55,186 research outputs found
An Event Structure Model for Probabilistic Concurrent Kleene Algebra
We give a new true-concurrent model for probabilistic concurrent Kleene
algebra. The model is based on probabilistic event structures, which combines
ideas from Katoen's work on probabilistic concurrency and Varacca's
probabilistic prime event structures. The event structures are compared with a
true-concurrent version of Segala's probabilistic simulation. Finally, the
algebraic properties of the model are summarised to the extent that they can be
used to derive techniques such as probabilistic rely/guarantee inference rules.Comment: Submitted and accepted for LPAR19 (2013
A Logic for True Concurrency
We propose a logic for true concurrency whose formulae predicate about events
in computations and their causal dependencies. The induced logical equivalence
is hereditary history preserving bisimilarity, and fragments of the logic can
be identified which correspond to other true concurrent behavioural
equivalences in the literature: step, pomset and history preserving
bisimilarity. Standard Hennessy-Milner logic, and thus (interleaving)
bisimilarity, is also recovered as a fragment. We also propose an extension of
the logic with fixpoint operators, thus allowing to describe causal and
concurrency properties of infinite computations. We believe that this work
contributes to a rational presentation of the true concurrent spectrum and to a
deeper understanding of the relations between the involved behavioural
equivalences.Comment: 31 pages, a preliminary version appeared in CONCUR 201
Coordination approaches and systems - part I : a strategic perspective
This is the first part of a two-part paper presenting a fundamental review and summary of research of design coordination and cooperation technologies. The theme of this review is aimed at the research conducted within the decision management aspect of design coordination. The focus is therefore on the strategies involved in making decisions and how these strategies are used to satisfy design requirements. The paper reviews research within collaborative and coordinated design, project and workflow management, and, task and organization models. The research reviewed has attempted to identify fundamental coordination mechanisms from different domains, however it is concluded that domain independent mechanisms need to be augmented with domain specific mechanisms to facilitate coordination. Part II is a review of design coordination from an operational perspective
The connection between radio and high energy emission in black hole powered systems in the SKA era
Strong evidence exists for a highly significant correlation between the radio
flux density and gamma-ray energy flux in blazars revealed by Fermi. However,
there are central issues that need to be clarified in this field: what are the
counterparts of the about 30% of gamma-ray sources that are as yet
unidentified? Are they just blazars in disguise or they are something more
exotic, possibly associated with dark matter? How would they fit in the
radio-gamma ray connection studied so far?
With their superb sensitivity, SKA1-MID and SKA1-SUR will help to resolve all
of these questions. Even more, while the radio-MeV/GeV connection has been
firmly established, a radio-VHE connection has been entirely elusive so far.
The advent of CTA in the next few years and the expected CTA-SKA1 synergy will
offer the chance to explore this connection, even more intriguing as it
involves the opposite ends of the electromagnetic spectrum and the acceleration
of particles up to the highest energies.
We are already preparing to address these questions by exploiting data from
the various SKA pathfinders and precursors. We have obtained 18 cm European
VLBI Network observations of E>10 GeV sources, with a detection rate of 83%.
Moreover, we are cross correlating the Fermi catalogs with the MWA
commissioning survey: when faint gamma-ray sources are considered, pure
positional coincidence is not significant enough for selecting counterparts and
we need an additional physical criterion to pinpoint the right object. It can
be radio spectral index, variability, polarization, or compactness, needing
high angular resolution in SKA1-MID; timing studies can also reveal pulsars,
which are often found from dedicated searches of unidentified gamma-ray
sources. SKA will be the ideal instrument for investigating these
characteristics in conjunction with CTA.
(abridged)Comment: 12 pages, to be published in the proceedings of "Advancing
Astrophysics with the Square Kilometre Array", PoS(AASKA14)15
Measuring Youth Program Quality: A Guide to Assessment Tools
Thanks to growing interest in the subject of youth program quality, many tools are now available to help organizations and systems assess and improve quality. Given the size and diversity of the youth-serving sector, it is unrealistic to expect that any one tool or process will fit all programs or circumstances. This report compares the purpose, history, structure, methodology, content and technical properties of nine different program observation tools
Distributed Non-Interference
Information flow security properties were defined some years ago (see, e.g.,
the surveys \cite{FG01,Ry01}) in terms of suitable equivalence checking
problems. These definitions were provided by using sequential models of
computations (e.g., labeled transition systems \cite{GV15}), and interleaving
behavioral equivalences (e.g., bisimulation equivalence \cite{Mil89}). More
recently, the distributed model of Petri nets has been used to study
non-interference in \cite{BG03,BG09,BC15}, but also in these papers an
interleaving semantics was used. We argue that in order to capture all the
relevant information flows, truly-concurrent behavioral equivalences must be
used. In particular, we propose for Petri nets the distributed non-interference
property, called DNI, based on {\em branching place bisimilarity}
\cite{Gor21b}, which is a sensible, decidable equivalence for finite Petri nets
with silent moves. Then we focus our attention on the subclass of Petri nets
called {\em finite-state machines}, which can be represented (up to
isomorphism) by the simple process algebra CFM \cite{Gor17}. DNI is very easily
checkable on CFM processes, as it is compositional, so that it does does not
suffer from the state-space explosion problem. Moreover, we show that DNI can
be characterized syntactically on CFM by means of a type system
Automated in situ observations of upper ocean biogeochemistry, bio-optics, and physics and their potential use for global studies
The processes controlling the flux of carbon in the upper ocean have dynamic ranges in space and time of at least nine orders of magnitude. These processes depend on a broad suite of inter-related biogeochemical, bio-optical, and physical variables. These variables should be sampled on scales matching the relevant phenomena. Traditional ship-based sampling, while critical for detailed and more comprehensive observations, can span only limited portions of these ranges because of logistical and financial constraints. Further, remote observations from satellite platforms enable broad horizontal coverage which is restricted to the upper few meters of the ocean. For these main reasons, automated subsurface measurement systems are important for the fulfillment of research goals related to the regional and global estimation and modeling of time varying biogeochemical fluxes. Within the past few years, new sensors and systems capable of autonomously measuring several of the critical variables have been developed. The platforms for deploying these systems now include moorings and drifters and it is likely that autonomous underwater vehicles (AUV's) will become available for use in the future. Each of these platforms satisfies particular sampling needs and can be used to complement both shipboard and satellite observations. In the present review, (1) sampling considerations will be summarized, (2) examples of data obtained from some of the existing automated in situ sampling systems will be highlighted, (3) future sensors and systems will be discussed, (4) data management issues for present and future automated systems will be considered, and (5) the status of near real-time data telemetry will be outlined. Finally, we wish to make it clear at the outset that the perspectives presented here are those of the authors and are not intended to represent those of the United States JGOFS program, the International JGOFS program, NOAA's C&GC program, or other global ocean programs
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