The impetus of unsustainable consumption coupled with major environmental concerns has renewed our society's investment in new energy production methods. Solar energy is the poster child of clean, renewable energy. Its favorable environmental attributes have greatly enhanced demand resulting in a spur of development and innovation. Photovoltaics, which convert light directly into usable electrical energy, have the potential to transform future energy production. The benefit of direct conversion is nearly maintenance free operation enabling deployment directly within urban centers. The greatest challenge for photovoltaics is competing economically with current energy production methods. Lowering the cost of photovoltaics, specifically through increasing the conversion efficiency of the active absorbing layer, may enable the invisible hand to bypass bureaucracy. To accomplish the ultimate goal of increased efficiency and lowered cost, it is essential to develop new material systems that provide enhanced output or lowered cost with respect to current technologies. However, new materials require new understanding of the physical principles governing device operation. It is my hope that elucidating the dynamics and charge transfer mechanisms in novel photovoltaic material systems will lead to enhanced design principles and improved material selection. Presented is the investigation of electron dynamics in two materials systems that show great promise as active absorbers for photovoltaic applications: inorganic semiconductor quantum dots and organic semiconductors. Common to both materials is the strong Coulomb interaction due to quantum confinement in the former and the low dielectric constant in the latter. The perceived enhancement in Coulomb interaction in quantum dots is believed to result in efficient multiexciton generation (MEG), while discretization of electronic states is proposed to slow hot carrier cooling. Time-resolved two-photon photoemission (TR2PPE) is utilized to directly map out the hot electron cooling and multiplication dynamics in PbSe quantum dots. Hot electron cooling is found to proceed on ultrafast time scales (< 2ps) and carrier multiplication proceeds through an inefficient bulk-like interband scattering. In organic semiconductors, the strong Coulomb interaction leads to bound electron-hole pairs called excitons. TR2PPE is used to monitor the separation of excitons at the model CuPc/C₆₀ interface. Exciton dissociation is determined to proceed through "hot" charge transfer states that set a fundamental time limit on charge separation. TR2PPE is used to investigate charge and energy transfer from organic semiconductors undergoing singlet fission, an analog of multiple exciton generation. The dynamic competition between one and two-electron transfer is determined for the tetracene/C₆₀ and tetracene/CuPc interfaces. These findings allow for the formulation of design principles for the successful harvesting of hot or multiple carriers for solar energy conversion. / text

Eukaryotic centromeres are the region upon which kinetochores assemble, directing attachment of spindle microtubules and faithful segregation of chromosomes during mitosis and meiosis. Except for a transient disruption in mitosis when chromosomes are segregated, centromeres of fission yeast Schizosaccharomyces pombe remain closely associated with the nuclear periphery. Similar to multicellular eukaryotic centromeres, they also maintain unique chromatin architecture, with a central core defined by the presence of the conserved centromeric histone H3 variant CENP-A, designated Cnp1 in S. pombe, that is flanked by histone H3 containing heterochromatin. While much progress has been made in understanding chromatin-associated factors important for proper centromere function, many questions remain. In order to gain a better understanding of the factors involved in centromeric chromatin structure, we affinity purified and defined by mass spectrometry interactions among select proteins that had been implicated in proper Cnp1 localization and centromere function. These biochemical purifications revealed several proteins that may be involved in Cnp1 localization. Purification and analyses of Cnp1 also led us to the identification of the Mlp1/Tpr nucleoporin homolog Nup211. We have found that Nup211 interacts with components of the inner nuclear basket of the nuclear pore, and co-purifies with centromeric chromatin proteins. Cells lacking Nup211 have substantial chromosome segregation defects, as observed by synthetic growth assay, flow cytometric analysis, and fluorescent microscopy. A series of immunoprecipitation experiments have revealed that Nup211 associates with centromeric DNA, and that, surprisingly, cells lacking Nup211 have increased histone H3 lysine 9 methylation, a marker of heterochromatin, and a reduction in Cnp1 levels at the central core. Moreover, cells lacking Nup211 have decreased transcription at centromeric loci, disruption of the stereotypical nucleosome structure found at the central core of S. pombe, and show striking changes in the distribution of heterochromatic foci in the nucleus. By demonstrating that Nup211 is essential for the maintenance of normal central core chromatin state, these studies have shed light on a novel role for Nup211 in proper centromere structure and function in S. pombe, and suggest that Nup211 may play a role in preventing the invasion of flanking pericentric heterochromatin into the central core of centromeres.

The Taimyr Peninsula is a key element in the circum-Arctic region and represents thenorthern margin of the Siberian Craton. The Taimyr Peninsula is a late Paleozoic fold andthrust belt and preserves late Paleozoic through Mesozoic siliciclastic sedimentarysuccessions and providing an ideal location to investigate the Paleozoic to Mesozoictectonic evolution associated with the Uralian orogeny, the Siberian Trap magmatism andopening of Amerasia Basin within a circum-Arctic framework. Multiple methods areadopted, including petrography, heavy mineral analysis and detrital zircon U-Pbgeochronology for provenance investigation, apatite fission track dating for revealingthermal history and balanced cross section for understanding the deformation style ofTaimyr.The results of this thesis indicate that the Late Carboniferous to Permian sediments ofsouthern Taimyr were deposited in a pro-foreland basin of the Uralian orogen during theUralian orogeny. In the Triassic, the siliciclastic deposits still show a strong Uraliansignature but the initiation of Siberian Trap-related input begins to be significant. Erosionof the Uralian orogen has reached a deep metamorphic level. By Late Jurassic andCretaceous time, the deposition setting of southern Taimyr is an intracratonic basin.Erosion and input from Uralian sources waned while greater input from SiberianTrap-related rocks of the Taimyr region dominated. The Taimyr Peninsula underwent atleast three cooling and uplifting episodes: 280 Ma, 250 Ma and 220 Ma, corresponding tothe Uralian orogeny, the Siberian Traps and the late Triassic transpression. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 2: In press. Paper 3: Manuscript. Paper 4: Manuscript.</p>

Since its discovery, the phenomenon of nuclear fission is the object of extensive theoretical and experimental studies. However, we are still far from a complete understanding of the fission process. Nuclear theory can satisfactorily explain the process of neutron-induced fission at thermal neutron energies, but it meets problems at high neutron energies. However, new applications are nowadays developed involving neutron-induced fission in this energy domain. An example of such an application is accelerator-driven systems (ADS) which are dedicated to transmutation of highly radioactive nuclear waste. Conceptual studies of ADS require new nuclear data on neutron-induced reactions within a wide incident energy range. Along with structural, spallation target and other materials, data on neutron-induced fission are especially required for two nuclides, 232Th and 238U. At present, however, there are no published neutron-induced fission yield data for either 232Th or 238U at energies above 20 MeV. In this thesis, I present measurements of fission fragment mass yields at neutron energies from 10 to 60 MeV for 232Th and 238U. The experiment was done at the Louvain-la-Neuve quasi-monoenergetic neutron beam facility. A multi-section Frisch-gridded ionization chamber was used as the fission fragment detector. The fission fragment mass yields were measured at peak neutron energies of 33, 45, and 60 MeV. In addition, data for the neutron-energy intervals 9-11, 16-18, and 24-26 MeV were also extracted from the low-energy tail. The measurement results show that the symmetric fission component increases with incident neutron energy for both uranium and thorium, but it is more enhanced for thorium. The uranium results were compared to the only existing set of experimental data for neutron energies above 20 MeV. Reasonable agreement was found. However, our data show a lower symmetric fission component. For thorium, the present data are the first above 20 MeV. Model calculations with the TALYS code have also been done. This code is based on the multi-modal random neck-rupture model extended for higher excitation energies. We included a phenomenological model into the code and achieved a good description of our experimental results. / Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 723

Uranium (U) exhibits a high temperature body-centered cubic (bcc) allotrope that is often stabilized by alloying with transition metals such as Zr, Mo, and Nb for technological applications. One such application involves U–Zr as nuclear fuel, where radiation damage and diffusion (processes heavily dependent on point defects) are of vital importance. Metallic nuclear fuels swell under fission conditions, creating fission product gases such as helium, xenon and krypton. Several systems of U are examined within a density functional theory framework utilizing projector augmented wave pseudopotentials. The bulk modulus, the lattice constant, and the Birch–Murnaghan equation of state for the defect free bcc uranium allotrope are calculated. Defect parameters calculated include energies of formation of vacancies in the α and γ allotropes, as well as self-interstitials, Zr, He, Xe and Kr interstitial and substitutional defects. This work is utilized in the construction of modified Embedded-Atom Method interatomic potentials for the bcc phase of uranium as well as the binary systems of U-Xe, U-Kr and U-He. Using this potential, equilibrium volume and elastic constants are calculated at 0 K and found to be in close agreement with previous first principles calculations. Further, the melting point, heat capacity, enthalpy of fusion, thermal expansion and volume change upon melting are calculated and found to be in reasonable agreement with experiment. Calculations of dilute fission gas defects show reasonable agreement with first principles calculations. Finally, void and xenon bubble energetics are analyzed as a function of temperature.

Dsk1 is the Schizosaccharomyces pombe functional homolog of human SRPK1, an SR protein kinase that regulates localization and function of SR protein splicing factors involved in transcription, alternative splicing, and mRNA export. It has been shown that a Dsk1 deletion strain of S. pombe is sensitive to exposure to butylated hydroxyanisole (BHA), a phenol derivative commonly used as a food preservative. Little is known about how BHA interacts with cells on a functional level, although it has been shown to be cytotoxic and tumorigenic. The aims of this thesis are to study the effect of BHA on eukaryotic cells and the possible involvement of Dsk1 protein kinase in the cellular response network to BHA through the use of fluorescence microscopy. The results showed that in BHA-treated cells, Dsk1 exhibits reduced nuclear localization and increased incidence of cytoplasmic clusters as well as a series of changes in cellular morphology. These observations imply that the function of Dsk1 is altered in response to BHA, consistent with genomic data collected by the Tang Lab. Thus, this study provides a basis for a series of future studies that will reveal in more detail how BHA affects fission yeast cells, and potentially gene or protein functional homologs in human cells.

The Paparoa Metamorphic Core Complex developed in the Mid-Cretaceous due to continental extension conditioning the crust for the eventual breakup of the Gondwana Pacific Margin, which separated Australia and New Zealand. It has two detachment systems: the top-NE-displacing Ohika Detachment at the northern end of the complex and the top-SW-displacing Pike Detachment at the southern end of the complex. The structure is rather unusual for core complexes worldwide, which are commonly characterised by a single detachment system. Few suggestions for the kinematics of the core complex development have been made so far. In this study structural-, micrographic- and fission track analyses were applied to investigate the bivergent character and to constrain the kinematics of the core complex. The new results combined with reinterpretations of previous workers’ observations reveal a detailed sequence of the core complex exhumation and the subsequent development. Knowledge about the influence and the timing of the two respective detachments is critical for understanding the structural evolution of the core complex. The syntectonic Buckland Granite plays a key role in the determination of the importance of the two detachment systems. Structural evidence shows that the Pike Detachment is responsible for most of the exhumation, while the Ohika Detachment is a mere complexity. In contrast to earlier opinions the southwestern normal fault system predates the northeastern one. The Buckland Pluton records the ceasing pervasive influence of the Pike Detachment, while activity on the Ohika Detachment had effect on the surface about ~8 Ma later. Most fission track ages are not related to the core complex stage, but reflect the younger late Cretaceous history. They show post core complex burial and renewed exhumation in two phases, which are regionally linked to the development of the adjacent Paparoa Basin and the Paparoa Coal Measures to the southwest and to the inception of seafloor spreading in the Tasman Sea in a larger context.

This dissertation describes two independent studies related to charged aerosols. The first study examines the role of electrical conductivity on the amounts of charge and mass emitted during the break-up of charged droplets via Coulombic fission. The second study examines the hygroscopic behavior of mixed particles. The results from both studies are presented here in detail along with an in-depth discussion of pertinent literature and applications in modern technologies. Charged droplets break-up via a process termed Coulombic fission when their charge density reaches a certain level during which they emit a portion of their charge and mass in the form of progeny microdroplets. Although Rayleigh theory can be used to predict the charge level at which break-ups occur, no equivocal theory exists to predict the amounts of charge or mass emitted or the characteristics of the progenies. Previous investigations have indicated that the electrical conductivity of a charged droplet may determine how much charge and mass are emitted during its break-up via Coulombic fission. To further examine this supposition, charged droplets having known electrical conductivities were observed through multiple break-ups while individually levitated in an electrodynamic balance. The amounts of charge and mass emitted during break-ups were determined using a light scattering technique and changes in the DC null point levitation potentials of the charged droplets. Here, electrical conductivity was found to increase and decrease the amounts of charge and mass emitted, respectively, while having no effect on the charge level at which break-ups occurred. The findings of this investigation have significant bearing in nanoparticle generation and electrospray applications. The hygroscopic behavior of atmospherically relevant inorganic salts is essential to the chemical and radiative processes that occur in Earth’s atmosphere. Furthermore, studies have shown that an immense variety of chemical species exist in the atmosphere which inherently mix to form complex heterogeneous particles with differing morphologies. However, how such materials and particle morphologies affect the hygroscopic behavior of atmospherically relevant inorganic salts remains mostly unknown. Therefore, the effects of water insoluble materials, such as black carbon, on the hygroscopic behavior of inorganic salts were examined. Here, water insoluble solids were found to increase the crystallization relative humidities of atmospherically relevant inorganic salts when internally mixed. Water insoluble liquids however, were found to have no effect on the hygroscopic behavior of atmospherically relevant inorganic salts. The findings of this investigation have significant bearing in atmospheric modeling.

En France, l'énergie électrique est majoritairement produite (78 %) grâce au fonctionnement de 58 REP (Réacteurs à Eau Pressurisée). Lors du fonctionnement de ces réacteurs, de nombreux produits de fission (PF) sont générés dans le combustible qui est de l'UO2 enrichi à environ 4% en 235U. Parmi eux, il est important de connaître le comportement du xénon et du krypton, produits de fission gazeux qui sont abondamment produits (près de 15 % des produits de fission stables). De plus, de par leur nature chimique, ces deux gaz ont une très faible solubilité dans le combustible et vont donc avoir tendance à se regrouper sous forme de bulles (pour minimiser la tension de surface) pouvant ainsi engendrer un gonflement de la pastille d'UO2. Le gaz formé peut aussi être libéré hors de la pastille, entrainer une augmentation substantielle de la pression dans la gaine de combustible et ainsi limiter l'utilisation du combustible. Cependant, les mécanismes de migration, traditionnellement étudiés de manière indirecte en mesurant la quantité de gaz relâché après irradiation, ne sont pas encore totalement compris. Il est fréquemment supposé que la diffusion atomique est le seul mécanisme susceptible d'entrainer une migration du xénon. L'objectif de cette thèse est de mettre en évidence de manière directe les différents mécanismes gouvernant le comportement thermique et sous irradiation du xénon dans UO2. Pour cela, nous avons utilisé l'implantation ionique qui nous permet d'introduire du xénon dans des échantillons de dioxyde d'uranium. Cette implantation engendre un profil de concentration quasi-gaussien de xénon (variation de la concentration en fonction de la profondeur) dans les 300 premiers nanomètres de l'échantillon. Suite à différents traitements qui sont d'une part des recuits entre 1400°C et 1600°C afin d'étudier l'impact de la température et d'autre part des irradiations avec des ions afin de simuler l'impact des produits de fission dans le combustible, les profils de concentration ont été mesurés par microsonde ionique (SIMS). Bien que la faisabilité de la mesure du xénon ait été démontrée dans différents articles, aucun profil de concentration n'avait jusqu'à présent été présenté dans la littérature. Dans le dioxyde d'uranium, un traitement classique des données SIMS n'est pas adapté. Un nouveau logiciel de traitements des données a donc été développé au cours de cette thèse qui permet l'obtention de profils reproductibles. Aucune diffusion du xénon n'a pu être observée lors des recuits à 1400°C et à 1600°C indiquant une absence de mobilité du xénon dans ces conditions. Des études complémentaires de caractérisation de défauts de type lacunaire et de bulles de xénon ont été effectuées par spectroscopie d'annihilation de positrons (PAS) et par microscopie électronique par transmission (MET). Elles montrent des modifications importantes de la microstructure d'UO2 induites par la formation de bulles à 1400°C et 1600°C pouvant expliquer l'absence de diffusion observée. Les études sous irradiation à fort (dE/dx) électronique ont montré une diffusion et un transport du xénon dépendants des températures d'irradiation. Pour les irradiations à 600 et 1000°C, les caractérisations de la microstructure, mettent en évidence la formation de bulles de xénon alignées avec la direction du faisceau d'ions incidents. A contrario, les chocs balistiques (irradiation avec des ions Argon de 800keV) n'ont causé aucune modification significative des profils quelle que soit la température d'irradiation.

This document gives an overview of the proposed MSc study. The main goal of the study is to model the cases listed in the code benchmark study of the International Atomic Energy Agency CRP–6 fuel performance study (Verfondern & Lee, 2005). The platform that will be employed is the GETTER code (Keshaw & van der Merwe, 2006). GETTER was used at PBMR for the release calculations of metallic and some non–metallic long–lived fission products. GETTER calculates the transport of fission products from their point of fission to release from the fuel surface taking into account gas precursors and activation products. Results show that for certain experiments the codes correspond very well with the experimental data whilst in others there are orders of magnitude differences. It can be seen that very similar behaviour is observed in all codes. Improvements are needed in updating the strontium diffusion coefficient and in understanding, on a deeper level, the transport of silver in TRISO particles and how it deviates from simple diffusion models. / Thesis (M.Sc. Engineering Sciences (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2012.