Now showing items 61-80 of 314

    • On hybrid classification using model assisted posterior estimates 

      Ghosh, Anil K.; Godtliebsen, Fred (Journal article; Tidsskriftartikkel; Peer reviewed, 2012)
      Traditional parametric and nonparametric classifiers used for statistical pattern recognition have their own strengths and limitations. While parametric methods assume some specific parametric models for density functions or posterior probabilities of competing classes, nonparametric methods are free from such assumptions. So, when these model assumptions are correct, parametric methods outperform ...
    • 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 ...
    • 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 ...
    • Surface mass balance and stable oxygen isotope ratios from shallow firn cores on Fimbulisen, East Antarctica 

      Schlosser, E; Anschütz, Helgard; Isaksson, E.; Martma, T; Divine, Dmitry V; Nøst, O.-A. (Journal article; Tidsskriftartikkel; Peer reviewed, 2012)
      The mass balance of Antarctica is one of the crucial factors for determining sea-level change in a warming climate. The marginal zones of the continent, namely the ice shelves, are most sensitive to climate change. During the 2009/10 austral summer an extensive glaciological field campaign was carried out on Fimbulisen, an ice shelf in East Antarctica, to investigate its recent surface mass balance. ...
    • 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 ...
    • Robustness of predator-prey models for confinement regime transitions in fusion plasmas 

      Zhu, H; Chapman, Sandra; Dendy, R.O. (Journal article; Tidsskriftartikkel; Peer reviewed, 2013)
      Energy transport and confinement in tokamak fusion plasmas is usually determined by the coupled nonlinear interactions of small-scale drift turbulence and larger scale coherent nonlinear structures, such as zonal flows, together with free energy sources such as temperature gradients. Zero-dimensional models, designed to embody plausible physical narratives for these interactions, can help to ...
    • 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. ...
    • Hamming weights and Betti numbers of Stanley–Reisner rings associated to matroids 

      Johnsen, Trygve; Verdure, Hugues (Journal article; Tidsskriftartikkel; Peer reviewed, 2013)
      To each linear code C over a finite field we associate the matroid M(C) of its parity check matrix. For any matroid M one can define its generalized Hamming weights, and if a matroid is associated to such a parity check matrix, and thus of type M(C) , these weights are the same as those of the code C . In our main result we show how the weights d1,…,dk of a matroid M are determined by the N -graded ...
    • ENSO dynamics: Low-dimensional-chaotic or stochastic? 

      Zivkovic, Tatjana; Rypdal, Kristoffer (Journal article; Tidsskriftartikkel; Peer reviewed, 2013)
    • Elemental carbon measurements in European Arctic snow packs 

      Forsström, S.; Isaksson, Elisabeth; Skeie, Ragnhild Bieltvedt; Ström, Johan; Pedersen, CA; Hudson, S.R.; Berntsen, Terje Koren; Lihavainen, H.; Godtliebsen, Fred; Gerland, Sebastian (Journal article; Tidsskriftartikkel; Peer reviewed, 2013-12-26)
      Black carbon (BC) and other light-absorbing particles deposited on snow and ice are known to perturb the surface radiative balance. There are few published observations of the concentration of these particles in the snow in Scandinavia and the European Arctic. We measured BC concentrations in snow samples collected in this region from 2007 to 2009, and we present the results here. The data set ...
    • 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 ...
    • 2d gauge theories and generalized geometry 

      Salnikov, Vladimir; Strobl, Thomas; Kotov, Oleksii (Journal article; Tidsskriftartikkel; Peer reviewed, 2014)
    • Surface water conditions and calcium carbonate preservation in the Fram Strait during marine isotope stage 2, 28.8–15.4 kyr 

      Zamelczyk, Katarzyna; Rasmussen, Tine Lander; Husum, Katrine; Godtliebsen, Fred; Hald, Morten (Journal article; Tidsskriftartikkel; Peer reviewed, 2014-01-14)
      We present a high-resolution record of calcium carbonate preservation alongside the distribution pattern of planktic foraminifera from the Fram Strait. The record covers the marine isotope stage (MIS) 2, 28.8 to 15.4 kyr, including the Last Glacial Maximum (LGM) and the early deglaciation in multidecadal temporal resolution. The investigation is based on the distribution patterns of planktic ...
    • A semiautomatic tool for prostate segmentation in radiotherapy treatment planning 

      Schulz, Jörn; Skrøvseth, Stein Olav; Tømmerås, Veronika Kristine; Marienhagen, Kirsten; Godtliebsen, Fred (Journal article; Tidsskriftartikkel; Peer reviewed, 2014-01-25)
    • Statistical significance of rising and oscillatory trends in global ocean and land temperature in the past 160 years 

      Østvand, Lene; Rypdal, Kristoffer; Rypdal, Martin Wibe (Journal article; Tidsskriftartikkel, 2014-03-20)
      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 general ...
    • 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 ...
    • Stanley-Reisner resolution of constant weight linear codes 

      Johnsen, Trygve; Verdure, Hugues (Journal article; Tidsskriftartikkel; Peer reviewed, 2014-08)
      Given a constant weight linear code, we investigate its weight hierarchy and the Stanley–Reisner resolution of its associated matroid regarded as a simplicial complex. We also exhibit conditions on the higher weights sufficient to conclude that the code is of constant weight.
    • 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 ...
    • The gap phenomenon in parabolic geometries 

      Kruglikov, Boris; The, Dennis (Journal article; Tidsskriftartikkel; Peer reviewed, 2014-09-14)
      The infinitesimal symmetry algebra of any Cartan geometry has maximum dimension realized by the flat model, but often this dimension drops significantly when considering non-flat geometries, so a gap phenomenon arises. For general (regular, normal) parabolic geometries of type (G,P), we use Tanaka theory to derive a universal upper bound on the submaximal symmetry dimension. We use Kostant’s version ...
    • 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 ...