This thesis investigates the application of two different modeling techniques for simulating nuclear fuel rods: Constructive Solid Geometry (CSG) with Boolean operations in Serpent and mesh-based modeling in OpenFOAM. The purpose of the study was to evaluate how a mesh-based model performs compared to a CSG-based model when conducting simulations on a relatively simple geometric configuration. The reasons for using mesh-based geometry include the ability to couple Serpent with OpenFOAM, enabling simulations in both codes using the same geometry, and accommodating users who might be more comfortable with mesh-based software. By performing a direct comparison between the results from the two modeling methods, the project aimed to assess the accuracy, efficiency, and practical usability of mesh-based geometry in nuclear simulations. The results indicate that mesh-based modeling, particularly with finer mesh, can achieve a level of detail and accuracy comparable to that of CSG models. However, the simulations with finer mesh took significantly longer to complete, highlighting the need for careful consideration of mesh size depending on the specific requirements of the simulation. The study encompasses several critical aspects, including computational speed and the precision of the resulting simulation data. The analysis demonstrates that while mesh-based modeling offers high precision and flexibility, it is more computationally intensive. In contrast, CSG is faster and simpler to implement for less complex geometries, but may not adequately capture more intricate details. The conclusions suggest that mesh-based modeling can be a viable alternative for complex simulations, provided that the computational resources are available. By highlighting the potential and limitations of mesh-based modeling in comparison to traditional CSG techniques, the study provides valuable insights. Utilizing mesh-based models is highly advantageous when CFD simulations are planned, as it avoids the need to simulate one model in Serpent and another in CFD. Thus, mesh-based geometry is a promising toolkit for achieving high precision and efficiency in detailed and intricate simulations within the nuclear field.

Renormalization group analysis is a useful tool for studying critical behaviour of stochastic systems. In this thesis, field-theoretic renormalization group will be applied to the scalar model representing directed percolation, known as Gribov model, in presence of the random velocity field. Turbulent mixing will be modelled by the compressible form of stochastic Navier-Stokes equation where the compressibility is described by an additional field related to the density. The task will be to find corresponding scaling properties.

This paper considers the statistical mechanics occupation of the edge of a single helix of DNA by simple polymers. Using Fisher's exact closed form solution for dimers on a two-dimensional lattice, a one-dimensional lattice is created mathematically that is occupied by dimers, monomers, and holes. The free energy, entropy, average occupation, and total charge on the lattice are found through the usual statistical methods. The results demonstrate the charge inversion required for a DNA helix to undergo DNA condensation.

Quantum dots, also known as artificial atoms, are created by tightly confining electrons, and thereby quantizing their energies. They are important components in the emerging fields of nanotechnology where their potential uses vary from dyes to quantum computing qubits. Interesting properties to investigate are e.g. the existence of atom-like shell structures and lifetimes of prepared states. Stability and controllability are important properties in finding applications to quantum dots. The ability to prepare a state and change it in a controlled manner without it loosing coherence is very useful, and in some semiconductor quantum dots, lifetimes of up to several milliseconds have been realized. Here we focus on dots in semiconductor materials and investigate how the confined electrons are effected by their experienced potential. The shape of the dot will effect its properties, and is important when considering a suitable model. Structures elongated in one dimension, often called nanowires, or shaped as rings have more one-dimensional characteristics than completely round or square dots. The two-dimensional dots investigated here are usually modeled as harmonic oscillators, however we will also consider circular well models. The effective potential confining the electrons is investigated both in regard to how elliptical it is, as well as how results differ when using a harmonic oscillator or a circular well potential. By mixing spin states through spin-orbit interaction transitioning between singlet and triplet states becomes possible with spin independent processes such as phonon relaxation. We solve the spin-mixing two-electron problem numerically for some confinement, and calculate the phonon transition rate between the lowest energy singlet and triplet states using Fermi's golden rule. The strength of the spin-orbit interaction is varied both by changing the coupling constants, and by applying an external, tilted, magnetic field. The relation between magnetic field parameters and dot parameters are used to maximize state lifetimes, and to model experimental results. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 3: Manuscript.</p>

Graphene, the world's first truly two-dimensional material, is unique for having an electronic structure described by an effective Lorentz invariant theory. One important consequence is that the ratio or Coulomb energy to kinetic energy is a constant, depending only on conditions within the lattice rather than on the average charge density as in a typical Galilean invariant material. Given this unusual property, a natural question would be how do phenomena, such as screening of a Coulomb impurity, happen in graphene? Moreover, how does the addition of uniaxial strain enhance or diminish this behavior? Here I discuss our work to calculate the charge density distribution in a lattice of strained graphene under the effect of an external Coulomb impurity. Graphene can have its band structure significantly altered by the application of uniaxial strain. Two cases are here explored: relatively weak strain at some finite chemical potential, and extreme strain with zero chemical potential. In the first system, the strain induces elliptic Dirac cones, engendering some inherent directionality to graphene's electronic properties that did not exist before. This anisotropy manifests itself in the polarization function, and so too in the screening charge density. A finite chemical potential in this case is necessary for any screening to take place in graphene since, without it, there are no electron states near the Fermi level to polarize. Both in the strained and unstrained case, decaying oscillations known as Friedel oscillations are observed. The result of strain is a multifaceted anisotropy of the charge distribution: the amplitude, frequency, and the position of the first peak in the oscillations are each varied depending on the direction one observes. In the second system, extreme strain in graphene leads to a merging of Dirac cones, yielding a transition to a new energy spectrum. This band structure is unusual in that it becomes quadratic along the direction of strain while remaining linear along the perpendicular. We evaluate the screening response to a Coulomb impurity in this case at zero chemical potential, and yet long-range distribution tails are still observed. The result is a very exotic charge distribution, in which the radial distribution of charge and the angular distribution are highly coupled, and at various distances, both screening and anti-screening regions are observed around the impurity. The anti-screening regions are local, and the net induced charge density still satisfies the accepted model of screening.

Sea state is a subjective quantity whose accuracy depends on an observer’s ability to translate local wind waves into numerical scales. It provides an analytical tool for estimating the impact of the sea on data quality and operational safety. Tasks dependent on the characteristics of local sea surface conditions often require accurate and immediate assessment. An attempt to automate sea state classification using eleven years of ship motion and sea state observation data is made using parametric modeling of distribution-based confidence and tolerance intervals and a probabilistic model using sea state frequencies. Models utilizing distribution intervals are not able to exactly convert ship motion data into various sea states scales with significant accuracy. Model averages compared to sea state tolerances do provide improved statistical accuracy but the results are limited to trend assessment. The probabilistic model provides better prediction potential than interval-based models, but is spatially and temporally dependent.

Organic solar cells have been showing promise as a way of producing renewableenergy with the help of light, flexible, and production effective materials.The efficiencies and lifetimes reached in organic solar cells have steadily beenincreasing over the years as more research in the field is being conducted.One way of increasing the efficiency in organic solar cell devices is introducingan interlayer between the photoactive material and the anode, referred toas the ’hole transport layer’. Most commonly used as a hole transport layer isthe material PEDOT:PSS, which offers desired properties such as transparency,simple processing and good ohmic contact between anode and photoactive material.PEDOT:PSS is also known to be a degradation site in organic solar cells,as it will corrode the electrode in the presence of water.This project has consisted of investigating PEDOT:PSS along with two othercandidates that may one day come to replace PEDOT:PSS as the most commonlyused material, molybdenum trioxide (MoO3) and phosphomolybdic acid(PMA). The aim was to investigate how the different materials energy bandstructure would be affected upon exposure to sunlight, air and annealing, byobserving the work function under different conditions.

HEAT-grenades are wing-stabilized grenades using shaped charge technology. Theshaped charge is a method, producing a jet-beam, with the use of a copper linerin which the aim is to focus the detonation energy to be able to penetrate armourand structures. This jet-beam is only eective under a rotational frequency of 15Hz, any frequency above this and the produced jet-beam loses its eciency and willnot be able to penetrate its target. One approach to minimize the inner body'srotation is by using bearings. By the use of ball bearings the intention is to with-hold transferring the angular momentum from the outer rotating body to the innercylinder body. This thesis have been analysing how much rotation the warhead haveacquired from the outer rotation of the grenade divided in an acceleration phase anda ying phase. During the acceleration phase the rotation of the warhead is reach-ing a frequency of 0.35 Hz. Proposals are presented for improving and lowering therotational speeds for future studies.

We present a novel modelling approach for the morphology formation from ternary mixtures upon evaporation, which takes into consideration two different length scales of the interaction, and further allows for these length scales to be altered. A quantitative study of the interfacial energy hints towards the existence of a mesoscopic regime - further research is needed to verify the validity of this claim however. We also demonstrate that the solvent initially follows a Fickian law of diffusion, then deviates from this behaviour, presumably due to the phase separated regions produced by the two remaining (active) components. We also attempt to bridge the gap between this work and a hypothetical three-dimensional model by considering a top-down view of the system. Here, we observe domain growth dominated by Ostwald ripening, with some coalescence. The domain growth was further characterised using Fourier image analysis. / Vi presenterar en ny modellansats för morfologiformation från trekomponentsblandningar under avdunstning, som tar hänsyn till två olika längdskalor hos interaktionen, samt möjliggör förändring av dessa längdskalor. En kvantitativ studie av energin vid domängränserna tyder på att det finns en mesoskopisk regim - ytterligare forskning är dock nödvändig för att verifiera giltigheten av detta påstående. Vi visar också att lösningsmedlet ursprungligen följer en Fickiansk diffusionslag, för att senare avvika från detta beteende, förmodligen på grund av de tydliga domänerna som produceras av de två återstående (aktiva) komponenterna. Vi försöker också minska klyftan mellan det här arbetet och en hypotetisk tredimensionell modell genom att behandla systemet uppifrån. Här observerar vi domäntillväxt dominerad av 'Ostwald ripening', med viss koalescens. Domäntillväxten karakteriserades vidare med hjälp av Fourier-bildanalys.

Water pollution is one of many environmental problems that currently exists and inadequate treatment of industrial wastewater is contributing to further pollution. SpinChem AB's Rotating Bed Reactor (RBR) technology offers the possibility of water treatment by carrying out reactions between a solution and a solid phase. To move further in the field of large scale water treatment, SpinChem AB developed a prototype of a mobile reactor, i.e. a raft, carrying the RBR technology. The prototype proved that a mobile reactor can greatly reduce the process time for larger water volumes compared to a stationary RBR. The aim of this thesis is to develop the next version of the mobile reactor, with increased operational stability and autonomous driving (autopilot) as main goals. This work covers all parts in the development of the new mobile reactor which involves design, simulation, construction, electronics, software implementations and testing. The presented mobile reactor is a twin hull surface vehicle with the possibility of using two RBRs for water treatment. The steering is based on differential motor thrust and the autonomous driving was achieved using sensor data from a GPS, magnetometer and accelerometer, together with a proportional-integral-derivative (PID) type control system. The autopilot was put to the test on two different travel routes with a P and PI controller. The mobile reactor successfully followed the given routes, thus verifying that the developed mobile reactor can be used for future autonomous large scale water treatment.