4,562 research outputs found
Formation of '3D' multiplanet systems by dynamical disruption of multiple-resonance configurations
Assuming that giant planets are formed in thin protoplanetary discs, a '3D'
system can form, provided that the mutual inclination is excited by some
dynamical mechanism. Resonant interactions and close planetary encounters are
thought to be the primary inclination-excitation mechanisms, resulting in a
resonant and non-resonant system, respectively. Here we propose an alternative
formation scenario, starting from a system composed of three giant planets in a
nearly coplanar configuration. As was recently shown for the case of the Solar
system, planetary migration in the gas disc (Type II migration) can force the
planets to become trapped in a multiply resonant state. We simulate this
process, assuming different values for the planetary masses and mass ratios. We
show that such a triple resonance generally becomes unstable as the resonance
excites the eccentricities of all planets and planet-planet scattering sets in.
One of the three planets is typically ejected from the system, leaving behind a
dynamically 'hot' (but stable) two-planet configuration. The resulting
two-planet systems typically have large values of semimajor axial ratios (a1/a2
< 0.3), while the mutual inclination can be as high as 70{\deg}, with a median
of \sim30{\deg}. A small fraction of our two-planet systems (\sim5 per cent)
ends up in the stability zone of the Kozai resonance. In a few cases, the
triple resonance can remain stable for long times and a '3D' system can form by
resonant excitation of the orbital inclinations; such a three-planet system
could be stable if enough eccentricity damping is exerted on the planets.
Finally, in the single-planet resulting systems, which are formed when two
planets are ejected from the system, the inclination of the planet's orbital
plane with respect to the initial invariant plane -presumably the plane
perpendicular to the star's spin axis- can be as large as \sim40{\deg}.Comment: 9 pages, 5 figures, published in MNRA
An Automated Approach to Auditing Disclosure of Third-Party Data Collection in Website Privacy Policies
A dominant regulatory model for web privacy is "notice and choice". In this
model, users are notified of data collection and provided with options to
control it. To examine the efficacy of this approach, this study presents the
first large-scale audit of disclosure of third-party data collection in website
privacy policies. Data flows on one million websites are analyzed and over
200,000 websites' privacy policies are audited to determine if users are
notified of the names of the companies which collect their data. Policies from
25 prominent third-party data collectors are also examined to provide deeper
insights into the totality of the policy environment. Policies are additionally
audited to determine if the choice expressed by the "Do Not Track" browser
setting is respected.
Third-party data collection is wide-spread, but fewer than 15% of attributed
data flows are disclosed. The third-parties most likely to be disclosed are
those with consumer services users may be aware of, those without consumer
services are less likely to be mentioned. Policies are difficult to understand
and the average time requirement to read both a given site{\guillemotright}s
policy and the associated third-party policies exceeds 84 minutes. Only 7% of
first-party site policies mention the Do Not Track signal, and the majority of
such mentions are to specify that the signal is ignored. Among third-party
policies examined, none offer unqualified support for the Do Not Track signal.
Findings indicate that current implementations of "notice and choice" fail to
provide notice or respect choice
Privacy Implications of Health Information Seeking on the Web
This article investigates privacy risks to those visiting health- related web
pages. The population of pages analyzed is derived from the 50 top search
results for 1,986 common diseases. This yielded a total population of 80,124
unique pages which were analyzed for the presence of third-party HTTP requests.
91% of pages were found to make requests to third parties. Investigation of
URIs revealed that 70% of HTTP Referer strings contained information exposing
specific conditions, treatments, and diseases. This presents a risk to users in
the form of personal identification and blind discrimination. An examination of
extant government and corporate policies reveals that users are insufficiently
protected from such risks
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
Taking Chemical EOR Data from Lab Results to Simulation
Imperial Users onl
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&
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
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
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