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norskFakultet for naturvitenskap og teknologi
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Challenges and Strategic Research Plans for Earth and Heliosphere: Research Infrastructures, Projects and Initiatives
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-07-24)We describe existing research infrastructures relevant for space weather and open issues of space weather research including the need for sustainable observation networks and for high-quality data products as basis for model development. The local relevance in Europe for studies of the ionosphere at high latitude is described. We propose as possible a way forward to sustain space weather research ... -
The configuration, sensitivity and rapid retreat of the Late Weichselian Icelandic ice sheet
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-02-03)The fragmentary glacial-geological record across the Icelandic continental shelf has hampered reconstruction of the volume, extent and chronology of the Late Weichselian ice sheet particularly in key offshore zones. Marine geophysical data collected over the last two decades reveal that the ice sheet likely attained a continental shelf-break position in all sectors during the Last Glacial Maximum, ... -
A Theoretical Model of Drumlin Formation Based on Observations at Múlajökull, Iceland
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-11-20)The drumlin field at the surge‐type glacier, Múlajökull, provides an unusual opportunity to build a model of drumlin formation based on field observations in a modern drumlin‐forming environment. These observations indicate that surges deposit till layers that drape the glacier forefield, conform to drumlin surfaces, and are deposited in shear. Observations also indicate that erosion helps create ... -
Deep kernelized autoencoders
(Peer reviewed; Book; Chapter, 2017-05-19)In this paper we introduce the deep kernelized autoencoder, a neural network model that allows an explicit approximation of (i) the mapping from an input space to an arbitrary, user-specified kernel space and (ii) the back-projection from such a kernel space to input space. The proposed method is based on traditional autoencoders and is trained through a new unsupervised loss function. ... -
Range-Doppler Mapping of Space-Based Targets Using the JRO 50 MHz Radar
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-12-02)The Jicamarca Radio Observatory (JRO) two-dimensional square array radar system operating at ~ 6-m wavelength was used to study the Moon and low Earth orbit satellites using the Range-Doppler inverse synthetic aperture radar technique also known as Delay-Doppler imaging. The radar data was collected on Oct 21, 2015. A circularly polarized coded pulse was transmitted from a quarter-array antenna ... -
Relationship between frequency power spectra and intermittent, large-amplitude bursts in the Alcator C-Mod scrape-off layer
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-08-21)Fluctuations in the boundary region of the Alcator C-Mod tokamak have been analyzed using gas puff imaging data from a set of Ohmically heated plasma density scan experiments. It is found that the relative fluctuation amplitudes are modest and close to normally distributed at the separatrix but become increasingly larger and skewed towards the main chamber wall. The frequency power spectra are ... -
Modeled deposition of nitrogen and sulfur in Europe estimated by 14 air quality model systems: evaluation, effects of changes in emissions and implications for habitat protection
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-07-17)<p>The evaluation and intercomparison of air quality models is key to reducing model errors and uncertainty. The projects AQMEII3 and EURODELTA-Trends, in the framework of the Task Force on Hemispheric Transport of Air Pollutants and the Task Force on Measurements and Modelling, respectively (both task forces under the UNECE Convention on the Long Range Transport of Air Pollution, LTRAP), have brought ... -
Advancing relativistic electronic structure methods for solids and in the time domain
(Doctoral thesis; Doktorgradsavhandling, 2018-08-28)Effects arising from the special theory of relativity significantly influence the electronic structure and properties of molecules and solid-state materials containing heavy elements. At the same time, the inclusion of the relativistic effects in theoretical and computational models increases their methodological complexity and the computational cost. In the solid state, additional challenges ... -
Structural glaciology of Isunguata Sermia, West Greenland
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-08-26)We present a 1:42,000 scale map of Isunguata Sermia, a land-terminating outlet glacier draining the western-sector of the Greenland Ice Sheet. Structure-from-Motion software applied to ∼3,600 aerial images collected by a fixed-wing unmanned aerial vehicle in July 2015 allowed us to produce a high resolution (0.3 m ground sampling distance (GSD)) orthomosaic and digital elevation model (DEM; 1.5 m ... -
BedMachine v3: Complete bed topography and ocean bathymetry mapping of Greenland from multi-beam echo sounding combined with mass conservation
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-09-18)Greenland's bed topography is a primary control on ice flow, grounding line migration, calving dynamics, and subglacial drainage. Moreover, fjord bathymetry regulates the penetration of warm Atlantic water (AW) that rapidly melts and undercuts Greenland's marine‐terminating glaciers. Here we present a new compilation of Greenland bed topography that assimilates seafloor bathymetry and ice thickness ... -
Robust clustering using a kNN mode seeking ensemble
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-12-02)In this paper we present a new algorithm for parameter-free clustering by mode seeking. Mode seeking, especially in the form of the mean shift algorithm, is a widely used strategy for clustering data, but at the same time prone to poor performance if the parameters are not chosen correctly. We propose to form a <i>clustering ensemble</i> consisting of repeated and bootstrapped runs of the recent kNN ... -
Enantioselective incorporation of CO2: status and potential
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-09-09)CO<sub>2</sub> is a promising and sustainable carbon feedstock for organic synthesis. New catalytic protocols for efficient incorporation of CO<sub>2</sub>into organic molecules are continuously being reported. However, little progress has been made in the enantioselective conversion of CO<sub>2</sub>to form enantioenriched molecules. In order to allow CO<sub>2</sub>to become a versatile carbon ... -
Direct measurements of meltwater runoff on the Greenland ice sheet surface
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-12-05)Meltwater runoff from the Greenland ice sheet surface influences surface mass balance (SMB), ice dynamics, and global sea level rise, but is estimated with climate models and thus difficult to validate. We present a way to measure ice surface runoff directly, from hourly in situ supraglacial river discharge measurements and simultaneous high-resolution satellite/drone remote sensing of upstream ... -
New ways of looking at very small holes – using optical nanoscopy to visualize liver sinusoidal endothelial cell fenestrations
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018-01-10)Super-resolution fluorescence microscopy, also known as nanoscopy, has provided us with a glimpse of future impacts on cell biology. Far-field optical nanoscopy allows, for the first time, the study of sub-cellular nanoscale biological structures in living cells, which in the past was limited to electron microscopy (EM) (in fixed/dehydrated) cells or tissues. Nanoscopy has particular utility in the ... -
KAIRA - The Kilpisjärvi Atmospheric Imaging Receiver Array
(Doctoral thesis; Doktorgradsavhandling, 2018-08-24)The Kilpisjärvi Atmospheric Imaging Receiver Array (KAIRA) is a phased-array radio detector located in Arctic Finland, where auroral electron precipitation is common. This unique deployment of a modern radio telescope in an unconventional location has resulted in a novel and powerful instrument capable of carrying out a large variety of remote-sensing, geoscience experiments. This work presents a ... -
Data-driven detrending of nonstationary fractal time series with echo state networks
(Journal article; Tidsskriftartikkel, 2016-12-14)In this paper, we propose a novel data-driven approach for removing trends (detrending) from nonstationary, fractal and multifractal time series. We consider real-valued time series relative to measurements of an underlying dynamical system that evolves through time. We assume that such a dynamical process is predictable to a certain degree by means of a class of recurrent networks called Echo ... -
Late Pliocene–early Pleistocene deep-sea basin sedimentation at high-latitudes: mega-scale submarine slides of the north-western Barents Sea margin prior to the shelf-edge glaciations
(Journal article; Tidsskriftartikkel; Peer reviewed, 2015-10-01)At high‐latitude continental margins, large‐scale submarine sliding has been an important process for deep‐sea sediment transfer during glacial and interglacial periods. Little is, however, known about the importance of this process prior to the arrival of the ice sheet on the continental shelf. Based on new two‐dimensional seismic data from the NW Barents Sea continental margin, this study documents ... -
Interstellar Interloper 1I/2017 U1: Observations from the NOT and WIYN Telescopes
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-11-30)We present observations of the interstellar interloper 1I/2017 U1 ('Oumuamua) taken during its 2017 October flyby of Earth. The optical colors B – V = 0.70 ± 0.06, V – R = 0.45 ± 0.05, overlap those of the D-type Jovian Trojan asteroids and are incompatible with the ultrared objects that are abundant in the Kuiper Belt. With a mean absolute magnitude <i>H <sub>V</sub></i> = 22.95 and assuming a ... -
Octaiodoporphyrin and Octaiodocorrole: Isolation of a Cis Porphyrin Tautomer
(Doctoral thesis; Doktorgradsavhandling, 2018-09-28)Iodinated aromatics are excellent starting materials for further elaboration via transition-metal-catalyzed cross-coupling reactions. Considering the diverse applications of porphyrins and corroles - as photosensitizers in photodynamic therapy, dye sensitized solar cells, near-infrared dyes, gas sensors, nonlinear optical materials, and catalysts - the synthetic potential of β-polyiodinated or ... -
On the symmetry algebras of 5-dimensional CR-manifolds
(Journal article; Tidsskriftartikkel; Peer reviewed, 2017-11-13)We show that for a real-analytic connected holomorphically nondegenerate 5-dimensional CR-hypersurface <i>M</i> and its symmetry algebra <i>s</i> one has either: (i) dim <i>s</i> = 15 and <i>M</i> is spherical (with Levi form of signature either (2,0), or (1,1), everywhere), or (ii) dim <i>s</i> ≤ 11 where dim <i>s</i> = 11 can only occur if on a dense open subset <i>M</i> is spherical with Levi ...
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