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norskFakultet for naturvitenskap og teknologi: Recent submissions
Now showing items 3701-3720 of 5327
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Deep Learning: From Data Extraction to Large-Scale Analysis
(Master thesis; Mastergradsoppgave, 2018-05-15)We aim to give an insight into aspects of developing and deploying a deep learning algorithm to automate biomedical image analyses. We anonymize sensitive data from a medical archive system, attempt to replicate and further improve published methods, and scale out our algorithm to support large-scale analyses. Specifically, our contributions are described as follows. First, to anonymize and extract ... -
Intermittent electron density and temperature fluctuations and associated fluxes in the Alcator C-Mod scrape-off layer
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-04-10)The Alcator C-Mod mirror Langmuir probe system has been used to sample data time series of fluctuating plasma parameters in the outboard mid-plane far scrape-off layer. We present a statistical analysis of one second long time series of electron density, temperature, radial electric drift velocity and the corresponding particle and electron heat fluxes. These are sampled during stationary plasma ... -
Improving Doppler frequency estimation from Envisat data
(Journal article; Tidsskriftartikkel; Peer reviewed, 2014-11-06)This paper shows that Envisat ASAR data are degraded by a small periodic variation in gain between internal calibration cycles of the antenna, which introduces a significant bias when we try to estimate line-of-sight surface velocities from the estimated Doppler frequency shifts. We investigate the impact of the gain problems on the derived surface velocity product and propose a simple correction ... -
Cenozoic tectonosedimentary development and erosion estimates for the Barents Sea continental margin, Norwegian Arctic
(Doctoral thesis; Doktorgradsavhandling, 2018-04-26)The Barents Sea shelf has been experienced extensive uplift and erosion in the Cenozoic. However, the pre-glacial erosion has been so far less constrained in comparison to the glacial erosion. This paper aims to better understand the early–middle Cenozoic erosion in the western Barents Sea and the late Cenozoic erosion in the northern Barents Sea by using the mass-balance approach. The study utilizes ... -
Erratum to: Almost complex structures in 6D with nondegenerate Nijenhuis tensors and large symmetry groups
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-02-23)We correct an error in the second part of Theorem 3 of our original paper. -
Subband Extraction Strategies in Ship Detection With the Subaperture Cross-Correlation Magnitude
(Journal article; Tidsskriftartikkel; Peer reviewed, 2012-01-27)The subaperture cross-correlation magnitude (SCM) has previously been proposed as a statistic that improves the contrast between small ship targets and the surrounding sea in synthetic-aperture-radar images. This preprocessing technique utilizes the fast decorrelation of open-water surface ripples on the scale of the SAR wavelength relative to coherent targets such as a ship. However, optimization ... -
Late Weichselian ice-sheet dynamics and deglaciation history of the northern Svalbard margin
(Doctoral thesis; Doktorgradsavhandling, 2018-05-04)This thesis presents new results from marine geological and geophysical studies based on sediment gravity cores, airgun, subbottom acoustic and high-resolution swath bathymetric data from fjords, the continental shelf and slope north of Nordaustlandet, Svalbard. From these records, the glacial landform assemblages as well as the glacial and postglacial sedimentary environments were interpreted. Where ... -
Benthic communities at high-Arctic cold seeps: Faunal response to methane seepage in Svalbard
(Doctoral thesis; Doktorgradsavhandling, 2018-03-20)Cold seeps are chemosynthetic habitats found in both deep sea and shallow ocean-shelves worldwide, including the polar regions. At seeps, hydrocarbons, sulfide, and other reduced compounds emerge from the seafloor, providing energy to fuel chemoautotrophic production. Microbial assemblages, supported by the oxidation and reduction of gases and fluids, form the base of a food web composing unique and ... -
A new genus and two new species of Thyasiridae associated with methane seeps off Svalbard, Arctic Ocean
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-05-16)Bivalves have been found in unique benthic assemblages associated with active methane seeps and mounds along the western and southern margins of the Svalbard shelf (75–79°N) at 350–380 m depth. Among the samples collected were a number of shells of Thyasiridae that are distinct from any species previously described. Here we describe one new genus Rhacothyas gen. nov. and two new species Thyasira ... -
Diagenetically altered benthic foraminifera reveal paleo-methane seepage
(Doctoral thesis; Doktorgradsavhandling, 2018-05-02)Methane is a powerful greenhouse gas and its atmospheric concentrations varied throughout the geological history. Large amounts of methane are stored in seafloor sediments and society is apprehensive that some of this methane may enter the water column and atmosphere. Vestnesa Ridge, located offshore north-western Svalbard, is one of the northernmost known active methane seeps. This PhD project ... -
Geological controlling parameters on seismic imaging of igneous intrusions on Svalbard
(Master thesis; Mastergradsoppgave, 2017-05-15)Imaging and mapping igneous intrusions such a sills and dykes has been one of the challenges in recent years. However, igneous intrusions in seismic data have properties that make them good targets for visualization, such as high amplitude and sophisticated shapes. 3D visualization methods are especially well suited for sill reflections. One of the main limitations of tying offshore seismic data to ... -
Characterization of a neuraminic acid synthase from the psychrophilic organism Moritella viscosa
(Master thesis; Mastergradsoppgave, 2013-05-15)Sialic acids are family of nine carbon α-keto acids found to have important roles mammals and bacteria. They are negatively charged sugars which have found to play critical roles in the cognitive development, as well as being a part of the innate immune system and being targets for pathogens. Mammalian cells express sialic acids to confer self to the immune system, a trait being exploited by some ... -
Statistical significance of rising and oscillatory trends in global ocean and land temperature in the past 160 years
(Journal article; Tidsskriftartikkel, 2014-03-20)Various interpretations of the notion of a trend in the context of global warming are discussed, contrasting the difference between viewing a trend as the deterministic response to an external forcing and viewing it as a slow variation which can be separated from the background spectral continuum of long-range persistent climate noise. The emphasis in this paper is on the latter notion, and a general ... -
Optimization of Pure-Component LNG Cascade Processes with Heat Integration
(Journal article; Tidsskriftartikkel, 2018-01-15)Liquefaction of natural gas is an energy-intensive process in which the energy efficiency depends on the number of compressors stages and the heat integration scheme. The aim of the study is to systematically evaluate process performance of pure component cascade processes, present optimized designs for all relevant numbers of compression stages and compare energy consumption between processes with ... -
Ice intelligence retrieval by remote sensing - Possibilities and challenges in an operational setting
(Peer reviewed; Chapter; Bokkapittel, 2017)Detecting ice drift velocity when operating offshore in ice-covered waters is crucial during marine operations, as ice actions affect station keeping and ice management. Furthermore, other ice data/intelligence such as ice concentration and thickness are important parameters to determine ice resistance, evaluate performance of icebreakers and predict ice actions on structures. Different sensors are ... -
Probability distribution functions for intermittent scrape-off layer plasma fluctuations
(Journal article; Peer reviewed; Tidsskriftartikkel, 2018-01-24)A stochastic model for intermittent fluctuations in the scrape-off layer of magnetically confined plasmas has been constructed based on a super-position of uncorrelated pulses arriving according to a Poisson process. In the most common applications of the model, the pulse amplitudes are assumed exponentially distributed, supported by conditional averaging of large-amplitude fluctuations in experimental ... -
Cascading lake drainage on the Greenland Ice Sheet triggered by tensile shock and fracture
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-03-14)Supraglacial lakes on the Greenland Ice Sheet are expanding inland, but the impact on ice flow is equivocal because interior surface conditions may preclude the transfer of surface water to the bed. Here we use a well-constrained 3D model to demonstrate that supraglacial lakes in Greenland drain when tensile-stress perturbations propagate fractures in areas where fractures are normally absent or ... -
Glacigenic sedimentation pulses triggered postglacial gas hydrate dissociation
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-02-12)Large amounts of methane are stored in continental margins as gas hydrates. They are stable under high pressure and low, but react sensitively to environmental changes. Bottom water temperature and sea level changes were considered as main contributors to gas hydrate dynamics after the last glaciation. However, here we show with numerical simulations that pulses of increased sedimentation dominantly ... -
Magnetotelluric signatures of the complex tertiary fold–thrust belt and extensional fault architecture beneath Brøggerhalvøya, Svalbard
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-12-18)Magnetotelluric (MT) data were recently collected on Brøggerhalvøya, Svalbard, in a 0.003–1000 s period range along a curved WNW–ESE profile. The collected data manifested strong three-dimensional (3D) effects. We modelled the full impedance tensor with tipper and bathymetry included in 3D, and benchmarked the result with determinant data two-dimensional (2D) inversion. The final inversion results ... -
EURODELTA-Trends, a multi-model experiment of air quality hindcast in Europe over 1990-2010
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-09-05)The EURODELTA-Trends multi-model chemistry-transport experiment has been designed to facilitate a better understanding of the evolution of air pollution and its drivers for the period 1990–2010 in Europe. The main objective of the experiment is to assess the efficiency of air pollutant emissions mitigation measures in improving regional-scale air quality. <br>The present paper formulates the ...
