Browsing by Department "University of Tokyo"

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  • Cometary plasma science: Open science questions for future space missions
    (2021) Goetz, C.; Gunell, H.; Volwerk, M.; Beth, A.; Eriksson, A.; Galand, M.; Henri, P.; Nilsson, H.; Wedlund, C. Simon; Alho, M.; Andersson, L.; Andre, N.; De Keyser, J.; Deca, J.; Ge, Y.; Glassmeier, K. H.; Hajra, R.; Karlsson, T.; Kasahara, S.; Kolmasova, I.; LLera, K.; Madanian, H.; Mann, I.; Mazelle, C.; Odelstad, E.; Plaschke, F.; Rubin, M.; Sanchez-Cano, B.; Snodgrass, C.; Vigren, E.
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Comets hold the key to the understanding of our Solar System, its formation and its evolution, and to the fundamental plasma processes at work both in it and beyond it. A comet nucleus emits gas as it is heated by the sunlight. The gas forms the coma, where it is ionised, becomes a plasma, and eventually interacts with the solar wind. Besides these neutral and ionised gases, the coma also contains dust grains, released from the comet nucleus. As a cometary atmosphere develops when the comet travels through the Solar System, large-scale structures, such as the plasma boundaries, develop and disappear, while at planets such large-scale structures are only accessible in their fully grown, quasi-steady state. In situ measurements at comets enable us to learn both how such large-scale structures are formed or reformed and how small-scale processes in the plasma affect the formation and properties of these large scale structures. Furthermore, a comet goes through a wide range of parameter regimes during its life cycle, where either collisional processes, involving neutrals and charged particles, or collisionless processes are at play, and might even compete in complicated transitional regimes. Thus a comet presents a unique opportunity to study this parameter space, from an asteroid-like to a Mars- and Venus-like interaction. The Rosetta mission and previous fast flybys of comets have together made many new discoveries, but the most important breakthroughs in the understanding of cometary plasmas are yet to come. The Comet Interceptor mission will provide a sample of multi-point measurements at a comet, setting the stage for a multi-spacecraft mission to accompany a comet on its journey through the Solar System. This White Paper, submitted in response to the European Space Agency’s Voyage 2050 call, reviews the present-day knowledge of cometary plasmas, discusses the many questions that remain unanswered, and outlines a multi-spacecraft European Space Agency mission to accompany a comet that will answer these questionsby combining both multi-spacecraft observations and a rendezvous mission, and at the same time advance our understanding of fundamental plasma physics and its role in planetary systems.
  • Continuous Metal-Organic Framework Biomineralization on Cellulose Nanocrystals
    (2019-03-18) Richardson, Joseph J.; Tardy, Blaise L.; Guo, Junling; Liang, Kang; Rojas, Orlando J.; Ejima, Hirotaka
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Growing metal-organic frameworks (MOFs) around biomolecules has recently emerged as a promising method to combine natural and synthetic materials. In parallel, cellulose nanocrystals (CNCs) have found use for forming a wide range of renewable nano- and macroscopic materials because of their bio-derived nature, high surface area, and high strength. Herein, we demonstrate the continuous nucleation of MOFs from the surface of CNCs, thereby forming hybrid hydrogels, aerogels, and porous assemblies that can be pre- or postloaded with functional cargo. With simple mixing of CNCs with MOF precursors, the biomineralization is initiated and takes place continuously where the MOFs simultaneously coat and cross-link the CNCs across a wide range of CNC and MOF precursor concentrations. Additionally, CNCs can be extruded into the premixed MOF precursors to yield CNC-MOF filaments that can be preloaded with functional enzymes or postloaded with small fluorophores. Overall, our approach enables the rapid structural control of functional composites promising for a range of applications.
  • The extreme HBL behaviour of Markarian 501 during 2012
    (2018-12) Ahnen, M. L.; Ansoldi, S.; Antonelli, L. A.; Arcaro, C.; Babić, A.; Banerjee, B.; Bangale, P.; Barres de Almeida, U.; Barrio, J.A.; Becerra-González, J.; Bednarek, W.; Bernardini, E.; Berti, A.; Bhattacharyya, W; Blanch, O.; Bonnoli, G.; Carosi, R.; Carosi, A.; Chatterjee, A; Colak, S M; Colin, P.; Colombo, E.; Contreras, J. L.; Cortina, J.; Covino, S.; Cumani, P; Da Vela, P.; Dazzi, F.; De Angelis, A; De Lotto, B.; Delfino, M; Delgado, J; Di Pierro, F.; Doert, M.; Domínguez, A.; Dominis Prester, D.; Doro, M.; Eisenacher Glawion, D.; Engelkemeier, M.; Fallah Ramazani, V.; Fernández-Barral, A.; Fidalgo, D.; Fonseca, M. V.; Font, L.; Fruck, C.; Galindo, D.; García López, R.J.; Garczarczyk, M.; Gaug, M.; Giammaria, P.; Godinović, N.; Gora, D.; Guberman, D.; Hadasch, D.; Hahn, A.; Hassan, T.; Hayashida, M.; Herrera, J.; Hose, J.; Hrupec, D.; Ishio, K.; Konno, Y.; Kubo, H.; Kushida, J.; Kuveždić, D.; Lelas, D.; Lindfors, E; Lombardi, S.; Longo, F.; López, M.; Maggio, C.; Majumdar, P.; Makariev, M.; Maneva, G.; Manganaro, M.; Maraschi, L.; Hovatta, Talvikki; Lähteenmäki, Anne; Tornikoski, Merja; Tammi, Joni
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    A multiwavelength campaign was organized to take place between March and July of 2012. Excellent temporal coverage was obtained with more than 25 instruments, including the MAGIC, FACT and VERITAS Cherenkov telescopes, the instruments on board the Swift and Fermi spacecraft, and the telescopes operated by the GASP-WEBT collaboration. Mrk 501 showed a very high energy (VHE) gamma-ray flux above 0.2 TeV of ∼ 0.5 times the Crab Nebula flux (CU) for most of the campaign. The highest activity occurred on 2012 June 9, when the VHE flux was ∼ 3 CU, and the peak of the high-energy spectral component was found to be at ∼ 2 TeV. This study reports very hard X-ray spectra, and the hardest VHE spectra measured to date for Mrk 501. The fractional variability was found to increase with energy, with the highest variability occurring at VHE, and a significant correlation between the X-ray and VHE bands. The unprecedentedly hard X-ray and VHE spectra measured imply that their low- and high-energy components peaked above 5keV and 0.5 TeV, respectively, during a large fraction of the observing campaign, and hence that Mrk 501 behaved like an extreme high-frequency- peaked blazar (EHBL) throughout the 2012 observing season. This suggests that being an EHBL may not be a permanent characteristic of a blazar, but rather a state which may change over time. The one-zone synchrotron self-Compton (SSC) scenario can successfully describe the segments of the SED where most energy is emitted, with a significant correlation between the electron energy density and the VHE gamma-ray activity, suggesting that most of the variability may be explained by the injection of high-energy electrons. The one-zone SSC scenario used reproduces the behaviour seen between the measured X-ray and VHE gamma-ray fluxes, and predicts that the correlation becomes stronger with increasing energy of the X-rays.