3,020 research outputs found
Extreme State Aggregation Beyond MDPs
We consider a Reinforcement Learning setup where an agent interacts with an
environment in observation-reward-action cycles without any (esp.\ MDP)
assumptions on the environment. State aggregation and more generally feature
reinforcement learning is concerned with mapping histories/raw-states to
reduced/aggregated states. The idea behind both is that the resulting reduced
process (approximately) forms a small stationary finite-state MDP, which can
then be efficiently solved or learnt. We considerably generalize existing
aggregation results by showing that even if the reduced process is not an MDP,
the (q-)value functions and (optimal) policies of an associated MDP with same
state-space size solve the original problem, as long as the solution can
approximately be represented as a function of the reduced states. This implies
an upper bound on the required state space size that holds uniformly for all RL
problems. It may also explain why RL algorithms designed for MDPs sometimes
perform well beyond MDPs.Comment: 28 LaTeX pages. 8 Theorem
Tackling student binge drinking: pairing incongruent messages and measures reduces alcohol consumption
Objectives: Excessive alcohol consumption is a persistent problem in Northern European cultures. Across a 2-week period, we tested the effect of varying message frames, message types, and response measures, in reducing alcohol consumption. Design: Three hundred and twenty-three respondents were allocated to a 2 (message frame: gain vs. loss) × 2 (message type: health vs. social) × 2 (response type: engaging vs. refraining) mixed design. Method: Binge drinking and units consumed were measured at Time 1 and Time 2 (2 weeks later). Participants read (following Time 1) a gain- or loss-framed message on binging emphasizing either social or health consequences and answered engaging in or refraining from drinking attitude measures. Results: No main effects were identified. The key finding was that gain-framed messages, when used in conjunction with engage response measures (an incongruous pairing), were highly effective in reducing alcohol consumption 2 weeks later compared with the other message frame/response measure combinations. Conclusions: We suggest that for prevention behaviours, gain-framed messages, when paired with engage response measures, initiate an inconsistency resolution process. Together, our findings emphasize the importance of message frame and response type when seeking to reduce alcohol consumption using persuasive health messages
A case of Muir-Torre syndrome associated with mucinous hepatic cholangiocarcinoma and a novel germline mutation of the MSH2 gene
Muir-Torre syndrome (MTS) is a rare cancer-predisposing syndrome that is autosomal dominantly inherited and characterized by the development of sebaceous skin lesions (adenomas, epitheliomas, basaliomas and carcinomas). These lesions are typically associated with tumors that belong to the spectrum of hereditary nonpolyposis colorectal cancer (HNPCC) (i.e. tumors of the colorectum, endometrium, stomach or ovary). Biliary malignancy in association with MTS has only rarely been reported. We report a case of Muir-Torre syndrome associated with intrahepatic cholangiocarcinoma, a location not previously described, and associated with a novel missense mutation of the MSH2 gene (c.2026T>C), predicted to disrupt the function of the gen
A Hydrodynamic model for a dynamical jammed-to-flowing transition in gravity driven granular media
Granular material on an inclined plane will flow like a fluid if the angle
the plane makes with the horizontal is large enough. We employ a
modification of a hydrodynamic model introduced previously to describe Couette
flow experiments to describe chute flow down a plane. In this geometry, our
model predicts a jammed-to-flowing transition as is increased even
though it does not include solid friction, which might seem necessary to
stabilize a state without flow. The transition is driven by coupling between
mean and fluctuating velocity. In agreement with experiments and simulations,
it predicts flow for layers with a thickness H larger than a critical value
and absence of flow for
Electron correlation in C_(4N+2) carbon rings: aromatic vs. dimerized structures
The electronic structure of C_(4N+2) carbon rings exhibits competing
many-body effects of Huckel aromaticity, second-order Jahn-Teller and Peierls
instability at large sizes. This leads to possible ground state structures with
aromatic, bond angle or bond length alternated geometry. Highly accurate
quantum Monte Carlo results indicate the existence of a crossover between C_10
and C_14 from bond angle to bond length alternation. The aromatic isomer is
always a transition state. The driving mechanism is the second-order
Jahn-Teller effect which keeps the gap open at all sizes.Comment: Submitted for publication: 4 pages, 3 figures. Corrected figure
Lattice-Boltzmann Method for Geophysical Plastic Flows
We explore possible applications of the Lattice-Boltzmann Method for the
simulation of geophysical flows. This fluid solver, while successful in other
fields, is still rarely used for geotechnical applications. We show how the
standard method can be modified to represent free-surface realization of
mudflows, debris flows, and in general any plastic flow, through the
implementation of a Bingham constitutive model. The chapter is completed by an
example of a full-scale simulation of a plastic fluid flowing down an inclined
channel and depositing on a flat surface. An application is given, where the
fluid interacts with a vertical obstacle in the channel.Comment: in W. Wu, R.I. Borja (Edts.) Recent advances in modelling landslides
and debris flow, Springer Series in Geomechanics and Geoengineering (2014),
ISBN 978-3-319-11052-3, pp. 131-14
Salmeterol for the prevention of high-altitude pulmonary edema.
BACKGROUND: Pulmonary edema results from a persistent imbalance between forces that drive water into the air space and the physiologic mechanisms that remove it. Among the latter, the absorption of liquid driven by active alveolar transepithelial sodium transport has an important role; a defect of this mechanism may predispose patients to pulmonary edema. Beta-adrenergic agonists up-regulate the clearance of alveolar fluid and attenuate pulmonary edema in animal models.
METHODS: In a double-blind, randomized, placebo-controlled study, we assessed the effects of prophylactic inhalation of the beta-adrenergic agonist salmeterol on the incidence of pulmonary edema during exposure to high altitudes (4559 m, reached in less than 22 hours) in 37 subjects who were susceptible to high-altitude pulmonary edema. We also measured the nasal transepithelial potential difference, a marker of the transepithelial sodium and water transport in the distal airways, in 33 mountaineers who were prone to high-altitude pulmonary edema and 33 mountaineers who were resistant to this condition.
RESULTS: Prophylactic inhalation of salmeterol decreased the incidence of high-altitude pulmonary edema in susceptible subjects by more than 50 percent, from 74 percent with placebo to 33 percent (P=0.02). The nasal potential-difference value under low-altitude conditions was more than 30 percent lower in the subjects who were susceptible to high-altitude pulmonary edema than in those who were not susceptible (P<0.001).
CONCLUSIONS: Prophylactic inhalation of a beta-adrenergic agonist reduces the risk of high-altitude pulmonary edema. Sodium-dependent absorption of liquid from the airways may be defective in patients who are susceptible to high-altitude pulmonary edema. These findings support the concept that sodium-driven clearance of alveolar fluid may have a pathogenic role in pulmonary edema in humans and therefore represent an appropriate target for therapy
Decoupling with unitary approximate two-designs
Consider a bipartite system, of which one subsystem, A, undergoes a physical
evolution separated from the other subsystem, R. One may ask under which
conditions this evolution destroys all initial correlations between the
subsystems A and R, i.e. decouples the subsystems. A quantitative answer to
this question is provided by decoupling theorems, which have been developed
recently in the area of quantum information theory. This paper builds on
preceding work, which shows that decoupling is achieved if the evolution on A
consists of a typical unitary, chosen with respect to the Haar measure,
followed by a process that adds sufficient decoherence. Here, we prove a
generalized decoupling theorem for the case where the unitary is chosen from an
approximate two-design. A main implication of this result is that decoupling is
physical, in the sense that it occurs already for short sequences of random
two-body interactions, which can be modeled as efficient circuits. Our
decoupling result is independent of the dimension of the R system, which shows
that approximate 2-designs are appropriate for decoupling even if the dimension
of this system is large.Comment: Published versio
A case of Muir-Torre syndrome associated with mucinous hepatic cholangiocarcinoma and a novel germline mutation of the MSH2 gene.
Muir-Torre syndrome (MTS) is a rare cancer-predisposing syndrome that is autosomal dominantly inherited and characterized by the development of sebaceous skin lesions (adenomas, epitheliomas, basaliomas and carcinomas). These lesions are typically associated with tumors that belong to the spectrum of hereditary nonpolyposis colorectal cancer (HNPCC) (i.e., tumors of the colorectum, endometrium, stomach or ovary). Biliary malignancy in association with MTS has only rarely been reported. We report a case of Muir-Torre syndrome associated with intrahepatic cholangiocarcinoma, a location not previously described, and associated with a novel missense mutation of the MSH2 gene (c.2026T &gt; C), predicted to disrupt the function of the gene
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