Blar i forfatter "Rypdal, Martin"

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    • Dynamics and entropy in the Zhang model of Self-Organized Criticality 

      Kruglikov, Boris; Rypdal, Martin (Working paper; Arbeidsnotat, 2005-09-12)
      We give a detailed study of dynamical properties of the Zhang model, including evaluation of topological entropy and estimates for the Lyapunov exponents and the dimension of the attractor. In the thermodynamic limit the entropy goes to zero and the Lyapunov spectrum collapses.1

    • Entropy via multiplicity 

      Kruglikov, Boris; Rypdal, Martin (Working paper; Arbeidsnotat, 2005-09-30)
      The topological entropy of piecewise affine maps is studied. It is shown that singularities may contribute to the entropy only if there is angular expansion and we bound the entropy via the expansion rates of the map. As a corollary we deduce that non-expanding conformal piecewise affine maps have zero topological entropy. We estimate the entropy of piecewise affine skew-products. Examples of ...

    • Modeling temporal fluctuations in avalanching system 

      Rypdal, Martin; Rypdal, Kristoffer (Working paper; Arbeidsnotat, 2008-07-22)
      We demonstrate how to model the toppling activity in avalanching systems by stochastic differential equations (SDEs). The theory is developed as a generalization of the classical mean field approach to sandpile dynamics by formulating it as a generalization of Itoh’s SDE. This equation contains a fractional Gaussian noise term representing the branching of an avalanche into small active clusters, ...

    • A Parsimonious Description and Cross-Country Analysis of COVID-19 Epidemic Curves 

      Rypdal, Kristoffer; Rypdal, Martin (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-09-06)
      In a given country, the cumulative death toll of the first wave of the COVID-19 epidemic follows a sigmoid curve as a function of time. In most cases, the curve is well described by the Gompertz function, which is characterized by two essential parameters, the initial growth rate and the decay rate as the first epidemic wave subsides. These parameters are determined by socioeconomic factors and ...

    • A piece-wise affine contracting map with positive entropy 

      Kruglikov, Boris; Rypdal, Martin (Working paper; Arbeidsnotat, 2005-04-10)
      We construct the simplest chaotic system with a two-point attractor.

    • Statistical significance of rising and oscillatory trends in global ocean and land temperature in the past 160 years 

      Østvand, Lene; Rypdal, Kristoffer; Rypdal, Martin (Journal article; Tidsskriftartikkel, 2014-10-30)
      Various interpretations of the notion of a trend in the context of global warming are discussed, contrasting the difference between viewing a trend as the deterministic response to an external forcing and viewing it as a slow variation which can be separated from the background spectral continuum of long-range persistent climate noise. The emphasis in this paper is on the latter notion, and a ...

    • A stochastic theory for temporal fluctuations in self-organized critical systems 

      Rypdal, Martin; Rypdal, Kristoffer (Journal article; Tidsskriftartikkel; Peer reviewed, 2008)

    • A stochastic theory for temporal fluctuations in self-organized critical systems 

      Rypdal, Martin; Rypdal, Kristoffer (Working paper; Arbeidsnotat, 2008-07-22)
      A stochastic theory for the toppling activity in sandpile models is developed, based on a simple mean-field assumption about the toppling process. The theory describes the process as an anti-persistent Gaussian walk, where the diffusion coefficient is proportional to the activity. It is formulated as a generalization of the Itˆo stochastic differential equation with an anti-persistent fractional ...

    • The Structure of Climate Variability Across Scales 

      Franzke, Christian L.E.; Barbosa, Susana; Blender, Richard; Fredriksen, Hege-Beate; Laepple, Thomas; Lambert, Fabrice; Nilsen, Tine; Rypdal, Kristoffer; Rypdal, Martin; Scotto, Manuel G; Vannitsem, Stephane; Watkins, Nicholas W.; Yang, Lichao; Yuan, Naiming (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-03-05)
      One of the most intriguing facets of the climate system is that it exhibits variability across all temporal and spatial scales; pronounced examples are temperature and precipitation. The structure of this variability, however, is not arbitrary. Over certain spatial and temporal ranges, it can be described by scaling relationships in the form of power laws in probability density distributions and ...

    • To tolerate weather and to tolerate pain: two sides of the same coin? The Tromsø Study 7 

      Farbu, Erlend Hoftun; Rypdal, Martin; Skandfer, Morten; Steingrimsdottir, Olöf Anna; Brenn, Tormod; Stubhaug, Audun; Nielsen, Christopher Sivert; Höper, Anje Christina (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-09-09)
      It is a common belief that weather affects pain. Therefore, we hypothesized that weather can affect pain tolerance. This study used data from over 18,000 subjects aged 40 years or older from the general population, who participated in the Tromsø Study 7. They underwent a one-time assessment of cuff algometry pressure pain tolerance (PPT) and cold pain tolerance (CPT), tested with a cold pressor test. ...