http://hdl.handle.net/1956/909 Search the Channel search http://bora.uib.no/simple-search http://hdl.handle.net/1956/2393 Title: On the Nordic Seas’ role in the Atlantic Meridional Overturning Circulation <br/> <br/>Authors: Iovino, Doroteaciro <br/> <br/>Abstract: In the present climate, the North Atlantic thermohaline circulation (THC) plays a fundamental role in the global transport of heat at high latitudes. The response of the North Atlantic Ocean-Nordic Seas THC to surface forcing and basin geometries in an idealized one-hemisphere basin is analyzed to better understand the processes that are fundamental to the modeled circulation. Focusing on the dynamics of the Nordic Seas, analytical and numerical modeling highlight the relevance of a sill (Greenland-Scotland Ridge) in setting the properties of the water masses formed in and exported from a marginal sea. Finally, the influence of the convective activity in the Greenland Sea for the overflow, and thus the overturning, is assessed using hydrographic data (from 1950 to present), a regional ocean model, and a unique tracer release experiment. Greenland Sea Gyre water is estimated to contribute less than 1 Sv, and there is no evidence for causality between changes in the Greenland Sea and the overflow. http://hdl.handle.net/1956/2393 Title: On the Nordic Seas’ role in the Atlantic Meridional Overturning Circulation <br/> <br/>Authors: Iovino, Doroteaciro <br/> <br/>Abstract: In the present climate, the North Atlantic thermohaline circulation (THC) plays a fundamental role in the global transport of heat at high latitudes. The response of the North Atlantic Ocean-Nordic Seas THC to surface forcing and basin geometries in an idealized one-hemisphere basin is analyzed to better understand the processes that are fundamental to the modeled circulation. Focusing on the dynamics of the Nordic Seas, analytical and numerical modeling highlight the relevance of a sill (Greenland-Scotland Ridge) in setting the properties of the water masses formed in and exported from a marginal sea. Finally, the influence of the convective activity in the Greenland Sea for the overflow, and thus the overturning, is assessed using hydrographic data (from 1950 to present), a regional ocean model, and a unique tracer release experiment. Greenland Sea Gyre water is estimated to contribute less than 1 Sv, and there is no evidence for causality between changes in the Greenland Sea and the overflow. http://hdl.handle.net/1956/2373 Title: Charged Higgs boson searches and SemiConductor Tracker commissioning for the ATLAS experiment <br/> <br/>Authors: Mohn, Bjarte Alsaker <br/> <br/>Abstract: The ATLAS (A Toroidal Lhc ApparatuS) experiment is one of four major experiments presently being installed at the upcoming Large Hadron Collider (LHC) at the European Centre for Nuclear Research (CERN) outside Geneva. In this thesis we present work done on both the simulation of the ATLAS physics potential for a charged Higgs boson and the construction of the Semiconductor Tracker (SCT) - a subdetector within the ATLAS Inner Detector. The discovery of a charged Higgs boson would be an unambiguous sign of physics beyond the Standard Model (SM) and it is thus of great interest to study the ATLAS potential for a charged Higgs discovery. Two such studies have been conducted for this thesis. In the first study a large-mass-splitting Minimal Supersymmetric Standard Model (MSSM) is assumed in which the charged Higgs boson decays into a W boson and a neutral Higgs may receive a large branching ratio.We conclude, however, that charged Higgs searches in this decay channel are made difficult by a large irreducible SM background. Despite its small brancing ratio at high masses for the charged Higgs boson, the decay mode H± →τν remains the most powerful decay mode for a charged Higgs discovery. Discovery through this channel depends heavily on excellent detector performance and understanding of the background.We show that with detector full simulation and with more complete background samples this channel still remains the most powerful decay mode. We also show that it is possible to connect the discovery countour for charged Higgs boson masses below and above the top-quark mass. The SCT detector is a tracking detector based on silicon microstrip detector technology. It is a highly modular detector consisting of 4088 detector modules that are mounted on 4 barrels and 9x2 end cap disks. Some 320 of the SCT barrel detector modules were built by a Scandinavian collaboration and presented here are the results of this work and procedures for building and quality assurance. Each SCT detector module is powered by an individual high and low voltage supply and thus a large scale and robust power supply control system is needed for controlling the SCT detector. Presented in this thesis is work done to prepare the SCT power supply software for this task, as well as the results obtained during testing and development. As a part of the commissioning of the completed SCT barrel, a series of cosmic runs were performed. Data from these runs allowed for first studies of the detector alignment and alignment results and conlusions thereof are presented in this thesis. http://hdl.handle.net/1956/2368 Title: Modeling of atmospheric circulation at mid- and high latitudes of the northern hemisphere – evaluation studies using ARPEGE <br/> <br/>Authors: Song, Yongjia http://hdl.handle.net/1956/2357 Title: Crude oil components with affinity for gas hydrates in petroleum production <br/> <br/>Authors: Borgund, Anna Elisabet <br/> <br/>Abstract: Some crude oils are believed to contain natural inhibiting components that can prevent hydrate plugging of oil pipelines in petroleum production. A method for classification of the oils that form hydrate plugs, as opposed to those that are not problematical, can change the hydrate inhibiting strategies for oil companies, and result in both economical savings and environmental improvements. Furthermore, an identification of natural hydrate plug inhibiting components can eventually give rise to development of more economical and environmentally friendly inhibitors that can be added to crude oil in pipelines. This thesis addresses the issues of chemical characterisation of crude oil with respect to identification of natural plug inhibiting components. Natural plug inhibiting components are probably hydrate surface active, e.g. an acid fraction has previously been shown to be able to convert a plugging oil into a non-plugging oil when added in a low concentration. In this work, methods for extraction of surface active compounds in crude oil have been established; two methods for acid extraction have been tested (liquid-liquid and ion exchange), and in addition components with affinity for freon hydrate and ice surfaces have been extracted. The extracts have been characterised with chromatographic and spectroscopic methods, e.g. an HPLC method for separation of extracts into four groups have been developed; non-polar compounds, saturated carboxylic acids, phenolic compounds and polyfunctional compounds. The results show that the ion exchange is more effective than the liquidliquid method for extraction of acids from crude oil. Freon hydrates are found to extract a specific fraction with polar compounds from crude oil, while ice does not seem to be a good surface for extraction of components. Compounds which absorb to hydrate surfaces are found to be dominated by saturated carboxylic acids, and to contain lower amounts of phenols and polyfunctional compounds. In general, crude oil extracts primarily contain components of intermediate molecular weights. This means that neither high-molecular compounds such as asphaltenes, nor simple low-molecular petroleum acids and bases are present to a large extent in these extracts. FTIR analysis can to some degree differentiate between freon hydrate extracts from plugging and non-plugging crude oils. GC-MS is not suited for the extracts used in this thesis due to limitations regarding molecular weights and low volatility. LC-MS analysis with Ion Trap MS has been tested at the University of Newcastle, but was not optimal for our samples. The freon hydrate extracts have been analysed for compounds similar to a biosurfactant structure, but no such compounds could be found. No structural identification of the natural inhibiting components have been obtained. However, new methods for extraction of components with affinity for freon hydrate and ice surfaces have been developed and acid extraction methods from the literature have been tested. In addition, a set of analytical methods that can characterise the fractions have been established. One reason for the difficulty of identifying the natural inhibiting components can be that they are present in very low amounts, but it may also be that the distribution of compounds in the fractions is as important as the presence of specific molecules. http://hdl.handle.net/1956/2357 Title: Crude oil components with affinity for gas hydrates in petroleum production <br/> <br/>Authors: Borgund, Anna Elisabet <br/> <br/>Abstract: Some crude oils are believed to contain natural inhibiting components that can prevent hydrate plugging of oil pipelines in petroleum production. A method for classification of the oils that form hydrate plugs, as opposed to those that are not problematical, can change the hydrate inhibiting strategies for oil companies, and result in both economical savings and environmental improvements. Furthermore, an identification of natural hydrate plug inhibiting components can eventually give rise to development of more economical and environmentally friendly inhibitors that can be added to crude oil in pipelines. This thesis addresses the issues of chemical characterisation of crude oil with respect to identification of natural plug inhibiting components. Natural plug inhibiting components are probably hydrate surface active, e.g. an acid fraction has previously been shown to be able to convert a plugging oil into a non-plugging oil when added in a low concentration. In this work, methods for extraction of surface active compounds in crude oil have been established; two methods for acid extraction have been tested (liquid-liquid and ion exchange), and in addition components with affinity for freon hydrate and ice surfaces have been extracted. The extracts have been characterised with chromatographic and spectroscopic methods, e.g. an HPLC method for separation of extracts into four groups have been developed; non-polar compounds, saturated carboxylic acids, phenolic compounds and polyfunctional compounds. The results show that the ion exchange is more effective than the liquidliquid method for extraction of acids from crude oil. Freon hydrates are found to extract a specific fraction with polar compounds from crude oil, while ice does not seem to be a good surface for extraction of components. Compounds which absorb to hydrate surfaces are found to be dominated by saturated carboxylic acids, and to contain lower amounts of phenols and polyfunctional compounds. In general, crude oil extracts primarily contain components of intermediate molecular weights. This means that neither high-molecular compounds such as asphaltenes, nor simple low-molecular petroleum acids and bases are present to a large extent in these extracts. FTIR analysis can to some degree differentiate between freon hydrate extracts from plugging and non-plugging crude oils. GC-MS is not suited for the extracts used in this thesis due to limitations regarding molecular weights and low volatility. LC-MS analysis with Ion Trap MS has been tested at the University of Newcastle, but was not optimal for our samples. The freon hydrate extracts have been analysed for compounds similar to a biosurfactant structure, but no such compounds could be found. No structural identification of the natural inhibiting components have been obtained. However, new methods for extraction of components with affinity for freon hydrate and ice surfaces have been developed and acid extraction methods from the literature have been tested. In addition, a set of analytical methods that can characterise the fractions have been established. One reason for the difficulty of identifying the natural inhibiting components can be that they are present in very low amounts, but it may also be that the distribution of compounds in the fractions is as important as the presence of specific molecules. http://hdl.handle.net/1956/2355 Title: Effects of initial anaerobic biodegradation on crude oil and formation water composition <br/> <br/>Authors: Skaare, Bent Barman <br/> <br/>Abstract: The e ect of initial biodegradation on oil and formation water was studied using both laboratory degradation schemes and biodegraded oils from the reservoir comprising Troll C. The e ects of biodegradation on the molecular level of oil may be heteroge- neous even in systems that ought to have the same starting point. This is true for both laboratory incubations and for biodegradation processes inside model reservoirs. Simultaneous depletion in di erent oil constituents and compound groups occurs at di erent relative rates, as a result of di erences in the bacterial activity. The dependence of the molecular e ects on the active microbial com- munity is also valid in reservoirs. This makes assessing biodegradation di cult on a molecular level because the e ects may vary according to the prevailing bacterial community in each reservoir. As a result of these di erences using multivariate analysis, e.g. principal component analysis, may provide valuable information that would not have been apparent using univariate ratios. The composition of organic acids in the water phase of the model reservoirs studied are highly dependent on the biodegradation processes it has encoun- tered, as it oods through the system. The identi cation of metabolites speci c for anaerobic biodegradation of naphthalene, 2-methylnaphthalene and tetralin in the formation water from Troll C indicates that the composition of such wa- ter might be dependent on the ongoing biodegradation in the reservoirs as well as in the model reservoirs. The water solubility of such metabolites, along with the assumption that biodegradation occurs at or near the oil water contact, can make identi cation of the metabolites easier in formation water than in the corresponding oils. Hence, the composition of formation waters may contribute information which is not available from the water composition. This was thecase in the samples from Troll C. http://hdl.handle.net/1956/2353 Title: Gelatinous zooplankton in western Norwegian fjords : ecology, systematics and comparisons with adjacent waters <br/> <br/>Authors: Hosia, Aino <br/> <br/>Abstract: Gelatinous zooplankters, also known as jellies, are ubiquitous in the marine pelagic. Medusae, siphonophores and ctenophores are voracious predators that can, when abundant, have significant structuring effects on the pelagic community. Many jellies exhibit opportunistic life history characteristics such as short generation times, asexual reproduction or hermaphrodism, high fecundity, rapid growth, and ability to exploit high food concentrations effectively. While siphonophores and ctenophores are generally holoplanktonic, most scypho- and hydromedusae are meroplanktonic with a benthic polypoid stage. These characteristics contribute to the naturally pulsed occurrence of jellies in the plankton. In order to assess the role of jellies in the fjord ecosystems, information on the identity, seasonal abundance, distribution and behaviour of the species constituting the gelatinous community is necessary. This thesis attempts to fill in several gaps in knowledge regarding the systematics and ecology of gelatinous zooplankton in western Norwegian fjords. In order to do so, both net based sampling and remotely operated vehicles (ROVs) have been utilized. Seasonal changes in the gelatinous community as a whole as well as the abundances of the individual species in Korsfjord and Fanafjord, western Norway, were examined. The gelatinous communities showed a clear seasonal succession, with maximum diversity and abundance occurring in April-June. Aglantha digitale was numerically dominant in both fjords. Meroplanktonic hydromedusa species appeared sequentially and were most common during the summer months. During the winter, the siphonophores Nanomia cara, Lensia conoidea and Dimophyes arctica formed the bulk of the community especially in Korsfjord. While the two fjords had rather similar faunas, they differed in terms of the relative importance of the observed groups. Siphonophores were prominent in the more oceanic Korsfjord, while Fanafjord was characterized by meroplanktonic hydromedusae. A community of deep-water hydromedusae was found at the deeper stations at Korsfjord. Two new species presumed to be members of this deep-water community, Foersteria quadrata and Parateclaia norvegica, are described in this thesis. The vertical distribution of animals in a fjord has relevance in terms of degree of overlap with prey and predator distributions as well as the likelihood of being advected from the fjord. Exchange of fjord water is most pronounced in the layers occurring above sill depth, while the sill promotes the retention of basin water. The holoplanktonic Aglantha digitale and Nanomia cara both seem to facilitate their retention in the fjords by residing below sill depth when mature. Younger stages of both species are known to have a shallower distribution, and may thus be more susceptible to advective transport. Comparison with results from the northern portions of the Mid-Atlantic Ridge (MAR) show that the same species of planktonic cnidarians (A. digitale, N. cara, L. conoidea and D. arctica) dominated the epipelagic both in Korsfjord and the corresponding latitudes at the MAR. However, the mesopelagic siphonophores and medusae common at the MAR (e.g. Chuniphyes multidentata, Gilia reticulata, Pantachogon haeckeli and Aeginura grimaldii) seem to have been unable to colonize the fjords. The notable exception to the above rule is Periphylla periphylla, a coronate midwater scyphomedusa with abundant populations in certain west Norwegian fjords. Large P. periphylla in Lurefjord were shown to feed primarily on Calanus spp., but also on krill and ostracods. They behaved as ramming predators, approaching their prey tentacles first in order to minimize fluid disturbance, and were found to have clearance rates comparable with other gelatinous predators of similar size. The horizontal and vertical distributions of siphonophores were found to be negatively correlated with P. periphylla distribution.