12,333 research outputs found

    On the mechanical simulation of habit-forming and learning

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    This paper discusses digital techniques by which habit-forming and learning may be simulated. After classifying the types of simulation mechanisms it discusses types of habit-forming and learning to be simulated, focusing attention upon reinforcement. It uses the language of computer programming to describe the flow of control, and the language of mathematical probability to analyze the effect of various reinforcement functions on the asymptotic behavior of simulating programs. It shows further, again in programming terms, how the “delayed random selector” part of the simulating process may be “factored out” as a separate unit applicable either to habit-forming or learning, which latter are distinguished by whether the reinforcements are applied immediately or upon “comparison with a goal.”Several reinforcement models are considered, including the “linear asymptotic” model used extensively by Bush and Mosteller, two simple “absorbing boundary” models, and a “nonlinear asymptotic” model currently being investigated by Bush, Galanter, and Luce. A sketch is given of the Harris-Bellman-Shapiro analysis of the linear asymptotic model. Contrasted with this, a complete analysis is given of the simpler absorbing boundary model, with explicit proof of eventual absorption, and formulae for probability of absorption in n trials, and the expected number of steps to absorption. Finally, a special example is given of the second absorbing boundary model to show how its structure differs from the others

    Expectations, Learning and Macroeconomic Persistence

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    This paper presents an estimated model with learning and provides evidence that learning can improve the fit of popular monetary DSGE models and endogenously generate realistic levels of persistence. The paper starts with an agnostic view, developing a model that nests learning and some of the structural sources of persistence, such as habit formation in consumption and inflation indexation, that are typically needed in monetary models with rational expectations to match the persistence of macroeconomic variables. I estimate the model by likelihood-based Bayesian methods, which allow the estimation of the learning gain coefficient jointly with the "deep" parameters of the economy. The empirical results show that when learning replaces rational expectations, the estimated degrees of habits and indexation drop near zero. This ?nding suggests that persistence arises in the model economy mainly from expectations and learning. The posterior model probabilities show that the specification with learning fits significantly better than does the specification with rational expectations. Finally, if learning rather than mechanical sources of persistence provides a more appropriate representation of the economy, the implied optimal policy will be different. The policymaker will also incur substantial costs from misspecifying private expectations formation.Persistence, Constant-gain learning, Expectations, Habit formation in consumption, Inflation inertia; Phillips curve; Bayesian econometrics; New-Keynesian model.

    THE IMAGINATIVE REHEARSAL MODEL – DEWEY, EMBODIED SIMULATION, AND THE NARRATIVE HYPOTHESIS

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    In this contribution I outline some ideas on what the pragmatist model of habit ontology could offer us as regards the appreciation of the constitutive role that imagery plays for social action and cognition. Accordingly, a Deweyan understanding of habit would allow for an understanding of imagery in terms of embodied cognition rather than in representational terms. I first underline the motor character of imagery, and the role its embodiment in habit plays for the anticipation of action. Secondly, I reconstruct Dewey's notion of imaginative rehearsal in light of contemporary, competing models of intersubjectivity such as embodied simulation theory and the narrative practice hypothesis, and argue that the Deweyan model offers us a more encompassing framework which can be useful for reconciling these approaches. In this text I am mainly concerned with sketching a broad picture of the lines along which such a project could be developed. For this reason not all questions are given equal attention, and I shall concentrate mainly on the basic ideas, without going directly into the details of many of them

    Expectations, Learning and Macroeconomic Persistence

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    This paper presents an estimated model with learning and provides evidence that learning can improve the fit of popular monetary DSGE models and endogenously generate realistic levels of persistence. The paper starts with an agnostic view, developing a model that nests learning and some of the structural sources of persistence, such as habit formation in consumption and inflation indexation, that are typically needed in monetary models with rational expectations to match the persistence of macroeconomic variables. I estimate the model by likelihood-based Bayesian methods, which allow the estimation of the learning gain coefficient jointly with the `deep' parameters of the economy. The empirical results show that when learning replaces rational expectations, the estimated degrees of habits and indexation drop near zero. This finding suggests that persistence arises in the model economy mainly from expectations and learning. The posterior model probabilities show that the specification with learning fits significantly better than does the specification with rational expectations. Finally, if learning rather than mechanical sources of persistence provides a more appropriate representation of the economy, the implied optimal policy will be different. The policymaker will also incur substantial costs from misspecifying private expectations formation.persistence, constant-gain learning, expectations, habit formation in consumption, inflation inertia, Phillips curve, Bayesian econometrics, New-Keynesian model.

    Learning and judgment shocks in U.S. business cycles

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    This paper examines the role of judgment shocks in combination with other structural shocks in explaining post-war economic volatility within the context of a New Keynesian model. Agents form expectations using constant gain learning then augment these forecasts with judgment. These judgments may be interpreted as a reaction to current news stories or policy announcements that would influence people's expectations. I allow for the possibility that these judgments be informatively based on information about structural shocks, but judgment itself may also be subject to its own stochastic shocks. I estimate a standard New Keynesian model that includes these shocks using Bayesian simulation methods. To aid in identifying expectational shocks from other structural shocks I include data on professional forecasts along with data on output gap, inflation, and interest rates. I find judgment is largely not informed by macroeconomic fundamentals; most of the variability in judgment is explained by its own stochastic shocks. Impulse response functions from the estimated model illustrate how shocks to judgment destabilize the economy and explain business cycle fluctuations.Learning; judgment; add-factors; New Keynesian model; Metropolis-Hastings

    Ab initio Modelling of the Early Stages of Precipitation in Al-6000 Alloys

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    Age hardening induced by the formation of (semi)-coherent precipitate phases is crucial for the processing and final properties of the widely used Al-6000 alloys. Early stages of precipitation are particularly important from the fundamental and technological side, but are still far from being fully understood. Here, an analysis of the energetics of nanometric precipitates of the meta-stable β′′\beta'' phases is performed, identifying the bulk, elastic strain and interface energies that contribute to the stability of a nucleating cluster. Results show that needle-shape precipitates are unstable to growth even at the smallest size β′′\beta'' formula unit, i.e. there is no energy barrier to growth. The small differences between different compositions points toward the need for the study of possible precipitate/matrix interface reconstruction. A classical semi-quantitative nucleation theory approach including elastic strain energy captures the trends in precipitate energy versus size and composition. This validates the use of mesoscale models to assess stability and interactions of precipitates. Studies of smaller 3d clusters also show stability relative to the solid solution state, indicating that the early stages of precipitation may be diffusion-limited. Overall, these results demonstrate the important interplay among composition-dependent bulk, interface, and elastic strain energies in determining nanoscale precipitate stability and growth

    Optical Mineralogy in a Modern Earth Sciences Curriculum

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    Provides pedagogical insight concerning the skill of studying minerals The resource being annotated is: http://www.dlese.org/dds/catalog_SERC-NAGT-000-000-000-651.htm

    Affective neuroscience, emotional regulation, and international relations

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    International relations (IR) has witnessed an emerging interest in neuroscience, particularly for its relevance to a now widespread scholarship on emotions. Contributing to this scholarship, this article draws on the subfields of affective neuroscience and neuropsychology, which remain largely unexplored in IR. Firstly, the article draws on affective neuroscience in illuminating affect's defining role in consciousness and omnipresence in social behavior, challenging the continuing elision of emotions in mainstream approaches. Secondly, it applies theories of depth neuropsychology, which suggest a neural predisposition originating in the brain's higher cortical regions to attenuate emotional arousal and limit affective consciousness. This predisposition works to preserve individuals' self-coherence, countering implicit assumptions about rationality and motivation within IR theory. Thirdly, it outlines three key implications for IR theory. It argues that affective neuroscience and neuropsychology offer a route towards deep theorizing of ontologies and motivations. It also leads to a reassessment of the social regulation of emotions, particularly as observed in institutions, including the state. It also suggests a productive engagement with constructivist and poststructuralist approaches by addressing the agency of the body in social relations. The article concludes by sketching the potential for a therapeutically-attuned approach to IR
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