for exoplanet candidate validation
Context. The TESS and PLATO missions are expected to find vast numbers of new
transiting planet candidates. However, only a fraction of these candidates will
be legitimate planets, and the candidate validation will require a significant
amount of follow-up resources. Radial velocity follow-up can be carried out
only for the most promising candidates around bright, slowly rotating, stars.
Thus, before devoting RV resources to candidates, they need to be vetted using
cheaper methods, and, in the cases for which an RV confirmation is not
feasible, the candidate's true nature needs to be determined based on these
alternative methods alone.
Aims. We study the applicability of multicolour transit photometry in the
validation of transiting planet candidates when the candidate signal arises
from a real astrophysical source. We seek to answer how securely can we
estimate the true uncontaminated star-planet radius ratio when the light curve
may contain contamination from unresolved light sources inside the photometry
aperture when combining multicolour transit observations with a physics-based
contamination model.
Methods. The study is based on simulations and ground-based transit
observations. The analyses are carried out with a contamination model
integrated into the PyTransit v2 transit modelling package, and the
observations are carried out with the MuSCAT2 multicolour imager installed in
the 1.5 m TCS in the Teide Observatory.
Results. We show that multicolour transit photometry can be used to estimate
the amount of flux contamination and the true radius ratio. Combining the true
radius ratio with an estimate for the stellar radius yields the true absolute
radius of the transiting object, which is a valuable quantity in statistical
candidate validation, and enough in itself to validate a candidate whose radius
falls below the theoretical lower limit for a brown dwarf.Comment: Accepted to A&
Kepler-77b: a very low albedo, Saturn-mass transiting planet around a metal-rich solar-like star
We report the discovery of Kepler-77b (alias KOI-127.01), a Saturn-mass
transiting planet in a 3.6-day orbit around a metal-rich solar-like star. We
combined the publicly available Kepler photometry (quarters 1-13) with
high-resolution spectroscopy from the Sandiford@McDonald and FIES@NOT
spectrographs. We derived the system parameters via a simultaneous joint fit to
the photometric and radial velocity measurements. Our analysis is based on the
Bayesian approach and is carried out by sampling the parameter posterior
distributions using a Markov chain Monte Carlo simulation. Kepler-77b is a
moderately inflated planet with a mass of Mp=0.430+/-0.032 Mjup, a radius of
Rp=0.960+/-0.016 Rjup, and a bulk density of 0.603+/-0.055 g/cm^3. It orbits a
slowly rotating (P=36+/-6 days) G5V star with M*=0.95+/-0.04 Msun,
R*=0.99+/-0.02 Rsun, Teff=5520+/-60 K, [M/H]=0.20+/-0.05, that has an age of
7.5+/-2.0 Gyr. The lack of detectable planetary occultation with a depth higher
than about 10 ppm implies a planet geometric and Bond albedo of
Ag<0.087+/-0.008 and Ab<0.058+/-0.006, respectively, placing Kepler-77b among
the gas-giant planets with the lowest albedo known so far. We found neither
additional planetary transit signals nor transit-timing variations at a level
of about 0.5 minutes, in accordance with the trend that close-in gas giant
planets seem to belong to single-planet systems. The 106 transits observed in
short-cadence mode by Kepler for nearly 1.2 years show no detectable signatures
of the planet's passage in front of starspots. We explored the implications of
the absence of detectable spot-crossing events for the inclination of the
stellar spin-axis, the sky-projected spin-orbit obliquity, and the latitude of
magnetically active regions.Comment: 13 pages, 10 figures, 3 tables. Accepted for publication in A&A. This
version includes referee comments. Planet's name changed from KOI-127b to
Kepler-77
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