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Browsing Fakultet for naturvitenskap og teknologi by Title
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Hanssen, Øyvind (Master thesis; Mastergradsoppgave, 1994)[+][-]
Abstract: I denne hovedfagsavhandlinga undersøkes avbildningsmekanismer mellom ANSAware applikasjoner og en føderativ omgivelse. Dette gjøres innefor rammen av ODS-gruppas arbeid med samvirkende informasjonssystemer. For å få kunnskap om problemområdet og om hvordan avbildning effektivt kan utføres, utvikles et rammeverk for modellering, design og implementasjon av avbildningsmekanismer. Vi fokuserer spesielt på hvordan man i føderasjonen kan gi inntrykk av ANSAware objekter som persistente. Vi baserer oss på en persistensmodell som innebærer at vi stiller ulike krav til objekt-identitet. Vi trenger bare permanent identitet for noen få objekter. For disse er det behov for mekanismer for transparent forvaltning (aktivisering/passivisering). Vi undersøker to logiske komponenter som samarbeider om avbildning: Objekt-adapter som har ansvaret for forvaltning og objekt-identitet og språkbindinger som representerer programmeringsgrensesnitt for den aktuelle klient-omgivelse og realiserer aksess-transparens ved hjelp av stubs. Vi innfører begrepet proxy-objekt som representerer identifikasjon av objekter i objekt-adapter og presenterer en konseptuell modell for interaksjon med klient. Et gjenbrukbart objekt-orientert rammeverk er realisert. Dette representerer design og delvis implementasjon av objekt-adapter. Denne påbygges med applikasjonsspesifikk software for å bli komplett. En notasjon for definisjon av forvaltning av permanente objekter blir utviklet. Egenskaper ved språkbindinger blir undersøkt. Her gjøres et skille mellom direkte binding hvor klient er i samme prosess og binding via eksplisistt grensesnitt (kanonisk språk). Ei språkbinding til C++ er realisert, og det er skissert et rammeverk for binding til FRIL som er et funksjonelt og objektorientert språk for integrasjon og samvirke mellom ulike informasjonssystemer. Description: Dette er en hovedoppgave URI: http://hdl.handle.net/10037/1248 File(s) in this item: 1
thesis.pdf (2.110Mb) -
Grydeland, Tom (Master thesis; Mastergradsoppgave, 01-Mar-1998)[+][-]
Abstract: The thesis describes observations of strongly enhanced incoherent scatter plasma lines in the auroral ionosphere which were made with the EISCAT UHF radar in 1985. The linear theory of plasma instabilities is reviewed, and several possible explanations are discussed. The observations were found to be of insufficient resolution to unambiguously resolve which one would be the correct explanation. Finally, a new radar experiment design capable of making observations with higher resolution was realised and is presented in some detail. URI: http://hdl.handle.net/10037/239 File(s) in this item: 2
appendix.pdf (10.72Mb)thesis.pdf (1.166Mb) -
Valladares, C.E.; Van Eyken, A.P.; Alcaydé, D.; Rodriguez, J.V.; Ruohoniemi, J.M. (Journal article; Peer reviewed, 1999)[+][-]
Abstract: We report important results of the first campaign specially designed to observe the formation and the initial convection of polar cap patches. The principal instrumentation used in the experiments comprised the EISCAT, the Sondrestrom, and the Super DARN network of radars. The experiment was conducted on February 18, 1996 and was complemented with additional sensors such as the Greenland chain of magnetometers and the WIND and IMP-8 satellites. Two different types of events were seen on this day, and in both events the Sondrestrom radar registered the formation and evolution of large-scale density structures. The first event consisted of the passage of traveling convection vortices (TCV). The other event occurred in association with the development of large plasma jets (LPJ) embedded in the sunward convection part of the dusk cell. TCVs were measured, principally, with the magnetometers located in Greenland, but were also confirmed by the line-of-sight velocities from the Sondrestrom and SuperDARN radars. We found that when the magnetic perturbations associated with the TCVs were larger than 100 nT, then a section of the high-latitude plasma density was eroded by a factor of 2. We suggest that the number density reduction was caused by an enhancement in the O+ recombination due to an elevated Ti, which was produced by the much higher frictional heating inside the vortex. The large plasma jets had a considerable (>1000 km) longitudinal extension and were 200-300 km in width. They were seen principally with the Sondrestrom, and SuperDARN radars. Enhanced ion temperature (Ti) was also observed by the Sondrestrom and EISCAT radars. These channels of high Ti were exactly collocated with the LPJs and some of them with regions of eroded plasma number density. We suggest that the LPJs bring less dense plasma from later local times. However, the recent time history of the plasma flow is important to define the depth of the density depletion. Systematic changes in the latitudinal location and in the intensity of the LPJs were observed in the 2 min time resolution data of the SuperDARN radars. The effect of the abrupt changes in the LPJs location is to create regions containing dayside plasma almost detached from the rest of the oval density. One of these density features was seen by the Sondrestrom radar at 1542 UT. The data presented here suggest that two plasma structuring mechanisms (TCVs and LPJs) can act tens of minutes apart to produce higher levels of density structures in the near noon F-region ionosphere. URI: http://hdl.handle.net/10037/609 File(s) in this item: 1
article.pdf (1.289Mb) -
Henriksen, K.; Rees, D.; Smith, R.W.; Signernes, F.; Brandstrom, U.; Harris, M.; Maskall, G. (Journal article, 1998)[+][-]
Abstract: Two Doppler imaging systems (DIS) or wide-field imaging Fabry-Perot interferometers (FPI), have recently been commissioned, one at the Auroral Station, Adventdalen, Longyearbyen, Svalbard, and the second at the IRF, Kiruna, Sweden. These instruments can provide wide-field (600 * 800 km) images of neutral wind flows in the upper thermosphere, by measuring the Doppler shift of the atomic oxygen forbidden near 630 nm, which is emitted from an altitude of approximately 240 km. From the instrument in Svalbard, at mid-winter, it is possible to observe the dayside polar cusp and the polar cap throughout the entire day, whereas from Kiruna, the night-time auroral oval is observable during the hours of darkness. Measurements of thermospheric dynamics from the DIS can be used in conjunction with observations of ionospheric plasma flows and thermal plasma densities by the EISCAT-Svalbard radar (ESR) and by EISCAT, along with other complementary observations by co-located instruments such as the auroral large-scale imaging system (ALIS). Such combined data sets will allow a wide range of scientific studies to be performed concerning the dynamical response of the thermosphere and ionosphere, and the important energetic and momentum exchange processes resulting from their complex interactions. These processes are particularly important in the immediate vicinity of the polar cusp and within the auroral oval. Early results from Svalbard in late 1995 will be discussed. The DIS in Kiruna observed two interesting geomagnetic disturbances in early 1997, the minor geomagnetic storm of 10, 11 January, and the disturbed period from 7–10 February. During these events, the thermospheric wind response showed some interesting departures from the average behaviour, which we attribute to the result of strong and variable Lorenz forcing (ion drag) and Joule and particle heating during these geomagnetic disturbances. URI: http://hdl.handle.net/10037/567 File(s) in this item: 1
article.pdf (479.5Kb) -
Pless, Gustav (Master thesis; Mastergradsoppgave, 15-May-2009)[+][-]
Abstract: The high-resolution 3D seismic survey EL0001 allowed to document the subsurface fluid migration system and fluid accumulations within Veslemøy High, SW Barents Sea. Fluids migrate both through Cretaceous and Tertiary sediments, but also through younger glacial sediments. Veslemøy High is a structurally isolated high at the Cretaceous and Tertiary levels bounded by N-S trending west-dipping normal faults. Cretaceous to Miocene sediments that consists of deep marine shales dominate in the older part and Plio-Pleistocene successions deposited by glaciomarine processes dominate in the upper part. Fluid accumulations are identified in L. Paleocene to E. Eocene sediments, and in Pliocene to Pleistocene sediments of glacial origin. An extensive high-seismic amplitude anomaly of 790 km2 appears to occur in a fan system within the eastern section of the 3D survey extending into Tromsø Basin. High and negative seismic amplitudes indicate appreciable gas accumulations within the fan. On the seafloor the existence of pockmarks suggest that pockmark formation most likely occurred after the ice-sheet retreat and thus between 15 ka and 12.5-11.5 ka. Pockmarks may represent fluid flow events from violent eruptions associated with deglaciation processes. Some evidence exists that gas may have been generated in deeper basins. Fluids migrated into Veslemøy High primarily along Plio-Pleistocene strata from Sørvestsnaget Basin in the west and along Creataceous-Paleogene strata from Tromsø Basin in the east. As the fluids reach the apex of Veslemøy High vertical migration through giant chimneys and along normal faults dominate. It is important to note that there is no geophysical evidence for fluid migration from Cretaceous sediments that lie directly below the high. URI: http://hdl.handle.net/10037/1910 File(s) in this item: 1
thesis.pdf (9.943Mb) -
Ivanova, Maria (Journal article; Tidsskriftartikkel; Peer reviewed, 2011)[+][-]
Abstract: The issue of oil spill emergency response in north-west Russia has become increasingly important following a substantial increase in maritime transport and major offshore developments in Russian waters. This study is an initial effort to outline the public and private agencies and organizations involved in handling oil spills in the Murmansk region and the structure of the oil spill emergency response system in the region. This study examines the formal relationships between federal and regional authorities and between the different subsystems at the regional level. Due to the paucity of academic literature and public documentation on this topic, this study to a large extent bases itself on interview data. A main finding is that the regional oil spill response system has not been fully developed. It further concludes that the system lacks a clearly formulated state policy, a single governing authority and a unified structure. Finally, the study demonstrates that the agencies and organizations involved in tackling oil spill emergencies in the Murmansk region are hampered by insufficient funding, which probably reduces their preparedness to combat oil spills. Description: This article is part of Maria Sydnes' doctoral thesis, which is available in Munin at http://hdl.handle.net/10037/4180 URI: http://hdl.handle.net/10037/4056 File(s) in this item: 1
article.pdf (331.9Kb) -
Lychagin, Valentin V.; Goldberg, Vladislav V. (Working paper; Arbeidsnotat, 13-Dec-2008)[+][-]
Abstract: We present a complete description of a class of linearizable planar geodesic webs which contain a parallelizable 3-subweb. URI: http://hdl.handle.net/10037/1854 File(s) in this item: 1
article .pdf (102.2Kb) -
Ghosh, Anil K.; Godtliebsen, Fred (Journal article; Tidsskriftartikkel; Peer reviewed, 2012)[+][-]
Abstract: Traditional parametric and nonparametric classifiers used for statistical pattern recognition have their own strengths and limitations. While parametric methods assume some specific parametric models for density functions or posterior probabilities of competing classes, nonparametric methods are free from such assumptions. So, when these model assumptions are correct, parametric methods outperform nonparametric classifiers, especially when the training sample is small. But, violations of these assumptions often lead to poor performance by parametric classifiers, where nonparametric methods work well. In this article, we make an attempt to overcome these limitations of parametric and nonparametric approaches and combine their strengths. The resulting classifiers, denoted the hybrid classifiers, perform like parametric classifiers when the model assumptions are valid, but unlike parametric classifiers, they also provide safeguards against possible deviations from parametric model assumptions. In this article, we propose some multiscale methods for hybrid classification, and their performance is evaluated using several simulated and benchmark data sets. URI: http://hdl.handle.net/10037/4948 File(s) in this item: 1
article.pdf (3.990Mb) -
Lychagin, Valentin V.; Goldberg, Vladislav V. (Chapter; Bokkapittel, 03-Dec-2008)[+][-]
Abstract: We present some old and recent results on rank problems and linearizability of geodesic planar webs Description: Rettighetshaver (Forfatter) har gitt oss tillatelse til å legge ut artikkelen (forfatternes aksepterte versjon) URI: http://hdl.handle.net/10037/2044 File(s) in this item: 1
article .pdf (236.6Kb) -
Lychagin, Valentin V.; Goldberg, Vladislav V. (Journal article; Tidsskriftartikkel; Peer reviewed, 21-Nov-2004)[+][-]
Abstract: We find relative differential invariants of orders eight and nine for a planar nonparallelizable 3-web such that their vanishing is necessary and sufficient for a 3-web to be linearizable. This solves the Blaschke conjecture for 3-webs. As a side result, we show that the number of linearizations in the Gronwall conjecture does not exceed fifteen and give criteria for rigidity of 3-webs. Description: Dette er forfatternes aksepterte versjon. URI: http://hdl.handle.net/10037/2055 File(s) in this item: 1
article.pdf (414.7Kb) -
Asplin, Jo; Mehus, Sindre (Research report; Forskningsrapport, Jan-1997)[+][-]
Abstract: Volume rendering is an important and CPU-intensive technique for visualizing large scalar fields. In essence, a volume renderer performs two activites on behalf of the user: loading a new data set, and rendering the current one. At one level, the performance of an individual activity is important. At another level, the erformance of the session as a whole, in particular switching from one activity to the next, should be addressed. In this paper we present PARFUM, a parallel volume renderer based on a controller/worker model in a network of workstations. PARFUM has three essential properties that increase the performance of a parallel volume renderer. First, dynamic load balancing is employed during a rendering activity. Second, workers may enter or fail without affecting the correctness of a session. Third, a user may easily abort the current activity in favour of a new one. These properties may more easily be achieved by accepting (rather than fighting) the inherent asynchrony in a distributed system. As a consequence, PARFUM attempts to minimize causal dependencies in the interaction between the user and the controller as well as between the controller and the workers. We evaluate two implementations based on the TCP and UDP transport protocols respectively. URI: http://hdl.handle.net/10037/375 File(s) in this item: 1
report.pdf (336.4Kb) -
Eliassen, Frank; Hanssen, Øyvind (Conference object; Konferansebidrag, Aug-1995)[+][-]
Description: Paper presented at 8th ERCIM Database Research Group Workshop on Database Issues and Infrastructure in Cooperative Information Systems URI: http://hdl.handle.net/10037/2446 File(s) in this item: 1
article.pdf (147.6Kb) -
Hall, Chris (Journal article; Peer reviewed, 2002)[+][-]
Abstract: By measuring fading times of radar echoes from underdense meteor trails, it is possible to deduce the ambipolar diffusivities of the ions responsible for these radar echoes. It could be anticipated that these diffusivities increase monotonically with height akin to neutral viscosity. In practice, this is not always the case. Here, we investigate the capability of neutral turbulence to affect the meteor trail diffusion rate. URI: 1432-0576 (elektronisk) File(s) in this item: 1
article.pdf (205.2Kb) -
Fredriksen, Åshild; Mishra, Lekha Nath; Gulbrandsen, Njål; Miloch, Wojciech Jacek (Journal article; Tidsskriftartikkel; Peer reviewed, 2010)[+][-]
Abstract: Plasma parameters and the subsonic flow from a capacitively coupled, cylindrical plasma source of the Njord helicon device are investigated by means of a Mach probe and a retarding field energy analyzer (RFEA). 13.56 MHz and 600 W RF power is inserted into the argon working gas under low-pressure conditions and moderate magnetic field. By means of a downstream field coil, the magnetic field is shaped from a purely expanding field to a configuration with more parallel field lines. It is shown that the downstream plasma density along the outer rim of the source increases significantly and there is a sudden increase by nearly 20 V in the plasma potential already after a moderate increase in the downstream magnetic field. The investigation of the flow indicates that current ratios derived from the Mach probe result in an apparent flow in the direction towards the source, while the current bratios derived from the RFEA indicate a flow in the direction away from the source. PIC simulations demonstrate that the acceptance angle of the probes, being nearly 180o for the Mach probe, and about 45o for the RFEA, can critically affect the current ratios and hence the subsonic flow measured by the probes in the weakly magnetized plasma in our device. The first section in your paper URI: http://hdl.handle.net/10037/3560 File(s) in this item: 1
article.pdf (336.4Kb) -
Hall, Chris (Journal article; Peer reviewed, 2000)[+][-]
Abstract: Strong wind shears may result in dynamic instability, often characterised by the Richardson number lying between zero and 0.25. The extent to which electric-field driven ion flow may induce such neutral wind shears is examined. Further, it is proposed that, in the ionosphere, it is possible for electric fields to drive ion winds such that the collisionally induced neutral air response may be comparable to viscous damping of neutral motion. We shall present an analogy to the Reynolds Number Re to quantify this effect. In the same way that Re may be used to evaluate the likelihood of a flow being turbulent, the analagous metric may also indicate where in the atmosphere plasma dynamics may be strong enough to destabilise the neutral dynamics. URI: http://hdl.handle.net/10037/574 File(s) in this item: 1
article.pdf (129.8Kb) -
Kellerman, A. C.; Hansen, Truls Lynne; Makarevich, R. A.; Honary, F. (Journal article; Tidsskriftartikkel; Peer reviewed, 02-Feb-2009)[+][-]
Abstract: In this study, the relationship between auroral absorption, electrojet currents, and ionospheric plasma convection velocity is investigated using a series of new methods where temporal correlations are calculated and analysed for different events and MLT sectors. We employ cosmic noise absorption (CNA) observations obtained by the Imaging Riometer for Ionospheric Studies (IRIS) system in Kilpisj¨arvi, Finland, plasma convection measurements by the European Incoherent Scatter (EISCAT) radar, and estimates of the electrojet currents derived from the Tromsø magnetometer data. The IRIS absorption and EISCAT plasma convection measurements are used as a proxy for the particle precipitation component of the Hall conductance and ionospheric electric field, respectively. It is shown that the electrojet currents are affected by both enhanced conductance and electric field but with the relative importance of these two factors varying with magnetic local time (MLT). The correlation between the current and electric field (absorption) is the highest at 12:00– 15:00MLT (00:00–03:00MLT). It is demonstrated that the electric-field-dominant region is asymmetric with respect to magnetic-noon-midnight meridian extending from 09:00 to 21:00MLT. This may be related to the recently reported absence of mirror-symmetry between the effects of positive and negative IMF By on the high-latitude plasma convection pattern. The conductivity-dominant region is somewhat wider than previously thought extending from 21:00 to 09:00MLT with correlation slowly declining from midnight towards the morning, which is interpreted as being in part due to highenergy electron clouds gradually depleting and drifting from midnight towards the morning sector. The conductivitydominant region is further investigated using the extensiveIRIS riometer and Tromsø magnetometer datasets with results showing a distinct seasonal dependence. The region of high current-absorption correlation extends from 21:00 to 06:00MLT near both equinoxes, however, it is narrower and rotated towards the morning (02:00–07:00MLT) in summer, while in winter the correlation shows much greater variability with MLT. During periods of high current-electricfield correlation, the relationship between electric field and absorption can be described as an inverse proportionality, which can be explained by limitation of the electrojet current by the magnetospheric generator. Possible cases of electron heating absorption are also investigated with absorption showing no obvious dependence on the ion velocity or electron temperature. Description: This is the publisher’s version/PDF (Published in Annales Geophysicae, an open access journal of the European Geosciences Union) URI: http://hdl.handle.net/10037/2386 File(s) in this item: 1
angeo-27-473-2009.pdf (6.676Mb) -
Havnes, Ove; Næsheim, Lars Irgens (Journal article; Tidsskriftartikkel; Peer reviewed, 2007)[+][-]
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Descomps, Alexandre Pierre (Master thesis; Mastergradsoppgave, 30-Jun-2008)[+][-]
Abstract: The present work is on the total synthesis of a natural compound found in a mixture of secondary metabolite produced by an alga nearby the cost of Australia. The target molecule, the 4-bromo-3-butyl-5-(dibromomethylene)furan-2(5H)-one, has not previously been proposed. The synthetic route described in this thesis uses cheap and readily available starting materials and the target is reached after six synthetic steps. Several new results have been obtained: selective monolithiation of a dibromofuran; Suzuki coupling with butyl boronic acid; a regioselective photo-oxidation of furan. The final step of the synthesis, a dibromoolefination, has not yet been accomplished. URI: http://hdl.handle.net/10037/1641 File(s) in this item: 1
thesis.pdf (12.00Mb) -
Strømme, Jann H. (Master thesis; Mastergradsoppgave, 19-May-2009)[+][-]
Abstract: Abstract The present work is on the synthesis of a pyrylium salt, 8-hydroxy-2,4-diphenyl-5,6,7,8-tetrahydrochromenylium tetrafluoroborate, a precursor for interesting transition metal ligands. Different routes are presented with the aim of making an affordable precursor for the variety of syntheses possible from these versatile pyrylium salts. New findings include a preparative non optimized 2-hydroxy â cyclohexanone synthesis. It includes high resolution measurements not found in literature for several substrates. Keywords Triphenylpyrilium, 8-oxo-2,4-diphenyl-5,6,7,8- tetrahydrobenzopyrylium tetrafluoroborate, Ichiis reagent, CBS reductions, oxygen insertions, DIBAL reductions, singlet oxygen, Magtrieve⢠oxidation, Oxone⢠oxidations, manganese oxidation, Oppenauer and Meerwein Schmidt Ponndorf Verley transfer hydrogenations. URI: http://hdl.handle.net/10037/2077 File(s) in this item: 1
thesis.pdf (2.731Mb) -
Ludwig, Patrick; Miloch, Wojciech Jacek; Kählert, Hanno; Bonitz, Michael (Journal article; Tidsskriftartikkel; Peer reviewed, 2012)[+][-]
Abstract: The theoretical description of complex (dusty) plasmas requires multiscale concepts that adequately incorporate the correlated interplay of streaming electrons and ions, neutrals and dust grains. Knowing the effective dust–dust interaction, the multiscale problem can be effectively reduced to a one-component plasma model of the dust subsystem. The goal of this paper is a systematic evaluation of the electrostatic potential distribution around a dust grain in the presence of a streaming plasma environment by means of two complementary approaches: (i) a high-precision computation of the dynamically screened Coulomb potential from the dynamic dielectric function and (ii) full 3D particle-in-cell simulations, which self-consistently include dynamical grain charging and nonlinear effects. The range of applicability of these two approaches is addressed. URI: http://hdl.handle.net/10037/5054 File(s) in this item: 1
article.pdf (3.319Mb)
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