Now showing items 1-20 of 314

    • 25 years of self-organized criticality: concepts and controversies 

      Watkins, Nicholas W.; Pruessner, Gunnar; Chapman, Sandra; Crosby, Norma B; Jensen, Henrik J (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-05-28)
      Introduced by the late Per Bak and his colleagues, self-organized criticality (SOC) has been one of the most stimulating concepts to come out of statistical mechanics and condensed matter theory in the last few decades, and has played a significant role in the development of complexity science. SOC, and more generally fractals and power laws, have attracted much comment, ranging from the very ...
    • 2d gauge theories and generalized geometry 

      Salnikov, Vladimir; Strobl, Thomas; Kotov, Oleksii (Journal article; Tidsskriftartikkel; Peer reviewed, 2014)
    • Abelian equations and rank problems for planar webs 

      Goldberg, Vladislav V.; Lychagin, Valentin V. (Journal article; Tidsskriftartikkel; Peer reviewed, 2006-05-04)
      We find an invariant characterization of planar webs of maximum rank. For 4-webs, we prove that a planar 4-web is of maximum rank three if and only if it is linearizable and its curvature vanishes. This result leads to the direct web-theoretical proof of the Poincar´e’s theorem: a planar 4- web of maximum rank is linearizable. We also find an invariant intrinsic characterization of planar 4-webs ...
    • Algebraforståelse blant studentene i brukerkurs i matematikk ved UiT 

      Malyutina, Elena; Søvik, Øistein; Huru, Hilja Lisa (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-02-24)
      Ved Institutt for matematikk og statistikk UiT – Norges arktiske universitet ble Brukerkurset i matematikk høsten 2020 lagt om til et prosjektbasert emne og ny eksamensform med avsluttende muntlig gruppeeksamen. Et av målene for vår studie er å kartlegge ferdigheter og forståelse i algebra i begynnelsen av semesteret og hvordan studentene videre møter de algebraiske aktivitetene i prosjektene. I ...
    • Almost every path structure is not variational 

      Kruglikov, Boris; Matveev, Vladimir S. (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-10-15)
      Given a smooth family of unparameterized curves such that through every point in every direction there passes exactly one curve, does there exist a Lagrangian with extremals being precisely this family? It is known that in dimension 2 the answer is positive. In dimension 3, it follows from the work of Douglas that the answer is, in general, negative. We generalise this result to all higher dimensions ...
    • Analysis of free text in electronic health records for identification of cancer patient trajectories 

      Jensen, Kasper; Soguero-Ruiz, Cristina; Mikalsen, Karl Øyvind; Lindsetmo, Rolv-Ole; Kouskoumvekaki, Irene; Girolami, Mark; Skrovseth, Stein Olav; Augestad, Knut Magne (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-04-07)
      With an aging patient population and increasing complexity in patient disease trajectories, physicians are often met with complex patient histories from which clinical decisions must be made. Due to the increasing rate of adverse events and hospitals facing financial penalties for readmission, there has never been a greater need to enforce evidence-led medical decision-making using available ...
    • Anomaly of linearization and auxiliary integrals 

      Kruglikov, Boris (Chapter; Bokkapittel, 2007-12-20)
      In this note we discuss some formal properties of universal linearization operator, relate this to brackets of non-linear differential operators and discuss application to the calculus of auxiliary integrals, used in compatibility reductions of PDEs.
    • Antarctic climate variability on regional and continental scales over the last 2000 years 

      Stenni, Barbara; Curran, Mark A.J.; Abram, Nerilie J.; Orsi, Anais; Goursaud, Sentia; Masson-Delmotte, Valerie; Neukom, Raphael; Goosse, Hugues; Divine, Dmitry V; Van Ommen, Tas; Steig, Eric J.; Dixon, Daniel A.; Thomas, Elizabeth R.; Bertler, Nancy A.N.; Isaksson, Elisabeth; Ekaykin, Alexey; Werner, Martin; Frezzotti, Massimo (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-11-17)
      Climate trends in the Antarctic region remain poorly characterized, owing to the brevity and scarcity of direct climate observations and the large magnitude of interannual to decadal-scale climate variability. Here, within the framework of the PAGES Antarctica2k working group, we build an enlarged database of ice core water stable isotope records from Antarctica, consisting of 112 records. ...
    • Arctic hydroclimate variability during the last 2000 years: current understanding and research challenges 

      Linderholm, Hans W.; Nicolle, Marie; Francus, Pierre; Gajewski, Konrad; Helama, Samuli; Korhola, Atte; Solomina, Olga; Yu, Zicheng; Zhang, Peng; D'Andrea, William J.; Debret, Maxime; Divine, Dmitry V; Gunnarson, Björn E.; Loader, Neil J.; Massei, Nicolas; Seftigen, Kristina; Thomas, Elizabeth K.; Werner, Johannes; Andersson, Sofia; Berntsson, Annika; Luoto, Tomi P.; Nevalainen, Liisa; Saarni, Saija; Väliranta, Minna (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-04-10)
      Reanalysis data show an increasing trend in Arctic precipitation over the 20th century, but changes are not homogenous across seasons or space. The observed hydroclimate changes are expected to continue and possibly accelerate in the coming century, not only affecting pan-Arctic natural ecosystems and human activities, but also lower latitudes through the atmospheric and ocean circulations. However, ...
    • Are there multiple scaling regimes in Holocene temperature records? 

      Nilsen, Tine; Rypdal, Kristoffer; Fredriksen, Hege-Beate (Journal article; Tidsskriftartikkel; Peer reviewed, 2016-04-28)
      In this article it is discussed how temperature variability on centennial timescales and longer can be described in a simplistic way. By analysing the scaling in late Holocene temperature reconstructions and longer temperature records from Greenland and Antarctic ice cores, we find that the choice of model depends heavily on the data material and timescale one chooses to emphasize. Ignoring data ...
    • Are there multiple scaling regimes in Holocene temperature records? 

      Nilsen, Tine; Rypdal, Kristoffer; Fredriksen, Hege-Beate (Journal article; Tidsskriftartikkel, 2015-07-17)
      The concept of multiple scaling regimes in temperature time series is examined, with emphasis on the question whether or not a mono-scaling model can be rejected from the data at hand. A model with only one regime is simpler and is preferred if this 5 explains the observed variability. Our analysis of spectra from reconstructed air temperature from Greenland and Antarctica ice cores shows that ...
    • Assessing the performance of the BARCAST climate field reconstruction technique for a climate with long-range memory 

      Nilsen, Tine; Werner, Johannes; Divine, Dmitry V; Rypdal, Martin wibe (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-06-29)
      The skill of the state-of-the-art climate field reconstruction technique BARCAST (Bayesian Algorithm for Reconstructing Climate Anomalies in Space and Time) to reconstruct temperature with pronounced long-range memory (LRM) characteristics is tested. A novel technique for generating fields of target data has been developed and is used to provide ensembles of LRM stochastic processes with a prescribed ...
    • Associations and predictive power of dietary patterns on metabolic syndrome and its components 

      Moe, Åse Mari; Ytterstad, Elinor; Hopstock, Laila Arnesdatter; Løvsletten, Ola; Carlsen, Monica Hauger; Sørbye, Sigrunn Holbek (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-10-31)
      Background and aims: Metabolic syndrome (MetS) defines important risk factors in the development of cardiovascular diseases and other serious health conditions. This study aims to investigate the influence of different dietary patterns on MetS and its components, examining both associations and predictive performance.<p> <p>Methods and results: The study sample included 10,750 participants from ...
    • Attribution in the presence of a long-memory climate response 

      Rypdal, Kristoffer (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-11-18)
      Multiple, linear regression is employed to attribute variability in the global surface temperature to various forcing components and prominent internal climatic modes. The purpose of the study is to assess how sensitive attribution is to long-range memory (LRM) in the model for the temperature response. The model response to a given forcing component is its fingerprint and is different for a zero ...
    • Attribution in the presence of a long-memory climate response 

      Rypdal, Kristoffer (Journal article; Tidsskriftartikkel, 2015-08-10)
      Multiple, linear regression is employed to attribute variability in the global surface temperature to various forcing components and prominent internal climatic modes. The purpose of the study is to asses how sensitive attribution is to long-range memory 5 (LRM) in the model for the temperature response. The model response to a given forcing component is its fingerprint, and is different for a ...
    • Automatic nematode detection in cod fillets (Gadus morhua L.) by hyperspectral imaging 

      Sivertsen, Agnar Holten; Heia, Karsten; Hindberg, Kristian; Godtliebsen, Fred (Journal article; Tidsskriftartikkel; Peer reviewed, 2012)
      Detection of objects embedded in tissue, using visible light, is difficult due to light scattering. The optical properties of the surrounding tissue will influence the spectral characteristics of the light interacting with the object, and the spectral signature observed from the object will be directly affected. A method for calibrating the spectral signature of small objects, embedded in translucent ...
    • Automatic Segmentation of Dermoscopic Images by Iterative Classification 

      Zortea, Maciel; Skrøvseth, Stein Olav; Schopf, Thomas Roger Griesbeck; Kirchesch, Herbert M.; Godtliebsen, Fred (Journal article; Tidsskriftartikkel; Peer reviewed, 2011)
      Accurate detection of the borders of skin lesions is a vital first step for computer aided diagnostic systems. This paper presents a novel automatic approach to segmentation of skin lesions that is particularly suitable for analysis of dermoscopic images. Assumptions about the image acquisition, in particular, the approximate location and color, are used to derive an automatic rule to select small ...
    • Bayesian Computing with INLA: A Review 

      Rue, Håvard; Riebler, Andrea Ingeborg; Sørbye, Sigrunn Holbek; Illian, Janine B.; Simpson, Daniel Peter; Lindgren, Finn Kristian (Journal article; Tidsskriftartikkel, 2016-12-23)
      The key operation in Bayesian inference is to compute high-dimensional integrals. An old approximate technique is the Laplace method or approximation, which dates back to Pierre-Simon Laplace (1774). This simple idea approximates the integrand with a second-order Taylor expansion around the mode and computes the integral analytically. By developing a nested version of this classical idea, combined ...
    • Bayesian modeling and significant features exploration in wavelet power spectra 

      Divine, Dmitry V; Godtliebsen, Fred (Journal article; Tidsskriftartikkel; Peer reviewed, 2007)
    • Bayesian multiscale analysis of images modeled as Gaussian Markov random fields 

      Thon, Kevin Otto; Rue, Håvard; Skrøvseth, Stein Olav; Godtliebsen, Fred (Journal article; Tidsskriftartikkel; Peer reviewed, 2012)
      A Bayesian multiscale technique for the detection of statistically significant features in noisy images is proposed. The prior is defined as a stationary intrinsic Gaussian Markov random field on a toroidal graph, which enables efficient computation of the relevant posterior marginals. Hence the method is applicable to large images produced by modern digital cameras. The technique is demonstrated ...