6,945 research outputs found
Retractable Contracts
In calculi for modelling communication protocols, internal and external
choices play dual roles. Two external choices can be viewed naturally as dual
too, as they represent an agreement between the communicating parties. If the
interaction fails, the past agreements are good candidates as points where to
roll back, in order to take a different agreement. We propose a variant of
contracts with synchronous rollbacks to agreement points in case of deadlock.
The new calculus is equipped with a compliance relation which is shown to be
decidable.Comment: In Proceedings PLACES 2015, arXiv:1602.0325
Profiles of Emotion Regulation: Understanding Regulatory Patterns and The Implications for Posttraumatic Stress
Trauma survivors often experience posttraumatic stress (PTS) and report concurrent difficulties with emotion regulation (ER). Although individuals typically use multiple regulatory strategies to manage emotion, no studies yet examine the influence of a constellation of strategies on PTS in a community sample. We assessed six ER strategies and investigated whether specific profiles of ER (i.e. the typical pattern of regulation, determined by how often each strategy is used) were related to PTS. A hierarchical cluster analysis indicated that four distinct profiles were present: Adaptive Regulation, Active Regulation, Detached Regulation, and Maladaptive Regulation. Further analyses revealed that an individual\u27s profile was not related to frequency of past trauma, but had the power to differentiate symptom severity for overall PTS and each symptom cluster of posttraumatic stress disorder. These findings highlight how profiles characterising multiple regulatory strategies offer a more complete understanding of the ways ER can account for PTS
Minimisation of event structures
Event structures are fundamental models in concurrency theory, providing a representation of events in computation and of their relations, notably concurrency, conflict and causality. In this paper we present a theory of minimisation for event structures. Working in a class of event structures that generalises many stable event structure models in the literature, (e.g., prime, asymmetric, flow and bundle event structures) we study a notion of behaviour-preserving quotient, taking hereditary history preserving bisimilarity as a reference behavioural equivalence. We show that for any event structure a uniquely determined minimal quotient always exists. We observe that each event structure can be seen as the quotient of a prime event structure, and that quotients of general event structures arise from quotients of (suitably defined) corresponding prime event structures. This gives a special relevance to quotients in the class of prime event structures, which are then studied in detail, providing a characterisation and showing that also prime event structures always admit a unique minimal quotient
On the origin of fluorine in the Milky Way
The main astrophysical factories of fluorine (19F) are thought to be Type II
supernovae, Wolf-Rayet stars, and the asymptotic giant branch (AGB) of
intermediate mass stars. We present a model for the chemical evolution of
fluorine in the Milky Way using a semi-analytic multi-zone chemical evolution
model. For the first time, we demonstrate quantitatively the impact of fluorine
nucleosynthesis in Wolf-Rayet and AGB stars. The inclusion of these latter two
fluorine production sites provides a possible solution to the long-standing
discrepancy between model predictions and the fluorine abundances observed in
Milky Way giants. Finally, fluorine is discussed as a possible probe of the
role of supernovae and intermediate mass stars in the chemical evolution
history of the globular cluster omega Centauri.Comment: 7 pages, 4 figures. MNRAS in pres
Characterising and Verifying the Core in Concurrent Multi-Player Mean-Payoff Games (Full Version)
Concurrent multi-player mean-payoff games are important models for systems of
agents with individual, non-dichotomous preferences. Whilst these games have
been extensively studied in terms of their equilibria in non-cooperative
settings, this paper explores an alternative solution concept: the core from
cooperative game theory. This concept is particularly relevant for cooperative
AI systems, as it enables the modelling of cooperation among agents, even when
their goals are not fully aligned. Our contribution is twofold. First, we
provide a characterisation of the core using discrete geometry techniques and
establish a necessary and sufficient condition for its non-emptiness. We then
use the characterisation to prove the existence of polynomial witnesses in the
core. Second, we use the existence of such witnesses to solve key decision
problems in rational verification and provide tight complexity bounds for the
problem of checking whether some/every equilibrium in a game satisfies a given
LTL or GR(1) specification. Our approach is general and can be adapted to
handle other specifications expressed in various fragments of LTL without
incurring additional computational costs.Comment: This is the full version of the paper with the same title that
appears in the CSL'24 proceeding
Stokes trapping and planet formation
It is believed that planets are formed by aggregation of dust particles
suspended in the turbulent gas forming accretion disks around developing stars.
We describe a mechanism, termed 'Stokes trapping', by which turbulence limits
the growth of aggregates of dust particles, so that their Stokes number
(defined as the ratio of the damping time of the particles to the Kolmogorov
dissipation timescale) remains close to unity. We discuss possible mechanisms
for avoiding this barrier to further growth. None of these is found to be
satisfactory and we introduce a new theory which does not involve the growth of
small clusters of dust grains.Comment: 30 pages, 4 figures. Revised version has improved concluding remarks,
extended discussion of sticking velocit
A Framework for Transactional Consistency Models with Atomic Visibility
Modern distributed systems often rely on databases that achieve scalability by providing only weak guarantees about the consistency of distributed transaction processing. The semantics of programs interacting with such a database depends on its consistency model, defining these guarantees. Unfortunately, consistency models are usually stated informally or using disparate formalisms, often tied to the database internals. To deal with this problem, we propose a framework for specifying a variety of consistency models for transactions uniformly and declaratively. Our specifications are given in the style of weak memory models, using structures of events and relations on them. The specifications are particularly concise because they exploit the property of atomic visibility guaranteed by many consistency models: either all or none of the updates by a transaction can be visible to another one. This allows the specifications to abstract from individual events inside transactions. We illustrate the use of our framework by specifying several existing consistency models. To validate our specifications, we prove that they are equivalent to alternative operational ones, given as algorithms closer to actual implementations. Our work provides a rigorous foundation for developing the metatheory of the novel form of concurrency arising in weakly consistent large-scale databases
Men after feminism: whatâs left to say?
In a paper first delivered at the University of Barcelona (2006), Segal focuses on the future of men after the feminist movement. Among the many topics Segal broaches is that masculinity(ies) studies should not be viewed as usurping women's studies in the academy
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