We calculate tree-level scattering amplitudes in φ^3 theory and Yang-Mills theory by means of the perturbiner expansion. This involves solving the Euler-Lagrange equations of motion perturbatively via a multi-particle ansatz, and using Berends-Giele recursion relations to extract the solution from simple on-shell data. The results are Berends-Giele currents which are then used to calculate the scattering amplitudes. The theoretical calculations are implemented into a Mathematica script which effectively handles recursive calculations and allows us to calculate amplitudes for an arbitrary number of particles.

Nuclear power is a foundational part of our electrical grid in the present and through our transition towards more sustainable and renewable alternatives. However, given the serious consequences of reckless and/or dangerous operation of nuclear power plants, they are subject to strict regulation and supervision by the Swedish radiation protection authority (SSM) and other regulating bodies (e.g. IAEA). In order to prove that a nuclear power plant is operating in a safe and accident preventative manner, the “Safety Analysis Report” (SAR) is created and submitted. The SAR categorizes and ranks all possible incidents and operation affecting events in terms of risk and available countermeasures to ensure that the radioactive release from the power plant and impact on a third party from any event is at acceptable levels. This projects limits its analysis to flooding of the reactor building or “internal flooding events” as described in the SAR. To determine the affected areas and impacted systems of any flooding event, deterministic safety analyses (DSA) are employed. The goal of this project is to develop a comprehensive thermohydraulic model of the Forsmark 2 reactor building and evaluate its performance with respect to the previously used MATLAB model. The model  should allow for a detailed nodalisation of the reactor building as well as realistic modelling of structural components such as doors, hatches, stairwells and drainage systems. The resulting thermohydraulic model  can be used to evaluate different flooding incidents dynamically and follow the spread of water and/or steam throughout the reactor building. Furthermore, the resulting pressure changes and heat generation in the reactor building can also be evaluated. The model allows for the possibility to couple the thermohydraulic reactor building model with the existing power plant systems model to holistically evaluate the power plant response to flooding related incidents. / Kärnkraft är en grundläggande del av vårt elnät i nuläget och under vår övergång mot mer hållbara och förnybara alternativ. Men med tanke på de allvarliga konsekvenserna av vårdslös och/eller farlig drift av kärnkraftverk, är de föremål för strikt reglering och tillsyn av Strålsäkerhetsmyndigheten (SSM) och andra reglerande organ (t.ex. IAEA). För att bevisa att ett kärnkraftverk drivs på ett säkert och olycksförebyggande sätt, upprättas och inlämnas "Strålsäkerhetsanalysrapport" (SAR). SAR kategoriserar och rangordnar alla möjliga incidenter och händelser som påverkar driften i termer av risk och tillgängliga motåtgärder för att säkerställa att radioaktiva utsläpp från kraftverket och påverkan på tredje person från någon händelse är på acceptabla nivåer. Detta projekt begränsar sin analys till översvämning av reaktorbyggnaden eller "interna översvämningshändelser" enligt beskrivningen i SAR. För att fastställa de påverkade områdena och drabbade systemen vid en översvämningshändelse, används deterministiska säkerhetsanalyser (DSA). Målet med detta projekt är att utveckla en omfattande termohydraulisk modell av Forsmark 2 reaktorbyggnad och utvärdera dess prestanda i förhållande till den tidigare använda MATLAB-modellen. Modellen ska möjliggöra en detaljerad nodalisering av reaktorbyggnaden samt realistisk modellering av strukturella komponenter som dörrar, luckor, trapphus och dräneringssystem. Den resulterande termohydrauliska modellen kan användas för att dynamiskt utvärdera olika översvämningsincidenter och följa spridningen av vatten och/eller ånga genom reaktorbyggnaden. Dessutom kan de resulterande tryckförändringarna och värmegenereringen i reaktorbyggnaden också utvärderas. Modellen möjliggör koppling av den termohydrauliska reaktorbyggnadsmodellen med den befintliga kraftverkssystemmodellen för att holistiskt utvärdera kraftverkets respons på översvämningsrelaterade händelser.

Sweden's nuclear power industry plays a crucial role in meeting future energy needs and achieving climate goals where nuclear power is essential to this success. However, one of the biggest challenges in nuclear power is the management of spent nuclear fuel, which must be stored safely for long periods to protect people and the environment from radioactive radiation. To address this, Svensk Kärnbränslehantering AB (SKB) plans to build a capsule factory for encapsulating spent nuclear fuel. The capsule factory is a key component of the Swedish KBS-3 system for the final disposal of nuclear waste, where copper capsules will be used to safely seal and store the spent nuclear fuel for over 100,000 years, 500 meters underground. The purpose of this study was to evaluate two main scenarios for the construction of the capsule factory: an early construction, and a later construction, as well as to examine the opportunities and risks of reusing existing encapsulation equipment compared to investing in new equipment. To address the research questions and achieve the objectives of the report, the methods consisted of SWOT-analyses, surveys, risk assessments, and statistical analysis of the risks to evaluate the scenarios. The results show that an early construction start can reduce overall risks and enable a more efficient transition to full-scale production by the year 2036. A later construction start can reduce initial costs but may involve an increased risk of delays. Reusing existing equipment can also lower costs but may require extensive inspections and upgrades as it becomes outdated. New investments in equipment entail higher initial costs but offer more modern and efficient solutions with lower long-term maintenance requirements. In summary, an early construction start of the capsule factory is recommended, with a thorough assessment of the possibility of reusing existing equipment to maximize cost-effectiveness and minimize risks.

Materials at extreme conditions exhibit properties that differ substantially from ambient conditions. High pressure and high temperature expose anharmonic, non-linear behavior, and can provoke phase transitions among other effects. Experimental setups to study that sort of effects are typically costly and experiments themselves are laborious. It is common to apply theoretical techniques in order to provide a road-map for experimental research. In this thesis I cover computational algorithms based on first-principles calculations for high-temperature and high-pressure conditions. The two thoroughly described algorithms are: 1) the free energy studies using temperature-dependent effective potential method (TDEP), and 2) a higher-order elastic constants calculation procedure. The algorithms are described in an easy to follow manner with motivation for every step covered. The Free energy calculation algorithm is demonstrated with applications to hexagonal close-packed Iron at the conditions close to the inner Earth Core’s. The algorithm of elastic constants calculation is demonstrated with application to Molybdenum, Tantalum, and Niobium. Other projects included in the thesis are the study of effects of van der Waals corrections on the graphite and diamond equations of state. / Material vid extrema förhållanden uppvisar egenskaper som skiljer sig avsevärt från omgivningsförhållanden. Högt tryck och hög temperatur exponera anharmonicity, icke-linjärt beteende, och kan framkalla fasövergångar bland andra effekter. Experimentella uppställningar för att studera denna typ av effekter är vanligtvis dyra och experiment själva är mödosam. Det är vanligt att tillämpa teoretiska metoder för att ge en färdplan för experimentell forskning. I denna avhandling täcker jag beräkningsalgoritmer baserat på första principer beräkningar för hög temperatur och högt tryck. De två grundligt beskrivna algoritmer är: 1) den fria energin studier med temperaturberoende effektiv potentiell metod (TDEP), och 2) en högre ordning elastiska konstantberäkningsproceduren. Algoritmerna beskrivs i en lätt att följa sätt med motivation för varje steg som omfattas. Den fria energiberäkningsalgoritm visas med program till hexagonal tätpackad järn på villkoren nära jordens inre kärna. Algoritmen av elastiska konstanter beräkning demonstreras med tillämpning till molybden, tantal, och niob. Andra projekt som ingår i avhandlingen är effekterna av van der Waals-korrigeringar på tillståndsekvation och elastiska konstanter i grafit och diamant.

The aim of the study is to provide knowledge about how children explore, understand and reason about the physical phenomenon of friction. This study have been based on the younger children’s exploring. The method of the study has been observation in order to get as close to the environment that’s being investigated and to bring attention to the younger children’s actions. A nonparticipating observation was also used for the observer to influence the children as little as possible. The observations that have been made have taken place over two days and have been video recorded to ensure documentation of children's reasoning, body language and actions. The result shows how the children focused on overcoming the friction to get an object to slide instead of getting stuck. The participants’ interaction also emerged in the result as central to driving the exploration further. The conclusions drawn after the study is that the result can be linked to the preschool’s curriculum, which addresses the fact that the children should be given the opportunity to explore, discuss and develop understanding of physical phenomena. The study has also highlighted that hills can be used as a tool for teaching and exploring the phenomenon of friction.

We introduce slow-roll inflation in string theory on both a conceptual level and a detailed one. In order to do this we first briefly review important concepts of inflation and string theory. We then reconstruct models of string inflation in the so-called Racetrack scenario for two different cases where the difference being the number of Kähler moduli used as inflaton. Furthermore, we briefly relate our results to the more recent discussion on whether AdS/dS solutions actually exist in string theory. In this instance our results seem to indicate that uplifting is a crucial component to obtain AdS/dS solutions.

There are many clinical situations where magnetic resonance imaging (MRI) is preferable over other imaging modalities, while the major disadvantage is the relatively long scan time. Due to limited resources, this means that not all patients can be offered an MRI scan, even though it could provide crucial information. It can even be deemed unsafe for a critically ill patient to undergo the examination. In MRI, there is a trade-off between resolution, signal-to-noise ratio (SNR) and the time spent gathering data. When time is of utmost importance, we seek other methods to increase the resolution while preserving SNR and imaging time. In this work, I have studied one of the most promising methods for this task. Namely, constructing super-resolution algorithms to learn the mapping from a low resolution image to a high resolution image using convolutional neural networks. More specifically, I constructed networks capable of transferring high frequency (HF) content, responsible for details in an image, from one kind of image to another. In this context, contrast or weight is used to describe what kind of image we look at. This work only explores the possibility of transferring HF content from T1-weighted images, which can be obtained quite quickly, to T2-weighted images, which would take much longer for similar quality. By doing so, the hope is to contribute to increased efficacy of MRI, and reduce the problems associated with the long scan times. At first, a relatively simple network was implemented to show that transferring HF content between contrasts is possible, as a proof of concept. Next, a much more complex network was proposed, to successfully increase the resolution of MR images better than the commonly used bicubic interpolation method. This is a conclusion drawn from a test where 12 participants were asked to rate the two methods (p=0.0016) Both visual comparisons and quality measures, such as PSNR and SSIM, indicate that the proposed network outperforms a similar network that only utilizes images of one contrast. This suggests that HF content was successfully transferred between images of different contrasts, which improves the reconstruction process. Thus, it could be argued that the proposed multi-contrast model could decrease scan time even further than what its single-contrast counterpart would. Hence, this way of performing multi-contrast super-resolution has the potential to increase the efficacy of MRI.

Bacteria can quickly spread throughout the human body, making certain diseases hard or impossible to cure. In order to understand how the bacteria can initiate and develop into an infection, microfluidic chambers in a lab environment are used as a template of how bacteria reacts to different types of flows. However, accurately tracking the movement of bacteria is a difficult task, where small objects has to be captured with a high resolution and digitally analysed with computationally heavy methods. Popular imaging methods utilise digital holographic microscopy, where three-dimensional movement is captured in two-dimensional images by numerical reconstruction of the diffraction of light. Since numerical reconstructions become computationally heavy when a good accuracy is required, this master's thesis work focus on evaluating the possibility of using convolutional neural networks to quickly and accurately determine the spatial properties of bacteria. By thorough testing and analysis of state of the art and old networks a new network design is presented, designed to eliminate as many imaging issues as possible. We found that there are certain network design choices that help with reducing the overall error of the system, and with a well chosen training set with sensible augmentations, some networks were able to reach a 60% classification accuracy when determining the vertical rotation of the bacteria. Unfortunately, due to the lack of experimental data where the ground-truth is known, not much experimental testing could be performed. However, a few tests showed that images of high quality could be classified within the expected range of vertical rotation. / Bakterier kan snabbt sprida sig genom människokroppen, vilket försvårar starkt möjligheterna att kurera vissa sjukdomar. För att få en inblick i hur bakterier kan initiera och utvecklas till en infektion används som mall laborativa uppställningar med vätskekanaler i mikroskala när man söker förstå hur bakterier reagerar på olika typer av flöden. Att spåra dessa rörelser med god säkerhet är dock en utmaning, då man experimentellt söker fånga små skalor med hög upplösning, som sedan ska analyseras med datorintensiva metoder. Populära avbildningsmetoder använder sig utav digital holografisk mikroskopi, där tredimensionella rörelser kan fångas med hjälp av tvådimensionella bilder genom att numeriskt återskapa ljusets brytningsmönster mot objekten. Eftersom dessa metoder blir beräkningstunga när god säkerhet krävs så utforskar detta examensarbete möjligheterna att utnyttja faltningsnätverk för att snabbt och säkert bestämma vertikalrotationen hos bakterier avbildade med holografi. Genom nogranna tester av moderna samt äldre nätverk så presenteras en ny nätverksdesign, utvecklad i mål med att eliminera så många avbildningsproblem som möjligt. Vi fann att vissa designval vid nätverksutvecklingen kan hjälpa med att reducera klassificeringsfelen givet vårt system, och med en väl utvald träningsmängd med lämpliga justeringar så lyckades vi nå en klassificeringssäkerhet på över 60% med vissa nätverk. På grund av bristande experimentellt data där de riktiga värdena är kända så har ingen utförlig experimentell analys utförts, men några tester på experimentella bilder i god kvalité har visats ge resultat som tyder på en korrekt analys inom den förväntade vertikalrotationen.

The treatment plan for radiation therapy with protons is based on images from a computed tomography (CT) scanner. This is problematic since the photons in the x-ray beam from the CT scanner and the protons are affected differently by the tissue in the patient, which introduce an uncertainty in the track length of the protons. The hypothesis of this study is that a new generation of CT scanners (DECT), with the capacity to simultaneously scan the patient with two photon spectra of different mean energy, will improve the tissue characterisation and which in turn reduce the uncertainty in the track length of the protons. In this study, the accuracy and precision of a DECT-based method from the literature is compared to the conventional calibration method used today at the University clinics in Sweden to relate the attenuation of the photon beam to the slowing down of the protons. The methods are tested on CT images of a phantom, a plastic body containing tissue equivalent plastic inserts of known elemental composition. The results turned out to be inconclusive as there were large uncertainties in the measurements. The method has potential, as has been shown in the literature, but there are many questions that need to be answered before the method is ready to be implemented at the clinic. / En proton som färdas genom människokroppen deponerar endast en liten del av sin energi längs vägen innan den plötsligt deponerar allt i slutet på dess bana. Hur lång dess bana är beror på protonens ursprungliga energi och den atomära sammansättningen hos vävnaden den passerar igenom. Om sammansättningen är känd går det genom att justera den initiala energin bestämma banlängden. Denna egenskap gör protonen väldigt attraktiv för strålterpi, då det innbär möjligheten att behandla med hög precision samt bespara frisk vävnad onödig dos. Strålterapi med protoner planeras idag med bilder från en skiktröntgen (CT) som underlag. Ett problem med det är att röntgenstrålarna från CT-skannern påverkas annorlunda än protonerna av vävnaden, vilket introducerar en osäkerhet i protonernas banlängd. Hypotesen i denna studie är att en ny generation av CT-scanner (DECT), med möjlighet att simultant skanna patienten med två fotonspektran av olika medelenergi, på ett bättre sätt ska kunna bestämma den atomära sammansättningen för vävnaden och därmed reducera osäkerheten i protonernas banlängd. Noggrannhet och precision för en DECT-baserad metod från litteraturen jämförs med den SECT-baserade kalibreringsmetoden, som idag används på Universitetssjukhusen i Sverige för att relatera fotonstrålens dämpning i vävnaden till protonernas inbromsning. Metoderna testas på CT bilder av ett fantom, en plastkropp innehållandes olika cylindrar av vävnadsekvivalent plast med känd atomär sammansättning. Resultatet av den här studien är inte starkt nog för att bevisa hypotesen för studien. Det insamlade bildmaterialet innehåller höga brusnivåer jämfört med de som rapporteras i literaturen. Brusnivåer är så höga att det mesta av resultatet inte kan anses som statistiskt signifikant. Det är dessutom svårt att göra en direkt jämförelse av prestanda med befintlig teori för vävnadskaraktärisering, då bildmaterialet från de CT skanners som jämfördes är av olika typer. De resultat som publicerats i litteraturen visar att den DECT-baserade metoden har potential, men den här studien gör tydligt att det fortfarande finns frågor som måste besvaras innan metoden är redo att implementeras kliniskt.

This study aims to validate a screw joint simulation model used by BAE Systems in LS-DYNA during blast simulations. It is important that the screw joint simulation model is physically correct, since the simulation results can influence major design decisions. The study provides a short overview on the subject of bolts and screws, material deformation and stress and strain in materials, of the finite element method (FEM) and on some specific numerical methods used in this study. BAE Systems started a validation project of the screw joint simulation model in 2015, but it was not finished due to other priorities. In this older project some drop-tower tests measuring the axial force in a screw joint were conducted. These old tests can now serve as validation data for the screw joint simulation model. The screw joint simulation model used by BAE Systems is dependent on a special kind of finite element formulation; a so called beam element. This study provides a finite element analysis on this simulation model, which is implemented through an established industry FEM solver called LS-DYNA. The validation of the screw joint simulation model is done against three drop-tower experiments performed at 900, 1000 and 1100mm drop height respectively. The drop-tower experiments were replicated in LS-DYNA, with a prescribed velocity on the falling parts rather than simulating a free fall and non-elastic impact. A comparison between the simulation model using beam elements, that is used by BAE Systems, and a similar simulation model using solid elements is presented as part of the validation. To make sure that the result of the study is confident, a local mesh convergence study and a study of the mass scaling numerical method in LS-DYNA is also presented. The results show that the screw joint simulation model using beam elements is valid according to the available experimental data. In one of the experiments, where the drop-test was performed twice, an average maximum force on the screw was measured to be 33.5+-4.8 kN. Simulations of the same case, under the same conditions, using beam elements resulted in a maximum force on the screw of 35.4 kN, well within the experimental result range. In the other two drop-tower experiments, the simulated results showed correlation considering the error sources in the simulation model and the statistical spread that is present in the experimental results. The simulation model using beam elements is also similar to the results using solid elements, which also indicates that the beam model is valid. All in all, it is shown that the beam model can be used to produce safe results that either overestimate or place the simulations of the axial force in the screw in the upper spread of the measurements.