Viser treff 170-189 av 314

    • Limits to the quantification of local climate change 

      Chapman, Sandra; Stainforth, David A.; Watkins, Nicholas W. (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-09-16)
      Abstract Wedemonstrate how the fundamental timescales of anthropogenic climate change limit the identification of societally relevant aspects of changes in precipitation.Weshow that it is nevertheless possible to extract, solely from observations, some confident quantified assessments of change at certain thresholds and locations. Maps of such changes, for a variety of hydrologically-relevant, ...
    • Linear codes associated to symmetric determinantal varieties: Even rank case 

      Beelen, Peter; Johnsen, Trygve; Singh, Prasant (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-06-20)
      We consider linear codes over a finite field Fq, for odd q, derived from determinantal varieties, obtained from symmetric matrices of bounded ranks. A formula for the weight of a codeword is derived. Using this formula, we have computed the minimum distance for the codes corresponding to matrices upperbounded by any fixed, even rank. A conjecture is proposed for the cases where the upper bound is ...
    • Linear scaling Coulomb interaction in the multiwavelet basis, a parallel implementation 

      Jensen, Stig Rune; Juselius, Jonas; Durdek, Antoine Pacifique Romain; Flå, Tor; Wind, Peter; Frediani, Luca (Journal article; Tidsskriftartikkel; Peer reviewed, 2014-08-27)
      We present a parallel and linear scaling implementation of the calculation of the electrostatic potential arising from an arbitrary charge distribution. Our approach is making use of the multi-resolution basis of multiwavelets. The potential is obtained as the direct solution of the Poisson equation in its Green’s function integral form. In the multiwavelet basis, the formally non local ...
    • Linear slices of Hyperbolic polynomials and positivity of symmetric polynomial functions 

      Riener, Cordian Benedikt; Schabert, Robin Leonid (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-10-17)
      A real univariate polynomial of degree n is called hyperbolic if all of its n roots are on the real line. Such polynomials appear quite naturally in different applications, for example, in combinatorics and optimization. The focus of this article is on families of hyperbolic polynomials which are determined through k linear conditions on the coefficients. The coefficients corresponding to such a ...
    • Linearizability of d-webs, d ≥ 4, on two-dimensional manifolds 

      Goldberg, Vladislav V.; Lychagin, Valentin V.; Akivis, Maks A. (Journal article; Tidsskriftartikkel; Peer reviewed, 2004-03-31)
      We find d − 2 relative differential invariants for a d-web, d ≥ 4, on a two-dimensional manifold and prove that their vanishing is necessary and sufficient for a d-web to be linearizable. If one writes the above invariants in terms of web functions f(x, y) and g4(x, y), ..., gd(x, y), then necessary and sufficient conditions for the linearizabilty of a d-web are two PDEs of the fourth order ...
    • Long-memory effects in linear response models of Earth's temperature and implications for future global warming 

      Rypdal, Martin Wibe; Rypdal, Kristoffer (Journal article; Tidsskriftartikkel; Peer reviewed, 2014-07-15)
      A linearized energy-balance model for global temperature is formulated, featuring a scale-invariant longrange memory (LRM) response and stochastic forcing representing the influence on the ocean heat reservoir from atmospheric weather systems. The model is parameterized by an effective response strength, the stochastic forcing strength, and the memory exponent. The instrumental global surface ...
    • Long-range memory in Earth's surface temperature on time scales from months to centuries 

      Rypdal, Kristoffer; Østvand, Lene; Rypdal, Martin wibe (Journal article; Tidsskriftartikkel; Peer reviewed, 2013)
      The paper explores the hypothesis that the temporal global temperature response can be modeled as a long-range memory (LRM) stochastic process characterized by a Hurst exponent 0.5 < H≲1.0 on time scales from months to decades. The LRM is a mathematical representation of the multitude of response times associated with the various subsystems. By analysis of instrumental and reconstructed temperature ...
    • Long-Range Memory in Millennium-Long ESM and AOGCM Experiments 

      Nilsen, Tine (Others; Andre, 2014)
      Consider the Earth’s global mean surface temperature time series (GMST) as a realization of a stochastic process. Based on a number of studies, a long-range memory (LRM) stochastic process seems to describe the GMST better than a shortrange memory model, such as the AR(1)-process. We want to study the persistence in climate model simulations, to find out if simulated temperature data exhibit the ...
    • Long-range persistence in global surface temperatures explained by linear multibox energy balance models 

      Fredriksen, Hege-Beate; Rypdal, Martin Wibe (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-09-15)
      The temporal fluctuations in global mean surface temperature are an example of a geophysical quantity that can be described using the notions of long-range persistence and scale invariance/scaling, but this description has suffered from lack of a generally accepted physical explanation. Processes with these statistical signatures can arise from nonlinear effects, for instance, through cascade-like ...
    • Machine Learning in Chronic Pain Research: A Scoping Review 

      Jenssen, Marit Dagny Kristine; Bakkevoll, Per Atle; Ngo, Phuong; Budrionis, Andrius; Fagerlund, Asbjørn Johansen; Tayefi, Maryam; Bellika, Johan Gustav; Godtliebsen, Fred (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-04-02)
      Given the high prevalence and associated cost of chronic pain, it has a significant impact on individuals and society. Improvements in the treatment and management of chronic pain may increase patients’ quality of life and reduce societal costs. In this paper, we evaluate state-of-the-art machine learning approaches in chronic pain research. A literature search was conducted using the PubMed, IEEE ...
    • Mapping climate change in European temperature distributions 

      Stainforth, David A.; Chapman, Sandra; Watkins, Nicholas W. (Journal article; Tidsskriftartikkel; Peer reviewed, 2013)
      Climate change poses challenges for decision makers across society, not just in preparing for the climate of the future but even when planning for the climate of the present day. When making climate sensitive decisions, policy makers and adaptation planners would benefit from information on local scales and for user-specific quantiles (e.g. the hottest/coldest 5% of days) and thresholds (e.g. ...
    • Mapping the shape and dimension of three-dimensional Lagrangian coherent structures and invariant manifolds 

      Aksamit, Nikolas Olson (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-03-10)
      We introduce maps of Cauchy–Green strain tensor eigenvalues to barycentric coordinates to quantify and visualize the full geometry of three-dimensional deformation in stationary and non-stationary fluid flows. As a natural extension of Lagrangian coherent structure diagnostics, which provide separate scalar fields and a one-dimensional quantification of fluid deformation, our barycentric mapping ...
    • Matematisk kulturhistorie : artikkelsamling 

      Thorvaldsen, Steinar (Book; Bok, 2002-08)
    • Maximizing Interpretability and Cost-Effectiveness of Surgical Site Infection (SSI) Predictive Models Using Feature-Specific Regularized Logistic Regression on Preoperative Temporal Data 

      Kocbek, Primoz; Fijacko, Nino; Soguero-Ruiz, Cristina; Mikalsen, Karl Øyvind; Maver, Uros; Brzan, Petra Povalej; Stozer, Andraz; Jenssen, Robert; Skrøvseth, Stein Olav; Stiglic, Gregor (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-02-19)
      This study describes a novel approach to solve the surgical site infection (SSI) classification problem. Feature engineering has traditionally been one of the most important steps in solving complex classification problems, especially in cases with temporal data. The described novel approach is based on abstraction of temporal data recorded in three temporal windows. Maximum likelihood L1-norm ...
    • 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 modelling approach to assessing the timescale uncertainties in proxy series with chronological errors 

      Divine, D.V; Godtliebsen, F.; Rue, H. (Journal article; Tidsskriftartikkel; Peer reviewed, 2012)
      The paper proposes an approach to assessment of timescale errors in proxy-based series with chronological uncertainties. The method relies on approximation of the physical process(es) forming a proxy archive by a random Gamma process. Parameters of the process are partly data-driven and partly determined from prior assumptions. For a particular case of a linear accumulation model and absolutely dated ...
    • Modelling suggests limited change in the reproduction number from reopening Norwegian kindergartens and schools during the COVID-19 pandemic 

      Rypdal, Martin Wibe; Rypdal, Veronika Gjertsen; Jakobsen, Per Kristen; Ytterstad, Elinor; Løvsletten, Ola; Klingenberg, Claus; Rypdal, Kristoffer (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-02-25)
      <i>Background</i> - To suppress the COVID-19 outbreak, the Norwegian government closed all schools on March 13, 2020. The kindergartens reopened on April 20, and the schools on April 27 and May 11 of 2020. The effect of these measures is largely unknown since the role of children in the spread of the SARS-CoV-2 virus is still unclear. There are only a few studies of school closures as a separate ...
    • Möbius and coboundary polynomials for matroids 

      Johnsen, Trygve; Verdure, Hugues (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-06-28)
      We study how some coefficients of two-variable coboundary polynomials can be derived from Betti numbers of Stanley–Reisner rings. We also explain how the connection with these Stanley–Reisner rings forces the coefficients of the two-variable coboundary polynomials and Möbius polynomials to satisfy certain universal equations.
    • Multicentennial Variability of the Sea Surface Temperature Gradient across the Subpolar North Atlantic over the Last 2.8 kyr 

      Miettinen, A.; Divine, D.V.; Koc, N.; Godtliebsen, F.; Hall, I.R. (Journal article; Tidsskriftartikkel; Peer reviewed, 2012)
      A 2800-yr-long August sea surface temperature (aSST) record based on fossil diatom assemblages is generated from a marine sediment core from the northern subpolar North Atlantic. The record is compared with the aSST record from the Norwegian Sea to explore the variability of the aSST gradient between these areas during the late Holocene. The aSST records demonstrate the opposite climate tendencies ...
    • A Multiscale Wavelet-Based Test for Isotropy of Random Fields on a Regular Lattice 

      Thon, Kevin Otto; Geilhufe, Marc; Percival, Donald B. (Journal article; Tidsskriftartikkel; Peer reviewed, 2014-12-31)
      A test for isotropy of images modeled as stationary or intrinsically stationary random fields on a lattice is developed. The test is based on wavelet theory, and can operate on the horizontal and vertical scale of choice, or on any combination of scales. Scale is introduced through the wavelet variances (sometimes referred to as the wavelet power spectrum), which decompose the variance over ...