Viser treff 401-420 av 1276

    • First dust measurements with the Solar Orbiter Radio and plasma wave instrument 

      Zaslavsky, A.; Mann, I.; Soucek, J.; Czechowski, A.; Píša, D.; Vaverka, J.; Meyer-Vernet, N.; Maksimovic, M.; Lorfèvre, E.; Issautier, K.; Rackovic Babic, K.; Bale, S.D.; Morooka, M.; Vecchio, A.; Chust, T.; Khotyaintsev, Y.; Krasnoselskikh, V.; Kretzschmar, M.; Plettemeier, D.; Steller, M.; Štverák, Š; Trávnícek, P.; Vaivads, A. (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-12-14)
      Context - Impacts of dust grains on spacecraft are known to produce typical impulsive signals in the voltage waveform recorded at the terminals of electric antennas. Such signals (as may be expected) are routinely detected by the Time Domain Sampler (TDS) system of the Radio and Plasma Waves (RPW) instrument on board Solar Orbiter.<p> <p>Aims - We investigate the capabilities of RPW in terms of ...
    • Dynamics of nanodust in the vicinity of a stellar corona: Effect of plasma corotation 

      Czechowski, Andrzej; Mann, Ingrid (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-08-24)
      Context - In the vicinity of the Sun or other stars, the motion of the coronal and stellar wind plasma must include some amount of corotation, which could affect the dynamics of charged dust particles. In the case of the Sun, this region is now investigated in situ by the Parker Solar Probe. Charged dust particles coming from the vicinity of the Sun can also reach, and possibly be detected by, ...
    • Endocytic motif on a biotin-tagged hiv-1 env modulates the co-transfer of env and gag during cell-to-cell transmission 

      Barría, María Inés; Alvarez, Raymond A.; Law, Kenneth; Wolfson, Deanna; Huser, Thomas; Chen, Benjamin K. (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-08-31)
      During HIV-1 transmission through T cell virological synapses, the recruitment of the envelope (Env) glycoprotein to the site of cell–cell contact is important for adhesion and for packaging onto nascent virus particles which assemble at the site. Live imaging studies in CD4 T cells have captured the rapid recruitment of the viral structural protein Gag to VSs. We explored the role of endocytic ...
    • Charged dust in the D-region incoherent scatter spectrum 

      Gunnarsdottir, Tinna L.; Mann, Ingrid (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-09-14)
      We investigate the influence of charged dust on the incoherent scatter from the D-region ionosphere. Incoherent scatter is observed with high-power, large aperture radars and results from electromagnetic waves scattering at electrons that are coupled to other charged components through plasma oscillations. The influence of charged dust can hence be considered an effect of dusty plasma. The D-region ...
    • Towards automatic detection of dark features in the Barents Sea using synthetic aperture radar 

      Cristea, Anca; Johansson, Malin; Filimonova, Natalya A.; Ivonin, Dmitry; Hughes, Nick; Doulgeris, Anthony Paul; Brekke, Camilla (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-02-17)
      Increased human presence and commercial activities in the Barents Sea (fishing, offshore oil and gas exploration) are amplifying the need for large-scale operational ocean monitoring of the eventual oil spills in the region. The geographical location and climate impose additional constraints on satellite-based monitoring, making it necessary to use Synthetic Aperture Radar (SAR). Dark features or ...
    • A comparison of contact charging and impact ionization in low-velocity impacts: implications for dust detection in space 

      Antonsen, Tarjei; Mann, Ingrid; Vaverka, Jakub; Nouzák, Libor; Fredriksen, Åshild (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-06-15)
      We investigate the generation of charge due to collision between projectiles with sizes below ∼1 µm and metal surfaces at speeds ∼0.1 to 10 km s<sup>−1</sup>. This corresponds to speeds above the elastic limit and well below speeds where volume ionization can occur. Impact charge production at these low to intermediate speeds has traditionally been described by invoking the theory of shock wave ...
    • Ion Cloud Expansion after Hypervelocity Dust Impacts Detected by the MMS Electric Probes in the Dipole Configuration 

      Vaverka, Jakub; Pavlů, Jiří; Nouzak, Libor; Šafránková, Jana; Nemecek, Sdenek; Antonsen, Tarjei; Mann, Ingrid; Lindqvist, Per-Arne (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-11-08)
      Dust impact detection by electric field instruments is a well-established technique. On the other hand, not all aspects of signal generation by dust impacts are completely understood. We present a study of events related to dust impacts on the spacecraft body detected by electric field probes operating simultaneously in the monopole (probe-to-spacecraft potential measurement) and dipole (probe-to-probe ...
    • What is going on with Middle Eastern solar prices, and what does it mean for the rest of us? 

      Apostoleris, Harry; Al Ghaferi, Amal; Chiesa, Matteo (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-03-04)
      For the third time in a decade, solar energy pricing records are tumbling in the Persian Gulf. As each previous wave of new records was met with incredulity, only for these prices to become the new normal around the world within a few years, it would be unwise to once again dismiss low prices as unrepresentative outliers. In this study, we show how local conditions and global macroeconomic factors ...
    • Integrated nanophotonic waveguide-based devices for IR and Raman gas spectroscopy 

      Alberti, Sebastian; Datta, Anurup; Jágerská, Jana (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-10-30)
      On-chip devices for absorption spectroscopy and Raman spectroscopy have been developing rapidly in the last few years, triggered by the growing availability of compact and affordable tunable lasers, detectors, and on-chip spectrometers. Material processing that is compatible with mass production has been proven to be capable of long low-loss waveguides of sophisticated designs, which are indispensable ...
    • A Multimodal Feature Selection Method for Remote Sensing Data Analysis Based on Double Graph Laplacian Diagonalization 

      Khachatrian, Eduard; Chlaily, Saloua; Eltoft, Torbjørn; Marinoni, Andrea (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-11-13)
      When dealing with multivariate remotely sensed records collected by multiple sensors, an accurate selection of information at the data, feature, or decision level is instrumental in improving the scenes’ characterization. This will also enhance the system’s efficiency and provide more details on modeling the physical phenomena occurring on the Earth’s surface. In this article, we introduce a flexible ...
    • On the applicability of Taylor's hypothesis, including small sampling velocities 

      Pécseli, Hans L; Trulsen, Jan Karsten (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-12-03)
      Taylor's hypothesis, or the frozen turbulence approximation, can be used to estimate also the specific energy dissipation rate ϵ by comparing experimental results with the Kolmogorov–Obukhov expression. The hypothesis assumes that a frequency detected by an instrument moving with a constant large velocity <i><b>V</i></b> can be related to a wavenumber by <i><b>ω=kV</i></b>. It is, however, not obvious ...
    • Automatic Selection of Relevant Attributes for Multi-Sensor Remote Sensing Analysis: A Case Study on Sea Ice Classification 

      Khachatrian, Eduard; Chlaily, Saloua; Eltoft, Torbjørn; Dierking, Wolfgang Fritz Otto; Dinessen, Frode; Marinoni, Andrea (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-07-26)
      It is of considerable benefit to combine information obtained from different satellite sensors to achieve advanced and improved characterization of sea ice conditions. However, it is also true that not all the information is relevant. It may be redundant, corrupted, or unnecessary for the given task, hence decreasing the performance of the algorithms. Therefore, it is crucial to select an optimal ...
    • Planetary radar science case for EISCAT 3D 

      Tveito, Torbjørn; Vierinen, Juha; Gustavsson, Björn Johan; Narayanan, Viswanathan Lakshmi (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-05-12)
      Ground-based inverse synthetic aperture radar is a tool that can provide insights into the early history and formative processes of planetary bodies in the inner solar system. This information is gathered by measuring the scattering matrix of the target body, providing composite information about the physical structure and chemical makeup of its surface and subsurface down to the penetration ...
    • The CPV “toolbox”: New approaches to maximizing solar resource utilization with application-oriented concentrator photovoltaics 

      Apostoleris, Harry; Stefancich, Marco; Chiesa, Matteo (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-02-03)
      As the scaling of silicon PV cells and module manufacturing has driven solar energy penetration up and costs down, concentrator photovoltaic technologies, originally conceived as a cost-saving measure, have largely been left behind. The loss of market share by CPV is being locked in even as solar energy development encounters significant obstacles related to space constraints in many parts of ...
    • Multiresolution Dynamic Mode Decomposition (mrDMD) of Elastic Waves for Damage Localisation in Piezoelectric Ceramic 

      Kalimullah, Nur M. M.; Shelke, Amit; Habib, Anowarul (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-08-27)
      The performance of piezoelectric sensors deteriorated due to the presence of defect, delamination, and corrosion that needed to be diagnosed for the effective implementation of the structural health monitoring (SHM) framework. A novel experimental approach based on Coulomb coupling is devised to visualise the interaction of ultrasonic waves with microscale defects in the Lead Zirconate Titanate (PZT). ...
    • Monitoring a changing Arctic: Recent advancements in the study of sea ice microbial communities 

      Matero, Ilkka; Bellas, Christopher; Turpin-Jelfs, Thomas; Anhaus, Philipp; Graeve, Martin; Fripiat, Francois; Tranter, Martyn; Landy, Jack Christopher; Sanchez-Baracaldo, Patricia; Leu, Eva; Katlein, Christian; Mundy, C.J.; Rysgaard, Søren; Tedesco, Letizia; Haas, Christian; Nicolaus, Marcel (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-11-25)
      Sea ice continues to decline across many regions of the Arctic, with remaining ice becoming increasingly younger and more dynamic. These changes alter the habitats of microbial life that live within the sea ice, which support healthy functioning of the marine ecosystem and provision of resources for human-consumption, in addition to influencing biogeochemical cycles (e.g. air–sea CO2 exchange). With ...
    • Surface-based Ku-and Ka-band polarimetric radar for sea ice studies 

      Stroeve, Julienne C.; Nandan, Vishnu; Willatt, Rosemary; Tonboe, Rasmus; Hendricks, Stefan; Ricker, Robert; Mead, James; Mallett, Robbie; Huntemann, Marcus; Itkin, Polona; Schneebeli, Martin; Krampe, Daniela; Spreen, Gunnar; Wilkinson, Jeremy; Matero, Ilkka; Hoppmann, Mario; Tsamados, Michel (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-12-04)
      To improve our understanding of how snow properties influence sea ice thickness retrievals from presently operational and upcoming satellite radar altimeter missions, as well as to investigate the potential for combining dual frequencies to simultaneously map snow depth and sea ice thickness, a new, surface-based, fully polarimetric Ku- and Ka-band radar (KuKa radar) was built and deployed ...
    • A Theoretical Analysis of Deep Neural Networks and Parametric PDEs 

      Kutyniok, Gitta Astrid Hildegard; Petersen, Philipp; Raslan, Mones; Schneider, Reinhold (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-06-02)
      We derive upper bounds on the complexity of ReLU neural networks approximating the solution maps of parametric partial differential equations. In particular, without any knowledge of its concrete shape, we use the inherent low dimensionality of the solution manifold to obtain approximation rates which are significantly superior to those provided by classical neural network approximation results. ...
    • Self-Constructing Graph Convolutional Networks for Semantic Labeling 

      Liu, Qinghui; Kampffmeyer, Michael; Jenssen, Robert; Salberg, Arnt-Børre (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-02-17)
      Graph Neural Networks (GNNs) have received increasing attention in many fields. However, due to the lack of prior graphs, their use for semantic labeling has been limited. Here, we propose a novel architecture called the Self-Constructing Graph (SCG), which makes use of learnable latent variables to generate embeddings and to self-construct the underlying graphs directly from the input features ...
    • Multi-View Self-Constructing Graph Convolutional Networks With Adaptive Class Weighting Loss for Semantic Segmentation 

      Liu, Qinghui; Kampffmeyer, Michael; Jenssen, Robert; Salberg, Arnt Børre (Conference object; Konferansebidrag, 2020-07-28)
      We propose a novel architecture called the Multi-view Self-Constructing Graph Convolutional Networks (MSCG-Net) for semantic segmentation. Building on the recently proposed Self-Constructing Graph (SCG) module, which makes use of learnable latent variables to self-construct the underlying graphs directly from the input features without relying on manually built prior knowledge graphs, we leverage ...