Siste publikasjoner

• Erhardt, André Henrik (2021). Stability of weak solutions to parabolic problems with nonstandard growth and cross–diffusion. Axioms.  ISSN 2075-1680.  10(1), s 1- 7 . doi: 10.3390/axioms10010014
• Brualdi, R.A. & Dahl, Geir (2021). Sign-restricted matrices of 0's, 1's, and -1's. Linear Algebra and its Applications.  ISSN 0024-3795.
• Normann, Dag & Sanders, Sam (2021). The Axiom of Choice in computability theory and Reverse Mathematics with a cameo for the Continuum Hypothesis. Journal of Logic and Computation.  ISSN 0955-792X. . doi: https://doi.org/10.1093/logcom/exaa080
• Støle-Hentschel, Susanne; Nieto Borge, Jose Carlos & Trulsen, Karsten (2021). The deconvolution as a method to deal with gaps in ocean wave measurements. Ocean Engineering.  ISSN 0029-8018.  219 . doi: 10.1016/j.oceaneng.2020.108373 Vis sammendrag

  This work introduces the deconvolution as a technique to reconstruct missing information in data. While the method was originally developed for ocean waves, it will be useful in a wider range of applications where gaps in data may alter the statistics or spikes have to be eliminated without removing extreme values. For the application to ocean waves, it is estimated that gaps as long as half of the peak period may be reconstructed well. It is possible to reconstruct data of longer gaps, however, in total the amount of missing points should be less than 50% of all points and the missing data should not be clustered.

• Vanem, Erik; Aarsnes, Lars Holterud; Storhaug, Gaute & Astrup, Ole Christian (2021). Statistical Modelling and Comparison of Model-Based Fatigue Calculations and Hull Monitoring Data for Container Vessels, In  Practical Design of Ships and Other Floating Structures. Proceedings of the 14th International Symposium, PRADS 2019, September 22-26, 2019, Yokohama, Japan- Volume II.  Springer.  ISBN 978-981-15-4671-6.  paper.  s 517 - 536 Fulltekst i vitenarkiv.
• Rossow, Ingeborg Margrete; Amundsen, Ellen Johanna & Samuelsen, Sven Ove (2020). Socio‐economic differences in all‐cause mortality in people with alcohol use disorder: a prospective cohort study. Addiction.  ISSN 0965-2140.  116(1), s 53- 59 . doi: 10.1111/add.15070
• Landstad, Magnus Brostrup; Elliott, George A.; Bratteli, Tone; Digernes, Trond; Størmer, Erling; Robinson, Derek W; Kishimoto, Akitaka; Jorgensen, Palle E.T. & Evans, David E. (2020). Ola Bratteli and His Diagrams. Notices of the American Mathematical Society.  ISSN 0002-9920.  67(5), s 665- 675
• Barker, T.; Rauter, Matthias; Maguire, E. S. F.; Johnson, C. G. & Gray, J. M. N. T. (2020). Coupling rheology and segregation in granular flows. Journal of Fluid Mechanics.  ISSN 0022-1120.  909(A22) . doi: 10.1017/jfm.2020.973 Fulltekst i vitenarkiv. Vis sammendrag

  During the last fifteen years there has been a paradigm shift in the continuum modelling of granular materials; most notably with the development of rheological models, such as the μ(I) μ(I) -rheology (where μ μ is the friction and I is the inertial number), but also with significant advances in theories for particle segregation. This paper details theoretical and numerical frameworks (based on OpenFOAM) which unify these currently disconnected endeavours. Coupling the segregation with the flow, and vice versa, is not only vital for a complete theory of granular materials, but is also beneficial for developing numerical methods to handle evolving free surfaces. This general approach is based on the partially regularized incompressible μ(I) μ(I) -rheology, which is coupled to the gravity-driven segregation theory of Gray & Ancey (J. Fluid Mech., vol. 678, 2011, pp. 353–588). These advection–diffusion–segregation equations describe the evolving concentrations of the constituents, which then couple back to the variable viscosity in the incompressible Navier–Stokes equations. A novel feature of this approach is that any number of differently sized phases may be included, which may have disparate frictional properties. Further inclusion of an excess air phase, which segregates away from the granular material, then allows the complex evolution of the free surface to be captured simultaneously. Three primary coupling mechanisms are identified: (i) advection of the particle concentrations by the bulk velocity, (ii) feedback of the particle-size and/or frictional properties on the bulk flow field and (iii) influence of the shear rate, pressure, gravity, particle size and particle-size ratio on the locally evolving segregation and diffusion rates. The numerical method is extensively tested in one-way coupled computations, before the fully coupled model is compared with the discrete element method simulations of Tripathi & Khakhar (Phys. Fluids, vol. 23, 2011, 113302) and used to compute the petal-like segregation pattern that spontaneously develops in a square rotating drum.

• Chan, Tak Shing; Pedersen, Christian; Koplik, Joel & Carlson, Andreas (2020). Film deposition and dynamics of a self-propelled wetting droplet on a conical fibre. Journal of Fluid Mechanics.  ISSN 0022-1120. . doi: 10.1017/jfm.2020.834
• Arumugam, Gurusamy & Erhardt, André Henrik (2020). Existence and uniqueness of weak solutions to parabolic problems with nonstandard growth and cross diffusion. Electronic Journal of Differential Equations.  ISSN 1550-6150.  2020(123), s 1- 13 Fulltekst i vitenarkiv.
• Ivarsson, Bjorn; Kutzschebauch, Frank & Løw, Erik (2020). Factorization of symplectic matrices into elementary factors. Proceedings of the American Mathematical Society.  ISSN 0002-9939.  148(5), s 1963- 1970 . doi: 10.1090/proc/14891
• Grytten, Ivar; Rand, Knut Dagestad; Nederbragt, Alexander Johan & Sandve, Geir Kjetil (2020). Assessing graph-based read mappers against a baseline approach highlights strengths and weaknesses of current methods. BMC Genomics.  ISSN 1471-2164. . doi: 10.1186/s12864-020-6685-y
• Binde, Caroline Ditlev; Tvete, Ingunn Fride; Gåsemyr, Jørund Inge; Natvig, Bent & Klemp, Marianne (2020). Comparative effectiveness of dopamine agonists and monoamine oxidase type-B inhibitors for Parkinson’s disease: a multiple treatment comparison meta-analysis. European Journal of Clinical Pharmacology.  ISSN 0031-6970.  76(12), s 1731- 1743 . doi: 10.1007/s00228-020-02961-6 Fulltekst i vitenarkiv.
• Riiser, Even Sannes; Haverkamp, Thomas Hendricus Augustus; Varadharajan, Srinidhi; Borgan, Ørnulf; Jakobsen, Kjetill Sigurd; Jentoft, Sissel & Star, Bastiaan (2020). Metagenomic Shotgun Analyses Reveal Complex Patterns of Intra- and Interspecific Variation in the Intestinal Microbiomes of Codfishes. Applied and Environmental Microbiology.  ISSN 0099-2240.  86(6), s 1- 16 . doi: 10.1128/AEM.02788-19
• Mossige, Endre Joachim & Jensen, Atle (2020). Clog-free trilobite filtration: Tunable flow setup and velocity measurements. Micromachines.  ISSN 2072-666X.  11(10) . doi: 10.3390/mi11100904
• Grue, John & Osyka, Bogdan (2020). Runup on a vertical column in strong water wave events. Coastal Engineering.  ISSN 0378-3839.  163 . doi: 10.1016/j.coastaleng.2020.103775
• Grue, John (2020). Mini-tsunami made by ship moving across a depth change. Journal of waterway, port, coastal, and ocean engineering.  ISSN 0733-950X.
• Joki, Reidar Kvale; Grytten, Frode; Hayman, Brian & Sørensen, Bent Fruergaard (2020). A mixed mode cohesive model for FRP laminates incorporating large scale bridging behaviour. Engineering Fracture Mechanics.  ISSN 0013-7944.  239, s 1- 15 . doi: 10.1016/j.engfracmech.2020.107274 Fulltekst i vitenarkiv. Vis sammendrag

  A user defined cohesive material model is implemented in the LS-DYNA finite element code. The model is based on interface properties characterised from DCB specimens loaded with unequal bending moments. Different mode mixities are obtained by applying different ratios of moments to the two beams in the cracked part of the specimen. The mixed mode cohesive law is fitted for large scale bridging delamination through inverse modelling. In this way, the variations in stress and crack opening across the width of the specimen are taken into account. The J integral approach is used to find a starting point for the fitting procedure. Three properties from five moment configurations are evaluated to find a first estimate of the shape of the cohesive law: crack tip fracture energy, steady-state fracture resistance and crack end-opening at steady-state fracture resistance. The parameters of the cohesive law are then further adjusted using the optimisation tool LS-OPT. The implemented cohesive model is assessed by comparing numerical to experimental test results from the standardised ASTM double cantilever beam test and the ASTM mixed mode bending test.

• Greiner, Thomas Larsen; Hlebnikov, Volodya; Lie, Jan Erik; Kolbjørnsen, Odd; Kjeldsrud Evensen, Andreas; Harris Nilsen, Espen; Vinje, Vetle & Gelius, Leiv-J. (2020). Cross-streamer wavefield reconstruction through wavelet domain. Geophysics.  ISSN 0016-8033.  85(6), s 1ND- Z30 . doi: 10.1190/geo2019-0771.1 Fulltekst i vitenarkiv.
• Georgiev, Ivan; Kristiansen, Lars & Stephan, Frank (2020). Computable Irrational Numbers with Representations of Surprising Complexity. Annals of Pure and Applied Logic.  ISSN 0168-0072. . doi: 10.1016/j.apal.2020.102893 Fulltekst i vitenarkiv.
• Normann, Dag & Sanders, Sam (2020). Open sets in computability theory and reveres mathematics. Journal of Logic and Computation.  ISSN 0955-792X. . doi: 10.1093/logcom/exaa049
• Biagini, Francesca; Gnoatto, Alessandro & Hartel, Maximilian (2020). General Analysis of Long-Term Interest Rates. International Journal of Theoretical and Applied Finance.  ISSN 0219-0249.  23(1), s 2050002-1- 2050002-29 . doi: 10.1142/S0219024920500028
• Chan, Tak Shing; Kamal, Catherine; Snoeijer, Jacco H.; Sprittles, James E. & Eggers, Jens (2020). Cox–Voinov theory with slip. Journal of Fluid Mechanics.  ISSN 0022-1120.  900(A8) . doi: 10.1017/jfm.2020.499
• Agostini, Daniele; Améndola, Carlos & Ranestad, Kristian (2020). Moment Identifiability of Homoscedastic Gaussian Mixtures. Foundations of Computational Mathematics.  ISSN 1615-3375. . doi: 10.1007/s10208-020-09469-6
• Chan, Tak Shing; Yang, Fan & Carlson, Andreas (2020). Directional spreading of a viscous droplet on a conical fibre. Journal of Fluid Mechanics.  ISSN 0022-1120.  894(A26) . doi: 10.1017/jfm.2020.240
• Amine, Oussama; Baños, David & Proske, Frank Norbert (2020). Regularity properties of the stochastic flow of a skew fractional Brownian motion. Infinite Dimensional Analysis Quantum Probability and Related Topics.  ISSN 0219-0257.  23(1) . doi: 10.1142/S0219025720500058
• Boug, Pål; Cappelen, Ådne; Jansen, Eilev S & Swensen, Anders Rygh (2020). The Consumption Euler Equation or the Keynesian Consumption Function?. Oxford Bulletin of Economics and Statistics.  ISSN 0305-9049. . doi: 10.1111/obes.12394
• Bressan, Andrea & Lyche, Tom (2020). Local Approximation from Spline Spaces on Box Meshes. Foundations of Computational Mathematics.  ISSN 1615-3375. . doi: 10.1007/s10208-020-09467-8
• Li, Xin; Omland, Tron & Spielberg, Jack (2020). C*-algebras of right LCM one-relator monoids and Artin-Tits monoids of finite type. Communications in Mathematical Physics.  ISSN 0010-3616. . doi: 10.1007/s00220-020-03758-5
• Erhardt, André Henrik & Solem, Susanne (2020). On complex dynamics in a Purkinje and a ventricular cardiac cell model. Communications in nonlinear science & numerical simulation.  ISSN 1007-5704.  93 . doi: 10.1016/j.cnsns.2020.105511 Fulltekst i vitenarkiv.
• Raffo, Andrea & Biasotti, Silvia (2020). Weighted quasi-interpolant spline approximations: Properties and applications. Numerical Algorithms.  ISSN 1017-1398.  s 1- 29 . doi: 10.1007/s11075-020-00989-4
• Cuellar-Camacho, Jose Luis; Bhatia, Sumati; Reiter-Scherer, Valentin; Lauster, Daniel; Liese, Susanne; Rabe, Jürgen P; Herrmann, Andreas & Haag, Rainer (2020). Quantification of Multivalent Interactions between Sialic Acid and Influenza A Virus Spike Proteins by Single-Molecule Force Spectroscopy. Journal of the American Chemical Society.  ISSN 0002-7863.  142(28), s 12181- 12192 . doi: 10.1021/jacs.0c02852
• Kremer, Marcel; Benth, Fred Espen; Felten, Björn & Kiesel, Rüdiger (2020). Volatility and liquidity on high-frequency electricity futures markets: Empirical analysis and stochastic modeling. International Journal of Theoretical and Applied Finance.  ISSN 0219-0249.  23(4) . doi: 10.1142/S0219024920500272
• Pladsen, Arne Valebjørg; Nilsen, Gro; Rueda, Oscar M.; Aure, Miriam Ragle; Borgan, Ørnulf; Liestøl, Knut; Vitelli, Valeria; Frigessi Di Rattalma, Arnoldo; Langerød, Anita; Mathelier, Anthony; Engebråten, Olav; Kristensen, Vessela N.; Wedge, David C.; Van Loo, Peter; Caldas, Carlos; Børresen-Dale, Anne-Lise; Russnes, Hege Elisabeth Giercksky & Lingjærde, Ole Christian (2020). DNA copy number motifs are strong and independent predictors of survival in breast cancer. Communications Biology.  ISSN 2399-3642.  3 . doi: 10.1038/s42003-020-0884-6 Fulltekst i vitenarkiv.
• Normann, Dag (2020). Measure-theoretic Uniformity and the Suslin Functional. Computability - The Journal of the Assosiation.  ISSN 2211-3568. . doi: 10.3233/COM-190248 Fulltekst i vitenarkiv.
• Vollestad, Petter; Angheluta, Luiza & Jensen, Atle (2020). Experimental study of secondary flows above rough and flat interfaces in horizontal gas-liquid pipe flow. International Journal of Multiphase Flow.  ISSN 0301-9322.  125 . doi: 10.1016/j.ijmultiphaseflow.2020.103235
• Ciardo, Lorenzo (2020). A Fiedler center for graphs generalizing the characteristic set. Linear Algebra and its Applications.  ISSN 0024-3795.  584, s 197- 220 . doi: 10.1016/j.laa.2019.09.015
• Friederich, Pascal; Dos Passos Gomes, Gabriel; De Bin, Riccardo; Aspuru-Guzik, Alán & Balcells, David (2020). Machine learning dihydrogen activation in the chemical space surrounding Vaska's complex. Chemical Science.  ISSN 2041-6520.  11(18), s 4584- 4601 . doi: 10.1039/d0sc00445f
• Hubin, Aliaksandr; Storvik, Geir Olve & Frommlet, Florian (2020). Rejoinder for the discussion of the paper "A Novel Algorithmic Approach to Bayesian Logic Regression". Bayesian Analysis.  ISSN 1936-0975.  15(1), s 312- 333 . doi: 10.1214/18-ba1141 Vis sammendrag

  Logic regression was developed more than a decade ago as a tool to construct predictors from Boolean combinations of binary covariates. It has been mainly used to model epistatic effects in genetic association studies, which is very appealing due to the intuitive interpretation of logic expressions to describe the interaction between genetic variations. Nevertheless logic regression has (partly due to computational challenges) remained less well known than other approaches to epistatic association mapping. Here we will adapt an advanced evolutionary algorithm called GMJMCMC (Genetically modified Mode Jumping Markov Chain Monte Carlo) to perform Bayesian model selection in the space of logic regression models. After describing the algorithmic details of GMJMCMC we perform a comprehensive simulation study that illustrates its performance given logic regression terms of various complexity. Specifically GMJMCMC is shown to be able to identify three-way and even four-way interactions with relatively large power, a level of complexity which has not been achieved by previous implementations of logic regression. We apply GMJMCMC to reanalyze QTL (quantitative trait locus) mapping data for Recombinant Inbred Lines in Arabidopsis thaliana and from a backcross population in Drosophila where we identify several interesting epistatic effects. The method is implemented in an R package which is available on github.

• Hubin, Aliaksandr; Storvik, Geir Olve; Grini, Paul Eivind & Butenko, Melinka Alonso (2020). A Bayesian binomial regression model with latent gaussian processes for modelling DNA methylation. Austrian Journal of Statistics.  ISSN 1026-597X.  49(4), s 46- 56 . doi: 10.17713/ajs.v49i4.1124 Fulltekst i vitenarkiv. Vis sammendrag

  Epigenetic observations are represented by the total number of reads from a given pool of cells and the number of methylated reads, making it reasonable to model this data by a binomial distribution. There are numerous factors that can influence the probability of success in a particular region. Moreover, there is a strong spatial (alongside the genome) dependence of these probabilities. We incorporate dependence on the covariates and the spatial dependence of the methylation probability for observations from a pool of cells by means of a binomial regression model with a latent Gaussian field and a logit link function. We apply a Bayesian approach including prior specifications on model configurations. We run a mode jumping Markov chain Monte Carlo algorithm (MJMCMC) across different choices of covariates in order to obtain the joint posterior distribution of parameters and models. This also allows finding the best set of covariates to model methylation probability within the genomic region of interest and individual marginal inclusion probabilities of the covariates.

• Cunen, Celine Marie Løken; Hjort, Nils Lid & Nygård, Håvard Mokleiv (2020). Statistical sightings of better angels: Analysing the distribution of battle-deaths in interstate conflict over time. Journal of Peace Research.  ISSN 0022-3433.  57(2), s 221- 234 . doi: 10.1177/0022343319896843 Fulltekst i vitenarkiv.
• Ottem, John Christian & Gounelas, Frank (2020). Remarks on the positivity of the cotangent bundle of a K3 surface. Épijournal de Géométrie Algébrique (EPIGA).  ISSN 2491-6765.  4(8) Fulltekst i vitenarkiv.
• Valnes, Lars Magnus; Mitusch, Sebastian; Ringstad, Geir; Eide, Per Kristian; Funke, Simon Wolfgang & Mardal, Kent-Andre (2020). Apparent diffusion coefficient estimates based on 24 hours tracer movement support glymphatic transport in human cerebral cortex. Scientific Reports.  ISSN 2045-2322.  10 . doi: 10.1038/s41598-020-66042-5 Fulltekst i vitenarkiv.
• Ottem, John Christian & Benoist, Olivier (2020). Failure of the integral Hodge conjecture for threefolds of Kodaira dimension zero. Commentarii Mathematici Helvetici.  ISSN 0010-2571.  95, s 27- 35 Fulltekst i vitenarkiv.
• Ottem, John Christian & Suzuki, Fumiaki (2020). A pencil of Enriques surfaces with non-algebraic integral Hodge classes. Mathematische Annalen.  ISSN 0025-5831.  377, s 183- 197 . doi: 10.1007/s00208-020-01969-8 Fulltekst i vitenarkiv.
• Arumugam, Gurusamy & Erhardt, André Henrik (2020). Existence of weak solutions to a certain homogeneous parabolic Neumann problem involving variable exponents and cross-diffusion. Journal of Elliptic and Parabolic Equations (JEPE).  ISSN 2296-9020.  6(2), s 685- 709 . doi: 10.1007/s41808-020-00078-6 Fulltekst i vitenarkiv.
• Zengaffinen, Thomas; Løvholt, Finn; Pedersen, Geir Kleivstul & Muhari, Abdul (2020). Modelling 2018 Anak Krakatoa Flank Collapse and Tsunami: Effect of Landslide Failure Mechanism and Dynamics on Tsunami Generation. Pure and Applied Geophysics (PAGEOPH).  ISSN 0033-4553.  177, s 2493- 2516 . doi: 10.1007/s00024-020-02489-x
• Erhardt, André Henrik; Mardal, Kent-Andre & Schreiner, Jakob Emil (2020). Dynamics of a neuron-glia system: the occurrence of seizures and the influence of electroconvulsive stimuli. Journal of Computational Neuroscience.  ISSN 0929-5313.  48(2), s 229- 251 . doi: 10.1007/s10827-020-00746-5 Fulltekst i vitenarkiv.
• Stoltenberg, Emil Aas; Nordeng, Hedvig Marie Egeland; Ystrøm, Eivind & Samuelsen, Sven Ove (2020). The cure model in perinatal epidemiology. Statistical Methods in Medical Research.  ISSN 0962-2802. . doi: 10.1177/0962280220904092 Fulltekst i vitenarkiv.
• Friedemann, Christopher; Mortensen, Mikael & Nossen, Jan (2020). Two-phase flow simulations at 0 - 4° inclination in an eccentric annulus. International Journal of Heat and Fluid Flow.  ISSN 0142-727X.  83 . doi: 10.1016/j.ijheatfluidflow.2020.108586 Fulltekst i vitenarkiv.
• Kristiansen, Lars & Simonsen, Jakob Grue (2020). On the Complexity of Conversion Between Classic Real Number Representations. Lecture Notes in Computer Science (LNCS).  ISSN 0302-9743.  12098, s 75- 86 . doi: 10.1007/978-3-030-51466-2_7
• Kristiansen, Lars & Murwanashyaka, Juvenal (2020). On Interpretability between some weak essential undecidable theories. Lecture Notes in Computer Science (LNCS).  ISSN 0302-9743.  12098, s 63- 74 . doi: 10.1007/978-3-030-51466-2_6 Fulltekst i vitenarkiv.
• Zengaffinen, Thomas; Løvholt, Finn; Pedersen, Geir Kleivstul & Harbitz, Carl Bonnevie (2020). Effects of rotational submarine slump dynamics on tsunami-genesis – new insight from idealized models and the 1929 Grand Banks event. Geological Society Special Publication.  ISSN 0305-8719. . doi: 10.1144/SP500-2019-201 Fulltekst i vitenarkiv. Vis sammendrag

  Sediment slumps are known to have generated important tsunamis such as the 1998 Papua New Guinea (PNG) and the 1929 Grand Banks events. Tsunami modellers commonly use solid blocks with short run-out distances to simulate these slumps. While such methods have the obvious advantage of being simple to use, they offer little or no insight into physical processes that drive the events. The importance of rotational slump motion to tsunamigenic potential is demonstrated in this study by employing a viscoplastic landslide model with Herschel-Bulkley rheology. A large number of simulations for different material properties and landslide configurations are carried out to link the slump's deformation, rheology, its translational and rotational kinematics, to its tsunami-genesis. The yield strength of the slump is shown to be the primary material property that determines the tsunami-genesis. This viscoplastic model is further employed to simulate the 1929 Grand Banks tsunami using updated geological source information. The results of this case study suggest that the viscoplastic model can be used to simulate complex slump induced tsunami. The simulations of the 1929 Grand Banks event also indicate that a pure slump mechanism is more tsunamigenic than a corresponding translational landslide mechanism.

• Kristiansen, Lars & Murwanashyaka, Juvenal (2020). First-Order Concatenation Theory with Bounded Quantifiers (Preprint). arXiv.org.  ISSN 2331-8422. . doi: 10.1007/s00153-020-00735-6
• Rauter, Matthias; Barker, T. & Fellin, W. (2020). Granular viscosity from plastic yield surfaces: The role of the deformation type in granular flows. Computers and geotechnics.  ISSN 0266-352X.  122 . doi: 10.1016/j.compgeo.2020.103492 Fulltekst i vitenarkiv. Vis sammendrag

  Numerical simulations of granular flows with Navier–Stokes type models emerged in the last decade, challenging the well established depth-averaged models. The structure of these equations allows for extension to general rheologies based on complex and realistic constitutive models. Substantial effort has been put into describing the effect of the shear rate, i.e. the magnitude of the velocity gradient, on the shear stress. Here we analyse the effect of the deformation type. We apply the theories of Mohr–Coulomb and Matsuoka–Nakai to calculate the stresses under different deformation types and compare results to the theory of Drucker–Prager, which is formulated independently of the deformation type. This model is particularly relevant because it is the basis for many granular rheologies, such as the –rheology. All models have been implemented into the open-source toolkit OpenFOAM® for a practical application. We found that, within the context of these models, the deformation type has a large influence on the stress. However, for the geometries considered here, these differences are limited to specific zones which have little influence on the landslide kinematics. Finally we are able to give indicators on when the deformation type should be considered in modelling of landslides and when it can be neglected.

• Støle-Hentschel, Susanne; Trulsen, Karsten; Nieto Borge, José Carlos & Olluri, Shkurte (2020). Extreme Wave Statistics in Combined and Partitioned Windsea and Swell. Water Waves.  ISSN 2523-367X.  2, s 169- 184 . doi: 10.1007/s42286-020-00026-w
• Normann, Dag & Sanders, Sam (2020). Pincherle's theorem in reverse mathematics and computability theory. Annals of Pure and Applied Logic.  ISSN 0168-0072.  171(5) . doi: 10.1016/j.apal.2020.102788 Fulltekst i vitenarkiv.
• Landet, Tormod; Mardal, Kent-Andre & Mortensen, Mikael (2020). Slope limiting the velocity field in a discontinuous Galerkin divergence-free two-phase flow solver. Computers & Fluids.  ISSN 0045-7930.  196 . doi: 10.1016/j.compfluid.2019.104322
• Kristiansen, Lars & Murwanashyaka, Juvenal (2020). First-Order Concatenation Theory with Bounded Quantifiers. Archive for Mathematical Logic.  ISSN 0933-5846.  60(1-2), s 77- 104 . doi: 10.1007/s00153-020-00735-6 Fulltekst i vitenarkiv.
• Patrizi, Francesco & Dokken, Tor (2020). Linear dependence of bivariate Minimal Support and Locally Refined B-splines over LR-meshes. Computer Aided Geometric Design.  ISSN 0167-8396.  77 . doi: 10.1016/j.cagd.2019.101803 Fulltekst i vitenarkiv. Vis sammendrag

  The focus on locally refined spline spaces has grown rapidly in recent years due to the need in Isogeometric Analysis (IgA) of spline spaces with local adaptivity: a property not offered by the strict regular structure of tensor product B-spline spaces. However, this flexibility sometimes results in collections of B-splines spanning the space that are not linearly independent. In this paper we address the minimal number of Minimal Support B-splines (MS B-splines) and of Locally Refined B-splines (LR B-splines) that can form a linear dependence relation. We show that such minimal numbers are six for MS B-splines and eight for LR B-splines. Further results are established to help detecting collections of B-splines that are linearly independent.

• Arumugam, Gurusamy; Erhardt, André Henrik; Eswaramoorthy, Indurekha & Krishnan, Balachandran (2020). Existence of weak solutions to the Keller-Segel chemotaxis system with additional cross-diffusion. Nonlinear Analysis: Real world applications.  ISSN 1468-1218.  54 . doi: 10.1016/j.nonrwa.2020.103090 Fulltekst i vitenarkiv.
• Rabault, Jean; Sutherland, Graig; Gundersen, Olav; Jensen, Atle; Marchenko, Aleksey & Breivik, Øyvind (2020). An open source, versatile, affordable waves in ice instrument for scientific measurements in the Polar Regions. Cold Regions Science and Technology.  ISSN 0165-232X.  170 . doi: 10.1016/j.coldregions.2019.102955
• Trulsen, Karsten; Raustøl, Anne; Jorde, Stian & Rye, Lisa Bæverfjord (2020). Extreme wave statistics of long-crested irregular waves over a shoal. Journal of Fluid Mechanics.  ISSN 0022-1120.  882 . doi: 10.1017/jfm.2019.861 Fulltekst i vitenarkiv. Vis sammendrag

  We report laboratory experiments of long-crested irregular water surface waves propagating over a shoal. For a sufficiently shallow shoal we find that the surface elevation can have a local maximum of skewness and kurtosis above the shallower part of the shoal close to the edge on the incoming side, and a local minimum of skewness over the downward slope on the lee side of the shoal. We find that the horizontal fluid velocity can have a local maximum and minimum of skewness at the same locations as those for the surface elevation. However, the kurtosis of the horizontal fluid velocity can have a local maximum over the downward slope on the lee side of the shoal, different from the location of the maximum of kurtosis of the surface elevation.

• Hellesland, Jostein (2020). New and extended design moment formulations for slender columns in frames with sway. Engineering structures.  ISSN 0141-0296.  203 . doi: 10.1016/j.engstruct.2019.109804 Fulltekst i vitenarkiv. Vis sammendrag

  Present first-order based design code formulations for slender columns in frames with sway, employ sway magnification factors (for global second-order effects) also as moment magnifiers for the individual columns of the frame (storey). This approach ignores differences in magnification of individual column moments caused by local second-order effects in the columns. This difference can be significant. Better understanding of this aspect will strengthen approximate first-order based elastic methods, for which the important superposition principle is valid. Towards this end, local second-order effects are considered for shears, end moments and maximum mo- ments, applicable over the full range of axial loads. Specifically, end moment and maximum moment expressions of columns with sway are derived. These represent novel contributions that are suitable in typical design code formats, and in practical design work. They will allow more rational column assessments, and will allow more economical designs than present structural code procedures. Proposals are verified by comparison with results from second-order in-plane elastic analyses of single restrained columns and columns in frame panels. Also, extensions to the general case of load combinations that include both gravity and sideways loading are briefly presented.

• Brualdi, R.A. & Dahl, Geir (2020). Alternating Sign Matrices: Extensions, König-properties, and Primary Sum-Sequences. Graphs and Combinatorics.  ISSN 0911-0119.  36, s 63- 92 . doi: 10.1007/s00373-019-02119-x Fulltekst i vitenarkiv.
• Ottem, John Christian (2020). Nef cycles on some hyperkähler fourfolds. arXiv.org.  ISSN 2331-8422.
• Aiello, Valeriano; Conti, Roberto; Rossi, Stefano & Stammeier, Nicolai (2020). The inner structure of boundary quotients of right LCM semigroups. Indiana University Mathematics Journal.  ISSN 0022-2518.  s 1- 29 . doi: 10.1512/iumj.2020.69.8006 Vis sammendrag

  We study distinguished subalgebras and automorphisms of boundary quo-tients arising from algebraic dynamical systems (G,P,θ). Our work includes a complete solution to the problem of extending Bogolubov automorphisms from the Cuntz algebra in 2≤p<∞ generators to the p-adic ring C*-algebra. For the case where P is abelian and C*(G) is a maximal abelian subalgebra, we establish a picture for the automorphisms of the boundary quotient that fix C*(G) pointwise. This allows us to show that they form a maximal abelian subgroup of the entire automorphism group.The picture also leads to the surprising outcome that, for integral dynamics, every automorphism that fixes one of the natural Cuntz subalgebras pointwise is necessarily a gauge automorphism. Many of the automorphisms we consider are shown to be outer.

• Bryder, Rasmus Sylvester; Ivanov, Nikolay A. & Omland, Tron (2020). C*-simplicity of HNN extensions and groups acting on trees. Annales de l'Institut Fourier.  ISSN 0373-0956.
• Fauske, Maria Fleischer; Mannino, Carlo & Ventura, Paolo (2020). Generalized periodic vehicle routing and maritime surveillance. Transportation Science.  ISSN 0041-1655.  54(1), s 164- 183 . doi: 10.1287/trsc.2019.0899 Fulltekst i vitenarkiv.
• Shaw, Kristin & Kummer, Mario (2020). The separating semigroup of a real curve. Annales de la Faculté des Sciences de Toulouse (AFST).  ISSN 0240-2963. . doi: 10.5802/afst.1624
• Christiansen, Snorre H & Licht, Martin Werner (2019). Poincaré-Friedrichs inequalities of complexes of discrete distributional differential forms. BIT Numerical Mathematics.  ISSN 0006-3835.  s 1- 27 . doi: 10.1007/s10543-019-00784-1 Fulltekst i vitenarkiv.
• Steinbakk, Gunnhildur Högnadóttir; Aarsnes, Lars Holterud; Aldrin, Magne Tommy; Astrup, Ole Christian; Haug, Ola; Storhaug, Gaute & Vanem, Erik (2019). Statistical Approximation to Synthetic Midship Hull Girder Stress Response. Journal of Ship Research.  ISSN 0022-4502.  64(03), s 266- 277 Vis sammendrag

  Combined hydrodynamic and structural models are used to simulate structural responses on ship hulls in a seaway for design and risk assessment purposes. From a safety and inspection perspective, there is demand for continuously monitoring the ship hull conditions to estimate the structural utilization in real time. However, setting up the computer models and running the analysis are time consuming and costly, preventing such models from being used operationally. We developed a statistical model that approximates the wave bending moment output from the computer model, by linking the wave bending moment to ship design parameters and environmental information. This statistical model is computationally cheap and much faster to run than a hydrodynamic model, and may thus act as a virtual indicator sensor for structural condition monitoring. The approximated wave bending moment can also be used to compute fatigue damage for a ship as an indicator for crack risk. Although somewhat sensitive to the training dataset, a validation study reveals that the statistical model performs decently well. For fatigue rates, relative errors range from 1.4% to 60% for out-of-sample results with weighted least squares, which is deemed acceptable for an indicator model used for screening a fleet of vessels.

• Lyche, Tom & Muntingh, Agnar Georg P (2019). B-spline-like bases for C2 cubics on the Powell–Sabin 12-split. SMAI Journal of Computational Mathematics (SMAI-JCM).  ISSN 2426-8399.  S5, s 129- 159 Fulltekst i vitenarkiv. Vis sammendrag

  For spaces of constant, linear, and quadratic splines of maximal smoothness on the Powell–Sabin 12-split of a triangle, the so-called S-bases were recently introduced. These are simplex spline bases with B-spline-like properties on the 12-split of a single triangle, which are tied together across triangles in a Bézier-like manner. In this paper we give a formal definition of an S-basis in terms of certain basic properties. We proceed to investigate the existence of S-bases for the aforementioned spaces and additionally the cubic case, resulting in an exhaustive list. From their nature as simplex splines, we derive simple differentiation and recurrence formulas to other S-bases. We establish a Marsden identity that gives rise to various quasi-interpolants and domain points forming an intuitive control net, in terms of which conditions for C 0 -, C 1 -, and C 2 -smoothness are derived.

• Holter, Karl Erik; Kuchta, Miroslav & Mardal, Kent-Andre (2019). Sub-voxel Perfusion Modeling in Terms of Coupled 3d-1d Problem, In Florin Adrian Radu; Kundan Kumar; Inga Berre; Jan Martin Nordbotten & Iuliu Sorin Pop (ed.),  Numerical Mathematics and Advanced Applications ENUMATH 2017.  Springer Berlin/Heidelberg.  ISBN 978-3-319-96415-7.  Kapittel.  s 35 - 47 Fulltekst i vitenarkiv.
• Mongardi, Giovanni & Ottem, John Christian (2019). Curve classes on irreducible holomorphic symplectic varieties. Communications in Contemporary Mathematics.  ISSN 0219-1997.  22(7) . doi: 10.1142/S0219199719500780 Fulltekst i vitenarkiv.
• Ottem, John Christian & Schreieder, Stefan (2019). On deformations of quintic and septic hypersurfaces. Journal des Mathématiques Pures et Appliquées.  ISSN 0021-7824.  135 . doi: 10.1016/j.matpur.2019.12.013 Fulltekst i vitenarkiv.
• Stoltenberg, Emil Aas & Hjort, Nils Lid (2019). Multivariate estimation of Poisson parameters. Journal of Multivariate Analysis.  ISSN 0047-259X.  175, s 1- 19 . doi: 10.1016/j.jmva.2019.104545 Fulltekst i vitenarkiv.
• Claeskens, Gerda; Cunen, Celine Marie Løken & Hjort, Nils Lid (2019). Model Selection via Focused Information Criteria for Complex Data in Ecology and Evolution. Frontiers in Ecology and Evolution.  ISSN 2296-701X.  7 . doi: 10.3389/fevo.2019.00415 Fulltekst i vitenarkiv.
• Ciardo, Lorenzo (2019). A Fiedler center for graphs generalizing the characteristic set. Linear Algebra and its Applications.  ISSN 0024-3795.  584, s 197- 220 . doi: 10.1016/j.laa.2019.09.015 Fulltekst i vitenarkiv.
• Walløe, Lars; Hjort, Nils Lid & Thoresen, Marianne (2019). Why results from Bayesian Statistical analyses of clinical trials with a strong prior and small sample sixes may be misleading. Acta Paediatrica.  ISSN 0803-5253.  (108), s 1190- 1191 . doi: 10.111/apa.14800 Fulltekst i vitenarkiv.
• Malacarne, Sara & Neshveyev, Sergey (2019). Martin boundaries of the duals of free unitary quantum groups. Compositio Mathematica.  ISSN 0010-437X.  155(6), s 1171- 1193 . doi: 10.1112/S0010437X19007322 Fulltekst i vitenarkiv.
• Ayati, Anis Awal; Steiros, Konstantinos; Miller, A Mark; Duvvuri, Subrahmanyam & Hultmark, Marcus (2019). A double-multiple streamtube model for vertical axis wind turbines of arbitrary rotor loading. Wind Energy Science.  ISSN 2366-7443.  4(4), s 653- 662 . doi: 10.5194/wes-4-653-2019 Fulltekst i vitenarkiv.
• Rauter, Matthias & Köhler, Anselm (2019). Constraints on Entrainment and Deposition Models in Avalanche Simulations from High-Resolution Radar Data. Geosciences.  ISSN 2076-3263.  10(1) . doi: 10.3390/geosciences10010009 Fulltekst i vitenarkiv. Vis sammendrag

  Depth-integrated simulations of snow avalanches have become a central part of risk analysis and mitigation. However, the common practice of applying different model parameters to mimic different avalanches is unsatisfying. In here, we analyse this issue in terms of two differently sized avalanches from the full-scale avalanche test-site Vallée de la Sionne, Switzerland. We perform depth-integrated simulations with the toolkit OpenFOAM, simulating both events with the same set of model parameters. Simulation results are validated with high-resolution position data from the GEODAR radar. Rather than conducting extensive post-processing to match radar data to the output of the simulations, we generate synthetic flow signatures inside the flow model. The synthetic radar data can be directly compared with the GEODAR measurements. The comparison reveals weaknesses of the model, generally at the tail and specifically by overestimating the runout of the smaller event. Both issues are addressed by explicitly considering deposition processes in the depth-integrated model. The new deposition model significantly improves the simulation of the small avalanche, making it starve in the steep middle part of the slope. Furthermore, the deposition model enables more accurate simulations of deposition patterns and volumes and the simulation of avalanche series that are influenced by previous deposits

• Da Silva, Damiao N & Zhang, Li Chun (2019). A calibrated imputation method for secondary data analysis of survey data. Scandinavian Journal of Statistics.  ISSN 0303-6898.  s 1- 17 . doi: 10.1111/sjos.12435

Se alle arbeider i Cristin

• Ottem, John Christian (2020). Enriques surface fibrations with non-algebraic integral Hodge classes.
• Ottem, John Christian (2020). Tropical degenerations and stable rationality.
• Ottem, John Christian (2020). On (2,3)-fourfolds.
• Ottem, John Christian (2020). Tropical degenerations and stable rationality.
• Kristiansen, Lars (2020). On Interpretability Between some Weak Essentially Undecidable Theories.
• Øksendal, Bernt (2020). A financial market with singular drift and no arbitrage.
• Øksendal, Bernt (2020). A financial market with singular drift and no arbitrage.
• Øksendal, Bernt (2019). Introduction to White Noise Theory and Applications.
• Øksendal, Bernt (2019). Introduction to Stochastic Control Theory for Jump Diffusions.
• Øksendal, Bernt (2019). Introduction to Stochastic Control of Jump Diffusions, with Applications to Mathematical Finance.
• Øksendal, Bernt (2019). A financial market with a local time drift term and delay.
• Øksendal, Bernt (2019). Introduction to White Noise Theory and Applications.
• Øksendal, Bernt (2019). Introduction to Stochastic Control Theory for Jump Diffusions.
• Øksendal, Bernt (2019). A financial market with a local time drift term and delay.
• Øksendal, Bernt (2019). Introduction to Stochastic Control of Jump Diffusions, with Applications to Mathematical Finance.
• Tvete, Ingunn Fride; Natvig, Bent; Gåsemyr, Jørund Inge; Klemp, Marianne & Binde, Caroline Ditlev (2019). Sammenligning av medikamenter for behandling av Parkinson pasienter. NR-notat. SAMBA/01/19.

Se alle arbeider i Cristin