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  • 1
    Online Resource
    Online Resource
    Modulation of NTC frequencies by Pc5 ULF pulsations: Experimental test of the generation mechanism and magnetoseismology of the emitting surface : MODULATION OF NTC FREQUENCIES
    American Geophysical Union (AGU) ; 2009
    In:  Journal of Geophysical Research: Space Physics Vol. 114, No. A11 ( 2009-11), p. n/a-n/a
    Details
    In: Journal of Geophysical Research: Space Physics, American Geophysical Union (AGU), Vol. 114, No. A11 ( 2009-11), p. n/a-n/a
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/2009JA014270
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2009
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  • 2
    Online Resource
    Online Resource
    Wave emissions at half electron gyroharmonics in the equatorial plasmasphere region: CLUSTER observations and statistics
    Elsevier BV ; 2009
    In:  Advances in Space Research Vol. 43, No. 2 ( 2009-1), p. 253-264
    Details
    In: Advances in Space Research, Elsevier BV, Vol. 43, No. 2 ( 2009-1), p. 253-264
    Type of Medium: Online Resource
    ISSN: 0273-1177
    URL: Article
    DOI: 10.1016/j.asr.2008.06.007
    Language: English
    Publisher: Elsevier BV
    Publication Date: 2009
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  • 3
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    A quantitative test of Jones NTC beaming theory using CLUSTER constellation
    Copernicus GmbH ; 2007
    In:  Annales Geophysicae Vol. 25, No. 3 ( 2007-03-29), p. 823-831
    Details
    In: Annales Geophysicae, Copernicus GmbH, Vol. 25, No. 3 ( 2007-03-29), p. 823-831
    Abstract: Abstract. Non-thermal continuum (NTC) radiation is, with auroral kilometric radiation (AKR), one of the two electromagnetic emissions generated within the Earth's magnetosphere and radiated into space. The location of the source of NTC has been sought for several decades, with only limited success. The constellation formed by the four CLUSTER spacecraft provides the possibility of triangulation in the vicinity of the source, thus allowing progress in source localisation, while simultaneously revealing the beaming properties of NTC radio sources. We present a case event showing two beams localised on opposite sides of the magnetic equator. At any selected frequency, triangulation points to a single region source of small size. Its position is compatible with the range of possible loci of sources predicted by the radio window theory of Jones (1982) in a frame of constraints relaxed from the simple sketch proposed in early works. The analysis of similar observations from the Dynamics Explorer 1 by Jones et al. (1987) enabled the authors to claim validation of the radio window theory. CLUSTER observations, however, reveal a large beaming cone angle projected onto the ecliptic plane, a feature unobservable by Dynamics Explorer which had a different spin axis orientation. According to the radio window theory, such a large observed cone angle can only be formed by a series of point sources, each beaming in a narrow cone angle. This study demonstrates the difficulty of validating NTC linear generation mechanisms using global beaming properties alone.
    Type of Medium: Online Resource
    ISSN: 1432-0576
    URL: Article
    DOI: 10.5194/angeo-25-823-2007
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2007
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  • 4
    Online Resource
    Online Resource
    A note on the validity of the density matrix expansion
    Elsevier BV ; 1975
    In:  Nuclear Physics A Vol. 253, No. 1 ( 1975-11), p. 1-19
    Details
    In: Nuclear Physics A, Elsevier BV, Vol. 253, No. 1 ( 1975-11), p. 1-19
    Type of Medium: Online Resource
    ISSN: 0375-9474
    URL: Article
    DOI: 10.1016/0375-9474(75)90117-7
    Language: English
    Publisher: Elsevier BV
    Publication Date: 1975
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  • 5
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    Properties of the singing comet waves in the 67P/Churyumov-Gerasimenko plasma environment as observed by the Rosetta mission
    EDP Sciences ; 2019
    In:  Astronomy & Astrophysics Vol. 630 ( 2019-10), p. A39-
    Details
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 630 ( 2019-10), p. A39-
    Abstract: Using in situ measurements from different instruments on board the Rosetta spacecraft, we investigate the properties of the newly discovered low-frequency oscillations, known as singing comet waves, that sometimes dominate the close plasma environment of comet 67P/Churyumov-Gerasimenko. These waves are thought to be generated by a modified ion-Weibel instability that grows due to a beam of water ions created by water molecules that outgass from the comet. We take advantage of a cometary outburst event that occurred on 2016 February 19 to probe this generation mechanism. We analyze the 3D magnetic field waveforms to infer the properties of the magnetic oscillations of the cometary ion waves. They are observed in the typical frequency range (~50 mHz) before the cometary outburst, but at ~20 mHz during the outburst. They are also observed to be elliptically right-hand polarized and to propagate rather closely (~0−50°) to the background magnetic field. We also construct a density dataset with a high enough time resolution that allows us to study the plasma contribution to the ion cometary waves. The correlation between plasma and magnetic field variations associated with the waves indicates that they are mostly in phase before and during the outburst, which means that they are compressional waves. We therefore show that the measurements from multiple instruments are consistent with the modified ion-Weibel instability as the source of the singing comet wave activity. We also argue that the observed frequency of the singing comet waves could be a way to indirectly probe the strength of neutral plasma coupling in the 67P environment.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    URL: Article
    DOI: 10.1051/0004-6361/201834876
    RVK:
    UA 1000
    RVK:
    US 1090
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2019
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  • 6
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    Electric field measurements at the plasma frequency around comet 67P by RPC-MIP on board Rosetta
    EDP Sciences ; 2021
    In:  Astronomy & Astrophysics Vol. 652 ( 2021-8), p. A73-
    Details
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 652 ( 2021-8), p. A73-
    Abstract: Context. The Mutual Impedance Probe (RPC-MIP) carried by the Rosetta spacecraft monitored both the plasma density and the electric field in the close environment of comet 67P/Churyumov–Gerasimenko (67P), as the instrument was operating alternatively in two main modes: active and passive. The active mode is used primarily to perform plasma density measurements, while the passive mode enables the instrument to work as a wave analyzer. Aims. We are reporting electric field emissions at the plasma frequency near comet 67P observed by RPC-MIP passive mode. The electric field emissions are related to Langmuir waves within the cometary ionized environment. In addition, this study gives feedback on the density measurement capability of RPC-MIP in the presence of cold electrons. Methods. We studied the occurrence rate of the electric field emissions as well as their dependence on solar wind structures like stream interaction regions (SIRs) and coronal mass ejections (CMEs). Results. We are showing that strong electric field emissions at the plasma frequency near 67P were present sporadically throughout the period when Rosetta was escorting the comet, without being continuous, as the occurrence rate is reported to be of about 1% of all the measured RPC-MIP passive spectra showing strong electric field emissions. The Langmuir wave activity monitored by RPC-MIP showed measurable enhancements during SIR or CME interactions and near perihelion. Conclusions. According to our results, Langmuir waves are a common feature at 67P during the passage of SIRs. Comparing the plasma frequency given by the RPC-MIP passive mode during Langmuir wave periods with the RPC-MIP active mode observations, we conclude that the measurement accuracy of RPC-MIP depends on the operational submode when the cold electron component dominates the electron density.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    URL: Article
    DOI: 10.1051/0004-6361/201936633
    RVK:
    UA 1000
    RVK:
    US 1090
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2021
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  • 7
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    Online Resource
    Cold electrons at comet 67P/Churyumov-Gerasimenko
    EDP Sciences ; 2018
    In:  Astronomy & Astrophysics Vol. 616 ( 2018-8), p. A51-
    Details
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 616 ( 2018-8), p. A51-
    Abstract: Context. The electron temperature of the plasma is one important aspect of the environment. Electrons created by photoionization or impact ionization of atmospheric gas have energies ~10 eV. In an active comet coma, the gas density is high enough for rapid cooling of the electron gas to the neutral gas temperature (a few hundred kelvin). How cooling evolves in less active comets has not been studied before. Aims. We aim to investigate how electron cooling varied as comet 67P/Churyumov-Gerasimenko changed its activity by three orders of magnitude during the Rosetta mission. Methods. We used in situ data from the Rosetta plasma and neutral gas sensors. By combining Langmuir probe bias voltage sweeps and mutual impedance probe measurements, we determined at which time cold electrons formed at least 25% of the total electron density. We compared the results to what is expected from simple models of electron cooling, using the observed neutral gas density as input. Results. We demonstrate that the slope of the Langmuir probe sweep can be used as a proxy for the presence of cold electrons. We show statistics of cold electron observations over the two-year mission period. We find cold electrons at lower activity than expected by a simple model based on free radial expansion and continuous loss of electron energy. Cold electrons are seen mainly when the gas density indicates that an exobase may have formed. Conclusions. Collisional cooling of electrons following a radial outward path is not sufficient to explain the observations. We suggest that the ambipolar electric field keeps electrons in the inner coma for a much longer time, giving them time to dissipate energy by collisions with the neutrals. We conclude that better models are required to describe the plasma environment of comets. They need to include at least two populations of electrons and the ambipolar field.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    URL: Article
    DOI: 10.1051/0004-6361/201833251
    RVK:
    UA 1000
    RVK:
    US 1090
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2018
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  • 8
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    Conjugate ground and multisatellite observations of compression‐related EMIC Pc1 waves and associated proton precipitation
    American Geophysical Union (AGU) ; 2010
    In:  Journal of Geophysical Research: Space Physics Vol. 115, No. A7 ( 2010-07)
    Details
    In: Journal of Geophysical Research: Space Physics, American Geophysical Union (AGU), Vol. 115, No. A7 ( 2010-07)
    Abstract: We present coordinated ground satellite observations of solar wind compression‐related dayside electromagnetic ion cyclotron (EMIC) waves from 25 September 2005. On the ground, dayside structured EMIC wave activity was observed by the CARISMA and STEP magnetometer arrays for several hours during the period of maximum compression. The EMIC waves were also registered by the Cluster satellites for half an hour, as they consecutively crossed the conjugate equatorial plasmasphere on their perigee passes at L ∼ 5. Simultaneously, conjugate to Cluster, NOAA 17 passed through field lines supporting EMIC wave activity and registered a localized enhancement of precipitating protons with energies 〉 30 keV. Our observations suggest that generation of the EMIC waves and consequent loss of energetic protons may last for several hours while the magnetosphere remains compressed. The EMIC waves were confined to the outer plasmasphere region, just inside the plasmapause. Analysis of lower‐frequency Pc5 waves observed both by the Cluster electron drift instrument (EDI) and fluxgate magnetometer (FGM) instruments and by the ground magnetometers show that the repetitive structure of EMIC wave packets observed on the ground cannot be explained by the ultra low frequency (ULF) wave modulation theory. However, the EMIC wave repetition period on the ground was close to the estimated field‐aligned Alfvénic travel time. For a short interval of time, there was some evidence that EMIC wave packet repetition period in the source region was half of that on the ground, which further suggests bidirectional propagation of wave packets.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/2009JA014935
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2010
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    SSG: 16,13
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  • 9
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    Online Resource
    Impact of a cometary outburst on its ionosphere : Rosetta Plasma Consortium observations of the outburst exhibited by comet 67P/Churyumov-Gerasimenko on 19 February 2016
    EDP Sciences ; 2017
    In:  Astronomy & Astrophysics Vol. 607 ( 2017-11), p. A34-
    Details
    In: Astronomy & Astrophysics, EDP Sciences, Vol. 607 ( 2017-11), p. A34-
    Abstract: We present a detailed study of the cometary ionospheric response to a cometary brightness outburst using in situ measurements for the first time. The comet 67P/Churyumov-Gerasimenko (67P) at a heliocentric distance of 2.4 AU from the Sun, exhibited an outburst at ~1000 UT on 19 February 2016, characterized by an increase in the coma surface brightness of two orders of magnitude. The Rosetta spacecraft monitored the plasma environment of 67P from a distance of 30 km, orbiting with a relative speed of ~0.2 m s -1 . The onset of the outburst was preceded by pre-outburst decreases in neutral gas density at Rosetta, in local plasma density, and in negative spacecraft potential at ~0950 UT. In response to the outburst, the neutral density increased by a factor of ~1.8 and the local plasma density increased by a factor of ~3, driving the spacecraft potential more negative. The energetic electrons (tens of eV) exhibited decreases in the flux of factors of ~2 to 9, depending on the energy of the electrons. The local magnetic field exhibited a slight increase in amplitude (~5 nT) and an abrupt rotation (~36.4°) in response to the outburst. A weakening of 10–100 mHz magnetic field fluctuations was also noted during the outburst, suggesting alteration of the origin of the wave activity by the outburst. The plasma and magnetic field effects lasted for about 4 h, from ~1000 UT to 1400 UT. The plasma densities are compared with an ionospheric model. This shows that while photoionization is the main source of electrons, electron-impact ionization and a reduction in the ion outflow velocity need to be accounted for in order to explain the plasma density enhancement near the outburst peak.
    Type of Medium: Online Resource
    ISSN: 0004-6361 , 1432-0746
    URL: Article
    DOI: 10.1051/0004-6361/201730591
    RVK:
    UA 1000
    RVK:
    US 1090
    Language: English
    Publisher: EDP Sciences
    Publication Date: 2017
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  • 10
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    Machine Learning-Based Prediction of COVID-19 Severity and Progression to Critical Illness Using CT Imaging and Clinical Data
    XMLink ; 2021
    In:  Korean Journal of Radiology Vol. 22, No. 7 ( 2021), p. 1213-
    Details
    In: Korean Journal of Radiology, XMLink, Vol. 22, No. 7 ( 2021), p. 1213-
    Type of Medium: Online Resource
    ISSN: 1229-6929 , 2005-8330
    URL: Article
    DOI: 10.3348/kjr.2020.1104
    Language: English
    Publisher: XMLink
    Publication Date: 2021
    detail.hit.zdb_id: 2085349-X
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