Institutt for matematikk og statistikk: Recent submissions
Now showing items 101-120 of 412
-
On Multi-Rule and Probability-Dependant Adaptations of Conway’s Game of Life and Their Character
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022)We introduce some novel adaptations of Life-Like Automata. We focus mainly on some modifications of the original rules where the evolution of the system is depending from the step and the zone of the grid. We study also the properties of some novel non-deterministic adaptations. -
Effects of feedbacks for an energy balance model on a circle
(Mastergradsoppgave; Master thesis, 2022-05-31)A simple, North like, energy balance model on a circle is studied using boundary formulations derived with Green's functions for the stationary case, and a pseudo-spectral and finite difference solution for the time dependent case. The bifurcation software Auto-07p is also applied. The boundary formulation solution can be solved analytically in most cases, and is solved for bifurcation diagrams. ... -
Symmetry gaps for higher order ordinary differential equations
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-07-04)The maximal contact symmetry dimensions for scalar ODEs of order ≥ 4 and vector ODEs of order ≥ 3 are well known. Using a Cartan-geometric approach, we determine for these ODEs the next largest realizable (submaximal) symmetry dimension. Moreover, finer curvature-constrained submaximal symmetry dimensions are also classified. -
Data-Driven Robust Control Using Reinforcement Learning
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-02-21)This paper proposes a robust control design method using reinforcement learning for controlling partially-unknown dynamical systems under uncertain conditions. The method extends the optimal reinforcement learning algorithm with a new learning technique based on the robust control theory. By learning from the data, the algorithm proposes actions that guarantee the stability of the closed-loop system ... -
Symmetries of supergeometries related to nonholonomic superdistributions
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-06-06)We extend Tanaka theory to the context of supergeometry and obtain an upper bound on the supersymmetry dimension of geometric structures related to strongly regular bracket-generating distributions on supermanifolds and their structure reductions. -
Probabilistic Wind Power and Electricity Load Forecasting with Echo State Networks
(Mastergradsoppgave; Master thesis, 2022-05-15)With the introduction of distributed generation and the establishment of smart grids, several new challenges in energy analytics arose. These challenges can be solved with a specific type of recurrent neural networks called echo state networks, which can handle the combination of both weather and power consumption or production depending on the dataset to make predictions. Echo state networks ... -
Killing Tensors in Koutras-McIntosh Spacetimes
(Mastergradsoppgave; Master thesis, 2022-05-15)This thesis is concerned with the (non)existence of Killing Tensors in Koutras-McIntosh spacetimes. Killing tensors are of particular interest in general relativity, because these correspond to conserved quantities for the geodesic motion. For instance, Carter found such a conserved quantity in the Kerr metric which he used to explicitly integrate the geodesic equations. The equation defining ... -
Wachpress Conjecture Restricted To Arrangements Of Three Conics
(Mastergradsoppgave; Master thesis, 2022-05-15)This thesis discusses Wachpress conjecture restricted to arrangements of three conics. Wachpress conjectured the existence of a set of barycentric coordinates, namely Wachpress coordinates, on all polycons. Barycentric coordinates are very useful in many different fields as they can be used to define a finite element approximation scheme with linear precision. This thesis focuses on the conjecture ... -
On the effects of symmetry in the energy balance on a sphere
(Mastergradsoppgave; Master thesis, 2022-05-15)Simple climate models have gathered much attention as they have suggested the possibility of abrupt climate change associated with tipping points. Several simple climate models are found to have multiple equilibria, but in most cases similar equilibria do not appear or become too difficult to find in complex, fully coupled earth system models. In this thesis, we investigate a simple climate model, ... -
Greedy weights for matroids
(Journal article; Tidsskriftartikkel; Peer reviewed, 2020-12-19)We introduce greedy weights of matroids, inspired by those for linear codes. We show that a Wei duality holds for two of these types of greedy weights for matroids. Moreover we show that in the cases where the matroids involved are associated to linear codes, our definitions coincide with those for codes. Thus our Wei duality is a generalization of that for linear codes given by Schaathun. In ... -
Deep learning applied to fish otolith images
(Master thesis; Mastergradsoppgave, 2021-11-14)This thesis is concerned with classification and regression using deep learning applied to fish otolith images. Otoliths (earstones) are calcified structures in the inner ear of vertebrates, and are used, for instance, in fish stock assessment and fish age determination. We use convolutional neural networks – a class of deep learning models - on two specific problems: discrimination between Northeast ... -
Automatic detection of the mental foramen for estimating mandibular cortical width in dental panoramic radiographs
(Mastergradsoppgave; Master thesis, 2021-12-15)Screening tests are vital for detecting diseases, especially at early stages, where efforts can prevent further illness. For example, osteoporosis is a systemic skeletal disease characterized by low bone mass and microarchitectural deterioration of bone tissue, resulting in bone fragility and susceptibility to fracture. Dual-energy x-ray absorptiometry is commonly used to diagnose osteoporosis since ... -
Overview of the MOSAiC expedition: Physical oceanography
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-02-07)Arctic Ocean properties and processes are highly relevant to the regional and global coupled climate system, yet still scarcely observed, especially in winter. Team OCEAN conducted a full year of physical oceanography observations as part of the Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC), a drift with the Arctic sea ice from October 2019 to September 2020. ... -
25 years of self-organized criticality: concepts and controversies
(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 ... -
Classification of simply-transitive Levi non-degenerate hypersurfaces in C^3
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-06-24)Holomorphically homogeneous Cauchy–Riemann (CR) real hypersurfaces <i>M<i/><sup>3</sup>⊂C<sup>2</sup> were classified by Élie Cartan in 1932. In the next dimension, we complete the classification of simply-transitive Levi non-degenerate hypersurfaces <i>M<i/><sup>5</sup>⊂C<sup>3</sup> using a novel Lie algebraic approach independent of any earlier classifications of abstract Lie algebras. Central ... -
Constraining two climate field reconstruction methodologies over the North Atlantic realm using pseudo-proxy experiments
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-07-06)This study presents pseudo-proxy experiments to quantify the reconstruction skill of two climate field reconstruction methodologies for a marine proxy network subject to age uncertainties. The BARCAST methodology (Bayesian Algorithm for Reconstructing Climate Anomalies in Space and Time) is tested for sea surface temperature (SST) reconstruction for the first time over the northern North Atlantic ... -
Symmetry classification of viscid flows on space curves
(Journal article; Tidsskriftartikkel; Peer reviewed, 2020-11-01)Symmetries and differential invariants of viscid flows with viscosity depending on temperature on a space curve are given. Their dependence on thermodynamic states of media is studied, and a classification of thermodynamic states is given. -
Continuum mechanics of media with inner structures
(Journal article; Tidsskriftartikkel; Peer reviewed, 2020-11-05)We propose a geometrical approach to the mechanics of continuous media equipped with inner structures and give the basic (Navier–Stokes, mass conservation and energy conservation) equations of their motion. -
Exact semidefinite programming bounds for packing problems
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-05-25)In this paper we give an algorithm to round the floating point output of a semidefinite programming solver to a solution over the rationals or a quadratic extension of the rationals. This algorithm does not require the solution to be strictly feasible and works for large problems. We apply this to get sharp bounds for packing problems, and we use these sharp bounds to prove that certain optimal ... -
Lightboard – a new teaching tool at the Faculty of Science and Technology at UiT
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-05-05)We would like to present a new tool that was built by three lecturers at UiT last semester – Lightboard. This tool was used before in other countries and other universities, but never at UiT. The COVID-19 pandemic situation motivated the lecturers to find a way to do online lectures differently. Blackboard and chalk work well for natural sciences as long as the lecture is physical and the teacher ...