3,873 research outputs found
Detection of Laplace-resonant three-planet systems from transit timing variations
Transit timing variations (TTVs) are useful to constrain the existence of
perturbing planets, especially in resonant systems where the variations are
strongly enhanced. Here we focus on Laplace-resonant three-planet systems, and
assume the inner planet transits the star. A dynamical study is performed for
different masses of the three bodies, with a special attention to terrestrial
planets. We consider a maximal time-span of ~ 100 years and discuss the shape
of the inner planet TTVs curve. Using frequency analysis, we highlight the
three periods related to the evolution of the system: two periods associated
with the Laplace-resonant angle and the third one with the precession of the
pericenters. These three periods are clearly detected in the TTVs of an inner
giant planet perturbed by two terrestrial companions. Only two periods are
detected for a Jupiter-Jupiter-Earth configuration (the ones associated with
the giant interactions) or for three terrestrial planets (the Laplace periods).
However, the latter system can be constrained from the inner planet TTVs. We
finally remark that the TTVs of resonant three or two Jupiter systems mix up,
when the period of the Laplace resonant angle matches the pericenter precession
of the two-body configuration. This study highlights the importance of TTVs
long-term observational programs for the detection of multiple-planet resonant
systems.Comment: 8 pages, 8 figures, accepted in MNRA
A general introduction to glucocorticoid biology
Glucocorticoids (GCs) are steroid hormones widely used for the treatment of inflammation, autoimmune diseases, and cancer. To exert their broad physiological and therapeutic effects, GCs bind to the GC receptor (GR) which belongs to the nuclear receptor superfamily of transcription factors. Despite their success, GCs are hindered by the occurrence of side effects and glucocorticoid resistance (GCR). Increased knowledge on GC and GR biology together with a better understanding of the molecular mechanisms underlying the GC side effects and GCR are necessary for improved GC therapy development. We here provide a general overview on the current insights in GC biology with a focus on GC synthesis, regulation and physiology, role in inflammation inhibition, and on GR function and plasticity. Furthermore, novel and selective therapeutic strategies are proposed based on recently recognized distinct molecular mechanisms of the GR. We will explain the SEDIGRAM concept, which was launched based on our research results
Origin and continuation of 3/2, 5/2, 3/1, 4/1 and 5/1 resonant periodic orbits in the circular and elliptic restricted three-body problem
We consider a planetary system consisting of two primaries, namely a star and
a giant planet, and a massless secondary, say a terrestrial planet or an
asteroid, which moves under their gravitational attraction. We study the
dynamics of this system in the framework of the circular and elliptic
restricted TBP, when the motion of the giant planet describes circular and
elliptic orbits, respectively. Originating from the circular family, families
of symmetric periodic orbits in the 3/2, 5/2, 3/1, 4/1 and 5/1 mean-motion
resonances are continued in the circular and the elliptic problems. New
bifurcation points from the circular to the elliptic problem are found for each
of the above resonances and thus, new families, continued from these points are
herein presented. Stable segments of periodic orbits were found at high
eccentricity values of the already known families considered as whole unstable
previously. Moreover, new isolated (not continued from bifurcation points)
families are computed in the elliptic restricted problem. The majority of the
new families mainly consist of stable periodic orbits at high eccentricities.
The families of the 5/1 resonance are investigated for the first time in the
restricted three-body problems. We highlight the effect of stable periodic
orbits on the formation of stable regions in their vicinity and unveil the
boundaries of such domains in phase space by computing maps of dynamical
stability. The long-term stable evolution of the terrestrial planets or
asteroids is dependent on the existence of regular domains in their dynamical
neighbourhood in phase space, which could host them for long time spans. This
study, besides other celestial architectures that can be efficiently modelled
by the circular and elliptic restricted problems, is particularly appropriate
for the discovery of terrestrial companions among the single-giant planet
systems discovered so far.Comment: Accepted for publication in Celestial Mechanics and Dynamical
Astronom
Puzzling out the coexistence of terrestrial planets and giant exoplanets. The 2/1 resonant periodic orbits
Hundreds of giant planets have been discovered so far and the quest of
exo-Earths in giant planet systems has become intriguing. In this work, we aim
to address the question of the possible long-term coexistence of a terrestrial
companion on an orbit interior to a giant planet, and explore the extent of the
stability regions for both non-resonant and resonant configurations. Our study
focuses on the restricted three-body problem, where an inner terrestrial planet
(massless body) moves under the gravitational attraction of a star and an outer
massive planet on a circular or elliptic orbit. Using the Detrended Fast
Lyapunov Indicator as a chaotic indicator, we constructed maps of dynamical
stability by varying both the eccentricity of the outer giant planet and the
semi-major axis of the inner terrestrial planet, and identify the boundaries of
the stability domains. Guided by the computation of families of periodic
orbits, the phase space is unravelled by meticulously chosen stable periodic
orbits, which buttress the stability domains. We provide all possible stability
domains for coplanar symmetric configurations and show that a terrestrial
planet, either in mean-motion resonance or not, can coexist with a giant
planet, when the latter moves on either a circular or an (even highly)
eccentric orbit. New families of symmetric and asymmetric periodic orbits are
presented for the 2/1 resonance. It is shown that an inner terrestrial planet
can survive long time spans with a giant eccentric outer planet on resonant
symmetric orbits, even when both orbits are highly eccentric. For 22 detected
single-planet systems consisting of a giant planet with high eccentricity, we
discuss the possible existence of a terrestrial planet. This study is
particularly suitable for the research of companions among the detected systems
with giant planets, and could assist with refining observational data.Comment: Accepted for publication in A&
Predicting links in ego-networks using temporal information
Link prediction appears as a central problem of network science, as it calls
for unfolding the mechanisms that govern the micro-dynamics of the network. In
this work, we are interested in ego-networks, that is the mere information of
interactions of a node to its neighbors, in the context of social
relationships. As the structural information is very poor, we rely on another
source of information to predict links among egos' neighbors: the timing of
interactions. We define several features to capture different kinds of temporal
information and apply machine learning methods to combine these various
features and improve the quality of the prediction. We demonstrate the
efficiency of this temporal approach on a cellphone interaction dataset,
pointing out features which prove themselves to perform well in this context,
in particular the temporal profile of interactions and elapsed time between
contacts.Comment: submitted to EPJ Data Scienc
On the 3D secular dynamics of radial-velocity-detected planetary systems
Aims. To date, more than 600 multi-planetary systems have been discovered.
Due to the limitations of the detection methods, our knowledge of the systems
is usually far from complete. In particular, for planetary systems discovered
with the radial velocity (RV) technique, the inclinations of the orbital
planes, and thus the mutual inclinations and planetary masses, are unknown. Our
work aims to constrain the spatial configuration of several RV-detected
extrasolar systems that are not in a mean-motion resonance. Methods. Through an
analytical study based on a first-order secular Hamiltonian expansion and
numerical explorations performed with a chaos detector, we identified ranges of
values for the orbital inclinations and the mutual inclinations, which ensure
the long-term stability of the system. Our results were validated by comparison
with n-body simulations, showing the accuracy of our analytical approach up to
high mutual inclinations (approx. 70{\deg}-80{\deg}). Results. We find that,
given the current estimations for the parameters of the selected systems,
long-term regular evolution of the spatial configurations is observed, for all
the systems, i) at low mutual inclinations (typically less than 35{\deg}) and
ii) at higher mutual inclinations, preferentially if the system is in a
Lidov-Kozai resonance. Indeed, a rapid destabilisation of highly mutually
inclined orbits is commonly observed, due to the significant chaos that
develops around the stability islands of the Lidov-Kozai resonance. The extent
of the Lidov-Kozai resonant region is discussed for ten planetary systems (HD
11506, HD 12661, HD 134987, HD 142, HD 154857, HD 164922, HD 169830, HD 207832,
HD 4732, and HD 74156).Comment: Accepted for publication in A&
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