A Bivariate Measure of Redundant Information

We define a measure of redundant information based on projections in the space of probability distributions. Redundant information between random variables is information that is shared between those variables. But in contrast to mutual information, redundant information denotes information that is shared about the outcome of a third variable. Formalizing this concept, and being able to measure it, is required for the non-negative decomposition of mutual information into redundant and synergistic information. Previous attempts to formalize redundant or synergistic information struggle to capture some desired properties. We introduce a new formalism for redundant information and prove that it satisfies all the properties necessary outlined in earlier work, as well as an additional criterion that we propose to be necessary to capture redundancy. We also demonstrate the behaviour of this new measure for several examples, compare it to previous measures and apply it to the decomposition of transfer entropy.Comment: 16 pages, 15 figures, 1 table, added citation to Griffith et al 2012, Maurer et al 199

Accelerating Empowerment Computation with UCT Tree Search

Models of intrinsic motivation present an important means to produce sensible behaviour in the absence of extrinsic rewards. Applications in video games are varied, and range from intrinsically motivated general game-playing agents to non-player characters such as companions and enemies. The information-theoretic quantity of Empowerment is a particularly promising candidate motivation to produce believable, generic and robust behaviour. However, while it can be used in the absence of external reward functions that would need to be crafted and learned, empowerment is computationally expensive. In this paper, we propose a modified UCT tree search method to mitigate empowerment's computational complexity in discrete and deterministic scenarios. We demonstrate how to modify a Monte-Carlo Search Tree with UCT to realise empowerment maximisation, and discuss three additional modifications that facilitate better sampling. We evaluate the approach both quantitatively, by analysing how close our approach gets to the baseline of exhaustive empowerment computation with varying amounts of computational resources, and qualitatively, by analysing the resulting behaviour in a Minecraft-like scenario

Impact vaporization and Condensation: Laser Irradiation Experiments with Natural Planetary Materials

0000-0002-4414-4917The attached files are the published version of the article from the 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083), and the open access abstract (Geophysical Research Abstracts, Vol. 20, EGU2018-16223, 2018, EGU General Assembly 2018, © Author(s) 2018. CC Attribution 4.0 license.

Measuring Time with Minimal Clocks

© 2019 Massachusetts Institute of Technology. This is the accepted manuscript version of an article which has been published in final form at https://doi.org/10.1162/artl_a_00303Being able to measure time, whether directly or indirectly, is a significant advantage for an organism. It allows for timely reaction to regular or predicted events, reducing the pressure for fast processing of sensory input. Thus, clocks are ubiquitous in biology. In the present article, we consider minimal abstract pure clocks in different configurations and investigate their characteristic dynamics. We are especially interested in optimally time-resolving clocks. Among these, we find fundamentally diametral clock characteristics, such as oscillatory behavior for purely local time measurement or decay-based clocks measuring time periods on a scale global to the problem. We include also sets of independent clocks (clock bags), sequential cascades of clocks, and composite clocks with controlled dependence. Clock cascades show a condensation effect, and the composite clock shows various regimes of markedly different dynamics.Peer reviewe

Expanding the Active Inference Landscape: More Intrinsic Motivations in the Perception-Action Loop

Active inference is an ambitious theory that treats perception, inference, and action selection of autonomous agents under the heading of a single principle. It suggests biologically plausible explanations for many cognitive phenomena, including consciousness. In active inference, action selection is driven by an objective function that evaluates possible future actions with respect to current, inferred beliefs about the world. Active inference at its core is independent from extrinsic rewards, resulting in a high level of robustness across e.g., different environments or agent morphologies. In the literature, paradigms that share this independence have been summarized under the notion of intrinsic motivations. In general and in contrast to active inference, these models of motivation come without a commitment to particular inference and action selection mechanisms. In this article, we study if the inference and action selection machinery of active inference can also be used by alternatives to the originally included intrinsic motivation. The perception-action loop explicitly relates inference and action selection to the environment and agent memory, and is consequently used as foundation for our analysis. We reconstruct the active inference approach, locate the original formulation within, and show how alternative intrinsic motivations can be used while keeping many of the original features intact. Furthermore, we illustrate the connection to universal reinforcement learning by means of our formalism. Active inference research may profit from comparisons of the dynamics induced by alternative intrinsic motivations. Research on intrinsic motivations may profit from an additional way to implement intrinsically motivated agents that also share the biological plausibility of active inference

Designing Chatbots for Crises: A Case Study Contrasting Potential and Reality

Chatbots are becoming ubiquitous technologies, and their popularity and adoption are rapidly spreading. The potential of chatbots in engaging people with digital services is fully recognised. However, the reputation of this technology with regards to usefulness and real impact remains rather questionable. Studies that evaluate how people perceive and utilise chatbots are generally lacking. During the last Kenyan elections, we deployed a chatbot on Facebook Messenger to help people submit reports of violence and misconduct experienced in the polling stations. Even though the chatbot was visited by more than 3,000 times, there was a clear mismatch between the users’ perception of the technology and its design. In this paper, we analyse the user interactions and content generated through this application and discuss the challenges and directions for designing more effective chatbots

A sigmoidal fit for pressure-volume curves of idiopathic pulmonary fibrosis patients on mechanical ventilation: clinical implications

OBJECTIVE: Respiratory pressure-volume curves fitted to exponential equations have been used to assess disease severity and prognosis in spontaneously breathing patients with idiopathic pulmonary fibrosis. Sigmoidal equations have been used to fit pressure-volume curves for mechanically ventilated patients but not for idiopathic pulmonary fibrosis patients. We compared a sigmoidal model and an exponential model to fit pressure-volume curves from mechanically ventilated patients with idiopathic pulmonary fibrosis. METHODS: Six idiopathic pulmonary fibrosis patients and five controls underwent inflation pressure-volume curves using the constant-flow technique during general anesthesia prior to open lung biopsy or thymectomy. We identified the lower and upper inflection points and fit the curves with an exponential equation, V = A-B.e-k.P, and a sigmoid equation, V = a+b/(1+e-(P-c)/d). RESULTS: The mean lower inflection point for idiopathic pulmonary fibrosis patients was significantly higher (10.5 ± 5.7 cm H2O) than that of controls (3.6 ± 2.4 cm H2O). The sigmoidal equation fit the pressure-volume curves of the fibrotic and control patients well, but the exponential equation fit the data well only when points below 50% of the inspiratory capacity were excluded. CONCLUSION: The elevated lower inflection point and the sigmoidal shape of the pressure-volume curves suggest that respiratory system compliance is decreased close to end-expiratory lung volume in idiopathic pulmonary fibrosis patients under general anesthesia and mechanical ventilation. The sigmoidal fit was superior to the exponential fit for inflation pressure-volume curves of anesthetized patients with idiopathic pulmonary fibrosis and could be useful for guiding mechanical ventilation during general anesthesia in this condition

The mineralogy and alteration history of the Yamato-type (CY) carbonaceous chondrites

The CY chondrites are a group of thermally metamorphosed carbonaceous chondrites. Although they share similarities with the CM and CI chondrites, their primary properties argue for a distinct classification. Previous studies have highlighted their isotopically heavy bulk compositions (δ17O =10‰, δ18O=21‰, Δ17O =0‰) and exceptionally high sulphide abundances (10–30vol%). In this work we explore their petrography and alteration history. The CYs accreted low abundances of chondrules (15–20 area%) with average apparent diameters slightly larger (∼320–340µm) than the CM chondrites. In contrast to the CMs, the CYs record an early episode of brecciation prior to the main window of aqueous alteration. Subsequent fluid activity produced a range of alteration extents with both CY2 and CY1 chondrites documented. Phyllosilicate minerals in the CYs were a mix of serpentine and saponite (including occurrences of Na-saponite) with minor quantities of chlorite (within chondrules). An initial generation of Fe-sulphides formed by sulfidation of metal, and by precipitation from S-rich fluids. Three generations of carbonates are recognized, an early generation that infilled voids left by brecciation and co-precipitated with sulphide, a later generation that co-precipitated with magnetite and a final Fe-Mg-bearing generation which formed large (>100 µm) clasts. Only the first-generation carbonates are found in the CY2s, while the CY1s preserve all three generations. Phosphates occur as Ca-apatite or rarely as Mg-bearing apatite and have hydroxylapatite compositions, indicating low halogen activities in the alteration fluids. Refractory oxides (ilmenite and Cr-spinel) occur as precipitates adhering to the margins of phyllosilicates. They formed late in the alteration sequence and attest to oxidizing conditions. During the late-stages of aqueous alteration Fe-sulphides were replaced by magnetite. Thermal metamorphism (Stage II-IV: ∼300–750 °C) overprinted aqueous alteration leading to dehydration and recrystallization of the phyllosilicate matrix and the decomposition of some carbonate phases. Most Fe-sulphide grains survived heating without decomposition as initial partial decomposition from pyrrhotite to troilite under closed system conditions led to elevated ƒS2 gas and resulted in a stabilizing effect. Retrograde reactions between trapped S2 gas and metal/magnetite formed a final generation of Fe-sulphides. The survival of Fe-sulphides and their stochiometric troilite compositions are evidence for near-closed system heating. Analysis of organic matter by Raman spectroscopy supports an interpretation of short-duration heating (on the scale of minutes to days), at peak temperatures between 750 and 900°C. Thus, an impact event was the most likely cause of metamorphic heating

The effects of exercise training in a weight loss lifestyle intervention on asthma control, quality of life and psychosocial symptoms in adult obese asthmatics: protocol of a randomized controlled trial

Abstract\ud \ud Background\ud Asthma and obesity are public health problems with increasing prevalence worldwide. Clinical and epidemiologic studies have demonstrated that obese asthmatics have worse clinical control and health related quality of life (HRQL) despite an optimized medical treatment. Bariatric surgery is successful to weight-loss and improves asthma control; however, the benefits of nonsurgical interventions remain unknown.\ud \ud \ud Methods/Design\ud This is a randomized controlled trial with 2-arms parallel. Fifty-five moderate or severe asthmatics with grade II obesity (BMI ≥ 35 kg/m2) under optimized medication will be randomly assigned into either weight-loss program + sham (WL + S group) or weight-loss program + exercise (WL + E group). The weight loss program will be the same for both groups including nutrition and psychological therapies (every 15 days, total of 6 sessions, 60 min each). Exercise program will include aerobic and resistance muscle training while sham treatment will include a breathing and stretching program (both programs twice a week, 3 months, 60 min each session). The primary outcome variable will be asthma clinical control. Secondary outcomes include HRQL, levels of depression and anxiety, lung function, daily life physical activity, body composition, maximal aerobic capacity, strength muscle and sleep disorders. Potential mechanism (changes in lung mechanical and airway/systemic inflammation) will also be examined to explain the benefits in both groups.\ud \ud \ud Discussion\ud This study will bring a significant contribution to the literature evaluating the effects of exercise conditioning in a weight loss intervention in obese asthmatics as well as will evaluate possible involved mechanisms.\ud \ud \ud Trial registration\ud \ud \ud NCT02188940The study was supported by the São Paulo Research Foundation (FAPESP;\ud Grants 2012/16700-9 and 2012/16134-3) and Conselho Nacional de Pesquisa (CNPq Grants 485065/2012-6)