362 research outputs found
Optimistic Agents are Asymptotically Optimal
We use optimism to introduce generic asymptotically optimal reinforcement
learning agents. They achieve, with an arbitrary finite or compact class of
environments, asymptotically optimal behavior. Furthermore, in the finite
deterministic case we provide finite error bounds.Comment: 13 LaTeX page
Universal knowledge-seeking agents for stochastic environments
We define an optimal Bayesian knowledge-seeking agent, KL-KSA, designed for countable hypothesis classes of stochastic environments and whose goal is to gather as much information about the unknown world as possible. Although this agent works for arbitrary countable classes and priors, we focus on the especially interesting case where all stochastic computable environments are considered and the prior is based on Solomonoffâs universal prior. Among other properties, we show that KL-KSA learns the true environment in the sense that it learns to predict the consequences of actions it does not take. We show that it does not consider noise to be information and avoids taking actions leading to inescapable traps. We also present a variety of toy experiments demonstrating that KL-KSA behaves according to expectation
Treatment of obstructive sleep apnoea leads to improved microvascular endothelial function in the systemic circulation
Background: Obstructive sleep apnoea (OSA) is a common and potentially reversible cause of systemic hypertension. The mechanisms whereby OSA leads to hypertension and the effects of treatment on arterial function, however, are not well established. Microvascular arterial endothelial and smooth muscle function was assessed in subjects with OSA before and after treatment with continuous positive airways pressure (CPAP). Methods: Ten subjects of mean (SE) age 49 (8) years with at least moderately severe OSA had detailed forearm vascular reactivity studies before and after 3 months of CPAP treatment. The systemic circulation was assessed by measuring brachial artery pressure, flow and resistance responses to intra-arterial infusions of acetylcholine (ACh; an endothelium dependent vasodilator), sodium nitroprusside (SNP; an endothelium independent vasodilator), L-NMMA (a nitric oxide (NO) antagonist), and L-arginine (the substrate for NO). Results: Before CPAP, ACh and SNP infusions increased forearm blood flow in a dose dependent manner (p,0.01). After CPAP, endothelium dependent dilation to ACh was significantly increased (434 (23)% of baseline after CPAP v 278 (20)% before CPAP, p,0.001), whereas SNP induced dilation was unchanged. Resting NO production was higher after CPAP, evidenced by a significantly greater reduction in basal flow by L-NMMA (p = 0.05). L-Arginine reversed the effect of L-NMMA in all cases. Conclusion: In patients with OSA, treatment with CPAP improves baseline endothelial NO release and stimulates endothelium dependent vasorelaxation in the systemic circulation. This is a potential mechanism for improving systemic and vascular function in patients with OSA treated with CPAP
Sequential Extensions of Causal and Evidential Decision Theory
Moving beyond the dualistic view in AI where agent and environment are
separated incurs new challenges for decision making, as calculation of expected
utility is no longer straightforward. The non-dualistic decision theory
literature is split between causal decision theory and evidential decision
theory. We extend these decision algorithms to the sequential setting where the
agent alternates between taking actions and observing their consequences. We
find that evidential decision theory has two natural extensions while causal
decision theory only has one.Comment: ADT 201
The diverse nature of island isolation and its effect on land bridge insular faunas
Aim:
Isolation is a key factor in island biology. It is usually defined as the distance to the geographically nearest mainland, but many other definitions exist. We explored how testing different isolation indices affects the inference of impacts of isolation on faunal characteristics. We focused on land bridge islands and compared the relationships of many spatial and temporal (i.e., through time) isolation indices with communityâ, populationâ and individualâlevel characteristics (species richness, population density and body size, respectively).
Location:
Aegean Sea islands, Greece.
Time period:
Current.
Taxon:
Many animal taxa.
Methods:
We estimated 21 isolation indices for 205 islands and recorded species richness data for 15 taxa (invertebrates and vertebrates). We obtained body size data for seven lizard species and population density data for three. We explored how well indices predict each characteristic, in each taxon, by conducting a series of ordinary least squares regressions (controlling for island area when needed) and a metaâanalysis.
Results:
Isolation was significantly (and negatively) associated with species richness in 10 of 15 taxa. It was significantly (and positively) associated with body size in only one of seven species and was not associated with population density. The effect of isolation on species richness was much weaker than that of island area, regardless of the index tested. Spatial indices generally outâperformed temporal indices, and indices directly related to the mainland outâperformed those related mainly to neighbouring islands. No index was universally superior to others, including the distance to the geographically nearest mainland.
Main conclusions:
The choice of index can alter our perception of the impacts of isolation on biological patterns. The nearly automatic, ubiquitous use of distance to the geographically nearest mainland misrepresents the complexity of the effects of isolation. We recommend the simultaneous testing of several indices that represent different aspects of isolation, in order to produce more constructive and thorough investigations and avoid imprecise inference
Seroprevalence of HCV, HBV and HIV in two inner-city London Emergency Departments.
Summary: In this paper we build on work investigating the feasibility of human immunodeficiency virus (HIV) testing in emergency departments (EDs), estimating the prevalence of
hepatitis B, C and HIV infections among persons attending two inner-London EDs, identifying factors associated with testing positive in an ED. We also undertook molecular characterisation to look at the diversity of the viruses circulating in these individuals, and the presence
of clinically significant mutations which impact on treatment and control.
Blood-borne virus (BBV) testing in non-traditional settings is feasible, with emergency
departments (ED) potentially effective at reaching vulnerable and underserved populations.
We investigated the feasibility of BBV testing within two inner-London EDs. Residual samples
from biochemistry for adults (â©Ÿ18 years) attending The Royal Free London Hospital (RFLH)
or the University College London Hospital (UCLH) ED between January and June 2015 were
tested for human immunodeficiency virus (HIV)Ag/Ab, anti-hepatitis C (HCV) and HBsAg.
PCR and sequence analysis were conducted on reactive samples. Sero-prevalence among persons attending RFH and UCLH with residual samples (1287 and 1546), respectively, were
1.1% and 1.0% for HBsAg, 1.6% and 2.3% for anti-HCV, 0.9% and 1.6% for HCV RNA,
and 1.3% and 2.2% for HIV. For RFH, HBsAg positivity was more likely among persons of
black vs. white ethnicity (odds ratio 9.08; 95% confidence interval 2.72â30), with anti-HCV
positivity less likely among females (0.15, 95% CI 0.04â0.50). For UCLH, HBsAg positivity
was more likely among non-white ethnicity (13.34, 95% CI 2.20â80.86 (Asian); 8.03, 95%
CI 1.12â57.61 (black); and 8.11, 95% CI 1.13â58.18 (other/mixed)). Anti-HCV positivity
was more likely among 36â55 year olds vs. â©Ÿ56 years (7.69, 95% CI 2.24â26.41), and less likely
among females (0.24, 95% CI 0.09â0.65). Persons positive for HIV-markers were more likely
to be of black vs. white ethnicity (4.51, 95% CI 1.63â12.45), and less likely to have one ED
attendance (0.39, 95% CI 0.17â0.88), or female (0.12, 95% CI 0.04â0.42). These results indicate that BBV-testing in EDs is feasible, providing a basis for further studies to explore provider and patient acceptability, referral into care and cost-effectiveness
Neuroscience in gambling policy and treatment: an interdisciplinary perspective
Neuroscientific explanations of gambling disorder can help people make sense of their experiences and guide the development of psychosocial interventions. However, the societal perceptions and implications of these explanations are not always clear or helpful. Two workshops in 2013 and 2014 brought together multidisciplinary researchers aiming to improve the clinical and policy-related effects of neuroscience research on gambling. The workshops revealed that neuroscience can be used to improve identification of the dangers of products used in gambling. Additionally, there was optimism associated with the diagnostic and prognostic uses of neuroscience in problem gambling and the provision of novel tools (eg, virtual reality) to assess the effectiveness of new policy interventions before their implementation. Other messages from these workshops were that neuroscientific models of decision making could provide a strong rationale for precommitment strategies and that interdisciplinary collaborations are needed to reduce the harms of gambling
Me, My Girls, and the Ideal Hotel: Segmenting Motivations of the Girlfriend Getaway Market Using Fuzzy C-Medoids for Fuzzy Data.
Segmenting the motivation of travelers using the push and pull framework remains ubiquitous in tourism. This study segments the girlfriend getaway (GGA) market on motivation (push) and accommodation (pull) attributes and identifies relationships between these factors. Using a relatively novel clustering algorithm, the Fuzzy C-Medoids clustering for fuzzy data (FCM-FD), on a sample of 749 women travelers, three segments (Socializers, Enjoyers, and Rejoicers) are uncovered. The results of a multinomial fractional model show relationships between the clusters of motivation and accommodation attributes as well as sociodemographic characteristics. The research highlights the importance of using a gendered perspective in applying well established motivation models such as the push and pull framework. The findings have implications for both destination and accommodation management
Re-Arrest Among Juvenile Justice-Involved Youth: An Examination Of The Static And Dynamic Risk Factors
The purpose of this study is to investigate the static and dynamic risk factors for re-arrest among detained youth by examining gender, race/ethnicity, age, special education and mental health variables (i.e., anger/irritability, depression/anxiety, somatic complaints, suicide ideation, thought disturbances, and traumatic experiences). The demographic profiles of detained youth with one admit were also compared with those with multiple admits to the juvenile detention center. With regards to static risk factors, older, white, and special education were significantly at risk of re-arrest. Concerning dynamic risk factors, only anger/irritability predicted re-arrest. Practice implications are also discussed
Radiocarbon dating and cultural dynamics across Mongoliaâs early pastoral transition
All necessary permits were obtained for the described study, which complied with all relevant regulations. Collaboration contract between the Max Planck Institute for the Science of Human HIstory and the National University of Mongolia began on the 10th November, 2016. Export number 10/413 (7b/52) was received on the 2nd Feb, 2017 (#A0109258, MN DE 7 643). This research was supported by the Max Planck Institute for the Science of Human History. Special thanks to Dr. Katerina Douka and the Oxford Radiocarbon Accelerator Laboratory for conducting 14C analysis, and to all of the original excavators and authors who published the radiocarbon dates cited in this study.Peer reviewedPublisher PD
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