62 research outputs found

    Geometry of Refractions and Reflections Through a Biperiodic Medium

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    Mechanistic models for West Nile virus transmission: a systematic review of features, aims and parametrization

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    Mathematical models within the Ross-Macdonald framework increasingly play a role in our understanding of vector-borne disease dynamics and as tools for assessing scenarios to respond to emerging threats. These threats are typically characterized by a high degree of heterogeneity, introducing a range of possible complexities in models and challenges to maintain the link with empirical evidence. We systematically identified and analysed a total of 77 published papers presenting compartmental West Nile virus (WNV) models that use parameter values derived from empirical studies. Using a set of 15 criteria, we measured the dissimilarity compared with the Ross-Macdonald framework. We also retrieved the purpose and type of models and traced the empirical sources of their parameters. Our review highlights the increasing refinements in WNV models. Models for prediction included the highest number of refinements. We found uneven distributions of refinements and of evidence for parameter values. We identified several challenges in parametrizing such increasingly complex models. For parameters common to most models, we also synthesize the empirical evidence for their values and ranges. The study highlights the potential to improve the quality of WNV models and their applicability for policy by establishing closer collaboration between mathematical modelling and empirical work

    Ergodic infinite group extensions of geodesic flows on translation surfaces

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    We show that generic infinite group extensions of geodesic flows on square tiled translation surfaces are ergodic in almost every direction, subject to certain natural constraints. Recently K. Fr\c{a}czek and C. Ulcigrai have shown that certain concrete staircases, covers of square-tiled surfaces, are not ergodic in almost every direction. In contrast we show the almost sure ergodicity of other concrete staircases. An appendix provides a combinatorial approach for the study of square-tiled surfaces

    Mind the gap: Balancing alliance network and technology portfolios during periods of technological uncertainty

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    While clique-embeddedness is generally considered to enhance firm performance, there are also reasons to expect that under conditions of technological turbulence clique-membership is less beneficial or might even become a liability. To address this, we study the innovative performance of clique members during periods of both technological change and technological stability. We find support for the idea that companies’ ability to adapt their alliance network (i.e. forming ties beyond the scope of the clique) and their ability to adapt their technology portfolios (i.e. access to novel technological knowledge) positively influences their innovative performance during technologically turbulent periods

    On semiparametric M-estimation in single-index regression

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