Blar i tittel Artikler, rapporter og annet (matematikk og statistikk)

Viser treff 142-161 av 314

    • Instance Segmentation of Microscopic Foraminifera 

      Johansen, Thomas Haugland; Sørensen, Steffen Aagaard; Møllersen, Kajsa; Godtliebsen, Gustav (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-07-16)
      Foraminifera are single-celled marine organisms that construct shells that remain as fossils in the marine sediments. Classifying and counting these fossils are important in paleo-oceanographic and -climatological research. However, the identification and counting process has been performed manually since the 1800s and is laborious and time-consuming. In this work, we present a deep learning-based ...

    • Institutt for matematiske realfag 1972-1992. IMR 20 år. Knutepunkter i instituttets historie og perspektiver på fag og fremtid 

      Jervell, Herman Ruge; Johnsen, Ben (Research report; Forskningsrapport, 1992)

    • Integrability via Geometry: Dispersionless Differential Equations in Three and Four Dimensions 

      Calderbank, David M. J.; Kruglikov, Boris (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-11-25)
      We prove that the existence of a dispersionless Lax pair with spectral parameter for a nondegenerate hyperbolic second order partial differential equation (PDE) is equivalent to the canonical conformal structure defined by the symbol being Einstein–Weyl on any solution in 3D, and self-dual on any solution in 4D. The first main ingredient in the proof is a characteristic property for dispersionless ...

    • Integrable Systems in Four Dimensions Associated with Six-Folds in Gr(4, 6) 

      Doubrov, Boris; Ferapontov, Evgeny V; Kruglikov, Boris; Novikov, Vladimir S (Journal article; Tidsskriftartikkel, 2018-01-29)
      Let Gr(d, n) be the Grassmannian of <i>d</i>-dimensional linear subspaces of an <i>n</i>-dimensional vector space <i>V</i>. A submanifold <i>X</i> ⊂ Gr(<i>d, n</i>) gives rise to a differential system Σ(X) that governs <i>d</i>-dimensional submanifolds of <i>V</i> whose Gaussian image is contained in <i>X</i>. We investigate a special case of this construction where <i>X</i> is a six-fold in Gr(4, ...

    • Inter-outbreak stability reflects the size of the susceptible pool and forecasts magnitudes of seasonal epidemics 

      Rypdal, Martin Wibe; Sugihara, George (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-05-30)
      For dengue fever and other seasonal epidemics we show how the stability of the preceding inter-outbreak period can predict subsequent total outbreak magnitude, and that a feasible stability metric can be computed from incidence data alone. As an observable of a dynamical system, incidence data contains information about the underlying mechanisms: climatic drivers, changing serotype pools, the ecology ...

    • Interplay between advective, diffusive and active barriers in (rotating) Rayleigh-Bénard flow 

      Aksamit, Nikolas Olson; Hartmann, Robert; Lohse, Detlef; Haller, George (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-08-22)
      Our understanding of the material organization of complex fluid flows has benefited recently from mathematical developments in the theory of objective coherent structures. These methods have provided a wealth of approaches that identify transport barriers in three-dimensional (3-D) turbulent flows. Specifically, theoretical advances have been incorporated into numerical algorithms that extract ...

    • Invariant characterization of Liouville metrics and polynomial integrals 

      Kruglikov, Boris (Journal article; Tidsskriftartikkel; Peer reviewed, 2007-09-04)
      A criterion in terms of differential invariants for a metric on a surface to be Liouville is established. Moreover, in this paper we completely solve in invariant terms the local mobility problem of a 2D metric, considered by Darboux: How many quadratic in momenta integrals does the geodesic flow of a given metric possess? The method is also applied to recognition of other polynomial integrals ...

    • Invariants and submanifolds in almost complex geometry 

      Kruglikov, Boris (Chapter; Bokkapittel, 2007-12-20)
      In this paper we describe the algebra of differential invariants for GL(n,C)-structures. This leads to classification of almost complex structures of general positions. The invariants are applied to the existence problem of higher-dimensional pseudoholomorphic submanifolds.

    • Invariants of pseudogroup actions: Homological methods and Finiteness theorem 

      Kruglikov, Boris; Lychagin, Valentin V. (Working paper; Arbeidsnotat, 2005-12-07)
      We study the equivalence problem of submanifolds with respect to a transitive pseudogroup action. The corresponding differential invariants are determined via formal theory and lead to the notions of l-variants and l-covariants, even in the case of non-integrable pseudogroup. Their calculation is based on the cohomological machinery: We introduce a complex for covariants, define their cohomology ...

    • Involutivity of field equations 

      Kruglikov, Boris (Working paper; Arbeidsnotat, 2009-02-10)
      We prove involutivity of Einstein and Einstein-Maxwell equations by calculating the Spencer cohomology of these systems. Relation with Cartan method is traced in details. Basic implications through Cartan-Kähler theory are derived.

    • Is there a break in scaling on centennial time scales in Holocene temperature records? 

      Nilsen, Tine; Rypdal, Kristoffer; Fredriksen, Hege-Beate (Conference object; Konferansebidrag, 2017)

    • Jet-determination of symmetries of parabolic geometries 

      Kruglikov, Boris; The, Dennis (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-04-24)
      We establish 2-jet determinacy for the symmetry algebra of the underlying structure of any (complex or real) parabolic geometry. At non-flat points, we prove that the symmetry algebra is in fact 1-jet determined. Moreover, we prove 1-jet determinacy at any point for a variety of non-flat parabolic geometries—in particular torsion-free, parabolic contact, and several other classes.

    • Joint Invariants of Linear Symplectic Actions 

      Andreassen, Fredrik; Kruglikov, Boris (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-12-07)
      We review computations of joint invariants on a linear symplectic space, discuss variations for an extension of group and space and relate this to other equivalence problems and approaches, most importantly to differential invariants.

    • Kausale design – Et gjennombrudd i samfunnsfagene eller keiserens nye klær? 

      Rypdal, Kristoffer (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-02-03)
      Statistiske metoder som regresjonsanalyse og kausale design basert på naturlige eksperi-menter har etter hvert blitt hyllevare innen de fleste fag som behandler store datamengder,ikke minst innen epidemiologi, meteorologi og klimavitenskap.1 Et eksempel er prinsipalkomponentanalyse (PCA), som brukes til å finne karakteristiske mønstre i geofysiske felt.Mønstrene, eller prinsipalkomponentene, ...

    • Kayas identitet og valgets kval 

      Rypdal, Kristoffer (Chronicle; Kronikk, 2017-08-21)
      <i>Ingress</i>: Det Kayas identitet viser oss er for det første at for å redusere utslippene må vi gjøre noe med befolkningsveksten og/eller en eller flere av de tre intensitetene.

    • Killing tensors in Koutras-McIntosh spacetimes 

      Kruglikov, Boris; Steneker, Wijnand Sebastiaan (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-11-03)
      The Koutras–McIntosh family of metrics include conformally flat pp-waves and the Wils metric. It appeared in a paper of 1996 by Koutras–McIntosh as an example of a pure radiation spacetime without scalar curvature invariants or infinitesimal symmetries. Here we demonstrate that these metrics have no 'hidden symmetries', by which we mean Killing tensors of low degrees. For the particular case of Wils ...

    • Kinetic energy-free Hartree–Fock equations: an integral formulation 

      Jensen, Stig Rune; Durdek, Antoine Pacifique Romain; Bjørgve, Magnar; Wind, Peter; Flå, Tor; Frediani, Luca (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-07-18)
      We have implemented a self-consistent feld solver for Hartree–Fock calculations, by making use of Multiwavelets and Multiresolution Analysis. We show how such a solver is inherently a preconditioned steepest descent method and therefore a good starting point for rapid convergence. A distinctive feature of our implementation is the absence of any reference to the kinetic energy operator. This is ...

    • Klimakrisen og økonomisk politikk 

      Rypdal, Kristoffer (Chronicle; Kronikk, 2015-11-14)

    • The Kobayashi pseudodistance on almost complex manifolds 

      Overholt, Marius; Kruglikov, Boris S. (Working paper; Arbeidsnotat, 1997-03-06)
      We extend the definition of the Kobayashi pseudodistance to almost complex manifolds and show that its familiar properties are for the most part preserved. We also study the automorphism group of an almost complex manifold and finish with some examples.

    • Kontinuitet i overgangen fra skole til universitet - Implikasjoner av Fagfornyelsen for MNT-fagene 

      Pedersen, Ida Friestad; Huru, Hilja Lisa; Coucheron, David Andre (Conference object; Konferansebidrag, 2023-03)
      Med LK20 Fagfornyelsen innføres det nye læreplaner i skolen, der antall kompetansemål i de ulike fagene er noe redusert for å gi mer rom til dybdelæring, samt at læreplanene i matematikk og fysikk har et større fokus på utforsking, modellering og bruk av numeriske metoder enn tidligere (Ludvigsen et al., 2015; Utdanningsdirektoratet, 2020, 2021). I dette bidraget presenterer vi hvordan en gruppe ...