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Les occultations stellaires sont une méthode puissante pour étudier les petits corps du Système Solaire, trop faibles ou lointains pour être étudiés par d’autres techniques. Cette méthode consiste à observer le corps passant devant une étoile d’arrière plan. Le flux lumineux stellaire est alors intercepté quelques instants, ce qui permet de caractériser la forme de l’objet et d’étudier son environnement (anneau, atmosphère ou satellite). Deux anneaux denses et étroits ont été découverts en Juin 2013 pour la première fois autour du plus gros des Centaures Chariklo (corps central : 250 km de diamètre ; anneaux : 800 km). Cette thèse présente les 16 occultations par Chariklo et ses anneaux observées depuis 2013. Ces données représentent les seules observations aujourd’hui existantes de ce système planétaire. Une première étude de leur structure et de leur géométrie est détaillée dans ces travaux. Mes travaux ont également porté sur une occultation par la planète naine Haumea observée en Janvier 2017. Celle-ci nous a révélé la présence d’un anneau dense de rayon ~2281 km autour de ce corps tri-axial. Haumea est donc le deuxième corps en dehors des planètes géantes à posséder un anneau. Cette occultation permet notamment de déduire la forme, la taille (1161x852x513 km) et la densité d’Haumea. Cette seconde découverte tend à montrer que les anneaux autour des petits corps ne sont pas si rares. La publication du catalogue Gaia DR1 en 2016 a permis d’améliorer considérablement la précision de nos prédictions donc nos observations. Les prochaines années seront consacrées à scanner plus en détails les anneaux de Chariklo et d’Haumea, mais aussi à chercher des anneaux autour d’autres petits corps afin de comprendre les mécanismes de formation et d’évolution de ces systèmes. / Stellar occultations are a very powerful tool to study small bodies of the Outer Solar System, which are usually too faint or too far away to be studied by others techniques. They occur when a body passes in front of a background star. The stellar flux will then be intercepted during several seconds/minutes. Observation of the occulted star in time allows us to study the shape and size of the occulting object and its vicinity (ring, atmosphere or satellite). For the first time, two dense and narrow rings have been discovered on June 2013 around the biggest known Centaur Chariklo (body’s diameter: 250 km and rings diameter: 800 km). My work shows the 16 observed occultations by Chariklo and/or its rings since 2013. Those data are the only one available about this planetary system today. A first study of their structure and their geometry is conducted. Another part of my work was to study an occultation by the dwarf planet Haumea recorded on January 2017. It revealed the presence of a ring of radius ~2281 km around this tri-axial body. This discovery made Haumea the second body with a ring orbiting around except the four giant planets. This occultation allows us to derive the shape, size (1161x852x513 km) and density of the main body. This second discovery tends to show that rings in small planetary systems are more common that we thought. The release of Gaia DR1 catalog in 2016 greatly improved our predictions of such occultations. In the forthcoming years, efforts will be made on detailed and localized studies of Chariklo’s and Haumea’s rings, but also on search for other small rings systems in order to better understand the origins and the evolution mechanisms of such systems.

<div><div><div><p>The exponential growth of space debris poses a significant threat to humankind’s activities in orbit. It is thus worthwhile to investigate debris-generating events and uncover their causes, consequently informing debris-mitigation guidelines and safer spacecraft design. This work sets out to examine three fragmentation events pertaining to Centaur upper stages which have yet to be fully understood. Critical breakup characteristics such as breakup epoch, fragment velocities, and angular distributions for the Centaur events, as well as select historic fragmentation events are presented. Subsequently, hypotheses regarding the causes of the events are postulated. The Centaur fragmentations stray from breakup patterns exhibited by ’typical’ upper stage fragmentations such as those of the historic explosive Delta upper stage events. Only one of the three events, 2018-079B, appears to have fragmented due to the combustion of leftover propellant. 2009-047B, on the other hand, likely endured a structural failure – inferred from clustered fragments and low fragment spreading speeds. A torus-shaped fragment distribution is observed for the 2014-055B event, suggesting a collision with a small piece of debris may have taken place.</p></div></div></div>

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Background: The presence of muscular deficiency seems to be a major cause of back pain that requires counteractions. Considering that the autochthonous back muscles, responsible for straightening and stabilizing the spine, cannot be activated voluntarily, they can be strengthened only through specific training. The computer-supported test and training system (CTT) Centaur (BfMC GmbH, Leipzig, SN, Germany) seems well suited for this purpose. To show its potential as a reliable diagnostic and training tool, this study aimed to evaluate the test-retest reliability of this 3D spatial rotation device. Methods: A prospective pilot study was conducted in 20 healthy volunteers of both sexes. For test-retest reliability analysis, three measurements were performed with a two-day interval between each measurement. Each measurement consisted of a one-minute endurance test performed in eight different positions (transverse plane). During the test, the subject was tilted by 90° in the sagittal plane from a neutral, upright position. Meanwhile, the subject's level of upper body stabilization along the body axis was assessed. All trunk movements (momentum values) were quantified by a multicomponent force sensor and standardized relative to the subject's upper body mass. The range of motion was assessed by 95% confidence ellipse analysis. Here, all position-specific confidence ellipses for each measurement were merged to a summarized quantity. Finally, ICC analysis using a single-rating, absolute agreement, two-way mixed-effects model and a Bland-Altman plot was performed to determine the reliability. Results: Considering all measurements (t1, t2, t3), the ICC for reliability evaluation was 0.805, and the corresponding 95% confidence interval (CI) was [0.643, 0.910]. Moreover, the Bland-Altman plots for all three pairs of time points did not show significant differences. Conclusion: This study concludes that the CTT Centaur shows good test-retest reliability, indicating it can be used in clinical practice in the future.

This study aims to understand how police officers in Sweden are affected by their line of work in their personal life. The study is based on qualitative research where the empirical material has been gathered from interviews with Swedish police officers. A total of eight police officers have contributed to this study. The main theoretical concept used in this study is Göran Ahrnes notion of the “organizational centaur”. Alongside this concept, the essay also covers police culture and organizational concept. The results of this study reveal that several police officers find it hard to combine their line of work with their personal life. Not only does the occupation affect the police officers themselves, it also affects their family and acquaintances. Moreover, the results demonstrate how police officers relate to their profession in their spare time. Finally, the results of this study express how changes within the police organization has affected the work situation for many police officers in Sweden.

This study examines employees who, during the spread of the Covid-19 virus, have had to switch from working in the workplace to digital teleworking. The aim of the study is to achieve a deeper understanding of how the informants are experiencing their social work environment in digital teleworking, by examining how they experience their relationships with colleagues, managers and cohabitants, as well as how they experience their organizations’ handling of the social work environment. The empirical data consists of 6 qualitative, semi-structured interviews. The theoretical framework of the study consists of Jahoda’s Deprivation theory and Ahrne’s theory of the Organizational centaur, both of which concern the importance of social contact in the workplace. The result of the study show how the respondent’s collegial relationships are affected or even deteriorative by the digital telework during Covid-19 , and how the relationships with cohabitants have changed their dynamics by becoming more work oriented. The result also shows that the respondents perceived lack of organizational management of the social work environment during their new work circumstances caused by Covid-19. Meanwhile, the experiences of employee engagement for digital social contact has increased, as well as perceived social support from those whose partners also work from home. The conclusions of the study are that work seems to fulfill an unintentional social function that is irreplaceable, and that employee initiatives for social interaction increase when the employees feel that the employer invests too much in organizational goals / Denna studie undersöker arbetstagare som under spridningen av Covid-19 har behövt ställa om från arbete på arbetsplatsen till digitalt distansarbete. Studiens syfte är att nå en djupare förståelse av hur respondenterna upplever den sociala arbetsmiljön i det digitala distansarbetet, genom att undersöka hur de upplever relationerna till kollegor, chefer och samboende samt hur de upplever organisationernas hantering av den sociala arbetsmiljön. Den empiriska datan består av 6 stycken kvalitativa, semistrukturerade intervjuer i vilket respondenterna fått berätta om sina upplevelser. Studiens teoretiska ramverk utgörs av Jahodas deprivationsteori och Ahrnes teori om den organisatoriska kentauren, vilka båda berör vikten av social kontakt i arbetet. Resultaten som framkommer vittnar om försämrade eller uteblivna kollegerelationer i det digitala distansarbete som orsakats av Covid-19, en ändrad relationsdynamik med samboende och upplevd bristande organisationshantering av den sociala arbetsmiljön i det digitala distansarbetet. Samtidigt återfinns dock upplevelser av ett ökat medarbetarengagemang för digital social kontakt, samt ett socialt stöd från partners som också arbetar hemifrån. Slutsatserna blir att arbetet verkar fylla en oavsiktlig social funktion som är oersättlig, samt att medarbetarinitiativen för socialt umgänge ökar då arbetstagarna upplever att arbetsgivaren satsar för mycket på organisatoriska mål.