224 research outputs found
New Deterministic Algorithms for Solving Parity Games
We study parity games in which one of the two players controls only a small
number of nodes and the other player controls the other nodes of the
game. Our main result is a fixed-parameter algorithm that solves bipartite
parity games in time , and general parity games in
time , where is the number of distinct
priorities and is the number of edges. For all games with this
improves the previously fastest algorithm by Jurdzi{\'n}ski, Paterson, and
Zwick (SICOMP 2008). We also obtain novel kernelization results and an improved
deterministic algorithm for graphs with small average degree
The Complexity of Admissibility in Omega-Regular Games
Iterated admissibility is a well-known and important concept in classical
game theory, e.g. to determine rational behaviors in multi-player matrix games.
As recently shown by Berwanger, this concept can be soundly extended to
infinite games played on graphs with omega-regular objectives. In this paper,
we study the algorithmic properties of this concept for such games. We settle
the exact complexity of natural decision problems on the set of strategies that
survive iterated elimination of dominated strategies. As a byproduct of our
construction, we obtain automata which recognize all the possible outcomes of
such strategies
Atomically Resolved Chemical Reactivity of Small Fe Clusters
Small metal clusters have been investigated for decades due to their beneficial catalytic activity. It was found that edges are most reactive and the number of catalytic events increases with the cluster's size. However, a direct measurement of chemical reactivity of individual atoms within the clusters has not been reported yet. We combine the high-resolution capability of CO-terminated tips in scanning probe microscopy with their ability to probe chemical binding forces on single Fe atoms to study the chemical reactivity of atom-by-atom assembled Fe clusters from 1 to 15 atoms on the atomic scale. We find that the chemical reactivity of individual atoms within flat Fe clusters does not depend on the cluster size but on the coordination number of the investigated atom. Furthermore, we explain the atomic contrast of the investigated Fe clusters by relating the force spectra of individual atoms with atomic force microscopy images of the clusters
Qualitative Analysis of Partially-observable Markov Decision Processes
We study observation-based strategies for partially-observable Markov
decision processes (POMDPs) with omega-regular objectives. An observation-based
strategy relies on partial information about the history of a play, namely, on
the past sequence of observations. We consider the qualitative analysis
problem: given a POMDP with an omega-regular objective, whether there is an
observation-based strategy to achieve the objective with probability~1
(almost-sure winning), or with positive probability (positive winning). Our
main results are twofold. First, we present a complete picture of the
computational complexity of the qualitative analysis of POMDP s with parity
objectives (a canonical form to express omega-regular objectives) and its
subclasses. Our contribution consists in establishing several upper and lower
bounds that were not known in literature. Second, we present optimal bounds
(matching upper and lower bounds) on the memory required by pure and randomized
observation-based strategies for the qualitative analysis of POMDP s with
parity objectives and its subclasses
Intensive statin therapy compared with moderate dosing for prevention of cardiovascular events: a meta-analysis of >40 000 patients
Aims Statin therapy is associated with important benefits for patients at risk of, and with, established cardiovascular disease. There is widespread interest in whether intensive dosing of statins yields larger treatment effects. We aimed to determine if intensive dosing is clinically important using a meta-analysis of randomized clinical trials (RCTs). Methods We conducted comprehensive searches of electronic databases from inception to December 2010. We included any RCT evaluating a larger dose with a clinically common dose. Two reviewers independently extracted data, in duplicate. We performed random-effects meta-analysis and a trial sequential analysis. Results We identified 10 RCTs enrolling a total of 41 778 participants. Trials followed patients for a mean of 2.5 years. We did not find statistically significant effects on all-cause mortality [relative risk (RR) 0.92, 95% confidence interval (CI), 0.83-1.03, P = 0.14, I2 = 38%] or cardiovascular disease (CVD) deaths (RR 0.89, 95% CI, 0.78-1.01, P = 0.07, I2 = 34%). When we pooled the composite endpoint of coronary heart disease (CHD) death plus non-fatal myocardial infarction (MI), we found a significant protective effect of intensive statin dosing (RR 0.90, 95% CI, 0.84-0.96, P ≤ 0.0001, I2 = 0%). We also found a significant effect on non-fatal MIs (RR 0.82, 95% CI, 0.76-0.89, P ≤ 0.0001, I2 = 0%) and a significant reduction in the composite of fatal and non-fatal strokes (excluding transient ischaemic attacks) reported in 10 RCTs (RR 0.86, 95% CI, 0.77-0.96, P = 0.006, I2 = 0%). A subgroup analysis of three trials examining acute coronary syndrome patients found significant effects on all-cause (RR 0.75, 95% CI, 0.61-0.91, P = 0.005, I2 = 0%) and CVD mortality (RR 0.74, 95% CI, 0.59-0.94, P = 0.013, I2 = 0%) with intensive dosing. Applying an analysis of optimal information size on the primary analysis, we found that the evidence for CHD death plus non-fatal MIs is conclusive. The evidence for CVD deaths alone is not yet conclusive. Conclusions Available evidence suggests that intensive statin therapy reduces the risk of non-fatal events and may have a role in reducing mortalit
Response of the topological surface state to surface disorder in TlBiSe
Through a combination of experimental techniques we show that the topmost
layer of the topo- logical insulator TlBiSe as prepared by cleavage is
formed by irregularly shaped Tl islands at cryogenic temperatures and by mobile
Tl atoms at room temperature. No trivial surface states are observed in
photoemission at low temperatures, which suggests that these islands can not be
re- garded as a clear surface termination. The topological surface state is,
however, clearly resolved in photoemission experiments. This is interpreted as
a direct evidence of its topological self-protection and shows the robust
nature of the Dirac cone like surface state. Our results can also help explain
the apparent mass acquisition in S-doped TlBiSe.Comment: 16 pages, 5 figure
Symmetric Strategy Improvement
Symmetry is inherent in the definition of most of the two-player zero-sum
games, including parity, mean-payoff, and discounted-payoff games. It is
therefore quite surprising that no symmetric analysis techniques for these
games exist. We develop a novel symmetric strategy improvement algorithm where,
in each iteration, the strategies of both players are improved simultaneously.
We show that symmetric strategy improvement defies Friedmann's traps, which
shook the belief in the potential of classic strategy improvement to be
polynomial
Automated vessel centerline extraction and diameter measurement in OCT Angiography
Optical Coherence Tomography Angiography (OCTA) is a non-invasive imaging technique that enables the visualizationof perfused vasculature in vivo. In ophthalmology,it allows the physician to monitor diseases affecting the vascular networks of the retina such as age-related macular degeneration or diabetic retinopathy. Due to the complexity of the vasculature in the retina,it is of interest to automatically extract vascular parameters which describe the condition of the vessels. Suitable parameters could improve the diagnosis and the treatment during the course of therapy.We present an automated algorithm tocompute the diameters of the vessels in en face OCTA images. After segmentingthe images, the vessel centerlinewascomputed using a thinningalgorithm.The centerline wasrefined by detecting invalid pixelssuch as spursandbycontinuing the centerline until the endsof the vessels. Lastly, the diameter wascomputed by dilating a discrete circle at the position of the centerline or by measuring the distance between both borders of the vessels. The developed algorithms were applied to in vivo images of human eyes. Certainly, no ground truth was available. Hence, a plausibility check was performed by comparing the measured diameters of two different layers of the retina (Superficial Vascular Complex (SVC) and Deep Vascular Complex (DVC)). Each layer exhibits a different characteristic vasculature.The algorithm clearly reflectedthe differences from both retinal layers. The measured diameters demonstrate that the DVC consists of more capillaries and considerably smaller vessels compared to the SVC.The presented method enables automated analysis of the retinal vasculature and forms thereby the basis for monitoringdiseases influencing the vasculature of the retina. The validation of the method using an artificial ground truth is still neede
Games on graphs with a public signal monitoring
We study pure Nash equilibria in games on graphs with an imperfect monitoring
based on a public signal. In such games, deviations and players responsible for
those deviations can be hard to detect and track. We propose a generic
epistemic game abstraction, which conveniently allows to represent the
knowledge of the players about these deviations, and give a characterization of
Nash equilibria in terms of winning strategies in the abstraction. We then use
the abstraction to develop algorithms for some payoff functions.Comment: 28 page
Non-Zero Sum Games for Reactive Synthesis
In this invited contribution, we summarize new solution concepts useful for
the synthesis of reactive systems that we have introduced in several recent
publications. These solution concepts are developed in the context of non-zero
sum games played on graphs. They are part of the contributions obtained in the
inVEST project funded by the European Research Council.Comment: LATA'16 invited pape
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