The objectives of this thesis were to explore how effectiveness of school-based anti-bullying interventions (SBABI) evolves over time and to assess the possibility to predict the medium-term or long-term effectiveness of SBABIs on the basis of their short-term effectiveness. The first step included a literature review in order to understand the study designs and evaluation techniques that researches used to assess the effectiveness. This literature review described the methodologies based on which researchers collected evidence and concluded on the effectiveness of their SBABIs. In order to address the thesis objectives, a collaborative project was established, named SET-Bullying (“Statistical modelling of the Effectiveness of school based anti-bullying interventions and Time”). The above-mentioned literature review was used to identify potentially eligible studies. After addressing a call for collaboration to the corresponding authors of these studies, this project included data from two of them, the DFE-SHEFFIELD study from United Kingdom and the RESPEKT study from Norway. Both of these studies have used pupil self-reported frequencies on being bullied and bullying others as an effectiveness measure, but using different instruments to elicit this information. Thus, the subsequent step of this thesis was to harmonize the data from these studies using polychoric principal components analysis, in order to be able to perform the same analysis with the data from both studies. The data from both studies were analysed using mixed effect models in order to take into account the hierarchical (i.e. the responses of pupils from the same school may be more correlated with each other as opposed to the responses of pupils from different schools) and the longitudinal structure (i.e. same pupils are more likely to respond in a similar way in the repeated measurements of each studies) of the data. With regard to the primary objective of the thesis, it was observed that effectiveness (where it is observed) may evolve either in a linear fashion or a “delayed effect” may be observed. This refers to a minimal evolution of effectiveness over the first study measurements and a sharper evolution at the later study measurements. This finding is only hypothesis generating at this point. Would this be confirmed in future studies, it will have important implication of the design, implementation and evaluations of SBABIs. About the secondary objective of this thesis, there were some preliminary findings of the possibility to predict the medium-term or long-term effectiveness based on the short-term effectiveness. However, these predictions in some cases seemed to be very variable. Future research should focus on how to make these predictions more accurate in order that this allows for dynamic and adaptable delivery of SBABIs. / Doctorat en Santé Publique / info:eu-repo/semantics/nonPublished

Ce travail consiste en une étude des phénomènes de coalescence dans un nuage de gouttes, par la simulation numérique directe d'un écoulement turbulent gazeux, couplée avec une approche de suivi Lagrangien pour la phase dispersée. La première étape consiste à développer et valider une méthode de détection des collisions pour une phase polydispersée. Elle est ensuite implémentée dans un code couplé de simulation directe et de suivi Lagrangien existant. Des simulations sont menées pour une turbulence homogène isotrope de la phase continue et pour des phases dispersées en équilibre avec le fluide. L'influence de l'inertie des gouttes et de la turbulence sur le taux de coalescence des gouttes est discutée dans un régime de coalescence permanente. Un aperçu est donné de la prise en compte d'autres régimes de collision et de coalescence entre gouttes. Ces simulations sont la base de développement et de validation des approches utilisées dans les calculs à l'échelle industrielle. En particulier, les résultats des simulations sont comparés avec les prédictions d'une approche Lagrangienne de type Monte-Carlo et de l'approche Eulerienne 'Direct Quadrature Method of Moments' (DQMOM). Différents types de fermeture des termes de coalescence sont validés. Les uns sont basés sur l'hypothèse de chaos-moléculaire, les autres sont capables de prendre en compte des corrélations de vitesses des gouttes avant la collision. Il est montré que cette derniere approche prédit beaucoup mieux le taux de coalescence par comparaison avec les résultats des simulations déterministes. / Coalescence in a droplet cloud is studied in this work by means of direct numerical simulation of the turbulent gas flow, which is coupled with a Lagrangian tracking of the disperse phase. In a first step, a collision detection algorithm is developed and validated, which can account for a polydisperse phase. This algorithm is then implemented into an existing code for direct numerical simulations coupled with a Lagrangian tracking scheme. Second, simulations are performed for the configuration of homogeneous isotropic turbulence of the fluid phase and a disperse phase in local equilibrium with the fluid. The influence of both droplet inertia and turbulence intensity on the coalescence rate of droplets is discussed in a pure permanent coalescence regime. First results are given, if other droplet collision outcomes than permanent coalescence (i.e. stretching and reflexive separation) are considered. These results show a strong dependence on the droplet inertia via the relative velocity of the colliding droplets at the moment of collision. The performed simulations serve also as reference data base for the development and validation of statistical modeling approaches, which can be used for simulations of industrial problems. In particular, the simulation results are compared to predictions from a Lagrangian Monte-Carlo type approach and the Eulerian 'Direct Quadrature Method of Moments' (DQMOM) approach. Different closures are validated for the coalescence terms in these approaches, which are based either on the assumption of molecular-chaos, or based on a formulation, which allows to account for the correlation of droplet velocities before collision by the fluid turbulence. It is shown that the latter predicts much better the coalescence rates in comparison with results obtained by the performed deterministic simulations.