Univ., Diss., 2009--Kassel.

Stuttgart, Univ., Diss., 2008.

Young adults spend a lot of their time on social media where they share their lives with friends, family, colleagues, acquaintances, ect. Wesch (2009) explains that things posted on social media such as YouTube can be viewed by anybody, everybody, and nobody, anywhere in the world all at once. This becomes a problem for young adults as several different audiences blend into one (i.e. context collapse) (Brandtzaeg, Lüder & Skjetne,2010). For example, how would it feel if your mother saw a video of you at a party which was posted for friends to joke about? However, Brandtzaeg and Lüders (2018) states that is not the only problem. Social media also blurs the line between the present and the past. One example can be a friend commenting on a silly post on facebook you made years ago, then it appears in everyone's feed again making it seem as if you have posted it recently. Both of these problems make young adults change how they chose to self-presentate themselves on social media. In addition, since social media is asynchronous as content does not take place in real-time, it provides time to be more strategic as well as for more polished forms of self-presentation and self-censorship(Gardner & Davis, 2013; Lindgren, 2017). With foundation in this, this study is going to examine which strategies young adults use that are related to self-presentation on the occasion of facing context and time-collapse. The study will focus on to what extent the participants use the tactics mentioned in earlier literature as well as how different aspects relate to the tactics one chooses to use. In order to create an understanding of context- and time collapse previous research has been examined. Furthermore, previous research about self-presentation in general and self-presentation on social media inparticular is examined to connect to how self-presentation can be disturbed by context- and time collapse. Finally, theories and research about privacy is used to gather an understanding of how young adults experiencecontext and time collapse as a problem for their privacy. Through a survey, data have been collected from 226 respondents to be examined, presented and analyzed. The respondents were born between the years 1997 and 2004. The result showed that all of the strategies were used yet the extent varied depending on the strategy. However, the most commonly used strategies were connected to self-censoring. Moreover, there are relations between the strategies and for example gender, how long one had social media, how one perceives oneself etc.However, surprisingly the relations were for the most part weak even though some stand out as a bit stronger. / Unga vuxna spenderar mycket av deras tid på sociala medier där de delar sina liv med vänner, familj, kollegor, bekantskapskretsar, etc. Wesch (2009) förklarar att saker som är publicerade på sociala medier så som YouTube kan bli sedda av vem som helst, alla, ingen och var som helst i världen på samma gång. Detta blir ett problem för unga vuxna då flera olika publiker samlas och blandas på ett och samma ställe (d.v.s kontext kollaps) (Brandtzaeg m fl., 2010). Ett exempel är hur skulle det kännas ifall din mamma såg en video på dig från en fest som du postat till vänner för att skoja? Dock konstaterar Brandtzaeg och Lüders (2018) att det inte är det enda problemet. Sociala medier suddar ut linjen mellan nutid och dåtid. Ytterligare ett exempel kan vara när vänner kommenterar ett töntigt inlägg du gjorde för flera år sen som då hamnar i allas flöden igen, vilket får det att verka som att du har publicerat det nyligen. Båda dessa problem gör att unga vuxna ändrar hur de väljer att presentera sig själva på sociala medier. Dessutom då sociala medier är “asynchronous” då innehåll inte händer i realtid, möjliggör detta tid att vara mer strategisk men även visa mer polerade former av självpresentation och självcensurering  (Gardner & Davis, 2013; Lindgren, 2017). Denna studie kommer med grund i ovanstående undersöka vilka strategier unga vuxna använder som är relaterade till självpresentation vid bemötande av kontext och tids kollaps. Studiens fokus kommer att ligga på vilken utsträckning deltagarna har använt sig av de olika taktikerna som är nämnda av tidigare forskning men även hur olika aspekter relaterar till de taktiker som beslutats att användas.   Genom att skapa en förståelse för kontext- och tid kollaps, har tidigare forskning blivit undersökt. Fortsättningsvis har forskning gällande självpresentation överlag på sociala medier i särskildhet undersökts för att knyta ihop hur själv presentationen kan bli rubbad av kontext- och tids kollaps. Slutligen så har teorier och forskning gällande integritet används för att bilda en förståelse för hur unga vuxna upplever att kontext - och tids kollaps är en problematisk faktor för deras integritet. Genom en enkät har data samlats för analys, undersökning och presentation från 226 deltagare. Deltagarna föddes mellan åren 1997 och 2004. Resultatet visade att alla strategier var använda till viss del, dock varierade det till vilken grad strategierna användes. De mest använda strategierna var länkade till självcensurering. Fortsättningsvis, är det relationer mellan strategier och exempelvis kön, hur länge man har haft sociala medier, hur man ser sig själv o.s.v. Oavsett är det överraskande att relationerna mellan variablerna var till större delen svaga, dock stod vissa ut i mängden som lite starkare.

We review the current state on the thermodynamic behavior and structural phases of self- and mutually-attractive dilute semiflexible polymers that undergo temperature-driven transitions. In extreme dilution, polymers may be considered isolated, and this single polymer undergoes a collapse or folding transition depending on the internal structure. This may go as far as to stable knot phases. Adding polymers results in aggregation, where structural motifs again depend on the internal structure. We discuss in detail the effect of semiflexibility on the collapse and aggregation transition and provide perspectives for interesting future investigations.

I perform and analyse the first ever calculations of rotating stellar iron core collapse in {3+1} general relativity that start out with presupernova models from stellar evolutionary calculations and include a microphysical finite-temperature nuclear equation of state, an approximate scheme for electron capture during collapse and neutrino pressure effects. Based on the results of these calculations, I obtain the to-date most realistic estimates for the gravitational wave signal from collapse, bounce and the early postbounce phase of core collapse supernovae. I supplement my {3+1} GR hydrodynamic simulations with 2D Newtonian neutrino radiation-hydrodynamic supernova calculations focussing on (1) the late postbounce gravitational wave emission owing to convective overturn, anisotropic neutrino emission and protoneutron star pulsations, and (2) on the gravitational wave signature of accretion-induced collapse of white dwarfs to neutron stars. / Ich präsentiere die ersten Computer-Simulationen des rotierenden Kollapses stellarer Eisenkerne, die in der {3+1}-Zerlegung der Allgemeinen Relativitätstheorie durchgeführt werden und Vorsupernova-Sternmodelle aus Sternentwicklungsrechnungen, eine heiße nukleare Zustandsgleichung und ein näherungsweises Verfahren zur Beschreibung des Elektroneneinfangs enthalten und Neutrinodruck-Effekte berücksichtigen. Basierend auf den Ergebnissen dieser Rechnungen erhalte ich die zur Zeit realistischsten Vorhersagen für das Gravitationswellensignal der Kollaps, Abprall, Abkling und frühen Nach-Abprallphase einer Kern-Kollaps-Supernova. Neben den {3+1} Simulationen diskutiere ich newtonsche axisymmetrische Kern-Kollaps-Supernova-Simulationen mit Schwerpunkten auf: (1) der Gravitationswellenabstrahlung in der späten Nach-Abprallphase durch Konvektionsströmungen, anisotropische Neutrinoemission und Proto-Neutronenstern Pulsationen und (2) der Gravitationswellensignatur des Kollapses weißer Zwergsterne zu Neutronensternen, der durch Akkretion eingeleitet wird.

This Thesis puts its focus on the physics of neutron stars and its description with methods of numerical relativity. In the first step, a new numerical framework the Whisky2D code will be developed, which solves the relativistic equations of hydrodynamics in axisymmetry. Therefore we consider an improved formulation of the conserved form of these equations. The second part will use the new code to investigate the critical behaviour of two colliding neutron stars. Considering the analogy to phase transitions in statistical physics, we will investigate the evolution of the entropy of the neutron stars during the whole process. A better understanding of the evolution of thermodynamical quantities, like the entropy in critical process, should provide deeper understanding of thermodynamics in relativity. More specifically, we have written the Whisky2D code, which solves the general-relativistic hydrodynamics equations in a flux-conservative form and in cylindrical coordinates. This of course brings in 1/r singular terms, where r is the radial cylindrical coordinate, which must be dealt with appropriately. In the above-referenced works, the flux operator is expanded and the 1/r terms, not containing derivatives, are moved to the right-hand-side of the equation (the source term), so that the left hand side assumes a form identical to the one of the three-dimensional (3D) Cartesian formulation. We call this the standard formulation. Another possibility is not to split the flux operator and to redefine the conserved variables, via a multiplication by r. We call this the new formulation. The new equations are solved with the same methods as in the Cartesian case. From a mathematical point of view, one would not expect differences between the two ways of writing the differential operator, but, of course, a difference is present at the numerical level. Our tests show that the new formulation yields results with a global truncation error which is one or more orders of magnitude smaller than those of alternative and commonly used formulations. The second part of the Thesis uses the new code for investigations of critical phenomena in general relativity. In particular, we consider the head-on-collision of two neutron stars in a region of the parameter space where two final states a new stable neutron star or a black hole, lay close to each other. In 1993, Choptuik considered one-parameter families of solutions, S[P], of the Einstein-Klein-Gordon equations for a massless scalar field in spherical symmetry, such that for every P > P⋆, S[P] contains a black hole and for every P < P⋆, S[P] is a solution not containing singularities. He studied numerically the behavior of S[P] as P → P⋆ and found that the critical solution, S[P⋆], is universal, in the sense that it is approached by all nearly-critical solutions regardless of the particular family of initial data considered. All these phenomena have the common property that, as P approaches P⋆, S[P] approaches a universal solution S[P⋆] and that all the physical quantities of S[P] depend only on |P − P⋆|. The first study of critical phenomena concerning the head-on collision of NSs was carried out by Jin and Suen in 2007. In particular, they considered a series of families of equal-mass NSs, modeled with an ideal-gas EOS, boosted towards each other and varied the mass of the stars, their separation, velocity and the polytropic index in the EOS. In this way they could observe a critical phenomenon of type I near the threshold of black-hole formation, with the putative solution being a nonlinearly oscillating star. In a successive work, they performed similar simulations but considering the head-on collision of Gaussian distributions of matter. Also in this case they found the appearance of type-I critical behaviour, but also performed a perturbative analysis of the initial distributions of matter and of the merged object. Because of the considerable difference found in the eigenfrequencies in the two cases, they concluded that the critical solution does not represent a system near equilibrium and in particular not a perturbed Tolmann-Oppenheimer-Volkoff (TOV) solution. In this Thesis we study the dynamics of the head-on collision of two equal-mass NSs using a setup which is as similar as possible to the one considered above. While we confirm that the merged object exhibits a type-I critical behaviour, we also argue against the conclusion that the critical solution cannot be described in terms of equilibrium solution. Indeed, we show that, in analogy with what is found in, the critical solution is effectively a perturbed unstable solution of the TOV equations. Our analysis also considers fine-structure of the scaling relation of type-I critical phenomena and we show that it exhibits oscillations in a similar way to the one studied in the context of scalar-field critical collapse. / Diese Arbeit legt seinen Schwerpunkt auf die Physik von Neutronensternen und deren Beschreibung mit Methoden der numerischen Relativitätstheorie. Im ersten Schritt wird eine neue numerische Umgebung, der Whisky2D Code entwickelt, dieser löst die relativistischen Gleichungen der Hydrodynamik in Axialymmetrie. Hierzu betrachten wir eine verbesserte Formulierung der sog. "flux conserved formulation" der Gleichungen. Im zweiten Teil wird der neue Code verwendet / um das kritische Verhalten zweier kollidierenden Neutronensternen zu untersuchen. In Anbetracht der Analogie, um Übergänge in der statistischen Physik Phase werden wir die Entwicklung der Entropie der Neutronensterne während des gesamten Prozesses betrachten. Ein besseres Verständnis der Evolution von thermodynamischen Größen, wie der Entropie in kritischer Prozess, sollte zu einem tieferen Verständnis der relativistischen Thermodynamik führen. Der Whisky2D Code, zur Lösung Gleichungen relativistischer Hydrodynamik wurde in einer „flux conserved form“ und in zylindrischen Koordinaten geschrieben. Hierdurch entstehen 1 / r singuläre Terme, wobei r der ist, die entsprechend behandelt werden müssen. In früheren Arbeiten, wird der Operator expandiert und die 1 / r spezifisch Therme auf die rechte Seite geschrieben, so dass die linke Seite eine Form annimmt, die identisch ist mit der kartesischen Formulierung. Wir nennen dies die Standard-Formulierung. Eine andere Möglichkeit ist, die Terme nicht zu expandieren, den und den 1/r Term in die Gleichung hinein zu ziehen. Wir nennen dies die Neue-Formulierung. Die neuen Gleichungen werden mit den gleichen Verfahren wie im kartesischen Fall gelöst. Aus mathematischer Sicht ist keine Unterschiede zwischen den beiden Formulierungen zu erwarten, erst die numerische Sicht zeigt die Unterschiede auf. Versuche zeigen, dass die Neue-Formulierung numerische Fehler um mehrere Größenordnungen reduziert. Der zweite Teil der Dissertation verwendet den neuen Code für die Untersuchung kritischer Phänomene in der allgemeinen Relativitätstheorie. Insbesondere betrachten wir die Kopf-auf-Kollision zweier Neutronensterne in einem Bereich des Parameter Raums, deren zwei mögliche Endzustände entweder einen neuen stabilen Neutronenstern oder ein Schwarzes Loch darstellen. Im Jahr 1993, betrachtete Choptuik Ein-Parameter-Familien von Lösungen, S [P], der Einstein-Klein-Gordon-Gleichung für ein masseloses Skalarfeld in sphärischer Symmetrie, so dass für jedes P> P ⋆, S[P] ein Schwarzes Loch enthalten ist und jedes P <P ⋆, S [P] eine Lösung ohne eine Singularität. Er studierte das numerisch Verhalten von S [P] als P → P ⋆ und stellte fest, dass die kritische Lösung, S[P ⋆], universell in dem Sinne ist, dass die Lösung nahe des kritischen Wertes unabhängig von den Anfangsdaten ist. Alle diese Phänomene haben die gemeinsame Eigenschaft, dass sobald sich P P ⋆ annähert, auch S[P] S [P ⋆] annähert und dass alle physikalischen Größen von S [P] nur noch von | P - P ⋆ | abhängen. Die erste Studie der kritischen Phänomene über den Frontalzusammenstoß von zwei Neutronensternen wurde von Jin und Suen im Jahr 2007 durchgeführt. Insbesondere untersuchten sie eine Reihe von Anfangsdaten gleicher Neutronensternmasse, mit einer idealen EOS, die aufeinander zu beschleunigt werden. Variiert wurden die Massen der Sterne, ihr Abstand, die Geschwindigkeit und die polytropen Index der EOS. Auf diese Weise konnten sie kritische Phänomen des Typ I beobachten. In weiteren Versuchen, führten sie ähnliche Simulationen frontal kollidierender Materie in Gauß Verteilungen durch. Auch in diesem Fall fanden sie Typ-I-kritisches Verhalten. Zudem führten sie eine störungstheoretische Analyse der Anfangsobjekte als auch der stabilen Endobjekte durch. Wegen der beträchtlichen Unterschiede in den Eigenfrequenzen in beiden Fallen, schlossen sie daraus, dass die kritische Lösung keine linear-gestörten Tolmann-Oppenheimer-Volkoff (TOV) Sterne im Gleichgewicht darstellen. In dieser Arbeit untersuchen wir die Dynamik der Frontalzusammenstoß zweier Neutronensterne gleicher Masse mit ähnlichem Setup wie oben besprochen. Während wir bestätigen, dass die erzeugten Objekte ebenfalls ein Typ-I-kritische Verhalten aufweisen, wiedersprechen wir der der Aussage, dass sich die kritische Lösung nicht als Gleichgewichtslösung dargestellt werden kann. In der Tat zeigen wir, dass die kritische Lösung als linear-gestörte instabile Lösung eines TOV-Sterns dargestellt werden kann. Unsere Analyse berücksichtigt auch die Feinstruktur der Skalenverhältnisse Typ-I-kritischer Phänomene und wir zeigen ebenfalle, dass hier Oszillationen auftreten, die bereits in ähnlichen Studien zum Kollaps kritischer Skalar-Feld gefunden wurden.

The purpose of this thesis work is to evaluate how the physical behaviour of a pipe bend is affected by the pipe bending procedure. Effects such as initial ovalization, thinning, thickening and plastic hardening from the bending procedure are examined and the mechanical properties of pipe bends containing these effects are investigated. This has been evaluated by creating a detailed Finite Element model of a pipe that is being bent. Then the differences compared to a bent tube in a virgin state, so called Elbow elements and an analytical in-house program have been evaluated. The virgin state refers to a model of a pipe that is bent from the beginning, thus having a homogeneous thickness and not containing any plastic hardening. The Elbow element is a calculationally cheap element, specially developed for accurate calculations of pipe bends in an initially virgin state. The goal with the thesis work is to get a better picture of what happens to a pipe as it is being bent, how this affects the mechanical properties and to evaluate the possibility to develop an easy method for taking these effects into account when using the Elbow element. This report describes the layout of the work and how the detailed FE-model has been constructed. One step to being able to use the Elbow element with respect to changes in shape and plastic hardening from the manufacturing process has been presented, the differences are though considered being too big to be able to use the Elbow elements with enough confidence in the results. The problems that remain are presented and discussed and proposals for further work are presented.

<p>The purpose of this thesis work is to evaluate how the physical behaviour of a pipe bend is affected by the pipe bending procedure. Effects such as initial ovalization, thinning, thickening and plastic hardening from the bending procedure are examined and the mechanical properties of pipe bends containing these effects are investigated.</p><p>This has been evaluated by creating a detailed Finite Element model of a pipe that is being bent. Then the differences compared to a bent tube in a virgin state, so called Elbow elements and an analytical in-house program have been evaluated. The virgin state refers to a model of a pipe that is bent from the beginning, thus having a homogeneous thickness and not containing any plastic hardening. The Elbow element is a calculationally cheap element, specially developed for accurate calculations of pipe bends in an initially virgin state.</p><p>The goal with the thesis work is to get a better picture of what happens to a pipe as it is being bent, how this affects the mechanical properties and to evaluate the possibility to develop an easy method for taking these effects into account when using the Elbow element.</p><p>This report describes the layout of the work and how the detailed FE-model has been constructed. One step to being able to use the Elbow element with respect to changes in shape and plastic hardening from the manufacturing process has been presented, the differences are though considered being too big to be able to use the Elbow elements with enough confidence in the results. The problems that remain are presented and discussed and proposals for further work are presented.</p>

Fires in buildings are dangerous in many ways, one big hazard is the risk of building collapse. This is a hazard both to occupants in the building and to the fire service, who might have to enter the building for their firefighting. The consequences of a building collapse can become severe, both in terms of damage to the building and in terms of injuries to people. Despite this, there are few methods to determine how stable a construction is, when exposed to stress from a fire. This thesis has tried to find connections between occurred events where buildings have collapsed, both by a literature study and by looking into some occurred collapses. This has been done by analysing some specific events more deeply, to find out what went wrong in that specific case, and by looking into a broader base of occurred building collapses which has been presented as statistics. Finally contact with personnel from two different fire brigades was taken, to perform a questionnaire and collect information of how they work with the dangers in reality. All of these studies has shown that there are some connections between which buildings collapse more often than others, one example is that small houses collapse more frequently than residential buildings and that roofs is the part of the building which collapses most often. This is confirmed by some of the people from the fire brigades, who thinks it reflects their own experiences regarding building fires. Even though some connections like these can be shown, they can have several explanations as for example, there are many more small houses than residential buildings in Sweden which makes it natural to believe that they collapse more often. Still, some connections are clear and this information can be used to base further studies on and perhaps gain more knowledge to be able to make better judgements on whether a construction is stable or not.

Efterfrågan av väderskyddande ställningar inom byggproduktion har ökat under de senaste åren. En konsekvens vid användning av väderskydd är att ställningen tar upp större laster vid vind och nederbörd, vilket ökar risken för att konstruktionen kollapsar. Under vintern 2016/2017 rasade två väderskydd på Kungliga Tekniska Högskolans område efter ett kraftigt snöfall vilket gav författarna idén till denna examensrapport. Syftet med rapporten är att utreda varför väderskyddade ställningar rasar genom att undersöka processen för uppförande och användande av väderskydd i produktion samt gällande lagar och regler. Rapporten gjordes i samarbete med Skanska och således studerades enbart företagets egna tillvägagångssätt. Litteraturstudier och en genomförd kvalitativ undersökning på tre projekt ligger till grund för rapportens diskussion och slutsatser. Genom studie av Arbetsmiljöverkets föreskrifter (AFS) drogs slutsatsen att dessa är tillräckliga för att förebygga att olyckor sker. Studierna visade även att Skanskas säkerhetsarbete är välutvecklat med detaljerade arbetsmetoder för ett säkert arbete med ställningar och väderskydd. Skanska har även gjort egna tillägg som kompletterar AFS:en för ett säkrare arbete. Rapporten påvisar även ett behov av utredningar från Arbetsmiljöverket när väderskydd kollapsar för att förebygga allvarliga olyckor i framtiden. / The demand for weather protected scaffolding in building production has increased during recent years. A consequence when using weather protection is that the scaffolding will have to endure bigger loads from wind and snow, which increases the risk of a collapse. During the winter of 2016/2017 two weather protected scaffoldings collapsed by heavy snowfall at the site of KTH (the Royal Institution of Technology) in Stockholm, Sweden. This gave the authors the idea of this report. The purpose of the report is to investigate why weather protected scaffoldings collapses by examining the procedure of building and using weather protection in production and also a study of the current regulations regarding the subject. The report was made in cooperation with Skanska and therefore only the company’s intern procedure was studied. During the studies of the Swedish Work Environment Authority’s statute book a conclusion was made that the statute book was sufficient enough to prevent accidents to occur. The studies also showed that Skanska’s safety work is well developed with it’s detailed working methods for a safe work environment regarding scaffolding and weather protection. Skanska has made own additions to the statute book in order to improve safety even more. The report also shows a need of an investigation made of the Swedish Work Environment Authority when a weather protected scaffolding has collapsed to prevent serious accidents in the future.