Artikler, rapporter og annet (matematikk og statistikk): Recent submissions
Now showing items 181-200 of 353
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Differential invariants of Kundt waves
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-07-17)Kundt waves belong to the class of spacetimes which are not distinguished by their scalar curvature invariants. We address the equivalence problem for the metrics in this class via scalar differential invariants with respect to the equivalence pseudo-group of the problem. We compute and finitely represent the algebra of those on the generic stratum and also specify the behavior for vacuum Kundt ... -
Relative profiles and extended weight polynomials of almost affine codes
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019)In this paper we study various aspects concerning almost affine codes, a class including, and strictly larger than, that of linear codes. We use the combinatorial tool demi-matroids to show how one can define relative length/dimension and dimension/length profiles of flags (chains) of almost affine codes. In addition we show two specific results. One such result is how one can express the relative ... -
On the Ewald Oseen scattering formulation for light scattering: stability, singularity and parallelization.
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-11-15)In this paper we discuss some of the mathematical and numerical issues that have to be addressed when calculating wave scattering using the Ewald Oseen scattering (EOS) formulation which is newly developed for solving linear and nonlinear scattering problems. The discussion is framed in context of light scattering by objects whose optical response can be of a nonlinear and/or inhomogeneous nature. ... -
Warming trends and long-range dependent climate variability since year 1900: A Bayesian approach
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-08-21)Temporal persistence in unforced climate variability makes detection of trends in surface temperature difficult. Part of the challenge is methodological since standard techniques assume a separation of time scales between trend and noise. In this work we present a novel Bayesian approach to trend detection under the assumption of long-range dependent natural variability, and we use estimates of ... -
The effects of terlipressin and direct portacaval shunting on liver hemodynamics following 80% hepatectomy in the pig
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-01-15)Liver failure is the major cause of death following liver resection. Post-resection portal venous pressure (PVP) predicts liver failure, is implicated in its pathogenesis, and when PVP is reduced, rates of liver dysfunction decrease. The aim of the present study was to characterize the hemodynamic, biochemical, and histological changes induced by 80% hepatectomy in non-cirrhotic pigs and determine ... -
Quality of life in substance use disorder patients with and without attention deficit hyperactivity disorder 12 months after treatment: a naturalistic follow-up study
(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 ... -
Surface mass balance and stable oxygen isotope ratios from shallow firn cores on Fimbulisen, East Antarctica
(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. ... -
Recent advances in hyperspectral imaging for melanoma detection
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-04-22)Skin cancer is one of the most common types of cancer. Skin cancers are classified as nonmelanoma and melanoma, with the first type being the most frequent and the second type being the most deadly. The key to effective treatment of skin cancer is early detection. With the recent increase of computational power, the number of algorithms to detect and classify skin lesions has increased. The overall ... -
Arctic hydroclimate variability during the last 2000 years: current understanding and research challenges
(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, ... -
Inter-outbreak stability reflects the size of the susceptible pool and forecasts magnitudes of seasonal epidemics
(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 ... -
Maximizing Interpretability and Cost-Effectiveness of Surgical Site Infection (SSI) Predictive Models Using Feature-Specific Regularized Logistic Regression on Preoperative Temporal Data
(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 ... -
Homogeneous integrable Legendrian contact structures in dimension five
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-07-04)We consider Legendrian contact structures on odd-dimensional complex analytic manifolds. We are particularly interested in integrable structures, which can be encoded by compatible complete systems of second order PDEs on a scalar function of many independent variables and considered up to point transformations. Using the techniques of parabolic differential geometry, we compute the associated ... -
Differential invariants of self-dual conformal structures
(Journal article; Tidsskriftartikkel; Peer reviewed, 2016-06-17)We compute the quotient of the self-duality equation for conformal metrics by the action of the diffeomorphism group. We also determine Hilbert polynomial, counting the number of independent scalar differential invariants depending on the jet-order, and the corresponding Poincaré function. We describe the field of rational differential invariants separating generic orbits of the diffeomorphism ... -
Emergent Scale Invariance and Climate Sensitivity
(Journal article; Peer reviewed, 2018-11-28)Earth’s global surface temperature shows variability on an extended range of temporal scales and satisfies an emergent scaling symmetry. Recent studies indicate that scale invariance is not only a feature of the observed temperature fluctuations, but an inherent property of the temperature response to radiative forcing, and a principle that links the fast and slow climate responses. It provides a ... -
Climate variability in the subarctic area for the last 2 millennia
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-01-25)To put recent climate change in perspective, it is necessary to extend the instrumental climate records with proxy data from paleoclimate archives. Arctic climate variability for the last 2 millennia has been investigated using statistical and signal analyses from three regionally averaged records from the North Atlantic, Siberia and Alaska based on many types of proxy data archived in the ... -
Differential invariants of Einstein-Weyl structures in 3D
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-05-22)Einstein–Weyl structures on a three-dimensional manifold <i>M</i> are given by a system <i>E</i> of PDEs on sections of a bundle over <i>M</i>. This system is invariant under the Lie pseudogroup <i>G</i> of local diffeomorphisms on <i>M</i>. Two Einstein–Weyl structures are locally equivalent if there exists a local diffeomorphism taking one to the other. Our goal is to describe the quotient equation ... -
Reflection groups, arrangements, and invariant real varieties
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-10-18)Let <i>X</i> be a nonempty real variety that is invariant under the action of a reflection group <i>G</i>. We conjecture that if <i>X</i> is defined in terms of the first <i>k</i> basic invariants of <i>G</i> (ordered by degree), then <i>X</i> meets a <i>k</i>-dimensional flat of the associated reflection arrangement. We prove this conjecture for the infinite types, reflection groups of rank at most ... -
On the Isotypic Decomposition of Cohomology Modules of Symmetric Semi-algebraic Sets: Polynomial Bounds on Multiplicities
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-04-30)We consider symmetric (under the action of products of finite symmetric groups) real algebraic varieties and semi-algebraic sets, as well as symmetric complex varieties in affine and projective spaces, defined by polynomials of degrees bounded by a fixed constant <i>d</i>. We prove that if a Specht module, S<sup>λ</sup>, appears with positive multiplicity in the isotypic decomposition of the ... -
On the equivariant Betti numbers of symmetric definable sets: vanishing, bounds and algorithms
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-03-02)Let R be a real closed field. We prove that for any fixed <i>d</i>, the equivariant rational cohomology groups of closed symmetric semi-algebraic subsets of R<sup><i>k</i></sup> defined by polynomials of degrees bounded by <i>d</i> vanishes in dimensions <i>d</i> and larger. This vanishing result is tight. Using a new geometric approach we also prove an upper bound of [mathematical formula] on the ... -
Assessing the performance of the BARCAST climate field reconstruction technique for a climate with long-range memory
(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 ...