The Brightness of Density Structures at Large Solar Elongation Angles: What is Being Observed by STEREO/SECCHI?

We discuss features of coronal mass ejections (CMEs) that are specific to heliospheric observations at large elongation angles. Our analysis is focused on a series of two eruptions that occurred on 2007 January 24-25, which were tracked by the Heliospheric Imagers (HIs) onboard STEREO. Using a three-dimensional (3-D) magneto-hydrodynamic simulation of these ejections with the Space Weather Modeling Framework (SWMF), we illustrate how the combination of the 3-D nature of CMEs, solar rotation, and geometry associated with the Thomson sphere results in complex effects in the brightness observed by the HIs. Our results demonstrate that these effects make any in-depth analysis of CME observations without 3-D simulations challenging. In particular, the association of bright features seen by the HIs with fronts of CME-driven shocks is far from trivial. In this Letter, we argue that, on 2007 January 26, the HIs observed not only two CMEs, but also a dense corotating stream compressed by the CME-driven shocks.Comment: 5 pages, 2 figures, accepted for ApJ Lette

Learning Interpretable Rules for Multi-label Classification

Multi-label classification (MLC) is a supervised learning problem in which, contrary to standard multiclass classification, an instance can be associated with several class labels simultaneously. In this chapter, we advocate a rule-based approach to multi-label classification. Rule learning algorithms are often employed when one is not only interested in accurate predictions, but also requires an interpretable theory that can be understood, analyzed, and qualitatively evaluated by domain experts. Ideally, by revealing patterns and regularities contained in the data, a rule-based theory yields new insights in the application domain. Recently, several authors have started to investigate how rule-based models can be used for modeling multi-label data. Discussing this task in detail, we highlight some of the problems that make rule learning considerably more challenging for MLC than for conventional classification. While mainly focusing on our own previous work, we also provide a short overview of related work in this area.Comment: Preprint version. To appear in: Explainable and Interpretable Models in Computer Vision and Machine Learning. The Springer Series on Challenges in Machine Learning. Springer (2018). See http://www.ke.tu-darmstadt.de/bibtex/publications/show/3077 for further informatio

Backgrounds of language delays of young children in East Groningen

Oost-Groningen is een gebied met traditioneel veel leerlingen met taalachterstanden. Recent reviewonderzoek heeft dat nog eens bevestigd. Inmiddels is veel bekend over de achtergronden van taalachterstanden. Desondanks stagneert de achterstandsbestrijding in deze regio. In deze bijdrage wordt getracht na te gaan op welke manier achtergrondkenmerken van ouders uit Oost-Groningen, hun verwachtingen van hun kinderen, hun opvattingen ten aanzien van onderwijs en aspecten van informele educatie een verklaring vormen voor de taalontwikkeling van 4-jarige kinderen in groep 1. Uit toetsing van het gepresenteerde theoretische model met LISREL blijkt dat opvattingen en verwachtingen van ouders in Oost-Groningen substantieel mediëren tussen achtergrondkenmerken van ouders en de taalontwikkeling, ook als gecontroleerd wordt intelligentie en verbaal geheugen van de kinderen. Ook mediëren opvattingen en verwachtingen tussen de achtergrondkenmerken en aspecten van informele educatie. Informele educatie medieert echter niet tussen de achtergrondkenmerken en taalontwikkeling. Het belang van informatieve geletterdheid van ouders en van opvattingen en verwachtingen wordt besproken. Het feit dat opvattingen en verwachtingen als leefstijlkenmerk doorwerken in de proximale processen, maar tevens verankerd zijn in de culturele leefstijl van ouders weerspiegelt de complexiteit van het vraagstuk

Particle kinetic analysis of a polar jet from SECCHI COR data

Aims. We analyze coronagraph observations of a polar jet observed by the Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) instrument suite onboard the Solar TErrestrial RElations Observatory (STEREO) spacecraft. Methods. In our analysis we compare the brightness distribution of the jet in white-light coronagraph images with a dedicated kinetic particle model. We obtain a consistent estimate of the time that the jet was launched from the solar surface and an approximate initial velocity distribution in the jet source. The method also allows us to check the consistency of the kinetic model. In this first application, we consider only gravity as the dominant force on the jet particles along the magnetic field. Results. We find that the kinetic model explains the observed brightness evolution well. The derived initiation time is consistent with the jet observations by the EUVI telescope at various wavelengths. The initial particle velocity distribution is fitted by Maxwellian distributions and we find deviations of the high energy tail from the Maxwellian distributions. We estimate the jet's total electron content to have a mass between 3.2 \times 1014 and 1.8 \times 1015 g. Mapping the integrated particle number along the jet trajectory to its source region and assuming a typical source region size, we obtain an initial electron density between 8 \times 109 and 5 \times 1010 cm-3 that is characteristic for the lower corona or the upper chromosphere. The total kinetic energy of all particles in the jet source region amounts from 2.1 \times 1028 to 2.4 \times 1029 erg.Comment: A&A, in pres