Master's thesis "Communication strategy of NASA during space programs Mercury, Gemini and Apollo space programs in 1958-1972" is a summary of the work of National Aeronautics and Space Administration (NASA) in the field of external communications. This diploma thesis maps the communication strategy during the first space programs Mercury, Gemini and Apollo in the 50s-70s. of the 20th century. It also puts it in a wider historical, social and media context. It is also devoted to the emergence of NASA, to individual programs and the emergence of space interest in the United States.

Over the past few decades there have emerged greater possibilities for users and consumers of media to create or engage in the creation of digital media technologies. This PhD dissertation explores the ways in which the broadening of possibilities for making technologies, specifically software, has been taken advantage of by new producers of digital culture – freelancers, aspiring digital media creators and small studios – in the production of digital visual media. It is based on two empirical case studies that concern the making of free software for computer graphics animation production in two contexts: by a loose collective of anime fans in Siberia, Russia, and by a small animation studio in Amsterdam, Netherlands. The case studies are presented and analysed in the scope of four journal articles and one book chapter which form the core of the dissertation. The dissertation draws on a media practice perspective and an understanding of software as an artefact that concentrates and mediates specific infrastructural arrangements that entangle politics of technological production, economic interests and practice-related concerns. The analytical focus of the research problematises in particular practices of software decommodification and its further repair and development by non-programmers; the anchoring of software development and repair in actual production practices of computer graphics animations; and a commitment to sharing software, animations and other artefacts online as commons. The thesis combines several concepts from anthropology and science and technology studies to theorise these practices: – politics and regimes of value (Appadurai, 1986); repair and artful integrations (Jackson, 2014; Suchman, 2000); gifting (Baudrillard, 1981; Mauss, 1925/2002) and autonomy (cf Bourdieu, 1993). Bringing together these concepts, the dissertation regards them as constitutive and indicative of what I refer to as ‘media-related infrastructuring practices’, or practices in which non-programmers generate infrastructures through creating and mediating arrangements around technical artefacts like software. The results of the dissertation indicate how making free software for computer graphics media is entangled in diverse conditions of technological unevenness that may enable, but also limit, the possibilities of aspiring media creators to improve their status or work positions in the broader field of digital media. / Under det senaste decenniet har nya medieteknologier för kommunikationoch digitalt skapande möjliggjort för såväl professionella medieproducentersom amatörer att skapa och sprida olika typer av medieinnehåll. Samtidigt finns fler möjligheter än tidigare att bidra till utvecklingen av digitala medieteknologer, såsom programvaruverktyg och infrastrukturer för att producera och cirkulera medieinnehåll (t.ex. Coleman, 2013; Kannengießer,2016; Kubitschko, 2017; Löwgren and Reimer, 2013; Ratto, 2011; Rosneroch Fox, 2016; Toombs et al., 2014). Denna avhandling undersöker hur dessa ökade möjligheter för skapandet av teknologier och infrastrukturer för digital medieproduktion, i synnerhet programvara, har tagits tillvara av mediekreatörer som arbetar, eller strävar efter att arbeta, med datorgrafik. Avhandlingen fokuserar på kulturella, teknologiska och ekonomiska praktiker genom vilka frilansare, oetablerade mediekreatörer och mindre produktionsbolag skapar användardrivna programvaror. Med användardriven avser jag programvara som utvecklas av dess användare: digitalkonstnärer, amatörer och professionellaskapare av digitalt visuell media, snarare än de industriella producenter som traditionellt satt de tekniska ramarna för medieproduktion. Avhandlingen baseras på två empiriska fallstudier som rör skapandet av fri programvara för datoranimation. Med fri programvara avses program där användarna har frihet att använda, kopiera, distribuera, studera, ändra och förbättra programvaran (GNUProject, 2017). De huvudsakliga forskningsfrågorna är: a) hur skapare av datorgrafik utvecklar, formar och guidarde fria programvaror som utgör ett alternativ till industriella programvarorför digital animation, och b) vilken mening dessa alternativ tillskrivs när de används i medieproduktion. Den första fallstudien fokuserar på arbetet av Blender Institute, en oberoende animationsstudio i Amsterdam, Nederländerna. Sedan 2006 har studion arbetat med att utveckla och förbättra en populär programvara för 3D-animation, Blender. Detta har skett genom skapandet av så kallade ‘open-source animation films’, korta animerade filmer med höga produktionsvärden genom vilka programvara, filmelement och utbildning i programvaranhar delats online. Genom den här fallstudien har jag diskuterat programvaruutveckling i en kontext av delningsekonomi. Jag har visat hur strategiskt delande kan vara ett sätt att erövra en maktposition inom digitalmedieproduktion. Jag har också belyst de olika spänningar som uppstår när kulturproducenter söker förena olika perspektiv på programvaror, individuella ambitioner och existerande marknadsstrukturer. Den andra fallstudien fokuserar på praktikerna av Morevna project, ett kollektiv av animé-fans, geografiskt situerade i staden Gorno-Altaysk, i ryska Sibirien. Kollektivet har skapat korta datoranimerade filmer genom vilka man utforskat, lagat och distribuerat den fria programvara de använt i sina produktioner: Synfig för 2D animering. I denna fallstudie har jag argumenterat för värdet av att undersöka spänningar, misslyckanden och lagning snarare än innovationer för att förstå hur alternativa infrastrukturerför digital medieproduktion kan uppstå i kontexter starkt präglade av piratverksamhet. Fallstudierna presenteras och analyseras i fyra olika tidskriftsartiklar och ett bokkapitel, som alla ingår i denna avhandling. De tre första artiklarna svarar mot den första forskningsfrågan och de två sista artiklarna mot den andra. Metodologiskt utgår avhandlingen ifrån kvalitativa ansatser, såsom grounded theory och etnografi. Det empiriska materialet har samlats inmellan 2012 och 2016. Som en del av fältarbetet har jag genomfört kvalitativaintervjuer med 37 informanter. Bland dessa ingår skapare av datorgrafikoch animationer, programmerare och projektledare på Blender Institute och i Morevna. Teoretiskt utgår avhandlingen från ett perspektiv på medier som praktik (Couldry, 2004, 2012). Specifika praktiker som analyseras och teoretiseras i artiklarna är dekommodifiering av programvara; förankrandet av lagningav programvara i medieproduktion; samt delning online av programvara, filmer och filmmaterial; produktionsarbete; samt utbildningsmaterial. Praktikerna analyseras genom begreppen politics and regimes of value (Appadurai, 1986); repair och artful integrations (Jackson, 2014; Suchman,2000); och gifting (Baudrillard, 1981; Mauss, 1925/2002). Jag har också utgått från begreppet autonomi (jfr. Bourdieu, 1993) för att utforska frågan om meningsproduktion vid utveckling av användardriven fri programvaraför medieproduktion. Begreppen beskriver hur olika relationer upprätthålls mellan digitala artefakter, ekonomi och personer. Jag förenar dem i ett gemensamt teoretiskt ramverk genom begreppet infrastructuring (Karasti och Syrjänen, 2004) från science and technology studies. Genom detta begrepp vidgar jag perspektivet på medier som praktik med fokus på praktiker där icke-programmerare och amatörer skapar digitala infrastrukturer genom att integrera nya verktyg och teknik med socialt praktik. Resultaten av denna studie visar hur skapandet av fri programvara av frilansare, oetablerade mediekreatörer och mindre produktionsbolag är ett sätt att skapa infrastrukturell trygghet på en osäker arbetsmarknad. Olika former av autonomi förhandlas i relation till olika konfigurationer av infrastrukturer för teknikproduktion och distribution, till exempel infrastrukturerför piratkopiering eller för att komma runt industriellt skapade begränsningar i förändringen av programvara. I linje med Jackson (2014) betonar jag vikten av att väga upp diskursen kring ‘användarinnovation’ (von Hippel, 2005) genom att betrakta misslyckanden, förfall och haverier som en del av processen av att utveckla nya medier och ny medieteknik, och på så sätt omförhandla uppdelningen och hierarkin mellan olika medieproducenter. Programvaruförfall, dekommodifiering och åldrande kan göra programvaror till ‘residual media’ (Acland, 2007), som i sig kan fungera som en plats där mening, värde och maktförhållanden omförhandlas och skapas på nytt. Dessa omförhandlingar är inte sprungna ur snabba och spontana förändringsprocesser möjliggjorda genom nätverk av kommunikationsteknologier. Snarare karakteriseras de av långsamhet (Paper 3), strategi, dolt kapital (Paper 2), samt konstant förhandling mellan olika intressen (Paper 1, 4 och 5). Litteratur som behandlar organisationen av öppen medieproduktion baserad på allmänningar såsom fri programvara och digitala artefakter som delas online har ofta beskrivits som något som utvecklas organiskt när de frikopplats från etablerade upphovsrättsformer (t.ex. Benkler, 2006; Shirky, 2009). Denna avhandling visar dock att det krävs strategiskt och långsiktigt engagemang för att skapa och etablera en programvara, engagera grupper av användare och integrera programvaran i aktuell medieproduktion. Dessutom antas det ofta att det är hackare, programmerare eller ingenjörer som har makten att tänka ut och realisera faktiska infrastrukturer för digital medieproduktion. Denna studie visardock att mikroanställningar och retorik gör det möjligt även för användare att initiera och påverka medieteknikutvecklingen (Paper 5). Genom att anlägga ett perspektiv på medier som praktik och utveckla det perspektivet med begreppet infrastructuring till det jag kallar för ‘mediarelated infrastructuring practices’ har jag visat hur användardriven programvara och infrastrukturer för datografik skapas och stabiliseras genom att skapa nya och integrera existerande resurser i det digitala medielandskapet. Detta perspektiv öppnar upp möjligheter för att etablera kopplingar mellan olika delfält inom medievetenskapen som fokuserar på medieproduktion, såsom studier av industriell medieproduktion; amatördriven öppenteknikproduktion; samt studier av medieinfrastruktur. Genom infrastructuring kan man se hur medieproducenter skapar nya, förändrar och kritiserar existerande arbetsrelationer, ekonomiska relationer samt kunskapsrelationer. Dessutom kan det växande fältet av infrastrukturstudierutvecklas genom att byta fokus från studier av stora etablerade medieinfrastrukturertill processer av pågående infrastrukturformering av mindre och nya aktörer i det digitala medielandskapet. Sammanfattningsvis bidrar denna avhandling med empiriskt material vilket skapar en större förståelse för formeringen av delar av de digitalamedieproduktionsinfrastrkturer genom en analys av skapandet av användardrivenfri programvara för digital animation. Den bidrar också teoretiskt till en utveckling av perspektivet på medier som praktik (Couldry, 2012). Metodologiskt bidrar den genom att betona värdet av platsbaserad deltagande observation och etnografi även i sammanhang av decentraliserad medieproduktionspraktik. Den bidrar även till att skapa en större förståelse för produktionen av tekniken som underbygger och möjliggör de visuella uttrycken som präglar det mesta av vårt digitala medieinnehållsutbud idag.

Tracy K. Smith's Pulitzer Prize winning collection of poetry, Life on Mars, has been celebrated and analyzed as an elegy to Smith's father by many reviewers and scholars. And while this reading is valid and has been openly endorsed by Smith herself, our understanding of this collection and Smith's father is incomplete without Smith's treatment of motherhood and religion, two previously unexplored fields in relation to Life on Mars that complete our picture of Smith's father. Smith uses her own new role as a mother and her religious questions about the afterlife and her father's fate to address her father's passing. This paper first discusses the previously hidden role of Smith's unborn daughter Naomi, specifically hearkening to poems in the fourth section of Life on Mars which describe Naomi's conception and the painful process of giving birth. This is followed by an analysis of Smith's father and mother and their interconnected relationship to both Smith and her child. The third section of this paper complicates Smith's more idyllic depictions of her family members with universal examples of violence, specifically violence towards women that can lead to unwanted motherhood like rape. The final section of this paper takes previous discussions of motherhood, parenthood, and violence to describe Smith's interest in the living and the dead and how the poems in Life on Mars tie together these disparate groups through the shared experience of loss and gain. This blurred boundary between life and death culminates in Smith's vision of the future, a future Earth which will be incomplete and "hollow" without children, just as Smith's past would be empty without her familial relationships. This link between the deceased and unborn makes Smith's imagined future meaningful and invites further scholarship on Life on Mars, asking for scholars previously interested in only Smith's father to include Smith's descriptions of motherhood and religion in their analysis of Smith's work.

This diploma thesis deals with electron microscopy. Examined equipment is environmental scanning electron microscope (ESEM), namely scintillation a detector of the microscope. There is solved the influence of the profile of holes in diaphragms to the resulting pressure and gas flow on the path of secondary electrons at the detector. Introductory part of thesis informs about microscopy in general, with concentration on electron microscopy; especially on scanning microscope, because research is taken just on the environmental scanning electron microscope. Another part informs about both general principles of dynamics of gases and with finite volume method. Another part deals with concrete used software and with setting of individual parameters for calculation. At the beginning of calculation are used five basic profiles of holes in diaphragms for pressure 1000 Pa in the chamber of the sample. For modelling individual shapes is used 3D parametric modeller SolidWorks. Analysis of circulation of secondary electrons through detector is made by using Cosmos FloWorks module. The most suitable type of diaphragms is chosen from measured models. Another part of diploma thesis deals with measuring of chosen types of diaphragms for more pressures in the chamber of the sample; the pressure is 200, 400, 600, 800 and 1000 Pa. The outcomes of this research are both models of pressure and speed of circulation inside the detector and graphically processed values by using different diaphragms, respectively one type of a diaphragm in different pressures. Production drawings of each diaphragm, together with calculated models, are enclosed.

This diploma thesis deals with the spiritual poetry of Rudolf Jurolek from a religionistic- theological perspective. First, it determines the context of the poet's work through the delimitation of the concept of spiritual poetry and the characteristics of its contemporary form. The thesis then contains a detailed literary-religionistic analysis of individual Jurolek's poetry collections (Dobrovoľná samota, Život je možný, Smrekový les, Poľné vety, Posunok, Putovanie Jakuba z Rána, Hierografia) with an increased interest in spiritual themes and motifs. Subsequently, based on the results of the first two steps, the thesis determines mysticism as a suitable interpretative framework for religionistic-theological research. Among the focal points of Jurolek's spiritual search, nature and poetry, the thesis reveals the connection with mysticism, both on a thematic-motivic level through the figures of particular saints (St. Francis of Assisi, St. Hildegard of Bingen, Plotinus) and through individual phases of mysticism (awakening, purification, enlightenment). The thesis also finds a connection with mysticism in the poet's way of writing which, from the point of view of philosophy, recalls the procedures of Husserl's phenomenology. At the same time, the thesis observes where Jurolek comes closer to the...

Since the mid-20th century, global average temperatures have dramatically risen mostly due to the increasing amount of greenhouse gas emissions in the atmosphere. The effects of this recent global warming are already evident and could be exacerbated in the near future if no real action is taken. Recent ice loss in West Antarctica, monitored by satellite measurements and other techniques, gives cause for concern in such a warming world. A major part of this loss has been driven by warm water masses penetrating underneath the ice shelves in this region. This has led to a flow acceleration of the inland outlet glaciers and a greater discharge of ice to the ocean. The actual resulting contribution of West Antarctica to sea-level rise is estimated to be around 0.2 mm per year between 1992 and 2011, i.e. about one third of the ice-sheet contribution (Antarctica and Greenland), and is expected to increase in the near future.<p><p>In this thesis, we first clearly demonstrate that modeling grounding-line (the boundary between grounded and floating ice) migration depends on both the numerical approach and the physical approximation of the ice-sheet model used. Ice-sheet models prescribing the ice flux at the grounding line and using appropriate physical level and numerical approach converge to the same steady-state grounding-line position irrespective of the grid size used. However, the transient behavior of those models is less accurate than other models and leads to an overestimated grounding-line discharge. Therefore, they need to be used with particular attention on short time scales. Furthermore, the non-inclusion of vertical shear stress in those models increases the effective viscosity and gives steady-state grounding-line positions further downstream when compared to full-Stokes models.<p><p>The second major finding of this thesis is the high control of geometry (glacier width and bedrock topography) on Thwaites Glacier, one of the fastest-flowing outlet glaciers in West Antarctica. A flowline finite-difference Shallow-Shelf Approximation (SSA) model is applied to the glacier and shows that ice-flow convergence (through width parameterization) slows down the grounding-line retreat when compared to simulations where the width is constant. A new buttressing parameterization is also tested on the glacier and permits a better understanding of this effect. Finally, the three-dimensional version of the model above is applied to Thwaites Glacier and highlights the strong control of lateral variations in bedrock topography on grounding-line migration./Depuis le milieu du 20e siècle, les températures moyennes globales ont fortement augmenté principalement à cause de l'augmentation des émissions de gaz à effet de serre d'origine humaine. Les effets de ce réchauffement global récent sont déjà détectables et pourraient s'accentuer dans un futur proche si aucune mesure réelle n'est prise. La perte récente de glace en Antarctique de l'Ouest, enregistrée par mesures satellites et d'autres techniques, est préoccupante dans un monde qui se réchauffe. Une grande partie de cette perte de glace est due à la pénétration de masses d'eau chaude sous les plateformes de glace flottante dans cette région. Cela engendre une accélération de l'écoulement des glaciers émissaires et une plus grande décharge de glace vers l'océan. Ainsi, la contribution récente à la hausse du niveau de la mer de l'Antarctique de l'Ouest s'élève à environ 0.2 mm par an entre 1992 et 2011, c'est-à-dire près du tiers de la contribution des calottes glaciaires (Antarctique et Groenland). On estime que cette contribution va continuer à augmenter dans le futur proche.<p>Dans cette thèse, nous démontrons clairement que la modélisation de la migration de la ligne d'ancrage (frontière entre glaces posée et flottante) dépend de l'approche numérique et de l'approximation physique du modèle cryosphérique utilisé. Les modèles cryosphériques qui prescrivent le flux glaciaire à la ligne d'ancrage et qui utilisent un niveau de physique et une approche numérique appropriés convergent vers la même position d'équilibre de la ligne d'ancrage quelle que soit la taille de maille utilisée. Cependant, le comportement transitoire de ces modèles est moins précis que d'autres modèles et mène à une surestimation du flux à la ligne d'ancrage. Dès lors, ces modèles doivent être utilisés avec précaution sur de courtes périodes de temps. De plus, la non inclusion des contraintes verticales de cisaillement dans ces modèles augmente la viscosité effective et donne des positions d'équilibre de la ligne d'ancrage plus en aval en comparaison avec les modèles « full-Stokes ».<p>La seconde découverte majeure de cette thèse est le contrôle important exercé par la géométrie (largeur du glacier et topographie du lit rocheux) sur Thwaites Glacier, l'un des glaciers émissaires les plus rapides en Antarctique de l'Ouest. Un modèle « Shallow-Shelf Approximation » (SSA) résolvant les différences finies le long d'une ligne d'écoulement est appliqué au glacier et montre que la convergence de l'écoulement glaciaire (au travers de la paramétrisation de la largeur) ralentit le retrait de la ligne d'ancrage comparé aux simulations où la largeur est constante. Une nouvelle paramétrisation de l'effet arc-boutant est testée sur le glacier et permet de mieux comprendre cet effet. Finalement, la version en trois dimensions du modèle ci-dessus est appliquée à Thwaites Glacier et met en évidence le contrôle important des variations latérales de l'altitude du lit rocheux sur la migration de la ligne d'ancrage. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Antarctic ice shelves control the ice flux from the continent to the ocean. As such, they play a major role in the stability of the ice sheet and its potential contribution to sea level rise, especially in the context of global change. Below some of these ice shelves, marine ice can be found which is a product of the Deep Thermohaline Circulation. Due to its specific genetic process, marine ice has intrinsic physical (grain size, ice fabric, bubble content, ) and chemical (impurities, water stable isotopes) properties, that differ from those of 'meteoric ice' formed on the continent through snow metamorphism or 'sea ice' resulting from sea water freezing at the ocean-atmosphere surface. Until now however, the effect of these specific properties on marine ice rheology is still very poorly understood.<p><p>The principal objective being to include realistic mechanical parameters for marine ice in ice shelf flow models, uniaxial compression experiments have been performed on various types of marine ice samples. Technical developments are an important component of this thesis has they were necessary to equip the laboratory with the appropriate tools (pneumatic rig, automatic ice fabric data handling).<p><p>Results from experimental compression on isotropic marine ice show that it represents the higher boundary for meteoric ice viscosity throughout the whole temperature range, thereby validating Cuffey and Paterson's relationship with an enhancement factor equals to 1.<p><p>Marine ice is however often quite anisotropic, showing elongated crystals and wide single maximum fabric, that should impact its mechanical properties. Experiments on pre-oriented marine ice samples have therefore been carried out combining the study of epsilon_{oct} vs. tau_{oct} with a thorough analysis of microstructural data 'before' and 'after' the experiment. <p><p>Depending on the orientation of the sample in the applied stress field and on the intensity of the latter, anisotropic marine ice can be harder or softer than its isotropic counterpart, with n=4 often observed in Glen's flow law. Associating the experimental geometrical settings to potential natural equivalent, results suggest that anisotropic marine ice would strengthen ice shelf flow in most areas (for a same given temperature), apart from suturing areas between individual ice streams as they merge to form the ice shelf, where it could become weaker than meteoric ice in certain circumstances.<p><p>Finally, preliminary sensitivity studies, using a simple ice shelf model with our experimental parameters of Glen's flow law have allowed us to discuss the potential impact of rift location, rift size and thermal regime in the ice shelf behavior. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Dans le contexte actuel du changement climatique, les glaciers arctiques contribuent de manière importante à l’élévation du niveau marin. Parmi eux, les glaciers dits « polythermaux » sont relativement répandus mais leur comportement demeure toujours mal connu. Afin de mieux comprendre la réponse de ces glaciers aux modifications du climat, nous nous somme intéressés au glacier McCall, situé en Alaska arctique, une zone marquée par un réchauffement du climat relativement prononcé.<p>Nous avons utilisé les techniques modernes de radio-écho sondage (radar) et de modélisation numérique, en combinaison avec des observations et mesures de terrain, afin d’identifier les processus physiques responsables de l’évolution de ce glacier ces dernières décennies.<p>Les données radar ont permis de reconstituer la géométrie actuelle du glacier, de distinguer les zones de glace « froide » (dont la température est située sous le point de fusion) des zones de glace « chaude » (température au point de fusion), ainsi que de détecter la présence d’eau à la base du glacier.<p>Ces informations ont été introduites dans un modèle à deux dimensions d’écoulement de la glace, afin de simuler le retrait du glacier depuis le Petit Age de la Glace (fin du 19ème siècle) selon différents scenarios.<p>Les résultats montrent que le modèle est capable de simuler l’évolution du glacier ces dernières décennies de manière réaliste et que le glacier McCall peut-être considéré comme un bon indicateur du changement climatique. Ils démontrent également que le retrait du front du glacier est principalement dû aux perturbations de son bilan de masse, chaque jour plus négatif. Cependant, la percolation et le regel d’une partie de l’eau de fonte sont des processus essentiels pour expliquer le maintien du glacier. Ceux-ci ont pour effet d’ajouter de la glace à l’ensemble du système qui serait autrement perdue par écoulement et drainage. De plus, ils ont paradoxalement pour effet de diminuer la température de la glace et participent donc à ralentir sa perte de masse.<p>En conclusion, la tendance générale au retrait du glacier McCall se confirme pour les années à venir et sa disparition semble inévitable. Cependant, nos résultats suggèrent que cette évolution future pourrait être moins rapide qu’annoncé, en raison de phénomènes complexes de regel d’une partie de l’eau de fonte jouant un rôle « tampon » en contrebalançant les effets directs du réchauffement atmosphérique dans la région.<p> / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

The Antarctic ice sheet is increasingly contributing to sea-level rise because of accelerated mass losses at its floating extensions -- its ice shelves. By floating while remaining attached to the grounded ice sheet, ice shelves buttress (i.e. restrain) the inland ice in such a way that ice-shelf losses lead to accelerated ice discharge in the ocean. This thesis investigates the stability of Antarctic ice shelves -- so crucial for the stability of the entire ice sheet -- using the Roi Baudouin Ice Shelf (RBIS), Dronning Maud Land, East Antarctica, as a case study. The RBIS has remained relatively stable over the last millennia and presents various kilometre-scale features (pinning point, ice-shelf channels and englacial lakes) with potential impact on its present and future stability.We first derive a horizontal velocity field, combining interferometry and speckle tracking with Synthetic Aperture Radar images from ERS 1/2 and ALOS-PALSAR, respectively. The resulting velocities and associated shear-strain rates represent the most detailed fields, currently available for the RBIS and clearly resolve small-scale features of the RBIS: significant slow-down and shearing are observed upstream of a small pinning point and ice converges at ice-shelf channels. We then combine our flow field with high-resolution elevations from TanDEM-X to infer the Basal Mass Balance (BMB) of the RBIS. This method relies on mass conservation in a Lagrangian frame and enables us to finely detect spatial variability in the BMB. We show that the BMB of the RBIS varies substantially on sub-kilometre scales. Our technique is promising and could easily be applied more widely.Additionally, the flow field is used to investigate how considering/ignoring small pinning points in observations (geometry and velocities) impacts data initialisation of poorly known parameters (e.g. basal friction, ice viscosity) and subsequent ice-sheet modelling with BISICLES. We find that overlooking the pinning point in the bathymetry leads to erroneous ice-shelf properties whereas accurately capturing the pinning point in velocities is of secondary importance. Finally, before concluding the thesis, we discuss the stability of the RBIS and its neighbouring ice shelves. Most studies agree that the ice shelf has remained stable over the last decades to millennia and would likely remain so in the absence of external forcing. We however point out to three potential triggers of instabilities: (i) large quantities of surface meltwater are formed in the grounding zone and subsequently stored on the ice shelf, thereby providing fuel for hydrofracturing; (ii) ice-shelf channels are found to significantly incise the ice inland and (iii) a bathymetric trough beneath the RBIS forms a potential gateway for warm water intrusions the ice-shelf cavity, which could destabilise the ice shelf from below. We close with a short essay on the importance of outreach, where we argue that public engagement as a scientist should be considered as being part of science and should be valued for its worth. This chapter gives us the opportunity to present outreach activities undertaken in the frame of this thesis. We conclude that, just like ice shelves control Antarctic ice losses, science communication determines transfers of scientific expertise to public knowledge. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Cosmic rays reach Earth from beyond the Milky Way and with energies up to 10^20 eV.The responsible accelerators have to date not been discovered. However, multi-messenger astronomy can shed light on the question, based on the principle that protons and nuclei accelerated in dense and energetic environments would also produce gamma rays and neutrinos. Such environments may be found in "blazars", which are therefore cosmic ray accelerator candidates. Their gamma-ray emission has been observed to increase, sometimes by orders of magnitude, during "flares" as observed in light curves taken by the Large Angle Telescope on the Fermi satellite. When the latter was launched in 2008, the IceCube Neutrino Observatory had also started taking data, detecting the Cherenkov light from high-energy neutrino interactions in the glacier ice under the geographic South Pole. These two experiments have enabled multi-messenger searches for neutrinos in time correlation with the gamma-ray emission from blazars. This work builds on this principle and extends it by "stacking" the signal from multiple blazar flares. Thus, their individually undetectable neutrino emission could still be discoverable. One first analysis focused on the blazar TXS 0506+056, whose flare in 2017 coincided with arrival of the neutrino IceCube-170922A. Extending into a lower energy range than the alert, the search found no additional excess neutrinos associated with the flare. A second analysis used 179 bright and variable blazars. They were divided in two specific blazar classes and weighted relatively to each other, with two weighting schemes motivated physically using the observed gamma-ray luminosity and a third, generic weighting to cover unconsidered scenarios. No significant neutrino excess was found in the unblinded likelihood fits for any of the source catalogues and weighting schemes. Their combined trial-corrected p-value was p=(79.1 +/- 0.3)%. The limits derived from this analysis are also discussed and its relation with other searches considered. Since that was the first "blazar flare stacking", this work also proposes further improvements to the analysis which will help advance the search for cosmic ray accelerators. / Les rayons cosmiques proviennent d'au-delà de la Voie lactée et atteignent la Terre avec des énergies pouvant aller jusqu'à 10^20 eV. Les objets qui accélèrent ces rayons cosmiques n'ont toujours pas été découverts. Toutefois, l'astronomie multimessager peut apporter un élément de réponse à cette question, en supposant que les protons et les noyaux accélérés dans des environnements denses et énergétiques pourraient également produire des rayons gamma et des neutrinos. Les "blazars" sont de possibles candidats pour les accélérateurs de rayons cosmiques. Une augmentation de leurs émissions de rayons gamma, parfois de plusieurs ordres de grandeur, a été observée lors de phénomènes qu'on appelle "éruption", comme le montrent les courbes de lumière prises par le télescope spatial Fermi-LAT. Lorsque ce dernier a été lancé en 2008, l'observatoire de neutrinos IceCube avait également commencé à prendre des données, détectant la lumière Tcherenkov provenant d'interactions de neutrinos à haute énergie dans la glace qui se trouve sous le Pôle Sud géographique. Ces deux expériences ont permis de mener à bien des recherches multi-messagers de neutrinos en corrélation temporelle avec l'émission de rayons gamma des blazars. Ce principe est le point de départ de cette thèse, qui va plus loin en employant la méthode du "stacking", qui consiste à combiner les signaux provenant de plusieurs éruptions de blazars. Ainsi, leurs émissions individuelles de neutrinos, habituellement indétectables, pourraient être découvertes après combinaison. Une première analyse s'est concentrée sur le blazar TXS 0506+056, dont l'éruption en 2017 a coïncidée avec l'arrivée de l'évènement IceCube-170922A. En considérant une gamme d'énergie inférieure à celle de l'alerte 170922-A, pas d’autres neutrino excédentaire n’a été associé à l'éruption. Une deuxième analyse est basée sur 179 blazars lumineux et variables. Ces blazars ont été répartis en deux classes spécifiques, et chacun d'entre eux a reçu un poids relatif. Trois schémas de pondération ont été considérés :les deux premiers étant motivés par des observations, le troisième étant plus générique. Aucun excès significatif de neutrinos n'a été observé après avoir effectué des ajustements par maximum de vraisemblance sur les données non masquées, pour les différents catalogues de sources et schémas de pondération. Leur valeur-p combinée est de p=(79.1 +/- 0.3)%. Les limites dérivées de cette analyse sont discutées ainsi que leur rapport avec les résultats d'autres recherches. Puisqu'il s'agit du premier stacking d'éruptions de blazars, nous suggérons également des améliorations à apporter à l'analyse afin de permettre la poursuivre de la recherche d'accélérateurs de rayons cosmiques. / Kosmische straling afkomstig van buiten de Melkweg bereikt de Aarde met energieën tot wel 10^20 eV. De astrofysische bronnen waarin deze deeltjes worden versneld zijn tot op heden nog niet ontdekt. De multi-boodschapperastronomie kan een nieuw licht werpen op de oorsprong van kosmische straling, aangezien protonen en atoomkernen die worden versneld in een dichte en energetische omgeving ook gammastralen en neutrino’s produceren. „Blazars” zijn mogelijke kandidaat-versnellers. Observaties van blazars, gemaakt met de ruimtetelescoop Fermi-LAT ,tonen aan dat hun gammastraling tijdens zogenaamde „flakkers” toeneemt. Rond de tijd dat deze werd gelanceerd, begon het IceCube Neutrino Observatorium ook gegevens te verzamelen. Deze laatste detecteert hoog-energetische neutrino’s aan de hand van het Cherenkovlicht dat geproduceerd wordt tijdens hun interacties met de ijskap bij de geografische zuidpool. Deze twee experimenten hebben het mogelijk gemaakt om een multibooschapperzoektocht te verrichten naar neutrino’s van blazars die een tijdscorrelatie hebben met diens flakkers van gammastraling. Dit is het uitgangspunt van dit proefschrift, waarbij er ook een zogenaamde „stapelmethode” wordt toegepast. Op deze manier kan de neutrino-emissie van indivuele blazarflakkers, die afzonderlijk te zwak is om te detecteren, gecombineerd worden en mogelijks toch worden ontdekt. Een eerste analyse legt de focus op de blazar TXS 0506+056, waarvan een flakker in 2017 samenviel met de aankomst van het neutrino IceCube 170922-A. In een relatief lager energiebereik wordt er geen surplus aan neutrino’s gevonden gecorreleerd met de flakker. In een tweede analyse maken we gebruik van de stapelmethode om neutrino’s te zoeken afkomstig van 179 heldere en variabale blazars. Deze worden onderverdeeld in twee specifieke klassen en krijgen elks een zeker gewicht in de stapelanalyse. Hiervoor worden twee wegingsschema’s gebruikt die gemotiveerd zijn door de geobserveerde gammastraling, alsook een derde generieke weging. Ook hierwordt er geen significant neutrinosignaal geobserveerd. De gecombineerde p waarde is p=(79.1 +/- 0.3)%. Hieruit worden limieten afgeleid, en worden de verbanden met andere zoekacties besproken. Aangezien dit werk de eerste analyse omvat naar neutrino’s afkomstig van blazarflakkers gebruik makende van een stapelmethode, worden er in dit werk ook verdere verbeteringen van de analyse voorgesteld. Deze zullen als een startpunt dienen voor toekomstige zoektochten naar de nog onbekende bronnen van kosmische straling. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished