Nye registreringer

  • 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 ...
  • An integrated seismic and well data study of shallow fluid accumulations in Snøhvit, SW Barents Sea 

    Arntzen, Andreas (Master thesis; Mastergradsoppgave, 2018-07-12)
    In the vicinity of the Snøhvit hydrocarbon reservoir in the Hammerfest Basin a number of fluid flow phenomena occur, e.g. free gas accumulations, pockmarks and potential indicators of gas hydrates.The presence of shallow gas may cause major blowouts during drilling. To reduce the risk, it is important to locate the shallow gas and gas hydrates. CO2 has been injected into the Snøhvit reservoir since ...
  • Iceberg Drift-Trajectory Modelling and Probability Distributions of the Predictions 

    Baadshaug, Ole (Master thesis; Mastergradsoppgave, 2018-06-29)
    Moving icebergs represent a major problem for shipping, as well as for oil and gas installations in ice infested waters. To be able to take actions against hazardous icebergs, it is necessary to develop models for prediction of iceberg drift trajectories. Many models have been developed in order to do so, using different approaches. These approaches can be divided into two main categories, dynamic ...
  • Kara-Siberian sea ice anomaly and its impact on the atmosphere 

    Balafkan, Nozhan (Master thesis; Mastergradsoppgave, 2018-05-15)
    The behavior of the autumn and winter weather pattern over Europe and Eurasia was investigated during two periods of high and low ice concentration in September over the Kara-Siberian sea. A statistically significant anomalous energy flux from the east Siberian sea to the atmosphere was detected during October of low ice years. Furthermore, an anomalous behavior in the atmospheric circulation was ...
  • 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 ...
  • Angle Dependent Reflectance and Performance of Solar Cells and Absorbers 

    Jordheim, Øystein (Master thesis; Mastergradsoppgave, 2018-05-14)
    In this thesis, the reflectance was measured for angles from 10 deg to 80 deg for different n-type silicon based solar cells and for solar absorbers. The measurements were done with unpolarized, p polarized and s polarized light. The reflectance results show that both the solar cells and solar absorbers perform well under small variation from perpendicular angle well but as the angle of incidence ...
  • Uncertainty Modeling and Interpretability in Convolutional Neural Networks for Polyp Segmentation. 

    Wickstrøm, Kristoffer Knutsen (Master thesis; Mastergradsoppgave, 2018-05-14)
    Colorectal cancer is one of the leading causes of cancer-related deaths worldwide, with prevention commonly done through regular colonoscopy screenings. During a colonoscopy, physicians manually inspect the colon of a patient using a camera in search for polyps, which are known to be possible precursors to colorectal cancer. Seeing that a colonoscopy is a manual procedure, it can be susceptible to ...
  • Temperature and thermal emission of cosmic dust around the Sun, Vega and Fomalhaut 

    Myrvang, Margaretha (Master thesis; Mastergradsoppgave, 2018-05-14)
    Many stars are known to have dust disks, which are created through collisions between planetesimals, comparable to comets and asteroids in our solar system. Cosmic dust around a star absorbs electromagnetic radiation and re-radiates at a longer wavelength, determined by its temperature. The thermal emission of the dust can be observed. In certain systems, including the solar system, some of the dust ...

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