344 research outputs found
Monitoring Networks through Multiparty Session Types
In large-scale distributed infrastructures, applications are realised through communications among distributed components. The need for methods for assuring safe interactions in such environments is recognized, however the existing frameworks, relying on centralised verification or restricted specification methods, have limited applicability. This paper proposes a new theory of monitored π-calculus with dynamic usage of multiparty session types (MPST), offering a rigorous foundation for safety assurance of distributed components which asynchronously communicate through multiparty sessions. Our theory establishes a framework for semantically precise decentralised run-time enforcement and provides reasoning principles over monitored distributed applications, which complement existing static analysis techniques. We introduce asynchrony through the means of explicit routers and global queues, and propose novel equivalences between networks, that capture the notion of interface equivalence, i.e. equating networks offering the same services to a user. We illustrate our static-dynamic analysis system with an ATM protocol as a running example and justify our theory with results: satisfaction equivalence, local/global safety and transparency, and session fidelity
Explicit connection actions in multiparty session types
This work extends asynchronous multiparty session types (MPST) with explicit connection actions to support protocols with op- tional and dynamic participants. The actions by which endpoints are connected and disconnected are a key element of real-world protocols that is not treated in existing MPST works. In addition, the use cases motivating explicit connections often require a more relaxed form of mul- tiparty choice: these extensions do not satisfy the conservative restric- tions used to ensure safety in standard syntactic MPST. Instead, we de- velop a modelling-based approach to validate MPST safety and progress for these enriched protocols. We present a toolchain implementation, for distributed programming based on our extended MPST in Java, and a core formalism, demonstrating the soundness of our approach. We discuss key implementation issues related to the proposed extensions: a practi- cal treatment of choice subtyping for MPST progress, and multiparty correlation of dynamic binary connections
Hybrid Session Verification through Endpoint API Generation
© Springer-Verlag Berlin Heidelberg 2016.This paper proposes a new hybrid session verification methodology for applying session types directly to mainstream languages, based on generating protocol-specific endpoint APIs from multiparty session types. The API generation promotes static type checking of the behavioural aspect of the source protocol by mapping the state space of an endpoint in the protocol to a family of channel types in the target language. This is supplemented by very light run-time checks in the generated API that enforce a linear usage discipline on instances of the channel types. The resulting hybrid verification guarantees the absence of protocol violation errors during the execution of the session. We implement our methodology for Java as an extension to the Scribble framework, and use it to specify and implement compliant clients and servers for real-world protocols such as HTTP and SMTP
SOPHIE velocimetry of Kepler transit candidates XVII. The physical properties of giant exoplanets within 400 days of period
While giant extrasolar planets have been studied for more than two decades
now, there are still some open questions such as their dominant formation and
migration process, as well as their atmospheric evolution in different stellar
environments. In this paper, we study a sample of giant transiting exoplanets
detected by the Kepler telescope with orbital periods up to 400 days. We first
defined a sample of 129 giant-planet candidates that we followed up with the
SOPHIE spectrograph (OHP, France) in a 6-year radial velocity campaign. This
allow us to unveil the nature of these candidates and to measure a
false-positive rate of 54.6 +/- 6.5 % for giant-planet candidates orbiting
within 400 days of period. Based on a sample of confirmed or likely planets, we
then derive the occurrence rates of giant planets in different ranges of
orbital periods. The overall occurrence rate of giant planets within 400 days
is 4.6 +/- 0.6 %. We recover, for the first time in the Kepler data, the
different populations of giant planets reported by radial velocity surveys.
Comparing these rates with other yields, we find that the occurrence rate of
giant planets is lower only for hot jupiters but not for the longer period
planets. We also derive a first measurement on the occurrence rate of brown
dwarfs in the brown-dwarf desert with a value of 0.29 +/- 0.17 %. Finally, we
discuss the physical properties of the giant planets in our sample. We confirm
that giant planets receiving a moderate irradiation are not inflated but we
find that they are in average smaller than predicted by formation and evolution
models. In this regime of low-irradiated giant planets, we find a possible
correlation between their bulk density and the Iron abundance of the host star,
which needs more detections to be confirmed.Comment: To appear in Astronomy and Astrophysic
Globally Governed Session Semantics
This paper proposes a bisimulation theory based on multiparty session types
where a choreography specification governs the behaviour of session typed
processes and their observer. The bisimulation is defined with the observer
cooperating with the observed process in order to form complete global session
scenarios and usable for proving correctness of optimisations for globally
coordinating threads and processes. The induced bisimulation is strictly more
fine-grained than the standard session bisimulation. The difference between the
governed and standard bisimulations only appears when more than two interleaved
multiparty sessions exist. This distinct feature enables to reason real
scenarios in the large-scale distributed system where multiple choreographic
sessions need to be interleaved. The compositionality of the governed
bisimilarity is proved through the soundness and completeness with respect to
the governed reduction-based congruence. Finally, its usage is demonstrated by
a thread transformation governed under multiple sessions in a real usecase in
the large-scale cyberinfrustracture
On the relative expressiveness of higher-order session processes
By integrating constructs from the λ-calculus and the π-calculus, in higher-order process calculi exchanged values may contain processes. This paper studies the relative expressiveness of HOπ, the higher-order π-calculus in which communications are governed by session types. Our main discovery is that HO, a subcalculus of HOπ which lacks name-passing and recursion, can serve as a new core calculus for session-typed higher-order concurrency. By exploring a new bisimulation for HO, we show that HO can encode HOπ fully abstractly (up to typed contextual equivalence) more precisely and efficiently than the first-order session π-calculus (π). Overall, under session types, HOπ, HO, and π are equally expressive; however, HOπ and HO are more tightly related than HOπ and π
The SOPHIE search for northern extrasolar planets. XI. Three new companions and an orbit update: Giant planets in the habitable zone
We report the discovery of three new substellar companions to solar-type
stars, HD191806, HD214823, and HD221585, based on radial velocity measurements
obtained at the Haute-Provence Observatory. Data from the SOPHIE spectrograph
are combined with observations acquired with its predecessor, ELODIE, to detect
and characterise the orbital parameters of three new gaseous giant and brown
dwarf candidates. Additionally, we combine SOPHIE data with velocities obtained
at the Lick Observatory to improve the parameters of an already known giant
planet companion, HD16175 b. Thanks to the use of different instruments, the
data sets of all four targets span more than ten years. Zero-point offsets
between instruments are dealt with using Bayesian priors to incorporate the
information we possess on the SOPHIE/ELODIE offset based on previous studies.
The reported companions have orbital periods between three and five years and
minimum masses between 1.6 Mjup and 19 Mjup. Additionally, we find that the
star HD191806 is experiencing a secular acceleration of over 11 \ms\ per year,
potentially due to an additional stellar or substellar companion. A search for
the astrometric signature of these companions was carried out using Hipparcos
data. No orbit was detected, but a significant upper limit to the companion
mass can be set for HD221585, whose companion must be substellar.
With the exception of HD191806 b, the companions are located within the
habitable zone of their host star. Therefore, satellites orbiting these objects
could be a propitious place for life to develop.Comment: 12 pages + tables, 7 figures. Accepted for publication in Astronomy &
Astrophysic
The SOPHIE search for northern extrasolar planets VIII. A warm Neptune orbiting HD164595
High-precision radial velocity surveys explore the population of low-mass
exoplanets orbiting bright stars. This allows accurately deriving their orbital
parameters such as their occurrence rate and the statistical distribution of
their properties. Based on this, models of planetary formation and evolution
can be constrained. The SOPHIE spectrograph has been continuously improved in
past years, and thanks to an appropriate correction of systematic instrumental
drift, it is now reaching 2 m/s precision in radial velocity measurements on
all timescales. As part of a dedicated radial velocity survey devoted to search
for low-mass planets around a sample of 190 bright solar-type stars in the
northern hemisphere, we report the detection of a warm Neptune with a minimum
mass of 16.1 +- 2.7 Mearth orbiting the solar analog HD164595 in 40 +- 0.24
days . We also revised the parameters of the multiplanetary system around
HD190360. We discuss this new detection in the context of the upcoming space
mission CHEOPS, which is devoted to a transit search of bright stars harboring
known exoplanets.Comment: 11 pages, 9 figure
The SOPHIE search for northern extrasolar planets VIII. Follow-up of ELODIE candidates: long-period brown-dwarf companions
Long-period brown dwarf companions detected in radial velocity surveys are
important targets for direct imaging and astrometry to calibrate the
mass-luminosity relation of substellar objects. Through a 20-year radial
velocity monitoring of solar-type stars that began with ELODIE and was extended
with SOPHIE spectrographs, giant exoplanets and brown dwarfs with orbital
periods longer than ten years are discovered. We report the detection of five
new potential brown dwarfs with minimum masses between 32 and 83 Jupiter mass
orbiting solar-type stars with periods longer than ten years. An upper mass
limit of these companions is provided using astrometric Hipparcos data,
high-angular resolution imaging made with PUEO, and a deep analysis of the
cross-correlation function of the main stellar spectra to search for blend
effects or faint secondary components. These objects double the number of known
brown dwarf companions with orbital periods longer than ten years and reinforce
the conclusion that the occurrence of such objects increases with orbital
separation. With a projected separation larger than 100 mas, all these brown
dwarf candidates are appropriate targets for high-contrast and high angular
resolution imaging.Comment: 17 pages, 9 figures, accepted in A&
One of the closest exoplanet pairs to the 3:2 Mean Motion Resonance: K2-19b \& c
The K2 mission has recently begun to discover new and diverse planetary
systems. In December 2014 Campaign 1 data from the mission was released,
providing high-precision photometry for ~22000 objects over an 80 day timespan.
We searched these data with the aim of detecting further important new objects.
Our search through two separate pipelines led to the independent discovery of
K2-19b \& c, a two-planet system of Neptune sized objects (4.2 and 7.2
), orbiting a K dwarf extremely close to the 3:2 mean motion
resonance. The two planets each show transits, sometimes simultaneously due to
their proximity to resonance and alignment of conjunctions. We obtain further
ground based photometry of the larger planet with the NITES telescope,
demonstrating the presence of large transit timing variations (TTVs), and use
the observed TTVs to place mass constraints on the transiting objects under the
hypothesis that the objects are near but not in resonance. We then
statistically validate the planets through the \texttt{PASTIS} tool,
independently of the TTV analysis.Comment: 18 pages, 10 figures, accepted to A&A, updated to match published
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