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

Statistical results for solar energetic electron spectra observed over 12 yr with STEREO/SEPT

This work presents a statistical analysis of near-relativistic solar energetic electron event spectra near 1 au. We use measurements of the Solar Electron and Proton Telescope (SEPT) on board STEREO in the energy range of 45–425 keV and utilize the SEPT electron event list containing all electron events observed by STEREO A and STEREO B from 2007 through 2018. We select 781 events with significant signal-to-noise ratios for our analysis and fit the spectra with single or broken-power-law functions of energy. We find 437 events showing broken power laws and 344 events only showing a single power law in the energy range of SEPT. For those events with broken power laws, we find a mean break energy of about 120 keV. We analyze the dependence of the spectral index on the rise times and peak intensities of the events as well as on the presence of relativistic electrons. The results show a relation between the power law spectral index and the rise times of the events with softer spectra belonging to rather impulsive events. Long rise-time events are associated with hard spectra as well as with the presence of higher-energy (>0.7 MeV) electrons. This group of events cannot be explained by a pure flare scenario but suggests an additional acceleration mechanism, involving a prolonged acceleration and/or injection of the particles. A dependence of the spectral index on the longitudinal separation from the parent solar source region was not found. A statistical analysis of the spectral indices during impulsively rising events where the rise times are below 20 minutes is also shown.Agencia Estatal de Investigació

Zur Thermodynamik der festen Loesungen von Caesiumchlorid und Caesiumbromid

Copy held by FIZ Karlsruhe; available from UB/TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Perceptions of service quality, customer satisfaction and customer loyalty in mobile telephony in South Africa

MBA thesis - WBSThe South African mobile telephony sector is reaching saturation and churn rates are extremely high. The market is becoming more competitive with the advent of fixed mobile convergence, disruptive technologies and deregulation of the sector. Faced with all these challenges operators need to identify ways to keep customers loyal while ensuring that subscribers continue to increase their spending. The purpose of this paper is to investigate the crucial factors that lead to customer loyalty in the South African mobile telephony sector, namely service quality and customer satisfaction. Furthermore the antecedents, mediating and consequent relationships of customer loyalty, service quality and customer satisfaction was also examined. Data was obtained from 168 mobile phone users from the three MNO’s (mobile network operators) using a survey compiled from existing literature. The survey was confined to the Gauteng province. The data was analysed using structural equation modelling in order to test the relationships between the constructs. The findings support the proposed hypotheses and are consistent with other literary studies. Pricing, value added services and customer support services are the most significant service quality dimensions influencing customer satisfaction. Customer satisfaction has a direct positive impact on customer loyalty. Customer satisfaction was found to be the mediator between service quality and customer loyalt