Ocean Islands Basalts provide important windows into the compositional variations of the Earth's mantle, which in tum constrains models for mantle convection and evolution. The Canary Islands show contrasting styles of eruption and evolution of magmas in an ocean island setting. U-Th-Ra disequilibrium have been used to constrain rates and timescales of melt generation and differentiation beneath ocean islands, and to estimate the buoyancy flux, potential mantle temperature and the depth and degree of melting. The Canary Islands provide a rare opportunity to observe U-Th-Ra disequilibrium, because they are underlain by a region of low buoyancy flux, and were expected to show significant disequilibrium. Tenerife is underlain by numerous magma chambers, in which magmas have time to differentiate from basanites to phonolites, erupting to form large strato-volcano complexes. The fissure and small vent eruptions of unusually primitive basanites and alkali basalts from Lanzarote show little evidence of magma chambers, unless of substantial size and longevity at depth. The U-Th results indicate that lavas underwent rapid transport from the melt region. The historic and recent pre-historic eruptions (1824, 1730-36, Corona) from Lanzarote have some of the most primitive compositions found on oceanic islands with low SiO² contents (< 51 %), Mg numbers of 67-74 and high Cr and Ni contents. The rocks are restricted in Sr, Nd and Pb isotopes, being displaced from MORB towards the HIMU om field. The major and trace elements have been modelled by mixing a deep smaller degree (1 %) melt and a shallower larger degree (4%) melt. Negative K anomalies were observed in the small degree melts indicating that melt generation may have continued at a shallow level, perhaps to within the lithospheric mantle with melting in the presence of residual phlogopite. The Lanzarote source was modelled as a mixture of HIMU and EMIl asthenospheric mantle, with a small contribution from a shallow, lithospheric source. Thermal erosion of the lithospheric mantle is required for melting at depths (58 and 73 km) modelled from the major and trace elements. The Lanzarote lavas exhibit significant (²³⁰Th/²³⁸U) disequilibrium with ²³⁰Th excesses of 6 - 81 %. This was modelled by dynamic melting giving a calculated melt rate of 0.125 x 10^-3 kg.m^-1.yr^-1, a timescale of melt generation (matrix transfer time) of 270 ka for the 1 % melt and 1,100 ka for the 4 % melt. A consistent upwelling rate of I cm.yr^-1 and an assumption that the melting process has remained consistent over tens of km at depth. The Teide-Pico Viejo complex lavas have undergone fractionation and mixing to form compositions from basanite to phonolite. Crystallising phases differ in the Pico Viejo series, where amphibole is dominant in the more evolved lavas, and Pico Teide series, where olivine in the major control. The more evolved lavas require assimilation and fractional crystallisation to explain the range in ⁸⁷Sr/⁸⁶Sr. (²³⁰Th/²³⁸U) ranges from 1.004-1.39 and gives information regarding the timescales of differentiation within the magma chambers, not least because the youngest mafic rocks have the highest (²³⁰Th/²³⁸U) and the most evolved phonolites have the lowest. The timescale of differentiation from basanite to phonolite is of the order of 150,000 years, which links to the periodicity of the eruption cycles on the island. A Ra-Th 'pseudo' whole rock isochron gave an age of fractionation for the Montafia Blanca eruption of 2.3 ka ± 80, which is a maximum of 300 years prior to eruption, indicating that fractionation of plagioclase as a possible trigger of an eruption.

<div>Detecting hidden/smuggled special nuclear materials (SNM) is one of the unsolved problems in the safeguards industry. The biggest challenge is to quantify and track SNM and prevent the use of these materials for illicit purposes. The goal is to detect smallest quantity of SNM in large cargo containers, at the ports of entry, in the shortest amount of measurement time. Currently passive detection techniques, which is based on long-lived isotopes, are used to detect hidden SNM. This technique is not very reliable, as appropriate shielding of the SNM can reduce detection signals from these long-lived isotopes. Accelerator based active interrogation methods are proposed to solve the SNM problem. Besides SNM, another challenge in the nuclear industry is to meet the demand and supply of medical radioisotopes, particularly Tc-99m (half-life 6 hours). Mo-99, which decays to Tc-99m, is one of the fission products found in nuclear reactors. Because of short half-life of 66 hours, Mo-99 cannot be stockpiled. The shutdown of various research reactors globally disrupted the supply of Mo-99. Because of the financial and regulatory burden on the nuclear reactors, accelerator-based systems can be used to produce Mo-99.</div><div><br></div><div>With the aim to solve these two major challenges, a preliminary study is done to understand the neutrons behavior on milliseconds (or shorter) time steps in an accelerator driven subcritical system. A pulsed external neutron source, i.e. Deuterium-Deuterium (DD) generator, drives the assembly. Using first principles, the transient equations are derived and the neutron population at different time stamps is calculated. The Li-6 detector’s response to the neutron population is predicted. Experiments are performed to compare the predicted behavior with the observed behavior. The model is extended further to investigate the case of no uranium fuel inside the system. Transient measurements, in the absence of the uranium fuel, are made and the neutron die-away time is determined. This die-away time is compared with the predicted time.</div>

The climatology of the seasonal cycle of water mass variation and transformation in Bass Strait, south-eastern Australia, is studied using a high resolution three-dimensional sigma-coordinate hydrodynamic model coupled with data from observations and previous studies. Model forcing consists of the principal tidal constituents from the Australian National Tidal Centre and long-term monthly mean atmospheric forcing fields from NCEP reanalysis. The initial density field is established using temperature and salinity means and annual and semi-annual harmonics from the CARS2000 hydrographic atlas. This is also used to prescribe incoming water mass properties at model open-sea boundaries with seasonal variation. Far-field forcing is included with open-sea boundary parameterisation of residual sea-level representing both the South Australian Current and the East Australian Current. Lagrangian and Eulerian tracer methods are used to derive transport timescales, such as age, residence times and flushing times. These are used to examine and summarise model predictions and as a diagnostic tool in sensitivity studies. Currents, sea-level and water mass properties in the model compare favourably with previous studies and observations, despite limitations in the model and in the data used for comparison. The seasonal cycle, in model results, is characterised by formation of a shallow (< 20 m) saltier surface-layer in late spring to summer and subsequent downward mixing and erosion of the salinity field in autumn to winter with water mass from the west. This leaves behind water mass with positive age and salinity anomalies in areas of low flushing. In late winter-early spring most parts of this water mass leave the Strait interior. These areas are thought to be related to the source water of the Bass Strait Cascade. The residual circulation in all model experiments is shown to be related to seasonal-mean sea-level anomalies, arising from both barotropic and baroclinic adjustment, both in and surrounding the Strait.

Throughout Europe, the introduction of Solvency II is forcing companies in the life assurance and pensions provision markets to change how they estimate their liabilities. Historically, each solvency assessment required that the estimation of liabilities was performed once, using actuaries' views of economic and demographic trends. Solvency II requires that each assessment of solvency implies a 1-in-200 chance of not being able to meet the liabilities. The underlying stochastic nature of these requirements has introduced significant challenges if the required calculations are to be performed correctly, without resorting to excessive approximations, within practical timescales. Currently, practitioners within UK pension provision companies consider the calculations required to meet new regulations to be outside the realms of anything which is achievable. This project brings the calculations within reach: this thesis shows that it is possible to perform the required calculations in manageable time scales, using entirely reasonable quantities of hardware. This is achieved through the use of several techniques: firstly, a new algorithm has been developed which reduces the computational complexity of the reserving algorithm from O(T2) to O(T) for T projection steps, and is sufficiently general to be applicable to a wide range of non unit-linked policies; secondly, efficient ab-initio code, which may be tuned to optimise its performance on many current architectures, has been written; thirdly, approximations which do not change the result by a significant amount have been introduced; and, finally, high performance computers have been used to run the code. This project demonstrates that the calculations can be completed in under three minutes when using 12,000 cores of a supercomputer, or in under eight hours when using 80 cores of a moderately sized cluster.

No description available.

CoordenaÃÃo de AperfeÃoamento de Pessoal de NÃvel Superior / This study aims to develop a planning system on multiple spatial and temporal scales, and apply it to the Brazilian electric sector and Cearà State, Jaguaribe Metropolitan System. For realization of this proposal, we have been considered some temporal scales: short-term (up to 1 month), short term (up to one year) and medium to long term (1-10 years and 10-30 years, respectively). To obtain estimates of the flow of short-term rainfall forecasts from atmospheric models for later entry in the hydrological rainfall-runoff model are used. To short term scale were considered stochastic and statistical models, as the Periodic Autoregressive type (PAR), Periodic Autoregressive with exogenous variables (PARx) and K-nearest neighbor models, and the use of global atmospheric models as input to hydrological rainfall-runoff model Soil Moisture Accounting Procedure (SMAP). For the range of the medium term were considered auto regressive models (AR) and Fourier and wavelets. We used data from the Coupled Model Intercomparison Project Phase 5 (CMIP5) as input in hydrological rainfall-runoff model for long-term scale. For the weather forecast, as the rain threshold adopted in the construction of the contingency table increases, the quality of the forecasts decreases, except for the adjustment index. Thus, the system of numerical prediction proves efficient in detecting the occurrence of rainfall of less intensity, with most satisfactory results in the North and Northeast regions of Brazil. On seasonal scale the models feature up better than the climatology. Likewise, in the range of medium-term models based on Fourier series and wavelets have better likelihood than the weather. In multi-scale, there are differences in the future shown by the projections of the CMIP5 models that were analyzed for RCP8.5 and RCP4.5 the XXI century scenarios, but in the North sector of the National Interconnected System (SIN), most models indicate negative trend, diverging only in magnitude. / O presente trabalho visa elaborar um sistema de planejamento em mÃltiplas escalas temporais e espaciais e aplicÃ-lo ao setor elÃtrico brasileiro e ao sistema Jaguaribe-Metropolitano do Estado do CearÃ. Para realizaÃÃo desta proposta, foram consideradas algumas escalas temporais: curtÃssimo prazo (atà um mÃs), curto prazo (atà um ano) e mÃdio e longo prazo (1 a 10 anos e atà 30 anos, respectivamente). Para obtenÃÃo das previsÃes de vazÃes de curtÃssimo prazo sÃo utilizadas as previsÃes de precipitaÃÃo a partir de modelos atmosfÃricos, para posterior entrada no modelo hidrolÃgico chuva-vazÃo. Para escala de curto prazo foram considerados modelos estocÃsticos e estatÃsticos, como do tipo PeriÃdico Autorregressivo (PAR), PeriÃdico Autorregressivo com variÃveis exÃgenas (PARx) e K-vizinhos, e o uso de modelos atmosfÃricos globais como entrada do modelo hidrolÃgico chuva-vazÃo Soil Moisture Accounting Procedure (SMAP). Na escala de mÃdio prazo foram considerados modelos autorregressivos (AR) e as transformadas de Fourier e ondeletas. Para escala de longo prazo foram utilizados dados provenientes do Coupled Model Intercomparison Project Phase 5 (CMIP5) como dados de entrada no modelo hidrolÃgico chuva-vazÃo. Quanto à previsÃo de tempo, à medida que o limiar de chuva adotado na construÃÃo da tabela de contingÃncia aumenta, a qualidade das previsÃes diminui, exceto para o Ãndice acerto. Dessa forma, o sistema de previsÃo numÃrica mostra-se eficiente em detectar a ocorrÃncia de chuvas de menor intensidade, apresentando resultados mais satisfatÃrios nas regiÃes Norte e Nordeste do Brasil. Na escala sazonal, os modelos apresentam-se melhor que a climatologia. Da mesma forma, na escala de mÃdio prazo, os modelos baseados na sÃrie de Fourier e ondeletas apresentam melhor verossimilhanÃa do que a climatologia. Na escala plurianual, hà divergÃncias quanto ao futuro mostrado pelas projeÃÃes dos modelos do CMIP5 que foram analisados para os cenÃrios RCP8.5 e RCP4.5 do sÃculo XXI, porÃm no setor Norte do Sistema Interligado Nacional (SIN), a maioria dos modelos sinaliza tendÃncia negativa, divergindo apenas em magnitude.

To rigorously study hot stars, we need to determine their properties as accurately as possible. This thesis focuses on improving the accuracy of parameters of two hot stars and contributes to the collection of stars with more known parameters. While photometric and spectroscopic data sets on hot stars δ Ori A and ω CMa are plentiful, the former is a triple star that suffers from having a faint spectrum of the secondary, which complicates its analysis, and the latter is a Be star, the origin, formation, and long-term variability of whose gaseous envelopes (veils) remain unexplained. Using mathematical techniques (Fourier transforms) and modelling software PHOEBE 1, properties of δ Ori A are determined, and conjecture on the presence of a circumstellar envelope in δ Ori A might be true by considering the shape changes of the Hα line. A conjecture that period changes of ω CMa correlate to the mass of the circumstellar envelopes seems to be proved true by considering variations of radial velocities, V/R ratio, and determining profile line asymmetry. 1

No description available.

No description available.

Cette thèse présente une étude de la dynamique des plages sableuses ouvertes dominées par la houle, au travers d’une base de données originale, couvrant une période de 29 mois, et composée de 150 levés DGPS couvrant 750m de linéaire côtier, donnant accès à la morphodynamique du site de Biscarrosse à différentes échelles de temps. Dans un premier temps, l’analyse du jeu de données à l’échelle des événements (tempêtes et successions de tempêtes appelées clusters) nous a permis de montrer que la réponse des plages sableuses aux clusters ne résulte pas de la somme des impacts induits par chaque tempête d’un cluster. Ainsi, l’effet cumulé des clusters, rapporté sur d'autres sites dans la littérature, n’est ici pas vérifié. L'impact de l’enchainement des tempêtes a également été étudié et il en résulte que lors d’un cluster, un changement des conditions hydrodynamique, à savoir, une augmentation des hauteurs de vagues et/ou du niveau d’eau, est nécessaire pour que la tempête suivante ait un impact érosif significatif sur le système. Dans un second temps, nous avons étudié la dynamique saisonnière du système plage/dune, que ce soit la saison hivernale ou estivale, dans le but de mettre en relief les principaux processus impliqués à cette échelle. Nos travaux montrent que la réponse hivernale de la plage ne dépend pas uniquement des conditions énergétiques et du profil pré-hivernal de la plage, mais également du séquençage des événements, comme lors d'un cluster. Mes travaux confirment également la nécessité de prendre en compte de nombreux paramètres dans l’étude de la dynamique hivernale des littoraux sableux : les conditions hydrodynamiques, le séquençage des évènements érosifs mais également reconstructifs, en particulier le ré-engraissement post-évènement, les transports sédimentaires cross-shore et longshore, ainsi que la position de la barre interne et des courants d’arrachements. La saison estivale est, quant-à-elle, marquée par la reconstruction de berme. Elle semble être liée à la fois aux conditions hydrodynamiques et aux caractéristiques des barres sableuses. L’étude de deux étés et deux hivers successifs a ainsi permis d’identifier les interactions entre les saisons et l’impact de la saison hivernale sur l’estivale, et l’influence de la dynamique événementielle sur la dynamique saisonnière. Elle a aussi permis de mettre en relief l’impact de l’urbanisme et des stratégies d’aménagement dans la réponse du système, à différentes échelles de temps. / This thesis presents a study of an open sandy beach wave-dominated, based on an original dataset, covering 29 months and composed by 150 DGPS surveys recorded along 750m of sandy shore, giving an access to the morphodynamic of Biscarrosse beach at different timescales. In a first time, event scale analysis showed that sandy beach response to clusters is not the result of the sum of the impact generated by each storm of a cluster on the system. Thus, the cumulated effect of clusters, described in the literature is not verified here. The storm sequencing has also been studied: during a cluster, changes in hydrodynamics conditions (rising of the water level and/or wave height) are necessary to provoke a significant erosion of the system by the second storm. In a second time, we studied the seasonal scale dynamic of the beach/dune system (winter and summer seasons) with the purpose to highlight dominant processes involved at this timescale. Beach response to winter seasons not only depends on hydrodynamic conditions and previous beach profile, but also on erosion/recovery event sequencing, post-storm recovery, cross-shore and longshore sediment transport, the barline characteristics and RIP current positions. Summer seasons are here defined by the berm reconstruction. Recovery periods are both linked to hydrodynamic conditions and barline characteristics (e.g. position and shape).The study of successive winters and summers allowed us to identify interactions between seasons, and the influence of short-scale dynamics on the seasonal one. It also emphasizes the impact of urbanism and coastal management strategies on the system’s response, at different timescales.