Increasing energy consumption and its environmental impacts make it necessary to look for alternative energy sources. Solar energy as huge energy source which is able to cover the terms sustainability is considered as a favorable alternative. Solar cells and solar fuels are two kinds of technologies, which make us able to harness solar energy and convert it to electricity and/or store it chemically. Metal oxide semiconductors (MOSs) have a major role in these devices and optimization of their properties (composition, morphology, dimensions, crystal structure) makes it possible to increase the performance of the devices. The light absorption, charge carriers mobility, the time scale between charge injection, regeneration and recombination processes are some of the properties critical to exploitation of MOSs in solar cells and solar fuel technology. In this thesis, we explore two different systems. The first one is a NiO mesoporous semiconductor photocathode sensitized with a biomimetic Fe-Fe catalyst and a coumarin C343 dye, which was tested in a solar fuel device to produce hydrogen. This system is the first solar fuel device based on a biomimetic Fe-Fe catalyst and it shows a Faradic efficiency of 50% in hydrogen production. Cobalt catalysts have higher Faradic efficiency but their performance due to hydrolysis in low pH condition is limited. The second one is a photoanode based on the nanostructured hematite/magnetite film, which was tested in a photoelectrochemical cell. This hybrid electrode improved the photoactivity of the photoelectrochemical cell for water splitting. The main mechanism for the improvement of the functional properties relies with the role of the magnetite phase, which improves the charge carrier mobility of the composite system, compared to pure hematite, which acts as good light absorber semiconductor. By optimizing the charge separation and mobility of charge carriers of MOSs, they can be a promising active material in solar cells and solar fuel devices due to their abundance, stability, non-toxicity, and low-cost. The future work will be focused on the use of nanostructured MOSs in all-oxide solar cell devices. We have already obtained some preliminary results on 1-dimensional heterojunctions, which we report in Chapter 3.3. While they are not conclusive, they give an idea about the future direction of the present research.

Climate modeling and tropical cyclone forecasting are two significant is- sues that are continuously being improved upon for more accurate weather forecasting and preparedness. In this thesis, we have studied three climate models and formulated a new model with a view to determine the outgoing longwave radiation (OLR) budget at the top of the atmosphere (TOA) as ob- served by the National Oceanic and Atmospheric Administration’s (NOAA) satellite based Advanced Very High Resolution Radiometer (AVHRR). In 2006, Karnauskas proposed the African meridional OLR as an Atlantic hur- ricane predictor, the relation was further proven in 2016 by Karnauskas and Li. Here we have considered a similar study for all other tropical cyclone basins.

<p>This thesis describes an analysis of the influence of dose and dose rate from low LET radiation on the induction of a cytotoxic bystander effect. The general direction was as follows:</p> <p>a) Utilize a well – established reporter cell line with two types of low – LET radiation across varying dose and dose rates in order to assess the possibility of a dose rate effect. These results identified the recovery of bystander cell survival to control levels after high dose treatment. Additionally, dose rate effects were seen at high dose treatments following electron irradiation as well as between similar low – LET sources.</p> <p>b) Apply aggressive radiation treatment for toxic medium production in order to elicit a bystander cell death response in a cell line with no previous observed effect. Results indicated a similar response to a reporter line including an increase in cell survival at high doses. Transforming growth factor β1 (TGF-β1) was identified as necessary to the observed effect.</p> <p>c) Develop a dosimetry model for <em>in vitro</em> bystander studies following toxic medium production with a β-emitting radiopharmaceutical. Furthermore, use this model to re-examine survival fraction data in comparison with traditional external beam treatment. A code-base and application were developed. Comparison between treatments indicated a similar survival curve shape with differences in the magnitude of the response. This is possibly the result of cell response to low – dose rates from radiopharmaceutical treatment.</p> <p>The overall conclusion points to the importance of dose rate in observed bystander cell death as well as the differentiating response at high doses. Additionally, the similarity in survival curve behaviour across differing cell type's further points to common underlying critical mechanisms. However, it is believed that further data acquisition and aggregation is required in order to build a robust model for the influence of these factors.</p> / Doctor of Philosophy (PhD)

<p>Simultaneous dual-isotope SPECT imaging has a number of applications, for exam- ple, cardiac, brain and cancer imaging. The major concern in simultaneous dual- isotope SPECT is the significant crosstalk contamination between the different isotopes used. The current study focuses on a method of crosstalk compensation between two isotopes in simultaneous dual isotope SPECT acquisition applied to cancer imaging using ^99mTc/¹¹¹In and breast SPECT using ^99mTc/¹²³I. Monte Carlo (MC), which is thought to offer the most realistic crosstalk and scatter compensation modelling, in typical implementations, has inherent long calculation times (often several hours or days) associated with it. This makes MC unsuitable for clinical applications. We have previously incorporated convolution based forced detection into SIMIND Monte Carlo (MC) program which have made MC feasible to use in clinical time frames. In order to evaluate the accuracy of our accelerated MC program a number of point source simulation results were compared to experimentally acquired data in terms of spatial resolution and detector sensitivity. We have developed an iterative MC based image reconstruction technique that simulates the photon down-scatter from one isotope into the acquisition window of a second isotope. The MC based estimation of scatter contamination contained in projection views is then used to compensate for the photon contamination during iterative reconstruction. We use a modified ordered subset expectation maximization (OSEM) alogrithm, named as simultaneous ordered subset-expectation maximization (Sim-OSEM), to perform this step. We have undertaken a number of simulation tests and phantom studies to verify this approach in case of both of the dual-isotope combinations (i.e. ^99mTc/¹¹¹In and ^99mTc/¹²³I). In breast SPECT studies three different breast sizes were simulated. For each of the breast sizes ten combinations of lesions with 3 lesions per combination, were selected randomly for acquisition and reconstruction of simulation data. The images reconstructed using Sim-OSEM showed crosstalk compensation when compared with images reconstructed using simultaneously (with crosstalk) acquired projection data using analytical attenuation based reconstruction. In case of Sim-OSEM the lesion to background ratios were much closer to actual values compared to images reconstructed for both separately (without crosstalk) and simultaneously (with crosstalk) acquired projection data using analytical attenuation based reconstruction. Activity estimation is also possible with Sim-OSEM and yielded accurate estimates of lesion activities with relatively small error compared to deposited activities. The proposed reconstruction technique also evaluated by reconstruction of experimentally acquired projection phantom data in case of ^99mTc/¹¹¹In. Reconstruction using Sim-OSEM showed very promising results in terms of crosstalk and small angle scatter compensation and uniformity of background compared to analytical attenuation based reconstruction after triple energy window (TEW) based scatter correction of projection data. In our case images obtained using Sim-OSEM showed more uniform background even when compared to the images reconstructed for separately acquired projection data using analytical attenuation based reconstruction may be due to better correction of photons scattered at small angle and got detected under photopeak.</p> / Master of Science (MSc)

<p>We study bifurcations of periodic travelling waves in granular dimer chains from the anti-continuum limit, when the mass ratio between the light and heavy beads tends to zero. We show that every limiting periodic wave is uniquely continued with respect to the mass ratio parameter and the periodic waves with the wavelength larger than a certain critical value are spectrally stable. Numerical computations are developed to study how this solution family is continued to the limit of equal mass ratio between the beads, where periodic travelling waves of granular monomer chains exist.</p> / Master of Science (MSc)

<p>Position sensitive detectors represent a class of particle detectors widely used in high-energy physics, astrophysics, biophysics and medicine for imaging the spatial distribution of various radioactive sources. In recent years, a new class of gas based detectors, so-called micropattern gas detectors (MPGDs), has emerged. While modern MPGDs rival solid state detectors in terms of spatial and temporal resolution, their cost of production is significantly lower. A Thick Gaseous Electron Multiplier (THGEM) imaging detector, with a two-dimensional delay line readout, has been constructed as a concept for a large area imaging detector with reasonable spatial resolution. The delay line based THGEM imaging detector is robust, easy to manufacture and cost effective alternative to direct readout techniques which frequently employ a large number of channels. Featuring an active area of 40 x 40 mm<strong>2</strong>, the prototype has been constructed using two 0.4 mm THGEMs and successfully operated in a low pressure, propane based, gas mixture. Two sets of orthogonal electrodes, connected to individual delay lines, serve as a two-dimensional anode readout. Adjacent electrodes are separated by approximately 3.4 ns of time delay and allow the interaction position to be calculated by measuring the time difference between delay line output signals corresponding to a common axis. Using modern field programmable gate arrays (FPGAs), a time-to-digital (TDC) data acquisition (DAQ) system has been developed. The TDC DAQ performs the position reconstruction algorithm and is capable of continuous event rates up to 1.8 MHz. The imaging capabilities of the detector have been assessed using a collimated alpha source and a wide X-ray beam. Under these aforementioned conditions, the detector was able to successfully resolve 1 mm diameter holes spaced 3 mm apart. With higher operating pressures, and using Xenon based gas mixture, it is expected the imaging detector should achieve sub-mm spatial resolution. The investigations presented in this thesis serve as a framework for the development of future THGEM imaging detectors.</p> / Doctor of Philosophy (PhD)

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.

The goal of this thesis has been to find a means of i) designing an active square particle, and ii) continuously varying its degree of activity with the objective of understanding the effects of activity on the various phases of granular matter. The motivations, results and limitations of our methods of creating active particles are discussed in this thesis. The applicability of a stochastic model based on the Langevin equation in 2D as well as implications for future experiments are also discussed.

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.