43,263 research outputs found
Formalization of the fundamental group in untyped set theory using auto2
Full text linkWe present a new framework for formalizing mathematics in untyped set theory
using auto2. Using this framework, we formalize in Isabelle/FOL the entire
chain of development from the axioms of set theory to the definition of the
fundamental group for an arbitrary topological space. The auto2 prover is used
as the sole automation tool, and enables succinct proof scripts throughout the
project.Comment: 17 pages, accepted for ITP 201
An Empirical Study of 'Fringe Benefits' and Performance of the Korean Firms
Get PDFThis paper examines the effects of fringe benefits in the compensation package on performance of the Korean firms. Theoretically, fringe benefits have two implications in relation to employees: they are effective instruments that provide incentives; at the same time, some fringe benefits, especially the power-related benefits, are often used for exploitation of self-interests. Using a six-year panel data of the Korean manufacturing firms, we do a regression analysis and identify the links between fringe benefits and performance of the Korean firms. Our results suggest that, in general, these types of compensations do not promote good performance of firms. The results also imply that perhaps some designs in pay for performance in Korea are not efficient.published_or_final_versio
Using Unobserved Causes to Explain Unexpected Outcomes: The Effect of Existing Causal Knowledge on Protection From Extinction by a Hidden Cause
Full text linkPeople often rely on the covariation between events to infer causality. However, covariation between cues and outcomes may change over time. In the associative learning literature, extinction provides a model to study updating of causal beliefs when a previously established relationship no longer holds. Prediction error theories can explain both extinction and protection from extinction when an inhibitory (preventive) cue is present during extinction. In three experiments using the allergist causal learning task, we found that protection could also be achieved by a hidden cause that was inferred but not physically present, so long as that cause was a plausible preventer of the outcome. We additionally showed complete protection by a physically presented cue that was neutral rather than inhibitory at the outset of extinction. Both findings are difficult to reconcile with dominant prediction error theories. However, they are compatible with the idea of theory protection, where the learner attributes the absence of the outcome to the added cue (when present) or to a hidden cause, and therefore does not need to revise causal beliefs about A. Our results suggest that prediction error encourages changes in causal beliefs, but the nature of the change is determined by reasoning processes that incorporate existing knowledge of causal mechanisms and may be biased toward preservation of existing beliefs
Sustainable built asset management performance indicators and attributes : a UK social housing case study example
Get PDFThis paper aims to identify key performance indicators (KPI), and their corresponding
attributes, required to successfully manage asset management sustainably in a built environment
context. Improving the sustainability of existing housing stock is a major challenge facing the UK social
housing sector. There is a lack of support to navigate the growing and often incongruent information
relating to sustainable development and how to operationalise it. The problem is twofold; firstly, the
current (single criterion) condition-based approach to maintenance planning constrains Asset
Managers and does not fully address the social, environmental and economic aspects of sustainability.
Secondly, the toolkits available for assessing the sustainability of housing are often generic and are
time consuming and expensive to implement. This paper reports the findings of a participatory
research project with a leading London based housing association, using a series of landlord and
tenant workshops to derive a set of attributes associated with key performance indicators (KPIs) to
fully reflect the local requirements of the landlord and their interpretation of the sustainability
agenda. Five KPIs considered to be measurable, directly affected by maintenance work and
independent of each other were identified by this landlord (comfort, running costs, adaptability,
maintenance costs and community).The resulting outputs, in a policy context, will provide a clear
route-map to social housing landlords of how to improve the sustainability of their housing stock with
the additional benefits of addressing fuel poverty, carbon emissions targets whilst at the same time
help create and maintain housing in which people want to live. The proposed approach is flexible
enough to incorporate the individual requirements of landlords, be able to adapt to changes in
government policy (local and central) in a timely, robust, transparent and inclusive format
Retardation of Acquisition After Conditioned Inhibition and Latent Inhibition Training in Human Causal Learning
Full text linkInhibitory stimuli are slow to acquire excitatory properties when paired with the outcome in a retardation test. However, this pattern is also seen after simple nonreinforced exposure: latent inhibition. It is commonly assumed that retardation would be stronger for a conditioned inhibitor than for a latent inhibitor, but there is surprisingly little empirical evidence comparing the two in either animals or humans. Thus, retardation after inhibitory training could in principle be attributable entirely to latent inhibition. We directly compared the speed of excitatory acquisition after conditioned inhibition and matched latent inhibition training in human causal learning. Conditioned inhibition training produced stronger transfer in a summation test, but the two conditions did not differ substantially in a retardation test. We offer two explanations for this dissociation. One is that learned predictiveness attenuated the latent inhibition that otherwise would have occurred during conditioned inhibition training, so that retardation in that condition was primarily due to inhibition. The second explanation is that inhibitory learning in these experiments was hierarchical in nature, similar to negative occasion-setting. By this account, the conditioned inhibitor was able to negatively modulate the test excitor in a summation test, but was no more retarded than a latent inhibitor in its ability to form a direct association with the outcome
Inhibitory Summation as a Form of Generalization
Full text linkInhibitory learning after feature negative training (Aþ/AB–) is typically measured by combining the Feature B with a separately trained excitor (e.g., C) in a summation test. Reduced responding to C is taken as evidence that B has properties directly opposite to those of C. However, in human causal learning, transfer of B’s inhibitory properties to another excitor is modest and depends on individual differences in inferred causal structure. Here we ask whether instead of opposing processes, a summation test might instead be thought of in terms of generalization. Using an allergist task, we tested whether inhibitory transfer would be influenced by similarity. We found that transfer was greater when the test stimuli were from the same semantic category as the training stimuli (Experiments 1 and 2) and when the test excitor had previously been associated with the same outcome (Experiment 3). We also found that the similarity effect applied across all self-reported causal structures. We conclude it may be more helpful to consider transfer of inhibition as a form of conceptual generalization rather than the arithmetic summation of opposing processe
Network-analysis-guided synthesis of weisaconitine D and liljestrandinine.
Get PDFGeneral strategies for the chemical synthesis of organic compounds, especially of architecturally complex natural products, are not easily identified. Here we present a method to establish a strategy for such syntheses, which uses network analysis. This approach has led to the identification of a versatile synthetic intermediate that facilitated syntheses of the diterpenoid alkaloids weisaconitine D and liljestrandinine, and the core of gomandonine. We also developed a web-based graphing program that allows network analysis to be easily performed on molecules with complex frameworks. The diterpenoid alkaloids comprise some of the most architecturally complex and functional-group-dense secondary metabolites isolated. Consequently, they present a substantial challenge for chemical synthesis. The synthesis approach described here is a notable departure from other single-target-focused strategies adopted for the syntheses of related structures. Specifically, it affords not only the targeted natural products, but also intermediates and derivatives in the three families of diterpenoid alkaloids (C-18, C-19 and C-20), and so provides a unified synthetic strategy for these natural products. This work validates the utility of network analysis as a starting point for identifying strategies for the syntheses of architecturally complex secondary metabolites
Biochemical properties of Paracoccus denitrificans FnrP:Reactions with molecular oxygen and nitric oxide
Get PDFIn Paracoccus denitrificans, three CRP/FNR family regulatory proteins, NarR, NnrR and FnrP, control the switch between aerobic and anaerobic (denitrification) respiration. FnrP is a [4Fe-4S] cluster containing homologue of the archetypal O2 sensor FNR from E. coli and accordingly regulates genes encoding aerobic and anaerobic respiratory enzymes in response to O2, and also NO, availability. Here we show that FnrP undergoes O2-driven [4Fe-4S] to [2Fe-2S] cluster conversion that involves up to 2 O2 per cluster, with significant oxidation of released cluster sulfide to sulfane observed at higher O2 concentrations. The rate of the cluster reaction was found to be ~6-fold lower than that of E. coli FNR, suggesting that FnrP can remain transcriptionally active under microaerobic conditions. This is consistent with a role for FnrP in activating expression of the high O2 affinity cytochrome c oxidase under microaerobic conditions. Cluster conversion resulted in dissociation of the transcriptionally active FnrP dimer into monomers. Therefore, along with E. coli FNR, FnrP belongs to the subset of FNR proteins in which cluster type is correlated with association state. Interestingly, two key charged residues, Arg140 and Asp154, that have been shown to play key roles in the monomer-dimer equilibrium in E. coli FNR are not conserved in FnrP, indicating that different protomer interactions are important for this equilibrium. Finally, the FnrP [4Fe-4S] cluster is shown to undergo reaction with multiple NO molecules, resulting in iron nitrosyl species and dissociation into monomers
Formulation and performance of variational integrators for rotating bodies
Get PDFVariational integrators are obtained for two mechanical systems whose configuration spaces are, respectively, the rotation group and the unit sphere. In the first case, an integration algorithm is presented for Euler’s equations of the free rigid body, following the ideas of Marsden et al. (Nonlinearity 12:1647–1662, 1999). In the second example, a variational time integrator is formulated for the rigid dumbbell. Both methods are formulated directly on their nonlinear configuration spaces, without using Lagrange multipliers. They are one-step, second order methods which show exact conservation of a discrete angular momentum which is identified in each case. Numerical examples illustrate their properties and compare them with existing integrators of the literature
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