Feedback information and the reward positivity

The reward positivity is a component of the event-related brain potential (ERP) sensitive to neural mechanisms of reward processing. Multiple studies have demonstrated that reward positivity amplitude indices a reward prediction error signal that is fundamental to theories of reinforcement learning. However, whether this ERP component is also sensitive to richer forms of performance information important for supervised learning is less clear. To investigate this question, we recorded the electroencephalogram from participants engaged in a time estimation task in which the type of error information conveyed by feedback stimuli was systematically varied across conditions. Consistent with our predictions, we found that reward positivity amplitude decreased in relation to increasing information content of the feedback, and that reward positivity amplitude was unrelated to trial-to-trial behavioral adjustments in task performance. By contrast, a series of exploratory analyses revealed frontal-central and posterior ERP components immediately following the reward positivity that related to these processes. Taken in the context of the wider literature, these results suggest that the reward positivity is produced by a neural mechanism that motivates task performance, whereas the later ERP components apply the feedback information according to principles of supervised learning

Public & Private Spillovers, Location and the Productivity of Pharmaceutical Research

While there is widespread agreement among economists and management scholars that knowledge spillovers exist and have important economic consequences, researchers know substantially less about the "micro mechanisms" of spillovers -- about the degree to which they are geographically localized, for example, or about the degree to which spillovers from public institutions are qualitatively different from those from privately owned firms (Jaffe, 1986; Krugman, 1991; Jaffe et al., 1993; Porter, 1990). In this paper we make use of the geographic distribution of the research activities of major global pharmaceutical firms to explore the extent to which knowledge spills over from proximate private and public institutions. Our data and empirical approach allow us to make advances on two dimensions. First, by focusing on spillovers in research productivity (as opposed to manufacturing productivity), we build closely on the theoretical literature on spillovers that suggests that knowledge externalities are likely to have the most immediate impact on the production of ideas (Romer, 1986; Aghion & Howitt, 1997). Second, our data allow us to distinguish spillovers from public research from spillovers from private, or competitively funded research, and to more deeply explore the role that institutions and geographic proximity play in driving knowledge spillovers.

Beyond dichotomies in reinforcement learning

Reinforcement learning (RL) is a framework of particular importance to psychology, neuroscience and machine learning. Interactions between these fields, as promoted through the common hub of RL, has facilitated paradigm shifts that relate multiple levels of analysis in a singular framework (for example, relating dopamine function to a computationally defined RL signal). Recently, more sophisticated RL algorithms have been proposed to better account for human learning, and in particular its oft-documented reliance on two separable systems: a model-based (MB) system and a model-free (MF) system. However, along with many benefits, this dichotomous lens can distort questions, and may contribute to an unnecessarily narrow perspective on learning and decision-making. Here, we outline some of the consequences that come from overconfidently mapping algorithms, such as MB versus MF RL, with putative cognitive processes. We argue that the field is well positioned to move beyond simplistic dichotomies, and we propose a means of refocusing research questions towards the rich and complex components that comprise learning and decision-making

Divergence-Free Adaptive Mesh Refinement for Magnetohydrodynamics

In this paper we present a full-fledged scheme for the second order accurate, divergence-free evolution of vector fields on an adaptive mesh refinement (AMR) hierarchy. We focus here on adaptive mesh MHD. The scheme is based on making a significant advance in the divergence-free reconstruction of vector fields. In that sense, it complements the earlier work of Balsara and Spicer (1999) where we discussed the divergence-free time-update of vector fields which satisfy Stoke's law type evolution equations. Our advance in divergence-free reconstruction of vector fields is such that it reduces to the total variation diminishing (TVD) property for one-dimensional evolution and yet goes beyond it in multiple dimensions. Divergence-free restriction is also discussed. An electric field correction strategy is presented for use on AMR meshes. The electric field correction strategy helps preserve the divergence-free evolution of the magnetic field even when the time steps are sub-cycled on refined meshes. The above-mentioned innovations have been implemented in Balsara's RIEMANN framework for parallel, self-adaptive computational astrophysics which supports both non-relativistic and relativistic MHD. Several rigorous, three dimensional AMR-MHD test problems with strong discontinuities have been run with the RIEMANN framework showing that the strategy works very well.Comment: J.C.P., figures of reduced qualit

Dark solitons in atomic Bose-Einstein condensates: from theory to experiments

This review paper presents an overview of the theoretical and experimental progress on the study of matter-wave dark solitons in atomic Bose-Einstein condensates. Upon introducing the general framework, we discuss the statics and dynamics of single and multiple matter-wave dark solitons in the quasi one-dimensional setting, in higher-dimensional settings, as well as in the dimensionality crossover regime. Special attention is paid to the connection between theoretical results, obtained by various analytical approaches, and relevant experimental observations.Comment: 82 pages, 13 figures. To appear in J. Phys. A: Math. Theor

Plasmodium falciparum Hep1 is required to prevent the self aggregation of PfHsp70-3

The majority of mitochondrial proteins are encoded in the nucleus and need to be imported from the cytosol into the mitochondria, and molecular chaperones play a key role in the efficient translocation and proper folding of these proteins in the matrix. One such molecular chaperone is the eukaryotic mitochondrial heat shock protein 70 (Hsp70); however, it is prone to self-aggregation and requires the presence of an essential zinc-finger protein, Hsp70-escort protein 1 (Hep1), to maintain its structure and function. PfHsp70-3, the only Hsp70 predicted to localize in the mitochondria of P. falciparum, may also rely on a Hep1 orthologue to prevent self-aggregation. In this study, we identified a putative Hep1 orthologue in P. falciparum and co-expression of PfHsp70-3 and PfHep1 enhanced the solubility of PfHsp70-3. PfHep1 suppressed the thermally induced aggregation of PfHsp70-3 but not the aggregation of malate dehydrogenase or citrate synthase, thus showing specificity for PfHsp70-3. Zinc ions were indeed essential for maintaining the function of PfHep1, as EDTA chelation abrogated its abilities to suppress the aggregation of PfHsp70-3. Soluble and functional PfHsp70-3, acquired by co-expression with PfHep-1, will facilitate the biochemical characterisation of this particular Hsp70 protein and its evaluation as a drug target for the treatment of malaria

Surveillance, performativity and normalised practice: the use and impact of graded lesson observations in Further Education colleges

In little over a decade, the observation of teaching and learning (OTL) has become the cornerstone of Further Education (FE) colleges’ quality systems for assuring and improving the professional skills and knowledge base of tutors. Yet OTL remains an under-researched area of inquiry with little known about the impact of its use on the professional identity, learning and development of FE tutors. This paper examines the specific practice of graded OTL and in so doing discusses findings from a mixed-methods study conducted in 10 colleges situated across the West Midlands region of England. Data from a questionnaire survey and semi-structured interviews were analysed within a theoretical framework that drew largely on aspects of Foucauldian theory as well as the twin phenomena of new managerialism and performativity. This analysis revealed how OTL has become normalised as a performative tool of managerialist systems designed to assure and improve standards, performance and accountability in teaching and learning. It is argued that FE has now outgrown graded OTL and it is time for a moratorium on its use. Colleges and tutors need to be given greater professional autonomy with regard to OTL and be allowed to develop their own systems that place professional learning and development at the forefront, rather than the requirements of performance management systems

Shop stewards’ leadership, left-wing activism and collective workplace union organisation

Providing an account of the dynamic interrelationship between shop steward leadership and membership interaction, Ralph Darlington focuses particular attention on the much-neglected crucial role that left-wing political activists can play in shaping the nature of collective workplace relations