Sea ice drift and deformation, namely sea ice dynamics, play a significant role in atmosphere–ice–ocean coupling. Deformation patterns in sea ice can be observed over a wide range of spatial and temporal scales, though high-resolution objective quantification of these features remains difficult. In an effort to better understand local deformation of sea ice, we adapt the trajectory-stretching exponents ...

We show the global dynamics of spatial correlation of Pc2 wave activity can track the evolution of the 2015 St. Patrick's Day geomagnetic storm for an 8 hr time window around onset. The global spatially coherent response is tracked by forming a dynamical network from 1 s data using the full set of 100+ ground-based magnetometer stations collated by SuperMAG and Intermagnet. The pattern of spatial ...

This thesis first introduces some theory on coding theory and matroids, and properties that are shared between these, and then we will investigate derived matroids. In 1979 Longyear made a construction of derived matroids for binary matroids, which illuminates "dependencies among dependencies". The construction was later generalized to representable matroids by Oxley and Wang, where the derived ...

On page 206 in his lost notebook, Ramanujan recorded the following enigmatic identity for his theta function φ(q): φ(e^{−7π√7}) = 7^{−3/4}φ(e^{−π√7}){1 + ( )^{2/7} + ( )^{2/7} + ( )^{2/7}}. We give the three missing terms. In addition, we calculate the class invariant G_{343} and further special values of φ(e^{−nπ}), for n = 7, 21, 35, and 49.

The density ridge framework for estimating principal curves and surfaces has in a number of recent works been shown to capture manifold structure in data in an intuitive and effective manner. However, to date there exists no efficient way to traverse these manifolds as defined by density ridges. This is unfortunate, as manifold traversal is an important problem for example for shape estimation in ...

Students of physics in Norway typically spend a lot of time on mandatory problemsolving exercises that they must get a passing grade on to be allowed to take the exam. This is often a primarily summative assessment, which can limit the learning potential. <p> <p>In this contribution, we present an intervention in which traditional mandatory assignments are modified to put more emphasis on ...

We use the recent frame-indifferent theory of diffusive momentum transport to identify internal barriers in wall-bounded turbulence. Formed by the invariant manifolds of the Laplacian of the velocity field, the barriers block the viscous part of the instantaneous momentum flux in the flow. We employ the level sets of single-trajectory Lagrangian diagnostic tools, the trajectory rotation average ...

We consider a q-analogue of abstract simplicial complexes, called q-complexes, and discuss the notion of shellability for such complexes. It is shown that q-complexes formed by independent subspaces of a q-matroid are shellable. Further, we explicitly determine the homology of q-complexes corresponding to uniform q-matroids. We also outline some partial results concerning the determination of homology ...

The arithmetic mean/geometric mean inequality (AM/GM inequality) facilitates classes of nonnegativity certificates and of relaxation techniques for polynomials and, more generally, for exponential sums. Here, we present a first systematic study of the AM/GM-based techniques in the presence of symmetries under the linear action of a finite group. We prove a symmetry-adapted representation theorem and ...

Statistiske metoder som regresjonsanalyse og kausale design basert på naturlige eksperi-menter har etter hvert blitt hyllevare innen de fleste fag som behandler store datamengder,ikke minst innen epidemiologi, meteorologi og klimavitenskap.1 Et eksempel er prinsipalkomponentanalyse (PCA), som brukes til å finne karakteristiske mønstre i geofysiske felt.Mønstrene, eller prinsipalkomponentene, ...