This is the Master’s Thesis of Eirik Timo Bøe Vilpponen, and was writtenat the Department of Physics at the Norwegian University of Science andTechnology (NTNU). The thesis is twofold, the first part being the comple-tion of a project undertaken during the fall of 2010. The project concernedthe setup of a solar cell current-voltage characterization lab [4] at the sameDept. of Physics.The second part is an analysis of the current-voltage characteristics ofNTNU-made quantum-dot intermediate band solar cells. A strong focus isput on exploring the possibility of utilizing the Two-Diode Model as a meansof analysis. The two-diode model has been found to have a good potential forthis use, but that it requires a specially made curve fitting computer programto fulfill this potential.

In this thesis the Minimum Ignition Energy, in a hydrogen-air system, is studied by Direct Numerical Simulations (DNS) in a program called the Pencil Code. The heat source used to achieve ignition is modeled by a Gaussian temperature distribution. Three different geometries of the heat source are looked upon, one with spherical geometry in three dimensions, one with cylindrical geometry in two dimensions and the last in one dimension. The results show that the dimensionality of the heat source has a strong impact on ignition.In addition, a new simpler zero dimensional simulation method is proposed with the goal of replicating the results from the Pencil Code. This method needs less calculation power, and uses ignition delay time data together with the heat equation to simulate ignition. The model has proven itself useful since it reproduces the Pencil Code results very well.

The theory of laser-induced liquid-liquid interface deformation has been presented and used to derive a differential equation describing the shape of the deformation. The differential equation has been investigated and solved numerically, and the results have been compared to the experimental results of the Bordeaux group. A model describing the maximum depth of the deformation based on the theory of a sphere in an electric field has also been investigated.The deformations from the numerical solutions of the differential equation are too wide compared to the experimental results. The shoulder-shape that has been observed in the experiments is not present in the numerical solutions. There is reason to believe that the differential equation may be too simple in order to describe the liquid-liquid interface deformation for nonlinear cases. There may be thermal effects that changes the liquid properties due to local temperature variations induced by the laser, causing the liquid parameters to change along the deformation.The model used to estimate the deformation depth does not give reasonable results, as it leads to a deformation that is more than 100 times larger than what is observed in the corresponding experiments. The assumptions made for this model may not be valid, and a discussion on what should be done in order to improve the model is included in this text.

This report is a study of how polarized light can improve our understandings of physical phenomena, such as local organization of anisometric nanoparticles dispersed in a liquid.The first part of the thesis considers the theoretical aspects of polarized light. The Maxwell's equations are considered together with the Stokes formalism and the Mueller matrix. The Mueller matrix is analyzed in depth by looking at different ways it can be decomposed into several matrices, each clearly representing the physical phenomena of depolarization, diattenuation and retardance. The physics behind the phenomena will then be shortly addressed.The second part of the thesis describes the Mueller Matrix Imaging (MMI) ellipsometer, developed in the Applied Optics Group at NTNU. The results of Mueller imaging of air will be presented and discussed in order to get more understanding of the ellipsometer.The third and main part of the thesis, focuses on applying the MMI ellipsometer in order to study complex phenomena in clay dispersion. By looking at the development of samples of aqueous clay dispersions, the creation of different phases will be recorded. Some of those phases have crystalline properties and a Mueller matrix imaging can reveal much about its structure. A decomposition of the Mueller matrix can tell even more about the properties of the phases.

Hyperbolic relaxation systems is an active field of research, with a largenumber of applications in physical modeling. Examples include modelsfor traffic flow, kinetic theory and fluid mechanics. This master’s thesis is a numerical and theoretical analysis of such systems, and consists of two main parts: The first is a new scheme for the stable numerical solution of hyperbolic relaxation systems using exponential integrators. First and second-order schemes of this type are derived and some desirable stability and accuracy properties are shown. The scheme is also used to solve a granular-gas model in order to demonstratethe practical use of the method. The second and largest part of this thesis is the analysis of the solutionsto 2 × 2 relaxation systems. In this work, the link between the the sub-characteristic condition and the stability of the solution of the relaxationsystem is discussed. In this context, the sub-characteristic condition andthe dissipativity of the Chapman–Enskog approximation are shown to beequivalent in both 1-D and 2-D. Also, the dispersive wave dynamics of hyperbolic relaxation systems isanalyzed in detail. For 2 × 2 systems, the wave-speeds of the individualFourier-components of the solution are shown to fulfill a transitional sub-characteristic condition. Moreover, the transition is monotonic in thevariable ξ = kε, where ε is the relaxation time of the system and k is thewave-number. A basic 2 × 2 model is used both as an example-model in the analyticaldiscussions, and as a model for numerical tests in order to demonstratethe implications of the analytical results.

Silicone oil droplets containing synthetic smectite clay submerged in another immiscible organic oil have been studied by observing clay particle movement, oil circulation and drop deformation when an electric field is applied. Results show how electric field strength, electrohydrodynamics, dielectric and conductive properties determines the fluid flow, clay particle formation and drop deformation.

In this thesis we theoretically examine spin-polarized non-local transport in two junctions built up by materials with superconducting and magnetic properties. The first consists of a Zeeman-split superconductor placed between two normal metals. We find that such systems can generate a spin-polarized non-local current even when the injected current is unpolarized. The effect is however mostly geometric and take place also when the superconductor is switched with a normal metal. The second system is built up by two ferromagnetic wires coupled by a superconductor via spin-active interfaces. We investigate the circumstances which allow for an inverse spin-valve effect. For certain parameter ranges we find that a crossover between positive and negative magnetoresistance is possible as a function of temperature.

Motivation: Cartilage is a robust but flexible connective tissue found in most joints of the body. The collagen fibres present in the extracellular matrix of cartilage contribute to its tensile strength and stiffness. The purpose of this study is to develop and implement methods to determine the orientation and anisotropy of collagen fibres in 3-D images gen- erated with multi-photon microscopy. The motivation behind developing these techniques is to improve the foundation for further studies on understanding the characteristics of the cartilage matrix. This in turn would give a better foundation for developing artificial matrices and mechanical models, as well as improve diagnostics.Material and methods: The two methods developed in this study are based on analysing the frequency domain. One is an expansion of a previous developed method by Chaudhuri et al. [1]. This method is based on evaluating the average intensity at different directions in the frequency domain. The direction with the least average intensity is equivalent to the direction of the fibres. The other method is based on thresholding the frequency domain according to intensity followed by fitting an ellipsoid to the remaining data set. The direction of the collagen fibres is equivalent to the direction of the shortest axis of the ellipsoid. These methods are called the sector and ellipsoid method, respectively. To determine how robust these methods are a series of tests were developed. The focus of these tests was to determine if the methods are rotational invariant and if the results are influences by different preprocessing techniques. These preprocessing techniques are: median filtering, deconvolution and skeletonization of the original image containing the collagen fibres. It is also important to determine the sensitivity of the ellipsoid method according to the chosen threshold value. In addition data generated fibres and frequency domains were made to determine the accuracy of the methods.Results and conclusion: The sector method was not very robust. For most cases there is not one specific direction that has the least average intensity in the frequency domain. Instead there is a quite large minimum area. The ellipsoid method shows promising results. It managed to find the correct direction both for the data generated data sets, but also for the real images. It seems like no preprocessing nor frequency filtering, except for thresholding, is needed to still find the correct direction and its anisotropy. The only remark is that the automatically chosen threshold value was to low for one of the samples. This can probably be improved by making a slight change in the process for choosing a threshold value.

The effect of thermophoresis on the particle deposition on a cooled cylinderin non-isothermal laminar gas ow has been studied using Direct NumericalSimulations (DNS). Simulations where thermophoresis have been taken intoaccount for different Stokes numbers and particle-to-gas thermal conductivityratios, Λ, have been performed at Reynolds number Re = 380. In additionreference cases, simulations where thermophoresis have not been taken intoaccount, have been performed both for isothermal and non-isothermal owfor Re = 20 and Re = 380.The ratio between the front side particle impaction efficiency in the non-isothermal reference case and the isothermal reference case for the smallestStokes numbers considered was expected to be proportional to the ratio ofthe free stream temperature and the cylinder temperature, according to an-analytical considerations. The simulations for Re = 20 was in good agreementwith this relation, but for Re = 380 the front side particle impaction efficiency for the smallest particles was lower in the non-isothermal referencecase compared to the isothermal reference case. This is believed to havebeen caused by inaccuracies in the numerical method for the non-isothermalsimulation at Re = 380.Thermophoresis was not found to affect the particle impaction for thelargest Stokes numbers. For intermediate and small Stokes numbers the effect of thermophoresis depended on Λ. The particle impaction efficiency wassignificantly higher, both for the front side and the back side, in the ther-mophoretic simulations compared to the non-isothermal reference case forparticles with Λ = 1 and Λ = 100. The particle impaction efficiency forparticles with Λ = 1000 was lower, both for the front side and the back side,in the thermophoretic case compared to the non-isothermal reference case.

A numerical model for predicting icing on offshore structures and vessels has been developed and implemented. The model calculates the icing caused by freezing sea spray, and focuses on two distinct sources of spray - spray from droplets blowing off whitecaps on the sea surface, and spray from waves colliding with the vessel. The implementations of both wind-induced and wave-induced sea spray are based on existing theoretical models, and are combined with a thermodynamic model for the icing process. The model may be used to calculate icing on reference objects or structures on the vessel. In addition, algorithms have been developed so that the model can be applied to polygon-based vessel geometries, calculating the icing distribution over the entire vessel. The model has been applied to meteorological observations and hindcast data for locations in the Norwegian Sea and Barents Sea, in particular at the locations of the Norne field and the undeveloped Skrugard and Shtokman fields. The results indicate that the icing will be comparable at the locations of Skrugard and Shtokman, and that both the frequency and severity of icing events will be far greater for these two locations than for Norne. Although conditions at Shtokman are colder than at Skrugard, the higher winds and waves near Skrugard will increase the available sea spray in the model, thus making the number of severe icing events more similar for the two locations.