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

A comparison of open and closed loop applications of the minimum distance guidance technique

A comparison is made of open and closed loop applications of a second order guidance algorithm, using the minimum distance strategy. A nonlinear reoptimization procedure is used as the ideal guidance history. The system model used for the comparison is a low-thrust vehicle performing a minimum time, three-dimensional, heliocentric Earth-Mars transfer. For the example problem considered, closed loop guidance proves to be much more accurate on satisfaction of the final state than the open loop procedure. On the other hand, closed loop guidance proves to be much more vulnerable to perturbation by highly nonlinear regions in the trajectory. Finally, the results indicate that for this problem the best loop closure interval is at each integration step, about one day, or more often, if possible

Distortions to Agricultural Incentives in Australia and New Zealand

In 1990, Australia and New Zealand were ranked around 25th and 35th in terms of GNP per capita, having been the highest-income countries in the world one hundred years earlier. The poor performance over that long period contrasts markedly with that of the past 15 years, when these two economies out-performed most other high-income countries. This difference in growth performance is due to major economic policy reforms during the past two to three decades. We provide new evidence on the extent of governmental distortions to agricultural incentives in particular in the two economies since the late 1940s, both directly and indirectly (and negatively) via manufacturing protection.Distorted incentives, agricultural and trade policy reform, Agricultural and Food Policy, F13, F14, Q17, Q18,

Changing Patterns of Sexual Risk Behavior Among London Gay Men: 1998-2008

Objectives: To examine changes in the sexual behavior of London gay men between 1998 and 2008. Methods: Gay men using London gyms were surveyed annually between 1998 and 2005, and again in 2008 (n = 6064; range, 482–834 per year). Information was collected on human immunodeficiency virus (HIV) status of the respondent, unprotected anal intercourse (UAI) in the previous 3 months, type (main or casual) and HIV status of partner for UAI. Nonconcordant UAI (ncUAI) was defined as UAI with a partner of unknown or discordant HIV status. Concordant UAI (cUAI) was defined as UAI with a partner of the same HIV status (“serosorting”). Results: Between 1998 and 2008, the percentage of men reporting UAI increased from 24.3% to 36.6% (P = 0.07). This overall increase concealed important differences between nonconcordant and concordant UAI. While the percentage of men engaging in cUAI increased steadily between 1998 and 2008 (9.8%, 20.8%; P = 0.01), the percentage reporting ncUAI increased between 1998 and 2001 (14.5%, 23.7%; P < 0.001), decreased between 2001 and 2005 (23.7%, 15.6%; P < 0.001), and then leveled off between 2005 and 2008 (15.6%, 15.7%; P = 0.2). However, the percentage of men reporting ncUAI with a main partner increased between 2005 and 2008 for HIV-positive men (2.5%, 8.1%; P < 0.05) and HIV negative men (2.1%, 5.5%; P = 0.06). While the percentage of HIV negative men who reported cUAI with a main partner (i.e., serosorting) increased between 1998 and 2008 (12.4%, 21.1%; P < 0.05), less than half established seroconcordance by testing together. Conclusions: The patterns of sexual behavior among London's gay men between 1998 and 2008 were dynamic and complex. Our data suggest that HIV risk with a main partner and HIV testing among couples should be given greater priority by health promotion programmes

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 Solomonoff’s 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

Labor Trafficking Victimization among Farmworkers in North Carolina: Role of Demographic Characteristics and Acculturation

Human trafficking is a hidden domestic and international problem of unknown numbers and unsubstantiated estimates. Most research on labor trafficking has focused on known cases through conducting stakeholder interviews and reviewing police and court case files. This limited prior research suggests that demographic characteristics and level of acculturation may impact one’s risk for labor trafficking victimization. However, these relationships have not been consistently demonstrated. The current research explores two primary research questions: (1) how prevalent is labor trafficking and other labor exploitation among farmworkers in North Carolina; and (2) do individual-level characteristics or circumstances place a person at greater risk of labor trafficking or other labor exploitation. This was accomplished by conducting 380 inperson interviews with migrant farmworkers in North Carolina. We used three strategies to identify migrant farmworkers: (1) attendance at community events; (2) lists of labor camps known to advocacy organizations; and (3) other public venues farmworkers visit. Based on descriptive statistics and a logistic regression analysis, we present results on the extent of farmworker abuse and exploitation, and discuss future research in this area

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

Women After War: Weaving Nostos in Homeric Epic and in the Twenty-First Century

While women play a circumscribed role in ancient epic, Homer\u27s Odyssey depicts both Helen and Penelope as undergoing their own forms of homecoming, or nostos, after the Trojan War: Helen returns to her husband Menelaus after experiencing the war firsthand at Troy and a ten-year separation; Penelope stays home, but Odysseus\u27 return is in many ways as much a challenge for her as it is for him and the Odyssey portrays her domestic ordeal as a form of heroic nostos. In this essay, I explore female ways of homecoming in the Odyssey and draw connections between Homeric heroines and members of Team Lioness returning home from Afghanistan and Iraq in the twenty-first century. The 2008 documentary Lioness gives voice to some of these women, the country\u27s first generation of female combat veterans, as they struggle to reconcile their experience of war in Iraq with their lives at home. While the ancient Greeks could not have conceived of women experiencing battle in the way the members of Team Lioness did, Helen\u27s and Penelope\u27s marginalized roles in the Odyssey open a window into the contemporary experience of women soldiers and veterans and provide ways of understanding the challenges of the trauma of war and female homecoming in the twenty-first century

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

Self-Reported Barriers of Middle-Aged and Older Adults Entering a Home-Based Physical Activity Program

The purpose of this study was to assess barriers experienced by mid-older adults upon entering a homebased, telephone-delivered physical activity (PA) program and examine differences in barriers for subgroups. Methods: Three hundred eighty four participants recruited from Tennessee, California, and Illinois for the Active Choices program, which was part of Active for Life®, completed one face-to-face counseling session and received follow-up telephone counseling. Barriers were analyzed qualitatively and quantitatively for subgroups of mid-older adults. Results: Personal, social, and environmental themes emerged as barriers. Lack of motivation was most salient for men while health barriers were more prominent for women; however, no significant differences were found between men and women. Both whites and African Americans reported lack of motivation as the most frequent barrier to PA. Health and weather barriers were more prominent for the oldest group of older adults. Few differences were reported by PA or weight status. Conclusions: In a large sample of mid-older adults varying in age, race, gender, and health status, multiple barriers to PA were reported. Differences across subgroups may have implications for future PA interventions