Institutt for matematikk og statistikk: Recent submissions
Now showing items 41-60 of 412
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Probabilistic load forecasting with Reservoir Computing
(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 ... -
Numerical evaluation of line, surface and toroidal integrals on level sets of toroidally symmetric functions
(Journal article; Tidsskriftartikkel; Peer reviewed, 2023-08-05)We investigate strategies to numerically integrate closed lines and surfaces that are implicitly defined by level sets (iso-contours) of continuously differentiable toroidally symmetric functions. The “grid-transform” approach transforms quantities given in non-surface-aligned coordinates onto a numerically constructed surface-aligned grid. Here, line and surface integrals, as well as so-called ... -
Interplay between advective, diffusive and active barriers in (rotating) Rayleigh-Bénard flow
(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 ... -
A finite volume flux coordinate independent approach
(Journal article; Tidsskriftartikkel; Peer reviewed, 2023-07-03)We present a novel family of schemes as the merging between a one-dimensional advection scheme with the flux coordinate independent approach. The scheme can be used to discretize the field-aligned NavierStokes equations in three dimensions. Our approach consists of three major steps: (i) the formulation of the one-dimensional scheme in a locally field-aligned coordinate system, (ii) a numerical ... -
Evaluating Deep Q-Learning Algorithms for Controlling Blood Glucose in In Silico Type 1 Diabetes
(Journal article; Tidsskriftartikkel; Peer reviewed, 2023-10-07)Patients with type 1 diabetes must continually decide how much insulin to inject before each meal to maintain blood glucose levels within a healthy range. Recent research has worked on a solution for this burden, showing the potential of reinforcement learning as an emerging approach for the task of controlling blood glucose levels. In this paper, we test and evaluate several deep Q-learning algorithms ... -
Generalized Teleparallel de Sitter geometries
(Journal article; Tidsskriftartikkel; Peer reviewed, 2023-10-30)Theories of gravity based on teleparallel geometries are characterized by the torsion, which is a function of the coframe, derivatives of the coframe, and a zero curvature and metric compatible spin-connection. The appropriate notion of a symmetry in a teleparallel geometry is that of an affine symmetry. Due to the importance of the de Sitter geometry and Einstein spaces within General Relativity, ... -
Geographical study of the stroke incidence and mortality rates using Bayesian analysis
(Master thesis; Mastergradsoppgave, 2023-09-21)There is large geographical variation in the stroke incidence rate worldwide. In addition, stroke is one of the diseases with highest mortality rate. In this thesis, our main focus is to examine if there are any geographical variation in stroke incidence and mortality rates in Norway. We approach this study using models within the Bayesian framework. Before performing analysis, we first introduce ... -
On elementary particles as representations of the Poincaré group
(Master thesis; Mastergradsoppgave, 2023-08-14)This thesis is concerned with the definition of elementary particles as irreducible projective unitary representations of the Poincaré group. During the contents of this work, we will introduce the relevant prerequisites and results. Concerning differential geometry, we will discuss smooth manifolds, Lie groups and Lie algebras. About quantum mechanics, we will introduce Hilbert spaces and the basic ... -
The poset of Specht ideals for hyperoctahedral groups
(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>. ... -
Linear slices of Hyperbolic polynomials and positivity of symmetric polynomial functions
(Journal article; Tidsskriftartikkel; Peer reviewed, 2023-10-17)A real univariate polynomial of degree n is called hyperbolic if all of its n roots are on the real line. Such polynomials appear quite naturally in different applications, for example, in combinatorics and optimization. The focus of this article is on families of hyperbolic polynomials which are determined through k linear conditions on the coefficients. The coefficients corresponding to such a ... -
A Heterotic Kodaira--Spencer Theory at One-Loop
(Journal article; Tidsskriftartikkel; Peer reviewed, 2023-10-23)We consider a heterotic version of six-dimensional Kodaira-Spencer gravity derived from the heterotic superpotential. We compute the one-loop partition function and fnd it can be expressed as a product of holomorphic Ray-Singer torsions. We discuss its topological properties and potential gauge and gravitational anomalies. We show these anomalies can be cancelled using Green-Schwarz-like ... -
The South American monsoon approaches a critical transition in response to deforestation
(Journal article; Tidsskriftartikkel; Peer reviewed, 2023-10-04)The Amazon rainforest is threatened by land-use change and increasing drought and fire frequency. Studies suggest an abrupt dieback of large parts of the rainforest after partial forest loss, but the critical threshold, underlying mechanisms, and possible impacts of forest degradation on the monsoon circulation remain uncertain. Here, we use a nonlinear dynamical model of the moisture transport ... -
Laplace transformation of Lie class ω = 1 overdetermined systems
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-01-20)In this paper, we investigate overdetermined systems of scalar PDEs on the plane with one common characteristic, whose general solution depends on one function of one variable. We describe linearization of such systems and their integration via Laplace transformation, relating this to Lie's integration theorem and formal theory of PDEs. -
Is there a break in scaling on centennial time scales in Holocene temperature records?
(Conference object; Konferansebidrag, 2017) -
Second-order PDEs in four dimensions with half-flat conformal structure
(Journal article; Tidsskriftartikkel; Peer reviewed, 2020-01-29)We study second-order partial differential equations (PDEs) in four dimensions for which the conformal structure defined by the characteristic variety of the equation is half-flat (self-dual or anti-self-dual) on every solution. We prove that this requirement implies the Monge–Ampère property. Since half-flatness of the conformal structure is equivalent to the existence of a non-trivial dispersionless ... -
Real Root Finding for Equivariant Semi-algebraic Systems
(Conference object; Konferansebidrag, 2018)Let <i><b>R</b></i> be a real closed field. We consider basic semi-algebraic sets defined by <i>n</i>-variate equations/inequalities of s symmetric polynomials and an equivariant family of polynomials, all of them of degree bounded by 2<i>d</i> < <i>n</i>. Such a semi-algebraic set is invariant by the action of the symmetric group. We show that such a set is either empty or it contains a point ... -
Extreme Event Statistics in Dst, SYM-H, and SMR Geomagnetic Indices
(Journal article; Tidsskriftartikkel; Peer reviewed, 2023-03-20)Extreme space weather events are rare, and quantifying their likelihood is challenging, often relying on geomagnetic indices obtained from ground-based magnetometer observations that span multiple solar cycles. The Dst index ring-current monitor, derived from an hourly average over four low-latitude stations, is a benchmark for extreme space weather events, and has been extensively studied ... -
Temporal evolution of under-ice meltwater layers and false bottoms and their impact on summer Arctic sea ice mass balance
(Journal article; Tidsskriftartikkel; Peer reviewed, 2023-03-31)Low-salinity meltwater from Arctic sea ice and its snow cover accumulates and creates under-ice meltwater layers below sea ice.These meltwater layers can result in the formation of new ice layers, or false bottoms, at the interface of this low-salinity meltwater and colder seawater. As part of the Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC), we used a ... -
Seafood production in Northern Norway: Analyzing variation and co-development in aquaculture and coastal fisheries
(Journal article; Tidsskriftartikkel; Peer reviewed, 2023-07-27)Norway is one of the leading ocean-based food production nations. Its seafood industry comprises wild-capture fisheries and farmed fish production. Both industries play a provisional role but also contribute to economic development of the country and help sustain coastal communities, particularly, in Northern Norway. Coastal fishery has been the staple industry in Northern Norway for centuries, while ... -
Mapping the shape and dimension of three-dimensional Lagrangian coherent structures and invariant manifolds
(Journal article; Tidsskriftartikkel; Peer reviewed, 2023-03-10)We introduce maps of Cauchy–Green strain tensor eigenvalues to barycentric coordinates to quantify and visualize the full geometry of three-dimensional deformation in stationary and non-stationary fluid flows. As a natural extension of Lagrangian coherent structure diagnostics, which provide separate scalar fields and a one-dimensional quantification of fluid deformation, our barycentric mapping ...