This thesis describes the use of centrifugal photosedimentation, for the particle size analysis of soil clays and clay minerals. The instrument that was used is the Horiba, CAPA 500. It has a lower limit to particle size analysis for clays of 20nm (Stokes' diameter) and gives a high degree of size resolution. The initial output is a relationship between turbidity and Stokes' diameter over a limited range of particle sizes. Use of the centrifugal photosedimentometer with materials containing a broad range of particle sizes, such as clays, by combining results from runs with overlapping size ranges is described. In order to maximize sensitivity it was necessary to use higher initial suspension concentrations when analysing for small particles, compared to those used when analysing for larger particles. Typically clays contain particles that are both greater and smaller than the wavelength of light in the dispersing medium (400 nm in this case). It is therefore important to correct for the variation in light extinction with particle size and those aspects of light scattering and absorption theory that are relevant to photosedimentation data analysis are reviewed. For particles that are smaller than 100nm absorption makes a significant contribution to light extinction. Therefore the absorption coefficients of a range of contrasting clays were estimated from reflectance measurements taken from diluted clays (in powder form). These samples provided a set of standards that allowed the absorption coefficients of other clays to be estimated by visual comparison. In very force fields disc-like particles sediment so that they are oriented with their minimum dimension in the direction of motion. Light scattering is sensitive to particle orientation, hence photosedimentation was used to estimate the orientation state of sedimenting particles. Estimates of the maximum advisable centrifugal speed for use with the various particle sizes are given. These were obtained from both simple theory and from experimental results. Although repeatable results were obtained from photosedimentation, the particle size distributions calculated from the relationship between turbidity and Stokes' diameter did not agree with those from gravimetric size analysis, when traditional theories (e.g. Mie) were used to correct the experimentally obtained turbidity data prior to the calculation of particle size distribution. However, satisfactory semi-empirical scattering efficiencies are suggested for the 100nm to 10 μm size range, but they need further testing. Photosedimentation analysis produced the same shape of particle size distribution for TEM size analysed samples, however the positions of these size distributions in terms of mean particle size did not always coincide. Despite the various sources of uncertainty in the particle size distributions that are obtained from photosedimentation data analysis, the high degree of size resolution and good repeatability of the instrument make it suitable for many applictions in Soil Science. Centrifugal photosedimentation was found to be particularly useful for studying the effect of saturating cation on the particle size distributions of dispersed bentonite. Further work is suggested to extend the range of semi-empirical values of extinction efficiency that are given and also to quantify the biasing that can result from samples which have a variation of axial ratio and/or chemical composition with particle size.

Aim: To determine the criterion validity of the Activ8a and VitaMoveb activity monitors (AM) in measuring body postures and movements (P&M) in adults with spastic cerebral palsy (CP) with different gross motor functional abilities in a simulated free-living environment. Methods: In this observational validation study participants were included between March and June 2016. Participants were divided into two groups: ambulatory and non-ambulatory adults (wheelchair users). For ambulatory adults, three Activ8 monitors (attached to the frontal thigh, lateral thigh, and in the pant pocket) and three synchronized VitaMove monitors (attached to the chest and each leg) were worn while participants were video recorded when performing a standardized activity protocol. For non-ambulatory adults, two synchronized Activ8 monitors (attached to the dominant wrist and wheelchair wheel) and three VitaMove monitors (attached to the chest and each wrist) were worn while participants were video recorded when performing a standardized wheelchair protocol. A native Dutch student provided standardized instructions while the author video recorded participants. Activities were performed in a movement laboratory and simulated free-living environment. Output data of the Activ8 and the VitaMove monitors were compared with video observation as a criterion measure. Absolute and relative time differences were calculated for each detected body P&M and for total measurement time for each participant. The following body P&M categories were detected: sitting, standing, walking, running, cycling, wheelchair driving, active upper body (stable wheelchair), and assisted driving. Agreement between the Activ8 and VitaMove during activity measurement was determined for each activity using Spearman Rho correlation coefficients, which were then compared with Meng’s test. Adapted Bland-Altman plots were completed to determine agreement at an individual level and Wilcoxon Signed-Rank tests were calculated to evaluate differences between detected P&M time across measures. Relative time differences of <10% between measures were indicative of acceptable validity. Results: Fifteen adults with spastic CP [10 men; mean(SD) age, 35.7(13) years; Gross Motor Function Classification System distribution: level I (n=6), level II (n=5), level III (n=3), level IV (n=1)] were included. For ambulatory adults (n=14), criterion validity of the Activ8 at the lateral thigh location during basic and complex daily life activities was moderate to good (average relative time differences: 0.25% for sitting, 4.69% for standing, 2.46% for walking, 3.19% for cycling, and 1.96% for light-to-moderate upright activity), except for running (34.6% average difference) The criterion validity of the VitaMove was acceptable, with the exception of standing and running (average relative time differences: 1.69% for sitting, 12.3% for standing, 4.84% for walking, 9.70% for cycling, 23.8% for running, and 0.91% for light-to-moderate upright activity). Spearman Rho correlation coefficients were significantly greater between video/lateral thigh Activ8 than video/frontal thigh Activ8 and video/pant pocket Activ8 for P&M categories sitting, basic standing, basic walking, and light-to-moderate upright activity (p<0.01 for all). Moreover, Spearman Rho correlation coefficients were significantly greater between video/Activ8 than video/VitaMove for basic walking and light-to-moderate upright activity P&M categories (p<0.01). In non-ambulatory, wheelchair users (n=3), the Wheelchair Activ8 demonstrated greater validity than the VitaMove monitor, when compared to video observation, for the detection of sedentary upper body and active upper body behaviours. Conclusion: The Activ8, positioned on the lateral thigh, demonstrates adequate validity as a tool for monitoring of body P&M during free-living activities in ambulatory adults with spastic CP. The Activ8 demonstrated superior validity as a direct measure of body P&M compared to the VitaMove AM. The sample size of non-ambulatory adults was small (n=3) and allowed for descriptive and exploratory analysis only; therefore, validity of the Wheelchair Activ8 for has to be further examined in a larger number of participants. Clinical relevance: The Activ8 and Wheelchair Activ8 shows promise as a clinical measurement tool of physical behaviour for adults with CP across GMFCS levels I-IV. The Activ8 could be used in the future development of health promotion initiatives, due to the features of goal setting and user feedback, while providing researchers greater insight in activity data than consumer-grade AMs. Suppliers: a. Activ8, trademark of Remedy Distribution Ltd. (original equipment manufacturer is 2M Engineering Ltd.), John F Kennedylaan 3, 5555XC, Valkenswaard, The Netherlands b. VitaMove, 2M Engineering Ltd., John F Kennedylaan 3, 5555XC, Valkenswaard, The Netherlands / Thesis / Master of Science (MSc)

Cette thèse est centrée sur le développement de modèles numériques pour simuler le comportement physique des plasmas présents dans un réacteur d'implantation ionique à immersion plasma. Ces modèles ont pour but d'estimer l'impact des réglages opérationnels du réacteur sur les paramètres plasma pertinents pour l'implantation, comme le flux ionique sur le substrat et la distribution en énergie des ions. La géométrie complexe du réacteur rend difficile sa modélisation d'un seul tenant, du fait des importants gradients temporels et spatiaux attendus pour les densités ioniques et la température électronique. Une stratégie de simulation en deux étapes a donc été adoptée : - Un modèle quasi-homogène, couplé à un module de chimie en volume élaboré, permet de représenter des deux portions de la source plasma et d'obtenir l'évolution de la composition du plasma en fonction de la puissance radiofréquence injectée. - Un modèle unidimensionnel de type PIC-MC permet de décrire la dynamique de la gaine ionique qui se forme près du substrat du fait du potentiel imposé, ainsi que de déterminer la distribution de l'énergie d'impact des ions et les flux d'implantation correspondants. Au final, ces travaux de recherche ont permis d'aboutir à une meilleure compréhension de l'impact des paramètres opérationnels du réacteur sur le flux ionique et la distribution en énergie des ions arrivant sur le substrat. La connaissance des couplages physiques entre la source plasma et la chambre d'implantation autorise l'optimisation du processus de dopage, puisque les paramètres opérationnels peuvent être réglés de manière à minimiser la profondeur de dopage après implantation. / Numerical models have been developped to simulate the plasma present inside a plasma immersion ion implantation reactor. Their goal is to estimate the impact of the reactor’s settings on the plasma parameters relevant for ion implan-tation. The complex geometry of the reactor renders its modelling difficult, because of the stiff spatial and temporal gradients expected, so a two-step simulation stra-tegy was adopted : – A global model of the plasma source, coupled to a detailed volume chemistry module, allows to determine the time evolution of the plasma composition according to the radio-frequency power injected in the source.– A 1D PIC-MC model of the sheath facing the substrate describes the dyna-mics of the expanding sheath and allows to determine the ion impact energy distribution function and corresponding implantation profiles. Determination of the couplings between the plasma source and the implantation chamber makes possible to optimize the doping process, since the reactor’s opera-tional settings can then be adjusted to minimize the doping depth after implanta-tion.

This single-case study examines the influence of social media practices on tennis players’ physical behaviours in the context of Swedish tennis club. Through semi-structured interviews with tennis club members, the research aims to understand how social media practices impact tennis players’ physical behaviours. The study draws on theoretical frameworks that highlight social media’s influence on both the production and consumption of content, which can shape tennis players’ physical behaviours. The findings reveal that social media practices affect tennis players’ physical behaviours. Firstly, these practices can lead to changes in coaching approaches as coaches adapt their strategies and techniques based on social media trends and feedback. Tennis players may develop new habits influenced by what they observe and engage with on social media platforms. Additionally, social media practices can impact tennis players’ societal position, influencing their interactions with others and potentially affecting their social dynamics within the sports community. In conclusion, this study emphasizes the importance of considering social media practices beyond online engagement and their impact on physical behaviours. The findings provide valuable insights for sports organizations aiming to develop strategies that promote positive social media practices among tennis players while mitigating negative influences. Moreover, the study contributes to the research field by exploring the influence of social media practices on tennis players’ physical behaviours in offline settings. Researchers interested in further investigating this topic can draw upon the methodology and findings of this study as a guide for their own investigations.