184 research outputs found
Folk Theorems on the Correspondence between State-Based and Event-Based Systems
Kripke Structures and Labelled Transition Systems are the two most prominent
semantic models used in concurrency theory. Both models are commonly believed
to be equi-expressive. One can find many ad-hoc embeddings of one of these
models into the other. We build upon the seminal work of De Nicola and
Vaandrager that firmly established the correspondence between stuttering
equivalence in Kripke Structures and divergence-sensitive branching
bisimulation in Labelled Transition Systems. We show that their embeddings can
also be used for a range of other equivalences of interest, such as strong
bisimilarity, simulation equivalence, and trace equivalence. Furthermore, we
extend the results by De Nicola and Vaandrager by showing that there are
additional translations that allow one to use minimisation techniques in one
semantic domain to obtain minimal representatives in the other semantic domain
for these equivalences.Comment: Full version of SOFSEM 2011 pape
A Compact 3H(p,gamma)4He 19.8-MeV Gamma-Ray Source for Energy Calibration at the Sudbury Neutrino Observatory
The Sudbury Neutrino Observatory (SNO) is a new 1000-tonne D2O Cerenkov solar
neutrino detector. A high energy gamma-ray source is needed to calibrate SNO
beyond the 8B solar neutrino endpoint of 15 MeV. This paper describes the
design and construction of a source that generates 19.8-MeV gamma rays using
the 3H(p,gamma)4He reaction (``pt''), and demonstrates that the source meets
all the physical, operational and lifetime requirements for calibrating SNO. An
ion source was built into this unit to generate and to accelerate protons up to
30 keV, and a high purity scandium tritide target with a scandium-tritium
atomic ratio of 1:2.0+/-0.2 was included. This pt source is the first
self-contained, compact, and portable high energy gamma-ray source (E>10 MeV).Comment: 33 pages (including 2 table, 12 figures) This is the revised
manuscript, accepted for publication in NIM A. This revision relfects minor
editorial changes from the previous versio
Simulation-Based Graph Similarity
We present symmetric and asymmetric similarity measures for labeled directed rooted graphs that are inspired by the simulation and bisimulation relations on labeled transition systems. Computation of the similarity measures has close connections to discounted Markov decision processes in the asymmetric case and to perfect-information stochastic games in the symmetric case. For the symmetric case, we also give a polynomial-time algorithm that approximates the similarity to any desired precision
Algorithms for Game Metrics
Simulation and bisimulation metrics for stochastic systems provide a
quantitative generalization of the classical simulation and bisimulation
relations. These metrics capture the similarity of states with respect to
quantitative specifications written in the quantitative {\mu}-calculus and
related probabilistic logics. We first show that the metrics provide a bound
for the difference in long-run average and discounted average behavior across
states, indicating that the metrics can be used both in system verification,
and in performance evaluation. For turn-based games and MDPs, we provide a
polynomial-time algorithm for the computation of the one-step metric distance
between states. The algorithm is based on linear programming; it improves on
the previous known exponential-time algorithm based on a reduction to the
theory of reals. We then present PSPACE algorithms for both the decision
problem and the problem of approximating the metric distance between two
states, matching the best known algorithms for Markov chains. For the
bisimulation kernel of the metric our algorithm works in time O(n^4) for both
turn-based games and MDPs; improving the previously best known O(n^9\cdot
log(n)) time algorithm for MDPs. For a concurrent game G, we show that
computing the exact distance between states is at least as hard as computing
the value of concurrent reachability games and the square-root-sum problem in
computational geometry. We show that checking whether the metric distance is
bounded by a rational r, can be done via a reduction to the theory of real
closed fields, involving a formula with three quantifier alternations, yielding
O(|G|^O(|G|^5)) time complexity, improving the previously known reduction,
which yielded O(|G|^O(|G|^7)) time complexity. These algorithms can be iterated
to approximate the metrics using binary search.Comment: 27 pages. Full version of the paper accepted at FSTTCS 200
Inheritance of Temporal Logic Properties
Abstract. Inheritance is one of the key features for the success of object-oriented languages. Inheritance (or specialisation) supports incremental design and re-use of already written specifications or programs. In a for-mal approach to system design the interest does not only lie in re-use of class definitions but also in re-use of correctness proofs. If a provably correct class is specialised we like to know those correctness properties which are preserved in the subclass. This can avoid re-verification of already proven properties and may thus substantially reduce the verifi-cation effort. In this paper we study the question of inheritance of correctness prop-erties in the context of state-based formalisms, using a temporal logic (CTL) to formalise requirements on classes. Given a superclass and its specialised subclass we develop a technique for computing the set of for-mulas which are preserved in the subclass. For specialisation we allow addition of attributes, modification of existing as well as extension with new methods.
Observational Constraints on Chaplygin Quartessence: Background Results
We derive the constraints set by several experiments on the quartessence
Chaplygin model (QCM). In this scenario, a single fluid component drives the
Universe from a nonrelativistic matter-dominated phase to an accelerated
expansion phase behaving, first, like dark matter and in a more recent epoch
like dark energy. We consider current data from SNIa experiments, statistics of
gravitational lensing, FR IIb radio galaxies, and x-ray gas mass fraction in
galaxy clusters. We investigate the constraints from this data set on flat
Chaplygin quartessence cosmologies. The observables considered here are
dependent essentially on the background geometry, and not on the specific form
of the QCM fluctuations. We obtain the confidence region on the two parameters
of the model from a combined analysis of all the above tests. We find that the
best-fit occurs close to the CDM limit (). The standard
Chaplygin quartessence () is also allowed by the data, but only at
the level.Comment: Replaced to match the published version, references update
Quantum walks: a comprehensive review
Quantum walks, the quantum mechanical counterpart of classical random walks,
is an advanced tool for building quantum algorithms that has been recently
shown to constitute a universal model of quantum computation. Quantum walks is
now a solid field of research of quantum computation full of exciting open
problems for physicists, computer scientists, mathematicians and engineers.
In this paper we review theoretical advances on the foundations of both
discrete- and continuous-time quantum walks, together with the role that
randomness plays in quantum walks, the connections between the mathematical
models of coined discrete quantum walks and continuous quantum walks, the
quantumness of quantum walks, a summary of papers published on discrete quantum
walks and entanglement as well as a succinct review of experimental proposals
and realizations of discrete-time quantum walks. Furthermore, we have reviewed
several algorithms based on both discrete- and continuous-time quantum walks as
well as a most important result: the computational universality of both
continuous- and discrete- time quantum walks.Comment: Paper accepted for publication in Quantum Information Processing
Journa
The Sudbury Neutrino Observatory
The Sudbury Neutrino Observatory is a second generation water Cherenkov
detector designed to determine whether the currently observed solar neutrino
deficit is a result of neutrino oscillations. The detector is unique in its use
of D2O as a detection medium, permitting it to make a solar model-independent
test of the neutrino oscillation hypothesis by comparison of the charged- and
neutral-current interaction rates. In this paper the physical properties,
construction, and preliminary operation of the Sudbury Neutrino Observatory are
described. Data and predicted operating parameters are provided whenever
possible.Comment: 58 pages, 12 figures, submitted to Nucl. Inst. Meth. Uses elsart and
epsf style files. For additional information about SNO see
http://www.sno.phy.queensu.ca . This version has some new reference
Risk profiles and one-year outcomes of patients with newly diagnosed atrial fibrillation in India: Insights from the GARFIELD-AF Registry.
BACKGROUND: The Global Anticoagulant Registry in the FIELD-Atrial Fibrillation (GARFIELD-AF) is an ongoing prospective noninterventional registry, which is providing important information on the baseline characteristics, treatment patterns, and 1-year outcomes in patients with newly diagnosed non-valvular atrial fibrillation (NVAF). This report describes data from Indian patients recruited in this registry. METHODS AND RESULTS: A total of 52,014 patients with newly diagnosed AF were enrolled globally; of these, 1388 patients were recruited from 26 sites within India (2012-2016). In India, the mean age was 65.8 years at diagnosis of NVAF. Hypertension was the most prevalent risk factor for AF, present in 68.5% of patients from India and in 76.3% of patients globally (P < 0.001). Diabetes and coronary artery disease (CAD) were prevalent in 36.2% and 28.1% of patients as compared with global prevalence of 22.2% and 21.6%, respectively (P < 0.001 for both). Antiplatelet therapy was the most common antithrombotic treatment in India. With increasing stroke risk, however, patients were more likely to receive oral anticoagulant therapy [mainly vitamin K antagonist (VKA)], but average international normalized ratio (INR) was lower among Indian patients [median INR value 1.6 (interquartile range {IQR}: 1.3-2.3) versus 2.3 (IQR 1.8-2.8) (P < 0.001)]. Compared with other countries, patients from India had markedly higher rates of all-cause mortality [7.68 per 100 person-years (95% confidence interval 6.32-9.35) vs 4.34 (4.16-4.53), P < 0.0001], while rates of stroke/systemic embolism and major bleeding were lower after 1 year of follow-up. CONCLUSION: Compared to previously published registries from India, the GARFIELD-AF registry describes clinical profiles and outcomes in Indian patients with AF of a different etiology. The registry data show that compared to the rest of the world, Indian AF patients are younger in age and have more diabetes and CAD. Patients with a higher stroke risk are more likely to receive anticoagulation therapy with VKA but are underdosed compared with the global average in the GARFIELD-AF. CLINICAL TRIAL REGISTRATION-URL: http://www.clinicaltrials.gov. Unique identifier: NCT01090362
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