Fakultet for naturvitenskap og teknologi: Recent submissions
Now showing items 3521-3540 of 5314
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Multi-frequency radar remote sensing of sea ice. Modelling and interpretation of polarimetric multi-frequency radar signatures of sea ice
(Doctoral thesis; Doktorgradsavhandling, 2018-06-08)This thesis deals with polarimetric multi-frequency radar signatures of sea ice. It presents a thorough background on the topic and three case studies. The first study presents a global sensitivity analysis of the fully polarimetric radar backscatter response from snow covered sea ice. The analysis is global in the sense that it takes into account the observed ranges of sea ice properties that ... -
Bayesian Computing with INLA: A Review
(Journal article; Tidsskriftartikkel, 2016-12-23)The key operation in Bayesian inference is to compute high-dimensional integrals. An old approximate technique is the Laplace method or approximation, which dates back to Pierre-Simon Laplace (1774). This simple idea approximates the integrand with a second-order Taylor expansion around the mode and computes the integral analytically. By developing a nested version of this classical idea, combined ... -
Rapid Surface Lowering of Benito Glacier, Northern Patagonian Icefield
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-05-01)The Patagonian Icefields, which straddle the Andes below 46°S, are two of the most sensitive ice masses on Earth to climate change. However, recent mass loss from the icefields along with its spatial and temporal variability is not well-constrained. Here we determine surface elevation changes of Benito Glacier, a 163 km2 outlet glacier draining the western flank of the North Patagonian Icefield, ... -
New geophysical evidence for a revised maximum position of part of the NE sector of the Greenland ice sheet during the last glacial maximum
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-06-26)The extent and dynamics of the north-eastern sector of the Greenland ice sheet (GIS) during the last glacial still remain very uncertain, and maximum ice extents to inner-shelf, mid-shelf and outer-shelf positions have been suggested. Here we argue that the margin of the GIS reached the shelf break along part of its NE sector during the last glacial maximum. Swath-bathymetry and sub-bottom profiler ... -
Ice-stream dynamics of the SW Barents Sea revealed by high-resolution 3D seismic imaging of glacial deposits in the Hoop area
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-03-07)Recent developments in seismic acquisition systems and seismic data visualization have contributed to improve the imaging of seismic geomorphologies over a broad range of topics. This study focuses on a new high-resolution P-Cable 3D seismic cube located in the Hoop area in the SW Barents Sea. The scientific motivations of the study are (1) to document glacial landforms on a meter-scale, (2) to study ... -
Cenozoic tectonostratigraphy and pre-glacial erosion: A mass-balance study of the northwestern Barents Sea margin
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-03-26)<p>The evolution of the northwestern Barents Sea continental margin, part of a NW-SE trending mega shear zone, has been reconstructed in order to quantify the sedimentation and erosion affecting this area during and after its formation in the Paleogene–Neogene. This development was closely related to the sea-floor opening of the Norwegian-Greenland Sea. Our study incorporated 2D seismic data, well ... -
Emulating sentinel-1 Doppler radial ice drift measurements using envisat ASAR data
(Journal article; Tidsskriftartikkel; Peer reviewed, 2015-08-05)Using data from the Envisat Advanced Synthetic Aperture Radar (ASAR) instrument, this paper demonstrates how the high-precision radial surface velocity product, which will become available with the European Space Agency's Sentinel-1 satellite, can complement the analysis of sea ice motion. High-resolution Doppler frequency measurements are used to estimate the subsecond line-of-sight motion of ... -
Relating 3D surface displacement from satellite- and ground-based InSAR to structures and geomorphology of the Jettan rockslide, northern Norway
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-12-13)This study combines remote sensing data from ground- and satellite-based radar to calculate 3D displacement vectors for the Jettan rockslide, Troms, northern Norway. Using 3D displacement vectors, aspect data and strain rates in conjunction with structure (foliation, faults, fractures), geomorphological elements (ridges, scarps, terraces, depressions), topography and borehole data, we identify zones ... -
Interplay of twist angle and solvents with two-photon optical channel interference in aryl-substituted BODIPY dyes
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-10-11)Channel interference plays a crucial role in understanding the physics behind multiphoton absorption processes. In this work, we study the role of channel interference and solvent effects on the two-photon absorption in aryl-substituted boron dipyrromethene (BODIPY) dyes, a class of intramolecular charge-transfer (ICT) molecules. For this purpose, we consider fourteen dyes of this class with various ... -
The Elephant in the Room of Density Functional Theory Calculations
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-03-14)Using multiwavelets, we have obtained total energies and corresponding atomization energies for the GGA-PBE and hybrid-PBE0 density functionals for a test set of 211 molecules with an unprecedented and guaranteed μHartree accuracy. These quasi-exact references allow us to quantify the accuracy of standard all-electron basis sets that are believed to be highly accurate for molecules, such as Gaussian-type ... -
One electron changes the entire story: NMR versus pNMR
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-11-28)<sup>11</sup>B NMR chemical shifts of structurally similar diamagnetic and paramagnetic molecules are obtained using four-component relativistic DFT calculations. The calculated chemical shifts of the diamagnetic molecules are compared with those of the paramagnetic molecules to get an insight on the influence of the unpaired electron on the <sup>11</sup>B chemical shifts. -
The gap phenomenon in parabolic geometries
(Journal article; Tidsskriftartikkel; Peer reviewed, 2014-09-14)The infinitesimal symmetry algebra of any Cartan geometry has maximum dimension realized by the flat model, but often this dimension drops significantly when considering non-flat geometries, so a gap phenomenon arises. For general (regular, normal) parabolic geometries of type (G,P), we use Tanaka theory to derive a universal upper bound on the submaximal symmetry dimension. We use Kostant’s version ... -
Paleoceanographic development in Storfjorden, Svalbard, during the deglaciation and Holocene: evidence from benthic foraminiferal records
(Journal article; Tidsskriftartikkel; Peer reviewed, 2014-08-07)Brines can have a profound influence on the relative abundance of calcareous and agglutinated foraminiferal faunas. Here we investigated the distribution of benthic foraminiferal species in four cores from a brine‐enriched environment in Storfjorden, Svalbard. Stratigraphically, the cores comprise the last 15 000 years. The purpose of the study was to reconstruct changes in the palaeoecology and ... -
3D Seismic Investigation of a Gas Hydrate and Fluid Flow System on an Active Mid‐Ocean Ridge; Svyatogor Ridge, Fram Strait
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-05-12)Tectonic settings play a large role in the development of fluid flow pathways for gas migrating through sedimentary strata. Many gas hydrate systems worldwide are located on either passive continental margins, in large contourite deposits on the slopes of passive continental margins or on subduction margins. The Svyatogor Ridge, however, located at the northwestern flank of the Knipovich Ridge and ... -
Retreat patterns and dynamics of the Sentralbankrenna glacial system, central Barents Sea
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-06-26)The Barents Sea Ice Sheet (BSIS) is a good palaeo-analogue for the present day West Antarctic Ice Sheet. Both were marine-based ice sheets, particularly vulnerable to ocean warming and sea-level rise. Understanding the BSIS ice dynamics and patterns of retreat since the Last Glacial Maximum (LGM) is useful in developing our knowledge of spatial and temporal variations during marine-based ice sheet ... -
Aldol condensations on a 3-alkylidene-2,5-diketopiperazine - synthesis of two marine natural products
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-06)The synthesis of two marine natural products containing a 3-alkylidene-6-arylidene-2,5-diketopiperazine scaffold by employing two consecutive aldol condensations starting with 1,4-diacetyl-2,5-diketopiperazine is reported. The target compounds contain a phenol or an imidazole group as aryl substituents, respectively, and suitable conditions for the aldol condensation of 1-acyl-3-alkylidene-2,5-dik ... -
Calculations of the EPR g-tensor using unrestricted two- and four-component relativistic approaches within the HF and DFT frameworks
(Journal article; Tidsskriftartikkel; Peer reviewed, 2016-06-08)Approaches and programs for calculations of the EPR g-tensor in the framework of the two- and four-component methods are still very rare. There are three main reasons for this: the wider community's unawareness of the importance of second- and higher order spin–orbit effects on the g-tensor, the methodological problems associated with performing such calculations and the lack of understanding of ... -
Large subglacial meltwater features in the central Barents Sea
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-02-01)During the last glacial period large parts of the Arctic, including the Barents Sea, north of Norway and Russia, were covered by ice sheets. Despite several studies indicating that melting occurred beneath much of the Barents Sea ice sheet, very few meltwater-related landforms have been identified. We document ∼200 seafloor valleys in the central Barents Sea and interpret them to be tunnel valleys ... -
High frequency copolymer ultrasonic transducer array of size-effective elements
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-01-05)A layer-by-layer deposition method for producing dual-layer ultrasonic transducers from piezoelectric copolymers has been developed. The method uses a combination of customized and standard processing to obtain 2D array transducers with electrical connection of the individual elements routed directly to the rear of the substrate. A numerical model was implemented to study basic parameters effecting ... -
Efficient disease detection in gastrointestinal videos – global features versus neural networks
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-07-19)Analysis of medical videos from the human gastrointestinal (GI) tract for detection and localization of abnormalities like lesions and diseases requires both high precision and recall. Additionally, it is important to support efficient, real-time processing for live feedback during (i) standard colonoscopies and (ii) scalability for massive population-based screening, which we conjecture can be done ...