Viser treff 216-235 av 314

    • Pairwise scale space comparison of time series with application to climate research 

      Godtliebsen, Fred; Holmström, L.; Miettinen, A.; Erästö, P.; Divine, Dmitry V; Koc, Nalan (Journal article; Tidsskriftartikkel; Peer reviewed, 2012)
      In this paper, we study how sea surface temperature variations in the North Atlantic and the Norwegian Sea are correlated with the climate in the Northern Hemisphere in late Holocene. The analysis is performed by testing statistical hypotheses through novel scale space methodologies. In late Holocene, the proposed techniques reveal that the climate development in the subpolar North Atlantic has been ...
    • Paris-toppmøtet og spillet om CO2-kvotene 

      Rypdal, Kristoffer (Chronicle; Kronikk, 2015-11-25)
    • 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 ...
    • Penalised Complexity Priors for Stationary Autoregressive Processes 

      Sørbye, Sigrunn Holbek; Rue, Håvard (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-05-23)
      The autoregressive (AR) process of order p(AR(p)) is a central model in time series analysis. A Bayesian approach requires the user to define a prior distribution for the coefficients of the AR(p) model. Although it is easy to write down some prior, it is not at all obvious how to understand and interpret the prior distribution, to ensure that it behaves according to the users' prior knowledge. In ...
    • Penalising Model Component Complexity: A Principled, Practical Approach to Constructing Priors 

      Simpson, Daniel; Rue, Håvard; Riebler, Andrea Ingeborg; Martins, Thiago Guerrera; Sørbye, Sigrunn Holbek (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-04-06)
      In this paper, we introduce a new concept for constructing prior distributions. We exploit the natural nested structure inherent to many model components, which defines the model component to be a flexible extension of a base model. Proper priors are defined to penalise the complexity induced by deviating from the simpler base model and are formulated after the input of a user-defined scaling parameter ...
    • 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.
    • Poincaré function for moduli of differential-geometric structures 

      Kruglikov, Boris (Journal article; Tidsskriftartikkel, 2019)
      The Poincaré function is a compact form of counting moduli in local geometric problems. We discuss its property in relation to V. Arnold’s conjecture, and derive this conjecture in the case when the pseudogroup acts algebraically and transitively on the base. Then we survey the known counting results for differential invariants and derive new formulae for several other classification problems in ...
    • Point classification of 2nd order ODEs: Tresse classification revisited and beyond 

      Kruglikov, Boris (Chapter; Bokkapittel, 2008-09-26)
      In 1896 Tresse gave a complete description of relative differential invariants for the pseudogroup action of point transformations on the 2nd order ODEs. The purpose of this paper is to review, in light of modern geometric approach to PDEs, this classification and also discuss the role of absolute invariants and the equivalence problem.
    • A polymatroid approach to generalized weights of rank metric codes 

      Ghorpade, Sudhir R; Johnsen, Trygve (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-09-15)
      We consider the notion of a (<i>q,m)</i>-polymatroid, due to Shiromoto, and the more general notion of (<i>q,m</i>)-demi-polymatroids, and show how generalized weights can be defined for them. Further, we establish a duality for these weights analogous to Wei duality for generalized Hamming weights of linear codes. The corresponding results of Ravagnani for Delsarte rank metric codes, and Martínez-Peñas ...
    • The poset of Specht ideals for hyperoctahedral groups 

      Debus, Sebastian; Moustrou, Philippe; Riener, Cordian Benedikt; Verdure, Hugues (Journal article; Tidsskriftartikkel, 2023)
      Specht polynomials classically realize the irreducible representations of the symmetric group. The ideals defined by these polynomials provide a strong connection with the combinatorics of Young tableaux and have been intensively studied by several authors. We initiate similar investigations for the ideals defined by the Specht polynomials associated to the hyperoctahedral group <i>B<sub>n</sub></i>. ...
    • Power availability of PV plus thermal batteries in real-world electric power grids 

      Foldvik Eikeland, Odin; Kelsall, Colin C.; Buznitsky, Kyle; Verma, Shomik; Bianchi, Filippo Maria; Chiesa, Matteo; Henry, Asegun (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-07-25)
      As variable renewable energy sources comprise a growing share of total electricity generation, energy storage technologies are becoming increasingly critical for balancing energy generation and demand.<p> <p>In this study, a real-world electricity system was modeled rather than modeling hypothetical future electric power systems where the existing electricity infrastructure are neglected. In ...
    • Power Flow Balancing With Decentralized Graph Neural Networks 

      Hansen, Jonas Berg; Anfinsen, Stian Normann; Bianchi, Filippo Maria (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-08-01)
      We propose an end-to-end framework based on a Graph Neural Network (GNN) to balance the power flows in energy grids. The balancing is framed as a supervised vertex regression task, where the GNN is trained to predict the current and power injections at each grid branch that yield a power flow balance. By representing the power grid as a line graph with branches as vertices, we can train a GNN that ...
    • Preservice and inservice teachers’ views on digital tools for diverse learners in mathematics education 

      Meaney, Tamsin Jillian; Huru, Hilja Lisa; Kvivesen, Mona (Journal article; Tidsskriftartikkel; Peer reviewed, 2023)
      Although teachers are expected to use digital tools in their mathematics teaching in many countries, little is known about preservice and inservice teachers’ digital competence, especially in relationship to specific groups of school students. Results from a survey of 394 preservice teachers and 61 inservice teachers, at three Norwegian institutions, provide information on how they considered different ...
    • Probabilistic load forecasting with Reservoir Computing 

      Guerra, Michele; Bianchi, Filippo Maria; Scardapane, Simone (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-12-15)
      Some applications of deep learning require not only to provide accurate results but also to quantify the amount of confidence in their prediction. The management of an electric power grid is one of these cases: to avoid risky scenarios, decision-makers need both precise and reliable forecasts of, for example, power loads. For this reason, point forecasts are not enough hence it is necessary to adopt ...
    • Probabilistic Load Forecasting With Reservoir Computing 

      Guerra, Michele; Bianchi, Filippo Maria; Scardapane, Simone (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-12-15)
      Some applications of deep learning require not only to provide accurate results but also to quantify the amount of confidence in their prediction. The management of an electric power grid is one of these cases: to avoid risky scenarios, decision-makers need both precise and reliable forecasts of, for example, power loads. For this reason, point forecasts are not enough hence it is necessary to adopt ...
    • Projectable Lie algebras of vector fields in 3D 

      Schneider, Eivind (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-06-15)
      Starting with Lie’s classification of finite-dimensional transitive Lie algebras of vector fields on <b>C<sup>2</sup></b> we construct transitive Lie algebras of vector fields on the bundle <b>C<sup>2</sup> x C</b> by lifting the Lie algebras from the base. There are essentially three types of transitive lifts and we compute all of them for the Lie algebras from Lie’s classification. The simplest ...
    • A propagation-separation approach to estimate the autocorrelation in a time-series 

      Divine, Dmitry V; Polzehl, J; Godtliebsen, Fred (Journal article; Tidsskriftartikkel; Peer reviewed, 2008)
    • A quadratic reciprocity law for elliptic curves 

      Verdure, Hugues (Journal article; Tidsskriftartikkel; Peer reviewed, 2008)
      If E is an elliptic curve, then the Galois group of the extension generated by the n-torsion points acts on these points. We prove a quadratic reciprocity law involving this group action. This law is an extension of the usual quadratic reciprocity law.
    • Quality of life in substance use disorder patients with and without attention deficit hyperactivity disorder 12 months after treatment: a naturalistic follow-up study 

      Flores, Lizbett; Lensing, Michael B.; Ytterstad, Elinor; Eisemann, Martin (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-03-22)
      There is sparse research on quality of life (QoL) as an outcome measure in patients with substance use disorders (SUD), with or without attention deficit hyperactivity disorder (ADHD). We aimed to investigate whether SUD patients with and without ADHD (SUD + ADHD vs. SUD − ADHD) differed in QoL at baseline and at a 12-month follow-up after SUD treatment. The groups were additionally compared with ...
    • A quasi-objective single buoy approach for un- derstanding Lagrangian coherent structures and sea ice dynamics 

      Aksamit, Nikolas Olson; Scharien, Randall K.; Hutchings, Jennifer; Lukovich, Jennifer (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-04-11)
      Sea ice drift and deformation, namely sea ice dynamics, play a significant role in atmosphere–ice–ocean coupling. Deformation patterns in sea ice can be observed over a wide range of spatial and temporal scales, though high-resolution objective quantification of these features remains difficult. In an effort to better understand local deformation of sea ice, we adapt the trajectory-stretching exponents ...