Efficiency of particle acceleration at interplanetary shocks: Statistical study of STEREO observations

Context. Among others, shocks are known to be accelerators of energetic charged particles. However, many questions regarding the acceleration efficiency and the required conditions are not fully understood. In particular, the acceleration of electrons by shocks is often questioned. Aims. In this study we determine the efficiency of interplanetary shocks for $<$100 keV electrons, and for ions at $\sim$0.1 and $\sim$2 MeV energies, as measured by the Solar Electron and Proton Telescope (SEPT) instruments aboard the twin Solar Terrestrial Relations Observatory (STEREO) spacecraft. Methods. We employ an online STEREO in situ shock catalog that lists all shocks observed between 2007 and mid 2014 (observed by STEREO A) and until end of 2013 (observed by STEREO B). In total 475 shocks are listed. To determine the particle acceleration efficiency of these shocks, we analyze the associated intensity increases (shock spikes) during the shock crossings. For the near-relativistic electrons, we take into account the issue of possible ion contamination in the SEPT instrument. Results. The highest acceleration efficiency is found for low energy ions (0.1 MeV), which show a shock-associated increase at 27% of all shocks. The 2 MeV ions show an associated increase only during 5% of the shock crossings. In the case of the electrons, the shocks are nearly ineffective. Only five shock-associated electron increases were found, which correspond to only 1% of all shock crossings

Interpretation of increased energetic particle flux measurements by SEPT aboard the STEREO spacecraft and contamination

Context. Interplanetary (IP) shocks are known to be accelerators of energetic charged particles observed in-situ in the heliosphere. However, the acceleration of near-relativistic electrons by shocks in the interplanetary medium is often questioned. On 9 August 2011 a Corotating Interaction Region (CIR) passed STEREO B (STB) that resulted in a flux increase in the electron and ion channels of the Solar Electron and Proton Telescope (SEPT). Because electron measurements in the few keV to several 100 keV range rely on the so-called magnet foil technique, which is utilized by SEPT, ions can contribute to the electron channels. Aims. We aim to investigate whether the flux increase in the electron channels of SEPT during the CIR event on 9 August 2011 is caused by ion contamination only. Methods. We compute the SEPT response functions for protons and helium utilizing an updated GEANT4 model of SEPT. The CIR energetic particle ion spectra for protons and helium are assumed to follow a Band function in energy per nucleon with a constant helium to proton ratio. Results. Our analysis leads to a helium to proton ratio of 16.9% and a proton flux following a Band function with the parameters $I_0 = 1.24 \cdot 10^4$ / (cm2 s sr MeV/nuc.), $E_c = 79$ keV/nuc. and spectral indices of $\gamma_1 = -0.94$ and $\gamma_2 = -3.80$ which are in good agreement with measurements by the Suprathermal Ion Telescope (SIT) aboard STB. Conclusions. Since our results explain the SEPT measurements, we conclude that no significant amount of electrons were accelerated between $55$ keV and $425$ keV by the CIR

E-Learning in der universitären Lehre am Beispiel der Entwicklung und Evaluation eines hybriden Onlineseminars zur computergestützten Text- und Inhaltsanalyse

In dieser Arbeit wird auf der Basis von Klassifikationsmodellen zu E-Learning in der Hochschullehre, didaktischen Modelle zur Strukturierung der Onlinelehre und der Synopse von bisherigen Praxiserfahrungen mit Onlineseminaren sowohl ein didaktisches Modell, als auch eine technische Lernplattform entwickelt. Am Beispiel der Vermittlung der Text- und Inhaltsanalyse am Fachbereich Erziehungswissenschaften, wird das Modell in einem vierstufigen Zyklus eingesetzt, erprobt und formativ und summativ evaluiert. Daraus lassen sich Erkenntnisse über grundlegende Gestaltungsprinzipien, Möglichkeiten und Grenzen der Lehrform "hybrides Onlineseminar" ableiten

The longitudinal distribution of energetic particles in the inner heliosphere - multi-point observations with STEREO-

The datasets of the STEREO spacecraft, utilized in this thesis, built an unprecedented platform to investigate longitudinal particle distributions in the inner heliosphere. In contrast to previous space missions these two nearly identical spacecraft fly on Earth-like orbits around the Sun with successively increasing longitudinal separation to Earth. One spacecraft, therefore, runs ahead of the Earth, STEREO A, while the other one, STEREO B, trails behind. Beside plenty of up to date instruments carried by the STEREO spacecraft, one of the main advantages of the mission is the radial distance to the Sun which is nearly the same as that of the Earth. This is of great use when investigating energetic particles because radial effects can almost be neglected. Another important advance is that both spacecraft do not orbit the Sun ’blindly’: In addition to a number of in-situ experiments they are also equipped with several remote sensing instruments. These provide optical observations of the Sun and the corona at different wavelengths which were only available from the Earth’s viewpoint previous to the STEREO mission. In the region of STEREO’s orbit, two energetic particle populations lend themselves for longitudinal investigations: Energetic particles associated with corotating interaction regions (CIRs), and solar energetic particles (SEPs). The first part of this thesis deals with the former and the different effects which can cause variable CIR observations and associated particle increases. For this purpose, the special configuration of the STEREO spacecraft enables us to disentangle temporal and spatial effects. Furthermore, local interactions with transient structures were observed which obviously favor the local particle acceleration. The second part of this thesis presents investigations of solar energetic particle events which show remarkably wide particle spreads of up to 360 degrees in longitude in the inner heliosphere. These so-called wide-spread events are of special interest because the processes, yielding to these unexpectedly wide distributions, are not completely understood yet. On the basis of a detailed study of such an event and comparison with a 3D propagation model, we conclude that particle transport perpendicular to the mean magnetic field in the interplanetary medium cannot be neglected for wide spread events. In a second study we identified 21 of such wide-spread events and investigate these in a statistical manner. As a key characteristic the longitudinal anisotropy distribution is also investigated. By means of this information different types of events could be distinguished. In contrast to the first study where strong perpendicular diffusion was supposed to play the main role, several observations require a pre-distribution of the particles over large angular ranges close to the Sun. The second study, therefore, concludes that it is likely that both processes, perpendicular diffusion in the interplanetary medium as well as a lateral distribution in the corona (due to coronal transport, a shock or another so far unknown process) must be present at the same time to explain the majority of our observations

Evaluation of a press-fit osteochondral poly(ester-urethane) scaffold in a rabbit defect model

The purpose of this study was to evaluate the impact on osteochondral healing of press-fitted multiphasic osteochondral scaffolds consisting of poly(ester-urethane) and hydroxyapatite into a cylindric osteochondral defect in the distal non-weight bearing femoral trochlear ridge of the rabbit. Two scaffolds were investigated, one with and one without an intermediate microporous membrane between the cartilage and the bone compartment of the scaffold. A control group without a scaffold placed into the defect was included. After 12 weeks macroscopic and histomorphometric analyses were performed. The scaffold was easily press-fitted and provided a stable matrix for tissue repair. The membrane did not demonstrate a detrimental effect on tissue healing compared with the scaffold without membrane. However, the control group had statistically superior healing as reflected by histological differences in the cartilage and subchondral bone compartment between control group and each scaffold group. A closer analysis revealed that the difference was localized in the bone compartment healing. However, given the observed degree of healing in some of the animals in this study with the scaffold, the ease of its insertion and its stability, biodegradable elastomeric PUR/nHA scaffolds should be further investigated as potentially suitable carriers for a regenerative approach of articular cartilage injuries. Das Studienziel war, den Einfluss von mehrphasigen Poly(ester- urethan)/Hydroxyapatit Scaffolds in einem zylindrischen osteochondralen Defekt im medialen Rollkamm des Kaninchenfemurs, in Bezug auf die Gewebeheilung zu untersuchen. Zwei unterschiedliche Scaffolds wurden im Rahmen der Studie untersucht: Beide bestehen aus einem Knorpel- und einem Knochenbereich und unterscheiden sich durch das Vorhandensein/Abwesenheit einer mikroporösen separierenden Membran zwischen den unterschiedlichen Bereichen des Scaffolds. Eine Kontrollgruppe mit einem leeren Defekt wurde ebenfalls untersucht. Nach 12 Wochen wurden makroskopische und histomorphometrische Untersuchungen durchgeführt. Die Scaffolds konnten ohne Probleme mittels press- fit Technik implantiert werden und lieferten eine stabile Matrix für die Geweberegeneration. Die An- bzw. Abwesenheit der Membran zeigte keinen Einfluss auf die Heilung. Jedoch zeigte die Kontrollgruppe eine statistisch signifikant bessere Heilung im Vergleich zu den Gruppen mit einem implantierten Scaffold, was hauptsächlich auf Unterschiede im Knochenbereich zurückzuführen ist. Allerdings konnte in einigen Tieren mit implantiertem Scaffold eine beginnende Heilungstendenz beobachtet werden. In Kombination mit der einfachen Implantierungstechnik und der Biodegradibilität der PUR/nHA Scaffolds, führt dies zum Schluss, dass die Scaffolds weiter untersucht werden sollten, besonders in ihrer Eignung als regenerative Carrier für Knorpelverletzunge

Energetic particle cross-field propagation early in a solar event

Solar energetic particles (SEPs) have been observed to easily spread across heliographic longitudes, and the mechanisms responsible for this behaviour remain unclear. We use full-orbit simulations of a 10 MeV proton beam in a turbulent magnetic field to study to what extent the spread across the mean field can be described as diffusion early in a particle event. We compare the full-orbit code results to solutions of a Fokker-Planck equation including spatial and pitch angle diffusion, and of one including also propagation of the particles along random-walking magnetic field lines. We find that propagation of the particles along meandering field lines is the key process determining their cross-field spread at 1 AU at the beginning of the simulated event. The mean square displacement of the particles an hour after injection is an order of magnitude larger than that given by the diffusion model, indicating that models employing spatial cross-field diffusion cannot be used to describe early evolution of an SEP event. On the other hand, the diffusion of the particles from their initial field lines is negligible during the first 5 hours, which is consistent with the observations of SEP intensity dropouts. We conclude that modelling SEP events must take into account the particle propagation along meandering field lines for the first 20 hours of the event.Comment: 5 pages, 4 figures; Accepted for publication in Astrophysical Journal Letter

An Approach to Calculate and Visualize Intraoperative Scattered Radiation Exposure

During the intraoperative radiograph generation process with mobile image intensifier systems (C-arm) most of the radiation exposure for patient, surgeon and operation room personal is caused by scattered radiation. The intensity and propagation of scattered radiation depend on different parameters, e.g. the intensity of the primary radiation, and the positioning of the mobile image intensifier. Exposure through scattered radiation can be minimized when all these parameters are adjusted correctly. Because radiation is potentially dangerous and could not be perceived by any human sense the current education on correct adjustment of a C-arm is designed very theoretical. This paper presents an approach of scattered radiation calculation and visualization embedded in a computer based training system for mobile image intensifier systems called virtX. With the help of this extension the virtX training system should enrich the current radiation protection training with visual and practical training aspects