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norskArtikler, rapporter og annet (matematikk og statistikk): Nye registreringer
Viser treff 221-240 av 316
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A generalization of weight polynomials to matroids
(Tidsskriftartikkel; Journal article; Peer reviewed, 2015-11-11)Generalizing polynomials previously studied in the context of linear codes, we define weight polynomials and an enumerator for a matroid M. Our main result is that these polynomials are determined by Betti numbers associated with N0-graded minimal free resolutions of the Stanley-Reisner ideals of M and so-called elongations of M. Generalizing Greene’s the- orem from coding theory, we show that ... -
A generalization of Kung’s theorem
(Journal article; Tidsskriftartikkel; Peer reviewed, 2015-10-01)We give a generalization of Kung’s theorem on critical exponents of linear codes over a finite field, in terms of sums of extended weight polynomials of linear codes. For all i=k+1,…,ni=k+1,…,n, we give an upper bound on the smallest integer m such that there exist m codewords whose union of supports has cardinality at least i. -
Stanley-Reisner resolution of constant weight linear codes
(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. -
Betti numbers associated to the facet ideal of a matroid
(Journal article; Tidsskriftartikkel; Peer reviewed, 2015-01-06)To a matroid M with n edges, we associate the so-called facet ideal F(M)⊂k[x1,…,xn] , generated by monomials corresponding to bases of M. We show that when M is a graph, the Betti numbers related to an ℕ0-graded minimal free resolution of F(M) are determined by the Betti numbers related to the blocks of M. Similarly, we show that the higher weight hierarchy of M is determined by the weight hierarchies ... -
Stem cell regulation: Implications when differentiated cells regulate symmetric stem cell division
(Journal article; Tidsskriftartikkel; Peer reviewed, 2015-05-19)We use a mathematical model to show that if symmetric stem cell division is regulated by differentiated cells, then changes in the population dynamics of the differentiated cells can lead to changes in the population dynamics of the stem cells. More precisely, the relative fitness of the stem cells can be affected by modifying the death rate of the differentiated cells. This result is interesting ... -
Dørene lukkes for klimamålene
(Journal article; Tidsskriftartikkel, 2016)FNs klimapanel har utarbeidet en rekke prognoser for økningen i global middeltemperatur basert på ulike scenarier for utviklingen av utslipp av drivhusgasser og partikler fra menneskelig aktivitet. Disse prognosene er i hovedsak basert på en lang rekke svært komplekse modeller. De mest komplekse, såkalte jordsystemmodeller, omfatter sirkulasjonen i atmosfære og hav, men også isdynamikk, og kjemiske ... -
Holdbarhet på klippfisk. Vekst av rødmidd i klippfisk lagret ved forhøyede temperaturer (AP2)
(Research report; Forskningsrapport, 2016-02)I prosjektet «Holdbarhet på klippfisk» er det foretatt studier for å fastsette holdbarhet på klippfisk basert på vekst av rødmidd. Denne rapporten referer til studier hvor klippfisk er lagret ved forhøyede temperaturer. Rød misfarging skyldes vekst av rødmidd som er en ekstrem halofil bakterie og denne blir naturlig tilført fisken gjennom saltet. Emballert loins av klippfisk og flekket klippfisk ble ... -
Limits to the quantification of local climate change
(Journal article; Tidsskriftartikkel; Peer reviewed, 2015-09-16)Abstract Wedemonstrate how the fundamental timescales of anthropogenic climate change limit the identification of societally relevant aspects of changes in precipitation.Weshow that it is nevertheless possible to extract, solely from observations, some confident quantified assessments of change at certain thresholds and locations. Maps of such changes, for a variety of hydrologically-relevant, ... -
Computer-aided decision support for melanoma detection applied on melanocytic and non-melanocytic skin lesions: a comparison of two systems based on automatic analysis of dermoscopic images
(Journal article; Tidsskriftartikkel; Peer reviewed, 2015)Commercially available clinical decision support systems (CDSSs) for skin cancer have been designed for the detection of melanoma only. Correct use of the systems requires expert knowledge, hampering their utility for nonexperts. Furthermore, there are no systems to detect other common skin cancer types, that is, nonmelanoma skin cancer (NMSC). As early diagnosis of skin cancer is essential, there ... -
Attribution in the presence of a long-memory climate response
(Journal article; Tidsskriftartikkel; Peer reviewed, 2015-11-18)Multiple, linear regression is employed to attribute variability in the global surface temperature to various forcing components and prominent internal climatic modes. The purpose of the study is to assess how sensitive attribution is to long-range memory (LRM) in the model for the temperature response. The model response to a given forcing component is its fingerprint and is different for a zero ... -
Network analysis of geomagnetic substorms using the SuperMAG database of ground-based magnetometer stations
(Journal article; Tidsskriftartikkel; Peer reviewed, 2015-09-26)The overall morphology and dynamics of magnetospheric substorms is well established in terms of the observed qualitative auroral features seen in ground-based magnetometers. This paper focuses on the quantitative characterization of substorm dynamics captured by ground-based magnetometer stations. We present the first analysis of substorms using dynamical networks obtained from the full available ... -
Klimakrisen og økonomisk politikk
(Chronicle; Kronikk, 2015-11-14) -
Long-memory effects in linear response models of Earth's temperature and implications for future global warming
(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 ... -
Dørene lukkes for klimamålene
(Chronicle; Kronikk, 2015-11-10) -
Global warming projections derived from an observation-based minimal model
(Journal article; Tidsskriftartikkel, 2015-09-18)A simple conceptual model for the global mean surface temperature (GMST) response to CO2 emissions is presented and analysed. It consists of linear long-memory models for the GMST anomaly response ∆T to radiative forcing and atmospheric CO2 - 5 concentration response ∆C to emission rate. The responses are connected by the standard logarithmic relation between CO2 concentration and its radiative ... -
Attribution in the presence of a long-memory climate response
(Journal article; Tidsskriftartikkel, 2015-08-10)Multiple, linear regression is employed to attribute variability in the global surface temperature to various forcing components and prominent internal climatic modes. The purpose of the study is to asses how sensitive attribution is to long-range memory 5 (LRM) in the model for the temperature response. The model response to a given forcing component is its fingerprint, and is different for a ... -
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 ... -
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 ...
