Embodied Active Learning of Relational State Abstractions for Bilevel Planning

State abstraction is an effective technique for planning in robotics environments with continuous states and actions, long task horizons, and sparse feedback. In object-oriented environments, predicates are a particularly useful form of state abstraction because of their compatibility with symbolic planners and their capacity for relational generalization. However, to plan with predicates, the agent must be able to interpret them in continuous environment states (i.e., ground the symbols). Manually programming predicate interpretations can be difficult, so we would instead like to learn them from data. We propose an embodied active learning paradigm where the agent learns predicate interpretations through online interaction with an expert. For example, after taking actions in a block stacking environment, the agent may ask the expert: "Is On(block1, block2) true?" From this experience, the agent learns to plan: it learns neural predicate interpretations, symbolic planning operators, and neural samplers that can be used for bilevel planning. During exploration, the agent plans to learn: it uses its current models to select actions towards generating informative expert queries. We learn predicate interpretations as ensembles of neural networks and use their entropy to measure the informativeness of potential queries. We evaluate this approach in three robotic environments and find that it consistently outperforms six baselines while exhibiting sample efficiency in two key metrics: number of environment interactions, and number of queries to the expert. Code: https://tinyurl.com/active-predicatesComment: Conference on Lifelong Learning Agents (CoLLAs) 202

China’s industrial policy fosters collusion

China’s economic growth is often attributed to the rapid proliferation of special economic zones (SEZ). New research suggests that gains to firms arising from the preferential tax and regulatory incentives for locating inside an SEZ, may come at a cost to consumers. Clustering may equally promote competition and collusion among firms in SEZs; could benefits from collusion outweigh the costs

Geography, ties and knowledge flows: evidence from citations in mathematics

Using data on academic citations, career and educational histories of mathematicians, and disaggregated distance data for the world's top 1000 math departments, we study how geography and ties affect knowledge flows among scholars. The ties we consider are co-authorship, past colocation, advisor-mediated relationships, and alma mater relationships (holding a Ph.D. from the institution where another scholar is affiliated). Logit regressions using fixed effects that control for subject similarity, article quality, and temporal lags, show linkages are strongly associated with citation. Controlling for ties generally halves the negative impact of geographic barriers on citations. Ties matter more for less prominent and more recent papers and show no decline in importance in recent years. The impact of distance - controlling for ties - has fallen and is statistically insignificant after 2004

Understanding brønsted-acid catalyzed monomolecular reactions of Alkanes in Zeolite Pores by combining insights from experiment and theory

Acidic zeolites are effective catalysts for the cracking of large hydrocarbon molecules into lower molecular weight products required for transportation fuels. However, the ways in which the zeolite structure affects the catalytic activity at BrOnsted protons are not fully understood. One way to characterize the influence of the zeolite structure on the catalysis is to study alkane cracking and dehydrogenation at very low conversion, conditions for which the kinetics are well defined. To understand the effects of zeolite structure on the measured rate coefficient (k(app)), it is necessary to identify the equilibrium constant for adsorption into the reactant state (Kads-H+) and the intrinsic rate coefficient of the reaction (k(int)) at reaction temperatures, since k(app) is proportional to the product of Kads-H+ and k(int). We show that Kads-H+ cannot be calculated from experimental adsorption data collected near ambient temperature, but can, however, be estimated accurately from configurational-bias Monte Carlo (CBMC) simulations. Using monomolecular cracking and dehydrogenation of C-3-C-6 alkanes as an example, we review recent efforts aimed at elucidating the influence of the acid site location and the zeolite framework structure on the observed values of k(app) and its components, Kads-H+ and k(int)

Genetic and clinical assessment of 2009 pandemic influenza in southern China

Introduction: South China has a proven role in the global epidemiology of previous influenza outbreaks due to its dual seasonal pattern. We present the virologic, genetic and clinical characterization of pandemic H1N1 influenza infection (pH1N1) in Shantou and Nanchang, cities in southern China, during the second wave of the 2009-2010 pandemic. Methodology: Nasopharyngeal swabs were collected from 165 individuals with influenza-like illness (ILI) who presented to the hospitals in Shantou and Nanchang. Laboratory diagnosis and characterization was performed by real-time PCR, virus isolation in embryonated chicken eggs, and sequencing. Results: pH1N1 activity was sustained in three different temporal patterns throughout the study period. The overall positivity rate of pH1N1 was 50% with major distribution among young adults between the ages of 13 and 30 years. High fever, cough, expectoration, chest pain, myalgia, nasal discharge and efficient viral replication were observed as major clinical markers whereas a substantial number of afebrile cases (17%) was also observed. Rate of hospitalization and disease severity (39%) and recovery (100%) were also high within the region. Furthermore, severe complications were likely to develop in young adults upon pH1N1 infection. Genetic characterization of the HA and NA genes of pH1N1 strains exhibited homogenous spread of pH1N1 strains with 99% identity with prototypic strains; however, minor unique mutations were also observed in the HA gene. Conclusion: The study illustrates the detailed characteristics of 2009 influenza pandemic in southern parts of China that might help to strategize preparedness for future pandemics and subsequent influenza seasons.</br

Borders and Distance in Knowledge Spillovers: Dying Over Time or Dying with Age? - Evidence from Patent Citations

This paper explores the effects of distance as well as subnational and national borders on international and intranational knowledge spillovers through patent citations across the 39 most patent-cited countries and 319 metropolitan statistical areas (MSAs) within the U.S. In contrast to previous findings that knowledge localization fades over time, border and distance effects increase over time for the same-age citations. This increasing effect of borders and distance is associated with strengthened knowledge agglomeration over time. Nevertheless, both border and distance effects decrease with the age of patents. Aggregate border effects are often overestimated due to various aggregation bias. Moreover, industrial specialization and business travels effectively attenuate the effect of subnational borders in knowledge flows

International Trade, Technology Diffusion, and the Role of Diffusion Barriers

This paper assesses the welfare impact of trade and technology diffusion as well as the change in the cross-country distribution of GDP due to removal of trade costs and diffusion barriers. The model extends the multi-country Ricardian trade model of Alvarez and Lucas (2007) to include technology diffusion with diffusion barriers. A key feature of the model is that some countries export goods produced by foreign technology via diffusion. The model is calibrated to match the world GDP distribution, the merchandise trade and technology diffusion shares of GDP, and real GDP per capita for a sample of 31 countries. Data on international trade in royalties, license fees, and information intensive services are used as proxies for international technology diffusion. There are three key findings. First, the welfare gains from removing diffusion barriers are 4--60% across countries, generally larger than the gains from removing trade costs (8--40%). The main reason is that diffusion has a larger impact on the nontradable sector due to the substitutability between trade and diffusion in the tradable sector. Second, removing trade costs and diffusion barriers has little impact on reducing the dispersion of real GDP per capita (measured by Gini index) across countries. Compared to the benchmark, free diffusion decreases the Gini by 4%, and free trade decreases the Gini by 2%. Third, removing diffusion barriers increases trade, which indicates that diffusion may enhance trade

International Trade, Technology Diffusion, and the Role of Diffusion Barriers

This paper assesses the welfare impact of trade and technology diffusion as well as the change in the cross-country distribution of GDP due to removal of trade costs and diffusion barriers. The model extends the multi-country Ricardian trade model of Alvarez and Lucas (2007) to include technology diffusion with diffusion barriers. A key feature of the model is that some countries export goods produced by foreign technology via diffusion. The model is calibrated to match the world GDP distribution, the merchandise trade and technology diffusion shares of GDP, and real GDP per capita for a sample of 31 countries. Data on international trade in royalties, license fees, and information intensive services are used as proxies for international technology diffusion. There are three key findings. First, the welfare gains from removing diffusion barriers are 4--60% across countries, generally larger than the gains from removing trade costs (8--40%). The main reason is that diffusion has a larger impact on the nontradable sector due to the substitutability between trade and diffusion in the tradable sector. Another reason is that diffusion barriers are generally larger than trade costs. Second, removing trade costs and diffusion barriers has little impact on reducing the dispersion of real GDP per capita (measured by Gini index) across countries. Compared to the benchmark, free diffusion decreases the Gini by 4%, and free trade decreases the Gini by 2%. Third, removing diffusion barriers increases trade, which indicates that diffusion may enhance trade