Artikler, rapporter og annet (matematikk og statistikk)
https://hdl.handle.net/10037/950
2024-07-19T18:33:03ZIncreasing fluctuations in the Arctic summer sea ice cover are expected with future global warming
https://hdl.handle.net/10037/34055
Poltronieri, Anna; Bochow, Nils Ole Ronald; Boers, Niklas; Rypdal, Martin Wibe<br />
The loss of Arctic sea ice (ASI) represents a major transformation in the Arctic region, impacting regional and global climate, ecosystems, and socio-economic structures. Observational and reanalysis data have consistently shown a notable shift in polar environmental conditions over recent decades, marked by a substantial reduction in the ASI area and a rise in the variability in its coverage and distribution. Utilizing data from the latest Coupled Model Intercomparison Project phase, our study reveals a consistent pattern highlighting a fundamental shift in ASI dynamics preceding total loss. We observe increasing fluctuations in the September ASI area as the threshold for an ice-free Arctic is approached across various scenarios and models. This pattern is particularly concentrated in the Central Arctic (CA) sub-region. Spatial analyses reveal increasing variance along the CA's northern coastlines, accompanied by a substantial increase in open water coverage, underscoring the shift from stable to highly variable ice conditions in this region. Additionally, our findings suggest a potential link between increased ASI fluctuations and variability in surface wind speeds. These specific results underscore the urgency of multidisciplinary approaches in addressing the challenges posed by ASI variability, with implications for marine ecosystems, Indigenous communities, and navigational safety.<br />
2024-06-11T00:00:00ZIncreasing fluctuations in the Arctic summer sea ice cover are expected with future global warmingPoltronieri, AnnaBochow, Nils Ole RonaldBoers, NiklasRypdal, Martin WibeThe loss of Arctic sea ice (ASI) represents a major transformation in the Arctic region, impacting regional and global climate, ecosystems, and socio-economic structures. Observational and reanalysis data have consistently shown a notable shift in polar environmental conditions over recent decades, marked by a substantial reduction in the ASI area and a rise in the variability in its coverage and distribution. Utilizing data from the latest Coupled Model Intercomparison Project phase, our study reveals a consistent pattern highlighting a fundamental shift in ASI dynamics preceding total loss. We observe increasing fluctuations in the September ASI area as the threshold for an ice-free Arctic is approached across various scenarios and models. This pattern is particularly concentrated in the Central Arctic (CA) sub-region. Spatial analyses reveal increasing variance along the CA's northern coastlines, accompanied by a substantial increase in open water coverage, underscoring the shift from stable to highly variable ice conditions in this region. Additionally, our findings suggest a potential link between increased ASI fluctuations and variability in surface wind speeds. These specific results underscore the urgency of multidisciplinary approaches in addressing the challenges posed by ASI variability, with implications for marine ecosystems, Indigenous communities, and navigational safety.IOP PublishingJournal articleTidsskriftartikkelPeer reviewedPoltronieri, Bochow, Boers, Rypdal. Increasing fluctuations in the Arctic summer sea ice cover are expected with future global warming. Environmental Research: Climate. 2024Environmental Research: ClimateArctic summer sea ice loss will accelerate in coming decades
https://hdl.handle.net/10037/34052
Poltronieri, Anna; Bochow, Nils Ole Ronald; Aksamit, Nikolas Olson; Boers, Niklas; Jakobsen, Per Kristen; Rypdal, Martin Wibe<br />
The Arctic sea ice (ASI) is expected to decrease with further global warming. However, considerable uncertainty remains regarding the temperature range that would lead to a completely ice-free Arctic. Here, we combine satellite data and a large suite of models from the latest phase of the Coupled Model Intercomparison Project (CMIP6) to develop an empirical, observation-based projection of the September ASI area for increasing global mean surface temperature (GMST) values. This projection harnesses two simple linear relationships that are statistically supported by both observations and model data. First, we show that the September ASI area is linearly proportional to the area inside a specific northern hemisphere January–September mean temperature contour <i><b>T</i></b><sub>c</sub>. Second, we use observational data to show how zonally averaged temperatures have followed a positive linear trend relative to the GMST, consistent with Arctic amplification. To ensure the reliability of these observations throughout the rest of the century, we validate this trend by employing the CMIP6ensemble.Combiningthesetwolinearrelationships, we show that the September ASI area decrease will accelerate with respect to the GMST increase. Our analysis of observations and CMIP6 model data suggests a complete loss of the September ASI (area below 10<sup>6</sup> km<sup>2</sup>) for global warming between 1.5<sup>◦</sup>C and 2.2<sup>◦</sup>C above pre-industrial GMST levels.<br />
Source at <a href=https://iopscience.iop.org/journal/1748-9326></a>.<br />
2024-06-17T00:00:00ZArctic summer sea ice loss will accelerate in coming decadesPoltronieri, AnnaBochow, Nils Ole RonaldAksamit, Nikolas OlsonBoers, NiklasJakobsen, Per KristenRypdal, Martin WibeThe Arctic sea ice (ASI) is expected to decrease with further global warming. However, considerable uncertainty remains regarding the temperature range that would lead to a completely ice-free Arctic. Here, we combine satellite data and a large suite of models from the latest phase of the Coupled Model Intercomparison Project (CMIP6) to develop an empirical, observation-based projection of the September ASI area for increasing global mean surface temperature (GMST) values. This projection harnesses two simple linear relationships that are statistically supported by both observations and model data. First, we show that the September ASI area is linearly proportional to the area inside a specific northern hemisphere January–September mean temperature contour <i><b>T</i></b><sub>c</sub>. Second, we use observational data to show how zonally averaged temperatures have followed a positive linear trend relative to the GMST, consistent with Arctic amplification. To ensure the reliability of these observations throughout the rest of the century, we validate this trend by employing the CMIP6ensemble.Combiningthesetwolinearrelationships, we show that the September ASI area decrease will accelerate with respect to the GMST increase. Our analysis of observations and CMIP6 model data suggests a complete loss of the September ASI (area below 10<sup>6</sup> km<sup>2</sup>) for global warming between 1.5<sup>◦</sup>C and 2.2<sup>◦</sup>C above pre-industrial GMST levels.IOS PressJournal articleTidsskriftartikkelPeer reviewedPoltronieri, Bochow, Aksamit, Boers, Jakobsen, Rypdal. Arctic summer sea ice loss will accelerate in coming decades. Environmental Research Letters. 2024Environmental Research Lettersinfo:eu-repo/grantAgreement/EC/H2020/820970/Norway/Tipping Points in the Earth System/TiPES/info:eu-repo/grantAgreement/EC/H2020/956170/Norway/Multiscales and Critical Transitions in the Earth System/CriticalEarth/Beyond the Oberbeck-Boussinesq and long wavelength approximation
https://hdl.handle.net/10037/33357
Held, Markus; Wiesenberger, Matthias<br />
We present the first simulations of a reduced magnetized plasma model that incorporates both arbitrary wavelength polarization and non-Oberbeck–Boussinesq effects. Significant influence of these two effects on the density, electric potential and <i><b>E</i></b> × <i><b>B</i></b> vorticity and non-linear dynamics of interchange blobs are reported. Arbitrary wavelength polarization implicates so-called gyro-amplification that compared to a long wavelength approximation leads to highly amplified small-scale <i><b>E</i></b> × <i><b>B</i></b> vorticity fluctuations. These strongly increase the coherence and< lifetime of blobs and alter the motion of the blobs through a slower blob-disintegration. Non-Oberbeck–Boussinesq effects incorporate plasma inertia, which substantially decreases the growth rate and linear acceleration of high amplitude blobs, while the maximum blob velocity is not affected. Finally, we generalize and numerically verify unified scaling laws for blob velocity, acceleration and growth rate that include both ion temperature and arbitrary blob amplitude dependence.<br />
2022-12-22T00:00:00ZBeyond the Oberbeck-Boussinesq and long wavelength approximationHeld, MarkusWiesenberger, MatthiasWe present the first simulations of a reduced magnetized plasma model that incorporates both arbitrary wavelength polarization and non-Oberbeck–Boussinesq effects. Significant influence of these two effects on the density, electric potential and <i><b>E</i></b> × <i><b>B</i></b> vorticity and non-linear dynamics of interchange blobs are reported. Arbitrary wavelength polarization implicates so-called gyro-amplification that compared to a long wavelength approximation leads to highly amplified small-scale <i><b>E</i></b> × <i><b>B</i></b> vorticity fluctuations. These strongly increase the coherence and< lifetime of blobs and alter the motion of the blobs through a slower blob-disintegration. Non-Oberbeck–Boussinesq effects incorporate plasma inertia, which substantially decreases the growth rate and linear acceleration of high amplitude blobs, while the maximum blob velocity is not affected. Finally, we generalize and numerically verify unified scaling laws for blob velocity, acceleration and growth rate that include both ion temperature and arbitrary blob amplitude dependence.IOP PublishingJournal articleTidsskriftartikkelHeld, Wiesenberger. Beyond the Oberbeck-Boussinesq and long wavelength approximation. Nuclear Fusion. 2023;63(2)Nuclear FusionOn uniqueness of submaximally symmetric parabolic geometries
https://hdl.handle.net/10037/33306
The, Dennis<br />
Among (regular, normal) parabolic geometries of type (<i>G,P</i>), there is a locally unique maximally symmetric structure and it has symmetry dimension dim(<i>G</i>). The symmetry gap problem concerns the determination of the next realizable (submaximal) symmetry dimension. When <i>G</i> is a complex or split-real simple Lie group of rank at least three or when (<i>G,P</i>) = (<i>G<sub>2</sub></i>, <i>P</i><sub>2</sub>), we establish a local uniqueness result for submaximally symmetric structures of type (<i>G,P</i>).<br />
2024-01-24T00:00:00ZOn uniqueness of submaximally symmetric parabolic geometriesThe, DennisAmong (regular, normal) parabolic geometries of type (<i>G,P</i>), there is a locally unique maximally symmetric structure and it has symmetry dimension dim(<i>G</i>). The symmetry gap problem concerns the determination of the next realizable (submaximal) symmetry dimension. When <i>G</i> is a complex or split-real simple Lie group of rank at least three or when (<i>G,P</i>) = (<i>G<sub>2</sub></i>, <i>P</i><sub>2</sub>), we establish a local uniqueness result for submaximally symmetric structures of type (<i>G,P</i>).World Scientific PublishingJournal articleTidsskriftartikkelPeer reviewedThe. On uniqueness of submaximally symmetric parabolic geometries. International Journal of Mathematics. 2024International Journal of MathematicsPreservice and inservice teachers’ views on digital tools for diverse learners in mathematics education
https://hdl.handle.net/10037/33305
Meaney, Tamsin Jillian; Huru, Hilja Lisa; Kvivesen, Mona<br />
Although teachers are expected to use digital tools in their mathematics teaching in many countries, little is known about preservice and inservice teachers’ digital competence, especially in relationship to specific groups of school students. Results from a survey of 394 preservice teachers and 61 inservice teachers, at three Norwegian institutions, provide information on how they considered different digital tools would support differentiated teaching, related to a student’s mathematical progress, and in multilingual classes. The results suggest that preservice and inservice teachers evaluated similarly the usefulness of different digital tools for differentiated mathematics teaching and in multilingual classrooms. However, for the majority of tools, the standard deviations indicate that the responses were somewhat spread, suggesting uncertainty in how they could use digital tools to support specific groups of students.<br />
Source at <a href=https://ncm.gu.se/nomad/>https://ncm.gu.se/nomad/</a>.<br />
2023-01-01T00:00:00ZPreservice and inservice teachers’ views on digital tools for diverse learners in mathematics educationMeaney, Tamsin JillianHuru, Hilja LisaKvivesen, MonaAlthough teachers are expected to use digital tools in their mathematics teaching in many countries, little is known about preservice and inservice teachers’ digital competence, especially in relationship to specific groups of school students. Results from a survey of 394 preservice teachers and 61 inservice teachers, at three Norwegian institutions, provide information on how they considered different digital tools would support differentiated teaching, related to a student’s mathematical progress, and in multilingual classes. The results suggest that preservice and inservice teachers evaluated similarly the usefulness of different digital tools for differentiated mathematics teaching and in multilingual classrooms. However, for the majority of tools, the standard deviations indicate that the responses were somewhat spread, suggesting uncertainty in how they could use digital tools to support specific groups of students.NCM, Gøteborgs universitetJournal articleTidsskriftartikkelPeer reviewedMeaney T, Huru HL, Kvivesen M. Preservice and inservice teachers’ views on digital tools for diverse learners in mathematics education. Nordisk matematikkdidaktikk. 2023;28(3-4):103-123Nordisk matematikkdidaktikkBiogeographic gradients of picoplankton diversity indicate increasing dominance of prokaryotes in warmer Arctic fjords
https://hdl.handle.net/10037/33243
Hörstmann, Cora; Hattermann, Tore; Thomé, Pauline C.; Buttigieg, Pier Luigi; Morel, Isidora; Waite, Anya M.; John, Uwe<br />
limate change is opening the Arctic Ocean to increasing human impact and ecosystem changes. Arctic fjords, the region’s most productive ecosystems, are sustained by a diverse microbial community at the base of the food web. Here we show that Arctic fjords become more prokaryotic in the picoplankton (0.2–3 µm) with increasing water temperatures. Across 21 fjords, we found that Arctic fjords had proportionally more trophically diverse (autotrophic, mixotrophic, and heterotrophic) picoeukaryotes, while subarctic and temperate fjords had relatively more diverse prokaryotic trophic groups. Modeled oceanographic connectivity between fjords suggested that transport alone would create a smooth gradient in beta diversity largely following the North Atlantic Current and East Greenland Current. Deviations from this suggested that picoeukaryotes had some strong regional patterns in beta diversity that reduced the effect of oceanographic connectivity, while prokaryotes were mainly stopped in their dispersal if strong temperature differences between sites were present. Fjords located in high Arctic regions also generally had very low prokaryotic alpha diversity. Ultimately, warming of Arctic fjords could induce a fundamental shift from more trophic diverse eukaryotic- to prokaryotic-dominated communities, with profound implications for Arctic ecosystem dynamics including their productivity patterns.<br />
2024-03-02T00:00:00ZBiogeographic gradients of picoplankton diversity indicate increasing dominance of prokaryotes in warmer Arctic fjordsHörstmann, CoraHattermann, ToreThomé, Pauline C.Buttigieg, Pier LuigiMorel, IsidoraWaite, Anya M.John, Uwelimate change is opening the Arctic Ocean to increasing human impact and ecosystem changes. Arctic fjords, the region’s most productive ecosystems, are sustained by a diverse microbial community at the base of the food web. Here we show that Arctic fjords become more prokaryotic in the picoplankton (0.2–3 µm) with increasing water temperatures. Across 21 fjords, we found that Arctic fjords had proportionally more trophically diverse (autotrophic, mixotrophic, and heterotrophic) picoeukaryotes, while subarctic and temperate fjords had relatively more diverse prokaryotic trophic groups. Modeled oceanographic connectivity between fjords suggested that transport alone would create a smooth gradient in beta diversity largely following the North Atlantic Current and East Greenland Current. Deviations from this suggested that picoeukaryotes had some strong regional patterns in beta diversity that reduced the effect of oceanographic connectivity, while prokaryotes were mainly stopped in their dispersal if strong temperature differences between sites were present. Fjords located in high Arctic regions also generally had very low prokaryotic alpha diversity. Ultimately, warming of Arctic fjords could induce a fundamental shift from more trophic diverse eukaryotic- to prokaryotic-dominated communities, with profound implications for Arctic ecosystem dynamics including their productivity patterns.Springer NatureJournal articleTidsskriftartikkelPeer reviewedHörstmann C, Hattermann T, Thomé, Buttigieg PL, Morel, Waite AM, John U. Biogeographic gradients of picoplankton diversity indicate increasing dominance of prokaryotes in warmer Arctic fjords. Communications Biology. 2024;7Communications BiologyLinear codes associated to symmetric determinantal varieties: Even rank case
https://hdl.handle.net/10037/33172
Beelen, Peter; Johnsen, Trygve; Singh, Prasant<br />
We consider linear codes over a finite field Fq, for odd q, derived from determinantal varieties, obtained from symmetric matrices of bounded ranks. A formula for the weight of a codeword is derived. Using this formula, we have computed the minimum distance for the codes corresponding to matrices upperbounded by any fixed, even rank. A conjecture is proposed for the cases where the upper bound is odd. At the end of the article, tables for the weights of these codes, for spaces of symmetric matrices up to order 5, are given.<br />
2023-06-20T00:00:00ZLinear codes associated to symmetric determinantal varieties: Even rank caseBeelen, PeterJohnsen, TrygveSingh, PrasantWe consider linear codes over a finite field Fq, for odd q, derived from determinantal varieties, obtained from symmetric matrices of bounded ranks. A formula for the weight of a codeword is derived. Using this formula, we have computed the minimum distance for the codes corresponding to matrices upperbounded by any fixed, even rank. A conjecture is proposed for the cases where the upper bound is odd. At the end of the article, tables for the weights of these codes, for spaces of symmetric matrices up to order 5, are given.ElsevierJournal articleTidsskriftartikkelPeer reviewedBeelen P, Johnsen T, Singh P. Linear codes associated to symmetric determinantal varieties: Even rank case. Finite Fields and Their Applications. 2023;91(October)Finite Fields and Their ApplicationsExceptionally simple super-PDE for F (4)
https://hdl.handle.net/10037/33170
Santi, Andrea; The, Dennis<br />
For the largest exceptional simple Lie superalgebra F(4), having dimension (24|16), we provide two explicit geometric realizations as supersymmetries, namely as the symmetry superalgebra of super-PDE systems of second and third order respectively.<br />
2024-02-01T00:00:00ZExceptionally simple super-PDE for F (4)Santi, AndreaThe, DennisFor the largest exceptional simple Lie superalgebra F(4), having dimension (24|16), we provide two explicit geometric realizations as supersymmetries, namely as the symmetry superalgebra of super-PDE systems of second and third order respectively.Journal articleTidsskriftartikkelPeer reviewedSanti, The. Exceptionally simple super-PDE for F (4). Communications in Contemporary Mathematics. 2023Communications in Contemporary MathematicsODEs whose Symmetry Groups are not Fiber-Preserving
https://hdl.handle.net/10037/33166
Kruglikov, Boris Serafimovich; Schneider, Eivind<br />
We observe that, up to conjugation, a majority of higher order ODEs (ordinary differential equations) and ODE systems have only fiber-preserving point symmetries. By exploiting Lie's classification of Lie algebras of vector fields, we describe all exceptions to this in the case of scalar ODEs and systems of ODEs on a pair of functions. The scalar ODEs whose symmetry algebras are not fiber preserving can be expressed via absolute and relative scalar differential invariants, while a similar description for ODE systems requires us to also invoke conditional differential invariants and vector-valued relative invariants to deal with singular orbits of the action. Investigating prolongations of the actions, we observe some interesting relations between different realizations of Lie algebras. We also note that it may happen that the prolongation of a finite-dimensional Lie algebra acting on a differential equation never becomes free. An example of an underdetermined ODE system for which this phenomenon occurs shows limitations of the method of moving frames.<br />
Source at <a href=https://www.heldermann.de/JLT/JLT33/JLT334/jlt33048.htm>https://www.heldermann.de/JLT/JLT33/JLT334/jlt33048.htm</a>.<br />
2023-01-01T00:00:00ZODEs whose Symmetry Groups are not Fiber-PreservingKruglikov, Boris SerafimovichSchneider, EivindWe observe that, up to conjugation, a majority of higher order ODEs (ordinary differential equations) and ODE systems have only fiber-preserving point symmetries. By exploiting Lie's classification of Lie algebras of vector fields, we describe all exceptions to this in the case of scalar ODEs and systems of ODEs on a pair of functions. The scalar ODEs whose symmetry algebras are not fiber preserving can be expressed via absolute and relative scalar differential invariants, while a similar description for ODE systems requires us to also invoke conditional differential invariants and vector-valued relative invariants to deal with singular orbits of the action. Investigating prolongations of the actions, we observe some interesting relations between different realizations of Lie algebras. We also note that it may happen that the prolongation of a finite-dimensional Lie algebra acting on a differential equation never becomes free. An example of an underdetermined ODE system for which this phenomenon occurs shows limitations of the method of moving frames.Heldermann VerlagJournal articleTidsskriftartikkelPeer reviewedKruglikov BS, Schneider E. ODEs whose Symmetry Groups are not Fiber-Preserving. Journal of Lie theory. 2023;33(4):1045-1086Journal of Lie theoryDecomposable (5, 6)-solutions in eleven-dimensional
supergravity
https://hdl.handle.net/10037/33103
Chi, Hanci; Chrysikos, Ioannis; Schneider, Eivind<br />
We present decomposable (5, 6)-solutions M<sup>1,4</sup>×M<sup>6</sup>
in eleven-dimensional supergravity by solving the bosonic supergravity equations for a variety of non-trivial flux forms. Many of the bosonic backgrounds presented here are induced by various types of null flux forms on products of certain totally Ricci-isotropic Lorentzian Walker manifolds and Ricci-flat Riemannian manifolds. These constructions provide an analogy of the work performed by Chrysikos and Galaev [Classical Quantum Gravity 37, 125004 (2020)], who made similar computations for decomposable (6, 5)-solutions. We also present bosonic backgrounds that are products of Lorentzian Einstein manifolds with a negative Einstein constant (in the “mostly plus” convention) and Riemannian Kähler–Einstein manifolds with a positive Einstein constant. This conclusion generalizes a result of Pope and van Nieuwenhuizen [Commun. Math. Phys. 122, 281–292 (1989)] concerning the appearance of six-dimensional Kähler–Einstein manifolds in eleven-dimensional supergravity. In this setting, we construct infinitely many non-symmetric decomposable (5, 6)-supergravity backgrounds by using the infinitely many Lorentzian Einstein–Sasakian structures with a negative Einstein constant on the 5-sphere, known from the work of Boyer et al. [Commun. Math. Phys. 262, 177–208 (2006)].<br />
2023-06-08T00:00:00ZDecomposable (5, 6)-solutions in eleven-dimensional
supergravityChi, HanciChrysikos, IoannisSchneider, EivindWe present decomposable (5, 6)-solutions M<sup>1,4</sup>×M<sup>6</sup>
in eleven-dimensional supergravity by solving the bosonic supergravity equations for a variety of non-trivial flux forms. Many of the bosonic backgrounds presented here are induced by various types of null flux forms on products of certain totally Ricci-isotropic Lorentzian Walker manifolds and Ricci-flat Riemannian manifolds. These constructions provide an analogy of the work performed by Chrysikos and Galaev [Classical Quantum Gravity 37, 125004 (2020)], who made similar computations for decomposable (6, 5)-solutions. We also present bosonic backgrounds that are products of Lorentzian Einstein manifolds with a negative Einstein constant (in the “mostly plus” convention) and Riemannian Kähler–Einstein manifolds with a positive Einstein constant. This conclusion generalizes a result of Pope and van Nieuwenhuizen [Commun. Math. Phys. 122, 281–292 (1989)] concerning the appearance of six-dimensional Kähler–Einstein manifolds in eleven-dimensional supergravity. In this setting, we construct infinitely many non-symmetric decomposable (5, 6)-supergravity backgrounds by using the infinitely many Lorentzian Einstein–Sasakian structures with a negative Einstein constant on the 5-sphere, known from the work of Boyer et al. [Commun. Math. Phys. 262, 177–208 (2006)].AIP PublishingJournal articleTidsskriftartikkelPeer reviewedChi, Chrysikos I, Schneider E. Decomposable (5, 6)-solutions in eleven-dimensional
supergravity. Journal of Mathematical Physics. 2023Journal of Mathematical Physics