2,908 research outputs found
Perfect simulation for interacting point processes, loss networks and Ising models
We present a perfect simulation algorithm for measures that are absolutely
continuous with respect to some Poisson process and can be obtained as
invariant measures of birth-and-death processes. Examples include area- and
perimeter-interacting point processes (with stochastic grains), invariant
measures of loss networks, and the Ising contour and random cluster models. The
algorithm does not involve couplings of the process with different initial
conditions and it is not tied up to monotonicity requirements. Furthermore, it
directly provides perfect samples of finite windows of the infinite-volume
measure, subjected to time and space ``user-impatience bias''. The algorithm is
based on a two-step procedure: (i) a perfect-simulation scheme for a (finite
and random) relevant portion of a (space-time) marked Poisson processes (free
birth-and-death process, free loss networks), and (ii) a ``cleaning'' algorithm
that trims out this process according to the interaction rules of the target
process. The first step involves the perfect generation of ``ancestors'' of a
given object, that is of predecessors that may have an influence on the
birth-rate under the target process. The second step, and hence the whole
procedure, is feasible if these ``ancestors'' form a finite set with
probability one. We present a sufficiency criteria for this condition, based on
the absence of infinite clusters for an associated (backwards) oriented
percolation model.Comment: Revised version after referee of SPA: 39 page
Loss network representation of Peierls contours
We present a probabilistic approach for the study of systems with exclusions,
in the regime traditionally studied via cluster-expansion methods. In this
paper we focus on its application for the gases of Peierls contours found in
the study of the Ising model at low temperatures, but most of the results are
general. We realize the equilibrium measure as the invariant measure of a
loss-network process whose existence is ensured by a subcriticality condition
of a dominant branching process. In this regime, the approach yields, besides
existence and uniqueness of the measure, properties such as exponential space
convergence and mixing, and a central limit theorem. The loss network converges
exponentially fast to the equilibrium measure, without metastable traps. This
convergence is faster at low temperatures, where it leads to the proof of an
asymptotic Poisson distribution of contours. Our results on the mixing
properties of the measure are comparable to those obtained with
``duplicated-variables expansion'', used to treat systems with disorder and
coupled map lattices. It works in a larger region of validity than usual
cluster-expansion formalisms, and it is not tied to the analyticity of the
pressure. In fact, it does not lead to any kind of expansion for the latter,
and the properties of the equilibrium measure are obtained without resorting to
combinatorial or complex analysis techniques.Comment: 42 pages. Revised version after the first referee repor
Processes with Long Memory: Regenerative Construction and Perfect Simulation
We present a perfect simulation algorithm for stationary processes indexed by
Z, with summable memory decay. Depending on the decay, we construct the process
on finite or semi-infinite intervals, explicitly from an i.i.d. uniform
sequence. Even though the process has infinite memory, its value at time 0
depends only on a finite, but random, number of these uniform variables. The
algorithm is based on a recent regenerative construction of these measures by
Ferrari, Maass, Mart{\'\i}nez and Ney. As applications, we discuss the perfect
simulation of binary autoregressions and Markov chains on the unit interval.Comment: 27 pages, one figure. Version accepted by Annals of Applied
Probability. Small changes with respect to version
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From Curatorial Files to Linked Open Data: Cataloging the Art Collection at Columbia University
Columbia University is relatively unique among American educational institutions with regard to its art collection. Rather than being housed in a traditional museum environment, artwork instead is organized as a special collection within Avery Architectural and Fine Arts Library. Overseen by the Art Properties department, the collection of over 12,000 works of art encompasses all time periods, cultures, and media. This paper presents a case study in which item-level records for the collection were exposed in the library’s online catalog and, in just five years, evolved from being an unsearchable resource to becoming an international model of linked open data for records for works of art. The first part of this presentation describes the original museum-style documentation used for organizing the collection, and the library cataloging standards implemented in recent years
Bradycardia and atrial fibrillation in patients with stable coronary artery disease treated with ivabradine: an analysis from the SIGNIFY study
Aim: The aim of this study was to determine the impact of emergent bradycardia and atrial fibrillation (AF) on cardiovascular outcomes in 19 083 patients with stable coronary artery disease (CAD) receiving ivabradine or placebo (SIGNIFY, Study assessInG the morbidity–mortality beNefits of the If inhibitor ivabradine in patients with coronarY artery disease).
Methods and results: Emergent bradycardia (resting heart rate <50 b.p.m. on 12-lead electrocardiogram) with ivabradine was reported in 3572 patients (37.4%) overall, and in 2242 (37.2%) patients with Canadian Cardiovascular Society (CCS) class ≥2 angina. There was no difference in outcomes over the course of the study in ivabradine-treated patients with and without emergent bradycardia in the whole population (2.5 vs. 2.9% per year, respectively, for primary composite endpoint of cardiovascular death or non-fatal myocardial infarction) or in the angina subgroup (2.5 vs. 3.2% per year). Neither was there an increase in the rate of primary endpoint after emergent bradycardia was recorded compared with those without emergent bradycardia. There were 754 cases of emergent AF on treatment (2.2% per year ivabradine vs. 1.5% per year placebo) and 469 in the patients with angina (2.2 vs. 1.5% per year). While outcomes occurred more frequently in patients in whom emergent AF had been recorded, there was no treatment–placebo difference in outcomes, including stroke, and no difference in treatment effect in patients with limiting angina.
Conclusion: Both in the overall population as well as in the angina subset, bradycardia was common in ivabradine-treated patients, but did not appear to impact outcomes. Emergent AF was relatively rare and did not appear to have an impact on outcomes relative to placebo
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