Studying the small-scale structure of a polarization jet during the April 20, 2018 geomagnetic storm

In this work, we study the small-scale structure of a polarization jet in the subauroral region during the April 20, 2018 geomagnetic storm. We report measurement results of plasma parameters inside the polarization jet with a maximum sampling rate of up to 1 kHz, obtained with Langmuir probes installed on the NorSat-1 microsatellite. The study establishes the presence of temperature and electron density inhomogeneities inside the polarization jet with spatial dimensions of tens to hundreds of meters. The previously known features of the polarization jet evolution have been confirmed. We have also found that the distribution of the electron temperature inside the jet forms two separate peaks as the geomagnetic activity develops during the storm.

Studying the small-scale structure of a polarization jet during the April 20, 2018 geomagnetic storm

In this work, we study the small-scale structure of a polarization jet in the subauroral region during the April 20, 2018 geomagnetic storm. We report measurement results of plasma parameters inside the polarization jet with a maximum sampling rate of up to 1 kHz, obtained with Langmuir probes installed on the NorSat-1 microsatellite. The study establishes the presence of temperature and electron density inhomogeneities inside the polarization jet with spatial dimensions of tens to hundreds of meters. The previously known features of the polarization jet evolution have been confirmed. We have also found that the distribution of the electron temperature inside the jet forms two separate peaks as the geomagnetic activity develops during the storm.

Variations in shape among observed Lyman-α spectra due to intergalactic absorption

Lyman-α (Lyα) spectra provide insights into the small-scale structure and kinematics of neutral hydrogen (HI) within galaxies as well as the ionization state of the intergalactic medium (IGM). The former defines the intrinsic spectrum of a galaxy, which, in turn, is modified by the latter. These two effects are degenerate. Using the IllustrisTNG100 simulation, we studied the impact of the IGM on Lyα spectral shapes between z ∼ 0 and 5. We computed the distribution of the expected Lyα peaks and of the peak asymmetry for different intrinsic spectra, redshifts, and large-scale environments. We find that the averaged transmission curves that are commonly applied give a misleading perception of the observed spectral properties. We show that the distributions of peak counts and asymmetry can lift the degeneracy between the intrinsic spectrum and IGM absorption. For example, we expect a significant number of triple-peaked Lyα spectra (up to 30% at z ∼ 3) if the galaxies’ HI distribution become more porous at higher redshift, as predicted by cosmological simulations. We provide a public catalog of transmission curves for simulations and observations to allow for a more realistic IGM treatment in future studies.

Cellular automata in operational probabilistic theories

The theory of cellular automata in operational probabilistic theories is developed. We start introducing the composition of infinitely many elementary systems, and then use this notion to define update rules for such infinite composite systems. The notion of causal influence is introduced, and its relation with the usual property of signalling is discussed. We then introduce homogeneity, namely the property of an update rule to evolve every system in the same way, and prove that systems evolving by a homogeneous rule always correspond to vertices of a Cayley graph. Next, we define the notion of locality for update rules. Cellular automata are then defined as homogeneous and local update rules. Finally, we prove a general version of the wrapping lemma, that connects CA on different Cayley graphs sharing some small-scale structure of neighbourhoods.