A systematic literature review on the quality of moocs

This paper presents the findings from a systematic literature review on the quality of massive open online courses (MOOCs). The main research question was “How can the quality criteria for MOOCs identified in the analysed studies from the systematic literature review be best organ-ised in a categorisation scheme?” The systematic literature review was conducted using the PRISMA procedures. After conducting the screening and eligibility analysis according the pre-defined crite-ria, 103 studies were finally selected. The analysis was done in iterative cycles for continuous im-provements of the assignments and clustering of the quality criteria. The final version was validated in consensus through the categorisation and assignment of all 103 studies in a consistent way to four dimensions (pedagogical, organisational, technological, and social) and their sub-categories. This quality framework can be re-used in future MOOC research and the discussion of the analysed studies provides a current literature overview on the quality of MOOCs

Ejecta cloud distributions for the statistical analysis of impact cratering events onto asteroids’ surfaces: A sensitivity analysis

This work presents the model of an ejecta cloud distribution to characterise the plume generated by the impact of a projectile onto asteroids surfaces. A continuum distribution based on the combination of probability density functions is developed to describe the size, ejection speed, and ejection angles of the fragments. The ejecta distribution is used to statistically analyse the fate of the ejecta. By combining the ejecta distribution with a space-filling sampling technique, we draw samples from the distribution and assigned them a number of representative fragments so that the evolution in time of a single sample is representative of an ensemble of fragments. Using this methodology, we analyse the fate of the ejecta as a function of different modelling techniques and assumptions. We evaluate the effect of different types of distributions, ejection speed models, coefficients, etc. The results show that some modelling assumptions are more influential than others and, in some cases, they influence different aspects of the ejecta evolution such as the share of impacting and escaping fragments or the distribution of impacting fragments on the asteroid surface

A Density-Based Approach to the Propagation of Re-Entry Uncertainties

The proposed study aims at implementing a density-based approach for the propagation of uncertainties in the initial conditions and parameters for the analysis and prediction of spacecraft re-entries. Using the continuity equation together with the re-entry dynamics, the joint probability distribution function of the uncertainties is propagated and the final uncertainties in the re-entry corridor, impact location, and casualty area are quantified. The paper considers uncertainties in the initial conditions at re-entry and in the ballistic coefficient of the satellite for different types of re-entry scenarios, studying the effects that such uncertainties have on the impact location and entry corridor

A Density-Based Approach to the Propagation of Re-Entry Uncertainties

The proposed study aims at implementing a density-based approach for the propagation of uncertainties in the initial conditions and parameters for the analysis and prediction of spacecraft re-entries. Using the continuity equation together with the re-entry dynamics, the joint probability distribution function of the uncertainties is propagated and the final uncertainties in the re-entry corridor, impact location, and casualty area are quantified. The paper considers uncertainties in the initial conditions at re-entry and in the ballistic coefficient of the satellite for different types of re-entry scenarios, studying the effects that such uncertainties have on the impact location and entry corridor