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norskInstitutt for matematikk og statistikk: Nye registreringer
Viser treff 281-300 av 391
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Are there multiple scaling regimes in Holocene temperature records?
(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 ... -
Spatiotemporal Long-Range Persistence in Earth’s Temperature Field: Analysis of Stochastic-Diffusive Energy Balance Models
(Journal article; Tidsskriftartikkel; Peer reviewed, 2015-11-01)A two-dimensional stochastic–diffusive energy balance model (EBM) formulated on a sphere by G. R. North et al. is explored and generalized. Instantaneous and frequency-dependent spatial autocorrelation functions and local temporal power spectral densities are computed for local sites and for spatially averaged surface temperature signals up to the global scale. On time scales up to the relaxation ... -
Late quaternary temperature variability described as abrupt transitions on a 1/f noise background
(Journal article; Tidsskriftartikkel, 2015-11-09)We show that in order to have a scaling description of the climate system that is not inherently non-stationary, the rapid shifts between stadial and interstadial conditions during the last glaciation cannot be included in the scaling law. The same is true for the 5 shifts between the glacial and interglacial states in the quaternary climate. When these events are omitted from a scaling analysis ... -
Overlevelsesanalyse med tidsavhengige forklaringsvariabler med bruk av Cox proporsjonal hasard regresjonsmodell
(Master thesis; Mastergradsoppgave, 2015-12-15)I denne mastergradsoppgaven ble det brukt overlevelsesanalyse med tidsavhengige variabler til å estimere en Cox proporsjonal hasard regresjonsmodell. Variablene stammet fra forskningsprosjektet ''Kvinner og kreft'' (The Norwegian Women and Cancer post genome cohort study - NOWAC) ved universitetet i Tromsø og besto av 57 561 kvinner. Modellen ble brukes til lage en modell av hasard raten til kvinnene ... -
Linear scaling Coulomb interaction in the multiwavelet basis, a parallel implementation
(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 ... -
Institutt for matematiske realfag 1972-1992. IMR 20 år. Knutepunkter i instituttets historie og perspektiver på fag og fremtid
(Research report; Forskningsrapport, 1992) -
Eilertsen-bløffen
(Chronicle; Kronikk, 2015-06-27)Kristian Eilertsen i Troms FRP prøver i Nordlys 24. juni febrilsk å justere fakta etter sine politiske oppfatninger – og ikke motsatt – når han oppdager at seriøse argumenter mot menneskeskapte klimaendringer forsvinner som dugg for solen. Han er heldigvis på kollisjonskurs med FRPs egen olje- og energiminister, som sammen med direktøreni Statoil har erklært at det skjer en menneskeskapt global ... -
En investering i tvil
(Journal article; Tidsskriftartikkel, 2015-07-30)Ifølge Ole Henrik Ellestads innlegg i Nordlys 20. juli er alle modeller som ikke stemmer overens med observasjoner gale. Det kan man godt si, men det betyr at alle modeller er gale. En modell er en forenklet versjon av virkeligheten, og vil alltid avvike noe fra observasjonene. Man lærer likevel mye av å bruke modeller.Klimamodellene er gode på å forutsi forventet temperaturrespons på eksterne ... -
The Unidirectional Pulse Propagation Equation for Cylindrical Vector modes
(Master thesis; Mastergradsoppgave, 2015-07-27)A new model for the unidirectional pulse propagation equations (UPPE) was developed by Per Jacobsen[1], this model is based on the assumption of cylindrical vector (CV) modes. The model will be strong for CV type electrical eld representations where only a few modes will be excited. In this thesis we will investigate the model further. The model will be implemented as a pseudo spectral method where ... -
Regional melt-pond fraction and albedo of thin Arctic first-year drift ice in late summer
(Journal article; Tidsskriftartikkel; Peer reviewed, 2015-02-09)The paper presents a case study of the regional ( ≈ 150 km) morphological and optical properties of a relatively thin, 70–90 cm modal thickness, first-year Arctic sea ice pack in an advanced stage of melt. The study combines in situ broadband albedo measurements representative of the four main surface types (bare ice, dark melt ponds, bright melt ponds and open water) and images acquired by a ... -
Arctic tipping points
(Master thesis; Mastergradsoppgave, 2015-05-15)The Arctic is warming much faster than the entire planet, and this causes severe melting of sea ice. However, the climate of different regions of the Earth is interconnected, and changes in the amount of ice in the Arctic can dramatically affect the climate across the whole planet. Some scientists claim that a possible tipping point is the event of the ice-free Arctic Ocean in summer. Certain ... -
Tipping points and crises in financial markets
(Master thesis; Mastergradsoppgave, 2015-05-15)Electricity spot markets and other financial markets are complex systems, and it is difficult to forecast their behaviour, especially uncontrolled and unmanageable situations, such as power crises and deflation of financial bubbles. An energy crisis is any price rise in the supply of energy resources to an economy. It has undesirable consequences, occasionally irreversible. The most known of these ... -
Separation of fish stocks by otoliths: Image representation, Fourier approximation and discrimination
(Master thesis; Mastergradsoppgave, 2015-05-18)In this thesis the entire process of Fourier Contour Analysis have been investigated for potential sources of bias. No potential biases has been found when creating the contour, however it has been shown there is a slight bias in which otoliths get invalidated by breakage. A probablity based sampling strategy has been suggested instead of the previously used stratification based. It has been shown ... -
Simplicial complexes, Demi-matroids, Flag of linear codes and pair of matroids.
(Master thesis; Mastergradsoppgave, 2015-05-15)We first describe linear error-correcting codes, and show how many of their most important properties are determined by their associated matroids . We also introduce the simplicial complex of the independent sets of a matroid. We then proceed to study flags of linear codes, and recall the definition of demi-matroids, and how such demi-matroids associated to flags can describe important properties ... -
Homological methods applied to theory of codes and matroids
(Master thesis; Mastergradsoppgave, 2015-05-15)In this thesis we first give a survey of linear error-correcting codes, and how many of their most important properties only depend on the matroids derived from their parity check matrices. We also introduce the Stanley-Reisner ring associated to the simplicial complex of the independent sets of a matroid. We then recall in particular how some important properties of linear codes, including their ... -
Towers of Betti Numbers of Matroids and Weight Distribution of Linear Codes and their Duals
(Master thesis; Mastergradsoppgave, 2015-05-15)The main notion behind the study of matroids is linear dependence. In this thesis, we give a survey of the concepts and properties of linear error-correcting codes over finite fields being dependent only on the matroids derived from these codes. In particular, the weight distributions of linear codes, and their extensions, over bigger fields are only dependent on the N-graded Betti numbers of these ... -
A Multiscale Wavelet-Based Test for Isotropy of Random Fields on a Regular Lattice
(Journal article; Tidsskriftartikkel; Peer reviewed, 2014-12-31)A test for isotropy of images modeled as stationary or intrinsically stationary random fields on a lattice is developed. The test is based on wavelet theory, and can operate on the horizontal and vertical scale of choice, or on any combination of scales. Scale is introduced through the wavelet variances (sometimes referred to as the wavelet power spectrum), which decompose the variance over ... -
2d gauge theories and generalized geometry
(Journal article; Tidsskriftartikkel; Peer reviewed, 2014) -
A semiautomatic tool for prostate segmentation in radiotherapy treatment planning
(Journal article; Tidsskriftartikkel; Peer reviewed, 2014-01-25) -
Symmetry transformation groups and differential invariants
(Master thesis; Mastergradsoppgave, 2014-11-15)There exists a local classification of finite-dimensional Lie algebras of vector fields in two complex dimensions. We lift the Lie algebras from this classification to three complex dimensions.
