Light is electromagnetic radiation that could be shown in a spectrum with a wide range of wavelengths. Blackbody radiation is a type of thermal radiation and is an important topic to explore due to it being an ideal body that materials’ properties are often described in comparison to it. Therefore, it helps in understanding how materials behave on the quantum level. One must understand its interaction with light spectrum and how electron excitation happens. Thus, concepts such as Planck’s law, energy quantization and band theory will be discussed to try to grasp of how light interacts with materials.

In this thesis, I study fluctuations and rare events of time-additive observables of discrete-time Markov chains on finite state spaces. The observable of interest is the mean node connectivity visited by a random walk running on instances of an Erdős-Rényi (ER) random graph. I implement and analyze the Adaptive Power Method (APM) which converges to the driven process, a biased random walk defined through a control parameter that simulates trajectories corresponding to rare events of the observable in the original dynamics. The APM demonstrates good convergence and accurately produces the desired quantities from a single trajectory. Due to the bulk-dangling-chain structure in the ER graph, the driven process seems to undergo a dynamical phase transition (DPT) for infinitely large graphs, meaning the behavior of the trajectories changes abruptly as the control parameter is varied. Observations show that the random walk visits two distinct phases, being de-localized in the bulk or localized in the chain. Through two simpler models capturing the bulk-dangling-chain property of the ER graph I study how the DPT occurs as the graph size increases. I observe that the trajectories of the driven process near the transition show intermittent behavior between the two phases. The diverging time scale of the DPT is found to be the average time that the random walk spends in a phase before it transitions to the other one. On the ER graph the trajectories are also intermittent but the form of the time scaling remains open due to computational limits on the graph size.

In the global transition from fossil fuels to renewable energy sources, hydrogen is predicted to play a large role. It is particularly interesting in areas where batteries and electrification are not viable options, as well as stabilisation of power deliverance from volatile, green energy production. This expansion on top of current, industrial applications create a large demand for green hydrogen.  DalaVind AB is a regional wind power company looking to implement reversible hydrogen production at a future wind park site. In order to streamline the planning and implementation they need the ability to simulate different scenarios and building components.  In this study, a rudimentary computational planning tool was developed and used to test different cases. By supplying the application with preexisting data we were able to estimate the production of energy, hydrogen gas and usable heat as well as the net earnings as compared to an identical wind park without hydrogen production. / Vätgas förväntas spela en viktig roll i den globala omställningen från fossila till förnybara energikällor. Det är av särskilt intresse inom områden där elektrifiering och batterier inte ses som rimliga alternativ, samt för stabilisering av varierande produktion från förnyelsebar elproduktion. Den här expansionen, utöver den redan etablerade industriella användningen medför en stor efterfrågan på grön vätgas.  DalaVind AB är ett regionalt vindkraftsbolag som planerar att inkorporera vätgasproduktion vid en framtida vindkrafts park. För att kunna effektivisera planeringen och genomförandet av projektet behöver DalaVind kunna simulera olika scenarion och kombinationer av komponenter.  I det här projektet skapades ett beräkningsverktyg som sedan användes för att simulera olika fall. Genom att ge verktyget tillgång till existerande data kunde vi uppskatta produktion av el, vätgas och värme samt net-intäkter jämfört med en identisk vindpark utan vätgasproduktion.

The aim of this study is to contribute to more knowledge about how pedagogical link-making can be used to make the subject content of physics visible in systematic investigations. The method used is a didactic exemplification in a design study, where pupils have been observed in the teaching through audio recording and field notes. The study was carried out in two teaching cycles and the sample of pupils consisted of two classes in 4th grade. We studied whether the subject content in a systematic investigation could be made visible to the pupils through specific pedagogical link-making processes. The result showed that link-making was less favorable in the practical aspects of a systematic investigation, but it created opportunities for feedback that promoted learning, together with emotional involvement. It turned out that the emotional involvement of the pupils does not alone lead to learning. Feedback on subject content was required to be able to lead the pupils towards new knowledge. It is therefore important that the teaching is not only planned based on creating an emotional commitment but also to link back to the subject content in different ways. Based on this insight, the original didactic model was revised, and a new draft of a didactic model was produced. The teacher needs to take responsibility for meeting the pupils in their emotions about the teaching and try to connect these with different types of knowledge to promote pupil learning, which was made visible in the new model. / Syftet med denna studie är att bidra med mer kunskap om hur pedagogiskt länkskapande kan användas för att synliggöra fysikens ämnesinnehåll i systematiska undersökningar. Metoden som använts är en didaktisk exemplifiering i en designstudie, där elever har observerats i undervisningen genom ljudupptagning och fältanteckning. Undersökningen genomfördes i två undervisningscykler och elevurvalet bestod av två klasser i årskurs 4. Studien undersökte, om ämnesinnehållet i en systematisk undersökning kunde synliggöras för eleverna genom olika pedagogiskt länkskapande processer. Undersökningen visade att länkskapning var mindre gynnsamt i de praktiska momenten i en systematisk undersökning, men att det skapade möjligheter för en återkoppling som tillsammans med känslomässigt engagemang främjade ett lärande. Det visade sig att känslomässigt engagemang hos eleverna inte ensamt leder till ett lärande, utan det krävdes en återkoppling till någon form av ämnesinnehåll för att kunna leda eleverna vidare mot nya kunskaper. Det blir därmed av betydelse, att undervisningen inte enbart planeras utifrån att skapa ett känslomässigt engagemang, utan även för att koppla tillbaka till ämnesinnehållet på olika sätt. Utifrån denna insikt reviderades den ursprungliga didaktiska modellen och ett nytt utkast till en didaktisk modell togs fram. Läraren behöver ta ett ansvar i att möta eleverna i deras känslor för undervisningen och försöka koppla samman dessa med olika typer av kunskaper för att främja lärandet hos eleverna, detta synliggjordes i den nya modellen.

Geophysical methods have been widely used to investigate the subsurface in various ap-plications, such as mineral exploration, geotechnical and environmental studies. Among these methods, electrical resistivity tomography (ERT) has gained popularity due to its non-invasive and high-resolution capability in mapping subsurface resistivity variations. In this report, we provide an overview of the theoretical principles behind ERT and discuss its practical applications. We highlight the importance of inversion in ERT data processing and explain how different filtering methods and parameters can affect the results. Our investigation shows that running 2D and 3D inversion in a cloud service is more than feasible and that filtering can significantly reduce the error between the model and reality. We demonstrate that the error can be reduced to less than a 0.1 % in the tested dataset with careful parameter selection. Overall, our findings emphasize the potential of ERT as a powerful tool for subsurface characterization and shed light on its practical implementation for various geophysical applications. / Geofysiska metoder har använts flitigt för att utforska underjordiska strukturer inom olikaforskningsområden, såsom mineralutforskning, geotekniska studier och miljöstudier. Bland dessa metoder har elektrisk resistivitetstomografi (ERT) vunnit popularitet på grund av dess icke-invasiva natur och förmågan att kartlägga resistivitetsvariationer med hög noggrannhet. I detta arbete presenterar vi en översikt över de teorier bakom ERT och diskuterardess praktiska tillämpningar. Vi poängterar betydelsen av inversion vid bearbetningen av ERT-data och förklarar hur olika filtreringsmetoder och parametrar kan påverka resultatet. Vår undersökning visar att det är fullt genomförbart att utföra 2D- och 3D-inversion i en molntjänst och att filtrering kan signifikant minska felet mellan modellen och verkligheten. Vi demonstrerar att felet kan reduceras till mindre än 0,1 %. Sammantaget belyser våra fynd potentialen hos ERT som ett kraftfullt verktyg för karakterisering av underjorden och belyser dess praktiska implementering inom olika geofysiska områden.

This thesis aimed to investigate the relativistic magnetron (RM), which is a high-power microwave (HPM) source. Since the RM can generate high-intensity microwave radiation, it can be used as a pulsed electromagnetic weapon to target electronic systems in different objects, such as drones, missiles, or vehicles. Other applications include electromagnetic compatibility (EMC) testing. In this thesis, a novel design of an RM with a transparent cathode configuration was investigated. This RM, referred to as the FOI-magnetron, was developed with the goal of generating the more advantageous TE11 mode of microwaves. This thesis starts with an in-depth theoretical exploration of the physics surrounding the RM, followed by a proof-of-concept study, where we compare our simulation results against published data. We then investigate the FOI-magnetron to determine if the transparent cathode configuration is more favourable than a solid cathode configuration. Particle-in-cell (PIC) simulations in MAGIC3D were used to study the RM, and extensive parameter studies were conducted for the FOI-magnetron to optimise its performance. The simulations revealed that the FOI-magnetron suffered from leakage currents. Moreover, parameter studies of the FOI-magnetron with transparent cathode demonstrated favourable TE11-mode emission of microwaves with a peak output power reaching 590 MW after 15 ns, having a frequency of 2.56 GHz, and an efficiency of 37%. Comparisons between thetransparent and solid cathode for the FOI-magnetron showed a slightly lower output power and efficiency for the transparent cathode, with minimal difference in the rise time of microwaves. Additionally, the transparent cathode exhibits a higher overall impedance and leakage currents. On the other hand, a lower back-current density on the transparent cathode and emitter was shown, resulting in less damage to the material. In this study, we found that we could reduce leakage currents by extending the interaction region without impacting the performance of the FOI-magnetron. Also, the frequency was shown to change with either a shorter emitter or a longer interaction region, allowing for frequency control. Lastly, a modified design of an RM with a semitransparent cathode showed a promisingly high efficiency of 46% with an output power of 600 MW. This design utilised endcaps, which are useful for significantly reducing leakage currents

Networks of nodes and links are powerful tools to model complex systems, however, when the number of nodes and links grows to the thousands then even the network becomes too complex to comprehend unless we can simplify and highlight the networks underlying structure. The map equation is a method developed by the researchers at IntegratedScience Lab that uses an information theoretic approach to reveal community structure using the flow of information on the network modeled with random walks. Describing these random paths using Huffman codes and utilizing the duality between compression and finding regularities changes the problem of finding community structure into a compression problem. The success of the map equation method depends on the user’s understanding of the method. This thesis describes the design and implementation of a web-based demo application to showcase the mechanics of the map equation aimed to make the map equation more accessible to individuals with no prior knowledge of the method. / Nätverk av noder och länkar är ett kraftigt verktyg för att modellerakomplexa system. Problemet nätverk har är att när antalet noder och länkar växer upp till tusentals noder och länkar, då blir dem snabbt väldigt svåra att tyda och nästan omöjliga att förstå om vi inte kan förenkla och lyfta fram nätverkets underliggande struktur. Kartekvationen är en metod som utvecklats av forskarna vid Integrated Science Labsom använder informationsteori för att avslöja ett nätverks underliggandestruktur med hjälp av informationsflöden på nätverket modellerat med slumpmässiga vandringar. Vi beskriver slumpvandrarens bana när den rör sig på nätverket med Huffman-kodord och använder oss av dualiteten mellan att komprimera data och att hitta regelbundenheter i den data vilket då ändrar problemet av att hitta nätverksstrukturen till ett komprimeringsproblem. Kartekvationens framgång är beroende av användarens förståelse av metoden. Integrated Science Lab vill ha en webbaserad demoapplikation för att introducera användare till kartekvationen och visa upp hur metoden fungerar. Den här avhandlingen beskriver designen och implementationen av den web-baserade demoapplikationenför kartekvationen med syftet att göra kartekvationen mer tillgänglig för individer utan förkunskaper om metoden.

A relativistic magnetron (RM) is a high-power microwave (HPM) source. The main objective of the RM is to generate directed electromagnetic pulses with high power, which can be used in e.g. HPM weapons and for electromagnetic compatibility testing. These pulses can disturb or damage electronic equipment. One of the main challenges when designing an RM is to generate the advantageous TE11 wave mode to the circular waveguide and antenna with high efficiency and peak power. This thesis investigates a new design of the RM, developed at the Swedish Defence Research Agency (FOI), referred to as the FOI magnetron. This design is based on the A6-magnetron and employs four large and two small cavities in the diffraction output of the RM, compared to the conventional design that has six identical cavities. The FOI magnetron has previously shown results that indicate the possibility of generating the TE11 wave mode. In this thesis, a literature study was performed to better understand the governing physical laws of the RM. This was followed by parametric studies using the ​​particle-in-cell code MAGIC3D for simulating the RM. To validate the simulation models, a model of a conventional RM was constructed and the results were compared against the published simulation results by Daimon and Jiang (2008).  Lastly, different geometrical properties, applied magnetic field, and applied voltage of the FOI magnetron were studied to see how they impacted the RM performance. Apart from the diffraction output, the geometry of the interaction region was studied to investigate the effect on frequency and power. The goal was to generate a clean TE11 mode in the waveguide of the RM with high efficiency. The validation yielded results that were in good agreement with the ones obtained by Daimon and Jiang (beam-to-microwave efficiencies of 37% and 36% respectively). The parameter studies of the FOI magnetron gave results that indicate a clean TE11 mode with a beam-to-microwave efficiency of ∼35% and peak powers up to 1 GW at frequencies of approximately 2.5 GHz. The studies on the interaction region showed that a shift of approximately 0.12 GHz was possible when making the rear part of the interaction region 4.5 cm longer. It was found that the length of the front of the interaction region can to some extent affect the output power. Lastly, it was found that a fraction of the output power (∼10−17%) that leaves the interaction region propagates back toward the input region and the voltage source.

Until now the quantum field theory (QFT) that successfully describes the electric, weak and strong interactions (three out of the four fundamental forces) between particles is the Standard Model, but it omits gravity. The prime candidate for a quantum theory of gravity is string theory. However, recent developments in string theory suggest that a portion of the alternative quantum field theories that are being considered, are incompatible with gravity. In 2005, this led string theorists to outline the conditions an effective field theory (EFT) should satisfy in order to be consistent with a quantum theory of gravity. These conditions are the ones that separate the so-called landscape from the swampland. An EFT that satisfies these conditions is said to reside in the landscape, while EFTs that do not satisfy these conditions belong to the swampland. This mapping out of EFTs to the swampland gives rise to a number of predictions that are related to the physics of the Early universe and the nature of dark energy. The de Sitter conjecture and the Trans-Planckian censorship conjecture are some of these conditions and will be the main focus of this thesis. The main purpose behind this work is to gain a deep understanding of each criterium, as well as unravel their implications and predictions related to the dynamics of the Early Universe. We do this by writing a pedagogical introduction of the topic and by introducing some possible alternative to the inflationary scenario, cosmologies that seem to be consistent with the aforementioned constraints.

This master thesis is framed in the striking correspondence between gravity theories in Anti-de Sitter spacetime (AdS) and Conformal Field Theories (CFT). This is usually known as AdS/CFT duality and relates gravity theories in the bulk with CFTs that live in their conformal boundary. We start by presenting the notion of CFTs and some of the results and techniques that are widely used in this field. This includes conformal correlators for scalar and spin operators, the state-operator correspondence and the operator product expansion (OPE) of operators. The embedding formalism and the index-free notation to encode tensors in polynomials are also discussed and used throughout this work. The basic notions of AdS are outlined and CFT at finite temperature is then introduced. We include a review of thermal blocks and thermal coefficients for a thermal two-point function between scalar fields in mean field theory. We then analyse the thermal two-point function for conserved currents, which was not known in the literature. Finally, we start a study of its thermal blocks and thermal coefficients for the mean field theory application.