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  • Light and photosynthetic microalgae: A review of cellular- and molecular-scale optical processes 

    Lehmuskero, Anni Maria; Chauton, Matilde Skogen; Boström, Tobias (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-09-08)
    Light and its interaction with microalgae are essential concerns in the context of microalgae studies. The optical properties of microalgae have a great impact on the remote sensing ocean color, underwater light distribution and biomass accumulation, to mention some areas. A deep understanding of these processes requires knowledge on both the physical light interaction mechanisms with algae, and ...
  • Comets as a possible source of nanodust in the Solar System cloud and in planetary debris discs 

    Mann, Ingrid (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-05-29)
    Comets, comet-like objects and their fragments are the most plausible source for the dust in both the inner heliosphere and planetary debris discs around other stars. The smallest size of dust particles in debris discs is not known and recent observational results suggest that the size distribution of the dust extends down to sizes of a few nanometres or a few tens of nanometres. In the Solar System, ...
  • Challenges and Strategic Research Plans for Earth and Heliosphere: Research Infrastructures, Projects and Initiatives 

    Mann, Ingrid; Kauristie, Kirsti; Bamford, Ruth; McCrea, Ian; Moen, Jøran Idar; Oksavik, Kjellmar; Yamauchi, Masanori; Johnsen, Magnar Gullikstad; Turunen, Esa (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 ...
  • Deep kernelized autoencoders 

    Kampffmeyer, Michael C.; Løkse, Sigurd; Bianchi, Filippo Maria; Jenssen, Robert; Livi, Lorenzo (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 

    Kesaraju, Saiveena; Mathews, J. D.; Milla, M.; Vierinen, Juha (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 

    Theodorsen, Audun; Garcia, Odd Erik; Kube, Ralph; LaBombard, Brian; Terry, Jim L. (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 ...
  • New ways of looking at very small holes – using optical nanoscopy to visualize liver sinusoidal endothelial cell fenestrations 

    Øie, Cristina Ionica; Mönkemöller, Viola; Hübner, Wolfgang; Schüttpelz, Mark; Mao, Hong; Ahluwalia, Balpreet Singh; Huser, Thomas Rolf; McCourt, Peter Anthony (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 ...
  • Data-driven detrending of nonstationary fractal time series with echo state networks 

    Maiorino, Enrico; Bianchi, Filippo Maria; Livi, Lorenzo; Rizzi, Antonello; Sadeghian, Alireza (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 ...
  • Interstellar Interloper 1I/2017 U1: Observations from the NOT and WIYN Telescopes 

    Jewitt, David; Luu, Jane; Rajagopal, Jayadev; Kotulla, Ralf; Ridgway, Susan; Liu, Wilson; Augusteijn, Thomas (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 ...
  • Spectral clustering using PCKID – A probabilistic cluster kernel for incomplete data 

    Løkse, Sigurd; Bianchi, Filippo Maria; Salberg, Arnt-Børre; Jenssen, Robert (Journal article; Tidsskriftartikkel; Peer reviewed; Preprint, 2017-05-19)
    In this paper, we propose <i>PCKID</i>, a novel, robust, kernel function for spectral clustering, specifically designed to handle incomplete data. By combining posterior distributions of Gaussian Mixture Models for incomplete data on different scales, we are able to learn a kernel for incomplete data that does not depend on any critical hyperparameters, unlike the commonly used RBF kernel. To evaluate ...
  • Statistical properties of a filtered Poisson process with additive random noise: distributions, correlations and moment estimation 

    Theodorsen, Audun; Garcia, Odd Erik; Rypdal, Martin Wibe (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-04-19)
    Filtered Poisson processes are often used as reference models for intermittent fluctuations in physical systems. Such a process is here extended by adding a noise term, either as a purely additive term to the process or as a dynamical term in a stochastic differential equation. The lowest order moments, probability density function, auto-correlation function and power spectral density are derived ...
  • The Science of Sungrazers, Sunskirters, and Other Near-Sun Comets 

    Jones, Geraint; Knight, Matthew; Battams, Karl; Boice, Daniel; Brown, John; Giordano, Silvio; Raymond, John; Snodgrass, Colin; Steckloff, Jordan; Weissman, Paul; Fitzsimmons, Alan; Lisse, Carey M; Opitom, Cyrielle; Birkett, Kimberley; Bzowski, Maciej; Decock, Alice; Mann, Ingrid; Ramanjooloo, Yudish; McCauley, Patrick (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-12-18)
    This review addresses our current understanding of comets that venture close to the Sun, and are hence exposed to much more extreme conditions than comets that are typically studied from Earth. The extreme solar heating and plasma environments that these objects encounter change many aspects of their behaviour, thus yielding valuable information on both the comets themselves that complements other ...
  • Dynamics of nanodust particles emitted from elongated initial orbits 

    Czechowski, Andrzej; Mann, Ingrid (Journal article; Tidsskriftartikkel; Peer reviewed, 2018)
    <p><i>Context</i>: Because of high charge-to-mass ratio, the nanodust dynamics near the Sun is determined by interplay between the gravity and the electromagnetic forces. Depending on the point where it was created, a nanodust particle can either be trapped in a non-Keplerian orbit, or escape away from the Sun, reaching large velocity. The main source of nanodust is collisional fragmentation of ...
  • Analysis of evolving oil spills in full-polarimetric and hybrid-polarity SAR 

    Espeseth, Martine Mostervik; Skrunes, Stine; Jones, Cathleen Elaine; Brekke, Camilla; Holt, Benjamin; Doulgeris, Anthony Paul (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-04-25)
    Oil spill detection using a time series of images acquired off Norway in June 2015 with the uninhabited aerial vehicle synthetic aperture radar is examined. The relative performance of a set of features derived from quad-polarization versus hybrid-polarity (HP) modes in detection of various types of slicks as they evolve on a high wind driven sea surface is evaluated. It is shown that the HP mode ...
  • Can we extend local sea-ice measurements to satellite scale? An example from the N-ICE2015 expedition 

    Rösel, Anja; King, Jennifer; Doulgeris, Anthony P.; Wagner, Penelope M.; Johansson, Malin; Gerland, Sebastian (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-12-17)
    Knowledge of Arctic sea-ice conditions is of great interest for Arctic residents, as well as for commercial usage, and to study the effects of climate change. Information gained from analysis of satellite data contributes to this understanding. In the course of using in situ data in combination with remotely sensed data, the question of how representative local scale measurements are of a wider ...
  • An objective global climatology of polar lows based on reanalysis data 

    Stoll, Patrick; Graversen, Rune; Noer, Gunnar; Hodges, Kevin (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-04-16)
    Here we present an objective global climatology of polar lows. In order to obtain objective detection criteria, the efficacy of several parameters for separating polar lows from other cyclones has been compared. The comparison and the climatology are based on the ERA‐Interim reanalysis from 1979 ‐ 2016 and the high‐resolution Arctic System Reanalysis from 2000 ‐ 2012. The most effective parameters ...
  • Emulating sentinel-1 Doppler radial ice drift measurements using envisat ASAR data 

    Kræmer, Thomas; Johnsen, Harald; Brekke, Camilla (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 ...
  • High frequency copolymer ultrasonic transducer array of size-effective elements 

    Decharat, Adit; Wagle, Sanat; Habib, Anowarul; Jacobsen, Svein Ketil; Melandsø, Frank (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 ...
  • Poleward energy transport: is the standard definition physically relevant at all time scales? 

    Liang, Minyi; Czaja, Arnaud; Graversen, Rune; Tailleux, Remi (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-05-17)
    Poleward energy transport in the atmosphere and oceans constitutes an important branch of the global energy budget, and its role in the climate system has been the subject of many studies. In the atmosphere, the transport is affected by “eddies” and large scale meridional cells, both with zero net mass transport across latitude circles, but also partly by processes associated with a net transport ...
  • Accurate estimation of the illumination pattern’s orientation and wavelength in sinusoidal structured illumination microscopy 

    Lahrberg, Marcel; Singh, Mandeep; Khare, Kedar; Ahluwalia, Balpreet Singh (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-01-05)
    Structured illumination microscopy is able to improve the spatial resolution of wide-field fluorescence imaging by applying sinusoidal stripe pattern illumination to the sample. The corresponding computational image reconstruction requires precise knowledge of the pattern’s parameters, which are its phase (φ) and wave vector (<b>p</b>). Here, a computationally inexpensive method for estimation of ...

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